On the effect of a xylanase post-treatment as a means of reducing the yellowing of bleached hardwood kraft pulp

The effect of an enzymatic post-treatment of bleached hardwood kraft pulp in order to improve the brightness stability was studied using two commercially available endoxylanases. The results clearly show that the yellowing was significantly reduced for two pulps of different origins bleached in different ways. The beneficial effect on the brightness stability was linked to a removal of hexenuronic acid (HexA) from the pulps. The practical applicability of the results needs to be considered in relation to the cost of the enzyme and to indications that there is some yield loss due to the treatment.