Semester Courses

The following academic courses related to Papermaking Chemistry and related fields are available (as of 2022) at the Department of Forest Biomaterials at North Carolina State University. If interested, please consider registering as a student. We have programs at both the undergraduate and graduate levels.

PSE 322 001 Course Syllabus

PSE 322 001 – Wet End & Polymer Chemistry

Section (just one lecture section; two lab sections)

Fall 2022

4 Credit Hours

Course Description

Wet End & Polymer chemistry prepares undergraduate students (especially third-year students having a background in chemical engineering and chemistry) for careers in the papermaking industry. The focus is on applications of chemistry to improve the efficiency and quality outcomes of the paper manufacturing process. Emphasis is on the chemistry, mechanisms of action, and effects of chemical additives to the paper machine.

Learning Outcomes

By the end of the course students will be able to do the following:

Identify technical terminology related to the chemistry, materials, and processes of paper manufacture.
Explain the functions and principles of engineering unit operations and equipment commonly used in papermaking, repulping, and wastewater remediation.
Explain the functions and engineering principles of using different chemicals that are added during papermaking.
Calculate first-pass retention, addition rates (employing conversion factors), and solve problems requiring a use of chemical engineering concepts.
Apply knowledge of polymers, including identification of polymers as random, block, or alternating, determination of charge equivalents, and anticipation of whether a polymer is likely to be soluble in water.
Correctly distinguish between related colloidal chemical concepts, such as zeta potential vs. charge demand.
Apply concepts of chemical interactions with surfaces and with each other.

Course Structure

Lecture:

The course is organized as 41 lectures, which are scheduled in a uniform pattern over the semester. Each lecture is to be presented in class, with a Panopto Capture version being auto-recorded for study purposes. Each lecture contains a couple of “lecture questions”. When these come up in lecture, each student makes notes so that they can later supply an answer via the Moodle site. The deadline for lecture questions for a given week is 11 PM on the Friday of that week. Each week the student completes a ten-question multiple choice quiz, with questions randomly drawn from a large pool. Students who wish to may take the quiz as many as ten times. Quiz scores are averaged. For these, the deadline again is Friday of that same week at 11 PM. Each week the student also completes a homework set. Questions in the homework sets are often covering quantitative aspects of the topic, following content provided in one of the lectures for the week. Students are randomly assigned different versions, for which the numerical results are different. The deadline is Wednesday of the week after the homework was assigned, at 11 PM.

Laboratory:

The laboratory is organized into four segments, which will be referred to as quarterly blocks. There will be 13 one-a-week sessions (with about 2 core hours each), for each of the two lab cohorts (a Tuesday group and a Thursday group). Assignment of students to 4-member (and occasionally 5-member) teams is done by random numbers. The first session is an orientation session in which the team system and individual responsibilities within each team are explained, the lab manual is presented and explained, the assignments are explained, and there is a brief overview of the procedures used in the class. Every team get assigned unique sets of data to process, interpret, run statistical tests, and use as the basis for accepting or rejecting one or more assigned hypotheses. Each team gets assigned four unique hypotheses of the course of the semester. These will be associated with four of the following six work stations:

Station 1: Charge demand titrations (Emtec CAS-touch!)

Station 2: Drainage rates (Mutek DFR-05)

Station 3: Properties of paper handsheets

Station 4: Retention of fine particles (Britt jar)

Station 5: Fiber-pad streaming potential

Station 6: Flocculation (Rank Bros. PDA)

The third and final week of each quarterly block involves a presentation by each of the teams to the whole assembled cohort. Any critical input received by the team during the presentation is required to be dealt with in the final report, which is due by the following week (6 days after the presentation by 11 PM).

Laboratory location:

Orientation session and presentation sessions: Zoom (to be arranged during lab core hours)

Laboratory work sessions: Paper Labs (Biltmore) 2226 (undergraduate laboratory)

Course Policies

Students are expected to complete lecture questions, quizzes, and homework by their own efforts. However, with respect to the homework they are encouraged to use available resources as they learn the material in an integrated way. For example, they can discuss issues related to homework with people whom they know, as long as in the end they do the homework themselves.

Instructors

Dr Martin A Hubbe (hubbe) – Instructor
Email: hubbe@ncsu.edu
Web Page: http://www4.ncsu.edu/~hubbe
Phone: 919-513-3022
Office Location: Biltmore (Paper Labs) 1206
Office Hours: Monday and Wednesday 10 AM to 11 AM or by appointment (contact me at hubbe@ncsu.edu to set up something specific)

Course Meetings

Lecture

Days: MWF
Time: 11:45 am – 12:25 pm (nominal)

Location: Paper Labs 2221

Laboratory

Days: (Separate Tuesday and Thursday cohorts)
Time: 1:55 pm – 3:45 pm (core hours required attendance)

The lab will open at about 1 PM and remain available to students until at least 5 PM. Teams wishing to use these extra hours need to have at least two team members present during those times. Groups that have accumulated enough data to fully address all of the points of their hypothesis statements, with suitable replication, may ask the instructor whether they can be excused from the second session in a quarterly block.

Location: Paper Labs 2226 (for the work sessions); Zoom meetings will be arranged for the orientation session (first week of lab) and for each presentation session (weeks 4, 7, 10, and 13).

Course Materials

Textbooks

None. A full course-pack (22 PDF chapters) is included at the Moodle site.

Also, a full laboratory manual is provided (PDF) at the Moodle site.

Expenses

None.

Materials

None.

Transportation

This course will not require students to provide their own transportation. Non-scheduled class time for field trips or out-of-class activities is NOT required for this class.

Safety & Risk Assumptions

None.

Grading

Grade Components

Component	Weight	Details
Lecture questions	10	Two lecture questions per lecture. All contribute equally to the final score. Student provide their answer by Moodle. The deadline for these questions to be answered at the Moodle site is Friday of the week by PM. Manually graded by the instructor.
Class participation	10	Numerous questions per period are directed to students, by name, from randomized lists. Assessment emphasizes attentiveness, effort, and the clarity of the response.
Quizzes	10	Quizzes refer to content for the assigned week. Most quizzes cover three lectures. Multiple choice questions are drawn randomly from a pool. Students answer ten questions. Students can take a quiz up to ten times, with a new set of random questions (and occasional return questions). The average score is reported. Deadline Friday, 11 PM.
Homework sets	10	Homework sets pertain to the content covered during a certain week of lectures. Completed homework is uploaded to Moodle and graded manually by the instructor. Deadline Wed, 11 PM.
Mid-term exam	15	The mid-term test covers roughly the first half of the course content. Typically it covers lectures 1 through 21, plus Appendix A (ethical principles). The exam consists of about 25 multiple choice questions (75% of the test score) plus either 3 or 4 essay questions (25% of the test score).
Final exam	20	The final exam covers the whole course, but emphasis is on the second half of the course content. Specifically it covers lectures 1 through 41, plus Appendix A (ethical principles) and Appendix C (statistics and data analysis). The exam consists of about 25 multiple choice questions (75% of the exam score) plus either 3 or 4 essay questions (25% of the exam score).
Laboratory	25	The laboratory component is scored based on equal weights of the following five components: Laboratory notebook and organizing the initial planning by the group (5% of the course grade) Analysis and graphing, including statistics using Excel (5% of the course grade) Preparation and coordination of the group presentation (5% of the course grade) Assembly and primary writing of a final report for the team’s work (5% of the course grade) Peer scoring by other members of the team of 4 or 5 with the student (5% of the course grade, but with faculty oversight)

Letter Grades

This Course uses the Following (Non-Standard) Letter Grading Scale:

96.67	≤	A+	≤	100
93.34	≤	A	<	96.66
90.00	≤	A-	<	93.33
86.67	≤	B+	<	89.99
83.34	≤	B	<	86.66
80.00	≤	B-	<	83.33
76.67	≤	C+	<	79.99
73.34	≤	C	<	76.66
70.00	≤	C-	<	73.33
66.67	≤	D+	<	69.99
63.34	≤	D	<	66.66
60.00	≤	D-	<	63.33
0	≤	F	<	59.99

Requirements for Credit-Only (S/U) Grading

Performance in research, seminar and independent study types of courses (6xx and 8xx) is evaluated as either “S” (Satisfactory) or “U” (Unsatisfactory), and these grades are not used in computing the grade point average. For credit only courses (S/U) the requirements necessary to obtain the grade of “S” must be clearly outlined.

Requirements for Auditors (AU)

Information about and requirements for auditing a course can be found at http://policies.ncsu.edu/regulation/reg-02-20-04.

Policies on Incomplete Grades

If an extended deadline is not authorized, an unfinished incomplete grade will automatically change to an F after either (a) the end of the next regular semester in which the student is enrolled (not including summer sessions), or (b) by the end of 12 months if the student is not enrolled, whichever is shorter. Incompletes that change to F will count as an attempted course on transcripts. The burden of fulfilling an incomplete grade is the responsibility of the student. The university policy on incomplete grades is located at http://policies.ncsu.edu/regulation/reg-02-50-03.

Late Assignments

Late assignments will result in a loss of points commensurate with the degree of lateness. For instance, an assignment two weeks late may be docked up to 10 percentage points if there is no notice and no explanation. Students can avoid loss of points due to lateness by (a) letting the instructor know that there will be a delay, and (b) on a regular basis letting the instructor know the revised schedule when the work will be completed. In other words, communication is the key. It is understood that most students in the course are working full-time jobs, and many of the jobs entail occasional extended work schedules, night work, unexpected travel, and coverage of responsibilities beyond one’s usual work. This is expected, but it is the student’s responsibility to keep the instructor informed.

Attendance Policy

For complete attendance and excused absence policies, please see http://policies.ncsu.edu/regulation/reg-02-20-03

Attendance Policy

This is a 100% online course. There is no “attendance”.

Absences Policy

This is a 100% online course. There is no “absence”.

Makeup Work Policy

See earlier statement about late work.

Additional Excuses Policy

None.

Academic Integrity

Students are required to comply with the university policy on academic integrity found in the Code of Student Conduct found at http://policies.ncsu.edu/policy/pol-11-35-01

No additional statement.

Academic Honesty

See http://policies.ncsu.edu/policy/pol-11-35-01 for a detailed explanation of academic honesty.

No additional statement.

Honor Pledge

Your signature on any test or assignment indicates “I have neither given nor received unauthorized aid on this test or assignment.”

The same policy applies to lecture questions, quizzes, and term papers, even though there is no place for a signature. In the case of homework, it is OK for the student to accept help to understand the material, as long as the student completes the whole homework set by their own efforts. In other words, the policy on homework is “open book” and “open ability to ask people to explain things”.

Digital Course Components

Students may be required to disclose personally identifiable information to other students in the course, via digital tools, such as email or web-postings, where relevant to the course. Examples include online discussions of class topics, and posting of student coursework. All students are expected to respect the privacy of each other by not sharing or using such information outside the course.

Digital Course Components: Wolfware MOODLE, which includes the streaming lectures (created in Mediasite and delivered as YouTube)

Accommodations for Disabilities

Reasonable accommodations will be made for students with verifiable disabilities. In order to take advantage of available accommodations, students must register with the Disability Resource Office at Holmes Hall, Suite 304, Campus Box 7509, 919-515-7653. For more information on NC State’s policy on working with students with disabilities, please see the Academic Accommodations for Students with Disabilities Regulation (REG02.20.01) (https://policies.ncsu.edu/regulation/reg-02-20-01/).

Non-Discrimination Policy

NC State provides equal opportunity and affirmative action efforts, and prohibits all forms of unlawful discrimination, harassment, and retaliation (“Prohibited Conduct”) that are based upon a person’s race, color, religion, sex (including pregnancy), national origin, age (40 or older), disability, gender identity, genetic information, sexual orientation, or veteran status (individually and collectively, “Protected Status”). Additional information as to each Protected Status is included in NCSU REG 04.25.02 (Discrimination, Harassment and Retaliation Complaint Procedure). NC State’s policies and regulations covering discrimination, harassment, and retaliation may be accessed at http://policies.ncsu.edu/policy/pol-04-25-05 or https://oied.ncsu.edu/divweb/. Any person who feels that he or she has been the subject of prohibited discrimination, harassment, or retaliation should contact the Office for Equal Opportunity (OEO) at 919-515-3148.

Course Schedule

NOTE: The course schedule is subject to change.

Lecture MWF 11am – 11:50 am — Session 1: Introduction — 08/10/2020 – 08/10/2020

Introduction to the course FB 522, Chemical Principles for the Papermaking Process Engineer. Learning outcomes. Lecture system. Lecture questions. Quiz instructions. Homework instructions. Term paper overview. Grading. Start of overview of chemistry, costs, and fiber material background.

Lecture MWF 11am – 11:50 am — Session 2: Stock preparation — 08/12/2020 – 08/12/2020

Fiber dimensions. Fiber structure. Wood structure. Chemical components of wood. Start of background of pulping and bleaching. Refining background.

Lecture MWF 11am – 11:50 am — Session 3: Paper machine system — 08/14/2020 – 08/14/2020

Paper machine system. Flow diagrams. Unit operations. Chests. Hydrocyclones. Screening. Hydrodynamic shear levels. Case study (spots in the paper).

Lecture MWF 11am – 11:50 am — Session 4: Paper forming & drying — 08/17/2020 – 08/17/2020

Paper forming and drying. Headboxes. Flows from the slice. Hydrofoils. Vacuum boxes. Wet pressing. Capillary forces involved with sheet consolidation. Drying. Pocket ventilation in the dryer section.

Lecture MWF 11am – 11:50 am — Session 5: Aqueous chemistry — 08/19/2020 – 08/19/2020

Aqueous chemistry. Hydrogen bonding. Dissociation. Chemical equilibria. pH. Acidity and alkalinity. Weak acids, etc. Solubility products. Electrical conductivity.

Lecture MWF 11am – 11:50 am — Session 6: Charge of a fiber surface — 08/21/2020 – 08/21/2020

Charge of a fiber surface. Hemicellulose. Dissociation of carboxylic acid groups vs. pH. Calculations related to pH. Stability of charge and the typical signs of charge of various components in the paper machine system. Effects of pH

Lecture MWF 11am – 11:50 am — Session 7: Polymers & polymerization — 08/24/2020 – 08/24/2020

Polymers & polymerization. Relative sizes of different items in the papermaking furnish. Linear, branched, and crosslinked polymers. Random and block polymers. Classes of starch. Molecular mass averaging systems. Intrinsic viscosity. Condensiation reactions. How pH affects the charge of a non-quaternary amine-type polymer.

Lecture MWF 11am – 11:50 am — Session 8: Retention chemistry — 08/26/2020 – 08/26/2020

Retention chemistry. The ionic double-layer. Zeta potential vs. pH. Free radiccal polymerization. Inversion of an emulsion concentrate polymer. Case study of loss of dry air supply in the head space of a polymer emulsion tank. Salt-based emulsion system.

Lecture MWF 11am – 11:50 am — Session 9: Retention of fines — 08/28/2020 – 08/28/2020

Retention of fines. Paper machine primary circuit of flow. First-pass retention definition and calculations. Effect of hydrofoils on retention. Distribution of fine particles in the Z-direction of paper. Filtration mechanism. Washing mechanismm. Effect of retention aids on Z-directional distribution. Disk savealls. Examples of retetion aid systems.

Lecture MWF 11am – 11:50 am — Session 10: Retention mechanisms — 08/31/2020 – 08/31/2020

Retention mechanisms. Britt jar lab test. Agglomeration of fines. Attachment of fines to fibers. TEM micrographs showing retention aid molecules. Two-component retention aid system. Charged patch mechanism. Effects of different chemical additives.

Lecture MWF 11am – 11:50 am — Session 11: Time effects — 09/02/2020 – 09/02/2020

Time effects. Time vs. optimum dosage. Inverse size-exclusion chromatography. Pore sizes of cellulosic fibers. Process control issues when using retention aids. Automatic control of a retention aid program.

Lecture MWF 11am – 11:50 am — Session 12: Surface chemistry — 09/04/2020 – 09/04/2020

Surface chemistry. Hydrogen bonding at surfaces. Hydrogen bonding within cellulose. Lignin chemistry. Extractives chemistry. Force-distance relationships. Why simple geometrical rules are not expected to apply well when predicting forces between materials of interest to papermakers. What component makes the biggest difference in terms of fiber charge.

Lecture MWF 11am – 11:50 am — Session 13: Forces of interacton — 09/07/2020 – 09/07/2020

Forces of interaction. Van der Waals forces. Thermal diffusion and electrostatic attraction and their net effects. Zeta potential measurements. Energy barriers and prediction of coagulation rates. Case study: Factors affecting rates of settling in a clarifier.

Lecture MWF 11am – 11:50 am — Session 14: Stability and coagulation — 09/09/2020 – 09/09/2020

Stability and coagulation. Effects of salts and multivalent ions. The Schultze-Hardy rule. Steric stabilization. Nonionic surfactants. Case study: Ion exchange system.

Lecture MWF 11am – 11:50 am — Session 15: Process additives — 09/11/2020 – 09/11/2020

Process additives. Hydrodynamic shear levels in a typical paper machine system. Effects of different types of retention aid systems vs. level of hydrodynamic shear. Defoamers. Mechanical deaeration aystem. Acids and bases. Introduction to alum chemistry. Polyaluminum chloride. Case study: Order of addition.

Lecture MWF 11am – 11:50 am — Session 16: Chemical preparation — 09/14/2020 – 09/14/2020

Chemical preparation. Three ways in which materials are received at a paper mill: Non-returnable container, tote bin, and bulk. Justifying capital to install a bulk handling system. Hydropulper. Eductor. Definitions. Filtering of additives. Chemical feed calibration. Static mixers. Stuff box addition. Adding of chemicals at the top of a chest.

Lecture MWF 11am – 11:50 am — Session 17: Functional additives — 09/16/2020 – 09/16/2020

Functional additives. Criteria and examples of functional additives. Repulpability. Testing of paper at the paper mill and comparison to how the customer evaluates paper. Contrasting ways to innovate. Disruptive innovations. Patenting. Price erosion. Cost-revenue diagrams.

Lecture MWF 11am – 11:50 am — Session 18: Rosin sizing systems — 09/18/2020 – 09/18/2020

Rosin sizing systems. Hercules size test. Cobb size test. Bristow wheel. Lucas-Washburn theory and equation. What a sizing agent has to be able to do. Four main types of sizing agents. Rosin and its fortification reaction. Rosin soap. Resin emulsion. Rosin sizing. Why acidic paper breaks down during storage. Problem when attempting to rosin size in the presence of calcium carbonate.

Lecture MWF 11am – 11:50 am — Session 19: ASA, AKD, & surface sizing — 09/21/2020 – 09/21/2020

ASA, AKD, & surface sizing. Factors that make it inherently challenging to render paper resistant to water. Specific surface areas of minerals. ASA chemistry and reactions. Formulation of ASA. Breakdown of ASA vs. time, pH, and temperature. Autocatalytic effects. AKD. Surface sizing, as affected by internal sizing.

Lecture MWF 11am – 11:50 am — Session 20: Starch preparation — 09/23/2020 – 09/23/2020

Starch preparation. Starch granules. Pasting and gelatiniization temperatures. Batch cooking and jet cooking of starch. Viscosity changes during start preparation. Retrogradation. Amylose and amylopectin. Cationic starch. Opposite charges of cationic starch and the fiber surface. Synergistic effects between refining and addition of strength agents.

Lecture MWF 11am – 11:50 am — Session 21: Starch systems for strength — 09/25/2020 – 09/25/2020

Starch systems for strength. Fraction of fiber breakage, depending on sheet strength. Relative bonded area. Adding strength agent so that more of it goes onto long fibers. Refining effects relative to chemical effects. Limitation on how much cationic starch can be used at the wet end. Effects of the uniformity of formation relative to paper strength.

Lecture MWF 11am – 11:50 am — Session 22: Wet strength agents — 09/28/2020 – 09/28/2020

Wet strength agents. Glyoxylated PAM and temporary wet strength agents. Polyamido-amine epichlorohydrin and permanent wet strength agents. Urea-formaldehyde. Melamine-formaldehyde. Where to add a wet strength agent in a paper machine system. Factors that affect wet strength agent performance.

Lecture MWF 11am – 11:50 am — Session 23: Dyes and paper’s color — 09/30/2020 – 09/30/2020

Dyes and paper’s color. Measuring brightness. Measuring opacity. Dye types. Color space. Substractive coloration. Metamerism. Fluorescent whitening. Factors affecting the performance of fluorescent whitening agents. Case study: poor affinity and graniting.

Lecture MWF 11am – 11:50 am — Session 24: Fillers for paper — 10/02/2020 – 10/02/2020

Fillers for paper. PCC, GCC, kaolin, TiO2. Size vs. surface area. Disproportionate effects of filler on surface area. Light scattering vs. particle shape. Kubelka-Mulk analysis. Refractive index. Retention of fillers. Dissolution of calcium carbonate by acids. Particle size distributions. Fillers vs. paper strength.

Lecture MWF 11am – 11:50 am — Session 25: Retention aid theory — 10/05/2020 – 10/05/2020

Retention aid theory. Diffusion vs. convection. Guided tour through different size scales. Diffusion rates and likeiihood of collisions. Convection as a mechanism of collsion in an agitated suspension. Rate laws. How typical rates compare, depending on the level of hdyrodynamic shear. Zeta potential decay.

Lecture MWF 11am – 11:50 am — Session 26: Drainage enhancement — 10/07/2020 – 10/07/2020

Drainage enhancement. Blocking of drainage channels by fines. Effects of retention aids on drainage. Refining vs. rates of dewatering. Effects of basis weight and fines content on dewatering. Chemical systems to promote drainage. How to trade away increased drainage in favor of a more uniform sheet formation. Average fiber orientation from the headbox. Water retention values.

Lecture MWF 11am – 11:50 am — Session 27: Advanced dewatering systems — 10/09/2020 – 10/09/2020

Advanced dewatering systems. Charge neutralization vs. charged patches. Microparticle and nanoparticle systems. Sols and gels as options. Enzymes as a way to achieve faster dewatering.

Lecture MWF 11am – 11:50 am — Session 28: Uniformity of formation — 10/12/2020 – 10/12/2020

Uniformity of formation. Persistent floc structures held together by friction. Hard flocs and soft flocs. Strategic use of hydrodynamic shear. Selective detachment. Opposite effects for gravity and vacuum dewatering. Options of where to add a retention aid.

Lecture MWF 11am – 11:50 am — Session 29: Effects of anionic colloids and polymers — 10/14/2020 – 10/14/2020

Effects of anionic colloids and polymers. Optimization of the charge demand. Adverse effects of dissolved and colloidal anionics on strength. Adverse effects on retention and drainage. Interference with bridging mechanism. Strategies to deal with dissolved and colloidal anionics. Enzymatic breakdown of certain dissolved polymer anionics. Case study.

Lecture MWF 11am – 11:50 am — Session 30: Cationic demand testing — 10/16/2020 – 10/16/2020

Cationic demand testing. Streaming current device. Titrations. Effects of salts on the titration. Colorimetric procedure for cationic demand testing. Fiber pad streaming potential measurements. Microelectrophoresis. Case study: Reduced fresh water usage in a paper machine system.

Lecture MWF 11am – 11:50 am — Session 31: Analysis of deposits — 10/19/2020 – 10/19/2020

Analysis of deposits. Solubility in acid, base, and solvent. Wood extractives in deposits. FTIR. Ignition factors of inorganics. Case study: TiO2 content in a deposit. Ways to combat deposits. How deposits can affect the bottom line. Pareto analysis. Felt cleaning.

Lecture MWF 11am – 11:50 am — Session 32: Anti-deposit strategies — 10/21/2020 – 10/21/2020

Anti-deposit strategies. Tackiness vs. temperature, molecular mass, purity. Talc effects. Microbological (slime) deposits. Holes in the paper. Boil-outs. Case study: build-up of a deposit on a smooth surface.

Lecture MWF 11am – 11:50 am — Session 33: Foam causes and effects — 10/23/2020 – 10/23/2020

Foam causes and effects. Water, air, agitation, a stabilizer, and something to slow internal drainage. Surfactants. Critical micelle concentration. Entrained air vs. drainage and sheet properties. Air content vs. defoamer feed rate. Mechanical deaeration vs. paper machine speed.

Lecture MWF 11am – 11:50 am — Session 34: Foam and problem solving — 10/26/2020 – 10/26/2020

Foam and problem solving. Defoamer composition. Defoamer mechanism. Oil content in defoamers. Adverse effects of defoamers. Air removal devices. Carbon dioxide in entrained air. Wet web strength.

Lecture MWF 11am – 11:50 am — Session 35: Coating and rheology — 10/28/2020 – 10/28/2020

Coating and rheology. Coating components. Pigments. Binders. Additives. Immobilization. Newtonian. Pseudo-plastic. Dilatent. Thixotropic. Typical shear rates.

Lecture MWF 11am – 11:50 am — Session 36: Coating optimization — 10/30/2020 – 10/30/2020

Coating optimization. Equivalent spherical diameter. Coating clay particle size distributions. Hydroxyethylated starch. Modification of starch for the size presss. Latex binders. Protein binders. Coating formulations. Parts of pigment. Worked example.

Lecture MWF 11am – 11:50 am — Session 37: Paper recycling steps — 11/02/2020 – 11/02/2020

Paper recycling steps. Types of ink. Methods of deinking. Screening of stickies. Cleaning and washing. Flotation. The ragger. Pulper chemistry for recycling.

Lecture MWF 11am – 11:50 am — Session 38: Strategies for paper recycling — 11/04/2020 – 11/04/2020

Strategies for paper recycling. Saponification. Swelling. Peroxide bleaching. Washing. HLB values. Agglomerative deinking. Detackification. Ropes and sticks: What happens to fibers in paper when it is dried. Loss of bonding ability.

Lecture MWF 11am – 11:50 am — Session 39: Process control issues — 11/06/2020 – 11/06/2020

Process control issues. Fiber-related tests. Consistency. Refining control. Sources of variablity. Fiber length monitoring. Zeta potential vs. catonic demand. Charge control. Retention control. Statistics related to process control.

Lecture MWF 11am – 11:50 am — Session 40: Wastewater treatment — 11/09/2020 – 11/09/2020

Wastewater treatment. Freshwater usage vs. year. Energy usage vs. year. Effluent quality measures. Cluster rule. Wastewater clarifier. Secondary wastewater treatment. Aeration. Activated sludge system. Anaerobic treatment of wastewater. Thickening of sludge. Membrane filtration for polishing of treated water or intake water.

Lecture MWF 11am – 11:50 am — Session 41: Sustainability and the environment — 11/11/2020 – 11/11/2020

Sustainability and the environment. Life cycle assessment. Definitions. Some environmental challenges. Fuorocarbons. Nanocellulose. Barrier coatings. Saveall systems. Kidney systems. Bioreactors. Obtaining value for a company: Earning money and meeting responsiblity to people’s health and the environment.

Special Provisions for the COVID19 Pandemic

Due to the COVID-19 pandemic, public health measures continue to be implemented across campus. Students should stay current with these practices and expectations through the Protect the Pack website (https://www.ncsu.edu/coronavirus/). The sections below provide expectations and conduct related to COVID-19 issues.

Health and Participation in Class

We are most concerned about your health and the health of your classmates and instructors/TAs.

If you test positive for COVID-19, or are told by a healthcare provider that you are presumed positive for the virus, you should not attend any hybrid or face-to-face (F2F) classes and work with your instructor on any adjustments necessary; also follow other university guidelines, including self-reporting (Coronavirus Self Reporting): Self-reporting is not only to help provide support to you, but also to assist in contact tracing for containing the spread of the virus.
If you feel unwell, even if you have not been knowingly exposed to COVID-19, please do not come to a F2F class or activity.
If you are in quarantine, have been notified that you may have been exposed to COVID-19, or have a personal or family situation related to COVID-19 that prevents you from attending this course in person (or synchronously), please connect with your instructor to make alternative plans, as necessary.
If you need to make a request for an academic consideration related to COVID-19, such as a discussion about possible options for remote learning, please talk with your instructor.

Health and Well-Being Resources

These are difficult times, and academic and personal stress are natural results. Everyone is encouraged to take care of themselves and their peers. If you need additional support, there are many resources on campus to help you:

Counseling Center (NCSU Counseling Center)
Student Health Services (Health Services | Student)
If the personal behavior of a classmate concerns or worries you, either for the classmate’s well-being or yours, we encourage you to report this behavior to the NC State CARES team: (Share a Concern).
If you or someone you know are experiencing food, housing or financial insecurity, please see the Pack Essentials Program (Pack Essentials).

Community Standards related to COVID-19

We are all responsible for protecting ourselves and our community. Please see the community standards (which have been updated for 2021) and Rule 04.21.01 regarding Personal Safety Requirements Related to COVID-19 RUL 04.21.01 – Personal Safety Requirements Related to COVID-19 – Policies, Regulations & Rules

Course Expectations Related to COVID-19:

Face Coverings: All members of the NC State academic community are expected to follow all university policies and guidelines, including the Personal Safety Rule and community standards, for the use of face coverings. Face coverings are required in instructional spaces. Face coverings should be worn to cover the nose and mouth and be close fitting to the face with minimal gaps on the sides.
Course Attendance: NC State attendance policies can be found at: REG 02.20.03 – Attendance Regulations – Policies, Regulations & Rules. Please refer to the course’s attendance, absence, and deadline policies for additional details. If you are quarantined or otherwise need to miss class because you have been advised that you may have been exposed to COVID-19, you should not be penalized regarding attendance or class participation. However, you will be expected to develop a plan to keep up with your coursework during any such absences. If you become ill with COVID-19, you should follow the steps outlined in the health and participation section above. COVID 19-related absences will be considered excused; documentation need only involve communication with your instructor.
Technology Requirements: This course may require particular technologies to complete coursework. Be sure to review the syllabus for these expectations, and see the syllabus technical requirements for your course. If you need access to additional technological support, please contact the Libraries’ Technology Lending Service: (Technology Lending).

Course Delivery Changes Related to COVID-19

Please be aware that the situation regarding COVID-19 is frequently changing, and the delivery mode of this course could change accordingly, including from in-person to remote. Regardless of the delivery method, we will strive to provide a high-quality learning experience.

Due to the Coronavirus pandemic, public health measures have been implemented across campus. Students should stay current with these practices and expectations through the Protect the Pack website (https://www.ncsu.edu/coronavirus/). The sections below provide expectations and conduct related to COVID-19 issues.

Grading/Scheduling Changing Options Related to COVID-19

If the delivery mode has a negative impact on your academic performance in this course, the university has provided tools to potentially reduce the impact:

Enhanced S/U Grading Option: https://studentservices.ncsu.edu/your-resources/covid-19/spring2020-sat-grading/
Late Drop: https://studentservices.ncsu.edu/your-resources/covid-19/spring2020-latedrop/

In some cases, another option may be to request an incomplete in the course. Before using any of these tools, discuss the options with your instructor and your academic advisor. Be aware that if you use the enhanced S/U, you will still need to complete the course and receive at least a C- to pass the course.

Other Important Resources

Keep Learning: https://dasa.ncsu.edu/students/keep-learning/
Protect the Pack FAQs: https://www.ncsu.edu/coronavirus/frequently-asked-questions/
NC State Protect the Pack Resources for Students: https://www.ncsu.edu/coronavirus/reactivating-campus/resources-for-students/
NC State Keep Learning, tips for students opting to take courses remotely:
https://dasa.ncsu.edu/students/keep-learning/
Introduction to Zoom for students:
https://youtu.be/5LbPzzPbYEw
Learning with Moodle, a student’s guide to using Moodle:
https://moodle-projects.wolfware.ncsu.edu/course/view.php?id=226

Click here for 5-minute promotional video of “Chemical Principles for the Papermaking Process Engineer”

FB 522601 Course Syllabus

FB 522601 – Chemical Principles for the Papermaking Process Engineer

Section Only one section

Fall 2020

3 Credit Hours

Course Description

Chemical principles for the Papermaking Process Engineer provides a foundation in aqueous chemistry and the applications of polyelectrolytes. The course is intended for professionals employed in the paper manufacturing industry and related industries, such as chemicals suppliers to paper manufacturers. Topics include the papermaking process, acids and bases, polymers, water-resistance, paper strength, colorants, retention and dewatering aids, deposit control, coatings, recycling, and wastewater treatment. Lectures are by streaming video (Moodle). The course-pack, quizzes, and readings are on Moodle. Intended for off-campus students. On-campus students would need permission from the instructor.

Learning Outcomes

By the end of the course students will be able to do the following:

Identify technical terminology related to the chemistry, materials, and processes of paper manufacture.
Explain the functions and principles of engineering unit operations and equipment commonly used in papermaking, repulping, and wastewater remediation.
Explain the functions and engineering principles of using different chemicals that are added during papermaking.
Calculate first-pass retention, addition rates (employing conversion factors), and solve problems requiring a use of chemical engineering concepts.
Apply knowledge of polymers, including identification of polymers as random, block, or alternating, determination of charge equivalents, and anticipation of whether a polymer is likely to be soluble in water.
Correctly distinguish between related colloidal chemical concepts, such as zeta potential vs. charge demand.
Apply concepts of chemical interactions with surfaces and with each other.
Synthesize course material, plus supplemental reading material into an original, clear, professional, and useful term paper.

Course Structure

The course is organized as a series of 41 lectures, which are scheduled in a uniform pattern over the semester. Each lecture is delivered by streaming video (implemented with YouTube files, but created in Mediasite). Each lecture contains a couple of “lecture questions”, at which point the student pauses the lecture and immediately responds with a short descriptive answer to the question. Each week the student completes a ten-question multiple choice quiz, with questions randomly drawn from a large pool. Students who wish to may take the quiz as many as ten times. Quiz scores are averaged. Each week the student also completes a homework set. Questions in the homework sets are often covering quantitative aspects of the topic, following content provided in one of the lectures for the week. Students are randomly assigned different versions for which the numerical results are different. Near to the end of the semester the students are asked to submit their final version of a term paper, the topic of which has been decided after a discussion with the instructor.

Course Policies

Students are expected to complete lecture questions, quizzes, homework, and term paper assignment by their own efforts. However, with respect to the homework they are encouraged to use available resources as they learn the material in an integrated way. For example, they can discuss issues related to homework with people whom they know, as long as in the end they do the homework themselves. There is a strict rule to answer the lecture questions immediately in the course of listening to and watching the streaming content: The instructor wants to have the opportunity to check whether students are understanding the material and paying attention, without delaying the process of listening to the rest of a streaming lecture.

Instructors

Course Meetings

Lecture

Days: MWF
Time: 11am – 11:50 am
Campus: Main
Location: Online only
This meeting is required.

Course Materials

Textbooks

None.

Expenses

None.

Materials

None.

Requisites and Restrictions

Prerequisites

None.

Co-requisites

None.

Restrictions

None.

General Education Program (GEP) Information

GEP Category

This course does not fulfill a General Education Program category.

GEP Co-requisites

This course does not fulfill a General Education Program co-requisite.

Transportation

This course will not require students to provide their own transportation. Non-scheduled class time for field trips or out-of-class activities is NOT required for this class.

Safety & Risk Assumptions

None.

Grading

Grade Components

Component	Weight	Details
Lecture questions	25	Two lecture questions per lecture. All contribute equally to the final score. Manually graded by the instructor.
Quizzes	25	Quizzes refer to content for the assigned week. In most cases means that a quiz includes content from three lectures. Multiple choice questions are drawn randomly from a very large pool of question. Students answer ten questions. If students want to, they can take a quiz up to ten times, with a new set of random questions (and occasional return questions) each time. The average score is reported. Scoring is automatic.
Homework sets	25	Homework sets pertain to the content covered during a certain week of lectures. Completed homework is uploaded to Moodle and graded manually by the instructor.
Term paper	25	This comes due near the end of the semester. The topic is chosen jointly by the student and instructor. Usually the instructor will attempt to make the topic suitably narrow so that it falls within an area of expressed interest by the student but will require some searching through literature to find parts of a good answer to a posed question.

Letter Grades

This Course uses the Following (Non-Standard) Letter Grading Scale:

96.67	≤	A+	≤	100
93.34	≤	A	<	96.66
90.00	≤	A-	<	93.33
86.67	≤	B+	<	89.99
83.34	≤	B	<	86.66
80.00	≤	B-	<	83.33
76.67	≤	C+	<	79.99
73.34	≤	C	<	76.66
70.00	≤	C-	<	73.33
66.67	≤	D+	<	69.99
63.34	≤	D	<	66.66
60.00	≤	D-	<	63.33
0	≤	F	<	59.99

Requirements for Credit-Only (S/U) Grading

Requirements for Auditors (AU)

Information about and requirements for auditing a course can be found at http://policies.ncsu.edu/regulation/reg-02-20-04.

Policies on Incomplete Grades

If an extended deadline is not authorized by the Graduate School, an unfinished incomplete grade will automatically change to an F after either (a) the end of the next regular semester in which the student is enrolled (not including summer sessions), or (b) by the end of 12 months if the student is not enrolled, whichever is shorter. Incompletes that change to F will count as an attempted course on transcripts. The burden of fulfilling an incomplete grade is the responsibility of the student. The university policy on incomplete grades is located at http://policies.ncsu.edu/regulation/reg-02-50-03. Additional information relative to incomplete grades for graduate students can be found in the Graduate Administrative Handbook in Section 3.18.F at http://www.fis.ncsu.edu/grad_publicns/handbook/

Late Assignments

Late assignments will result in a loss of points commensurate with the degree of lateness. For instance, an assignment two weeks late may be docked up to 10 percentage points if there is no notice and no explanation. Students can avoid loss of ponts due to lateness by (a) letting the instructor know that there will be a delay, and (b) on a regular basis letting the instructor know the revised schedule when the work will be completed. In other words, communication is the key. It is understood that most students in the course are working full-time jobs, and many of the jobs entail occasional estended work scheules, night work, unexpected travel, and coverage of responsilities beyond one’s usual work. This is expected, but it is the student’s responsibility to keep the instructor informed.

Attendance Policy

For complete attendance and excused absence policies, please see http://policies.ncsu.edu/regulation/reg-02-20-03

Attendance Policy

This is a 100% online course. There is no “attendance”.

Absences Policy

This is a 100% online course. There is no “absence”.

Makeup Work Policy

See earlier statement about late work.

Additional Excuses Policy

None.

Academic Integrity

Students are required to comply with the university policy on academic integrity found in the Code of Student Conduct found at http://policies.ncsu.edu/policy/pol-11-35-01

No additional statement.

Academic Honesty

See http://policies.ncsu.edu/policy/pol-11-35-01 for a detailed explanation of academic honesty.

No additional statement.

Honor Pledge

Your signature on any test or assignment indicates “I have neither given nor received unauthorized aid on this test or assignment.”

Electronically-Hosted Course Components

Students may be required to disclose personally identifiable information to other students in the course, via electronic tools like email or web-postings, where relevant to the course. Examples include online discussions of class topics, and posting of student coursework. All students are expected to respect the privacy of each other by not sharing or using such information outside the course.

Electronically-hosted Components: Wolfware MOODLE, which includes the streaming lectures (created in Mediasite and delivered as YouTube)

Accommodations for Disabilities

Non-Discrimination Policy

Course Schedule

NOTE: The course schedule is subject to change.

Lecture MWF 11am – 11:50 am — Session 1: Introduction — 08/10/2020 – 08/10/2020

Lecture MWF 11am – 11:50 am — Session 2: Stock preparation — 08/12/2020 – 08/12/2020

Fiber dimensions. Fiber structure. Wood structure. Chemical components of wood. Start of background of pulping and bleaching. Refining background.

Lecture MWF 11am – 11:50 am — Session 3: Paper machine system — 08/14/2020 – 08/14/2020

Paper machine system. Flow diagrams. Unit operations. Chests. Hydrocyclones. Screening. Hydrodynamic shear levels. Case study (spots in the paper).

Lecture MWF 11am – 11:50 am — Session 4: Paper forming & drying — 08/17/2020 – 08/17/2020

Paper forming and drying. Headboxes. Flows from the slice. Hydrofoils. Vacuum boxes. Wet pressing. Capillary forces involved with sheet consolidation. Drying. Pocket ventilation in the dryer section.

Lecture MWF 11am – 11:50 am — Session 5: Aqueous chemistry — 08/19/2020 – 08/19/2020

Aqueous chemistry. Hydrogen bonding. Dissociation. Chemical equilibria. pH. Acidity and alkalinity. Weak acids, etc. Solubility products. Electrical conductivity.

Lecture MWF 11am – 11:50 am — Session 6: Charge of a fiber surface — 08/21/2020 – 08/21/2020

Lecture MWF 11am – 11:50 am — Session 7: Polymers & polymerization — 08/24/2020 – 08/24/2020

Lecture MWF 11am – 11:50 am — Session 8: Retention chemistry — 08/26/2020 – 08/26/2020

Lecture MWF 11am – 11:50 am — Session 9: Retention of fines — 08/28/2020 – 08/28/2020

Lecture MWF 11am – 11:50 am — Session 10: Retention mechanisms — 08/31/2020 – 08/31/2020

Lecture MWF 11am – 11:50 am — Session 11: Time effects — 09/02/2020 – 09/02/2020

Lecture MWF 11am – 11:50 am — Session 12: Surface chemistry — 09/04/2020 – 09/04/2020

Lecture MWF 11am – 11:50 am — Session 13: Forces of interacton — 09/07/2020 – 09/07/2020

Forces of interacton. Van der Waals forces. Thermal diffusion and electrostatic attraction and their net effects. Zeta potential measurements. Energy barriers and prediction of coagulation rates. Case study: Factors affecting rades of settling in a clarifier.

Lecture MWF 11am – 11:50 am — Session 14: Stability and coagulation — 09/09/2020 – 09/09/2020

Stability and coagulation. Effects of salts and multivalent ions. The Schultze-Hardy rule. Steric stabilization. Nonionic surfactants. Case study: Ion exchange system.

Lecture MWF 11am – 11:50 am — Session 15: Process additives — 09/11/2020 – 09/11/2020

Lecture MWF 11am – 11:50 am — Session 16: Chemical preparation — 09/14/2020 – 09/14/2020

Lecture MWF 11am – 11:50 am — Session 17: Functional additives — 09/16/2020 – 09/16/2020

Functional additives. Criteria and examples of fuctional additives. Repulpability. Testing of paper at the paper mill and comparison to how the cultomer evaluates paper. Contrasting ways to innovate. Disruptive innovations. Patenting. Price erosion. Cost-revenue diagrams.

Lecture MWF 11am – 11:50 am — Session 18: Rosin sizing systems — 09/18/2020 – 09/18/2020

Lecture MWF 11am – 11:50 am — Session 19: ASA, AKD, & surface sizing — 09/21/2020 – 09/21/2020

Lecture MWF 11am – 11:50 am — Session 20: Starch preparation — 09/23/2020 – 09/23/2020

Lecture MWF 11am – 11:50 am — Session 21: Starch systems for strength — 09/25/2020 – 09/25/2020

Lecture MWF 11am – 11:50 am — Session 22: Wet strength agents — 09/28/2020 – 09/28/2020

Lecture MWF 11am – 11:50 am — Session 23: Dyes and paper’s color — 09/30/2020 – 09/30/2020

Lecture MWF 11am – 11:50 am — Session 24: Fillers for paper — 10/02/2020 – 10/02/2020

Lecture MWF 11am – 11:50 am — Session 25: Retention aid theory — 10/05/2020 – 10/05/2020

Lecture MWF 11am – 11:50 am — Session 26: Drainage enhancement — 10/07/2020 – 10/07/2020

Lecture MWF 11am – 11:50 am — Session 27: Advanced dewatering systems — 10/09/2020 – 10/09/2020

Advanced dewatering systems. Charge neutralization vs. charged patches. Microparticle and nanoparticle systems. Sols and gels as options. Enzymes as a way to achieve faster dewatering.

Lecture MWF 11am – 11:50 am — Session 28: Uniformity of formation — 10/12/2020 – 10/12/2020

Lecture MWF 11am – 11:50 am — Session 29: Effects of anionic colloids and polymers — 10/14/2020 – 10/14/2020

Lecture MWF 11am – 11:50 am — Session 30: Cationic demand testing — 10/16/2020 – 10/16/2020

Lecture MWF 11am – 11:50 am — Session 31: Analysis of deposits — 10/19/2020 – 10/19/2020

Lecture MWF 11am – 11:50 am — Session 32: Anti-deposit strategies — 10/21/2020 – 10/21/2020

Lecture MWF 11am – 11:50 am — Session 33: Foam causes and effects — 10/23/2020 – 10/23/2020

Lecture MWF 11am – 11:50 am — Session 34: Foam and problem solving — 10/26/2020 – 10/26/2020

Foam and problem solving. Defoamer composition. Defoamer mechanism. Oil content in defoamers. Adverse effects of defoamers. Air removal devices. Carbon dioxide in entrained air. Wet web strength.

Lecture MWF 11am – 11:50 am — Session 35: Coating and rheology — 10/28/2020 – 10/28/2020

Coating and rheology. Coating components. Pigments. Binders. Additives. Immobilization. Newtonian. Pseudo-plastic. Dilatent. Thixotropic. Typical shear rates.

Lecture MWF 11am – 11:50 am — Session 36: Coating optimization — 10/30/2020 – 10/30/2020

Lecture MWF 11am – 11:50 am — Session 37: Paper recycling steps — 11/02/2020 – 11/02/2020

Paper recycling steps. Types of ink. Methods of deinking. Screening of stickies. Cleaning and washing. Flotation. The ragger. Pulper chemistry for recycling.

Lecture MWF 11am – 11:50 am — Session 38: Strategies for paper recycling — 11/04/2020 – 11/04/2020

Lecture MWF 11am – 11:50 am — Session 39: Process control issues — 11/06/2020 – 11/06/2020

Lecture MWF 11am – 11:50 am — Session 40: Wastewater treatment — 11/09/2020 – 11/09/2020

Lecture MWF 11am – 11:50 am — Session 41: Sustainability and the environment — 11/11/2020 – 11/11/2020

FB 501 “Research Methods” – Course Syllabus

Section 001

Fall 2021

2 Credit hours

Special Notes

The course Research Methods is required for all on-campus graduate students in the Department of Forest Biomaterials. Students enrolled at the Masters degree level take FB 501. Students enrolled at the PhD level take FB 701. Distance education students may select FB 501 as an elective (section typically listed as “FB 501 section 601”).

Course Description

This is an introductory course to familiarize graduate students with basic research methods. It will cover conduct of research by the scientific method, literature searching, applying green technologies and sound conceptual approaches to research, the writing and critiquing of scientific articles, rules for assigning credit for the work of others, basic research ethics, basic statistics and analysis of data, experimental design, and making a research presentation.

Learning Objectives

1. Understand and be able to apply the scientific method.

2. Perform a literature search on their research topic

3. Acknowledge credit in research by appropriate designation of authorship and proper referencing.

4. Understand laboratory safety, etiquette and common practices.

5. Appreciate ethical issues in research.

6. Use basic statistics to analyze experimental data and design experiments.

7. Present data in figures and tables.

8. Write a research paper with the appropriate sections and content.

9. Make a professional research presentation.

Course Structure

Week	Lecture Topics	Assignments Due
1	Course introduction & syllabus The scientific method	Brief curriculum vitae (CV), 1-2 pages
2	Searching the literature for a research project	1. Produce a list of at least 10 relative literature references from searches of the keywords. 2. Writing exercise: Prepare a paragraph (one-half to one page) that cites at least four or your collected references. Aim to prepare a paragraph that you would be proud to include in a draft of the Introduction section of a PhD thesis. Make sure that you citations follow a widely accepted, consistent style.
3	1. Implementing green technology principles in research 2. Insisting upon the use of sound concepts in research	Reading: Hubbe, M. A. (2021). “Insisting upon meaningful results from adsorption experiments,” Separation & Purification Reviews, early availability, article ID LSPR 1888299. DOI: 10.1080/15422119.2021.1888299
4	1. The basics of a research paper 2. Plagiarism – acknowledging credit and how to appropriately reference prior work 3. Example of how plagiarism can be easily detected by a journal editor	Reading: The scientific method (essay) Reading: Example of plagiarism Reading: Marulier et al. 2015 article Reading: Eichhorn et al. 2011 article Writing: Brief statement of career goals, ~ 1p.
5	Basic statistics Presentation of experimental data	1. Writing assignment: Produce 1-3 pages of literature review pertaining to your research topic, with at least ten proper references. 2. Skim and be ready to discuss “Running statistical tests in Excel”.
6	1. Correlation and regression 2. Experimental design	1. Given a set of data, calculate basic statistics: mean, standard deviation, and confidence limits (please specify the degree of confidence that you chose). Then use the student-t test to determine whether or not the means of two populations are statistically different from each other.
7	1. What is an MS degree about? 2. What is a PhD degree about? 3. Being ready to make an “elevator talk” (due next week).	1. Plot data on an x-y chart; perform linear regression; show error bars. Use the regression output to report the coefficient of determination, the slope, and the intercept. Below the plot, indicate what the error bars are showing (for example, what kind of confidence interval). 2. Reading assignment: Look through the graduate school’s rules for electronic document submission and be ready to discuss issues that interest you.
8	1. Introductory overview of lab methods for characterization of cellulosic materials: Spectroscopy, chromatography, and thermal analysis	1. Reading assignment: Kim, Lee, and Kafle, 2013, Characterization of crystalline cellulose in biomass: Basic principles, applications, and limitations of XRD, NMR, IR, Raman, and SFG. 2. Be prepared to briefly discuss at least one thing that you liked about the article. Be prepared to briefly discuss at least one error in the article or something that you think that the authors could have done better.
9	1. Critique of content of some relatively bad examples of writing and graphics in articles that have recently appeared in the peer-reviewed literature.	1. Reading assignment: You are asked to quickly read two drafts of articles that were submitted for publication. One of them (“grafted cellulose flocculant”) had been peer reviewed by the instructor, and he will be discussing the comments that he had sent to the authors. The other one (An article by Marulier et al., 2015, about 3D analysis of paper microstructures) is required reading to enable you to complete your homework assignment. Focus not on the content, but on how the article is structured and written. 2. Produce an additional 3 pages (pages 4-6) for your literature review.
10	1. Preparation and delivery of a research presentation	1. Reading assignment: Presentation of research 2. Writing assignment: Produce yet another 3 pages of research paper (Materials, Methods, Research plan) with references. Turn in the accumulated draft (now with 9 pages, 20 references).
11	1. Ethics in research 2. Dealing with stakeholders having different ethical approaches 3. Discussion of Franzen’s real-life experiences	1. Reading assignment: The news story of Dr. Franzen (to prepare for the discussion in class) 2. Prepare the PowerPoint document (10 or more slides) for presentation of your research work (to be critiqued by the instructor).
12	Student presentations	1. Prepare at least one page of additional content of your draft research paper (maybe distributed in more than one place in the article) that discusses theoretical implications of the work, how your work differs from all previous work, and what were the main motivations fort this type of work. Make sure that there has been sufficient work on a statement of novelty of your work appearing near to the end of the Introduction section. When you pass in your draft, make sure that it includes any changes that you made in response to input from the instructor so far.
13	Student presentations	1. This is your last chance to submit a non-final draft of your research paper and get feedback from your instructor before the final draft is due next week.
14	1. Student presentations 2. Discussion and role playing related to the oral defense of a thesis.	1. Final drafts of written paper are due.

Course Meetings: 2102 Biltmore Hall (Robertson wing), Wednesdays, 3:00 PM to 4:50 PM

Course Materials: All are provided within this Moodle site; nothing needs to be purchased.

Requisites and Restrictions: None

General Education Program (GEP) Information

This course does not fulfill a General Education Program category or co-requisite.

Transportation

This course will not require students to travel. Distance-education students will be able to participate in non-simultaneous manner, with recording of the audio and computer screen from each class.

Safety and Risk Assumptions: None

Grading Components

Component	Weight	Details
Written homework	50%	This item includes all written homework assigned during the course. The grade will be apportioned based on items, not length, so that the grade is spread about equally over the semester.
Final writing assignment	30%	This item is based on your final writing assignment and emphasized both the overall quality of the work and the degree of learning that was demonstrated over the semester
Final presentation	20%	This item is based on your final presentation to the class as an indication of your ability to use what you have learned during the course.

Letter Grades

This course uses the following (non-standard) letter grading scale:

96.6667 ≤ A+ ≤ 100

93.3334 ≤ A < 96.6666

90.0000 ≤ A- < 93.3333

86.6667 ≤ B+ < 89.9999

83.3334 ≤ B < 86.6666

80.0000 ≤ B- < 83.3333

76.6667 ≤ C+ < 79.9999

73.3334 ≤ C < 76.6666

70.0000 ≤ C- < 73.3333

66.6667 ≤ D+ < 69.9999

63.3334 ≤ D < 66.6666

60.0000 ≤ D- < 63.3333

0 ≤ F < 59.9999

Requirements for Credit-Only (S/U) Grading

Requirements for Auditors (AU)

Information about and requirements for auditing a course can be found at http://policies.ncsu.edu/regulation/reg-02-20-04.

Policies on Incomplete Grades

Late Assignments

Unexcused late assignments will be penalized by 10% of their numerical grade.

Attendance Policy

For complete attendance and excused absence policies, please see http://policies.ncsu.edu/regulation/reg-02-20-03

Attendance Policy: Students unable to attend a session must alert the instructor and be prepared to complete all assignments.

Absences Policy: Each unexcused absences will be penalized 2 points of the final grade.

Makeup Work Policy: As noted under “late assignments, late work will be penalized by 10% of the grade of the item.

Additional Excuses Policy: None.

Academic Integrity

Students are required to comply with the university policy on academic integrity found in the Code of Student Conduct found at http://policies.ncsu.edu/policy/pol-11-35-01 None.

Academic Honesty

See http://policies.ncsu.edu/policy/pol-11-35-01 for a detailed explanation of academic honesty. None.

Honor Pledge

Your signature on any test or assignment indicates “I have neither given nor received unauthorized aid on this test or assignment.”

Electronically-Hosted Course Components

There are no electronically-hosted components for this course.

Accommodations for Disabilities

Reasonable accommodations will be made for students with verifiable disabilities. In order to take advantage of available accommodations, students must register with the Disability Resource Office at Suite 304, University College Commons, Campus Box 7509, 919-5157653. For more information on NC State’s policy on working with students with disabilities, please see the Academic Accommodations for Students with Disabilities Regulation (REG02.20.01) (https://policies.ncsu.edu/regulation/reg-02-20-01/).

Non-Discrimination Policy

NC State University provides equality of opportunity in education and employment for all students and employees. Accordingly, NC State affirms its commitment to maintain a work environment for all employees and an academic environment for all students that is free from all forms of discrimination. Discrimination based on race, color, religion, creed, sex, national origin, age, disability, veteran status, or sexual orientation is a violation of state and federal law and/or NC State University policy and will not be tolerated. Harassment of any person (either in the form of quid pro quo or creation of a hostile environment) based on race, color, religion, creed, sex, national origin, age, disability, veteran status, or sexual orientation also is a violation of state and federal law and/or NC State University policy and will not be tolerated. Retaliation against any person who complains about discrimination is also prohibited. NC State’s policies and regulations covering discrimination, harassment, and retaliation may be accessed at http://policies.ncsu.edu/policy/pol-04-25-05 or http://www.ncsu.edu/equal_op/. Any person who feels that he or she has been the subject of prohibited discrimination, harassment, or retaliation should contact the Office for Equal Opportunity (OEO) at 919-515-3148.

Course Schedule

See the “Course Structure” table earlier in this document.

Special Provisions for the COVID-19 Pandemic

Health and Participation in Class

We are most concerned about your health and the health of your classmates and instructors/TAs.

If you test positive for COVID-19, or are told by a healthcare provider that you are presumed positive for the virus, you should not attend any hybrid or face-to-face (F2F) classes and work with your instructor on any adjustments necessary; also follow other university guidelines, including self-reporting (Coronavirus Self Reporting): Self-reporting is not only to help provide support to you, but also to assist in contact tracing for containing the spread of the virus.
If you feel unwell, even if you have not been knowingly exposed to COVID-19, please do not come to a F2F class or activity.
If you are in quarantine, have been notified that you may have been exposed to COVID-19, or have a personal or family situation related to COVID-19 that prevents you from attending this course in person (or synchronously), please connect with your instructor to make alternative plans, as necessary.
If you need to make a request for an academic consideration related to COVID-19, such as a discussion about possible options for remote learning, please talk with your instructor.

Health and Well-Being Resources

Counseling Center (NCSU Counseling Center)
Student Health Services (Health Services | Student)
If the personal behavior of a classmate concerns or worries you, either for the classmate’s well-being or yours, we encourage you to report this behavior to the NC State CARES team: (Share a Concern).
If you or someone you know are experiencing food, housing or financial insecurity, please see the Pack Essentials Program (Pack Essentials).

Community Standards related to COVID-19

Course Expectations Related to COVID-19:

Face Coverings: All members of the NC State academic community are expected to follow all university policies and guidelines, including the Personal Safety Rule and community standards, for the use of face coverings. Face coverings are required in instructional spaces. Face coverings should be worn to cover the nose and mouth and be close fitting to the face with minimal gaps on the sides.
Course Attendance: NC State attendance policies can be found at: REG 02.20.03 – Attendance Regulations – Policies, Regulations & Rules. Please refer to the course’s attendance, absence, and deadline policies for additional details. If you are quarantined or otherwise need to miss class because you have been advised that you may have been exposed to COVID-19, you should not be penalized regarding attendance or class participation. However, you will be expected to develop a plan to keep up with your coursework during any such absences. If you become ill with COVID-19, you should follow the steps outlined in the health and participation section above. COVID 19-related absences will be considered excused; documentation need only involve communication with your instructor.
Technology Requirements: This course may require particular technologies to complete coursework. Be sure to review the syllabus for these expectations, and see the syllabus technical requirements for your course. If you need access to additional technological support, please contact the Libraries’ Technology Lending Service: (Technology Lending).

Course Delivery Changes Related to COVID-19

Grading/Scheduling Changing Options Related to COVID-19

If the delivery mode has a negative impact on your academic performance in this course, the university has provided tools to potentially reduce the impact:

Enhanced S/U Grading Option: https://studentservices.ncsu.edu/your-resources/covid-19/spring2020-sat-grading/
Late Drop: https://studentservices.ncsu.edu/your-resources/covid-19/spring2020-latedrop/

Other Important Resources

Keep Learning: https://dasa.ncsu.edu/students/keep-learning/
Protect the Pack FAQs: https://www.ncsu.edu/coronavirus/frequently-asked-questions/
NC State Protect the Pack Resources for Students: https://www.ncsu.edu/coronavirus/reactivating-campus/resources-for-students/
NC State Keep Learning, tips for students opting to take courses remotely:
https://dasa.ncsu.edu/students/keep-learning/
Introduction to Zoom for students:
https://youtu.be/5LbPzzPbYEw
Learning with Moodle, a student’s guide to using Moodle:
https://moodle-projects.wolfware.ncsu.edu/course/view.php?id=226

COURSE SYLLABUS Ver. Jan. 6, 2022
FB 516: “Forest Products Colloids & Surfaces”
Spring, even-numbered years

Instructor:
Dr. Martin A. Hubbe
Biltmore Hall 1206
Telephone: (919) 513-3022
E-mail: hubbe@ncsu.edu
Moodle course management system:
https://wolfware.ncsu.edu/
Website: http://www4.ncsu.edu/~hubbe
Class sessions: Tuesday and Thursday, 11:45 AN to 1:00 PM, Biltmore 2006
Office hours for student consultation: To be posted
Course Description:
This graduate-level class deals with surface and interfacial science as it relates to uses of
lignocellulosic materials. Fundamentals of the physical chemistry of surfaces, dispersions and suspensions are brought to life with examples from such fields as paper and biomaterials science, nanocellulose, composites, and cellulose processing and transformation. Topics include colloidal stability, flocculation, surface and capillary forces, polyelectrolyte behavior, electrokinetics, adhesion, surfactancy, and self-assembly. Water-cellulose interactions, including wettability, swelling, and hydrogen bonding effects are highlighted.
Course Rationale:
This is one of four courses selected by the faculty of the Department of Forest Biomaterials to serve as core courses for the department’s graduate program for students interested in forest products, lignocellulosic and renewable materials. Topics related to colloid and surface science can be critical to the success of existing and emerging technologies that rely on the processing of biomass and/or renewable materials. The term “forest products” identifies this course as part of the department’s primary focus. The term “colloids” indicates a fundamental approach to phenomena happening within short distances of surfaces within aqueous systems, e.g. forces that bring about coagulation, wetting, adhesion, friction, etc. Likewise, “surfaces” highlights the fact that the top layer of a material, its surface, is most critical in terms of interactions with the surrounding; regardless if it deals to binding of an enzyme for cellulose to sugar conversion or to
the adsorption of a strength-enhancer additive. Students in our degree programs need to fully understand such concepts as they prepare for careers in which they may have opportunities to apply those concepts in innovative ways.
Student Learning Outcomes:
Students who complete the course will be able to accurately describe physical chemical
principles related to interactions involving surfaces and interfaces, e.g. surface free energy,
WPS 516 Page 2
wetting, capillary forces, double layer forces, adsorption of polyelectrolytes, flocculation,
effects of surfactants, swelling, development of hydrogen bonding.
Students completing the course will be able to identify and explain factors that affect the
results of interactions between surfaces or between cellulosic materials and aqueous
solutions, e.g. the effects of pH or salt conditions on agglomeration and settling of
suspensions.
Students who complete the course will be able to efficiently find and understand facts from recently published literature and to use those facts to explain phenomena of importance in such emerging fields as cellulosic nanotechnology, new paper product development, and pretreatment of biomass.
Textbooks
The course makes extensive use of recent articles selected from the scientific literature. Copies of these articles are made available to all class participants via a password-limited Internet site, using the Moodle online course management system.
The instructor of the course, together with co-authors, has written a series of scholarly review article with the purpose of that they would serve as the primary background text for the present course. Each of these reading assignments has a corresponding set of online quiz questions (Moodle system). The articles are freely available at http://www.bioresources.com, and the citations are as follows:
 Hubbe, M. A., and Rojas, O. J. (2008). “Colloidal stability and aggregation of lignocellulosic materials in aqueous suspension: A review,” BioResources 3(4), 1419-1491;
 Hubbe, M. A., Ayoub, A., Daystar, J. S., Venditti, R. A, and Pawlak, J. J. (2013).
“Enhanced absorbent products incorporating cellulose and its derivatives: A review,”
BioResources 8(4), 6556-6629;
 Hubbe, M. A., Rojas, O. J., and Lucia, L. A. (2015). “Green modification of surface
characteristics of cellulosic materials at the molecular or nano scale: A review,”
BioResources 10(3), 6095-6229;
 Hubbe, M. A., Gardner, D. J., and Shen, W. (2015). “Contact angles and wettability of
cellulosic surfaces: A review of proposed mechanisms and test strategies,” BioResources
10(4), 8657-8749.
In addition, the following texts are optional, but recommended to be read by students of the course:
 Habibi, Y., Lucia, L. A., and Rojas, O. J. (2010). “Cellulose nanocrystals: Chemistry, selfassembly, and applications,” Chem. Rev. 110, 3479-3500.
 Zhang, Y., Nypelo, T., Salas, C., Arboleda, J., Hoeger, I. C., and Rojas, O. J. (2013).
“Cellulose nanofibrils: From strong materials to bioactive surfaces,” J. Renewable Mater.
1(3), 195-211.
 Hubbe, M. A., Rojas, O. J., Lucia, L. A., and Sain, M. (2008). “Cellulosic nanocomposites:
A review,” BioResources 3(3), 929-980.
Text descriptions and links to other resources are provided by means of the Moodle system.
These resources fulfill the role of a textbook, making it unnecessary to consider purchase of a textbook.
WPS 516 Page 3
Course Organization and Scope
Main Topics (approximate number of hours in parentheses)
Overview of lignocellulosic surfaces (3 class sessions)
Adsorption from solution (4 class sessions)
Colloidal interactions of cellulosics (4 class sessions)
Nanocellulose (4 class sessions)
Swelling and porosity (3 class sessions)
Modification of cellulosic surfaces (4 class sessions)
Wettability and adhesion (4 class sessions)
Student presentations of class projects (25 min. each)
Schedule of Reading Assignments
Due dates shown in the following list are based on the example of an on-campus semester at North Carolina State University. Distance-education students will ordinarily receive the classroom content asynchronously via Panopto, for which a link will be provided at the Moodle page. See the website for the current due dates!
Everyone is responsible for reading and understanding this material as it is assigned.
Watch the “Assignments” page on the website to know what has been assigned by what
deadline. The following schedule is approximate. The detailed schedule is what appears
in the Wolfpack Moodle system for each current semester.
Period (No. of Periods)
Topic
1 3 1. Overview of lignocellulosic surfaces
o Wood, pulp fibers, other fibers, regenerated cellulose, thin films
o Hemicelluloses, lignin-related surfaces
o Cellulosic nanomaterials
o Reading assignment and online quiz.
2 o Surfaces affected by lignin and its byproducts
o Extractives
3 o Lignocellulosic biopolymers
o Reading assignment and online quiz.
4 4 2. Adsorption from solution
o Thermodynamic considerations: surface excess, isotherms
o Kinetics of adsorption onto cellulosic surfaces
o Reading assignment and online quiz.
o Due date: Rough draft of first essay (critical review of a scientific
article: student-selected topics related to treatments of
lignocellulosic materials and their effects on surface behavior)
5 o Examples: Ions, surfactants, polyelectrolytes, papermaking
additives
o Due date: Final draft of first essay
o Reading assignment and online quiz.
6 o Self-assembly, micellization
7 o Complex deposition, layer-by-layer assembly
o Reading assignment and online quiz.
WPS 516 Page 4
8 4 3. Colloidal interactions of cellulosics
o Hamaker constants
9 o Double layer forces:
o Charged groups on lignocellulosic surfaces
o Zeta potential
10 o Agglomeration: Coagulation (DLVO)
11 o Flocculation, steric stabilization
o Friction between wetted surfaces, sediment structure
o Reading assignment.
12 4 4. Nanocellulose
o Refining, ultra-refining and factors affecting it
13 o Isolation of nanostructures: enzymatic, acid hydrolysis,
cryocrushing
o Factors affecting accessibility: pulping, bleaching, drying,
dissolution
o
14 o Properties and behaviors of cellulosic nanoparticles and thin films
15 o Nanocomposites
16 Mid-term test
o Reading assignment and online quiz.
17 3 5. Swelling and porosity
o Evaluations of surface area and porosity of cellulosics
o Types of water associated with cellulosics
o Factors affecting swelling, water retention
18 o Donnan equilibrium and other theories related to swelling
19 o Penetration of fluids and chemicals into cellulosic materials
o Factors affecting surface area, including effects of drying
o Reading assignment and online quiz.
o Due date: Rough draft of your second essay (hypothesis question)
20 4 6. Modification of cellulosic surfaces
o Chemical derivatization
o Grafting
21 o Adsorption
o Surfactants and lignocellulosic surfactants
22 o Composites
23 o Self-assembly
o Complexes involving lignocellulosic materials
o Reading assignment and online quiz.
o Due date: Final draft of your second essay (hypothesis question)
24 4 7. Wettability and adhesion
o Due date: Presentation draft
o Contact angles
o Surface free energy
25 o Cellulosic composites and nanocomposites
26 o Solubility parameters
o Acid-base theory applications
o Drying and bond development, loss of swelling ability
27 o Student Presentations
28 o Student Presentations
WPS 516 Page 5
Schedule of Homework Due Dates, Quizzes, and Tests
The detailed assignments for the class are specified in the Moodle learning management system pages. The preceding table (see 5, Schedule of Reading Assignments) for a general list. The most significant homework assignments will consist of two essays and one presentation to the class. These are described below:
First essay assignment: The written version, due early in the course is a two-three page critical review of a published article. A different article is assigned to each student, based on their choice of a semester project topic (see later). The review is required to conform to the style and format of an example given in the course pack. Students are also recommended to read relevant sections for the course-pack material before completing their essay. An example essay is provided at the Moodle site under “Resources”.
As shown on the course schedule in Moodle, the first written assignment comes due is just a short time. Students are urged to act promptly to “claim” their first and second choices of a focus topic for their semester projects, which include two written assignments and a presentation. E-mail is a recommended way to stake the claim – or they can tell the instructor. It is recommended to watch the due dates on the calendar. An e-mail or a comment from the instructor will be the indication of which claims were successful.
For full credit, the format of the critical review must closely match the criteria and example shown in the course-pack. A professional level of grammar, spelling, and clarity are expected. Headings and other features must follow the format illustrated. Figures, if included must be the student’s own original figures (not scanned from a publication). The minimum length is 1.5 pages, single-spaced, with a 12-point font. The maximum length is approximately 3 pages. The goal is quality and originality of the essay, not its length.
Second written assignment. The subject of the second written assignment will be from a list provided by the instructor. Once a student has successfully claimed a topic, the instructor will make recommendations of relevant publications, and the student also is urged to use the NC State University library system to obtain relevant articles. It is recommended to read the relevant articles thoroughly and think about it so that the student can write the essay completely on his/her own words, not those of the cited authors. The minimum length is 3 pages, single-spaced, 12-point font. The target length is four pages. The report will be graded according to the following scoring table:
20% set the context with a good background section
20% answer the question and support your answer
20% use logic, and factual accuracy in explaining theory and experimental support
20% show how the focus question is related to practical results
20% spelling, grammar, and accurately follow the format
Class presentation: Class presentations, based on the same material as the second written
assignment, will be scheduled. Off-campus students can use their imagination in coming up with suitable ways to make a class presentation. The following methods have been used by off-campus students of this course in the past: PowerPoint digital presentation with narration text provided to the instructor to read; PowerPoint digital presentation with narration included in the file (this may be difficult, but not impossible to send by e-mail), hard-copy visuals and text, visuals and audio-cassette tape. The minimum length of the presentation is 15 minutes and the maximum is about 30.
Tests
Mid-term exam (one hour)
Grading System
Evaluation Method Weighting for Graduate
Course (%)
Assigned questions & class participation/email etc. 25
Online quizzes 15
First essay, a review of a recent scientific article 10
Second essay, addressing a challenge question 15
Oral presentation related to second essay topic 10
Mid-term test 25
All academic integrity rules are strictly enforced.
Grading Scale:
A+ 100.00-96.67
A 96.66-93.34
A- 93.33-90.00
B+ 89.00-86.67
B 86.66-83.34
B- 83.33-80.00
C+ 79.00-76.67
C 76.66-73.34
C- 73.33-70.00
D+ 69.00-66.67
D 66.66-63.34
D- 63.33-60.00
F
below
60
Instructor’s Policies on Incomplete Grades and Late Assignments
Points with a maximum value of 10% of the assignment will be deducted from assignments that are late by one week or less (relative to the due date as defined in the previous sentence, above). Points with a maximum value of 20% will be deducted from an assignment that is more than a week but less than two weeks late. Assignments more than two weeks late may be docked additional points at the discretion of the instructor. These penalties may be waived in cases where the student has obtained permission for the delay and has kept the instructor informed of progress on a consistent basis.
Distance-education students are strongly urged to stay “with the class” for the sake of class participation, the efficiency of the grade accounting system, and the efficient use of teaching resources. Limited exceptions can be made for bone-fide changes in life situation, including job relocations, extended medical conditions, or unexpected, extended travel, etc. Please contact the instructor right away if you believe that this applies to your case.
Instructor’s Policies on Absences and Scheduling Makeup Work
On-campus students are expected to attend all scheduled classes and any classes that are
rescheduled due to weather emergencies or other situations causing closure of the facilities.
Exceptions will be made in case of excused absences, such as illness, if documented by a note from the appropriate authority. Attendance policies are explained in more detail in the following
link: http://policies.ncsu.edu/regulation/reg-02-20-03
Course Prerequisites or Restrictive Statements
Students are expected to have graduate standing or permission of the instructor. Undergraduate students can be admitted to the course based on their record of strong academic performance.
Academic Integrity Statement
All academic integrity rules of the Department and University are strictly enforced. Students are encouraged to work together, if desired, when completing homework assignments and project work. No collaboration is permitted when completing quizzes, tests, and on-line quiz homework.
Please refer to NC State Student Code of Conduct policy in http://policies.ncsu.edu/policy/pol-11-35-01 and the definition of Academic Dishonesty: http://policies.ncsu.edu/policy/pol-11-35-01
A video prepared by Dr. Rojas with OIS on academic integrity as it applies to international
students can be found in the following link:
http://mediasite.online.ncsu.edu/online/Viewer/?peid=2fa0059a484c4f8caf30aafde20246ef1d
Students are expected to participate actively in classroom discussions and case studies. Distance students satisfy this requirement by means of their e-mail, phone, or FAX correspondence. There is no penalty for a wrong answer during class discussions. Students are expected to take initiative in making sure that they understand the material and ask questions when they do not. Questions about the material are welcome during class, during office hours, or at any time that the instructor is available in person or through e-mail.
NC State Policy on Working with Students with Disabilities
Students with disabilities are encouraged to schedule an appointment with Dr. Hubbe to discuss their accommodation needs. Please refer to http://policies.ncsu.edu/regulation/reg-04-20-06 for more information
Safety
There are no special safety requirements for this course, and there is no laboratory component.
Statement on “Pass-Through” Charges
There are no pass-through charges for this course.
Class Evaluations
Online class evaluations will be available for students to complete during the last two weeks of class. Students will receive an email message directing them to a website where they can login using their Unity ID and complete evaluations. All evaluations are confidential; instructors will never know how any one student responded to any question, and students will never know the ratings for any particular instructors.
Evaluation website: https://classeval.ncsu.edu; Student help desk: classeval@ncsu.edu;
More information about ClassEval: http://www2.acs.ncsu.edu/UPA/classeval/index.htm

COVID-19 INFORMATION
Due to the COVID-19 pandemic, public health measures continue to be implemented across campus. Students should stay current with these practices and expectations through the Protect the Pack website (https://www.ncsu.edu/coronavirus/). The sections below provide expectations and conduct related to COVID-19 issues.
Health and Participation in Class
We are most concerned about your health and the health of your classmates and instructors/TAs.
 If you test positive for COVID-19, or are told by a healthcare provider that you are
presumed positive for the virus, then you should not attend any face-to-face (F2F) classes
or face-to-face component of a hybrid class. Work with your instructor on any adjustments necessary; also follow other university guidelines, including self reporting (Coronavirus Self Reporting): Self-reporting is not only to help provide support to you, but also to assist in contact tracing for containing the spread of the virus.
 If you feel unwell, even if you have not been knowingly exposed to COVID-19, please do not come to a F2F class or activity.
 If you are in quarantine, have been notified that you may have been exposed to COVID-19, or have a personal or family situation related to COVID-19 that prevents you from attending this course in person (or synchronously), please connect with your instructor to make alternative plans, as necessary.
 If you need to make a request for an academic consideration related to COVID-19, such as a discussion about possible options for remote learning, please talk with your instructor.
Health and Well-Being Resources
These are difficult times, and academic and personal stress are natural results. Everyone is
encouraged to take care of themselves and their peers. If you need additional support, there are many resources on campus to help you:
 Counseling Center (NCSU Counseling Center)
 Student Health Services (Health Services | Student)
 If the personal behavior of a classmate concerns or worries you, either for the classmate’s well-being or yours, we encourage you to report this behavior to the NC State CARES team: (Share a Concern).
 If you or someone you know are experiencing food, housing or financial insecurity, please see the Pack Essentials Program (Pack Essentials).
Community Standards related to COVID-19
We are all responsible for protecting ourselves and our community. Please see the community standards and Rule 04.21.01 regarding Personal Safety Requirements Related to COVID-19 RUL 04.21.01 – Personal Safety Requirements Related to COVID-19 – Policies, Regulations & Rules
Course Expectations Related to COVID-19:
 Face Coverings: All members of the NC State academic community are expected to
follow all university policies and guidelines, including the Personal Safety Rule and
community standards, for the use of face coverings.
 Course Attendance: NC State attendance policies can be found at: REG 02.20.03 –
Attendance Regulations – Policies, Regulations & Rules. Please refer to the course’s
attendance, absence, and deadline policies for additional details. If you are quarantined or
otherwise need to miss class because you have been advised that you may have been
WPS 516 Page

To access LEGACY files, including critical review essays and essays based on challenge questions, you will need to go to separate FB 527 (Legacy Files) items on the menu (not this item).

FB 527 Course Syllabus

FB 527 – Wet End & Colloidal Chemistry

Section TBD

Spring 2019

3 Credit Hours

Special Notes

Moodle and streaming video based course primarily aimed at off-campus (paper industry) students, with availability also for on-campus students a assynchronous mode. There are 13 chapters, each of which has a corresponding “course-pack” text. The streaming video sessions have “lecture questions” to be completed by students during the viewing. Chapters 2 through 13 have final quizzes. Fourteen homework assignments draw upon fourteen selected texts (mainly review articles). Two essays are assigned: (a) a critical review; and (b) the student’s responses to a “challege question” from the instructor, usually on a topic related to their initial choice of an article to review.

Course Description

The primary purpose of this course is to prepare graduate-level students to solve problems and create product development innovations in the area of paper machine wet-end chemistry. One of the key foundations for this ability is a broad understanding of how finely divided suspended particles, fibers, monomers, and polymeric materials interact with each other, i.e. the subject of colloids. Another key foundation is the practical understanding of state-of-art strategies used by papermakers, i.e. wet-end chemistry.

Wet-end and colloidal chemistry is an inter-disciplinary field relating to the efficient operation of paper machines and the achievement of paper property objectives. A wet-end chemist has knowledge and skills that apply most specifically to papermaking, but also to other fields such as water and wastewater treating, wet-laid nonwovens manufacture, mining separations technology, and various unit operations in paper recycling. Because colloid chemical concepts are thoroughly integrated into the course, the student is prepared to deal with issues involving new materials, new chemical strategies, or new product goals. Some of the most critical process issues involve retention of fine materials, drainage, and the uniformity of the resulting paper. Some key paper property issues related to chemical use are absorbency (or “sizing”), optical properties, and strength.

Learning Outcomes

1. Prepare graduate-level students to solve wet-end chemical-related problems and to achieve paper product innovations with a rigorous knowledge base in the area of wet-end chemistry, with an emphasis on application of colloidal chemistry.

2. Provide opportunities for students to practice with problem sets and case studies and demonstrate their ability to use wet-end chemical principles.

Course Structure

All assignments are listed on the Moodle page

Course Policies

Students are free to “work ahead” and complete course requirements ahead of time.

Distance-education students can request schedule adjustments in order to accommodate their professional commitments. Please contact the instructor at your earlier convenience when this need arises.

It is requried that the all written content from students by freshly composed by them. In other words, if a student finds a “perfect answer” to a question in a published source, they have to paraphrase it in their own words.

“Lecture questions” are to be answered promptly, in the course of listening to a streaming lecture session. The goal of these questions is to encourage active engagement with the sessions. Therefore, polished answers or researched answers are not expected for the lecture questions.

Instructors

Course Meetings

None.

Course Materials

Textbooks

None.

Expenses

None.

Materials

None.

Requisites and Restrictions

Prerequisites

None.

Co-requisites

None.

Restrictions

None.

General Education Program (GEP) Information

GEP Category

This course does not fulfill a General Education Program category.

GEP Co-requisites

This course does not fulfill a General Education Program co-requisite.

Transportation

This course will not require students to provide their own transportation. Non-scheduled class time for field trips or out-of-class activities is NOT required for this class.

Safety & Risk Assumptions

None.

Grading

Grade Components

Component	Weight	Details
Online quizzes (twelve of them)	20	Students take a quiz after reading the coursepack text and listening and watching the lecture session. There are twelve quizzes in all, and they are administered through Moodle. In each case, the questions that a student sees are drawn randomly from a larger pool of questions.
Responses to lecture questions	20	The lecture questions are incorporated into the streaming video. The student is required to answer the question before the streaming will continue. The goal is to encourage engagement with the streaming content.
Homework essays	30	There are 14 homework assignments spaced out over the course session. In each case, students are asked to respond to their selection of a question from one or more options. In a few cases, all students are asked to address the same question. Minimum length is 100 words. Quality of the answer is emphasized over quantity. In each case, the student has at their disposal a review article to use as source material in putting together their answer to the selected question.
Critical review essay	15	The student selects a recent scientific article from an approved list (only one student per available article). They write a critical review, aiming to make it similar in format and style to a provided example. Grading is based on a rubric.
Essay in response to a challenge question	15	The student writes an essay in response to a challenge question from the instructor. Each question is uniqe. In most cases the question is related to the article that they selected for their critical review. The quesiton usually goes beyond anything that was explicitly discussed or concluded in the published literature, thus encouraging the student to speculate.

Letter Grades

This Course uses the Following (Non-Standard) Letter Grading Scale:

96.6667	≤	A+	≤	100
93.3334	≤	A	<	99.6666
99.0000	≤	A-	<	99.3333
86.6667	≤	B+	<	89.9999
83.3334	≤	B	<	86.6666
80.0000	≤	B-	<	83.3333
76.6667	≤	C+	<	79.9999
73.3334	≤	C	<	76.6666
70.0000	≤	C-	<	73.3333
66.6667	≤	D+	<	69.9999
63.3334	≤	D	<	66.6666
60.0000	≤	D-	<	63.3333
0	≤	F	<	59.9999

Requirements for Credit-Only (S/U) Grading

Requirements for Auditors (AU)

Information about and requirements for auditing a course can be found at http://policies.ncsu.edu/regulation/reg-02-20-04.

Policies on Incomplete Grades

Late Assignments

Unexcused late assigments, without prior notification of the instructor, will be subject to reduced credit.

One week: 5 percentage points.

More than one week: Ten percentage points

Attendance Policy

For complete attendance and excused absence policies, please see http://policies.ncsu.edu/regulation/reg-02-20-03

Attendance Policy

This is an assynchronous course. Students are expected to complete each assignment, but there is no such thing as attendance.

Absences Policy

Not applicable

Makeup Work Policy

Not applicable.

Additional Excuses Policy

Not applicable.

Academic Integrity

Students are required to comply with the university policy on academic integrity found in the Code of Student Conduct found at http://policies.ncsu.edu/policy/pol-11-35-01

All text provided by a student (in their essay assignments, in their homework, and in response to lecture questions) is expected to be their own original composition. Pasted content from published sources is not acceptable.

Academic Honesty

See http://policies.ncsu.edu/policy/pol-11-35-01 for a detailed explanation of academic honesty.

Honor Pledge

Your signature on any test or assignment indicates “I have neither given nor received unauthorized aid on this test or assignment.”

Electronically-Hosted Course Components

Electronically-hosted Components: Wolfpack Moodle

Accommodations for Disabilities

Reasonable accommodations will be made for students with verifiable disabilities. In order to take advantage of available accommodations, students must register with the Disability Services Office at Suite 2221, Student Health Center, Campus Box 7509, 919-515-7653. For more information on NC State’s policy on working with students with disabilities, please see the Academic Accommodations for Students with Disabilities Regulation (REG02.20.01) (https://policies.ncsu.edu/regulation/reg-02-20-01/).

Non-Discrimination Policy

Course Schedule

NOTE: The course schedule is subject to change.

First week — 01/07/2019 – 01/13/2019

Streaming video: Chapter 1, course introduction (one recording session)

Coursepack text: Chapter 1, course introduciton

Second Week — 01/14/2019 – 01/20/2019

Streaming video: Chapter 2, Papermaking process overview (two recording sessions)

Coursepack text: Chapter 2, Papermaking process overview

Quiz for chapter 2

Pass in first draft of critical review essay

Third Week — 01/21/2019 – 01/27/2019

Streaming video: Chapter 3, Papermaking materials: Fibers & fillers (three recording sessions)

Coursepack text: Chapter 3, Papermaking materials: Fibers & fillers

Quiz for chapter 3

Background text for first homework assignment: Manipulating of cellulosic colloidal behavior

First homework assignment

Fourth Week — 01/28/2019 – 02/03/2019

Streaming video: Chapter 4, Chemical additives (three recording sessions)

Coursepack text: Chapter 4, Chemical additives

Quiz for chapter 4

Background text for 2nd homework assignment: Dissolved & colloidal substances

Second homework assignment

Pass in final draft of critical review essay

Fifth Week — 02/04/2019 – 02/10/2019

Streaming video: Chapter 5, Interactions (three recording sessions)

Coursepack text: Chapter 5, Interactions

Quiz for chapter 5

Background text for 3rd homework assignment: Flocculation & redispersion

Third homework assignment

Sixth Week — 02/11/2019 – 02/17/2019

Streaming video: Chapter 6, Sizing & absorbancy (three recording sessions)

Coursepack text: Chapter 6, Sizing & absorbancy

Quiz for chapter 6

Background text for 4rd homework assignment: Paper’s resistance to wetting

Fouth homework assignment

Background text for 5th homework assignment: Bonding between cellulosic fibers

Fifth homework assignment

Seventh Week — 02/18/2019 – 02/24/2019

Streaming video: Chapter 7, Strength of paper (two recording sessions)

Coursepack text: Chapter 7, Strength of paper

Quiz for chapter 7

Background text for 6th homework assignment: Prospects for retaining strength of paper

Sixth homework assignment

Eighth Week — 02/25/2019 – 03/03/2019

Background text for 7th homework assignment: Paper’s appearance

Seventh homework assignment

Ninth Week — 03/11/2019 – 03/17/2019

Streaming video: Chapter 8, Paper’s appearance (two recording sessions)

Coursepack text: Chapter 8, Paper’s appearance

Quiz for chapter 8

Background text for 8th homework assignment: Fillers for papermaking

Eighth homework assignment

Tenth Week — 03/18/2019 – 03/24/2019

Streaming video: Chapter 9, Retention (two recording sessions)

Coursepack text: Chapter 9, Retention

Quiz for chapter 9

Background text for 9th homework assignment: Fillers for papermaking

Ninth homework assignment

Pass in first draft of your essay in response to a challenge question.

Eleventh Week — 03/25/2019 – 03/31/2019

Streaming video: Chapter 10, Drainage (two recording sessions)

Coursepack text: Chapter 10, Drainage

Quiz for chapter 10

Background text for 10th homework assignment: Fillers for papermaking

Tenth homework assignment

Twelfth Week — 04/01/2019 – 04/07/2019

Streaming video: Chapter 11, Uniformity (two recording sessions)

Coursepack text: Chapter 11, Uniformity

Quiz for chapter 11

Background text for 11th homework assignment: Wet-laid nonwovens manufacture

Eleventh homework assignment

Submit final version of your second essay in response to the challenge question

Thirteenth Week — 04/08/2019 – 04/14/2019

Streaming video: Chapter 12, Productivity (three recording sessions)

Coursepack text: Chapter 12, Productivity

Quiz for chapter 12

Background text for 12th homework assignment: Control of tacky deposits

Twelfth homework assignment

Fourteenth Week — 04/15/2019 – 04/21/2019

Streaming video: Chapter 13, Process control (two recording sessions)

Coursepack text: Chapter 13, Process control

Quiz for chapter 13

Background text for 13th homework assignment: Control of tacky deposits

Thirteenth homework assignment

Fifteenth Week — 04/22/2019 – 04/28/2019

Background text for 14th homework assignment: Accurate charge-related measurements

Fourteenth homework assignment

OUR LITERATURE REVIEWS

Spring 2009 Critical Reviews

“Alkaline rosin sizing using microparticulate aluminium-based retention aid systems in a fine paper stock containing CaCO3” by Hedborg F. and Lindström T., 1993 Nordic Pulp Paper Res.J. 8(3): 331. Reviewed by Olga Vdovina, 2009.

“The use of ozone as a biocide in paper machine recycled white water.” Susanna Korhonen and Tuula Tuhkanen. TAPPI Journal (2000). – Reviewed by Scott Ewers, Spring 2009

“The influence of colloidal interactions on fiber network strength”
by A. Elisabet Horvath and Tom Lindstrom, 2007 Journal of Colloid and Interface Science, 309. Reviewed by Scott Wagner, 2009.

Spring 2008 Critical Reviews

“Flocculation of Clay Particles with Poorly and Well-Dissolved Polyethylene Oxide” by D. Kratochvil, B. Alince, and T.G.M. Van De Ven, Journal of Pulp and Paper Science: Vol. 25 No. 9, September 1999; Reviewed by Justin Zoppe, 2008.

“Papermaking Technology Evolution: Its Impact on Wet-end Retention” by Juntai Liu, 2005, Paper Technology, 31; Reviewed by Kelley Spence, 2008

“Dendrimers: A New Retention Aid For Newsprint, Mechanical Printing Grades and Board.”
by Allen L., Polverari M., PARICAN, Ponite Claire, Canada; Reviewed by Ying Xue, 2008

“Transfer of Adsorbed Alum from Cellulosic Fibres to Clay Particles” by L. Odberg, P. Barla and G. Glad-Nordmark, 1995 Journal of Pulp and Paper Science, J250; Reviewed by Joscelin Diaz, 2008.

“On the mechanism of cationic-polyacrylamide-induced flocculation and re-dispersion of a pulp fiber dispersion”, Daniel Solberg, SCA Packaging Research, Sweden and Lars Wagberg, Royal Institute of Technology, Sweden, Nordic Pulp Paper Res. J. 18(1), 51 (2003); Reviewed by Maria Soledad Peresin, Spring 2008.

“Core shell: the latest innovation in polymer technology for the paper industry” by Alessandra Gerli, Sandra Berkhout and Xavier Cardoso, Paper Technology 44(2), 38-42 (2003); Reviewed by Hao Chen, Spring 2008.

“Polymer Transfer During Fines Detachment Under Turbulent Flow: Mechanism and Implications” by T. Asselman and G. Garnier, 2001 J Pulp Paper Sci., Vol. 27, No. 2, 60-65; Reviewed by Eugene F. Douglass, Spring 2008.

“A bridging model for the effects of a dual component flocculation system on the strength of fiber contacts in flocs of pulp fibers: Implications for control of paper uniformity”, by B.-U. Cho, G. Garnier, T.G.M. van de Ven, and M. Perrier; Colloids and Surfaces A: Physiochem. Eng Aspects 287 (2006) 117-125; Reviewed by Rachel Ernest, 2008.

“Competitive Absorption of Cationic Polyacrylamides with Different Charge Densities onto Polystyrene Latex, Cellulose Beads and Cellulose Fibres” by H. Tanaka, A. Swerin, L. Odberg and S. –B. Park, 1999 Journal of Pulp and Paper Science, 25; Reviewed by Magaly A. Ramírez Vicéns, 2008

“Aminated poly – N – vinyl formamide as modern retention aid of alkaline paper sizing with acid rosin sizes,” by Fei Wang and Hiroo Tanaka, Department of Forest Products, Faculty of Agriculture, Kyushu University, Fukuoka 812-8581, Japan, J. Applied Polymer Sci. 78, 1805-1810 (2000); Reviewed by V. Vivek, Spring 2008.

“Polyacrylamide as a Filler Retention Aid for Bagasse Paper Pulp” by Ibrahem, A. A., Nada, A. M. A., El-Saied, H., and El-Ashmawy, A.E. (2005).Ang. Makromol. Chem. 127, 89; Reviewed Xiaomeng Liu, Jan. 22, 2008.

“A Model Colloid for Flocculant Testing” by R. Cong, T. Smith-Palmer, and R. Pelton, J. Pulp Paper Sci. 27 (11), 2001; Reviewed by Douyong Min, 2008

“Retention Aid Chemicals for High Speed Paper Machines” by Y. Kamijo and T. Miyanishi, 2002 Japan Tappi Journal 56(6), 110-119; Reviewed by Takashi Yamaguchi, 2008.

“Adding Retention aid before filler addition – retention, water removal and formation” by K. Ryösö, Paper Technology, 42(8), 52-55; Reviewed by Charles W. Gordon, 2008

Spring 2007 Critical Reviews

“Competitive Adsorption of Alkyl Ketene Dimer (AKD) on Pulp Fibers and CaCO3 Fillers” by Petteri Voutilainen, Department of Paper Chemistry, Abo Akademi Univ., Turku, Finland; Reviewed by Sameerkumar Patel, Spring 2007

“On the mechanism of cationic-polyacrylamide-induced flocculation and re-dispersion of a pulp fiber dispersion” by Daniel Solberg, Nordic Pulp and Paper Research Journal, Vol. 18, No. 1/2003; Reviewed by Norris Pike, 2007.

“Nanoparticulars on Colloidal Retention” by Carr. D, Proc. Wet End Chemistry Conf. Boston, MA, PIRA International, Letherhead, UK 2005, Reviewed by Anthony Atamimi, 2007

“Modern Approach for Precise Sizing Measurement” by Shawn Hickey, Sylvain Renaud and Wolfgang Falkenberg, BTG Americas Inc Norcross, GA 30071; Reviewed by Ning Wu, 2007

“Practical experiences in Additive Screening Using a Torque-based Flocculation Analyzer” by: Anker, L. S. Proc. TAPPI 2001 Paper makers conf., TAPPI Press, Atlanta 2001; Reviewed by Ronalds W. Gonzalez, Spring 2007.

“On the Mechanism behind Wet Strength Development in Papers Containing Wet Strength Resins”
by L. Wågberg and M. Björklund, SCA Research AB, Sundsvall, Sweden; Reviewed by Ilari Filpponen
January 2007

“Filler Flocculation Technology – Increasing Sheet Filter Content Without Loss in Strength or Runnability Parameters” by S. Mabee, Industrial Technologist, Technical Service Department and R. Harvey, Consultant, Grain Processing Corporation, Muscatine, Iowa, 2000 Papermakers Conference Proceedings; Reviewed by Lu Athnos, 2007

“The Mechanism of Polyvinylamine Wet-Strengthening” by John-Louis Diflavio, Robert Bertoia, Robert Pelton and Marc Leduc, 13th Fundamental Research Symposium, Cambridge, UK, Para International, Leatherhead, UK, September 2005; Reviewed by Max F. Farmer, Jr., Spring 2007

Spring 2006 Critical Reviews

“Activity Predictions for Single Wire Machines for Various Frequencies”
by V. Wildfong and D. Bousfield, TAPPI 2004 Spring Technical Conference, TAPPI Press, Atlanta, 2004; Reviewed by James Ronning, January 2006

“Benefits of Cationic Ground Calcium Carbonate” by Loreen Goodwin, Tappi J. 72 (8):109-112 (1989); Reviewed by Irma Sofia Contreras Sulbaran, 2006.

“Influence of Alkalinity and pH Stability on Wet End Chemistry” by Molin, U., and Puutonen, P., Proc. Wet End Chemistry, Nice, France, May 11-12, 2004, Pira International, Leatherhead, UK.; Reviewed by: Sanjay Chakravarty, 2006

“Real Time Assessment of Microbial Activity in Paper Coatings and Additives”
by S.Ramesh and R. Banks, 2002 TAPPI Paper Summit; Reviewed by Keiko Fujita, 2006

“Establishing a comprehensive stickies treatment Programs by utilising the Kemira Organic Deposit Test (KODT)”
by T. Miller, C. Campbell, K. Curham and M. Nelson, 2004 TAPPI Spring Technical Conference; Reviewed by Enrique Yago, January 2006.

“Effect of Cationic Polymers, Salts and Fibers on the Stability of Model Micro-Stickies”
by X. Huo, R.A. Venditti and H.-M. Chang, J. Pulp Paper Sci. 27(6): 207-212 (2001); Reviewed by Kristin Koenig, January 2006

“Alkyl ketene dimer sizing efficiency and reversion in calcium carbonate filled papers”
by William J. Bartz, Michael E. Darroch, and Frederick L. Kurrle, Tappi J. 77(12): 139 (1994); Reviewed by: Wendy McKinnon, 2006

“Analysis and Retention Behavior of Cationic and Amphoteric Starches on Handsheets”
By J. YOSHIZAWA, A. ISOGAI and F. ONABE, J. Pulp Paper Sci.24(7): 213-218 (1998); Reviewed by Gang Hu, January 2006

“Stability and deposition tendency of colloidal wood resin” by Anna-Liisa Sihvonen, Kenneth Sundberg, Anna Sundberg and Bjarne Holmbom Nordic Pulp Paper Res. J. 13(1): 64 (1998).

“Shear strength in papermaking suspensions flocculated by retention aid systems”
By Swerin, A., Risinger, G., and Ödberg, L., Nordic Pulp Paper Res. J. 11 (1): 30-35 (1996); Reviewed by Jun-Young Cho, 2006

Fall 2004 Critical Reviews

“Effects of system closure on retention aids for SC-grade manufacture”
by Polverary, M., Sitholé, B., and Allen, L.H., TAPPI J. 3(7):32(2004). Reviewed by Carlos Garcia, November 9, 2004

“The Buildup of Dissolved Solids in Closed White Water Systems”
by Yufeng Xu, Yulin Deng, Tappi Journal (2004), 3(8), 17-21.Reviewed by Junlong Song, November 2004

“Vinylformamide – Based Cationic Polymers as Retention Aid in Alkaline Papermaking”
by Wang, F., Kitaoka, T., and Tanaka, H., Tappi J. 2 (12): 21 (2003). Reviewed by Yun Wang, Nov., 2004
“Automatic Control of Additives with Modern Online Measurement Technology Raises Papermaker Productivity,”
by R. Berger, D. Watzig, H. Ziegler and M. Fasth,
2004 TAPPI Spring Technical Conference;
Reviewed by Lambrini Adamopoulos, November, 2004
“Advanced wet-end System with Carboxymethyl-cellulose”
by Watanabe, M.; Gondo, T.; Kitao, O., TAPPI Journal, May 2004. Reviewed by Robert Bunzey, November 2004

Fall 2003 Critical Reviews
“Prediction and optimization of sizing response using adaptive machine learning and integrated management of wet-end chemistry” by Michael T. Plouff, TAPPI Summit 2002, paper 11-3. Reviewed by: Zhoujian Hu, November 10, 2003
“A Superior New Approach to Paper Contaminant Control,” by Charles D. Angle, TAPPI Summit 2002, paper 23-4; Reviewed by Jeff Wallace, November 11, 2003
“Industrial Refining of Unbleached Kraft Pulp-The Effect of pH and Refining Intensity” by Ulla-Britt Mohlin; Reviewed by Neeraj Sharma, November 11, 2003

“The Use of Synthetic Polymers to Enhance Sheet Strength And Improve Machine Efficiency” by Darren K. Swales and Richard Zemke, TAPPI Paper Summit 2002; Reviewed by Chang Woo Jeong
November 11, 2003.

“Characterizing Refining Action in PFI Mills”, by Kerekes, R.J., TAPPI Paper Summit 2002; Reiewed by: Kathy M. Austin, November 11, 2003

“Indicators for Forecasting Pitch Season”, by Blazey, M. A., Grimsley, A., and Chen, G.C., TAPPI Summit 2002, paper 23-2; Reviewed by Jeff McKee,
November 2003

Fall 2002 Critical Reviews

“Applying Automatic Chemical Control from Stock Prep to the Machine” by Sylvain Renaud, Teresa Burke, and Roland Berger, 2002 TAPPI Paper Summit. Reviewed by Sa Yong Lee, November 7, 2002

“Characterizing Refining Action in PFI Mills” by R.J. Kerekes, Tappi Paper Summit 2002. Reviewed by Jung Myoung LEE, November 10, 2002

“Retention of Fibers, Fillers and Fiber Fines at Individual Dewatering Elements of Gap Former” by M. Kosonen, J. Muhonen and J. S. Kinnunen, TAPPI Summit 2002, paper 35-1. Reviewed by Yong Sik Kim
November 12, 2002.

“A New Analysis of Filler Effects on Paper Strength” by Linda Li, Robert Pelton and Andrea Collis, TAPPI Paper Summit 2002. Reviewed by Qirong Fu,
November 15, 2002.

“Optimized Deaeration Leads to Substantial Process and Quality Improvements in Paper Manufacturing” by R. Rauch and T. Burke, TAPPI Summit 2002, paper 11-4. Reviewed by Chris Dozier, November 22, 2002.

“Deposition Synergy between Mechanical and Deinked Pulps,” by Lawrence H. Allen, TAPPI Paper Summit 2002, paper 23-1, Reviewed by Troy Watkins
November 18th, 2002

“Furnish Compatibility and Efficacy of Oxidizing Slimicides,” by Sweeny, P., and Ludensky, M., 2001 Papermakers Conf., Reviewed by Steven A. Fisher
Dec. 2, 2002

“Novel Biocide Provides Effective Microbiological Control Without Adversely Affecting The Papermaking Process” by C. K. Davis and G. Casini, TAPPI Summit 2002. Reviewed by Kevin Copeland,
December, 2002.

“A Superior New Approach to Paper Machine Contaminant Control” by Charles D. Angle, 2002 TAPPI Paper Summit. Reviewed by Marc Azzi,
December, 2002.

“PCC Application Strategies to Improve Papermaking Profitability. Part I. Thick Stock Precipitated Calcium Carbonate Addition,” by T. M Haller et al., (2001 Papermakers Conf.) Reviewed by Daniel Duarte, January 14, 2003

Fall 2001 Critical Reviews

“Investigations of the Flocculation Behavior of Microparticle Retention Systems” by Erich Gruber and Peter Muller, Proc. TAPPI 2001 Engineering and Papermakers Conference. Reviewed by Tim Schleining, November 2001.

“Starch-Related Operational Problems at the Size Press” by Steven Abell and Terence L. Knowles, Proc. TAPPI 2001 Engineering and Papermakers Conference. Reviewed by Ting-Feng Yeh, 2001.

“Monitoring Flocculation of Newsprint in the Laboratory and on a Paper Machine” by Keiser, B. A., and Govoni, S. T., Tappi 2001 Papermakers Conf. Reviewed by Taweewat Tripattharanan, November, 2001.

“Process Optimization at a Newsprint Mill by Continuous Charge Measurement in Thick Stock” by J. Nikkinen and L. Bley, Proc. TAPPI 2001Engineering and Papermakers Conf. Reviewed by Juan Bastidas, November 2001.

“Effects of System Closure on Retention and Drainage Aid Performance in TMP Newsprint Manufacture, Part II” by M. Polverari, L. Allen, and B. Sithole, 2001 Papermakers Conference, Reviewed by Jason Persinger, November 2001

“New Cationic Polymers for Enhanced Runnability and Paper Quality in Closed Water Systems” by A. Moormann-Schmitz and A. Esser, Proc. TAPPI 2001 Papermakers Conf. Reviewed by Julie Cheng, December, 2001.

“Controlled Filler Preflocculation – Improved Formation, Strength and Machine Performance” by S.W. Mabee, Proc. TAPPI 2001 Engineering and Papermaker’s Conf. Reviewed by Mathias Lindstrom, Dec. 2001 .

“Effect of a Wet-End Additive on the Components of Formation of Tissue” by Jean-Philippe Bernie and W.J. Murray Douglas; Reviewed by Robert Lowe, Dec. 6, 2001.

“Potential Application of Predictive Tensile Strength Models in Paper Manufacturing: Part I – Development of a Predictive Tensile Strength Model from the Page Equation” by Garg, P. and Scott, W.E. Paper Science and Engineering Department, Miami University, Reviewed by Betsy Whitley, 2001.

“Potential Application of Predictive Tensile Strength Models in Paper Manufacture: Part II – Integration of a Tensile Strength Model with a Dynamic Paper Machine Material Balance Simulation,” W. Scott, Proc. TAPPI 2001 Papermakers Conf.; Reviewed by Jay Scott, Dec. 2001.

“The Effect of Molecular Weight on the Performance of Paper Strength Enhancing Polymers,” Zhang, J., Pelton, R., Wagberg, L., and Rundlof, M., “The Effect of Molecular Weight on the Performance of Paper Strength Enhancing Polymers,” 2001; Martina Hakansson, November 17, 2001

“Dynamic Drainage Measurement – A Quick, Expressive, and Automated Method” by L. Bley and W. Falkenberg, 2001 Papermakers Conference. Reviewed by Mason Mead, 2001

“The Effects of Base Sheet Properties and Wet-End Chemistry on Surface Sized Paper” by Francis Aloi, Ralph M. Trksak, and Victor Mackewicz. 2001 Papermakers Conference. Reviewed by Robert Cheatham, December 1, 2001.

“Troubleshooting ‘Slimy’ Paper Machine Deposits,” by M. A. Blazey, S. A. Grelmsley, and G. C. Chen, Proc. TAPPI 2001 Engineering and Papermakers Conference. Reviewed by Evan Hafla, January 2002.

Fall 2000 Critical Reviews

“Alkyl ketene dimer sizing efficiency and reversion in calcium carbonate filled papers” by William J. Bartz, Michael E. Darroch, and Frederick L. Kurrle, Tappi J. 77 (12): 139 (1994). Reviewed by Neal Dressler, Nov. 16, 2000.

“Some Factors Affecting Desorption of Silicate in the White Water System of a Paper Machine” by Saastamoinen, S., Neimo, L., and Paulapuro, H., Paperi Puu 77 (3): 127 (1995). Reviewed by Kati Kautonen, November, 2000

“The effect of temperature, pH and alkalinity on ASA sizing in alkaline papermaking” by Raija M. Savolainen, proc. 1996 Paper Conference 289. Reviewed by Tien-wang Wu, November 18, 2000.

“The Relationship Between Single Fiber Contact Angle and Sizing Performance” by Krueger, Jeffrey, J., and Hodgson, Kevin, T., Tappi Journal 78(2): 154(1995). Reviewed by Fred Humphreys, November 10, 2000.

“Effect of Pulping Liquor on Drainage Aid Performance with Recycled Fiber” by T.H. Wegner, Tappi Press, 1990, Recycling Paper, from Fiber to Finished Product, Vol 1, 185. Reviewed by Diana Carroll, November, 2000.

“Size Reversion In Alkaline Paper-Making”, by Robert Novak and Dominic Rende, Proc. TAPPI 1993 Papermakers Conference, 437; Reviewed by Cameron Morris, Dec. 2000

“Interactions of Alkyl Ketene Dimer with Other Wet-end Additives,” by A. R. Colasurdo and I. Thorn, Tappi Journal 75 (9): 143 – 149 (1992); Reviewed by Rita Edwards November 29, 2000

“Evaluation of Cationic Debonding Agents in Recycled Paper Feedstocks” by C. Poffenberger and N. Jenny 1996 Recycling Symposium, 289. Reviewed by Maxine Klass-Hoffman, 2000.

“Cationic Polystyrene-based Paper Sizing Agents”, by Hiroshi Ono and Yulin Deng, Proc. TAPPI 1997 Engineering & Papermakers Conference, P837-849; Reviewed by Shunju Xiong, December 8, 2000

“The Influence on Paper Strength of Dissolved and Colloidal Substances in the White Water” by T. Lindstrom, C. Soremark and L. Westman, Svensk Papperstidning 80 (11): 341 (1977); Reviewed by Wes Giles, Fall 2000.

“Transfer of Cationic Retention Aid from Fibers to Fine Particles and Cleavage of Polymer Chains Under Wet-End Papermaking Conditions,” by Tanaka, H., Swerin, A., and Odberg, L., Tappi J. 76 (5): 157 (1993); Reviewed by Ryan Tomasiewicz, Fall 2000.

“Use of a Fixative in Combination with Cationic Starch in Peroxide-Bleached TMP” by V. Bobacka, Journal of Pulp and Paper Science 25 (3): 100-103 (1999); Reviewed by Melanie Gray-Walker, December 9, 2000.

“The Effect of Contact Time Between Cationic Polymers and Furnish on Retention and Drainage”, by S. Forsberg and G. Strom; Journal of Pulp and Paper Science: Vol. 20 (3) March 1994. Reviewed by Kelli Farmer, November 10, 2000

“Performance of Wet-End Cationic Starches in Maintaining Good Sizing at High Conductivity Levels in Alkaline Fine Paper,” by Beaudoin, R. Gratton and R.Turcotte J. Pulp Paper Sci. 21 (7): J2388 (1995) Reviewed by Will Smith, Fall 2000.

“Influence of Dissolved Ions on Alum Cationicity Under Alkaline Papermaking Conditions” by C. E. Farley, TAPPI J. 75 (11): 193 (1992). Reviewed by Carrie M. Johnson, December 2000.

“Enhanced Flocculation and Dispersion of Colloidal Suspensions through Manipulations of Polymer Conformation” by P. Somasundaran, T. V. Vasudevan, and K. F. Tjipangandjara, Dispersion Aggregation, Proc. Eng. Found. Conf.1992, 403-418. Reviewed by Susan D. Stewart, 10 December 2000.

“Practical Aspects of Alkaline Sizing: Alkyl Ketene Dimer in Mill Furnishes” by Marton J., Tappi J. 74 (8): 187 (1991), Reviewed by Gaurav K. Agarwal, December 2nd, 2000.

“The Use of Britt Jar Retention-RPM Curves and Microscopic Analysis to Determine the Aggregation State of a Papermaking Furnish” by Li, H.M. and Scott, W.E.; 2000 TAPPI Papermakers Conference and Trade Fair, Tappi Proceedings 733-755. Reviewed by: Gaurav K. Agarwal, December 13, 2000.

“The Effect of C14-labelled Cationic and Native Starches on Dry Strength and Formation” by J. C. Roberts, C. O. Au, and G. A. Clay, Tappi J. 69 (10): 88, 1986. Review by Tricia Hughes, December 14, 2000.

“Adsorption of Cationic Starches on Microcrystalline Cellulose“, by Van de Steeg, H. G. M., De Keizer, A., Cohen Stuart, M. A., and Bijsterbosch, B. H., Nordic Pulp Paper Res. J. 8 (1): 34 (1993); Reviewed by Wendy F. Hendricks, December 2000

“The Role of Polymers in AKD Sizing”, by Catherine Cooper, Peter Dart, John Nicholass and Ian Thorn, PAPER TECHNOL. 36 (4): 30 (1995). Reviewed by Takao Sezaki, December 2000.

“Micromechanics: A new approach to Studying the Strength and Breakup of Flocs” by K.C. Yueng and Robert Pelton. Journal of Colloid and Interface Science 184, 579-585 (1996). Reviewed by J. Dagnall on December 21,2000.

“Competitive Adsorption of Alkyl Ketene Dimer (AKD) on Pulp Fibers and CaCO3 Fillers” by Petteri Voutilainen, proc. 1996 International Paper and Coating Chemistry Symposium pp.195-204. Reviewed by James K. Lim, Decemeber 20, 2000

“Dryer Section Passivation: A Novel and Effective Method of Preventing Dryer Section Deposition and Linting,” by Thord Hassler (Hercules Incorporated) and Hiroshi Sokiya (Mainteeb Co.), Proc. 2000 TAAPI Papermakers Conference and Trade Fair. Reviewed by Abbas Alagheband, January, 2001.

Fall 1999 Critical Reviews

“On-Line Charge Monitoring – A Wet End Strategy” by L. Bley and E. Winter, Proc. TAPPI 1997 Engineering and Papermakers Conf., 297. Reviewed by Jill Scherrer

“Wet-End Optimization for a Neutral PCC-Filled Newsprint Machine”, by Takanori Miyanishi Tappi J. 82 (1): 220, 1999. Reviewed by Judy Delaney, November 5, 1999

“Interactions between Cationic Starch and Anionic Trash of a Peroxide-Bleached TMP at Different Salt Concentrations” by V. Bobacka, J. Nasman, and D. Eklund, J. Pulp Paper Sci. 24 (3): 78 (1998). Reviewed by Edmund A. Pozniak Jr. November 6, 1999

“On the Mechanism Behind Wet Strength Development in Papers Containing Wet Strength Resins,” Lars Wagberg and Mirjam Bjorklund, SCA Research AB, Sundsvall, Sweden, Wagberg, Nordic Pulp and Paper Research Journal (1): 53 (1993), Reviewed by Matt Gregersen, November 8, 1999.

“Prevention of pitch and stickies deposition on paper forming wires via adsorption of cationic polymer associated with anionic species,” by D. Y. Nguyen and D. D. Dreisbach, Proc. TAPPI 1996 Papermakers Conf., 511.
Two students prepared review of this article.
CLICK HERE for a review by Sandra Beder-Miller, November 4, 1999
CLICK HERE for a review by Steve Henry, November 26, 1999.

“Alkaline Rosin Sizing Using Microparticulate Aluminium Based Retention Aid Systems in a Fine Paper Stock Containing Calcium Carbonate” by Fritz Hedborg and Tom Lindstrom, Nordic Pulp and Paper Research Journal 8 (3): 331 (1993). Reviewed by Pankaj Kaprwan, Nov. 30, 1999.

“Formation Improvements with Water Soluble Micropolymer Systems” by Honig, D. S., Harris, E. W., Pawlowska, L. M., O’Toole, M. P., and Jackson, L. A., Tappi J. 76 (9): 135 (1993). Reviewed by David Szurley, Nov. 2, 1999.

“The Analysis and Chemistry of Aluminum Based Paper Machine Deposits” by Frederick S. Potter, Proc. TAPPI 1996 Papermakers Conf., 315. Reviewed by Tim Dumm – UPM Blandin Paper, November 15, 1999“

“A New Approach to Wet End Drainage / Retention / Formation Technology,” by Vaughan, C. W., Proc. TAPPI 1996 Papermakers Conf., 439. Reviewed by Julie Dellemann, January, 2000.

SPRING 2001

“Transfer of Adsorbed Alum from Cellulosic Fibres to Clay Particles” by L. Odberg, P. Barla, and G. Glad-Nordmark, Journal of Pulp and Paper Science, Vol. 21 No. 7, 1995. Reviewed by Kyle Yarbrough, April, 2001

“Strategies to Reduce AKD Deposits on Paper Machines” by T. Ahlskog, A.J. Juppo, and L. Petander, Paperi Puu 80 (2): 100, 1998. Reviewed by Zachary Guy, May 2, 2001

FB 572 LEGACY FILES “OUR LITERATURE REVIEWS”

Spring 2009 Critical Reviews

“The use of ozone as a biocide in paper machine recycled white water.” Susanna Korhonen and Tuula Tuhkanen. TAPPI Journal (2000). – Reviewed by Scott Ewers, Spring 2009

Spring 2008 Critical Reviews

“Papermaking Technology Evolution: Its Impact on Wet-end Retention” by Juntai Liu, 2005, Paper Technology, 31; Reviewed by Kelley Spence, 2008

“Dendrimers: A New Retention Aid For Newsprint, Mechanical Printing Grades and Board.”
by Allen L., Polverari M., PARICAN, Ponite Claire, Canada; Reviewed by Ying Xue, 2008

“A Model Colloid for Flocculant Testing” by R. Cong, T. Smith-Palmer, and R. Pelton, J. Pulp Paper Sci. 27 (11), 2001; Reviewed by Douyong Min, 2008

“Retention Aid Chemicals for High Speed Paper Machines” by Y. Kamijo and T. Miyanishi, 2002 Japan Tappi Journal 56(6), 110-119; Reviewed by Takashi Yamaguchi, 2008.

“Adding Retention aid before filler addition – retention, water removal and formation” by K. Ryösö, Paper Technology, 42(8), 52-55; Reviewed by Charles W. Gordon, 2008

Spring 2007 Critical Reviews

“Nanoparticulars on Colloidal Retention” by Carr. D, Proc. Wet End Chemistry Conf. Boston, MA, PIRA International, Letherhead, UK 2005, Reviewed by Anthony Atamimi, 2007

“Modern Approach for Precise Sizing Measurement” by Shawn Hickey, Sylvain Renaud and Wolfgang Falkenberg, BTG Americas Inc Norcross, GA 30071; Reviewed by Ning Wu, 2007

Spring 2006 Critical Reviews

“Benefits of Cationic Ground Calcium Carbonate” by Loreen Goodwin, Tappi J. 72 (8):109-112 (1989); Reviewed by Irma Sofia Contreras Sulbaran, 2006.

“Real Time Assessment of Microbial Activity in Paper Coatings and Additives”
by S.Ramesh and R. Banks, 2002 TAPPI Paper Summit; Reviewed by Keiko Fujita, 2006

Fall 2004 Critical Reviews

“Effects of system closure on retention aids for SC-grade manufacture”
by Polverary, M., Sitholé, B., and Allen, L.H., TAPPI J. 3(7):32(2004). Reviewed by Carlos Garcia, November 9, 2004

“The Buildup of Dissolved Solids in Closed White Water Systems”
by Yufeng Xu, Yulin Deng, Tappi Journal (2004), 3(8), 17-21.Reviewed by Junlong Song, November 2004

“Characterizing Refining Action in PFI Mills”, by Kerekes, R.J., TAPPI Paper Summit 2002; Reiewed by: Kathy M. Austin, November 11, 2003

“Indicators for Forecasting Pitch Season”, by Blazey, M. A., Grimsley, A., and Chen, G.C., TAPPI Summit 2002, paper 23-2; Reviewed by Jeff McKee,
November 2003

Fall 2002 Critical Reviews

“Applying Automatic Chemical Control from Stock Prep to the Machine” by Sylvain Renaud, Teresa Burke, and Roland Berger, 2002 TAPPI Paper Summit. Reviewed by Sa Yong Lee, November 7, 2002

“Characterizing Refining Action in PFI Mills” by R.J. Kerekes, Tappi Paper Summit 2002. Reviewed by Jung Myoung LEE, November 10, 2002

“Retention of Fibers, Fillers and Fiber Fines at Individual Dewatering Elements of Gap Former“ by M. Kosonen, J. Muhonen and J. S. Kinnunen, TAPPI Summit 2002, paper 35-1. Reviewed by Yong Sik Kim
November 12, 2002.

“A New Analysis of Filler Effects on Paper Strength” by Linda Li, Robert Pelton and Andrea Collis, TAPPI Paper Summit 2002. Reviewed by Qirong Fu,
November 15, 2002.

“Deposition Synergy between Mechanical and Deinked Pulps,” by Lawrence H. Allen, TAPPI Paper Summit 2002, paper 23-1, Reviewed by Troy Watkins
November 18th, 2002

“Furnish Compatibility and Efficacy of Oxidizing Slimicides,” by Sweeny, P., and Ludensky, M., 2001 Papermakers Conf., Reviewed by Steven A. Fisher
Dec. 2, 2002

“A Superior New Approach to Paper Machine Contaminant Control” by Charles D. Angle, 2002 TAPPI Paper Summit. Reviewed by Marc Azzi,
December, 2002.

Fall 2001 Critical Reviews

“Starch-Related Operational Problems at the Size Press” by Steven Abell and Terence L. Knowles, Proc. TAPPI 2001 Engineering and Papermakers Conference. Reviewed by Ting-Feng Yeh, 2001.

“Effect of a Wet-End Additive on the Components of Formation of Tissue” by Jean-Philippe Bernie and W.J. Murray Douglas; Reviewed by Robert Lowe, Dec. 6, 2001.

“Dynamic Drainage Measurement – A Quick, Expressive, and Automated Method” by L. Bley and W. Falkenberg, 2001 Papermakers Conference. Reviewed by Mason Mead, 2001

“The Effects of Base Sheet Properties and Wet-End Chemistry on Surface Sized Paper“ by Francis Aloi, Ralph M. Trksak, and Victor Mackewicz. 2001 Papermakers Conference. Reviewed by Robert Cheatham, December 1, 2001.

Fall 2000 Critical Reviews

“The effect of temperature, pH and alkalinity on ASA sizing in alkaline papermaking” by Raija M. Savolainen, proc. 1996 Paper Conference 289. Reviewed by Tien-wang Wu, November 18, 2000.

“Size Reversion In Alkaline Paper-Making”, by Robert Novak and Dominic Rende, Proc. TAPPI 1993 Papermakers Conference, 437; Reviewed by Cameron Morris, Dec. 2000

“Interactions of Alkyl Ketene Dimer with Other Wet-end Additives,” by A. R. Colasurdo and I. Thorn, Tappi Journal 75 (9): 143 – 149 (1992); Reviewed by Rita Edwards November 29, 2000

“Evaluation of Cationic Debonding Agents in Recycled Paper Feedstocks” by C. Poffenberger and N. Jenny 1996 Recycling Symposium, 289. Reviewed by Maxine Klass-Hoffman, 2000.

“Cationic Polystyrene-based Paper Sizing Agents”, by Hiroshi Ono and Yulin Deng, Proc. TAPPI 1997 Engineering & Papermakers Conference, P837-849; Reviewed by Shunju Xiong, December 8, 2000

“Influence of Dissolved Ions on Alum Cationicity Under Alkaline Papermaking Conditions” by C. E. Farley, TAPPI J. 75 (11): 193 (1992). Reviewed by Carrie M. Johnson, December 2000.

“Practical Aspects of Alkaline Sizing: Alkyl Ketene Dimer in Mill Furnishes” by Marton J., Tappi J. 74 (8): 187 (1991), Reviewed by Gaurav K. Agarwal, December 2nd, 2000.

“Adsorption of Cationic Starches on Microcrystalline Cellulose”, by Van de Steeg, H. G. M., De Keizer, A., Cohen Stuart, M. A., and Bijsterbosch, B. H., Nordic Pulp Paper Res. J. 8 (1): 34 (1993); Reviewed by Wendy F. Hendricks, December 2000

“The Role of Polymers in AKD Sizing”, by Catherine Cooper, Peter Dart, John Nicholass and Ian Thorn, PAPER TECHNOL. 36 (4): 30 (1995). Reviewed by Takao Sezaki, December 2000.

Fall 1999 Critical Reviews

“On-Line Charge Monitoring – A Wet End Strategy” by L. Bley and E. Winter, Proc. TAPPI 1997 Engineering and Papermakers Conf., 297. Reviewed by Jill Scherrer

“Wet-End Optimization for a Neutral PCC-Filled Newsprint Machine”, by Takanori Miyanishi Tappi J. 82 (1): 220, 1999. Reviewed by Judy Delaney, November 5, 1999

“Prevention of pitch and stickies deposition on paper forming wires via adsorption of cationic polymer associated with anionic species,” by D. Y. Nguyen and D. D. Dreisbach, Proc. TAPPI 1996 Papermakers Conf., 511.
Two students prepared review of this article.
Review by Sandra Beder-Miller, November 4, 1999
Review by Steve Henry, November 26, 1999.

“A New Approach to Wet End Drainage / Retention / Formation Technology,” by Vaughan, C. W., Proc. TAPPI 1996 Papermakers Conf., 439. Reviewed by Julie Dellemann, January, 2000.

SPRING 2001

“Strategies to Reduce AKD Deposits on Paper Machines” by T. Ahlskog, A.J. Juppo, and L. Petander, Paperi Puu 80 (2): 100, 1998. Reviewed by Zachary Guy, May 2, 2001

Introduction

In this article the authors try to make an analysis of the influence of different parameters and achieve optimum conditions for alkaline rosin sizing. During the experimental work the authors discovered several conditions that influence the quality of alkaline rosin sizing. On the other hand the article appears incomplete and leaves the reader with a series of questions. Besides, in this article only one side of the topic was discerned – the influence of different conditions on alkaline rosin sizing, whereas another side of this question, the influence of the same conditions on the retention, was not discerned, and the authors devoted only a few sentences in consideration of the contradictory influence of the same parameters.

Background

In recent years neutral and alkaline papermaking have received considerable attention, especially for the manufacture of uncoated wood-free printing papers containing calcium carbonate, coated papers, and board. At the same time commercial practice has shown that dispersion sizes are easier to apply and more suited for neutral or alkaline sizing conditions. However, the application of a traditional alum/rosin sizing system under these conditions is not practical, due to the fact that the aluminium-resinate complex becomes anionic at pH values exceeding 6.5. These sizing agents become more difficult to retain on the negatively charged fibres under neutral or alkaline conditions. Other explanations for decreasing of sizing quality at high pH values also exist. One way to solve this problem is by using the rosin sizing in combination with a cationic starch and aluminium hydroxide retention aid system under neutral or alkaline sizing conditions. Increasing interest to alkaline rosin sizing may also be connected with the possibility of adding certain desired properties to the paper product.

Discussion

In this experimental work polyaluminium chloride and NaOH+Al2(SO4)3 retention aid systems were used and compared with each other. The peculiarity of this article is that it contains experimental data having a nature that prompts the reader to think about underlying reasons to explain the observed behaviour of system. But these experimental data are insufficient to answer the questions that arise. For instance, the authors write about the effect of aluminium addition on the degree of sizing and say that quality of sizing increases with increasing addition of aluminium, and that polyaluminium chloride works better than the NaOH+Al2(SO4)3 system. These results leave the reader questioning why this is so. Moreover, the range of results for aluminium addition given on figures is narrow. Thus the article does not help one to understand how a further increase in aluminum addition might change the quality of sizing, especially in the case of the NaOH+Al2(SO4)3 system, for which the graphics look like straight lines. By portraying the results in this graphical form, it is difficult to understand whether there are saturation limits for aluminium addition to the system.

Another discomfort of this article is that the authors show the influence of different parameters all together in one figure. This makes perception and understanding of information in these figures more difficult.

In the part of article titled “Studies on the kinetics of sizing” the authors state conclusions from the experimental results regarding the existence of an optimum contact time between rosin size addition and sheetforming and about decrease of sizing with increase of R-value (the amounts of alkali). These conclusions cause the reader to think about reasons underlying these experimental results, but they don’t give answers to these questions. Indeed, the experimental datas are not sufficient to fully address these questions. But it is very important to understand the mechanism of reactions inside the system because it gives the possibility to regulate and control this system.

The big defect of this article is that the authors consider the problem of alkaline rosin sizing only from one side, the influence of different conditions on sizing itself, whereas another side of this problem, the influence of the same conditions on retention, is not discerned in the article. The authors only sometimes mentioned about contradictory influence of the same parameters on sizing and retention and they don’t give any experimental results for retention. But both of these exponents have a complex interest for paper maker.

When the authors investigated the influence of different conditions on alkaline rosin sizing they neglected to consider or explain the role of cationic starch addition. For the reader, the question of influence of quantity and charge of cationic starch on the sizing can be very interesting. Another interest is to know the how quantity and charge of cationic starch are connected with quantity and R-value of aluminium addition.

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The Use Of Ozone As A Biocide In Paper Machine Recycled White Water. Susanna Korhonen and Tuula Tuhkanen. TAPPI Journal (2000). – Reviewed by Scott Ewers, Spring 2009

The authors of this article I thought produced a well organized research paper on the topic of “ozonation as a biocide”. In my opinion the only area(s) that may have needed more detailed explanations / descriptions was in the introduction section that addressed the potential microbiological problems in a closed paper machine water system, and the concept of chemical oxygen demands (COD) referenced in the Material and Methods section. All other sections— Results, and Discussion were addressed adequately. Methods for data collection were defined well and data analysis was clearly presented in tables and graphs.

I feel the introductory section lacked adequate description of the specific microbiological problems in a white water system. The paper presents several problems associated with biological growth in a closed water system, one of them being spore forming thermophilic bacterial growth. The article did not provide any background information on the specific spore-forming organisms. While credit should be given to the authors for citing a reference for the topic of thermophilic organisms, a short description of the particular spore-forming organisms might have provided a worthy insight into the biology of the problem causing organism. A biological description, specifically the life processes, of the thermophilic organisms could have provided the reader with background information that may have lead to a better understanding of how a bacteria organism colonizes the water system as well as an understanding of the thermophilic nature of the particular organism. The authors stated that thermophilic bacteria growth is favored in water temperature above 50 degrees Celsius. An additional temperature range, “mesophilic” temperatures range (20 – 35 degrees Celsius), was mentioned as well but the authors did not say whether or not bacterial growth occurs in the lower mesophilic range and if it is problematic for a white water system. More discussion may have been worthwhile to compare bacterial development in both temperature ranges. As presented, I would assume that bacterial growth in the water system at the lower range was negligible or did not occur.

The principal objective of the study was to determine the ozone dose that is required to control bacterial growth in a paper machine white water system. The authors also stated a secondary objective that compares the efficiency of ozone to remove “the aerobic heterotrophic bacteria versus the bacterial spores”. No information was provided in the article that described heterotrophic bacteria. Given that tests were conducted to gather data on the growth and control of both the heterotrophic bacteria and bacterial spores, you would expect some description and even a comparison of the two types of organisms being researched. The last critical aspect of the article was with the authors statement that antimicrobial activity of chemicals used as biocides can “impair the efficiency of the biological wastewater treatment plant” when lost in effluent but they do not provide a follow up example(s) of how a paper mill wastewater treatment system is impaired. One or two examples listing environmental or process problems in handling paper mill effluent could have served to frame the problem (or potential problem) that traditional biocide products can cause.

I feel the authors needed to expand on their description of the methods they used for physiochemical analysis of water. The term chemical oxygen demand (COD) was stated to represent the amount of organic material in water samples and the Standard Method SFS 5504 was referenced. I think more detail on the COD concept was needed since the ozone dose used in their experiments was based on the concept (mgO3/mgCOD).

Overall, the authors presented their goals in the study, the test methods they used, and an analysis of data in a manner that was easy to interpret, and they acknowledge areas of the study that require further research on the effectiveness of ozonation in a white water system.

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In this paper written by Horvath and Lindstrom, the two authors investigate the influence of colloidal interactions on fiber network strength by varying the surface charge density, electrolyte concentration, and the type of counterion used. However, the paper fails to expound upon findings and assumptions made by others who provided contributions to work in this area, thus leaving the reader to accept their work as scientifically valid.

BACKGROUND

In a flowing suspension of papermaking fibers, there are various forces governing the fiber to fiber interactions which can cause fiber flocculation. Flocs are localized fiber concentrations higher than the average and can adversely affect sheet properties such as formation index, opacity and sheet strength. The investigation into fibers flocking together has been directly linked to fiber charge. Increasing the charge density on the fibers surface decreases the floc size due to an increase in the repulsion forces between the fibers. It was first believed that these colloidal forces were the sole reason for fiber flocculation however, it was later discovered that mechanical surface linking and elastic fiber bending also caused fibers to flocculate as well. Mechanical surfaces linking results from fibers becoming entangled with each other and becoming permanently bent or have a fibrillated surface. Elastic fiber bending results from fibers coming to rest in a strained position as the paper sheet is formed. The colloidal probe microscope (CPM) is an important tool that is used to study the normal forces acting between the fibers on a macroscopic level as they approach each other. The factors that dominate this type of interaction are electrolyte concentration and charge density. As the charge density increases, the swelling of the cellulose fibers increases, which is directly related to the electrolyte concentration. An effective combination could have a positive effect on fiber to fiber interactions in a flowing suspension and therefore influence sheet strength by reducing the likelihood of fiber flocs.

DISCUSSION

The paper investigates the role electrostatic and electrosteric interactions played in fiber to fiber interactions using never-dried ECF bleached softwood kraft fibers. The approach used was a two part study; the first part used a CPM to study the effects of electrolyte concentration, counterion (H+, Na+, Ca2+), and charge density on approaching fiber surfaces. In the second part of the study, colloidal interactions on a macro scale (effective network strength) through rheological measurements are examined.

Two cellulosic surfaces are used to conduct the experiment; regenerated cellulose beads and a cellulose coated wafer. The methods used to perform the experiment including the preparation of the cellulosic surfaces and the use of the rheometer were effectively communicated. The cellulose beads are prepared for carboxymethylation. Carboxymethyl cellulose (CMC) is grafted onto the fiber surfaces as a way to increase the charge density. The exact amount of CMC attached to the cellulose surfaces in the experiment was difficult to determine, so a graph was used to show the attached amount of CMC to be a direct function of the CMC dosage. There was no explanation as to why the results were different for the two surfaces or if similar results were found under a different set of conditions. This leaves the reader wondering.

Measurements are conducted between the cellulose sphere and a flat cellulose surface in NaCl, HCl, and CaCl2 solution at three different electrolyte concentrations. The results are plotted for the distance between the two surfaces versus the repulsive forces. A sharp increase in repulsion appears at 10nm for the 10-5M solution. However; the authors can only speculate as to the reason to be related to electrosteric repulsion and do not discuss why this is only unique at this concentration. At this point, the authors discuss the influence charge density plays in the experiment and provide a plot showing that increasing the surface charge density largely increases the repulsion between the two surfaces.

The remainder of the paper discusses how the apparent yield stress as a function of network strength is affected on a macroscopic level through rheological measurements. Plots are presented showing the apparent yield stress as a function of consistency with different surface charge densities and in various electrolyte concentrations. Here the authors do a good job in discussing what the results indicate and what forces are dominant but do not present data for consistencies below 1%, at which most paper makers operate the headbox. Also, no mention is made of frictional forces or hydrogen bonding if any. In the end, definitive conclusions are drawn showing surface charges and the type of counterion used are important factors during fiber interactions and that they do have an impact on network strength.

The information in this paper can be quite useful for the papermaker. Understanding the effects that ionic strength, charge density, and counterion have on the interaction between cellulosic surfaces can be beneficial in achieving a superior final product. As this experiment was performed using never dried ECF bleached kraft softwood, it is suggested the authors conduct additional experiments using other fiber species (hwd, eucalyptus…) and other pulp types (sulfite, tmp…) to see if similar results are observed. This would give the paper maker a complete understanding of the interactions regardless of the fiber source or process.

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“New advances in microparticle retention technologies” by Rosa M. Covarrubias, Joseph Parack, and Saleem Mirza, 56th Appita Annual Conference, March 2002.

Reviewed by Guy Joseph, 2009

Introduction

In the article by Covarrubias, Parack, and Mirza a brief review of the industry accepted and effective microparticle retention, drainage, and formation programs is presented. The authors mention the global market and the pressure it has placed on costs for the paper industry. The authors provide a few case studies from laboratory work as well as mill applications. The overall discussion is on three new products from Buckman Labs, called the Mosaic System. The products are a new anionic synthetic inorganic microparticle (MP810), a new cationic microparticle (MP820), and a new proprietary emulsion cationic polyacrylamide (MP830/835). The intent of the article is assumed to be an introduction of new technology that can improve performance and one would expect to lower costs. It is unclear from the article what the true innovations to microparticle technology are considering two examples are of the MP830/835 emulsion and only one is with the MP810 microparticle hectorite.

Background

Microparticle technology is an accepted and widely used drainage, retention, and formation improvement technology used in the paper industry. Silica, bentonite and various polyacrylamide retention aids are relatively inexpensive additives in the paper industry. The use of microparticle systems in general applications will enhance drainage, reduce floc size resulting in more uniform formation, and improve overall retentions on the machine. Further improvements to the microparticle systems would be beneficial to the industry as costs continue to escalate and machines are continually pushed to run higher tonnage rates without major capital investments. Therefore enhanced microparticle systems to lower operating costs and improve production would be beneficial.

Discussion

The laboratory studies provided in the article were done on newsprint and packaging furnishes. The newsprint involved a furnish of 50%TMP/50% de-inked pulp with a conductivity of 2000 micro Siemens and a cationic demand of 200 meq/lt. The packaging furnish was 100% OCC with a cationic demand of 1000 meq/lt. The cationic demand of the OCC furnish was not reported and should be considered as this is an important factor when dealing with OCC. In both lab studies it was determined that a new microparticle approach could improve performance through decreased drainage time and improved retention on newsprint and lower turbidity for the OCC furnish. While lab studies are a key part of developing application strategy in a mill environment, it is not uncommon to not match the results on a paper machine. Further laboratory testing on ore systems would be beneficial to show consistent improvements over bentonite and silica.

The current applications discuss improved performance in a fine papers application, a trial in a newsprint application, and a coated freesheet mill. Data was provided for the trials but the article is premised on innovations to microparticle retention technologies. Only one application uses the traditional approach to microparticle, the MP810 application in the newsprint mill. The other applications referenced are of the cationic polyacrylamide emulsion. This approach requires equipment for make down and is not a like in kind match to a bentonite or colloidal silica approach.

It is assumed this presentation was intended to help promote the use of the Buckman Mosaic System in other mills. The article gives a good discussion of the traditional bentonite and silica systems currently in wide use but the applications discussed for the mosaic system tend to vary from a traditional approach. The new systems require make down equipment and are not the simple low cost approach that silica and bentonite provide. The article is overall a good discussion of new systems available to paper makers but would be more enlightening with a wider discussion of laboratory and mill applications. When considering the work involved when conducting a trial on a paper machine making real time production, the article should provide some more compelling information if it is intended to promote the Mosaic program.

“Flocculants for precipitated calcium carbonate in newsprint pulps” by A. Gibbs, H. Xiao, Y. Deng, and R. Pelton. (1996) Tappi Journal Vol 80: No4. Pages: 163-170.

Reviewed by Ingrid C. Hoeger, 2008

Introduction

In this paper Gibbs, et al., the authors, compared the retention and flocculation efficiency of experimental copolymers, prepared in their laboratory, with leading commercial retention aids. The work was done with a peroxide-bleached mechanical pulp. They focused on retention of precipitated calcium carbonate (PCC). The flocculants were used as combinations of two sequential additives. The maximum PCC retention was achieved by using either the experimental PFR/poly(AM/MEPEGMA) system or the commercial CPAM1/CLAY system. They obtained over 50% of PCC retention with these retention aids, which is a high value when compared with 12% of retention without polymer addition. If there is a significant weakness in this study, it may lie in the fact that readers cannot easily compare the two main retention aid programs considered. The experiments with PFR/poly(AM/MEPEGMA) and CPAM1/CLAY could easily have been designed and carried out and the results presented in such a way as to facilitate a comparison between them.

Background

Retention and drainage aids are used in newsprint mills to improve fines retention, increase drainage on the paper machine, control deposits, improve filler retention, increase sheet dryness exiting the press section, improve runnability, reduce linting and improve pressroom performance. However, newsprint and related paper grades are particularly challenging applications for polymeric retention aids, because the paper machines usually have very turbulent drainage and rapid dewatering, which can destroy polymer flocs. The action of cationic additives is inhibited by high levels of dissolved and colloidal substances.

Discussion

Concerning the outline of the paper in the experimental section, the authors cite the commercial polymers and then they give a description of the components and synthesis of their experimental copolymers. This is really interesting, that the authors give a good description of the materials and procedures that they used in the study. Unfortunately, the display of the graphics and tables from the results don’t always coincide with the explications given in the text, so a better arrangement could have been made for their display in order to help the reader visualize the explanation and not to confuse them.

The authors determined PCC retention in the furnish in the presence of commercial and experimental polymeric flocculants by Dynamic Drainage Jar (DDJ) tests and a paper industry flocculation test. They also studied the effect of temperature on PCC retention and the effect of the external crystal habit of PCC on retention.

Though the authors start by presenting and analyzing PCC retention induced by cationic polymers, they fail to give any explanation for what, on its surface, would appear to have been rather arbitrary and unequal dosages of the different polymers. They used two commercial cationic polymers and two experimental polymers. They obtained maximum retention with CPAM1/CLAY (1:10). But a higher polymer dose was used than those of the other polymers. In one of their next results they show the influence of CLAY concentration and the type of PCC on retention in the CPAM1/CLAY, they obtain that the optimum retention corresponded to a polymer-to-bentonite (CLAY) ratio of (1:1). The reader is left to wonder why did the authors conduct the study of PCC retention by cationic polymers with the ratio (1:10)? When from the test of the influence of CLAY they were able to observe that with this ratio (1:10) the retention is descending?

Concerning the effectiveness of their experimental cationic polymers, the poly(NIPAM/DADMAC) showed little promise as a PCC retention aid, and the poly(AM/MAPTAC/MPEGMA) gave good retention at a small polymer dose, although that polymer lost virtually all flocculation activity after 3 month storage at room temperature.

Regarding PCC retention, the anionic polymers were, as expected, not as effective as cationic polymers in papermaking suspensions. It’s worth mentioning that their experimental anionic polymer “poly(AM/AA/MPEGMA)” achieved a better retention than the anionic commercial polymer that was used in this study.

In the PCC retention induced by nonionic polymers, the authors compared a very high molecular weight PEO homopolymer with a nonionic experimental copolymer “poly(AM/MEPEGMA) ”. Both required the addition of a phenolic resin (PFR) cofactor and a further increased in PCC retention was obtain when Na2CO3 was used. In their results the PFR/ poly(AM/MEPEGMA) was the most effective combination of additives for PCC retention. The readers might have liked to see what happen to the PCC retention at a higher polymer dose. Does the retention decrease? The experiment should have been carried out and the results presented in such a way as to facilitate comparison with the CPAM1/CLAY system.

The authors showed that the electrophoretic mobility of the filler particles could be changed, depending on the content and nature of polyelectrolytes in the solution. The PCC’s electrophoretic mobility was measured as functions of the concentration of various additives. With no additives the PCC particles were positively charged. Using polygalacturonic acid, an anionic water-soluble polymer produced during peroxide bleaching, caused charge reversal, because it was adsorbed onto the positively charge PCC. The behavior showed with the cofactor (PFR) was similar. Finally, with cationic terpolymer poly(AM/MAPTAC/MPEGMA) addition increased the PCC mobility, suggesting that the cationic polyelectrolyte adsorbed onto the cationic particles.

Most of the experiments where carried out at room temperature, because in the paper mill we can find higher temperatures, they studied the effect of temperature on PCC retention and didn’t find a significantly effect in the retention by an increase from 22 to 50°C.

Finally, when the authors proposed a mechanism to account for their observations, they did not appear to provide any justification for their proposal. The authors believed that a bridging mechanism is responsible for the retention of PCC by both CPAM1/CLAY and poly(AM/MEPEGMA) systems. It would have been helpful to the reader to explain how they reached this conclusion or where a reader can find information about it.
According to the researchers this study could show similar results in a mill. So it can be extrapolated to the industry. For the authors the PFR/ poly(AM/MEPEGMA) was the most effective combination of additives for PCC retention with the addition of Na2CO3. They left a number of answered issues, as noted above, that could be addressed in future work.

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“The use of oppositely charged polyelectrolytes as flocculants and retention aids,” by Petzold, G.; Buchhammer, H.-M. and Lunkwitz , K., Colloids and Surfaces A 119 (1996) 87-92

Reviewed by: Deusanilde Silva

Introduction

The cited article, published by Petzold and co-authors deals with the flocculation of a cellulose and clay blend using a dual system of polyelectrolyte. This kind of retention system involves the use of a polycation and a polyanion as flocculating agents. In the case of this study, the authors used PDMDAAC (poly(dimethyldiallylammonium chloride)) as the positive polyelectrolyte, paired with one of four other additives as the negatively charged polyelectrolyte, with different molecular weight These were (a) P(MS-e-MeSty – Poly(maleic acid-co-α-methylstyren Na salt, (b) P(MS-Sty)/Leum – 500/10 – Poly(maleic acid-co-styrene) di-Na salt, (c) PAA – Poly(acrylic acid), and (d) P(AM-AA)/Praest2o5l 30 (30 mol% acid) – Poly(acrylamide-co-acrylic acid.

In accordance with the article, the flocculation of cellulose and clay blend was verified by three practical techniques: (a) polyelectrolyte titration, (b) a dewatering test, and (c) measuring the residual turbidity.
The trials showed that the molecular weight of the anionic polyelectrolyte could define the flocculation mechanism and its effectiveness. The mechanism observed were complexation, charged patches and polymer bridging.

Background

In papermaking, some process and product parameters have shown considerable importance. The operational variables, retention and drainage, and the paper sheet quality formation are continuously verified during the papermaking. These variables could be affected by the flocculation mechanism, considering constant other parameters, such as the pulp slurry, the quality of the process water, the fines content, pH, anionic trash, and conductivity, etc.

In general, the flocculation mechanism has had to evolve along with the evolution of the paper machine, including its increase in speed over the years. In other words, a lot of new products, including retention and drainage agents, as well as wet- and dry-strength additives have been introduced with the aim to improve operational and functional parameters of papermaking.

The impossibility of exactly reproducing of the flocculation mechanism as it happens in a paper mill is accepted, considering the large number of variables that we can find in each papermaking process and the difficulty in reproducing the real conditions of the process, residence times, shear forces, dosage points, etc. Therefore, some effects could be verified in an isolated way using lab trials. The results from these trials showed fundamental importance to understand and solve some mill trouble.

Some lab trials were carried out with filler only. When the trials are carried out with pulp and filler, this kind of trial is more complex to do in the lab. In other words, it can be increasingly difficult to verify that a given effect is significant when we increase the number of components of the system. Another important thing that we have to consider is the methodology used by the authors to verify the effects. This methodology has to be very close to the real conditions, if the goal is to be able to apply the results with confidence in the actual running of the paper machine. In addition, the work has to be as detailed as possible to be repeated and understood.

Discussion

In my opinion, this article has some advantages. The authors carried out the trials not only with filler, but also in presence of fiber. Another advantage is that the authors use relatively simple methods, and the equipment was similar to what easily can be found in a typical paper mill lab.

On the other hand, I did not think that is of sufficient interest to contrast the results with those presented in another article, e.g. [Ref. 1]. The explanation about the mechanism was superficial. The authors could explain these mechanisms more deeply.

The conditions of the trials could be closer to mill conditions in term of conductivity and anionic trash. In addition, I think that the methods could be explained more completely, even when the authors are describing work carried out in cited work. The particular circumstances described in each paper are important.
It is also possible to make some general criticisms of the article. Although the authors have cited retention and drainage in the focus of their work, the results were discussed more in terms of drainage.
The graphics were not so good. The scale for the variable drainage could be better adjusted.

Even with these negative points, the article was able to show that in this kind of system, a polycation with higher molecular weight showed better results for a specific molar ratio of negative and positive charge, i.e, there is an optimum point. After that, the efficiency of the process is inverted, maybe because of an imbalance in charge.

The best results were found for the anionic polyelectrolyte with the highest molecular weight. This means that the bridging mechanism was more efficient in terms of promoting drainage. Considering these results, I can conclude that the molecular weight of the polyelectrolyte is an important parameter that we have to consider in the flocculation mechanism.

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Reviewed by Justin Zoppe, 2008.

Introduction

In this paper, Kratochvil et al. discuss the efficiency of polyethylene oxide (PEO) as a retention aid for fines in mechanical grade papers. The authors studied the efficiency of flocculation in terms of the history of the PEO solution. In particular, the time of mixing and storage are considered. The authors use clay to model fines in papermaking. They failed to mention how the flocculation of clay can be related to fines. Most of their conclusions seem to be well supported, but I also believe there is a need to discuss the chemistry of PEO as a molecule to help support their conclusions. They also fail to study temperature effects.

Background

PEO is commonly used as a retention aid in a PEO-cofactor system for fines in mechanical grade papers. It has been reported that the efficiency of PEO to retain fines sometimes declines with time, and freshly dissolved PEO flocculates latex faster than an aged solution. The authors hypothesize that PEO has large entanglements in poorly dissolved solutions. This makes the molecules behave as if they have higher molecular weight and increases the efficiency of flocculation. They perform flocculation experiments with clay using different concentrations of PEO, different mixing times of PEO solution prior to addition of clay particles, and the effect of addition of a cofactor of sulfonated kraft lignin (SKL). To understand the gradual disappearance of entanglements as solutions are stirred, they performed pressure drop experiments across a valve caused by flow of PEO solutions. For these molecules to effective at flocculating, they must adsorb to the surface of the clay particles and they must reach out past the electrostatic double-layer to bridge with an adjacent particle. Discussion

During the authors’ flocculation experiments, they used clay suspensions of 400 mg/L and added PEO and SKL using a syringe after different stirring times of the PEO solutions alone. They presented the data in terms of a stability ratio W obtained by comparing rates of flocculation at an experimental condition to a maximum rate of flocculation in the presence of salt. So, when W goes to infinity, the system remains stable and dispersed. When W is equal to 1, the rate of flocculation is very fast. To find the rate of fast flocculation, the stability of clay suspensions were studied with KCl. They showed the stability ration W, decreasing with increasing concentrations of salt. Next, they studied the rates of flocculation in presence of a fresh solution PEO, after stirring PEO solutions for 1 hour, and 1 day. They varied the concentration of polymer from 0.5 to 5.0 mg/g clay. They showed freshly dissolved PEO flocculated clay particles faster than salt, regardless of the concentration of polymer solution. Solutions stirred for 1 hour showed the typical V-shape curve for polymer bridging. Solutions stirred for 1 day did not flocculate clay whatsoever.

In my opinion, it would be important to discuss the chemical behavior of PEO in solution in addition to the idea of entanglements. It is known that PEO behaves strangely, being a nonionic polymer. At higher temperatures, PEO is more difficult to dissolve because of the increased exposure of alkyl parts of the polymer chain in aqueous solution. If temperature is decreased, PEO is more likely to fold on itself with oxygen groups in closer contact with water which will dissolve better. This behavior should be taken into account in addition to stirring. Not only will stirring remove entanglements as the authors claim, but individual chains will tend to straighten out. This will also decrease its effect on flocculation. The evidence that they showed for disentanglement makes sense in pressure drop experiments, but they should have mentioned individual molecule behavior as well. They showed larger pressure drops for fresh solutions and they decreased with increasing stirring time. The effect of addition of cofactor SKL was also considered. They showed mostly the same behavior for PEO solutions, except that the solution stirred for 1 day then showed the typical V-shaped curve for polymer bridging. So, it seems that the disentanglements are still occurring, but the addition of SKL into the suspensions forms complexes large enough to still overcome the double-layer to bridge with adjacent particles. They argued that disentangled PEO molecules adsorb to clay, but are not large enough in hydrodynamic radius to overcome the double-layer, thus they repel and do not flocculate.

The authors concluded that PEO is not degraded as has been claimed in the past, but these polymers become disentangled after the solution has aged or been stirred for prolonged periods. This claim seems validated by the results shown, but the authors failed to mention the individual behavior of PEO polymer in aqueous solution. The more the solution is stirred (higher temperature), the harder it becomes for PEO to be dissolved in solution. They did not mention the temperature at which these experiments were conducted, and that will have a great effect on their results.

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“Papermaking Technology Evolution: Its Impact on Wet-end Retention” by Juntai Liu, 2005, Paper Technology, 31.

Reviewed by Kelley Spence, 2008

Introduction

In this journal article, Juntai Liu discusses the state-of-the-art papermaking technology in China and its effect on retention aids. Liu describes the new technology that has been implemented in China during the last 10 years that affects the paper machine wet-end. This is particularly related to lower grammage requirements, new pulping techniques, increased filler levels, the Telioform retention system, machine improvements, and online measurement with closed-loop control. The article thoroughly shows that China’s papermaking technology improvements have a negative effect on retention aids, but results are not substantiated by data or literature, and many improvements are not described thoroughly enough for the reader to successfully comprehend.

Background

Retention aids are used to keep smaller particles such as fines in the wet web. They are also used to obtain good first pass ash retention, which is needed to meet ash targets and for better machine runnability, but improvements in retention can lead to poorer formation and drainage. Record-breaking speeds and other modern papermaking technology in China (the current technological leader in the paper industry) have resulted in a need for an improvement in retention aid performance.

Discussion

The first issue investigated is the use of deinked pulps for newsprint and mechanical pulps for fine paper. Alkaline deinking is commonly used to remove contaminants from recycled pulp, but it introduces residual chemicals such as sodium silicates to the wet-end, reducing the effectiveness of the retention aid. Figure 1 in the article shows the effects of sodium silicate on retention aid performance by measuring turbidity. This figure is sufficient proof that sodium silicates harm retention aid performance, but it does not prove that other residuals have a significant effect. An investigation of replacing sodium silicate with other chemicals to improve retention aid performance would have strengthened the author’s argument. Alkaline peroxide mechanical pulping also introduces residual chemicals to the wet-end. The author states that “the effect is significant when the chemicals are overdosed or if the pulp washing is inadequate,” but offers no proof of the significance. The author could also suggest monitoring and improvement of the chemical dosage and pulp washing systems to prevent residuals from reaching the wet-end.

In recent years, China has seen a decrease in grammages for newsprint, business paper and containerboard. Reducing the grammage results in a decrease in retention values that are typically achieved through the entrapment of small particles in the wet web while on the forming fabric. Figure 2 in the article successfully shows that it is difficult to obtain high first pass retention at lower grammages, but the data points appear to be scattered, with no error bars displayed to determine the statistical significance of the results. There is also no mention of new forming fabric technology that could improve retention without a major change in the chemical system.

Higher whiteness and increased fiber content have also been implemented in China; typical sheet brightness is 110 ISO brightness with 29% filler content for copy paper. To obtain the high brightness levels, florescent whitening agents (FWAs) are used. The author reports that “FWAs raise the level of anionicity of the furnish and affect the performance of the retention aids markedly,” but the article lacks proof of a significant effect. The author needs to present production data to substantiate this statement.

To improve retention in the wet-end, new retention systems have been implemented. The Telioform retention system, which uses a combination of organic and inorganic microparticles, claims to decouple the effects of retention, drainage and formation. It was observed that the Teliform system could improve retention under high ash and high whiteness paper production. This article does not elaborate on the Telioform system and how it works, leaving readers confused by the lack of information and the claim that it is able to decouple retention, drainage and formation. Explanations of this statement or production data to prove Teliform’s success are needed to support the author’s claim.

Paper machines using direct dyes have been converted to pigment dyes because they have a less significant effect on retention aid performance. The author supports this statement with a graph that displays b and l values for the pigment and the direct dye, but this figure only proves that dyes can be replaced with pigments; it does not confirm that they improve retention as well. This section also does not elaborate on the effects of the dye or the pigment on the retention aid system. The author only states that pigments are better than direct dyes, with no supporting details. A figure showing the retention of a system when using the two different dyes would be useful to support the author’s argument.

The new paper machines in China are equipped with online measurements and closed-loop control of the wet-end system. These systems allow for immediate changes to the wet-end in order to maintain nearly constant first pass retention, but they are not sufficiently described in the article. Online charge sensors have been installed to optimize wet-end retention as well as the online measurement of white water and headbox solids. The article, however, does not explain how this works. Finally, a new system for retention aid dosing is introduced with Figure 10. The article states that the system is successful but does not elaborate why or how the system actually works. An explanation of the figure would be useful for the reader.

Liu successfully describes the technology improvements in China associated with the paper industry’s rapid growth, but does not substantiate many of the statements with production data or literature proof. The reader is left confused about how the improvements work and the results they could potentially provide.

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“Dendrimers: A New Retention Aid For Newsprint, Mechanical Printing Grades and Board.”
by Allen L., Polverari M., PARICAN, Ponite Claire, Canada

Reviewed by Ying Xue, 2008Introduction

The authors, Allen L. et al, 2000, came up with a great idea of trying to use a relatively low molecular weight, highly three dimensionally branched, and highly charged cationic polymer, instead of a traditional high molecular weight, linear, low charged polyelectrolytes to enhance the retention of fine matter at the wet end in paper machine, and they found it maybe would be very promising in industrial use. They did a lot of excellent work on different kinds of paper from different paper mills and simulated the real conditions of the wet end. However, some of the figures and charts used in this paper lack evidence to support the author’s theories, while most of the results make sense.Background

Imagine a point, and from that point two branches stick out, giving two branches. Then each end of the branches divides into two branches, giving four branches. Then this process happens again, and one has eight branches, then 16, 32, and 64, etc. —- Finally, a ball-like dendrimer is synthesized after several steps. The dendrimers used in the cited paper have relatively low molecular weight; they only have 4-64 branches, but have high charge on their surfaces.

According to the data presented in the paper, dendrimers can be very effective for retention and drainage purposes for both virgin pulp and deinked pulp even under severe closure conditions (using 2 cubic miters process water). Another benefit of using a dendrimer is that it can help to coagulate resin in pulp at wet end, therefore contributing to the control of pitch control. When used in combination with flocculants, dendrimers would give higher gains in retention and drainage. Pretreatment of fillers will help to enhance the retention performance of dendrimer. Discussion

Firstly, a question related to this paper is whether the data support the assertion that innovative retention aid with three-dimensional branches and high charge density can function the same as a traditional retention aid having a linear structure and low charge density. It seems so. But in this regard it is suggested to look closely at figures 2 and 3. The tendency of the line in figure 2, which indicates the first pass retention of Poly SKA would be higher than that for the dendrimers when the polymer dosage becomes higher. In figure 3, the dendrimer performs even worse than Poly SKA at low concentrations. The same situation is clear in figures 5 and 6. To conclude the ideas above, maybe the following sentence would be more suitable to describe the author’s data: “the retention and drainage performance of dendrimers is as good or better compared to that of a linear polyelectrolyte between the polymer dosage of 5kg/t and 20kg/t,” for instance.

Secondly, even if the dendrimer can perform as well as (or even better than)a cationic retention aid of the traditional kind, it is not clear whether we can draw the conclusion from the data in this paper that this retention aid ability is endowed by the nature of three dimensional branched or highly charged on the surface.
The second question can be divided into two parts.

Let’s think about the first part of the second question in another way: whether the charming structure of dendrimer is really necessary. Because linear polyelectrolytes will have longer chain to contact with fillers in a longer range, while the ball-like dendrimers will only contact with the fillers around itself, powerful though, but, are there indeed that lot of fillers that would need such a powerful contact in a tiny place? Maybe a linear structure would give a more even retention and drainage performance, and would be strong enough for contact with fillers along its chain area.

The second part of this question could also be asked in the following way: whether the high charge on the surface is necessary. If the high charge on the surface of dendrimers is quite useful, the result of using PA4 and PA64 should be different. Referring to fig. 2., “first pass retention” there is no obvious difference between the performance of PA64 and PA4. Similar situations also could be found in figure7, 8, etc.

Last but not least, it is worth asking whether a dendrimer product has the potential to become popular in industrial use. This kind of polymer has a very low molecular weight, and in some sense this means that it will not require a large amount of raw materials to produce. However, the synthesis of dendrimer is conducted in separated steps, which means a lot of labour and work, labour and work means not only time, it means money at the same time. Traditional polyelectrolytes, on the other hand, are much more easier to produce.

Anyway, it is a very good trial; the author’s method is very smart, which simulate the situations with brilliant ideas, and at the same time, the picture of dendrimer can give the readers a lot of inspiration and a means of more fully understanding the mechanism that are involved.

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“Transfer of Adsorbed Alum from Cellulosic Fibres to Clay Particles” by L. Odberg, P. Barla and G. Glad-Nordmark, 1995 Journal of Pulp and Paper Science, J250.

Reviewed by Joscelin Diaz, 2008.

Introduction

In this paper, the authors show the effects of increasing addition level of clay in reducing the amount of aluminum on fibres, using different OH/Al ratios. The study of some variables such as stirring time, pre-adsorption, stirring rate, electrolyte concentration, and polyaluminum chloride (PAC) help to determine the optimum process conditions. However, there are some experimental difficulties in the measurement of alum on the clay particles that gave rise to a few incoherent results. More experimentation is needed to understand the retention process and the transfer of alum to clay particles. These findings will help to understand the kinetic processes that affect added paper chemicals in the wet end paper machine. It also will help to elucidate the location for addition of paper chemicals. All this aspects will facilitate the optimization of the papermaking process.

Background

Papermakers use alum in many ways, such as pH-control, sizing, charge neutralization, pitch control, and coagulation. Small amounts of alum used in alkaline papermaking in cationic or neutral form enhance efficiency of anionic retention aids, enhance and stabilize sizing, enhance runnability, and help in neutralization of interfering substances. Also, alum acts as a retention aid for fibrous and non-fibrous additives.

For all this advantages, it is important for a papermaker who uses alum to understand how some variables affect the transfer of alum ions to the clay because then they can have a basis for understanding the kinetic processes that affect the performance of chemicals added in the paper machine wet end.
Alum is a cheap source of highly cationic complexes which can be used as a coagulant for colloidal material both on a paper machine and in water clarification (by adding an electrolyte to an electrostatic colloid); that is why it has been used in the papermaking industry. But, the role of alum as a retention aid on modern high-speed machines, where hydrodynamic forces are strong, is limited. Polymers, especially cationic polyelectrolytes, are now commonly used as retention aids to optimize paper production. However, alum can be used in many processes, and to find the effective conditions in which the retention is higher could have positive effects in the strength of the paper.

Discussion

In the first part of the study, the adsorption of alum on the fibres was determined for two different cases; with and without addition of clay to the sample. The information obtained was shown in graphic curves. By comparing the curves it is easy for the reader to see that less aluminum was found on the fibres when clay was added. These studies were compared with the value obtained of the total mass balance for alum, and quite acceptable agreement was found. However, that value did not prove that the alum had been transferred to the clay particles. The first purpose was to know how much of the Al-flocs remained on the fibres at different OH/Al ratios. The results were given in percentages, and those were approximations.

Another purpose of the study was to measure the adsorption of a high molecular weight polyacrylamide on the fibres and on the clay particles to get an estimate of the available charges on these particles. However, these adsorption results were neither discussed nor compared with the amount of Na2SO4 used previously.

To continue this study, some possible variables on the transfer were investigated, while maintaining a constant OH/Al ratio. This ratio was implemented using the report obtained from other investigations. First, the stirring time was changed to study of the effect of this variable on the transfer of aluminum. The results obtained were not clear in this study, because they did not use an adequate mathematic methodology to measure the transfer.

The pre-adsorption time was also investigated. The results obtained were represented and compared in a graphic form. The authors confirmed that this variable does not influence the amount transferred of aluminum, and the results were compared with a cited reference. At this point, they cited the influence on pre-adsorption time using a high molecular weight polymer, but they do not show any data, despite the fact that they stated a conclusion related to this point.

The stirring rate was studied using only two levels of agitation, and the data obtained were represented in a graphic form. The authors concluded, based on the two different stirring rates, that this influence is moderate relative to the amount transferred; they did not express this issue clearly and did not make comparison with the aggregation of clay in the suspension.

The electrolyte concentration was studied by changing the concentration of Na2SO4. The data were analyzed and clearly they showed the optimum concentration in which there is more transfer of aluminum to the clay.
The last discussion was based on the influence of polyaluminum chloride (PAC) with different degrees of prehydrolysis. The data were analyzed and compared with the data obtained by using aluminum. The authors concluded that these results are similar to the results of alum, but they did not show how do they obtained those.

Since the authors did not show any calculations, a new report with all these details should be helpful to the reader who wanted to clarify the effect of the variables studied. There are too many weak points, such as the fact that they did not study any alkali other than Na2SO4, and they just emphasizes their work in the OH/Al ratios as the most important variable to determinate the absolute amounts adsorbed and transferred of aluminum.

It is suggested that the authors publish a follow-up version of this journal article with the use of results obtained from modern high-speed machines and use efficient math methodology to obtain clear results.

From the above discussion, it can be concluded that more work is still needed to establish a detailed understanding in factors such as the study of alum solution chemistry, because this issue was not considered, as well as the relation of the increase of alum in the transfer (alum dosage) and the adsorption time on the fiber before the addition of fillers. The pH also was no considered as a function of the adsorption of aluminum to understand the aqueous equilibrium and predict the interactions of aluminum species with other materials in the papermaking system. It is important to control pH and aluminum concentration to obtain stability at the wet end. For all these reasons and to achieve better results, more study should be implemented to understand the retention process.

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“Polymer Transfer During Fines Detachment Under Turbulent Flow: Mechanism and Implications” by T. Asselman and G. Garnier, 2001 J Pulp Paper Sci., Vol. 27, No. 2, 60-65.

Reviewed by Eugene F. Douglass, Spring 2008.Introduction

In this paper Asselman and Garnier discuss their study of the concept of polymer transfer during fines detachment in turbulence in a paper manufacturing process. Polymer flocculants are used in paper making to improve first pass retention of solid materials.

Background

In the production of paper, people have used various substances to enable fibers to stick together efficiently over the years. Water-soluble polymer flocculants were developed to hold in the slurry small wood fibers, that would in their absence drain through the mesh and be lost in the waste water. This is a study of a variety of polymers, how much fines are retained, and the simulated mechanism of their retention. The objective of their paper is to analyze the findings of previous studies in the context of papermaking.Discussion

“In the first part, the critical experiments of fines-fiber coflocculation are presented and compared to a combination of fundamental models… in the second part, these results extrapolated to paper making conditions…” They then state the results are determined by simulation and the effects are inferred.

The authors’ statement regarding “simulation” is the first major problem I have with this paper. They have not proven in this paper, and I have no evidence to show they have proven in previous papers, any direct correlation between lab results and real-world conditions.

One example is related to their description of the polyethyleneimine they use in the experiments; they say it is believed to be highly branched and give a set of previous references. What does that mean? Believed to be? They need to give evidence of what it is, if they are going to come to conclusions on their own results.

Another example is that they say “full polymer coverage was achieved by stirring the fibers in a polymer solution for 5 minutes.” They provide no proof for this blanket statement other than a previous reference. How do they know it was full coverage? They need to provide the evidence, if the reader is to believe the results. They then state 5 minutes is “largely sufficient” to coat the fiber surfaces. In this context “largely sufficient” means nothing, because these results are then treated as numbers in a mathematical simulation and in mathematics unknown errors are compounded in simulations.

They then give a series of experimental results that show only that when fines are mixed with polymer-coated fibers, the concentration increased with longer mixing time. That is obvious, of course it would, as fines are mixed with “sticky” fibers, more will become attached.

The next major problem with the article is that the results are said to be determined by simulation, whereas the results really are just inferred by the authors. Real world conditions are not simulated sufficiently to make conclusions that are inferred meaningful. Currently there is no super-computer powerful enough to simulate, in the strict sense of the word, what they are trying to show, and then come to real conclusions, that have real world results. Their simulations may have value, but in the absence of the previous data, that the reader can discern this for himself, their conclusions become essentially opinions with no clear foundation for them.

The rest of the paper is filled with estimations, possibilities and even guesses as to what they believe is happening.

The last statement the authors make illustrates the main problem I have with the whole of this paper “The kinetics of this phenomenon is still poorly quantified, but reconformation within 5 s has been reported in the literature” again with more external references, the kinetics they studied had simulated results. Simulations are not real; they are models at best. They poorly quantified their simulated results; and then they state real world observations with the pretense their simulation predicts the real world results. This is classic circular reasoning. An example, the fines become “permanently detached,” whereas they have no proof to make such a blanket statement.

Lastly they say “these results can explain the observed loss in retention on high speed paper machines.” This statement does NOT mean anything; there can be other reasons for the observations of loss of retention of fines on a paper machine in real life. What really was accomplished in the study, the writing and conclusions that come from this paper? I don’t know of much.

Conclusions

Readers of studies similar to this one need to bear in mind the severe limitations of laboratory studies that are meant to simulate real-world situations. Even if one accepts the use of the author’s term “simulation” for this kind of work, the experimental results, leading to inferred conclusions, are still a long way away from reality. Their value for industry is questionable.

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Reviewed by Rachel Ernest, 2008.

Introduction

In this article, B.-U. Cho et al. describe the development of a mathematical model to predict the bridging strength of different levels of a cPAM/bentonite retention aid system. The bridging strength calculations corresponded quite well to experimental measurements of paper formation. Although the authors used simple addition schemes with two different furnishes, they had small dissimilarities in the consistencies and addition points for the two furnishes. Also, by using a pilot machine and filler, the author leaves the reader questioning other aspects of the papermaking process which might be more dominant in creating paper uniformity. Even with these questions, the authors have provided evidence for the appropriate blends of retention aid polymer and micro-particles.

Background

Papermakers are quite concerned about drainage and uniformity. If a slurry contains too many loose fines, they tend to clog the drainage routes which decreases drainage rates. Many papermakers use a high-mass cationic polymer (cPAM) as a flocculant to form bridges between fines and fibers. Unfortunately, these bridges also form between fibers, and the bridges are often too strong and irreversible which leads to poor uniformity. However, with the addition of a small anionic mineral (like bentonite), these bridges become more reversible and the polymer can coil around the bentonite – these two actions lead to reduced fiber flocculation and increased drainage.

The bridge strength is only one aspect that can affect the paper uniformity. Papermakers must also consider crowding number (the number of contact points of fibers), slurry consistencies, and filler concentrations (in this article, precipitated calcium carbonate (PCC)). The crowding number will mainly be a function of fiber consistency and fiber length – more long fibers will result in a higher crowding number and, therefore, higher fiber flocculation and reduced formation quality. Controlling filler-to-polymer proportions is also important because fillers can pull (and break) polymers from fiber surfaces which can lead to weaker bridges and reduced fiber flocculation.

Discussion

Overall, Cho et al. were quite clear in their explanations about how bentonite coverage of cPAM is important to reduce fiber flocculation. With their data from SwBKP, the authors were able to prove that their model could predict formation quality. Their explanations about their model were complete, although their estimation for the relative bond strength between fiber and polymer (αpol) is not explained thoroughly.

The researchers used two different furnishes (a softwood bleached kraft, SwBKP, and a softwood/hardwood bleached kraft, HwBKP & SwBKP) for their experiments. By using a furnish with all long fibers and another with long and shorter fibers, the authors could more confidently comment on uniformity based on fiber contact (of course, the blended fiber furnish had better formation). However, the researchers failed to report the blended fiber furnish’s formation index in relation to the retention aid system. With the shorter fiber blend’s expected higher uniformity, this article leaves the reader wondering what cPAM/bentonite balance is best for a blended furnish. More importantly, for this article, the authors did not provide evidence that their bridging simulation model can also predict formation for a blended furnish.

The authors attempted experiments to show how basis weight affected formation. Their descriptions for their results are somewhat obscure; moreover their experiment design seems flawed. First, they did not have analogous consistencies for the two furnishes – the range for the SwBKP was extremely small in comparison to the blended furnish’s range. Also, the dosages for the cPAM was different for each furnish, as well. In designing an experiment, the reader expects to see more comparable treatments for different materials.

The researchers left the reader questioning other parts of their design. For both furnishes, the PCC filler was added before the cPAM/bentonite retention aids, as expected. However, the researchers were not consistent in their method or addition points – for the SwBKP, PCC 30% slurry was added at the blend chest and for the HwBKP/SwBKP, the PCC 10% slurry was added to the fan pump. For a reader, determining the possible effects of these differences is distracting.

The authors brought up interesting possible future research by asking whether fillers improve formation by either filling voids in the fiber network or by reducing the fiber flocs by blocking fiber bonding sites. When retention aids are used, there are remaining questions about how fillers affect bridging strength, as well.

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Reviewed by Magaly A. Ramírez Vicéns, 2008

Introduction

The effects of retention and drainage aids, as well as dry-strength additive, have been studied in order to improve their function in the papermaking process. Examples of components with these properties include the polyacrylamide (PAM) derivatives, which are frequently used by papermakers. Their adsorption onto papermaking components under different conditions has been investigated. In the reviewed article Tanaka et al. present a study of the individual and competitive adsorption of cationic polyacrylamides with different charge densities but similar molecular weight.

Background

It is known that fibers have anionic surfaces mostly composed by carboxylic groups. These anionic surfaces usually interact with cationic compounds as a result of electrostatic forces. Due to the anionic character of polyacrylamides (PAMs), these are usually not adsorbed unless a cationic compound is applied to promote their retention. To avoid the need of cationic promoters, cationic PAMs have become a useful alternative as wet end additives. Their effects are dependent of their molecular weight (MW) and their charge density (CD). Evidently, there is no barrier when cationic polymers adsorb on a negatively charge surface. However their adsorption will be controlled by collision frequencies that can be induced either by diffusion or by shear. According to previously studies developed by Tanaka et al., it has been reported that the effect of MW of C-PAMs (cationic PAMs) on the adsorption to anionic surfaces was small when performed under shear. However, the effect of the CD of polyelectrolytes on the adsorption under shear conditions has to be studied in more detail. There are three types of manufactured C-PAM used in papermaking. These are the ones manufactured by the Mannich reaction, the Hoffman reaction, and copolymerization reactions. The first two methods mentioned are carried out in homogenous systems. In the reviewed study the polymers were prepared by the Hoffman method. However, according to the authors of the article the adsorption of cationic polymers with a heterogeneous distribution remains under investigation.

Discussion

As stated in this research article, the experiments were carried out under different conditions, varying the CD and MW of the polymer and also trying different substrates. All the parameters were well defined except for the shear level, which was estimated to be 2000 s-1. This factor can influence the results, since the shear level is not accurately known. While discussing the results of the individual charge adsorbed onto PSL, the authors stated that the adsorbed amount of charge was 2.1-2.2 μeq/g PSL, which is 1.2-1.3 times higher than the CD (1.7 μeq/g) of PSL. They attributed these results to the existence of segments of polymers that extend out into solution, but this is still unclear since the authors didn’t confirm their reasoning. In the competitive adsorption of mixed polymers (C-PAM + DC- PAM) onto PSL, the total amount of charges adsorbed were practically the same as in the individual adsorption. It was expected that there would be a preferential adsorption of the C-PAM having the highest CD, but the results indicated the opposite tendency. The authors justified this behavior explaining that the adsorption of C-PAM onto negatively surfaces is governed by shear-induced collisions. To confirm this interpretation, an adsorption experiment was carried out using a 1:1 mixture by weight of C-PAM 1 and DC-PAM. The adsorbed amount of C-PAM 1 (low CD) was slightly higher than that of DC-PAM (high CD). The authors concluded that this result confirms that the main factor in this competitive adsorption is the shear induced collisions. The reader is left wondering if the author’s conclusion applies for all types of polymer or if this is just an interpretation for this specific case. Why the shear collisions induced a high adsorption amount of the polymer with lower CD (charge density) and not the one with the higher CD?

Two other experiments were carried out, the individual and competitive adsorption of cellulose beads and fibres. The results of the individual adsorption of C-PAMs and DC-PAM onto cellulose beads were almost the same when extrapolated to zero time, as also occurred with PSL. The individual adsorption of C-PAMs onto cellulose fibres was similar to the adsorption onto cellulose beads, although the larger pores gave an easier penetration leading to higher fraction of polymer charge adsorbed. The article continues explaining the results obtained with cellulose beads and fibres, but this time with the competitive adsorption of mixed polymers (C-PAM1 + DC-PAM). The effects were almost the same as on PSL. The amount of polymer charge adsorbed increased with time. However, the increase in adsorption of C-PAM1 in the case of competitive adsorption was much slower that in the case of individual adsorption whereas the rates of increase of DC-PAM with high CD were very similar to the individual adsorption case. The authors concluded that this behavior suggests that preadsorbed DC-PAM also blocks adsorption of C-PAM1. But why does the preadsorbed DC-PAM block the adsorption of C-PAM1 and the adsorption of DC-PAM remain the same for both, competitive and individual? Could it be possible that an amount of preadsorbed DC-PAM blocks the adsorption of C-PAM1 in the individual adsorption?

Finally the authors ended their discussion by explaining the adsorption onto cellulose fibres. According to the results obtained the adsorption onto cellulose fibres was analogous to that onto cellulose beads, although the adsorbed amounts extrapolated to zero time was higher than the amounts on beads. The authors attributed this to the higher CD on fibres and to the larger pore sizes in the cellulose fibres.

It is evident that this project needs to be followed up, since there are some unclear concepts for the reader. I would also recommend to the authors to study other parameters related to adsorption other than charge or mass adsorption. This project was conducted in homogeneous systems, but it can be useful to study the behavior of heterogeneous systems.

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Reviewed by V. Vivek, Spring 2008.

Introduction and Background:

The paper by Wang and Tanaka describes the use of a new polymer APNVF (partially aminated poly –N- vinyl formamides) that uses a dual retention aid system (second component: alum) to enhance the sizing efficiency of neutral to alkaline sizing systems. The paper further describes the use of this polymer in the retention of calcium carbonate as fillers. It’s a well-known fact that use of calcium carbonate helps in getting printing properties and more importantly print gloss, if used as filler or used in the pre coat recipe of coating formulations. The author suggests that the use of APNVF should be useful, as it consists of primary amino group and a formamide group in the same polymer chain. Lastly the author directs the reader to the effects of addition of this polymer addition to wet and dry strength improvements.

Discussion:

The authors here in the paper have chosen acidic sizing for conducting the experiment, which in past has been abandoned my many papermakers due to newer sizing methodologies and also due to the problems faced by the user when acidic sizing is done. The paper rightly takes the reader to the issue of filler retention and strength improvement, which is a major challenge faced by paper makers today. The reader is then encouraged to ask several questions that are related about the size retention, fibre source, presence of sulphide and chloride ions in the system, chemical addition sequence, etc.

The following are some points, which if the authors would have highlighted them, could have made APNVFs more effective for immediate machine use. The study has been mainly conducted on HBKP. The pulp was beaten in the lab beater using the standard methods. But in real practice there are a large number of fibre sources that are used for papermaking. The study should have included more varieties of fibres . The paper does not describe how the sizing retention was tested. The Stockigt method gives the sizing value (Cobb), but not how much of the sizing chemical was retained. The paper does not illustrate when the sizing was checked, i.e. whether immediately or after 24 hours. In the latter case one can presume that on machine curing is not feasible in this case. Also attention may be drawn to the fact that retention aids are effected by the presence of sulphide and chloride ions too, which may exist in the paper making system, a little consideration of this aspect would have made the paper even more understandable. The paper says that handsheets with known consistency were prepared and a sheet of 60 gsm was prepared using the standard TAPPI method. Usually certain other chemicals are also added in the system, and as the paper suggests, calcium carbonate retention was also studied, but the preparation of handsheets does not mention the order of addition. The cationic demand of the solution was also not measured in the process. It is always essential to address the amount the entrained air in the system which affects sizing to a large degree.The paper gives a good illustration on the retention of calcium carbonate and a comparison with the sizing achieved. As the dual polymer in the retention system studied in the paper consists of APNVF and alum, the author does not describe whether the analytical grade of alum used was ferric or non ferric.

The paper gives an excellent SEM image of the sizing effect on the pulps, which enables the reader to appreciate the use of APVNFs to the emulsified rosin sizes. The paper defines well about how each of the different APVNFs acted with specified dosages of alum and rosin. The paper usefully determines the effect of polymer on the wet and dry strength of paper. But it seems after reading the necessary parts of the paper that either this APNVF can be used for calcium carbonate retention or as a strength improvement polymer at one time only.

However even after these above mentioned points the reader is hopeful that further investigations on APNVFs can make it a multifunctional, cost effective additive and ready for industrial use.

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“Polyacrylamide as a Filler Retention Aid for Bagasse Paper Pulp” by Ibrahem, A. A., Nada, A. M. A., El-Saied, H., and El-Ashmawy, A.E. (2005).Ang. Makromol. Chem. 127, 89.

Reviewed Xiaomeng Liu, Jan. 22, 2008.

Introduction

In this paper the authors showed that the polyacrylamide (PAM) could be used as a retention aid, especially in the case of a sample that had been hydrolyzed for 2 hours. The PAM was used in papermaking processes and the effects of adding PAM, including the prepared PAMs hydrolyzed for 2 and 4 hours, as well as a commercial polymer (Accostrength 86) were compared in terms of the retained amount of different paper fillers. The authors also considered the effects of the different retention aids on the strength properties of the paper sheet. All of these results demonstrated that the authors comprehensively considered the basic functions of PAM as a filler retention aid for bagasse paper pulp. However, there are some incompletely analyzed figures and unclear conclusions from the experimental results.

Background

During the processes of papermaking, fillers are usually added to increase the opacity, brightness, smoothness, printability, density, and improve the appearance, especially in printing, writing and coated grades. The commonly used fillers are calcium carbonate, titanium dioxide, silica, and talc, etc. However, the use of more fillers in these grades will tend to decrease physical strength of paper sheets, and because of various mechanical and chemical factors, the losses of fillers will increase especially in the formation section. To balance these advantages and disadvantages of addition of fillers in the printing paper, it is necessary to add a retention aid to increase the strength properties of paper and the retention rate, which means to prevent the losses of inorganic fillers, as well as cellulosic fines. The retention aids such as AM-dextran graft copolymer, cationic starch, blends of nonionic and cationic surfactants and hydrolyzed PAM are usually chosen in the processes of practical production. The authors in this paper studied the effects of the different forms of hydrolyzed PAM on the retention of different fillers during the formation of the bagasse paper and the strength properties of this kind of prepared paper sheets.

Discussion

In the experimental part there are some omissions about the actual experiment which can be expected to be confusing to the reader. In my opinion, the authors should introduce what the commercial polymer, Accostrength 86, is and what kinds of properties it has. They should also explain in detail regarding how the prepared PAMs were produced and the basic characteristics of them, such as the molecular weights and the charge densities, as well as the chemical analyses of the aids to help the readers understand the chemical principle of the effects of different PAMs on the strength properties of paper sheet.

In the first part of results, the authors observed the individual effects of each of the substances used as retention aids – the different concentrations of them on the strength properties of paper sheets. By doing so they could find the meaningful concentration of the different retention aids to make the later work much more valuable and not time consuming. They clearly explained the trends of the breaking length and burst factor with respect to the increasing of the different polymer addition. However, there is a lack of specific explanation to justify to the readers why they neglected the original decrease from the blank values, what happened during that processes and how they conclude that “the addition of 0.5% polymer slightly affects the strength properties.” Based just on the figures, the readers cannot be expected to observe any special differences to be able to reach the conclusion that the 0.5% level should be selected polymer addition to study its efficiency as a retention aid. Since all the later work was done under this specific addition of 0.5% polymers, this is a serious omission, which could not convince readers to believe that the authors could draw the later experiment and the conclusion of this paper. If the authors could add the explanations, such as considering that the use of more retention aid will have the negative effects on the strength properties of the prepared paper sheets, because the function of electrostatic and charge stabilization on the surface of solids in the furnish could resist the solids flocculation, the choose of the favorable addition of polymers should be based on the lowest treatment level of the polymers, this part of conclusion will be more convincing.

The authors investigated the effects of adding PAMs on the retained amount of different paper fillers, including titanium dioxide, silica and kaolin. They used different concentrations of fillers with 0.5% retention aids to test the retained amount of these fillers during the processes of sheets formation. They reached the clear conclusion that the higher saving of the fillers could be obtained when PAM that had been hydrolyzed for 2 hours was used to increase the retaining amount of no matter what kinds of fillers used.

After showing the well-known effects of addition on the retention rate with changes in the types and amount of fillers during the formation of paper sheet, the authors demonstrated that it was important to test the strength properties when different fillers were used in the presence of PAMs. They tried to draw conclusions based on the effects of PAMs with the different concentration of titanium dioxide, silica and Kaolin on the physical properties of paper sheets. However, when they made some descriptions and conclusions, the analysis began to get confusing. The figures concentrate on the percentage of retained fillers but not the adding fillers, which are the totally different concepts. They analyzed how the strength properties change with the amount of added fillers, but from the figures one cannot see any relationship between how much fillers will be retained and how much fillers were added. Perhaps the authors know that the answer, but they have not shared that information with the readers. Based on this kind of analysis they could not convince the readers to believe that their conclusions from the figures make sense. I suggest that there should be a table which could give the relationship between the adding fillers and the retained fillers besides the figure or they could analyze the strength properties through the relationship between the retained fillers and the physical properties.

Finally, the authors draw some general conclusions from the results. In the first conclusion they summarize that “PAM can be successfully used as a retention aid in paper processing”, but in the present paper they just could get the conclusion that the PAM as a filler retention aid is effective for bagasse paper pulp or a similar pulp. The second conclusion also gives readers some confusion, because the words “partially hydrolyzed PAM” also includes the sample hydrolyzed for 4 hours. It is necessary to be clear that the favorable results were achieved by PAM that had been hydrolyzed for 2 hours.

In conclusion, this paper depicted a comprehensive way to analyze the effects of PAMs as fillers retention aids on the retention rate of the fillers during the formation of sheets and on the physical properties of these prepared paper. It is suggested that the authors supply some more details about the properties regarding the retention aids, especially in the case of the PAMs, and fill in some omitted details that tend to blur the analysis from the resulting figures. With such improvements, this paper would be much more convincing to the readers.

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“A Model Colloid for Flocculant Testing” by R. Cong, T. Smith-Palmer, and R. Pelton, J. Pulp Paper Sci. 27 (11), 2001

Reviewed by Douyong Min, 2008

Introduction

In this study, authors proposed a new colloidal model, i.e. dextran sulphate-modified precipitated calcium particles (DS-PCC), to narrow the gap between practice and laboratory bench. Due to dextran sulphate’s negative charge, it can absorb on positive PCC surfaces, thus changed the PCC’s surface charge, and stabilized the PCC particles in suspension. The authors characterized this new model and demonstrated its flocculation behaviors in the presence of some commonly used retention aids such as polyacrylamide, cationic polyacrylamide, poly (ethylene oxide) in conjunction with commercial cofactor. By these works, the authors discussed some experiments’ results and gave possible explains about flocculant mechanism. Besides praising authors’ creative idea and instructive works, readers should recognize some flaws of these works.

Background

In paper industry, there are many water-soluble polymers employed to enhance the deposition of colloidal filler particles onto the fiber surfaces and improve the physical properties of the product paper. There are three main mechanisms to explain the flocculant process, charge neutralization, charged patches, sweep, and bridging, respectively. Because there are special components of the mechanical pulp i.e. a high concentration mixture of dissolved and colloid substances (DCS), it is very difficult to clear its flocculant mechanism. Although there were some procedures to mimic this special flocculant process, they didn’t draw satisfied conclusions. Because there is plenty of negative DSC, authors proposed a new model to demonstrate this special procedure. PCC absorbed with dextran sulphate (DS) on the surface to model the fillers in mechanical pulp. They then characterized its properties and demonstrated its flocculation behaviors interacting with different flocculants. After all, these works are very important to explore the flocculant mechanism and the development of practical produces.

Discussion

To begin, the authors prepared the DS-PCC and characterized its various properties. As described in the article, the DS-PCC is synthesized from different concentration DS solutions mixed with standard PCC solution. The amounts of adsorbed DS were determined though back titration using polybrene and PVSK. But a problem appeared when authors used the same method to determine how much DS would desorb from the PCC’s surfaces. Due to electrostatic attraction, the negative DS adsorbs on the positive PCC’s surfaces; if there were any desorbed DS, they would adsorb on the additional pure PCC’s surfaces. So the amount of the desorbed DS couldn’t be calculated by back titration method. If authors wanted that result, they could use de-ionized water to substitute pure PCC solvent. In the paper, authors prepared two sample groups with pH 7.7 and 7.5 respectively. However, only electrophoretic mobility was done with pH 7.5 group. So did it mean that the DS-PCC’s electrophoretic mobility in pH=7.5 was same as pH=7.7? But I don’t think so, because in different acid levels they would have different electrophoretic mobilities due to different charge screen impaction. And authors didn’t compare these two different pH systems to show any different flocculant results. Thus, I think authors should do electrophoretic mobility trial in pH=7.7, and focused on it.

Secondly, authors said that the optimal flocculation occurred when 16 mg/L DS were present in the 1g/L PCC suspension and 8mg/L DS was absorbed and 8mg/L was free. Readers can only get that the system (16 mg/L DS mixed with1g/L PCC) had the best relative turbility result and can’t have an idea about that there were 8mg/L free DS in these systems from authors’ data. The second question is that author said the charge density of cationicity of the CPAM didn’t have any influence on flocculant results. As authors said in the paper, adsorbed different DS and with different free DS, the PCC’s charge must be different. So it is common that different charge density of CPAM will have different influence on flocculant with different DS-PCC based on the electrostatic attraction or mechanism of neutralization. For example, CPAM35 maybe could have more efficiency with more free DS or higher charge density PCC than CPAM15, because CAPM35 can neutralized more free negative DS and higher charge density PCC. So in the case of CAPM35 the optimal flocculation maybe occurred when there was 20mg/L DS in the 1g/L PCC suspension. Thus I think authors should do more research to demonstrate absorption details. In addition, it is said that in low concentrations, PAM was a more effective flocculant than CPAM, and described this phenomenon as being a result of bridging between PAM and DS-PCC. Yes, it’s right because there is a well known bridging mechanism to explain flocculation. There are some attracted effects between particles and polymer chains. Surely, there are many factors to affect these impacts, such as particle and chain ratio, initial particle’s concentration, flocculation’s condition. Thus, if PAM has such effect, the CPAM also can do this because they are both long-chain polymers. So authors should give more information to rule out the possibility that CPAM doesn’t have such influence. At last, authors compared CPAM and PAM with different molecular weights. I think the results would have been more representative if the authors had compared the same or close molecular weight flocculants.

The DS-PCC model gives some useful information, and can explain some phenomenon. But the model is still very simple. In practice, there are many byproducts from cellulose, hemicellulose, lignin and extractive with different charge, molecular structure, and mass and so on. So there is still much work to do to fully demonstrate the mechanisms of flocculant action in mechanical pulp furnish.

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Reviewed by Maria Soledad Peresin, Spring 2008

Introduction

In this work, the authors analyze the effects of adsorption of cationic polyacrylamide on pulp fibers at contact times relevant to the practical application of retention aids in papermaking. The main objective of this study is to analyze whether there is a correlation between the surface coverage and the flocculation at very short contact times. In my opinion, they clearly explain basic concepts that are useful to understand the mechanism of flocculation and re-dispersion, developing ideas from the general to the particular, thus making the article “easy to read”.

Background

The authors start their publication by stating that cationic polyacrylamide is a system used as retention aids in papermaking processes in order to retain fiber fragments and mineral fillers. Among the concepts explained by the authors, there are:

Phases of the flocculation process induced by this polymer:
Adsorption of the polyelectrolyte onto the fiber surfaces
Formation of flocs
The fundamentals of the adsorption process of the polyelectrolyte on the fiber surface (Brownian motion or turbulent transport make the polyelectrolyte collide with fibers with the consequent adsorption followed by reconformation and finally penetration when it is feasible).
Times required for the release of ions

The nature and characteristics of the adsorption process of cationic polyacrylamide onto cellulose:
Electrosorption process where the driving force is entropic.
There do not exist any non-electrostatic interactions (recent investigations show that these kind of interactions exist on films of cellulose)
Mechanisms of flocculation: bridging and “patch”-flocculation. The authors suggest that polyacrylamide-induced fiber flocculation is described by the bridging flocculation model, and finally they draw the conclusion that bridging plays a significant role.

Discussion

By the experiments carried out (adsorbed amount and flocculation index) the authors effectively analyze what are the factors that could be affecting the change of the adsorption of C-PAM on the fiber surface with time. They are:

Reconformation of the polymer from a looped to a flat conformation: this is expected to be reflected in an increase of the adsorption which is emphasized with contact time. Even though the process of reconformation can take several days, the experimental available data from the investigations are based on shorter contact times (from half a minute to 30 min).
During the experiment, the adsorption of the C-PAM achieved a level of 100%, but only in the case of low levels of addition. Under those conditions, adsorption is not affected by the contact time. The C-PAM adsorption after few seconds is significantly lower than at equilibrium after 30 minutes. The authors hypothesize that that situation could be originated by a kind of initial saturation due to electrosorption (charge on the polymer is combined with those charges present on the surface).
C-PAM size: it has a high molecular weight and unavailable to enter into the fiber, so the amount of charge will remain independently of contact time. A non-electrostatic barrier can be result of a geometric saturation of the fiber surface. The initial conformation of the polymer on the surface is the same as in solution which causes a non-equilibrium adsorption barrier, formed by non-neutralized cationic groups preventing the further adsorption of the polymer. These two factors explain why at full surface coverage, there were just 2% of adsorbed charges over the total fiber charge but after 30 minutes, the percent of adsorbed charges was 15%.

One interesting feature of the work of Solberg and Wagberg is that the measurements of polymer adsorption and fiber flocculation were made simultaneously. This fact allowed them to represent fiber flocculation as a function of the adsorbed amount of polymer and to calculate a maximum in flocculation which correlates with the model for bridging flocculation by La Mer and Healy: around 50% surface coverage by the polymer.

As a conclusion, Solberg and Wagber assert that cationic polyacrylamide adsorption is not influenced with time on the time scale relevant for standard papermaking conditions. Solberg and Wagber explain that as time increases, the positive charges of the cationic polymer are neutralized by the negative charges on the surface of the fibers as the polyelectrolyte reconforms to a flat conformation on the surface. Besides this, they found the flocculation maximum at 50% surface coverage situated below of the point of charge neutralization. This fit as a good correlation with the model for bridging flocculation (La Mer and Healy).

Finally, they demonstrate that fiber fines have a large influence on the flocculation by C-PAM. Pulp suspension with C-PAM become difficult to disperse when there is present a considerable amount of fines but in the experiences but the authors found out that dispersion is difficult even when the amount of fines present is small. They indicated that it is due to a synergistic interaction between fines and the C-PAM, but this aspect of the work is still in development.

As regards to the experimental section, Solberg and Wagberg present a good description of the materials and reagents that were used during this work. However, all the observations are developed with use of a totally chlorine-free, refined and bleached (TCF) softwood kraft pulp. It would have been reasonable for the authors to have carried out similar experiments with raw material of different composition (e.i. Hardwood) to reach a valid conclusion (or at least do not generalize the conclusions). The fact that they used a Dynamic Drainage Jar to determine the fine contents is important because this device works in conditions of both turbulence and high rates of hydraulic shear (papermaking conditions).

The influence of presence of the amount of fines in flocculation processes represents a problem for the papermaking industry and the mechanism of induced flocculation and re-dispersion of pulp fibers is essential to obtain a high quality final product. Because of this, it is necessary to have a strict control in this aspect and it is the counteracting effect of the use of C-PAM in the process. This article clearly summarizes the fundamentals of the mechanism of flocculation of C-PAM and also provides evidence of this, as well of the influence of contact time of the polymer in flocculation. On the other hand, it also sets some key points for future works as regards to the influence of fines in this mechanism. Solberg and Wagberg correlate their experimental work and the discussion of results, also they use expressions that even though technical, are yet completely understandable.

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“Core shell: the latest innovation in polymer technology for the paper industry” by Alessandra Gerli, Sandra Berkhout and Xavier Cardoso, Paper Technology 44(2), 38-42 (2003).

Reviewed by Hao Chen, Spring 2008

Introduction

In this paper the authors present the practical application of a new polymer technology, which is named “Core Shell,” in the papermaking process. Experiments were carried out in laboratories and commercial paper machines. The results showed that Core Shell polymer on could provide a significant increase in on-machine retention of fines and fillers compared to conventional dry and emulsion polymers. Core Shell polymer can produce a higher floc-shear resistance when the retention program was under high turbulence. The authors also emphasized that the Core Shell polymer could be used as a single flocculant program or in combination with microparticles.

Background

With the development of modern papermaking technology, an increasing amount of filler is being added to furnish. Paper mills can benefit a lot by adding filler, including saving the cost of raw materials, lower energy consumption, and improved print quality. However a great deal of filler and fines tend to be pulled out of the sheet during the formation process, which could undoubtedly cause economic loss. Papermakers are motivated to find ways to enhance the retention of fines and fillers. A wide range of chemicals is currently being used as retention additives. The first retention and drainage program were based on a single polymeric flocculant component. But In the past years, most specialty chemical companies pay more attention to the development of multi-component systems, because these systems allow the papermaker to achieve a balance between retention, drainage and formation. Core Shell is a polymer technology recently launched by the Nalco chemical company. Core Shell liquid polymer showed significant advantages when was added to stock as a retention additive, compared to conventional emulsion and dry polymers.

Discussion

The main goal of this study was to provide proof for the significant benefits by implementation of Core Shell polymers in the papermaking industry. For this purpose, a series of experiments were carried out in the laboratory and several cases obtained from paper mill were studied.

In the first part of the study, the authors describe how Core Shell improved on-machine retention. In simple words Core Shell polymer was added into the furnish in combination with 0.5kg/t of Nalco 8692. Then, ash retention data were collected by using Dynamic Drainage Jar (DDJ) testing techniques. With simple bar charts, they clearly demonstrated that the addition of Core Shell improve the ash retention significantly compared to others retention additives, including the utilization of dry polymers and cationic charge emulsion polymers. The authors also compared data that were obtained by the application of Scanning Laser Microscopy (SLM). According to the authors’ explication, the Mean Chord Length (MCL, or mean particle size) is an instrument output of SLM, and the maximum Mean Chord Length achieved after flocculation addition (△MAC) is proportional to the first pass retention data obtained by using the DDJ. This experiment showed that Core Shell could engender a higher retention rate. It is worth mentioning here that with the increasing dose of Core Shell from 0.25kg/t to 0.5kg/t, the retention rate rose remarkably in the mean time.

After achieving their first goal, the authors went to the next stage and focused on the shear resistance of flocs produced by Core Shell. Experimental results revealed that the initial floc size created by dry polymer decayed much more rapidly than in the case of the Core Shell polymer, which indicated that Core Shell polymer could produce a floc having a higher floc shear resistance. In this period, experiments were designed to compare the floc-shear resistance produced by Core Shell polymer and microparticle system. As showed in a figure, Mean Chord Length data collected after addition of Core Shell was higher and could come to a peak value in a shorter time than those obtained by adding dry polymer in combination with bentonite. Furthermore, the drainage that resulted from Core Shell polymer, under the same furnish conditions, was significantly higher than that produced by the microparticle programme. The subsequent research showed that the reflocculation ability of Nalco 8692 was improved when the micropaticle was used in combination with Core Shell polymers. That means Core Shell polymer made the ultra POSITEK microparticle operate more efficiently.

Core Shell polymer technology was not only developed in the laboratory stage, but also applied to a real word commercial system. The last part of this paper took recycled board, uncoated free sheet and newsprint as examples. Case studies demonstrated that using Core Shell polymer could provide significant papermaking benefit such as better and more stable retention, improved paper quality and improved system cleanliness.

In summary, this paper described the advantage of Core Shell polymer. But I think everything has two sides, if the authors could write something about its shortcoming, the authors’ points of view would be more convincing.

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Competitive Adsorption of Alkyl Ketene Dimer (AKD) on Pulp Fibers and CaCO3 Fillers” by Petteri Voutilainen, Department of Paper Chemistry, Abo Akademi Univ., Turku, Finland

Reviewed by Sameerkumar Patel, Spring 2007

Introduction

Although it is difficult to understand the whole mechanism and complexity of adsorption phenomena, this paper provides fundamental information that can be utilized to enhance sizing of paper within the papermaking process. The author, Petteri Voutilainen, provides fundamental concepts of surface morphology of fillers and fibers, and adsorption of AKD on the surface of fillers and/or fibers. This paper is focused on adsorption of AKD on pulp fiber (cellulose) and CaCO3 fillers (PCC-Precipitated Calcium Carbonate and GCC- Granulated Calcium Carbonate (chalk)) and provides very useful information about the surface phenomenon of fiber/fillers. I believe this paper provides basic information, which is essential to understand surface phenomena of fillers/fiber, which could increase efficiency of papermaking process, but the research did not reach its full potential due to certain limitations like this research carried out on the basis of “no other additives.”, and extrapolations of results based on assumptions.

Background

AKD is the most widely used sizing agent for the manufacture of paper. In the sizing of paper one creates a layer of AKD on fillers and fibers surfaces by physical and/or chemical means to reduce water wetability of paper. It is very important to understand adsorption mechanism of sizing agent, as it allows us to determine when and where we have to add fillers or/and sizing agent in wet end of a paper machine. This research paper is about adsorption of AKD particles on fillers (PCC and chalk) and fiber (cellulose) surfaces. The author took two filler/softwood kraft fiber mixtures, one containing chalk as filler, and other containing scalenohedral PCC as filler, and carried out AKD adsorption on those mixtures. The author studied how much AKD adsorbed on filler (chalk and PCC) versus fiber (cellulose) surfaces, and why the adsorption was less on fiber as compared to filler. The author also carried out extraction of non-reacted AKD by THF (tetrahydrofuran) to study how much AKD was reacted with filler and fiber. He found chalk adsorbed more AKD than PCC and, provided justifications for that. He also found there was no major change in adsorption of AKD on fiber surfaces when the adsorption was carried out either with chalk/fiber or PCC/fiber with increase in the % filler addition. He found PCC adsorbed more effectively on cellulose surface than chalk due to the strong interaction between negative cellulose and positive PCC than negative cellulose and negative chalk. This research was carried out with radioactive 14C-labled AKD. Non- adsorbed AKD was analyzed with a scintillation counter, filler particle size was measured by wet sedimentation, and surface analysis was determined by ESCA.

Discussion

As the adsorption phenomenon is quite complex and difficult to understand within the context of a single theory, the author did lots of cross-referencing to establish a proper understanding of surface phenomena of filler and fiber. I think, by providing this fundamental information about adsorption of sizing agent on filler and fiber surfaces, the author did a great job on the behalf of papermakers; we could utilize this information for our core research or to improve process efficiency. Although this paper provides some very good information about adsorption of AKD on fiber/filler, it could not able to explain some questions that may arise by reading it like what is optimum amount of AKD could adsorbed on PCC, chalk, and fiber, and this research was carried out on the basis of “no other additives.” which means that it was carried out only with the filler, fiber, and AKD, while in an actual case the wet end of a paper machine contains other additives like recycled furnish, and different types of fibers such as recycled fibers, that could have great effect on the adsorption of AKD on fiber/filler surfaces. I think this omission could affect greatly the results of this research when an attempt is made to replicate the results at a commercial scale.

According to basic understanding, fillers with higher surface areas are expected to have higher affinity for adsorption due to the availability of free space for adsorption, but in this case, chalk (surface area=2.0 m2/g) had less surface area than PCC (surface area=7.3 m2/g) even though it showed higher affinity for adsorption of AKD on surface at low addition level on AKD. This is attributed to the presence of the inorganic oxides (Al- and Si-) on the surface of chalk; furthermore, chalk has an anionic surface charge due to adsorbed polyacrylates and/or phosphates could increase affinity for adsorption of AKD. Both chalk and PCC adsorbed almost same amount of AKD, but the chalk had approximately 4 times less surface area than PCC. These results imply that the chalk had 4 times more adsorption capacity in comparison to PCC. We might think why would PCC had less capacity for adsorption even though it had higher surface area. This was due to presence of weak positive charge on the surface of PCC, which reduced affinity of cationic starch particle to adsorb on PCC surface, but PCC had some negative sites on particle due to CO3-2 that could contribute to adsorption of AKD on its surface. Overall, due to all these factors PCC had less affinity for adsorption than chalk. Non-extractable AKD on PCC surface was found higher than chalk due to the interaction between AKD and PCC, as PCC had uniformity in its crystal structure the intercrystalline voids were responsible for strong adsorption of AKD on its surface. While in case of chalk, there is no such uniformity in micro structure, so, it has less amount of non-extractable AKD on its surface as compared to PCC. Here the author mentioned other factors that might be responsible for this, but did not provided any theoretical or practical justification that could support those factors. I believe the provided reasons are plausible, but if author provided some evidence that would make good impression on readers.

The fiber surface has a low affinity for adsorption as compared to filler. The difference can be attributed to a lower surface area as compared to filler, but cellulose fiber has a natural capability to adsorb AKD due to the presence of anionic charge on its surface, which found to be limited, so overall adsorption would be remain limited. When we think about different pulping techniques and fibers produced by those techniques; surface area of fibers mainly depends on pulping techniques. Mechanical fiber has a higher adsorption capacity than unrefined fiber as it was beaten and had a high specific surface area than unrefined fibers and this could be factor that governs adsorption of AKD on fiber’s surface. In addition to that, filler loading would not have much effect on AKD adsorption on fiber surfaces, and the amount of AKD adsorbed on fiber surfaces was limited to small amounts in both types of fillers. In justification of that statement the author made an assumption that only a portion of the adsorbed AKD became reacted to cellulose. In the case of PCC, adsorption of AKD onto the fiber surface was increased due to PCC interacting more significantly and it increased with increase of filler addition due to the incomplete separation of filler and fiber phases that could increase the AKD retention onto fiber surface. While in the case of chalk, adsorption of AKD on fiber surface was remained constant with increase of filler addition and it was limited to about 0.2 mg/g of fiber fraction, which was almost less than half of AKD adsorbed on fiber surface when PCC was used as filler. This is due to separation of filler (chalk) and fiber phases and weaker interaction between negative cellulose and negative chalk. Non-extractable AKD was also found less in chalk as compared to the PCC, but both cases support there was reaction between cellulose and AKD and probably the formation of covalent bond between AKD and cellulose, and such covalent bonds would not let AKD to go away from the surface of the fiber. However, the study, as well as other references, indicated that there were an existence of covalent bond between AKD and fiber surface, readers should have to account that results were only based on the extraction of non-reacted AKD. I think there should be formation of covalent bond between the filler and AKD, and the fiber and AKD, as sufficient amount of AKD retained on the surfaces and would not extracted by THF furthermore, I think PCC has higher capacity to form covalent bond as it retained higher amount of AKD on its surface and on the fiber surface, but it required further study.

Finally, I believe this was a fundamental study and we should have to appreciate the author’s work as a means of achieving gains in a theoretical understanding. The results are quite useful for further study of covalent bond between AKD & fiber and AKD & filler and surface behavior at elevated temperature. We can also utilize these results to enhance efficiency of papermaking process. As I mention earlier, this research had been done with “no other additives.” and ambient temperature. Therefore, we should have to consider these parameters when we would like to implement or utilize the fundamental principles of this research paper. This paper is very useful source for further study of AKD and chalk and/or PCC interaction with other types of fiber or filler/additives.

Competitive Adsorption of Alkyl Ketene Dimer (AKD) on Pulp Fibers and CaCO3 Fillers” by Petteri Voutilainen, Department of Paper Chemistry, Abo Akademi Univ., Turku, Finland

Reviewed by Sameerkumar Patel, Spring 2007

Introduction

Discussion

“Practical experiences in Additive Screening Using a Torque-based Flocculation Analyzer”
by: Anker L., S. Proc. TAPPI 2001 Paper makers conf., TAPPI Press, Atlanta 2001.

Reviewed by Ronalds W. Gonzalez, 2007.

Introduction

Lawrence S. Anker, in this paper, presents the practical application of the torque-based flocculation analyzer (TBFA) in the determination of the effects of polymers as flocculating and coagulating agents, and also analyzes the behavior of this “new” technology (in this field) with respect to commonly used techniques. With the TBFA, it is possible to evaluate the effects of different polymers in the formation of flocs and also graphically observe the resistance of these flocs to shear forces. Experiments were carried out in several mills under different scenarios. TBFA could be a useful tool in the selection of new potential polymers that could eventually be tested under real-operational conditions. The results from the TBFA clearly show a high relationship (statistic correlation) between the loads of the impeller motor and the retention-drainage values as measured using standard techniques; nevertheless, it would be important that the final results reported by this technique were presented in usual retention and drainage units instead of Newton units. The author emphasizes that TBFA can give us technical-analytical data about fiber flocculation (and it is supported), but the author fails in providing reliable evidence about the retention of fine particles.

Background

In the papermaking process, flocculation is the first step in the formation of the paper web. Papermakers try to control the level of fiber flocculation in the paper machine, specifically in the headbox. If we look through a sheet of paper (in presence of light) it is possible to observe some dark areas, these areas represent the agglomeration of fibers, known as fiber flocs; this non-uniformity of the paper reduces some strength properties of the sheet (uniformity of paper appearance is a product differentiation in some market segments). Besides the mere fact that flocculation is the first step in the paper formation; flocculation makes it possible to attach functional and process additives onto fiber surfaces. In order to increase the retention of fines particles, papermakers add flocculating additives (in some cases the speed or run ability of the paper machine could be limited by the drainage and particle retention). The effectiveness of these polymers can determine bonding formation between fibers and particles; for example, the fixation of fillers onto the fiber surfaces is strongly required in uncoated free sheet paper production to achieve brightness or opacity properties. The flocculation and particle retention values can be estimated using several methods including Modified Schopper-Riegler (MSR), the Canadian Standard Freeness (CSF) and the Dynamic Drainage Jar (DDJ), as well as first pass retention and first pass ash retention. New techniques that give us more complete information are always welcomed in order to improve the technical analysis at mill.

Discussion

As a first step the author describes how the TBFA works, in simple words: it is added an aliquot of furnish to a sample cup, in the sample cup is inserted a impeller, a cell in the motor impeller register the changes of rotation resistance in the solution, when flocculants or coagulants are added to the sample, flocculants begin to form, which make the impeller movement lower or with more friction, this resistance is registered, as the impeller continues its rotation, flocs begin to break down. All the process is registered, so it is possible to have a complete set of values that displayed in a graphic can be observed the effect of polymers in the formation of flocs as well as resistance of flocs to shear forces. The set of values in a graphic is very interesting as it can be examined the performance of the polymer in flocculating in function of time, is this info of practical concern? Yes, we must know very well the time of reaction of these polymers.

As part of the goals of the research, experiments carried out with the TBFA also were done using traditional methods. A total of seven experiments were performed in different in-mill conditions. The relationships between the peaks of flocculation and the values obtained form traditional methods correlate very well, but applying the TBFA results come faster. The reader should be wondering about the effectiveness of this technique in the determination the fines retention, and in the way that the data and info are presented, it is understandable to believe that the TBFA can be useful for flocculation recognition but that it can failed in determine the retention of fine particles.

It is expected that after some application of shear forces during short time fiber flocs should breakdown as can be seen in figure 18, 19 and let’s say also figure 24, but figures 22, 15 and 17 show that after applying shear forces the flocculation levels “are” too high in comparison with other polymers tested, it would be interesting to find out why these flocks do not disintegrate during the period of observation, may be it is needed to expand the time of observation/testing?

The calibration of the torque-based flocculation analyzer is an import step when testing new polymers, the friction of the impeller with some particle in the solution could give erroneous result about the action of polymers in flocculation.

In conclusion, it can be said that this technique is useful in identifying the chemical and the dosage where occurs better flocculation (the author proved the application). Although in most of the cases there is a strong correlation between the torque of the sample with the retention or drainage, this equipment does not measure this properties directly, one solution could be adjust (with specific slurry condition) a multivariable model that besides give result in Newton also give results in (e.g.) ml. Advantages: quick results in comparison with traditional equipments: quick decision making.

“On the mechanism of cationic-polyacrylamide-induced flocculation and re-dispersion of a pulp fiber dispersion” by Daniel Solberg, SCA Packaging Research, Sweden and Lars Wagberg, Royal Institute of Technology, Sweden, Nordic Pulp and Paper Research Journal, Vol. 18, No. 1/2003.

Reviewed by Norris Pike, 2007.

Introduction

In this paper by Solberg and Wagberg, the authors speak about measuring cationic polyacrylamide adsorption on pulp fibers. They attempt to force the fibers to flocculate during time periods that are pertinent to normal retention aids applications. They found that flocculation was maximized at approximately 50% surface coverage. At above 100% surface coverage, the fibers were re-dispersed, according to the authors’ research findings. In my mind, Solberg and Wagberg tend to overcomplicate the process and its description. They use technical terms derived from Latin in cases where simpler words would have sufficed. I had to use a dictionary and glossary as well as enlist the aid of the course instructor throughout the paper. While I realize flocculation induction is needed in helping to attach fillers to fibers sometimes, in papermaking, there can also be such a thing as too much of a “good” thing.

Background

Solberg and Wagberg assert that cationic polyacrylamides (C-PAM) are the major basis for retention aids for adsorbing fiber particles and mineral fillers in papermaking. The authors describe that this happens in two phases. First the polyelectrolyte is adsorbed onto the surfaces of the fibers. After this, flocs are formed. They state that this is accomplished either through “Brownian motion” (somewhat random movement of particles susperded in a liquid) or through “turbulent transport” (occurring during the flow of liquid through approach system pipes or in chests with agitators). Solberg and Wagberg state that the action of the cationic polyacrylamide has been previously reported to be due to “electrosorption” which probably means the molecules are attached through the attraction of oppositely charged molecules. The authors’ findings also state that adsorbed charges after a short contact time account for only 2% of the total fiber charge, but the adsorbed charges contribute 15% of the total charge after 30 minutes. They surmise that this adsorption after a short time indicates that the process is not solely controlled by the charges. The authors believe that this shows there may be a “non-equilibrium charge” or “steric barrier” hindering adsorption at short contact times.

Discussion

Solberg and Wagberg state that the main purpose for their research was to ascertain whether there is a relationship between surface coverage and flocculation at the shorter contact times which are more relevant to papermaking. The authors then go on to describe their experimental methods and materials used while attempting to research their objective. They procured totally chlorine-free, bleached Kraft pulp from Sweden from which they subsequently removed the fines through a spraying and filtering process. These fines were removed so that any measurements conducted in the research would be solely on the fibers themselves while looking for possible effects. It appears they attempted to be meticulous about not introducing extraneous ions to the experiment through the use of deionized water. Although they used deonized water in most of the experiment, I noticed they refined the pulp in tap water though. I would tend to think that this refining in tap water might actually force unwanted ions into the fibers themselves. Previously in the paper the authors point out that, through an “ion exchange” process, there is adsorption even at low ionic strength levels.

Solberg and Wagberg go on to report that polymers used as retention aids are normally added during papermaking operations just before the headbox, allowing for 1 to 10 seconds before reaching the headbox. It has been previously found that these polymers are substantially adsorbed at contact times of less than one second. The adsorption of the polyacrylamide after a few seconds of contact with the fibers was measured to be almost 100 % at low addition levels but not at addition levels at a higher amount, namely above 0.4 % mg/g polymer addition. The resulting flocculation of fibers and polymer was found to be greater after being adsorbed for one second compared to two seconds, according to this article. The quality of their research and experimental conditions seems to be very good. Their theories appear to be well supported by their experimental data.

Solberg and Wagberg present a credible writing style while presenting their case. The authors found that when cationic polyacrylamide was added to a fines-containing pulp suspension, the suspension could not be dispersed. This is probably due to the higher surface area associated with fines upon which the C-PAM deposits itself. In the “real world” of papermaking, one will normally encounter fines in papermaking furnishes. As I previously stated, this leads me to the assumption that, in the case of induced flocculation (as with many other things in life), there may be too much of a “good’ thing. While flocculation induction by cationic polyacrylimide addition for the purpose of adhering filler to fibers may be a good thing, flocculation can also be detrimental to other aspects of papermaking.

Based upon my own experience, flocs formed from this flocculation can hinder the appearance of the formation in the paper sheet. These flocs are normally indicative of randomly distributed higher basis weight regions in the paper sheet. Higher basis weight regions also mean there will be lower basis weight areas in the sheet. These lower basis weight regions can contribute to weak spots in the sheet. These weak spots can affect wet web runnability. They can also affect strength properties such as tensile and tear. In filter paper, these flocs will also make air permeability highly variable throughout the sheet. In the more flocculated (higher basis weight regions), the CFM will tend to be lower than in the lower basis weight areas where there are less fibers present to restrict the airflow.

Outside of these last few points, though, it appears the authors have done a reasonably good job in reinforcing their main objective. That goal being, as they stated, to research the relationship between surface coverage and flocculation in the practical contact times associated with “real world” papermaking. Once the terminology is understood, it appears that Solberg and Wagberg have presented a logical description that is consistent with their experimental findings.

“On the Mechanism behind Wet Strength Development in Papers Containing Wet Strength Resins”
by L. Wågberg and M. Björklund, SCA Research AB, Sundsvall, Sweden

Reviewed by Ilari Filpponen
January 2007

Introduction

In this paper the authors described in detail how the wet and dry strengths of the paper can be improved by using polyamideamine epichlorohydrine (PAE) as a wet strength resin. Furthermore, mechanistic aspects related to the interactions with carboxyl groups of the fibres and added wet strength resin are used to support the observed improvements in the wet strength of the paper. As a matter of fact, the investigations with Fourier Transform Infrared Spectroscopy (FTIR) combined with tensile strength tests are pointing out that the reaction between aforementioned carboxyl groups and PAE is taking place, leading to a formation of a saturated ester.

Background

The wet strength of paper is described as the ability of paper to maintain a percentage of its tensile strength when it has been saturated with water. As is well known, the introduction of water to paper will cause swelling phenomena as the hydrogen bond network is ruptured. For decades researchers have been investigated different approaches to improve the wet strength properties of paper. The major focus has been on wet strength additives that are typically polymeric chemicals, such as urea formaldehyde (UF), melamine formaldehyde (MF) and PAE. Despite the extensive studies of different wet strength additives there has been no agreement with respect to the operating mechanisms of these chemicals. However, it is widely believed that UF and MF are conveying wet strength via internal cross linking with themselves. On the contrary, for the PAE resin it has been suggested by several investigators that carboxyl groups on the fibres react with the resin, leading to the formation of ester linkages.

Discussion

The main target of this study was to provide indisputable proof for the aforementioned formation of ester linkage between cellulosic fibres and PAE resin. For this purpose a series of carboxymethylated pulps with different degrees of substitution (D.S.) were selected, since the D.S. was believed to have a strong effect on the final wet strength properties of PAE treated paper. Furthermore, the effect of addition levels of PAE resin in bond strengths was evaluated as a function of D.S. of the pulps.

In the first part of the study, developments of both dry and wet strength were determined for carboxymethylated pulps with different levels of PAE addition. It was found that the wet and dry strength followed the same trends, and they increased not only as a function of D.S., but also with increased PAE levels. This indicates that the strength development is restricted by the bond strength between the fibers. It is worth mentioning here that both dry and wet strength developments leveled off at higher additions of PAE. Although the authors did not provide definite explanation for the strength leveling off phenomena, they are suggesting that increased swelling due to the carboxyl groups in the fiber leads to a higher adsorption of the PAE resin on the interior parts of the fibre wall, where they are not contributing to bond strengths between the fibers. Subsequently, the surface “saturation” point is reached, i.e. increased amount of PAE does not improve the wet strength properties. In addition, the adsorption of PAE is not only governed by the D.S., but also by the geometrically available area, which in turn means that the strength properties cannot be improved infinitely by increasing the carboxyl group content of pulp. It can be concluded that these results point toward the ester formation between PAE and cellulosic fibers as the strength properties are improved along the higher levels of D.S. as well as elevated uptake of PAE.

In order to distinguish the effects of carboxymethylation and PAE resin to the strength improvements, a constant concentration of PAE was used with pulps having different D.S. values. Experimental results indicated that the change in D.S. is more significant for the dry strength properties, whereas the presence of PAE promotes wet strength properties, as the sheet becomes more resistant to the swelling. By reason of the perceived positive effect of carboxymethylation to the dry strength properties, the authors decided to determine the relative bonded areas (RBA) of the sheets. The light scattering studies indicated that RBA increased with the carboxymethylation, which means that the improvements in strength properties were provided by virtue of improved bonding between fibres (addition of PAE) as well as increased bonded area between the fibres. Based on the information above it can be concluded that carboxymethylation seems to develop the strength properties at least in three different ways: by increasing the PAE uptake, by forming ester bonds with PAE and by escalating the RBAs.

The interaction of PAE and carboxyl groups was subsequently studied by preparing sheets with diverse RBA values. The results revealed similar behavior to the previous investigations, i.e. the carboxyl groups enhanced the efficiency of PAE, most likely via ester formation. The final evidence of existing ester linkage was provided by FTIR, as the carboxymethylated sheets with and without PAE resin were measured separately and obtained spectra were then subtracted. After subtraction three absorption bands were remaining. One of them possessed characteristic wavenumbers for saturated esters while other two were derived from the PAE resin itself.

Finally, the reader would have liked to have been offered a few comments regarding practical applications of the findings. First of all, what would be the importance of these findings in a mill scale, as the carboxymethylation hardly is a feasible or an economical approach in perspective of wet end chemistry. Secondly, it would be more convincing to compare the observed FTIR spectrum versus a control sheet without added PAE as the carboxyl groups in carboxymethylated pulp may also react with available hydroxyl groups to form an ester that should appear in very similar region in FTIR spectrum than the suggested ester linkage between PAE resin and cellulosic fibers.

“Nanoparticulars on Colloidal Retention”
by Carr. D, Proc. Wet End Chemistry Conf. Boston, MA, PIRA International, Letherhead, UK 2005,

Reviewed by Anthony Atamimi, 2007

Introduction
In this paper Carr compares the bridging retention mechanism between current commercially available micro-particles and silica nano-particles. Carr also illustrates the advantages of silica-nanoparticles to paper mill operations, and shows how charge neutralization, the main critical feature, promotes shear resistance in order to improve colloidal retention. The author also describes the mechanism.

Carr starts explaining the bridging mechanism from the initially known micro-particles that are normally applied in a colloidal retention using cationic PAM (cPAM) and anionic colloidal silica. The author uses micro-particles of delaminated montmorillonite and cPAM in the colloidal retention system for his work. Montmorillonite has a thickness of 1 nm but length and width at 600 nm; for comparison silica nano-particles that have 5 nm diameter, when considering the approximately spherical primary particles.

Concept and Principle

Montmorillonite relies on a bridging mechanism between the strands of cPAM absorbed on fibers. The bonding is stronger than that between fibers and cPAM due to a greater electrostatic attraction, especially due to the fact that the surface of montmorillonite is more anionic than that of fibers. In the meantime, because of its smaller dimension, silica nano-particles have a farther penetration mechanism of anionic silica nano-particles to fibers in continuation to cPAM’s bridging mechanism between fines and fibers. The addition of anionic silica nano-particles to fibers causes charge neutralization, which brings particles close together, overcoming the charge repulsive forces, and relies on van der Waal’s forces to bind fines material microflocs into fibers. [3]

Carr is not critical of a statement by Penniman [3], who wrote that van der Waal’s forces would be strong enough to bind the fine materials onto fibers. My opinion is that the papermaker relies on hydrogen bonds in order to make a good sheet of paper. The London dispersion component of van der Waal’s forces is too weak, and normally overwhelmed with other forces that act over distances in the colloidal size range. Despite the neutralization happened, there must be electrostatic forces due to a patch-like coverage of various surfaces with oppositely charged materials.

However, the nano-particle’s effect doesn’t take place with cPAM until the silica nano-particles are imparted to the structure of cPAM in which the loops and tails are micro-bridged. [5] According to Anderson and Lindgren, if the amylopectin branches are separated by a distance 5-7 nm, then a <5 nm sol may be optimum for charge neutralization.

Discussions

Effect of particle size on retention and selective deflocculation: Carr places stress on the relevance of micro-particles and their small sizes to shear resistance based on the previous work by Hubbe; the shear resistance of particles attached to a surface is inversely proportional to its size, the smaller the particle, the greater the shear resistance. [8] Carr emphasizes that the key is getting the particles attached to fiber in the first place. It’s therefore advantageous to get fine particles attached to fibers in their smallest dimension as these offer the greatest shear resistance.

With regard to sizing, Carr tries to explain about selective deflocculation based on the work by Odberg, Swerin, and Tanaka; if the internal sizing agent is added before the filler addition in order to try and to keep it on the fiber, there is still considerable transfer of size to fillers. [9] Carr suggests that if the sizing agent can be associated with microflocs of particles closely bound to the fiber, then it is less likely to be transferred to and build up on filler particles. I think that this is a hypothetical opinion by Carr, it may need a further research to prove how strong the correlation between the dosage of silica nano-particles and the degree of hydrodynamic shear required for detachment. Effect of mechanism on shear resistance and selective flocculation: According to Swerin and Odberg, when using the retention system using cPAM and montmorillonite, it is possible to increase shear resistance and at the same time to produce more flocculation- though a smaller floc size. [11] Carr explains that in presence of an optimized charge neutralization mechanism by silica nano-particles, it will give a selective flocculation and stronger bonding between fines and fibers against the shear, and reflocculation effect once shear has been passed. Carr relies on the work by van de Ven and Mason, if the fine material can be deposited on the fiber prior to the high shear of the headbox, it will demonstrate greater resistance than fiber-fiber flocs by entanglement and fiber-fines by polymer bridging. [12]

Effect of reflocculation and mechanism on environment: The author has clearly demonstrated how the above-mentioned concept and principle take place in various data, tables and graphics.In brief summary, Carr finds that (1). The fast drainage time is consistently positive with increased dosage, (2). The high shear rate reduces the capability of reflocculation, (3). The smaller size of nano-particles improves the effectiveness of retention, (4). The high quality of potato starch gives a very positive correlation to total retention and ash retention. Table 1 and Table 2 shows evidence that reflocculation happens. Results of the third experiment that was done on white top liner machine also show a reduction of starch residual in the white water.

Carr tries, but not convincingly, to prove that the degree of structure aspect of the nano-particle is directly correlated to the retention effectiveness. I cannot see the trend consistent in the change of degree of structure. Table 3 shows that total retention and ash retention respectively increase when degree of structure decreases from high to medium. Graph 2 shows that starch retention is larger in the case of a higher degree of structure, in comparison to the case of a medium degree versus low degree of structure. Graph 1, nano-particle of 3 nm with high degree of structure, shows that the starch retention decreases with the increased dosage. I find that Carr suggests that neutralization doesn’t happen, without giving a very clear and solid explanation.

The experiments described in Graph 3 under 700 rpm, which is lower than 1100 rpm described in previous Graphs and Tables, have opened 3 questions and opportunities to new research; (1) What is the trend of starch retention if we change the silica nano-particles’ degree of structure from low to high or the other way around?, (2) What is the aspect that causes the contradictive trend shown in Graph 1; is the size of nano-particles or the degree of structure the more important parameter? Table 3, Graph 1 and Graph 2 are not consistently supporting the trend of starch retention; especially Graph 2 has 5 nm with low degree of structure. We are not sure that the lower starch retention is caused by the larger size of particle or the low degree of structure. I wish the author had used a nano-particle having a low degree of structure with 3 nm diameter in the experiment represented in Graph 2 in order to see the consistency of aspect of size of nano-particles, (3) Are the shear rate and degree of structure together playing significant roles in different result of 3 nm with high degree of structure between Graph 1 and 3?

This article is principally able to guide us in the application of microparticle retention aid systems in the case of a modern hydraulic headbox with high shear stress, and whether we should be focusing on use of retention aid system capable of reflocculation. Based on the reported findings, I would suggest utilizing 3 nm silica nano-particles size with a medium degree of structure. The dosages of the additives need to be checked further with the shear stress rate corresponding to that in a modern hydraulic headbox, so that the additives have the optimum dosage to achieve the maximum starch retention. The use of a high quality of starch will significantly help the fine particle retention and ash retention, and reduce the starch residual, or improve the reflocculation. The careful selection of addition points of filler, sizing agent, starch, cPAM, and silica before the headbox are required to ensure that the fines are bound effectively to the fibers.

Reviewed by Lu Athnos, 2007

Introduction

Grain Processing Corporation has patented a system that they call Filler Flocculation Technology. In this paper, Mabee and Harvey maintain that the preflocculation of filler materials via the Filler Flocculation Technology can provide a significant increase in sheet filler content without loss in strength, optical, or runnability parameters. This paper presented the Filler Flocculation Technology in detail and summarized the advantages which may be provided through use of the process on a commercial basis. The authors did a good job introducing the technology to the public with sufficient facts to back up their statements.

Background

In the papermaking industry, it’s always a challenge to optimize the right mixture of fiber and filler. Increasing filler content in paper can provide the papermaker with numerous benefits, including savings in the cost of raw materials, lower steam consumption for drying, improved optical properties including opacity and brightness, and better print quality. However, there are limits to the amount of filler that can be substituted for papermaking fiber. At high filler contents, paper can suffer losses in both wet and dry strength properties, stiffness, sizing, paper machine runnability and product quality. With the Filler Flocculation Technology that was introduced by Mabee and Harvey, the authors state that paper mills will be able to overcome these limitations and utilize the advantages of increasing the filler content in paper.

Discussion

This paper has a very good structure to describe the context of the authors’ findings. Fist it started by explaining what “Filler Flocculation Technology” is. It is a method in which filler particles are preflocculated using a cationic reagent. In addition, a controlled level of shear is applied to the filler/flocculant combination, providing an end product with controlled particle size and charge characteristics. This leads to improved filler distribution and increased formation uniformity. The treatment system also improved filler distribution, and formation improves strength, optical and runnability parameters for a given filler level.

The paper then reported on two studies conducted at the Western Michigan University, comparing the use of preflocculated and untreated filler addition. The authors used data and figures to compare the results of using flocculated fillers and unflocculated fillers. The results included retention, burst strength properties, stiffness, opacity, and sizing efficiency. The five figures clearly indicated benefits when using preflocculated filler.

When technology is only found in the laboratory stage(s), then the technology is not going to benefit the real world commercial applications. Fortunately the Grain Processing Corporation was granted permission to conduct an extended trial on a 600 ton-per-day, twin-wire paper machine producing reprographic and bond papers. This paper went into the details of describing this commercial application trial. They introduced the Commercial Filler Flocculation Equipment and also provided with a diagram of the system, which was shown in Figure 6 of the article. After describing the trial program procedures, this paper provided four figures showing some critical parameters collected by the mill’s computer system. These figures showed comparisons on the specific Sub 20 grade between a three-month time period prior to the trial and the last two weeks of the trial period. It is a powerful tool to conduct “before” and “after” comparisons. It is a very convincing argument that using the preflocculated filler has made a difference in the paper making process. (It would be better if the authors put the figures right after the text, instead of putting all of the figures at the end of the paper. It would make it easier for readers to see the results right away).

To make it more convincing, the paper went into detail discussing the results on retention, ash content, basis weight, stiffness, bulk, formation, opacity, machine runnability, and internal bond. The authors used numbers and figures supporting their point of view.

One point in the paper that caught my attention was that it was indicated that the commercial unit is capable of being tied into the mill Distributed Control System (DCS). Distributed Control Systems are becoming more and more popular in the papermaking industry. The authors were very wise in making the point that the commercial unit is capable of being tied into the mill DCS. That’s a big “plus” for readers who are fans of the DCS system. This capability will increase the interest level of some paper mills that already have a DCS system and want to have all of their controls integrated.

The material presented in this paper was “in-depth” to the proper degree and was also made applicable to the actual papermaking process. The authors made it clear that the Filler Flocculation Technology allows the papermaker to increase filler content while maintaining specified physical sheet properties without loss in machine performance. Readers of this paper can see the theories as well as applications concerning the Filler Flocculation Technology. It is obvious that all the benefits came down to creating “significant” mill savings.

One thing that this paper was “lacking of” is that the authors didn’t discuss any shortcomings of the Filler Flocculation Technology. I had a big “question mark” in my mind after reading this paper, i.e. “If the filler pretreatment strategies are this effective and beneficial, why isn’t every mill using them?”

“Modern Approach for Precise Sizing Measurement” by Shawn Hickey, Sylvain Renaud and Wolfgang Falkenberg, BTG Americas Inc Norcross, GA 30071

Reviewed by Ning Wu, 2007

Introduction

In this paper the authors present a modern approach for precise measurement of sizing – the ultrasonic-attenuation method. Considering the weaknesses and limitations of past sizing measurement, the authors demonstrated advantages of this modern method and introduced a device employing ultrasonic-attenuation analysis, which can report important and otherwise unattainable information about the penetration dynamics of liquids such as water, ink, coating color, acids, and oils. However, the author didn’t explain in detail some terms treated related to the results and the conditions under which this method can be applied. Besides, the author ought to introduce better the application of the new method. It seems thin and weak to demonstrate unparalleled advantages of a modern approach in just two sizing trials. Overall, this paper gives beneficial information and offers further R&D ideas for a more complete picture of sizing measurement.

Background

Sizing measurement is critical, due to the influence of the dominant paper production and converting processes. Available measurements such as HST and Cobb are best suited for incompletely and highly sized papers; they do not precisely match the requirements and specifications of all sized paper markets. Moreover, they are slow and inaccurate. Other methods, such as the contact angle method, are limited to specific applications. The author believed that, with a combination of low weight, ease of handling, high speed, and reliability, the measurements will be an ideal instrument for the field service staff of chemical suppliers. In the paper, the authors provided useful information about the modern ultrasonic-attenuation sizing analysis, which can report important and otherwise unattainable information about the penetration dynamics of water, ink, coating color, acids, and oils. Its special characteristic is that measurement starts immediately after liquid contact. This highly efficient method provides information about the surface characteristics of the paper/board. The method also supplies significant process-related information before the material is printed, glued, coated, or impregnated. To the paper producer, this technique is proving to be an unparalleled asset for the purposes of R&D and/or quality assurance.

Discussion

The ultrasonic-attenuation method was found to be a good method for precise sizing measurement, as the authors described in sections denoted “Basic Function” and “Measurement Apparatus.” However, in my opinion, the authors fail to convince the reader that, in fact, the method is truly superior to other methods. The authors just concluded that the ultrasonic sizing tester lends itself ideally to quick and simple testing of the surface properties of paper/board up to 800 g/m2, whereas HST and Cobb are also used within a wide range of basis weight papers. About its useful applications, the author didn’t give us an adequate explanation, such as applications in quality assurance at the paper machine. It has been known to us that paper quality includes many aspects other than sizing; it can also have many quality standards according to the use requirements. In addition, the authors didn’t mention the conditions under which this method can be applied, such as the temperature, humidity, the types of samples that can be tested, and requirements of sample preparation.

The author explained the dynamic penetration curve and characteristic parameters such as the surface characteristic W, wettability S and absorption characteristic A. for further analysis. By illustrating the received signal intensity changes through five steps (wetting, swelling, penetration, and saturation phases), from the time a paper sample comes into contact with the test liquid, the author drew a link between the physical processes of the paper to liquid interaction and observable changes in ultrasonic-attenuation.

It is possible to draw conclusions from the characteristic changes in intensity from the intensity-time diagram, but the authors didn’t give sufficient supporting information about the influence on important paper parameters such as surface sizing, surface porosity, printability, internal sizing, and wettability.

At the end of the paper, the authors described two trials done at a paper mill to demonstrate the application of the new method. It is a pity that the author didn’t provide a real solution that satisfies the purpose of the paper mill. In other words, the study results presented just a partial story. It is unilateral to draw the conclusion that the ultrasonic-attenuation method provided the precise resolution needed to predict that internal size addition had a positive impact on the newsprint printing properties, or consider it is a great achievement.

The author should have explained how to achieve the optimum surface sizing and internal sizing, what the relationship is between them, and how people can control it properly to achieve the best results. It is far from enough to provide information that the results with sizing are better, than without.

In summary, this paper described a very good way to measure sizing. If the author can provide more data and figures about the advantages of this new method and specific examples of superiority to other methods, it might be more convincing. Because every discussion has two sides, if the author could write something about its shortcomings rather than only providing utmost praise, the author’s points would be more credible.

Reviewed by Max F. Farmer, Jr., Spring 2007.

Introduction

The authors took regenerated cellulose films and laminated them together using polyvinylamine (PVAm), and used wet peel delamination forces to demonstrate the mechanism by which they feel PVAm increases the wet strength of paper. Findings leave the reader with very little doubt as to the mechanism by which this process happens.

Background

It has been known for over 50 years that the addition of PVAm to a stock slurry increased the wet strength of paper, but no definitive answer as to what has to happen that causes the increase in wet strength. The swelling of the joints of the fibre-fibre bonds during the saturation of water caused the bonds in paper to weaken and break apart. During some situations, such as repulping and paper recycling, the breakdown of the bonds is needed to allow the paper to revert back to a slurry. Yet during the manufacture and use of packaging, towels, and tissue require the wet strength to be at a higher level to maintain the bonds to keep the product from breaking down in water. The traditional approach to measure wet strength is to prepare handsheets with resin-treated fibre suspensions and measure the wet tensile compared to the amount of polymer used. Handsheets are prepared at different densities and wet to dry strength are compared. A better understanding of how PVAm causes this increase in wet strength of the paper would enable the more efficient use of PVAm as a wet strength additive.

Discussion

A model adhesion experiment was developed in which two regenerated cellulose films were laminated together using the wet strength resin PVAm. A ninety degree peel delamination force indicated the measure of adhesion. If the laminate was never dried, the delamination, or peel force, corresponded to the wet-web strength but if the laminate was dried and rewet, the results simulated wet strength measurements. The amount of the polymer PVAm used was carefully controlled, the results were measurable and reproducible, and the surface of the laminate was examined before and after the peeling.

Two methods were used to apply the resin PVAm to the cellulose films. For the majority of the experiments, the polymer solution was directly spread on the wet cellulose, this was called the Direct Application Method. For the other experiments, one or both of the cellulose films were exposed to a polymer solution to a point of saturation. This method was called Adsorption Application. Finally the experiments were oxidized by a catalyst in order to introduce carboxyl and aldehyde surface groups. The dried laminates were soaked in aqueous solution and kept wet during the peel force measurements.

Experiments were done using both methods with several variables. The variables were compared with the peel force applied as follows:

Oxidation time.
Polymer surface coverage.
Polymer molecular weight.
Soak time.
Degree of hydrolysis.
Laminate drying temperature on adhesion.
Influence of pH on adhesion.

The oxidation time from 0.1 to 1 minute had very little effect, but from 1 minute to 4 minutes, the amount of peel force needed increased greatly, more than any other time period. As the oxidation time neared 10 minutes, the peel force needed to separate the laminates leveled out and oxidation time after the 10 minute period did not increase the force needed. As the surface area coverage by the polymer solution increased, so did the force needed to separate the laminate sheets. The adsorption application method far exceeded the direct application method in increasing the amount of force needed to separate the laminate fibers.

Other variables that increased the peeling force needed were an increase in molecular weight of the polymer and the degree of hydrolysis up to a point of 55%. Soak time had only a slight effect as to the increase in peel force. Laminates drying temperature had very little effect on peel force and a pH range of 3 to 9 had very little effect but the peel force dropped drastically from a pH of 9 to 12.

The writers concluded that the primary amine groups on PVAm are the active agents for wet strength since adhesion increases with the molecular weight of the polymer. The oxidation of cellulose gave a six-fold increase in wet adhesion supporting the hypothesis that imine and aminal bonds between cellulose and PVAm contribute to wet strength. They also concluded that wet strength was independent of pH between 3 and 9, suggesting that in addition to covalent bonding, electrostatic interactions between carboxyls and amines contributed to wet adhesion.

For the papermaker, the information in this article would be very helpful. The author’s thoroughness pertaining to the number of variables used during the experiments would allow the papermaker to start their own trials in a more controlled manner. Based on the pH of his wetend, he would know the approximate time needed for the wet strength to bind to his fibers. He would then know where to add the polymer to get the best results.

The one thing this experiment could not tell the reader was what this increase in wet strength would do to the operation of the paper machine. Would he be able to dry the sheet? What would the draw at the press section do? What would the overall runnability be? The authors’ whole paper is based on the assumption that a cellulose film laminated with PVAm is a model for fibre-fibre adhesion. They are taking a giant leap in this assumption. Fiber joints are approximately 20 um wide whereas the laminate strips tested were 20 mm wide. The reader has to also take this leap to assume any of the facts in this paper are true. These are questions that can only be answered by applying this PVAm to the paper machine and doing his own trials using this article as a starting point.

“Activity Predictions for Single Wire Machines for Various Frequencies”
by V. Wildfong and D. Bousfield, TAPPI 2004 Spring Technical Conference, TAPPI Press, Atlanta, 2004

Reviewed by James Ronning,
January 2006

Introduction

In this paper Wildfong and Bousfield model the free surface fluid effects of multiple foil blades in a conventional fourdrinier. Although the use of foil blades to generate “activity” has been commonplace for many years, the fundamental understanding of the mechanism by which they operate is not well studied. Drainage as well as suction has been well evaluated, but activity has not. Table activity is considered to be responsible for formation uniformity. Although fluid research in a complex system requires many assumptions, the results of this and further research may lead to new innovation in this segment.

Background

It is widely understood by operators of fourdrinier machines that small-scale activity of moderate amplitude will produce a sheet of paper with the most regular formation. Properly tuning a fourdrinier table is one of the areas which fall under the “art” of papermaking. Considerable research has been performed on the drainage rates of foils and the pressure pulses produced by them. Fundamental research has also been conducted with regard to the pressures and drainage mechanisms of twin-wire forming over a single blade. Other than the earlier work of Wildfong and Bousfield little fundamental research has tried to describe the fluid activity of a fourdrinier table.

The earlier work by Wildfong & Bousfield attempted to describe mathematically the action of a single foil blade working in the free-surface geometry of a fourdrinier table. As those familiar with tuning a fourdrinier table know well, table activity is generally produced by a multiple of blades on a fourdrinier table producing some kind of operational frequency, and a single blade will have little effect of activity.

Discussion

The fluid mechanics of a fourdrinier are complex well beyond a simple mechanical model. Many assumptions must be made to simplify the real-world case into a working mathematical model. The path is assumed to be sinusoidal and there is no downward dewatering. The fluid is assumed to be Newtonian with no fibers.

The input variables to the model consist of foil spacing, amplitude of deflection, velocity, and the fluid thickness.

The model is solved for several cases. In the first case, the fluid inertia is not used, and the excitation decreases with recurring events. This is exactly the opposite of paper mill events. When the fluid inertia is included the outputs begin to change. In the first case, it depicts a spout as the initial event forming decreasing-scale ripples with increasing time. This is still not representative of paper mill events where the activity greatly increases with additional foil blades, especially with no dewatering.

When the following inputs are entered with the inertial terms, the results seem to be the most promising:

Deflection – 0.05mm (.002″)
Speed – 10 m/s (1970 fpm)
Fluid thickness – 10 mm (.40″)
Foil spacing – .125 m (5″)

These values are realistic with field data. The deflection value produced an out-of-bounds excitation at 3.8m. This is similar to the build-up of activity on a paper machine with these conditions. Even the shapes of the curve with small ripples quickly turning to spouts is indicative of a well set-up table.

The paper is noteworthy in that:

The fluid mechanics of the fourdrinier table are incredibly complex. Any fundamental research on the fluid mechanics of this event is laudable. Several papers have discussed drainage rates but little work has been performed in characterizing the condition of the free surface.

Although it was not validated in a true sense, some of the findings do seem to agree with industry experience.

Future research would be beneficial to include:

The motion of the fabric is clearly not sinusoidal. This is fine for a simple model, but the shape should be derived as a function of the pressure curve. This is a solvable exercise. Knowing the downward suction or pressure and the fabric tension, a localized estimation of deflection can be obtained. With a deflection term incorporated the actual shape of the foil can be modeled and some of the early attempts at curved, angled or notched blades can be modeled.

Validation of the model on a pilot machine would be very beneficial, especially if it included variation of some of the model parameters with matching changes in the operation. Variation of foil spacing and speed on a pilot machine and comparing the model predictions would be quite interesting. Even if the exact values turned out to be different the trends should show similar results.

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“Effect of Cationic Polymers, Salts and Fibers on the Stability of Model Micro-Stickies”
by X. Huo, R.A. Venditti and H.-M. Chang, J. Pulp Paper Sci. 27(6): 207-212 (2001).

Reviewed by Kristin Koenig, January 2006

Introduction

In this paper by Huo et al, the authors provided an excellent follow-up study on the behavior and stability of micro-stickies to complement their previous work with macro-sized sticky particles. A number of parameters were examined to supply a comprehensive analysis of these problematic particles. These included cationic polymer, starch, fiber and salt interactions. One shortcoming, however, was that in some cases, it is difficult to determine how and if this technology can be applied to the paper mill. Overall, this paper gives beneficial information and offers further study ideas for a more complete picture of micro-sticky behavior.

Background

The agglomeration of stickies during the papermaking and recycling processes has become a more frequent occurrence due to the increased amount of adhesive materials used in paper production. Micro-stickies are those particles which can pass through 0.006″ slots and tend to accumulate in the white water and eventually deposit on the machine leading to web breaks and spots on the paper sheet. In a previous study, Huo et al showed that some components of the papermaking system had an effect on macro-sized stickies after pulping. The behavior of micro-stickies however with fibers, cationic polymers, starch and salt solutions has yet to be determined. By studying solution turbidity, titrations, and the count of sticky particles using a hemacytometer, it will be possible to illustrate the changes that micro-stickies may go through during mill conditions. Before trying these experiments on a paper machine, a chemical model of typical adhesive stickies must be created to predict possible behavior of these particles. By evaluating interactions of stickies with common papermaking compounds, it is hoped that removal methods can eventually be developed and sticky stability can be better understood.

Discussion

Several techniques have been proposed for the removal of secondary stickies throughout the papermaking process. Precipitation of the particles has been observed with highly charged cationic polymers. The adsorption of stickies on solids depends on pH, time, temperature, and the presence of retention and deinking chemicals. Some research has shown that adsorption also depends on the hydrophobic and hydrophilic nature of the sticky surface. There are many factors that seem to affect sticky behavior and it is believed that one or more could help with the removal of the particles from papermaking. Huo et al tried to test as many of these theories as possible. At first this seemed like a daunting and nearly impossible task, but they proved it could be done and their results show a promising future for the removal of stickies.

An adhesive emulsion of acrylic micro-spheres was used as the model compound for stickies. The particle sizes within the emulsion ranged from 1-50µm, which is the same for micro-stickies. The overall research goal was to compare the behavior of the compound in salt, cationic starch, and poly-DADMAC solutions.

In the previous study it was noted that because fibers and micro-stickies carry a negative charge, cationic starch was able to coat the stickies, rendering them less tacky. This allowed the particles to be broken down more easily. In this research the goal was to determine just how much polymer was needed. At this point there was a lot of discussion regarding charge demand and charge ratio. There was little introduction and information provided and this section was confusing. Unfortunately, charge ratio played a large role in determining experimental parameters and the reasoning behind the procedure remained unclear. The only information gained by this section was that excess polymer restabilized the stickies and that the flocs formed by the cationic starch and the poly-DADMAC were different. The cationic starch was less effective in flocculating the micro-stickies. Unfortunately, the addition of poly-DADMAC into the papermaking process would cause competition for surface area with the starch and the situation would become even more problematic. At this point, it was hard to determine just how this information could be applied to the process and introduced into the mill without causing further complications.

Another possible aspect of micro-sticky stability studied was the presence of a double-layer. The coagulation of the particles in a salt solution matched closely with the Schultz- Hardy rule, illustrating that the particles’ stability was affected by the presence of an electrical double layer. Little mention was made to the Schultz-Hardy rule so there was a small information gap for the reader. This section also showed that unlike polymer addition, an over-dose of salt did not increase the stability of the micro-stickies. This provides a practical link to the mill: the normal concentrations of Al3+ in a mill using alum may cause sticky destabilization depending on the pH. It is unclear, however, what would happen at a mill that does not use alum.

Several studies were performed to evaluate the effects of fibers on sticky stability. This section was confusing because there many experiments and the results varied greatly. The overall conclusions drawn by this research were very general due to the complicated nature of the problem. Further research ideas were presented, illustrating the incompleteness of the data. Although the problem is complicated, the results obtained establish general relationships between micro-sticky behavior and starch, fibers, cationic polymers and salt concentration. Together with their previous research, Huo et al were able to add on to the sticky knowledge-base and shine light on this problematic and complicated issue.

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“Benefits of Cationic Ground Calcium Carbonate”
by Loreen Goodwin, Tappi J. 72 (8):109-112 (1989).

Reviewed by Irma Sofia Contreras Sulbaran, 2006.

Introduction

In this paper the author L. Goodwin explains the advantages of using cationic ground calcium carbonate (CGCC) in place of other compounds that are usually used to the same purpose, such as ground calcium carbonate (GCC), precipitated calcium carbonate (PCC) and mixtures of the two. The author provides information about how CGCC affects the sheets and their production and compares CGCC with the other filler compounds mentioned before, showing that the use of CGCC is better than the others through the results of the studies made in a pilot paper machine and in a mill. However the author doesn’t explain in detail some terms treated in the results and the process conditions to obtain CGCC to allow the reader to judge the practicality of this technology. Besides, the author ought to introduce better the CGCC product and focus less in the comparison between PCC and GCC, because the main topic of the article is the advantages in using CGCC.

Background

In the production of paper there are some fillers that are added to the papermaking furnish to give some qualities to the final product. One of the most used as fillers is CaCO3 because it makes bright, opaque paper at minimum cost. In other words, the addition of CaCO3 provides a sheet with better optical properties than an all-fiber sheet. The main goal of all industries is to produce its product with high quality with the lowest production cost, so the addition of CaCO3 is important for this achievement. This compound can be found in two different forms, as precipitated calcium carbonate (PCC) or as ground calcium carbonate (GCC). In this paper the author compares both of them and makes a study for introducing and showing the advantages of a new compound, cationic ground calcium carbonate (CGCC), which is a mixture of GCC with water that contains a cationic polymer, which imparts a cationic charge to the individual CaCO3 particles.

Discussion

In the first part of the paper the author talks about the using of CaCO3 and the properties that it gives to the sheet with low cost, the forms in which it can be found (PCC and GCC), and then the author makes a comparison between them, showing the advantages if GCC is used in the papermaking process over PCC. But this is not the main idea the author try to show and he focused pretty much in that at the beginning.
After introducing the use of PCC and GCC in the process of paper, the article explains the different properties affected by adding these products, like brightness and abrasion. Is in this part of the paper, where the author starts to talk about CGCC that is the main idea of the publication. Then the author gives a little explanation of how the CGCC is prepared but doesn’t explain it in detail this process. To begin the development of main idea in this paper some results from laboratory tests are shown, comparing CGCC with GCC and PCC in terms like opacity, FPR, FPAR and the quantities of cationic retention aids that are needed to retain CGCC. All the results confirm that using of CGCC is the best option; however, they are not specific and too very informative, because only the values of FPR and FPAR are considered.

Then the author continues with the trials done in a pilot plant and in a mill. These results are presented in tables with specific data, but there is no discussion about all of them. In the pilot trial there was a problem, since when using CGCC, the retention was high, and it was necessary to reduce the amount of pulp and CGCC. This fact proves that it is important to check all the variables and make the necessary studies of a compound that is to be used in the production of paper. Some trials in the pilot plant were made with mixtures of CGCC and TiO2 and compared with PCC and GCC. The rest of the results obtained in those studies (even in pilot plant and in a mill) show that CGCC is a good option to improve FPR, FPAR, and the quality of the paper in opacity and sizing, with lower costs. The studies in the mill were done in the production of copier paper and 40lb opaque paper; maybe the study must be wider than this in order to evaluate the results in the production of other kind of paper.

The samples of the trial paper were sent to the laboratory to test printing and abrasion. It was shown that PCC and GCC can be replaced by CGCC without affecting paper abrasiveness. There was no conclusion about the opacity because of the presence of TiO2, but in the tables it is shown the property is improved with CGCC. In the print testing only high-opacity samples were tested, and the paper ran so cleanly that it was considered to be the best they had tested. There was more uniformity in the ash distribution through the sheets with CGCC than the sheets with PCC. Another advantage shown by the results of using CGCC is the production of equivalent surface strength properties at higher loadings.

All the discussion in this paper is useful for papermakers to make higher the use of CGCC (improving the qualities mentioned before) and make lower the cost of the production in a papermaking machine.

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“Alkyl ketene dimer sizing efficiency and reversion in calcium carbonate filled papers”
by William J. Bartz, Michael E. Darroch, and Frederick L. Kurrle, Tappi J. 77(12): 139 (1994)

Reviewed by: Wendy McKinnon, 2006

Introduction

In this paper Bartz, Darroch, and Kurrle analyze sizing properties of alkyl ketene dimer (AKD) with calcium carbonate using many different variables. The main idea of the paper is to study the reversion of sizing and what are the most probable causes. The aspects considered are the morphology of calcium carbonate additives, particle size, paper drying temperature, precipitated calcium carbonate (PCC) filler concentration, and the AKD concentration. Also discussed are the differences between ground calcium carbonate (GCC) and PCC as fillers. There was no reversion testing for GCC. There are so many variables included in this study that it is at times difficult to follow; however the results are very interesting. The authors are successful at achieving the main objective of this analysis, which is to have a better understanding of the interactions between AKD and PCC.

Background

Paper production in North America made the change from acid to alkaline processing for many reasons. Stronger and smoother sheets, lower costs, and better durability over longer periods of time are a few of advantages. The main factor, however, seems to be the development of low cost PCC as a filler. One problem that has arisen from the use of PCC is the interaction with AKD size. This interaction has been found to cause reversion, which is the loss of water repellency over time. Many different aspects of papermaking are scrutinized as to how they affect the bonding between calcium carbonate fillers and AKD size. If this problem can be solved, more wet-end filler can be used in the place of fiber, giving a great economic benefit.

Discussion

It has been shown that different sizing losses occur in papers having about the same levels of AKD. While most studies have focused on the reaction of AKD with fibers, this examination focuses on other paper making variables such as the surface area of the filler, drying temperatures and size dosages. Using the combination of these aspects created a bit of information overload, but the authors managed to come up with some interesting results.

The first study compared increased drying temperatures when applying AKD on handsheets made separately with 10% GCC (0.7 m) and 10% PCC (1.4 m). Hercules Size Testing (HST) decreased on the handsheets as the temperature increased with the use of PCC. With GCC, the sizing ability increased as the temperature increased. This is attributed to the fact that the melted size could have seeped into the pores of PCC and that, in comparison, GCC has no internal pore structure so there was better surface coverage. The graph clearly shows that the only temperature at which the PCC performed better than the GCC was at 180oF, but typical dryer cans operate at much higher temperatures so this is a negative aspect of using PCC.

Once it was determined that PCC does indeed absorb more of the AKD, variables were added to establish if a higher fill amount or larger particle size would improve the HST. A constant trend was not established to prove that either aspect reduced size reversion. Using only PCC for this study, the filler level was increased from 11% – 30% and the handsheets were treated with both 3.5 and 4.0 lb/ton AKD. The addition of 1.4µm PCC showed no improvement with an increase in filler level. The larger particle sizes faired a little better initially as well as with increased filler level up to about 22% where the HST began to decrease. This seems to be another negative for PCC due to the fact that 1.4µm is the standard particle size used in the paper making process. Reversion studies were completed at 10 weeks. This is where things could be improved. There are eight graphs showing the results for each particle size at the various filler levels and AKD dosages. This information would be easier to absorb if there were a table containing the numerical values instead of looking at eight different figures. Also adding to the confusion is that the figures are two pages away from the text so there is quite a bit of flipping back and forth. After wading through all of this information the authors state that the largest particle fillers had very little reversion at filler levels below 20%, but higher fill levels had significant reversion. Then an exception was made for the 1.4 µm PCC at 11.5% because it had reversion at 3.5 and 4.0 lbs/ton. It is then stated that increasing pigment diameter up to the intermediate sized PCC resulted in increases in sizing efficiency and improvements in size stability and that the large diameter PCC provided no additional sizing benefits. However, when looking through the graphs, there are a couple of examples where this is not the case.

In summary, results found here support earlier findings by Colasurdo and Thorn, who reported that size reversion was connected more to fines and filler than with the actual paper fiber. According to this study an increase of AKD size reduced size reversion for all PCC pigments, but in some cases this difference was minimal and in other cases it was not totally accurate. One useful piece of information is that there is a point where the PCC particle size does not increase, and at times decreases, sizing efficiency. It would have been interesting for some of the variables to be held constant and have more comparisons with GCC since it seems to have some improved properties over PCC.

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“Influence of Alkalinity and pH Stability on Wet End Chemistry”
by Molin, U., and Puutonen, P., Proc. Wet End Chemistry, Nice, France, May 11-12, 2004, Pira International, Leatherhead, UK.

Reviewed by: Sanjay Chakravarty, 2006

Introduction

In this paper Molin and Puutonen have provided insight into a novel process to control pH and alkalinity of wet end of papermaking system. The new method developed by Linde AG known as ADALKA process stabilizer uses a combination of carbon dioxide and caustic soda (NaOH) to regulate and stabilize the pH. It enhances the system alkalinity i.e. buffering capacity, thus stabilizing wet end chemistry and unit operations like beating and mixing and providing excellent opportunities for optimization of chemical additions. I think the authors have written this paper from commercial point of view without giving any specific details and drawbacks of the system.

Background

Papermaking system pH influences most unit operations, such as swelling tendency of fibers, dissolution of organic substances, calcium carbonate dissolution, and sizing efficiency. Most importantly, as most of the paper mills are moving towards closed systems due to environmental regulations, it is imperative that papermakers should have better control on pH of the system. Calcium carbonate is present in many papermaking systems these days due to benefits as higher brightness and lower net cost of materials in the paper. Conditions in paper machines are often such that CaCO3 starts to dissolve at low pH = 6.5, which causes runnability problems, precipitation of calcium ions, deposits problems and foaming problem, leading to higher chemical consumptions. In this paper researchers have tried to demonstrate a CO2 based application where conditions in stock preparation and short circulation need to be stable.

Materials and Methods

Occasionally problems that occur in papermaking system are associated with process fluctuation, but mechanisms leading to process disturbances are not well understood. In this article the authors have done a very nice job to explain the changes in the chemical state of the process and its observed effect on runnability and quality problems. This report summarizes the state of the art information concerning the following:

1. Factors that have effects on the chemical state of the process
2. Available control methods

In this way, the article sets a foundation for future work aiming at improved methods for controlling alkalinity and pH stability of the papermaking system. The report discusses the new process developed by the authors and their results from several mill trials conducted with different papermaking furnish. However there are some points which are likely to be unclear to readers regarding facts stated in the paper.

The authors have given brief and in some respects incomplete description about the process developed by Linde AG for producing sodium bicarbonate solution for better control of pH and stability and discussed some of their results from mill application. Sodium carbonate based solution was made on-site from carbon dioxide and caustic soda in Linde AG’s Alkalinity control unit reactor (ACU). Alkalinity and pH can be adjusted independently by adjusting the NaOH/CO2 ratio according to the process requirement. The authors have discussed some of their experience from actual mill cases. One of the mills was having problem of low pH (5.4) in their kraft pulp going to the paper machine. Trials were taken with NaOH, NaHCO3 powder and ADALKA solutions. With ADALKA solution they were able to increase the alkanity independent of pH. In this study they did not mention the source of calcium carbonate or the point of addition of ADALKA solution. The authors also did not mention about what ratio they used for ADALKA solutions a, b and c.

In case of mill A, there was variation of pH of 1 unit in the clear filtrate tower from dithionite bleaching stage. The authors mentioned that there were several variables involved in determining the dosage of solution, but they only write about the how addition rate of solution changes with the amount of dithionite bleaching liquor. It is not clear how variation in pH in clear filtrate tower affects the performance of paper machine. The reader is not told whether they were using this water for dilution purposes at wet end for stock preparation.

In another case a trial was carried out on a paper machine where mechanical pulp was used as furnish and with calcium carbonate as filler. CO2 was used to acidify the mechanical pulp, as it contains CaCO3 particles from system water used for dilution at different stages. The authors mention that the calcium level increases when pH goes down, but peroxide bleaching is done at a pH of 8- 10. No reasons are provided to justify acidification of the pulp with carbon dioxide. For another paper machine, the authors initially mention that the machine produces paper from mechanical pulp, chemical pulp, and CaCO3 but later they talk about adding bicarbonate solution by ADALKA process to coated broke tower. The reader is not able to understand why they are adding the solution to coated broke when they have not mentioned its being added to the furnish.

Discussion

The chemistry discussed by the authors can be useful for the papermaker. The authors have given very sound understanding how the process variables are affected by changes in pH. It is evident from their study that it is more important to have a stable pH than to have to have an ideal pH. However the authors appear to have presented this paper to market their process, without any giving sufficient details of how they prepare the solution. They have talked about the brighter side of their process. They have not mentioned limitations of the process and what problems they might have faced during implementing this process. For example, they do not discuss whether this process is able to eliminate the usage of defoamer on paper machine. Overall this is a novel process for controlling the alkalinity and pH of a wet end system, and the technology has the potential to significantly improve paper machine efficiency.

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“Analysis and Retention Behavior of Cationic and Amphoteric Starches on Handsheets”
By J. YOSHIZAWA, A. ISOGAI and F. ONABE, J. Pulp Paper Sci.24(7): 213-218 (1998)

Reviewed by GANG HU, January 2006

Introduction:

The authors of this paper tested the chemical structure of substituents in cationic and amphoteric starches by NMR. They analyzed the retention behavior of starches at the wet end of papermaking relative to their chemical structures. The degree of subsitutioin (DS) of ionic groups and amylase/amylopection ratios in starch derivatives were obtained by NMR. Hydrolysis of starch components in the handsheets helped to determine the contents of starch derivatives in handsheets by glucose sensor. The authors believed starches were retained in paper sheet was primarily due to the formation of ionic bonds between the cationic groups in the starch derivatives and the carboxyl groups in fibers or fines and that nonionic interactions partly helped trap starches in the pulp mat.

Background:

Cationic starches have been widely used in paper industry to improve strength properties of paper, retention of fillers, fines and sizes, and drainage behaviors. Amphoteric starches and anionic starches have also been introduced to improve paper quality and machine runnability. Amphoteric starches have been believed to be superior to conventional ones. Chemical structures of substituents in starch, degree of substitution, molecular weight and its distribution, amylose/amylopection ratios or degrees of branch structures and purity factors influence the effect of starches and their handling. Different ways can be used to obtain DS of cationic groups in starch derivatives. The starch-iodine methods are generally used for determining starch extracted from the paper sheet with hot water. Mechanisms of the retention of starch derivatives have been studied in the lab with colorimetric methods and starch-iodine methods adopted to determine starches adsorbed on microcrystalline cellulose, pulps and calcium carbonate fillers. Enzymatic hydrolysis of starch derivatives to glucose by enzyme provided a new method to test the starch contents. The glucose can be determined by a glucose sensor. By analyzing the structure and DS of starch derivatives, as well as the retention behavior, the author thought ionic bonds were the main reason why starches were retained in pulp fibers and fines.

Discussion:

By dissolving commercial diethylaminoethyl (DEAE) starch and 2-hydroxyl-3-trimethyl-ammoniumpropyl (HPTMA) in NaOD/D2O, the authors tested their DS with 1H- and 13C- NMR analysis. The results from 1H-NMR were believed to be better than elementary analysis or nitrogen content determination because inorganic compounds did not influence the results. Carboxyl groups were blocked by methylamide groups as shown by 1H-NMR analysis. On the other hand, through analysis of the graphs of starch and starch derivatives obtained from 13C-NMR analysis, the ratios of amylose/amylopectin of these starches were obtained by comparison the peaks of C6(a1-4) and C6(a1-6) in different starches. These analyses can help understand how starch could work with fibers.

The enzymatic hydrolysis of starch to glucose was found to be a good method to test the retention of starch in handsheets. By hydrolysis of the original starches, starches spread on handsheets, starched in handsheets through wet-end addition and handsheets themselves, the author proved the selectivity of the enzymes and the effectiveness of this method. The glucose was tested with glucose sensors. This paper shows than DEAE and HPTMA have similar retention activity. At about 1% addition levels, the retentions were about 80%. With the increase of addition level, retention went down. Amphoteric starches (HPTMA) showed higher retention than cationic starches (DEDA). However, the authors did not give explanation of why there was this difference. They also did not specify whether the handsheet was made from the HW pulp or the treated fine-free pulp, which might give more information about the hypothesis of the mechanisms they put forth.

Further experiments were carried out to check the retention in handsheets made from normal pulp and carboxyl group-blocked pulp. The author compared the retention of different starches on these two kinds of pulps and noticed much higher retention was in the normal pulp than in the carboxyl-group-blocked pulp. They then drew the conclusion that cationic and amphoteric starches were primarily retained at the carboxyl groups in pulp fibers and fines through ionic bonds with cationic groups in starch derivatives. What if anionic starch were used in the same handsheets under the same conditions? This might prove their hypothesis or disprove it. The authors did not have any information about this.
Fine fiber and beating/refining effect were also checked relative to the effect on the retention. It is noteworthy that fines-free pulp retained less starches of all kinds here, including HPTMA starches and ampho-HPTMA starches, than the normal pulp. With the relationship of HPTMA and ampho-HPTMA checked against beating, starch retention went up with the degree of beating. The author explained this by assuming that the accessibility of more active carboxyl groups as more surface was exposed and more fines were created by beating. However, the author did not explain why there was this difference from their experiments on fines. If more active carboxyl groups were present, the more starched would be kept in handsheets once more starches were added. But there was no information on this. The author did give an explanation about the difference why amphoteric starches behaved differently from cationic starches, the reason was said to involve the intermolecular ionic interactions between their own cationic and anionic groups. Therefore, competition from other cationic groups at the wet end will affect the presence of retention of amphoteric starches in fibers or fines. It is not clear whether this inference is shared by the author.

The authors also checked the retention behaviors of starches against pH values of pulp suspensions. For cationic DEAE and it amphoteric forms, retention both increased from pH 2 to 5, then decreased as the pH increased to 11 except that cationic seemed to reach a peak value at about 6; amphoteric HPTMA showed similar behavior; but its cationic forms had different behavior. Its retention kept going up with increasing pH value to about 9. The author attributed this effect to more dissociated carboxyl groups that are available for bonding. The author mentioned that the formation of intermolecular ionic linkages between cationic and anionic groups in amphoteric DEAE starch molecular caused the higher retention and wide peak showed in their experiments. This is confusing, since with the formation of intermolecular ionic bonds, there is less chance for amphoteric starch to form ionic bonds with fibers; and then there must be some other factors that make it have higher retention than the corresponding cationic starches? What’s it? Can the nonionic interactions like London-Van Der Waals interaction mentioned by the authors explain this? One also could suggest self-association as a retention mechanism. Or there may be some physical factors like capillary force affecting these differences.

This paper provided a very good way to evaluate the retention of starches by use of a glucose sensor. If the author had compared results from SW and other pulps, it might have been more convincing, because that can help explain the difference because of their different chemical compositions. Some points might need to be proved or confirmed from further experiments or references to other published literature.

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“Real Time Assessment of Microbial Activity in Paper Coatings and Additives”
by S.Ramesh and R. Banks, 2002 TAPPI Paper Summit.

Reviewed by Keiko Fujita, 2006

Introduction:

This paper describes a new method developed by Ondeo Nalco Company for assessment of microbial activity in the papermaking process. Additives such mineral slurries, starch, protein, polymers, and coatings etc. can be nutrients for microorganisms. Their growth in the process can cause negative effects resulting in plugged flow meters, fouled nozzles, and form deposits. Also they can cause changes of pH, viscosity, rheology and the development of malodors or lumps in the coating formulations or their ingredients. In order to prevent microbial growth, various biocides are used, and to determine the amount of such growth, measuring the quantity of microorganisms is necessary. One of the ways to predict microbiological activity is by incubating microorganisms, taken from the process water, on a nutrient culture media plate. Disadvantages of this method are 1) it requires 48 hours for detection, and 2) plating often does not culture the problematic organisms. Another way utilized is the ATP method, using the reaction between firefly lucifirase and ATP to detect live organisms. This can provide quick results, but this method is incompatible with opaque, light scattering additive materials. Some industries use HPLC methods to determine residual biocide concentration, but that is an indirect approach and does not check the microbiological status of the sample.

Background:

In order to prevent microbial contamination, it is necessary to regularly monitor the coating and additives materials for microbial activity in a rapid and accurate way. Also when screening new biocide chemicals, a rapid selection method is required. To meet these needs, the authors have developed a new technology. Its advantages are 1) providing results in a six- hour period. 2) measuring true microbiological activity, and 3) minimal operator involvement. As a result, the values obtained are 1) improved monitoring efficacy of biological programs, and 2) producing a higher quality of finished products.

Discussion:

The most advantageous point of this newly developed microbial activity method is obtaining quicker results compared to the plate counts. As for the new method, a flourogenic dye is added to a sample and is allowed to react with the microorganisms present in the sample. The flourogenic dye reacts with microbial enzyme to form a flourogenic byproduct, which can further react to form a non-flourogenic product. To be able to accurately determine microbial activity, reading the fluorescence at frequent intervals of 5 minutes or less for the entire 6- hour period is necessary. The higher the microbial activity, the quicker the results were obtained. As stated, plate counts require 48 hours to determine the microbiological status of sample.

Also, with respect to accuracy, the plate count method has the risk of detecting inactivated microorganisms. When a biocide is used, the activity of microorganisms is inhibited, but if they are on the plate with a favorable environment of surplus nutrients and optimum growth temperature, these can form colonies. Therefore, the newly developed approach, actually counting the microbial activity, can provide a more accurate estimation of the level of microbial contamination of a sample than a plate count.

As a member of a laboratory staff, I was often asked about a better way to predict the amount of bacteria in the papermaking process water. Especially when slime problems are happening, they want to take quick action by adding a proper amount biocides into the process. Using excess preservatives are not allowed since such use would have a negative impact on the environment. However, taking a 48-hour period is too long for them. Also, the microorganism status can be change in this period. I always recommend them to use an ATP- lucifirase detection kit that can provide the results within 30 minutes. A Japanese food manufacturing company, Kikkoman, has developed chemical kits and a handy detector set mainly for food sanitary purposes, but the kit also can be applied to the pulp and paper industries.

The authors stated that the ATP method is incompatibles with opaque, light scattering additive materials. Their new method also uses a fluorescence detector, and they conducted the experiments to measure the biological activity in latex polymer, but the paper does not discuss the accuracy of its detection. The new method would be better compared to plate counts. However, they do not give enough benefits compared to the ATP method. Industries avoid using dangerous chemicals, so if the dye of the new method has toxicity, then companies would not apply the method. The price of the kits and custom-made detector can also have an effect on the decision- making so that if the kits were much cheaper than conventional methods, then they would be competitive in the market.

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“Stability and deposition tendency of colloidal wood resin”
Anna-Liisa Sihvonen, Kenneth Sundberg, Anna Sundberg and Bjarne Holmbom Nordic Pulp Paper Res. J. 13(1): 64 (1998).

Reviewed by Kacee Des Jarlais, 2006.

Introduction

Pitch deposits in a paper mill can wreak havoc by causing deposits on the paper machine and spots in the final paper product. The pitch comes from the resinous material in the wood material and the deposition tendency of the resin is dependent upon a variety of factors. The purpose of this study was to characterize the different factors that determine the deposition of the resinous materials that can be found in pulp. Although much valuable information is given, the authors lack a clear correlation to actual papermaking conditions and how the presented material can be used to lower pitch problems in a mill.

Background

Although resin materials cannot be completely avoided during most papermaking processes, a good understanding of the chemistry of the resinous colloidal suspensions could help to lower the damaging effects. Resin can be transferred from the pulping process to the paper machine by being adsorbed on fiber surfaces, carried inside of parenchyma cells, or colloidally dispersed in the mobile phase of the slurry. Colloidal resin is often the largest cause of problems during the papermaking process. There are factors that affect the stability of the dispersion by electrostatic or steric interactions. Some of these factors include pH, electrolyte concentration, viscosity, temperature, and the chemical composition of the resin. The authors used a model dispersion prepared from thermomechanical pulp (TMP) of Norway spruce and varied the chemical composition by adding dehydroabietic acid (to mimic naturally occurring resin acid), linoleic acid (to mimic naturally occurring fatty acids), glucommanans (to mimic naturally occurring sugars), lignin, and taking away resinous and linoleic acid via hydrolysis. The conditions that were tested included electrolyte concentration and water hardness (with Ca+2). In addition, the tests were performed at pH 5 and pH 8, most probably to represent acidic and alkaline papermaking.

Discussion

An initial experiment with only the model dispersion was conducted to evaluate the stability against NaCl and CaCl2. These results showed that the different chemical compositions change how the suspension acts, depending upon pH and ion valence charge. At a pH of 5, the fatty and resin acids increased the amount of deposits but at a pH of 8, the fatty and resin acids acted as an emulsifier and actually decreased deposition frequency. The authors then took this idea one step further and measured the stability of the model suspension with added dehydroabietic acid or linoleic acid and a suspension of pine heartwood resinous material. This was done to prove the fact that different species of wood have different compositions of pitch-forming materials. However, the addition of electrolytes changed the circumstances.

The model suspension was most stable against NaCl at pH 8, and most stable against CaCl2 at pH 5. This is because at a higher pH the particles were more negatively charged and more resistant to the Na+ attack but the Ca2+ acted by forming soaps with the fatty and resin acids. Both suspensions with NaCl were more stable than those with CaCl2. When NaCl was added at a pH of 5, the model dispersion was the least stable, the dispersion with dehydroabietic acid next, then the dispersion with linoleic acid, and the most stable was the pine heartwood. In this instance, the pine heartwood contained much more fatty and resin acids, leading to increased colloidal stability against NaCl at a pH of 5. A different result was noted when the different suspensions were tested against CaCl2 at a pH of 8. Now, a low concentration of fatty and resin acids was needed for stability since the Ca+2 caused the formation of insoluble and sticky soaps.

Glucomannans and lignin-glucomannan stabilization was studied next. The addition of glucomannans and the lignin-glucomannan complex decreased deposit formation for all of the different suspensions under study. It was suggested that the glucomannans sterically stabilize the colloidal resins. This effect was mostly seen with CaCl2 addition at a pH of 5 and had very little to no effect at a pH of 8.

The material presented in this paper was very in-depth but could have been made more applicable to the actual papermaking process. No matter what results were found, the end goal would be to decrease the tacky pitch deposits that cause problems during papermaking. The authors also neglect to discuss in depth the different types of pulp (mechanical, chemical) and how they would pertain to the resinous compositions required for pitch deposition or the effect different papermaking additives would have on the colloidal stability. A good foundation of resin colloid suspension chemistry was supplied.

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Reviewed by Enrique Yago, January 2006.

Introduction

The authors of this article propose, with considerable success, a global and exhaustive approach to controlling stickies problems. Their approach involves consideration of all parts of a paper machine system that are affected by stickies, auditing these each unit operation step by step, and putting the results obtained to use in a comprehensive program. The authors also describe a Kemira test method and its application in the case of an SCA tissue mill North America. Notably, one of the co-authors, Mr. Nelson, is introduced as Kemira´s Account Manager.

The articles states that traditional stickies treatments, offered by a great number of chemicals suppliers, are based on a relatively few technologies. Competing chemical suppliers even may use the same treatment steps in the process, but the results are not necessarily effective in cost nor in reducing the problems resulting from stickies.

Basing their analysis on a classical point of view, the authors propose a comprehensive treatment program, including an interesting and particularised vision of the problem of stickies control.

Background

Stickies contamination is an important issue in the manufacturing of recycled paper. In fact, the problem in increasing in recent years due to increased use of recycled fibers. As the recycling of fibers becomes increasingly widespread, an increased proportion of the fibers become recycled multiple times. As a consequence, there is a tendency for the raw material to become more and more contaminated, and the presence of pitch deposition tends to increase with the passage of time.

Because most unit operations in a paper mill are affected by stickies, it follows that one must take corrective actions that affect many different parts of the production line equipment. On the other hand, stickies are able to change their chemical structure and also they are able to interact with another substances (contaminants, fillers, aids). All of this takes place in the range of temperature and pH used in the paper process. Chemical technologies provide a wide range of treatments, a lot of them listed in the article, based in different techniques, but these are not 100% effective for all cases. All of these factors, taken together, mean that we can expect to face considerable challenges in dealing with stickies, and that the solutions proposed until now are good but not truly sufficient to solve the problems that we face.

The approach recommended by the authors is to view stickies-related problems not as a whole, but in particular, this is, by considering each part of the paper process individually, checking each section of the paper machine with the KODT. After the diagnosis is complete, an effective chemical method to control pitch contaminants can be optimized for each unit operation..

Opinion

One of the most valuable features of the article is a very useful classification of stickies, including the composition and source of such materials, together with the most common treatment technologies. All this be helpful when one is attempting to choose between all of the different possible treatment strategies that suppliers could offer.

In my opinion an especially useful the part of the article is headed “Deposit Control Process Survey.” The authors provide an interesting check list that one can use as a tool for making an evaluation of your system. The evaluation includes estimating the impact of the contaminant, including its financial impact. You can take such an analysis as a first step and as a starting point in order to attack the problem.

Regarding the KODT test itself, it seems to be more accurate than methods which are based in counting the stickies by means of pulling them up or by staining the pitch particles. The Kemira method uses a system with a digital image analysis and statistics, based in a visual rating average of depositions on the test element. With respect to such methods, I am most familiar with Tappi Test method T277, and I consider the KODT to be much better and more fully developed. In any case, the KODT method is a commercial test to evaluate the action of Kemira additives, and so it has a stronger technical and financial support behind it, in comparison to a lab method.

The authors show that results obtained by using the KODT control program can be very effective in addressing stickies problems. In addition, they have demonstrated their proficiency in the formulation of the assay and in their ability to present their work to others.

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“Shear strength in papermaking suspensions flocculated by retention aid systems”
By Swerin, A., Risinger, G., and Ödberg, L., Nordic Pulp Paper Res. J. 11 (1): 30-35 (1996)

Reviewed by Jun-Young Cho, 2006

Introduction

In this paper the authors consider the influence of chemical flocculants on the viscoelastic properties of fiber suspensions. They investigate the influence of single polymeric and two-component microparticle flocculant systems on the shear strength of fiber networks using a rheometer. The effect of NaCl concentration on the shear strength of fiber networks is examined to know how the retention chemical performs in the different electrolyte conditions. Also, the influence of mineral filler on the fiber network strength is evaluated as a recommended method in comparison with optical methods. The authors believe that the measurement of shear strength in flocculated suspensions is an effective way to examine flocculation in papermaking suspensions, a phenomenon that has been known difficult to evaluate by other methods. However the authors failed to clearly explain their proposed mechanism in terms of specific chemical interactions or reactions between the flocculants and fibers.

Background

One of the most important mechanisms of retention aid action, bridging, results in fibers and particles sticking to each other in aqueous solution. Since various combinations of additives produce higher efficiency and drainage results, papermakers commonly employ multi-component retention programs such as the following: (a) a high-charge cationic polymer followed by a very-high mass cationic polymer (usually cPAM or PEI copolymer), (b) a high-charge cationic polymer followed by a very-high-mass anionic polymer (usually aPAM), or (c) a very high-mass cationic polymer followed by an anionic microparticle such as colloidal silica, bentonite, or a micropolymer. During papermaking the increased retention due to retention aid systems often is achieved at the expense of an impaired formation uniformity of the finished sheet because retention chemicals cause increases in fiber flocculation. Though, theoretically, flow fields should disperse all fiber flocs, dispersed fibers tend to refloccculate rapidly due to flow-induced collisions. The shearing history, which the initial hydrodynamic shear tends to leave fibers in a bent state, and the fibers tend to lock together in flocs as they attempt to straighten themselves out, is the main reason of reflocculation of dispersed fibers. Though the viscoelastic character of papermaking fiber suspensions was studied, and fiber suspension’s shear strength properties are explained as a mathematical model by previous work, the influence of chemical flocculants on the viscoelasic properties has been rarely studied so far.

Discussion

In the first part of the article the authors discuss the value of the elastic shear modulus G’ of a single-component flocculant systems consisting of a cationic polyacrylamide, C-PAM having either high or low charge density (degree of substitution DS=0.02 and 0.14). In Fig. 1 and Fig. 2, the value of G’, the shear strength, increases by increasing of the amount of C-PAM. The authors explain that a bridging flocculation of fibers is the reason for the increase of the shear strength by increasing the amount of C-PAM. Also, the authors support their idea by citing the previous research done by Swerin that the polymeric flocculant increases the number of contact points per fiber. However I think that the authors should propose a specific chemical reaction or physical interaction between C-PAM and fibers which can clearly explain their relationship.

In part 2 of the article, the effect of contact time between the combination of microparticles and C-PAM and fiber suspension is investigated by measuring the elastic shear strength. An experiment to investigate the effect of added amount of montmorillonite (Mont) is performed. In Fig. 4. the flocculating effect by the montmorillonite is very obvious. At three times the added amount of C-PAM, montmorillonite showed the biggest value of elastic shear strength compared to C-PAM without microparticles. However, in this experiment, the authors mentioned a certain ratio of C-PAM and montmorillonite for which the lowest amount of C-PAM addition (0.1 mg/m) yielded shear strength that was lower than for C-PAM alone. With this problem, the authors assume that a measuring problem of rheometer might be the reason to bring out this problem. But there is no specific number of repetitions of the test showing strange data. Also, a test using a sample having the ratio of C-PAM-Mont lower than 0.1mg/g should be carried out.

When looking at the test carried out with the C-PAM-Mont systems to examine the effect of electrolyte concentration, Fig. 5 shows results for a C-PAM of DS=0.14 and Fig. 6 for DS=0.03. With increasing electrolyte concentration, the flocculation decreases. The authors explain these results in terms of changes in the adsorption behavior of C-PAM on both fiber and on montmorillonite. However, the authors don’t provide a clear explanation why the effect of shear strength is greater at DS=0.02 than at DS=0.14.

Finally, the effect on the fiber network strength of the addition of mineral filler is examined. In Fig.7. the shear strength resulting when C-PAM was first added to the fiber suspension before adding filler was almost as same as when C-PAM was added alone. However, when filler was added first and C-PAM was added later, the result was different. The author explains the difference by noting that there is competitive adsorption because when C-PAM is added to the fiber-clay mixture, a large amount of polymer is adsorbed by filler particles and gives filler flocs.

Several sets of experiments are carried out to evaluate the influence of chemical flocculants on the viscoelastic properties of fiber suspensions. The authors show that the shear strength in papermaking suspensions increases with the addition of retention aids. However, some data the authors provide are not easy to explain. In addition, if the authors had provided stoichiometric relationships to explain how the reaction between retention aids and fibers occurred, then their experiments and interpretation of the results might be clearer and more credible.

“Effects of system closure on retention aids for SC-grade manufacture”
by Polverary, M., Sitholé, B., and Allen, L.H., TAPPI J. 3(7): 32(2004).

Reviewed by: Carlos Garcia
Date: November 9, 2004

Introduction

This paper presents the effects of increasing water closure systems on retention aids for peroxide-brightened TMP pulp. Polverary et al. have studied the behaviour of twelve different retention aids (5 flocculants, 2 coagulants, and 5 dual component systems) on three different degree of water closure system (DWCS) – 55, 20 and 3 m3 of fresh process water make-up for each metric ton. In one hand, the experimental set up and the authors´ goals make this paper very attractive for a papermaker reader. But, on the other hand, this paper presents statements and procedures with vague scientific support, confused conclusion results, hard to read graphs and tables, and an improvable paper structure organization.

Background

Papermakers search for process water reduction because it reduces effluent and water treatment costs, it achieves energy and fibre savings, it achieves compliance with effluent regulations, and it makes possible a wider choice of paper mill locations. When papermakers increase the water closure systems, the concentration of dissolved and colloidal material (DCM) in the furnish increases. DCM interacts with retention aids, reducing their efficiency of retention onto the fibre, which creates deposits or contamination along the circuit. These deposits can produce paper defects such as paper breaks, dirt and holes, and downtimes for wash-ups which would reduce the runnability and productivity of the paper machine. In addition, the presence of DCM in the furnish and white water reduces the drainage rate by blocking the spaces between fibres at the wet web. At low drainage rates, more water is kept inside the fibre mat, which makes it harder to remove by pressing and drying, resulting in high production costs either by reducing the paper machine speed or by consuming more steam. Therefore, papermakers try to obtain the optimal retention aid system to reduce the consequences of reducing water use in the paper mill.

Discussion

In the first part of this paper, a detail description of the retention aids properties is presented in a nice table which is very helpful while reading the results section. On the other hand, the authors make a vague reference, which lacks of scientific information, on the specific surface area of the bentonite clays used in this study. Polverari et al. describe very well the way the stock samples are prepared for the three different DWCS. The samples for each DWCS are prepared at the same consistency and pH, but they are taken from different paper mill points and have different preparation procedures, and the authors avoid any scientific references or explanations. So, at this point the reader could ask the following questions: Why are the samples prepared that way?; Why are the 20 m3 and 3m3 sample not prepared in the same way?; Is it representative to compare the results of the three different DWCS?; What are the best stock parameters and values that better describe the target DWCS?; Why is the DCM removed from the samples? It would have helped the reader to know the target stock properties for the three different DWCS. The authors use a few tables in this paper for clarification. Some of them are useful and clear for the reader, like Table I-Material Properties, Table II-Experimental Procedures for DDJ Studies and Table V-Analysis of Stock Samples, but there are other tables that are either not useful for this study, like Table III-Bleaching Conditions, or hard to understand, like Table IV – Pulp Characteristics.

In the second part of this paper Polverari et al. present and comment on their study results. Dynamic Drainage Jar (DDJ) retention, DDJ ash retention, drainage rate and dryness percent have been plotted versus different dosages of flocculants, coagulants, and combined retention aid systems. Although the way the authors have exposed the experimental results is good, in this part the reader can get confused. In some graphs, the results are hard to see since there are crossing and overlapping data points and lines. According to the authors, CPAM-2 and CPAM-4 obtain the best DDJ retention for the DWCS of 55m3 and 3m3, but in the 55m3 DWCS graph it is shown that one of the highest, if not the highest, DDJ retention is obtained by CPAM-3 at a low dosage rate. In addition, the authors say that the PEO/Phenolic resin enhancer systems performed the best for the DDJ retention at all DWCS, but the graphs show that for the 55m3 and 3 m3 DWCS the best performing system was PEO/Polysulfone resin. Another confusing fact is when the authors make the comments on the drainage rate results; in general, increasing the polymer dosage leads to lower drainage rate and higher DDJ retention but the graphs results show that not all the polymers follow this “rule.” Finally, the authors say that polymers with higher DDJ retention and lower drainage rates results in lower dryness values but it is not straight forward to follow this trend in the results graphs.

At the end the authors go over the discussion and conclusions. It is surprising to see that a new piece of information is presented in this section: Table V – Analysis of Stock Samples. This table includes good pieces of information, such as conductivity, cationic demand, colloidal fraction, etc, but it would have been better placed it in the experimental approach section so that the reader can see the differences between the different DWCS samples. In addition, this table presents some information that is not either used or discussed in this study. The authors write better and longer discussions, but the reader has to go back and forth to verify or check conclusion within the results. It is still confusing when the authors make the discussion/conclusion about the flocculants. According to the authors the polymer chain length and, to a lesser extent, charge density are important parameters in the choice of retention aid for system closure. The results show that at the highest WCS CPAM3 (molecular weight =7000 kDaltons and a charge density of 0.03 meq/g) obtains worse results than CPAM2 (5500 kDaltons and 1.29 meq/g) and CPAM4 (6000 kDaltons and 3 meq/g). On the other hand, the authors make good and clear discussions/conclusion on the behaviour of the dual component system as the water closure system is increased.

From my personal point of view, this paper presents information that could be used for the selection of a retention aid system as the water reduction is increased, but this paper does not discuss what could be interesting for a papermaker, such as maximum retentions and optimal retention aid dosage for each DWCS, what other dual component systems could work, and what other type of coagulant could have been tried to obtain results.

Literature Used

[1] “Water use reduction in the pulp and paper industry”, AGRA Simons, NLK Consultants and Sandwell Inc. Pointe-Claire, Quebec: PAPRICAN, 2001.
[2] WPS 527 course pack

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“The Buildup of Dissolved Solids in Closed White Water Systems”
by Yufeng Xu, Yulin Deng, Tappi Journal (2004), 3(8), 17-21.

Reviewed by Junlong Song,
November 2004

Introduction

In this paper by Yufeng Xu and Yulin Deng, a mathematical model has been developed to predict how the dissolved solids will build up after the white water system of a paper machine is closed to different degrees. In the closing of a mill system, any reduction in the paper machine water consumption will be accompanied by an increase in the dissolved and colloidal solids in white water. According to the model, the dissolved solids coming into the system will not build up endlessly, no matter how many times they are recycled and how tightly the system is closed. The final equilibrium concentration of any dissolved solids will be less than the flow-proportional average concentration of that species in all outside water sources entering the system. As a consequence, the authors concluded that the solids coming into the system in dissolved form will not precipitate out of the water solely because of the concentration increase, no matter how many times they are recycled and no matter what the degree of closure is. This consequence seems very interesting and exciting for the papermakers. Is it true? It would be interesting to know whether there are any restriction on the validity of these results. On the other hand, it would be interesting to know whether the results can be generalized to other applications.

Background

Closing up process water loops in paper and paperboard mills has tremendous environmental appeal, and there are significant economic benefits to this process in terms of fiber and energy savings. Strong world-wide interest in the environmental impacts of the pulp and paper industry, as well as an acceleration of trends toward greater closure of white water systems cause numerous of problems in paper making processes.

In an “open” water system, where a relatively large percentage of the water is discharged, there is a continuous and substantial purge of dissolved substances from the system. As the mill closes the water system by recirculation of a greater percentage of its water, the dissolved substances will increase. When present in sufficient concentrations, these substances will cause production difficulties such as increased deposits, foaming, biological activity, corrosion, and poorer retention. They may also impair the physical properties of paper.

Understanding of fundamentals of contaminant buildup in a paper machines is the key to reducing the fresh water consumption. It is well known that papermaking is a very complicated and sophisticated procedure. It is necessary to simplify it to get ideal model. But sometimes the simplified model is too simple to include all of the essential information, and consequently the results may deviate significantly from the real operation.

There are two categories of mathematic models to predict the tendency of the buildup of dissolved solids in closed white water systems. One is EF, the enrichment factor, but it doesn’t account for the adsorption of dissolved solids on fibers. The other one is the model by Yufeng Xu and Yulin Deng, which takes adsorption into consideration. This method has a better understanding for the closed system of white water, but it considers only part of dissolved substances, not all the dissolved substances. Although the model neglects much important information for paper machine, its conclusion got from the simplest condition still can apply to other complicated conditions.

Discussion

Now let’s analyze the model set up by the authors. From the model we can see, all the substances coming in the paper machine come out in two ways. One is P, gone with paper; the other is S, gone with discharge. When the authors calculated the amount of dissolved substance return the system, they use the following term: R*Cr,1. We know that, Cr,1=(Y+RCr,0)(1-K)/H, and H=R+P+S. This means flow P and flow S have the same concentration with R, Cr,1. What’s more, we can see in the figure 1-water flows in a paper mill, there is a save-all. The function of a save-all is to separate solid materials, plus any chemicals remaining adsorbed onto those solid particles, and clarified white water. But from the author’s balance, the save-all seems to have no function.

Neglecting the functions of save-all is a shortcoming of the model.

According to the affinity of dissolved substance to fiber and other solids, we can classify all the substance dissolved in water into two groups: one group is the substances which have no affinity to fibers and other solids; the other group is the substances which have affinity to fibers and other solids. This means they will have different properties when filtration, that is in the stages of forming and save-all. Group 1 will distributed evenly in water no matter how fibers and other solids distribute, while group 2 will be thickened on the slurry side and will be thinned on the filtrate side. Usually, the term buildup is used to refer to two types’ buildup, DCS (dissolved polymeric and colloidal anionic substances) and salt buildup (electricity conductivity). DCS belongs to group 2 and salt belongs to group 1, where it is assumed that the ion exchange capacity of the solids for salt already has been satisfied. Based on this assumption, the model set up by Yufeng Xu and Yulin Deng can only apply to salt.

This model can only apply to salt or substances have no affinity to fibers and solids from its principle; this is the model’s restriction.

For DCS, the concentration of recycled white water should be little higher than the concentration of white water in the tray due to the fact that the save-all system recovers almost all the fine solids and chemical. Let’s assume there is an efficiency coefficient for the save-all, a, where a = Cr,1*/ Cr,1, and where Cr,1=concentration in tray. The parameter Cr,1* equals theconcentration in the recycled stream
We can get a>1. We take the new parameter into the equation; we can get the new concentration Cr,n at last:
Cr,n=

and we can get the same equilibrium concentration as the author got. If, on the other hand,

then we can’t get the same solution as above. But this is impossible, because r=M/H, and as we know, usually the fiber concentration of income is about 4%, fiber concentration in headbox is about 0.5-1% and fiber concentration of outcome is about 12%. The approximate value of r is in the range of 0.125~0.25. However the approximate value of a is no more than 1.33. Based on this analysis, a has no use for changing the equilibrium state, except shorten the time to reach it.

In the analysis above the discharge S comes out of the system and doesn’t return to this system. As we known, more and more mills want to reduce the amount discharge to effluent. They use extensive filtration of the clear filtrate, so that it can be reused in showers, as well as for stock dilution. This means that an additional amount of fine solids and salts, not considered by the authors, will come back to the system. It is worth asking whether or not for this condition the dissolved substances will buildup for a long run? For this situation, we can only consider the extreme state for the closure system and see what the equilibrium condition is. The extreme state is like this, 100 percent white water closed, no white water discharged, that is S=0.

From the mass balance we can get M=P. The adsorption coefficient also is K, so we can get the following:

MCm =HChK+PCr

Cr= (MCm-HChK)/M

Cr= Cm-HChK/M

Now we get the final answer, Cr < Cm. If k=0, the white water reaches its maximum concentration Cr = Cm. for most cases, Cr< Cm, and the buildup will not proceed further in this system since the final equilibrium concentration is lower than Cm.

To summarize, the limiting cases considered in this essay represent widely different physical situations for the buildup of dissolved substance in recycle system. Despite the wide range of assumptions, each model leads to the same general conclusion: whatever the substance is, it will not accumulate or buildup endlessly. Rather, it will reach its equilibrium state and the equilibrium state can be estimated by Cm. But we must note that, the new M after recycling is much smaller than normal amount, so the Cm is much larger than the figure with no recycle. What’s more, from our derivation we can see, this equation also can apply to non-dissolved substances. For non-dissolved substance, we can simply take K as retention rate. Though the accuracy of the analysis by Xu and Deng are expected to be inaccurate in detail, their overall conclusion probably can be characterized as “true” in the following sense:

The conclusion of the model based on equilibrium assumptions is qualitatively correct and it can be generalized to all the substances involved in the recycle.

Minor Points

In addition to the concerns with the analysis, there are also some little mistakes in the paper. For example, Equation 11 is wrong; The correct equation should multiply H, not divide by H. Equation 10 also is wrong; it makes a mistake of writing Cr,n as Cr,4 . These little mistakes possibly indicate carelessness during preparation or editing of the paper. It is expected that this error would not change the final equilibrium state, although DCS will be disproportionately retained in the wet due to hydrodynamic shear. This is because that from the analysis of extreme state we got an equation:
Cr= Cm-HChK/M
K maybe becomes smaller due to the hydrodynamic shear, but its minimum is 0. So it must have some effect on the equilibrium state, whether or not it affects the time required to reach equilibrium.

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“Vinylformamide – Based Cationic Polymers as Retention Aid in Alkaline Papermaking”
by Fei Wang, Takuya Kitaoka, and Hiroo Tanaka, Tappi J. 2 (12): 21 (2003)

Reviewed by Yun Wang,
November, 2004

Introduction:

In this paper the authors introduce a new kind of retention system, vinylformamide-based cationic polymers, which is used in alkaline papermaking. Generally speaking, this paper is excellent. However there are still some small flaws.

Background:

As we know, one of the trends in the papermaking industry is to change from acidic papermaking to neutral or alkaline papermaking. This trend is fueled, at least in part, by the advantages of using CaCO3 as a filler. But this trend tends to make the rosin-alum sizing system inefficient. The rosin-alum sizing system is relatively inexpensive, and it is widely used in acidic papermaking. If this sizing system could also be used efficiently in alkaline papermaking, the cost of papermaking could be decreased. And some research indicates that a new kind of polymer, vinylformamide-based cationic polymers, can be used as a retention aid for rosin-alum sizing under alkaline conditions.

Discussion:

In their introduction section the authors suggest that the vinylamine class of polymers has an important effect relative to the efficiency of sizing with rosin. To support their assertion, it would have made sense for the authors to compare the efficiency of rosin sizing with and without cationic polymers under different pH conditions. However, Fig. 3 of the cited work shows only the sizing efficiency curve of the rosin – alum sizing system with cationic polymers. That is to say, the authors only compare the sizing efficiency of two cationic polymers and do not compare it with the rosin-alum sizing system without cationic polymers. In my opinion, this mistake will render the conclusion – that the cationic polymers are very efficient – meaningless.

To indicate the influence of molecular mass of the polymer used in the sizing system, authors research the sizing degree and sizing retention vs. different mass of polymers. From this figure, the authors conclude that molecular mass is an important factor for sizing degree. According to the authors, the reason is related to the pore structure of paper, which permits low mass polymers to fall into the pores easily and lose their effect. However, the authors don’t explain the trend of sizing retention. Though maybe it is not important compared with sizing degree in this paper, the authors still need to give one or two sentences to explain their result. Otherwise the reader will be confused. For instance, a possible explanation for the authors’ results is that the polymers might not be important for retention of the sizing agent, and the main factor governing sizing retention is same as in the rosin-alum sizing system in acid papermaking, i.e. alum is the factor of size retention, not the cationic polymers. As we know, the alum is the anchor for rosin size.

In the final section, the authors research the mechanism of this kind of polymer. But their paragraph of explanation prompts the following question: Where is the alum? Is alum still the anchor of rosin? Based on the authors’ data and analysis, there still is no way to rule out the possibility that alum is still the primary anchor for the size. The paper would have been more valuable if this point could have been spelled out more clearly, especially when the paper is read by a person knowing few about papermaking.

Result:

The polymer discussed in this paper can be quite useful in alkaline papermaking. Using this kind of cationic polymer, we can also use the inexpensive rosin-alum sizing system under alkaline papermaking conditions. However, whether use of the system proposed by the authors can reduce the cost of papermaking still needs be researched. We need to compare the price of these polymers, in combination with rosin, versus ASA or AKD systems, which can be used as sizing agents in alkaline papermaking, to see which alternative is the cheapest.

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“Automatic Control of Additives with Modern Online Measurement Technology Raises Papermaker Productivity,”
by R. Berger, D. Watzig, H. Ziegler and M. Fasth,
2004 TAPPI Spring Technical Conference

Reviewed by Lambrini Adamopoulos
November, 2004

Introduction

This paper by Berger et al. provides insight into the measuring technology that enables the automatic control of wet end additives in paper and paperboard machines. The authors give a clear and methodical description of the strategies and methods that they used to implement their control systems. Furthermore, they outline difficulties encountered as well as remedies found. Nevertheless, the paper seems slightly incomplete towards the end.

Background

Papermaking systems have become increasingly complex over the years. Laboratory testing is no longer sufficient to monitor and correct processes and product levels. They fail to capture the synergy of all the processes involved at the paper machine, and representative samples as well as representative simulations are hard to obtain. Furthermore, laboratory trials are often time consuming, in that small fluctuations are not corrected as soon as they occur, and there is often quite a delay between the occurrence of a problem, such as a variation from specifications, and its rectification.

Process control through inline and online measuring procedures provides a solution to the control issue. It allows for reproducible results, maximum precision and speedy feedback. Effective control loops identify problems and modify process variables to automatically correct for these, almost as soon as they occur. In a paper machine, such control loops can be applied to chemical additives in order to achieve enhanced paper properties.

Materials and Methods

Berger at al. investigate a high-speed newsprint machine in Sweden, in order to show that the total stability at the wet end can be improved by stabilizing subsystems using modern measuring and control technology. Instruments are strategically added at points clearly shown in the process flow diagram presented in the study. Moreover, the instruments’ specifications as well as their modes of action are explained in great depth.

The study itself deals with closed-loop control of de-aerator chemicals, retention aids and fixatives. For all three, the authors first assessed the existing levels and control strategy. Then, the automatic control loops were implemented. The analysis of the original situation is very important since it serves as the basis for comparison.

In de-aerator chemical dosage control, the gas content was sampled at two points, in order to determine the situation at both high and low consistencies. A figure coupling the gas content and de-aerator dosage (controlled manually), with respect to time was then generated. It clearly shows large fluctuations. The control loop installed to control the de-aerator begins by measuring dissolved and entrained gases on-line using a gas analyzing system. The control parameters such as the delay time and set point are then selected and optimized. In this manner, controlled amounts of de-aerator chemicals are added to the white water.

The authors manage to run the control loop, stable and problem free. Within a few days, they observe a 29% reduction in de-aerator dosages, without any side effects in paper quality or paper machine speed. In addition, the authors were able to add an alarm as an extra feature in this loop, in order to prevent the production of broke. Finally, they undoubtedly showed, in a graph of gas contents and de-aerator dosages without and with control, that the control loop reduces the variations in gas content and de-aerator dosage. What’s more, the authors claim there is a 37% saving on de-aerator costs within a period of two months.

On the paper-machine, the automatic control of retention aids is achieved by using in-line white water consistency transmitters. The online retention control system detects particles such as fibers, fines and fillers in real time, due to inline measurements. This is coupled with a retention control analyzer which measures the total and ash consistencies of the pulp suspension by drawing samples from a pipeline, which are de-aerated and deflocculated. Once again, the installation process is time consuming, since sensors need to be calibrated, and this requires a minimum of twenty measurements. However, automatic retention control in the white water is expected to keep the consistency constant and in this manner ensure smooth running of the paper machine, little variation of basis weights and overall wet end stability. The fluctuations of retention aid were monitored over a period of several weeks with both the existing sensor and with the inline sensor. The comparison shows that the inline retention control shows a much smaller variation of retention dosages. Also, the retention control analyzer is proved to be much more accurate and precise than the existing sensor, as far as correlating the results to those of the lab, as shown by correlation coefficient calculations.

When looking at the wet end, the authors discovered that the fixatives added failed to sufficiently neutralize anionic trash. They looked at the streams at a location before dilution with white water. The TMP and DIP streams exhibit heavy charge variation. The authors then sought a suitable location for a fixative control loop. This was found to be the blend chest because it enabled the impact of all three stock streams, (TMP, DMP, broke) to be taken into account so that the charge level could be stabilized. A measuring position after the machine chest was selected, at an adequate distance from the starch dosing point to avoid unwanted effects on measurement results. Again, the authors find a noticeable long-term charge variation, made even more pronounced when testing with highly bleached TMP pulp. This could seriously affect subsequent chemical additions and should be rectified. Based on on-line cationic and anionic demand of colloidally dissolved materials, as measured by the particle charge titrator, fixatives can be controlled to a specific anionic trash set point. However, the authors show no work in controlling the charge demand and retention aid dosage. They relate the variation that is present to the production speed and the requirements of retention aid dosage, but no plan is implemented. The authors simply state that as the charge levels are stabilized downstream of the machine chest, the retention aid dosages can be kept at a constant level.

Discussion

Overall, this lack of a plan for controlling retention aid makes this article incomplete. This is a shame since the authors have shown very clear results obtained methodically, and implemented progressively, while working out all the kinks. Another reproach would be that the authors spend a lot of time defining equipment and specifications rather than the closed control loop, and how it works. The beginning of the paper gives the impression of a technical paper. A simple explanation of PID control, and its role in process optimization would have been appropriate.
Also, one must remain skeptical as far as the economic benefits of controlling of de-aerator chemicals and fixative are concerned. The control equipment itself may be pricey. Furthermore, the lost production time imposed by the trial and error involved with the setup of the optimal control parameters, as well as the start-up and shutdown each time a factor is modified, may result in further unexpected costs. Furthermore, if the control loops begin to have instability problems, the whole setup process may need to be repeated many times and further costs may be incurred. Moreover, what if the instability cannot be corrected, or requires further capital expenditures and equipment replacement?

Another issue that the authors neglect is how the savings on costs were calculated. What considerations and assumptions are implied? The 37% de-aerator cost reduction is a figure that is not backed by any proof. In addition, we must keep in mind that this all applies to a sample mill; these figures will change for other mills that wish to implement such control systems. And so, each mill will need to study its own system carefully.
Finally, the authors do not discuss how important it actually is to reduce the fluctuations, as far as improving wet end stability. How significant are the fluctuations? Is there an actual improvement in stability through automatic control loops?

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“Advanced wet-end System with Carboxymethyl-cellulose”
by Watanabe,Masasuke; Gondo, Tomohisa; Kitao, Osama, TAPPI Journal, May 2004.

Reviewed by Robert Bunzey, November 2004

As the papermaking industry increases it’s usage of secondary fibers, speeds up it’s production lines (which may reduce first pass retention) and closes it’s water systems, the use of wet-end chemicals plays an increasingly important role. This trend has, in effect, caused chemical manufacturers and papermakers to look for new technologies and new applications of older chemistries. The authors of this paper continue to look into the usage of carboxymethyl-cellulose adsorbed onto the fiber surfaces to increase retention, strength and runnability.

Earlier research conducted by these investigators, showed that because of electrical repulsion, it was very difficult to adsorb the CMC to the fibers. By reducing the pH of the slurry, with the CMC present, they were able to get sufficient adsorption. But the conditions necessary were not practical for papermaking operations. Additional research resolved these problems, which was the basis for this paper. The investigators used CMC with low levels of degrees of substitution in conjunction with the adjustment of electrical conductivity (electrolyte concentration) of the pulp slurry. Carboxymethyl-cellulose adsorption was increased resulting in improved efficacy of wet-end additives.

In part 1 of this study, the investigators beat hardwood kraft pulp to 450ml CSF and adjusted the electrolyte conductivity with soduim sulfate. The pulp consistency was held to 2%. They then added carboxymethyl-cellulose with different degrees of substitution, but kept the degree of polymerization steady in order to study the adsorption. Using colloidial titration, the amount of adsorption was determined. Data was presented that showed that as the electrical conductivity increased, the amount of CMC adsorbed was also increased to a certain level then seemed to hold steady. What was presented was that a lower degree of substituted CMC had a better early adsorption that increased with conductivity. Adsorption was only minimally affected by a temperature increase.
Based on this information, the authors looked into the electrical conductivity of raw materials under practical mill conditions. They stated that the electrical conductivity depended on the method of white water recovery and on the recovery rate; but offered no information or data to back up these claims.

Additional work using dosages of CMC showed that the physical properties tested were improved using the carboxymethyl-cellulose adsorbed by increasing the electrical conductivity method described earlier. Tensile index numbers increased from approximately .20 to .25. In addition, data was presented that showed increases in retention of dry strength additive, wet strength additives and rosin sizinge agent. Because of these increases, the authors claimed that the most significant result of this investigation was that handsheets made from CMC treated pulp needed 30-50% less chemicals added than usual to achieve the same physical properties. The optimum level of CMC addition was at .1% on the dry pulp, which showed a balance between adsorption of CMC and reduction of additional chemicals.
Part two of this study involved the addition of CMC to a mixed pulp slurry. Using 10% semibleached softwood kraft pulp, 30% thermomechanical pulp, and 60% deinked pulp, the investigators followed the same addition routine as was used in the first study. Again the sizing degree of these handsheets increased, however, there was a bigger boost when the CMC was added to the TMP first.

Zeta potentials of the individual pulps were recorded and the investigators found that the TMP zeta potential changed from a -7mV to a -5.5mV as a result of the addition of CMC. They theorized that the major improvement in the efficacy of the sizing agent with the pre addition of CMC to the TMP resulted in the equalization of the surface charges of these pulps. They believe that if there are various kinds of pulp in the mix, wet-end chemicals will adsorb preferentially onto the pulp that has the more anionic surface charge. This produces an uneven adsorption of wet-end chemicals and, in turn, means that the sizing agent will be unevenly distributed across the sheet.
The increase in anionic charge (ie: increasing the negative charge of the zeta potential) by the addition of CMC minimized the surface charge differential between the different pulps present, leading to a more uniform adsorption of the sizing agent. Graphs presented seem to support this hypothesis.

The investigators carried out mill trials based on their lab findings. In trial number one, CMC at .1% was added to the pulp chest of a kraft paper, with the result being a 33% reduction in the PAM addition and a 15% reduction in the level of the sizing agent used.
Mill trial two used a furnish that contained titanium dioxide. Addition of the CMC to the mixing chest increased the first pass retention of the TiO2 from 40% to 70%. This in turn led to a 15% reduction in the dosage level of the TiO2. Without offering any evidence, the investigators stated that the addition of the CMC incresed the anionicity of the pulp, thus increasing the number of adsorption sites for the titanium dioxide, and improved the effectiveness of the cationic additives, which increased the first pass retention of the TiO2.

Discussion:

This paper was very hard to understand and follow. The investigators talk about the carboxymethyl-cellulose adsorbing onto the fibers due to hydrogen bonding but failed to consider any carboxyl functionality. They also talk about CMC with a lower degree of substitution having more “pure cellulose units”, than CMC with a higher level of substitution, but offer no explanation of “pure cellulose units” and how that may affect their study or the results.

They also talk about the white water recovery rate and type being responsible for controlling the electrical conductivity of the raw materials. Again, they offer no evidence to support these assertions. They do not discuss the different types of white water recovery or rate, and how either of these may affect conductivity.

In table two, the investigators present data that shows the zeta potential of TMP pulp before the addition of CMC was at -7.1mV and after the addition of CMC the zeta potential was measured at -16mV. However, when discussing the zeta potential in the body of the paper, they stated that the zeta potential went from a -7.1mV to a -5.5mV. They then build a case for equilibration based on these numbers and state that this minimized the surface charge differences between the pulps used, which led to a more uniform adsorption of the sizing agent. Clearly there is much confusion here.

Finally, the investigators try to build a case for uneven sizing adsorption as a result of the CMC being adsorbed preferentially onto pulps with a higher zeta potential. While this makes some sense, conceptually, the pulp should be equally and evenly distributed throughout the sheet which would negate their theory about uneven distribution.

” Prediction and optimization of sizing response using adaptive machine learning and integrated management of wet-end chemistry” by Michael T. Plouff, TAPPI Summit 2002, paper 11-3.

Reviewed by: Zhoujian Hu
Date: November 10,2003

Introduction

In this article the author, Michael T. Plouff, in order to predict and optimize multiple papermaking process variables, chose adaptive machine learning methods. Approximately 300 data related to the parameters of rosin-sizing chemistry were used in the initial training and confirmation stages. Implementation data using the trained models showed a good general agreement between the model data and the actual machine data and can get a lower-cost for a given chemical program than do the traditional controlling methods. This article gives us some information about adaptive machine learning methods, neutral-network methods, computational algorithms and the logic of using an adaptive machine learning method in rosin-sizing control. This article is important for papermaking to use adaptive machine learning methods to control multiple papermaking process variables.

Background

The traditional procedure for wet-end chemical management is a trial-and-error method of linear optimization. This way runs very well for independent linear variables. However, in the wet-end, many variables have non-linear correlations. With the advance of chemical program technologies, closed whit-water loops, and lower-cost raw materials used to increase frequency, the traditional or normal approach can’t lead to a satisfactory result. This is the key reason why one wants to find a better way to control the parameters in the wet-end. An adaptive machine learning method involves a generalized computational method, often based on neutral networks, which analyze linear and non-linear, complex interrelations among data for the prediction, control and optimization of a desired target. This adaptive machine learning method is characterized by the ability to learn from underlying data trends. It is used to structure process control strategies, but has not often been applied to the wet-end chemistry of a paper machine.

Discussion

In this article the adaptive machine learning algorithms used were a combination of neural networks, a genetic algorithm and an advancement in the technology called a Free Form Mesh. In Free Form Mesh, the software iMODEL was used. The author chose sizing chemistry as a case study, using an adaptive machine learning method. The factors which affect the efficiency of rosin sizing were analyzed. These factors, such as pH, conductivity, charge demand, and so on, are interdependent, that is, non-linear interactions. Therefore, the traditional method (linear) used can’t get a satisfactory result in controlling the efficiency of rosin sizing. Sample points were selected and data were collected. Sample points were headbox, machine chest, kraft chest, chemical feed injection points and reel. Data collected were charge demand, pH, conductivity, dosages and COBB&HST values. After about 300 data were collected, the author ran initial adaptive learning model and analyzed them. He refined the model and analyzed the data. Finally, he implemented the model on the wet-end of a paper machine.

Initial adaptive learning model shows us the linear tendency of the underlying regression model, determined by the relationship between sizing dosage and a linear combination of the dosage for pH control, the sizing response variables COBB and HST, the charge demand of the headbox and the pH at the headbox sample point. The correlation coefficient was 0.8. Then a series of new data were put into this model. A better constraint was obtained. Unfortunately, the method that improves the model through eliminating variables will deteriorate the linear regression model.

However, when the neuro-genetic mesh software was used in training the model, the relationship between the variables and the results from the software had a high correlation between the original data and the model. Therefore, the author implemented this model on the paper machine. Then, an alum model and a dispersed rosin size model were used simultaneously (ratio of alum: dispersed rosin size was maintained). The result shows us there was a good agreement between the model data and the actual machine data. When the ratio (not normally controlled) between the alum and the dispersed rosin size was used as a control variable, the result showed correlation coefficient up to 0.7(not high). But the model result can track the actual ratio. That’s to say, we can use this model for other parameters not normal controlled.

In the end, this article discussed the optimization and economic efficiency. Since the model result can track the machine value very well, the consumption of chemicals will be decreased. The raw cost decreased by 35% in rosin sizing. That is a good deal for paper mill.

This article gives a good idea for controlling multiple variables in the wet-end. This is useful and helpful for integrated wet-end chemical management and achieves a high cost-performance for a given chemical program compared to the traditional approach controlling to the wet-end additives.

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“A Superior New Approach to Paper Contaminant Control,” by Charles D. Angle, TAPPI Summit 2002, paper 23-4

Reviewed by Jeff Wallace,
November 11, 2003

Principal Theories

This article explores the use of a new and superior combined method to improve paper machine contaminant control, which could improve machine productivity and paper quality. Hercules Inc. developed this new method and it combines an amphoteric, surface-active, structured protein with a highly charged cationic polymer. The structured protein was theorized to both increase the stability and reduce the thickness of colloidal contaminants. The approach combines three different method of control:

· Stabilizing the colloidal material with a dispersant
· Reducing the tackiness of the colloidal material using a detackifier
· Removing the contaminants from the system together with the paper using a highly charged cationic polymer

Combining these methods had traditionally provided few additional benefits and the methods have not been complementary. But with the use of the structured protein, it is theorized that all three methods can be combined to be totally more effective than the conventional methods. The structured protein performs its function through adsorption on to colloidal material, enhancing colloidal stability, modifying the contaminant surface to reduce adhesion, and combining with the contaminants, thereby allowing them to be fixed to the sheet and removed from the system by a cationic fixative.

Supporting Evidence

The theory of using the structured protein to improve contamination control was supported by the data presented in the article, and the author was very thorough in separating out the effects of different variables. The relationship between the structured protein and its effectiveness at improving the adsorption onto the surface of hydrophobic materials can be shown by data that supports a reduction in zeta potential of a colloidal suspension of those materials. The data showed a reduction in zeta potential of colloidally dispersed polystyrene with increased addition of the structured protein. This indicated that the adhesion of the structured protein onto the hydrophobic polystyrene and its attraction to hydrophobic surfaces.

It is preferred that this adsorption is strong is strong enough not to be easily washed off or displaced from the surface in dilution steps, refiners, pumps, etc. To measure this, hydrophobic material was treated with the structured protein and water was applied to the surface to measure the contact angle. A low contact angle demonstrates that the surface of the material is modified to exhibit lower hyrdophobicity. The hydrophobic material was then washed several times to determine how easily the structured protein could be removed from the surface during washing or dilution steps. A conventional detackifier was compared against the structured protein and lower contact angles after washing indicated that structured protein is more resistant to removal from hydrophobic surfaces even at higher washing levels. In my opinion, the author was thorough in this study.

With a reduction in charge by adsorption of the structured protein, colloidal stability between contaminant particles is more a function of interfacial or steric stabilization. Proprietary methods were used to verify that steric stabilization increased with application of the structured protein and it was shown in the data that if contaminants are treated with the structured protein, then greater colloidal stability could be expected. This reduces the tendency of treated contaminants to agglomerate and deposit.

To test how the structured protein could reduce tackiness, the author did a good job in presenting data on how it could modify the surface to reduce tack and depositability. Its adsorption onto the surface allows for the building of physical and water layers around the contaminant. These layers interfere with the adhesion of the contaminants to other surfaces. The percentage reduction in the required tack, or force, is termed the percent detackification. Data showing the effectiveness of the structured protein versus other proteins and the relative effectiveness of detackification versus a known, commercially available detackifier were found in this study. In both cases it was found that small amounts of the structured protein are almost able to eliminate the tack of the adhesives.

To reduce the content of contaminants in the papermaking system, the complex formed by the structured protein and the contaminant must be able to be retained. Reaction with cationic polymers to fix or bridge a complex onto a fiber surface is a common method of retention. The demonstrate how structured protein reduces the content of contaminants, the author presented data on tests that were conducted in a mill producing 100% recycled paper, double lined kraft, and clippings. The percent reduction in the turbidity of the filtrate is used to correlate with colloidal contaminant content and as a measure of colloidal retention. An accelerating reduction in turbidity, above that of cationic polymer alone, was seen in the presence of a constant concentration of structured protein and increasing fixative addition.

Further Opportunities for Study

One area where further work could be done is with the size of the furnish used. There was no study done in this report to demonstrate how increased levels in fine content could increase colloidal stability in the presence of structured proteins. It is theorized that smaller particle size will contribute to better colloidal stability, so it would be interesting to see a study done on increasing fines content in relation to it. Apart from furnish size, it would also be a good idea to look at how the effects of viscosity and temperature could influence the depositability of contaminants in the presence of structured proteins. This is important because depositability is essentially the tackiness or adhesive properties of the contaminants. It also has been suggested that temperature shock can reduce colloidal stability, so that is another area that needs to be looked at in relation to structured proteins.

Practical Application

The author of this article clearly demonstrates practical use of structured proteins by discussing several industrial trials at different mills that produce different grades of paper. ‘Mill A’ produces corrugating medium from 100% recycled fiber using a conventional detackifier and treatments on the wire and rolls for control and pitch deposition. The structured protein was introduced in place of the traditional detackifier, and it was shown that the amount of topical treatment required on the wire and rolls was reduced by approximately 30% and stickies deposition at the rewinder was reduced indicating better performance. The retention of suspended solids tracked closely with increased and decreased addition of the structured protein, and it was shown in this study that a decrease in suspended solids in the presence of the structured protein indicating an increase in retention.

‘Mill B’ produces tissue paper with a range of 50% to 100% recycled fiber and also added a traditional detackifier to the waste furnish to control stickies deposition in the wet end on the felts. A trial of the structured protein was initiated on a grade consuming 50% waste paper. 1.8 kg/ton of the detackifier was replaced with 0.5 kg/ton of the structured protein. After three hours, stickies that were seen at the air/water interface in the stock and white water chests disappeared, and sheet stickies content was visibly reduced.

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“Industrial Refining of Unbleached Kraft Pulp-The Effect of pH and Refining Intensity” by Ulla-Britt Mohlin

Reviewed by Neeraj Sharma
Date 11/11/2003

Introduction

In this paper, author has studied the effect of refining intensity and pH on sheet properties for machine-made paper and hand sheets simultaneously. The author has shown that properties developed in hand sheets and machine made paper are different. He has successfully explained the causes of these differences. Other than that he has explained the effect of refining intensity and pH in terms of plate gap. In this work at some places author hasn’t made statements clear and at some places results are over-stated.

Background

Refining of pulp is one of the most crucial steps in making stock for paper. A lot of study has been done to understand role of refining on strength properties of paper. Still there is only little understanding of the process. Usually two parameters, refining energy and refining intensity, are used to describe refining conditions. It has been shown in past that the chemical environment during refining is important for the efficiency of refining. It is found that pH and presence of electrolytes affect refining efficiency. Optimal pH for refining efficiency is 9-10 and as minimum as possible electrolyte concentration is favorable. Refining increases water retention value of a pulp by internal and external fibrillation and fines creation. These developments change the bonding properties of fibers. Other changes by refining are fiber shortening and changes in fiber curl.

As this work concentrates on the effect of refining intensity and pH on sheet properties, author has intentionally chosen unbleached kraft pulp for experimental work. The unbleached pulp has unassociated carboxyl groups, which enhance swelling at higher pH.

Discussion

In this paper the author has shown that change in refining due to pH or refining intensity is directly associated to plate gap. A higher degree of refining at higher pH values is a result of decrease in plate gap at higher pH. As for the same refining energy if plate gap is less, it will lead to more refining intensity leading to higher degree of refining. This reduction in plate gap may be due to a change in stiffness, which leads to change in compressibility of the fiber mat. Or it may be due to less friction between the fibers or between the fibers and refining plates for swollen fibers or due to all of these. The author has also shown that the high degree of refining for lower production is also associated to plate gap, if the refining energy is same for two pulps. The author has used term refining activity (WRV*production) instead of WRV to show this relation. The concept behind using refining activity is that if the pulp production is higher, the energy provided by refiner will be distributed over a higher amount of pulp, which is proportional to the pulp production. This means that for a certain plate gap refiner will be able to produce certain refining activity irrespective of production rate or pH. This information is very useful from the point of view that for any production rate or pH value we can predict and control WRV just by controlling the plate gap.

As other than increase in WRV two effects, fiber shortening and change in fiber curl, occur during refining so author has investigated if the fiber length and shape factor can also be correlated to refining gap, independent of refining conditions. Here it seems over-generalized statement that at a certain refining gap fiber shortening started to occur independent of refining conditions. There are not enough data available to support this statement as for some pulps refining gap data before this particular value are not available and for some other pulps data after this point are not available. Author hasn’t stated the reason why plate gap couldn’t be read for some refining conditions. As at high WRV, there are more fines in the pulp and they can affect tensile index negatively. Here it would have been more explanatory had they shown data for fractionated pulps. In the experimental section they have talked about fractionation of both refined and unrefined pulps but they have not shown any data for fractionated pulp.

For the machine made paper there was no general relationship between sheet properties and WRV. They found that at the higher level of production the density was lower for the pulps refined at pH 5 while at the lower level of production the pulp refined at pH 8 gave the lowest density. The difference in effect of refining on hand sheets and machine made sheets is partially due to the difference in forming consistency. The mechanical properties of the machine made papers correlated well with the power input during refining independent of production level during refining. It cannot be said whether it is power or refining gap, which is more important factor in refining.

For a higher level of production there was a direct correlation between plate gap and sheet density and other sheet properties but for the refining at the lower production level there was a lower density at pH 8 at a certain plate gap. The reason could not be explained in this paper. This means that in case of higher production level plate gap is a better parameter than refining intensity and refining energy to predict sheet properties. But at low production level this parameter can’t be used effectively. Some more work is needed to investigate the difference in sheet properties for same plate gap at lower production levels.

This paper presents a new refining parameter ‘plate gap’, which along with refining activity can successfully be employed to control product strength properties in case of high production level through refiners.

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“The Use of Synthetic Polymers to Enhance Sheet Strength And Improve Machine Efficiency” by Darren K. Swales and Richard Zemke, TAPPI Paper Summit 2002.

Reviewed by Chang Woo Jeong
November 11, 2003.

Introduction

In this paper by Swales and Zemke, the authors studied a novel polymer to enhance sheet strength and improve machine efficiency. The use of synthetic resins based on polyamide chemistry not only increases the strength of bonds but also takes an active role in the dewatering process. Their suggestion can increase machine speed. However, they did not consider obstacles which can occur in the application of the chemical in a real paper mill. Assumptions that were too simplified regarding the relation between various wet-end chemicals and the properties of the product could bring many questions to the reader. These findings provide the papermaker with an additional effective tool to improve the overall production process in spite of such drawbacks.

Background

The drainage of the paper web on a machine wire involves a dynamic separation of the paper web from the white water. Thus, the rate of drainage for the stock on the wire is a fundamental factor determining the speed of the paper machine. However, the two factors, retention and drainage, often are closely linked: the higher the drainage, the lower the retention and vice-versa. Several decades ago, modern retention aids such as synthetic polymers were discovered to improve retention and drainage at the wet end of the paper machine. Most recently with the inclusion of wet strength technology, novel polymers have been developed that not only produce higher degrees of dry strength, but also function synergistically with other wet end additives, namely starch, or starch based additives and colloidal silica. Thereby, this three-component system provides higher levels of strength, dewatering, and formation control than has been previously possible. Combining the beneficial effects of pulping and refining under alkaline conditions, along with synthetic additives that additionally enhanced the strength characteristics, provides the papermaker with tools to increase efficiency.

Discussion

The authors produced sheets with a basis weight of 200gsm. The desired amount of strength additive was added to 1000g of 3.0% consistency thick stock and stirred at 250rpm for 15 minutes. 275g of the stock was diluted in the sheet mould with municipal tap water (23 mg/L hardness as CaCO3). The sheets were rotary pressed at 450 kPa and drum dried at 105C for 60 seconds. The produced sheets were measured for zero span tensile, burst strength and ring crush. The evaluations were performed under standard conditions using the TAPPI Test Methods. Significant strength improvements were observed with the polymer strength additive(PSA) alone. The increases of turbidity, drainage and permeability in the sheet with PSA were evaluated by Dynamic Drainage Analyzer(DDA). Before machine evaluations, the complete additive system was investigated. When the system included the PSA, starch and colloidal silica greater impact on the fiber-fiber interaction, drainage and retention was observed. The three components worked synergistically indicating optimum dosage levels of starch and PSA.

The mill produces an average of 820 tons per day of 150-360 gsm ( 31-74 lb/1000 sq.ft) bleach top and natural linerboard grades, and various weights of high performance bleach top and natural linerboard. A Beloit Fourdrinier with Concept III primary headbox forms the primary ply and Beloit Concept IV secondary headbox and Bell-Liner twin wire former forms the secondary ply. The base ply consists of OCC, (old corrugated containers), and broke. In the paper mill the authors demonstrated that refining enhanced the strength of sheet but it could not avoid deteriorating drainage. However, the sheets with PSA improved sheet strength as well as drainage. The increase of drainage is related to the machine speed, in other words, process efficiency.

The research focused on only drainage and the authors omitted the relationship between retention and PSA dosage. Generally, high drainage can render poor retention. If there was poor retention, then the paper mill would not escape various problems, for instance, deposit problems, high load on save-all and increase of two-sideness and bubble foam. They should have investigated whether there were problems to prove feasibility in usage of PSA. In addition, the novel polymer can react with other chemicals other than starch and colloidal silica in the complex wet-end system. This interaction might be expected to decrease strength of sheets or the rate of drainage. High drainage is able to have bad influence on the sheet formation uniformity, which degrades the quality of sheet. They overlooked the survey of fine content in the white water, because higher fine content in the closed system means that the mill needs a lot of clean water which increases the cost of product. Finally, to achieve higher machine productivity, they could have carried out more research on the amount of PSA which can optimize the machine efficiency in terms of stoichiometry, since the change of charge in the system by overdose of PSA can reduce productivity and the quality of paper.

The wet-end system can be readily influenced by numerous unexpected factors. For this reason, it is not easy for us to predict the results. Even though the authors did not demonstrate whole effects of novel polymer in the papermaking system, the addition of the polymeric strength additive to the linerboard machine provided the papermaker with a tool that not only provided additional strength but also improved the overall system efficiency and economy.

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“Characterizing Refining Action in PFI Mills”, by Kerekes, R.J., TAPPI Paper Summit 2002

Reiewed by: Kathy M. Austin
November 11, 2003

Secondary Source: Beirmann, Christopher J., Handbook of Pulping and Papermaking, Second Edition, Academic Press; San Diego, 1996.

Introduction

Papermakers utilize refining to improve paper strength and formation. Refining uses physical forces to brush, cut and compress fibers to increase pliability and degree of fibrillization. Refined fibers have more bonding ability, which increases paper strength, even though the individual fibers are weakened. Though refining has the ability to increase paper strength and improve formation, it often decreases the average fiber length and is a very energy intensive process. Consequently, there is often a trade off in the positive and negative aspects of refining. Refining is an important part of papermaking and thus lab refiners are important pieces of equipment in many laboratories.

Today the most commonly used lab refiner is the PFI mill. The PFI mill uses refiner bars on a rotating disk against a smooth bed to refine pulp. The PFI mill is able to refine the pulp to the desired degree quickly and with little fiber damage. Refining results can also be reliably repeated with the PFI mill, which adds to its popularity in lab settings. However, PFI mills impart about one tenth the refining intensity of typical industrial refiners. The gentle nature of the PFI mill makes reproducing machine conditions difficult. Though the intensity is low, the specific energy of the PFI mill is roughly ten times that of industrial refiners.

Comparison of the PFI Mill to Other Refiners

A closer fit to large industrial refiners is the Escher-Wyss laboratory refiner (EW). EW refiners work much the same way as industrial refiners and tend to produce results very close to those found in paper mills. When refined to a common specific energy, EW refiners produce stronger pulps that more closely resemble those produced by industrial refiners.

The differences in the lab refiners’ nature can also be seen in freeness measurements. At equal levels of specific energy, the EW refiner drops the CSF value of the pulp dramatically, while the PFI mill gradually decreases the freeness. This change in freeness suggests a difference in external fibrillation. Electron micrographs show significantly more fibrillization on pulp refined with an EW refiner than a PFI mill. When the specific surface of the pulp is measured, the EW pulp has roughly twice the surface area of the PFI pulp. However, when the pulps are separated by fiber length, the long fiber surface areas of the two pulps are very close. One can rationalize from this information that the external fibrils produced in the EW pulp are weakly attached to the fibers and are able to pass through the screens when classified.

Comparing the characteristics of the PFI mill pulp with those produced with other laboratory refiners can help characterize the effects of PFI mill refining. Pulps produced with a device that rolls a ball over pulp yields very similar results to those produced with zero relative velocity between the rotor and housing of the PFI mill. This is evidence that one of the main sources of refining in the PFI mill is fiber compressions. Another rolling device, in which there is little to no fiber mixing and consequently results in nonuniform refining of the pulp, reaches a tensile strength plateau rather quickly. Since the PFI mill does not plateau until much later in the refining process, it can be concluded that there is sufficient mixing during PFI refining resulting in homogeneous refining.

Conclusion

The PFI mill, while common in papermaking laboratories, may not be the best tool when a comparison between lab results and actual paper mill data. The gentle, homogeneous refining process of the PFI mill produces very positive results, but often very different results from the heterogeneous, at times harsh refining of industrial refiners. The EW refiner is a closer fit to the full-scale refiners, but even this device deviates from the industrial refiners.

For all its merits, it seems strange that there has not been a movement in the papermaking industry to recreate the positive effects of a PFI mill on an industrial scale. Rather than finding ways to recreate the industrial refiners on a laboratory scale, it would seem as though a more positive task would be developing better industry refiners. Perhaps in the future a refiner will be developed and used in the industry with reduced fiber cutting and increased fiber brushing to increase surface area while maintaining the average fiber length. The PFI mill has its faults, as does any refiner, but in many ways it is better than those used in papermaking industry.

Article Critique

Though this article could be a useful tool to explain the differences between common refiners, nearly all of the claims made in the paper are based on estimates. The estimations and simplifications used could greatly reduce the usefulness of the calculated results. As an example, when the author estimates the working zone of the PFI mill, he states that there is an estimation of the “upper limit” and “lower limit”. Neither of these limits are exact and from these the author calculates a single estimation of the refining intensity. This simplification gives the illusion of a hard, calculated value, when in reality it may have been better to offer a range of refining intensity.

The article initially seems like a regular summary of a researcher’s findings. However, a closer inspection reveals that very little research was actually done by the author. Primarily this article is a literature review. While this fact makes the paper no less useful in understanding the effects of PFI mill refining, it may have been more accurate if the author had added “A literature review” to the title.

Overall, this is a well organized and information-rich paper that would be invaluable to someone whose research relies heavily on pulp refining.

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“Indicators for Forecasting Pitch Season”, by Blazey, M. A., Grimsley, A., and Chen, G.C., TAPPI Summit 2002, paper 23-2.

Reviewed by Jeff McKee,
November 2003

Introduction

The authors start this paper by talking about how the current industry trends are increasing the potential for severe pitch outbreaks. The trends mentioned include the increased use of high yield pulps, closure of white-water systems, and reduced chip-aging time. Today’s market requires mills to reduce cost by any means possible. Machine downtime and downgraded paper caused by pitch must be avoided for mills to stay competitive in today’s market, therefore mills need to be proactive in controlling pitch outbreaks. This means that they will need some way to predict when a pitch outbreak is approaching. Mills using pitch control chemicals also need to be able to optimize their pitch program chemical dosages to keep cost down, which requires some type of measurement that indicates or predicts pitch problems. The authors’ analysis of TMP samples indicate that pitch out breaks are due to the composition of pitch rather than the amount of pitch present in a system. The objective of this paper was to examine the factors that contribute to pitch season and methods that can be used to monitor them.

Background

For a paper-maker to understand when pitch season is starting and ending they need to understand the factors that influence and contribute to their pitch seasons. Based on the authors’ findings, pitch seasons will vary depending on geographical locations and wood storage time. This is mainly due to the different climate temperatures, which affect the reaction between pitch components.

Wood pitch is made up of compounds such as resin acids, fatty acids, triglyceride esters, steryl esters, and waxes. To simplify, the composition can be placed in two groups, “ester pitch” and “acid pitch”. The authors’ state that “ester pitch” is widely believed to be the driving factor that causes pitch particles to agglomerate and create problems for the paper-maker. The reason being the ester pitch contains triglycerides and steryl esters, which are a non-polar neutral species and are more hydrophobic than the acid pitch materials. The water-hating nature of these particles can increase the probability for the colloidal pitch particles to agglomerate and create deposits.

The ester pitch composition is affected by the seasoning of wood. As the wood ages, the triglyceride component of the ester pitch can hydrolyze into fatty acids. Therefore, as the wood ages, the ester pitch to acid pitch ratio decreases, and should lead to a reduction in pitch problems. This rate of hydrolysis for the triglyceride component decreases with decreasing temperatures, which is the reason that a mill’s geographical location has a big impact on their pitch season.

Discussion

Since the ester pitch component is being directly connected to pitch deposit problems, the ester pitch to acid pitch ratio can be used to determine a mill’s pitch season. A gas chromatograph can be use to quantitativly measure the triglycerides, resin acid, and fatty acids in process samples. With this data one can calculate the ester to acid pitch ratio.

The authors’ used a case study to prove their findings. A southern newsprint mill running 100% Southern Pine was used in their case study. This particular mill had experienced pitch deposit problems around the same time every year. Samples of post-refined TMP from June (outside pitch season) and February (during pitch season) were extracted and analyzed using a gas chromatograph. The following observations were made: a) total extractables decreased by 67% in the winter sample, but pitch deposit outbreaks were significantly worse during the winter, b) the resin acid content decreased by a factor of 4 in the winter sample, c) the triglyceride concentration increased significantly in the winter sample, d) the ester pitch to acid pitch ratio increased eleven-fold in the winter sample.

The authors’ point out that these results are from only one mill, but the correlation of the “pitch composition” with “pitch season” is believed to be widely applicable. They also state that the fiber source and geographical location could have some affect on the correlation between the pitch composition and pitch seasons.

Conclusion

Pitch outbreaks are always a challenging and costly time for paper-makers. Based on the authors’ findings, the ester pitch to acid pitch ratio can be used to determine a mill’s pitch season and or a potential pitch outbreak. The findings in this paper could be quite useful for the paper-maker that experiences issues with controlling pitch outbreaks. Not all mills will have a gas chromotograph readily available, but they should be able to utilize their R&D support or find an out-source for the needed chromotagraphy information. The problem here is sample turn-around time since it could take several weeks to obtain the needed chromotagraphy analysis results. A mill needs to have an effective tool to quickly and rapidly determine if they are approaching their pitch season or a pitch out-break. If the results are readily available they can be used to adjust chemical dosages to optimize the treatment and prevent or diminish an outbreak on the paper machine.

Further work is needed to find a simple method to determine these components that make up pitch. My suggestion would be to focus on measuring only the triglyceride component of pitch since it appears to be the main driving factor related to pitch problems. If a simple and quick method was developed, such as a spectrophotometer method, then a mill could run this test every day and develop trends. These trends could then be monitored, control charted, and used to be proactive and head-off any pitch outbreaks.

I also suggest that it is critical for a mill to have good pH and temperature control systems. Any swings in these two variables will significantly increase the possibility for pitch out-breaks. As far as the future goes, I see the enzyme technology that is used to promote the hydrolysis of triglycerides to play a big role in pitch control systems.

“Applying Automatic Chemical Control from Stock Prep to the Machine” by Sylvain Renaud, Teresa Burke, and Roland Berger, 2002 TAPPI Paper Summit

Reviewed by Sa Yong Lee
November 7, 2002

Introduction

In this paper by Renaud, Burke, and Berger, the authors provided a further understanding of wet end chemistry control. They present new results for both retention aid control using white water consistency and charge control using on-line cationic demand measurement. A practical example is provided which shows the benefits of combining both control techniques. However, even though the authors explained the difference between charge demand and zeta potential, and provided a summary of wet end chemistry system, they simplified everything too much, especially during explaining the charge survey and white water consistency control. Their assumption that the readers would have some basic knowledge of wet-end chemistry makes the readers have many questions. But what they said can be important for controlling wet-end part in order to get uniformity of paper and stability of mill process.

Background

Nowadays, less than 15% of the world’s paper producers use water consistency measurement for control of retention aid addition, even though the control strategy is well know and has proven efficient and beneficial. Most mills either under-dose or over-dose their coagulants or fixatives because operators lack not only on-line information to optimize dosages and reduce variability but they also are adding their luxury chemicals without understanding or control.

In order to determine the optimum location for an on-line Particle Charge Titrator installation for measuring charge demand, a complete charge survey should be done by measuring zeta potential and charge demand. Zeta potential describes the surface charge conditions of solids-fibers and fillers in an aqueous medium expressed in mV. The measurements provide information concerning of the fiber activity, i.e. the capacity of fibers to adsorb an additive carrying an opposite charge. The Particle Charge Detector (PCD) method, which uses an oppositely charged polyelectrolyte for titration up to the point of neutral charge, can determine the charge of dissolved material – anionic trash and cationic fixatives.
Usually, when a change occurs in the retention, it is very difficult to determine if it is due to the changes of white water or headbox consistencies. But white water consistency control provides a tool to optimize retention aid and overall retention. Thereby, white water consistency is the most responsive control strategy to stabilized paper machine operation.

For these reasons, controlling not only retention aid by white water consistency control, but also coagulant and fixative dosages by on-line charge demand measurement, can improve the paper making process significantly. Especially, controlling charge level makes it possible to control white water consistency more stably and smoothly.

Discussion

During the authors’ explaining of “Wet End Chemistry Concept,” they laid some emphasis on the accurate and complete charge survey, because of the importance of measuring the charge at the proper injection points of every wet end additive as each of them can have effects on the process stability. Thereby, the authors’ provided only one figure and some data of charge balance of MODO fine paper mill in Hallein, Austria for explaining the importance of whole, complete charge survey. Isn’t it too simple? They didn’t give us any detail information about the fixing agent, filler, and retention aid. There are some important facts we should know. Actually, zeta potential values aren’t always linearly proportional to the charge densities of fiber surfaces, and the fiber fines and long fibers have the same kinds of pH dependency of zeta potential. There can be also a lot of anionic trash and cationic materials. So, the real situation of the wet end can be more complicated than what we can imagine. For readers’ clear understanding, more charge survey examples are needed, which contain the more detail, specific information, and data.
Secondly, according to what the authors said, “retention on the paper machine is a calculation based on the consistency at the headbox(es) and the white water(s).” So, if there were some changes in the retention calculation, it would be really impossible to say which of the consistencies was affected. Thereby, the most responsive control strategy to stabilize paper machine operation and stabilizing first pass retention is not controlling the retention aid chemicals but controlling white water consistency. But they didn’t say a lot about how to control the white water consistency except mentioning the retention aid, which may result in the readers not knowing which system is used. There are several retention systems, i.e. alum and cationic starch, PEI and cationic acrylamide, dual retention aid, and microparticle programs. The characteristics of each system are different. There are also some physical and mechanical factors, such as headbox consistency, the fineness of forming fabric, the type and adjustment of hydrofoil blades, the speed of the paper machine, the jet speed, and vacuum. In order to get some efficiency with on-line wet end control strategies, which the authors said, these other factors should be optimized, and the whole system should be considered to ensure the minimum variations in these factors.

Actually, wet end chemistry is very complex, but it’s not impossible to understand it. The wet end process control by on-line wet end control strategies is also not impossible. Only if we don’t try to resolve the whole issue with just one online device, we can consider what the authors said is one of the essential method to control wet end system and finally, we can get high returns for our efforts in stabilized paper mill operations and product quality.

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“Characterizing Refining Action in PFI Mills” by R.J. Kerekes, Tappi Paper Summit 2002

Reviewed by Jung Myoung LEE
November 10, 2002

Introduction

Generally, papermakers have believed that results with the PFI mill are quite different compared to those from commercial refining equipment. However, papermakers are used to it as an indication for mill equipment because it has good reproducibility with different operators. In this study of PFI mills and their action, the author was trying to compare the difference between the PFI mills, the laboratory refiner, and the conical type Escher-Wyss laboratory refiner in terms of refining intensity and energy. Although the data presented by the author were based on theoretical assumptions for simplifying the complicated refining variables, this paper showed that characteristics of PFI mill compared to commercial refiners and allowed us to calculate easy conversion into mill equipment instead of a mill manager’s instincts or accumulated experiences.

Background

Refining processing is of great importance to the paper industry, since pulp must be treated to make it as suitable as possible for the desired paper grades. This kind of stock treatment is a significant economic issue, consisting of 3 per cent of the cost of the pulp or more in some cases. There are many types of laboratory refiners for evaluating the pulp properties before applying it in the mill. Of them, the PFI mill is getting popular as an alternative to the Valley beater due to its consistent reproducibility and time-saving operation. There are two distinct objectives in use of a laboratory refiner. In the first place, this equipment is used for research studies, since this technique more closely reflects what happens in the mill process. Another is used by mill operators to evaluate new pulps and to provide a more meaningful basis for process control when using variable pulp sources. Thereby, the idealized refining conditions produce the optimal capability to their stock treatment in order to produce the greatest properties of pulp for a given freeness. However, the main drawback is that the data with laboratory refiner do not match data with commercial refiners, or even with other laboratory refiners. In this paper, the author was trying to review published papers and then compare the PFI mill to commercial refiners and other laboratory refiners in order to improve better understanding of refining process itself in terms of “C-factor” defined the capacity of a refiner to inflict impacts upon fibers.

Discussion

The author was trying to quantify the PFI mill’s refining actions in terms of specific energy and refining intensity with data in already published papers (Table 1). As mentioned by the author, the PFI mill has not been characterized in terms of specific energy and refining intensity, but rather has been described by the number of revolutions. The author focused on specific energy and refining intensity due to two basic variables: the number of impacts imposed per unit mass of pulp, N, and the intensity of each impact, I. Together, these two parameters account for expenditure of energy, E, on pulp. Thus, refining energy may be directly related to the number of impacts and the intensity of each impact. Furthermore, he divided the problem into two parts in order to calculate the working zone of PFI mill: upper limits in which some bar contact took place with the pulp pad; and lower limits that a zone extending over an arc of 3 rotor bars. Under these assumptions and C-factor, he estimated refining intensity as the energy expended on a fiber during one impact. He found the PFI mill uses 10 times more energy than the commercial refiners and the refining intensity is one tenth compared to does the commercial refiners. However, he did not consider the bar material, radius of leading edge, secondary small-scale fiber deflections and the mechanism of how fibers behave between passing bars. Although he had simplified many variables relating beating actions, we can easily characterize commercial refiners and other laboratory refiners in the terms of energy and intensity.

Before getting into a comparison of pulp properties changed by each refiner, the author concluded, based on other research work, that the Escher-Wyss laboratory refiner (EW) is more similar to industry conical and disc refiners than is the PFI mill. After establishing the different characteristics of each refiner, the author compared the refiners in the term of a given freeness and at equal specific energy. The valuable finding is that the strength development by PFI mill was lower than that of the EW at equal specific energy although the PFI mill showed superior strength development at a given freeness in Figs 2 – 6. To explain the causes, the author showed data of hydrodynamic specific surface (Table II) and photomicrographs (Fig. 7). The author also compared the different level of intensity to explain the observed differences between the two devices (Fig. 8). Although the observed difference came from the degree of external fibrillations and fine contents, the author did not fully explain the different mechanical action, and consequently, its impact into fiber itself and paper formation. He noticed that there are differences in the refining actions between each other, but these could not be explained by specific energy and refining intensity.

To characterize the PFI mill actions, the author reviewed other researcher works. He summarized the PFI mill as a cyclic compression device that imposes a high ratio of compressive to shear forces, compared to commercial refiners that are characterized by a shearing action. The reason why the PFI mill consume so much energy to achieve appropriate strength relates to uniform distribution of forces among fibers in a network and results in homogeneous treatment of pulp with PFI mills. A high proportion of the applied energy is consumed for internal fibrillation of fiber. Finally, he skeptically concluded that the greater compressive shear force is responsible for the higher internal fibrillation, and lower external fibrillation and fiber shortening, without data carried out by himself.

In this work, the author was trying to characterize the PFI mills, which are becoming the dominant choice for a standard laboratory refiner, since they give a consistent reproducibility and homogeneous treatment. From other works and theoretical assumptions based on two variables such as energy and intensity, the author draws a conclusion of the difference between the PFI mill and commercial refiners in a theoretical way. Although, this paper is based on other works and many assumptions to simplify complicated refining variables, the author shows why the PFI mills are different, and how we can compare its data with those of refiners in the mill.

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“Retention of Fibers, Fillers and Fiber Fines at Individual Dewatering Elements of Gap Former” by M. Kosonen, J. Muhonen and J. S. Kinnunen, TAPPI Summit 2002, paper 35-1.

Reviewed by Yong Sik Kim
November 12, 2002.

Introduction

In this paper the authors provided a novel method of calculating the element retention of individual dewatering elements, based on a mass balance model of the forming and press sections when water flows and their consistencies are known. In additional, they suggested that the same model could be used to calculate precise dryness development along the wet end if dry content of the paper after press is known. The authors verified the novel method in a modern pilot machine using different retention levels with adjusting of the retention aid dosage. But there exist information gaps and assumption in practical paper mills. However, this kind of study helps to understand the fundaments of wet end processes and provides a tool for system optimization.

Background

Papermaking is basically a filtration process. The paper machine wire can be regarded as being a continuous filter on which a proportion of the solids in the stock is retained. The unretained solids drain through the wire along with the majority of the liquid to form the white water. Thus, wire retention has a strong effect on the properties of the paper produced and machine runnability as well as minimizing pollution and cost.
Conceptually, retention describes the amounts of a given materials in the press section relative to the amount present at headbox solids of the paper making process. Nowadays, the paper industry commonly uses different methods to approximate theses values: true retention, first-pass retention and comprehensive retention. But these values show only general trends of retention behavior because these methods are based on a stabilized system. However, if water flows and their consistencies are known, retention values for individual dewatering elements can be calculated, based on a mass balance model of the forming and press sections. Therefore, this new method could be better for calculating retention values, which more closely correspond to the behavior of retention on a paper machine system.

Discussion

The authors established a calculation procedure based on a retention definition, a conception of retention of individual dewatering elements, and some assumptions before the new method was applied for calculating the element retention. In this portion, the authors provided a reasonable approach to examining the retention values, using a mass balance consideration at gap formers, the flows and consistencies values of white water, and a reverse calculation method. Since the goal of this work was to provide a better tool for calculating the element retention of individual dewatering elements, this basic concept gives the useful information. However, there was no proposed method to measure fines content of the paper sheet. Thus, they used TAPPI standard method, originally to measure the fines content of the stock samples, by making re-pulped paper samples.

After establishing the calculation procedure, the authors first determined white water composition of individual dewatering elements (i.e. headbox, forming roll, blade section, suction dewatering and press dewatering) and consistencies of each mass component in all white water fractions using 5 different retention aid dosages. The results can be seen that all consistencies and retention values reflect the polymer dosages reasonable well. For example, when the polymer dosage is high, retention tends to be higher than with lower polymer dosages. The readers are left wondering that this new method can calculate real retention values because the authors only used fibers, fillers and fiber fines as stock suspension in this study. I think other factors, such as salt and dissolved lignin concentration and pulp types, should be considered. These factors will cause the retention variations, more closely resembling to the behavior of retention on paper machine system.

The remainder of the paper discusses total retention, ash and fiber fines retention as well as outgoing web consistency of every element. From the results it can be seen that retention values reflect the polymer dosage in general. But there is an odd result related to fiber fines retention. This is because there is no proposed method to measure fines content of the paper sheet. So the authors used the same methods that originally were used to measure the fine content of the stock. Probably, fiber fines particles are so strongly attached to the long fibers during drying that many of them will not detached without mechanical stress. I think this problem could be avoided if we know the total input amount of fines and amount of fines of white water at every element. Assuming the white water should not be recycled, we can indirectly know fines retention at paper web or sheet.

The new method can be used to evaluate the operations from forming to press sections. It is suggested that the authors consider other factors such as salt and dissolved lignin concentration at white water as well as pulp types. In addition more care should be taken that when this method is applied for individual components, and fiber fines. Although there is no relationship between retention values and paper quality variables, this reader believes that this kind of study helps to understand the fundamental of wet end processes and provides a tool for system optimization.

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“A New Analysis of Filler Effects on Paper Strength” by Linda Li, Robert Pelton and Andrea Collis, TAPPI Paper Summit 2002.

Reviewed by Qirong Fu,
November 15, 2002.

Introduction

In this paper by Li and her coworkers, the authors presented a new approach to study the effects of filler properties on paper strength and showed that their results compared favorably with the predictions of two semi-empirical models. The authors studied the inter-ply strength of the filled handsheets by ninety-degree peeling. They proposed a more useful model to evaluate the effect of fillers on paper strength, which included the effect of fillers basic properties, such as filler types, size, and concentration, on the peel force. The analysis method based on BDT theory (provided by Beazley, Dennison and Taylor) is very practical to evaluate the filler effect in the paper industry.

Background

Fillers are used as additives in paper to improve fine-scale uniformity by filling the porosity of paper, to increase paper smoothness, brightness, opacity, printability and dimensional stability and also reduce paper cost. On the other hand, fillers have some negative effects on paper sheets. It is generally accepted that fillers do not form effective bonding with fibers after paper is filled and the filler particles interfere with fiber/fiber bonding. The Page equation relates the tensile strength of paper to individual fiber strength and fiber bond strength. BDT theory accounts for filler effects on tensile strength. Based on the Page equation, BDT equation involves the effect o fiber/filler specific bond strength and filler specific surface area on the tensile strength of paper. Garg, described a new tensile strength model derived from the Page equation. Many factors related to refining, dry strength additives and filler levels were incorporated into the model. The relative bonded area of filler was involved in this model, not including filler types and the effective size distribution of fillers in paper. But these properties also give some effects on paper strength. One of the experimental difficulties in filler studies is the control and characterization of the filler distribution in the sheet. The authors in this article applied a new analysis method to study the effects of filler properties on paper strength.

Discussion

How to distribute the fillers uniformly in paper is a chief focus to study the filler effects. In the article, a sparse layer of filler particles was first deposited uniformly onto a membrane. Parts of filler particles were transferred to the laminated handsheets by pressing and then peeling off with the membrane. The filler contents of the laminated handsheets were obtained by the mass change on the membranes, which is a new method to quantitatively analyze the filler content. In the following experiments, two-ply handsheets were prepared by pressing a wet filler coated handsheet against a wet filler-free handsheet. In general, a complete sample is sandwiched between two double-sided adhesive tapes during the measurement of the internal bond strength of paper. In this article, in order to evaluate the effect of fillers, it is suggested to press a wet filler coated handsheet and a wet filler-free handsheet and then delaminate them. In this way, the fillers can be distributed uniformly in paper and can not aggregate together. But because most of the fillers dispersed on the top of fibers, it is not a real case of paper. It is a theoretic situation to consider the filler to distribute on the two in-plane plies, not including the fillers in the z-direction of paper. So it can be used only in this kind of model. In the delamination test, two handsheets interpolated with a sparse layer of fillers were delaminated by peel force. Different peel forces were required according to varied inter-ply filler contents. In short, this method is useful to evaluate the qualitative relationship between peel force and filler content.

Some surprising results about the effect of spherical polystyrene particles can also be obtained by the delamination experiments. It showed that the effect of spherical polystyrene particles is different from other fillers. Compared to PCC, the polystyrene particles had only a minor effect on delamination force and the effects were not sensitive to particle size. Especially the small latex particles accumulated in the voids between the fibers and could not take part in the bonding. Due to its negative charge and spherical shape, latex particles can roll away from the fiber/fiber junction and have minor effect on paper strength.

In the results section, the authors presented scanning electron micrographs (SEMs) of polycarbonate membranes before and after transfer of PCC1 in Figure 1. The readers can directly perceive the differences before and after transfer of fillers from a membrane to paper. The authors wanted to compare different filler particle contents in two ply surfaces in Figure 2. But it seemed that they only presented an SEM of a ply after peeling, not including the other ply. So there is no obvious visual contrast when the reader compares the results.

This work also gave some new insights into the effects of fillers on paper strength. Because mechanical properties of a composite material are correlated with filler content, filler size, and shape, the authors suggested a more sophisticated model that is based on BDT theory. The authors extended the theory to predict delamination behavior, not following the simple treatment of the mechanical properties of a binary composite material, which proposed that properties have a linear relation with the volume fraction. The authors proposed that there are some problems with this extended BTD theory. Equation 7 does not predict zero adhesion, and it does not account for particle shape effects. So the authors endeavored to improve the model equation. The authors introduced an ingenious method to calculate a dimensionless debonding area, which was derived from the combination of equation 3 and 8. Paper strength, the amount of filler in paper and particle size can be integrated by this method. They drew the conclusion that paper strength was much more sensitive to the amount of filler than to the particle size. But the cause of this behavior remains confusing. The author’s model predicts that large particles should have a relatively bigger effect on debonding. But it seems that the predictions are in conflict with the general concept that the smallest fillers have the most detrimental effect on paper strength. Furthermore, based on the experiments, the authors found that highest specific surface area of clay did not contribute to higher delamination strength, compared with the relatively large PCC2 particles. So the specific debonding factor ß was suggested to measure the tendency of filler to weaken paper. It has the same unit as specific surface area. The authors extended the conclusion that the specific surface area, like the specific debonding factor, would rank fillers in terms of their effects on paper strength for particles of a similar morphology. Comparing different types of fillers, the specific debonding factor is useful.

The new model discussed in this paper is quite useful to the paper industry when evaluating the effect of fillers and their application. Different filler types and filler effective size distribution, besides the specific surface area of fillers, have great effect on paper strength. The experimental model introduced in the article has some limitation when considering the filler distribution in z-direction of paper, not only relating to two in-plane plies. It hopes that the study will be extended in the future.

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“Optimized Deaeration Leads to Substantial Process and Quality Improvements in Paper Manufacturing”
by R. Rauch and T. Burke, TAPPI Summit 2002, paper 11-4.

Reviewed by Chris Dozier, 2002.

Introduction

In this paper by Rauch and Burke, the authors, explain problems that are caused by high air / gas contents in pulp and paper manufacturing. They provide a chemical explanation of how the air / gas is formed and they also provide excellent graphics as evidence to what can happen when air / gas is in high amounts in a paper machine system. The authors also provide the reader with possible options on ways to deaerate the pulp with in the process. By giving the reader experimental results and possible explanations on how this phenomenon occurs, papermakers that experiences problems closely associated to the ones mentioned here, can gain some benefits from this report.

Background

Most paper mills rely on the quality and performance of their paper to keep the business running. A lot of the older paper mills are upgrading their paper machines in order to keep up with all the new innovations that are coming out. Improved printing ability, high performance paper coatings, and strength are just a few important areas that paper companies have entered into. Thus, in order for a paper machine to run these upgrades, a papermaker needs to have better process control. As explained by Rauch and Burke, air or gas and dissolved gases tend to form in pulp suspensions as the decomposition of calcium carbonate forms carbon dioxide. Carbon dioxide is very easily dissolved in water, and as the pulp begins to be released onto the wire, there is a drop in the surrounding pressure. This drop in pressure will release the gases that are dissolved with in the pulp suspension. According to Rauch and Burke, these gases can constitute a serious problem in papermaking. These gases can be responsible for higher pump energy demands, deposits, pinholes, foaming and several other problems as well. Results have shown that determining these levels of entrained and dissolved gases online enables the optimization of preventive measures such as mechanical or chemical deaeration. Rauch and Burke also show results that online control of deaeration chemicals can lead to substantial cost reductions, process improvements and quality improvements in paper manufacturing.

Discussion

Many factors can cause the development of air or gases in a paper machine system. Closed water loops, high machine speeds, hydrophobic material accumulating in the system and the use of calcium carbonate are just to name a few. These factors can cause poor formation, porosity and printability problems, specks, pinholes and strength losses. The production of carbon dioxide, by the use of calcium carbonate, can be held liable by causing most of the dissolved gases that form in a system. This is because carbon dioxide has a higher solubility in water compared to the other gases, such as nitrogen and oxygen, to which the furnish is exposed during the unit operations. Carbon dioxide tends to be formed around pH 7 and released around pH 4. Also, when the pressure is reduced, this will cause the CO2 to be released from the pulp suspension. Dissolved gases that are released due to a pressure drop tend to produce pinholes and holes in a paper product, which can affect the printing and coating operations. Air bubbles cause undesirable flotation effects, especially with low grade paper, that causes deposits of white pitch or other types of hydrophobic materials in the white water circuit. These hydrophobic materials can form on the sheet and cause coating or printing ink not to adhere to the paper.

The authors used an online gas analyzer to determine both entrained and dissolved gases. This analyzer provides a measuring range of 0.00 to 8.00 % by volume and an accuracy of 0.02 % by volume to measure the gases. The gas bubbles are measured by compressing a sample in a measuring cell and the dissolved gases are measured by expanding a cell. The analyzer can be installed at any locations with in a system, but it is typically installed before the control device and before the headbox. This enables the degassing effect to be analyzed before the pulp enters the headbox and this also can help determine how much deaeration chemical may be needed. Mechanical deaerators and chemical deaerators can aid the degassing effect. Deaerator chemicals can be defined as hydrophobic (defoamers) in nature or hydrophilic (deaerators) in nature. Defoamers attack the air bubbles on the surface and deaerators attack the gases in a suspension forcing the air to the surface.

A study was performed in a Swedish paper mill investigating the impact of free and dissolved gases on the white pitch deposit tendency. Deposits consisting of coating binder and pigments constituted a major problem in machine performance. By optimizing the dosage of deaerator chemical, the gas levels were reduced to 0.1% by volume of free gas and 2 – 3 % by volume of dissolved gases, which relieved the problem of white pitch deposits. Also, another trial was run at a German paper mill consisting of LWC coated base stock. Degassing was optimized and showed reductions of 94% in gas at the headbox as well as a cost savings of 30% on deaeration chemicals. These two trials can demonstrate the benefits of an online gas analyzer for optimizing deaeration chemicals.

The theories and analysis discussed in this paper can be very useful for paper mills utilizing high ink and coating materials. On the other hand, mills that make heavy liner or unbleached kraft paper may not find these results as useful. Understanding the effects of gases and air in paper machine systems will aid in some problem solving ability of situations in this area. As mentioned by the authors, there are quality and performance improvements in determining gas content, but as we papermakers know, in this industry, it is customer driven. If the customer does not notice or complain about these flaws, then the company will, more than likely not, invest into a system like the one mentioned.

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“Deposition Synergy between Mechanical and Deinked Pulps,” by Lawrence H. Allen, TAPPI Paper Summit 2002, paper 23-1

Reviewed by Troy Watkins
November 18th, 2002

Introduction

In this paper, by Lawrence H. Allen, an overview is provided of the possible causes of an increased rate of pitch deposition potential for paper machines using a combination of mechanical and deinked pulps. It is a collection of the theories and observations of a large number of people who have performed work in this area, a list of whose material are referenced at the end of the article. From this information, a conceptual model has been proposed, based on the rate of particle deposition on a stationary glass surface by an impinging jet apparatus. Unfortunately, the article does not contain any experimental evidence to support this equation. However, it is regarded as a good empirical method of testing the deposition synergy between different pulp and / or water streams, without necessarily knowing the precise cause.

Background

In the last few decades, there has been a strong growth in the use of recycled fibres. When combined with an existing mechanical pulping operation, the amount of pitch deposition problems on the paper making equipment increases significantly. It has been observed that there is a synergistic effect in the rate of deposition when combining mechanical pulp and deinked pulp. There could be a number of causes of this effect, such as an increased level of contaminants known to increase pitch deposition. A large number of these contaminants are identified in this article.

To prove the synergistic effect in a laboratory setting, equipment was devised to show that the rate of deposition is greater from a mixture of mechanical pulp and deinked pulp than would be expected from individual data for each of the pulps added together. To understand this phenomena, the author suggests that this increased deposition can be explained by considering the known contaminants in the individual pulps. From this assumption, he developed a conceptual model from fundamental principles.

Discussion

This article provides a good list of possible contributing factors to reduce the problems some mills have with deposition caused by mixing virgin mechanical pulp with deinked pulp. However, it is not always possible for an established mill to alter some of these factors. Examples would include, for instance, a mill that is forced to use a raw material which is not ideal, such as a high quantity of pine in a mechanical furnish, or a reduced quality of recycled paper. Also, within the next few decades it will be expected that many paper mills become more efficient users of fresh water and lower their discharge of effluent. The only possible method to achieve this is to have a more closed water system, with efficient thickening and washing of the pulps, and a method of purifying the internal water loops. The method and efficiency of these clarification processes will dictate the build-up of many of the undesirable substances that the author has presented.

A point of confusion in the article was at what pH a virgin mechanical paper mill should operate at if an amount of calcium carbonate is introduced by the addition of a deinked pulp. At a pH above 6.0, the pitch components begin dissociating and could potentially produce hard water soap deposits. At a pH below 8.0, calcium carbonate begins dissolving, increasing the problems with associated with dissolved calcium and air in stock. Another issue, which is not mentioned in this article, is that a pH much above 7.0 is not desirable for a mechanical furnish due to alkali darkening of the pulp. In reality, there does not appear to be an ideal pH to operate at, as conditions are always compromised. Mill trials would be needed to dictate the most productive and cost effective position to operate the paper machine.

The model proposed in the article accounts for deposition on a stationary surface. It makes the reasonable assumption that deposition potential is dictated by the colloidal stability of the particle, the amount of shear, and a factor defined as a coefficient of stick. One issue with this model is that it does not account for deposition being caused by the agglomeration of material in a suspension. One of the obvious locations for this to happen in a mill that uses virgin mechanical pulp and deinked pulp is the mixing chest. At this point, it has been confirmed that the steric stability of the dispersed resin is decreased, and when combined with the salts present in the deinked pulp, agglomeration can occur. Once material is agglomerated, the possibility that it will deposit on a surface increases.

This article provides a list of conditions that lead to an increased potential for deposition of wood resin. This is valuable when attempting to identify opportunities to improve the efficiency of a paper mill. However, as identified in the above discussion points, sometimes it is not possible to achieve these desirable conditions. There is often issues created by such things as existing plant layout, availability of raw material, or restrictions on effluent discharge. With these issues in mind, often mill trials are required to dictate the most productive and cost effective position to operate a paper machine.

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“Furnish Compatibility and Efficacy of Oxidizing Slimicides,” by Sweeny, P., and Ludensky, M., 2001 Papermakers Conf.

Reviewed by Steven A. Fisher
Dec. 2, 2002

Why are the findings significant to the paper industry?

Paper machine water systems are rich breeding grounds for microbial activity, and if not controlled, they will destroy the product, the machinery, and even the health of the personnel. Controlling biological growth requires chemicals that are aggressive enough to degrade other useful additives in the papermaking system. The oxidizing class of biocides is (by design) very reactive with organics, which makes it important to find the right concentration that will deter microbes while preserving the precious additives and their functions.

The reviewed article has a narrow application in that it only considers the compatibility of free-halogen biocides. The focus of this paper is further narrowed to feature only one of these biocides. The free halogen-based oxidizing slimicide considered, is presumably offered by Lonza Inc., It is a hydantoin-stabilized form of oxidant called Dantobrom®, and the halogen present is bromine only. It is a brominated-methylethylhydantoin, or BrMEH for short. This particular free halogen compound is approved for food contact, and the new “stabilized” form is compared with the traditional form of hypobromous acid (HOBr). This article is essentially an advertisement for a new biocide for food contact paper.

What is the author’s point?

Using two oxidants (BrMEH versus the control HOBr), the author determines their individual compatibilities with typical paper machine furnish components (PAE, A-PAM, Cationic Starch, C-PAM, AKD, an OBR, and cellibiose). The BrMEH showed lower interaction with the furnish components than did the HOBr when compared at 2 ppm, and the BrMEH also showed much greater efficiency reducing microbe counts when compared at 20 ppm.

What is the evidence presented?

Furnish Component Interaction: Interaction with furnish components was measured by the persistence of measurable free-halogen in the mixture as determined by a standard free-chlorine tests (referred to as “DPD” tests). This method assumes that any harmful interaction with furnish components will involve an oxidation reaction which will consume the measurable free-halogen. The tests showed that in the five minutes expected to elapse between machine chest and head box, there will only be 0.1 ppm of oxidant loss.

Microbial Growth: Microbial growth was illustrated using a standard plate method in a mill white water sample known to contain AKD sizing residual and a viable microbe count. The oxidant addition rates in the white water sample were 10 times that of the component interaction test, and the results were extrapolated down to the 2 ppm level. This extrapolation is a questionable way to draw conclusions about data. The author is perhaps unaware that the bacteria always have a threshold of resistance to a biocide, and there is a minimum concentration necessary to begin reducing the population. This principle prohibits the assumption that you can calculate the kill rate at 2 ppm using data at 20 ppm. The kill rate usually can be linearly represented after the concentration threshold of resistance is established, but the author did not perform tests to find the threshold. The efficacy of the biocide was only demonstrated at 20 ppm, and more data is needed at lower biocide concentrations to make the comparison with the “Furnish Component Interaction” tests.

Are there other ways to account for their observations?

The author did not demonstrate that the biocide concentration used for the Furnish Component Interaction test was the appropriate level for biological control. It was not appropriate to extrapolate the results of the Microbial Growth test down to the concentration of the Interaction test.
The Interaction test conclusion result is based on the assumption that persistence of free halogen concentration is an indication of the level of chemical interaction with furnish components. This assumption is logical, but only accounts for the interaction associated with the oxidation reaction. It does not consider other ways the biocide may interfere with the function of the additives, or how any of these unknown interferences may differ from the traditional hypobromous acid (HOBr).

What can you suggest for future work in the same field?

Future work could come in the form of “Microbial Growth” tests performed at a wide range of biocide concentrations and then use the appropriate concentration for the “Furnish Component Interaction” tests. Other work may increase the number and type of oxidizing biocides tested in the same manner to demonstrate their relative performance.

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“Novel Biocide Provides Effective Microbiological Control Without Adversely Affecting The Papermaking Process” by C. K. Davis and G. Casini, TAPPI Summit 2002.

Reviewed by Kevin Copeland,
December, 2002.

Introduction

In this paper by Davis and Casini, the authors provide a compelling argument for the use of this new novel biocide against more widely used biocides in the papermaking industry. This biocide shows many advantages to the use of other biocides; it provides less additive usage, better effluent, and less deposition on the papermaking fabrics. But one point not made in this paper is what, if any, disadvantages come along with the implication of this new technology. This question is not to discourage the readers’ interest but to raise notion that something must be negative about this new novel biocide, if not everyone should be using it.

Background

In the papermaking process paper streams contain may substances that consume oxidizers, many biocides are oxidizers, such as additives, dyes, and fiber. With this consumption, biocides must be added in excess to effectively regulate the microbial populations in the papermachine streams and surfaces. This over-addition of biocide can result in reduced felt life, increased use of papermaking additives, and increased corrosion rates. This new biocide promises to eliminate most if not all of these problems. Most biocides are strong oxidizers and this adds to the problems stated earlier. The novel biocide in question, however, is a weak oxidizer. This weak oxidizer is shown to help in most if not all areas of interests while also eliminating the amount of halogenated organic compounds (AOX) commonly associated with strong biocides. One issue seen with the introduction of the novel biocide, ammonium bromide solution with sodium hypochlorite and fresh water, is that it must be made onsite because it begins to degrade upon production. This issue also needs to be looked at as a question of if this technology is better than the older more standard biocide use or if it just sounds better.

Discussion

With all these benefits one might ask he or she why isn’t the use of this new biocide technology spreading like wildfire throughout the papermaking industry. Two questions brought up earlier in this report were: Does this biocide have negative effects not mentioned in this paper? And does this onsite mixing technology cater to mills limited by space? All things being equal this new biocide seems to improve every aspect known to be affected by typical biocide usage. The use of less additives, less dyes, increase effluent quality, less number of breaks, and less on machine deposition all point to the use of this product. The advantages of this new product are not my concern it is the question if the reader is being told the entire story. The chart below lists the advantages of this novel biocide.

Features	Benefits
Effective at reducing microbial populations (including filamentous bacteria, unicellular bacteria, yeast and mold, and anaerobic bacteria)	Reduced sheet breaks Reduced sheet defects
Exhibits a low oxidizing potential (weak oxidizer	Reduced consumption of costly wet-end additives Reduced halogenated organic compound
Is not consumed by organics, ammonia, or other compounds that typically act as oxidizers	Prevents oxidizer overfeed Oxidizer residuals remain in system for longer time, which improves microbiological population control
Residual is easily measured by total combined chlorine	Simple monitoring can optimize feed rates
Degrades readily into non-toxic ions	No negative effect on activated sludge plants (at dosage rates of up to 10 times higher than normal)

In each of these mill trills the new biocide technology improved each problem the mills were having with their paper machine. Mill A had decreases of more than 99% of bioactivity due to the decrease in AKD sizing. This alone, with strict governmental guidelines in cluster rules, could be ample reason to take a long look at this new technology. Also, the number of machine breaks decreased from two breaks per day to almost one per week. Mill B had similar success using this new biocide with a total decrease of bacterial counts of almost 95% as in Mill A. Another positive was the amount of deposited material left before a boilout decrease 30 grams and sloughing was prevented. Dye and chemical usage was the gains from the third mill tested. A decrease of 75% dye and almost 50% sodium hypochlorite to go along with the bacterial decrease and optical properties.

All these tests being looked at over a three-mill span, it is seen that an improvement in a papermaking system will be seen. However, it all depends on the individual mill process on what this new biocide will do for it. I just feel that the report should have answered some questions to make the product more interesting to a potential customer. What was the cost for these improvements? The cost of putting this new technology into place, fresh water usage and capitol costs. This novel technology must come with a price tag or some other issue that papermakers might need to resolve in order to implement it as their own. Special training must be needed to maintain an on site dosing operation. This article provides a significant argument for the implementation of this new novel technology and should be see as a great step in the negative effects of biocide usage in papermaking. The article provides that argument but the question still remains is this article being used to tell the entire story of this biocide as a production tool for papermakers or as a marketing tool for the company producing this product.

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“A Superior New Approach to Paper Machine Contaminant Control” by Charles D. Angle, 2002 TAPPI Paper Summit.

Reviewed by Marc Azzi,
December, 2002.

Introduction

This paper describes a new approach for solving the problem of stickies deposition. The author made an excellent introduction, detailing the different parameters affecting deposition, as well as the most common chemical methods aiming at finding a solution to the recycled paper inherent problem. Supporting data included laboratory tests and mill case histories. The paper however failed to give any detailed description about the innovative structured protein or any information about the method and location of application. It also failed to mention any side effects that could limit its use in certain mills (such as protein denaturation by pH or high temperature).

Background

Recycled fiber has become a major raw material for the modern paper mill. Reasons for the increase include environmental concerns, economic considerations, government legislation, and the market demand for paper containing recycled fibers. In the US for example, it is estimated that half of the paper mills use 50% recycled paper while the second half uses 100 %. One of the major limiting factors in the utilization of recycled paper is their inclusion of contaminants. Contaminants such as pressure sensitive adhesive, hot melt, waxes inks, seam bindings, latexes and resins can severely increase machine downtime. Originally, paper mills relayed on equipments such as screens, cleaners and floatation cells to reduce the effect of stickies. Over the past years, chemical companies have put great effort into finding a chemical solution to the stickies problem, supplementing the mechanical onemeasures they have taken.

Discussion
Many parameters affect the extent of stickies deposition. They can be summarized as the content of the contaminant, their depositability and colloidal stability, and the surface affinity for deposition. The author believes that addressing the highest numbers of parameters will achieve the best result in deposition reduction. Current available chemical methods for the management of stickies include stabilization, detackification, and fixation and removal. Only by combining all these methods that could the previous goal could be achieved. This was not possible previously because some of these methods would conflict with each other mechanistically. The new approach cited by D. Angle applies the introduction of a novel amphoteric, surface-active structured protein with a cationic fixative.

The supportive evidence of the superior performance of the structured protein can be divided into two parts:

1- Laboratory experiments. They supported the following facts:
a- Adsorption of the structured protein to the surface of hydrophobic material, made evident by the reduction of the zeta potential of the colloidal suspension.
b- The tenacity of the structured protein to adhere to the hydrophobic material surface, supported by the relatively small increase in the contact angle after several washings compared to commercially marketed detackifiers. Note however, that it would have helped if a comparison of the reduction in contact angle of the hydrophobic material without treatment, to a different detackifier including the structured protein, were plotted.
c- The superior detackifying ability of the structured protein as compared to other proteins and a conventional detackifier. The results of this experiment rely on the “detackification percentage” with no clear reference to the method used to test for the force required for separating the adhesive surfaces.
d- The superior ability of the structured protein to stabilize the colloidal suspension. Again, the author refers to “proprietary methods” to test for the colloidal stability. Figure 3 shows a plot of “colloidal stability” versus the addition rate of the structured protein with no clues about the units of the former. In addition, it would be helpful to have a comparison between the structured protein and another stabilizing polymer on the same graph similarly to the following experiment.
e- The accelerated removal rate of contaminants in the presence of the structured protein as compared to the cationic polymers alone.

2- Mill case histories. They included three mills:
a- A corrugating medium mill running on 100% MOW and OCC. The stickies limited the utilization rate of the MOW to 25%. The mill was using a conventional detackifier and a topical treatment of the wire. The effect of the structured protein was to reduce the topical treatment by 30% and to increase the MOW utilization to 28%. The author relies on the reduction of suspended solids from samples collected from the machine chest and the head box to show the efficiency of the structured protein. While this test is relevant to the performance evaluation of the chemical in use, it would be more appropriate to complement it with another type of stickies test usually practiced by paper mills.
b- A tissue mill running on 50-100% MOW. The mill suffered from the presence of stickies in the air / water interface of the stock and the white water that were eventually present in the sheet. The substitution of the detackifier with the structured protein eliminated the stickies in the sheet. It would have been more informative if the type of the traditional detackifier was disclosed (mineral, polymer…).
c- Another tissue mill running on 100% recycled paper was handicapped by the high number of washes per day caused by the deposition of stickies. The use of the structured protein increased the mill production by reducing considerably the number of shutdowns and improved the mill effluent quality by reducing the quantity of solvent used. The evidence of SEM photographs showing the detackifying effect of the structured protein supported this case. It would have been more appropriate if the new approach were tested to a mill running a conventional program rather than a mill running originally without one.

This paper really points out the advantages of the new approach in the control of the stickies deposition. The well-organized introduction and the supporting data, especially the mill case histories, support the fact that this approach has a lot going for it. However, as a complete study, it would have been educative to have additional information about the effect of issues that are of importance to the paper maker such as the effect of system closure (high TDS), different pH, high temperature, and the addition location on the performance of the structured protein.

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“PCC Application Strategies to Improve Papermaking Profitability. Part I. Thick Stock Precipitated Calcium Carbonate Addition,” by T. M Haller et al., (2001 Papermakers Conf.)

Reviewed by Daniel Duarte,
January 14, 2003

Introduction:
In this paper authored by Haller and associates, a very comprehensive review of the factors that must be considered to optimize filler/fiber substitution is presented. Moreover, and more importantly, the authors present different PCC application strategies which that minimize the negative aspects of using precipitated calcium carbonate (PCC) at the wet-end. Overall, the paper is well written and quite comprehensive. The authors show that their proposed PCC application strategies can be used in varied scenarios and they also demonstrate the full array of benefits which that can be achieved. Perhaps, one of the drawbacks of writing a comprehensive paper is that in some sections, the material is not detailed. For example, I found that in many of the case studies presented, the authors do not give enough information with respect to process conditions and final sheet properties to allow others either to verify the work or fully understand its implications.

Background:
It is well known that the push to alkaline papermaking conditions, especially during the 1980’s and 90’s was primarily due to the fact that papermakers wanted to increase the quantity of calcium carbonate that could be used, and thus decrease the cost of using expensive fiber and/or titanium dioxide. Not only is the cost of fiber reduced, there are other paper property advantages associated to increasing the PCC content. For example, optical properties are enhanced, formation is improved, smoothness is increased, printability is superior, and dimensional stability is enhanced. Unfortunately, there is a limit to how much PCC can be used. This limit is due to fact that when PCC is added, strength is negatively affected (interference with fiber to fiber bonding); also, machine runability problems can occur. Therefore when using PCC, a tradeoff is expected. However, if PCC could be introduced in such a fashion that strength issues would be minimized, this would lead to substantial savings for the papermaker.

Discussion:
In this paper the authors clearly indicate how they managed to achieve this goal. Firstly, they explain how the various technological breakthroughs which led to the development of the proposed PCC application strategies, occurred. Secondly, the authors demonstrate how their application strategies works in terms of process conditions. And finally, regarding the mechanism and application benefits, the material is presented in a logical and easy to understand fashion.

In the report, two types of data are presented: (1) laboratory evaluations and (2) case studies. With respect to the Laboratory laboratory Evaluationsevaluations, various sequences were explored. For example, in some experiments, PCC was added in only the thin stock or only the thick stock, or both. Also, in the cases were PCC was added in either the thick or thin stock, starch was not necessarily added at the same consistency. Through-out the Laboratory Evaluation section, the authors do an excellent “job” of conveying key information to the reader. Some examples are the discussions pertaining to (1) the importance of mixing time and (2) effects of PCC and starch addition on internal bond strength.

In the Mechanism section of the paper, an excellent explanation is given regarding the observation that when PCC is fixed in the thick stock, – paper strength improves, is given. The authors explain that by adding PCC filler in the thick stock it can penetrate past fibrils of the fiber and come into intimate contact with the fibers themselves (and of course some loading was occurring). In the Mechanism section, several other key observations – followed by logical explanations – are given. For example, when PCC is added to the thick stock but starch is not added at the thick stock, little strength improvements occur. Based on the proposed mechanism, the authors suggests that PCC is not locked into place and PCC comes back out of the lumen and intimate contact with the fibers when dilution water is added.

Several case studies were also performed – and results presented in this paper. My overall appreciation of this section is very good. Very diversified case studies were performed, and, more importantly, quantification of benefits are presented (manufacturing cost savings were quantified for each case study). Unfortunately, as mentioned in the introduction, the authors do not give enough information with respect to process conditions and final sheet properties.

After reading the Case Study section, I was slightly confused regarding a statement given by the authors. It is stated that only 20 paper mills have adopted split PCC addition as of the end of 1999. One of my main complaints is that an adequate explanation to why this strategy has been adopted by so few mills was not given. It seems that the cost to add another PCC lines line to the thick stock is very low (only $15000 to $25000), and the results are very positive. A bit more elaboration on this topic would have been interesting.

Conclusion:
To conclude, I found that the authors did an excellent “job” in this paper with respect to explaining how their application strategy works and the benefits which can be derived from its use. Moreover, in terms of recommendations, the authors give what I found to be an complete and comprehensive list. My overall appreciation of this paper is very high.

“On-Line Charge Monitoring – A Wet End Strategy” by L. Bley and E. Winter, Proc. TAPPI 1997 Engineering and Papermakers Conf., 297. Reviewed by Jill Scherrer, 1999

On-line charge monitoring has attracted increasing interest as a means to control wet end chemistry on the paper machine. The authors of this article give a good review of the buildup of anionic colloidal materials in modern paper mills and its impact on paper machine runnability. A detailed approach is described for identifying the source of the colloidal materials and optimizing a control system using an on-line charge measurement device. The article is somewhat limited, since the authors discussed only one type of charge measurement device and provided rather general supporting evidence of actual results achieved in paper mills. The control recommendations appear to be of practical use in the industry, as long as the on-line charge measurement device proves to be sufficiently rugged for industrial use.

There is increasing demand for on-line charge measurement as modern trends in paper mills lead to the buildup of anionic colloidal materials in the paper machine furnish. Trends towards alkaline papermaking conditions, closed water systems, and increased levels of recycled fiber all tend to increase the amount of ionic materials either coming into the mill with the raw materials or building up in the furnish. These charged materials may interfere with chemical additives in the wet end of the paper machine and cause system instability due to fluctuations in the charge demand of the furnish. Accurate on-line measurement is an essential prerequisite to controlling charge demand and mitigating its effects on paper machine runnability.

The authors of this article gave a good discussion of the use of coagulants (also called fixing agents or scavengers) to control the charge demand of the paper machine furnish. An excellent approach is outlined for identifying the optimum addition points and control strategy for a coagulant. The translation is very poor, however, such that someone not already familiar with the subject would find some parts of the article incomprehensible. Although some solid examples of this control system in action would have improved the credibility of the recommendations, the article provides enough detail to encourage further investigation.

This article recommends controlling charge variation as close to its source as possible. Systematic laboratory testing should be performed at sample points throughout the paper machine wet end from the thick stock to the headbox. This data will provide a detailed map of the charge demand and variation so that the greatest contributors may be easily identified. The fixing agent needs to be similar in nature and opposite in charge to the ionic material it is intended to neutralize, e.g. a low molecular weight, highly cationic polyelectrolyte. An on-line charge measurement device should be used soon after the addition of the coagulant to provide feedback control and maintain a constant level of charge demand in the paper machine furnish, as illustrated in Figure 10.

A good example of the impact of on-line charge control was given in Figure 7. The measurement of cationic demand is illustrated over a 14 day period, during which the coagulant addition pump broke down for several days. The point at which the coagulant addition ceased is clearly evident, as the cationic demand showed a sharp increase and became highly variable as well. After the pump was repaired, the cationic demand returned to a low, stable level. Several other examples of the benefits of on-line charge control were cited, supported by two rather general examples of paper mill experience.

Both examples of paper mill experience which were cited in the article provided good support of the authors’ conclusions, but some missing details cast doubt on the validity of the presented data. Figure 8 shows a correlation between white water charge demand and retention, but the authors failed to explain the severe retention swings that occurred over a one hour period. Since this data is intended to prove charge demand may be a suitable indicator of retention aid demand, an obvious loss of retention control should have been explained. Figure 9 illustrates a correlation between white water charge and paper machine breaks. Clearly, runnability suffered when the white water charge was cationic and highly variable. However, careful study of the data leads the reader to wonder if a paper machine can really thread up fast enough to experience 10 – 12 breaks per 8 hour shift for almost two days.

This article does provide enough information to encourage further investigation of the use of on-line charge measurement as a wet end control strategy. Since only one on-line charge measurement device was discussed, a comparison between other types and brands would give further information on the best method by which to control charge demand. Another subject near and dear to the hearts of most readers would be some discussion as to the maintenance requirements of the on-line charge analyzer. Some information on the number and type of mills using this control strategy would also be useful – is it used primarily on tissue machines, fine paper machines, etc.? It would also have been helpful if the authors had mentioned the furnish and grade(s) produced for each paper machine example that was discussed in the article.

Overall, this article gives a sound discussion of the basic details of on-line charge control for the paper machine. Enough information is given for the reader to complete a detailed map of the level of charge demand and its variability in a given paper machine system. This map would provide the information necessary both to determine whether on-line control would be a useful goal for a particular system and how to optimize the control system. The reader could then research the various types of charge measurement devices on the market, and user lists would provide references as to the reliability and maintenance requirements of the on-line measurement device and the impact of control on paper machine runnability.

Bley, L. and Winter, E., “On-Line Charge Monitoring – A Wet End Strategy,” Proc. 1997 Engineering and Papermakers Conference, 297.

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“Wet-End Optimization for a Neutral PCC-Filled Newsprint Machine”, by Takanori Miyanishi Tappi J. 82 (1): 220, 1999. Reviewed by Judy Delaney, November 5, 1999

This article reports on work done to explore the unchartered waters of using precipitated calcium carbonate (PCC) in neutral newsprint applications. The prime motivation for this work is high brightness and opacity of the sheet. Preliminary laboratory work was done to test the viability of using PCC in neutral newsprint before running a 12-hour trial on a 229-inch width, twin wire former paper machine. Running the trial necessitated going from an acid to a neutral papermaking process.

Product quality issues encountered in the trial included two-sidedness in the sheet. The two-sidedness resulted in unsatisfactory print tests due to linting and sent researchers “back to the drawing board”, i.e., the laboratory, to find solutions. Handsheet study results allowed researchers to theorize that the two-sidedness/linting issue was not due to the neutral process and could be addressed with careful use of retention aid in a subsequent trial.

The word “careful” is used here because, in the first trial, the retention aid was added just prior to the headbox and resulted in such poor sheet formation that the use of retention aid was discontinued. The ramification of discontinuing the retention aid was poor filler retention, to the tune of more than 40% of the PCC going “down the drain”, so to speak. A 23-hour trial was run with the retention aid addition moved to pre-screen. The results of this trial included good sheet formation, high brightness and opacity. The filler retention improved over the no-retention aid portion of the first trial. However, the percent improvement was not noted in the article. A “passing grade” on the print tests for the linting issue was achieved in this second trial. Miyanishi concludes that using a neutral newsprint papermaking process with PCC as a filler is possible.

The neutral papermaking process offers advantages over the acid process, including paper permanence (versus the yellowing/aging traditionally plaguing acid papers) and improved recylcability of the paper. A side benefit of a neutral versus acid process is reduced “wear and tear” on equipment due to less corrosive additives in the process streams.

Another advantage to having a neutral papermaking process and the main focus of this work is that it allows the use of PCC as a filler. As previously stated, the desired quality benefits from PCC in the sheet are high brightness and opacity. The economic benefit of using PCC is that it is an inexpensive replacement for expensive fiber and other raw materials. Given these advantages, the work done by Miyanishi seems a worth-while endeavor and could lead to a valuable contribution to the newsprint industry.

One of the first clues I look for in determining the level of credibility of an article is to see who wrote it. If the author is promoting a product and he is employed by the company supplying the product, the needle on the credibility meter takes a dramatic swing to the low number range. Miyanishi is a senior research manager for Nippon Paper Industries Co., Ltd, Central Research Laboratory. Unless this is a well disguised manufacturer of PCC, the credibility meter shows an initial satisfactory reading.

During the trials, laboratory analysis included on-line retention, zeta potential, sheet formation, pH and conductance measurements. Process data collected included basis weight, reel ash, freeness. Paper samples were chemically analyzed for cationic demand, aluminum ion, dissolved and colloidal materials, etc. Graphs including Zeta potential versus first pass retention and pH effect on surface strength are presented in the article as well as SEM photographs of neutral newsprint samples from both machine trials. The type of data collected as well as the completeness of the presented graphs and photographs leads to the conclusion that the data presented is credible.

However, a concern arises over Miyanishi’s summary statement. Miyanishi concludes that neutral newsprint production is technically possible, but its development hinges on an understanding of fundamental theories of papermaking and wet end chemistry. I believe the development of this process goes beyond the fundamentals and requires increased trial work and optimization of both filler loading and retention chemical usage.

The machine trials were 12 and 23 hours in length. In our “neck of the woods”, these are called qualification trials and the sole objective is to see if there are any major “knock-outs” that disqualify the idea or product from being used in a longer machine trial. If this first hurdle is jumped, then the longer trial, ranging from one to several weeks, is scheduled. Therefore, writing an article on what I consider qualification trials seems premature. Additionally, short trials do not give an accurate picture of possible consequences of running the trial parameters longer term. An example of a negative outcome for this work could be a pitch deposit outbreak. It would be far more advantageous to know this might happen while still in the trial work stage than to have it occur after the process changes were permanently implemented/institutionalized.

In addition to longer trials, designed experimentation could be used to achieve optimal PCC and retention aid dosages. This statistically based, systematic experimentation would result in multiple variations using the least amount of machine time, laying a solid knowledge foundation of what different chemical combinations will or will not do. This method could be used in improving/optimizing the earlier reported poor retention of the PCC.

In summary, this work provides a solid basis for further exploration/experimentation and could potentially lead to an important development in the newsprint industry. If I worked in this branch of the industry and was interested in pursuing this process change, then I would have the laboratory work duplicated in our research/technical center to see if the concept was viable for our particular application.

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Reviewed by Edmund A. Pozniak Jr. November 6, 1999

Synopsis of Article.

The authors wish to show that medium-charge density cationic starch can be used by papermakers to neutralize and suspend anionic trash in a furnish comprised of peroxide-bleached thermo-mechanical pulp(TMP). TMP pulps contain significant concentrations of lignin, galacturonic acid, and other detrimental substances known as “anionic trash”. To expand the study, the furnishes were prepared at different salt concentrations, to show their effects on cationic starch addition levels. The salts utilized were Sodium Chloride (NaCl) and Calcium Chloride (CaCl2 ), keep in mind that NaCl is monovalent and CaCl2 is divalent. Four samples for each salt were prepared at concentration levels of .1, .01, .001, and .0001 mol/L. The pH of each suspension was 8. The experimental procedure was as follows:
1. Fiber and distilled water were added together to form a 1% fiber consistency. The suspension was heated to 60 C and agitated for 3 hours.
2. Consistency was then dropped to 0.5%
3. Adjustment of the ionic strength with NaCl or CaCl2.
4. The suspension was centrifuged at 850G for 30 minutes.
5. Cationic starch was added to the supernatant and allowed to adsorb for 30 minutes.
6. The solution was then centrifuged at 850 g for 30 minutes.
7. The supernatant was then analyzed for residual turbidity and starch concentration.

Results. With the NaCl solutions, complete destabilization of the anionic trash took place at starch additions of 65 mg/L for .01 mol/L Nacl, 165 mg/L for .001 mol/L NaCl and 210 mg/l for .0001 mol/L. Only partial destabilization was achieved at 40 mg/L at .1 mol/L NaCl. Continued additions of starch past the point of destabilization eventually caused restabilization of the wood substances.

With the CaCl2 solutions, , complete destabilization of the anionic trash took place at starch additions of 60 mg/L for .001 mol/L CaCl2 and 105 mg/L for .0001 mol/L CaCl2. Total destabilization took place at the .1 and .01 mol/L CaCl2 concentrations before the starch was added. Continued additions of starch past the point of destabilization eventually caused restabilization of the wood substance.

Why the article is or is not important.

At this point in the research the article has some potential applications, especially for close-stock systems where salt and anionic trash concentrations can become quite high. Closed stock systems where salt concentrations can become quite high are a candidate. High yield pulps, like TMP, ground wood, CTMP, CMP, etc., are rich in lignin, galaturonic acid and other anionic trash could also benefit from study. If qualified, cationic starch would give papermakers another alternative to additives they are already using, like higher cost synthetic retention aids. It must be emphasized though, that this study is only the first step of many more studies needed to qualify cationic starch as retention aid in the aforementioned systems.

Whether the data are credible.

The conditions and procedures used in the experiments lend the results to be very credible. The pulp samples were taken from a normal pulp mill process and not artificially produced in a lab, so they reflect a real life process. The samples were frozen to preserve freshness. Sample were re-prepared by heating in a 1% solution to 60 degrees Celsius, in order to dissolve wood substances that aggregated during freezing. Salt concentrations were measured, added, and mixed. PH was held constant at 8. The resulting material was centrifuged of fibers to prevent them from contaminating the data. Starch was then added to the supernatant and mixed for 30 minutes, a reasonable time for starch to be added in a normal stock system. The solution was then centrifuged, leaving residual turbidity and unreacted starch.

Things that the authors should have said or done or ways that the work ought to be extended.

The authors point out that further studies are needed in order to evaluate the application of cationic starch as a retention aid. To see how we can expand on this paper, we need to look at TMP. The nature of TMP lends itself to utilization in many printing grades(especially newsprint) where the addition of cationic starch is necessary to ensure a high degree of printability and sheet strength. Much of the effectiveness of cationic starch come from its ability to bridge between anionic particles. In clean water, repulsion forces cause the starch molecules to expand and spread out. In a salt solution, the charges are screened and the starch will stay in a balled up shape, thus significantly affecting the starch’s ability to bridge. In the study, we see that precise amounts of starch will destabilize the wood products, but when additional levels of starch are added, the anionic trash stabilizes again. How the salt solution affects the physical properties brought on by the cationic starch must be determined. If it is necessary to add more starch past the destabilization point, to over come the negative affects of the salt, then starch has no use as a retention aid.

The test conditions were run at a pH of 8 or alkaline conditions. It would be interesting to see the results of this trial, when run at acid papermaking norms(pH 4-5). I would expect to see a reduction in the salt concentration where destabilization would occur. At the lower pH, the acid would react with the carboxylic groups in the lignin, requiring less starch to neutralize the rest of the anionic trash.

It would have been appropiate for the authors to elaborate further on the CaCl2 solutions with .1 and .01 mol/L concentrations. Both solutions completely destabilized the wood products(anionic trash), before the addition of cationic starch. Without further data, I would assume the high salt concentrations totally screened out the anionic charge in the wood products.

Lets not forget are dear friend alum. Although alum does not function well in a high pH environment, if introduced early in the process, it may effectively neutralize the anionic trash.

How the results could or could not be put into practice in the industry.

Provided that cationic starch qualified for a particular process, this study would be an important tool for a papermaker in optimizing his process. By monitoring white water salt concentration, a stock prep operator could adjust the addition rate of cationic starch to provide for maximum destabilization of the anionic trash.

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Principal Theories

This article explores the mechanism with which polyamidamine epichlorohydrin (PAE) polymer interacts with fiber and develops wet strength in paper. The article theorizes that with higher fiber carboxyl concentration more PAE is adsorbed on the fibers and more wet strength is developed. Also, at a constant rate of PAE addition, increasing carboxyl group concentration will increase the shear bond strength between fibers. It is also theorized that PAE forms an ester linkage with the carboxyl groups on the fibers. The study was conducted using reference pulp and a carboxymethylated pulp with varying degrees of substitution to determine the effect of carboxyl content on wet strength development.

Supporting Evidence

These theories are well supported by the data presented in the article, and the authors were careful in separating the effects of different variables. The relationship between the carboxyl content and wet strength effectiveness are supported by three main pieces of wet and dry tensile strength data. Spectroscopic techniques using FTIR equipment were used to examine the ester linkage development between PAE and fiber carboxyl groups.

The first set of experiments described to support the carboxyl content theories involved determining wet strength, dry strength, and PAE adsorption for different degrees of substitution (D.S.) or carboxyl contents on carboxymethylated pulps. As the D.S. increases the quantity of PAE adsorbed increases at a linear rate. Both the wet and dry strength increase as well until they level out at a degree of substitution near 0.07. Sheet dryness was measured after the dry tensile tests to determine if PAE content had an effect on dryness. No large differences were found.

In an attempt to separate the effects of the fiber carboxyl content from the quantity of polymer adsorption, wet and dry tensile experiments were conducted using the various D.S. pulps with and without PAE. The PAE was added at a constant rate that was low enough for full adsorption at all D.S. during this portion of the experiment. The dry strength plots showed an increase in strength at the lower D.S. for the pulp with PAE added, but at the higher D.S. there was no advantage. However, with PAE, the wet strength increased with increased D.S. while the wet strength did not for the pulp that was not treated with the PAE. It was demonstrated that increases in carboxymethylation resulted in increased relative bonded area (RBA). This may have allowed more of the PAE adsorbed on the fibers to interact with other fibers, thus explaining the increase in wet strength at higher levels of carboxyl content even though the PAE addition was not changed.

The third experiment conducted involved varying press loads to vary the relative bonded area of the sheets. These experiments were conducted on carboxymethylated pulps and the non carboxymethylated base pulps. The non carboxymethylated pulp was beaten in a PFI beater so that the water retention value was equal to the carboxymethylated pulp it was being compared to, so the pulps would have similar pressing response. Plots were made, for both pulp types, of tensile strength as a function of RBA with and without PAE addition. The carboxymethylated pulp showed a larger change in the calculated bond shear strength improvement with PAE addition than the base pulp. This larger delta indicates that the increased carboxyl content improved the efficiency of the PAE resin.

To further clarify the function of the PAE, PAE resin was added at increasing rates to pulp of constant carboxyl content. The RBA and tensile strength were measured at the different PAE levels. The dry strength increased with increased PAE addition, while the RBA did not increase as determined by light scattering data. Increasing strength at constant light scattering indicates that the PAE resin increased fiber bond strength, not relative bonded area.

The arguments for the ester linkage formation consists of spectral analysis data. Spectral analysis using FTIR equipment was performed on sheets formed with and without PAE and on the resin itself. The difference spectrum between the two sheets is plotted, where the sheet spectrum from the sheet without PAE is removed from the spectrum of the sheet with PAE. The remaining plot has the same shape as the absorbence spectrum of the PAE polymer. Except, the sheet difference spectrum as an additional peak at 1735 cm-1 that is not evident in the plot for the PAE resin. The distinctness of this peak provides evidence of the ester linkage formed between PAE and the pulp carboxyl groups.

Further Opportunities for Study

Evidence is presented that at higher degrees of carboxyl content and PAE adsorption there is a leveling off in dry and wet strength. It appears that for the pulp used in the article a maximum dry strength of about 50 kNm/kg can be achieved by additional PAE addition or higher carboxyl content. It is proposed that the strength begins to level off as the breakage mechanism switches from bond breakage to fiber breakage. Zero span tensile testing could be done to verify this by measuring the fiber strength, or the fracture points could be evaluated microscopically to determine if the fiber breaking is occurring at the high levels of strength. A suggested explanation for the wet strength leveling off, proposed by the authors, is that at higher degrees of substitution fiber swelling increases and more PAE passes into the interior of the fibers leaving a constant concentration of the PAE molecules on the surface, and therefore a constant level of wet strength. However, with a higher D.S. the relative bonded area should increase and the wet strength should improve. The authors suggest that more work is needed to clarify the leveling off of strength.

One area where further work could be done is with the furnish used. All the work for the article was done with the fines removed. Additional work should be done to determine the effect of fines since they have a large impact on paper strength.

Practical Application

The article clearly demonstrates that increasing carboxyl content of the pulp increases the wet strength both with a constant dosage of PAE and with increasing levels of PAE adsorption. Therefore, to increase wet strength, measures could be taken to increase the carboxyl group content of the pulp such as operating at a higher pH of using higher yield pulp.

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Two students prepared reviews of this article. The following is by Steve Henry, November 26, 1999.
Click here to skip down to the other review that was prepared by Sandra Beder-Miller

Introduction

Pitch and stickies deposition on forming wires is a problem throughout the paper industry. Pitch is a result of the natural resins of wood. Stickies are waxy substances that are prevalent in recycled fiber furnishes. Both pitch and stickies fill in a forming wire, which results in holes in the sheet, other sheet quality issues, and runnability issues. These issues result in downtime and off-spec product, which is costly for the papermill. The article by Nguyen and Dreisbach examines a method of coating the forming wire with a cationic polymer to prevent deposition of pitch and stickies.

Principal Theories

The article focuses on manipulating surface affinity to reduce the deposition of pitch and stickies. Pitch and stickies are hydrophobic, so they deposit on the forming wire since it is a hydrophobic surface in contact with the stock slurry. If the forming wire surface could be hydrophilic, pitch and stickies would be less likely to deposit on the wire. The authors’ objective was to reduce the hydrophobicity of the wire “via adsorption of complexes of a cationic polymer associated with anionic species on such surfaces.” The article uses standard tape detackification test, surface tension, and streaming potential to evaluate the effectiveness of various polymers. Finally, the article also suggests that contact angle measurements can be used to measure the hydrophobocity/hydrophilicity of a forming wire surface.

Supporting Evidence

The authors describe how the test solution was formulated. They used TMP, linerboard, and akaline fine paper whitewater filtrate in the testing. The authors used a variety of whitewaters to demonstrate that their work could be applied to many different grades of paper. However, I thought the use of multiple filtrates diluted the results of the testing. The article could be improved if one filtrate type had been utilized rather than three. The authors describe the test equipment and procedure for each test. All of the tests were straightforward with the exception of the contact angle measurement. This procedure is more involved requiring both a goniometer and a tensiometer. The authors go into enough detail to understand how to reproduce the contact angle measurement.

There are extensive tape detackification test results with all three filtrates. Polymer A and Polymer B, both cationic polymers, show that they are the superior passivation polymers in all three filtrates. The authors then use the surface tension test to explore why Polymer A is better than Polymer C. A high molecular weight nonionic polymer. Polymer A has a more significant reduction in surface tension as compared to Polymer A. The authors theorize that the surface tension reduction is due “to the formation of complexes between the cationic polymer and water soluble anionic species.” The article then uses a synthetic white water formulation with further surface tension and streaming potential testing to confirm this interaction. Finally, the authors then use contact angle measurements to determine when the forming wire surface becomes hydrophilic. This test essentially measures how well the passivation polymer prevents the deposition of pitch and stickies. For the contact angle testing, the authors only test with the linerboard filtrate. The lower contact angle represents the better the expected results of the passivation polymer. A 5-PPM treatment of Polymer B gave superior results in the contact angle test. Based on these results, it is expected Polymer B would perform the best in practical applications.

Although the supporting evidence could be improved, the article does clearly demonstrate that cationic polymers are effective for passivation. It is clear that cationic polymers can significantly decrease the deposition of pitch and stickies. A hydrophobic wire can be coated with cationic polymer to render the forming wire surface hydrophilic.

Practical Application

The article offers several excellent visual aids (Figures 10 and 13) which help depict how the polymer coating works. These figures can be used effectively to help non-technical personnel understand how the wire passivation theory works.

The article also includes three case histories. Each case history involves different furnishes and different final products. The article indicates that Polymer B from the study worked well in each of the three practical applications. However, it is disappointing that the authors do not provide more quantitative results from the practical applications. In each case, they vaguely describe how Polymer B was successfully used in the application. It would also be beneficial if there was information on whether the wire passivation had any impact on drainage, felt life, or other paper making variables.

Further Opportunities for Study

Although the authors selected Polymer B because it had the best results in the tape detackification test, it would have been beneficial to include Polymer A in the contact angle measurements. The authors contrasted the differences between filtrate, Polymer B, and Polymer C in the contact angle measurements. It would be useful to see contact angles for Polymer A since it performed well in the tape detackification test to compare to Polymer B.

It would have been useful if the authors had provided more information about the polymers used in the article. The authors used generic names for each polymer. They gave vague descriptions of the polymers. In particular, they evaluated four cationic polymers but did not give the reader enough information to apply or even reproduce the results from the article. The authors merely stated the four cationic polymers were “of various degrees of molecular weight and charge density.” The reader must use trial and error to reproduce the results of this trial.

Finally, it would be interesting to see if wire passivation has any impact on forming wire life and drainage rates. I would expect the wire passivation treatment to have a minimal impact on wire life. It would be interesting to see if the treatment affects drainage rates.

“Prevention of Pitch and Stickies Deposition on Paper Forming Wires via Adsorption of Cationic Polymer Associated with Anionic Species,” Nguyen, D.Y. and D.D. Dreisbach, TAPPI 1996 Papermakers Conference. Review by Sandra Beder-Miller, November 4, 1999

Why is this article important?

This article describes additives that may be useful in reducing deposition of some common paper mill contaminants. These contaminants build up in pipes, tanks, pulp washers, and on the paper machine. Pitch deposition is a common problem in the pulp and paper mill. The problem is more pronounced depending on the wood species used for papermaking. Today, most mills are using an increased amount of recycled fiber in their furnish. Increases in pitch, dirt and stickies have been observed on the paper machine. Contaminants can plug the paper machine wires, break off of pipes and inside of tank walls and find their way into the paper machine furnish. They are usually the cause of holes and paper machine breaks. Reducing breaks and downtime on the paper machine is always desirable.

Deposition control falls into two main technologies, dispersion and detackification. Dispersion involves reducing the size of the stickies to improve sheet quality and by stabilizing these small particles to prevent agglomeration. Detackification tires to eliminate the tackiness of pitch and stickies and also attempts to stabilize the contaminants. However, there is no attempt to reduce the size of the particles. It is possible to control these deposit through certain control strategies at the wet end of the paper machine such as:

(1) Fix colloidal pitch particles on fibers
(2) Use a highly charged cationic polymer of a low molecular weight (less than 100,000) along with alum.
(3) Reduce pitch deposition by using a solid absorbent such as talc. However, this approach would not work for stickies. The talc particles would only coat the larger sized stickies particles.

By nature, pitch and stickies are hydrophobic. One method of control called wire passivity exploits this property. A water-soluble cationic polymer is continually sprayed on forming wires and reduces its hydrophobicity so that the contaminant won’t adhere. This article investigates the effectiveness of wire passivity to control pitch and stickies deposition on the paper machine.

Are the data credible?

Yes. The results seem to make sense based on the theory taught in class. The author used several grades of white water in the testing from TMP, linerboard and alkaline fine paper. A synthetic medium of kraft lignin (Indulin C), oleic acid, and abietic acid were also used. The experiment measured surface tension, contact angle, particle charge, and tackiness using a standard tape detackification test. Tapes were made of styrene butadiene rubber and vinylic esters to mimic stickies since these materials have been shown to cause deposition. A “coupon” of polyester film was used to mimic a paper machine wire. The “wire” was treated with 5 polymers of various molecular weights and charge density only identified as polymer A, B, C (nonionic), D, and E. A “peel force” measurement was taken to evaluate the tackiness of the “stickies” tape to the “wire”.

According to the author, the “wire” has become hydrophilic after treating it with a polymer. The polymer formed complexes with anionic products in the white water. Now, the stickies and pitch could not deposit. Surface tension was measured for each white water sample prepared for the experiment to demonstrate the interaction between the cationic polymer and the water-soluble anionic species present in the white water. Polymer A was shown to reduce surface tension by the greatest amount. Synthetic white water was used was used to confirm that reduction in surface tension is due to the formation of complexes between the cationic polymer and water soluble anionic products such as lignin or fatty acids.

In further testing, Polymer B was applied to the synthetic white water along with various amounts of surfactant. It was compared to a white water sample exposed to only various surfactant levels. The white water exposed to Polymer B and surfactant exhibited three distinct breakpoints when graphed. A lowering of surface tension was showed at a surfactant concentration of 15 ppm, which could have been caused by a reduction in electrical repulsion “between head groups of the surfactant allowing more surfactants to adsorb at the air/water interface”. The next breakpoint was at 60 to 105 ppm. Here the “interaction between the anionic surfactants and cationic polymer leads to a constant surface activity until the polymer is saturated with surfactant molecules”. This is near the critical association concentration and is shown to be around 95 ppm. Finally beyond 105 ppm, the surface tension reaches a maximum of 47 dyne/cm at 370 ppm. This was due to the formation of insoluble surfactant-polymer complexes. In all cases, Polymer B lowered the surface tension more than in the case of adding surfactant only to the white water. Only when excess of surfactant was added did the two curves approach each other in surface tension.

Streaming potential was also measured for the synthetic white water with and without the addition of 20 ppm of Polymer B and under various amounts of surfactant. The streaming potential of white water without the polymer addition was highly anionic and didn’t change much with increasing concentration. However, with the addition of Polymer B, the streaming potential of the white water decreased from a positive value (cationic) to a negative value (anionic) as the concentration of anionic surfactant was added. This shows that the cationic polymer formed complexes with the anionic surfactants found in the white water.
Adhesives (stickies) are hydrophobic and have a low surface energy (20 – 40 dyne/cm). The surface energy of a forming wire is about 43 dyne/cm, which is less hydrophobic than adhesives. So, contaminants having a lower surface energy than the wire will tend to deposit. If we can raise the surface energy of the “wire” close to the surface tension water (72dyne/cm) or white water (-62 dyne/cm), then the wire will become hydrophilic. Deposits are less likely to form since the surface energy of the adhesive is much higher than the surface energy of the wire coated with water (0 dyne/cm).

Contact angle is an indication of wettability. The interaction of a liquid with a solid is called wetting, which looks at the spreading of a liquid over a surface. A low contact angle is an indication of high wettability. Contact angle measurements of the polyester wire were made after applying Polymer B and nonionic Polymer C. Polymer B was shown to reduce the contact angle, which indicates that the polyester has become hydrophilic. The author feels this can be attributed to the adsorption of the complex formed between the cationic polymer and anionic species in the white water on the polyester wire. The standard tape detackification tests results were also consistent (exhibited lower values).

Contact angle measurements were not included for Polymer A. Peel force, surface tension and streaming potential were included for Polymer A. Polymer B appears to be the best choice for reducing deposition with “A” the next best. It would have been interesting to see the comparison. The article mentions in the conclusion that cationic polymers A and B adsorb on the polyester “wire” and make it hydrophilic but failed to report all pertinent tests for Polymer A.

What could have been extended in the study?

The authors used a “polyester coupon” as a surrogate paper machine wire to test the amount of contaminant deposition after treatment with various polymers. I don’t understand why the author didn’t use cut up samples of actual paper machine wires from several different major suppliers. I feel that this addition to the study would have made the results more meaningful to mill engineers reading the article. There is no mention of addition rates and appropriate strength of polymer to the wire surface. This information is needed to put this idea into practice.

Could the results be put into practice in industry?

All polymers (A, B, C, D and E) were only identified in general terms of molecular weight and charge density. I believe that the mill engineer would be interested in having more specifics about the product used. I think that appropriate application points could be in shower water at the forming section. However, the author failed to suggest some guidelines as to the minimal amount and application rate needed to maintain the wire in a hydrophilic condition. This is an important cost consideration to the mill. It may be cheaper to boil out periodically than to apply another additive at a constant rate throughout the production day.

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The paper aims to show the possible benefits of using Alum/ PAC (polyaluminum chloride) in combination with cationic potato starch (CPS) as a microparticulate retention drainage system, with anionic dispersion rosin size in a fine paper stock using calcium carbonate as filler in neutral/alkaline papermaking. During the last two decades there has been a prominent shift of papermaking
from traditional alum-rosin sizing to neutral / alkaline papermaking with the use of synthetic sizes such as AKD/ASA , which has enabled the papermakers to avail themselves of the benefits of using cheap calcium carbonate in the form of higher brightness , higher opacity of the paper products and ageing stability. The use of alum/PAC has been limited to stabilising synthetic sizing, to form a microparticulate retention/dewatering system with amphoteric CPS. The difficulty of using alum-rosin sizing under alkaline conditions are well known and can be attributed to the following reasons:

(1) Tendency of the cationic alum-rosin complex to turn anionic, making it difficult to retain on anionic furnish
(2) Premature agglomeration of the complex at the isoelectric point
(3) Decreased hydrophobicity of complex
(4) Destabilisation of alum rosin size by non-anchored rosin acids.

The laboratory study done by the authors of this paper aims at the possibility of alkaline rosin sizing using CPS/ aluminum hydroxide retention systems and to see if good sizing is achievable along with good retention.A 60% bleached kraft pulp and 40% bleached pine kraft pulp furnish were taken. 20% calcium carbonate was added, which was amphoteric in nature due to the presence of silicates as impurities. CPS which is amphoteric in nature (due to presence of negatively charged phosphoric esters) was used. Rosin size used was commercially available fortified dispersion size. PAC or NaOH and alum with different R values was taken. R is the mole ratio of NaOH to Altot, the total amount of aluminum. CPS followed by aluminum salts and then the rosin size was the sequence of addition always to the pulp furnish. That is, reverse sizing was followed to favour the aluminum-rosin complex formation ,and to prevent the the formation of calcium resinate which reduces and destabilizes sizing. The results obtained by reverse sizing and sizing by adding rosin before aluminum salts confirm the above said result of getting lower Cobb test values for reverse sizing for same amount of aluminum salts and rosin size. PAC-rosin system ( R=1.5) showed greater sizing results compared to NaOH/Al2(SO4)3 (R=1.3) system due to the greater hydrophobicity in PAC system and the interference of SO42- in the alum system. The addition of CPS first helped in making the chemical environment of the stock net positive and thus making the environment electrostatically healthy for anionic dispersion size and aluminum salts to decrease the zeta potential towards isoelectric point and increase sizing efficiency in alkaline environment. CPS utilizes charge mechanism as well as bridging mechanism.

Kinetics of sizing was studied and it was found out that thePAC/rosin system showed a lower contact time for optimum sizing compared to the NaOH/alum /rosin system for same amounts of rosin and Altot. The authors proposed that this was due to the very fact that a greater amount of transient cationic species were present in the PAC system whereas the alum system has lower in transient cationic species. The presence of sulphate ions will increase the rate of polymerization to form amphoteric aluminum hydroxide species which lower the reactivity of alum to rosin size. The added benefit of this final polymerization product (Al(OH)3) which is formed in both the systems (alum and PAC ) although at different rates is that it is amphoteric in nature. This allows alum to form an efficient microparticle retention/dewatering system with amphoteric CPS. So in the case of the alum system we can make up for its slower reactivity to rosin by its additional benefit of aiding drainage and dewatering. Higher retention values were noted in tests with Britt’s jar.

Thus the study opens up a door for doing reverse alum/rosin sizing with amphoteric starch in the neutral/alkaline conditions with the advantage of utilizing cheap calcium carbonate and imparting paper properties with a combination of benefits from acid and alkaline sizing. But in my opinion I have certain reservations which need to be addressed and are as follows:

1.In future work it would be beneficial if actual papermill conditions can be simulated.
2.The shear sensitivity of CPS needs to be evaluated in actual conditions as it added very early in the process.
3.The effectiveness of reverse rosin sizing in actual conditions needs to be evaluated for sizing contact time.
4.Britt’s jar was used for retention trials but actual papermaking shear values are different.
5.Tap water was used whereas mills today are moving towards closed white water systems.
6.The kinetics and behaviour of calcium carbonate needs to be analysed with rosin alum sizing under neutral/alkaline systems similar to commercial practice.

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Abstract

In the article [1], Honig, et.al. with CYTEC Industries, discuss the possibilities and limitations of “water soluble micropolymers” (WSM). The authors claim that WSM, a new class of retention aids, in effect, organic microparticles, and result in superior formation at equal or higher retention and at comparable drainage in comparison to inorganic microparticles.

Background

Papermakers want it all.

Papermakers demand that the suppliers of the chemicals that comprise the Retention/Drainage/Formation system (R/D/F) deliver high first pass retention (FPR), with high drainage and excellent formation. It is obvious that high FPR is important to ensure cost-effective use of raw materials, decreased levels of total suspended solids (TSS) and biological oxygen demand (BOD), as well as improved machine cleanliness to minimize spots and holes in the web and sheet breaks. Further, high drainage is important for line speed and its effect on productivity. Formation is critical for optimum sheet strength and, in the case of printing papers, for optimal printability.

Prior art in the use of retention aids has abundant data to support an inverse relationship between FPR and formation. In other words, at higher FPR, formation is poorer. The introduction of organic microparticle systems consisting of silica or bentonite in combination with cationic starch or cationic polymers resulted in better formation at equivalent levels of FPR in comparison with dual polymer retention systems.

In the subject article, Honig, et.al. claim that WSM result in better formation than inorganic microparticle systems at equal or better retention and at comparable drainage.

Water soluble micropolymers (WSM)

The authors claim that the ideal WSM would be a material having the optimum features of inorganic microparticles combined with those of polymeric coagulants and flocculants. The WSM that are the subject of this paper are organic micropolymers with an ionic nature and with a filamentous structure due to cross-linking of predominantly hydrophilic composition.

Potential markets for WSM

Until the advent of inorganic microparticles, programs consisting of a polymeric coagulant and a high molecular weight flocculant systems were the most widely used systems for retention and drainage, particularly for highly filled grades. One of the major disadvantages of this technology is the adverse effect that the flocculant has on formation.
Review of the article

The authors investigated polymeric microspheres to determine if organic materials consisting of an ionic surface, sub-micron particle size and a three-dimensional structure would behave similarly to the inorganic microparticles.

Drainage tests were conducted comparing the two systems. Unfortunately, the test used to compare the two can be confounded by, in the author’s words: “holes in the sheet” from overfloccing. Nonetheless, the authors were sufficiently encouraged by the results to extend the work to micropolymers of a sub-micron size, but with a filimentary micronetwork structure.

Conclusions that were drawn from the lab work indicated that, in combination with promoters like alum, micropolymers of various compositions and structures would allow papermakers to select a product to improve drainage at comparable formation, or to obtain significantly better formation at a slight deterioration in drainage.

Once again, quoting the authors: “…review of the data simply indicates that micropolymers with a micronetwork structure can perform in the laboratory. It suggests that they might also work in practical situations.”

Several trials were conducted on paper machines manufacturing a variety of grades such as coated papers, uncoated fine papers and board. The goal of the trials was improved formation rather than increases in retention and drainage.

In general, formation improvements during the machine trials ranged from slight to dramatic. In those trials where formation was only slightly improved, retention was better. Similarly, in the trials where formation was only slightly improved, the formation was either very good to begin with, or the formation of the paper was less sensitive to the retention system, possibly more highly affected to furnish properties, or machine conditions.

As of the writing of the article, the effect of the micropolymer system on highly filled grades has not been trialed on machine. On the other hand, lab work indicates that, at high filler contents, the micropolymer system has a significant drainage advantage over bentonite.

Critical commentary

In general, the authors did a reasonable job laying out the lab work to, firstly, prove that organic microparticles would work similarly to inorganic microparticles. Subsequently, the authors extended this line of reasoning by comparing the performance of organic microspheres to organic micropolymers. The primary objective of this piece of work was to demonstrate that, compared to inorganic microparticles, that formation could be improved at comparable levels of drainage and retention.
The quality of the author’s data is seriously in question as a result of their dependence on a drainage test that is affected by “holes in the sheet” due to overfloccing. If one overlooks this fact, as well as the subjective evaluation of the formation of handsheets, then one can make a giant leap of faith and conclude, as the authors conclude, that the data indicates that micropolymers with a micronetwork structure can perform in the laboratory and that it suggests that they might also work on the paper machine.
After this revelation, the next logical extension of this program was a series of trials on paper machines making a variety of different grades. The information regarding the machine trials is sketchy at best and it can only be assumed that the trials were conducted in a scientific manner, such as in a designed experiment, so that the data could be analyzed statistically. It is my belief that this was not the case, and, as is so prevalent in our industry, I believe that the trial was an Edisonian probe with little consideration for the design of the experiment, the data gathering plan or statistical analysis of the data upon completion of the trial. Trials like this are subject to interpretation, which is dependent on the perspective of the observer. It is obvious that, in this case, the perspective is from the standpoint of a chemical peddler trying to sell his magic foo foo juice to us poor, unsuspecting papermakers.

Nowhere in the article does the author reveal what WSM are, or pose a hypothesis to explain why micropolymers deliver superior formation at comparable levels of drainage and retention.

Jasper Mardon wrote the X commandments of paper chemistry. Three of the commandments are: “(III.) Know the nature of your chemicals, (IV.) Know the purpose of your chemicals, and (V.) Know the interactions of your chemicals.” From the information presented in this article, It is impossible to determine what WSM are, how they work, or the possible adverse interactions that might occur with other wet end additives.

After reading the article or after listening to a sales presentation, potential customers might ask several questions. Specifically, a customer with some knowledge of wet end chemistry might ask: What are WSM and how do they work?
WSM technology is patented and is the subject of at least three patents [2, 3, 4]. The patents claim the materials that are co-polymerized to make WSM, a method to make and emulsify the WSM, as well as the use of WSM to flocculate fines and fillers in papermaking processes.

The patents shed some light on the polymers, or types of polymers that are the backbone of what the authors call WSM. Reading between the lines, one may hypothesize that WSM can include polymers such as polyacrylamides that have been crosslinked. The patents stress the importance of an ionic, organic microbead less than 750 nanometers, more preferably less than 300 nm if cross-linked, and an ionicity of at least 1%. In this case, the particle size is the size of the discontinuous phase droplets in which the polymer is made. On the other hand, the patent does little to explain the mechanism by which WSM improve formation in comparison with inorganic microparticles.

Firstly, one might ask what are the critical differences between WSM and inorganic microparticles? WSM and inorganic microparticles are both sub-micron in size, have a three dimensional structure and an ionic surface. Inorganic microparticles are sub-micron in size, commonly 3-5 nm. In comparison with conventional polymers used as flocculants, molecular mass is greater, and due to its three-dimensional structure, the hydrodynamic volume is larger.

Another question a potential customer might ask is: What accounts for the difference in performance between the two types? In reference to the obvious questions papermaking technologists may ask regarding how to account for formation differences, the authors claim that: “This review of the data simply indicates that micropolymers with a micronetwork structure can perform in the laboratory. It therefore suggests (emphasis is mine) that they might also work in practical applications.”

The customer should also ask: How do WSM work? It is apparent from reading the subject article and the patent literature that the crosslinking of the polymers is an integral feature of the WSM. Further, one might hypothesize that the crosslinking might be the key difference between WSM and conventional polymers in R/D/F systems. To explain the possible differences, it is important that we understand the implications of crosslinking to structure of the WSM, and, therefore, to its performance. Crosslinking of the polymer may make the polymer chain less flexible. The conventional wisdom is that the flexible polymer chain can be attached to the fibers and fines leaving loops and tails away from the particle surface to provide bridging between that particle and other particles. A stiffer chain would be less flexible and resist the conformation of the polymer chain to the surface upon time that reduces efficiency permitting lower levels of the polymer for retention and drainage. Crosslinking may also result in the three-dimensional structure claimed in the paper. A three-dimensional structure will result in a polymer with high hydrodynamic volume, which can sweep out larger volumes as it rotates in the liquid phase. Higher hydrodynamic volume could result in more collisions with particles, resulting in greater efficiency, thus better retention and drainage. The larger mass, although simultaneously more susceptible to cleavage due to shear, will still have a large enough mass to effectively bridge between particles. Furthermore, the larger volume and the many charged sites that this implies, will result in more sites for attachment of fines and fillers within the chains of the micropolymer, such that more fine material will be agglomerated and attached to the fiber surfaces. The net effect of these four hypothetical considerations might be better retention and drainage at lower dosages of the polymer, thus reducing its negative effect on formation when compared to conventional polymers or microparticles at equal retention.

Summary and conclusions

In summary, I would not run a trial of this system based on the data in this article.

References
(1.) Honig, D.S., Harris, E.W., Pawlowska, L.M., O’Toole, M.P., and
Jackson, L.A., “Formation improvements with water soluble micropolymer
systems”, Tappi J. 76(9): 135 (1993).
(2.) Honig, D.S., Harris, E., U.S. pat. 5167,766 (Dec. 1, 1992).
(3.) Ryles, R.G., Honig, D.S., Harris, E.W., Neff, R.E., U.S. pat. 5,171,808
(Dec. 15, 1992).
(4.) Honig, D.S., Harris, E., U.S. pat. 5,274,055 (Dec. 28, 1993).

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A Few More “Clues” to Help You Solve the Alum Deposit “Blues”

You may have only heard about them, or they may come and go in your in your system with little effect, but if you are one of the many experiencing a “nightmare on alum street” due to alum based deposit problems in your paper machine system, then you may be interested in some of the new ideas presented in this article. The article “The Analysis and Chemistry of Aluminum Based Paper Machine Deposits” by Frederick S. Potter discusses the different forms of complex deposits derived from aluminum compounds in rosin size containing systems. The paper also describes two different types of analytical equipment, the FTIR (fourier transform infrared spectroscopy) and x-ray fluorescence spectroscopy, and how this equipment is utilized to evaluate the various forms of aluminum based paper machine deposits studied in this article.

Deposit formation in paper machine systems have always been a prevalent nuisance to papermakers. The ability to successfully analyze paper machine deposits, whether from aluminum compounds as discussed in this paper, or from other means, is critical to paper machine operation and efficiency. Because of the huge array of types of furnish, additives, and system conditions that exist in most paper making operations, having a tool to evaluate and trace where different deposits are derived is a major asset to problem solving.

The work completed in this article involved the evaluation of both paper machine deposits and so called “synthetic” deposits which were prepared in the lab under various controlled conditions. The paper machine deposits were obtained from throughout the different parts of a paper machine system which utilizes aluminum compounds for rosin sizing. The “synthetic” deposits were developed under lab conditions for three different aluminum compounds – alum, PAC (polyaluminum chloride), and sodium aluminate. Individual synthetic conditions were developed for each of the three different aluminum compounds in pH conditions ranging from pH 5 to pH 10. Aluminum hydroxide was also prepared in the lab under the same conditions and used as a control. Synthetic deposits were created for each of the aluminum ions at each individual pH target ranging from 5 to 10. The pH level was adjusted using 2N NaOH. The FTIR, which was utilized to evaluate the composition of each deposits, gives data which is plotted graphically. The graphs show different spectra wavelengths which depict bands which vary depending on the composition of the deposit. The X-ray diffraction utilized on these same deposits gives both a qualitative and quantitative measure of the composition, however in this study, they were not able to utilize the X-ray diffraction results because the samples were not in crystalline form. In question here was if the “synthetic” deposits varied in composition when the pH changed and if the “synthetic” deposits were comparable to the deposits collected from the paper machine systems. Also in question in this study was if the deposits collected were in the form of aluminum hydroxide – Al(OH)3 or another complex form of aluminum. It is known from other analytical studies that the form of active surface sites on these Al(OH)3 aggregates changes as the pH is raised form 5 to 10. Al(OH)3 exists as a positively charged species up to a pH 8.5-9.0 due to the adsorption of hydrolysis products onto the precipitate.

What Did the Article Really Tell Us

The analytical work completed shows the formation of two distinct aluminum precipitates that are found in the pH ranges 5-7 and 8-10 and are comparable for each of the three different aluminum compounds evaluated. The precipitates found at pH 5-7 for both alum and alum/sodium aluminate matched the paper machine deposits and were referred to as aluminum based deposits or complexed aluminum hydroxide. The precipitates found at pH 8-10 appear to be a form of aluminum hydroxide. None of the IR spectra from any of the precipitates prepared from the three aluminum salts were identical matches for aluminum hydroxide. Also, it was found that the aluminum values of the precipitates are affected by more than just changes in pH. It was concluded that exposure to heat and length of time also effect the aluminum values of the precipitates. The spectra from the deposits formed for pH 5, 6, and 7 were similar for alum and sodium aluminate, and also comparable to the paper machine deposits obtained. There were some differences between the alum and sodium aluminate spectra, and the PAC spectra in this pH range. For the three higher pH ranges, 8, 9, and 10, the spectra were identical to each other, but more comparable to the spectra for hydrated aluminum hydroxide and not the paper machine deposits. FTIR and X-ray fluorescence do appear to be important analytical tools for accurately determining the presence of aluminum based deposits in paper machine systems, but in this case, limited for use in identifying exact aluminum species.

What Did We Really Learn

The authors did not discuss the types of paper machine systems from which the deposits used for comparison were derived from (type of paper machine, pH of the system, type of furnish, other additives, etc), only where the deposits were obtained. This information would be key to more thorough understanding as it would be interesting to see if the same results and conclusions were apparent in different paper making systems. I would classify the article as interesting, but limited in terms of supporting data. The authors of this paper were trying to pinpoint exact aluminum species under varying conditions, a task that would appear to require a much more in-depth study due to the number of variations of aluminum compounds possible and the number of conditions which can alter the species. Thorough understanding and the establishment of convincing material would require additional case studies. The paper does give a good overview of paper machine chemistry and recommendations when using aluminum compounds and rosin size. The paper stresses the critical need for a strong background in wet end chemistry and knowledge of the operating history of a paper machine to successfully interpret and solve deposit problems. From my experience in paper machine operations, I would also stress the need for on-site analytical equipment for successful evaluation of paper machine deposits. Deposit control is very critical in all paper machine systems and loss of control can result in costly problems in a very short period of time.

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“A New Approach to Wet End Drainage / Retention / Formation Technology,” by Vaughan, C. W., Proc. TAPPI 1996 Papermakers Conf., 439. Reviewed by Julie Dellemann, January, 2000.

Making progress in one area of papermaking may require a compromise in quality or performance in another area. Craig W. Vaughan offers a new approach that may be customized in its application to provide drainage, retention, and formation benefits. The technology is based on a combination of two water soluble products: a cationic, high molecular weight, dispersion or emulsion polymer and a modified lignosulfonate. Vaughan attempts to show at low dosages that there are improvements in drainage with small loss in formation. The impact of the new program was examined through laboratory and pilot paper machine studies reporting the variables such as product dosages, ratios, feed points, on acid and alkaline furnish drainage, retentions, and sheet formation.

Laboratory Experimental

Alkaline Furnish Prepartion: A laboratory test was conducted using a synthetic alkaline or acid furnish.

Fiber	Filler	Other additives	Consistency	pH
50% HWK	15% GCC	0.25% Cat. starch	0.5%
50% SWK	15% Kaolin	1% Rosin size, 0.7% alum		4.8
350 ml CSF		0.7% AKD		8.0

Stock Freeness Test: Stock freeness or drainage rate was measured under the following conditions. A 500 mL sample was put into a one liter rectangular mixing jar with a stirrer and variable speed controller. The stock was treated as follows:

Simulated
Chemical Mixing
@Mix Time(sec) Feed Point Speed (rpm) Comments
time zero ————– 1200 Begin mixing stock
time five Pre-screen 1200 Add HMW polymer
time thirty ————– 600 Reduce mix speed
time forty Post-screen 600 Add D/R/F aid
time sixty ————— —— Stop stirring

The stock sample was transferred to a 500 ml drainage tube fitted at one end with a 100 mesh screen and rubber stopper. The drain tube was inverted five times. The bottom plug was opened and the drainage rate was measured as a function of volume.

Handsheet formation test: Handsheets were formed from the stock samples in the freeness test.

Pilot Paper Machine Test Conditions: A high speed, pilot paper machine was used to conduct experiments under acid and alkaline conditions. The experiments sought to test the laboratory predictions and compare the performance of the new D/R/F program.

RESULTS AND DISCUSSION:

Impact of Feed Points/Shear Alkaline furnish drainage-lab study: When increasing the mix time or shear with the high-molecular-mass polymer there were dramatic effects on drainage when the product was used with the modified lignosulfonate than when used alone. Increased shear on the single polymer, D/R led to a loss in drainage performance. The new two-product D/R/F program showed an increase in drainage when used with high shear. Contrastingly, when the modified lignosulfonate of the new product was subjected to increasing mix time or shear, the performance of drainage worsened progressively before it flattened out. Overall, the two product D/R/F could be manipulated by adjusting the degree of shear.

Alkaline furnish drainage-pilot paper machine studies: The pilot paper machine drainage data with changes in chemical feed points or applied shear differed from the laboratory test data. This was explained by the fact that drainage performance was dependent upon thorough distribution of the drainage/retention aid through the stock. There were short mix times and a lower degree of applied shear with less mixing energy imposed on the very high molecular polymer. The two-polymer system showed a slight drop in drainage performance with an increase of shear on the HMW polymer component. This led to a loss in drainage performance.

Total and filler retentions- pilot paper machine studies: In response to the applied shear, the total FPR and filler FPAR retentions on the pilot machine varied. The single polymer decreased FPR and FPAR with increased shear. There trend was the same for the two-product D/R/F program.

Uncoupling Drainage and Sheet Formation: Usually drainage/ retention and sheet formation are inversely coupled. Under the new two product program these parameters were manipulated separately. This holds true under applied shear and the ration of HMW polymer to modified lignosulfonate, D/R/F aid. Drainage and formation was manipulated independently through changes in the product ratio with constant shear. Optimum drainage was achieved between a 1:1 and 3:1 ratio of HMW polymer to D/R/F aid. At a 1:1 active product ratio, drainage and sheet formation became uncoupled so it was possible to increase sheet formation while the optimum drainage rate was obtained.

Impact of Recycled Fiber on Performace: Under alkaline conditions on the pilot paper machine, the new D/R/F program was addressed. The change in fiber source had a small impact on drainage, retentions, or formation.

Impact of Acid Fine Paper Conditions on Performance: The new D/R/F program in a laboratory test under acid furnish showed significant improvement in drainage over the cationic polymer D/R aid at a comparable sheet formation.

2 LEGACY FILES “OUR FACT BOOK”, CHALLENGE QUESTION ESSAYS

Name: Olga Vdovina
Date: April 13, 2009.

Topic: “In acidic papermaking why does a high degree of neutralization of aluminum (high R value) tend to give high retention, whereas a low R value tends to give high rosin sizing?”

Why this subject is important:
For sizing under acidic conditions, papermakers usually use rosin soap or rosin acid emulsion. The optimum aluminum species for rosin sizing depends on the type of rosin that will be used, because the sizing mechanisms are different for soap size and for dispersed acid size. In the case of rosin soap, this size is dissolved in water, and the best way to retain this rosin sizing in paper is a chemical reaction between soap form of rosin and other chemical substance such as Al3+ which make strong attachment of rosin molecules to fiber surface. In the case of rosin acid emulsion, acid particles of rosin don’t dissolve in water and these particles are little reactive; that is why the main way to guarantee the sizing is a retention of rosin particles inside the paper during the formation of sheet. After this, the rosin particles attach to the fiber surface with the aid of alum at the stage of sheet drying at high temperature. In this case the aluminium should guarantee the high retention of acid rosin particles inside the paper at the stage of sheet formation in the first place.
The aluminium is used not only for precipitation of soap form of rosin on the fiber surface, retention acid form of rosin inside the paper, but also for better retention of fines during formation of the paper, for promoting drainage, and for pH control. All of these factors assist of improvement of paper properties and make it possible to speed up the papermaking process. This is possible owing to the complex and changeable structure of aluminium compounds. The structure depends on the degree of aluminium neutralization (R value). That is why it is important to know how the aluminium structure in solution depends on the degree of neutralization and how change the aluminium properties in solution with change of its structure. This can help to use the aluminium with different structure and as a result with different properties for making specific tasks and also have an influence on the structure of aluminium in solution, changing it for a particular task.

Answer to the assigned question:
One of the most important steps leading to good sizing is a fixation of sizing agent on the fiber surface. For acidic papermaking, in the case of rosin sizing, Al3+ shows the most chemical activity toward the soap form of rosin. This Al3+ ion can be considered as a linking section between the negative charge of carboxylate groups of rosin soap and the negative charge of fiber surfaces. The aluminum ions complex with the carboxylate groups, then precipitate particles of aluminum rosinate onto the anionic fiber surfaces. The degree of neutralization for Al3+ is zero. The increasing of degree of neutralization lead to decreasing the amount of Al3+ in solution and to increasing the amount of small and medium-sized polymeric aluminium species. Polymeric Al can’t make strong bonds with rosin ions; it can make only weakly bond complexes. But these bonds are strong enough to cause the coagulation of fine particles (and sizing agents onto fiber fines) around polymeric Al in solution. This coagulation helps to hold small particles inside the paper sheet during formation, because the size of particles after coagulation are much more than previous and they can be held by the fiber mat. That is why the high degree of neutralization of aluminum (high R value) tends to give high retention. The increasing of neutralization leads to increasing the quantity of polymeric Al in solution (small and middle polymeric Al). The positive charges of polymeric Al attract negative charges of carboxylate groups of fines and lead to coagulation.

Logical or theoretical support for answer:
According to Shuping Bi and co-authors (1) at R<0.2, pH = 4.1, the main Al species in the solution are Al3+ and monomeric Al. At 0.2 < R < 2.5, the main Al species are small/middle polymeric Al, such as Al2(OH)42+, Al3(OH)45+, Al4(OH)84+, Al5(OH)132+, Al6(OH)128+, and Al10(OH)228+.   At 2.5 < R < 3.0, 4.6 < pH <9.3 the main Al species are large polymeric Al species such as Al13(OH)327+; Al14(OH)3210+; Al15(OH)3015+ and sol/gel Al(OH)3. The positively charged complexes of Al in solution can form chemical complexes with carboxylate groups at the surface of suspended and polymeric materials, thus neutralizing the negative charges. Such neutralization and complexation tends to coagulate the fine particles. After coagulation, fine particles can be held easily by the fiber mat. In this connection, this can be supposed, that an increasing quantity of polymeric Al in solution (Higher R value) with total positive charge higher than positive charge of one Al3+ ion leads to coagulation of a larger quantity of negatively charged fines around one molecule of polymeric Al. In this case, the agglomerate that is formed around the polymeric Al will contain a lot of negatively charged particles such as fines, sizing agents and other substances. The sizing agents also can be attached to the fiber fines that coagulate around the polymeric Al. The sizes of these agglomerates are big enough to be seived by the fiber mat or forming fabric.
            According to Edward Strazdins (2,3), the Al compounds show the best retention property in acidic papermaking at the highest value of cationic titratable charge of Al compounds. The cationic titratable charge depends on the Al concentration in solution and the degree of neutralization of aluminum. According to the author, the highest cationic titratable charge corresponds to the next degree of neutralization of aluminum: 1-2 OH- ions per Al3+ ion. This degree of neutralization of aluminum corresponds to pH value 4.1-4.6 and the region in which the main Al species are the small and middle polymeric Al. Further increasing the degree of neutralization of aluminum leads to a decrease in the titratable charge of aluminum and to decrease the retention property of aluminum. This can be connected with increasing part of sol/gel Al in solution during increasing the degree of neutralization of aluminum.
            The culminating moment in any mechanism of rosin sizing (sizing with rosin soap or rosin acid emulsion) is the formation of aluminium resinate, that is, the formation of strong bond between hydrophobic rosin molecule and fiber surface through an aluminum complex. The place of formation of aluminium resinate is different for soap and for acid form of rosin size. In the case of soap rosin the reaction goes very fast in the solution. Opposite to this, the reaction between the acid form of rosin and aluminum takes place only at high temperature during drying of paper sheet. This can be connected to low activity of rosin molecule in its acid undissociated form. As far as we discern the influence of aluminum in the sizing system in water solution, for acid form of rosin in solution the main role will play retention ability of aluminum. The influence of degree of neutralization of aluminum in solution on the retention ability of aluminum was discerned earlier.
            In the case of rosin soap we may deal with water soluble size, which in water solution dissociates to ions and rosin ions having strong negative charge. Water soluble compounds, in contrast to insoluble compounds, can be held on the surface of fibers only by making strong bound complexes, leading to precipitation the rosin complexes on the fiber surface. According to Joseph Marton and co-authors (6) and also Dr Juntai Liu (4) Al3+ ion (R=0) shows the highest activity to rosin ions in solution. The Al3+ ions have the biggest positive charge per Al ion; as a result Al3+ ions have high electrostatic force of attraction and can form strong bond complex. The neutralization of this positive charge by negative charge of rosin ions in solution leads to precipitation mono and dialuminium resinate size on the fiber surface. For maximum interaction the neutralization of aluminum should be low; in this case the main Al species in the solution are Al3+ ions.

Experimental support for answer:
            Shuping Bi and co-authors (1) determined points of transition from one form of Al compounds to another in water solution by a potentiometric titration experimental method. Six characteristic points were obtained from a potentiometric titration curve. Among them, the critical point is the crossing point of two neighboring tangent lines passing through the inflection point, while the inflection point is where the second derivative’s value is zero on a potentiometric curve equation. The three critical points express different meanings: 1 point (R=0.2) – mononuclear Al begins to convert into small/middle polynuclear Al; 2 point (R=2.5) – the small/middle polynuclear Al begins to form the large polynuclear Al; 3 point (R=3.0) – the amorphous gel or sediment begins to dissolve. The meanings of the three inflection points are: at R=1.0 – small polymeric Al will change into medium sized polymeric Al; at R=2.8 – large polymeric Al will change into gel or sediment, at R=3.3 – Al(OH)3 will dissolve as Al(OH)4-. Conclusions about structure of aluminum in solution at different degree of neutralization was made from “Core-links” model and “Cage-like” Keggin-Al13 model, and also the both models were joined to one “Continuous” model.
            Edward Strazdins (2,3) determined cationic charge of Al compounds in water solution by titration with an anionic polyelectrolyte (polyvinyl sulfate potassium salt – PVS-K). This was based on the premise that the interaction of cationic aluminum ions with the polyelectrolyte would adequately mimic the aluminum ion’s interaction with paper furnish components. From the series of experiments were drawn graphs showing the dependence between titratable charge of aluminum sulfate as a function of pH and Al concentration or titratable charge of Al as a function of degree of neutralization and concentration. From these graphs were determined the field of maximum titratable charge of aluminum sulfate in solution, which corresponds to pH value 4.2-4.6 and changes according to Al concentration in solution. Then the analogy was made between the dry strength development (consequently between polymer retention and retention of fines) and degree of neutralization of aluminum, and also cationic charge of aluminum. It was established that the dry strength maximum well agrees with the maximum of cationic charge of aluminum. The same analogy was obtained for retention of rosin dispersion (maximum retention of rosin dispersion corresponds to maximum titratable charge of aluminum in solution).
            Alum has been used to develop sizing with rosin soap since 1807. It was determined that good sizing can be achieved at low values of pH (to 4.5), and the quality of sizing is significantly decreased with further increasing of pH (in contrast to dispersed rosin sizing). As was mentioned earlier, this connects with a different mechanism of retention of rosin size in paper. The soluble soapy rosin sizes dissociate into so-called resinate anions, which then react with soluble aluminium cations to form an insoluble aluminium resinate, which precipitates on the negative charges of fiber surfaces (4). Good precipitation of aluminium resinate from solution on the fiber surface at low value of pH is favored by the presence of a large quantity of Al3+ ions in solution with strong positive charge per Al ion (1). This charge conditions the appearance of strong electrostatic (ionic) forces of attraction between Al3+ ions, rosin ions, and negatively charged fiber surface. The neutralization between these ions leads to formation of strong bonds rosin-Al-fiber and precipitation of aluminium resinate on the fiber surface. The polyaluminium compounds can’t form such strong bonds with rosin ions. This favors better sizing by rosin soap at low degree of neutralization of aluminum (R value is low). In this case the part of Al3+ ions in solution is high.

Situations in which the findings can be useful:
As was shown, the compounds of aluminum in water solution have very complex and changeable structure, which depends on the degree of neutralization of aluminum, and also on other variables such as temperature of solution, concentration of aluminum in solution, the presence of outside admixtures, and so on. The different structures of aluminum complex in solution are inclined to show different properties. Understanding of how the structure of aluminum in solution changes with degree of neutralization and ability to manage of aluminum structure and as a result to manage aluminum properties can help to use different aluminum complex with different degree of neutralization for decision of specific tasks correctly.
For example, as was mentioned earlier, aluminum with a low degree of neutralization is the most suitable for good rosin sizing in the case of rosin soap. On the other hand, for good retention of rosin dispersion on the fiber surface, the aluminum with a higher degree of neutralization will be more effective, because this aluminum shows better retention ability. This also can be useful when aluminum is employed as retention agent for keeping fines and different additives ub the paper sheet during the papermaking process. This property of aluminum is connected with the ability of soluble aluminum products to form chemical complexes with carboxylate groups at the surfaces of suspended and polymeric materials, thus neutralizing the negative charges. Such neutralization and complexation tends to coagulate the fine particles. In this case the mechanism of retention is the same as for retention of a rosin dispersion; consequently the best retention also will be obtained when the aluminum products have a degree of neutralization in the range R=1-2. As we know, retention is very important factor for good papermaking. Good retention helps to minimize losses of solids and additives, to make basis weight more stable, to optimize sheet structure, and to improve properties of paper.

Literature Cited

Bi, S., Wang, C., Cao, Q., Zhang, C. “Studies on the mechanism of hydrolysis and polymerization of aluminum salts in aqueous solution: correlations between the “Core-links” model and “Cage-like” Keggin-Al13 model”. Coordination Chemistry Reviews 248: 441-455 (2004).
Strazdins, E. “The chemistry of alum in papermaking”. Tappi Journal, April 111-114 (1986).
Strazdins, E. “Theoretical and practical aspects of alum use in papermaking”, Tappi Journal 128-134 (1989).
Liu, J. “Sizing with rosin and alum at neutral pH”. Paper technology, October 20-24 (1993).
Kitaoka, T., and Tanaka, H. “Fiber charge characteristics of pulp suspension containing aluminum sulfate”. Journal of Wood and Science. 48(1): 38-45 (2002).
Marton, J., “Mechanistic difference between acid and soap sizing”. Nordic Pulp and Paper Research Journal 4(2): 77-80 (1989).
Bottero, J.-Y. “Aluminum chemistry in aqueous solution”. Nordic Pulp and Paper Research Journal 2: 81-89 (1989).

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Name: Guy D. Joseph
Date: April 25, 2009

Topic: Based on what you know about their effects, how do you expect that microparticles interact with retention aid polyelectrolytes in solution? Do some of the published results suggest that the retention aid polymers “wrap themselves around” the microparticles, for instance?

Why this subject is important: The subject of microparticle and retention aid polyelectrolyte interaction is important because the microparticle addition is intended to affect drainage and formation on the paper machine. These two factors have significant impacts on machine production costs and paper quality. Improved drainage will allow for higher production rates on dryer limited machines and will lower the overall cost per ton of steam supplied to the machine. Improved formation has the potential to increase sheet strength properties which is important in packaging grades and visual appearance of the paper which is important for printing and writing grades. An understanding of how microparticles accomplish this change in drainage and formation should be understood to develop proper addition procedures and to aid in the analysis of the results of the addition whether expected or unexpected. The use of dual retention aid systems based on microparticles has proven to be effective on many paper machines. Continued optimization of their use will stem from a proper understanding of the drainage and formation mechanisms. Typical dual retention aid systems based on microparticles are the use of cationic starch with silica sols and cationic polyacrylamide (CPAM) with bentonite. More recent programs involve the use of anionic micropolymers or silica gels which have a linear or chain like form.

Answer to the assigned question: The theoretical answer to the question is that the charge difference between the anionic microparticle and the cationic retention aid will cause a change in the conformation of the polyelectrolyte. The expected result would be for the high mass cationic polyelectrolyte with extended loops and tails to collapse and take on a smaller radius of gyration. Based on theoretical information to some degree the analogy of the polyelectrolyte “wrapping itself around” the microparticle is accurate. The literature cited to answer this question suggests that there is not a single mechanism for the interaction of the microparticle and retention aid and that the size and type of retention aid, starch or polyacrylamide, and microparticle determines the mechanism. The smaller silica sols in the range of 4-5 nanometers will penetrate and collapse the branched cationic polymers while still providing the ability to bridge between polymer segments. The larger plate like bentonite (montmorillonite) microparticles will have more of a bridging effect as opposed to penetrating the polymer. The overall mechanism for the microparticle systems on a paper machine is to bridge sheared flocs due to the high anionic charge and allows for good retention with better drainage.

Logical or theoretical support for answer: In general practice when using cationic polyelectrolytes for retention aids in combination with microparticles the addition points are set up in the following manner. The high mass, usually cationic, polyelectrolyte is added prior to a point of high shear, typically the fan pump or the machine screen. The polymer induced flocs are then re-dispersed and the microparticle, usually highly charged and anionic, is added prior to the headbox where the flocs will undergo moderate to low levels of shear. The addition of polymer prior to the machine screen will tend to have a net negative impact on drainage and retention as opposed to the polymer added past the screen, in the absence of high shear. The reason for this is likely due to the irreversible breaking of the polymer bridges formed with the polyelectrolyte and the furnish components; fines, fibers and sometimes fillers. It should be mentioned for some clarification at this time that the retention aid polyelectrolyte is often interacting with colloidal substances formed by highly charged coagulants added earlier in the process. This could be a polyvinyl amine or some other proprietary coagulant. Cationic starch can act as the source of the cationic charge in this scenario as well, although it does not possess the same charge characteristics of a synthetic coagulant.

The addition of the anionic microparticle in common practice results in improved retention opposed to the pre-machine screen addition and a marked increase in drainage. This leads to the conclusion that a fundamental shift in the resulting flocculation mechanism has occurred. Over time, improved retentions can have a positive impact on drainage as the white water loop will be cleaned up and fewer fines and other components that impede drainage will be present in the system. This can be demonstrated as a gradual speed up of a machine or gradual reduction in steam load in the dryer section. The retention aid/microparticle systems impact on drainage is typically immediate with a large shift in the dry-line on the forming section of the fourdrinier.

Literature supports the concept of the reversibility of floc formed with microparticle systems and the formation of a more compressed floc. So, the combination of the cationic polyelectrolyte with the highly anionic microparticles will cause a change in the conformation of the floc, or a compression of the floc that will expel water and improve overall drainage on the machine (3). In addition, the more uniform formation cited as a result of the flocculation mechanism will lead to better dewatering on the machine. The usual consequence of increased porosity using microparticle support the concept of more open drainage channels.

Experimental support for answer: Wall et al (6) discuss the kinetics of flocculation between cationic starch and colloidal anionic silicic acid. The importance of this work is in respect to the question of whether the polymers will wrap themselves around the microparticle. Their work is based on the measure of turbidity and it’s relation to particle flocculation and size. The size of the cationic amylopectin, or cationic starch, is several hundred nanometers compared to the silica used which is in the range of 5.5 to 21nm in their study. Their work shows that the smaller highly charged anionic microparticles screen the larger branched polymer chains of the cationic starch. The consequence is that the starch molecules contract and take on a smaller radius of gyration. They state that the starch polymer can be assumed to be a cluster of regions of polymer chains with the space between the clusters containing solvent. One can make a logical step to conclude that in the papermaking process this solvent would be expelled and thus aid in dewatering. Their work also shows that the smaller the microparticle the smaller the floc. This is the conclusion from looking at the turbidity of starch and silica solutions of different sizes where the turbidity shows no reduction with the addition of the larger microparticle, 21nm. The 5.5nm particle size shows a reduction in turbidity after initial flocculation. From this they propose that the smaller particle can penetrate the polymer and collapse the chains. The concept of bridging then follows from the results of the 21nm microparticle.

Swerin and Odberg (5) discuss the flocculation mechanisms when dealing with anionic montmorillonite and cationic polyacrylamide (CPAM). Cellulosic fiber suspensions were treated with cationic polyacrylamide or cationic polyacrylamide then montmorillonite and subjected to varying shear levels and a corresponding flocculation index was assigned. Under low shear there was a similar flocculation index between the CPAM alone and the CPAM/montmorillonite. The flocculation index was higher and the average floc diameter was larger for the CPAM/montmorillonite combinations in their study. The flocculation index decreased and the floc average diameter decreased with increased shear in the absence of the montmorillonite. Their conclusion states a demonstration of an interaction between the polyacrylamide and the montmorillonite; in this case one can assume the flocs are bridged by the polymer adsorbed on individual cellulosic fibers and the anionic microparticle.

Asselman and Garnier (2) discuss the mechanism of microparticulate and retention aid systems. The key points, based on work with CPAM/montmorillonite addition, pertain to the platelets acting as a bridging agent, the reversibility of the flocs, and the idea of stronger flocs formed after re-dispersion from high shear and the subsequent addition of the microparticles.

Andersson and Lindgren (1) discuss the properties of the colloidal silica, in particular the charge density and particle size. These have shown to have a significant effect on the conformation of the cationic polymer. The starch and silica combination appear to have a synergistic effect at as particle size of 5nm while the CPAM require a microparticle size of roughly 8 to 10 times larger. There study states the main mechanisms of the silica system are charge neutralization and bridging.

The cited literature explains the results seen in real world applications with the use of microparticle programs with respect to drainage and retention mechanisms. Overall drainage has marked improvement and retention efficiencies can be improved. The question with regard to the interaction of microparticles and retention aid polyelectrolytes are a bridging mechanism with re-dispersed polymer induced flocs. In addition the charge relationship between the relatively small high anionic charged microparticles and the high mass retention aids result in a change in the conformational chemistry of the flocs, one that results in a collapsing of the floc. An analogy would be that the polymer “wraps itself around” the microparticle as it collapses.

Situations in which the findings can be useful: The finding can be useful in the understanding and proper selection of different microparticle programs. As noted in the literature there are programs involving silica, bentonite (montmorillonite), and there are micropolymer programs available as well (3). There appears to be a strong retention factor to the use of CPAM and bentonite with a strong drainage relationship with cationic starch. Both show improved drainage and retention but with varying wet end chemistry programs on different paper machines the correct selection will be important. A CPAM/bentonite approach may be more applicable to a strength grade such as linerboard while cationic starch and silica may be more advantageous for fine papers. Trial work is always appropriate but the finding gives some insight into which approaches to look at first.

Literature Cited

Anderson K., Lindgren E. and Nobel E., “Important properties of colloidal silica in microparticulate systems,” Nordic Pulp and Paper Research Journal, no. 1 (1996)
Asselman T. and Garnier G., “The Flocculation Mechanism of Microparticulate Retention Aid Systems,” Journal of Pulp and Paper Science, Vol. 27 No. 28 (August 2001)
Covarrubias, R., Paracki, J., Mirza, S., “New advantages in microparticle retention technologies” Appita Journal, Vol. 55 No.4 (July 2002)
Hubbe, M., “Microparticulate Programs for Drainage and Retention,” In Rodgriguez, J.M. Ed., Micro and Nanoparticles in Papermaking (2005)
Swerin, A. and Odberg, L., “Flocculation of cellulosic fibre suspensions by a microparticulate retention aid system consisting of cationic polyacrylamide and anionic montmorillonite,” Nordic Pulp and Paper Research Journal no. 1 (1996)
Wall S., Samuelsson, P., Degerman, G., Skoglunds P. and Samuelsson, A., “The Kinetics of Heteroflocculation in the System Cationic Starch and Colloidal Anionic Silicic Acid,” Journal of Colloid and Interface Science, Vol. 151 No. 1 (June 1992)

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Name: Scott Wagner
Date: April 20, 2009.

Topic: “Please explain various reasons why these authors did not find any evidence consistent with a polymer bridging mechanism, especially in systems where fiber suspensions were treated with carboxymethylcellulose (CMC).”

Why this subject is important:
Treating a cellulose fiber suspension with CMC offers many potential benefits in terms of fiber properties. CMC is an anionic polyelectrolyte and usually does not absorb well onto fiber surfaces; however, there are modifications that can be made to overcome this barrier. The three basic methods used to attach CMC to fiber surfaces are by heating the solution with a certain concentration of salt, such as calcium chloride to repress the electrostatic repulsion during fiber treatment, use a low-charge-density CMC, and grafting reactions.
This process has allowed researchers to discover facts about colloidal interactions such as the effects of ionic strength, charge density, and counterions on the interaction between two cellulose fiber surfaces. Research has shown that sorption of CMC onto fiber surfaces can lead to an increase in water retention values (WRV) due to an increase in the number of charged groups. This would be an important application in the absorbent products industry where articles such as baby diapers would see an increase in overall capacity (g/g).
Handsheet properties are also affected by the sorption of CMC. An increase in swelling of the fibers makes them more flexible, thus increasing their ability to bond during the sheet forming process. Thus, higher WRV lead to higher tensile and internal strengths. In research performed by Blomstedt et al (4), the tensile index increased between 20 and 60% over the reference pulp. This would be an added benefit not only to the paper industry, but to the textile industry as well.

Answer to the assigned question:
In the research conducted by Hovath et al (6), the influences of colloidal interactions on fiber network strength were studied by varying the surface charge density of cellulosic surfaces with grafted high molecular mass CMC. While their work did not discuss the mechanisms involved, their work did show a larger decrease in repulsion for the CMC treated cellulose when the electrolyte concentration was increased due to an even larger collapse of the CMC chains.

Similar research was done by Blomstedt et al (4), where CMC attachment with varying degrees of substitution (DS 0.2 to 0.43) without calcium was studied. It was suggested but not confirmed that CMC may be adopting a similar chain conformation to crystalline cellulose, enabling the adsorption. The article does state that further studies are needed to fully understand the mechanism behind the CMC adsorption. In contrast, another related study by Laine et al showed a different mechanism may exist, as sorption of CMC using higher degrees of substitution (>0.4) in the presence of large amounts of calcium were successful while no attachment under electrolyte-free conditions took place. Added electrolyte screens the electrostatic repulsion between anionic fibers and anionic CMC. While a mechanism does exist, research has failed to show evidence of a polymer bridge to attach CMC to fiber surfaces.

In yet another study conducted by Blomstedt et al (5) where optimizing CMC sorption to improve tensile stiffness on hardwood was conducted, researchers were able to attach lower degrees of substitution CMC to the fiber surfaces in the absence of salts, meaning that the repulsion is smaller. It is suggested that the CMC sorption in this study is driven by the conformational similarity between CMC and the cellulose in the microfibrils on the fiber surface. The amount of CMC attached did decrease when the DS was increased.

Finally, in a fractionation study by Blomstedt et al (2) research was conducted to determine the distribution between fibers and fines. The CMC content of the fines fraction was higher than the fiber fraction; however it was even further increased when salts were added, but to what degree remains unknown.

In summary, experiments have shown there are several variables that affect sorption of CMC onto fiber surfaces. Some research has shown a low DS in the absence of salts is successful while others have had success with a high DS in the presence of salts. CMC and cellulose are so closely related, attachment by charge neutralization is not what is at work here. Polymer bridging is based on opposite charges. Some systems however, can be pre-treated as anchoring sites for anionic polymers. So to answer the question, there are too many other variables to consider which affect CMC sorption to support evidence for a polymer bridging system.

Logical or theoretical support for answer:
In general, the process for grafting CMC onto fiber surfaces involves a treatment process and is influenced by such variables as CMC addition, temperature, pH, beating of pulp fibers, degree of substitution of CMC, and electrolyte concentration. While the adsorption percentage of CMC onto fiber surfaces seems to depend on several variables, repeated attempts of the same grafting variables have found different results, suggesting other factor may be involved or different mechanisms. One interesting feature based on work done by Blomstedt et al is that adsorption onto hardwood fibers is less that it is for softwood fibers under the same conditions (2).
The polymer bridging mechanism is less dependent on charge neutralization because the molecules are so large. But these mechanisms tend to break down under high shear conditions. In order for the CMC to attach itself, a moderate amount of shear is required to aid in the attachment and once it is attached, it is not reversible. Some of the benefits include a stronger sheet. It has been theorized that the CMC penetrates between the microfibrils, leading to a denser sheet. Also, the water retention values (WRV) increase on CMC treated pulp. This is explained by an increase in the amount of charged groups present. Polymer bridging mechanisms tend to work over a larger distance and are controlled by kinetic factors rather than charge. These factors do not support a bridging mechanism at work here.

Experimental support for answer:
Blomstedt et al (4) developed a method to attach CMC onto the surfaces of Kraft fibers in an easy fashion. The cellulose surface is negatively charged and CMC which is an anionic polyelectrolyte does not adsorb well. Their research showed the process could be done without high temperatures or electrolyte additions to obtain an irreversible sorption of CMC, provided a low level of substitution was used (< 0.5). The beating of the pulp fibers to a moderate level increased adsorption. The amount adsorbed onto the fibers was also influenced by the DS of the CMC, decreasing when the DS was increased. Similar studies by Laine et al showed higher degrees of substitution (> 0.4) was possible when large amounts of calcium were added; however, in this study CMC with DS of 0.43 was successfully attached in high amounts in the absence of calcium. Furthermore, lowering the pH from 12.5 to 10.0 enhanced sorption of CMC. However, this again was in contrast to the same study by Laine et al who found a decrease in the amount of CMC attached when the pH was lowered.   Based on these differences, the research points out that two different mechanisms are at work in these two studies. The work performed by Laine et al used a substantial amount of electrolyte addition. One theory is given to explain a possible mechanism at work. CMC may be adopting a chain conformation similar to cellulose and with a low DS adsorption is possible. It is then able to associate with the cellulose microfibrils. Their concluding remarks do state that further research is needed to determine the sorption mechanism which is still the subject of debate before any industrial applications can be made because little is know about the behavior of CMC treated fibers with other wet end chemicals.
Other research performed by Blomstedt et al (1) involved the treatment of CMC modified fibers with cationic surfactants. Here, the addition of a surfactant further increased the strength of the sheet. Rope-like bridges were seen using an ESEM. The research is clear to point out that CMC is first permanently attached to the fiber surface and then the surfactant is added, making it unlikely that a CMC-surfactant phase exists. The chains are stiff for cellulose and CMC so any micellular aggregates are not formed. The researchers theorized that the surfactants associate with CMC on the anionic fiber surfaces by ionic and hydrophobic interactions. However, concluding remarks do state future work is needed to understand the interactions in the fiber-CMC-surfactant system and the reasons why sheet strength is improved.
Further work by Blomstedt et al (5), in which bleached hardwood pulp was treated with CMC under specified conditions, showed similar results for increased sheet strength and WRV properties. In this study the degree of substitution was smaller, meaning the repulsion was much less between surfaces. The research suggested the mechanism for attachment was driven by conformational similarity between CMC and the cellulose in the microfibrils on the fiber surfaces. The article goes onto to say that what they are suggesting is mere speculation and further research is needed to confirm the exact mechanism.
In a fractionation study performed by Blomstedt et al (2), hardwood pulp was treated with CMC under specified conditions. The pulp was then fractionated using a hydrocyclone and DDJ apparatus. The reject fraction had a longer fiber length, width, curl, cell wall thickness, and coarseness compared to the accept fraction. The corresponding handsheets were twice the strength of the accept fraction. On the other hand however, the CMC content of the accept fraction was higher. The research does not suggest a plausible reason for this observation but it does state that a calcium salt should be added to maximize adsorption of CMC.
One final piece of research in this are was performed by Blomstedt et al (3) involved the modification of eucalyptus pulp with CMC. Again, an increase in sheet strength properties was realized in comparison to untreated reference pulp. But taking it a step further realized a difference in strength properties from those of birch (hardwood). The increase in strength properties for the eucalyptus was attributed to less fiber curl and lower vessel content. But no plausible mechanism of CMC attachment was given.
After careful examination of the research performed in this area, it is clear that discovering the true mechanism behind the attachment of CMC to cellulosic surfaces is needed. At this point, research has only been able to suggest a mechanism or identify that more than one mechanism is involved.

Situations in which the findings can be useful:
While the exact mechanism of how CMC attaches to cellulose is unknown, the method itself can be beneficial in the paper industry, where a stronger fiber network is desirable. Improvements in tensile and stiffness would be useful in packaging material applications. As discussed earlier, the added benefit of varying the surface charges to study interactions of other colloidal substances allows for researchers to discover how particles interact with ions, polymeric substances, and what affects the double layer. The findings can provide some insight into future research opportunities.

Literature Cited

Blomstedt M, Vuorinen T (2007) Modification of softwood kraft pulp with carboxymethyl cellulose and cationic surfactants. The Japan Wood Research society. 53:223-228.
Blomstedt M, Vuorinen T (2006) Fractionation of CMC-modified hardwood pulp. Appita 59:44-49.
Blomstedt M, Vuorinen T, Eero K (2007) Surface modification of eucalyptus pulp by carboxymethylcellulose: effects on fiber properties and sheet strength. 51-63 (June 2007).
Blomstedt M, Mitikka-Eklund M, Vuorinen T (2007) Simplified modification of bleached softwood pulp with carboxymethyl cellulose. Appita Journal v. 60 no. 4: 309-314 (July 2007).
Blomstedt M, Vuorinen T, Eero K (2007) Optimising CMC sorption in order to improve tensile stiffness of hardwood pulp sheets. Nordic Pulp and Paper Research Journal vol. 22, no. 3:336-342.
Horvath A, Lindstrom T (2007) The influence of colloidal interactions of fiber network strength. Journal of Colloid and Interface Science, 309:511-517.
Swenson J, Smalley M, Hatharasinghe H. L. M (1999) Structure of bridging polymers. Journal of Chemical Physics, vol. 110, no. 19:9750-9756.

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Name: Scott Ewers
Date: June 13, 2009

Topic: “Based on published articles, what slime control strategies would you expect to be particularly suitable for application in the case of a paper recycling operation?”

Why this subject is important: Slime development, often referred to as biofilm, is likely the most troublesome microbiological problem for the paper industry according to Hassler et al. [4] Slime management in a paper recycling operation is important, since ignoring the biofilm will eventually cause problems with product quality, equipment maintenance, production efficiencies, odors, and might lead to hazardous working conditions. Like most paper manufacturing operations, the recycling paper process utilizes fresh and re-circulated / closed water systems that are ideal environments for microbiological growth. According to Hassler et al. [4], process water that has a continuous supply of nutrients, adequate pH, temperature, salt concentration and a few other parameters are well within the range for microbiological growth. The biofilm formation is a dynamic process that involves several stages: 1) base layer development, 2) surface colonization, 3) biofilm formation, 4) biofilm maturation, and 5) dislodging of biofilm [4]. In base layer development no microbe life is required to start the layering process. Extractives begin to settle on clean surfaces to develop a “conditioning” layer that microbe will begin to colonize. As time progresses microbes will settle and colonize surfaces and eventually create the “biofilm” layer. As further detailed by Hassler et al. [4], the biofilm layer becomes an attachment area for microbes that is irreversible. It is this permanent attachment stage that facilitates a jelly-like / slime matrix known as EPS (extracellular polysaccharides). The biofilm layer continues to grow in thickness as other microscopic organisms like nematodes begin to colonize the slime layer. The most common way to control a biofilm formation is to rely on the use of antimicrobial agents known as biocides / “slimicides” along with conventional boil-out cleaning [2]. The use of hydrogen peroxide as a biocide in a paper recycling mill operation is an interesting one due to the presence of catalase enzyme and its inherent ability to decompose the peroxide. Based on the research by Ng and Davies [5] I would say that hydrogen peroxide use in paper recycling operation would have good merits in managing slime, as well as working as a brightening agent.

Answer to the assigned question: Based on articles reviewed concerning slime control in the paper industry, there are several suitable slime control strategies that are in use in typical pulp and paper mill process water systems that should be effective for a paper recycling operation. Based on Edwards’ TAPP article [2], it seems logical that the first-line of defense in the paper industry against a slime build up is disinfection. According to Daignault and Jones [1], boil-outs are a very important part of deposit control in a paper machine to minimize slime build up. The limiting factor for the boil-outs is the downtime that a mill will have to incur. The use of chemical biocides helps to reduce this potential downtime. Monitoring microbial growth and the use of biocides such as chlorine dioxide, hydrogen peroxide, and Bimogard are some products used to manage slime build up in a mill’s process water and equipment. Wadsworth and Simpson [6] describe the properties and efficiencies of chlorine dioxide used to control biofilm. Wadsworth and Simpson listed ClO2 characteristics as follows: very fast rate of disinfection, effective at low dosages, non-reactive with most organics and ammonia, and disinfection independent of pH. Hydrogen peroxide is a commonly used slime control chemical in paper recycling, but when in use it has to overcome the effects of the catalase enzyme. In nature catalase has the purpose of destroying peroxides both in and outside the cell during a cell’s normal metabolic process. Ng and Davies’ research [5] looked at appropriate hydrogen peroxide dosing levels to overcome this decomposing effect has on peroxide. Bimogard is a relatively new product that Hassler et al. describe as being a multi-stage approach to controlling a biofilm build up. The Bimogard chemical approach uses a combination of a surfactant component and non-biocidal sulphonated lignin derivate that is formulated into one product [4].

Logical or theoretical support for answer: Besides scheduled boil-outs, monitoring microbe levels by obtaining total bacterial counts is a good starting point for a typical mill slime control program. According to Goldstein [3] microscopic examination of deposits should be used to allow for quick identification of biologicals, so problem solving can begin immediately. Goldstein further states that maintaining proper biological control of mill in-coming fresh water supply is often neglected. The use of fresh water is seen as a likely entry point for many microorganisms. Microbiological dip slide test, Dye-Based tests, and ATP Luminescence test devices can be used in to estimate microbial population in process water [6]. All three tests are alternatives to the more time-consuming bacterial plate count method. It is not clear whether chlorine dioxide still can be considered to be a popular biocide treatment for mill operations today because of safety concerns with use and site ClO2 generation. But based on Wadsworth and Simpson’s article [6], chlorine dioxide is an efficient biocide, particularly if Dairyman’s Standards have to be met. The reversion of chlorine dioxide to chlorite ion is one major observation cited by Wadsworth and Simpson [6]. The researchers explained the dynamic role the chlorite ion plays in further control of biofilm formation. It is reported that the chlorite ion reacts with organic acids produced by bacteria in the biofilm layer to reform chlorine dioxide, or the organic acids lowers the pH in parts of the biofilm layer so that chlorous acid is formed. The chlorous acid will also revert to chlorine dioxide. Wadsworth and Simpson [6] further outline several other bacterial control chemicals: alkyl dimethyl benzyl ammonium chloride, 2,2-dibromo-3-nitrilpropinonamide, dodecyl guanidine hydrochloride, methylene bisthiocynanate, glutaraldehyde, carbamates, isothiazoline, and sulfones. The problem of catalases production when using hydrogen peroxide in wastepaper pulp mill operations is eliminated when adequate higher dosage of hydrogen peroxide is used. According to Ng and Davies [5] research the high residual level of hydrogen peroxide is carried over into mill whitewater and overwhelms the ability of bacterial catalase to decompose it. Ng and Davies also report that significant gain in pulp brightness is produced with higher dosage of hydrogen peroxide. Hassler et al. [4] detail some of the biocide use legislation that has been implemented in the European Union since 1998 and gradually phased in by 2010. Bimogard, a product developed in response to the new regulations, is continuously applied in low dosage to minimize biofilm formation, interfere with formation of sticky EPS layer, and works to delay the lag phase of biofilm formation where vigorous microorganism growth starts [4].

Experimental support for answer: A 30-month study is summarized by Daignault and Jones [1] on the importance of cleaning and deposit control through boil-outs. Their data illustrates a trendline that shows a continual reduction of daily web breaks on a test mill’s paper machine over the 30-month period. The efficiency improvements were attributed to the mill’s scheduled and intensive cleaning efforts. Ng and Davies’ [5] experimental biocide trial indicated a 0.5% hydrogen peroxide pulper dosage was an optimized level to increase pulp brightness gain and after two weeks of use in the test mill, the high dosage was found to have eliminated the catalase enzyme and slowly wipe out the bacteria in the whitewater system.

Situations in which the findings can be useful: Hassler et al. [4] reported that Bimogard system is an acceptable alternative to the use of conventional methods for microbiological growth control, and is in compliance with the European Biocide Directive. Bimogard studies were reported to show a significant reduction of extracellular polysaccharides (EPS) in the biofilm layer, particularly on seven different mill bacteria. The findings by Hassler et al. [4] should be very useful for the paper industry in Europe since the more stringent biocide use regulations will prohibit many traditional biocide chemicals.

Literature Cited:

1.   Daignault, L. and Jones, D.R., “The Importance of Cleaning and Deposit Control in Improving Paper Machine Efficiency”, Pulp & Paper Canada 104:8 (2003).
2.   Edwards, J., “Biocides—Bug Killers that Enhance Pulpmaking and Papermaking Processes”, TAPPI Journal (79) No. 7 (1996).
3.   Goldstein, S. D., “Some Overlooked Fundamentals of Slime Control”, Appita (40) No. 3 (1987).
4.   Hassler, T., Mangnus, Linberg and Schenker, “Sime and Again”, Paper360 28-32 (2007).
5.   Ng, B. ,and Davies, D., “Methods for Controlling catalase in a Deink Pulp Mill”, TAPPI Journal (80):4 (1997).
6.   Wadsworth, J., and Simpson, G., “Control of Biofilm in Alkaline Whitewater System with Chlorine Dioxide”, Engineering & Papermakers Conference 1095-1105 (1997).

Name: Joscelin Diaz
Date: April 9, 2008.

Topic: “Why do the amounts of adsorbed aluminum and “transferred” aluminum depend on the degree of neutralization of the aluminum cations and also on [SO4-2]?”

Why this subject is important:

Electrostatic charges of dissolved and suspended materials in paper furnish directly influence the retention behavior of fines, fillers, and various wet-end additives that improve paper quality and the process runnability.

Alum has been widely applied to practical papermaking processes to control the charge properties of the anionic substances at the wet end, and it has thus performed as an agent for enhanced drainage, retention, and sizing.

Alum, as a retention aid, has the ability to reduce electrostatic repulsive forces. It is used as a coagulant for colloidal material because it is a source of highly cationic complexes, fights disturbing anionic substances by precipitation or by adsorption on cationic Al-flocs, and also is still used to regulate pH. However, it is ineffective in papermaking systems where hydrodynamic forces are strong. That is why polymers, especially cationic polyelectrolytes, are now commonly used in retention aid additive programs.

Structural and electrostatic properties of aluminum compounds in aqueous media are susceptible to the pH of the system, its temperature, the shearing forces in the liquid flow, and other conditions.

Quantitative analyses of aluminum components present in paper sheets are indispensable for investigating A1 adsorption behavior on pulp fibers at the wet end.

For all these reasons, it is important to understand the kinetic processes that affect added paper chemicals in the paper machine wet end (transfer of paper chemicals between furnish components) in order to choose the dosage position of paper chemicals or to make mathematical simulations of a paper machine and to optimize paper production.

Answer to the assigned question:

The adsorption of aluminum is a function of the pH and the concentration of sulfate ions[1]. Increasing the ion neutralization by increasing the pH results in a change in the aqueous chemistry of the aluminum ion. At low pH, the Al+3 ions are the first species to be adsorbed in the fibers. Then, by increasing the pH, there will be a formation of aluminum hydroxide flocs. These Al-flocs can be adsorbed to the fibers due to the ion exchange interaction with the ionizable surface groups. Once the aluminum gets adsorbed, it can be transferred to the clay particles or other surfaces. The concentration of the sulfate ions interfered with the adsorption on aluminum on the fibers because the sulfate ions can shift the cationic charge of the Al-flocs, and these can get detached and stay in the solution. That is why, the transfer of aluminum decreases while the concentration of sulfate ions increase.

Logical or theoretical support for answer:

According to Arson and Stratton [2], when the pH increases, the carboxyl groups ionize and the adsorption of a simple cation increases. The increase suggests that a soluble hydrolyzed species of higher charge is being formed and adsorbed. And also, that at higher pH, a colloidal precipitate is formed.

Kitaoka and Tanaka [3] reported that the optimum neutralization of A1 solutions obtained by titratable charge measurements under equilibrium conditions was about 1.5-2.0.These differences probably arise from the carboxyl groups of the pulp fibers, which act as an acid in the neutralization procedures. In the pH 5 condition, alum cations adsorbed uniformly and performed well to control charge properties of fibers at the wet end. Excess neutralization procedures produced nonionic aluminum flocs on the fibers.

Research carried out by Ödberg and Nordmark [1], showed that the addition of clay reduced the amount of aluminum on the fibers. Different OH/Al ratios (AlOH) are the most sensitive parameter. If it is increases, increases the pH. They noted that by increasing the electrolyte concentration and the stirring rate decreases the transfer of aluminum to clay particles and the adsorption of aluminum on the fibers.

Experimental support for answer:

Arson and Stratton [2] demonstrated that the trivalent cation Al3+ is the dominant ionic aluminum species at pH 4.2 (here the aluminum adsorption is not affected by concentration) and there is a simple ion exchange mechanism where Al3+ is the primary species to adsorb. At pH 4.65-4.75 there is a mixture of Al3+ and complex hydrolysis products (the majority of carboxyl groups are in the ionized form) and the trivalent cation is highly adsorbed onto the fibers in this region because its high concentration.
At pH 5.5, aluminum is converted to the cationic colloidal precipitate and there is a reduction in the carboxyl content. The sulfate ions, whether incorporated into the precipitate or not, are apparently more effective than the monovalent anions in reducing the charge on the precipitate, thereby reducing the interaction between adsorbed flocs. Also, aluminum concentration influences the amount of adsorbed aluminum only in excessively high pH regions.

In the study made by Kitaoka and Tanaka [3], streaming potentials of the pulp suspensions containing aluminum sulfate with various degrees of alkalinity, the relative amounts of a1uminum element present only on the fiber surfaces, and the aluminum content of the pulp sheets were determined by the streaming current method (using PCD apparatus), XPS (X-ray photoelectron spectroscopy), and XFA (X-ray fluorescence analysis), respectively. The surface charge properties of the pulp fibers at the various pHs of the suspensions were investigated with regard to adsorption behavior of Al components on the pulp fibers estimated by the quantitative and dispersive differences of the Al components on the fiber surfaces. The positive regions appeared on the pulp fibers owing to adsorption of Al cations on the fiber surfaces. By adding a dilute NaOH solution in limited amounts to the suspension, the fiber surface charge converts from slightly negative to positive in the narrow range of around pH 5. Moreover, rapid decreases of streaming potentials by further alkali additions were observed at > pH 5.2. In general, positive charges due to the cations present on the solid surfaces were immediately consumed according to the adsorption of OH- ions via simple ionic interaction. The Al species in the pulp suspensions, however, distinctly contributes to cationization of the fiber surfaces by adding OH- ions. Maximum streaming potential value (ca. +160mV) was detected when the OH/Al molar ratio in the system was about 2.5. Therefore, they indicated that the adsorption behavior of Al species at around pH 5 implies the formation of noncoagulable and cationic A1 complexes on the fiber surfaces. Excessive alkali supplements, however, spoil the effective Al cations and produce only the useless nonionic Al flocs.

Ödberg and Nordmark [1] experimented with the transfer of alum from cellulosic fibers to clay particles at defined stirring levels in a Britt Jar. In the first part of the study, the adsorption of alum on the fibres was determined for two different cases; with and without addition of clay to the sample at different OH/Al ratios. The addition of clay reduced the amount of aluminum on the fibers. This is attributed to a transfer of Al-flocs from fibers to clay particles. These studies were compared with the value obtained of the total mass balance for alum and quite acceptable agreement was found. Also, some possible variables on the transfer were investigated, while maintaining a constant OH/Al ratio of 1.5 (where the aluminum ion is neutralized). First, the stirring time was changed to study the effect of this variable on the transfer of aluminum. Based on the two different stirring rates, this influence is moderate relative to the amount transferred. However, by increasing it, more Al-flocs are going to be in the solution rather than on the fibers, and the transfer decreases. The pre-adsorption time was also investigated, but the authors confirmed that this variable does not influence the amount transferred of aluminum. The electrolyte concentration was studied by changing the concentration of Na2SO4. They showed that by increasing the concentration of sulfate ions, the adsorption decreases and also the transfer. The reason is that the sulfate ions shift the positive charge of the aluminum flocs.

Conclusions:

The optimum alkali additions stimulated the preferential and uniform adsorption of Al cations on the fiber surfaces at around pH 5. Excess neutralization procedures produced nonionic aluminum flocs on the fibers.

The hydroxyl ions in Al-containing pulp suspensions probably play an important role in promoting adsorption of effectual A1 cations onto the fiber surfaces accessible for the wet-end additives and other substances.

The preferential aluminum adsorption behavior on the fiber surfaces, by utilizing the required amounts of hydroxyl ions, probably accounts for the effective cationization of the fibers under acidic to neutral papermaking conditions.

When aluminum ion neutralization increases: Al+3 ions decreases and aluminum hydroxide flocs begin to form.

In studies about the transfer of polymeric retention chemicals (like cationic retention aid) between furnish components (fines and fillers), these showed that the transfer depends on some factors such as: shear level, molecular weight and adsorption time. Increasing OH/Al ratio increases the amount transferred to clay, and increasing [SO42-] decreases the transfer.

As a hydrophilic adsorbate, pulp fibers adsorb simple cations only through a specific ion exchange interaction with ionizable surface groups. For bleached pulps, these ions exchange sites are primarily carboxyl groups. As a result, when the pH increases, the carboxyl groups ionize and the adsorption of a simple cation increases. Here, the aluminum hydroxide flocs can be transferred to clay particles.

Situations in which the findings can be useful:

Aluminum ions originating from aluminum sulfate added to the paper stock have some impact on drainage and retention behavior because they affect the charge properties of the fiber surfaces at the wet end. That is why it is so important to study and improve the efficiency of Al compound usage.

Even if the alum is added to the thick stock and the Al-flocs are to a large extent adsorbed on the fibres, a large proportion can be transferred to fine particles at the wet end, especially on a machine where the retention is slow. This can hurt the level of sizing of the fibers.

The method of application of alum depends on the mill condition (pH, type of size used, temperature, concentration of alum, fines, composition of white water, etc). So, it is important for a papermaker who uses alum to understand how some variables affect the transfer of alum ions to the clay because then they can have a basis for understanding the kinetic processes that affect the performance of chemicals added in the paper machine wet end.

The adsorption characteristics of fillers such as clay affect retention and the effectiveness of alum in the system. If clay is not also retained either, it will affect interfiber bonding capacity and thus sheet strength. Also, it will affect the optical properties of the sheet.

In a papermaking system, once the adsorption sites are satisfied, the unabsorbed aluminum builds up in the recycled white water system and eventually is purged into the wastewater system.

Literature cited:

[1] Ödberg, L and Nordmark, G. J. “Transfer of adsorbed alum from cellulosic fibers to clay particles” Pulp and Paper Science. 21 (7):J250 (1995).

[2] Arson, T.R. and Stratton, R.A. “The adsorption of complex aluminum species by cellulosic fibers”. Tappi Journal. 66t 12 v. 72 (1983).

[3] Kitaoka, T. and Tanaka, H. “Fiber charge characteristics of pulp suspension containing aluminum sulfate”. Journal of Wood and Science. 48(1): 38-45 (2002).

[4] Farley, C. “Influence of dissolved ions on alum cationicity under alkaline papermaking conditions”. Tappi Journal. Volume 75: 193-199 (1992).

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Name: Ingrid Hoeger
Date: April 2008

“When does it make sense to use cationic additives, and at the same time to employ retention aids having ethylene oxide chains, i.e. PEO or brush polymers with pendant ethylene glycol branches?”

The importance of nonionic retention aids

One of the current trends in papermaking is to fully close mill water streams. The mill water closure will result in a significant increase of inorganic salts and organic anionic trashes in papermaking white water, which, in turn, affects the retention aid performance. Nonionic retention aids have proven to perform better than ionic retention aids in these conditions.

Background Information in Nonionic Retention Aids

Retention aids having ethylene oxide chains, such as PEO or brush polymers with pendant ethylene glycol branches, are nonionic. They are used preferably in mechanical pulp furnishes. Several studies have determined that the performance of PEO can be enhanced with the use of polymeric material that acts as a cofactor for PEO [3, 4]. It is believe that cofactors modify PEO by aggregating it or forming a complex with it or by providing a surface on which PEO can adsorb [4]. So a crucial step in flocculation is the adsorption of PEO/cofactor complex onto the target colloids. Consequently, the flocculation is sensitive to the surface chemistry of the colloid particle. In this aspect, positively charge precipitated calcium carbonate would be easy to flocculate because the adsorption is driven by electrostatic interactions [2].

This type of retention aids appear to be more tolerant to the presence of dissolved colloidal substances (DCS) than the cationic retention aids. Because of this, they can still perform well in mills with a moderate system closure of the white water [1]; but the percentage in the first pass retention does decrease when compare to that of a system with less DCS [1].

The type of cofactor use with PEO is affected by the composition of the mechanical pulp, and this implies that a particular PEO/cofactor combination does not perform equally well with every furnish. One has to use caution when choosing the PEO/cofactor system, because the one that gives the highest retention is not necessary the right option; for example, too high a retention of fines and fillers during sheet formation may slow the drainage rate and lead to runnability problems [4].

There also can be an effect on the performance of PEO/cofactor combination due to the quality and ionic contents of the white water; these can affect the solubility of the cofactors. A cofactor that has precipitated from solution may no longer be available to interact and form a complex with PEO. For example, the gains in retention can be reduced by the contamination in the white water with deinking liquor. [4]

Background Information in the use of Cationic Additives

Cationic polymers can form aggregates with dissolved colloidal substances, primarily lipophilic extractives, UV-absorbing substances and anionic hemicelluloses [5]. This interaction between them can be influenced by the characteristics of the polymer (molecular mass, charge density and structure). For example, at the optimum polymer dosage, polymers that are linear, low molecular mass and high charge density can have the highest aggregation efficiency with regard to wood components [5].

Answer to the Question

The cationic material might be added as a pretreatment to the furnish to form aggregates with excess dissolved colloidal substances; and this way permit a better interaction of the complex of PEO/cofactor and the fibers.

In theory, by helping the cofactor adsorb better in the fibers we can help the retention mechanism. So if the cationic material can be included as a monomer in preparing the copolymer used as a retention aid, this would improve the performance of PEO. Experimental data is still needed to corroborate this statement. However, it is worth mentioning that cofactors with modified structure have been developed. They include the addition of cationic groups (amine groups), for example the retention agent patent number US 6,306,256 B1 [6].

References

[1] Allen L. et al. (1999). Effect of system closure on retention- and drainage –aid performance in TMP newsprint manufacture. TAPPI Journal April
[2] Cong R. et al (2003) The influence of PEO/poly(vinyl phenol-co-styrene sulfonate) aqueous complex structure on flocculation. Journal of Colloid and Interface Science 261 65–73
[ 3] Gibbs A. et al. (1996) Flocculants for precipitated calcium carbonate in newsprint pulps. TAPPI Journal Vol 80 No4
[4] Laivins et al. (2001) Performance of PEO/cofactor retention aids in MP furnishes. TAPPI Journal Vol 86. No3 .
[5] Sundberg A. et al (1994). Interactions of cationic polymers with components in TMP suspensions. PAPER JA PUU Vol 76. No 9
[6] Rosengren et al. (2001). United States Patent No. US 6,306,256 B1

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Name: Maria Soledad Peresin

Date: April 22th, 2008

Topic: “Is it necessary that a retention aid molecular have an “extended” three-dimensional conformation, at the moment of formation of a polyelectrolyte bridge, in order to achieve strong attachment between two surfaces in a fibrous suspension? What is the experimental evidence? What are some logical reasons for or against this idea?“

The implication of conformation of retention aids in papermaking:

Basically the manufacturing of paper could be thought of as a set of simple operations; for instance: separation of cellulose fibers from wood, and their dispersion in water; mechanical treatment of the fibers; addition of some “additives”; and formation of the paper web with the subsequent elimination of water. However, the papermaking process is not that simple, and the interaction between the furnish components with water makes the picture even more interesting. Since the papermaking process is essentially a process based on the filtration mechanism, the use of retention aids is fundamental in order to achieve two important goals: (1) high retention values; and (2) good drainage rates. Retention aid usage also can help to make the process cost-effective retention of fiber fines and fillers [1] and ease of removal water, saving energy to dry it after the wet-end section [2].

There are two different mechanisms that can explain polymeric retention aids flocculation, depending on the kind of polymer used and the type of interaction with the components of the furnish. These two mechanisms are known as bridging and patch charge flocculation [1]. Bridging flocculation is of special interest in this topic, and it occurs when a high-mass cationic polymer, with not necessarily high charge density forms a “bridge” by getting attached to different negatively charged particles in an irreversible way. It has been thought that this kind of attachments is only able to be broken by breaking the polymer chain.

Getting close to the question of the topic, the conformation of retention aids plays a fundamental role at the moment of achieving strong attachment between two surfaces in a fibrous suspension. An accurate understanding of this conformation may be helpful in gaining a clear idea about the strength of the attachment and its lifetime under the papermaking conditions. Numerous research projects have been carried out In order to shed light on this idea; they will be discussed in this essay.

Answer to the assigned question:

In my opinion the answer to the assigned question per se is YES, an extended conformation is needed at the moment of forming a polymer bridge and forming a strong attachment between two surfaces in a fibrous suspension. But, what is next? What about immediately after the polymer bridge has been formed? What is about the conditions that this fibrous suspension is subject to?
Logical or theoretical support for answer:

When talking about the importance of conformation of the polymers, one of the main aspects to think about is the reconformation of the polymer after the induced flocculation. Since the papermaking process is not a steady process, and it is subjected to different levels of hydrodynamic shear, it is not possible to assign only one mechanism as responsible for the flocculation of the system. In fact, a combination of mechanisms is needed in order to explain the importance of the conformation of the retention aids molecules by the time to form a strong attachment between surfaces.

Other factors to consider as regard to this issue is the contact of time between the polymer and the furnish, the molecular mass of the polymer, and the kinetics of its adsorption. Effectively, it is necessary that the conformation of the retention aid needs to be extended in order to be effective at the moment of the flocculation, but definitely, the conditions that this flocculation is taking place, change the conformation of the polymer and as consequence, the mechanism of retention also changes during the wet-end papermaking step.

Experimental support for the answer:

The initial adsorption of the polymer on surfaces of fibrous suspensions is completed in just the first seconds of contact. During this time, the high-mass cationic polymer presents an extended conformation with loops and tails [2]. That characteristic provides the retention aid molecule with its characteristic effectiveness as a flocculant. The extended conformation confers to the polymer lesser free energy of adsorption, which makes possible the formation of “bridges” between two surfaces. During the first five seconds or so, electrostatic interactions between the negatively charged surfaces and the cationic polymer induce to its reconformation into a flatter conformation and further penetration into the fiber walls. This fact was deduced by Forsberg et al. [3] who studied the effect of the contact time of different retention aids in a fibrous suspension and its effect in drainage rate and fines retention.

Other studies of reconformation and penetration were also performed by observing the behavior of cationic retention aids as a function of the contact time under turbulent conditions and the kinetics of the adsorption. Ödberg et al [4] found that there is a higher probability of collisions frequency between two surfaces when the fibers have been quickly covered with a monolayer of random coils. This is consistent with the bridging model of flocculation.

There is some evidence that after a certain time applying relatively high hydrodynamic shear, some of the polymer chains break into lower molecular masses [4]. According to the adsorption isotherms, the initial adsorption of the polymer agrees with the mechanism of bridging flocculation. Furthermore, with the reconformation of the polymer after time, the predominant mechanism is charge neutralization by patch formation [5].

There is an original work published by Nanko et al. [6] where they using TEM technique to try to observe and demonstrate the differences in the adsorption behavior and conformational characteristics of some retention aids in cellulosic fibers. This kind of method has never been used to directly measure polyelectrolyte conformation on cellulose surface. These authors show a set of interesting TEM microphotographs claiming that the retention aid used (polyacrylamide), may take the form of simple extended strands and form bridging polymer. This is an interesting work and marks a trend as regards to the fact of actually see the conformation of the polymer, but in order to make the results more reliable, other kinds of experiments have to be done in parallel.

Situations in which the findings can be useful:

The findings related to this topic, can be used in an effort to obtain a correct understanding and eventual optimization of addition points of additives in general. The conformation of the polymer under the papermaking process conditions is of high importance relative to the main concerns of the wet-end operations: retention, drainage and formation. Retention aids, their addition points, and their interaction with different additives plays an important role in these three parameters and the understanding of its behavior, once added to the furnish, is fundamental when some modification in the process needs to be effective.

Literature cited:

[1] Jaycock, J., Swales, D., “The theory of retention” Roe Lee Paper Chemicals Co. Paper Technology 35 18: 26 (1994).
[2] WPS Part 4: Chemical additives
[3] Forsberg S., Strom G., “The effect of contact time between cationic polymers and furnish on retention and drainage (Polyacrylamides and cat starches)”, Journal of Pulp and Paper Science: Vol. 20, No. 3, 71:76 (1994)
[4] Odberg L., Tanaka, H., Swerin A., “Kinetic aspects of the adsorption of polymers on cellulosic fibers”. Nordic Pulp and Paper Research Journal 8(1): 6 (1993).
[5] Solberg, D., Wagberg, L.“On the mechanism of cationic-polyacrylamide-induced flocculation and re-dispersion of a pulp fiber dispersion”. Nordic Pulp and Paper Research Journal Vol. 18. N01. 51:54 (2003s)
[6] Nanko H., Pan S. “Visualization of polymer adsorption on pulp fiber 1: Polyacrylamide ”

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Name: Rachel Ernest
Date: April 2008

Topic: “Reasonably design a retention aid treatment program that is strong enough to retain almost 100 percent of the fine material onto fiber surfaces, but weak enough that the fiber flocs are easily broken down under flow conditions existing in a paper machine headbox.”

Introduction

Papermakers strive to improve their systems, especially in the areas of retention and formation in the wet-end of the paper machine. Retention is particularly important because poor retention could result in slower drainage, two-sidedness, unstable basis weight, deposits, insolubility, high conductivity, etc. [9, pg 9.2]. Poor formation could result in decreased paper strength and visual properties, as well as poor paper machine runnability, printing, and other converting applications.

Many research projects have focused on developing a retention aid treatment program that is designed to provide contacts between solid surfaces that are strong enough to retain almost 100% of the fine material onto fiber surfaces, but weak enough that the fiber flocs are easily broken down under conditions of flow existing in a paper machine headbox. Based upon the literature, this essay discusses the use of retention aid systems that form flocs that are easily broken in moderate shear conditions. Moreover, it is also proposed to use a general retention aid program that could offer high retention rates and reduced negative effects on paper sheet formation and uniformity without the need to rely on fiber floc breakdown in the headbox. Although the final proposed solution in this essay may not directly address the topic question, as it was originally written, the ultimate goal of breaking up fiber flocs (wherever it may happen) is to improve paper formation and uniformity while still retaining fine material.

Retention is usually accomplished through either sieving or colloidal mechanisms. Sieving mechanisms occur when material is big enough to be sieved by the fiber mat (usually do not require retention-based chemical additions). Colloidal mechanisms can occur even when material is too small to be sieved by the fiber mat; these systems rely upon either charge neutralization or flocculation. Charge neutralization is a relatively weak retention aid program, whereas flocculation can lead to substantially higher retention. Unfortunately, as retention increases, generally so do the floc sizes and the cloudy appearance (high point-to-point basis weight variations) in the paper sheet.

Figure 1: Retention mechanisms [10]

Britt and Unbehend [3] first described fiber flocculation in terms of soft flocs and hard flocs. Soft flocs are generally formed via charge neutralization and the patch mechanism (Fig 1). They break down at moderate shear levels but reform once shear levels diminish. On the other hand, hard flocs are products of the flocculation and bridging mechanisms (Fig 1). Hard flocs are stable at moderate shear, but they break down irreversibly at high shear. Hubbe [8] has supported “selective deflocculation” which explains that the shear required to remove fine material from fibers is much higher than the shear required for breaking fiber-fiber flocculation. Therefore, the size and tenacity of flocs cause variations in fine material retention and formation.

Formation is a somewhat subjective measurement that depends on what the analyzer deems as good formation. In research, formation number (larger numbers mean better formation), floc size (smaller flocs relate to better formation), and flocculation index (lower numbers mean better formation) are all commonly used to describe the formation of flocs and the uniformity of the paper sheet. Due to the differing analytical methods, comparing the research results of various formation studies is quite challenging. When using formation number, results lower than a formation number of 50 might be considered poor formation. For floc size, most papermakers would prefer to have small flocs (less than 1 mm) [9] that are uniform in size. High flocculation indices have shown to have negative effects on strength properties [14], especially if the index grows larger than about 0.5 on a relative scale.

Retention Aid Systems

Chemical retention aid systems are usually arranged into five categories: 1) charge neutralizers, 2) cationic polymers, 3) non-ionic, 4) dual component, and 5) micro-particle systems.

Charge neutralizers are highly dependent upon conductivity and overall charge of the furnish. This type of system forms soft flocs that readily reform with reduction in shear, so it is important to break them down either in the headbox (by using a tube expansion device [15]) or with special jet-to-wire configurations (“pressure forming” jet impingement [9]). However, it is important that a tight mat not be formed too quickly (causing poor dewatering), and the papermaker must also consider the influence of fiber alignment on the paper’s end use. Tripattharanan et al. [25] found in their studies that charge neutralization has little consequence on fines retention.

Cationic polymers include starches, PEI, and acrylamide products. Depending on the polymer applied, the binding mechanism is different: charge neutralization (polyDADMAC), charged patch (PEI), or bridging (cationic polyacrylamide, called c-PAM) [25]. Adding the polymers before extremely high-shear could result in decreased retention [26] and increased paper sheet uniformity (and vice-versa for adding after high shear [11]). These cationic polymer systems are affected by both polymer charge [2] and conductivity [5]. If the system becomes too charge-neutral (caused by over-dosage) through complexes with the cationic additive, then the retention aid programs will be less effective [9, pg9.12].

Non-ionic retention systems use a very high-mass polymer, such as polyethyleneoxide (PEO), added to a furnish containing a soluble phenolic cross-linking cofactor, such as lignin to maintain the entanglement of the polymer. These high-mass polymers form association-clusters [27] between fine materials and fiber surfaces. Gibbs et al. [6] has also found that higher DCS levels can actually improve efficiency of non-ionic retention aides. With the drive for more closed-water systems (potentially higher DCS levels), non-ionic retention aids show promise. Quite high first-pass retention has been reported with various derivatives of non-ionic systems [16], but little work has been published on floc tenacity or formation affects.

Some of the highest retention levels sometimes result from the dual polymer systems [3, 11]. High-charge cationic polymers are usually added before the pressure screens to attach to anionic fibers. Next, high-mass anionic polymers can be added after the pressure screens to create bridges with the cationic anchoring sites [9, pg9.14]. Flocs formed by dual polymer systems do have some shear sensitivity (but not at the weak shear conditions in the head-box). Therefore, large flocs (2-4 mm diameter) often remain even after shear [28]. These large, strong flocs retain fine materials, but they also create tenacious flocs and cause poor formation (Fig 3) [19].

In micro-particle systems, the bridging mechanism is predominant. A cationic polymer (usually c-PAM or cationic starch) is combined with an anionic micro-particle with a high aspect ratio (such as bentonite or colloidal silica). Swerin et al. [22] reported that applying high sheer (versus normal low shear) after the chemical combination showed negligible differences in flocculation levels. More commonly [12], though, the cationic polymer is added before the pressure screens where the fiber-to-fiber complexes of the hard flocs can be broken, but the fillers are still retained by the polymer bridges. After the pressure screens, the micro-particle is added to pull the chains of the cationic polymer closer to the fiber surface. This contraction of the polymer bridge creates a strong binding of fillers and fines to the fiber surface which are resistant to the headbox shear. Since the majority of the fiber flocs are broken in these retention systems before the headbox, there is little focus on whether the moderate shear of the headbox will disperse the flocs. These micro-particle systems are sensitive to extractive levels [13], so a sacrificial high-charge cationic additive may be used to increase effectiveness. [23]

Moderate Shear Effects

Shear conditions in the headbox can have significant effects on retention levels and floc dispersion. Tam Doo and coworkers developed a shear stress comparison of various headbox components and Dynamic Drainage Jar stirring speeds (Fig 2) [24]. Most of the headbox shear levels are at or below the “moderate” shear levels (~500 rpm) commonly used by researchers to analysis retention levels and floc size. Britt and Unbehend found that even systems with no retention aid had fines retention levels of at least 55% at these shear levels [3]; however, they did not directly measure the floc dispersion at their tested shear levels nor did they test retention of fillers.

Figure 2. Shear stress by headbox components and DDJ

A study by Tripattharanan et al. [25] has compared retention mechanisms in shear conditions. His work showed that a charge neutralization model (based upon polyDADMAC) did not improve retention even at moderate shear conditions. However, experiments with ethyleneimine (modified PEI) showed improved retention at both moderate and high shear conditions. Fiber-to-fiber contact caused by PEI-induced charged patches are expected to disperse in moderate shear as found in a headbox. Another group of researchers [1] found that the size decay of flocs induced by c-PAM are strongly dependent upon stirring speed, but 750 rpm (equivalent to flow distributors) decays the size of flocs much more quickly than lower impeller speeds. [1] Therefore, it might be recommended that with a c-PAM retention aid, a headbox should be fitted with flow distributor devices. Hubbe completed a series of projects to determine the minimum shear required to remove particles from surfaces. He demonstrated that by using c-PAM, shear stresses of nearly 7,000 Pa are required to dislodge TiO2 filler (~100 nm) and about 1,000 Pa for CaCO3 (~400 nm) [8]. Both these values are significantly above the shear stresses found in the headbox.

MIicro-Particle System

Of the five retention schemes mentioned, it is believed that the micro-particle system offers the highest retention with the least negative effect on formation. Unfortunately, no retention aid system reported in the literature creates 100% retention (particularly first-pass retention) and excellent formation. However, even if a papermaker can retain a high percentage of the small filler particles, then the adverse affects of low first-pass retention can be minimized.

As mentioned earlier, Hubbe demonstrated that a particle with a smaller radius will be less likely to detach from the fiber surface during shear [8]. This theory is commonly called selective deflocculation, and it describes how fiber-fiber adhesion can be broken by high shear while filler-fiber adhesion can remain intact. In the micro-particle systems, the fine material and fiber polymer bridges are strong enough to resist high-shear – the high shear even tends to create smaller flocs [21] which can lead to better paper sheet uniformity.

In two studies [18, 19], researchers have illustrated that traditional micro-particle programs have roughly the same affect on formation at varying levels of retention. As shown in Figure 3 and Figure 4 below, as retention increased, the formation decreased at relatively the same rates for all retention aid programs (Smith used handsheets and Svedburg used a pilot paper machine).

Interestingly, though, researchers have discovered that instead of the traditional high-mass linear cationic polymer, a low-mass moderately-charged branched cationic polymer can be used as the cationic polymer in a micro-particle system. Shin et al. [16, 17] have shown that these branched polymers create small, tenacious flocs that are not broken apart by shear levels, but they are initially small enough to not adversely affect formation. Therefore, the retention levels are kept high (Fig 5) while not sacrificing formation (Fig 6). Another positive consequence of these small tenacious flocs is that addition schemes are not as important because high shear is not necessary to break apart the flocs. This research has revealed that branched polymers work more effectively if colloidal silica is used rather than the more widely accepted bentonite. Inadvertently, Swerin et al. [22] support Shin et al.’s findings that moderately charged polymers are more effective with colloidal silica. Also, Shin et al. found that these small flocs were quite homogeneous which can create the illusion of better formation because there will be less point-to-point basis weight variation in the paper sheet.

Figure 3: Retention and formation by various retention aid systems, handsheets [19]

Figure 4: Retention and formation by various retention aid systems, pilot machine [20]

Figure 5: Retention levels for cationic polymer micro-particle systems [17]

Figure 6: Formation measurements for cationic polymer micro-particle systems [18] Another research group, [4] have also looked into cross-linked cationic polymers, but their results were not as positive as the branched polymers. Unfortunately, though, they did not use colloidal silica in their work, so it is difficult to compare their results to Shin et al.

Conclusions and Recommendations

In developing a retention aid program, increased retention and decreased flocculation of fibers is vital for proper paper machine runnability and to meet product specifications. Shear conditions in the headbox are able to disperse fiber flocs formed by cationic polymers (such as PEI) while still maintaining adequate retention levels. However, many papermakers are wary about waiting until the last piece of the approach flow system to break apart fiber flocs – especially soft flocs which have a tendency to quickly reform once shear levels decrease. Therefore, in reviewing the available research an effective system to reduce fiber flocculation and increase retention might be to use a highly-branched, moderately-charged cationic polymer followed by an anionic colloidal silica. Possibly adding a sacrificial cationic material (such as alum, starch, or PAC) would increase the effectiveness of the branched cationic polymer. This system should result in small uniform flocs that are resistant to shear (so fillers remain intact) and should be more favorable to better formation and uniformity.

Due to the commodity nature of the paper industry, as well as the drive for more closed-loop mills, retention and formation are of paramount importance to a papermaker. A recommendation for more research that directly addresses the inter-play between these two variables should be undertaken. Research seems to be moving more toward high shear work, but it is important to also look at the effect of moderate shear levels on retention aid programs. In the areas of micro-particles, only a handful of groups have studied the branched or cross-linked cationic polymers, yet they seem to show great promise in the struggle for the balance in retention and formation. Expressly, more research is needed in the affect of different micro-particles. Also, it would be interesting to see research on optimum refining levels with various retention aid programs. Beyond refining, it could be beneficial to look into different refining levels and furnishes (hardwood to softwood to recycled content ratios) since these different processes and fibers have inherent affects on formation. A final recommendation would be to normalize the reporting of formation so that comparison of research results can be more accurately compared. Retention aids and their formation outcomes certainly require more attention, but many researchers have laid the groundwork for many promising systems.

References

Alfano, J.C. et al. (1998): Characterization of the flocculation dynamics in a papermaking system by non-imaging reflectance scanning laser microscopy (SLM). Nordic Pulp Paper J, 13(2), 159-165.
Beaudoin, R. et al. (1995): Performance of wet-end cationic starches in maintaining good sizing at high conductivity levels in alkaline fine paper. J Pulp Paper Sci, 21(7), 238-243.
Britt, K.W. and Unbehend, J.E. (1976): New methods for monitoring retention. TAPPI J, 59(2), 67-70.
Brouillette, F. et al. (2005): A new microparticulate system to improve retention/drainage in fine paper manufacturing. Appita J, 58(1), 47-51.
Buontempo, J.T., et al. (1996): Effects of salts on the performance of cationic flocculants used as retention aids for alkaline fine paper. TAPPI Papermakers Conf., 49-58.
Gibbs, A. et al. (1999): The influence of dextran derivatives on polyethylene oxide and polyacrylamide-induced calcium carbonate flocculation and floc strength. Colloids and Surfaces A, 159(1), 31-45.
Hedborg, F. and Lindström, T. (1996): Some aspects on the reversibility of flocculation of paper stocks. Nordic Pulp Paper J, 11(4), 254-259.
Hubbe, M.A. (1986): Retention and Hydrodynamic Shear. TAPPI J, 69(8), 116-117.
Hubbe, M.A. (2007): Flocculation of cellulose fibers. BioResources, 2(2), 296-331.
Hubbe, M.A. (2008): Wet-end & colloidal chemistry coursepack. NCSU WPS 527.
Hubbe, M.A. and Wang, F. (2002): Where to add retention aid: issues of time and shear. TAPPI J (1), 28-33.
Hubbe, M.A. et al. (2001): Reversibility of polymer-induced fiber flocculation by shear. 2. multi-component chemical treatments. Nordic Pulp Paper J, 16(4), 369-375.
Johansson & Wallin (1994): Proc 79th CPPA, A347.
Linhart, F. et al. (1987): Monitoring and control of formation by means of a fibre optic flocculation sensor. Wochenbl. Papierfabr., 115(8), 331-338.
Nordström, B. and Norman, B. (1994): Influence of headbox nozzle contraction ratio on sheet formation and anisotropy. TAPPI Engineering Conf, (1), 225-228.
Peng, X. et al. (2006): Preparation and retention of poly(ethyleneoxide) – grafted cationic polyacrylamide micro-particles. J Applied Polymer Sci, 101(1), 359-363.
Shin, J-H, et al. (1997): Highly branched cationic polyelectrolytes: fines retention. TAPPI J, 80(10), 185-189.
Shin, J-H, et al. (1997): Highly branched cationic polyelectrolytes: filler flocculation. TAPPI J, 80(11), 179-185.
Smith, J.H. (1991): Laboratory comparison of various multi-component retention aid systems. TAPPI Papermakers Conf, 481-499.
Svedberg, A. (2007) Valuation of retention/formation relationships using a laboratory pilot-paper machine. Diss. Royal Institute of Technology, Stockholm, Sweden.
Swerin, A. and Ödberg, L. (1993): Flocculation and floc strength in suspensions flocculated by retention aids. Nordic Pulp Paper J, 8(1), 141-147.
Swerin, A. et al. (1993): Flocculation of cellulosic fibre suspensions by model microparticulate retention aid systems: Effect of polymer charge density and type of microparticle. Nordic Pulp Paper J, 8(4), 389-398.
Swerin, A. et al. (1996b): An extended model for the estimation of flocculation efficiency factors in multicomponent flocculation systems. Colloids Surf, 113(1-2), 25-38.
Tam Doo, P.A., et al. (1984): Estimates of maximum hydrodynamic shear stresses on fibre surfaces in papermaking. J Pulp Paper Sci., 10(4), J80-J88.
Tripattharanan, T. et al. (2004): Effect of idealized flow conditions on retention aid performance. 2. polymer bridging, charged patches, and charge neutralization. Appita J, 57(6), 448-454.
Tripattharanan, T. et al. (2004): Effect of idealized flow conditions on retention aid performance. 1. Cationic acrylamide copolymer. Appita J, 57(5), 404-410.
Van de Ven, T. et al. (2005): Association-induced polymer bridging by poly(ethyleneoxide) – Cofactor flocculation systems. Advances in Colloid and Interface Science, (114-115), 147-157.
Wågberg, L. and Lindström, T. (1987): Some fundamental aspects of dual component retention aid systems. Nordic Pulp Paper J, 4(2), 49-55.

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Name: Magaly A. Ramírez
Date: April 3, 2008

Topic: “When selecting a retention aid for papermaking system at neutral or weakly alkaline pH, in which there is a high level of anionic dissolved and colloidal substances (DCS), does it make more sense to use (a) a high-charge density cationic retention aid so that it over-powers the negative charges in the system, (b) a low- charge density cationic retention aid so that it does not form a strong complex with the DCS, (c) pretreatment with a high-charge-density cationic polymer, or (d) some other strategy involving cationic acrylamide copolymer retention aid?”

Why this subject is important: Retention is the process of keeping fine particles and fiber fines within the web of paper as it is being formed. Good retention is important to the efficiency of papermaking operation due to the large influence it has on furnish and production cost, as well as on the quality of the finished sheet. Low retention can lead to many problems, including poor runnability, increased deposits, sheet defects, higher additive cost, more downtime for wash-ups and higher sewer losses. However, papermakers have been trying to develop some retention aids in order to solve these problems. Retention aids are known to be effective for improving the retention of fines particles during formation of paper. Some examples of retention aids used in the papermaking industries are inorganic retention aids (aluminum salts), cationic starch, organic macro-molecules, polyacrylamides, polyethyleneimine and multi-component systems. However in the presence of anionic dissolved and colloidal substances, the performance of these retention aids can be affected. This is one of the reasons why the selection of a good retention aid has been so challenging for papermakers.

Answer to the assigned question: According to the information found in the literature the behavior of retention aids remains unclear. It has been found that the cationic polyacrylamide polymer performs well in the papermaking process and also the pretreatment of the system with this polymer as a flocculant can improve retention. However, it is difficult when it comes to discuss the behavior of a high charge density cationic retention aid compared to a low charge density cationic retention aid. Results in the literature can be found to be contradictory since both types of cationic retention aids have demonstrated good performance in the papermaking process. However, it is important to keep in mind that when selecting a retention aid for papermaking system, other than paying attention to the charge density, we have to be aware of the papermaking conditions we are going to use. And that is one of the reasons it can be difficult to decide whether a type of retention aid is effective when it is compared to other type of retention aid that have been used under completely or slightly different papermaking conditions.

Logical or theoretical support for answer: According to Jaycock et al (1994), at low adsorption densities polymer chains can bridge two particle surfaces or give patch interaction, but at higher adsorbed polymer densities the chains cannot interpenetrate sufficiently for bridging or patch interaction to be possible, repulsion drives the particles apart before this can happen. When repulsive forces exist between two particles, the Gibbs free energy, ∆G, of the system has to increase. The proximity of two high molar mass charged polymers will result in an increase in ∆G. At the same time the entropy decreases. This explains why low dosages of cationic polymer can lead to good retention and too high a dosage to a poor one. However, when dealing with retention aids is important to consider papermaking conditions. If we think about a system in the presence of salts, even they don’t have any effect in alkalinity or acidity of solution, they can raise the repulsive forces within a system. In this specific case we can apply the theory proposed by Jaycock (1994) and we can say that a system in the presence of high amount of salts can lead to a poor retention due to repulsive forces. This is just one example in order to understand the problems that can result due to a variety of papermaking conditions.

Experimental support for answer: Several research projects have been performed in order to understand and improve the retention of fiber fines within a web. Allen et al. (2000) demonstrated the effect of high cationic charge density polymers on retention. As part of their research project they studied the ability of some compounds called dendrimers which are small molecules with a star like structure that have shown to be more resistant to shear when compared to linear polyacrylamide. Two kinds of dendrimers were used, ethylenediamine (EDA) and diaminobutane (DAB). According to the results obtained both types of dendrimers showed effectiveness as retention aids. DAB increased the first pass retention for about 15% while the EDA increased it for about a 7%. Even the increase of the FPR with EDA was not as high as with DAB its use is more convenient since EDA cost less than DAB. Since the increase of the FPR with EDA was lower than for DAB they decided to add flocculant (C-PAM) in order to improve the FPR. The results showed that addition of C-PAM increased the FPR but not as much as the DAB did. This project has to be followed up since there is not a possible explanation of the behavior of the two types of dendrimers in the discussion section of the paper. A possible reason could be the difference in structures of both polymers and the papermaking conditions where they were applied. Other research performed by Nurmi et al. (2004) studied the interaction between cationic polyacrylamide and DCS. It has been found that cationic polymers form neutral complexes with dissolved and colloidal substances. The complexes can be adsorbed on the colloidal particles in the suspension and stabilize them both sterically and electrostatically. One of the objectives of the work performed by Nurmi et al. (2004) was to separate the dissolved and colloidal fractions of the pulp water from each other and to examine the interaction of the permeate and retentate fractions with C-PAM. These fractions were separated using cross flow filter with different pore sizes (0.1μm, 0.45μm, 0.65μm). The 0.45μm retentate fraction was mixed with different charge density cationic polyacrylamides. This fraction was chosen because of its high content of extractives. Results showed that particles size increased with increased amounts of C-PAM due to particle flocculation. However, the C-PAM polymer with the lowest charge density (1.2meq/g) was more effective increasing the particle size and resulting in best fiber fines retention. C-PAM polymer (2.2meq/g) and C-PAM polymer (3.4meq/g) showed increase in particle size. However, C-PAM polymer (3.4meq/g) showed an increase in particle size higher than C-PAM polymer (2.2meq/g) after a 0.10% of polymer addition. Explanation to this behavior was not found. However they concluded its project saying that C-PAM increased the particle size and lead to flocculation. I recommend a further study in order to understand better these results. In addition to this research project there are some other research projects that focus on polymer charge density in order to improve their retention effectiveness. Research performed by Tanaka et al. (1999) studied the effect of charge density on adsorption of C-PAMs onto cellulose beads. According to the results the rate of adsorption of C-PAM decreased significantly with increasing charge density. These results are probably due to the more extended conformation of DC- PAM than that of C-PAM with low CD. There was also a slower penetration of polymers with higher CD into pores. In the case of C-PAM2 with medium CD, the adsorbed amount at zero time was almost the same as that of the other C-PAMs. As part of their research, they also studied the competitive adsorption of these polymers in cellulose beads and cellulose fibres. In the competitive adsorption of mixed polymers (C-PAM + DC- PAM) onto PSL, the total amount of charges adsorbed were practically the same as in the individual adsorption. It was expected that there would be a preferential adsorption of the C-PAM having the highest CD, but the results indicated the opposite tendency. The authors justified this behavior explaining that the adsorption of C-PAM onto negatively surfaces was governed by shear-induced collisions. The reader is left wondering if the author’s conclusion applies for all types of polymer or if this is just an interpretation for this specific case. Why the shear collisions induced a high adsorption amount of the polymer with lower CD (charge density) and not the one with the higher CD? This concepts need to be study in detail.

Situations in which the findings can be useful: It is difficult to say whether or not these findings can be useful. Most of these projects were carried out under different papermaking conditions and this can be an explanation to the diverse experimental evidence found in the literature. Retention aid polymers include a variety of structures that can lead to different behaviors under certain papermaking conditions. For future work it is recommended to study the mechanism of different cationic charge density polymers varying the papermaking conditions. Some other recommendations include the comparison of homogeneous and heterogeneous systems and the study of multicomponent systems.

Literature cited

Jaycock, M., and Swales, D., “The theory of retention,” Paper technology 35 (12): 26 (1994).
Nurmi, M., Byskata, J., and Eklund, D., “On the interaction between cationic polyacrylamide and dissolved and colloidal substances in thermomechanical pulp,” Paper and Timber 86 (2): 109 (2004).
Tanaka, H., Odberg, L., Swerin, A., and Park, S., “Competitive adsorption of cationic polyacrylamides with different charge densities onto polystyrene latex, cellulose beads and cellulose fibres,” Journal of pulp and paper science 25 (8): 283 (1999)
Allen, L., and Polverari, M., “Dendrimers: A new retention aid for newsprint, mechanical printing grades, and board,” Nodic Pulp and Paper Research Journal 15 (5): 407 (2000)
Liu, J., “Papermaking technology evolution: Its impact on wet-end retention,” Paper technology (October 2005)

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Name: Kelley Spence
Date: April 22, 2008

Topic: “Does it make practical sense to use multicomponent retention aid programs under less challenging situations, such as when the cationic demand of the furnish is low, the basis weight is pretty high and shear levels are not excessive?”

Topic background: Multicomponent retention aid systems composed of a cationic acrylamide copolymer, a microparticle, and other additives such as alum, are increasingly being used in mills that are implementing new papermaking technology – particularly paper machines with higher reel speeds. Paper machines have reached their maximum practical sheet width and, as a result, increasing the production rate relies solely on increasing machine speed. Increasing machine speed requires faster dewatering rates, but many machines have reached this maximum as well. Increasing drainage and retention in order to increase machine speed typically has a negative effect on formation uniformity because the three variables are interrelated [4].

The retention aid system is the most sensitive chemical component of the wet-end; it is more sensitive to furnish fluctuations than other added chemicals [4]. Improvements in retention aids, such as the use of a multicomponent retention aid system can decrease this sensitivity and promote wet-end stability, resulting in decreased machine downtime. Several potential advantages of a multicomponent retention aid system are as follows: decreased cost of retention aid chemicals, increased retention of fines and fillers, improved effluent clarification, more uniform product, and increased dewatering speeds [5]. They can also increase the performance of the retention polymer in the presence of high quantities of anionic trash and other dissolved colloidal materials. Microparticle systems in particular are known for their ability to “clean-up” the white water loop by retaining the suspended and dissolved solids in the sheet instead of recirculating them in the loop [1].

Why this subject is important: The subject of multicomponent retention aid programs is important to the paper industry because improving drainage and retention generally decreases formation uniformity which could ultimately harm the final product properties. Multicomponent systems are able to improve drainage with minimal negative effects on formation. The multicomponent programs however are typically used on fast machines with low basis weights or a furnish with a high cationic demand (i.e. tissue); they could potentially be useful for other types of machines and grades such as an older (slower) machine producing recycled box board under severe drainage restrictions. Implementing a multicomponent retention aid system on a machine making higher basis weight products with a drainage limitation could potentially improve drainage and increase machine speed, something that all papermakers are trying to accomplish. On the other hand, using a multicomponent retention aid system on a machine in which the cationic demand of the furnish is low and the shear levels are not excessive may not be feasible.

Answer to assigned question: Based on the literature search, there is no evidence that using a multicomponent retention aid system on a machine with high basis weight products would hurt formation; the addition of the system could potentially improve drainage and increase machine speed. Adding the multicomponent system to a machine with a low cationic demand furnish and low shear does not appear to be as feasible. Adding a microparticle to a system with low cationic demand may cause a charge reversal in the system. Adding the system to a machine with low shear may result in larger, hard flocs, decreasing sheet uniformity and potentially harming mechanical properties of the final product.

Based on mill experience, it is not likely that multicomponent retention systems would be utilized. First, trials would have to be performed to determine which components and at which dosages would be optimum for each machine. This would cost the mill time and money. After trials were completed and enough data gathered to determine which components and dosages to use, the customer would need to inspect the sheet to determine if the chemicals had negative impacts on their required end use specifications.

Theoretical support: Many have hypothesized that patch, bridging, and complex types of mechanisms occur during flocculation. The most popular hypothesis appears to be the site-blocking effect (patch) and polymer bridging. It is hypothesized that coagulant adsorption onto a fiber surface blocks adsorption sites for the flocculant, preventing the flocculant from reconforming on the surface during and after high shear turbulence (Figures 1 and 2). Decreasing the addition interval between the coagulant and the flocculant also results in a higher effectiveness [3]. Microparticles promote flocculation but they block normal bridging sites. It is expected that these two mechanisms are the reason that multicomponent retention aid systems are successful in improving drainage without harming formation.

Figure 1: Site blocking effect [3, 7] Figure 2: Reconformation [3, 7]

It has been shown that the order of addition in a multicomponent retention aid system is very important ( Figure 3). According to Wå gberg, polymer bridging is the most important type of flocculation which occurs when the cationic polymer is allowed to adsorb onto the fiber surface first before adding the other polymers [8]. Multiple components of the retention aid system added in sequence result in synergistic effects on flocculation and the formed flocs are able to withstand high shear forces [7]. This observation proves that multicomponent systems must be thoroughly tested to determine optimum conditions.

Figure 3: Order of addition effects [8]

In the case of heavy weight paper and paperboard, rapid drainage is often important for maintaining high machine speeds, but formation must remain uniform to avoid negative effects on product properties [1]. In this situation, it is expected that more fines, fillers, and other particles will be retained through the filtration method (mechanical entrapment through the wet-web and the forming fabric) because they will have a thicker wet-web to travel through [4]. Adding a multicomponent retention system is likely to improve drainage rates so that the machine speed can be increased; however it is unknown if the system will have an effect on formation. It has been shown that high total and first-pass ash retention along with rapid initial drainage can result in the sheet forming too early on the forming table, resulting in adversely effected sheet formation and poorer sheet properties [2].

The operators of newer paper machines often implement multicomponent retention aid systems because they have higher production rates and, as a result, higher shear forces during the stock approach and on the forming table. These forces are likely to degrade flocs that are produced using a single component retention aid system because they are not typically strong enough to withstand excessive shear forces [4]. High molecular mass cationic polymers are typically used as the retention polymer and they are theorized to operate in a patch type or a bridging type of flocculation which are both sensitive to excessive shear. The addition of an oppositely charged polyelectrolyte can be added to make the flocs more shear resistant [8].

Finally, in the case of a machine with a high cationic demand furnish, the use of alum, bentonite, or a fixative in conjunction with a high molecular weight and a cationic high- charge density polymer results in a decrease in the adverse effect of the dissolved and colloidal particles in the furnish on the retention polymer [4]. Paper mills are continually closing the water system, and this closure results in increased concentrations of dissolved anionic wood-polymers, inorganic substances, and dispersed materials that can complex with the cationic polyelectrolyte, decreasing its effectiveness and requiring larger dosages to reach the same retention level [8]. Converting to a multicomponent retention aid system with bentonite, for example, has shown that the bentonite particles have the capability to adsorb colloidal materials (anionic and nonionic) in the furnish, decreasing adverse effects on the retention polymer and resulting in a furnish that is “cleaner” because it has less colloidal trash freely suspended in the aqueous phase [2].

Experimental support: Many multicomponent systems have been proven to work on newer paper machines. The TELIOFORM system by Ciba Specialty Chemicals has been optimized for high-speed machines under high whiteness and high ash conditions [4]. The system originated by discovering that a synergistic effect is observed when microparticle systems, anionic linear polymers, and micropolymers are used together [2]. Laboratory results are shown in figure 4 for fine paper. The new system has the best drainage, with the exception of bentonite alone.

Figure 4: TELIOFORM results [2]

Machine trials of the system showed that it was successful in decoupling drainage, retention, and formation. On a wood free coated paper machine, the first pass ash retention was improved, increased wet-end stability resulted in less machine downtime, and the machine speed was increased by 120m/min. On a Fourdrinier producing 45 to 120 grams/meter2 white top board, the system improved runnability, increased machine speed, and decreased headbox solids without having a negative affect on formation [2].

The Mosaic system composed of a coagulant/flocculant with an inorganic synthetic engineered polymer has been shown to improve drainage and retention with out harming sheet formation. The system has also resulted in a large reduction in TiO2 usage in fine paper and it works extremely well with a furnish that has a high cationic demand with large amounts of anionic trash [1].

The HSR-Tester can be used to predict retention, drainage, and formation properties of a furnish and the results can be related to a twin wire paper machine. Results of the HSR-Tester on various types of multicomponent retention aid systems found that some retention effectiveness were effected by dosage of cationic polymer and pulsation (turbulence) frequency whereas others were sensitive to the time delay between dosing the chemicals [6]. The different properties of the retention systems are important to determine in order to relate to industrial machines. Because tests on paper machines in industry can be expensive and not enough testing can be preformed to determine the best solution, the generation of laboratory scale data is more important so that it can be related to the paper machine and fewer trials can be ran to determine the optimum solution [5]. The polymers chosen must be tested to determine if they have a positive synergistic effect on the paper machine system, based on the machine characteristics and the furnish characteristics [5].

It has been shown by Lui et al., that increasing basis weight results in better first-pass retention, without changing the retention aid chemicals; the figure shows that lower basis weight sheets are less able to retain fillers and fines without the help of a retention aid [4]. It is expected that lower basis weight sheets would be more affected by the addition of a retention aid than the high basis weight sheets because of the filtration mechanism previously mentioned in the theoretical support section of this paper. It has also been shown that silica based microparticle systems resulted in machine speed increases of around 30%, resulting in a significant increase in production, offsetting the cost of the technology [2].

Situations in which the findings can be useful: Situations in which the findings in this paper can be useful are paper machines that need to improve retention aid effectiveness because of anionic trash in the furnish, machines that need to increase production and are drainage limited, and, finally, machines running low basis weight products. These findings could also be useful in less challenging situations such as a furnish with low cationic demand, high/medium basis weight, and low shear levels. Trials and laboratory experiments for these situations would need to be performed to determine the feasibility of implementing a multicomponent system in these situations. It is likely that the multicomponent system would be feasible for a high basis weight product but it may not be feasible in systems with low furnish cationic demand and normal levels of hydrodynamic shear.

Suggestions for future work: My first suggestion for future work would be to create a HSR-Tester for other types of paper machines. Creating laboratory testing equipment similar to the HSR-tester for Fourdriner type machines could provide valuable information on how different components of the multicomponent retention aid could affect drainage, retention, and formation on Fourdriner machines. After obtaining this information, I suggest to run multiple mill trials on machines that exhibit less challenging situations such as high basis weight, low furnish cationic demand, low filler content, and average shear. Mill trials would be able to determine how multicomponent retention systems are affected in less challenging situations, and potentially lead to a better understanding of how they work in challenging situations, such as low basis weight, high furnish cationic demand, high filler content, and excessive shear.

Literature cited:

Covarrubias, R. et al. “New Advances in Microparticle Retention Technologies.” Appita Journal. July 2002. 55 (4). p 272.
Harris, N. et al. “Decoupling – the Latest Developments in Retention and Drainage Technology.” Retrieved from: http://www.tappsa.co.za/archive2/APPW_2004/Title2004/Decoupling/decoupling.html
Kamijo, Y. and Miyanishi, T. “Retention Aid Chemicals for High Speed Paper Machines.” Japan TAPPI Journal. 56 (6) 2002. p 870-879.
Liu, J. “Papermaking Technology Evolution: Its impact on wet-end retention.” Paper Technology. Oct. 2005. p 31-36.
Petaja, T. “Fundamental Mechanisms of Retention with Retention Agents.” Kemia. Kemi. 1980. Vol. 5. p 261.
Siven, S. and Manner, H. “Multicomponent Retention Systems in Twin Wire Forming.” Appita Journal. Nov. 2001. 54 (6). p 523-526.
Swerin et al. “An Extended Model for the Estimation of Flocculation Efficiency Factors in Multicomponent Flocculant Systems.” Colloids and Surfaces. 1996. Vol. 113. p 25-38.
Wagberg, L. and Lindstrom, T. “Some Fundamental Aspects of Dual Retention Aid Systems.” Nordic Pulp and Paper Research Journal. 1987 (2). p 49-55.

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Name: Justin O. Zoppe
Date: April 22nd, 2008

Topic: “Polyethylene oxide is rather difficult to dissolve in aqueous solution. Some evidence suggests that it can be precipitated out of solution by addition of certain materials called “co-factors.” Would it be fair to say that PEO owes its effectiveness, as a retention aid, to its relatively poor solubility in water?”

Why this subject is important:

In order to retain fines and fillers in the wet-end of the paper machine, papermakers have been using retention aid systems for many years. Retaining fines and fillers is a way to increase the overall quality of the paper product and save manufacturing costs. A retention aid system can be represented by five main classes: charge neutralizers, cationic polymers, dual-component, microparticle, or nonionic. Each of these classes of retention aids uses different mechanisms of fines and filler retention. Polyethylene oxide (PEO) is a nonionic polymer that has been used as a retention aid for over 20 years. Ironically, this polymer is rather difficult to dissolve in aqueous solution, which is the main condition of papermaking. PEO consists of repeat units of ethylene oxide and has been shown to have a variable performance as a retention aid [4]. In order to improve this nonionic polymer’s performance and reduce its variability, a cofactor is used, and this becomes a dual retention aid system. A cofactor is usually phenolic in structure, and when mixed with the furnish, it acts as a performance enhancer for PEO. Another benefit is that lignin byproducts and residual lignin from the wood pulping process can serve as the role of cofactor.

Answer to assigned question:

The fact that PEO is difficult to dissolve in water and there is some evidence that suggests it is precipitated out of solution by addition of cofactors does tend to support the assumption that PEO is more effective in retention the less solubilized that it is.

Logical or theoretical support for answer:

Many studies have been done in order to understand the mechanism of PEO-cofactor dual retention systems. In general, three mechanisms have been proposed: network flocculation, complex bridging flocculation, and association-induced flocculation. The studies done in support of network flocculation were performed in test tubes and at typical PEO dosages; the theory of diffusion-controlled collisions predicts several seconds for network formation. Both of these facts make network flocculation a less likely scenario for papermaking, because the time scale is much smaller in the process. The idea of complex bridging explains interactions with fillers, but PEO does not have a strong affinity for fiber surfaces, because it is uncharged. The association-induced flocculation mechanism, which seems to be the most promising explanation, assumes that a PEO-cofactor complex can adsorb more strongly to fibers and fines [1]. It is also important to discuss the chemical behavior of PEO in solution in addition to the idea of entanglements with cofactors. It is known that PEO behaves strangely, being a nonionic polymer. At higher temperatures, PEO is more difficult to dissolve because of the increased exposure of alkyl parts of the polymer chain in aqueous solution. If temperature is decreased, PEO is more likely to fold on itself with oxygen groups in closer contact with water, causing it to dissolve better [6]. So, this idea can be applied to entanglements between different PEO chains. Entangled PEO polymers will act as a high molecular weight polymer that will not be strongly dissolved, and have more ability to bridge, thus behaving as a better retention aid. Furthermore, PEO-cofactor association complexes will have the same effect as a polymer bridge. In all of these cases, the PEO entanglements or PEO-cofactor complex can extend past the electrostatic double layer to form a proper bridge between adjacent fines for better retention. From these facts, regarding PEO and PEO-cofactor retention systems, I believe it is fair to say that PEO owes its effectiveness, as a retention aid, to its relatively poor solubility in water.

Experimental support for answer:

The work performed by van de Ven, Qasaimeh, and Paris [1] shows significant evidence for the idea of entangled PEO being poorly dissolved in solution and having higher retention of fines. They studied effects of stirring time, stirring intensity, storage time, concentration, and shear on flocculation efficiency of fines. They show that regardless of the concentration of PEO, efficiency of flocculation decreases with increased stirring time. Also, an increased stirring intensity causes a decrease in flocculation efficiency, after an optimum. Efficiency also decreases with increasing storage time, after an optimum of 1 day. They studied the effect of flow rate at an injection port on flocculation efficiency and found an overall decrease in efficiency with increasing flow velocity. All of their evidence suggests that over time, shear, or dilution, PEO entanglements between polymers disentangle into individual PEO coils which are more soluble, and they cannot exceed the electrostatic double layer repulsion between fine particles.

Work performed by Kratochvil, Alince, and van de Ven [3] showed some similar results with clay flocculation experiments. The authors used clay suspensions of 400 mg/L and added PEO and Sulfonated kraft lignin (SKL) cofactor using a syringe after different stirring times of the PEO solutions alone. They presented the data in terms of a stability ratio W obtained by comparing rates of flocculation at an experimental condition to a maximum rate of flocculation in the presence of salt. So, when W goes to infinity, the system remains stable and dispersed. When W is equal to 1, the rate of flocculation is very fast. To find the rate of fast flocculation, the stability of clay suspensions were studied with KCl. They showed the stability ratio W to be decreasing with increasing concentrations of salt. Next, they studied the rates of flocculation in presence of a fresh solution PEO, after stirring PEO solutions for 1 hour, and 1 day. They varied the concentration of polymer from 0.5 to 5.0 mg/g clay. They showed that freshly dissolved PEO flocculated clay particles faster than salt, regardless of the concentration of polymer solution. Solutions stirred for 1 hour showed the typical V-shape curve for polymer bridging. Solutions stirred for 1 day did not flocculate clay whatsoever. This work supports the same idea of entangled PEO or PEO-cofactor complex extending past the double layer to form polymer bridges.

In other work shown by Alince and van de Ven [5], they showed similar results with clay flocculation experiments on fibers with PEO and PEO-SKL. They showed again the importance of initial entanglements of PEO being able to bridge clay and fibers, and after prolonged mixing, the flocculation decreases, because the PEO can no longer extend beyond the double layer repulsion [2]. Work by Carignon, Garnier, and van de Ven showed that the sequence of addition of cofactor versus PEO is an important consideration. They also came to the conclusion that both cofactors studied showed increased flocculation efficiency when complexed with PEO.

Laivins, Polverari, and Allen [4] performed many studies on PEO performance on mechanical pulp furnishes. They studied eight different cofactors and their effect on PEO flocculation performance. Again, for all cofactors studied, they found increased first pass retention of not only fines, but also fillers with PEO. They show some cofactors were more efficient than others with PEO, but retention were increased for all compared to PEO alone. Again, this supports an improved bridging mechanism with a PEO-cofactor system compared to PEO alone.

Situations in which the findings can be useful:

All of these findings can be very useful in choosing a dual retention aid system based on PEO. These studies have all shown that the addition point of PEO should be closest to the head-box because the additive will be exposed to less shearing, and therefore a higher proportion of the entanglements can be preserved (i.e. the polymer remains somewhat less dissolved). The cofactor can be added in the stream before the fan pump because it is not as sensitive to shearing and needs to be well mixed. The studies of Laivins, Polverari, and Allen [4] can help in the decision of which cofactor to choose for a particular dual retention aid system. In general, all findings support the idea that PEO is more efficient in its initial entangled state (less dissolved), and can be assisted by addition of a cofactor to increase its efficiency as a polymer bridge.

Literature Cited

T.G.M. van de Ven, M. Abdallah Qasaimeh, J. Paris, Colloids and Surfaces A, 248, (2004) 151-156
B. Alince, T.G.M. van de Ven, TAPPI Journal, 80 (8), (1997) 181-186
D. Kratochvil, B. Alince, T.G.M. van de Ven, J. Pulp and Paper Sci., 25 (9), (1999) 331-335
G. Laivins, M. Polverari, L. Allen, TAPPI Journal 84 (3): 57, (2001)
A. Carignan, G. Garnier, T.G.M. van de Ven, J. Pulp and Paper Sci., 24 (3), (1998) 94-99
F.E. Bailey, Jr., J.V. Koleske, Alkylene Oxides and their Polymers. CRC Press 1991.

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Name: Hao Chen
Date: Apr 20. 2008

Topic: “What evidence is there that the detailed structure of retention aid polymers, rather than just their molecular mass and charge density, has a significant effect on their performance?”

Why this subject is important:

With the development of faster and more sophisticated paper machines and various chemical additives, papermaking technology has been continuously advancing. Since the presence of high amount of fines in the wet section influences retention, drainage, system closure, etc. promoting proper flocculation between fines, fillers and fibers, therefore improving retention efficiency for economic benefits is desirable. First of all, they don’t want to lose the costly materials that they put into the system so they need to reduce losses of any solids and additives. Re-circulation of white water through effective save-all systems can help with this, but normally, they still need to introduce some sort of chemicals to help with flocculation and retention. [1] Retention aid polymers have a lot to do with the efficient use of raw materials and reduced white water solids. Good first-pass retention can promote less “two-sidedness” in the paper sheet. It can help with retaining higher levels of filler in the paper and better brightness performance. Better retention can give better drainage and cleaner back-water systems as well as help with less filling of the paper machine felts. [2]

Background information of retention aid polymers:

The first retention and drainage programs were based on a single polymeric flocculants component. But In the past years, most specialty chemical companies pay more attention to the development of multi-component systems, because these systems allow the papermaker to achieve a balance between retention, drainage and formation.

Retention aid polymers cause the fibers, fines, fillers and other colloidal particles to form an aggregate by either patch or bridge mechanism depending on their molecular weight and charge density. A general belief is that polyelectrolyte with high molecular weight and low cationic charge density flocculate colloidal particles by bridging formation. Those with low molecular weight and high charge density form flocs by patch formation. Soft flocs formed by the patch formation mechanism are usually small and compact. Upon exposure to high turbulence, the soft flocs break easily, but when the turbulence subsides, the same level of aggregation can reoccur. This shows the reversible of nature of the flocs. To a varying degree, hard flocs formed through a bridging of polyelectrolyte have a loose, voluminous structure. They show some resistance to high turbulence for a short period. They break irreversibly after subjection to longer period of high shear. That means the hard flocs cannot form again after a longer period of high turbulence. Both flocculation mechanisms are therefore insufficient to explain other phenomena in the papermaking process. [3]

The ideal flocs from the papermakers’ viewpoint are those that have compact structure, appropriate size, resistance to shear, and high retention properties. Since most flocs generated by currently used flocculants are either too large or too weak in tenacity against shear. Highly branched cationic polyelectrolytes have been developed to improve filler and fines retention. A branched polymer is different from a linear polymer because it contains several ramifications or branches.

Answer to the assigned question:

Polymer tails determine the hydrodynamic thickness of the absorbed layer almost exclusively. Branches or tails on highly branched polymers may extend into the aqueous medium after absorption. [4] The bridging flocculation of colloidal particle using these stretched tails could occur despite low molecular weight. These special characters allow branched polymers perform better than traditional polymers when concerning retention efficiency.

Experimental support for answer:

Shin et al. [5] studied the particle size distribution curves of GCC and titanium dioxide used in their study with the floc size distribution curves after flocculating with 0.05% of C-PAM 1 (linear structure) and HBC-PAM (branched structure), respectively. Their figures show that unflocculated GCC shows greater average particle size and broader particle size distribution than titanium dioxide. They also found that the size distribution range and average size values reversed when flocculated with C-PAM 1 for 30 minutes. Their study shows greater average particle size and broader particle size distribution for titanium dioxide particles flocculated by C-PAM 1. When the same fillers are flocculated with HBC-PAM at the same conditions, flocs of smaller average size are obtained and the floc size distribution curves also have narrower width. Shin also investigated the effect of shear force on the floc size formed with various polymeric flocculants by changing the pump speed of the particle size analyzer. They compared C-PAM 1with a cationic starch and HBC-PAM. When increasing the pump speed, the average floc size decrease substantially for the linear C-PAM 1. This indicates their limited tenacity against high shear. The average floc size when exposed to strong shear decreases slightly with the cationic starch and remained unchanged with HBC-PAM. This finding indicates that the flocs formed by the branched polymer are smaller but more tenacious than those formed by the linear polymers.

Francois et al. [6] compared the effect of the linear polyacrylamide to the cross-linked and branched polymers at low (1100r/min) and high (2500r/min) rotational speed of the DDJ. Results show that all programs studied are effective at increasing both total (FPR) and (FPRPCC) retention at low and high turbulence levels. In all cases, the branched polymer performs better than the cross-linked and standard polymers. Although all polymers show a significant reduction in both total and PCC retention at higher rotational speed, their studies clearly demonstrated that the branched polymer can withstand higher shear levels compared to the other polymer studied.

Gerli et al. [7] focused on the shear resistance of flocs produced by Core Shell. Experimental results revealed that the initial floc size created by dry polymer decayed much more rapidly than in the case of the Core Shell polymer, which indicated that Core Shell polymer could produce a floc having a higher floc shear resistance. In this period, experiments were designed to compare the floc-shear resistance produced by Core Shell polymer and microparticle system. As showed in a figure, Mean Chord Length data collected after addition of Core Shell was higher and could come to a peak value in a shorter time than those obtained by adding dry polymer in combination with bentonite. Furthermore, the drainage that resulted from Core Shell polymer, under the same furnish conditions, was significantly higher than that produced by the microparticle program. The subsequent research showed that the reflocculation ability of Nalco 8692 was improved when the micropaticle was used in combination with Core Shell polymers. That means Core Shell polymer made the ultra POSITEK microparticle operate more efficiently.

Concluding remarks:

When using branched retention aid polymers as a flocculant for fillers and fine materials, smaller flocs with greater shear resistance are produced compared with the conventional linear polyelectrolytes of high molecular weight.

Literature Cited

[1] Scott, W., Principles of Wet-End Chemistry, TAPPI Press, 1996
[2] Scott, W. Wet-End Chemistry: An Introduction, TAPPI Press 1992
[3] Unbehend, J. E., Mechanism of soft and hard flocs formation in dynamic retention measurement, Tappi J. 59(10):74(1976)
[4] Scheuthens, J.J.H.M., Fleer, G. J., and Cohen Stuart , M. A., Colloids and surfaces 21:285(1986)
[5] Shin, J.H., Han, S.H., Sohn, C., Ow,K.S and Mah, S, Highly branched cationic polyelectrolytes: filler flocculation, Tppi J. 80(11):179(1997)
[6] Broulilette, F., Morneau, D., Chabot, B and Daneault, C., A new microparticle system to improve retention/drainage in fine paper manufacturing, Appita J. 58(01)
[7] Gerli, A., Berkhout, S and Cardoso, X., Core shell: the latest innovation in the polymer technology for the paper industry, Paper Technology 44(2): 38-42 (2003).

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Name: Eugene F. Douglass
Date: April 20, 2008

Question: “Based on the findings of various experimental studies, which of the following is a more important factor in explaining why suspensions that are flocculated by addition of cationic acrylamide copolymers of very high molecular mass do not become strongly flocculated again after they have been dispersed by application of intense hydrodynamic shear?
1 – Breakage of polymer chains, reducing the molecular mass.
2 – Change in conformation, such that the polyelectrolytes lie down flat on the surfaces after bridges “peel off” from some of the surfaces when hydrodynamic shear is applied.
3 – The polyelectrolytes gradually penetrate below the outer surfaces of the fibers.“

This subject is important because it helps us understand the nature of hard flocs, versus soft flocs, and how the high Mw additive affects fiber-fiber, fiber-fine, filler-fiber, and fines-additive interactions. But, based on my answer to the question, I am uncertain of the need for a definite answer to the question.

Answer:

The first option, “breakage of polymer chains, reducing the molecular mass,” seems to be the most logical answer. This is because I believe this answer incorporates the other ones. Smaller masses will make it easier for the polymer to lie down on the surface and achieve greater penetration.

Logical or theoretical support

When the fiber surfaces have a naturally negative charge, adding a cationic polymer will associate in many places along the fiber surfaces. This behavior is expected due to its large molecular weight, extension in a chain, and because of entropic effects. Electrostatic effects with ionic cPAM will promote multiple connections with anionic regions across a relatively long distance. Logically the ionic attachment will extend across gaps between fibers and fillers, the chain extended natural in a bridging form between fibers, fines and fillers. The long chain will flap around, on high shear; some of the bonds in the chain between fibers will have more tension on them, compared to individual ionic associations along the fibers. So, the polymer chains break, reducing the molecular mass. These free radical/break points will then quickly react with something else available to bond it into place, so proving this hypothesis would be UNLIKELY. I believe the papers I read, more serve to show what is NOT the mechanism.

Experimental Support:

Cadote et al. [1] came up with conflicting results, where with PEO, the flattening of the polymer on the fiber SEEMED (to them) to be the mechanism. cPAM was intermediate in their determination regarding the results, and cPAM was very sensitive to ionic strength. Obviously, PEO is a NONionic polymer. They then conclude that their lab results do not correspond with plant results. PEO lying down is logical because of Vander Waals forces, there will be short distance interactions, but then to discuss cPAM as being similar neglects basic polymer chemical differences.

Forsberg et al. [2], based on their results conclude there is a flattening mechanism of the cPAM along the fiber, and combined with the formation of bonds along the surface of the fibers. Their answer is kind of #2, and some of #1. Because they also suggest there is breaking of bonds of extended cPAM, because of the irreversibility of the process. From their data I did not see proof of flattening of the cPAM along the fibers as being the predominant mechanism. I believe their results more point to #1.

Allen et al. [3], investigated a whole variety of retention aids and their sensitivity to high shear. They take a more logical approach, and conclude a breaking of bonds is occurring, and then recreation of the ends into a less extended conformation, and molecular mass is lowered and so easier penetration of fiber walls can take place. So for them it is #1 and #3. [3,4] #3 is a logical follow-on to #1, because a lower molecular weight polymer will penetrate easier.

Hubbe [5] suggests that it is either a net colloidal attraction between the surfaces of the cPAM and the fibers or of polymer bridging weaker than the original ones. So, his results do seem to suggest #1, but he concludes that it is more complicated [5-6].

Shin et al. [7] conclude that flocculation of does not follow a charged patch or a bridging mechanism but is due to a compact structure formed by filler particles interconnected by flexible polymer tails. They do acknowledge the presence of flexible polymer tails, but with cPAM, if there is flexible polymer tails, logically there could be bridging across gaps. So, they don’t know the answer to the question, they just say it isn’t something, without proving the negative.

Swerin et al. [8] concludes that there is a polymer bridging mechanism, based on the number of contact points between the cPAM and the fibers. They follow a more logical approach and do provide some evidence to justify their suggested conclusion.

Situations where the findings can be useful

The findings are useful in perhaps explaining what is happening in real life, to the scientist who is curious to answer questions “why”. But, the fact of improvement in paper quality and improvements in process is what really matters anyway. Quantifying an art like papermaking is only necessary for those who want to know “why”s, whereas most papermakers will not care why, as long as the additive works to improve properties or process.Literature cited:

Cadotte, M., Tellier, M.-E., Blanco, A., van de Ven, T., and Paris, J. (2005). “Effects of various retention aids on fiber flocculation, filler retention and drainage,” Annual Meeting of the Pulp and Paper Technical Association of Canada (PAPTAC), Vol. A, A31-A38.
Forsberg, S., and Ström, G. (1994). “The effect of contact time between cationic polymers and furnish on retention and drainage,” J. Pulp Paper Sci. 20(3), J71-J76.
Allen, L. H., and Lapointe, C. L. (2005). “Effectiveness of retention aids for pitch control in TMP newsprint manufacture. Part 1. Low shear,” Pulp Paper Can. 106(12), 102-107.
Allen, L. H., and Lapointe, C. L. (2005). “Effectiveness of retention aids for pitch control in TMP newsprint manufacture. Part 2. High shear,” Pulp Paper Can. 106(12), 108-112.
Hubbe, M. A. (2000). “Reversibility of polymer-induced fiber flocculation by shear. 1. Experimental methods,” Nordic Pulp Paper Res. J. 15(5), 545-553.
Hubbe, M. A., and Wang, F. (2002). “Where to add retention aid: Issues of time and shear,” Tappi J. 1(3), 28-33.
Shin, J., Han, S., Sohn, C., Ow, S., and Mah, S. (1997). “Highly branched cationic polyelectrolytes: Filler flocculation,” Tappi J. 80(11), 179-185.
Swerin, A.; Risinger, Gunnel; Odberg, L. “Shear strength in papermaking suspensions flocculated by Retention aid systems,” Nordic Pulp Paper Res. J. 11(1), 30-35

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Name: Xiaomeng Liu
Date: April 2008

Topic:“ When developing or selecting an anionic retention aid polymer, what factors govern the optimization of anionic charge density?”

Why do papermakers need retention aids?

A primary goal of papermakers is to obtain high quality paper products with low capital and operating costs and without environmental pollution. The use of as little as possible retention aid during paper’s formation is a good basic strategy. The idea is to use only enough retention aid to keep the fillers and fiber fines retained well, and also to get the uniform appearance of the final paper products. Such a strategy can help papermakers satisfy the demands of a wide range of paper products. It is very reasonable that the correct selection of retention aid and the correct position of addition are very crucial during the typical paper making processes, because the addition of retention aids has indispensable effects on the fillers and fiber fines retention, dewatering efficiency, formation, and finally, the efficiency of the paper machine.

Which kinds of retention aid are used in papermaking industry? And do anionic retention aids have special characteristics as retention aids?

A non-ionic retention aid, poly-ethylene oxide (PEO) has not been widely accepted by the paper making industry. There are still some concerns regarding the use of PEO as a retention aid: high sensitivity to temperature and hydrodynamic shear, etc..However, it still holds great promise in the future development tendency of papermaking industry including the reduction of using the fresh water, because the uncharged PEO is not affected by high levels of salts or negatively charged colloidal material in the process water.

Cationic retention aids are among the most popular additives in the papermaking processes. Cationic retention aid chemicals include cationic starch, which is usually modified from the nature starch to positively charged products. Cationic acrylamide copolymers, which typically have molecular masses in the range from about 4 million to about 20 million grams per mole are perhaps the most commonly used retention aids.

An anionic retention aid such as anionic acrylamide retention aid is used for alkaline pulping and papermaking and they also could be used in acidic processes.

There are some special characteristics of anionic PAM as retention aids. Possibly the reason that they are not so commonly used as cationic retention aids is because the negatively charged polyelectrolyte needs a positively charged anchoring material such as alum, aluminum sulphonate or cationic polymer including polydimethalammonium-epichlorohydrin, poly-DADMAC,etc. to flocculate with the negative fiber surface in the pulp stock, while the cationic retention aid could react directly with the negatively charged fiber surfaces. However, one of the reasons anionic acrylamide copolymers are used as retention aids is that they can be cheaper in comparison to the cationic retention aids. The preparation can be relatively simple; for instance the anionic PAM can be prepared by hydrolyzing polyacrylamide for different time. Also in cases where there are mostly cationic particles which need to be retained, such as pure PCC calcium carbonate,etc., in the paper machine system, it may be good to choose an anionic PAM product as the retention aid.

In my project, I would like to classify the dual (cationic and anionic) polymer systems as belonging to the category of anionic retention aids, because we could consider the cationic charged polymer as the anchoring site which has the anchoring function in the anionic retention aid system. Britt presented his results showing that the effective mechanism of using dual (cationic and anionic) polyelectrolytes as retention aid systems can be augmented if the furnish system is firsttreated with a moderate-mass, high-charged cationic polymer (PEI) that could act as an anchoring site, such as dimethylamine-epichlorohydrin condensation product. and then treated with a high mass anionic acrylamide copolymer, yielding higher retention efficiency in comparison to the sole use of cationic PAM or a PEI product by itself.

What are the main factors that could affect the efficiency of the anionic retention aids? What factors govern the anionic charge density?

The charge density of an anionic retention aid is one of the main factors of selecting a correct retention aid, because the electrical charges on the surfaces of fibers, retention aids polymers and other materials in a papermaking furnish have profound effects on the process and the final products. Chen, Hubbe, and Heitmann [5] used a titration test to show the importance of the charge density of the typical retention aids in their paper. According to Chen et a. the performance of retention aids could be directly affected by the balance of the surface charges in a papermaking machine system. The charges in the system also could affect the dewatering rates, the physical properties of the final paper products.

There are some factors that may be expected to have some obvious effects related to selecting a suitable charge density of the anionic retention aids. The salt concentration in the paper machine system is one of the main factors to consider. Because of the tendency for increasingly closed-water cycles used in the paper machine system, increasing amounts of salt can be expected in the white water that is reused to dilute the thick fiber stock. The conformation of the retention aid polymers will shrink or swell when the salt concentration changes. In fact in the forming section, the retention aids polymers will shrink with increasing salinity. To avoid the shrinking phenomenon, increasing the charge density of the retention polymers could help the polyelectrolyte remain more extended, so it would be reasonable to use the high retention aid charge density. The need to achieve strong interactions with anchoring sites also should be considered when the papermakers choose a type of anionic retention aid. Even if there are the same amount of anchoring site in the paper machine system, there will be much more opportunities to reaction with the cationic particles when the high charge density of anionic retention aid is used. The solubility is another factor that could affect the retention efficiency, as well as the ease of handling and make-down of the product. The high solubility with high retention efficiency could be achieved by using the anionic retention aid with high charge density.

Molecular weight is another factor which has the profound effect on selecting an anionic retention aid polymer; with the increasing of the molecular weight of the anionic retention aid polymer the retention efficiency is expected to increase.

Where is the optimum position to add an anionic retention aid?

After selecting a correct retention aid, another important issue is to choose a suitable addition point. According to the papermakers’ experience and the scientists’ research, a good addition point for a retention aid could be right after the pressure screen, where such a product is expected to give the highest retention efficiency and there is expected to be the minimum of negative effects on the retention aid’s molecular weight when using a medium molecular weight product. Another alternative is to add the retention aid before the screen, possibly achieving a better balance between formation uniformity and retention. In fact the typical point to add the retention aid should depend on the special retention aid, such as the ability of flocks to resist degradation from shear forces, as well as turbulence in the headbox and in the forming elements. Ideally a retention system needs to flocculate effectively at a minimum dosage level and to be somewhat shear resistant without adversely affecting sheet structure.

What kinds of evidence are supplied in the current reviewed literatures?

As previously mentioned, retention aid programs not only enhance retention but also improve the rate of dewatering in the formation section. Using a high charge density of anionic retention aid with high molecular weight is good for the retention efficiency; however, Blanco, Negro and Tijero [2] presented evidence that flocculation resulting from the use of retention aids could negatively affect the formation, especially if big flocks persist in the suspension during the formation of the sheet. In their paper, they provided a fundamental understanding of the effect of anionic polyacrylamide retention aids on the flocculation of the fiber stock and the final paper properties. They showed that use of an anionic polyacrylamide retention aid with high anionic charge and medium molecular weight could have the optimum retention behavior of fiber suspensions, as well as providing high bonding strength of the final products. Anionic polyacrylamide retention aid products are commonly used in alkaline pulp and paper processes by papermakers. The flock size and the flock properties which are the crucial factors influencing retention, drainage and formation has been investigated. In the cited article by Blanco, Negro, and Tijero [2] the authors presented a study of control the addition of different characteristics of anionic polyacrylamide and the relationship between the retention efficiency, the molecular weight, and the charge density.

Britt and Unbehend [3] gave evidence that the dual (cationic and anionic) retention aid system could withstand moderately high hydrodynamic shear up to about 1000rpm at a moderately high retention aid additon level. The rate of flocculation was rapid under all conditions of polymer concentration, charge density, salt concentration, and shear. The size and strength of flocs were affected by these variables. Results were consistent with a bridging mechanism of flocculation.

Literature Cited

1. Negro, C., Blanco, A., Fuente, E., Sánchez, L. M., & Tijero, J. Influence of flocculant molecular weight and anionic charge on flocculation behaviour and on the manufacture of fibre cement composites by the hatschek process. Cement and Concrete Research, 35(11), 2095-2103 (2005)..
2. Blanco, A., Negro, C., and Tijero, J., Modelling drainage in the wire section of a Fourdrinier machine, PIRA International, Leatherhead, UK, (1997).
3. Hubbe, M., Selecting and interpreting colloidal charge measurements,Proceedings of Scientific and Technical Advances in Wet-End Chemistry PIRA International conference. Spain, June, (2000).
4. Britt, K.W., Mechanisms of Retention During Paper Formation,Tappi 56(10):46-50(1973)
5. Chen, J., Heitmann, J. A., Hubbe, M. A., Dependency of polyelectrolyte complex stoichiometry on the order of addition.1.Effect of salt concentration during streaming current titration with strong poly-acid and poly-base.Colloids Surf. A 223(1-3), 215-230, (2003).
6. Hubbe, M. A., Chen, J., and Heitmann, J. A., The Measurement and Impact of Charge in the Paper Machine System, Solutions 87 (11), 47-49 (2004).

==========

Name: Ying Xue
Date: April 2008

Question: The most commonly used retention aids are very high mass linear poly electrolytes having relatively low charge density, but a few publications suggest that similar effects can be achieved with densely branched, highly charged cationic polymers. Does the evidence really suggest that these two classes of materials can have similar effects when added to paper making furnish? If so, can the similarity be explained by the three dimensional character of these two kinds of poly electrolytes, either due to their very low length or due to their highly branched nature?

Introduction:

Dendrimers are three-dimensional macromolecules intensively investigated recent years by papermaking scientists. They are highly branched, round shaped, stepwise synthesized polymers with a high density of cationic terminal function groups. The reason why paper makers are interested in this kind of star-like polymer is that they can be used as highly efficient retention and drainage aids in the wet end of a paper machine, and the efficiency is higher than conventional linear retention / drainage aid polymers in some kinds of furnishes, with pitch control as an additional benefit.

Answers to questions:

Why is the subject significant to paper industry?

There are three main reasons:

First of all, more and more paper mills nowadays are switching to closed systems, for the advantage of being economical and environmentally friendly. However, circulating of white water will cause an accumulation of non-substantive materials in the white water, which means colloidal matter in the furnish will increase as time goes on. Meanwhile, the anionic concentration will also increase will time. Both of these aspects can introduce a decrease of efficiency of retention and drainage.

Secondly, almost all the paper makers want to make paper machine faster, Slow drainage speed would retard the development of high speed paper machine, because the wet paper mat needs to achieve a certain dryness before going to the next section on the machine. On the other hand, a conventional linear drainage aid cannot endure high shear force caused by the high speed of paper machines.

Thirdly, papermakers are adding a great variety of chemicals into pulp furnish to achieve different kinds of purposes, sometimes the retention aid and drainage aid would be disturbed by these chemicals, especially when the retention or drainage aid polymers are low in molecular weight and low in charge density.

Therefore, the conventional linear retention and drainage aids sometimes are not efficient enough for the wet end in today’s paper machines. We need to seek for a noval retention and drainage aid, possibly having a higher charge density, with the goal that it can give a better retention and drainage performance.

What are various authors’ points of view on this topic?

Allen et al, mentioned in their United State Patent statement, 2002, a dendrimer can increase the retention of fillers in paper and decrease the loss of filler materials in white water waste from paper making. It can increase the retention of cellulosic fines and fibers in the paper making process and increase drainage on the paper machine.

Yang et al., Chen et al., Lin et al., and Alince et al. report that tje PEI – calcium carbonate bond is not as strong as a dendrimer- calcium carbonate bond, which indicates a potential of better retention and drainage performance in the wet end when using a dendrimer, compared to conventional PEI.

Allen et al, 2000, also compared the efficiency of dendrimer as a drainage and retention aid for several kinds of pulp furnishes, including newsprint, supercalendared grade, and paperboard, in an open system and closed system, to the efficiency given by conventional PEI. His work showed that, advantage of dendrimer in wet end retention and drainage compared to regular PEI differs from variance kinds of furnishes. Allen pointed out at the end of this article that the lab experiments are important before applying dendrimers into pulp furnishes, because for some kinds of furnishes, the efficiency of dendrimer is higher than regular PEI, however, sometimes it is not.

Fu et al, 2006 showed that the environment of the application of dendrimers, including pH, rotor speed, retention time, and dendrimer dosage can affect the efficiency of its performance as a retention and drainage aid. They also mentioned another advantage, which is the better solubility of using dendrimers over linear retention aids. They conclude that the efficiency of dendrimer when using dendrimer at a low dendrimer dosage, long retention time, high pH value, and high shear force will be low.

Shin et al, conclude that when dendrimers are used as a flocculant for GCC and titanium dioxide particles, smaller flocs with greater shear resistance are produced compared with the conventional linear poly electrolytes of high molecular weight. Experimental results indicate that the flocs formed with dendrimer have a compact structure with filler particles interconnected by the flexible polymer tails. Results clearly show that flocculation but dendrimer does not follow either charged patch or bridge mechanism. The floc size can increase further by adding micro-particulated silica. This suggested the dendrimers have a potential in promoting retention of miroparticles in wet end.

What’s their evidence?

The evidence given by Allen et al. for the declaration in their patent is that the author did experiments on retention/drainage efficiency in 12 different wet end situations, including different fiber sources, different fillers, different head box consistency, for the comparison of PEI and dendrimer. The author found that at the same polymer dosage (weight based), 5 of them showed a higher drainage/ retention efficiency of dendrimer than PEI, while all of the experiments related to pitch control showed a much higher pitch dispersal efficiency of dendrimers than PEI.

The evidence of better retention and drainage efficiency of dendrimer over linear PEI by Yang et al. is in that:

Although linear PEI cannot affect the deposition of calcium carbonate particles onto fiber surfaces, they can decrease the velocity of detachment. Meanwhile, PEI has a high affinity to fiber surfaces, but it is poorly attracted to calcium carbonate. These evidences indicate that PEI- fiber bonding is weaker than fiber- calcium carbonate bonding, and PEI- calcium carbonate bonding is even weaker. The dendrimers, although they have the same kind of function group with PEI, the charge density of dendrimer is far higher than PEI. Experiments done by Koper et al. showed a high affinity between dendrimers and calcium carbonate.

The evidence to support the viewpoint that the advantage of dendrimer over PEI depends on the specie of pulp furnish lies in several experiment done for comparing the retention efficiency of dendrimers with regular PEI, in open and closed systems using the same furnish for newsprint grade, for supercalendar grade, and for board grade. Results of these experiments are, for newsprint grade in both open and closed system, the efficiency of all the dendrimers tested were higher than PEI, expecially at high dosage. However, when comes to dual polymer retention system, only EDA(PA)4 had obviously higher retention efficiency than PEI when employing deinked pulp and TMP; and EDA(PA)4, EDA(PA)8 , DAB(PA)64 have higher retention efficiency than PEI when employing TMP pulp only.

The reason why Fu et al. conclude that the application environment can affect the efficiency of dendrimers as a retention aid and drainage aid is several experiments on employing dendrimer at different pH, retention time with furnish rotor speed and dosage gives different retention efficiency.

Shin et al. have done several experiments related to the dependence of particle size on the flocculation time when treating GCC and titanium dioxide with dendrimer and CPAM. The result shows a much higher average floc size of GCC and titanium with dendrimer as flocculant.

Are there other ways accounts for their observations?

Maybe Fu’s conclusion can partially explain the phenomena observed by Allen in his paper, which indicates a difference in advantages of dendrimer efficiency as a retention aid using different pulps for different paper grades..

In Fu’s paper it is obvious that the environment can influence the efficiency of a dendrimer as a retention and drainage aid. Different white water systems might have quite different amounts and kinds of ionic trash and small particles, which can have a big effect on dendrimer efficiency. The environment also will change the efficiency of PEI, but no comparison of how ionic trash and small particles affect the drainage and retention efficiency of dendrimers vs. PEI has been reported.

Another way to explain why sometimes dendrimer do not have an obvious advantage over PEI is that, as mentioned in my critical review, for the furnish does not need a high cationic charge density of retention aid, PEI is already efficient enough for the retention purpose, therefore, the advantage of high cationic density of dendrimers is not obvious.

Peng et al. (2007) compared the retention efficiency at the same mass fraction of retention aid of PAM, ungrafted PEO, and grafted PEO. Results showed that the retention efficiency of ungrafted PEO was lower than PAM, however, when grafted, the retention efficiency was higher than PAM. From this experiment, we also can assume a higher retention efficiency of dendrimer than conventional linear retention aids.

What can you suggest for future work in the same field?

My suggestion on the future work in developing dendrimers as retention and drainage aid is:

1. Decrease the cost of dendrimer synthesis.
Up to this point the dendrimer synthesis has employed a stepwise method, which implies a high cost in terms of both of labour and equipment.

2. Modify dendrimer to make it suitable for other kinds of pulp.
If the function groups in dendrimer molecule are changed, the property will also be changed. Affinity of dendrimers to small filler particles and fiber fines can be enhanced, and charge density also can be changed by modification of function groups in dendrimer.

References:

Allen, L., and Polverari, M., 2000, Denrimers: a new retention aid for newsprint, mechanical printing grades, and board. Nordic, Vol 15 no.5/2000
US patent 6468396B2
Peng, X., et al., 2007, Synthesis and application of polyxyethylene-grafted cationic polyamidoamine dendrimers as retention aid. Journal of applied polymer science, Vol.106, 3468-3473
Fu ,Y., et al., 2007, Retention and drainage performance of star shape cationic polyacrylamide. China pulp and paper, Vol. 26, 4/2007
Yang, K., and Su W. synthesis and application in paper making of dendrimer
Shin J., et al., 1997, highly branched cationic poly electrolytes: filler flocculation. Tappi Journal, Vol. 80, No. 11.

==========

Name: Douyong Min
Date: April 20, 2008

Topic: “What really happens, on a molecular level, between retention aid polyelectrolytes and “interfering substances” (dissolved and colloidal anionic substances), causing a decrease in the effectiveness of the retention aids?”

Why this project is very important to paper industry?

To the paper industry, the wet end of papermaking is an area of extremely complex chemistry. There are many kinds of substances, organic materials such as fibers, fines, added retention polymer aids, inorganic materials such as fillers, microparticles used to improve the retention and others. In addition, all of these substances have different characters such as different surface areas, charge qualities: negative or positive, ions concentrations and charge densities. Now, to decrease the demand of fresh water and environment pollution, the water is used closed and thermal mechanical pulp (TMP) are used more and more. Both of these increase the complexity of the wet end chemistry. So to figure out what really happens between retention aid and interfering substances (dissolved and colloidal substances DCS) is very important to improve the effectiveness of the retention aids and the paper machine runnability.

What progress has been made to this problem?

It is the most important step to solve this question that what are the amount and components of DCS. Bjarne Holmbom [1] developed an analytical method to provide the detailed components of DCS.

Fig.1. Scheme for analysis of the main dissolved and dispersed components in paper mill waters

They used gas chromatography (GC) to determine the carbohydrates by the monomeric sugars obtained through acid methanolysis of free-dried samples. They also developed a convenient solvent extraction procedure combined with a short-column GC method for the analysis of lipophilic extractives. And the estimate of the total amount of aromatic lignin-related components in waters can be obtained from the UV absorption at 280 nm. So we can find that DCS are negative charge. Thus, when you added some cationic polymer aids into the slurry with DCS, such substances will interfere with the reaction between the cationic polymers and negative fibers and fines due to the charge neutralization. Furthermore, they will decrease the paper machine runnability and paper quality. [2, 3]

Upon addition of high-charge density, low-molecular-mass cationic polymers to fiber suspensions containing DCS, aggregates of colloidal substances can be formed by two different modes of action. These anionic DCS can adsorb onto Cationic polymers surfaces leaving some positively charged patches. Of course, these positive particles will adsorb onto negative fibers surfaces. Another possible mechanism is flocculation. These DCS with positively and negatively charged patches can form loose flocs with each other because of the electrostatic attraction. It is commonly assumed that to different cationic polymer aids, there are different mechanism between the polymer and DCS.

Some experimental evidence

The turbidity and electrophoretic mobility (EM) are used to analysis the mechanism. The EM of a suspension is increased with the increasing amount of cationic polymer. That means the negative fibers, fines and DCS are neutralized by the added cationic polymer aids. But to turbidity, there is flat part of the response curve (an optimum polymer dose) where the turbidity is close to zero, then turbidity will increase again due to the neutralized substances are restablized by more cationic polymers. To the suspension containing only neutral hemicelluloses, there is no such flat area. And the suspension only containing the DCS, there is also no such flat area. When the polymer added above the definite value, the turbidity and particle size distribution will be close to that of the original, untreated suspension. This restabilization at excess cationic polymer doses further supported patch flocculation or charge neutralization being the dominating mechanism for destabilization of DCS by cationic polymers. [4]

Another research done by Cong, R., Smith-palmer, T. and Pelton R. also showed that DCS have influence on the filler (PCC) flocculation. Due to the electrostatic attraction between the DCS and PCC, the PCC will change from positive to negative, so they will need more cationic polymer aids to flocculate them. There is an isotherm for the adsorption of DCS onto PCC and no obvious desorption of DCS from DCS-PCC particle surfaces. And the measurements using disc centrifugation and dynamic light scattering indicated that the average diameter of DS-PCC particles was smaller than that of unmodified PCC. Furthermore, they found that DS-PCC is harder than PCC to flocculated, and the supernatant contained no DS were much more efficient in terms of the amount of cationic polymer aids required. [5]
Compared three different pulps P-bleached, P-bleached enzyme treated and unbleached, it was found that DCS can be completely aggregated in TMP suspensions by highly cationic polymers. But more polymers are needed in P-bleached suspensions. But the polymer demand was less to the pulp treated with pectinase enzyme. The reason is that there are much pectic acids belonged to the DCS were degraded by pectinase enzyme. [6] P-bleached suspensions needed more cationic polymer than unbleached due to more anionic charge density of the fibers introduced by bleaching. All of these results showed that they would require more cationic polymers to neutralize if there are more DCS or negative charge density in the suspensions.

Conclusion

The neutralization mechanism between the negative DCS and the cationic polymer aids is very easy to imagine and accept because electrostatic attraction is a common physical rule. And many sets of avilable data can be used to demonstrate it.

The patch mechanism also based on the neutralization maybe can also explain some experimental results. Especially to high mass molecular weight cationic polymers, this mechanism between DCS and polymers is more possible. But there is more work to do to demonstrate this rule.

Further studies

It is well known that DCS can affect the function of added cationic polymer aids; thus they will an impact on the quality of paper and runnability of paper machine. Nowadays, most research has been based on a macro-level observation, but to this problem, we should explore on the molecular level.

Another focus of research concerns competition between the DCS and fibers when cationic polymer aids are added into the suspension, based on the above two mechanisms. So it is of iterest which one was first flocculated and how and when they are flocculated. This is in addtion to questions about influences between cationic polymers and negatively charged colloids during the process of flocculation.

Figuring out all of these questions is very helpful to determine the mechanism about the DCS and cationic polymer aids on the molecular level.

References

Holmbom, B. 1996. “molecular interactions in the wet end of papermaking” 1996, international paper and coating chemistry symposium
Lindstrom, T., Soremark, C. and Westman, L. 1977: Svensk Paperstidn. 80: 11, 341-345.
Wearing, J., Barbe, M. C. and Ouchi, M. D. 1985: J. Pulp Pap. Sci. 11: 4, J113-J121.
Horn D. and Linhart, F. 1991: In “Paper Chemistry,” Part 4. Edited by Roberts, J. C. Blackie & Son Ltd., London, pp 55-59.
Cong, R., Smith-palmer, T. and Pelton R. 2001: “a model colloid for flocculant testing” 2001, Journal of Pulp and Paper Science: Vol. 27 NO. 11
Sunder, A., Ekman, R., Holmbom, B., et al. “interactions between dissolved and colloidal substances and a cationic fixing agent in mechanical pulp suspensions”, Nord. Pulp Pap. J. 8 226-231, 1993

==========

Name: Robert Zschocher
Date: April 22, 2008

Topic: “Some recent articles suggest that the manner in which a retention aid polymer is mixed with papermaking furnish can play a big role with respect to the quality of the paper and the efficiency of first-pass retention, etc. What can such observations tell us about the mechanisms by which retention aids work?”

Introduction

The manner in which a retention aid polymer is mixed with the papermaking furnish must be optimized by the papermaker to ensure efficiency in runnability, appropriate cost utilization of materials and meeting the customer’s quality requirement. The retention aid polymers must be added to the furnish with sufficient mixing action so that the polymer will be uniformly distributed within the stock. Consideration must also be given as to where the retention aid should be added to attain the optimal contact time with the furnish. Finally, mixing additives that are incompatible with each other must be avoided.
The proper mixing of retention aid polymers have a direct effect on retention, drainage, and uniformity.

There are a multitude of variables when considering the addition of retention aids. Each individual paper machine operating team must take into account these variables when deciding the best method of adding the retention aid polymers. Some of the variables the papermaker must consider include the following;

stock consistency, quality and composition
method and velocity of injection, contact time
retention aid polymer chemistry and dosage
degree of dilution, quality of the feed water

The stock quality and composition are not variables that would be typically modified for the benefit of the retention aid polymer. However, the papermaker must take these variables into account when determining the means of injection. The simplest form of injection is by use of a “T” joint. This method of injection is the most likely form of injection to cause inadequate mixing action. The injection quill is an improved injection method which allows the retention aid to be added in the middle of the stock stream. The greater turbulence in the stream results in more uniform distribution of the retention aid. There also exist even more elaborate mixers which add the retention aid at several points within the cross section of the pipe.

The velocity of injection may vary between two to six times the velocity of the line speed. Typically higher consistencies require a greater injection speed. The turbulence and shear stress caused by the velocity creates a detached fiber network. The downstream distance must also be taken into account.

The degree of shear sensitivity of the retention aid polymer must be taken into account when determining a point of addition. A high molecular mass polymer will be irreversibly damaged with high shear. The efficiency of the retention aid polymer will determine the level of dosage required in light of the other variables.
The dilution of the retention aid improves the efficiency of the mixing. The dilution water may be fresh water or re-circulated. The re-circulated water will have a higher level of salt concentration which may have a detrimental effect on the performance of the retention aid.

Theory

Retention in the absence of a cationic polymer takes place through mechanical filtration. The cationic polymer provides retention through a colloidal mechanism. The cationic polymer must be dispersed evenly throughout the furnish to insure that the adsorption is on most of the fiber surface. Inadequate mixing may result in spots in the paper. Once the polymer adsorbs onto the surface, the initial conformation consists of “loops” and “tails” protruding from the surface of the fiber into the solution. After the initial adsorption the polymer will form a flatter conformation and may penetrate underneath fibrils at the fiber surface or into the fiber wall, resulting in a loss of performance.

Velocity of Injection

The effect of injection velocity and the resulting turbulence was studied extensively in two studies at the Institute of Paper Science and Technology at Georgia Tech by Gorges etal [1,2]. The experimental setup consisted of two transparent pipes; an inner pipe representing the injection of retention aid and an outer pipe for the flow of the stock. The mixing efficiency was analyzed through the use of four sampling probes that were located downstream from the injection point. The velocity ratios (velocity of fluid from inner pipe / velocity of fluid in outer pipe) of up to six were studied in mixtures of hardwood and softwood pulp. The consistencies of the stock were 0.9% to 4.0%. The authors studied the angle of the interface between the inner and outer fluid and termed this as the inner jet spread angle. As this angle increased there existed a greater distance for uniformity of mixing before reaching the sampling probes. At low values of velocity ratio the mixing action does not provide the required hydrodynamic shear stress to disrupt the fiber network. This resulted in non-uniformities in the machine and cross directions. Clearly in both studies, increasing the velocity ratio resulted in improved mixing efficiency.

Method of Injection

The method of injecting the retention aid into the stock stream is another important variable that the papermaker must consider. The T-line mixer is commonly used in the paper making industry for injection of process chemicals. Lamminem et al. evaluated a new model of static mixer that is marketed as the RetaMixer [3]. The RetaMixer was designed to improve the uniformity of addition into the stock stream. The static mixer consists of wedge shaped protrusions which are placed inside the feed pipe. These wedges are more durable than an injection quill, which sometimes may break off due to the constant wear. Each wedge contains three addition points across the cross section of the line. These wedges are shaped such that the leading and trailing edge surfaces are not blunt, which minimizes the formation of fiber clogs. The authors evaluated the efficiency of the mixers in computer simulation, laboratory evaluation and a mill trial.

The computer simulation and laboratory evaluation showed an impressive scattering of the chemicals throughout the cross section of the stock line. The injected fluid was more widely dispersed and more uniform in concentration in the mixing area in comparison to a T-line mixer. Finally the pilot trial confirmed the superiority of the RetaMixer. The mill trial allowed for a 10% reduction in the usage of the retention aid due to the improved mixing action of the new mixer. Also, equally impressive was the positive comments made by the mill personnel regarding the cosmetic appearance of the final product. The performance of the RetaMixer demonstrates that improvements can be made in the methods of injecting process chemicals, both in terms of the quality of the product and the runnability of the papermaking process.

Contact Time in Fines Retention

A study was completed by Forsberg and Strom that emphasized the importance of the contact time of the retention aid polymer with the furnish [4]. The authors evaluated additions of cationic starch with varying degrees of substitution and additions of polyacrylamide with varying levels of charge density. Additions of these polymers were evaluated in a dynamic drainage analyzer instrument, which has similar dimensions to a Britt jar. This instrument was able to accurately control the rotation of the stirrer, the time for dosage, and the time to open the bottom valve for drainage. Evaluations were also carried out in the absence of the retention aids to establish a baseline. The effect of contact time was compared to the fines retention, drainage time and the solids content of the fiber mat. The study clearly showed that the optimal contact time was between ten and twenty seconds for both the cationic starch and polyacrylamide. The drainage time increased with increasing time of contact. Furthermore, the cationic starch and polyacrylamide had the highest solids at ten to twenty seconds of contact time.

The retention in the absence of the cationic polymers was by mechanical filtration mechanism. The results of this study show that the cationic polymer retains the fines through colloidal retention, which at short contact time improves the retention and drainage. These results can be explained by the fine material which is flocculated onto the long fibers before the fiber matte is formed. There are less free fines to block drainage channels. The cationic polymer may create a more open structure which allows the sheet to be more easily dewatered.

The improved retention and drainage with time, at short times, can be attributed to the time required for the initial adsorption of the polymer onto the fiber. At the initial stage of adsorption the polymer has loops and tails. With time the polyacrylamide adopts into a flatter conformation and adsorbs into the fiber wall. The authors suggested that the decrease in performance of the cationic starch was more related to the cleavage close to the cationic group.

Contact Time in Pigment Retention

Another study that emphasized the importance of contact time was completed by Alince [5]. This study focused on the retention of pigment as opposed to retention of fines discussed previously. Retention aids must adsorb onto the fibers and the pigment particles initially, then the pigment particles will attach to the fibers within a few seconds. Alince discussed a series of rate constants for this process;

Kpf, the rate at which the polymer adsorbs onto the fiber surface
Kpc, the rate at which the polymer adsorbs onto the pigment
Kcf the rate at which the pigment deposits on fibers

By taking into account the frequency of collisions and the concentration of the pigment particles the author was able to calculate the rate constants and the time for half of the particles to deposit. These rate constants must be considered for both the perikinetic (thermal Brownian motion) and orthokinetic (convective hydrodynamic motion) collisions. The perikinetic motion favors collisions between big and small objects. The orthokinetic motion favors collisions increasingly with larger particle sizes. The differences of the types of motions illustrate how the degree of mixing (and particle size) will affect the rate of collisions. The slowest process may become the fastest process as the rate of mixing is increased.

The experimental work of Alince involved changes in the order of addition of the retention aid and the effect on the required contact time. The first set of conditions consisted of oppositely charged fibers and pigments. The fibers were pretreated with PEI and added to the clay or the clay was treated with the PEI and added to the fibers. These results represented an electrostatic interaction between the clay and fiber. The next conditions the authors investigated was cationic fibers, followed by polyethleneimine and finally the clay. In this condition the clay formed aggregates that then attached to the fiber. This method occurred much more quickly and allowed for more clay to be deposited. The final addition strategy discussed was the PEI addition to the fibers and clay. This method had performance between the other two sets of data. This method is between deposition by single particles and deposition of aggregates.

Conclusion

Further studies in contact time may be useful to the industry. In particular the study completed by Forsberg and Strom concluded that the optimal retention time for the cationic starch and polyacrylamide was ten to twenty seconds. To obtain this contact time the point of addition would be prior to the pressure screen. The pressure screen presents another variable that was not considered in this study. The retention aid is typically added after the pressure screens to optimize the first pass retention. When the retention aid is added prior to the pressure screen the performance is sacrificed to obtain improvements in uniformity. Future lab studies that take these characteristics of the manufacturing process into account will be highly beneficial to the industry.

Another topic for consideration when considering the manner in which retention aids are added is the trend in the reduction in freshwater consumption in the industry. As paper mills are becoming more interested in achieving a closed system, the retention aids will be diluted with re-circulated water. This will results in a loss of efficiency and consideration will need to be given to the required contact times (point of addition) between the cationic polymers and the furnish. Of course the use of re-circulated water will also require a reconsideration of dosage and other factors related to mixing.
There are many variables that a paper maker must consider when contemplating the means of addition of retention aid polymers into the furnish. The paper highlights only a few parameters that must be considered to optimize the quality of the paper, maintain stability in the manufacturing process, and insure effective cost utilization of raw materials. These variables must be given considered regardless of the grade of paper or the size of the paper machine.

Literature Cited

1.         Giorges, A.T., White, D.E., Heindel, T., TAPPI Journal, 3(5): Online Exclusive (2004)
2.         Giorges, A.T., White, D.E., Heindel, T., TAPPI Spring Technical Conference, (2003)
3.         Lamminen, P., Koponen, A., Houni, J., Leino, T., Laakkonen, K., Paperi Ja Puu, 87 (8): 512-516 (2005)
4.         Forsberg, S., and Strom, G., Journal Pulp and Paper Science 20 (3): J71-76 (1994)
5.         Alince, B., Tappi Journal 79 (3): 291-294 (1996)

==========

Name: Scott T Schnelle
Date: April, 2008

Topic: “If an amphoteric polyelectrolyte of high molecular mass is used as a retention aid, what would be its most likely mechanism of action, explaining how it can hold fine particles on fiber surfaces?”

Why this subject is important:

The process conditions in modern paper mills are ever becoming more challenging for the paper scientist. The demands of increased production speed, lower quality fiber stocks and the requirement to operate at high loadings of anionic trash and high ionic strength are requiring new solutions. Established techniques and material systems are increasingly not able to meet the demands of the more aggressive environments. New materials and better understanding of the mechanisms involved are required to meet these challenges.

Amphoteric retention aid polymers are high molecular weight, water soluble polymers which possess both cationic and anionic ionizable moieties on the same molecular backbone. Recent findings (5,6) have suggested that certain of these, high molecular weight amphoteric polymers can yield superior performance over traditional homogeneously charged polyelectrolytes when employed in several roles in the paper machine wet-end. Improvements in dry strength, formation, fines retention and dewatering have been documented. The use of amphoteric polymers in papermaking is relatively new and the study of the molecular mechanisms is ongoing.

Answer to the assigned question:

Fines retention by amphoteric polyelectrolyte macromolecules are believed take place by way of an extended bridging mechanism. The basic mechanisms appear similar to those witnessed for standard, homogeneously charged polyelectrolyte systems. The enhanced performance observed for amphoteric systems result from unique structural and kinetic properties which allow these macromolecules to adapt and conform to their chemical / electronic environment.

The fine materials load in a paper furnish is composed largely of charged colloidal particles originating from wood fibers, mineral fillers and chemical agents added to enhance the furnish properties. These charged particles when brought into contact with the charged functional groups on the polyelectrolyte polymers are able to form ionic associations. These associations can bind the fine particles, forming aggregates.

Logic and theoretical support:

The noted improvements in performance achieved by utilizing polyampholytes as retention aids and dry strength agents are believed to arise from unique structural characteristics exhibited by the adsorbed polymers. These polymeric structures result from the interplay of the oppositely charged functional groups constrained within single polymer chains. Compared to the truly, random coil configurations of large linear, homogeneously charged polyelectrolytes, amphoteric macromolecules appear somewhat ordered. The various charged groups within the polymer chains arrange themselves so as to minimize the forces imposed by neighboring electric fields. Detailed theoretical analyses of the potential macromolecular structures available to these polymers have been undertaken by several groups (1). The effects of charge density, charged group ratio and distribution of charge in the chain are all examined as they affect the overall morphology of the resultant macromolecules. External effects from solution salt concentration and density of surface charges on bonding interfaces are also examined. These elaborate theoretical models help to shed some light on what might be happening in a real paper furnish, allowing us to imagine what mechanisms might be at work, imparting the improved performances.

Reorganization due to charge polarization

Amphoteric polymers in solution, when they first contact a charged surface in the paper furnish can form an ionic bond. This bond, most likely a cationic functional group in the polymer chain bonding with a anionic group on the fiber surface (although it could be the other way around), would serve to anchor the polymer. The polymer chain, still loose and extended, but now tethered, would start to reorganize its structure so as to minimize the electrical forces arising from interactions between its charged groups. As detailed below, this reorganized polymeric configuration would tend to evolve into a layered or zoned structure. The negatively charged groups on the polymer would try to move away from the more negatively charged fiber or mineral surfaces. Likewise the positively charged groups would migrate toward the negatively charged surfaces and possibly from more bonds. In the process, layers or string like groupings of like charged groups form. This process of ionic charge reorientation tends to polarize the net charge of the macromolecule.

These fixed, bonded, now polarized macromolecular “globules” now have the ability to form further bonds with additional amphoteric polymers in solution. The predominantly homogeneously charged, molecular surfaces can form new bonds with oppositely charged groups in passing molecules. Once attached, this new random polymer will, itself start to reorganize in response to neighboring ionic/electronic forces. The net result is a somewhat organized layered / zoned, stack of polarized polymer molecules.

This somewhat complex molecular agglomeration allows amphoteric macromolecules to build up thicker more extended layers of polymer, providing for more bonding area and more water retention at the fiber surfaces than can be obtained with comparable homogeneously charged polyelectrolytes. Simple polyelectrolytes would at best be expected to form monolayers of adsorbed polymer and these monolayers might be expected to reconform over time by laying down on the charged surfaces, as they conform to external forces.

In addition to the enhanced adsorption of polymer resulting from the molecular reconfiguration described above, amphoteric polymers have a natural tendency to adsorb most heavily at just the pH ranges encountered in neutral to alkaline papermaking. At these pH ranges (~5-9) both types of ionizable groups on the polymer backbone are charged. The resultant electrostatic attractions between oppositely charged groups cause the polymer’s hydrodynamic radius to contract. These collapsing polymer coils are less soluble than their expanded, homogeneously charged counterparts and are much more likely to adsorb out on to available surfaces. This pH sensitive adsorption phenomena, coupled with the ability of polyampholytes to form multiple layers help to explain the high polymer adsorption values reported by several groups. (3,4,5) The expected presence of additional polymer and assumptions made about its extended morphology give insight into possible mechanisms responsible for the observed papermaking performance enhancements.
Experimental support:

Hubbe and Wang (et al.)(3) have demonstrated several lines of evidence to support the pH dependent polymer adsorption hypothesis. Solution viscosity data presented with Song (et al.)(5) show clearly that the viscosity of polyampholyte solutions are at a minimum in the pH range (~4-9) whereas the simple polyelectrolyes maintain a higher, near maximum viscosity over the same range. Very similar trends are observed for turbidity studies. The polyampholyte solutions tested exhibited a high level of light scattering over the same pH range where they had demonstrated low viscosity. This again is indicative of a collapsed, dense polymer conformation, bordering on precipitation. These polymers would be ripe for adsorption on available, compatible surfaces.

Ye (et. al.)(6) reports on the successful application of amphoteric polymers as retention aids in wheat straw furnishes containing high loadings of cellulosic fines. The ability of the amphoteric polymers to form extended networks of electrostaticly bound macromolecules not only retained suspended fines but aided in dewatering, often a problem for these non-wood systems prone to high degrees of swelling.
Mori (2), describes the measurement of the shear resistance of fiber flocs formed in pulp furnishes flocculated with various PAM polymers. He goes on to speculate on a mechanism to explain why the flocs formed by amphoteric polymers tended to break up easily, under low shear and then reform rapidly once the shear conditions moderated. This behavior is in contrast to what is observed for single PAM or dual PAM retention systems. Mori hypothesizes that the associations between stacked layers amphoteric PAM molecules is weaker than comparable associations formed between oppositely charged PAMs used as dual component aids. He theorizes that because of the presence of both positively and negatively charged groups in the proximity of the molecular interface, that the net force holding the molecules together must be the sum of the attractive and repulsive forces. The result of this condition is the desirable effect that flocs formed using amphoteric PAMs, tended to produce smaller, softer flocs than those formed when using homogeniously charged polymers. These amphoteric based flocs demonstrated the ability to reheal after being sheared. This repetitive break-down / rehealing capability is postulated to result due to the weaker electrostatic interactions between amphoteric molecules.

Similar electrostatic bonding between polyelectrolytes might be expected in the case of standard “dual polymer” systems, where two differing polymers each possessing only a single charge type, are allowed to complex. The strength of these associations however, are thought to be too strong to allow repetitive floc breakdown and re-coagulation. As traditional high molecular weight retention aid and dewatering agents are added, there is a danger that due to high shear, the polymers would either physically degrade (breaking bridges), effecting retention, or if added later(after the screen), may over-flocculate the furnish, resulting in poor formation and causing potential problems with de-watering. In contrast, the re-coagulation phenomena witnessed for the polyampholytes is thought to have beneficial effects on formation and drainage (2) especially in the newer, higher shear environments.

Concluding remarks:

The application of amphoteric polymers in papermaking is a relatively new area. The functional mechanisms are not yet completely understood. Promising test results from laboratory and industrial trials are encouraging, indicating that amphoteric polymers may have a bright future, not just as retention aids but potentially as wet-end additives enhancing paper strength, furnish dewatering and improving formation.

References:

1) Dobrynin, A.V., Obukhov, S.P. and Rubinstein, M. (1999); Long-Range Multichain Adsorption of Polyampholytes on Charged Surface, Macromolecules, 32, 5689.
2)   Mori, Y., (2007); Blended Amphoteric PAMs: High Performance as Retention Aids, Tappi J., December 2007, pg. 20.
3)   Wang,Y., Hubbe, M.A., Sezaki, T., Wang X., Rojas O.J. and Argyropoulos D.S. (2006); The Role of Polyampholyte Charge Density on its Interactions with Cellulose, Nord. Pulp Paper Res. J. September 2006.
4)   Hubbe, M.A., Rojas o.J., Sulic, N. and Sezaki, T. (2007): Unique Behavior of Polyampholytes as Dry-Strength Additives, Appita.
5)   Song J., Wang Y., Hubbe M.A., Rojas O.J., Sulic N.R., and Sezaki T. (2007); Charge and the Dry-Strength Performance of Polyampholytes. Part 1. handsheet properties and Polymer Solution Viscosity, J. Pulp Paper Sci. (2007)
6)   Ye, X.-C., Taanka, H., and Sumimoto,M. (1990). “Effects of Network-Type Polyacrylamides on the Drainage and Retention of Wheat Straw Pulp,” Mokuzai Gakkaishi 36(1), 64-68.

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Name: Charles W. Gordon
Date: April 30, 2008

Topic: “Propose some reasons why papermakers very seldom add retention aids before other additives.”

Why this subject is important:

Economic pressures in the paper industry are constant and unrelenting. As energy costs soar, mill managers press for higher efficiencies and greater cost reductions. Finding any potential savings is worth the effort. Retention aid systems can be difficult to adjust and expensive to operate. Paper machine managers are loath to make a change in a system that can be quite delicate and easily upset, especially when results are not guaranteed.

Answer to the assigned question:

Many reasons exist why papermakers very seldom add retention aids before other additives. The reasons vary, such as legacy, this is how they have been doing it for a long time. Fear, they might not gain as much as they could lose. Other reasons are more scientific; maximum drainage and retention efficiency occurs if sheet formation takes place shortly after retention aid addition.

Logical or theoretical support for answer:

Papermakers face many challenges in operating a paper machine effectively. Decisions must be made that maximize the production of the grade distribution currently being run or that are expected to be run in the future. For older mills, some of these decisions have already been made. Paper machine managers must work with the equipment that they have at their disposal in its current configuration. This legacy places restrictions on potential process adjustments or improvements. The papermaker must decide if this change can provide a benefit. He faces many reasons why it has been done the other way.

Addition Point Utilization:

Retention aids were a solution to an existing problem, filler retention. Fillers are added to provide or augment desirable properties. Retention aids are added to help achieve this goal and save on additive costs. Retention aids do not inherently add value to the sheet; they do so through their effects. Because of the evolutionary process, additive addition placement was maximized. As the need for retention aids became apparent, their addition point had to be placed around existing equipment. Potentially more optimum addition points may have already been occupied.

Technology Shift:

An older machine will become less competitive as more technologically advanced machines come online during its life span. The faster machines will be more competitive because they can produce more product at a lower cost. The papermaker is faced with finding a new grade that requires less volume but can command a higher price at market. The switch may require different additives to meet the customers demand. The added equipment will have to be engineered around existing equipment. This same issue could also come about because of a change in consumer technology that creates a demand for a new grade of paper.

Marginal Cost/ Benefit:

Papermakers also face a lot of fear while making a decision involving non-traditional methods. They must ask, “How much could we lose if this doesn’t work?” This leads to “What do we hope to gain by making this change?” If the second question does not out weight he first question by a lot nothing will come about because the marginal gain is minimal to the potential loss. The third question is “how much will this cost?” This cost should be small to make the effort worthwhile.

Experimental Support for answer:

The work by Hubbe and Wang (1) brings several points that are related to the question of retention aid/ filler addition order. First, if a large polymer is exposed to high amounts of shear, such as in a pressure screen, the polymer will be reduced in chain length due to breakage. This will affect the bridging ability of the polymer and ultimately the retention and drainage. Second, the longer a polymer is exposed to the fiber the more its activity will be reduced by absorption into the porous fiber wall [1]. Another point to consider is that polymer-bridging effects occur very rapidly. A late addition will be very effective if bridging is the primary flocculation and retention mechanism.

Hubbe and Wang also point out some good attributes to early addition of retention aids. The reduction of flocks by passage through a pressure screen to a more uniform, smaller size may be good for formation [1].

As shown by Forsberg and Strom (2) the point of maximum drainage and high retention coincide. The maximum rate of drainage occurred within 30 seconds of retention aid addition. In an effort to achieve large production rates, water removal can be a limiting factor and must be considered when making changes. First pass retention reached a maximum of 90% within 5 seconds of retention aid addition. At 60 seconds, first pass retention had reduced to 75%. After longer periods, the polymers begin to assume a flat conformation. Lieing down on the fiber reduces the polymers ability cause flocculation. The charged patch mechanism becomes the dominant means of retention. Cationic starch also exhibited a similar relationship with respect to contact time. The longer the starch was in contact with the furnish, the more its ability to increase bond strength was decreased [2]. The effect is due to hydrodynamic shear. Starch polymers can be very large, shear reduces chain length through breakage.

The work of Ryösö showed some of the positive affects of retention aid addition reversal [4]. These affect included increased retention and more uniform formation. It was noted that fillers should be added directly after the addition of the retention aid to maximize first pass retention. Waech found in his work that one could achieve a white water consistency half that of a normal retention aid addition [6]. However, retention aid dosages were higher than in the normal addition in order to achieve the reduction. Higher addition rates mean more money, not a good selling point to the mill manager. The work suggests that areas of further investigation include addition point optimization, Zeta potential studies or dual retention aid systems.

The authors’ works provide valuable insight into the scientific possibility of a reversed order retention aid system. Although there are many questions left to answer, it is clear that they should be answered.

Situations in which the findings can be useful:

When deciding upon an addition point for the retention aid system, one should consider the paper machine system as a whole. Issues of poor formation, increased retention, and better drainage might be addressed by addition order reversal. One faces questions on how to implement a new strategy in light of the current configuration. What equipment must be rearranged to facilitate the implementation?

The ideal situation to implement this reversed order would be during a new equipment installation or after a rebuild. Changes could be made at a time when production requirements are relatively low and process adjustments are high.

Literature cited:

Hubbe, Martin A., and Fei Wang. “Where to Add Retention Aid: Issues of Time and Shear.” TAPPI Journal 1.1 (2002): 28-33
Forsberg, S., and G. Strom. “The Effect of Contact Time Between Cationic Polymers and Furnish on Retention and Drainage.” Journal of Pulp and Paper Science 20.3 (1994): 71-76.
Alince, B.. “Time Factor in Pigment Retention.” TAPPI Journal 79.3 (1996): 291-294.
Ryösö, Kati. “Adding Retention Aid Before Filler Addition – Retention, Water Removal and Formation.” Paper Technology 42.8 (2001): 52-55.
Soberg, Daniel. “On the Mechanism of Cationic-polyacrylamide-induced Flocculation and Re-dispersion of a Pulp Fiber Dispersion.” Nordic Pulp and Paper Research Journal 16.1 (2003): 51-55.
Waech, T. G. “Improving Filler Retention by Adding Filler After Retention Aid Addition.” Tappi Journal 66 (1983): 137-139.

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Name: V. Vivek
Date: Spring, 2008

Topic: “Many studies have shown that the effectiveness of sizing agents improves when retention aids are added to increase the retention efficiency of sizing agents. However, such studies seldom have considered how changes in paper uniformity and structure, due to the retention aid treatment, might have further influence on the hold-out of fluids. What would be expected based on published studies of how retention aids affect paper structure and uniformity under practical conditions?”

Why this subject is important? :
It is a well known fact amongst papermakers that the demand for efficient sizing has increased in recent years. These days the end users are insisting on more narrow sizing ranges for specific applications across various segments in the industry. Papermakers realized quite early that the use of retention aids can be beneficial in achieving sizing targets. Some postulated that the retention aids help retain the emulsified particles of the sizing agents on the surface. It was not too long ago when the paper makers realized the use of calcium carbonate in their wet end applications for improving the brightness and opacity of the papers. But the early usage of acid sizing proved detrimental to the companies having calcium carbonate as filler, as lower pH caused the filler to dissociate and create foam problems in the system. Parallel studies in the industry revealed different mechanisms in which retention aids work. Charge neutralizers, cationic polymers, non-ionic, dual component, and micro-particle systems were some commonly accepted retention aids. Such additives can affect formation uniformity and paper structure, depending on where they were dosed, the charge on the polymers, their molecular mass, active species, etc. Thus a need for a study has been felt on how these retention aids might affect the holdout of fluids in the paper structure.

Answer to the assigned question:
According to me, retention aids ought to have an effect on the holdout of fluids and also on the paper structure. Retention aids chemically or ionically (depending on the type of retention aid) do interact with the sizing agents. One is also aware of the fact that retention aids affect formation uniformity too. It is known from the research the sizing agents and fillers compete with each other to occupy space on the fibers. These fillers, due to their large surface area would also interact with the retention aid more than the sizing agent present, though this depends on the relative amount of sizing agent present. As is the usual case as the retention aid is added last in the process, is it quite possible that it may also flocculate the sizing agent and the filler particles onto to the fiber surface. This is true in case of anionic retention aids. These flocs of sizing materials, though essentially small in size, but large in number, may bloc the passages that the retention aid has made with the fibers.

In the cases that will be explained below, it becomes clear that firstly, the filler particles tend to occupy the spaces in the fiber voids. These also offer a way by which sizing chemicals adhere to the filler particles due to their large surface area. However, kinetic considerations (effect of shear forces) also influence whether the sizing particles go towards the fibers or towards the fillers. A second factor is that of sizing agent particles that are mostly associated with the fiber surface. It is natural for them also to fill up the fiber void spaces when there are long exposure times. When a particle (filler or sizing agent) fills the void spaces in the fibers it can be flocculated using the retention aids and it’s quite possible that it affects the formation uniformity. The mechanism is illustrated in the accompanying figure. This can be sometimes seen on paper machines, wherein if there are lots of filler particles, there is reduction in strength. The water or the fluids that may be sandwiched between the two filler particles (water holdout) and the fiber surfaces on the other side covering water or fluid particles from all four directions, the water may not be easily removed in the press section as well as in the dryer section. There may be regions in the sheet that are excessively flocculated and that contain large amount of entrapped water and there may be some areas in the sheet that may be quite uniform and less entrapped water. Thus a higher/lower moisture sheet at the pope reel is the result. This when tested for sizing ought to have variation in the values. Sometimes when there is no sizing in the wet end there can be problems of curl which also affects formation uniformity. If you have excessive sizing, then it’s possible that either one has made a charge reversion on the surface or as stated above, sizing agents along with the fiber surfaces would entrap the liquid. This would again result in moisture variations in the sheet, and the liquid holdout is affected leading to variation in sizing tests also. Wet presses also have an effect on the liquid holdout. Paper when it leaves the press section may not be uniform and may have thick and thin areas. These thick areas may also give comparatively larger amount of resistance to the liquid as compared to the thin areas, as the liquid may require more time to penetrate into the thick sheet.

In the above discussion the focus is more on the water in the void spaces. It would also be interesting to note here about the water that may be present on the fiber surface and how retention aids affect it. From the papers referred to below, it is known that there can be a release of alkali when one treats the fiber with sufficient quantity of retention aid, sizing agent, and filler. As a step forward it can be thought that as more retention is added, there can be more retention of sizing agent. This would also lead to floccy appearance on the sheet affecting the formation uniformity. This when combined with the alkali that is released on the sheet, shall have an effect on the printing inks that may be used. As the paper becomes alkaline, i.e. release of OH- ions, these may increase the anionicity of the fibers and may hamper the ink receptivity, especially of anionic inks. On the other hand, there may be considerable adsorption of cationic inks. However, my claim needs to be verified by practical experimentation. Thus in one way, by knowing the nature of formation, one can easily gage ink receptivity and ink holdout. When one employs the size press for sizing, if the chemicals used are anionic in nature and at low pH, it has been found that one gets a clear print image. This can be directly related to the fact that that the alkali release (due to affect of retention aid , there was a change in formation pattern and sizing) one as able to get a good ink hold out, which can be measured by seeing the ink density differences at various points in the sheet.

Logical or theoretical support for answer:
In case of [4], starch was used as a retention aid. Starch traditionally is amphoteric in nature. This is due to the phosphate groups present in the starch, also that starch has a high amylopectin content, which shows that in extended conformation, with loops and tails extending towards the solution. The Cobb results were higher when alum was added followed by rosin and then cationic starch. A possible reason could be that the starch that was added at the end might have caused flocculation of alum and rosin as well, and it may have caused a reduced spreading of rosin on the fiber surface. The cationic starch too might have been adsorbed onto the surfaces only in the places not blocked by alum. At higher pH, it is quite possible that alum lost its cationicity, as well as there might have been dissociation of even the starch’s anionic group, leading to reduced adsorption and hence reduced sizing.

In the second case of reverse sizing when cationic starch was added first, it may have reduced the porosity of the fiber pad by bringing the fibers as well as the fines together. Due to the presence of calcium carbonate it’s quite possible that the expanded conformation of starch might have reduced, causing the fibers and the fines to come even closer. When the alum addition was followed, it may have caused further flocculation as well as neutralizing of the surface charges. The net surface energy might have also increased to prevent further reactions to take place. The net effect of this process is that the spaces that were available for the water to flow in the fiber mat might have been reduced considerably. Finally when you add rosin dispersed, it only reacts with the alum present there forming a complex, as well as a hydrophobic film over the fiber surface when it passes through the dryers.

In case of [6], also there was addition of rosin followed by the addition of alum and then APNVF. Based on the proposed model above the results in the experiments can be understood as that the retention aid added at the last might have caused flocculation to take place and it can also be said that most of the charges on the surface of the fibers might have been neutralized by alum and the retention aid. Thus the polymer brings together the materials fibers, fines, alum, and rosin close to each other and there is increased bonding as shown in the separate set of results in the experiment wherein the dry and the wet tensile strength are increased. Thus here to the porosity might have reduced, thus causing lower sizing values. The surface energy of this system might have also increased, thus causing no further interactions. In other cases as the authors say that necessary neutralization or over-charging might have taken place in case of other APNVFs. The theory can be summarized by saying that it covers and brings all the materials together; as the author states that the SEM results show that APNVF prevented the dissociation of OH- particles.

In the third case of [5], it is said that there has been no usage of retention aid. But the principle explained by the authors essentially states that the charges are neutralized by CPMP and CPMA themselves and that sizing is also provided by the polymers. The main constituent of these polymers was styrene. It was observed by the authors that the contact angle was also reduced on the addition of these polymers. Herein too as per the model proposed these polymers caused increase in the strength of the paper, meaning that they brought essentially the fibers and the fines closer, and reducing the porosity and increasing the surface energy.

In the case of [3], it is being mentioned by the authors that increase in the filler concentration in the wet end would increase the polymer transfer from fiber to filler, leading to weaker fiber flocs and better formation. Thus even though there was flocculation in all the above mentioned cases; one did not see any drop in the strength properties, as it can happen due to increased flocculation.

This is also said by [1] that if sufficient neutralization takes place, then one can have an agglomeration of anionic colloidal material.

Lastly for [2], the authors evidently show that much of the AKD is with the fines in the system. The authors studied fugitive sizing of AKD. It is also further stated that there was a higher amount of AKD in the fines and on the PCC surfaces. The paper states that for fugitive sizing the beta-keto ester bonds have to be broken. In all the experiments conducted, the sizing chemical was added first, followed by the retention programmes. Also, fillers such as PCC were used in several experiments. There was also usage of cationic starch. The results implied that retention aids acted in the way described above.

Experimental support for answer:
Hedborg and Lindstrom [4] showed in their experiments what happens when the order of addition was as follows: NaOH, alum/PAC, followed by cationic starch. Thus with about 0.5% rosin size and 0.15% alum, they could get a cobb of 26gms/m2 on a 75 gsm sheet. They also formulated a table for the reverse sizing order which included cationic starch, NaOH, alum/PAC. By varying the values of R, they could achieve a minimum Cobb of 24.5 gm/m2 in their experiments. These results could be used to justify that probably starch is flocculating the materials and not allowing them to spread on the fiber surface.

In the work of Wang and Tanaka [6], they prepared a retention aid for their tests and hydrolyzed it to various extents. They used Aminated Poly-N-Vinylformamide as a modern retention aid of alkaline paper sizing with acid rosin sizes. It was used in conjunction with alum and proposed as a dual retention aid system. They prepared a slurry of 1.2% solids and to adjust the pH they added NaOH/HCl. The charge density of the polymer was found using polyelectrolyte titration and using a fluorescence spectrophotometer. The authors expected that there would be changes in retention efficiency according to the charge variations, so they conducted experiments to determine the charges under pH from 2 to 10. According to the authors the rosin soap size gave higher Cobb values (16.4-22.2 s) as compared to the emulsion rosin sizes ( 23.5 to 29.3 s), wherein the sheets were kept at 7.2 pH and base sheets of 60.5 gsm were used. They were able to effectively determine the efficiency of APNVF-1 ( a/f=11/89) with an addition of 0.1%. The article also showed SEM images of the interactions wherein the authors proposed that APNVFs prevented the de-emulsification and dissociation of rosin size due to the action of OH-.The authors also compared the effect of charge density of different APNFs on the sizing degree and concluded that lower charge density polymers were better than the higher charge density polymers as they related it to the hydrogen bonding of polymer molecules with the coordination bonding of rosin molecules with the alum molecules. The authors are also effectively able to graph the relations between the sizing degrees and the filler retention as well as the improvements in dry strength as well as wet strengths in case of increasing dosages of APNVFs.

Ono and Deng [5] designed two polymers in this paper that would act as a retention aid as well as a sizing agent. The proposed that by the use of cationic polymeric microparticle (CPMP), that has been prepared by emulsion polymerization and cationic polymeric micro aggregate (CPMA), that has been polymerized in ethanol and then dispersed in water one can also get the required dry strength. This, if carefully noted, follows from the work of Wang and Tanaka, wherein they have related their polymers with sizing as well as strength improvement, making one think that there ought to be relation between the sizing retention as well as paper structure and uniformity. The authors propose the benefit of use of these polymers as they can effectively adsorb onto the anionic fibers within a broad pH range of 1 to 11. They tried these polymers on long fibers having a consistency of about 5%, and without employing any specific retention aid. Here too the authors believe that the sizing degree depends on the charge density of the polymers and also on particle size and cross linking degree. For testing CPMP, contact angles as well as the time of a water drop remaining on the paper surface was seen. At about 0.8% addition they could get a good sizing efficiency, as water stayed as a stable drop on the paper surface. They also went on to prove that crosslinking of polymer particles cannot be used as a sizing mechanism, wherein they can only deposit but not diffuse on the fiber surfaces. They compared the polymers CPMP and CPMA by their adsorption on fiber surfaces. In case of CPMA the dosage at which they could get good efficiency was only about 0.4%, thus providing more adsorption i.e. interaction of CPMA with the fibers. They also observed strength improvement wherein CPMA was found to be more efficient polymer than CPMP. They proposed the use of a dual system of CPMP and CCPMA for PCC retention that gave significantly better results as compared to CPMA alone that increased the first pass retention from 24 to 41%.

In the work done by Colasurdo and Thorn [2], the authors showed how fugitive sizing is related to the usage of Polyamine. The authors suggested that polyamine can be used for retention of fines and fillers and also for the promotion of AKD reaction. By checking the pH the authors rightly demonstrated the release of alkali during paper drying. They used data showing the incoming pH of PCC at about 8.5, while that of white water was 7 to 7.5, and that of paper extract was much higher. The authors used a mixture of hardwood and softwood fibers and compared the sizing affects using only anionic retention aid, then, cationic starch and anionic retention aid and then both of the two components and PCC. The authors pointed out that the interaction of AKD and PCC is beyond surface area and it has some relation with morphology or some other characteristics.

In this paper [3] the authors studied the flocculation mechanism and its effect on the paper uniformity. They identify various variables that would effect formation and subsequently uniformity and strength. The authors further stated that retention aid helps in bridging and the bond strength increases at the fiber contact points. They used a pilot paper machine and a micro-particle retention aid system to conduct the experiments. Here PCC was added near the fan pump and cationic poly-acrylamide before the screens and as the usual practice bentonite after the screens. The shear effects seemed to be low, as the paper machine runs only at 90 m/min. Keeping the bentonite dosage (5 mg/gm) constant, the authors were able to show the effect on formation (ROD) by cat. Poly acrylamide. In the second case reverse was also done, cat. Polyacrylamide was kept constant and bentonite’s effect on formation index (ROD ) was studied. It was shown here that cat. Polyacrylamide had a larger effect on formation index as compared to bentonite. The authors also studied the formation index (ROD) with the percentage of ash content. The headbox consistency was at 0.5%, and the filler content was about 17.5%. They varied the dosages of cat. PAM and bentonite from 0 to 1 and 0 to 5 mg/gm respectively. The authors also studied ash content, which was varied by varying the filler concentration in the headbox. For the SwBKP furnish, the mass flow rate of CPAM was 607 mg/min and that of bentonite was 1733 mg/min. For the HwBKP+ SwBKP furnish, the mass flow rate of CPAM was 720 mg/min and that of bentonite was 6160 mg/min. It is believed here that the filler particles would fill the voids in the fiber network, thus reducing the variation in the basis weight. In our view as stated above, it also is quite possible that retention aid rounds up these particles and adheres them to the fibers in the voids. In another sense, there is a change in porosity, thus directly relating to the fluid holdout. However the authors do not study the water/ liquid absorbency in this case, but here mention has been made to highlight the point that fillers fill up the spaces in the voids in the fibers.

Conclusions:
This topic of how formation is related to the fluid holdout is very important as one can improve the printing properties of paper. If one is able to determine retention aid affecting the printing, it is quite obvious that development of new retention aids would consider this point. As one sees PEO as a non-ionic retention aid, it would be very interesting to note on how these would affect the final fluid properties of the paper.

Literature References:

Carr, D., – “Nanoparticulars on colloidal retention.” Conference Preprint, Pira International.
Colasurdo, A. R. and Thorn, I. – “The interaction of alkyl ketene dimer with other wet end additives,” TAPPI Journal, September 1992, Pg.143-149.
Garnier, G., Cho, B. U., van de Ven, T. G. M., and Perrier, M. – “A bridging model for the effects of a dual component flocculation system on the strength of fiber contacts in flocs of pulp fibers: Implications for control of paper uniformity,” Colloids and Surfaces: A Physiochem. Eng. Aspects 287 (2006), Pg. 117-125.
Hedborg F., and Lindstrom T. – “Alkaline rosin sizing using micro particulate aluminum based retention aid systems in a fine paper stock containing CaCO3,” Nordic Pulp and Paper Research Journal, No.3, 1993, Pg.331-336
Ono, H., and Deng, Y. – “Cationic Polystyrene based paper sizing agents,” Engineering and Papermakers Conference. 1997, Pg.837- 849.
Wang, F. and Tanaka, H. – “Aminated poly-N-vinyl formamide as a modern retention aid for alkaline paper sizing with acid rosin sizes,” Journal of Applied Polymer Science, Vol.78, Pg.1805-1810 (2000).

Flocculation in the presence of filler and sizing agent] — Bonding between fibers.

Name: Norris Pike
Date: April 2007

Topic: “How to balance retention and flocculation with different retention aid systems during manufacture of paper”

Why this subject is important:

To flocculate or not to flocculate, that is the question. Papermakers have to kind of play their own version of the old game show, “Let’s Make a Deal!” They normally need to flocculate fines and fibers in the headbox of the paper machine but, if they flocculate too much, they can destroy the appearance of the sheet and/or detrimentally affect other important paper properties. Another item papermakers have to be concerned about is retention efficiency (which goes hand-in-hand with flocculation) normally measured by first-pass retention percent or overall retention percent. Overall (or total) retention is the ratio of the amount of material added with the stock at the wet end of the paper machine compared to the amount that is retained in the sheet on the reel at the dry-end of the paper machine [5]. Typical values for this are 90-95% [3]. First-pass retention is the ratio of the amount of material from the headbox leaving the headbox slice compared to the amount of material that is retained in the sheet in the paper web leaving the couch roll [5]. Typical values for first-pass retention can vary anywhere from 20% to 90% [3]. First-pass retention can even be sectioned off into three different categories of: first-pass fines retention, first-pass fiber retention, and first-pass ash retention [3].

Goal of the Essay

The purpose of this paper is basically two-fold. The first purpose is to give some background information and definitions pertaining to retention on the paper machine. The second purpose would be to attempt to identify some retention strategies. Coinciding with this second purpose, I would like to try to sort out which retention strategies might be best to utilize on a cylinder type of former that has low hydrodynamic shear but where one also needs to have good formation.

Background

It is important for paper manufacturers to be interested in retention efficiency. First of all, they don’t want to lose the costly materials that they put into the system so they need to reduce losses of any solids and/or additives. Re-circulation of white water through effective save-all systems can help with this, but normally, they still need to introduce some sort of chemicals to help with flocculation and retention. The only problem with this though is that if you have a lot of fines retained in the system, these can make it harder to control differences in basis weight and other variations in the paper sheet. At the same time, the manufacturer wants to get the best possible sheet structure he can while sustaining high production efficiency. Not only that, but if you have poor retention efficiency, this can also result in deposit issues which can be avoided many times through the use of a retention aid [6].

Retention also has a lot to do with the efficient use of raw materials and reduced white water solids. Good first-pass retention can promote less “two-sidedness” in the paper sheet. It can help with retaining higher levels of filler in the paper and better brightness performance. Better retention can give better drainage and cleaner back-water systems as well as help with less filling of the paper machine felts [6].

I spoke earlier about fines retention. Fines can be defined as the portion of the paper stock system that is less than 76 microns or any material that can pass through a 200-mesh screen [6]. Fines can even be further sub-divided into primary and secondary fines. Primary fines are produced during pulping and bleaching operations in chemical as well as mechanical pulps. They are more of a chunky material having a surface area of 1.5 to 2.5 m2/g, with a water retention value of 0.6 to 1.5 g water / fiber [6]. Secondary fines are produced during the refining process resulting from the flexing and abrasion of the fibers. These mainly come from the S1 and outer S2 layers of the fiber. Their surface area ranges anywhere from 2.5 to 10 m2/g, and have a water retention value of 2 to 5 g water /g fiber [6]. Fines can be determined in the laboratory through the use of multi-screen classifiers and Britt Dynamic Drainage Jars.

Due to their high-surface areas as compared to paper fibers, fines are important to be retained in the paper sheet because they can influence strength, structural, and optical properties of the paper product. Poor fines retention can be detrimental to the runnability, cleanliness, and chemical efficiency of a paper machine. Even the action of the paper machine itself while it is trying to get water out of the web can wash fines and fillers out so that retention strategies have to be implemented in an attempt to capture these fines and fillers before they can be lost in the system. This is normally accomplished through the use of retention aids or flocculating agents. At the same time, though these same retention aids can also possibly promote too much flocculation and this can cause poor sheet formation in the way of flocs [8].

Flocs are normally divided into two categories – hard and soft. The idea of soft vs. hard flocs is a measure of floc “tenacity”. It is a measure of how well a flocculated system “holds up” to shear and turbulence. The distinction is regarded as the degree to which flocs reform after shear and turbulence “subsides” and it is used as a way to classify chemical additive systems. By definition, a soft floc is a flocculation of fibers and fines that can be easily “broken down” when exposed to turbulence. When redispersed and reflocculated, soft flocs respond like the initial flocs with essentially equivalent retention [2]. One of the main methods by which soft flocs are produced is by charge neutralization which is actually a form of coagulation [1].

Hard flocs show very good fines retention over a wide range of turbulence and shear. This type of floc is highly “tenacious” [6]. On subsequent exposure, hard flocs don’t reform to their original floc strength [2]. These flocs are normally produced by bridging types of flocculation and by using high molecular weight polymers [4].

Mechanisms for retention can either be classified as colloidal or sieving. Colloidal retention is based on attraction forces. These forces have to do with coagulation, which is essentially charge neutralization, and flocculation which is accomplished through polymer bridging [6].

Charge neutralization has to do with adding some kind of a material that promotes a neutral charge. Without a charge-charge repulsion mechanism, the particles will tend to come together. This type of mechanism can be responsible for forming soft flocs. Soft flocs can also be formed as a result of van der Waals dispersion forces, charge-charge attractions or charge patch mechanisms [8]. Soft flocs are normally formed using lower molecular weight materials than what are used for producing hard flocs. These hard flocs are formed by polymer bridging. This bridging is accomplished by the series of loops and tails that get intertwined while extending from the higher molecular weight polyelectrolytes which adsorb on surfaces [1]. This promotes high levels of first pass retention and stability against shear and turbulence.

Sieving has to do with mechanical entrapment due to the fiber web. This mechanism will always retain whole fibers but only some of the fines and fillers due to the forming of kind of a “spider web” at different locations [8]. Mechanical entrapment is normally associated with the formation of soft flocs.

Examples of Retention Aid Program Types

The methods by which retention aids work are either by agglomeration of fine particles onto other fines which makes them larger and easier to retain in the web, or by attachment of the fine particles onto whole fibers [6]. Years ago, the main retention and forming aid papermakers used was alum. They used to use a cliché something like this: “If the paper isn’t forming right, add alum. If that doesn’t work, add more alum.” To a certain extent, alum does work for the purposes of retention and formation. Unfortunately, alum can also reduce strength properties due to the acidic pH conditions it produces. These same conditions can also corrode any mild steel components that are in the paper machine. They later discovered, in addition to this, that there was a loss in permanence properties in the paper that was made from this in such things as books. Because of this, other retention aid regimens had to be developed. One such system is a somewhat “old fashioned” system which still uses alum but also uses cationic starch. This system is for high basis weight products such as paperboard that are produced on slower paper machines under acidic conditions [8].

The alum in this type of program is normally introduced first to help to neutralize anionic charges of the particles in the system. Alum requires good mixing with the furnish before the cationic starch is added, so it is usually added after the stuff box as the thick stock enters the fan pump. The cationic starch is normally added after the pressure screens and fan pump. The purposes of the cationic starch are to retain fiber fines, promote drainage and even give a slight improvement in dry strength. The bridges formed by catatonic starch are not very shear resistant [4]. Because of this, a good use for the alum/cationic starch retention aid program might be in a cylinder type of former which has low hydrodynamic shear – that is as long as the product that is being produced can feasibly be made under acidic conditions.

Another retention aid program that has been developed uses PEI and cationic polyacrylamide [8]. This is a good system for a furnish which is highly anionic such as in mechanical pulp, unbleached kraft pulp, or a coated furnish. With this system, one starts out with something that is highly cationic like PEI. The idea is that the PEI will coat some of the materials in the furnish so that they don’t have as much of a tendency to stick together. This is especially useful in the area of pitch control in that once the particles are coated with a cationic charge, this will enable them to stick to the fibers. The PEI or even Poly DADMAC can be added to the thin stock after the fan pumps and cleaners but before the screens and headbox. One reason for the PEI is to also remove excess anionic materials so that the cationic PAM retention aid will be more efficient. The cationic PAM is then normally added after the pressure screens just before the headbox. This type of retention aid program is good under acidic to neutral conditions in a pH range of 5 to 7.5 where one also wants to increase retention and drainage. If you want to maximize formation, the cationic PAM can be added before the pressure screens [7]. In this way, depending upon the end paper product, this strategy could also be useful in a cylinder former with low hydrodynamic shear. This would probably be a better choice than the first program for the application, depending upon cost considerations, of course. This system can achieve high retention of fines while avoiding fiber flocculation.

A third retention aid program is the classic “dual polymer system.” The program is useful only if you are primarily interested in good retention but not necessarily insistent on good drainage and formation. This type of retention aid system utilizes patch type and bridging mechanisms. The program can exhibit very strong bridging and, in many cases, actually too much bridging. This dual retention aid system involves first introducing alum or some high-charge cationic polymer [1]. This could come in after the fan pumps just before the pressure screens. It could even enter the system earlier, as the thick stock is entering the fan pump. This is then followed by a very high mass anionic flocculant such as aPAM. This is normally added after the pressure screens just before the flow enters the headbox. This system can be very cost-effective if the only thing you’re interested in is retention.

A fourth retention aid program is the classic microparticle system [8]. In this system, a very-high-mass cationic polymer is added just after the fan pump, prior to the pressure screens. This is often preceded by a high charge cationic chemical either in the thin stock or thick stock (before the fan pump) in an effort to first somewhat balance the system so that the very-high-mass cationic polymer may work better. This cationic polymer could be cationic starch or some sort of cationic acrylamide retention aid. The microparticle used is usually either anionic silica or some form of bentonite. This is added after the cationic polymer and the stock enter the pressure screens where they are strongly agitated. The only things that can exit from the screens are the individual fibers with no flocs, breaking any polymer bridges and their associated hard flocs [4]. In this way, one can achieve good retention and formation since the microparticles are added after the pressure screens just before the flow enters the headbox [7]. Depending on cost considerations and machine conditions, this could be another very good strategy for a cylinder former with low hydrodynamic shear.

There is a new three-component retention aid system that is becoming increasingly popular. This system consists of first treating the system with poly-DADMAC to help to prepare the system by neutralizing excess anionic colloidal charges in the furnish. After this, cationic PAM is introduced somewhere before the pressure screens. This is then followed by colloidal silica after the screens [8].

Concluding Remarks

In the end, it appears which retention strategy one chooses to use on a cylinder type of former with low hydrodynamic shear depends on the actual situation and application. Many times one of the major considerations is the cost factor for a particular retention program. Another consideration is what kind of sheet formation is actually essential in the particular grade. In selecting a retention strategy, one also must look at whether the product can or should be produced under acidic or alkaline conditions. There are also factors to consider regarding possible drainage and dryer limitations for that specific paper machine. In addition to this, the strategy can depend on what type of pulp is being used in the furnish, including whether it is a mechanical or chemical pulp. So, in answer to the question of which retention strategy to utilize on a cylinder type of former with low hydrodynamic shear, one might have to answer, at least at first, quite succinctly – it depends!

Literature Cited

1. Hubbe, M. A., Flocculation and Redispersion of Cellulosic Fiber Suspensions: A Review of Hydrodynamic Shear and Polyelectrolytes, BioResources 1 (2), 2006.

2. Hubbe, M. A., Reversibility of Polymer-Induced Fiber Flocculation by Shear. 1. Experimental methods, Nordic Pulp and Pamper Research Journal, Vol. 15, No. 5/2000.

3. Scott, W., Principles of Wet-End Chemistry, TAPPI Press, 1996, ISBN: 0-89852-28-2.

4. Scott, W. Wet-End Chemistry: An Introduction, TAPPI Press 1992, ISBN: 0-898521-300-1.

5. Smook, G.A., Handbook for Pulp and Paper Technologists, TAPPI Press 1988, ISBN: 0-919893-00-7.

6. Unbehend, J., and Deodhar, S., 1995, Introduction to Papermaking Wet-End Chemistry Short Course, The Center for Professional Advancement, March 27-29, Atlanta, GA.

7. Wang, F., and Hubbe, M. A., Where to Add Retention Aid: Issues of Time and Shear, TAPPI J. 1 (1): 28-33 (2002).

8. Wet -End and Colloidal Chemistry, WPS527 Course- pack, Spring, 2007.

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Name: Sameerkumar V Patel
Date: – 04/24/2007

Topic: “What mechanism could account for particles of AKD coming off the fibers and transferring onto GCC upon addition of the filler? Why did GCC adsorb more AKD than PCC?“

Why this subject is important:

Since 1980, alkaline papermaking practice has become more popular, as it provides high brightness, opacity, and strength at lower cost compared to acidic papermaking. In an alkaline papermaking process, calcium carbonate is used as filler and buffering agent, and it also is able to give higher brightness compared to clay (that is normally used as filler in acidic papermaking practice). Basically, three types of calcium carbonate can be used in the paper making process depending upon the availability of the mineral products and property requirements of paper. Those are chalk, Ground Calcium Carbonate (GCC), and Precipitated Calcium Carbonate (PCC); all of these have similar chemical structure but have different physical properties and surface charges. Due to the differences in the physical and surface charges properties they are able to induce difference in properties to the paper. According to their physical and chemical properties they are able absorb and scatter light at different levels that induce different level of brightness to the paper. Moreover, they can interact differently with different chemicals used in the paper making process (retention aids, flocculants, sizing agents etc.). Due to all of these this subject is very important for papermakers. Several research projects have been carried out on this subject to make papermaking process more efficient.

Answer to the assigned question:

(1) To answer this question we need to understand the behavior of AKD in presence of filler and fiber. The papermaking process utilized emulsified AKD, and this emulsion was prepared by the cationic starch, so, emulsified AKD had a cationic charge on it. Fibers are normally hardwood fibers or softwood fiber or a mixture of both fibers according to the property requirements in the final product. Fibers have relatively less surface area as compared to GCC and have anionic charge on surface due to the presence of the carboxyl ions on it. GCC is prepared from the limestone by the different unit operations. It has relatively very high surface area. As we do not purify it before and after grinding, it has Al- and Si- oxides on its surface; in addition to that, generally, phosphates are added as a grinding aid and dispersant during the grinding process those are anionic in character. Due to these ions GCC has anionic charges on its surface.

Let’s suppose that we have a furnish that contains AKD and fiber. We can predict that some of the AKD could react with fiber and become attached by an ester linkage to it, and some AKD could become retained on the fiber surfaces due to cationic AKD and anionic fiber charge attraction and remaining remain in the furnish. Now, if we add GCC to the furnish, GCC would become adsorbed, while AKD remained in the furnish. The GCC would be expected not only to adsorb AKD from the furnish, but also to adsorb AKD retained on the fibers surfaces. This is due to the very high surface area and anionically charged surface; these two factors make adsorption much favored to GCC. From this we can say that fiber would be expected to retain AKD that is reacted with the fiber and linked to it by ester linkages.

(2) The main difference between GCC and PCC is the way it is manufactured, and due to that difference they have very different surface characteristics. PCC is manufactured by the precipitation from calcium hydroxide with carbon dioxide, while GCC is prepared directly from the limestone by grinding. As one manufactures PCC one has better control over surface area and purity in final product, compared to GCC. Normally, PCC does not contain any other minerals, but recent study has shown that it could have some amount of calcium hydroxide in it, as it is manufactured from the calcium hydroxide. PCC has a very high surface area, low particle size and different types of particle shape and crystal lattices, depending upon how one control precipitation during the manufacturing. From these we can expect that PCC could adsorb more AKD than GCC, but in reality it adsorbed less AKD than GCC on the basis of surface area. This can be mainly attributed to the presence of the anionic charges on surface of GCC, which make adsorption of AKD very much favorable and effective than PCC.

Logical or theoretical support for answer:

AKD is a most commonly used sizing agent, prepared from the fatty acid, emulsified with cationic starch, and able to give higher degree of sizing by making ester linkages with cellulose.

The primary reason for using PCC is to impart brightness and opacity to the paper products; moreover, it is cost-effective relative to other additives such as TiO2 and works well in alkaline papermaking processes.

The performance characteristics of an AKD size product are a function of physical factors related to its particle size distribution and mean particle size, particle shape, crystal type and brightness; the importance of surface potential, pH, and residual impurities are dependent upon specific applications.

The GCC is made directly by grinding limestone, and the PCC is manufactured by chemical reprecipitation techniques. Within the two major groups, there are several categories based on differences in particle size and particle shape. Normally, the GCC has a larger average particle size and a broader size range as compared to the PCC.

Calcium carbonate occurs in nature as either of two crystalline polymorphs, calcite or aragonite. Thermodynamically, calcite is the only stable form of calcium carbonate. It falls into the hexagonal-scalenohedral crystal class in the hexagonal system. Other commonly observed crystal habits in calcite are prismatic, tabular, cuboid, rhombohedral, and scalenohedral. Aragonite falls into the dipyramidal crystal class in the orthorhombic system. The crystal habits usually observed are elongated prismatic or acicular in form. Both, calcite and aragonite have identical refraction index, which is sufficient to make a meaningful contribution to opacity in most paper applications. Normally, GCC has wide variety of crystalline structures while PCC has only one or two crystalline structures as one can control the crystallization during the manufacturing of PCC, and those structures impart different properties to the final product. For example, a rosette structure gives bulk, smoothness, and opacity, whereas a rhombohedral structure gives bulk and dewatering characteristics. Moreover, these structures are able to give certain other properties such as surface area, size distribution, and particle size. Due to all these factors, PCC can have a very high surface area relative to GCC (almost 4-10 times higher depending up on the manufacturing technique), narrow size distribution, and smaller particle size.

As one manufactures PCC by a reprecipitation technique, impurities may be at very low level, and one does not use any dispersant during the manufacturing; it has cationic surface charges due to the presence of the calcium ions on its surface. By contrast, in the case of GCC the filler product does contain natural impurities such as Al and Si- ions, and one uses dispersant during the preparation of GCC from the limestone; it has anionic charges on its surface. These anionic charges play an important role in the retention of the AKD on the surface of the GCC.

Physical and chemical properties of fiber mainly depend on the pulping process, source of the fiber, and any treatment applied as it is being used in the papermaking process. Although thermo-mechanical pulp (TMP) fiber generally has high surface charges as compared to kraft pulp fiber, as there is presence of lignin in the TMP that can ionize at different pH during the papermaking process. While kraft pulp has higher surface area as it was refined during the process, we can improve surface area of any fiber by refining. The anionic surface charges of fiber surfaces plays a very important role in the retention of AKD on its surfaces as AKD is emulsified with cationic starch and could retain on the fiber surfaces due to the charge interaction. Some of the AKD molecules are able to bond with the –OH linkage of cellulose by covalent bond, ester linkages, able to give higher retention and sizing effect to the final product. From this we can say presence anionic surface charges are able to improve retention of AKD on the fiber surfaces significantly.

Experimental support for answer:

Hagemeyer [1] studied calcium carbonate and its properties with respect to different types of manufacturing techniques. He observed a wide variation in the crystal structures and surface properties in calcium carbonates, which were prepared by different techniques such as ground calcium carbonate, superfine calcium carbonate, and precipitated calcium carbonate. He observed 96.6% purity in GCC and more than 98% in PCCs (three different types of PCC; according to the precipitation techniques). The difference mainly was attributed to the presence of impurities such as Al-, Si-, and Fe- oxides. This value can be changed according to raw material. Another noticeable difference was pH, GCC typically had a lower pH (9.1) than PCC (9.4), and even more pH if precipitation was carried out with sodium carbonate (pH=10.3). This difference was mainly attributed to the purity of precipitate calcium carbonate (PCC), and presence of calcium hydroxide in PCC. The higher pH for precipitation with sodium carbonate is due to the evolution of sodium hydroxide as a byproduct. The surface area of the calcium carbonate whether it be either GCC or PCC, mainly depends upon the processing conditions. Generally, surface areas range from 3-7 m2/g for GCC and from 9-11 m2/g for PCC [1]. The zeta potential of GCC and/or PCC depends upon the several factors such as the presence of any anionic or cationic charges on the surfaces, as well as the presence of acid or base in the system, as this can able to give different dissociation ions of calcium carbonate [2]. Generally, GCC has a negative surface charge and PCC has a positive surface charge on its surfaces [2]. Furthermore, the zeta potential of calcium carbonate is pH-dependent, as calcium carbonate is able to give different ions such as H+, OH-, Ca+2, Ca-, OH+, and HCO- concentrations; additionally, if system has any other inorganic ions, the whole system can become more complex. These ions play an important role to change the zeta potential of the whole system [2]. Anderson and Yunko studied the affect of PCC, GCC, and filler clay on different properties of paper; they concluded PCC is able to give better brightness and tear strength with the moderate ash content than GCC, while GCC gives better tensile and burst than PCC [3].

Esser and Ettl studied physico-chemical aspects of AKD retention and sizing efficiency, and they found very interesting results [4]. They found that GCC adsorbed a higher amount of AKD than PCC per gram of filler. This difference was mainly attributed to surface charges and particle shape [4]. They also observed a sudden increase in retention with addition of smaller amount of filler (GCC and PCC as well) to the furnish. They also observed a higher amount of β-keto acid leading to ketone in PCC, compared to GCC, which is an undesirable side reaction of AKD, So, we can predict that PCC would not be able to give efficient retention as GCC does. Furthermore, this effect also depends on the addition sequence of additives [4]. Molecular weight and degree of substitution with cationic charge of AKD also play important roles in the retention of AKD on filler/fiber surfaces. References [5] and [6] show that low molecular weight, emulsified with highly charged cationic starch, small particle size, AKD was able to give very good sizing, however, we can have different results if system has cationic polymer present in furnish. Colasurdo and Thorn [7] also observed similar results. They observed a loss of AKD sizing over time with PCC as a filler and found negligible loss in sizing with chalk as a filler. They predicted that the lower level of initial sizing and the fact that there was no additional cure over the time was due to the very high ratio of filler to fiber surface area for PCC than chalk, which was almost three times higher than chalk. They also proposed there should be other factors such as surface chemistry and morphology influencing the observed phenomenon and competition between PCC and cellulose fiber for AKD.

The presence of carboxyl groups on the fiber surface also can play an important role in retention of AKD on the fiber surface. The AKD could further react with hydroxyl groups of the fiber and be able to give a high degree of sizing by forming ester linkages between cellulose and AKD. The authors of [8] studied the effect of carboxyl groups on fiber on retention of AKD. They observed very high retention of AKD on fiber surfaces when carboxyl groups were present on the surface and almost no retention in the absence of carboxyl groups on the surface. They also observed an increase in AKD retention with increase in AKD and cationic polymer in the case of the fiber having carboxyl groups on the surface. They suggested that there was formation of ionic linkages between polymer-AKD-fiber and that such attachments could be to give a higher level of retention of AKD on fiber surface.

Finally, from the above discussion, we can say that the retention of AKD on fiber and/or filler surfaces, that can gives good sizing of paper, is govern by several factors, but surface area and surface charges of the filler and fiber are major factors. Physical and chemical properties of AKD are also important and could affect retention in certain conditions. On the other hand, papermaking conditions such as pH, the presence of the other additives, and the order of addition of additives are also critical and can have significant effects on retention and sizing of paper. Generally, we can expect higher brightness and inferior sizing with PCC in comparison to GCC.

Situations in which the findings can be useful: – Now, as we know PCC can give high brightness, opacity and tear strength with insignificant sizing, compared to GCC, and GCC can give lower brightness, higher tensile and better sizing than PCC. We can use them according to our necessity. If our primary requirement is brightness and not much concern about sizing, we can go with PCC. If we are concerned about high level and longer duration of sizing, we can go with GCC. Other factors are availability and cost. In most part of the world calcium carbonate is readily available from natural resources, and GCC can be prepared easily that, but main concern is the purity of available calcium carbonate and manufactured GCC regarding to utilization in papermaking process. On the other hand, PCC has little cost factor as it is prepared by reprecipitation of calcium carbonate and required additional facility to manufacture, but we could accomplished required brightness and opacity at lower dosage of PCC as compared to GCC, which reconcile the cost associated with production of PCC. Finally, I believe as PCC can able to give high brightness and opacity with comparative sizing, it is better option and due to this reason it is used as filler in papermaking process world wide. For instance, for copy and printing grade brightness and opacity are prime requirement and required to use PCC as a filler to get those properties with minimum dosage and cost, as compared to GCC.

References

[1] Hagemeyer, R., “Pigments for Paper,” TAPPI Press, 1984.
[2] Madsen, L., “Surface Charge of Calcite,” Encyclopedia of Surface and Colloidal Science, 2002
[3]Anderson, T., and Yunko, A., “CaCO3 fillers: selection, use in alkaline papermaking systems,” Pulp and Paper, October, 1983
[4] Esser, A., and Ettl, R., “On the Mechanism of Sizing with AKD: Physico-chemical Aspects of AKD Retention and Sizing Efficiency,” Pira International, Vol 2, September 1997
[5] Ravnjak, D., “Deposition Kinetics of AKD Size on Pulp Fibers,” Colloid and Polymer Science, 1435-1536 (online), 2007
[6] Chew, Y., Peng, G., Roberts, J., Xiao, H., Nurmi, K., and Sundbeg, K., “Characteristics of AKD Emulsions Prepared Using Cationic Starches with Well-Defined Structures,” Pira International, Wet End Chemistry, May 2004
[7] Colasurdo, A., and Thorn, I., “The Interaction of AKD with other Wet End Additives,” Tappi Proceeding, Papermakers Conference, 1992
[8] Isogal, A., Kitaoka, C., and Onabe, F., “Effects of Carboxyl Groups in Pulp on Retention of AKD,” Journal of Pulp and Paper Science 23 (5): (1997)

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Name: Ronalds W. Gonzalez
Date: March 8, 2007

What are the logical and practical justifications, if any, in favor of actively controlling the level of fiber flocculation in the head box furnish to a target level?

It is right to say that fiber flocculation is the first step in the formation of the paper web. In fact, some authors have stated that “flocculation in the wet end of papermaking can be defined as the intermediate state between the raw material and the final product” (Blanco, 1994). But it is also right to say that papermakers work to achieve certain levels of coagulation and also work to avoid the formation of fiber flocs. Hubbe (2006), states that “paper that contains a lot of thick areas, due to the presence of flocs, also must contain a lot of thin, weak areas, adjacent to those flocs”. This non-uniformity of the paper lowers paper strength and appearance; also non-uniformity could affect runnability of the paper machine and also some operations as coating (Hua et al. 1996). As shown in figure 1, the control of fiber flocculation in the headbox furnish can avoid some operational problems in the paper machine (such as paper web break and dewatering problems). Yet as stated before and as will be explored in the next pages, fiber flocculation control can have a positive impact in paper properties: strength and optical.

Figure 1. Some effects to consider the control of fiber flocculation in the headbox

Papermakers also need some functional additives become part of the paper, so the use of retention aids is a very good alternative to increase the retention of these fines and fillers, but when we try to increase the retention of fines through retention aid agents, we are also helping to increase the extent of flocculation, so the application of shear forces is needed to prevent and break down fiber flocs in the slurry.

As we understand and see that paper production must be studied as a complete system, the interaction of different factor in the production can affect other variables of the process.

Some evidence

About 80-90 years ago papermakers used to sell paper just as a good (there were not too many options), but now and days with higher market competition and with too many quality standards to fulfill, the “paper” has become a service more than a good. That could explain why the paper that does not fulfill client specifications is not sold, and could be used only as recycled raw material. Nazhad et al (2000) found out that poor paper formation (by variation of fiber length and agitation) lowers the tensile strength of paper due to stress concentration caused by non-uniformity mass distribution. As expected, they observe that there is a relationship between lower basis weight and lower breaking length; this observation can be useful to explain why thinner area (weaker areas) around fiber’s flocs can contribute to lower the tensile strength of paper. These conclusions are also confirmed by Waterhouse (1993) who found that specific tensile strength was inversely affected by the coefficient of variation (CV %) of mass density. The same author demonstrated the inverse relationship between grammage and CV%.

Nazhad et al (2000) also states that handsheet paper formed at higher agitation resulted in higher breaking length, this information can be interpreted as higher agitation will help to minimize the formation of fiber flocs resulting in a more homogeneous paper.

Although most of the information presented here is referred to the relationship between paper strength and uniformity of paper formation, the other properties displayed in figure 1 must not be forgotten: optical properties. Hua (1996) showed (practically) a linear relationship between higher formation index and gloss of paper, also the same author presented a positive relationship between formation index and scattering coefficient. This information can have a higher implication depending on the kind of product elaborated. In the case of uncoated free sheet, the optical properties are very important; in fact there are some products that are specifically oriented to some market segments that require very special characteristic of brightness, opacity, scattering, etc. Also in the case of unbleached pulp to produce liner board, these optical properties can be significant to the product differentiation; in contrast, in the case of semi-chemical pulp (to produce medium board paper), optical properties should not be very significant.

So we could properly say that quality of formation affect paper strength or either paper quality specifications

Are there other ways to account for their observations?

But it is also known that formation of paper is affected by the drainage and retention of fines. That is why the use of retention aids must be reviewed. Doo Hoon, et al (2005) observed that when using branched PAM instead of linear PAM with filler addition, drainage time was decreased, air permeability was improved, and paper physical strength was increased. Thus questions about how retention aid polymers work and how and in what time shear forces breakdown fiber flocs can be partially answered with the help of electronic tools, which in an indirect way measure the formation of fiber floc and their degradation by agitation. Anker (2001) presented the application of a torqued-based flocculation analyzer in order to determine the effectiveness of retention aid polymer and the degradation of flocs in function of time. The author statically correlated the load motor of the impeller with the formation and degradation of flocs. This technique as others that will be considered later in this paper have the advantage to give results in function of time, in other words it is possible to evaluate fiber formation as an action of flocculants, and flocs degradation as a consequence of shear forces and/ or agitation.

These data about polymers performance and breakdown of flocs in function of time and shear forces are very useful to determine in a practical manner how to optimize unit operations in the production of paper. Blanco et al (2002) with the use of a focused beam reflectant measurement system (FBRMS) could study the evolution of flocculation process with different flocculants at different agitations (rpm) in function of time. Is this information useful? Yes, it is. Readers, and specially those who have worked or spent some time in a paper mill, should imagine the practical application of these data. In production, processes are very tightly controlled and the “time” between each unit of the production chain is known. So for example, if the operators of the paper machine are experiencing troubles with the uniformity of formation of paper as a result of a high level of floc formation, then the following should be reviewed:

The evolution of flocculation in function of time
The effects of shear forces or agitation in breaking down those flocs.

Results from reviewing the first point could give highlights about where add flocculant polymers. A result of point two would give details about if increasing the shear forces (if possible). However, this last point must be carefully analyzed, because some induced coagulation-agglomeration bonding (to help the retention of fines) could be irreversibly affected. This last interpretation could take us to think in some strategies to fix fillers onto fiber surfaces (resistant to agitation) and the use of selective deflocculation mechanism. This is a very interesting subject to discuss; however one should not loose sight of our discussion here “practical justification in favor of actively control the flocculation of fiber in the headbox”. As it was stated some paragraphs earlier, the production of paper must be studied systematically: one variable affects another.

Despite the fact of the importance of flocculation control, most of the electronic control equipment is not integrated to the paper machine. The control of the fiber flocculation in the paper machine should be controlled on line, as it can be controlled in the case of such variables as percent humidity, pH and temperature. This implies that most of the effort to be done in the future about fiber flocculation control should be oriented to developing automated alternatives in the same thin stock, and the best justification is that the level of fiber flocculation can determine the quality of our products, the yield of our operations, and our permanence in the market.

References

Anker, L. S. 2001. “Practical experiences in additive screening using a Torque-based flocculation analyzer,” Proc. TAPPI 2001. Papermakers Conf., TAPPI Press, Atlanta.

Blanco, A. et al. 1994. Flocculation control in papermaking. 1994 Papermakers conference, proceedings.

Blanco, A. et al. 2002. Focused beam reflectant measurement as a tool to measure flocculation. Tappi J. 1 (10) 14-20.

Eisenlauer, J. et al; 1987. Fiber-optic flocculation sensor for on-line control of retention and drainage aids efficiency. Nordic Pulp and Paper Journal 3 (4) 132.

Fuentes, E. et al; 2003. Monitoring Flocculation of fillers in papermaking. Paper Technology. 44 (8) 41-50

Hua, et al. 1996. Cited by: Hubbe, M. 2007. Flocculation and redispersion of cellulosic fiber suspensions: a review of effects of hydrodynamic shear and polyelectrolytes. In preparation.

Hubbe, M. 2007. Flocculation and redispersion of cellulosic fiber suspensions: a review of effects of hydrodynamic shear and polyelectrolytes. In preparation.

Nazhad, M. M., Harris, E.J., Dodson, C.T.J., and Kerekes, R.J. (2000). The influence of formation on tensile strength of paper made from mechanical pulps,” Tappi J. 83 (12), 63 [electronic document].

Waterhouse, J. 1993. Effect of papermaking variables on formation. Tappi J. Vol 76. (9), 129-134.

Yoon, D.-H., and Park, J.-M. Fibers flocculation and physical properties changes of paper depending on cationic polymer addition. Polpu, Chongi Gisul (2005), 37(1), 10-16.

==========

Name: Ilari Filpponen
Date: April 2007

Topic: “What evidence is there, if any, that the observed increase in wet-strength efficiency with increasing carboxyl content of fibers is due to covalent bond formation? What other mechanism (s) could explain the results?”

Why this subject is important for the paper industry: Paper is created when cellulose fibres are added to an aqueous suspension to form a wet layered mat which, upon consolidation and drying, leads to the final product. The strength properties of the formed fibrous network are determined by the intermolecular forces (van der Waals; hydrogen bonding) at the contact point between fibres. Nevertheless, hydrogen bonds are extremely sensitive to water, and as so, exposure to water will disrupt the inter- and intramolecular hydrogen bonding due to the swelling phenomena, which in turn decreases the strength properties of the final product. The wet strength of paper is described as the ability of paper to maintain a percentage of its dry tensile strength when it has been saturated with water. For decades researchers have been investigating different approaches to improve the wet strength properties of paper. The major focus has been devoted to wet strength additives that are typically polymeric chemicals, such as urea formaldehyde (UF), melamine formaldehyde (MF) and polyamideamine epichlorohydrine (PAAE).

Two mechanisms are typically used to explain wet strength development in paper, namely, protection and reinforcement. However, despite the extensive studies of different wet strength additives there is no agreement with operating mechanisms of these chemicals. It is widely believed that UF and MF are conveying wet strength via internal cross linking with themselves (protection). In addition, MF appears to operate by also reacting with cellulosic hydroxyl groups. On the contrary, for the PAAE resins it has been suggested by several investigators that carboxyl groups on the fibres react with the resin leading to the formation of ester linkages (reinforcement).

Answer to the assigned question: The relation between carboxyl group content and wet strength development has been studied by a number of investigators (1,2,3,4). In general, results have shown that wet strength is increasing with increased carboxyl content, but indisputable evidence of operating mechanism is still lacking. Some studies have provided spectroscopic data that directly points toward covalent bonding (an ester) between wet strength resin and fibers (3,5). However, the attempts to prove covalent bonding by using simple model compounds have failed (2). It has been explained that the positive effect of increased carboxyl content in fibers is due to the electrostatic interactions between the resin and carboxyl groups, which in turn will enhance resin adsorption and make it more effective. Based on the available information at the moment it is reasonable to conclude that more research is needed to confirm the reinforcement mechanism. Furthermore, it is impossible to exclude the existence of protection mechanism, as it has been evidenced that PAAE crosslinks with itself (2,6). So, the main question to address is whether the observed increase in wet strength is due to combination of these two mechanisms or only by self-crosslinking of PAAE?

Logical or theoretical support for answer: As shown in figure 1 below, two types of interactions have been proposed for PAAE resin. The reaction between cellulosic carboxylic groups with azetidinium ring to form corresponding esters follows the reinforcement mechanism. The second proposed reaction is self cross-linking of the resin. It is worth mentioning that both reactions may occur at the same time. However, on the chemistry point of view the self cross-linking seems more likely because amine is stronger nucleophile than carboxylate-ion. Also, the availability of carboxyl groups in fibers will be a limiting factor for the ester formation. However, it is possible to increase the amount of carboxylic groups in furnish by adding carboxymethylcellulose before the addition point of PAAE resin. As a matter of fact the aforementioned treatment is a common strategy to avoid over-charging in the case of high wet strength grade papers.

Fig.1. Azetidinium group on PAAE resin

Spectroscopic methods such as infrared- (IR) and nuclear magnetic resonance (NMR) spectroscopies are widely used tools for the wet-strength mechanism investigations (2,3). However, these techniques have some sensitivity limitations mainly related to the low amount of additives (as low as 1% based on dry fiber) as well as structural similarities with main- and side-reaction products. Model compounds are typically used to simulate the proposed reaction mechanisms in order to understand the behavior of certain wet strength additives in real systems. Although modeling provides a convenient tool to investigate reactions some issues, such as solubility and reactivity, need to be critically considered before final conclusions can be made.

Experimental support for answer: Espy and Rave found indirect evidence supporting the reaction of azetidinium resins with the carboxylate groups of pulp (5). Their investigations showed that low initial addition of PAAE (0.1-0.2%, based on dry fiber weight) improved wet strength significantly more than addition of more resin, on a per-unit-resin-retained basis. To further support this preliminary finding Wågberg and Björklund studied the possible formation of ester linkage between cellulosic fibres and PAAE resin (3). For this purpose a series of carboxymethylated pulps with different degrees of substitution (D.S.) were selected, since the D.S. was believed to have a strong effect to the final wet strength properties of PAAE treated paper. Furthermore, the effect of addition levels of PAAE resin in bond strengths was evaluated as a function of D.S. of the pulps. It was found that the wet and dry strength followed the same trends, and they increased not only as a function of D.S., but also with increased PAAE levels. This indicates that the strength development is restricted by the bond strength between the fibers.

In order to distinguish the effects of carboxymethylation and PAAE resin to the strength improvements, a constant concentration of PAAE was used with pulps having different D.S. values. Experimental results indicated that the change in D.S. is more significant for the dry strength properties whereas the presence of PAAE promotes wet strength properties, as the sheet becomes more resistant to the swelling. By reason of the perceived positive effect of carboxymethylation to the dry strength properties the authors decided to determine the relative bonded areas (RBA) of the sheets. The light scattering studies indicated that RBA increased with the carboxymethylation, which means that the improvements in strength properties were provided by virtue of improved bonding between fibres (addition of PAAE) as well as increased bonded area between the fibres. Based on the information above it can be concluded that carboxymethylation seems to develop the strength properties at least in three different ways: by increasing the PAAE uptake, by forming ester bonds with PAAE and by raising the value of the RBAs.

The interaction of PAAE and carboxyl groups was subsequently studied by preparing sheets with diverse RBA values. The results revealed similar behavior to the previous investigations i.e. the carboxyl groups enhanced the efficiency of PAAE, most likely via ester formation. The final evidence of existing ester linkage was provided by FTIR, as the carboxymethylated sheets with and without PAAE resin were measured separately and obtained spectra were then subtracted. After subtraction, three absorption bands were remaining. One of them possessed characteristic wavenumbers for saturated esters while other two were derived from the PAAE resin itself.

The study by Devore and Fischer, however, pointed out quite different results in terms of the possible covalent bonding between the PAAE resin and cellulose (2). In fact, carefully selected model compound experiments in combination with NMR analysis excluded the existence of such a bonding. On the contrary, the reaction between PAAE and simple amine showed higher reactivity, pointing toward a protection mechanism. Further evidence supporting a protection mechanism was that the tensile strengths of PAAE treated handsheets followed the additivity rule, consistent with the behavior of independent networks of resin and paper fibers. The resins that are known to form covalent bonds to paper fibers do not follow the additivity rule.

Concluding remarks: Although comprehensive understanding is still missing, it seems that covalent bonding between PAAE and cellulosic carboxyl groups does not predominate in development of wet strength of paper. On the contrary, it seems to be more likely that PAAE improves wet strength via self cross-linking and carboxymethylcellulose can be used as retention aid. Finally, it would be more convincing to compare the observed FTIR spectrum versus a control sheet without added PAAE as the carboxyl groups in carboxymethylated pulp may also react with available hydroxyl groups to form an ester that should appear in a very similar region in FTIR spectrum as the suggested ester linkage between PAAE resin and cellulosic fibers.

Literature cited

1. Stratton, R., A., “Dependence of sheet properties on the location of adsorbed polymer”, Nordic Pulp and Paper Research Journal 4 (2): 104-112 (1989).
2. Devore, D., I., and Fischer, S., A., “Wet-strength mechanism of polyaminoamide-epichlorohydrin resins”, Tappi Journal 76 (8): 121-128 (1993).
3. Wågberg, L., and Björklund, M., “On the mechanism behind wet strength development in papers containing wet strength resins”, Nordic Pulp and Paper Research Journal 8 (1): 4. Espy, H., “The mechanism of wet-strength development in paper: a review”, Tappi Journal 78 (4): 90-99 (1995).
5. Espy, H., and Rave, T., W., “The mechanism of wet-strength development by alkaline-curing amino polymer-epichlorohydrin resins”, Tappi Journal 71 (5): 133-137 (1988).
6. Fischer, S., “Structure and wet strength activity of polyaminoamide epichlorohydrin resins having azetidinium functionality”, Tappi Journal 79 (11): 179-186 (1996)

==========

Name: Anthony Atamimi
Date: April 17, 2006

Topic: “Given the high shear stress present in the modern hydraulic headboxes, should we be focusing on use of retention aid systems capable of reflocculation?”

Why is the subject significant to paper industry?

In the days of slow paper machines and low-turbulence headboxes, simple electrolytes such as alum were used to affect retention via charge neutralization. This practice is very susceptible to hydraulic shearing, such as induced by an increase in machine speed. The hydrodynamic forces generated in the paper former demand more tenacious flocculation [1]. A new state-of-the-art paper machine nowadays runs at about 5000 fpm, which is 2 or 3 times higher than that of 20 to 30 years ago. The turbulence generated by modern hydraulic headboxes may cause flocculation. In addition, fine particles being retained on fiber surfaces by colloidal retention may become redispersed by shear.

Cost and efficiency of using the chemical material are crucial for a paper mill. The right selection of retention system is critical. Otherwise expensive chemicals may be wasted and become ineffective after passing through the headboxes.

Besides the commercial aspect, the technical challenge in wet-end process is the balancing act between the strong flocculation of fibers, fines and filler with the issue of uniformity of their distribution in the suspension and on the web. The conventional retention system, using a high charge density cationic polymer along with a high molecular weight anionic polymer only offers a one sided-solution to the expected outcome. The papermaker can achieve a good retention level of fibers, fines, and filler in the suspension, without suffering from the poor dewatering, but may lose the uniform distribution of fibers in suspension and on web of paper.

Why do we need a retention system capable of reflocculation?

Colloidal retention systems in general can be divided in two main groups based on the number of chemical components, i.e. single and dual. The dual-component retention aid systems are nowadays more practical for the papermaking process because firstly their bonding action is stronger, such as between fiber and filler, and secondly the dual system can provide more control in the addition process of the two different polymers (cationic high charge density polymer and anionic high molecular weight polymer). The latter advantage offers the optimum time for the first cationic polymer to be adsorbed to fiber, making it possible to obtain an effective bridging mechanism from the second anionic polymer [2].

The mechanism of bridging formation from the high molecular weight retention aid polymer will stand up to relatively high levels of hydronamic shear and result in high retention of fine materials. One of the characteristics of “hard flocs”, a term introduced by Britt and Unbehend, is that they tend to break down irreversibly when exposed to sufficiently high shear stress.

Another type of dual-component system is the microparticle retention system, which offers reflocculation or reversibility of flocculation. This system can answer the challenges of modern hydraulic headboxes with its high speed. It allows the papermakers to balance their two contradictory goals between the strong flocculation effects, leading to potentially high retention efficiency, and also a relatively uniform fiber distribution in the suspension and in the wet web.

Microparticles systems can give a high degree of flocculation even at moderate flocs size, due to the reversible nature of the flocculation. When a static in-line mixer in the experiment disrupts large flocs, the suspension reflocculates to smaller size, and more compact flocs. Experiments with CPAM and montmorillonite particles without and with increased shear show the possible fiber flocculations mechanism and at the same time it also suggests the phenomenon of the improved dewatering process on paper machine [3].

What are various authors’ points of view on this topic?

In regard to the use of colloidal silica as the anionic microparticles, Carr described the bridging mechanism happened between the strands of CPAM absorbed on the fibers [4]. Van de Ven described the bonding of fiber-CPAM-montmorillonite-CPAM-filler as being much stronger than that resulting from fiber-CPAM-filler bonding [2]. In other words, the montmorillonite is bridging the strands of CPAM. Carr further explained that the stronger bonding was due to the electrostatic attraction from the higher anionic content of colloidal silica than that of fibers. The sphere size of 5 nm plays the bigger role for the microparticles or nanoparticles to penetrate to fibers. It was suggested that if the amylopectin branches were separated by a distance of 5-7 nm, then a <5 nm sol might be optimum for charge neutralization. In reality, the commercially available silica nanoparticles clearly exhibited characteristic of both charge neutralization and microparticles bridging, in which the bridging mechanism defined as the nanoparticles effect [4]

Despite the charge naturalization process that often results as a consequence of the addition of negatively charged montmorillonite or colloidal silica to a system that has been treated with a sufficiently high amount of cationic polymer, there must be electrostatic forces due to a patch-like coverage of various surface with oppositely charged materials that allow the reflocculation process to take place.

From practical papermaking experience, it is generally recognized that polymers which function by bridging flocculation mechanism tend to be poorer dewatering aids than more highly charged polymers, which are assumed to function according to a patch flocculation mechanism. Another study, by Hedborg and Lindstrom [5], of microparticles retention system was emphasized on the drainage or dewatering process. If a papermaking stock reflocculates after the turbulence generator in modern headboxes, it was conceivable that this would lead not only to a good retention of fines and fillers but also to a more open wet, improving drainage both on the wire and in the press section [5].

What’s their evidence?

In 1993 Swerin et al. [3] made a study of the fiber flocculation characteristics of some microparticles retention aid systems. They described the reflocculation mechanism as basically resulting from the reaction of anionic microparticles with pre-adsorbed cationic polymers, rather than a long-chained anionic polymer interacting with pre-adsorbed cationic polymers. In this study they observed the flocculation index and the average floc diameter (mm) against the added amount of montmorillonite (mg/g). The CPAM with montmorillonite (Mont) particles were used with and without increased shear using a static inline mixer for comparison. They evidently found that reflocculation took place after an increase in the shear. The larger flocs were broken down to smaller flocs, but the degree of flocculation was still high due to a reflocculation of smaller flocs. Despite the flocculation index with increased shear of 1 mg/g Mont (5 second measurement) had a 15% lower, but the flocculation index of 3 mg/g Mont was about the same between before and after the increased shear. Even the 4 mg/g Mont showed that the increased shear had a bigger flocculation index than that of without increased shear. In regards to the flocs size, the concentration of 1 mg/g Mont and 3 mg/g Mont had a 15% and a 30% smaller size respectively. Swerin et al. further suggested that the reformed flocs were more compact than the flocs were initially formed before the increased shear. This was one possible dewatering mechanism for microparticles systems, because a paper with smaller, more compact flocs would have a higher dewatering rate [3]. The smaller and compact flocs theoretically will also help and maintain the uniform distribution of fibers, fines and fillers in the suspension.

The 2005 study by Carr [4] demonstrated the concept and mechanism by which microparticles function. He used silica nanoparticles, i.e. 5 nm sphere diameter that had much smaller dimension than that of regular montmorillonite micro-particles’ size, i.e. 1 nm length and 600 nm width. Due to the much smaller size of silica nanoparticles, Carr preferably distinguished it from the term of microparticles. The study has further strengthened the previous study of the benefit of microparticles retention system in reflocculation. Using three different dimensions and degrees of structure of nanoparticles, the effect of reflocculation increased with the increased dosage. The reflocculation rate was measured by the percentage residual reduction; it increased from average 30% to 45% under 1# and 5# silica. We can see the second proof of reflocculation from the reduction of fiber and filler sewer loss in tons and the increase of total and ash retention of monthly production report. Originally the paper mill used CPAM baseline and changed to nanoparticles system; on the daily average production number (1) The filler sewer loss dropped about 60% from 4.53 to 1.83 tons, (2) The fiber sewer loss decreased about 62% from 3.63 to 1.39 tons, (3) Ash retention increased about 6% from 44.6 to 50.2% and (4) Total retention increased about 3% from 79.2 to 82.4%. Carr said that the key to getting the microparticles or nanoparticles retention aids to work well was to deliberately shear the stock and bring about the reflocculation that exposes more polymer loops and tails to silica nanoparticles. With the charge neutralization mechanism of patch-like coverage of surface, there was a strong reflocculation that takes place after the shear stress [4].

Are there others ways to account for their observations?

Work by Hedborg and Lindström in 1996 addressed the question of how a high level of reflocculation, which they called “reversibility,” was the prerequisite of good dewatering. The investigation was to compare the effects of microparticle-based dual-component retention aid systems with those of conventional dual polymers. The contrast between microparticles and conventional dual component retention systems is most particularly apparent when the nature of the bridging mechanism is considered. The reversible nature of microparticles is believed due to the bridging mechanism of anionic microparticles instead of with long-chained polymer. When long-chained polymers is used, such as in a conventional dual component system, the chain cleavage and reconformation of the polymers on the particle surface takes place, whereas these mechanisms apparently occur to a lesser extent when microparticles were used as the bridging aid [5]. In another words, it’s also said the cleavage and reconformation of polymer basically limit the reflocculation capability [6].

The investigation of Hedborg and Lindstrom was firstly on the single component retention system, the reversibility index for the low charge density CPAM decreases with increasing polymer addition, i.e. from 0.5 to 0.2, whereas the reversibility index for the high charge density polymer remained constant at about 1.0. Secondly overall the dual component retention system showed that the reversibility index increased with increasing polymer addition. Out of 4 different types of dual component, the conventional dual retention system was poorer than that of microparticles system. For example, Cationic starch with APAM gave a high retention, but poor dewatering and poor reversibility; reversibility index at 0.5% addition of APAM was about 0.2 whereas CPAM and Montmorillonite microparticles was about 1.4. Another microparticles system, i.e. Cationic starch and colloidal silica had the reversibility index of 1.4 at 0.3% addition of silica. At the same time, the addition of microparticles improved the dewatering capacity. In this case, the reversibility index may be a useful predictor of the dewatering capacity together with the retention value that also go along with the increasing trend [5]. This study indicates the commercial benefit of microparticles retention system capable of reflocculation as the dewatering performance has a positive correlation with the productivity of a paper mill.

Carr’s work on nanoparticles retention system also showed the same positive result about dewatering; the drainage time became faster with the increase of nanoparticles dosage. The smaller size of nanoparticles improved the retention of starch and the drainage time. The size of 3 nm had the higher % residual reduction, which reflected the retention, between 3-5% than that of 5 nm. The size of 3 nm had a faster drainage time in fraction of second, about a half second [4].

Conclusion and the future suggested works

Beside the relevance of modern hydraulic headboxes nowadays, it’s evidently important to put our focus on the retention system capable of reflocculation based on the commercial aspect. It has been shown on experimental and real paper machines that dual polymer and microparticles retention aid system can improve the retention and reduce chemical cost as compared to single component retention aids [2]. The studies with focus on dewatering indicate the commercial benefit of microparticles retention system because dewatering performance has a positive correlation with the productivity of a paper mill.

It will be very interesting to find out through the study by Carr on how much the cost effective between 3 nm and 5 nm sphere diameter of nanoparticles in regard to their productivity to paper machine. Is it commercially critical to use 3 nm considering the different of drainage time in fraction of second and the retention in range of 3-5%? Referring to Swerin, Risinger, and Odberg, in a sheared suspension of fibers less than one second is needed for high mass polymer to adsorb efficiently onto fiber surfaces and to create attachments between the solid materials [7].

References:

Sikora M.D, and Stratton R.A., “The shear stability of flocculated colloids”, Tappi Journal Vol.64, No.11, November; 97 (1981)
van de Ven T.G.M., “Filler and Fines Retention in Papermaking”, 13th Fundamental Research Symposium, Cambridge; 1209-1210 (2005)
Swerin A., Sjodin U., and Odberg L., “Flocculation of cellulosic fibre suspensions by model microparticulate retention systems”, Nordic Pulp and Paper Research Journal no.4; 389-398 (1993)
Carr. D, “Nanoparticulars on Colloidal Retention”, Proc. Wet End Chemistry Conf. Boston, MA, PIRA International, Letterhead, UK (2005)
Hedborg F., and Lindstrom T., “ Some Aspects on the reversibility of flocculation of paper stocks”, Nordic Pulp and Paper Research Journal no.4; 254-259 (1996)
Swerin A., Risinger G., and Odberg L., “Shear strength in papermaking suspensions flocculated by retention aid systems”, Nordic Pulp and Paper Research Journal no.1; 30 (1996)
Hubbe M.A. and Wang F., “Where to add retention aid; Issues of time and shear”, Tappi Journal 1(1); 29 (2002)

==========

Name: Ning Wu
Date: May 2007

Topic: “What do ultrasonic tests related to the rapid immersion of paper into test fluids really measure, and how should the results be interpreted?”

Why is fluid penetration significant to the paper industry?

Progress in scientific technology results in the changes in materials to meet emerging needs. Paper is a kind of network material, consisting mainly of fibers and pores [1, 2]. It has been known that papermaking fibers consist predominantly of hydrophilic cellulose, so it is not surprising that much concern has been focused on paper’s wetting behavior. However, since different paper has different fluid penetration properties due to the paper structure itself and chemicals added to satisfy various requirements, it is necessary to study paper’s fluid penetration characteristics.

It has been found by some researchers that the liquid wetting process can be viewed as a sum of coexistent sub-processes:

(1) Filling of pores and of the valleys of roughness at the surface,
(2) Liquid penetration through pores, cavities, and capillaries in the sheet,
(3) Movement along fiber surfaces,
(4) Liquid absorption into and diffusion inside fibers.

These dynamic processes are usually hard to differentiate from each other. Liquid penetration and absorption into paper go with diffusion, chemical reactions, fibers swelling, and fiber network structural changes [3, 6–8].

Paper’s wetting characteristics have been often adjusted by sizing (internal sizing and surface sizing), which not only influence paper’s wetting behavior but also can be an important working procedure in papermaking to make paper water repellent, further improving paper product performance in the end use. In other words, if we can precisely and quickly control aspects of the sizing procedure, then we can achieve paper fluid penetration properties that are better suited to the product being made. As we know, the purpose of internal sizing is to control the penetration of water and aqueous liquids by treating the fiber surfaces, while surface sizing controls liquid penetration into paper as well by adding surface sizing chemicals, such as starch. Usually they are spread on the paper in the size press [4]. Paper grades such as newsprint and printing papers, office papers, milk carton, food container papers, packaging papers, and wall papers are water repellent or resistant to liquid penetration [5]. They all play an absolutely necessary role in our daily life.

In recent years, researchers have been trying to find a simple, universal test method and apparatus. By that way, we can obtain much more benefit such as efficient production, optimal paper quality, and more interest at lower cost.

Available measurements such as the Hercules Size Test (HST) and Cobb test are best suited for incompletely and highly sized papers; they do not precisely match the requirements and specifications of all sized paper markets. Moreover, they are slow and imprecise. Other methods, such as the contact angle method, are limited to specific applications [10]. Our goal is to deeply understand liquid penetration processes by a simple, quick, and precise method in sizing measurement.

What are various methods on this topic and what do they really measure?

Some methods have been developed for measurement of sorption properties of paper, providing information about a certain liquid penetration into paper such as water, oils, inks, surfactants, or special chemicals [3, 9]. However, these are relatively slow tests, and they generally fall withing the following categories: (1) absorption capacity tests or absorption rate tests, (2) sizing degree tests [3], and (3) printability tests. With the need to understand the wetting characteristics of paper more deeply, the absorption rate test carries increasingly greater interest, and the absorption capability tests during short times become more critical to achieve rapid measurements [9].

Modern ultrasonic sizing measurement is a new tool for quick and simple test of the surface properties of paper/board up to 800 g/m2. It functions in the following manner: A paper sample is brought into contact with liquid in a measuring cell. From the moment of contact with the liquid, the paper sample is radiated in the Z-direction with high-frequency low-energy ultrasonic signals. These signals are received by a highly sensitive sensor, processed in the device, and transmitted to a personal computer. From the time a paper sample comes into contact with the test liquid, the received signal intensity changes through five steps (wetting, swelling, penetration, and saturation phases), illustrating a link between the observable changes in ultrasonic-attenuation and the physical processes of the paper to liquid interaction [10].

Another useful method is the light transmission test, which can optically monitor the wetting properties of paper by measuring the transmission of laser light through a paper sample. The light transmission the signal intensity during liquid penetration can determine the wetting properties of a specific kind of paper. The shape of the wetting-time curve can reveal the sub-processes of the liquid wetting process mentioned earlier [10]. With this method one can study the wetting dynamics of different varieties of paper. Compared to ultrasonic testing, this test can not only confirm earlier findings on paper wetting, but also reveal new features in the wetting process.

How should be results be interpreted?

Since the received ultrasonic signals are processed in the device and transmitted to a PC, they can be displayed in a user-friendly and beautiful dynamic penetration curve with characteristic parameters that can be used to interpret the results, such as the surface characteristic W, the wettability S, and the absorption characteristic A. The surface characteristic W reflects the surface roughness and surface porosity; the higher the roughness and porosity of a sample, the more gradual will be the initial slope of the curve. The wettability S is the time period (in milli-seconds) required to completely wet the paper and to attain maximum signal intensity. The absorption A describes the rate of liquid absorption, correlates with the sizing degree, and characterizes the water absorption up to a defined point of time A(t). Due to compression of the air trapped in the paper samples, the ultrasonic transmission curves rise to higher values, and the progression of water through the surface is slowed by the presence of the compressed air bubbles. [10].

By understanding aspects of the parameters described above, we can relate the penetration curve with different phases, since the signal intensity changes through the wetting, swelling, penetration, and saturation phases. At the moment of liquid contact, the paper is dry. There is a thin air film existing between the water and the paper surface, which would attenuate the transmitted signal. This is the reference point on the ultrasound intensity plot. After the wetting period the air film disappears, and the signal reflection at the surface disappears as well. Decreased reflection results in increased received signal intensity. After wetting is the penetration phase, with the opening of hydrogen bonds that bridge fibers to each other, and the strength of the fibrous structure is reduced. The compressed air in the wetting phase now flows back into the swollen structure and can generate air traps in the larger pores. The scattering of ultrasound by this air is extremely strong; consequently the ultrasound transmission and the received signal intensity decrease. In the last phase – saturation, the swollen fiber structure, the air contained in the original dry paper, and the penetrated water share the available space. The air has formed stable air traps, so that there is substantial scattering of the ultrasound, which further reduces the received intensity. It has been demonstrated by this type of test that the higher intensity and greater t(MAX) -time requirements for the fiber structure to start to swell correspond to the greater sizing degree of paper samples.

Two paper machine trials involving the ultrasonic sizing tester have been reported [10]. The ultrasonic-attenuation method provided the precise resolution to predict internal size addition levels that had a positive impact on the newsprint printing properties. Testing also showed that the ranking of sizing degree corresponded exactly with the comparative dosages of the alkaline sizing agent used in the production of paper samples. Little to no sizing development corresponded equally to the low level of sizing agent used in production.

The other light transmission method determined the wetting properties of a specific paper type by measuring the intensity of light transmitted through paper during liquid penetration. The shape of the light transmission–wetting time curves revealed the sub-processes mentioned earlier. This kind of study confirmed earlier findings on paper wetting, revealing new features in the wetting process, which could be compared to ultrasonic testing [11].

According to the results of ultrasonic transmission method and light scattering method, it has been found that the wetting processes appear very similar. The latter is well suited for dynamic testing of paper wetting and could be used for online measurement of paper wetting properties [11].

Are there others ways to account for their observations?

The modern ultrasonic-attenuation method effectively offers information about the paper/board’s surface characteristics. Meanwhile, it supplies significant process-related information as well before the material is printed, glued, or coated. In this way the method has unparalleled capability for predicting whether paper quality will meet the requirements of the end use. The results shown in the penetration curves highlight not only important information of surface and internal fiber structure, but also information related to roughness and porosity of the paper surface. It has been found that paper with starch at the surface prints better than paper without surface starch, and penetration dynamics improve to a lesser degree from starch addition than from the addition of the surface sizing agent [10]. However, different factors might affect the penetration process of liquids such as the moisture content of the sample, the temperature, the pressure, the surface tension and the viscosity of the penetrating liquid [5].

What can you suggest for future work in the same field?

Ultrasonic-attenuation test can report important and otherwise unattainable information about the penetration dynamics of liquids such as water, ink, coating color, acids, and oils. However, the wetting processes are described only by reference to ideal models, without considering the complex factors that may affect the results. Also or there might be other explanations, rather than present conclusions. Regarding of these, it is important to carry out more practical and realistic work and comprehensively research how to satisfy different requirements, and how to properly control paper’s wettability characteristics in order to achieve optimal results. It seems that more time and work might be involved in the research and development of this kind of measurement.

References:

[1] Sihtola H and Makkonen H 1977 Suomen Paperi-insinöörien Yhdistyksen oppi-ja käsikirja I: Puukemia (PI Handbook
vol I: Wood Chemistry) 2nd edn ed W Jensen (Helsinki: Academy of Technical Sciences) (in Finnish)
[2] Retulainen E, Niskanen K and Nilsen N 1998 Fibers and bonds Papermaking Science and Technology vol 16: Paper
Physics ed K Niskanen (Helsinki: Fapet)
[3] Neimo L 1999 Internal sizing of paper Papermaking Science and Technology vol 4: Papermaking Chemistry ed L Neimo
(Helsinki: Fapet)
[4] Lipponen E 1983 Paperin liimaus Suomen Paperi-insinöörien Yhdistyksen oppi-ja käsikirja III: Paperin valmistus
(PI Handbook vol III: Papermaking 2nd edn ed A Arjas (Turku: Turun Sanomat/Serioffset) (in Finnish)
[5] Arvela P 1983 Paperin sorptio-ominaisuudet Suomen Paperi- insinöörien Yhdistyksen oppi-ja käsikirja osa III:
Paperin valmistus (PI Handbook vol III: Papermaking) 2nd edn ed A Arjas (Turku: Turun Sanomat/Serioffset) (in Finnish)
[6] Salminen P 1988 Studies of water transport in paper during short contact times PhD Thesis (Turku: A° bo Akademi, Department of Paper Chemistry)
[7] Zauscher S et al 1996 The influence of water on the elastic modulus of paper part 1: extension of the H-bond theory Tappi J. 79 178
[8] Stor-Pellinen J et al 2002 Air-coupled ultrasonic transmission measurement through paper during wetting Meas. Sci. Technol. 13 770
[9] Levlin J-E 2000 General physical properties of paper and board Papermaking Science and Technology vol 17: Pulp and Paper Testing ed J-E Levlin and V Söderhjelm (Helsinki: Fapet)
[10] Hickey, S., Renaud, S., and Falkenberg, W., “Modern Approach for Precise Sizing Measurement,” Proc. TAPPI 2004 Spring Tech. Conf., TAPPI Press, Atlanta, 2004.
[11] Timo Karppinen et al2004Measuring paper wetting processes with laser transmission Meas. Sci. Technol. 15 (2004) 1223–1229

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Name: Lu Athnos
Date: May, 2007

Topic: “What are some logical or practical reasons that might explain why filler pretreatment strategies have failed to become popular, despite many publications demonstrating their effectiveness for maintaining paper strength at higher filler loadings?”

Why is this subject important for the paper industry?

There are two major headaches facing today’s papermakers… The first is the ever-increasing cost of raw materials, particularly “virgin fiber”. The second is the energy costs associated with turning their raw materials into saleable paper products. Recently scientists have developed several approaches to lessening these problems. One of the most attractive solutions is to increase the “filler loading” of the paper.

Increasing the “filler content” in paper can provide the papermaker with numerous benefits, including savings in the cost of raw materials, lower steam consumption for drying, improved optical properties including opacity and brightness, and better print quality. Unfortunately, it is not possible simply to substitute large amounts of low cost filler for the expensive fiber, because of both technical and process problems. At high “filler contents”, paper can suffer losses in both wet and dry strength properties, stiffness, sizing, paper machine runnability and product quality. A great deal of research has been done over the past few years to find ways of overcoming these problems.

What are some of the “filler pretreatment strategies” developed in the paper making industry?

The conventional filler systems have limitations. Heath and Hofreiter [3] found that for each percent of “filler content” in a sheet, paper strength on the average was reduced by 2.5%. It has been shown that the loss in strength properties can be compensated for by an activation of the filler. To help overcome these limitations, there are a range of approaches that have been used to pre-treat the fillers before adding it to the system. For instance, the application of agitation to the fillers, or coat the filler particles with polymer, to not agglomerate them, or preflocculate the filler particles using a chemical like cationic reagent, etc.

A typical method is the addition of a hydrophobic polymer made of polymerisable monomers to the filler in order to create a hydrophobic film on the surface of the filler particles and/or between adjacent filler particles. The filler is pretreated with the hydrophobic polymer so that it makes it more difficult for water to penetrate into the filler layer. Thus, the pretreatment of the filler can improve the wet strength and reduce the linting of the paper, board or the like to be made. [1]

The Grain Processing Corporation has developed and patented a method in which filler particles are preflocculated using a cationic reagent. [2] The process includes the addition of a cationic flocculant to the mill’s filler slurry. It is not limited to treating any one type of mineral: kaolin clays, ground calcium carbonate, precipitate calcium carbonate, titanium dioxide, etc… they all have been successfully flocculated using this technique. Following the addition of the flocculant to the filler stream, the flocculant/filler combination moves through a shear device, which imparts a controlled “particle size” and “charge” characteristics. This increased size and degree of positive charge causes the treated filler particles to have a greater affinity for the anionic surfaces of the fiber in slurry form. This leads to improved filler distribution through the fiber matrix before, and then after the stock is dewatered as well as improved formation. The results showed that the filler preflocculation technology provides many potential benefits to the papermaker.

Why have “filler pretreatment strategies” failed to become popular?

Despite some of the advantages shown from the “filler pretreatment strategies”, these technologies have not been implemented and widely used in the modern paper industry. We need to find out why the filler pretreatment strategies have failed to become popular.

First of all, it’s a fact that filler and fiber are completely different in many aspects like their origin, size, shape, chemical properties, and all of these parameters are important in papermaking. Increasing the “filler loading” affects some major problem areas of a papermaking process. High “filler loading” reduces wet web strength; it changes the dynamic balance of the retention; it dramatically increases wire abrasion; it also increases dusting and fluffing due to the reduction in surface “pick” strength. [4,5]

Let’s take a look at what the most important characteristics an “ideal” “preflocculated filler system” must require [4]:

The system must produce stable flocs, which are also shear resistant.
The floc size must be of the right magnitude and easy to control.
The system should contribute to sheet strength.
The system must produce good filler retention.
The entire system must be economically effective.

These are some important parameters that a “preflocculated filler system” must exhibit in order for it to be suitable. The researchers must take all of these parameters into consideration when developing “filler pretreatment systems”.

A study was done to compare four types of “preflocculation systems” that are in commercial use. The respective systems involved the use of polyacrylamide, cationic starch, a proprietary system called “snow floc,” and guar gums. The main areas of study were “floc stability”, “floc dimensions”, and the effect of “preflocculated filler” on physical hand sheet properties. These four systems were compared and the relative merits of each were considered. The results of the experimental study showed that none of the systems exhibited consistently “perfect” results on all of the studied parameters. In order to convince the papermakers to use a new technology, these parameters have to demonstrate more promising results.

Besides, there are some other factors that the paper mills have to consider in order to accept any new technology. They have to be able to justify the return on the initial investment before investing in the capital equipment and any related engineering work. For the “filler pretreatment technology system”, the major investment is going to be the filler pretreatment devices such as tanks, piping, instrumentation, and necessary automatic control systems and engineering work involved. The proper investment yield depends on the target return on capital. Currently there is not enough real-time data provided for the papermakers to make the investment.

There is something else to consider; the paper mill’s customers always expect a specific set of standard paper quality parameters. Examples include basis weight, brightness, stiffness, and tensile strength. Any changes made to the paper making process will ultimately have to meet with the end user’s satisfaction. If the paper contains more filler, some performance will fail to meet the standards. On the other hand, they may not like 40% “filler content” in their new products even though the paper quality parameters have met the standards. The paper may feel completely different with increased filler loading and won’t satisfy the end users.

Do we have alternatives to solve the problem?

Throughout history, virtually every sort of plant fiber has been used to make paper — from bamboo to agricultural byproducts such as cereal straw, bagasse, to industrial crops such as flax and sisal. Hemp is also a good woodfiber substitute for papermaking although it is classified as a controlled substance in the United States, making it illegal to grow. It has been reported that a number of U.S. and European companies sell writing paper containing small amounts of hemp fiber, usually blended with less expensive nonwood fibers[7]. Use of these fibers has generally been driven by local availability, and the paper they produce has formed an important part of some local economies and niche markets.

Estimates of world paper production attribute 11% to all nonwood fibers. In the United States, use of nonwood fiber for paper is very limited, less than 1% of total capacity. As industries search for more efficient ways to produce products and to conserve natural resources, such as forests, many of these fibers are being explored as wood pulp replacements and major sources of raw material for papermaking. Alternative fibers can help reducing wood fiber consumption and possible energy saving. It’s worth while exploring the possibilities.

Conclusion and the future suggested works

There is no doubt that “filler pretreatment” is one of the most attractive answers to the problems involved with decreasing wood fiber consumption and energy saving by increasing “filler loading” in paper. Future work is still needed to establish which type of “filler pretreatment strategy” is most effective. As with any new technical developments, the more information that is available about the techniques and processes involved, the easier it will become to understand them and put them into practice.

Therefore, I’m sure that more scientists and research and development groups will keep doing their studies in this area, this technology will become more popular in the paper-making industry in the near future.

Literature Cited:

1. Niinikoski, Mari (Rusko, FI), Malmstrom, Olof (Abo, FI), Nurminen, Markku (Raisio, FI)
Sundberg, Kenneth (Abo, FI), Zetter, Claes (Abo, FI), “Method for pretreatment of filler, modified filler with a hydrophobic polymer and use of the hydrophobic polymer”

2. S. Mabee, R. Harvey,“Filler Flocculation Technology – Increasing Sheet Filter Content Without Loss in Strength or Runnability Parameters”.

3. Heath, H.D., Hofreiter. Filler retention and dry-strength addtivies. “A modified handsheet evaluation procedure”. Tappi 61 (1978): 12.21-23.

4. Mrs A.J. Hayes. “40% Filler Loaded Paper… Dream or Reality?” The Julius Grant – PMATA Prize.

5. M.C. Riddell, B.Jenkins, A.Rivers and I. Waring. “Modification of fillers to allow higher retained ash content” in “Three developments at Wolvercote Paper Mill”

6. H.D. Heath, A.J. Ernst, B.T. Hofreiter, B.S. Phillips, and C.R. Russell. “Flocculating agent – starch blends for interfiber bonding and filler retention: comparative performance with cationic starches”.

7. Boise Cascade Environment Office, “Nonwood Alternatives to Wood Fiber in Paper”.

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Name: Max F. Farmer, Jr.
Date: August 5, 2007

Topic: “Is reactivity with the fiber surface an important aspect for robust and efficient wet-strength treatment?”

Why this subject is important: Wet-strength properties are important in a number of different paper grades. Some of the products are hand towels, facial tissues, paper bags and sacks, and some food grade products such as teabags and coffee filters. Others are such grades as poster board, photographic paper, wall paper, currency paper and label paper.

These grades have varying amounts of required wet-strength. Crisp [1] and Dulany [3] both suggest that products that retain more than 15% of their original dry tensile strength when subject to soaking conditions should be considered as wet-strengthened paper. Some require a large amount of wet-strength and it must remain with the product its entire life cycle. Initially the wet-strength of some of the grades must be high, and then gradually lose its wet-strength so the product can be disposed of. The knowledge of how the resins react with the paper fibers enables the papermaker to make an informed decision as to what kind and how much of a wet-strength resin to use for a specific product grade.

Answer to the assigned question: The addition of this wet-strength additive should add to or strengthen the existing bonds between the fibers. It should protect the fibers that are susceptible to water penetration or form a network of material that physically entangles with the fibers. It should repress the swelling of the fibers that would occur at the point of rewetting the sheet. Regardless of how the additive reacts, Espy [1] suggests that it must be located at the weak links of the fiber to fiber bonds if they are to be effective.

Even though the additive is used for increasing the wet-strength, the mechanical strength of the fiber network often contributes directly to dry-strength. An increase in dry-strength occurs due to this increase in fiber to fiber bonding. Espy [1] also states that it is possible to produce paper which can retain 50% of its dry-strength value when soaked in water, though 20 to 40% is a more typical range. This increase in both dry and wet-strength increases both the capacity and efficiency of the paper machine. This increase is in direct proportion to the level of profitability of the paper machine, fewer breaks, more up time, more product out the door.

The quality of the product sent to the customer is increased. It can be shipped at a higher moisture content, increased strength properties and with the ability to retain a greater percentage of its strength in high water usage conditions.

Logical or theoretical support for answer: Paper is a system of fibers bonded together in a water solution. The strength of the paper is determined by the forces holding the fibers together (hydrogen bonding) at the points of contact of the fibers. The presents of water disrupts the electrostatic forces between the fibers. An increase in the water content at this fiber to fiber bond decreases the overall strength of the paper.

Espy [4] says that there are two principal mechanisms used to explain the development of wet strength in paper:

Protective mechanism – It is sometimes referred to as restriction mechanism but it is often called homo-crosslinking. Once the wet-strength has absorbed onto the fibers, or perhaps diffused into the hemicellulose, it reacts within itself to form a crosslink network around and through fiber contacts when the paper is dried. This reaction is influenced by pH, the local concentration of the resin as water is removed and by temperature. When the paper is rewetted, the network of resin restricts the rehydration and swelling of the fibers while keeping the fibers entangled. It also protects the hydrogen bonds in the fiber to fiber contact areas. This ability to keep the fibers entangled preserves some of the original dry-strength of the paper.
Reinforcement mechanism – It is sometimes referred to as new bond mechanism but is better known as co-crosslinking. In this mechanism, the chemical function of the wet-strength reacts with the functional groups on the fiber surface to form covalent bonds between cellulose molecules and presumably between fibers. The effect is to crosslink fibers together. There is no reason why these polymer crosslinkings cannot self-cure as they do when dried alone. When the paper is rewetted, the chemical bonds remain after the naturally occurring hydrogen bonds are disturbed by the addition of water. This leads to a stronger and permanent level of wet-strength in the paper.

Experimental support for answer: The largest amount of experimental testing data was gathered by testing handsheets with different amounts and types of wet-strength resins and by the same comparisons when run on a pilot paper machine. These resins used had different molecular weights and cationic charge densities. The resin molecular weights and cationic structural properties obtained from spectroscopic and wet analytical methods were compared to the tensile strength properties on the pilot paper machine. The MD (machine direction) wet tensile strengths of these papers were compared to wet tensile tests from laboratory handsheets and wet-strength properties from paper made in commercial papermaking operations using the same resins.

According to research by Fischer [5], the best wet tensile strength can be achieved with a PAE resin of high molecular weight and a high cationic charge. In a separate study by Devore and Fischer [2], they determined that the mechanism by which PAE resin produced wet-strength was essentially one of fresh homo-crosslinking with electrostatic interactions between the PAE and paper governing the resins absorption.

In a separate study by Wagberg and Bjorklund [6], it shows that chemical reactions probably takes place between PAE and the carboxyl groups on the fibers. The results also showed the importance of the carboxyl groups in increasing the PAE absorption capacity of the fibers and the importance both of the relatively bonded area (RBA) and of the bond strength between the fibers. They determined that the RBA should be large and the carboxyl group content and the PAE concentration in the bonded regions should be as high as possible to reach a high wet and dry-strength sheet. The concentration of the PAE in the bonded regions is determined by not only the carboxyl group content but also by the geometrically available area. This is the limiting factor in increasing the carboxyl group content of the pulp to try to increase the strength properties of the sheet.

Handsheet tests alone are not conclusive enough due to the shear factor difference between the forming of the handsheets and the forming of the sheet on the pilot machine. Even though the handsheets give an indication of the usefulness of a particular wet-strength resin, the final decisions can only be made after running and testing on the pilot machine.

Situations in which the findings can be useful: The findings can be very useful in performing optimization trials on an individual paper machine. These previous trials ran with similar furnishes on your particular machine can minimize the amount of trials needed to run. The list of wet-strength resins that look favorable for your machine can be tested using the handsheet method. The resins that stand out after performing these handsheet trials can then be tested on your individual paper machine under normal operating conditions. These wet-strength resins can then be used with different machine operating parameters to optimize the test results.

The final decision as to what type of and amount of wet-strength resin to use cannot be based solely on the test results. You must look at cost, runnability of the paper machine, and the end use of the product. An increase in tests results do not necessarily correspond to an increase in machine efficiency, machine productivity or in product qualities.

Literature Cited:

1. Crisp, M., “Chemistry of wet strengthening paper: trends, recent developments and applications,” Wet end chemistry conference and COST workshop, 28-29 May 1997.

2. Devore, D. and Fischer, S., “Wet-strength mechanism of polyaminoamide-epichlorohydrin resins,” Tappi Journal, Vol. 76, No. 8, August 1993.

3. Dulany, M., “Wet Strength Resin Chemistry and Regulatory Considerations,” 1989 Papermakers Conference.

4. Espy, H., “The mechanism of wet-strength development in paper: a review,” Tappi Journal, Vol. 78, No. 4, April 1995.

5. Fischer, S., “Structure and wet strength activity of polyaminoamide epichlorohydrin resins having azetidinium functionality,” Tappi Journal, Vol. 79, No. 11, November 1996.

6. Wagberg, L. and Bjorklund, M., “On the mechanism behind wet strength development in papers containing wet strength resins,” Nordic Pulp and Paper Research Journal, Vol. 8, No. 1, 1993.

Name: Wendy R. McKinnon
Date: April 4, 2006

Topic: “Under what circumstances does it make sense to add cationic starch before of after adding calcium carbonate at the wet end of a paper machine?”

Why this subject is important: The use of calcium carbonate in papermaking has greatly increased with the trend shifting toward alkaline paper production. Calcium carbonate improves brightness and opacity and is cheaper than paper fibers. It also decreases the overall bulk of the sheet. One drawback is that it is hard to retain and has negative effects on the mechanical properties of the paper. To help offset some of these problems, cationic starch is used as an additive. The starch not only acts as a retention aid, but has dry strength properties as well [1]. The starch can decrease the opacity of the paper, but when used together with calcium carbonate the positive aspects of both additives become apparent. The order of addition concerning cationic starch and calcium carbonate can affect the outcome of certain paper qualities. The characteristics most discussed are how the order can change the efficiency of sizing as well as the paper strength. Different calcium carbonate-cationic starch applications are analyzed each one very different from the other, but the effect of addition order is just as drastic for each. When the final product rolls off of the paper machine and the sizing or strength is affected in a negative way, the end use of the product will be compromised, costing the paper mill revenue.

Answer to the assigned question: The order of addition of calcium carbonate and cationic starch is important depending on the method of production and the type of calcium carbonate used. In an alkaline setting, it is imperative to add the calcium carbonate, in this case precipitated calcium carbonate (PCC), before the cationic starch. The scalenohedral shaped particles have an open pore structure, which lend to the adverse effects on sizing abilities [2]. Adding it before the cationic starch helps to alleviate this problem to a point. In an acidic situation, like rosin-alum sizing systems, it is better to wait until closer to the fan pump to add the calcium carbonate and even then it must be pre-flocculated to reduce the reaction time with the acid environment. If it is added too soon in the system the acid renders it pretty much useless. In the final case of ground calcium carbonate (GCC), it was shown to be more versatile in that it could be added before or after the cationic starch with positive results. With no internal pore structure, the problematic reactions found with the previous two examples do not occur [3,4].

Logical or theoretical support for answer: In the first scenario, PCC is clearly shown to be more effective when added before the cationic starch and the qualities deteriorate quickly when added last in the chemical lineup. It is a possibility that the cationic starch increases the amount of reacted alkyl ketene dimer (AKD) by coating the PCC surface. If this is true, then adding the PCC so close to the fan pump is not allowing any time for the cationic starch to react with the PCC. It has also been shown that cationic starch forms a substrate for reaction of the AKD. If the amount of PCC is increased, but the starch is not, then all of the calcium carbonate surfaces are not being sufficiently passivated to allow AKD bonding. Also, if the starch is increased, not only is there enough coverage of PCC, but there will be enough to promote the attachment of AKD [5].

In the second situation, the pH of the system is more acidic due to the rosin-alum sizing being used. Calcium carbonate does not react well under acidic conditions. Lots of foam is created and the sizing of the final product can be affected. A specialized “pre-flocculated” calcium carbonate is used to diminish the amount of time that the additive is in contact with the alum. The particles of calcium carbonate are encapsulated in the ‘Snowfloc’ polymer, which also cause the particles to flocculate. This reduces the surface area available for contact with the acid and allowing it to react with the retention aid more effectively. The polymer lowers the rate of diffusion of the acid produced by the hydrolysis of alum in the rosin-alum system [6]. In this case the cationic starch is added well before the calcium carbonate with acceptable results.

Lastly GCC was reviewed and the determination was that it could be added before or after the cationic starch with convincing results. This seems to be largely based on the lack of internal pore structure associated with GCC. It is not as dependent on chemical reactivity since chemicals that would normally adsorb into the pores simply coat the surface of the GCC particles. Another explanation involved the pH of the systems using GCC. A pH of ~7.0 is normally found with GCC systems, while PCC ranges from 8.0 – 8.5. The lower pH slows AKD hydrolysis and may be one reason why size reversion has not been found to be a problem when using GCC as it has been with PCC [3,4].

Experimental support for answer: In the study by Brungardt, the main idea was to determine if the point of addition of PCC and cationic starch had an effect on sizing efficiency. Various addition sequences were carried out and the results were evaluated by comparing the effect of increasing AKD on Before Size Press Hercules Size Testing (BSP HST). The baseline of these sequences added the PCC before the cationic starch. In the second sequence, when the starch was added first, the BSP HST dropped dramatically, proving that the addition sequence is important. Another final variation added the PCC even earlier in the wet end than the baseline, increasing the amount of time between that and the addition of the other components [5]. This increased the BSP HST somewhat over the baseline, again showing how in this alkaline system the addition point is vital.

A second set of tests was also performed by Brungardt to analyze the sizing efficacy of naturally aged paper samples. These results were lower overall than the prior study, but showed the same trend. The baseline fell in the middle, while the 2nd sequence dropped off significantly and the 3rd sequence had much higher results.

Further exploring orders of addition, a different type of calcium carbonate was found to have completely opposite results. Brooks and Meagher found that when the pH of the system is more acidic, like in a rosin-alum sizing situation, the calcium carbonate should be added as close to the fan pump as possible. This is long after the cationic starch has been introduced. Experimentally Brooks and Meagher showed that the burst ratio decreases as the percent of retained filler increased, but to a lesser extent in the case of pre-flocculated calcium carbonate. The comparison was made to clay and untreated calcium carbonate. The clay had the lowest burst ratio, followed by the untreated calcium carbonate and finally the pre-flocculated CaCO3 [6]. Had the calcium carbonate been added before the cationic starch, the acid would have degraded the product causing it to be inefficient.

Literature referencing addition points of GCC was a little difficult to come by. The overall determination was that GCC could be added before or after the cationic starch. Bartz, Darroch, and Kurle compared GCC and PCC and their reactions to sheet drying temperature on AKD sizing efficiency. It was found that as the dryer surface temperature increased, the HST for the PCC decreased while the GCC results increased. This is due to the non-porous nature of GCC whereby the particle is coated with the AKD. The PCC adsorbs the AKD into its pores and the AKD is less effective. This study added the CaCO3 prior to the starch. Also, in a statement by Hubbe, it has been said “GCC point of addition is not so dependant on chemical reactivity. It is actually preferred to add some GCC to the thin stock [7].”

Situations in which the findings can be useful: The findings by Brungardt, Brooks, Meagher, and Hubbe collectively can be useful when attempting to maximize paper characteristics and qualities. Brungardt showed that for the sizing capabilities to be at their best then the calcium carbonate should be added before the cationic starch. And if even more improved sizing longevity is needed then the addition time between the calcium carbonate and the other additives may be increased. It is also useful to know that the amount of either product can affect the other significantly. A perfect balance must be found between the dosages of calcium carbonate, cationic starch and AKD to obtain the most desired attributes.

It is also helpful to have the conclusions of Brooks and Meagher on hand. It is extremely important to know that in an acidic environment, not only can the calcium carbonate not be added before the cationic starch, but that it needs to be in a specialized polymer-coated form. If standard PCC were to be added to such a system with the same order of addition, the paper would have very little strength and would not be sellable. There are other positive qualities that can be found by using this filler. Improvements such as higher retention, increased drainage and more rapid drying on the paper machine can save energy and increase production.

Finally, it is beneficial to know that GCC is a much more versatile option. Although PCC is desired due to its ability to be produced at a particular particle size, GCCs lack of pore structure allows for better results at high drying temperatures. GCC is not the calcium carbonate of choice in the United States, but Europe seems to like its qualities. In fact the loss of sizing associated with PCC is not found with GCC, again because of the differences in the structure of each.

Literature Cited

1. Gaiolas, C., Mendes, P., et. al., “The Role of Cationic Starch in Carbonate-Filled Papers,” Appita J. 58(4): 282(2005).
2. Bartz, J. M., Darroch, M. E., and Kurrle, F. L., “Alkyl Ketene Dimer Sizing Efficiency and Reversion in Calcium Carbonate Filled Papers,” Tappi J. 77(12): 139(1994).
3. Laufmann, M. and Forsblom, M., “GCC vs. PCC as the Primary Filler for Uncoated and Coated Wood-Free Paper,” Tappi J. 83(5): 2000.
4. DeDecker, M. “The Big Five Battle It Out,” Paperloop Online Edition: (8)1999.
5. Brungardt, B, “Effect of Wet End Additives on Ketene Dimer Retention and Reaction Efficiency,” PIRA 2000, PIRA International, Barcelona, Paper 16(15).
6. Brooks, K. and Meagher, J., “The Increasing Role of Calcium Carbonate in the Paper Industry,” Paper 18(1982).
7. www4.ncsu.edu/unity/users/h/hubbe/www/GCC.htm

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Name: Gang Hu
Date: April 12, 2006

Topic: “Under what kinds of papermaking conditions and for what reasons might it make most sense to use amphoteric starch, assuming that it’s cost will be higher than a comparable cationic wet-end starch?”

Why this subject is important : Cationic starches were first introduced to the paper industry for improved filler and first pass retention, and a reduction in effluent loading and losses. These initial evaluations also showed that cationic starches can improve strength. In the late sixties, amphoteric starches were found to further impact drainage and formation. The improvement of retention and drainage following application of starch can not only improve the properties of final product, they can also reduce the refining energy and increase productivity. The application of starch has also reduced the need for retention aid in some applications. Meanwhile, these improvements provide the possibility that papermaker can use raw material with lower quality. All these aspects could help papermaker to optimize the process conditions, save operation costs and better satisfy the requirements from customers. All in all, these applications can help papermakers make profits.

Answer to the assigned question: Overall , amphoteric starch has been proved to have better performances than cationic starch over a broad range of pH, from acidic papermaking to alkaline papermaking. However, there is no simple answer for this question. Different application strategies should follow the requirements of individual papermakers and their actual situations of papermaking process, including the raw used materials, wet-end additives, water consumption, etc. Since the papermaking process is a complex system, the price of one single component should not be the factor that decides us to use it or not. A comprehensive evaluation involving performance and cost should be made before it is decided which one should be used.

The source of these starches will also be an important factor that needs to be considered when screening. For example, Glittenberg [1] thought amphoteric potato starches had shown proven performances only in alkaline papermaking in North America and Europe with respect to drainage, retention, strength development and sizing efficiency.

Logic and theoretical support: Compared to cationic starch, amphoteric starches have both anionic and cationic charge groups in their molecules. Cationic starches have been believed to remain in paper sheet through ionic interaction between fibers’ carboxylic groups and the amine or ammonium groups in starches [2]. Amphoteric starch, however, can react with both cationic and anionic material, removing excess ionic material from the wet end [3]. This dual functionality increases the locations where the amphoteric starch can react. As a consequence, it helps to yield a more stable system without significantly altering the charge balance.

Starch can form micro flocs of fibers, fines, and fillers, allowing the water drain faster, while improving the first pass retention and ash retention. Compared to other synthetic polymers, micro-flocculation by starch can improve formation [3]. However, one major problem that can happen is over-flocculation [4]. Cationic starch can only act as a flocculant, while amphoteric starch can have both dispersing and flocculating ability at the same time, which could decrease the occurrence of over-flocculation. Meanwhile, amphoteric starch might partly have the same function as shown by dual micro-particle retention systems (Gang’s surmise), which improves the retention and drainage, and could lead to less retention aid usage. As a result, the reduction of retention aid can also increase the dewatering rate of a sheet to allow greater water drainage, further improving formation. Machine speed can therefore increase, too.

Experimental support : Yoshizawa, et al. [2] had shown that amphoteric 2-hydroxyl-3-trimethyl-ammoniumpropry (HPTMA) starch produced higher retention on handsheets than their cationic forms under different refining situation at pH 7. They also proved that amphoteric diethylaminoethyl (DEAE) starch had better retention over their cationic forms between pH 3 and 9, although this was only true at the pH range of 3 to 7 for HPTMA.

Dalidowicz [4] had shown that increased bound phosphorus groups in amphoteric starch increased the drainage rate. Glittenberg [1] got similar, but more convincing results on drainage improvement through comparison between cationic potato starches (which is actually amphoteric starch because of the natural phosphorous groups in them) with DS 0045 and waxy corn starch with respective DS 0040 and DS 0045. He also had comprehensive experimental results including improvements in tensile strength, internal bond, and Dennison wax pick. Experimental results from the study also included improved performance of amphoteric starch over cationic starch with respect to AKD sizing application.

McQueary had a series of real application examples that had obtained improvements on retention, strength, ash content and machine speed from different paper or paperboard products. These applications included groundwood pulp, linerboard, bleached board, cylinder board, wood-free coated paper, wood-free uncoated paper, tissue, toweling and napkins. These application examples were very good examples that amphoteric starches have very good overall performance in papermaking and were convincing evidence that they are good additives for papermakers.

Roberts et al. [5] had tested how starch in paper affected the formation by testing of coefficient of grey level. However, no more direct data from publication was found on formation, although there might have been a lot of such information in industry. Fortunately, we have reasons to believe that formation could be really improved, based on its relationship with strength properties.

Concluding remarks : It can be concluded that amphoteric starches in general have better performance in improving paper properties and runnability of paper machine, according to the published experience. However, no rules have been come up with regarding papermaking conditions under which amphoteric starch can be used and what is the mechanism behind it. For instance, zeta potential is one important characteristic that papermakers are concerned about. However, we lack data about how zeta potential can change with the application of amphoteric starch, even though we could reason that with the same amount of amphoteric starch and cationic starch, the latter would change zeta potential of a certain pulp more. If this hypothesis is true, then what information can zeta potential provide for us? Can we use zeta potential as a reference for the optimum dosage of amphoteric starch? Or is there any other technique that we can use to explore the mechanism how amphoteric starch products work? A lot of research on how salt content can affect the performance of cationic starches and other cationic additives has been done, and these results provide guidance on how to use these products in the paper industry. However, similar research results are lacking for amphoteric starches. Answers to all these questions could make papermakers understand amphoteric starch better. It could even provide information so that starch makers can tailor-design starches that work more effectively for specific papermaking conditions.

Fortunately, the fact that amphoteric starches have better performance over cationic starches has been realized, and they also have been widely used in industry, although the current understanding about the mechanism needs to be broadened and deepened.

References:

1. D. Glittenberg, “Starch Alternatives for Improved Strength, Retention, and Sizing”, Tappi Journal 76(11): 215-219 (1993)

2. J. Yoshizawa, A. Isogai and F. Onabe, “Analysis and Retention Behaviour of Cationic and Amphoteric Starches on Handsheets”, Journal of Pulp and Paper Science , 24(7):213-218 (1998)

3. R.T. Mcqueary, “Wet End Waxy Amphoteric Starch Impacts Drainage, Retention and Strength”, 1990 Papermakers Conference Proceedings , P137-142 (1990)

4. P.C. Dalidowicz, “Drainage Aids Containing Bound Phosphorus”, 2000 TAPPI Papermakers Conference and Trade Fair Proceedings , 119-123 (2000)

5. J.C. Roberts, C.O. AU, G.A Clay and C. Lough, “A Study of the Effect of Cationic Starch on Dry Strength and Formation Using C14 Labeling”, Journal of Pulp and Paper Science , Vol. 13(1):J1-J5 (1987)

6. J.C. Formento, M.G. Maximino, L.R. Mina, M.I. Srayh and M.J. Martinez, “Cationic Starch in the Wet End: Its Contribution to Interfiber Bonding”, Appita 47(4): 305-308 (1994)

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Name: Kristin Koenig
Date: April 2006

“Stickies Problems: Can interactions with other wet-end additives make such problems worse during papermaking?”

Introduction: The development of adhesives and other sticker-like materials has helped to make life easier and more pleasant for consumers. For the papermaking industry, however, these products create difficulties and inefficiencies, especially within the recycling sector. Stickies is the term used to describe this category of papermaking contaminants and they are most commonly found in pressure-sensitive adhesives, hot melts, seam bindings, labels, decals, stickers, waxes, inks, latexes and wet strength resins. Pressure-sensitive adhesives include stamps, post-its and other similar products which do not require wetting to create adhesion. These materials are formulated from polyvinylacetate (PVA) and styrene-butadiene latex [2]. In general, stickies are tacky, deformable, soft, hydrophobic, and have a low surface energy [2]. Because of their tacky nature, it is not realistic to sort through waste paper and remove stickies before processing. Stickies are, unfortunately, an inconvenience for the industry. Once in the recycling stream, they can build up on machinery and even become visible in the finished paper product. It is common for stickies to deposit near shear, refining, and pumping points and following drastic temperature changes [5]. As papermakers try to develop ways to combat stickies deposition, it has become increasingly important to determine what exactly causes the problem in the first place. By comparing multiple papermaking conditions and their resulting stickies levels and behaviors, it may be possible to determine the root of the problem. Current research has shown that wet-end additives often have negative effects on these particles and the resulting paper products. The main additives currently under investigation include alum and other aluminum-containing species, cationic polymers like starch and poly-DADMAC, and cations like calcium.

Significance to Industry: Deposition of contaminants is known to be the greatest problem for machine and product runnability for recycled paper manufacturing [4]. As a result of stickies deposition, papermaking systems also experience difficulties with fiber substitution, felt, wire and fabric lifetimes, converting, calendering, sheet breaks, and pickouts, holes, wrinkles, cockling and high dirt counts in the finished products. All of these issues cause a reduction in the runnability of the machine, the efficiency of printing and the quality of the product. There are also increased replacement costs because the life of many parts is reduced. In a sample cost calculation, Fogarty estimates that stickies can cost a mill over $6,200 per day [1]. When mills run 365 days each year, this can add up to over $2.26 million annually just as a result of stickies problems. This number is staggering and shows just how pervasive and expensive this stickies problem can be.

Some of the best ways to deal with these substances are to inhibit their growth and deposition and retain them with the furnish without causing self-agglomeration and deposition on the equipment [2]. Currently the industry uses detackifiers, coagulants, equipment treatments, and dispersants. These methods, however, have proven to be insufficient because each sticky particle is chemically and physically different. This means there is not one technique that will solve the problem completely; it must be a combination of several.

Theoretical and Experimental Evidence: The number of wet-end additives used in the papermaking industry increases daily. The behavior of these additives is sometimes complicated and becomes even more so when stickies are present. The purpose of additives is to improve machine runnability and quality of the final product. Unfortunately, the presence of stickies can sometimes counteract these improvements. Although undesirable, the interactions between stickies and some wet-end additives cannot be completely eradicated. Some of the issues surround alum and other aluminum-containing species, cationic polymers like starch and poly-DADMAC, and cations like calcium. These make up only a small number of the wet-end additives, but their behavior with stickies is the most categorized. The paragraphs that follow provide some selected examples that illustrate interactions between stickies and other papermaking additives.

Aluminum Species: Alum is specifically added to the furnish as a source of aluminum ions which help to retain rosin size and fiber fines throughout the wet-end, reduce foaming, control pitch and retain small particles. Aluminum is also needed to aid in the formation of hydrophobic aluminum rosinate sizing in the drier section 5 . Near stoichiometric levels of the cation are required for this reaction to proceed efficiently and completely. Unfortunately, the overuse of alum can counteract its beneficial effects. Alum can increase the presence of pitch, rosin and stickies deposits because the retention aid causes coagulation of these colloidal particles into large visible agglomerates. Excess of the aluminum cation gives a similar result. The negatively charged stickies react with the cationic aluminum ions and form globs. The under dosage of alum leads to poor performance of additives, but these effects are thought to be more harmful than those of overuse. Because of this mentality, over dosage is more acceptable.

During recycling, the secondary fiber source varies and therefore the level of anionic materials changes too. In order for alum to be effective, it must react stoichiometrically with the negative charges in the furnish [5]. Because the paper stock changes, it is difficult to add the appropriate amount of alum all the time. To combat the over dosage issue, it is essential to control the amount of un-reacted aluminum ions in the system. This can be accomplished by the use of additional furnish materials. These unnamed chemicals sequester free aluminum ions and reduce the frequency of agglomeration and stickies formation. Removing the residual aluminum ions does not affect the efficiency of the retention aid system. In the Ormerod study, four mills tested this sequestration method with positive results [5]. One mill was experiencing aluminum hydroxide (Al(OH)3 ) deposits. The sequestrant was able to reduce the deposits but did not adversely affect the retention aid system. At a second mill, the occurrence and dryer build-up of stickies was greatly reduced. This mill was a 95% closed system and the presence of aluminum salt build up was a major problem. After treatment, the level of unprecipitated aluminum and stickies increased in the process waters showing just how effective the sequestration was. Productivity at the third mill improved dramatically and the number of web breaks fell when the aluminum sequestration method was employed. The fourth mill experienced shorter downtimes and faster production rates. Overall, the sequestration method greatly improved machine runnability and efficiency while decreasing stickies deposits. With this new technology, it will be necessary to determine whether or not the sequestration additive has any effect on the paper’s strength or appearance characteristics. In addition, it will be increasingly important for the industry to develop a method to measure aluminum concentrations on-line.

Cationic Polymers: Cationic materials like starch and poly-DADMAC are critical to the strength and appearance of paper. These polymers are appropriate because of their cationic nature which allows them to react well with the anionic cellulosic fibers. As with many papermaking additives, there is a proper dosage for these substances and deviation from that dose can be quite detrimental to the operation and final product [3]. Poly-DADMAC, while interacting with fibers, also helps to destabilize stickies. At the neutral point there is maximum flocculation of the contaminants. The stickies agglomerations resulting from poly-DADMAC addition were large and irreversible once formed. Excess of this polymer, however, somewhat restabilized the stickies. Similarly, cationic starch was able to destabilize the stickies through dispersion. It is believed that the starch coats the surface of the stickies, rendering them less tacky. The stickies then unfold and are more susceptible to shear and breakage. An excess of this additive once again restabilizes the stickies. Some of the flocs formed by cationic starch are reversible. This means that the flocculation forces with the starch are weaker than those involved with the poly-DADMAC [3]. Although cationic polymers are utilized specifically for strength, they can also have positive effects for stickies control. Unfortunately, it is difficult to apply the appropriate dose of these polymers all of the time. Because the stock changes constantly the cationic demand does too, creating a situation where cationic polymer overdose is likely. In the ideal situation, if given the option, poly-DADMAC is more effective for controlling stickies than cationic starch.

Calcium and Other Cationic Species: One of the biggest concerns with cationic species like calcium and magnesium is on water hardness and other negative effects they can have on the papermaking process. The deposits and scale formed by these two cations are not good for papermaking so it is important to prevent them. In order to do this, the concentrations of calcium and magnesium must not build up within the water system. Huo et al tried to determine whether calcium and other dissolved cations present in the papermaking water system had an effect on stickies deposition and behavior [3]. First they showed that these particles have an electrical double layer. Based on the Shultz-Hardy rule, the critical coagulation concentration (CCC) should be proportional to the inverse of the sixth power of an ion’s valence. The CCC for calcium was calculated to be 659ppm. The average concentration of the ion is the system ranged from 95 to 270ppm. These levels show that the calcium concentrations, on average, are not high enough to destabilize stickies. In order for calcium to destabilize stickies particles, the concentration of the ion would have to be increased. This would more than likely lead to water hardness and scale build-up.

Further experiments during the Huo study reiterated that aluminum ions can help destabilize stickies [3]. The theoretical CCC for aluminum was 36ppm. During the testing, the observed aluminum concentrations ranged from 2 to 54ppm. Some of these levels exceeded the CCC and caused a destabilization of stickies. The study also showed that the CCC could be lowered if the pH was decreased and polynuclear species were formed. This evidence shows that ions and compounds with high valences are able to precipitate stickies at lower concentrations. Overdosing the system with these cations does not restabilize the stickies, but in most cases, it causes detrimental effects for the rest of the system. Once again there is a fine line between benefits for stickies control and end-product performance.

Conclusions and Future Work: Just by examining cation concentrations and polymer dosages, it is clear that the relationship between papermaking additives and stickies is very complex. Additives like alum, starch and calcium carbonate are all needed to improve the runnability of the machine and the properties of the finished product. Unfortunately, these additives in their current dosages are not ideal for stickies control. The common overdose of alum redisperses pitch, rosin, and stickies into the system. New techniques such as aluminum sequestration have proven effective for stickies control while simultaneously upholding retention aid efficiencies. Cationic polymers are also regularly overdosed, sometimes causing reversible flocculation and deposition of contaminants. Calcium does not help with the control of stickies but increasing its concentration in the system can lead to water hardness issues. There is a very delicate balance between proper and over-dosing of wet-end additives.

To continue this research, it will be important to establish priorities. Each group will have to decide whether machine performance is more important than stickies problems. An effective on-line aluminum testing method will greatly improve alum dosing. Another important test will be to determine the effects of under- and overdosing of the myriad of wet-end additives not only for stickies control but for machine efficiency, cost, and end-product characteristics.

Literature Cited

1. Fogarty, T.J., “Cost-effective, Common Sense Approach to Stickies Control,” TAPPI Journal 76 (3): 161 (1993).

2. Hubbe, M., “WPS 322 Coursepack,” North Carolina State University .

3. Huo, X., Venditti, R.A., and Chang, H.M., “Effect of Cationic Polymers, Salts and Fibres on the Stability of Model Micro-Stickies,” Journal of Pulp and Paper Science 27 (6): 207 (2001).

4. Ling, T.F., “Agglomeration Tendency of Contaminants in Recycled Fibers,” TAPPI Journal 81 (3): 161 (1998).

5. Ormerod, D.L., and Hipolit, K.J., “Aluminum Control Prevents Stickies Problems,” TAPPI Pulping Conference Proceedings 597 (1987).

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Name: Sanjay Chakravarty
Date: April 24, 2006

Topic: “Where in the paper machine system does it make sense to add a defoamer chemical? How does the answer to this question depend on the details of the paper machine system and other factors?”

Why is this subject significant to the paper industry?

Increasing production rates and ever stricter quality, economic and environmental requirements have attracted increased attention to entrained air and its detrimental effects on the papermaking process and paper properties [6] . Foam control in the mill is a very practical subject. The chemistry behind the foam is very fascinating and complicated. Good quality stock is the basis for efficient and competitive paper manufacturing [2]. Air in the papermaking has a negative effect on paper quality. But in some cases like floatation de-inking foam is desirable for the removal ink particles. Papermakers have long known the problems caused by air contents in fiber furnish. High content of air may give circular marks on the paper, pinholes, poor formation, porosity, and strength loss. Some other problems related to unwanted air are clogged valves, pump cavitations, occurrence of plugged lines, deposits in tanks and chest, dewatering problems, sheet breaks, and added expenses like the need for high pump capacity. The most common foam related problems in papermaking result from surface active agents such lignin, black liquor soaps, sizing agents, fillers like calcium carbonate, and variation of stock pH. High contents of dissolved gases can originate from a decomposition of CaCO 3 where CO 2 is formed. In comparison to air and its components, CO 2 is far more easily dissolved in water. The immense pressure drop at the wire and at the foils leads to dissolved gases being release.

Answer to the assigned question: Defoamers often are added in dilute solution either at a fan pump, just before hydrocyclone cleaners, and as surface sprays. A paper machine approach flow system is highly closed and pressurized system, therefore it is more vulnerable to access for the air into the system. Mixing of air and gases into the white water is very common during dewatering on modern high speed machine, where the removed water splashes and sprays before it falls into the white water tray and goes to the white water silo [1]. In hydrocylones due to pressure variation dissolved air gets converted to entrained air and it introduces air into the system. So the defoamer is added just before the hydrocyclones. The coated broke contain calcium carbonate; it could release carbon-dioxide, so to counter the problem defoamer can be added to the broke stream as a surface spray.

Some of the other places where air enters into the stock are as follows:

Leaking seals in the pumps
Up the center of the cyclone cleaners
Air or gas generated by wet-end chemical interactions
A drop leg pipe discharging stock or white water turbulence and thrashing in air

Logical or theoretical support for the answer: The composition of defoamer for one particular application differs from other application, so it is very important for the mill to conduct a laboratory testing and analysis before putting the defoamer at particular location. Defoamers have similar structure to surfactants but are more hydrophobic. Due to their lower solubility in water, they displace surfactants from air/water interface into the bulk solution. To be effective, a defoamer must be able to destabilize the layer of surface active agent present at the air-liquid interface, which results in foam rupture and coalescence

The addition of defoamer required for a given application depends strongly on the following factors

Type of stock
Stock solution pH
Stock temperature
Where the foam occurs
Stickies tendencies

Thick stock feed: Air in the thick stock feed mainly comes from the chest agitator if the level of the chest is below the agitator. The air content in the thick stock is typically as follows: entrained air 1-2%, dissolved gases 1-2%, and the total air content is 2.5-4.0% [2]. A defoamer can be added to the thick stock when the level of the chest goes down to reduce the air content

White water circulation: The dewatering devices, such as hydrofoils on the wire table are major source of introducing the air in the system. This is more serious problem with the high speed machine where dewatering is fast and introduces air into the white water silo.

The work done by Paaulapuro et al [3] have found that entrained before the headbox of paper machine is around 0.25% and the amount of dissolved air can be around 3.0% or higher, so it makes sense to add a defoamer in the white water silo. Defoamer is added to the white water to release the entrained air and helps to keep the balance between entrained air and dissolved gasses. The effect of defoamer dosage on air removal can be measured by monitoring the entrained and dissolved gases. The design of the paper machine approach flow system is very important for foam development. When the stock comes out of the slice there is a drastic change in pressure, which causes the dissolved air to get converted to entrained air.

Pumps: Centrifugal pumps are another source of introducing air into the system. Due to high shear forces the entrained air is transformed to dissolved gas [2]. In this amount of dissolved air increases and the entrained air decreases, but the total air content remains the same if there is no leakage from the pump sealing. Adding a defoamer before the primary centricleaner pump or fan pump will help to decrease the amount of dissolved air, which can become problematic when it reaches the headbox of the paper machine.

Methods employed to measure air content

There are different methods to measure air content in the stock. Below are some of the methods used by the authors

Boadway Method: This method is used because it can measure both dissolved and entrained air. It is based on the principle that there is very little expansion or contraction with fibers and water with change in pressure, while air in the bubble will expand or contract with such changes. In expansion method the dissolved gases will get released and can thereby be measured in addition to entrained air .

Online measurement of entrained air: The air content measurement principle introduced here is based on attenuation of ultrasound by air bubbles. The attenuation is very sensitive to the stabilized air bubbles, but insensitive to solid material in furnish. Attenuation is directly proportional to the amount of entrained air present; however it does not measure the amount of dissolved gases. This ultrasound method is a continuous, online measurement, which makes air measurement and the control of deaeration more efficient than with conventional methods used on paper machines.

Situations in which thefindings can be useful

The findings reported by various authors can be useful in optimizing the defoamer addition point into the papermaking system. Studies have also revealed that not only foam can be reduced by chemical methods, but there are some new mechanical methods available to reduce the level of entrained air and dissolved air in the system. The air in the papermaking can be a source of trouble, and it is difficult to trace source of origin. To pin point where the air is getting into the system it is very important to take the sample from thin stock system, back through the complete loop, before and after each piece of equipment especially before and after the pumps. With the proper application of mechanical and chemical methods the dissolved and entrained air can be completely removed. The measurement results achieved in various mills showed that determining the levels of entrained and dissolved gases online enables the optimization of prevention measures. The results also showed that online control of de-aerator chemicals based on the measurement values leads to substantial cost decreases, process improvements, and quality enhancements in paper manufacturing. Understanding the basic nature of foam is an important step to maximizing the performance of defoamers. Many defoamers are typically combined or formulated with other materials to produce cost-effective products that deliver a number of benefits. Their findings may help to consider several factors that must be considered in the development of a cost effective defoamer.

Concluding remarks

Chemical methods generally employ adding a defoamer or antifoam agent into the system where the problem is occurring. A defoamer needs to be added to a point of good mixing prior to where it is expected to do its job. Therefore defoamers are often custom formulated for an application. Often a defoamer that works well at one location will not perform as effectively when added to different location. Generally there are different kinds of defoamer which are added depending upon the origin of foam. Each foaming system is unique. In particular, many defoamers have an optimum range of temperature under which maximum efficiency is achieved. Over-use of defoamers should be avoided due to added increase in cost and reduce deposit problems.

Literature Cited:

1. Matula, J. P., Kukkamaki, E., “How to Deal with Difficult Passengers,” PPE 10 (1): 12-14 (1997

2. Matula, J. P., Kukkamaki, E., “New Findings of Entrained Air and Dissolved Gases in PM Wet End, Mill Case Study,” Proc. Tappi Coating/Papermakers Conference , 245-275 (1998

3. Helle, T., Meinander, P. O., Nykanen, R. J., Molander, K. S. and Paulapuro, H., “Air Removal Mill Trials Using Pomp Deaerator,” TAPPI J., 82 (6): 146-149 (1999).

4. May, O. W., Buckman, S. J., “Practical effects of air in papermaking” TAPPI J., 58 (2): 90-94 (1975).

5. Helle, T., Paulapuro, H., “Effect of precipitated gas bubbles in papermaking” APPITA J., 57(6): 444-447(2004)

6. Lorz, R. H., “Air content, retention and drainage: Important parameters in paper/board production” Pulp and Paper Canada., 88(10) 1987

7. Avery-Edwards., D. J., Elms, R., and Buckingham, A., “Silicone antifoams for nonwoven applications” TAPPI J., 77 (8): 235-238 (1994)

8. http://www4.ncsu.edu/~hubbe/TShoot/G_Foam.htm

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Name: James A. Ronning
Date: April 28, 2006

Topic: “Is it possible to optimize the level of activity in the forming section of a paper machine to achieve a more favorable balance between first-pass retention and the uniformity of formation?”

Why this subject is important: A large percentage of paper is produced on a fourdrinier-style paper machine, where issues of formation and retention are closely balanced through the “activity” on the fourdrinier table. Activity is the formation of localized waves or fluid disturbances caused by fabric deflections over stationary elements on the table. As the stock suspension passes over the foils, the opening angle of the foil with respect to the fabric causes a suction pulse to be created. This suction pulse is responsible for deflecting the fabric and promoting drainage. As the fabric is released from the suction pulse it snaps back into place. When this occurs on a regular time interval by a uniform spacing of foil blades it creates a harmonic wave known as activity. The action of suction pulses and activity creates hydrodynamic shear forces in the papermaking furnish. These shear forces tend to break up fiber flocs and promote a more uniform formation. These shear forces may also separate fine materials which are then not retained in the web. An ideal process would create an exact amount of shear to form the sheet as uniformly as is desired and no more than is needed to minimize fine material losses.

First pass retention is a measure of the difference of headbox and tray consistency divided by the headbox consistency. It is a simple measurement to determine solids leaving the wet end of the paper machine. Web solids consist of fibers, fiber fines, and fillers. The fibers are long enough to be largely captured by the forming fabric. The fines and fillers are small enough to pass through the forming fabric without additional means of retention. Retaining fines can be done through the actions of both colloidal chemistry and mechanical actions. Through chemistry the fines can become attracted and agglomerated to the fibers or to themselves to be large enough to be retained in the sheet. Through mechanical actions, the fiber mat itself becomes a filter which traps fine particles as the mat builds. There are components of both systems working in the paper machine at all times.

Agglomerated fibers, fines and fillers can be separated through the means of shear. All agglomerations have a fundamental mechanical property known as the yield stress [6]. This is the shear force required to cause motion within an agglomeration of fibers. It is known that the yield stress of a fiber system is dependant on several factors, including fiber length, consistency and chemistry. When the yield stress is exceeded on the fourdrinier table, it can separate fines and fillers from the agglomerated fiber flocs, which will lower first pass retention. Hydrodynamic shear forces are also responsible for the breaking of large flocs into smaller flocs, which increases the sheet formation uniformity. Another effect is that of sheet drainage. As the mat builds, localized areas of lower basis weight are able to flow more freely. These localized flow increases are believed to have the effect of evening the basis weight as the sheet forms, attracting more fibers and fines to the areas of greater local flow.

Formation uniformity is commonly a visual examination of a sheet of paper with a background light bright enough to enable a look-though. Sheets with high degrees of formation have a very even floc distribution; sheets with low formation have a flocky, uneven appearance. Formation is also evaluated by means of automated light pass-through devices such as the M/K tester in addition to ß -measurement devices such as Ambertec.

Answer to the assigned question: Industry professionals are able to balance formation uniformity and retention goals currently through a process of changing blade angles and spacing [2]. Several table elements have been invented to control activity by augmenting the fabric deflections through the use of vacuum, by applying alternating suction/pressure pulses, by variable blade spacing and even by electrical vibration. Although many new technologies are introduced in this sector, the industry has primarily moved to high-frequency harmonic forming tables as a solution to better formation on formation-sensitive grades of paper. This is a practice of regular intervals of foils generating a frequency in the range of 80-100 Hz. The advantages are said to be smaller-scale but higher intensity activity, and better formation. Miller sites a specific example where an increase in retention was noted together with an increase in formation.

Wildfong and Bousfield [1] have made a fundamental model of a series of foils in order to predict activity and shear forces in a fourdrinier table. With knowledge of the network strength of the furnish at a specific point in time one could predict the exact point where the fiber floc is stretched but not destroyed, to optimize the formation improvements while minimizing the negative retention effects. Geometry changes to foils blades such as curved shapes or irregular spacing can also be modeled to fine-tune the responses of drainage, retention and formation.

Logical or theoretical support for answer: Studies have shown that high molecular weight bridging-type retention aids break down in the presence of hydrodynamic shear [4,6]. High shear and high drainage velocities can lead to a separation of fiber fines and fillers, causing a loss in first pass retention on the machine. Several lab testing devices have been established to evaluate the performance of retention aids in the presence of shear. Most of the studies have tried to baseline the lab apparatus to give similar retention results as that of the paper machine [5,10].

Tam Doo [3] evaluated the hydrodynamic shear of a 3 degree foil based on experimental data available at that time. It is noted in this research that drainage volume flow rates have been found to be as low as forty percent of theoretical values. Logically one could expect there to be wide latitude in the ability of foil blades to generate hydrodynamic shear values. Also, the data generated consists of a single foil generating a single pulse. It is understood in the industry that activity is only possible through the action of multiple foils in series.

Wildfong and Bousfield [1] have taken a different approach in modeling the fundamental effects of foil blades on activity. By modeling activity of multiple blades in series, the model can predict how much shear and drainage velocity a foil and composite table is capable of. This data can be used to redesign the foil itself. For instance, if the shape of the pressure pulse was altered to give a longer, gentler suction pulse it may provide the same overall drainage (same area under the curve) with less drainage velocity and less shear. If the shear was chosen to be at a peak value less than the yield stress of the fines / filler / fiber matrix it could produce a better fine material retention. Also, the effects of foils spacing (both harmonic and non-harmonic) on shear and activity can be evaluated. Further studies are required to validate the effects on formation resulting from modifying the pressure pulses in this fashion.

Experimental support for answer: Burkhard and Wrist [7] showed the pressure pulse over a foil to be of the following nature:

The initial pressure at the nose of the foil is seen in the web as positive; the diverging angle of the foil creates a suction pulse, drawing the fabric with the foil until the fabric tension causes the fabric to separate from the foil releasing the suction. This initial positive pressure pulse is attributed for the washing action of the foils on fabric-side fines. As the water is forced into the underside of the sheet then quickly retracted it can cause a washing effect on fine materials.

The measurement of activity is performed through several means in the field. Most commonly it is evaluated by means of a stroboscope and done on a visual basis. Being a subjective test, the activity can be characterized by means of the Schmid Scale, which is a visual range estimate from 1 (no activity) to 10 (stock jump). Kiviranta and Paulapuro [9] developed a characterization system for measuring the activity on a pilot paper machine in terms of surface roughness, correlation length and scale by photographing the shadow cast by the spout formation and analyzing with a computer model. In their fine paper trials, formation improved up to a certain level of activity then decreased with further activity. On a 12% ash fine paper trial, the optimum retention did not correlate with optimum formation. Formation and retention were diverging targets; optimization of the two is a balancing act.

Many different testers have been developed to lab-test the performance of retention aids. Several testers are capable of varying the amount of shear applied to the furnish during mat formation. In particular, the Moving Belt Drainage Tester [8] would be a suitable lab device to model the performance effects of foil shape and frequency with regard to both formation and first-pass retention, although relevant observations regarding table activity may be difficult with this device.

Solutions in which the findings can be useful:

Optimizing formation and retention is useful for nearly every paper machine in operation. It is a daily goal to balance sheet quality with production efficiency. All paper is formation-sensitive to a certain degree. Many printing and writing grades, newsprint, etc. are produced with on-line testing to monitor sheet formation, and is a quality parameter that must be satisfied for the end-customer. But many grades which are not directly formation-dependant still require consistent formation values. Poor formation may lead to sheet breaks and downtime. Formation uniformity has a significant impact on sheet porosity and changes may affect machine speed. Unstable first-pass retention may lead to basis weight variation in the finished sheet. This can cause excessive fiber usage, as well as operational issues. Low ash retention can cause finished product to fail brightness or opacity testing. These parameters are central to many of the daily challenges of paper machine operation.

Literature cited

Wildfong, V., and Bousfield, D. W., “Activity Predictions for Single Wire Machines for Various Frequencies,” Proc. TAPPI 2004 Spring Tech Conf., TAPPI Press, Atlanta , 2004

Miller, D.C., “The Role of Pulse Frequency in Optimizing Table Operation,” Proc. TAPPI 1993 Wet-End Operations Short Course , TAPPI Press, Atlanta , 1993
Tam Doo, P.A., Kerekes, R.J. and Pelton, R.H., “Estimates of maximum Hydrodynamic Shear Stresses on Fibre Surfaces in Papermaking,” J. Pulp Paper Sci., J80-88, July 1984
Hubbe, M., “Retention and Hydrodynamic Shear,” Tappi Journal , Atlanta , 116-117, August 1986
Hubbe, M., “Selecting Lab Tests to Predict Effectiveness of Retention and Drainage Aid Programs,” Paper Technology , 44 (8) 20-34, 2003
Bennington , C.P.J., Kerekes, R.J. and Grace, J.R., “The Yield Stress of Fibre Suspensions,” Canadian J. Chem. Engr., 748-757, October 1990
Burkhard, G. and Wrist, P.E., “Investigation of High Speed Paper Machine Drainage Phenomena,” Proc. Canadian Pulp Paper Assoc., 1956
Raisanen, K., Karrila, S., and Palapuro, H., “Wire Section Simulation with the Moving Belt Drainage Tester (MBDT),” Proc. 1993 Papermakers Conf. , TAPPI Press, Atlanta , 103-113, 1993
Kiviranta, A. and Paulapuro, H. “The Role of Fourdrinier Table Activity in the Manufacture of Various Paper and Board Grades,” Proc. 1993 Papermaker Conf., TAPPI Press, Atlanta , 331-344, 1992
Karrila, S., Champine, J., and White, D., “Pulsating Forming at Headbox Consistency in Bench Scale Provides Close Imitation of a Single-Wire Machine – Or How to Tune a Lab Device for Desired Web Structure,” Proc. 2003 TAPPI Spring Tech. Conf. & Trade Fair , TAPPI Press, Atlanta, 2003

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Name: Keiko Fujita
Date: May 2006

Topic: “Slime Control Strategies: Which would make more sense, and why – slime monitoring on a test surface in continuous contact with papermaking furnish, or repeated, rapid tests on fresh surfaces?” Introduction

Problems caused by microscopic organisms in the papermaking process are a big issue. In order to deal with such problems, the following actions are usually carried out. I would like to review each of the following steps using related references and, at the end, propose slime control strategies that are likely to be effective.

Problems Caused

Hoekstra [1] reviewed slime problems as follows:

• Loss of production by breaks, unscheduled boilouts and washing

• Reduction in quality by slime spots, holes, odors in product

• Microbiological corrosion by damage to metals, including stainless steel

• Production of dangerous gases such as hydrogen, hydrogen sulfide, and methane.

On a modern, high speed paper machine, an hour of downtime may cost more than $20,000 in production. It can be easily understood that slime problems are serious for the industry.

Measuring slime

The traditional measurement method involves plate counting. The method is cheap and provides useful information such as potential slime growth and identification of the kinds of microorganisms. However, Ramesh et al [2] state that this method is inaccurate because of the following reasons:

• Plating exposes the microorganisms to a favorable environment of surplus nutrients and optimum growth, encouraging even the inactivated ones to grow.

• Plate counting requires 48 hours to obtain a result and during these periods, the status of slime continues to change in the paper machine system.

As a real-time assessment, Ramesh [2] developed new methods using a flourogenic dye. Results were obtained within six hours. Another benefit one of the methods is being able to apply it for variety of samples of different matrices and color. The ATP method, which also is rapid, takes only several minutes. However, according to Ramesh, the ATP method is incompatible with opaque, light scattering additive materials. In my opinion, Ramesh’s method, requiring six hours, is still too long to be able to effectively monitor the status of slime. According to Simons et al, one of the disadvantages of the ATP method is not giving information about which type and what quantities of microorganisms are present. This is also the same shortcoming for Ramesh’s method. However the question is whether identifying the type of microorganism is practical in the mill. In a major laboratory there may be several microorganism specialists, but at a production site it may be useful to have a more frequent indication of the amount of total microorganisms, making it possible to take prompt actions.

As more ideal methods, several researchers propose online monitoring methods. According to Dickinson [3], there already have been some indirect online measurements, but there are some drawbacks as follows:

• Optical attenuation method: The device is limited to the use of transparent surfaces or polished surfaces, neither of which may be representative of the desired machine surface.

• Heat transfer resistance method: The devices that measure heat transfer resistance require the use of a heated metal surface. The applied heat can interfere with microbial growth and can stimulate excessive mineral scaling.

Lie [4] proposes a unique online system based on the use of the Quarts Crystal Microbalance with Dissipation monitoring (QCM-D). This system measures the amount and the viscoelastic properties of adhered material on a quartz crystal. The author states based on the results of lab-scale tests, that this system could effectively monitor slime buildup on a surface. However, questions arise regarding whether stickier materials other than slime also deposit onto the crystal sensor. Also, it might be expected that the sensor may need to be washed after it has become covered by slime. , However, Lie does not mention anything about this issue in his paper (figure).

Figure: when the viscoelastic material is on the sensor, the response of frequency is changed.

Dickinson et al [3] proposed another type of monitor based on the pressure required to pass water through a packed bed. Surface deposits such as microbial cells and the associated debris found in biofilms can increase the media roughness, resulting in an increase in pressure. Dickinson and his coworkers invented a new differential pressure biofouling monitor with a packed column of metal beads that can provide a large surface area for fouling. In this way they were able to create a sensitive, reliable instrument. Furthermore, by supplemental nutrient addition, slime forming by microbial activity is accelerated, and they concluded that the system could provide advanced warning of biofouling. The questions I am wondering about is whether the pH and the temperature of white water a likely to influence the pressure, the microbial activities. and the numerical results obtained, as influenced by these factors.

Online monitoring is very attractive approach, since it can be used as an indicator of the slime-forming status of white water. The approach has the potential to be able to prevent problems in advance by monitoring the status on a daily basis. As a monitoring tool, I still believe that the ATP method is superior to others, since it is selective for the living cell.

Applying Chemicals

Once the degree or status of slime formation has been identified, chemicals are applied to kill the microorganisms. However, biocides are often toxic chemicals, and mill staff needs to be very careful. The choice of chemical additives needs to be made based on both safety and environmental perspectives. Halogenated chemicals are effective against microorganisms, but they can form organic halides (AOX) that may end up in the final products or in the environment. Simons et al . [5] state that paracetic acid, a non-halogenated oxidant, should be an excellent slime control agent, and subsequently it is broken down to carbon dioxide and water. Also it does not affect felt life, and is less corrosive than other oxidants. The downside, as Simons et al mention, is that it requires a rather long contact time. Robertson [6] evaluated lignosulfanate dispersants as slime control chemicals. However, they did not appear to inhibit the formation of bacterial biofilms. Since lignosulfanate contains sugars, formation of biofilms was actually increased.

Hoekstra [1] states in his paper that good house keeping is very important. Some mills conduct “boilouts” to kill slimes. As far as good house keeping is concerned, besides boilouts, installing a UV sterilizer might be one option. I have had experience growing seedlings by hydro-cultures; in such operations, ozone can be used for disinfections. Compared to halogenated chemicals, such use of oxidants might be safer.

Slime Control Strategies

Based on the discussion above, it is recommended to consider employing a sterilization procedure on a paper machine involving ozone or ultraviolet devices. The goal would be to maintain good houskeeping in the machine system, inhibiting the development of slime deposits . In addition, it is recommended to check the status of slime in the white water daily by the ATP method. Online monitoring should be considered as an ideal approach, but taking a sample once a day can be acceptable. Measuring itself is not time-consuming, and data correction based on temperature and pH should be carried out. When unusual slime growth is identified, non-halogenic chemicals should be applied.

References

1. Hoekstra et. al. ,”Fundamentals of Slime Control”, in 1991 Chemical Processing Aids pgs 55-68

2. Ramesh et.al., “Real Time Assessment of Microbial Activity in Paper Coating and Additives” , in Tappi Paper Summit 2002

3. Dickinson, W. H., “Biofouling Assessment Using and On-line Monitor”, Tappi 99 Proceeding, pgs 449 –457.

4. Lie et. al., “A new early warning system for slime formation in paper machines” , Paper Technol. 43(8), 2002

5. Simons et. al., “Improving Productivity through Microbial Deposit Control Management”, Paperi ja Puu, 86(5), 2004 pgs 349-352

6. Robertson et.al. “Biofilms and dispersants: a less-toxic approach to deposit control”, vol.77, No4, Tappi Journal 1994. pgs 99-103

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Name : Contreras S. Irma Sofia
Date : April 4 th , 2006 .

Topic: “Why haven’t cationic fillers become popular, despite literature publications indicating benefits in terms of retention and optical properties?”

Why is the subject significant to the paper industry?

One important objective of papermakers is to lower production costs without sacrificing the optical and physical properties of paper. An important class of additives they use to achieve that goal are fillers. Fillers are widely used in production of paper in order to reduce the materials cost per unit mass of paper, increased the opacity, and improve the smoothness. There are many types of fillers; they can be anionic or cationic, and depending on their charge, they can be deposited on fiber surfaces by different mechanisms. Cationic fillers have been promoted as improving retention when used in the wet end of a paper machine because they are self retained due to their attraction for the anionic fiber; they have a tendency to be distributed along the anionic sites of the fibers, thus the fiber to air to filler spaces tend to be greater and opacity and light scattering tend to be improved [4]. However, this mutual attraction doesn’t ensure that contact between filler particles and fibers will be sufficiently intimate to result in an irreversible deposition. The effectiveness of this deposition is important in the production of paper, because the quality of the product depends on that. Besides papermakers want to produce a good quality of paper at the lowest cost and they do many studies in order to make the best decision on which type of additives they must add to the process to reach their goal.

Several studies have been performed on the use of cationic fillers in the alkaline freesheet market, as well in the area of newsprint. PCC produced on site is the only widely used filler material that has cationic charge; also some TiO2 can be produced this way. Kaolin manufactures have examined producing cationically dispersed slurries as both fillers and coatings. However the nature of the kaolin particle makes it much more economical to disperse it anionically than cationically [1].

Cationic fillers have a good performance with respect to improvement of the optical properties of the paper, and then usually strength properties and sizing performance are compromised. Fillers tend to become adsorbed on the sites where fibers can be attached to each other and the paper can achieve greater strength. Sizing can be sensitive to the pre-treatment of the filler and to the filler loading. This is most probably due to the sensitivity of the retention of sizing agents to the surface charge balance of the furnish.

There is another option when working with fillers. Papermakers can also use anionic fillers and/or add retention aids in order to achieve good retention of fillers the surface of the fibers. Retention aids are cationic or anionic acrylamide polymers, like PEI (polyethylene imine), aPAM (anionic polyacrylamide), PEO (polyethylene oxide), etc. They maintain adequate efficiency, drainage and also can achieve adequate Z-directional uniformity to retain additives. They are used in several combinations called “retention aid programs”. When using these additives the retention is improved and it tends to be better than using just cationic fillers, because retention aids provide different mechanisms to achieve the retention. Some of those mechanisms are polymer bridges, charged patches, etc, that form flocs more resistant to shear than those in which just Van der Waals forces are present.

What are various authors’ points of view on this topic?

The retention of wet end additives results from filtration, when particles are mechanically entrapped in the forming web, or by deposition, when particles are attached to the fibers in suspension. The deposition can be done by two mechanisms, heterocoagulation, when filler particles deposit on fibers because of mutual attraction, and heterofloculation, when long-chain polymers provide a bridge between fibers and filler particles. Filtration doesn’t contribute significantly to filler retention, because fillers are smaller than the openings within the fiber web. In the case of cationic fillers the predominant mechanism is the mutual attraction of fillers and fibers. But a redispersion of deposited fillers can be achieved by slow mixing if the mutual attractions are weakened [3]. The effectiveness of hydrodynamic forces in removing particles increases with the increase of the size of the fillers. In other words, the retention of the cationic fillers on the fibers doesn’t result in an irreversible deposition, as it was expected; so it’s important to consider the use of another type of mechanism or another type of filler in order to improve the retention of those particles in the paper sheet.

The fact that removal of fillers takes place even under slow stirring indicates that no intimate contact between deposited fillers and fiber is achieved and that the system did not reach a deep potential energy minimum. Fillers apparently are kept apart from the fiber surface because of some steric hindrance. This might arise from a hydration layer, surface roughness or other unknown factor. For practical purposes it is important to realize that although deposition of oppositely charged additives on fibers is enhanced by mutual attraction as expected, the attachment of the filler particles can be weak [2]. Depending on their ability to establish good contact with fiber, they be removed from the fibers, even with the application of gentle agitation. The effective separation distance between particle and fiber is critical in determining the behavior of deposited particles. On the other hand, papermakers use retention aids to improve the retention of particles on fibers. These retention aids are polymers that, besides the improvement in retention, can maintain adequate efficiency, drainage and achievement of a good Z-directional uniformity in a paper sheet. When papermakers work with retention aids, the mechanism of retention is heteroflocculation that can form flocs. Some of those flocs can be reversible with the application of shear; they can be formed again. So, the retention of fillers on the fiber surfaces is improved and more stable if compared with deposition of fillers just by attraction of different charges.

Cationic fillers offer the apparent benefit of mutual attraction between them and fibers for filling applications. This is, however, often overstated, and the forces involved are relatively weak compared with the hydrodynamic forces generated in most papermaking systems [6]. One important point to be considered is the cost, and it has been published that cationic dispersion is expensive; the monomers used to prepare the polymers are apparently more expensive and more polymer must be used than anionic dispersion. This must be considered a serious point.

What is their evidence?

The authors cited made some studies in order to figure out how the mechanism of retention of cationic particles works, as well as the effectiveness of the retention on the fibers. One of those studies was done by Alince and Robertson [2], who studied the deposition of colloidal alumina and different sizes of cationic latex (polystyrene latexes) on fibers. The colloidal alumina had a mean radius of 12nm. Of the two types of cationic latex, PS 1 was monodisperse with a particle diameter of 120nm, and PS 2 was polydisperse with a particle diameter of 1000nm. It is important to keep in mind that colloidal alumina and PS 2 are smaller than fillers. In those studies they observed deposition of latex particles was different depending on the particle size. They applied slow mixing to the mixtures and figured out that that was enough to redisperse PS 2 but not the smaller PS 1 particles. Another experiment these authors made was the addition of 0.1M NaCl to the stirred suspension of fibers after completion of latex deposition. The response was different for each type of latex. PS1 (monodispersed and smaller particle size) remained deposited, while the larger latex, PS2, experienced a substantial removal. The behavior of the alumina was different because of much smaller particle size, which made it less sensitive to stirring, and which may permit better contact with the fiber. Another study was done by Alince and Lepoutre [3]. They worked with cationic clay particles of different sizes, A 0.20 micrometers, B 0.68 micrometers and C 3.00 micrometers. They found the same results as the studies described above. Deposition of the smaller particles (A) was more effective than the larger ones (C). Pigment retained decreased with time in the three cases, but the decrease was higher for the biggest particles.

Are there others ways to account for their observations?

The total potential energy among two kinds of hydrophobic particles is obtained by summation of the Van der Waals attractive energy and the electrostatic energy. In the case of cationic fillers adsorbing onto the fiber surface, they have opposite charges and the main force that keep them together is Van der Waals force, but it is not strong enough to make the retention irreversible. Particles need to get close enough to keep together, and this is easier for small particles, so in the case of filler particles it is difficult to get the necessary distance to make the deposition irreversible.

What can you suggest for the future work in the same field?

The best future work should be focused in the development of a new type of cationic filler with a better performance in the retention onto the fibers; it may be the development on a new particle with a different shape and/or a different chemical composition that enhance the performance of the filler. This study must be done considering the cost of the new material, because this is an important point in the industry when they decide to use any new material in their processes.

References

[1] Carter, Douglas and J. M. Huber Corp., “Cationic fillers and their role in retention”, 1994 Papermakers Conference, 509-515.

[2] Alince, B. and Robertson A., “Colloidal aspects of the retention of positively charged additives”, TAPPI Journal 61(11), November 1978, 111-114.

[3] Alince, B. and Lepoutre, P., “Interaction of cationic clay particles with pulp fibers”, TAPPI Journal, January 1983, 92-95.

[4] Goodwin, L. “Benefits of cationic ground calcium carbonate”, TAPPI Journal 72(8), August 1989, 109-112.

[5] Penniman, J., “Cationic calcium carbonate fillers”, 3 rd International Seminar on Paper Mill Chemistry, August 30 th .

[6] Bown, R., “Cationic pigments in papermaking”, ECC international LTD.

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Name: Kacee Des Jarlais
Date: May 7, 2006

Topic: “When does it make sense to adjust a paper mill’s chemical strategy for pitch control, based on the composition of deposit-forming materials and seasonal variations?”

What is Pitch?

Pitch can be used as a generic word to describe hydrophobic molecules, also called extractives, from wood. Some pitch chemicals are fatty acids, resin acids, sterols, steryl esters, triglycerides, and any other hydrophobic chemicals in the wood (Figure 1). The three common places for the pitch to be are on the fiber surfaces, inside parenchyma cells, and suspended in the process liquid. 1 These chemicals are insoluble in water and can form unstable colloids and then deposit on different surfaces of the paper machine. There is also the term “white pitch” which refers to sticky particles, normally styrene butadiene resin from coated broke. These, along with stickies, ethylene-bis-stearamid and sizing agent byproducts cause similar deposits to pitch but are not naturally occurring chemicals from the wood like the components of pitch are [3].

Figure 1: a) abietic acid salt – a model compound of resin acid and rosin size (which is produced from the tall oil)

b) linoleic acid salt – an example of a fatty acid

Significance to Industry:

Wood pitch can be extremely tacky. Because of the this, pitch is commonly found in mill deposits and actually acts as the glue that holds them together [3]. These deposits are of great concern to the industry because they can cause spots or holes in the final paper product which may render the product quality below specification. The build-ups also cost the industry money in terms of downtime required for boil-outs to clean out the paper machine, especially when the downtime was not planned.

Notice that it was stated that the wood pitch can be extremely tacky. Under the right process conditions and with the right additives, pitch can go through the paper-making process without causing any problems. There are many different factors that affect when the pitch will come out of solution. An in-depth understanding of the form of chemical species that form with different pH, and other additives along with incorporation of changes in the wood pitch entering the system due to seasoning variations is imperative to reducing pitch deposit formation.

When is Pitch Season?

Pitch season is, just as it sounds, a time period (during the winter season) that occurs every year where there is an increased amount of pitch deposition at paper mill. This causes many problems with the run-ability of the machines since the change in pitch conditions lead to deposit problems under conditions that have been used previously without problems. Many times the deposit problems are extreme enough to fill wires and felts, plug Uhle boxes, and leave pitch on surfaces such as press rolls [2].

There are a couple reasons for these cyclical peaks in pitch problems. The main chemical causes are actual changes in the composition of the pitch present in trees and the absence of proper chip aging prior to pulping. Some current industry changes that increase the frequency and severity of these situations are increased mechanical pulp usage, water system closure and “just-in-time” wood chip deliveries [2].

What Possible Pitch Compositions Exist?

There are a large number of factors involved in the mechanism of pitch deposition. Because this is a costly problem for paper mills, much research has been performed to determine the components responsible for and the mechanism of deposit formation. Each mill probably contains a different set of pitch problems due to different species of wood, different locations of wood origination, varying wood chip seasoning times and temperatures, and various chemical additives used during the paper production. All of the mentioned differences lend to complex situations of chemical interactions. It is the specific pitch chemicals, and forms of those chemicals, that is important. Once this is known, then the interactions with the papermaking additives and conditions can be studied in attempt to predict the timing and severity of an upcoming or current pitch season.

The amount of pitch present in wood actually decreases in winter because many extractives travel to the root of the trees during autumn and winter, but the presence of the pitch season proves that the concentration alone is not the reason for the increased deposition. One way in which pitch molecules can be divided is into “ester pitch” and “acid pitch.” The ester pitch contains more hydrophobic molecules and is considered to be the type that contributes more to the deposition tendencies of the pitch. These ester components are more prevalent in the winter season for many trees, but many species themselves have a higher ester ratio. The seasoning of the chips is necessary because hydrolysis of the esters to acids occurs through natural pathways and the ester ratio decreases [2].

On a molecular level, the actual size of the pitch dispersion particles has been shown to be important. The pH of the process conditions can change the form of the resin acids from the neutral form to the charged acid form. Although these are fundamentally the same molecule, the different forms lead to different activities in the paper machine.

What Solutions Exist?

A mill should have a proactive plan in place to monitor the composition and frequency of their pitch problem. This is especially true for mills in climates that have winter as they will have cyclical patterns and experience pitch seasons. The mill will have to change its pitch control strategy as the chemical cause for the deposits will be different from other times of the year. It would be expensive to use lots of pitch control additives and such when it was not necessary and expensive to not try to stop any amount of pitch problems that could be dealt with. Changes in the mill pitch control method should take place as soon as pitch problems develop, but preferably the methods should be adjusted when it is known or suspected that there has been a change in season, wood species used, or process conditions but before the pitch starts to cause major problems.

Although the mill people can not do anything about the natural changes that take place in a tree, they can try to adjust with those changes. Any amount of chip seasoning that can be done is good, but this is hard to do in cold weather as the weathering reactions do not occur as quickly [1]. There may be special kinds of chemicals that are available to interact with specific part of the problematic pitch, including possible use of enzymes.

The first thing that must be determined is the specific composition of the problematic deposits and the best guess at the mechanism of formation [1]. There are at least two thoughts on the size of the colloids in solution that reducing deposition. When differing amounts of the acids were studied, it was found that the deposition tendencies were dependent upon the amount of hydrogen bond interactions between the molecules, not some sort of additive affect of both the molecules solubilities [6].

Conflicting data has been reported describing whether or not larger colloids are good or bad, but it appears as though if the pitch can be adsorbed onto the fibers, there is less chance of pitch deposits from colloidal material. Changes in pH or electrolytes present in the process water also affect the stability of the colloids [5]. Therefore, water hardness should be monitored. Also, use of any recycled fiber that may have been processed at a different pH (acidic versus alkaline) should either not be used or the change in pH should be accounted for as soon as possible.

Although many solutions specific to variables in the pitch are possible, there are of course the usual methods that could be utilized such as talc and other detackifiers, cationic fixatives to adhere the pitch to the fibers, surfactant use although this can cause other problems such as foam production and increased pulp washing to try to remove the pitch from the system.

Experimental Proof?

Molecular modeling was used to substantiate the unexpected results of the solubilities of model pitch compounds. The more hydrogen bonds between the pitch molecules, the fewer hydrogen bonds that can occurred between the pitch and surrounding water, making the colloid less soluble. Aromatic rings and long, more saturated alkyl chains were found to be the best for increasing the solubility of the pitch. This all has to do with the type of hydrogen bonding that occurs. For example, aromatic rings form hydrogen bonds with the other pitch particles with the cloud of pi-electrons, leaving more of the molecule available to interact with water [6].

Allen proposes that the colloids are sterically stabilized and the velocity of the particles colliding with surfaces causes the stable system to collapse, thus forming a deposit [1]. Shetty et al found that addition of a cationic polymer increased the colloid size from 2 µm to about 10 µm by coalescence. The larger colloid size then helped the pitch be adsorbed onto the fibers and carried out with the final product instead depositing in the paper machine [4]. Although Shetty et al propose an interesting idea, more work would have to be done based upon their theory to see if it is actually true under conditions in a papermaking process because it has been found that deposits form where flow suddenly changes direction, supporting the idea that the impact of colloids with a surface is important for deposit formation [1].

As with many organic acid salts, the presence of cations, especially calcium and magnesium, can cause the organic acid salts to precipitate out of solution as tacky deposits. The pH also affects the pitch because it there will more present as the neutral phase at a lower pH, and as the pH is increased the pitch will leave the fiber surfaces more and form the acid salt, now ready to aggregate with hardness ions 5].

What Future Research Could be Useful?

The chemical composition and interactions of wood pitch molecules are very intricate and could still be studied. Computational chemistry has not been utilized very much for this area of research, but prediction of chemical interactions among pitch particles and the water molecules could lead to some very helpful discoveries. New development of enzyme treatments may help break down the pitch esters that seem to the root of the problem in seasonal pitch variations. Possible an assisted seasoning could be achieved with enzymes in areas where the cold weather prohibits the natural seasoning effects. Routine analysis of pitch in wood chips could possibly warn of pitch deposition problems before they get out of control in the mill. In general, the best way to handle pitch seasons would be to keep records of events each year, including different wood species and originations used, and to monitor wood chip extractives or deposit composition and frequency. This way, hopefully a change in pitch control methodology can be in place before the situation gets out of control.

Literature Cited

1. Allen, L. H., “Mechanisms and control of pitch deposition in newspring mills,” Tappi J. 63 (2): 81 (1980).

2. Blazey, M. A., Grimsley, S. A., Chen, G. C., “Indicators for forecasting ‘pitch season’,” Tappi J. 1 (10): 28 (2002).

3. Hubbe, M. A., Class Notes for “WPS-322: Wet-End and Polymer Chemistry,” Chapter 17, North Carolina State University , Fall 2005.

4. Shetty, C. S., et al , “A likely mechanicsm for pitch deposition and control,” Tappi J. 77 (10): 91 (1994).

5. Sihvonen, A., et al, “Stability and deposition tendency of colloidal wood resin,” Nordic PPRJ 13 (1): 64 (1998).

6. Vercoe, D., et al , “An innovative approach characterizing the interactions leading to pitch deposition,” J. Wood Chem. Tech. 24 (2): 115 (2004).

Name: Bob Bunzey
Date: September 6, 2004

Topic: Anionic Wet-End Starch

Questions:
1. Give your assessment of whether the proposed technology, involving anionic starch would be a good fit for an uncoated grade of your choice.
2. Discuss whether it would make more sense to remove the size press, or just take a gain in bonding strength.
3. Point out the most important barriers to implementation of an anionic starch wet-end system in the type of grade application that you consider – especially in cases where the author has not made a convincing case that the barriers can be overcome.

Primary Resource: Brouwer, Piet H.; Baas, Jan; Wielema, Thomas A., “A Wealth of Possibilities to Improve Paper Quality and/or Reduce Paper Costs,” TAPPI Paper Summit 2002

Why this Subject is Important: Starch is the most used polymer in the paper industry. According to the authors, in the year 2000, the world production of paper and board was 323 x 106 tons. The average composition of all paper grades was 89% fiber, 8% filler, 1.5% starch, 0.5% alum and 1% synthetic chemicals. This equates to approxomately 5.2 x 10^6 tons of starch used worldwide in the paper industry in 2000. Trends in the paper industry are toward the use of more weaker recycled fiber and more minerals (fillers and coating pigments). The negative consequences of these trends is a loss in strength which is compensated for by the use of more starch. Starch is also the least expensive hydrocolloid to impart dry-strength and is labeled a “green” chemical because it is renewable and is environmentally friendly.
Expressed in the most simple way, starch in papermaking functions as a glue. Applied in the wet-end, the strength increase by starch is theorized to assist in the extension of the bonded area between pairs of crossing fibers. Starch in the wet-end of paper machines differ from that used in the size press in one main property: moleculear weight. In the wet-end, non-degraded (maximum moleculear weight) starches are used while in the size press, reduced moleculear weight starch (degraded) is the choice. The molecules in non-degraded starches have such huge dimensions that the adsorption of these molecules takes place only onto the outer surfaces of fibers. This allows, in principle, every molecule of starch to be available to perform a “glueing” task. Lowering the moleculear weight of starch reduces the binding power of those starches, whether in the wet-end or in the size press application. The high viscosity of non-degraded starches limits their usage to the wet-end of a paper machine, because there the actual concentration of the starch is sufficiently lowered so that the high moleculear weight does not create unacceptable viscosities in the water. A consistency of 1% of the pulp and the addition of 1% wet-end starch on the pulp gives a starch concentration of only 0.01%.
Based on the previous information, it becomes readily apparent that it would be advantageous to leave out the size press and use only wet-end starch. To do so the wet-end chemistry must be controllable and enough wet-end starch should be retainable to acquire the desired strength properties. With cationic starch this is not attainable.
Anionic wet-end starches such as carboxymethylethers, phosphate-esters and sulfosuccinate-esters had been used during the 1960’s and 70’s. These were adsorbed onto the fibers by means of alum in acidic papermaking furnishes. Additional levels of more than 1.5% cannot be retained by alum however, because the addition of more starch means more alum and that lowers the pH. This in turn diminishes the ionization of the acid groups on the fiber, and lowers the number of anionic bonding sites. In addition, in neutral systems, cationic wet-end starch has been used as the fixative with a maximum dosage of the combined starchs at approximately 1.3%, a level consistent with cationic starch levels alone. The possibility of retaining anionic surface sizing-starches at a neutral pH by means of a cationic fixative with a suitable moleculese has been demonstrated.
Among the many trials run and presented in this paper is one that addresses the addition of a wet-strength resin as a fixative for potato starch phosphates (PSP). Wallpaper base was chosen as the grade, utilizing chemical pulp and groundwood. The chemicals previously used were a cationic wet-strength resin and .04% cationic wet-end starch. Preliminary charge measurments showed strongly cationic conditions. During regular production, the cationic starch had been added between the mixing chest and the machine chest.
Machine conditions for this trial stayed the same with the anionic starch added in the same position in the feed system and the wet-strenght resin added between the machine chest and the headbox. Conditions are shown in Table 1:

Wet-end Parameters	0.4%Cationic	0.4%PSP	0.6%PSP
PH (Headbox)	4.3
Conductivity (uS/cm)	2300
Total wet strength resin (%)	0.4	0.4	0.6
Zeta potential (headbox, mV)	+2	-1	-1
A/C Demand (HB, ueq/kg)	A 160	A 30	C 10
Free starch (white water, mg/L)	171	93	99
Starch retention (%)	75	96	94

The change in this trial to PSP reversed the charge situation of the wet-end which coincided with better starch retention. There was reduced dusting in the finished sheet and a lower starch content in the white water. This led to PSP now being used in production.
At first blush, this particular trial seems to be what we are looking for. Unfortunately there is no corresponding strength data available in this paper. The addition points are accessable and straightforward. We do not use a size press in the manufacture of base and rely on fiber blends, refining and binder fibers to develop strength properties. The biggest barrier to implementation of an anionic starch would be its affect on porosity of the finished sheet. Secondly, we would have to carefully monitor our discharge water.

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Name: Carlos García
Date: September 9, 2004

Topic: “What practical and theoretical problems do you expect to encounter if one attempted to put into practice a system to control the dosage of a highly charged cationic additive based on the system described in this article – monitoring the size of aggregated material in the white water of a paper mill?”

Primary resource: Blanco et al., “Focused Beam Reflectance Measurement as a Tool to Measure Flocculation,” Tappi Papermakers Conf., 2002.

Why this subject is important: Retention and drainage affect the efficiency, production rate and paper quality of the paper machine. The presence of fine material (FM) in the furnish and white water, reduces the drainage rate by blocking the spaces between fibers at the wet web. At low drainage rates, more water is kept inside the fiber mat, which makes it harder to remove by pressing and drying, resulting in high production costs either by reducing the paper machine speed or by consuming more steam. Fines material interacts with retention aids, reducing their efficiency of retention onto the fiber, which creates deposits or contamination along the circuit. In addition, paper quality can be affected by having a low fiber and fine retention by producing unstable paper basis weight and humidity. Also, production costs rise due to fiber, fines, and chemical additives lost in the white waters. Therefore, control of the fine material behavior helps to obtain a stable and efficient process.

Answer to the assigned question: The practical problems that I expect to encounter if one attempted to put into practice a system to control the dosage of a highly charged cationic additive base on monitoring the size of aggregated material in the white water of a paper mill are the need of additional filtrate equipment to prepare the white water samples, the need of a cleaning stage in the FBRM, and the adjustment variables to obtain “optimal data”. The theoretical problem that I expect to encounter is that the data given by the FBRM would not reflect all the fine material present in the white water sample.

Logical or theoretical support for answer: Practical problems – White water has different fine material size content depending on the wire mesh used at the paper machine and to the presence of fiber and fines coming from the broke system which helps the disc filters or deckers runnability. A wide distribution of the particles sizes (fibers up to 3mm and fine material less than 76 m) would give a wide range of particle size distribution that would make difficult to control the dosage of a highly charged cationic additive to act on the fine material. In addition, the presence of fibers, mineral fillers, sticky materials, etc, in the white water can produce deposits on the FBRM beaker walls and on the probe, producing erroneous information data for the additive control. Results such as data confusion or even lack of reality can be presented by FBRM since it has many variables that can affect the results, such as probe location, duration of the measure, and data averaging.

Theoretical problem – Hydrodynamic shear is present in most of the wet-end components of the paper machine. Flocs can break due to shear forces, producing smaller aggregates particle size. FBRM bases its data in the particle size (aggregates, flocs, etc). In a continuous paper machine process, the aggregates or flocs of white water are broken forming smaller size particles which are hard to read by FBRM.

Experimental support for answer: The authors show the behaviour of the flocculation process with the presence of shear forces. The flocs size increases when a flocculant is added to the sample at low agitation and when the agitation intensity increases it can be seen that the flocs start breaking by decreasing their sizes. The chord size distribution of fine material with no shear forces applied to it had larger sizes than the chord size distribution with shear forces applied to it.

Situations in which the findings can be useful: The findings of using focused beam reflectance measurement (FBRM) as a tool to measure flocculation can be useful for studying the relationship between different wet-end variables, such as retention and drainage rate, and different amounts of fine material. Blanco et al. showed the chord size distribution of dissolved and colloidal material (DCM) in a white water sample with no shear forces applied to it. Therefore, studies can be done by taking a known amount of DCM in a white water sample and by taking a well washed amount of pulp DCM free. Also, the findings of this paper can be useful for selecting the optimum adding point to the process of a specific polymer. The authors present a figure where it can be seen the flocculation behaviour was affected by different shear stress applied on the flocs formed by the addition of PAM. Finally, FBRM can be useful for the optimization of retention aids for different paper grades. Flocs size and strength affect retention efficiency and paper uniformity.

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Name: John T. Scott
Date: 4th. August 2004

Topic: Whether the author is able to support the vague and general-sounding statements that he makes in the abstract, introduction, and conclusion of the article.

Primary Source: “New Amphoteric Starch Technology for Improved Paper Quality and Optimal Wet-End Performance” by Lee Nester and Walter Maliczyssyn of National Starch & Chemical Company, Bridgewater, New Jersey, USA. TAPPI Papermakers Conf., 2001.

Introduction: According to G. G. Hawley in “The Condensed Chemical Dictionary”, amphoteric means “having the capacity of behaving either as an acid or a base.” At acid pHs an amphoteric product has cationic charge, as the anionic charge is suppressed by the hydrogen ions around. Modern amphoteric starches, have quaternary amine and phosphate groups, which should remain ionised at the normal papermaking pHs. For neutral pHs, both charge groups will be weakly ionised and you will get an advantage from both. However, the fines in a paper machine are anionic, although very ionically active and with a very large surface area, they will have affinity to the cationic charges in the amphoteric starch. Normally the only cationic charge in a paper furnish is that introduced with alum, charge neutralisers, retention aids, etc., although calcium carbonate also can have a mild cationic charge. Some clays may exhibit a cationic charge on either the face or edge, but extremely weak.

Discussion: As is illustrated in the third mill example, mills tend to over-use products for the wrong reasons. In this example a mill is obviously using too much retention aid (and probably charge neutraliser), as well as the size, in the hope of keeping more fibre on the wire, less in the white water and less in the effluent. They obviously do not have good control of their machine – not enough monitoring of their charge. The increased amount of ash retention could well be from the anionic charge on the starch, but would not happen if they did not over-cationise their system normally. In my limited experience, it is better to run paper machines with an anionic charge and not too close to the iso-electric point. They are more stable, and you get better retention and formation. Really not enough facts are given, as it could be that they require large amounts of size and starch to achieve their dry strength and Cobb specifications. Normally when you increase the refining, drainage drops off, and I do not understand why it is different in this case.

In the laboratory studies, the acid recycled furnish has alum added as a ‘charge neutraliser’, but giving some cationic charge to the fibres and fines, helping the anionic retention aid to be effective. You would expect then, that amphoteric starch, regardless of the age of the technology would be more effective, as the cellulose fibre has itself become less anionic, even partly amphoteric. No explanation is given, even tentative, for the Ring Crush to keep increasing with this new starch. They also have not explained why the drainage rate should improve. Possibly the formation is ‘shot’! 15 kgs./ton is considerably more than most papermills will use of starch, however cheap it is. The slight change in ash retention is not significant at the sort of levels that a mill would normally use. Scott Bond, a measure of paper strength in Z-direction, does not seem to be affected really, whichever form of starch is used. The slight differences could be experimental error.

In the first mill trial, at the start up, everything looks bad, and I fail to see why after one day the mill should be able to decrease the sheet weight and still get an increase in Ring Crush – I feel there must be some other factor in there. Noticeably when the mill went back to incumbent amphoteric starch, the Ring Crush did not drop markedly, nor was a major increase in sheet weight necessary. Increasing the amphoteric starch in the thin stock, would improve the fines retention, which would in turn improve the stiffness of the board. The amplitude of the oscillations of the ring crush results, is less with the incumbent starch, important for machine control.

In the second example, just as the results are starting to get interesting, the mill changed back to the potato starch. Even then there seems to be a greater oscillation in the results than with their normal product. From this short trial, possibly only six hours, you can only be encouraged, but you cannot be definite. Actually the basis weight went down, when the potato starch was put back on!

Conclusion: Generally I do not think their claims have been substantiated.

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Name: Junlong Song
Date: September 5, 2004

Topic: What evidence is there, if any, that there is a synergistic effect of using a combination of bentonite microparticles and anionic polymer to achieve retention and drainage?

Primary resource: Philip A. Ford, “A New Multi Component Organic/Inorganic System, The Path Forward for Microparticle Technology,” 2003 TAPPI Spring Technical Conference & Trade Fair.

Why this subject is important: The retention of fillers and fine particles can affect the operation of paper machine and the final product’s properties and quantity. A low rate of retention will reduce the uniform distribution in the Z direction and increase the consistency of fines or filler in white water and increase the cost of water treatment. The rate of drainage can affect the production rate because for most cases drainage is the key factor limited the production. If there is a synergistic effect of using a combination of bentonite microparticles and anionic polymer to achieve retention and drainage, it means we can reduce the chemical consumption and reduce products’ cost at the same production, or we can gain higher production at the same retention aids consumption.

Answer to the assigned question: There is no evidence to prove that there is a synergistic effect of using a combination of bentonite microparticles and anionic polymer to achieve retention and drainage in Ford’s paper.

Logical or theoretical support for answer: Fine materials can be retained either by colloidal mechanisms or by sieving. But sieving is favored by large size. Thus, if we want to retain something that is too small to be filtered by the fiber mat we have to use a colloidal mechanism to attach it to fibers or fiber fines at first. There are two types colloidal mechanisms. One is coagulation, which means use of an oppositely charged additive to neutralize the charge of fiber surface and reduce its zeta potential and let small fines can collide on it. The other mechanism is flocculation, which means use of a high mass polymer to bridge the fines; this procedure is independent of charge.

For the multi-component organic/inorganic system, cationic PAM works as contributor of cationic charge into the thin stock system and works as a bridge between fiber and fiber. Bentonite microparticles and micropolymers, which both have high negative surface charge and have large specific surface, have a high tendency to absorb fines, fillers etc. which are neutralized by cationic PAM and form flocs. These flocs then are bridged by the long chain of cationic PAM. But for bentonite microparticle and micropolymer, since “like charges repel”, they are unlikely to react with each other or bind together to form a structure which benefit to retention and drainage. So, there should be no synergistic effect of using a combination of bentonite microparticles and anionic polymer to achieve retention and drainage.

Experimental support for answer: The experimental evidence provided by Ford support my answer given earlier consists of (a) “white water solids and additoin rates for the new three component system paper grade A” and (b) “white water solids and addition rates for the new three component system paper grade B” and (c) “addition rates vs. formation for the new three component system, white water solids maintained at same level”. We can see, although 900g/t bentonite microparticles added in the grade A and B, only slightly lower the addition of cationic PAM and mciropolymer, there is little effect for the white water solids. And from graph 8, substituting 0.2kg/ton of micropolymer with 0.2kg/ton of silica, the paper machine maintained the same retention. “Synergistic” means that a combination of two things does something that is greater than the sum of the two things. From all these data, we didn’t find any synergistic effect of using a combination of bentonite microparticles and anionic polymer to achieve retention and drainage. But for formation, they do have a synergistic effect. .

Situations in which the findings can be useful: The findings reported by Ford can be useful when one is involved in the trouble of getting good formation. From this paper, we can see, multi-component organic/inorganic colloidal systems do have obvious effect for the formation. But for the retention and drainage, its effect is nil or limited at the same chemical addition. So, it is pretty arbitrary that the author claimed that there is a synergistic effect of using a combination of bentonite microparticles and anionic polymer to achieve retention and drainage from its effect on formation.

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Name: Yun Wang
Date: September 8, 2004

Topic: “Can the results shown in Figs. 8 through 11 be explained by the mechanisms that the author shows in Figs. 1-7 and describes in the text?”

Primary resource: Richardson, “Use of PAC in Conjunction with Polymers as a Retention System,” TAPPI 2003 Spring Tech. Conf.

Background of this paper: Obtaining a significant benefit is the most important consideration for the purchase of chemical additives for any manufacturing process. A papermaking factory is no exception. Using less fiber to make more paper is a keygoal of many papermaking facilities. How to achieve this goal? Retention efficiency can be part of the answer. The higher retention you can get in the forming process, the less fiber you will need to use. Coagulants and flocculants are widely used as a retention system in many factories. But the retention efficiency varies in different situations, depending on the furnish and the papermaking equipment. So finding the method to achieve the best retention efficiency is the key of increasing the factories’ profits. However before you make a conclusion you should learn the mechanism of this retention system first.

A flaw of this paper: This paper is focused on finding the mechanism of the retention system that was employed. But unfortunately there appears to be a flaw in this paper. The results shown in Figs. 8 through 11 cannot be explained completely by the mechanisms that the author shows in Figs. 1-7 and describes in the text.

Support: The first part of the paper gives many details about the mechanism of coagulants and flocculants. As it says, the mechanism of the interaction between coagulants and furnish is electrostatic patches. And with adding anionic flocculants, the cationic coagulants can be the bridge between furnish and anionic flocculants. If we add cationic flocculants to furnish, then the cationic coagulants will influence the adsorption between furnish and cationic flocculants to maintain the polymer extension of flocculants maintain which results in better bridging. These are the keys of mechanism in the paper.

In the second part of this paper, the author gives us some examples to support his conclusion. And in these examples, the author compares the drain times or ash retention when using different kinds of coagulants or no coagulants. In these examples, the drain times or ash retention are greatly improved after using coagulants. This phenomenon can be explained by the mechanism mentioned above. However, if one only compares the numbers obtained by changing the dose of coagulants, maybe the reasons cannot be explained by the mechanism in this paper. For example, in figure 10, all of the curves are high at the beginning. This observation is consist with the function of coagulants. But the red curve starts to go down when the dose is about 2(lb/ton). And another issue is that the configurations of these curves are very different. However in this paper the author doesn’t give the relationship between the dose and the efficiency. So I think according to the mechanism we can’t explain the experimental results completely.

Conclusion: The mechanism reported by the author can give some ideas about the function of coagulants and flocculants. As a paper engineer, this knowledge is very important because it can help them to understand whether they need to use coagulants and flocculants and when to add them. But he needs to research the dose and which kind of coagulants or flocculants can be used by themselves.

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Name: Lambrini Adamopoulos
Date: Sept.9th, 2004

Topic: Is it or is it not true that the composition of wood pitch is more important than the amount of wood pitch, relative to the probability and severity of pitch deposition outbreaks? In what ways, if any, is it appropriate to change not only the amount, but also the type of pitch control additives in response to seasonal changes in pitch composition?

Primary Resources: Blazey et al, “Optimizing a Pitch Season Forecast”, TAPPI 2003 Spring Technical Conference and Trade Fair
Blazey et al, “Indicators for Forecasting Pitch Season”, TAPPI Journal, December 2002
Secondary Resource: Fischer and Messner, “Reducing troublesome pitch in pulp mills by lipolytic enzymes”, TAPPI Journal, February 1992

Why this subject is important: Wood pitch deposits can be a very troubling issue in today’s papermaking industry. They often lead to plugged uhle boxes, pitch-covered press rolls and filled wires and felts. Mills look to avoid extended downtime and lost production days, since they wish to maximize their cost-effectiveness. Thus, being able to forecast a mill’s unique pitch season can prove to be an asset for the papermaker who seeks to capitalize on efficient control strategies. As a result, papermakers are actively searching for factors that may forecast the onset of a pitch season, and that can be tailored to every mill’s specifications, as well as effective methods of dealing with pitch when it does arise.

Answer to assigned question: The composition of wood pitch is a better indicator of the probability and severity of pitch deposition outbreaks than the amount of wood pitch present. Wood pitch is comprised of “ester pitch” and “acid pitch”. All pitch components, resin acids, fatty acids, triglyceride esters, steryl esters and waxes, are classified in one of the two categories. However, it is the “ester pitch”, composed of non-ionic and water-insoluble oily materials, that is believed to be responsible for pitch deposits. As a result, the ester pitch: acid pitch ratio is a better indicator of pitch outbreaks.

Furthermore, the concentration of ester pitch is very much affected by wood chip seasoning and seasonal variations. The ester content in green chips is high enough that pulping them eventually leads to pitch deposits. Ester pitch control additives seem essential in such processes. As chips are seasoned, the ratio of ester pitch to acid pitch species decreases. This results in less pitch problems and less need for control additives. Moreover, ester pitch content increases significantly in cold winter temperatures, relative to the summer. Thus, during the winter, mills are more prone to pitch outbreaks.

Ester pitch control additives, detackifiers such as talc, coagulants like alum and cationic polymers, and dispersants may be used to prevent severe pitch outbreaks. Nevertheless, a priority in pitch control is to avoid its growth and inhibit its deposition. In trying to control ester pitch, one must look into controlling materials such as triglycerides and steryl esters. A possible solution is to remove triglycerides by enzyme catalyzed hydrolysis. Adding lipase in pulping lowers the adhesiveness of the resins and decreases the pitch deposits.

Logical or theoretical support for answer: Ester pitch materials are neutral species that are more hydrophobic than their acid pitch counterparts. For that reason, the pitch particles have a tendency to aggregate and form deposits. It then seems reasonable that the ester pitch fraction be held accountable for the formation of pitch deposits.

In addition, triglyceride esters can hydrolyze into their component fatty acids over time. Thus, seasoning decreases the amount of ester pitch while increasing the amount of acid pitch present, thereby decreasing the ester pitch: acid pitch ratio.

Cold temperatures are instrumental in decreasing the rate of hydrolysis of ester pitch. So, the ester pitch component of wood resin is significantly higher in the winter than it is in the summer, thus creating more pitch deposits. This results in varying needs for pitch control additives.

Consequently, forcing the hydrolysis of triglyceride esters through the use of lipase enzymes, and collecting the liberated fatty acids with a sodium hydroxide solution seems like an effective way to decrease of pitch adhesiveness, and thus pitch deposits.

Experimental support for answer: The experimental evidence provided by Blazey et al. to support the answer given earlier is found in the case studies that they carried out. At a Northern Kraft mill, Blazey et al identified steryl/triterpenyl ester wood pitch deposits using FT-IR spectroscopy. Also, a plot of % extractables of the aspen chips versus the date suggests that the peak months for deposit outbreaks coincide with the % extractables of the aspen chips, which are related to the levels of esters in the chips. This is a first hint to the importance of the ester pitch: acid pitch ratio.

At a Canadian Newsprint mill, the FT-IR spectroscopy spectrum identified deposits which were rich in wood pitch triglyceride esters. At this mill, low pitch counts and warmer relative temperatures were misleading and did not warn the papermakers that severe deposit outbreaks would happen. However, the ester pitch: acid pitch ratios as well as a plot of pitch counts versus day, shows that the ester pitch: acid pitch ratio predicts outbreaks even though pitch levels are low.

At a newsprint mill using Southern pine, chromatograms were use to show the pitch distribution profiles in the summer and winter. Based on these, the quantitative data for various pitch species present was obtained for both seasons. This showed the correlation between pitch composition and pitch season. The ester pitch: acid pitch ratio is much higher in the winter. Finally, Fischer et al. used gas chromatography to identify the reduction of triglyceride content after hydrolysis by the lipase (within two hours). This showed that the enzyme can be used to degrade pitch in an acceptable amount of time.

Situations in which the findings can be useful: The findings reported by Blazey et al. are useful to every paper mill. Pitch season is costly to mills since they wish to optimize production, and one way of doing so is by minimizing pitch outbreaks. Therefore, any tool for estimating and assessing the probability of pitch outbreaks is valuable to papermakers since it allows them to adjust their pitch control program. As a final point, it is important to note that papermakers want to prepare for a pitch season as efficiently as possible in order to limit the need for damage control.

Name: Kathy M. Austin

Date: September 4, 2003

Topic: “Why do the authors think that an association between the PEO neutral macromolecule and a phenolic material allows the PEO to adsorb and form bridges?”

Primary Resource: Van de Ven, T. G. M., “Mechanisms of fines and filler retention with PEO/cofactor dual retention aid systems,” J. Pulp Paper Sci. 3 (9): J447 (1997).

Why this subject is important: The retention of fillers and fine particles plays vital roles in several aspects in the papermaking process. Filler particles are added to the stock to impart specific properties to the final product. Unretained particles cannot affect the final product in any way. Unretained fillers and fines make their way to the recirculation system and waste water treatment system where the cost of filtering the particles adds to the production costs. Papermakers are usually anxious to find improved retention aid systems to reduce the loss of fillers and fines and the energy needed for recirculation and wastewater treatment.

Answer to the assigned question: The authors believe that the ability of the PEO/phenolic cofactor systems allows the manipulation of the thickness of the adsorbed polymer layer (dpol) and the distance over which the electrostatic repulsive forces act (del).

Theoretical support for answer: The attraction and repulsion of the particles in a wet end system using a PEO/CF retention aid system is controlled by the thickness of dpol and del. As dpol becomes thicker than del, the attraction caused by the polymer layer will overshadow the repelling force of the electrostatic repulsion and the particles are drawn into flocculation. Since PEO will not bind to all substances, a cofactor which will bind to the PEO and the substances in the wet end system is added to assist the build up of the dpol layer.

Experimental support for answer: Experiments involving various papermaking additives and fibers showed that PEO alone would often do little or no good in flocculating particles. However, when a cofactor was added to the mixture, the PEO/CF caused flocculations to form in the system. The cofactor needed to create flocculation depends on the components of the system in question. For example, neither PEO or sulphonated kraft lignin (SKL), binds to the surface of CaCO3 particles alone in any appreciable amount. Yet when PEO/SKL complexes are added to CaCO3 solutions, the CaCO3 readily accepts the PEO/SKL complexes.

Situations in which the findings can be useful: In wet end systems in which the main goal in using a retention aid system is retaining a specific component of the system, a PEO/CF retention aid system could be useful. Unfortunately, the information presented by the author suggests that one must be very specific in the use of the retention aid when choosing the cofactor most appropriate for the system. For example, the author states that the PEO/SKL combination works well to bind CaCO3 and fibers, but the same combination will only weakly and temporarily bind clay to fibers. Therefore an operation using CaCO3 to add brightness and smoothness to a sheet may benefit from PEO/SKL addition. But an operation which contains a large amount of clay particles, from coated broke or recycled coated grades, may not profit from PEO/SKL use.

The findings could be helpful in determining the addition rates and addition points to use in a system. The author found that when flocculating PCC with PEO/SKL a PEO concentration that covered approximately half the CaCO3 particles resulted in the fastest flocculation. This information would be useful if the correct addition rate was needed to retain the CaCO3 in the system.

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Name: Chang Woo Jeong

Date: September 4, 2003

Primary source: Wågberg, L., and Björklund, M., “On the mechanism behind wet strength development in papers containing wet strength resins,” Nordic Pulp Paper Res. J. 8 (1): 53 (1993).

Why this subject is important: Paper is a layered mat consisting of a network of cellulose fibers bonded together. Each of the fiber-to-fiber contacts is formed together by hydrogen bonds which are very sensitive to water. Thus, hydrogen bonds of paper which is destroyed by water do not sustain fiber-to-fiber bonds. Wet-strength resins play important role to improve paper strength in wet condition. We should understand the mechanism behind wet strength development in papers containing wet strength resins, because there has been no direct evidence about the mechanism between wet-strength resin and fiber.

Answer to the assigned question: The evidence of covalent bond formation is the existence of an ester linkage between carboxyl group on fiber and polyamideamine epichlorohydrine (PAE) observed by FTIR investigation. Other mechanisms are an increase of relatively bonded area (RBA) and adsorption capacity of wet strength resins by fiber swelling which is caused by carboxymethylation

Logical or theoretical support for answer: The weakly Nucleophilic carboxylate ion can attack the unstable bond between carbon and cationic nitrogen on PAE. Thus, anionic charged carboxymethyl cellulose can react with -CH2 on PAE resin to form ester bond. Azetidinium chloride on PAE continue to cross-link resin itself. PAE can increase wet-strength by ester bond between carboxyl group and PAE and by cross-linking between PAEs. It is reasonable that carboxyl content on fibers efficiently increase, because ester bonds cannot be formed without carboxyl group. Carboxymethylation on celluloses can also increase degree of substitution (D.S). This phenomenon causes fibers to swell, because the increase of D.S means the increase of hydroxyl groups that have been replaced by carboxymethyl group. Swelling of fibers increases RBA which can affect strength of sheet and the capacity of the fibers to absorb wet strength resins. By these mechanisms, carboxyl content of fibers can increase wet-strength efficiently.

Experimental support for answer: The main experimental evidence provided by Wågberg and Björklund to support the answer given consists of the following: (a) Sheets from the pulp D.S=0.069 with and without the addition of PAE were evaluated by FTIR. The form of different spectrum from the sheets with and without the wet strength resin represented a saturated ester. (b) To investigate the effect of carboxyl groups, untreated pulp and carboxymethylated pulp were used to prepare sheets, with and without the addition of PAE resin. The amelioration in dry strength upon addition of the PAE resin is much better in the case of the sheets including the higher concentration of carboxyl groups. This demonstrates that the carboxyl groups absolutely magnify the efficiency of the wet strength resin and these results also sustain that there is a chemical reaction between the carboxyl groups on the fibers and wet strength resin.

Situations in which the findings can be useful: The findings reported by Wågberg and Björklund can be useful when those who try to improve wet-strength property in paper, because the authors showed that carboxymethylated pulp increases the effect of wet-strength resin and analyzed factors which affect tensil properties of wet sheet. They can effectively produce optimized wet-strength papers such as hygiene papers, packaging paper and specialty papers through this research material.

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Name: Neeraj Sharma

Date: 09/04/2003

Topic: “Do you agree with the authors that unbeaten kraft fibers have a higher affinity for cationic starch than beaten fibers? What else could explain their results?”

Primary resource: Roberts, J. C., et al., “The effect of C14-labelled cationic and native starches on dry strength and formation,” TAPPI J. 69 (10): 88 (1986)

Why this subject is important: Starch is used as a dry strength additive in the production of paper. As the retention of cationic starch is significantly higher than native starch, it becomes more important to study the retention behavior of cationic starch in slurry during production of paper. Beating of fibers is done to create fibrils, which provide higher area for bonding to provide strength to final product. Here it becomes important to see if retention of cationic starch is affected by pulp beating.

Answer to the assigned question: I agree with the authors that unbeaten kraft fibers have a higher affinity for cationic starch than beaten fibers. Table 1 in the article supports this conclusion, which shows that for bleached softwood sulfate pulp, on a 24-mesh screen retention of cationic starch for unbeaten pulp was 71.3 % while that for beaten pulp was only 61.1 %.

Logical or theoretical support for answer: Lower retention of cationic starch on beaten kraft fibers may be because of more fine percentage in beaten pulp or it may be inherently lower affinity of cationic starch to beaten fibers.

There are more fines contained in the beaten pulp. As fines have much higher surface area per unit mass than fibers, higher part of cationic starch is attached to these fines. When this pulp goes through a screen, fines are filtered. These fines take starch attached to these out of the pulp.

Experimental support for answer: The explanation based on the fines content does not hold for poor retention of cationic starch on beaten fibers as the retention of cationic starch on fibers that had been fractionated showed little difference from unfractionated fibers. The other reason for not entirely accepting the role of fines is that after continuous recycling there was only a slight decrease in cationic starch retention after a number of passes. This suggests that fines content do not play an important role in retention of cationic starch. This result also negates the role of fines for poor retention of cationic starch. Both of these results suggest that cationic starch has inherently lower affinity for beaten fibers than for unbeaten fibers.

Situations in which the findings can be useful: The findings can be useful in optimizing the extent of beating of fibers followed by addition of cationic starch to produce a paper with desirable strength. As the higher degree of beating provides a paper with higher strength properties but if cationic starch is to be used to improve strength properties, it should be kept in mind that a higher degree of beating will result in less retention of cationic starch. If during the machine run there is lowering of strength properties in paper, the point to be checked is if there is poor retention of cationic starch. Reducing the degree of beating of fibers can increase the retention of cationic starch hence the strength properties of paper produced.

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Name: Jeff Wallace

Date: September 4, 2003

Topic: “Is it meaningful and fair to compare the “rate of reaction” and the “rate of cure” in the way that the authors do?”

Primary resource: Cooper, C., et al., “The role of polymers in AKD sizing,” Paper Technol. 36 (4): 30 (1995).

Why this subject is important: Internal sizing agents such as AKD are important wet-end additives that can resist wetting and penetrations of various liquids into paper. There are several hydrophobic sizing agents for wet-end use, but they all differ in the ranges of pH values where they achieve their best effects. In the case of alkyl-ketene dimer (AKD), the optimum range can be extended downward to somewhat lower pH values by use of strongly cationic polymer. The role of these polymers was studied by the papermakers in the article, “The role of polymers in AKD sizing,” and the major areas of interest that they had was the effect of cure promoters on cationic demand, the effect of polymer addition on AKD reaction rate, and the effect of polymer addition on cure. Cure promoters (polymers) are of much importance because of their ability to emulsify the slow reacting AKD. As a consequence of the low reactivity of AKD, it often does not complete its curing process until after the paper has been made. Curing is the gradual increase in sizing with time and usually it is possible to develop most of the AKD sizing response by the time the paper comes off of the machine at the reel. However, the degree of sizing usually continues to rise during storage of the hot rolls of paper. This is off-machine curing and a problem with this is that it makes it trickier to predict the quality of paper that is being received by the customers.

Answer to the assigned question: It was meaningful and fair for the authors to compare “rate of reaction” and the “rate of cure”. They concluded that the rate of reaction and rate of cure were probably independent of each other, even though they were both aided by the cationic polyelectrolytes. The two different polyelectrolytes (polymers) used in this experiment were polyamine polymers and polydadmac polymers. The authors pointed out that a major flaw in a previous study was that only the AKD retained was measured and that no difference was made between what was actually removed from the sheet and that which required a cellulose-AKD reaction. The authors of this study found that AKD retention may be more important than cellulose-AKD reaction. This is just one aspect that was looked into when comparing the rates of reaction with rates of cure. Another major factor was the threshold values required for both the polydadmac and polyamine before the product is efficient at cure promotion. With all of these factors taken into account, the authors were able to make a meaningful and fair comparison between rate of reaction and rate of cure.

Logical or theoretical support for answer: As mentioned earlier, AKD reacts slowly and only a fraction of the AKD is able to react covalently with the hydroxyl groups on the fiber surfaces or starch present on those surfaces. Paper that has been freshly produced with AKD often still contains a lot of unreacted AKD, which is hydrophobic enough to contribute to sizing. This increase in the amount of AKD contributes to a gradual increase in sizing with time, which is known as cure. The retention of AKD in the wet-end of the paper machine helps to increase the rate of cure. But, there is also a threshold level for AKD before the paper is efficient for cure promotion. This threshold level is found by increasing the rate of size addition, which in turn increases the rate of reaction, till the maximum amount of AKD is retained.

Experimental Support for answer: The main experimental evidence provided by the authors to support the answer given earlier consists of (a) the study of the dependency of the AKD reaction rate on polymer addition, and (b) the study on the effect of polymer addition on cure. The first study suggests that the greater the AKD retained the slower the reaction, but this is irrelevant to the reaction of the final percentage. The author also notes that the charge neutralization effect has no direct correlation with initial levels of reacted AKD, final levels of AKD, or total AKD. The second study shows that the oven dried Cobbs revealed both that the AKD had been retained and the likely target for natural cure. This study also points out that there is a threshold value of molecular weight for both polyadmac and polyamine before the product is efficient at cure promotion. They also suggest that if the high and medium molecular weight polydadmacs had been compared in isolation, then the correlation between reaction and cure would be very good. These experimental studies support my conclusion that many factors were looked into when the authors compared the different rates.

Situations in which the findings can be useful: The finding that the threshold retention of AKD is necessary for sizing to be achieved could be very useful to process engineers when they are trying to decide on the optimum addition rate for the AKD to retain and cure for their paper grades. The finding that both reaction and cure rates are aided by cationic polymers could also help paper mills by allowing them to achieve threshold AKD retention with increased curing rate. Also, the finding in which AKD retention was a greater factor in cure promotion than the reaction with the fibers could help engineers in helping them to understand the effects of AKD threshold levels and the different polymers that promote the curing process.

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Name: Zhoujian Hu

Date: September 3, 2003

Topic: Why and under what kind of conditions is it possible to obtain negatively charged aluminum-based colloids under weakly alkaline papermaking conditions, e.g. at PH values above 7 but below 8.5?

Primary resource: Ohman, L.-O. and Wagberg, L., “Freshly Formed Aluminum (III) Hydroxide Colloids- Influence of Aging, Surface Complexation and Silicate Substitution,” J. Pulp Paper Sci. 3 (10): J475 (1997).

Why this subject is important: Aluminum chemicals are very popular in acidic papermaking. But there is difficulty to use alum/rosin sizing under neutral or alkaline conditions. That is because the cationic aluminum-resinate complex in traditional soap sizing becomes anionic at pH values exceeding 6.5 [1]. Can we find more efficient and more reproducible ways of using aluminum salts in alkaline papermaking applications? Some people [2] proposed that it is possible for alkaline rosin sizing to add certain positive properties to the paper product. Then alkaline rosin sizing using the cationic starch aluminum hydroxide retention aid systems was developed. For aluminum hydroxide retention aid systems, the zeta potential and the size of aluminum particles are very important. It was observed that higher negative zeta potential and larger size of them can achieve good results as a retention aid system [4].

Answer to the assigned question: It is possible to obtain negatively charged aluminum-based colloids under weakly alkaline papermaking conditions under mixing AlCl3/Na2 tartrate solutions with different proportions of NaOH/Na2SiO3 solutions at 25? (tartrate: 2.5% of the aluminum concentration and 0.01 mol/l +NaOH, 0.01 mol/l Na2SiO3 in this article)

Logical or theoretical support for answer: According to the chemistry of aluminum in aqueous solution, the aluminum ion is one of the most typical examples of a hard Lewis acid. That is to say, water molecules form relatively strong bonds to the Al3+ ion to Al(H2O)63+. The Al (H2O)63+ ion acts as weak Bronsted acid. So, Al3+ in water can become several ions. The most important ions and compounds are listed [3]. The figure of Al species vs. pH shows that there are alum floc, Al(OH)3 and Al(SO4)OH at PH=7-8.5. Those compounds are difficult to set rosin size on fiber surface.

As reported by Violame and Huang’s research, the presence of small amounts of foreign anions can have a profound effect on the properties and aging of aluminum hydroxide. Those anions, such as tartrate ions and citrate ions, act as surface-active complexents on the cationic surfaces and thereby delay or even inhibit particle growth and/or particle “aging”.

The silicate anion can be used to determine the size and the zeta potential of the particles, probably by forming mixed aluminum-hydroxosilicate precipitates.The silicate ions lead to the formation of small particles over the entire pH range. The particles formed in the presence of silicate gradually turn increasingly anionic in character as the proportion of silicate; the particle size passes a maximum, which approximately coincides with the pH at which zero mobility is registered. In pH=7-8.5, the particles is anionic.

Experimental support for answer: The main experimental evidence provided by Ohman, L.-O. and Wagberg, L. to support the answer given earlier consists of (a) neutralization curve, number-average particle size and particle zeta-potential as influenced by the presence of various amounts of tartrate ions, and (b) neutralization curve, number-average particle size and particle zeta-potential as influenced by the presence of various amounts of silicate ions.

Situations in which the findings can be useful: The findings reported by Ohman, L.-O. and Wagberg, L. can be useful to find more efficient and more reproducible ways of using aluminum salts in alkaline papermaking applications. This results help papermaker use aluminum chloride, sodium silicate and cationic starch as microparticle retention aid system in alkaline rosin sizing.

References:
1. Hedborg, F., et al., “Alkaline rosin sizing using microparticulate aluminum-based retention aid systems in a fine paper stock containing CaCO3,” Nordic Pulp and Paper Research Journal 8 (3): __ (1993)
2. Lindstrom, T., Hedborg, F. and Hallgren, H., Nord. Pulp Paper Res. J. 4 (2): 99 (1989).
3. Wps527 course-pack Part4
4. Ohman, L.-O., et al., “Freshly Formed Aluminum (III) Hydroxide Colloids- Influence of Aging, Surface Complexation and Silicate Substitution,” J. Pulp Paper Sci. 3(10): J475 (1997).

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Name: Jeffrey S. McKee

Date: September 18th, 2003

Topic: Why do the amounts of adsorbed aluminum and “transferred” aluminum depend on the degree of neutralization of the aluminum cations and also on [SO4-2]?

Primary resource: ODBERG, L., BARLA, P. and GLAD-NORDMARK, G., Transfer of Adsorbed Alum from Cellulosic Fibres to Clay Particles. Journal of Pulp and Paper Science, Vol. 21 (7) J250-254 July 1995.

Why this subject is important: It is important for a paper-maker who uses alum to understand how pH and aluminum ion neutralization affects the “transfer” of aluminum ions from the fibers to particles within the system. In most all cases it is essential that a reasonable amount of aluminum remain on the fibers. Some issues can arise if too much of the aluminum is transferred from the fibers. These include issues associated with sizing, pitch out-breaks, retention, decrease in couch consistency, and slack draws.

This study also indirectly emphasizes the importance of good pH control in the wet-end. With an understanding about how aluminum ion neutralization affects the way that alum works in a system, the paper-maker will realize just how critical that proper pH control is to running a paper machine. Alum is a very cost effective and important process chemical to most all paper-makers. Paper-makers use alum in many ways, such as pH-control, sizing, charge neutralization, pitch control, and coagulation. Alum is a very popular pH-control chemical because it produces a highly buffered system that is resistant to pH upsets or stock variability.

Answer to the assigned question: When the aluminum ion neutralization increases (increase in pH), the following occurs (a) Al+3 ions that are in solution will be decreased (b) aluminum hydroxide flocs will begin to form and will increase as the aluminum ion neutralization increases (c) the aluminum hydroxide flocs can be adsorbed onto the fibers and then be redistributed to the clay particles. Sulphate groups also affect the transfer of aluminum ions because they shield the cationic charges associated with the aluminum flocs. The transfer of aluminum ions from fibers to clay particles will decrease as the electrolyte concentration (SO4) increases.

Logical or theoretical support for answer: Aluminum is present in the form as Al+3 ions at 3.9 pH, and there are very few Aluminum flocs at this pH. A small amount of the Al+3 ions are attached to the fiber. This leaves a large amount of Al+3 ions in solution, which are available to adsorb onto clay particles. When the pH increases to 4.5, aluminum flocs start to form, and the amount of aluminum ions (Al+3) in solution decreases. As a result the aluminum flocs can adsorb onto the fibers, resulting in fewer available aluminum ions “free aluminum” to adsorb onto clay particles. The aluminum flocs that are adsorbed onto fibers are then able to redistribute and “transfer” aluminum ions to clay particles.

Experimental support for answer: Published graphs provided by Odberg and Nordmark. These graphs included the following:

The presence and absence of filler clay as a function of aluminum ion neutralization (OH/Al ratio).
The transfer of aluminum ions from fibers to clay particles as a function of aluminum ion neutralization.
Mass balances showing that the aluminum ions not found on the fibers were found in the drainage water.
The aluminum ions found on fibers in the presence and absence of clay as a function of stirring time, pre-absorption time, and electrolyte concentration.
Aluminum ions transferred from fibers to clay particles at different stirring rates as a function of aluminum ion neutralization.

Stirring time, pre-adsorption time, stirring rate, and electrolyte concentration were possible variables that could have had some influence on this experiment. Each of these was investigated under set conditions. Findings were as follows:

Stirring time showed some influence that could be possibly due to a breakdown of Aluminum flocs, but the standard deviation was within experimental error.
Pre-adsorption time showed to have almost no influence on the amount of aluminum ions transferred.
Stirring rate did have a slight affect on the transfer of aluminum ions. It appeared to affect the Aluminum floc formation, which had some impact on the adsorption onto the fibers.
Electrolyte concentration had the most affect on the experiment. The aluminum ion adsorption decreased when the electrolyte concentration was increased. The reason for this appears to be due to the fact that the sulphate groups shield the positive charges of the aluminum flocs.

Situations in which the findings can be useful: Paper-makers should always try to understand what is happening between the furnish components. A better understanding of this subject will provide a paper-maker the ability to choose the most advantageous injection point when adding process and functional chemicals. In this specific experiment, one would be able to use these findings to possibly enhance the performance of their alum chemistry, sizing, pitch control, and possibly first pass retention.

Name: Yong Sik Kim

Date: Sep. 03.2002

Topic: “Why did colloidal lignin tend to affect the strength of paper differently from hemicellulose or addition of salt?”

Primary resource: Tom Lindström, Christer Söremark and Lennart Westman, “The influence on paper strength of dissolved and colloidal substances in the white water,” Svensk Paperstidn. 80(11): 341(1977).

Why this subject is important: The closure of white water systems in paper mills results in higher concentrations of dissolved and colloidal materials in the white water. The material in the white water can be roughly divided into fibers, fines, ash, hemicellulose, lignin and rosin. The paper strength can be influenced by these substances because they might somewhat adsorb onto the fiber surfaces or act as fillers and as non-bonding spacers in fiber crossings. The swelling of the fiber material is important for the development of the strength during the consolidation process. In other words, if there are some substances that can decrease in swelling of the fiber materials, the paper strength may be somewhat decreased. Also if there are substances that can increase in swelling or can be adsorbed by the fibers to increase the number of hydrogen bonds, its strength may be increased in general. Thus, dissolved and colloidal substances in the white water tend to affect the paper strength.

Answer to the assigned question: Colloidal lignin tends to affect the strength of the paper differently from hemicellulose or addition of salt because phenolic hydroxyl groups of lignin will not be dissociated at pH 5~6.5. In general, they don’t begin to dissociate appreciably until the pH reaches about 9, which is higher than most wet-end system, assuming the phenolic hydroxyl groups of the dominant type of acidic groups present after kraft pulping.

Logical or theoretical support for answer: Two mechanisms that can account for the paper strength effects of different dissolved and colloidal material in the white water are theories of polyelectrolytic gels and surface charge properties of fibers and most other solids in water solution. The main idea behind the theories of polyelectrolytic gels is that the cellulosic fiber contains ionic groups having a pka-value sufficiently low to be at least partly ionized at neutral pH. These charged groups add swelling power to the fiber wall due to an increase in electrostatic free energy. When a salt is added this energy will be lowered since the charges are shielded. Increasing salt concentration is expected to lower the paper strength by diminishing the swelling of the fiber material.
The other mechanism is that surface charge properties of fibers and other solids in water solution are highly pH-dependent. Hemicellulose contains a lot of carboxylic acid, whereas kraft lignin contains a lot of phenolic hydroxyl groups. Dissolved hemicelluloses can thus contribute a strong negative colloidal charge to wet-end system because the pKa-value of carboxylic acid is about 4.5. However, the pKa-value of the phenolic hydroxyl groups of lignin is about 9. Therefore, the phenolic groups in the lignin particles do not contribute to colloidal charge to wet-end system.

Experimental support for answer: The main experimental evidence provided by Lindström, Söremark and Westman to support answer given consists of (a) the relative change in strength properties (tensile rupture stress, modulus of elasticity and Z-strength) at different levels of addition of salt concentration, hemicellulose and lignin, (b) relative change in strength properties at different levels of in-situ precipitated kraft-lignin retained by sheets and (c) WRV at different salt concentration as well as hemicellulose addition. The strength decreases in general for an increase both salt concentration and added amount of lignin (%). However, the hemicelluloses leads to an increase in tensile and Z-strength, whereas the modulus of elasticity remains more or less unchanged. No such relationship was observed in case of the 55% pulp when both salt and lignin added to the stock.

Situations in which the findings can be useful: The findings reported by Lindström, Söremark and Westman can be useful to explain some of the properties of sorption pulps and give information as to what will happen if lignin from black liquor is added to the stock in order to increase the yield. In particular, Lindström and co-workers showed that one has to be careful when drawing conclusions about the influence on paper strength of dissolved and colloidal substances in the stock. If some substances affect a strong negative colloidal charge of wet-end system, then there is a good chance that the paper strength increases in general.

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Name: Qirong Fu

Date: Sept. 2, 2002

Topic: “What factors and procedures are most important to the optimization of micropolymers that are added to enhance water removal during formation of paper?”

Primary resource: Honig D.S., et al., “Formation improvements with water soluble micropolymer systems.” Tappi J, 76(9): 135(1993)

The retention and drainage characteristics of furnish are closely related to sheet formation. The purpose of adding retention aids into furnishes is to improve fines and fillers retention. Three kinds of materials that are used in retention aid systems include inorganic retention aids, natural organic polymers and synthetic organic polymers. Microparticle systems are widely used in recent years. In these microparticle systems, cationic polymer (e.g. cationic polyacrylamide or cationic starch) is first added into the furnish, and then inorganic particles (e.g. colloidal silica, bentonites, or related materials) that have large specific surface area and high negative charge are also added. The microparticle systems can provide good flocculation effect that contributes to retention. In the article, the authors introduced a new water-soluble micropolymer system to play the role of microparticle and improve retention and drainage during formation of paper.

Answer to the assigned question: In the chemical system described by the authors the structure and charge density of the water-soluble micropolymer play an important role in formation improvement. The water-soluble micropolymers have a submicron, three-dimensional structure with flexible polymer strands, chains, tails, and loops of controlled ionic charge. These features combine to give superior performance, relative to that provided by inorganic microparticles, polymeric flocculants and coagulants. Moreover, the micropolymers contain a high charge, which is a secondary factor for this performance. Addition points of micropolymer in this system are different from other retention systems. In the micropolymer system, micropolymer is usually added after the screen. In systems that use a cationic polyacrylamide, the cationic polyacrylamide addition precedes the micropolymer and is usually before the fan pump.

Logical or theoretical support for answer: The micropolymers possessing the three-dimensional solid structure as inorganic microparticles show effective performance in flocculation under high shear conditions. The microparticles in the retention systems do two things. First, they are able to form reversible bridges between the loops and tails of cationic polymers that remain attached to the fiber surfaces. Second, they get inside the coils of these polymers. The cationic polymer coils wrap tightly around the little anionic particles. That makes the coils contract. The fact the polymer coils become less swollen with water helps the paper drain faster during the forming process (see WPS 322 course-pack).

The micropolymers contain a high charge, which means that micropolymers have many opportunities to approach and attract particles. Moreover, the higher charge density of micropolymers, the greater is the electrostatic repulsion between charged particles on the molecular chain. It would make polymers more flexible to expand and contract.

The cationic polyacrylamide is usually added before the fan pump or before a pressure screen. The cationic polyacrylamide makes fibers stick to each other in aqueous solution by a bridging mechanism. After the fan pump or screen, flocs are broken by high shear force and then disperse into small flocs. At that time, micropolymers are added to make these small flocs combine into smaller, denser, more uniform micronetworks, compared to the single cationic polymer system. In this way, the micropolymer system can increase fines and fillers retention and also improve drainage.

Experimental support for answer: The main experimental data given by Honig et al. consist of (a) figures about drainage and formation comparison when using micropolymers and inorganic microparticles retention aid system, and (b) drainage performance at high sheet filler content. The submicron micropolymers at low dosage levels can achieve superior drainage compared to inorganic microparticles systems. Especially when sheet filler levels increase above the 20% level, the micropolymer system shows significant drainage advantages. Figure 2 of the cited article shows that with the increase of microsphere particle dose and surface charge densities, the drainage rate drastically increases. The paper samples show that the sheets have good formation when using the micropolymer system.

Situations in which the findings can be useful: The findings reported by the authors can be useful when one considers using the micropolymer retention system in a paper machine. In particular the micropolymer systems show better drainage and retention when sheet filler content is beyond 20%. Moreover, the micropolymer having a submicron, three-dimensional structure with flexible polymer strands, chains, tails, and loops of controlled ionic charge can perform very well at low dose levels. However, charge conditions of the system show great effect on microflocculation. It is proposed that the authors should discuss the charge change in this micropolymer system and how different surface charge distributions affect the addition of micropolymer.

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Name: Sa Yong Lee

Date: Sept 3, 2002

Topic: “What are ‘promoters’ in the context of this article, and why are they important? How and why do they affect AKD sizing and the effects of time on the degree of sizing?”

Primary resource: Colasurdo, A.R. and Thorn, I., “The Interactions of Alkyl Ketene Dimer with Other Wet-End Additives,” Tappi Journal 75(9): 143-149 (1992).

Why this subject is important: Fugitivity (or sizing loss) refers to a condition in which paper is in-spec at the reel and, after the passage of time, some or all of the sizing is lost. As the quantity of alkyl ketene dimer (AKD) sized alkaline paper has grown, fugitivity has been a problem in North America, where cationic starch, precipitated calcium carbonate (PCC), a retention system, etc. are used for the wet-end additives. In AKD-sized paper fugitivity is believed by the authors of this article to be a result of the AKD hydrolysis reaction. In order to ensure that end-users get the expected sizing effect, we should understand the impact of other additives on AKD sizing and ways to avoid the AKD hydrolysis reaction should be investigated.

Answer to the assigned question: The promoters of the competing hydrolysis reaction reported by Colasurdo & Thorn, are the presence of PCC alkalinity, overuse of polyamine, and promoted AKD. What make these factors important is that, although each of them has an inherent function why it is added into wet-end system, it also has a negative effect causing the AKD hydrolysis reaction or preventing the formation of ß-ketoester bonds. The polyamine added for retention not only increases the retention of fines & filler but also promotes the hydrolysis reactivity of AKD. AKD dispersions supplied in North America have been polymer-stabilized, starch-based dispersions and promoted dispersion of both types. A promoted dispersion of AKD, i.e. one that containly a highly cationic polymer to promote its reactivity, has a higher rate of hydrolysis, compared to a standard AKD dispersion in the presence of PCC. PCC alkalinity becomes higher with the passage of time and the resulting alkalinity increases the hydrolysis reaction. PCC also attracts AKD due to surface charge, morphology, or some other characteristics of PCC rather than because of PCC’s surface area. These effects indicate that PCC either prevents the formation of ß-ketoester bonds or causes the hydrolysis of unbound AKD which otherwise could have contributed to sizing.

Logical or theoretical support for answer: According to the fugitivity model proposed by Colasurdo & Thorn, in order to get optimum sizing, it is necessary to optimize the reactivity level, or to improve the organic chemistry reactivity in wet-end system. The conditions, such as low moisture, high temperature, proper pH, AKD’s concentration on fiber, a catalyst to help the kinetics of the reaction, etc. are also needed in the dryer section. Optimum sizing requires a minimum level of bound AKD on fiber and proper portion of unbound AKD which is not associated with fines and filler. Alkalinity is a major factor to contribute to the effective reaction between AKD and cellulose. The optimum pH range for the reaction of AKD with fiber surfaces is 6 to 9. But, in case of using PCC, as time goes on, the extract pH of paper rises to 9.5~10.0. PCC attracts AKD and has high surface area. This fact means that the PCC increases the proportion of AKD that is not bound to cellulose. Consequently, the unbounded AKD has the possibility to undergo a hydrolysis reaction with H2O, especially under conditions of excessive alkalinity. Once hydrolyzed the AKD byproduct is no longer capable of the formation of ß-ketoester bonds with cellulose. In this case, it is apparent that sizing loss (fugitivity) takes place.

Experimental support for answer: The experimental evidence provided by Colasurdo & Thorn to support the answer given earlier consists of the following: (a) The impact of PCC on AKD modified fiber using AKD hydrophobized pulp prepared according to Gupta and adding the substances of interest one by one; and (b) AKD hydrolysis depended on the different sets of AKD formulation and additives. Comparing the cases with PCC and without PCC suggested that PCC attracts AKD and prevents the formation of ß-ketoester bonds and causes the hydrolysis of unbound AKD. Promoted AKD shows increasing rates of hydrolysis with PCC versus with chalk. Adding polyamine into promoted AKD with PCC shows higher hydrolysis rate than the other formulation without polyamine.

Situation in which the findings can be useful: The findings reported by Colasurdo & Thorn can be useful when one intends to avoid fugitivity. The authors showed that promoted AKD, polyamine over-usage and the association of AKD with fines and PCC in fugitive paper, all appear to work by increasing the hydrolysis reaction of AKD. If one want to avoid sizing loss, he or she needs to understand the roles of AKD, polyamine, and PCC and should choose the proper sets and application points to encourage the interaction of AKD with the long fiber

References
Scott, W.E., Principles of Wet-End Chemistry, TAPPI Press, 1996
Roberts, J.C., Paper Chemistry, 2nd Ed., Blackie, London, 1996
Reynolds, W.F. The Sizing of Paper, 2nd Ed., TAPPI Press, 1996

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Name: Troy Watkins

Date: 15 September 2002

Topic: “How and why does the level of salt affect the ability of cationic starch to cause precipitation of colloidal materials from mechanical pulp (with focus on Fig. 2 of the article)?”

Primary source: Bobacka, V., et al., “Interactions between cationic starch and anionic trash of a peroxide-bleached TMP at different salt concentrations,” J. Pulp Paper Sci. 24 (3): 78 (1998).

Why this subject is important: The increasing importance of producing environmentally friendly products has resulted in pulp and paper mills reducing the levels of both fresh water usage and effluent discharge. Naturally, this reduction in fresh water usage has meant an increase in the number of times water needs to be recycled within the pulp and paper making processes. This recycling of water has increased the potential build-up of detrimental substances, in particular anionic trash.

During the production of mechanical pulps, colloidal and dissolved substances are released. These detrimental substances, which are primarily released from the refining and bleaching processes, can significantly reduce the efficiency of pulp and paper making systems if not dealt with effectively.

Answer to the assigned question: An increase in the concentration of salt compressed the electric double layer of the colloidal material. This reduced the quantity of cationic starch required to destabilise, or coagulate, the colloidal material.

Logical or theoretical support for the answer: The main mechanisms involved in the rate of agglomeration due to a change in the concentration of ions in solution are: a) The compression of the ionic double layers, and b) adsorption of ions on to the surface. (See WPS 527 course pack, Chapter 5)

An increase in the concentration of a salt in solution increases the concentration of ions with an opposite net charge in the diffuse layer around a colloidal particle. This causes a compression of the particles ionic double layer, reducing the systems zeta potential. An absolute zeta potential close to the value of zero means that the repulsion force of the colloidal material is reduced closer to the dispersion attraction force, and the overall net potential energy approaches zero.

As shown by the following diagram, once the surfaces of two solid objects in a suspension get very close together, they get into a primary minimum of potential energy of interaction. This means that they remain in a coaguated state. However, to reach that state, the two objects need to overcome a potential energy barrier. Multiple valency ions increase the ionic strength of a solution more than single valency ions. Accordingly this reduces the particles ionic double layer to a greater extent. This has the effect of decreasing the potential energy barrier.

The adsorption of ions of opposite charge onto the surface of a particle reduces the net charge on the particle surface. This increases the probability of coagulation due to a reduction in the zeta potential of the particle surface. Like with the compression of the ionic double layers, adsorption of multiple valency ions is more effective at reducing the system zeta potential than single valency ions.

Experimental support for the answer: The experimental evidence that Bobacka, V., et al. used to support the theoretical answer was the measurement of residual turbidity after the addition of a salt and cationic starch. Also, the consumption of starch was detected by a radioactivity method. The salts used in the experiment were sodium and calcium chloride.

An increase in the concentration of sodium ions reduced the concentration of cationic starch required to destabilise the colloidal particles. This destabilisation of the colloidal particles, or flocculation, was measured by a reduction in residual turbidity.

At the lowest concentrations of calcium ions, the cationic starch was able to completely destabilise the colloidal particles. The sample with the lowest calcium ion concentration required the most starch. At the highest concentrations, the colloidal material was completely destabilised before the addition of the cationic starch.

Less starch was required to destabilise the colloidal particles when the calcium salt was added compared to the sodium salt.

Situations in which the findings can be useful: The type and concentration of ions in the pulp and white water systems can influence the choice of polyelectrolyte required to destabilise the colloidal particles. These factors will also influence the location in which a polyelectrolyte can be added to a system. It could be important to use a chelating agent to bind multiple valency ions so they do not increase to a concentration that allows the coagulation of colloidal particles or interferes with the efficiency of other additives.

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Name: Chris Dozier

Date: August 26, 2002

Topic: “Based on this article, how can you explain the hydrophobicity of paper treated with AKD and then extensively extracted?”

Primary Resource: Bottorf, K.J., “AKD sizing mechanism: a more definitive description,” Tappi J. 77 (4): 105 (1994).

Why this subject is important: Sizing agents are used in the paper industry for prevention of liquids from penetrating into the paper. Over the past few years, paper made under alkaline conditions has been increasing as opposed to acid conditions. This trend has led to an increase in the usage of so-called alkaline sizing agents such as AKD. Understanding the chemistry of AKD can provide the possibility for its effective use in sizing applications.

Answer to the assigned question: AKD (alkyl-ketene dimer) is a sizing agent suitable for neutral to weakly alkaline wet-end conditions that forms a beta-keto ester linkage with the hydroxyl groups of cellulose to produce a fiber surface that resists wetting. The AKD bonds with the cellulose in such an arrangement that there are hydrophobic groups on the surface of the fiber resulting in a high resistance to water. In many cases, unreacted AKD can also have an important role to the total amount of sizing obtained. On the other hand, AKD can be extensively extracted from paper by using a solvent containing a 50% dioxane-water mixture. This mixture hydrolyzes the covalently bound AKD from the cellulose. Any AKD that is unreacted or unbound to the cellulose can be extracted by various other organic solvents without hydrolyzing any bonds.

Logical or theoretical support for answer: There are several reactions that AKD can form when added to alkaline paper. AKD may react with cellulose to form beta-keto ester, with water to form beta-keto acid, with a base to form beta-keto salts, or with a base and more AKD to form oligomer. The acid and salt only provide low levels of AKD sizing. Oligomer provides AKD sizing at moderate levels. AKD size can also be affected by curing intervals. When a sheet is air-dried, most of the AKD remains unreacted. This unreacted AKD can contribute significantly to the overall sizing of the sheet. When paper is drum-dried, the AKD is in the more reacted form with cellulose. AKD can be extracted more easily in the unreacted form rather than in the reacted form. Solvent can be used to extract unreacted AKD, but for reacted AKD, more severe and extensive procedures need to be performed to break the covalent bond the AKD forms with the cellulose compound.

Experimental support for answer: The main experimental support given by Bottorff to the answer above is by the use of solid-state 13C NMR. He had several spectra graphs showing whether AKD was present within the different test specimens. Samples were treated with different percentages of AKD, as well as different curing methods and solvent extracted sheets. The unreacted AKD tended to disappear through extraction with tetrahydrofuran and extended drying. The remaining covalently bound AKD was completely extracted with a 50% dioxane-water mixture for 8 hours at 80oC. The experiment also showed that AKD mixed with calcium carbonate filler would transform over time into palmitone, which does not contribute to the overall size. In unfilled paper, the AKD transforms to palmitone and bound AKD, which is a very effective size. This transformation is a result of increased surface area with the filler and elevated levels of calcium hydroxide present in the paper.

Situations in which the findings can be useful: The findings reported by Bottorff can be useful when the papermaker wants to make a sheet that is more resistant to water. It can be most useful when adding size to filled or unfilled alkaline-based paper. As pointed out by Bottorff, when adding AKD to filled paper, it is important to notice that the AKD will gradually transform to palmitone and unless there is bound AKD left, the paper will show less than average water repelling abilities. As with adding any other wet-end chemicals, it takes the right ratio to get the optimum performance from the additives.

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Name: Kevin L. Copeland

Date: September 20, 2002

Topic: “What evidence does the article provide that the observed benefits were due to the neutralization of zeta potential?”

Primary resource: Miyanishi, T., “Wet end optimization for a neutral PCC filled newsprint machine,” TAPPI J. 82 (1): 220 (1999)

Why this subject is important: The use of fillers such as precipitated calcium carbonate (PCC) can effectively reduce raw material costs in a paper mill. The use of PCC in neutral papermaking has become well established, but some questions remain in the minds of papermakers regarding its benefits in the case of mechanical pulp furnishes. In the papermachine trials reported by Miyanishi, the physical properties of the paper made with PCC under alkaline conditions remained constant with those of acidic paper. It is reported in this article that acidic papermaking is the norm for newsprint in this industry, as well as the optical and printing properties. The only drawback noticed in the change from acidic to neutral was the problem of linting. Linting is the process of leaving residual product on the rolls and felts of a paper machine. This being the only problem associated with the change, the papermakers in this article were excited about the chance to run real mill trials, using retention aids to improve the paper, as well as fight the problem of linting. Also, three areas of interest to be looked at were paper machine runnability, paper sheet structure, and optical properties.

Answer to the assigned question: The article does not show a clear relationship between the neutralization of zeta potential versus, the potential advantages to neutral papermaking as opposed to acidic papermaking. The article provides some data for the benefits of what neutralizing the zeta potential can help, but this measurement alone does not support the entire structure of the argument. If it were that simple then the measurement of zeta potential would be more widely used to distinguish what a system would need. It is known however, that it is not that simple and that most systems react differently to changes than others do and that the measurement of zeta potential would possibly be independent of process being analyzed and not a standard for all processes.

Logical or theoretical support for answer: It is not logical to believe that the change in one variable in this process will successfully give the papermaker all he desires from his operation. In an industry with so many variables and less constants it is known that with the addition of a new species into a system, in this case PCC, many other factors must also change to absorb the shock this addition may have on the system. The papermaking process can easily change with the addition or subtraction of a known variable and it a long shot to believe that the neutralization of the zeta potential with the addition of PCC is any different. Chemical additives such as alum, starches, and retention aid must support the change in the system. This argument is can be supported both logically from a papermakers standpoint, and experimentally from a researchers point of view.

Experimental support for answer: During this trial the zeta potential went from -2 mV to -7 mV during increases in the amount PCC. This change in zeta potential was undesirable, according to the investigators, and needed to be changed. The dissociation of carboxyl groups and decrease of alum addition added to the zeta potential increase. As stated earlier the paper properties stayed much the same through the first part of these experiments. The addition of alum and retention aid brought the zeta potential to its desired level. Once the amount of PCC needed was stabilized and the chemical furnish was increased the zeta potential moved from -10 mV to its isoeletric point. The efficiency of the paper was best and the paper breaks on the machine decreased. The paper properties such as brightness and tear strength decreased slightly with the move from pH 4 to 8. Tensile strength and stiffness increased with the change in pH and the print image was good. The only problem being seen was linting. The use of retention aid was not only as a control device for the zeta potential but the introduction of the aid cut the linting problems by half. The fiber fines and fillers effectively attached to the fibers by colloidal forces. The only increased problem with the use of retention aid was ash content. A decrease in ash content was seen in the PCC paper when no retention aid was used but the introduction of the aid saw a three times higher amount of ash. As stated earlier the formation and two-sidedness became better with the use of a retention aid. The problems with retention aid are minimal considering the overall improvement on the system with the addition of the single polymer retention aid. With all this data being presented it is not clearly shown whether that the neutralization of the zeta potential was the single cause of the benefits associated with neutral papermaking. A wide range of other variables must be in place in order to successfully accomplish this goal.

Situations in which the findings can be useful: The research shown could be used in a mill looking for a more recyclable sheet or less raw material cost. With the economy being the way it is, a useful application of this research could save a company a large amount of raw material cost. Also, for an area like newsprint, that has a single time usage, this research could be great to lessen the raw material investment in this paper grade and the fiber could be used for higher quality printing grades.

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Name: Jung Myoung Lee

Date: September 3, 2002

Topic: “Why did the authors choose to use surface tension, contact angle, and streaming potential tests to explain the results of peel type detackification test?”

Primary resource: Nguyen, D.T., and Dreisbach, D.D., “Prevention of pitch and stickies deposition on paper forming wires via adsorption of cationic polymer associated with anionic species”, TAPPI 1996 Papermakers Conference: 511-519

Why the subject is important: As paper mills have increased the usage of wastepaper, the occurrences of pitch and stickies deposits and quality problems caused by sticky contaminants have increased. Wastepaper contains non-fibrous materials which can be present in many forms and the presence of all of these has a detrimental effect on sheet properties. These contraries entering the papermaking cycle during conversion are the most difficult to remove and create major problems during the recycling of paper and board products. By far the greatest problem is caused by the contaminants termed “stickies”. Stickies are complex chemicals which have their origin in adhesives applied during paper conversion and use. The common sources of stickies are labels and boxes to which hot melt adhesives have been applied. These sticky contaminants can be found as spots on forming fabrics, press felts and dryer fabrics. It causes sheet picking, wet web breaks, and dirt specks and holes in the finished product. It is necessary to control sticky contaminants to reduce the troubles in mills and further to meet customer needs. To facilitate the use of secondary fibers, sticky contaminants must be controlled.

Answer to the assigned questions: The surface characteristics of furnish are one of the important factors in terms of the properties of the final sheet of paper and runnability of papermaking processes. As mentioned previously, the depositions of sticky contaminants such as pitch and stickies on paper machine, especially forming wires, will cause many trouble in paper mills. In this paper, the authors are trying to control the trouble by the “wire passivation” using cationic polyelectrolytes applied via spray systems to forming fabrics to reduce deposition problems. The mechanism preventing deposition appears to be the retention of the added chemical on the surface of the forming fabric, thus creating a hydrophilic barrier between stickies and the surface of fabrics. To verify the mechanism of how the cationic surfactant interact the stickies and the surface of wire and the degree of detackification, the authors have chosen the surface tension, contact angle and streaming potential test.

Logical or theoretical support for answer: The surface energy (surface tension) of a material gives very important information about its surface characteristics which is determined by the interfacial contact angle against water and some organic liquids. Also, surface energy is related to the hydrophility and hydrophobicity of the surface. The contact angle between the liquid and solid surface tell us the wettability of its surface. At contact angle below 90 degree, the surface is wetted by water, which means the surface has hydrophilic features. The streaming potential can be able to measure the zeta-potential showing the state of surface charges. The surface charge has an important influence on interaction with chemicals.

Experimental support for answer: The authors were trying to explain why the cationic polymer is effective to alleviate the hydrophobic-hydrophobic interaction between sticky contaminants including pitch and stickies and the forming wire. They were used to surface tension measurement to verify the formation of complexes between the cationic polymer and water soluble anionic species such as lignin and/or fatty acids (hydrophobic) which has potential possibility of becoming to be deposit. In fig.7 and 8, the data show the effect of cationic and nonionic polymer. As the dosage of cationic polymer used increases, the surface tension is much more decreased compared to that of nonionic polymer. In addition, they measured the value of streaming potentials with/without the addition of cationic polymer. Without the polymer, the synthetic white water is highly negative. However, with polymer the value of streaming potential changes positive to negative as the concentration of the anionic surfactant is increased. This results show the cationic polymer can be formed the complexes with anionic trashes and more solids will be retained. Also, they also measured the contact angle indicating the wettability of a material. In fig. 12, the cationic polymer much more decreased the contact angle compared to nonionic polymer. Therefore, this result shows the surface of the forming fabric is more hydrophilic when treated with cationic polymer than nonionic polymer.

Situations in which the findings can be useful: As mentioned earlier, their findings are very effective in removing the sticky contaminants. Furthermore, the paper mills are going to close their water due to the environmental problems and running costs. Thereby, there are many potential chances to occur “sticky contaminants-like troubles”. They already showed that where their findings are suitable in this paper. They showed three kinds of case study to evaluate their finding into “real paper mills”, especially in the focus on the recycling.

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Name: Steven A. Fisher

Date: September 27, 2002.

Topic: “Why and how was the cationic character of colloidal byproducts of aluminum sulfate increased in the presence of calcium ions?”

Primary Resource: Farley, C. E., “Influence of dissolved ions on alum cationicity under alkaline papermaking conditions,” Tappi J. 75 (11): 193 (1992).

Why this subject is important: Alum is a favored additive to papermaking systems, and is sometimes called the “papermaker’s friend”. Its many benefits can be partially attributed to its cationic behavior in a colloidal system. It is used to reduce the cationic demand of the wet end, and to improve the performance of rosin sizing. Traditionally, the cationic behavior of alum was believed to be limited to acidic realm, more specifically in the pH range of 4 to 6. With the increase of alkaline papermaking, there is a need to define the cationic behavior of alum (if any) in the alkaline range of 7 to 9 pH.

Answer to the assigned question: First to state the observation that leads to the assigned question: The isoelectric point (where Zeta Potential = 0) of alum preparations shifts from a pH of about 7.5 to a pH of 9 or higher when calcium chloride (CaCl2) is added to the solution. The effect is significant at CaCl2 concentrations as low as 25 ppm. The first clue to answer the question is the fact that colloidal by-products exist at all from a reportedly soluble (ionizable) metal salt. There must be something special about this salt that causes it to form colloidal by-products. The consensus is that the trivalent character of the aluminum ion is responsible for this behavior. By definition the mixture at lower pH will exhibit more cationicity by virtue of the higher proportion of H+ ions in solution. Conversely it is expected that lower acidity (higher pH) will exhibit lower cationicity. In other words, hydrogen ions are relatively more concentrated at lower pH, therefore “cationicity” is more likely in the system. Calcium (Ca2+) is a divalent ion, therefore it contributes a potent positive charge relative to the space it occupies when added to the mixture. Calcium therefore allows the preparation to exhibit more cationicity at lower proportions of H+ ion (higher pH). The monovalent Na+ ion is not able to do this, because it has a relatively low positive charge relative to its size.

Logical or theoretical support for answer: The following table gives the atomic radius and ionic charge for the elements mentioned from the Periodic Table. Notice the large size of monovalent atoms Na and K compared to H.

Element	Atomic Mass	Radius (angstroms)	Ion Charge	Ion Charge / Atomic Radius
H	1	0.79	1	1.27
Na	23	2.23	1	0.45
Mg	24.3	1.72	2	1.16
K	39	2.77	1	0.36
Ca	40.1	2.23	2	0.90

Also, the divalent and trivalent atoms are quite small. The concentrated charge on the divalent ions relative to their size has a powerful effect on the isoelectric point observed in a colloidal system such as the one observed.

Experimental support for answer: Figure 3 of the article shows that addition of monovalent salts (NaCl, Na2SO4) have little or no affect on the pH at which the isoelectic point occurs. In contrast, the figure also shows that the addition of the divalent salts (MgCl2 and CaCl2) seem to cause a shift in the isoelectic point, causing it to occur at a higher pH. Addition of excess SO42- caused a partial reversal of the effect (Figure 8). The titratable cationicity of the mixture was increased across a wide pH range by the addition of CaCl2 (Figures 9 and 10). The mixture was better able to reduce the cationic demand of a bleached kraft furnish when CaCl2 was present (Figure 12). Figure 12 also shows the CaCl2 has an effect by itself, but the synergistic effect with alum is most pronounced at pH’s of 8-9. To extend these findings, based on Figure 4, it is still unclear whether Ca2+ was enhancing Al3+ mobility or if Al3+ was enhancing the mobility of Ca2+. Both ions have beneficial isoelectric influence in their own.

Situations in which the findings can be useful: Wherever alum is used in the papermaking process or other colloidal system where it is beneficial for the alum to a impart cationicity, this cationic effect may be enhanced and its pH range extended into the alkaline region by the addition of ionized calcium (as CaCl2 for example). Specifically, this enhancement of alum performance can apply to alkaline papermaking processes to reduce the cationic demand of fibers, or improve the pH range and alum dosage at which sizing agents have maximum performance.

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Name: Daniel Duarte

Date: September 27, 2002

Topic: “Why does there tend to be a poor correlation between apparent charge density and mean zeta potential when testing diverse samples of white water from paper mills?”

Primary resource: Sanders, N. D., and Schaefer, J. H., “Comparison of Electrophoretic Mobility Distributions in Synthetic Papermaking Furnishes with Streaming Potential and Polyelectrolyte Titration Data,” Proc. TAPPI 1994 Papermakers Conf., 629.

Why this subject is important: With the advent of system closure, neutral/alkaline papermaking conditions, and the increased usage of recycled paper; it is important that chemical additive programs are optimized. To maximize efficiency, appropriate charge measurement application strategies must be adopted. Several technologies/procedures are available to characterize charge. Two examples are (1) automated electrophoresis (DELS technique) which provides particle zeta potential, and (2) colloidal titration (CT) from which apparent charge densities (CD) and cationic or anionic demand can be derived. Before adopting a testing regimen, an understanding off the various charge measurement techniques is required. Mill personnel and/or researchers should be aware of the limitations, sensitivities, and interferences of the various available techniques to furnish variables.

Answer to assigned question: There are important distinctions to be made between the DELS and CT techniques; and these distinctions explain why there tends to be poor correlation between apparent charge density and mean zeta potential when white water samples are analyzed. Firstly, the two techniques measure different properties. Second, the techniques have sensitivities to different components/variables of a sample.

Logical or theoretical support for answer: Sanders and Schaefer have established that charge measurement techniques have sensitivities to different variables. For example, the DELS technique (which measures particle zeta potential) is more sensitive to fines/filler particles and Ca++ concentration, and the effect of alum and cationic starches; whereas CT (which measures the charge of a suspension of solubles and fine particles) is more sensitive to anionic “trash” and cationic promoters.

Since white water contains un-retained fines, filler, additive, etc., and has a very low consistency, a poor correlation between ZP and CT can be predicted. However, for each mill, the degree of correlation will be a function of the papermaking process (i.e., source of fiber; type, dosage, and addition point of additives; type of filler; conductivity and hardness of water; operating conditions; etc.).

Experimental support for answer: Although the paper does not present specific “white water” charge characterization case studies, the paper does contain several figures in which apparent CD of various furnishes are plotted against corresponding zeta potential. These various case studies demonstrate the effect of selected furnish variables on CT and ZP measurements.

For example, data (i.e., plots of CD vs. ZP) is shown which demonstrates how the degree of CT/ZP (or CD/ZP) correlation can be influenced by the order of starch/PCC addition. From the data it is seen that when starch was added (especially late addition), CT remained negative, although zeta potential was “pushed” positive. According to the authors, this demonstrated that polymer consumption (for CT test) was occurring due to presence of anionic “trash” not neutralized by the starch. Another factor to consider is that PCC (especially when added early) is effective at adsorbing anionic “trash” (i.e., decreasing CT).

Also, results from a case study in which the effect of Ca++ was investigated, are presented. The results (see Figure 4a and 4b) show a clear trend with respect to Ca++ and ZP for all PCC containing slurries, but not for other types of fillers (e.g., talc/clay). With respect to CT/ZP correlation, the results showed that the correlation was poor for slurries containing PCC. However slurries that did not contain any PCC showed”slightly better” correlations.

In another case study, the effect of sample fraction was investigated. The results show that ZP data for thick stock was similar to CT data for fines, however the CT for the other fractions (fiber, solubles) was different. With respect to thin stock samples, very poor CT/ZP correlation existed for all fractions.

Situation in which the findings can be useful: The recommendation given by Sanders and Schaefer must be taken into consideration if optimization of the chemical additive program is required. The findings demonstrate that an appropriate strategy for wet end charge characterization requires the knowledge of the relative sensitivities of available charge measurement techniques to furnish variables. Moreover, the paper’s usefulness resides in the fact that it demonstrates that DELS and CT are complementary techniques.

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Name: Marc Azzi

Date: September 28, 2002

Topic: “Why did the results depend on the zeta potential neutralization at the lower level of anionic polymer addition, but not at the higher level of anionic polymer addition?”

Primary Resource: Somasundaran, P., Vasudevan, T. V., and Tjipanganjara, K. F., “Enhanced flocculation and dispersion of colloidal suspensions through manipulation of polymer conformation”, Dispersion aggregation, Proc. Eng. Found. Conf. 1992 (Pub1994):403-418.

Why this subject is important: Flocculation is a key process used in pulp and paper mills around the world. Its main application is in the clarification of the machine white water (in equipment such as dissolved air flotation units) and in the clarification of the mill effluent water (in settling tanks). Other applications include improving the first pass retention on machine wires and improving sludge de-watering in screw presses and centrifuges for example. A large part of the flocculants used in the pulp and paper industry is of the organic polymer type. These products are expensive and they constitute a big portion of the mill expenditure on chemicals. It is the mill technical expert goal to optimize the polymer performance in order to reduce its running cost.

Answer to the assigned question: A simple explanation could be that at their respective IEP, the conformation of the polymer at low concentration was more extended than the conformation of the PAA at higher concentration, which will result eventually in better results in the earlier condition. In addition, the neutralization of the surface charges was the main contributor to the flocculation at low addition of polyacrylic acid concentration, while at high addition of polyacrylic acid concentration the bridging of the polymer played the major role.

Logical or theoretical support for answer: Flocculation can be achieved by charge neutralization of the colloids and by bridging of the agglomerated colloidal particles. At charge neutralization the particles are able to approach each other more easily because the repulsion have been reduced with the reduction of the surface potential. Bridging between particles occur due to the loops and trains of the polymer that extend out into the surrounding medium.

At lower levels of polymer addition, the change in the zeta potential did not induce any change in the conformation of the polymer and thus maximum flocculation is expected to be at the isoelectric point where the charges are neutralized and repulsion minimized. Note that the effect of bridging was present but not enhanced by the change of potential. In the case of higher level of polymer addition, the adsorption of the polymer in greater quantity on the surface of the particles affected in such that the conformation of the polymer is the determining factor in the flocculation rather than the neutralization of the surface charges. The change in the zeta potential affected the flocculation by affecting the coiling of the polymer and its ability to bridge.

Experimental support for the answer: If we are to simplify the results of the tests conducted by Somasudaran, and compress them in the following comparative table:

PAA	pH	Charge Neutralization	Conformation	Bridging
Low	IEP	High	High extension	High
High	IEP	High	Low extension	Moderate
High	Above IEP	Moderate	High extension	Moderate
Zero	IEP	High	Zero extension	Zero

From the above table we can conclude that best flocculation could be achieved at IEP for the low [PAA] by good charge neutralization and good bridging. Whereas, at high [PAA], the previous synergetic effect is not achievable.

Situations in which the findings can be useful: If we assume from a practical point of view that in a specific situation, a lower concentration of polymer at the proper zeta potential could generate a better or even an equal flocculation performance than at its higher concentration, could be a big source of reducing chemical expenses. What is certain however is that the conformation of the polymer is affected by many parameters, which in turn reflects directly into the polymer efficiency and consequently the operational cost.

Steve Henry, September 22, 1999

ALKENYL SUCCINIC ANHYDRIDE – A WET-END ADDITIVE FOR PAPER

Why Use Alkenyl Succinic Anhydride?

Since the 1800’s, papermakers have relied on internal sizing agents for moisture resistance and improved printability [1]. Essentially, the internal sizing agent forms a hydrophobic layer on the pulp fibers. This layer then resists rewetting. Size usage may vary from moderately sized for printing and linerboard grades to hard sized for water repellency on liquid container grades. Since the 1800’s, papermakers utilized alum/rosin sizing which required an acid pH wet-end chemistry system. Due to innovations in the paper industry in the 1980’s, papermakers began transitioning to alkaline processes that forced the paper industry to look for new sizing agents. In alkaline systems, the paper industry began primarily using one of two synthetic sizing agents: alkyl ketene dimer (AKD) or alkenyl succinic anhydride (ASA). ASA is primarily used where moderate sizing is required as opposed to hard sizing applications. ASA offers high reactivity that results in a quick cure time. Unlike AKD, ASA does not affect the coefficient of friction. This is particularly advantageous on recycled paper grades where friction is often an issue. ASA also works well over a wider pH range, which also benefits recycled paper grades [2]. In many cases, ASA is more cost-effective than AKD. Despite these benefits, AKD has been the dominant synthetic size due to its ease-of-use. However, ASA emulsification systems have been greatly improved in recent years. Due to the improved emulsification systems and the other benefits that ASA provides, ASA use is growing rapidly in the paper industry.

Alkenyl Succinic Anhydride Chemistry

As shown below, ASA consists of an isomerized alpha-olefin and an anhydride ring. The isomerized alpha-olefin is produced by polymerizing ethylene [3]. Then, the alpha-olefin is then subjected to random isomerization of the double bond position [1]. The alpha-olefin is typically in the C16 to C20 range and may be linear or branched [1]. Finally, in order to form the ASA molecule, the isomerized alkelene chain is reacted with maleic anhydride [3].

Alkenylsuccinic anhydride molecular formula

Figure from Reference [1]

The anhydride ring can “cleave on either side of the single bonded oxygen” and form an ester bond with the hydroxyl groups of cellulose or hemicellulose [2]. The ester bond reaction rate is very fast. Once the ASA molecule is bonded with the fiber, the long-chain isomerized alpha-olefin provides a hydrophobic layer for the fiber.

Alkenyl Succinic Anhydride’s Charged Nature and its Consequences

The ASA molecule itself is nonionic. It must be combined with a cationic starch or synthetic cationic polymer to be retained. The starch or polymer makes the ASA emulsion cationic, so it will be retained by the anionic fibers. While the sheet is in the dryer section of the paper machine, the ASA emulsion becomes anchored to the fiber by forming covalent bonds [3]. The ASA emulsion exhibits a fast reaction time, which benefits the papermaker. Typically, the paper is almost fully cured by the time it reaches the reel of the paper machine. This is a distinct advantage over AKD where it is common to allow the paper to “age” before running cobb tests. However, the fast reaction rate does have one drawback. Hydrolysis of ASA also exhibits a fast reaction time. Hydrolysis of ASA produces dicarboxylic acid that has been shown to be detrimental to sizing [2]. In addition, the salts of the dicarboxylic acid are extremely tacky which leads to deposits and picking problems in the press section of the paper machine [1]. To prevent hydrolysis, the papermaker must try to use the ASA emulsion immediately and minimize its contact with water.

Alkenyl Succinic Anhydride’s Size and its Consequences

ASA emulsion particle size plays a large role in how well it performs. Typical emulsion particle sizes are 0.5 to 3.0 mm [2]. Small emulsion particles (< 0.5 mm) would be ideal since these they allow very uniform distribution of the ASA molecules on the fibers. However, small emulsion particles are difficult to produce and experience high hydrolysis rates [1]. Large emulsion droplets (> 3.0 mm) are easier to produce. Even if the large droplets are uniformly distributed on the fiber surface, the result is not as uniform as a uniform distribution of smaller droplets. The large droplets can also lead to deposits on the paper machine. The ideal emulsion particle size is 1 to 2 mm which is a compromise between the small and large molecules. The intermediate-sized emulsion particles can be easily produced and are small enough to be distributed uniformly.

Methods of Application

Mills typically receive ASA as oil that looks similar to amber or yellow motor oil. Since the oil is insoluble in water, it requires emulsification with starch (or synthetic polymer) in order to work in wet end of a papermill. There are two main emulsification processes used with ASA. The first and less common method is using a low-shear venturi-type emulsifier. The most common method is high shear emulsification where the ASA is subjected to a high shear pump. The cationic starch or polymer acts as a protective colloidal when the high shear emulsification process is used. Also, the high shear method requires minimal surfactant as opposed to the venturi-type emulsifier [2]. This is beneficial because surfactants rewet the fibers, which is opposite what the papermaker is trying to accomplish. Both emulsification processes have several key variables that affect the quality of the ASA emulsion. These variables are the amount of energy put into the emulsifier, the starch (or synthetic polymer) ratio to ASA, the amount of surfactant, and the qualities of the starch (or synthetic polymer) [1]. A typical ratio of cationic starch to ASA is 3:1; a typical ratio of synthetic polymer to ASA is 0.4:1 [2]. Standard feed rates of ASA is 0.1 to 0.15% by mass based on oven dry tons of fiber [2].

It is best if the ASA emulsion is used immediately. If the emulsion must be stored for a period of time, it should be maintained at a pH of 3.5 or lower and temperatures slightly above freezing to minimize hydrolysis [2]. Since the ASA emulsion has a fast reaction rate and experiences hydrolysis when interacting with water, the emulsion is typically used immediately and injected at or after the fan pump. Finally, in order to retain size particles and minimize deposits, it is important to have good first pass retention to avoid hydrolysis while recirculating the paper machine white water. Retention aids are often used in concert with ASA to maximize the retention of ASA and minimize the hydrolysis of ASA.

References

1. Scott, W. E., Principles of Wet End Chemistry. Atlanta: TAPPI Press, 99-109 (1996).
2. Hodgson, K. T., “A review of paper sizing using alkyl ketene dimer versus alkenyl succinic anhydride,” Appita, 47(5): 402 (1994).
3. Andounian, W. J. “ASA sizing agents in alkaline fine paper,” PIMA Magazine, 75(7): 48 (1993).

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Pankaj Kaprwan, Sept. 13,1999

ALUM – A WET ADDITIVE FOR PAPER

Why use Alum?

Papermakers alum, aluminum sulfate is a true friend of papermaker in terms of the following roles it plays on the paper-machine:
1. It controls pH by virtue of the hydrolysis reactions of Al3+ ion.
2. It acts as a retention aid for fibrous and non-fibrous additives.
3. It is responsible for fixing rosin size to fiber and fines and then keeping the size stable.
4. It acts as a drainage aid.
5. It increases dry strength of the paper by acting as fixing agent for dry strength additives.
6. It helps in press reducing press picking and foam suppression.
7. Small amounts of alum used in alkaline papermaking in cationic or neutral form enhances efficiency of anionic retention aids, enhances and stabilizes sizing, enhances runnability and helps in neutralization of interfering substances.

Alum Chemistry:

Alum has the formula Al2(SO4)3.14H2O and is characterized by equivalent Al2O3 content. Commercial liquid alum contains 48.5% Al2(SO4)3.14H2O with an equivalent content of (8.0-8.3)% Al2O3.
The chemistry of alum revolves around the high charge density of aluminum ion i.e. +3 ionic charge and small ionic radius 0.50 A, because of which it acts as a Lewis acid electron pair acceptor and complexes with neutral or anionic ligands where ligands occupy coordination site in the octahedral structure.

Aluminum Sulfate in water exists as separate hydrated aluminum and sulfate ions. With increasing pH aluminum ions undergo hydrolysis to produce hydroxy aluminum species. The presence of sulfate ions results in replacement of hydroxy ligands in hydrolyzed species by SO42- ions and shifting of pH of formation of these various species to the lower side:
· At pH<4 it exists as Al3+ predominantly and some as AlSO4+.
· Above pH 4, it hydrolyses to produce a polynuclear species Al8(OH)10(SO4)54+ predominantly along with Al(OH)3 in a narrow pH range till 5. This is known as the active alum floc by virtue of high cationic charge, which helps in getting adsorbed onto the negatively charged fiber.
· Above this pH it begins to precipitate to irreversibly to form Al(OH)3 which reduces the cationic charge of the alum floc but nevertheless gets adsorbed onto fiber surface along with hydrolyzed products, and dominates upto pH 8.
· At pH >8 it forms Al(OH)4-

Activity of alum is by virtue of high cationic charge and the alum floc ( hydrolyzed products ) and the activity is maximum in the range of pH 4 to 5.5. It decreases then as charge lowers. Concentration of alum also affects pH as with increasing concentration of applied alum the pH of hydrolyses products shifts to the lower side.

Alum’s high charge density and its consequences:

The alum’s high charge density and formation of polynuclear species by virtue of hydrolysis is responsible for retaining the fibers, fillers by suppressing the zeta potential of these particles, reversing their charge and thereby allowing these particles to come close, collide and stick to each other. The high cationic charge of larger hydrolysis species is responsible for setting bonding sites for adhering rosin to fiber depending on pH and type of rosin ( rosin soap or dispersed rosin ). Basically active alum floc should have high positive charge which exists at pH 4 to 5.5 for effective reaction with anionic particles. Below this pH there is less of active floc and above this pH the positive charge is insufficient but may serve some purpose in neutral or alkaline papermaking.

Method of Application:

The method of application depends on the mill conditions, i.e. the pH we are working in, grade of paper, type of sizing, stock temperature and white water closure system mainly. Generally the rule of thumb is to have a minimum of 1:1 ratio of alum to rosin size to maintain net +ve charge. But because of its other jobs of retention aid and drainage aid, the ratio is (2-3): 1 – alum to rosin i.e. 0.1 to 0.15 % of alum on fiber. When using rosin soap size the pH is 4.0 to 4.5 and when using dispersed rosin size the recommended pH is 4.6 to 5.3. Alum is added after rosin size, nearer to the machine headbox, generally at fan pump, to prevent deactivation of alum rosin floc. Reverse sizing (alum added before) may be followed to offset bad effects of hard water. High acidity of white water needs to be brought down to keep alum floc active. Because of the broader range of ASA sizing ( pH 5-10 ) alum is added (20% of ASA weight) to ASA during emulsification to enhance sizing and reduce sticky deposits.

References:

1. David R. Cordier, Harris J. Bixler, “Measurement of aluminum hydrolysis in the Wet End” Tappi Journal, Pg. 99, November 1987.
2. Arnson R. “The chemistry of aluminum salts in papermaking” Tappi Journal, 65(3), 125-130, 1982.
3. William E. Scott, Chapter 11,13,14 of Principles of Wet End Chemistry, Tappi Press, 1996.
4. “Alum in Papermaking”, Trade Literature Cyanamid Alum, American Cyanamid Co.

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Thidarat Rodanant, Sept. 30, 1999

AMPHOTERIC STARCH – A WET-END ADDITIVE FOR PAPER

Why Use Amphoteric Strarch ?

In order to run higher speed machines with new designs of manufacturing equipment to improve product quality, paper mills need high performance polymers to achieve their targets. Amphoteric starch allows papermakers to obtain higher retention, better formation and faster drainage as well as strength. Also it can help solve problems when the system become over-cationized. In linerboard, amphoteric starch are used to increase strength, especially in cases where cationic starches have caused unmanageable foam problems [2].

Amphoteric Starch Chemistry

Starches are polymers with repeating units of glucose joined through hemi-acetal or glycosidic bonds by alpha configuration which in solution results in a helical conformation of linear segments that have about six repeating units per turn [1]. Starches are made up of two different molecular structures, amylose and amylopectin. Amylose is the linear chains of alpha-1,4 linked glucose residues while amylopectin is branched molecules which contains alpha-1,4 linked chain with branch points via alpha-1,6 linked most commonly and occasionally through carbon 3.

Amphoteric starch can be made by preparing native starches containing tertiary aminoethyl or quaternary amine ether and sulfate or carboxyl ether groups or phosphate ester groups with different molar ratios of anionic to cationic groups. A combination of charges and degree of substitution are alternatively involved as the use conditions vary [1]. Natural potato starch contains phosphate groupings. For this reason all cationic potato starches can be considered to be amphoteric starches.

Amphoteric Starch’s Charged Nature and its Consequences

Amphoteric starch has both cationic and anionic charges. It allows papermakers the flexibility to control strength development without changing the retention or drainage additives, because addition rate can be increased without negative effects as cationic starch do. The dual functionality to react with both anionic and cationic material helps remove excess ionic material from the wet-end. The ability to react with anionic or cationic sites increases the locations where the amphoteric starch can react. This also helps maintain the ionic stability in the wet-end, yielding a more stable system capable of handling upsets without significantly altering the charge balance [2].

Amphoteric Starch’s Size and its Consequences

The branched amylopectin is much higher molecular weight (1.6 million to 16 million) than linear amylose (160,000 – 710,000). Starch granules range in size from 2 to 100 microns. Different starch sources have varying levels of amylose and amylopectin. Higher molecular-weight molecules are not only adsorbed to a larger degree but are also more effective interfiber bonding agents per unit retained.

Charged polymers can form micro flocs of the fibers, fines and filler, allowing the water to drain faster while improving the first pass and ash retention. Unlike the macro flocs caused by some synthetic polymers, micro flocculation by starch can improve formation. Increases in first pass retention will allow the reduction of retention aid polymers, reducing the tendency to form macro flocs and yielding a more homogeneous fiber distribution. [2]

Methods of Application

Amphoteric starch can be used in alkaline, neutral and acid papermaking systems. In order to prepare aqueous pastes of starch, the batch system comprises a large cooking tank provided with steam injection and mixing equipment. A second storage tank is required from which the starch solution is metered to the machine. Batch cooking is usually done at concentration from 2%-8% and temperature around 88 degree C for about 30 minutes. Continuous cooking system use steam sparging to heat and gelatinize the paste. Variables in the process include put-through rate, temperature, back-pressure, and starch concentration. [1] For the optimum strength development, starch is commonly added to the thick stock where the relatively long dwell time ensures adsorption to the longer fibers. [2]

On a machine using groundwood pulp, problems of pitch deposits and paper rejects have been solved by replacing 2% of cationic starch with 1% of amphoteric starch. In linerboard, bleached board and cylinder board a 0.5% addition rate of amphoteric starch can help increase strength, improve drainage retention and formation, enhance machine speeds and develop product quality. Amphoteric starch helps reduce consumption of expensive titanium dioxide with improved formation in wood-free uncoated paper process. In the production of tissue, toweling and napkins amphoteric starch help increase strength and drainage that make manufacturer to reduce refining, lower basis weight, and substitute alternative fibers.

References

[1] , B.T. Hofreiter, ” Chapter 14 Natural Products for Wet-End Addition “, PULP AND PAPER, Chemistry and Chemical Technology, Third Edition Volume III,
[2] Robert T. McQueary, “Wet End Waxy Amphoteric Starch Impacts Drainage, Retention and Strength “, TAPPI, 1990 Papermakers Conference

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Judy Delaney, September 20, 1999

ANTIFOAMER – A WET-END ADDITIVE FOR PAPER

Why Use Antifoamer?

Antifoamer* is used to control foam that develops during the manufacture of pulp and paper. Specifically, foam occurs in Kraft pulping mills, pulp de-inking processes, pulp bleaching processes and on paper machines, both at the wet-end and at the coaters. The fact that antifoamers are widely used in the pulp and paper industry (millions of dollars are spent annually) to control foam leads to the natural conclusion that foam is an unwanted entity in these processes. The problems foam can cause range from the nuisance variety to those of serious consequence. These problems include, but are not limited to: 1) mechanical: valves clogging, pumps cavitating and lines plugging; 2) process: process slowdowns (due to mechanical issues and deposits in the system), poor runnability and product deterioration 3) paper machine issues: deposit build up, poor runnability, increased machine breaks, reduced machine speed (resulting in decreased production ) and final product quality issues such as spots and streaks.

Antifoamer Chemistry

There are five basic categories of antifoamers. The categories are based on oil content: 1) Oil-free (i.e., water-based), 2) Oil-water emulsion which contains more than 50% water (also referred to as water-based), 3) Oil-water emulsion, which contains less than 50% water (also referred to as water-extended) 4) Oil-based ( i.e., contains 0% water) and 5) Concentrates (i.e., contain 0% oil, 0% water).

Regardless of the category, an antifoamer product is generally comprised of several components (the exception is the concentrate): 1) a primary antifoam particulate which is usually hydrophobic and is the major contributor to defoaming capability, 2) a secondary antifoam particulate which is important to the overall performance of the antifoamer, but is less influential than the primary particulate, 3) a fluid carrier/ spreading agent, which comprises the majority of the product and should be insoluble in the process area to be defoamed 4) an emulsifying agent, which introduces the primary and secondary antifoam particulates into the process needing foam control 5) a stabilizing agent which maintains product stability and 6) a preservative which prevents microbiological growth in the antifoamer product.

An example of typical components for four of the basic categories of antifoamer follows (listed in this order: primary antifoam particulate (P), secondary antifoam particulate, fluid carrier (C) spreading agent (S) , emulsifying agent (E), stabilizing agent (ST) and, preservative (PR)): 1) Oil-free: fatty alcohol (P), hydrocarbon wax (S), water (C), surfactants (S, E, ), polymer (ST) and biocide (PR), 2) Oil-water emulsion: Hydrophobic silica (P), EBS (ethylene bis stearamide) (S), water (C) mineral oil (C, S), surfactants/ester (S,E) and biocide (PR). 3) Oil based: hydrophobic silica (P), EBS (S), Mineral oil (C, S), ester/surfactant (S), 4) Concentrated: usually 100% active or emulsions of PEG esters and surfactants.

*The words antifoamer and defoamer are commonly used interchangeably. The actual meanings differ: defoamers destabilize
foams that already exist, antifoamers inhibit foam formation by preventing the stabilizing surfactant from forming around developing air bubbles. Most products sold for foam control perform both functions, hence the intertwining of the terms. In cases where products contain either antifoamer or defoamer, the antifoamers are usually placed further back in the system versus defoamers, which are applied near, or to, the foam.

Antifoamers Charged Nature and its Consequences

The single reference to antifoamer’s charged nature found in the literature was that of the emulsifying agent (the antifoamer component that introduces the primary and secondary antifoam particulates into the process). Emulsifying agents were referred to as being either nonaionic or anionic. Additionally, on a local level, a laboratory PCD (Particle Charge Determination) test using a water-based antifoamer resulted in a slightly anionic charge.

Antifoamer’s Size and its Consequences

As previously stated, the main antifoaming constituent of an antifoamer product is usually a hydrophobic particulate. The particulate size range is from 1 to 100 microns.

Methods of Application

The safest course of action when introducing an antifoamer to a process is to pre-screen (i.e., in a laboratory setting) the product(s) to be trialed. This will avoid possible upsets to the process which could lead to lost production time and/or off -quality product.

Most antifoamers come in liquid form, however, brick and flake forms are available options. The liquids can either be in concentrated form or “made down” when they come to the manufacturing site. Antifoamer applications are usually metered on a continual basis by metering pumps. Methods of application and delivery system design will depend on the particular antifoamer product used. As observed from the previous information, antifoamers are available in a wide variety of formulations. In order to ensure the most advantageous application/delivery system, the product data sheet should be carefully reviewed and the antifoamer supplier should be consulted.

From a safety aspect, there are relatively minimal safety concerns surrounding antifoamers. However, in the case of oil containing antifoamers, a slip/fall hazard could exist. Personal protective equipment should include chemical goggles and chemically resistant rubber gloves. Ventilation must be adequate when antifoamers are used. The Material Safety Data Sheet (MSDS) must be consulted prior to use.

From a process impact aspect, lab analysis and trial planning should be carefully executed in order to avoid overuse of the product. Adverse affects on both the process and final product could result from antifoamer overuse.

References

1. Gardberg, L. (Nalco Chemical Company), “Water-based fixes for foam control,” PIMA Magazine, August 1995, 66.
2. Keegan, K.R. (Henkel Paper Chemicals), “Defoamer Theory and Chemistry,” 1991 Chemical Processing Aids/ 27, TAPPI Short Course.
3. Nelson, J.R., “Foam Control Agents,” Chemical Processing Aids in Papermaking: A Practical Guide, 155.

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Sandra E. Beder-Miller ,September 29, 1999

BIOCIDES – SLIME CONTROL AT THE PAPER MACHINE

Why Use Biocides?

Biocides are used to control the growth of microscopic organisms or bacteria usually referred to as “slime”. These organisms grow in stringy structures called filaments. The filaments form a net that can collect fines, fillers, pitch, clay, latex, or other paper making additives, and dirt. Slime can resemble a wet, sticky substance or appear as a stringy, granular or pasty mass [1]. It typically has an orange, red or pink color. The Paper Machine environment provides an ideal location for the growth of anaerobic bacteria. The two predominant anaerobic bacteria groups are Clostrida sp. and sulfate reducing bacteria. The major contributor to increased anaerobic growth in the paper mill as been due to the closure of mill water systems and the increased use of recycled fiber.

Products of anaerobic metabolism are volatile fatty acids (acetate, propionate, and butyrate), H2, CH4, and H2S. Anaerobic bacteria can cause such problems as:

(1) Strong odors due to degradation of stock and additives which leads to the formation of volatile fatty acids.
(2) H2S produced by some species of anaerobes can lead to equipment corrosion.
(3) Clostridia sp. may produce cellulase enzymes that degrade the cellulose polymers found in the wood fiber structure. If cellulase persists for a long time, the wood fiber will become weakened and decrease sheet strength.
(4) Hydrogen, H2S, and methane gas can be produced and accumulate in confined spaces and vessels and become explosive if allowed to accumulate.

These deposits can break loose and fall into the paper making furnish and cause defects such as holes and spots. Slime can be the cause of paper machine breaks and excessive downtime that leads to a loss in production.

Biocides Chemistry

In general, biocides must either kill the anaerobic population, slow the reproduction of organisms, or interfere with the organism’s ability to metabolize food. Biocides must be effective at killing cells in the vegetative state and keep spores from becoming active in the case of Clostridia sp.. They must also be persistent enough to be effective through extended periods of down time. Biocides used in the paper mill fall into several major categories:

(1) Organobromines
(2) Organosulfurs
(3) Cationics
(4) Isothiazolinones
(5) Thiocyanates
(6) Oxidizers

As an example, Boise Cascade uses Chlorine Dioxide and products supplied by NALCO in their biocide control program:

(1) NALCO 7650 is a mixture of acetic acid, hydrogen peroxide and peracetic acid. It is an oxidizer and highly flammable.
(2) NALCON 7648 is a microbiocide that is an aqueous solution of phosphate ester of triethanol amine and a quaternized alkyl dimethyl benzyl ammonium chloride. It is extremely corrosive.
(3) NALCON 7647 is a microbiocide that is an aqueous solution of substituted isothiazolinone.
(4) STABREX ST70 is an aqueous solution of sodium hypobromite, sodium hydroxide, and sodium salts.
(5) Chlorine Dioxide (8gpl to 12gpl strength) from the bleach plant is diluted with water to 2.5 gpl to 3.5 gpl.

Biocide’s Charged Nature and its Consequences

Biocides have no charged nature according to Nalco. One reference to “charge” was made in an article Roberston and Taylor [2]. They explored the use of nonionic polymer dispersants in the treatment of paper machine deposits.

Biocide’s Charged Size and its Consequences

Biocides are shipped in solution form, so reporting a particle size is not appropriate.

Methods of Application

In general, the paper maker should use enough Biocide to prevent quality and production problems. It is important to note that one generic control strategy will not fit every mill. It is important to assess each situation. The Slime control program could involve several products administered into a variety of paper machine locations:

(1) Broke System
(2) Blend Chest
(3) White Water Chest
(4) Saveall
(5) Starch Slurry
(6) Coating
(7) Clay or other fillers
(8) Tray Water at forming section
(9) Fresh Water Make-Up

Products may be added at different intervals throughout the day or continuously. Usually pumps will run for a short interval and then shut off for so many hours. Addition rate in ppm depends on the severity of the deposit problem balanced against the cost of the Biocide. Precautions must be taken to insure safe handling. Goggles, gloves, apron, and face shield should be worn when handling biocide products. One must also consider the frequency of paper machine boilouts. It is very important to monitor the following conditions around the paper machine that influence the growth of slime:

(1) Water Quality – it may be necessary to treat the water before it enters the paper machine system.
(2) Food – additives in the water, excessive amounts of starch, condition of broke, and the use of more secondary fiber adds more nutrients and microorganisms to the system.
(3) Temperature – wet end temperature normally operate at 500 F. A sudden drop in temperature (for example 400 F) helps fungi and bacteria grow better
(4) PH – fungi grow better in acid conditions whereas, bacteria prefer neutral conditions.
(5) Oxygen – Anaerobic bacteria (can not survive in the presence of molecular oxygen) usually live in chests where the stock is not well agitated or beneath deposits

REFERENCES:

(1) Hoekstra, Philip M., “Fundamentals of Slime Control”, 1991CHEMICAL PROCESSING AIDS, TAPPI Short Course Notes.
(2) Robertson, Linda R. and Taylor, Nicole R., “Biofilms and dispersants: A less-toxic approach to deposit control”, Tappi J.77(4):99-103(1994).
(3) Goldstein, Steve D.,”Some overlooked fundamentals of slime control”, Appita 40(3):213-216(1987).
(4) Stitt, John, “Slime and deposit control: THE ALKALINE CHALLENGE”, PIMA’S PAPERMAKER 79(9):54(1997).
(5) Schwingel, William R. The Implications of the Growth of Anaerobic Bacteria in the Papermaking Process. 1997. Biological Sciences Symposium.
(6) NALCO. Technical Publications for Customers.

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Jill Scherrer, September 23, 1999

BENTONITE – A WET-END ADDITIVE FOR PAPER

Why use bentonite?

Bentonite has many uses in the paper industry, but it is primarily used as part of a microparticle retention system. Typically, a medium to high molecular weight cationic polymer is added to the thin stock just before the fan pump. The polymer forms large flocs of fiber and filler material, which are then sheared into microflocs as they pass through the fan pump and pressure screens. Bentonite, an anionic microparticle of colloid dimensions, is then added to coagulate the microflocs1.

Microparticle retention systems are typically used when high retention is required and the use of a single component polymer system results in unacceptably high cost and poor formation2. The use of bentonite along with a cationic polymer results in significantly superior retention, with improved formation and drainage properties. Another advantage of this system is that it can be used in all pH conditions normally associated with papermaking1.

Bentonite Chemistry

Bentonite, by definition, is a rock that typically contains two or more minerals, one of which is from the smectite clay mineral group3. This rather loose definition leads to the grouping of materials with widely varying composition and characteristics under the same name. For this reason, bench studies are usually required to identify the specific product that will work most efficiently in a particular mill.

The basic chemical structure of a smectite crystal is shown below. The center of the smectite crystal consists of a layer of oxygen octahedra which contain metal ions, usually magnesium and/or aluminum. Layers of oxygen tetrahedra form on either side of the middle octahedral layer, typically each containing a silicon ion. The corners of the octahedra that are not sharing oxygen atoms with the tetrahedra consist of hydroxyl ions, or in some cases fluoride ions3.

Bentonite’s Charged Nature and its Consequences

There is a slight deficiency of structural cations in bentonite’s smectite crystals, resulting in a slight negative charge. This charge attracts cations to its surface which are mobile and readily exchanged for other cations. In water, these cations tend to diffuse away from the surface to form an electrical double layer of positive charges around the negatively charged crystal3. This double layer tends to keep the bentonite particles dispersed in solution, with large surface areas available for reaction.

Bentonite is introduced to a furnish consisting of finely dispersed, cationically charged microflocs. The addition of an anionically charged colloidal material reduces the charge of the electrical double layers until coagulation occurs. Coagulation of the microflocs produces dense aggregates of the furnish materials. This mechanism results in improved fines and filler retention and uniform formation characteristics compared to that achieved through a pure flocculation mechanism2.

Bentonite’s Size and its Consequences

Bentonite forms two dimensional crystals in the colloidal particle size range, with a uniform thickness of one unit cell (about 0.9 nanometers) and lateral dimensions varying from a few nanometers to a few micrometers. The very thin shape of the crystal leads to its high surface area, approximately 800 square meters per gram of clay3. Since the availability of this high surface area is the source of bentonite’s coagulant properties, adequate dispersion of the crystal aggregate is critical to its efficiency as a wet end additive.

The presence of any multivalent cation in the smectite structure inhibits dispersion by increasing the bonding strength between the individual crystals. Most commercially produced bentonite is made by treating calcium bentonite with sodium carbonate. The resulting sodium bentonite is usually very easily dispersed, often spontaneously swelling to several times it’s dry volume upon addition to water3.

Methods of Application

Bentonite is used as part of a microparticle retention system also involving a medium to high molecular weight cationic polymer. The polymer is added early in the thin stock system, forming large flocs of fiber and filler material through a bridging mechanism. As the large flocs pass through high shear areas of the thin stock approach system, the large flocs are sheared into much smaller sizes, sometimes referred to as “microflocs.” Bentonite is then added to the thin stock after the last point of high shear, usually at the discharge of the pressure screens1. The following figure provides a pictoral representation4:

The key to proper functioning of this retention system is to balance the surface area and charges of the dispersed, cationically charge furnish with the surface area and charges of the anionically charged bentonite1, while maintaining on-line control of first pass retention on the paper machine. Typically, the bentonite addition to the system will be base-loaded while the polymer addition is controlled by a feedback loop based on tray solids measurements (an indicator of first pass retention). In this case, the bentonite dosage should be periodically reevaluated to verify the optimal setpoint for target first pass retention. Since no paper machine operates under static conditions, this practice provides a means to correct for “drifts” in system requirements and ensures the most cost effective combination of additives will be used.

References

1 Langley, J. G. and Litchfield, E., “Dewatering Aids for Paper Applications,” Proc. TAPPI 1986 Papermaking Conference, 89.
2 Dixit, M. K., Maleike, T. A., and Jackowski, C. W., “Retention Strategies for Alkaline Fine Papermaking with Secondary Fibre: A Case History,” TAPPI Journal 74 (4): 107 (1991).
3 Knudson, M. I., “Bentonite in Paper: The Rest of the Story,” Proc. 1993 Papermakers Conference, 141.
4 Moberg, “A Visual Perspective on Microparticles,” TAPPI Instroduction to Wet-End Chemistry, 1999.

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Edmund A. Pozniak Jr., September 22, 1999

CATIONIC STARCH – A WET-END ADDITIVE FOR PAPER

Why use Cationic Starch?

Cationic starches are primarily utilized for improved dry strength in paper. These charged starches allow papermakers to use the additive as an alternative or in addition to other papermaking tools, to produce a high dry strength not attainable by available papermaking tools or not attainable without compromising other desirable paper properties. The dry strength parameters most often enhanced by cationic starch are internal bond, tensile strength, mullen burst, wax pick and folding endurance. Uncoated wood-free papers take advantage of cationic starch’s bonding ability by increasing the sheet’s ratio of cheaper components, such as hardwood and mineral fillers. Cationic starch is sometimes added separately as a retention aid for sizing. Cationic starches can be part of an overall retention plan for white water systems that are high in pH and zero-to-minimum alum content. Coated papers use cationic starch because the high z-directional strength it imparts to the sheet improves pick resistance. In turn, coating levels can sometime be reduced, improving porosity, glossing tendency and optical properties. Linerboard utilizes starch to lessen the amount of refining needed. Refining reduces drainage, causing the need to reduce machine speed and therefore also reducing tonnage. Also of note, cationic starches can reduce linting and dusting during printing and provide for clean slitting, die cutting and perforating.

Cationic Starch Chemistry

Starch is chemically similar to cellulose in that it is a polymer composed of glucopyranose units linked through carbons 1 and 4. Starches are cationized with either tertiary or quarternary amine groups. Most starches occur as a mixture of linear and branched molecules. The branched fraction is called amylopectin. Amylopectin contains a-1,4 linked chains with branch points primarily via a-1,6 links, and occasionally through carbon 3. On average, there is one branch point for every 18-27 glucose units. The linear amylose molecules have a greater tendency to associate in crystaline aggregates(starch retrogradation) than branched amylopectin molecules and so highly branched starches are preferred for wet end addition. Starch granules are 5 to 100 microns in size.

Cationic starch, amylose, and amylopectin

Cationic Starch’s Charged Nature and its Consequences

Starch is a white granular substance that occurs widely in plants, such as the seeds of corn and wheat, in roots and tubers of potatoes and tapioca, and in stem piths like the sago. Native starch has a retention rate of less than 40%. In order to make the use of starch efficient, it is necessary to add cationic substituents to the native starch. Once charged, cationic retention rate is near 100%.

Generally commercial cationic starches are prepared with nitrogen containing reagents. The reagent used may be a primary, secondary, tertiary, or quaternary amine. Primary and secondary amines are of limited value in wet end papermaking applications and usually tertiary or quaternary products are used. A typical reagent used for the preparation of a cationic starch with a tertiary group is 2-Chloroethyldiethylamine. 2,3Epoxypropyltrimethylammonium chloride, is a typical reagent used to form a quaternary cationic starch. The degree of substitution is typically in the 0.01 to 0.05 range. Tertiary groups begin to lose their charge at a pH of 6.0, while quaternary groups maintain their charge regardless of pH.

Cationic Starch’s Size and its Consequences

The molecular weight of starch will vary greatly with its source. For example, experiments conducted by Harvey[4] revealed potato starches ranging from 3,000,000 to 3,500,000 grams per mole, while corn starch samples ranged from 800,000 to 1,800,000. Corn and potato starch have a high amylopectin content, resulting in less reticulation of the starch molecules. Cationic starches have a high affinity for cellulose fibers and fillers used in papermaking, lending to increased areas of bonding between surfaces and promotes a greater degree of hydrogen bonding.

Methods of Application

Cationic starch is received as dry powder, crushed flake, or in solution. Powder form is only soluble in hot water, where crushed flake is soluble in cold water. In a batch operation, starch is added to an agitated tank at 4-5% solids, heated by direct steam to 95 degrees Celsius, and held for 20 to 30 minutes. The starch solution will then be diluted and cooled before adding to the stock system. In continuous cooking systems, the starch is slurried in water to 36% solids. The slurry is the diluted to 5% solids and jet-cooked inline.

Considerations in adding starch to the system include: (1) Proper preparation and dilution to 1% solids or less. Any addition of 2-2.5% will not be effective (2) Add starch to furnish at a point where good mixing will occur. (3) Starch should be added after all refining for maximum effect. (4) Add starch at a point where retention time will be no more then 20 minutes. (5) Do not allow the starch to come into contact with other additives that have not been mixed well or become absorbed by it. Minimize contact as much as possible with anionic additives. Keep all additives as separate as possible. (6) The starch adsorption capacity of fiber can be increased by raising the pH in the system.

Many furnishes may contain fine anionic polymeric and colloidal materials that may neutralize with the cationic starch. Addition of alum earlier into the stock system may prevent this problem.

References

1. Harvey, Klem, Bale, and Hubbard, Cationic Starches in Papermaking Applications, TAPPI 1979 Retention and Drainage Seminar Notes, Atlanta, GA

2. William E. Scott, Principles of Wet End Chemistry, TAPPI Press, Atlanta, GA, Pgs 51-56

3. Hagemeyer, Manson, and Kocurek, Pulp and Paper Manufacture Volume 6 Stock Preparation, McGraw-Hill, 1992, Pgs 87-96

4. Harvey, R. D. “The effect of wet end starch in neutral/alkaline papermaking systems.”, Proceedings of
TAPPI Neutral/Alkaline Papermaking Short Course, Orlando, FL. October 16-18, 1990.

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Matthew Gregersen, September 25, 1999

COLLOIDAL SILICA – A WET-END ADDITIVE FOR PAPER

Why Use Colloidal Silica?

Colloidal silica is used as a microparticle in microparticle retention systems, which provide excellent retention without the adverse affects on formation of more traditional retention aid systems. The other part of the microparticle retention system is a cationic additive or combination of cationic additives. The excellent retention and drainage characteristics of microparticle retention systems lead to several advantages
over traditional retention aids.

Microparticle flocculation will reform after shear, unlike traditional flocculation mechanisms and form tighter denser flocs [1-2]. These tighter denser flocs release water more easily and increase web porosity or microporosity thus yielding increased drainage [1-2]. This increased drainage can lead to increased machine speed.

The increased drainage afforded by microparticle systems can lead to improved formation by allowing increased headbox dilution, refining, and/or hardwood content [1]. The formation is also improved by the smaller denser flocs formed using a microparticle retention system [1]. This improved formation and small dense flocs can lead to better moisture profile, wet-press efficiency, and drying [1]. Runnability in the press may be improved by increasing dryness off the former and increasing press dryness due to the microporosity in the sheet associated with the small dense flocs formed with the microparticle retention system [2]. The improved formation and small uniform floc size allow more uniform contact with dryer cylinders which leads to the increased drying and more uniform moisture profile [1]. The increase in sheet porosity may also reduce the energy needed to dry the sheet [1].

In addition to the drainage and formation related improvements, machine productivity can be improved with microparticle retention systems due to the improved retention [1]. As white water and headbox consistencies are reduced there will be a corresponding decrease in the rate deposits form, thus increasing runnability by lowering the frequency of breaks [1]. The frequency that machine wash-ups are needed will also decrease [1].

Related to the improvement in formation microparticle systems can also lead to improved strength. This improved strength can be achieved through improved formation, increased refining, and higher retention of fines and strength additives that the microparticle systems increased drainage and retention allow [1].

Improved retention fillers is another benefit of the microparticle retention system [1]. Improved filler retention will improve filler distribution within the sheet or two sidedness [1]. This improved distribution of filler can in turn lead to higher opacity, coating hold out, and improved printing [1]. The improved retention of fines and fillers will also allow for greater filler levels, thus reducing furnish costs [1].

Also, the improved first pass retention of microparticle systems can reduce the use of other wet end additives [1]. With the increased retention, more of the fines and fibers are retained the first time through along with the associated additives. Therefore, the additives effectiveness is not wasted as the fines and fibers that are not retained circulate through the white water system. Also, increased retention can reduce the loss of fillers and additives to the mill effluent [1].

Colloidal Silica Chemistry

Colloidal silica is composed of small spheres of silica. The surfaces of these spheres are covered with hydroxyl groups [3]. Two forms of colloidal silica are used in paper making. The silica sol is made up of individual spheres. Structured silica or silica microgels are composed of linear or branched networks of smaller silica spheres. These two types of silica are shown in Figure 1.

Colloidal silica surface groups schematic

Figure 1. Colloidal Silica Sol and Gel. Courtesy of EKA Chemicals.

Colloidal silica is generally produced by the deionization of sodium silicate to produce silicic acid [3]. The silicic acid is then condensed to form 1 to 2 nm particles, which are then grown to the desired particle size [3].

Colloidal Silica’s Charged Nature and its Consequences

The charge of colloidal silica is pH dependent. Above a pH of 2 the hydroxyl groups on surface of the colloidal silica particles begin to ionize and the colloidal silica becomes anionic [3]. The level of ionization and charge is pH dependent increases with increasing pH [3]. The anionic charge causes the colloidal silica to form strong ionic bonds with cationic additives that have been absorbed onto the surfaces of the papermaking furnish, thus leading to the flocculation of the paper furnish components [1, 3]. As hydrogen bonds are replaced by these stronger ionic bonds the flocs tend to collapse around the silica particles [1]. The collapsing of these flocs causes the floc to release water more easily than a larger softer floc [1].

Colloidal Silica’s Size and its Consequences

Traditional colloidal silica sols have a 3-5 nm diameter [1, 3]. Structured colloidal silica or silica microgels are composed of smaller diameter particles (1-3 nm) in linear or branched silica chains [2, 3]. The small size of these particles lead to very high specific surface area and surface charge density [1]. The high surface area leads to efficient interaction with the cationic components of the microparticle system [1]. This efficiency is due to the high concentration of silica particles [1]. For example, with an addition rate of 1 lb/ton (dry basis) there will be a silica particle approximately every 0.25 microns in all directions in the headbox stock [1]. Related to size, the structured or microgel forms of colloidal silica are claimed to have higher effectiveness, on a per weight basis, due to their increased specific surface area compared to traditional colloidal silica sols [2,3].

Methods of Application

As mentioned before, colloidal silica is used as part of a microparticle retention aid system. The other major component of the microparticle retention aid system is a cationic additive or combination of additives [1]. Typically the cationic additive is a cationic starch or cationic polyacrylamide, but may include cationic guar gum, alum, or a low molecular weight high charge density cationic coagulant [1, 2]. Generally, the cationic polymer will be added ahead of the pressure screen or fan pump, where the initial flocculation will be broken up by the high shear of the screen or pump [2]. The colloidal silica will be added following the screen allowing the dispersed flocs to form the small dense flocs typical of microparticle retention systems [2]. The colloidal silica is injected with plenty of dilution water to assure good dispersion and mixing with the stock. Colloidal silica can be either produced on site or received as a slurry from the supplier [3].

References

1. Duffy, B. P., “A Microparticle Retention Approach to Papermaking,” Proc. TAPPI 1993 Papermakers Conf., 171.

2. Main, S., and Simonson, “Retention Aids for High-Speed Paper Machines,” Tappi J.82 (4): 78 (1999).

3. Moffet, R. H., “On-Site Production of Silica Based Microparticulate Retention and Drainage Aid,” Proc. TAPPI 1994 Papermakers Conf., 243.

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Tim Dumm: September 30, 1999

FILLER CLAY: A WET-END ADDITIVE

Why Use Filler Clay:

Conventional filler clays and various modified clay products are used for reasons that depend on the type of paper being produced and the desired sheet characteristics. Filler clay (hydrous kaolin) is one of the leading types of filler used in the paper industry. The primary reasons why filler clays are used are to improve optical properties (brightness, opacity, and whiteness) and reduce costs. Secondary reasons why filler clays are used are to improve sheet smoothness for offset printability, formation and ink absorption uniformity, and to control or adjust porosity and coefficient of friction. In supercalendered grades a high level of filler clay can contribute to gloss. Structured and designed (or specially engineered) pigments which are made from special blends and physically or chemically altered clays have also become popular to obtain certain desired characteristics in specific types of papers. While there are several positive reasons why filler clay is used, there are a number of potential negative impacts as well. Negative impacts include a reduction in sheet strength due to debonding. Increased abrasion, paper density, and paper machine water system fines content are also considered potential negative impacts.

Filler Clay Chemistry:

The most common form of filler clay is kaolinite and the content of kaolinite is also a measure of how suitable the mineral is as a filler. Kaolinite has a two-layer structure with one layer of silica tetrahedrons and one layer of aluminum octahedrons joined by oxygen atoms coordinated with Si and Al. Because kaolinite belongs to the triclinic system, it forms hexagonal plates that have a thickness of 7.2 angstroms. The degree of order between the different plates varies according to where the clay is mined. The plates are connected by hydrogen bonds between the OH- groups in the Al – layer and the 0 – atoms in the Si – layer. Kaolin has a hardness of 2 to 2.5 Moh, a density of 2.58 g/cm3, and a refractive index of 1.5%.

(In the above molecular diagram, the sizes of the spheres and the degrees of the angles are not intended to accurately represent the structure.)

Filler Clay Charged Nature and its Consequences

Kaolin clay in its natural state is amphoteric in that it has a cation and an anion exchange capacity. Though the surface is amphoteric, the edges of the clay platelets are positively charged, while the faces are negatively charged. Because of the larger surface area of the faces, the net charge is usually more negative. Because kaolin clay has this amphoteric character, it can be flocculated by either cationic or anionic polyelectrolytes. Most clays that are utilized for filler have been dispersed with anionic polyelectrolytes, mainly polyacrylates and polyphosphates, which are employed in preparation, handling, and storage. These anionic polyelectrolytes adsorb strongly onto particle surfaces, causing clay to have a high negative surface charge that leads to particle-particle repulsion and suspension stability. When filler clay with this high charge capacity is incorporated into the wet end of the paper machine it can greatly effect the behavior of other additives and even the fibers. Clay particles with these anionic dispersing agents can react with cationic retention aids rendering them ineffective. Filler clay addition points can be critical and different systems require different addition points to obtain optimal desired performance. Filler clay with a high charge characteristic will have a high affinity for certain particles and low affinity or repulsion for others. Retention, distribution, formation, drainage, and even sheet strength are properties that can be affected by a filler clay’s charge characteristics and addition points.

Filler Clay Size and its Consequences

Typical kaolin filler clay has an average particle size of 0.2-2.0 microns and a specific surface area of 10-25 m2/g. Structured clays, which include calcined clay, have an average particle size between 0.7 microns and 1.5 microns, but tend to have particle size distributions smaller than standard filler clays. The particle size and shape of both filler clays and structured clays affect a number of papermaking and sheet properties. Filler clay tends to have a very high specific surface area relative to fibers and thus tend to adsorb greater quantities of additives per unit weight than fibers. More surface area means the filler is more difficult to retain and also affects adsorption capacity. These adsorption characteristics will affect retention, sheet two-sidedness, and the effectiveness of other additives in the system. Particle size and shape will also affect interfiber bonding capability and thus sheet strength. One of the most apparent characteristics of filler clay size will be its affect on the optical properties of the sheet.

Methods of Application

Typical filler clay addition levels vary between 3% and 30%, depending on the type of paper being produced and the desired sheet characteristics. Filler clays may be added to systems in one or more addition points. In coated paper mills, broke systems typically supply the most of the filler clay to the sheet and an addition point is also located in the thin stock loop to control the percentage of ash in the sheet. In cases of very high filler loading, multiple addition points may be used to improve retention and sheet quality. Addition points will vary depending on the system configuration, filler loading level, system charge, and desired filler interaction the fibers and other additives. Filler clays are stored and shipped in either a powder form or in typically a 70% solids slurry. Filler clay is usually made-down to a lower solids level before added to the wet end of the paper machine. Most of the filler clay utilized in the United States is mined in Georgia. Papermaking friendly clays are also mined in England, Germany, Czechoslovakia, the Soviet Union, and Australia. Recently much effort has gone into the marketing of what appears to be a premium kaolin clay found in Brazil.

References

Eklund, D., and Lindstrom, T., “Paper Chemistry – An Introduction,” DT Paper Science 1991
Manasso, J. and Mueller, K., “Evolution of High Performance Paper Fillers,” TAPPI 1989
Welch, L., and Dahlquist, R. “Kaolin Clay in the Paper Industry,” revised October 1990

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Martin Hubbe, Sept. 1, 1999

GUAR GUM – A WET-END ADDITIVE FOR PAPER

Why Use Guar Gum?

Cationic guar gum offers three kinds of benefits to papermakers and their customers [1]. In some cases it improves the efficiency of production. In other cases it is used to enhance the dry strength of the product [1-2]. In yet other cases it has the potential to reduce effluent loads [3]. Production efficiency is enhanced, for example, when cationic guar is used as a retention aid during manufacture of containerboard. Users have reported improved drainage; a decrease in web breaks, and reduced deposits.

Cationic guar can be classed as a “beater adhesive” when its purpose is to increase the tensile strength, internal bond, stiffness, or crush resistance of paper and board products [1]. Though the historical term “beater adhesive” suggests that guar products are added before the pulp is refined, it has become much more common to add guar products in the same way as most other dry-strength chemicals – to pulp that already has been refined. The chemical structure of cationic guar gum favors its use in retaining dissolved organic matter that otherwise is likely to contribute to the biological oxygen demand of the liquid effluent from a paper mill [3].

Guar Gum Chemistry

Guar is a linear polymer belonging to the family of polysaccharides [1]. As shown below, the natural polymer has a linear backbone comprised of mannose, and randomly distributed galactose side groups. There is a tendency for the D-galactosyl groups to be arranged in groups of 2 to 4 units on successive mannose groups along a chain.

Unmodified guar is a water-loving polymer having sufficiently high molecular masses that dilute solutions are viscous and slimy. Guar gum is similar to cellulose with respect to how the subunits are linked together. Each mannose unit is linked to the next by means of a beta (1-6) ether. This linkage confers upon guar products a rod-like structure, quite unlike the helical structure of starch in solution. The relatively high affinity of guar products for cellulose surfaces may be due to the similarity in their backbones [1].

Guar Gum’s Charged Nature and its Consequences

Essentially uncharged guar gum products are obtained from the seen of the guar plant cyanoposis tetragonolobus [1]. This pod-bearing, nitrogen fixing legume has been cultivated from thousands of years in India and Pakistan. These same countries remain the primary source of supply.

Cationization is achieved by reaction with 3-chloro, 2-hydroxyproplytrimethylammonium chloride (CHTMA) or 2,3-epolxypropyl-trimethylammonium chloride (EPTMA) [1]. The degree of substitution is typically in the range 0.01 to 0.03. The products are available as dry powders or flakes. Because of the generally anionic colloidal charge of solids in the paper machine wet end, the cationic charge increases the retention of guar and makes it more effective as a strength additive and as a contributor to retention of fines.

Anionic guar products are commercially available. They depend on the presence of cationic materials such as alum for their efficient retention.

Guar Gum’s Size and its Consequences

Product literature for unmodified guar gums list molecular mass values in the range of about 200,000 to 2,000,000 grams per mole. Compared to typical synthetic polyelectrolytes of the type used for retention aids, guar’s molecular mass is not large. But the molecular mass of guar is high relative to amylose, which is perhaps guar’s closest rival in the paper industry. The relatively high mass of guar inhibits its migration into the cell walls of fibers. In theory, the presence of guar at the surface of fibers provides increased area of bonding between the surfaces and promotes a greater degree of hydrogen bonding.

Methods of Application

Powdered guar products require an eductor for efficient dispersal and subsequent dissolution in water at a solids level of 0.75% or less. It is recommended to let the initial solution stir for 30-120 minutes at a temperature of 20 to 50 oC. Certain cationic guar products require acidification or heating to achieve full dissolution. For critical applications, such as fine paper a 100-mesh filter or finer is recommended to eliminate problematic grit and any fish-eyes. For dry strength applications usage levels are typically in the range of zero to 0.2% of product (solids basis). In batch-wise papermaking operations it is common to add the prepared guar during hydropulping. Continuous paper machine systems typically add dry strength additives (such as cationic starch, guar products, or synthetic copolymers) to the thick stock at a location such as the machine chest or stuff box (usually downstream of the main refining.) When it is used as a retention aid it is recommended to add 0.02% to 0.05% (dry basis on product) to the thin stock at a ring-header or quill immediately following the pressure screens. If the wet end is heavily loaded with recirculating fines, then it is recommended to ramp up the dosage very gradually during the first trial run with cationic guar. At excessive levels of addition guar products are known to adversely affect drainage and retention.

References

1. Coco, C. E., “Derivatized guar for improved paper strength and pigment retention,” TAPPI 1980 Retention and Drainage Seminar Notes, Appleton, WI.
2. Dugal, H. S., and Swanson, “Effect of polymer mannan content on the effectiveness of modified guar gum as a beater adhesive,” Tappi J.55 (9): 1362 (1972).
3. Rojas, O. J., Neuman, R. D., and Mills, R. J., “Utilization of guar gums for white-water BOD reduction,” Proc. TAPPI 1998 Papermakers Conf., 145.

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David Szurley, October 1, 1999

PRECIPITATED CALCIUM CARBONATE (PCC) – A WET END ADDITIVE FOR PAPER

Why Use PCC?

PCC was first used in cigarette papers to control porosity and burning rate. In the 50’s and 60’s, wood-free coated mills such as the S. D. Warren Co., converted the wet end chemistry of their basepaper machines to alkaline to enable the use of higher levels of PCC in their coating and therefore took advantage of the benefits of PCC in the wet end [1].

Gill in [1] states that PCC is used as a filler to: (1) Increase brightness and opacity, (2) Improve formation, (3) Provide a smoother surface, (4) Provide enhanced printability, (5) Improve dimensional stability, (6) Provide cost savings when used as a replacement for fiber and (7) Provide a more “environmentally friendly” system reducing corrosion and producing a more environmentally acceptable effluent.

Further, since PCC is precipitated from a controlled chemical reaction the result is a purer product with less contamination and less variability than natural products [1]. In addition, the use of PCC or GCC in paper neutralizes acidic radicals in the atmosphere resulting in improved paper permanence.

PCC Chemistry

PCC is a mineral pigment.

Most PCC is manufactured by bubbling CO2 gas through a solution of milk-of-lime [2]. Important variables in PCC manufacturing are: (1) Starting temperature and temperature profile, (2) Type and degree of agitation, (3) Concentration of the gas, and (4) Types and dosages of various additives and production aids [3]. The quality of the lime and slaking of the CaO to Ca(OH)2 also affect the characteristics and size of the PCC.

PCC is incompatible with the alum in acid papermaking systems resulting in foam, soluble salts and products that are hard to retain. Recent developments in PCC technology include development of treated and neutrally buffered pigments that can extend the use of PCC to machines running acid/neutral furnishes, such as machines using mechanical pulps to manufacture directory and rotogravure grades [4]. PCC solubility increases as pH decreases and temperature decreases. After dissolution, a very tenacious carbonate scale will precipitate out onto machine surfaces when either the environment becomes more alkaline or the temperature increases.

The Charged Nature of PCC and its Consequences

PCC from the batch reactor has a natural positive charge generated by an amorphous layer of calcium ions concentrated at the surface [3]. However, to ensure stability of the 70% solids PCC manufactured by an off-site plant during shipment and storage, the slurry is dispersed with various phosphate and polyacrylate dispersants which adsorb onto the surface of the PCC resulting in a highly anionic charge. On the other hand, on-site PCC is supplied to the host mill at 20% slurry thus eliminating the need for dispersant addition [1].

The zeta potential of PCC is also dependent on specific ionic concentration [1]. Free lime in the PCC can result in high slurry pH thus affecting the pH of the wet end and the system zeta potential.

In use, the slightly cationic charge of the on-site PCC generally results in improved retention as opposed to the highly anionic charge of PCC shipped from off-site plants which necessitates higher levels of cationic chemicals to neutralize the anionic charge, coagulate and retain the pigment particles [1].

PCC Size, Morphology and its Consequences

PCC is available in average particle sizes ranging from 0.3-3.0 microns or even larger. The particle size distribution (PSD) and surface area also affect its performance.

PCC occurs in three crystalline polymorphs: (1) Calcite, (2) Aragonite and (3) Vaterite. Vaterite is a metastable form synthesized in the lab which irreversibly transforms to calcite and aragonite. Aragonite occurs as a needle-like acicular form. The calcite form can occur as prismatic, tabular, cuboid, rhombohedral, scalenohedral habits or in various combinations. The rhombohedral (barrel-shaped) and scalenohedral (rosette shaped) forms are the two types of commercial significance [5].

Particle size and crystal morphology both affect the performance of PCC on the paper machine, and determine its effect on paper properties.

For scalenohedral PCC (S-PCC), increasing the average particle size and, thus, reducing the surface area increased drainage. [6]

From a study by Gill reported in [6], increasing particle size did not improve retention significantly, it was the particle charge that had the biggest effect.

The crystal morphology also affects press solids. Fairchild and Clark in [7] report on a study at STFI where press solids increased from 40.2% up to 42.4% as the blend of S-PCC and rhombohedral PCC (R-PCC) was changed from 100% S-PCC to 100% R-PCC.

In general, as the particle size of PCC increases, retention increases, abrasion increases, the deleterious effect on fiber-fiber bonding decreases, light scattering decreases, bulk increases and the sheet becomes more porous.

Scalenohedral PCC has better scattering and a more deleterious effect on debonding than rhombohedral PCC.

At equal filler loading, PCC has higher bulk, lower breaking length, lower burst, lower bond and higher brightness than ground calcium carbonate (GCC) [8].

Method of Application

Prior to the ’60’s, beater addition of dry fillers was the most common method of application. Alternatively, the dry PCC for wet end addition could be slurried at 20% solids with medium to high shear dispersers, filtered, and pumped into storage tanks. In the ’70’s and ’80’s, to take advantage of the conveniences handling, storage and pumping slurries, the most common method of distribution of PCC from the manufacturer to the paper mill was as a slurry having 70% solids.

Beginning in the 70’s, on-site satellite PCC plants were built at host paper plants. The host plant provides CO2 gas from the lime kiln or power boilers to the PCC plant as well as utilities including power and water. On-site PCC provides the papermaker with the flexibility to tailor-make various PCC’s with different crystal habits and particle sizes to meet specific grade requirements [6].

Low solids PCC is usually stored in tile or stainless steel tanks from where it is distributed to the wet end of the machine. Most wet end additives are filtered prior to injection into the stock system.

Addition points for PCC can include addition to the beater dump chest, the blend chest, or in the thin stock system, usually into the suction of the fan pump. If TiO2 is also used as a wet end filler, suppliers recommend adding the PCC first (such as into the suction of the machine chest pump) to eliminate the floccing of TiO2 by the PCC and the resultant lower light scattering.

PCC can either be added as a percentage of the thick stock mass flow rate, i.e. as pounds of filler per ton of fiber, or the filler addition rate may be controlled by an on-line ash sensor using a sheet ash target.

The properties exhibited by PCC in paper are dependent not only on the characteristics of the filler, but also on how the PCC is applied. The type and dosage of the retention aids, as well as the addition point of the PCC affect its’ performance. One cannot generalize on the retention system that may be the best for each paper machine wet end system and the specific requirements of the grade.

References
1. Gill, R.A., “Precipitated CaCO3 Fillers for Papermaking”, Pigments for Paper, Tappi Press 1997.
2. Laine, J., “Manufacture of precipitated calcium carbonate”, Paperi ja Puu, No. 11, 1980, 725.
3. Clark, P.C. and Gill, R.A., Chapter 14 Precipitated Calcium Carbonate in Retention of Fines and Fillers During Papermaking, J.M. Gess, TAPPI Press, 1998.
4. Snowden, K.J., Rodriguez, J.M. and Fink, R., “Neutrally buffered precipitated calcium carbonate for use in newsprint mill where pH is maintained at levels below 7 without need for adding acid to the paper machine”, 1998 Coating/Papermakers Conference proceedings, Tappi Press, 469-480.
5. Hagemayer, R.W., Chapter 5-Calcium Carbonate, from Pigments for Paper, Tappi Press.
6. Gill, R.A., “The retention, drainage and optical performance of on-site synthesized PCC fillers”, Pulp & Paper Canada, 91:9 (1990) T342-T346.
7. Fairchild, G.H. and Clark, E.B., “PCC morphology and particle size effects in alkaline paper”, 50th Appita Annual General Conference, Vol. 2, 1996.
8. Han, Y-R and Seo, Y-B, “Effect of particle shape and size of calcium carbonate on physical properties of paper”, J. of Korea Tappi, 29(1) 1997.

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Julie Dellemann, September 28, 1999

Polyaminoamide-epichlorohydrin (PAE resin) – A WET END ADDITIVE FOR PAPER

Why use PAE resin?

A wet strength resin must perform two functions: 1) Adhere to the pulp (by adsorption or deposition) 2) Form a network that represses swelling of cellulose fibers, thus inhibiting the separation of fiber-fiber contacts when paper is rewetted. Wet strength resins share four attributes. 1) Water soluble (or water dispersible) thus allowing even dispersion and effective distribution on the fibers. 2) Cationic, thus facilitating adsorption onto anionic pulp fibers, usually by an ion-exchange mechanism. 3) Polymeric, with high-molecular-weight-polymers being more completely adsorbed and forming stronger bonds. 4)Reactive, thus promoting formation of cross linked networks with themselves or with cellulose that resist dissolution in water [1]. High levels of wet strength can be achieved with these resins, along with promoting good crepe in the drier section. Today, PAE (polyaminoamide-epichlorohydrin), resins are used extensively in practically all types of wet strength papers. Major examples include: household products such as paper towels, napkins, and facial tissue; packaging materials, such as liquid packaging, corrugated boxes, and paper bags; and specialties such as photographic papers, wrappings and disposables. PAE resins are usually recommended for coffee filter papers. The resins are not recommended for use with fluorescent whitening agents because of their quenching effect [2]. PAE resins are best known to papermakers by their trade names, including Kymene, Discostrength, Cascamid, and Amres.

PAE Chemistry

The preparation of polyamide resins is similar to that used in preparing 66 Nylon. A dibasic acid is condensed with diethylene triamine to give a water-soluble polyamide. The secondary amine groups of the polyamide are then alkylated with epichlorohydrin, and a number of reactions take place. Predominantly, tertiary amino-chlorohydrin groups are formed, which self-alkylate to form 3-hydroxyazetidinium groups which are responsible for the reactivity and the cationic character of this wet-strength resin. The azetidinium group will slowly react with water to form a non-reactive diol. Treatment with epichlorohydrin leads to some crosslinking and care has to be taken to control this and to retain water solubility [2].

PAE’s Charged Nature and its Consequences

Pahl and Espy have reviewed some of the practical aspects of using PAE resins in papermaking. Being highly charged cationic polymers, PAE resins are substantive to negatively charged fibres and are rapidly adsorbed when added to a papermaking furnish. At low dosages there is a steady increase in the wet strength obtained, but a point is reached where resin retention starts to decrease as the adsorption sites on the fibres (carboxyl groups) diminish and the furnish becomes less negatively charged. The carboxyl content of the pulp affects performance of the resin, and a higher wet strength can be achieved with unbleached kraft than bleached kraft. The most difficult to treat are bleached sulphite pulps due to the lower carboxyl content. Performance is affected by refining due to an increase in surface area. The effect is the greatest at higher dosages where more resin can be adsorbed by the refined pulp [2].

PAE resins are sensitive to anionic interfering substances whether they are naturally occurring (lignosulphonates) or anionic chemical additives (e.g. anionic dyes used to dye tissue). In both cases it is necessary either to add more resin to obtain the required effect, or use a high charge density cationic polymer to pretreat the pulp [2].

PAE Resin’s Size and Consequences

The resulting product consists of relatively low molecular weight polyamide backbones with many reactive side chains. Chloride counter-ions are formed as a result of epoxidation and, at the end of the manufacturing process, the resin is usually acidified to provide stability against gelation during storage. The acidity and presence of chloride ions requires that a high quality stainless steel or suitable plastic containers are used for storage [2]. The wet tensile strength of paper made with polyamide-epichlorohydrin (PAE) was found to depend on the resin’s relative equivalent weight based on azetidinium, the most reactive cross linking group in the resin. Molecular weight is an important characteristic of a PAE resin that greatly affects its performance, such as adsorption onto cellulose and other solid substrates. PAE resins are typically prepared by reacting a polyaminoamide with epichlorohydrin until a solution viscosity is reached that suggests an “effective molecular weight” (before thermosetting on paper) for developing wet-strength properties. The relative weight of the resins were determined by size exclusion chromatography (SEC) and the relative azetidinium content was measured by nuclear magnetic resonance (NMR) spectroscopy [3].

Methods of Application

Polyamide resins are provided at 12.5-30% solids, with neat resin pH between 3.0-6.0, requiring an acid resistant system. These resins may be used in systems with pH 5-9, though resin efficiency is best between pH 6.5-8.0. On machine cure is typically 50-60% at this pH range, with the remainder coming as the reel cools, usually within 24 hours [4].
The wet strength additive is unstable and loses activity on storage. Therefore it should be titrated for “active solids” content at the time of use to guarantee consistent product quality in production [5].

References

1. Espy, Herbert., “The mechanism of wet-strength development in paper: a review,”
Tappi J.78 (4): 90-99 (1995).
2. Dunlap-Jones, N., “Wet end Chemistry,” in Paper Chemistry, Chapman and Hall, New York: e.d. J.C. Roberts 1991 82-84.
3. Fischer, Steven A., “Structure and wet strength activity of polyaminoamide epichlorohydrin resins having azetidinium functionality,” Tappi J.79 (11) : 179-186 (Nov. 1996).
4. “Lissa” Dulany, Margaret A., “Wet strength Resin Chemistry and Regulatory Considerations,” TAPPI 1989 Papermakers Conference, 373.
5. Rahman, Matiur., and Turbak, Albin F., “The structure of kymene,” TAPPI Proceedings 1991 Nonwovens Conference., 299.

Semester Courses

Wet end and polymer chemistry (PSE 322): (each Fall semester, undergraduate)

PSE 322 001 Course Syllabus

PSE 322 001 – Wet End & Polymer Chemistry

Course Description

Learning Outcomes

Course Structure

Course Policies

Instructors

Course Meetings

Lecture

Laboratory

Course Materials

Textbooks

Expenses

Materials

Transportation

Safety & Risk Assumptions

Grading

Grade Components

Requirements for Credit-Only (S/U) Grading

Requirements for Auditors (AU)

Policies on Incomplete Grades

Late Assignments

Attendance Policy

Attendance Policy

Absences Policy

Makeup Work Policy

Additional Excuses Policy

Academic Integrity

Academic Integrity

Academic Honesty

Honor Pledge

Digital Course Components

Accommodations for Disabilities

Non-Discrimination Policy

Course Schedule

Lecture MWF 11am – 11:50 am — Session 1: Introduction — 08/10/2020 – 08/10/2020

Lecture MWF 11am – 11:50 am — Session 2: Stock preparation — 08/12/2020 – 08/12/2020

Lecture MWF 11am – 11:50 am — Session 3: Paper machine system — 08/14/2020 – 08/14/2020

Lecture MWF 11am – 11:50 am — Session 4: Paper forming & drying — 08/17/2020 – 08/17/2020

Lecture MWF 11am – 11:50 am — Session 5: Aqueous chemistry — 08/19/2020 – 08/19/2020

Lecture MWF 11am – 11:50 am — Session 6: Charge of a fiber surface — 08/21/2020 – 08/21/2020

Lecture MWF 11am – 11:50 am — Session 7: Polymers & polymerization — 08/24/2020 – 08/24/2020

Lecture MWF 11am – 11:50 am — Session 8: Retention chemistry — 08/26/2020 – 08/26/2020

Lecture MWF 11am – 11:50 am — Session 9: Retention of fines — 08/28/2020 – 08/28/2020

Lecture MWF 11am – 11:50 am — Session 10: Retention mechanisms — 08/31/2020 – 08/31/2020

Lecture MWF 11am – 11:50 am — Session 11: Time effects — 09/02/2020 – 09/02/2020

Lecture MWF 11am – 11:50 am — Session 12: Surface chemistry — 09/04/2020 – 09/04/2020

Lecture MWF 11am – 11:50 am — Session 13: Forces of interacton — 09/07/2020 – 09/07/2020

Lecture MWF 11am – 11:50 am — Session 14: Stability and coagulation — 09/09/2020 – 09/09/2020

Lecture MWF 11am – 11:50 am — Session 15: Process additives — 09/11/2020 – 09/11/2020

Lecture MWF 11am – 11:50 am — Session 16: Chemical preparation — 09/14/2020 – 09/14/2020

Lecture MWF 11am – 11:50 am — Session 17: Functional additives — 09/16/2020 – 09/16/2020

Lecture MWF 11am – 11:50 am — Session 18: Rosin sizing systems — 09/18/2020 – 09/18/2020

Lecture MWF 11am – 11:50 am — Session 19: ASA, AKD, & surface sizing — 09/21/2020 – 09/21/2020

Lecture MWF 11am – 11:50 am — Session 20: Starch preparation — 09/23/2020 – 09/23/2020

Lecture MWF 11am – 11:50 am — Session 21: Starch systems for strength — 09/25/2020 – 09/25/2020

Lecture MWF 11am – 11:50 am — Session 22: Wet strength agents — 09/28/2020 – 09/28/2020

Lecture MWF 11am – 11:50 am — Session 23: Dyes and paper’s color — 09/30/2020 – 09/30/2020

Lecture MWF 11am – 11:50 am — Session 24: Fillers for paper — 10/02/2020 – 10/02/2020

Lecture MWF 11am – 11:50 am — Session 25: Retention aid theory — 10/05/2020 – 10/05/2020

Lecture MWF 11am – 11:50 am — Session 26: Drainage enhancement — 10/07/2020 – 10/07/2020

Lecture MWF 11am – 11:50 am — Session 27: Advanced dewatering systems — 10/09/2020 – 10/09/2020

Lecture MWF 11am – 11:50 am — Session 28: Uniformity of formation — 10/12/2020 – 10/12/2020

Lecture MWF 11am – 11:50 am — Session 29: Effects of anionic colloids and polymers — 10/14/2020 – 10/14/2020

Lecture MWF 11am – 11:50 am — Session 30: Cationic demand testing — 10/16/2020 – 10/16/2020

Lecture MWF 11am – 11:50 am — Session 31: Analysis of deposits — 10/19/2020 – 10/19/2020

Lecture MWF 11am – 11:50 am — Session 32: Anti-deposit strategies — 10/21/2020 – 10/21/2020

Lecture MWF 11am – 11:50 am — Session 33: Foam causes and effects — 10/23/2020 – 10/23/2020

Lecture MWF 11am – 11:50 am — Session 34: Foam and problem solving — 10/26/2020 – 10/26/2020

Lecture MWF 11am – 11:50 am — Session 35: Coating and rheology — 10/28/2020 – 10/28/2020

Lecture MWF 11am – 11:50 am — Session 36: Coating optimization — 10/30/2020 – 10/30/2020

Lecture MWF 11am – 11:50 am — Session 37: Paper recycling steps — 11/02/2020 – 11/02/2020

Lecture MWF 11am – 11:50 am — Session 38: Strategies for paper recycling — 11/04/2020 – 11/04/2020

Lecture MWF 11am – 11:50 am — Session 39: Process control issues — 11/06/2020 – 11/06/2020

Lecture MWF 11am – 11:50 am — Session 40: Wastewater treatment — 11/09/2020 – 11/09/2020

Lecture MWF 11am – 11:50 am — Session 41: Sustainability and the environment — 11/11/2020 – 11/11/2020

Special Provisions for the COVID19 Pandemic

Chemical principles for the papermaking process engineer (FB 522) (each Fall semester, distance edition masters