Summaries of December 2004 peer-reviewed papers.

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SIZING

IMPROVEMENT OF ASA SIZING EFFICIENCY USING HYDROPHOBICALLY MODIFIED AND ACID-HYDROLYZED STARCHES

APPLICATION: ASA sizing was improved by attaching hydrophobic hydrocarbon chains by esterification and controlling the molecular weight of cationic corn starches.

ASA is an alkaline sizing agent that develops most of its effect on the machine by reacting with cellulose. It reacts rapidly, which is beneficial for on-machine sizing and size press holdout. This rapid reactivity increases hydrolysis, however, which is detrimental to sizing and machine runnability.

To improve the emulsion stability and ASA sizing efficiency, we prepared a new cationic corn starch using esterification with OSA (octenyl succinic anhydride). The pH of ASA emulsions prepared with the esterified starch remained constant, indicating that the hydrophobically modified starch molecules prevented ASA from hydrolyzing.

We used acid hydrolysis of starches as a way to prepare ASA emulsions with a small particle size. The small particle size serves to improve the distribution of ASA on paper surfaces.

The new starch substantially increases the sizing efficiency of ASA. We reduced hydrolysis by using hydrophobically modified starch and improved the surface distribution by controlling the molecular weight of the starch. The use of acid-hydrolyzed starch increased the adsorption of ASA size onto fibers, which is also helpful in improving sizing. View this paper online at http://www.tappi.org/index.asp?pid=31224&ch=1

At the time of this research, Hak Lae Lee, Jong Soo Kim, and Hye Jung Youn were with the Program in Environmental Materials Science, Dept of Forest Sciences, College of Agriculture and Life Sciences, Seoul National University, Seoul, Korea. Kim is now with Hankook Paper Mfg. Co., Ulsan, Korea. Email Lee at [e-mail].

SLUDGE RECYCLING

REPULPING FIBROUS RESIDUALS FROM PULP AND PAPER MILLS FOR RECYCLING IN CONCRETE

APPLICATION: By providing wastewater-treatment residuals that can be easily repulped, mills can help commercialize the production of durable concrete reinforced with these fibrous residuals.

Fibrous residuals from pulp and paper mills, or sludge, can be used as a source of microfibers in concrete. More fibers can participate in strengthening the concrete if the fibers are uniformly dispersed. Researchers at the Center for By-Products Utilization at the University of Wisconsin-Milwaukee have been studying this potential for reinforcing concrete with fibers from pulp and paper mill residuals.

The researchers took samples of fibrous residuals from various mills and repulped them in a high-speed mixer before adding them to concrete. Several sources of fibrous residuals were easy to repulp, but it was difficult to repulp some of the other sources of residuals. Apparently those that proved difficult were dewatered to a high degree at mill wastewater-treatment plants.

The test results showed that including fibrous residuals in concrete greatly improved the concrete's durability. In fact, the durability of concrete improved in direct proportion to the ease with which the fibrous residuals could be repulped. Those residuals that were not so thoroughly dewatered produced the best results.

Cellulose fibers are economical. In tensile strength, they are as strong as steel microfibers. Pulp and paper mills can contribute to better recycling results by providing concrete producers with either sufficiently wet residuals that can be readily repulped or residuals that are already dispersed well and ready for use in concrete. View this paper online at http://www.tappi.org/index.asp?pid=31225&ch=1

Yoon-moon Chun is a research associate and Tarun R. Naik is the director of the UWM Center for By-Products Utilization, Dept of Civil Engineering and Mechanics, College of Engineering and Applied Science. The University of Wisconsin-Milwaukee (UWM), P.O. Box 784, Milwaukee. WI 53201 Email Chun at [e-mail] and Naik at [e-mail].

COATING

OPERATIONAL ISSUES IN HIGH-SPEED CURTAIN COATING OF PAPER, PART 2: CURTAIN COATING OF LIGHTWEIGHT COATED PAPER

APPLICATION: Pilot coater trials are showing the potential of the high-speed curtain coating process to produce superior LWC coating coverage at low coat weight.

Curtain coating--a new coating process for specialty papers--is emerging as a potential method for coating printing paper grades as well. In Part 1, we discussed the operational principles of the process. In Part 2, we present results from pilot-coater trials that demonstrate: (a) the operational window of the process and potential defects, and (b) a value proposition for coating lightweight coated (LWC) papers. By removing the air layer traveling with the web (moving faster than 400 m/min), we have been able to coat LWC at web speeds as high as 1500 m/min. Coating at high speeds requires low air void volume in the coating color and viscosity control. The most challenging issue has been removal of air bubbles from the coating color that might break up the curtain at the slot die exit or create coating layer defects. Careful choice of coating formulations and deaeration has made high-speed curtain coating possible. We show that curtain coating can achieve low coat weights (5.8 g/[m.sup.2]) on LWC, with high coverage (85%), even at low coating solids (54%) to avoid detrimental bubbles in the coating. At a constant coat weight of 5-6 g/[m.sup.2], we saw nearly a 40% advantage in coating coverage using the curtain coating process instead of a metered size press. View this paper online at http://www.tappi.org/index.asp?pid=31226&ch=1

Nick Triantafillopoulos is with RohmNova LLC, Akron, Ohio, USA; Johan Gron is with Stora Enso, Publication Paper, Kymemlaasko, Finland; Iiro Luostarinen and Petri Paloviita are with Metso Paper Inc., Jarvenpaa, Finland. Email Triantafillopoulos at [e-mail].

FLOCCULATION 

INVESTIGATIONS OF THE FLOCCULATION BEHAVIOR OF MICROPARTICLE RETENTION SYSTEMS

APPLICATION: Controlling flocculation by adding the components of microparticle retention systems in the right dosage can improve runnability and paper quality.

Microparticle retention systems consist of a cationic polymer and anionic particles. These systems have been used successfully in papermaking over the last 20 years, but there is still some controversy about the underlying mechanisms and processes involved.

In this study we investigated the flocculation behavior of microparticle retention systems in different furnishes. The state of flocculation in the paper furnish was characterized by image analysis and by the scattering of laser light. The combination of these two methods leads to a more elaborate view of the flocculation mechanism. The dosage of cationic polymer was found to influence the floc size strongly, regardless of the kind of microparticle system used. The dosage of the microparticle component has an impact on the floc size only in the case of the system consisting of cationic polyacrylamide (CPAM) and bentonite. The floc index, measured by light scattering, is affected in both cases by the dosage of polymer and microparticle component. The floc index correlated well with filler retention during handsheet formation. View this paper online at http://www.tappi.org/index.asp?pid=31227&ch=1

Erich Gruber and Peter Muller are with Darmstadt University of Technology, Dept. of Macromolecular Chemistry, Alexanderstr. 10, D-64283 Darmstadt, Germany. Email Gruber at [e-mail].

WOOD CHIPS

CHIP PROPERTIES ANALYSIS FOR PREDICTING BLEACHING AGENT REQUIREMENTS FOR TMP PULPS

APPLICATION: The peroxide charges required to bleach TMP pulps to a required brightness can be predicted with respect to fluctuations in chip properties.

The objective was to model the relationship between the quality of chips and the pulp brightness. The model could then be used to evaluate the amount of peroxide needed to reach a target brightness as chip quality fluctuates. Regulating the charge of bleaching agent on the basis of chip quality could cut the cost of bleaching.

A neural network brightness predictor coupled with an optimizer was used to simulate peroxide bleaching. The chip quality was determined by six parameters of the chip management system. The simulation showed how chip quality influences the peroxide bleaching of TMP pulps. When the chip quality was increased, the brightness setpoint could be achieved at a lower peroxide charge. The chip management system (CMS) includes main and auxiliary sensors for characterizing wood chips online. The raw materials were different mixtures of black spruce, balsam fir, jack pine, and white birch. View this paper online at http://www.tappi.org/index.asp?pid=31228&ch=1

Luc Laperriere, Celine Leduc, and Claude Daneault are with the Universite du Quebec at Trois-Rivieres, Pulp and Paper Integrated Centre, C.P. 500, Trois-Rivieres, QC, Canada, G9A 5H7. Pierre Bedard is with the Centre de Recherche Industrielle du Quebec, Technologie des Pates et Papiers, 333 Franquet, Ste-Foy, QC, Canada, G1P 4C7. Email Laperriere at [e-mail].

BLEACHING

PULP PROPERTIES AND EFFLUENT CHARACTERISTICS FROM THE MG(OH)[.sub.2]-BASED PEROXIDE BLEACHING PROCESS

APPLICATION: Using magnesium hydroxide as a substitute for sodium hydroxide can improve the bleaching effluent characteristics in the bleaching of mechanical pulps.

Peroxide bleaching based on magnesium hydroxide (Mg(OH)[.sub.2]) has recently been used to brighten TMP. Compared with the conventional NaOH process, the Mg(OH)[.sub.2] process offers lower bleaching costs, less scaling, and decreases in COD and anionic trash.

We subjected a softwood TMP to peroxide bleaching under various conditions, using either Mg(OH)[.sub.2] or NaOH as the alkali source. We then determined various pulp properties, including the light-scattering coefficient, internal bonding strength, and surface strength. The Mg(OH)[.sub.2] process produces bleached TMP fibers with a light-scattering coefficient that is higher than that of the fibers produced by the NaOH process. The internal bonding and surface strength properties of the bleached pulps are not affected when Mg(OH)[.sub.2] is used as the alkali source instead of NaOH. We also characterized the dissolved substances in the bleaching effluent using NMR spectroscopy, UV spectroscopy, ion chromatography, and polyelectrolyte titration. The Mg(OH)[.sub.2]-based process offers a lower COD load in the bleaching effluent because less acetic acid and methanol are formed and because less lignin is dissolved. View this paper online at http://www.tappi.org/index.asp?pid=31229&ch=1

Zhibin He, Moses Wekesa, and Yonghao Ni are with the Limerick Pulp and Paper Centre University of New Brunswick, Fredericton, Canada E3B 6C2. Email Ni at [e-mail].

ONLINE EXCLUSIVE ECONOMICS

2004 NORTH AMERICAN PAPER INDUSTRY PERFORMANCE REPORT

APPLICATION: This annual financial analysis of the pulp, paper, and packaging industry compares and contrasts the performance of Canadian and United States firms. It is hoped that research findings provide useful insights for industry managers, government officials, and academics.

Since this annual study first analyzed pulp, paper, and packaging industry data in 1995, industry consolidation has been substantial. In the first study, the census of publicly traded firms included 24 Canadian firms, compared to eight in this year's study, and 42 U.S. firms, as compared to 25 for this report.

Total industry paper sales for the United States (US$ 101 billion) are almost tenfold those in Canada (US$ 11 billion), though firms in both countries experienced marginal declines (<-1%) in paper annual sales. In terms of total annual sales (paper, wood, and non-forest products). Canadian paper firms experienced more sales growth in 2002, up over 5% as compared to only a 1% increase in the United States.

The U.S. paper industry is a third more leveraged than Canada (debt to equity is 3 versus 2) and raised debt while Canadian firms lowered it. Canadian capital expenditures were smaller and decreased more than in the United States, on average US$ 103 (-36%) and U.S. firms averaged US$ 565 million (-7%). Almost all North American paper firms have foreign sales and operations, but Canadian firms depend much less on domestic sales (35% of all sales) as compared to U.S. firms (84%). Canada produces twice as many tons of pulp, paper, and board as it consumes domestically (46 million tons versus 23 million tons) as compared to U.S. production, which does not meet domestic consumption needs (135 million tons versus 142 million tons). Total industry foreign sales in both countries grew modestly, almost 6%. Despite global competition, falling prices, and reduced capital spending, only a quarter of U.S. and Canadian paper firms experienced declining foreign sales. View this paper online at http://www.tappi.org/index.asp?pid=31230&ch=1

Dorothy Paun is associate professor of forest products business and Fulbright Distinguished Chair; Vivek Srivastava, Reinier Voorwinde, Peter Stroble, Dan Thomson, and Abhilash Reddy are M.B.A. and M.S. students; Elizabeth Scott and Nan Hu are Ph.D. students; and Bill Spohnholtz is a B.S. student; University of Washington. Email Paun at [e-mail].