Use of Enzymes as One Stage in Pulp Bleaching, 1992 Environmental Conference Proceedings

The environmental impact of conventional waste bleach waters justify for environmentally benign and economically feasible bleaching techniques to be developed. It has been shown that the hemicelluloses remaining in kraft pulp are closely associated with, and even chemically bound to, the residual lignin. These covalent linkages apparently contribute to the difficulty in removing residual lignin from the fibers, even though a large part of the lignin network has been torn apart. We will describe how treatment of kraft pulp, with xylanases in particular, facilitate removal of residual lignin. The enzyme treatment results in a considerable release of lignin carbohydrate complexes from the pulps. The treatment has an enhancing effect on the removal of residual lignin from the pulp in subsequent bleaching stages. The application of hemicellulose-degrading enzymes as one stage of bleaching yields better pulp bleachability and pulp quality. The fully bleached kraft pulps, using enzymes as one stage of bleaching, have very compatible yields and physical properties compared to commercially produced pulps.