Abstract: A laccase mediator system was applied on pre treatment of wheat straw pulps.The characteristics of enzyme treated pulps and their bleaching abilities by several total chlorine free(TCF) bleaching sequences were investigated.The results show that bio treatment of laccase mediator system can enhances not only optical properties but also physical strength of the treated pulps.After laccase treatment,brightness gain of pulp was up to 12.9 units (%,ISO).Using an OEPP bleaching sequence,the bleached pulp brightness of laccase treated pulps was higher by 14 units than that of bleached initial pulp.Bleached by a QPP bleaching sequence,laccase treatment could improve the bleached pulp brightness by 18.3 units more than that from initial pulp.After QPaP sequence bleaching,brightness of laccase treated pulp was of 8.1 units higher than that of bleached initial pulp.If the target brightness was the same,laccase treatment could save much bleaching chemicals,that was beneficial to reduce the load of bleaching effluence.The strength of bleached laccase treated pulp was similar to or a little bit lower than that of bleached initial pulp.

Key words: laccase-mediator system, total chlorine free(TCF) bleaching, wheat-straw chemical pulp