TREATMENT OF SULPHATE PULP AT ACIDIC PH AND ELEVATED TEMPERATURE TO REMOVE HEXENURONIC ACID

摘要

Pulp, in particular hardwood pulps, is delignified in cooking and, when needed, further delignified with oxygen to a kappa number below (24), preferably below (14). The delignified pulp is heated and treated at a temperature of about 85 to 150 DEG C, preferably 90 to 110 DEG C, at a pH of about 2 to 5 in order to decrease the kappa number by 2 to 9 units by removing at least 50 % of the hexenuronic acid groups in the pulp. The treated pulp is bleached in at least one bleaching stage.