Investigation of pH effect on enzymatic bleaching efficiency of bagasse kraft pulp

It has been demonstrated that pulp bleaching can be enhanced by enzymatic pretreatment, but their efficiency differ with pulping method and raw materials. In present study, the effects of xylanase pH in bagasse kraft pulp pretreatments on D1ED2 (Dioxide chlorine 8% + Alkaline extraction + Dioxide chlorine 2% as active chlorine) bleaching sequence was investigated at laboratory scale. Bagasse kraft pulp with initial kappa number 20 was treated by commercial xylanase from Trichoderma viride at 5, 10, 25 and 50U/g doses, for reaction time 2 hours and two levels of pH (5, 7.5). The result showed that the efficiency of commercial xylanase in acidic pH was significantly higher (P<0.01), as compared to neutral pH in reduction of kappa number and yellowness and increase of brightness and opacity. Increasing enzyme content from 5U/g to 25U/g in both pH values led to improved brightness and in enzyme content 50U/g decreased brightness. In addition, yield loss was more in acidic pH than netural pH. Therefore, regarding the obtained results, acidic pH can be suggested as optimal in enzymatic prebleaching of bagasse kraft pulp.