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Summaries of August 2005 peer-reviewed papers.

TAPPI JOURNAL is a monthly publication that includes full-text, peer reviewed research papers exploring every aspect of pulp and papermaking. Each issue presents technically sound, applications-based research; special insights from the authors; and more. TAPPI Membership includes access to all TAPPI JOURNAL content online at www.tappi.org. In addition, convenient print and electronic subscription options are available; TAPPI members receive substantial subscription discounts.

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BLEACHING

STATISTICAL DETERMINATION OF THE EFFECTS OF ENZYMES ON BLEACHED PULP YIELD

APPLICATION: Knowing the potential effects of bleaching enzymes on pulp yield allows mills to make improved economic decisions about enzyme use.

Since the first commercial application of bleaching enzymes, their potential effect on pulp yield has been debated. Enzymes work by selectively removing various hemicellulose constituent of the fiber off the surface of the pulp. Older enzyme preparations contained extensive quantities of cellulases that reduced yield. Modern preparations are virtually cellulase free, but still rely upon xylanase to remove xylan from the fiber surface. Much or possibly all of this xylan would be removed in chlorine dioxide bleaching anyway. Thus, the debate as to the affect of enzymes on pulp yield continues.

For this study, we statistically analyzed several years of pulp yield data from an integrated bleached kraft mill. The data included yields obtained with and without enzymes. No statistically significant effect on pulp yield was found from enzyme usage. Variability in the results suggested interference from the industrial process, so new data were obtained. Several years of effluent BOD data from two different market pulp mills were obtained as a potential surrogate for pulp yield. Market pulp mill data were used to avoid interference of paper machine operation on BOD data. Statistical analysis of these data suggested the use of enzymes in pulp bleaching does not affect hardwood pulp yield. The data were somewhat inconclusive with respect to softwood. The softwood runs with enzymes had higher production rates than the runs without enzymes. These higher production rates could have altered the BOD levels sufficiently to explain these results. We concluded that the use of enzymes in pulp bleaching does not increase pulp yield and, at worst, it has an exceedingly small negative effect. View this paper online at http://www.tappi.org/index.asp?pid=32881&ch=1.

Peter W. Hart is with MeadWestvaco Corp, Fiber Development Group, Chillicothe, Ohio, USA; Harry F. Sharp, III is with Georgia State University, Department of Math and Statistics, Atlanta, Georgia, USA. Email Hart at pwh3@meadwestvaco.com.

PAPERMAKING

THE RELATIONSHIP BETWEEN ENERGY REQUIREMENT AND BARRIER PROPERTIES IN THE PRODUCTION OF GREASEPROOF PAPER

APPLICATION: This study shows product- and process-specific relationships between energy requirements and barrier properties in the production of greaseproof paper.

A full-scale mill trial surveyed the energy required to produce greaseproof paper. The furnishes studied were a 100% sulfite pulp and a 50/50 sulfite/sulfate pulp, refined to two freeness levels. The papers produced were then calendered at two line-loads using a soft-nip laboratory calender and tested with respect to air permeability, water vapor transmission rate, grease resistance, tear strength, and tensile strength.

The least energy-demanding (beating + drying) process was that used to produce the paper from 100% sulfite pulp of low freeness. This paper exhibited approximately the same water vapor transmission rate and grease resistance as the paper made from high freeness 100% sulfite pulp. The papers produced from 50/50 sulfite/sulfate furnish exhibited poorer barrier properties. The mechanical properties of all the papers produced satisfied the specifications for standard greaseproof paper. Beating improved the barrier properties, but required additional energy. Results showed that the same or better barrier properties can be achieved with calendering or surface coating, with lower energy input.

We also found that the furnish composition and beating and the calendering affected air permeability in different ways. The former affected both the pore volume fraction and the pore dimensions, while the latter mainly affected the pore volume fraction. View this paper online at http://www.tappi.org/index.asp?pid=32882&ch=1

Henrik Kjellgren is with Nordic Paper Seffle AB, Saffle, Sweden; Gunnar Engstrom is with Karlstad University, Department of Chemical Engineering, Karlstad, Sweden. Email Kjellgren at henrik.kjellgren@nordic-paper.com and Engstrom at gunnar.engstrom@kau.se.

RECYCLING

PSA PROPERTIES AND SCREENABILITY IN PAPER RECYCLING

APPLICATION: A fundamental understanding about the relationships between PSA properties and screenability can give PSA producers better insight into the design of new screenable PSAs.

Stickies arise mainly from pressure-sensitive adhesives (PSA). Producing screenable PSAs has been considered as a solution to the stickies problem in paper recycling. For PSAs to be screenable, they must form particles large enough to be caught by the cleaning screen. It would be desirable to produce PSAs that could be totally screened out during the screening process. Toward that goal, we explored the fundamental relationships between PSA properties and screenability.

Increased tack generally increases PSA screenability because tacky polymer particles adhere together more easily than do nontacky particles. Also, higher tack means the adhesive has greater ability to adsorb energy in deformation. Therefore, the PSA with higher tack does not easily break down into tiny particles during the repulping action.

PSAs with higher peel strength can form large particles with each other, making them easier to screen. A PSA with high elongation generally has good screenability because this kind of PSA can absorb more energy during repulping and does not easily break down into small particles. Both tensile and shear strength, which are the measure of the PSA internal resistance to force, have only marginal effects on screenability.

Generally, no single property is enough to determine the PSA screenability. It would be ideal for the PSA to have high tack, high peel adhesion, and good deformation ability. View this paper online at http://www.tappi.org/index.asp?pid=32883&ch=1

Yulin Zhao is with the Institute of Paper Science and Technology, Georgia Institute of Technology, 500 10th Street NW, Atlanta, GA 30332-0100. Zegui Yan is senior technical specialist at Franklin International, 2020 Bruck Street, Columbus, Ohio 43207. Yulin Deng is with the School of Chemical and Biomolecular Engineering at the Georgia Institute of Technology. Email Zhao at yulin.zhao@ipst.gatech.edu.

COATING

CHITOSAN AS A COATING ADDITIVE IN PAPER AND PAPERBOARD

APPLICATION: Coating paper with chitosan, an abundant material, improves its bending stiffness and MD tensile strength.

Recently, environmental regulations have become more important for fibrous-based products, especially for packaging. Consequently, the paper and paperboard industry is searching for more environmentally friendly products, such as biodegradable paper coating materials. Chitosan is an abundant, biodegradable product that can be used as pre-coating to give better adhesion and improve barrier properties.

We studied a chitosan from natural polysaccharide as a potential coating additive. We studied the mechanical and optical properties of chitosan-coated paper sheets. Bending strength was found to improve significantly, but tear index and tensile index improved only slightly. Water absorption was slightly reduced.

Chitosan has good adhesion onto cellulose and could be used as an environmentally friendly coating material. In future studies, we expect to concentrate on the odor and oxygen barrier properties of chitosan. View this paper online at http://www.tappi.org/index.asp?pid=32884&ch=1

Jurkka Kuusipalo and Marikki Kaunisto are with Tampere University of Technology, Institute of Paper Converting, Tampere, Finland. Antti Laine and Minna Kellomaki are with Tampere University of Technology, Institute of Biomaterials, Tampere, Finland. Email Kuusipalo at jurkka.kuusipalo@tut.fi

NONWOOD PULPING

REDUCING SHIVES LEVEL IN NONWOOD CHEMITHERMOMECHANICAL PULP

APPLICATION: This study suggests ways to improve wheat straw pulp properties for production of test liner and corrugating medium paper.

Packages Ltd. in Pakistan built the first high-yield pulping plant based on wheat straw using a unique pulping technique to produce a pulp ideally suited for manufacturing test liner and corrugating medium paper. This paper includes an overview of the mill's chemithermomechanical (CTMP) pulping process and associated pulp properties. Using this unique process, agricultural waste can be used to produce high strength board.

CTMP pulp from straw has more water-soluble compounds and many fines are generated during processing. Consequently, straw has lower yield than does wood. The straw pulp obtained from the CTMP process is characterized by high shives, high long fiber fraction, high bulk, high stiffness, high ring crush strength, and low smoothness. High stiffness and ring crush make it extremely suitable for high compressive strength-bearing corrugated containers. But the higher shives level is a great problem. Numerous studies have examined ways to reduce shives levels in this high strength pulp.

This paper describes a process by which the shives level is reduced without affecting pulp strength properties. In the first trial, differing chemical charges are used to reduce shive levels, without effect. Another trial reduced shives levels to a minimum by refining pulp at low consistency. Using this technique, we are quite successful in reducing this unwanted material from pulp. Refining at low consistency reduces energy consumption. View this paper online at http://www.tappi.org/index.asp?pid=32885&ch=1

Babar Ali conducts research and development at Packages Limited, Shahrah-E-Roomi, P.O. Amer Sidhu, Lahore 54760, Pakistan. Email Ali at babarali@packages.com.pk.

COATINGS

COMPARATIVE EVALUATION OF THE POTENTIAL FOR WAX-ALTERNATIVE PACKAGING COATINGS

APPLICATION: Box plant operators and linerboard producers may be able to use alternative coatings to produce wax-free corrugated containers.

Widely used for transporting produce and meat, waxed corrugated containers are not without problems as a reusable source of pulp. Alternatives to wax are being pursued by several companies. Are the boxes made with these products recyclable? Do they perform on a par with boxes curtain-coated with wax? For these products to gain acceptance, these kinds of questions need to be answered in objective studies.

The purpose of this IPST study was to analyze these products for their suitability as replacements for wax. Numerous trials were conducted. The wax-replacement containers consisted of coated linerboards and a treated, wet-resistant corrugating medium. In the best-case scenario tested, a wax-replacement container retained 34% of its original BCT, as opposed to 65% for a curtain-coated box, after exposure to simulated conditions for wet use. Some applications may not require as much water resistance as wax provides. On the other hand, additional treatment to improve performance would be expected to increase the cost.

In terms of repulping the containers, the commercial polymer formulations evaluated did not appear to present difficulties. However, some loss of sheet strength can be expected. View this paper online at http://www.tappi.org/index.asp?pid=32886&ch=1

Roman E. Popil is a senior research scientist, and Michael Schaepe is a senior research engineer at The Institute of Paper Science and Technology, Georgia Institute of Technology, 500 10th St. NW, Atlanta, GA 30332. Email Popil at roman.popil@ipst.edu.
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Title Annotation:TAPPI JOURNAL SUMMARIES
Publication:Solutions - for People, Processes and Paper
Date:Aug 1, 2005
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