EFFECT OF PULP SURFACES ON ENZYME-AIDED BLEACHING OF KRAFT PULPS

The effects of fibre surfaces on pulp bleachability and on enzyme-aide d blenching were studied by bleaching pine and birch kraft pulps, fibr es [i.e. pulps with fines (<100 mu m) removed] and mechanically peeled fibres with one stage of hydrogen peroxide treatment. The removal of the primary fines from the pulps resulted in a higher brightness after bleaching. The removal of the outer surface of the pine kraft fibres decreased the brightness after blenching, whereas no effect was observ ed with the birch kraft fibres. The xylanase treatment increased the b leachability of both types of pulps, fibres and mechanically peeled fi bres, suggesting that its effect on bleaching is not only a surface ef fect but a broader phenomenon. In the mannanase-aided bleaching of the pine kraft pulp, the presence of the outer surface of the fibres hind ered the enzymatic bleach-boosting effect. A positive effect of mannan ase oil the bleachability of the pine kraft pulp was observed only aft er the removal of the outer surface of the fibres.