Summaries of February 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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PAPERMAKING

IMPROVEMENT OF PAPER PROPERTIES USING STARCH-MODIFIED PRECIPITATED CALCIUM CARBONATE FILLER

APPLICATION: Starch-modified PCC may offer an economical option to increase filler content and improve paper qualities.

The paper industry uses fillers to reduce manufacturing costs and energy consumption. Fillers also add desired functionality and end-use properties to paper. However, increasing the filler content in paper beyond the conventional level generally reduces paper strength and increases size demand, abrasion, and dusting.

This paper introduces a new filler modification technology. The modified fillers were used to improve the strength in high filler content papers. Our research showed that handsheet physical properties--including tensile, tearing, and folding--could be improved dramatically with starch-coated filler compared to the conventional method. Handsheets containing starch-shell PCC made with different types of starches gave almost the same physical and optical properties. The potential application of this technology in the papermaking industry is very attractive because of the lower price of raw starch compared to cationic starch used in paper wet end. View this paper online at http://www.tappi.org/index.asp?pid=31693&ch=1

Yulin Zhao, Zeshan Hu, and Yulin Deng are with the School of Chemical & Biomolecular Engineering; Art Ragauskas is with the School of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, GA 30332. Email Deng at [e-mail].

RAW MATERIALS

EFFECTS OF EUCALYPTUS NITENS HEARTWOOD IN KRAFT PULPING

APPLICATION: Managers of kraft pulp mills in Chile can improve the pulping process and the quality of the pulp by setting the optimum percentage of heartwood when E. nitens is used as the raw material.

Research on eucalyptus species as a raw material for pulp has not drawn a distinction between the sapwood and heartwood of E. nitens. In fact, most of the research on eucalyptus has focused on E. globulus. However, E. nitens is quickly becoming an attractive alternative in Chile because it is in abundant supply in some of the southern districts.

We examined the physical and chemical properties of heartwood and looked at how an increasing percentage of heartwood influences the kraft pulping process and the quality of the pulp. Heartwood and sapwood were mixed in reciprocal percentages of 0%, 25%, 50%, 75%, and 100% for kraft pulping. The physical and chemical properties of heartwood and sapwood were measured by TAPPI methods.

The heartwood and sapwood densities were similar, but the fiber length and cell wall thickness were greater in the sapwood. Heartwood was higher in lignin and hemicellulose. Increasing the heartwood to over 50% increased the rejects rate and the kappa number of the pulp.

Mechanical strength, tensile index, and burst index were higher in pure heartwood pulp than in pure sapwood pulp. The tearing index and bulk were greater in the pure sapwood pulp. However, the correlation between the heartwood percentage and the pulp properties was not linear. View this paper online at http://www.tappi.org/index.asp?pid=31694&ch=1

Silvana Mariani, Marco Torres, Alicia Fernandez, and Eduardo Morales are with the Instituto de Tecnologia de Productos Forestales, Universidad Austral de Chile, Casilla 567, Valdivia, Chile. Email Mariani at [e-mail].

COATING

INFLUENCE OF SILICA AND ALUMINA OXIDE ON COATING STRUCTURE AND PRINT QUALITY OF INK-JET PAPERS

APPLICATION: This paper can help to guide coating formulators in the contribution of pigment characteristics to coating structure for matte coatings of ink-jet papers that can be on-machine coated.

Amorphous and precipitated silica and silica gels, prepared by the acidification of a solution of sodium silicate, are commonly used in premium matte coated ink-jet papers. Aqueous coatings for paper or paperboard applications use traditional coating pigments such as clay, calcium carbonate, and titanium dioxide. However, for matte coated ink-jet papers, precipitated and gelled silica are used for their unique morphological properties. The structure of these pigments provides an internal and packing porosity that enables the rapid diffusion of liquid inks into the coating layer. The rapid uptake of the ink immobilizes the anionic dyes at the surface of the coating. This accumulation of dye at the surface allows high optical print densities to be achieved. The particle size of precipitated and gelled silica is typically in the 3-16 mm range. Particles of this size significantly reduce gloss, which limits their use in glossy ink-jet media. Thus, they are primarily used in matte grades.

This study compared coatings of non-porous fumed silica, aluminum oxide, and precipitated silica in ink-jet media. We used a blade coat process on a cylindrical lab coater (CLC) rather than the cast coat process. We focused on the contribution of pigment chemistry, functionality, and particle size on coating structure, and coating influences on ink-jet print quality. The pigments used are commercially available and, because of this work, currently being used commercially. View this paper online at http://www.tappi.org/index.asp?pid=31695&ch=1

Hyun-Kook Lee, Margaret K. Joyce, Paul D. Fleming, and James E. Cawthorne are with the Department of Paper Engineering, Chemical Engineering and Imaging, Center for Coating Development, Western Michigan University, Kalamazoo, MI 49008. Email Fleming at [e-mail].

MAINTENANCE

GUIDELINES FOR INTEGRITY EVALUATION AND REMAINING LIFE ASSESSMENT OF RECOVERY BOILERS--CENIBRA'S EXPERIENCE

APPLICATION: This paper may serve as a guide for other pulp mills and help answer questions about the process of integrity evaluation and remaining life assessment of aged recovery boilers.

The need for integrity evaluations and remaining life assessments of boilers arises from technical, economic, and legal reasons. The pulp and paper industry has less experience and tradition in using this engineering discipline when compared to other industries such as oil, petrochemical, and power generation. The pertinent Brazilian legal standard (NR-13) is concise in establishing this requirement, without providing details of applicable technical procedures. Furthermore, recovery boilers are a special type of steam generator, being very specific as to their inherent in-service degradation mechanisms and inspection needs.

In view of the above scenario, pulp and paper mill engineers often have doubts and encounter diverse interpretations of the official regulations when they need to carry out integrity evaluations of quarter-century old recovery boilers. This paper relates CENIBRA's recent experience in evaluating its recovery boiler No. 1. View this paper online at http://www.tappi.org/index.asp?pid=31696&ch=1

Flavio A. Paoliello is a maintenance engineer with CENIBRA, Belo Oriente, MG, Brazil. Email Paoliello at [e-mail].

PROCESS CONTROL

MEASURING MOISTURE, FIBER, AND TITANIUM DIOXIDE IN PULP WITH IMPEDANCE SPECTROSCOPY

APPLICATION: By accurately measuring the pulp moisture at the wet end of the paper machine, papermakers can exercise more precise control over the early stages of paper production.

To measure the moisture content at the wet end accurately is important for precise moisture control in the early stages of paper production. With optimized control, larger quantities of water can be removed from the pulp by mechanical means, reducing energy spent on removing moisture by heating. Although the moisture content at the dry end can be measured with several types of sensors, measuring moisture at the wet end is more difficult. The concentration of additives varies, which precludes any approach based on a simple univariate linear calibration.

In a new approach, researchers have used impedance spectroscopy and fringing electric field sensors to measure the concentration of moisture, fiber, and titanium dioxide in the pulp. The sensors measure concentrations without contacting the pulp, so the technique can be put to work in a paper machine without disrupting the manufacturing process.

According to experimental results, the measurements are quite accurate when the moisture concentration varies from 94% to 86% and the concentration of other constituents in the pulp is between 0% and 7%. Furthermore, it takes only a few experimental data points to implement the calibration procedure. View this paper online at http://www.tappi.org/index.asp?pid=31697&ch=1

Kishore Sundara-Rajan, Leslie Byrd II, and Alexander V. Mamishev are with the Dept. of Electrical Engineering, Campus Stop 352500, University of Washington, Seattle, WA 98195. Email Sundara-Rajan at [e-mail], Byrd at [e-mail], and Mamishev at [e-mail].

ALKALI PULPING

ALKALI IMPREGNATION OF HARDWOOD CHIPS

APPLICATION: It should be possible to predict the time needed for a complete alkali impregnation of hardwood chips based on the chip thickness distribution.

To achieve optimal pulping efficiency and pulp uniformity requires a uniform distribution profile of pulping chemicals within wood chips. Chip thickness is the critical dimension for alkali impregnation. In both the tangential and radial directions in the wood, chip impregnation is a process of reactive diffusion. An advancing front separates a growing, swollen outer zone from an untouched inner zone.

The general pattern of the alkali impregnation of eucalyptus wood is similar to that of poplar wood. For poplar, the reaction zone becomes wider and its movement slows, but the mechanism is always the same. Consequently, for a given hardwood material, the advance of the impregnation front can be determined as a function of time. This information allows us to predict the time needed to impregnate a wood chip under given conditions. View this paper online at http://www.tappi.org/index.asp?pid=31698&ch=1

Miguel Zanuttini, Miguel Citroni, Victorio Marzocchi, and Cristina Inalbon are at ITC, Institute of Cellulose Technology, FIQ, UNL, Santiago del Estero 2654, S3000AOJ Santa Fe, Argentina. Email Zanuttini at [e-mail].