EVALUATION OF THE EFFECTS OF HEMICELLULASES ON THE BLEACHABILITY OF SULFITE PULPS

Sulphite pulps were prepared from spruce chips with four cooking methods, differing in cooking pH, the use of additives such as anthraquinone, and the cooking time and temperature. Considerable differences in carbohydrate composition, Lignin content and yield of the pulps were observed. The sulphite pulps were treated with Trichoderma reesei xylanases and mannanase prior to peroxide bleaching. The accessibility of xylan and glucomannan was greatly dependent on the cooking method used. The xylan was most accessible in the alkaline pulp, whereas glucomannan was most readily hydrolyzed in the two-stage sodium sulphite pulp. Despite enzymatic hydrolysis of pulp xylan or glucomannan, no clear improvement in the bleachability was observed in peroxide bleaching.