Obtaining biobleached eucalyptus cellulose fibres by using various enzyme combinations.

Various combinations of laccases, xylanase and cellulase were used to biobleach cellulose fibres from eucalyptus. The Trametes villosa and Myceliophthora thermophila laccases were used in combination with violuric acid (VA(TvL) system) and methyl syringate (MeS(MtL) system), respectively, as mediator. A dissimilar mode of action of the two systems was found: the VA(TvL) treatment released both hexenuronic acids and lignin, whereas the MeS(MtL) released lignin alone. Pulp properties were further improved by applying the mediator before the enzyme during treatment. Pulp properties comparable to those provided by industrial TCF sequences were obtained by inserting a xylanase pretreatment before VA(TvL), but no significant effect was observed after the cellulase pretreatment. As an added value, the resulting enzymatically bleached fibres possess a reduced hexenuronic acid content. The chemical oxygen demand of the effluents from each stage was also assessed.