Sequential pretreatments of wheat straw Soda-AQ pulp with Aspergillus niger xylanase and Basidiomycete sp. laccase before sodium hypochloride bleaching were studied. The effect of different treatments by synergistic action of xylanase (X) and laccase (L) on pulp hardness (KMn04 number) and brightness was discussed, and the optimum conditions concerning laccase dosage, mediator dosage and reaction time were also investigated. Results showed that the optimum conditions were laccase charge 2.5 U/g, mediator charge 0.1% and retention time 120 min.The KMn04 number decreased rate of the pulp treated by LMS under 1 kg/cm2 oxygen pressure was 31.6%, 21 percent higher than that treated without oxygen. The hardness of the pulp pretreated by L-X sequence was lower than that by X-L one, their bleached pulps brightness was respectively 3.9%ISO and 3.0%ISO higher than the control pulp.

Two fungi, wich produced an acid and an alkaline-stable xylanase, were isolated from soil and identified as strains of Aspergillus niger. The basic characteristics of both xylanases were studied and the conditions of pretreating wheat straw pulps with xylanases were also optimized. The results showed that enzyme-pretreated pulps can obtain higher brightness, or 20%-30% of hypochlorine can be reduced at the same final brightness level. It can be predicted that xylanase has a great potential economic and environmental benefits in non-wood pulp bleaching in the near future.