Introducing North Carolina State University's
Wet-End Chemistry Program


Martin A. Hubbe
Associate Professor
Buckman Distinguished Scientist
NCSU, Dept. of Wood & Paper Science
Box 8005; Raleigh, NC 27695-8005
Voice: (919) 513-3022; FAX: (919) 515-6302
E-Mail: m_hubbe@ncsu.edu
Website: http://www4.ncsu.edu/~hubbe


A critical need

How we use knowledge in the years ahead may be the key to survival of a strong paper industry. As noted by Bob Buckman of Buckman Laboratories, Inc., it is no longer enough just to develop modified products and processes by gradual evolution. Rather, the future demands that we manage knowledge - and that we digest and communicate that knowledge so that it can be put to use. The goal is to substitute knowledge in place of cost.

Nowhere is the need for technological innovation more critical than in wet-end chemistry. Fiber furnish and process water quality are changing. Factors prompting these changes include recycling and reductions in fresh water use. New instrumenta-tion and chemical additives are becoming available. As though that weren't enough, competition requires us to produce ever more uniform products, using an increasing level of automation.

Realizing the importance of wet-end chemistry to the future of our industry, Bob Buckman and his wife Joyce Mollerup gave $1 million dollars to endow a new program in Wet-End Chemistry education and research at North Carolina State University. The generous gift has enabled the Wood and Paper Science Dept. at NCSU to offer the new program that is described in this flier and on our website (see above).

Wet-end chemistry program

Our new program's mission is to serve the paper industry through wet-end-chemistry-related research and education. We believe that the two elements - research and education - have a synergistic relationship. Our goal is to provide the industry with the following kinds of benefits:

1. Solutions to technical problems
2. Talented people who have come through our undergraduate and graduate programs
3. Short courses tailored to meet the industrial needs
4. Initiatives in distance-learning, including the first-in-world MS-level distance course in wet-end chemistry (Fall 1999)
Research Priorities

The following set of research priorities was developed after extensive consultation. Many thanks are owed to those who helped us with their comments. Input came from people in paper companies, chemical suppliers to the paper industry, and instrument vendor companies. And maybe from you, too. If you have a "pet" project in wet-end chemistry that you think ought to be carried out at a university, please contact Marty Hubbe at (919) 513-3022 or m_hubbe@ncsu.edu.

1. Strategies for dealing with changing conditions of the fiber furnish and the impact of such changes on the performance of wet-end chemicals.

2. Wet-end sensing technology related to the automatic control of chemical additions.

3. Strategies to address strength and drainage issues with recycled fibers.

NC State Background

NC State is well known as an active and innovative partner of the pulp and paper industry. Our Wood and Paper Science program has 184 undergraduate and 24 graduate students. We have 13 full time pulp and paper faculty. Our faculty have established a worldwide reputation in the areas of pulping, bleaching, recycling, and other branches of pulp and paper technology.

Preventing strength loss

Which would you rather use as a source of fiber for papermaking, never-dried kraft fiber or repulped broke? Think of the benefits that one ought to get from using broke:
· Refining energy already has been put into the fibers.
· Strength additives such as cationic starch already have been paid for.
· The composition may be close to that of the grade you are making at the moment.

Did anyone change their vote? The awkward truth about kraft pulps is that they offer truly superior strength properties… (ahem)…. only the first time that they are used. Refined kraft fibers lose a lot of bonding potential the first time that they are dried. This fact is illustrated in Fig. 1.

Ellis data: Recycled pulp is lower in tensile strength at all freeness values.

As shown by the upper curve in Fig. 1, the never-dried pulp achieved tensile strength levels in excess of 6 km breaking length when the pulp was refined enough to decrease the freeness below 600 ml CSF. Results were much less favorable when the once-dried sheets were reslurried and formed into a first generation of recycled paper (curve no. 1). The strength was reduced relative to the refining curve for the virgin pulp. Further refining of the recycled pulp hurt the freeness without restoring most of the lost strength. It is worth noting that most of the strength loss occurred during the first cycle of drying.

Now let's compare kraft pulp with a high-yield pulp. As shown in Fig. 2, mechanical pulps usually do not suffer such a severe relative strength loss when they are first formed into paper.

Howard and Bichard data:  recycling weakens kraft pulp but not TMP.

Past efforts to address strength issues mainly have involved chemical treatments after the damage already has been done. Those few published studies involving never-dried pulps involved solvent-based chemical derivatization of the fiber surfaces. Our research interests are limited to strategies than can be implemented with existing equipment in a paper mill. Based on applications of colloidal chemistry and papermaking technology we have identified candidate materials that hold promise to prevent strength loss from happening in the first place. International Paper and Hercules have joined with us in offering this work as an Agenda 2020 project proposal. Out of a field of about 400 proposals, ours was among the 24 funded.

Charge analysis

When you stop to think about how many different cationic and anionic chemicals are added to a paper machine system it is amazing that the process works at all. Some paper mills have made great progress in achieving more effective and predictable results from their use of charged additives. Words such as "charge" and "zeta potential" still make many paper-makers uneasy. But some papermakers are starting to turn measurements of these quantities into increased profits.

Our research initiative in this area involves two very promising technologies, each of which has the potential to revolutionize the control of additive flows. Potential benefits include reduced chemical costs, more uniform products, and improvements in productivity. One of the technologies in question is known to the industry as "streaming current" (SC). The other method is known as fiber-pad streaming potential (SP).

As shown in Fig. 3, the SC method is based on the electrical signal generated when a Teflon® piston reciprocates within a closely spaced Teflon® cylinder.

Streaming current detector cell

The mechanical simplicity and rugged nature of SC-type devices has prompted their use in hundreds of paper mills around the world. Within the last five years many mills have begun to use on-line SC devices with titration procedures to automatically determine the level of colloidal charge in process water streams. The results are being used to make decisions, each involving millions of dollars of daily production.

A downside of the SC method always has been its lack of a firm theoretical foundation. In effect, users of the SC method are forced to accept a hypothesis that colloidal materials in the white water are able to adsorb onto the Teflon® probe surfaces. There has been no published study providing users with guidance as to what types of paper machine process samples can be used, and when is the hypothesis likely to be valid.

To help set priorities for our research work with SC technology we have held discussions with all six of the companies that have considered marketing their SC devices within North America. Each company helped us by completing an opinion survey of possible research priorities. The results were unambiguous; there is a clear mandate to investigate possible effects of chemicals that have potential to interfere with the test results.

The fiber-pad streaming potential (SP) method is diagramed in Fig. 4. The flow of water through a fiber pad produces an electrical potential that can be evaluated between two electrodes. Because the signal arises from events at the surfaces of the fibers themselves, the technique offers great promise. In certain mills on-line SP devices have been used for early detection and correction of changes likely to cause process upsets.

Fiber-pad streaming potential schematic

Relative to its potential value, industry has been slow to adopt SP technology. Signal interpretation has proven difficult in many cases. Figure 5 shows data obtained during a paper machine run. No study has fully explained or controlled the high-frequency variations in data of this type. There is evidence that some of the apparent noise is telling us about the inadequacy of current mixing strategies of chemical additives with pulp. Alternatively, if the method can be modified to remove the high-frequency variations, then it may be possible to extend applications of on-line SP devices over a wider range of paper grades.

Streaming potential data versus time in a process

Performance of wet-end additives in difficult furnish

It's been said that only a full-scale trial on a paper machine will convince the skeptics. A problem with most lab-scale and pilot-scale evaluations is that they fail often to match the contact times, stock consistencies, and levels of hydrodynamic shear found in real paper machine systems. These differences get important when we use a sequence of papermaking additives and when the pulp furnish already is rich with salts, surfactants, and colloidal materials. Unfortunately, a commercial paper machine is an expensive place to run trials in the interest of science.

Our idea of using a flow system to study pulp flocculation is not new. Much progress has occurred recently with image analysis and laser light scattering. Our research will depart from previous studies in the following respects:
· Emphasis placed on difficult furnish conditions and the effects of chemical additives
· Several on-line measuring strategies used in a new way
· Sensing devices will include on-line floc strength, streaming potential, drainage, and fine-particle retention (via turbidity).

Fig. 6 shows a sketch of the flow system we are in the process of putting together. Among the first studies with this device will be an analysis of how retention, drainage, and the charge balance are affected when the same white water is used repeatedly to reslurry wastepaper pulp and form it into recycled paper. The floc strength and floc size modules already have been developed and used in studies of floc stability and reversibility when exposed to shear.

Laboratory settup for flow experiments

New courses at NC State

Most readers will be aware that NC State's Department of Wood and Paper Science offers full undergraduate and graduate degree programs. Over the years we have built up an international reputation. As has been mentioned, our faculty has been recognized for leadership in the areas of pulping, bleaching, and paper recycling technologies. In addition, there are two new elements worth noting:

Short Courses

In June 1999 we rolled out the first edition of a three-day, hands-on short course in the area of Wet-End Chemistry. Our target audience for this course is the paper mill process engineer or technical sales rep taking on new responsibilities in the use of wet-end additives. Contact us to learn more.

A related course segment has been developed for the Chemistry of Wet-Laid Nonwovens. The segment was offered for the first time this April 21-22 as part of a Nonwovens Short Course open to members of the Nonwovens Cooperative, through the College of Textiles here at NCSU.

Don't overlook the other well-established short courses offered periodically at our Raleigh, NC facility. These include our five-day Introduction to Pulp and Paper, Hands-On Course. Send an E-Mail if you want to be alerted when the next such course is going to be held.

Consulting programs

Wet-end chemistry on-site consulting is available. Areas of teaching and/or consulting include wet-end chemistry, optimum use of chemical additives, colloidal chemistry, and optical properties. Please call to determine availability. Allow extra time if you need a customized short course at your facility. Additional information is given in our website.
Pilot Plant Technical Service

Our pilot facilities include a wide range of pulping, bleaching, and separation technologies from chipping to the finished sheet. A new 30,000 square foot addition to our pilot plant includes a Fourdrinier paper machine having a 12-inch deckle width and a speed range of 40 to 150 feet per minute. The machine is equipped with a wet-end shake, size press, calender stack, and Allen-Bradley controls. The machine is used for research, as well as for training and contract trials. Contact Med Byrd at (919) 515-5790 to learn more about technical service options.

You can be a part of our research

Companies can join with us to achieve needed innovations. For us the infusion of ideas from industry can be very helpful and can provide focus. Also we can use seed money to attract grant support for projects that we believe are worthy of your support. In-kind support can be just as valuable. For example, we can use a loan of a sensing device in cases where it meets our research needs. If your organization has some ideas, let's discuss them and see if they can fit into our educational and research goals.

While all of our work is open and publishable, there can be advantages of co-sponsorship. Research partners have the opportunity to help set project plans and priorities. There are opportunities for participants to hold exclusive licenses of any patentable technology developed.

Program manager

Let me close with a summary of my background. Maine is my home state. I did not necessarily intend to follow the family tradition and go into papermaking. But Millinocket at the time I was growing up had only 8000 people and eleven running Fourdrinier paper machines. I got hooked. My degrees are from Colby College (BA. Chem.), the Inst. of Paper Chem. (MS., Paper Technology), and Clarkson University (PhD., Colloidal Chemistry). After graduation I worked two years at American Cyanamid (now Cytec) developing alkaline sizing formulations. Before joining NCSU I spent twelve years with International Paper at their Corporate Research Center. My responsibilities included product development, alkaline conversions, color technology, and optimization of wet-end chemistry.

The other thing I did at International Paper was teach. My wet-end chemistry course was offered at least five times a year to groups of paper mills people. I also offered training in optical properties and wet-laid nonwovens. As I look back at it, those experiences played a big role in my decision to join a university. My goal is to share some of what I learned in industry with students. A further goal is to bring some solutions back from the university. I hope that you will join with us in helping develop and implement technical solutions.

I'd love to hear from you. You can call me at (919) 513-3022. Our website is http://www4.ncsu.edu/~hubbe, and you can E-mail me at m_hubbe@ncsu.edu.