Factors Affecting Bleachability of Eucalypt Pulp

Abstract

Unbleached and oxygen-prebleached pulps were produced both in industrial and laboratory scale using Eucalyptus urograndis woods from two different sites (A and B) as a raw material. Quantitative chemical analysis of wood and pulp was performed, aiming to find a correlation with bleaching performance. Fiber dimensions measurements in wood were also performed. Carbohydrates and lignin composition in wood from A and B were found to be similar, while extractives in acetone presented variations of about 0.5% between wood from site A and B. Laboratory-made unbleached pulps from A and B had brightness varying 0.3% ISO, whereas pulps from industry presented variations over 4% ISO from each other. By virtue of its high unbleached pulp brightness, the industry-made sample A presented a higher bleachability than its sample B counterpart. The higher bleachability of the industry-made sample A was traced to its much higher content of hexenuronic acids (HexA), which was caused by differences in pulping conditions in mill sites A and B.