APPLICATION OF XYLANASES IN THE PULP AND PAPER-INDUSTRY

Interest in hemicellulolytic enzymes has increased remarkably during r ecent years. This is mainly due to the new areas of application of the se enzymes within the pulp and paper industry. Among these, the most p romising seems to be utilization of hemicellulases, especially xylanas es, to increase the bleachability of kraft pulps. This is partly due t o the great potential of an environmentally safe method. The main enzy mes needed in the enzyme-aided bleaching have been shown to belong to the group of endo-beta-xylanases. Xylanases act mainly on the relocate d, reprecipitated xylan on the surface of the pulp fibres. Enzymatic h ydrolysis of this specific type of xylan renders the structure of the fibres more permeable, allowing enhanced extraction of residual lignin from the fibres. The hydrolysis of hemicelluloses in the inner fibre layers may also enhance the bleachability. The main goals in the enzym e-aided bleaching of kraft pulps have been the reduction of consumptio n of chlorine chemicals in the bleaching process, and consequent lower ing of the AOX of the effluents. In the production of totally clorine- free pulps, enzymes have also been successfully used for increasing th e brightness of pulp. Other suggested enzymatic modifications of fibre s are aimed at improved drainage (water removal) in the paper machine, improvement of fibre properties or production of dissolving pulps. Th e xylanolytic enzymes and their application areas are reviewed.