Enzyme-aided bleaching of industrial softwood kraft pulps

Enzyme-aided, totally chlorine-free bleaching of different industrial softwood kraft pulps was studied using purified Trichoderma reesei xylanase and mannanase. Both xylanase and mannanase treatments were found to increase the bleachability of the pulps, depending on the cooking method used in pulp production. The effect of xylanase treatment on brightness was highest in the conventional kraft pulps and in pulps produced by extended cooking methods. Higher amounts of lignin with higher average molecular mass also could be extracted from these pulps after xylanase treatment. The enzymes were especially effective in improving the bleachability of oxygen-delignified pulps