Summaries of September 2005 peer-reviewed papers.

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POLYMER PRETREATMENT 

DEPOSITION OF POLYELECTROLYTE COMPLEXES AS A MECHANISM FOR DEVELOPING PAPER DRY STRENGTH

APPLICATION: Dual treatment with dry-strength polymers may boost the strength of paper made from recycled copy paper.

Polymer treatments increased the strength of handsheets formed from recycled xerographic copy paper. These treatments involved a high-charge cationic polymer, poly-diallyldimethylammonium chloride (poly-DADMAC) followed by anionic carboxymethylcellulose (CMC). The amount of the first additive was varied, but the CMC was held constant.

The results were not the same as those of earlier work, in which the maximum strength was obtained when the amount of poly-DADMAC was just sufficient to saturate the adsorption capacity of unbleached kraft fibers. In the case of the recycled copy paper of this study, significantly higher tensile strength was obtained when the poly-DADMAC addition exceeded the saturation level by a factor of ten.

Tests were performed to evaluate a hypothesis that the strength increase was caused by the formation of polyelectrolyte complexes (PECs) in the bulk phase, with the PEC depositing on the fibers. The fibers were found to retain pre-formed complexes efficiently, especially when the fiber surfaces had been pretreated with poly-DADMAC.

Surprisingly, such pretreatment increased the retention efficiency of all of the PEC mixtures tested. PEC deposition yielded an additional increase of about 13% in dry strength beyond what could be achieved by treatments that did not involve complexation. View this paper online at http://www.tappi.org/index.asp?pid=33030&ch=1

Megan C. Lofton is a student at Howard University in Washington, D.C.; Stephanie M. Moore is a student at Appalachian State University in Boone, North Carolina; Martin A. Hubbe is Associate Professor at North Carolina State University, Raleigh; and Sa Yong Lee is a student at North Carolina State University. Email Hubbe at [e-mail].

CALENDERING 

INFLUENCE OF CALENDERING CONDITIONS ON PAPER SURFACE CHARACTERISTICS--A COMPARISON BETWEEN HARD-NIP, SOFT-NIP, AND EXTENDED SOFT-NIP CALENDERING

APPLICATION: A combination of traditional and new measurement techniques to analyze the effects of calendering on paper properties is introduced.

This study investigated the influence of different calendering conditions on newsprint surface and absorption characteristics, strength, and compression uniformity. We used a combination of traditional and new measurement techniques to evaluate newsprint calendered using a hard-nip, a conventional soft-nip, and an extended soft-nip. This study points out and compares the advantages and disadvantages of the respective calendering techniques.

In all cases, flocs carried the greater part of the load. The different calendering techniques yielded dissimilar compression patterns. At constant process parameters, flocs were flattened most in hard-nip calendering, which had a positive effect on smoothness, gloss, thickness uniformity, and ink hold out. However, it negatively affected tensile strength, gloss uniformity, and print mottle. Extended soft-nip calendering produced opposite effects, including a rougher surface, non-uniform thickness, and less print mottle. View this paper online at http://www.tappi.org/index.asp?pid=33031&ch=1

Isabel Endres is with STFI-Packforsk/Karlstad University, Box 5604, SE-11486 Stockholm, Sweden; Gunnar Engstrom is with Karlstad University, Department for Chemical Engineering, SE-65188 Karstad, Sweden. Email Endres at [e-mail].

RECOVERY

PARTIAL BORATE AUTOCAUSTICIZING TRIAL INCREASES CAPACITY AT SWEDISH MILL

APPLICATION: Partial borate autocausticizing is an easy way for a recausticizing-limited mill to increase its capacity without new equipment.

A full-scale partial borate autocausticizing trial has been running continuously and successfully since November 2002 at the Stora Enso Norrsundet mill in Sweden. The objective was to off-load the lime kilns and reduce the amount of purchased lime and subsequent lime mud disposal costs. The total lime requirement has been reduced by about 7%, while the autocausticizing level averaged around 9%-11% over this period. Overall, the presence of sodium borate in the liquors had little effect on the mill operations and the pulp properties and quality were unaffected. Results indicate that borates may enhance the pulp yield. View this paper online at http://www.tappi.org/index.asp?pid-33032&ch=1

Maria Bjork is with Stora Enso Pulp Competence Centre, Sweden; Tomas Sjogren and Tommy Lundin are with Stora Enso Pulp AB Norrsundet Mill, Sweden; Helen Rickards is with Borax Europe Limited, UK; Saied Kochesfahani is with US Borax Inc., USA. Email Rickards at [e-mail].

EUCALYPTUS PULP

PAPERMAKING POTENTIAL OF HARDWOOD PULPS FOR DECORATIVE PAPER: A COMPARATIVE STUDY

APPLICATION: Portuguese eucalyptus pulp is a favorable and appropriate furnish to select for producing decorative paper for lamination.

Most of the pulp produced in Portugal is from Eucalyptus globulus. Although this pulp has been used for high-quality printing and writing papers, it is now used as well for decorative papers for laminated products, which is a relatively new application.

Good structural and mechanical properties are important for decorative paper. In fact, a certain degree of porosity improves the absorption of inks and resins. The high level of filler incorporated in the paper requires that the fibers have good strength properties.

In this study, the objective was to evaluate the suitability of different hardwood kraft market pulps as raw materials for decorative papers. After testing the pulps, we evaluated the physical properties of both conventional handsheets and decorative paper made on a pilot machine. The pulps were also evaluated based on pairs of relevant properties, air permeance vs. tensile index and tear index vs. tensile index.

The results showed that papers produced with pulps from eucalyptus from Spain and Portugal require more beating energy but have the best combination of structural and mechanical properties. They both have high mechanical resistance and low air resistance. These factors make these pulps the most appropriate choices for this paper grade. View this paper online at http://www.tappi.org/index.asp?pid=33033&ch=1

Evelina Santos is with Portucel-Empresa Produtora de Pasta e Papel, Portugal. Hartmut Schulz is with Technocell Dekor, Burg Gretesch, Germany. Margarida Figueiredo is with the Chemical Engineering Dept. of Coimbra University, Portugal. Email Figueiredo at [e-mail].