BIOBLEACHING EFFECT OF STREPTOMYCES-THERMOVIOLACEUS XYLANASE PREPARATIONS ON BIRCHWOOD KRAFT PULP

The biobleaching effect of cellulase-free thermophilic xylanase prepar ations from Streptomyces thermoviolaceus on birchwood kraft pulp was d etermined. Enzyme pretreatment was found to be most affective at high pulp consistencies and resulted in the hydrolysis of hemicellulose and the release of chromophoric material from the pulp. Removal of residu al lignin was indicated by a reduction in Kappa number. The applicatio n of cyclic enzyme treatments coupled with intermediate alkaline extra ction stages increased the biobleaching effect however, more then two cycles resulted in a decrease in the physical strength of the paper. T he enzyme treatment process was optimized and found to be most effecti ve at 65 degrees C and pH 6.0, with the crude enzyme preparation blend ed to a pulp consistency of 5%. A 3 h enzyme pretreatment of pulp foll owed by single-stage peroxide bleaching yielded pulp with a brightness of >70 ISO units for the production of paper handsheets in which the physical strength of the fibers had been presented.