Cooking, oxygen delignification, and ECF bleaching characteristics of Scandinavian pine were studied using a recently implemented lab. scale displacement cooking system. Cooking with white liquor was varied over a wide range in order to produce pulps of varying delignification degrees and yields with const. impregnation and hot black liquor treatment. The pulps were then oxygen delignified and bleached with a D(EOP)DD sequence, again varying conditions in order to evaluate delignification and brightness development. Unbleached and bleached pulps were analyzed and tested in terms of PFI-beating and pulp strength. The results show that the alkali profile after the two-stage pretreatment with black liquors dets. the delignification speed and delignification selectivity in displacement kraft batch cooking. Bleachability, i.e. the active chlorine consumption to a certain brightness level, was significantly better for cooks done at higher alkali concns. Yield saving by using a low alkali charge impairs bleachability.
International Symposium on Wood and Pulping Chemistry, 8th, Helsinki, June 6-9, 1995