XYLANASE PREBLEACHING OF FRACTIONS OF DOUGLAS-FIR KRAFT PULP OF DIFFERENT FIBER LENGTH

A commercial xylanase from Trichoderma longibrachiatum was used to tre at the fractions of Douglas-fir kraft pulp of different fibre length. Enzymatic prebleaching was followed by chelation and peroxide bleachin g. An evaluation of both optical and physical properties of the distin ct fractions was conducted. A difference in susceptibility of the frac tions of different fibre length to xylanase prebleaching was observed. The bleach-boosting effect observed with all fractions appeared to be related to the high-molecular-mass UV-absorbing material solubilized during enzyme treatments. Xylanase treatments resulted in beneficial e ffects to handsheet density and roughness as well as to some of the st rength properties. However, the response to the xylanase treatments ex hibited by all fractions of different fibre length was not uniform, in dicating that fiber composition played a key role in the effectiveness of xylanase treatments.