Effect of Chemical Pretreatments of Never-Dried Pulp on the Strength of Recycled Linerboard, 2001 Papermakers Conference Proceedings

According to the American Forest and Paper Association (AF&PA) the recovery rate of corrugated boxes used in the US now exceeds 75%. In principle the recycling of boxes saves fiber resources and requires less total energy. However, further progress in old corrugated container (OCC) recycling faces a potential barrier. It is known that recycled kraft fibers have a reduced bonding ability. The approach taken in this study was to pre-treat the never-dried fibers before the first cycle of papermaking. New data have been obtained with never-dried, refined, unbleached kraft pulp. Simple drying, low-shear disintegration, and forming without further refining yielded a loss in compression strength in the range 19 to 26%, depending on the pulp batch. Pretreatment with various chemical agents was able to compensate for some of the strength loss. Two general classes of treatment agent were identified that were able to favorably affect the strength of recycled sheets. Certain low-molecular weight materials such as sucrose appeared to interfere with the mechanism of pore closure during the initial drying. In contrast, certain high-mass polyelectrolytes such as guar gum products, cationic starch, and polyelectrolyte complexes appeared to affect the adhesiveness of the fiber exteriors of the repulped fibers.