Summaries of November 2005 peer-reviewed papers.

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CURTAIN COATING

PRODUCTION EXPERIENCE WITH CURTAIN COATING FOR WOODFREE COATED PAPER 

APPLICATION: Curtain coating can be used in a mill to obtain graphic paper grades similar in quality to that of blade-coated paper.

For a long time papermakers have dreamed of applying a perfect layer of coating on the surface without touching the surface with any mechanical device. Curtain coating is now opening new possibilities for coated papers.

In this mill trial with a commercial curtain coater, the objective was to produce single-coated, glossy, woodfree paper. Coatings were applied in different amounts to point up the influence of coat weight on the final quality. The roughness of the base paper was also varied, through changing the pre-calender line load.

The coating color used was a blend of fine calcium carbonate and clay with styrene-butadiene latex. The optimum solids content and viscosity were determined in pre-trial tests on a pilot coater.

After coating, the rolls were calendered on a pilot multinip calender. Sheets were offset printed in a commercial printing shop, and a blade-coated paper was printed as a reference.

The results showed that the curtain principle can be applied to obtain graphic paper grades with quality similar to that of blade-coated paper. Surprisingly, pre-calendering had little influence on the final quality. View this paper online at http://www.tappi.org/index.asp?pid=33590

Michael Trefz and Uwe Frohlich are with Voith Paper GmbH & Co. KG, St. Poeltener Strasse 43, 89522 Heidenheim, Germany. Email Trefz at [e-mail].

ADDITIVES

HOW POLYMERS STRENGTHEN FILLED PAPERS

APPLICATION: This study evaluates the effectiveness of various combinations of polymers, fines, and PCC to strengthen paper.

We compared two strategies for strengthening filled papers. One used polymers to increase cellulose-cellulose adhesion, the other used polymers to increase cellulose-calcium carbonate adhesion. We made two-ply laminates from wet, filler-free hand-sheets with a sparse coating of precipitated calcium carbonate (PCC) in the ply-ply interface. After those had dried, we measured the force required to delaminated them. Polymer treatment of one or both plies increased the strength of laminates with low PCC contents due to enhanced cellulose-cellulose adhesion. However, at intermediate filler contents this strategy failed. Treatment of PCC with polymer to strengthen cellulose-PCC adhesion gave modest strength improvements. By far the strongest laminates were obtained when cellulose fines were present in the PCC layer. View this paper online at http://www.tappi.org/index.asp?pid=33591

Yaling Xu, Xiaonong Chen, and Robert Pelton are with the McMaster Centre for Pulp and Paper Research, Department of Chemical Engineering, McMaster University, 1280 Main Street West, Hamilton, Ontario, Canada, L8S 4L7. Email Pelton at [e-mail].

FIBER SUPPLY

FOUR ADDITIONAL HYBRID POPLARS WITH PAPERMAKING PROPERTIES SUPERIOR TO ASPEN

APPLICATION: Equal in strength and bleachability to pulps derived from aspen, pulps from hybrid poplars have great potential in papermaking as traditional supplies of hardwood fiber diminish.

How suitable are hybrid poplars for manufacturing kraft pulp and bleached refiner mechanical pulp (BRMP)? Are they equally as suitable as the poplars traditionally used in papermaking?

Faced with the prospect of shortfalls in hardwood fiber, some corporations have been developing plantations for hybrid poplars. Research has been aimed at identifying elite clones that have good chemical and physical properties for papermaking. One problem is that the papermaking properties are different for each clone and are different even for the same clone grown on different sites.

The objective of this research was to compare the papermaking properties of kraft and mechanical pulps derived from four hybrid poplars to the same properties of pulps derived from aspen and balsam poplar. All of the poplars were harvested in close proximity to each other.

The research showed that pulps could be derived from hybrid poplars that would be stronger and equally bleachable compared to pulps from aspen. Kraft pulps from the four hybrid poplars had tensile properties superior to those of pulps from aspen and balsam poplar. High strain and tensile energy absorption were found in paper sheets made from the hybrids. Three of the four hybrid poplar BRMP had bleached brightness and light scattering coefficient equal to those of aspen. In general, plantations of elite clones of hybrid poplars look promising as future sources of hardwood fiber. View this paper online at http://www.tappi.org/index.asp?pid=33592

Raymond C. Francis and Alton F. Brown are with Empire State Paper Research Institute, SUNY College of Environmental Science and Forestry, Syracuse, New York. R.P. Bosshart is now with Horizon AG-Products, Modesto, CA. Sidney E. Balch is with New England Forestry Foundation, Littleton, MA. Darrell M. Waite is with MeadWestvaco Corp., Chillicothe, OH 45601. Email Francis at [e-mail].

FILLERS

EFFECT OF THERMAL TREATMENT ON THE STRUCTURE OF PCC PARTICLES

APPLICATION: This study demonstrates the effects of thermal treatment on the structure of PCC particles and evaluates the potential of the ashing method to isolate these particles from filled papers.

Controlled combustion of paper is normally used to determine the filler content of paper. It can also be a valuable tool to isolate the mineral particles for extra characterization or additional applications. However, it is known that the ashing temperature greatly affects the filler particles.

The main goal of this study was to analyze the effects of paper calcinations on the intrinsic properties of precipitated calcium carbonate filler (PCC) by using distinct temperatures, from 400[degrees]C up to 1000[degrees]C. Both the original PCC particles and the ashes were characterized in terms of size, density, surface area, porosity, chemical composition, color and electrostatic charge. A commercial printing and writing paper (P & W) from an eucalyptus kraft based pulp was used.

We characterized the original PCC particles and the ashes obtained by the paper combustion in terms of the properties that most influence the paper performance, namely the morphological and the optical properties. We also determined the mineralogical and chemical composition and particle electrostatic charge.

The results showed that to preserve the structure of the PCC aggregates in terms of size, specific surface area, and porosity, 400[degrees]C is the most suitable temperature for paper controlled combustion but color and charge are still affected by the papermaking chemical residues. To overcome this situation 600[degrees]C is the optimum temperature for isolating the paper fillers so that their physical, chemical, optical, and electrical characteristics are adequately balanced and not too different from those of the original particles. View this paper online at http://www.tappi.org/index.asp?pid=33593

At the time of this research, Paulo Ferreira, Margarida Figueiredo, and Anselmo Mendes were with the Department of Chemical Engineering, University of Coimbra, 3030-215 Coimbra, Portugal, and Jose Velho was with Department of Geosciences, University of Aveiro, 3810-193 Aveiro, Portugal. Mendes is now with Clean Compounds--Industria de Polimeros, S.A. Email Ferreira at [e-mail].

BLEACH PLANTS

INORGANIC SCALE BUILDUP IN A BLEACH PLANT--A MILL CASE STUDY

APPLICATION: Antiscalant can inhibit scale formation in the bleach plant to improve washing, reduce chemical consumption, and increase production.

A mill modified its bleaching process in ways that benefited the environment but led to the precipitation of calcium carbonate scale. This scale builds up to 15 cm in the chute and the thick stock pump leading from the discharge of the E-stage washer to the inlet of the D, up-flow tube. The scale tends to build up and restrict the stock flow. Ultimately, it decreases production unless it is controlled.

The bleach plant is shut down for cleaning at a cost of US$ 62,000 per shutdown. Over the years, the mill personnel have devised a schedule based on operating experience to shut down the bleach plant every seven weeks. However, there are times when the mill has to shut down before the scheduled downtime because of excessive scaling. The last incident of unscheduled downtime prompted the mill personnel to try an antiscalant in the bleaching process.

During the trial period, the addition rate was varied and optimized, and the discharge pressure of the thick stock pump was monitored along with the daily production rate. The antiscalant added in the process at the upper pond flow on the E-stage washer controlled the excessive buildup of scale. The result was an increase in daily production of 10-50 tons/day. View this paper online at http://www.tappi.org/index.asp?pid=33595

Amin Manji and John Karagiannis are with Constant America Inc., 2120 Cabot, Montreal, Quebec, Canada. The company can be reached at [phone]. Email Manji at [e-mail].