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Polyamidoamine epichlorohydrin (PAAE) is a permanent wet strength resin used in papermaking. When applied to paperboard, some amount of resin is retained in the sheet, and some is lost to the white water. The papermaker usually knows the amount of PAAE charged to the pulp but has no idea how much chemical is retained in the sheet. In addition, the influence of PAAE dosage, freeness, zeta potential, and pulp kappa number variability on PAAE retention is not well understood. Factorial design experiments using unbleached and bleached softwood (loblolly pine) kraft pulps were conducted to understand the factors that affect PAAE retention. The results revealed that PAAE retention, wet tear index, and tensile index not only depended on the PAAE charged of the pulp but also depended significantly on the pulp freeness. In lieu of freeness, zeta potential data can be used to predict PAAE retention. In addition, at similar freeness, bleached pulp has the highest retention of PAAE compared to low and high kappa unbleached kraft pulps. The results also suggest that lignin may have potential as a wet strength agent. [ABSTRACT FROM AUTHOR]

Within the past 15 years, three North American pulp mills experienced catastrophic equipment failures while using 50 wt% hydrogen peroxide. In two cases, explosions occurred when normal pulp flow was interrupted due to other process problems. To understand the accidents, a kinetic model of alkali-catalyzed decomposition of peroxide was developed. Modeling a normal start-up condition where peroxide and sodium hydroxide flow to a mixer in a stoichiometric ratio does not show a significant pressure rise, but a scenario in which peroxide enters the pump in advance of the sodium hydroxide displays a rapid pressure rise that greatly exceeds the rated pressure for the pumps.

Coffee edge-wicking testing was conducted on two groups of highly-sized paperboard manufactured at two mills with similar manufacturing processes, but with vastly different local fiber sources. Although the Hercules size test (HST) indicated similar internal size levels between the two types of board, the edge-wicking behavior was noticeably different. Analysis of fiber structure revealed that the board with more edge-wicking had fibers with thicker fiber walls, which kept the fiber lumen more open after pressing and drying on a paper machine. It was demonstrated that liquid penetration through voids between fibers in highly-sized paperboard was limited, because the fiber surface was well protected by the presence of sufficient sizing agent. Nevertheless, freshly exposed fiber walls and lumens at the cut edge of the sheet were not protected by sizing material, which facilitated edge-wicking. The correlation between fiber structure and edge-wicking behavior was highlighted in this work to inspire development of novel sizing strategies that protect the freshly cut edge of the sheet from edge-wicking. [ABSTRACT FROM AUTHOR]

Recycled fiber-based papermaking in America is experiencing a persistent reduction in the strength of the incoming fiber. To maintain paper strength properties, paper mills respond by increasing basis weight, dry strength, etc. On average, the fiber cost component in recycled paper is approximately 40% of the total manufacturing cost. Increased fiber weight results in higher operating cost and has a negative effect on production rate, especially on dryer-limited paper machines. Increased pH and use of certain enzymes can improve strength during subsequent refining. The ProLab refiner was used to generate laboratory refining curves to evaluate changes in fiber bonding. The effect of pH and enzymes pretreatment on the strength development and change in drainage of recycled fibers with refining was evaluated. [ABSTRACT FROM AUTHOR]

The present work focused on characterizing the chemical and structural properties of isolated lignin from six hardwoods and their kraft pulps in an attempt to better understand the relationship between lignin's chemical properties and resultant oxygen delignification performance. Several hardwood samples were cooked under the same conditions with varying alkali charges to obtain unbleached pulps with kappa numbers between 19 and 20. These pulps were then subjected to an oxygen delignification stage. Both processes were evaluated for pulp quality, residual lignin, and O-stage delignification efficiency. The oxygen delignification stage was carried out under fixed conditions and evaluated with regards to kappa number, which was corrected for hexenuronic acid (HexA) contributions. Results revealed that different hardwood species exhibited differing oxygen delignification efficiencies. A high correlation was found between the O-stage delignification efficiency and the content of phenolic groups in the unbleached lignin, which confirmed that free phenolic groups are the reactive site for molecular oxygen attack. When different hardwood species were compared, the HexA contents were not found to affect O-stage delignification efficiencies. [ABSTRACT FROM AUTHOR]

The current trend to further reuse water within paper mills has resulted in more accumulated salts, as reflected by increased conductivity values. Although conductivity measurement is widely used in paper mills, its fundamental principles and interpretation are not often fully understood. This keeps papermakers from reaching the full benefits of using conductivity measurements to help manage the wet end chemistry of paper or board machines. High and variable conductivity affects the intrinsic properties of pulps, the performance of chemical additives, and the interaction between them. This paper reviews principles of conductivity; its measurement; its effect on important aspects of papermaking operations, such as retention, drainage, sizing, strength development and deposit control; and the fundamentals behind the effects of conductivity on the papermaking process. Specific mill examples are also provided. Potential solutions for operating a mill under high and variable conductivity conditions are discussed. [ABSTRACT FROM AUTHOR]

The use of eucalyptus as a partial replacement for mixed southern hardwoods can result in significant amounts of eucalyptus bark being incorporated into the chips going to the digester. When eucalyptus is first harvested, the bark peels off in large sheets, which will pass through chippers designed for southern hardwood. After being cut for more than about 4-6 weeks, the bark tightens onto the bole of the tree and again passes through chippers not designed for eucalyptus. As a result, significant quantities of eucalyptus bark could go to the digester. This study describes the effect of pulping eucalyptus bark in the laboratory. A series of control studies were performed on eucalyptus and mixed southern hardwood bark. The results show that incorporating bark into the cook results in increased kappa number, decreased pulp yield, and increased alkali consumption. If the percentage of applied active alkali is increased to counteract the increased alkali consumption, increased hexenuronic acid is generated. [ABSTRACT FROM AUTHOR]