Abstract: Using aspen alkaline peroxide mechanical pulp (APMP), chemithermomechanical pulp (CTMP), kraft pulp (KP) and wheat straw CTMP as material, before enzymatic bleaching, the pulp was moderately pretreated by ionic liquids of BmimCl 1.0%(relative to the amount of dry pulp, the below was the same ) and EmimDMP 1.2%, respectively. The results showed that ionic liquids could optimize the pulp enzymatic bleaching properties, and EmimDMP gave better results. The whiteness of poplar kraft pulp(KP) increased by 4.27 %(ISO), opaqueness increased by 2.46%, and the tensile index, burst index, ring crush index, tear index as well as the folding number of wheat straw chemithermomechanical pulp(CTMP) forming paper increased by 12.21 %, 29.80 %, 22.45 %, 44.82 % and 52.50 %, respectively, after the pretreatment of EmimDMP. The fiber quality analysis(FQA), X-ray diffraction(XRD), and scanning electron microscope(SEM) were employed to characterize its properties. After pretreated with ionic liquid, there was a improvement of fiber quality with the average length increasing, the fines content reducing, and the fiber crystalline increasing. The crystalline of EmimDMP pretreated poplar KP increased by 11.21 %. The surface of pulp occured obvious fibrillation, and this phenomenon could increase the penetration of liquids.

Key words: ionic liquids, pretreatment, enzymatic bleaching