| The technology of xylanase-assisted bleaching was originally advanced by Viikari et al in 1986, and soon thereafter it was confirmed that the technology could boost the bleachability of pulp, reduce the consumption of bleaching liquor and cut down the pollution load of bleaching effluent. Presently, the technology has been applied widely abroad, whose application at home has entered the start-up stage. However, as for the mechanism, unanimousness has not reached yet.In this paper, firstly, the conditions of treating KP with xylanase X I and xylanase XII were optimized respectively. The results showed that the optimum conditions, such as temperature, pH value, pulp consistency, treating time and enzyme dosage etc, were 50 C, 6.86, 12%, 120min, 30IU/g o.d in turn for X I and 50 C, 4.80, 12%, 120min, 20IU/g o.d in turn for XII.Secondly, the feasibility of applying the technology to APMP was studied. The influence of xylanase-treating on brightness was investigated by carrying enzyme-treating in different stage of APMP process. The results indicated that xylanase-treating worked no obvious effect on brightness of APMP by reason that APMP which was not cooked chemically contained excessive lignin, so the accessibility of xylan in APMP fibre wall was less than that in KP fibre wall.Thirdly, the mechanism of xylanase-assisted bleaching was probed by using SEM and UV techniques. Based on SEM photos and UV profiles, conclusions drawn in the first two parts were verified. In addition, the pledget extracted with benzene-alcohol was cooked with wood chips in order to study the effect of xylanase-treating on xylan reprecipitated during the cooking stage. Finally, the mechanism concerned was further discussed.
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