The Effect of High Pure Thermostable and Alkaline Tolerant Xylanase Pretreatment on ECF Bleaching of Wheat Straw Soda-AQ Pulp

The selectivity of pretreatment before ECF bleaching of wheat straw pulp and the effect of the preteatment on the ECF bleaching with a high pure thermostable and alkaline tolerant xylanase were studied.The results showed that the xylanase pretreatment had obviously high selectivity and assist-bleaching efficiency.With the pretreatment,the brightness of each stage in D0ED1D2 was much higher than that of the control at the same ClO2 dosage;certain prebleaching efficiency was achieved even at 1.0 IU/g xylanase dosage.The final brightness,close to 90%,of the bleached pulps with the XAD0ED1D2 bleaching sequence was 3 percentage points higher than that of the control at the same bleaching conditions.The ClO2 dosage in the D0 stage could be saved by 23.5%(14% of total ClO2 dosage) when the same brightness(87.0%) as the unpretreatment bleached pulp was achieved.The pretreatment conditions of high temperature and pH value(80℃,pH value 8.0) and wide range enzymes dosage(1.0～4.0 IU/g) could make the xylanase to be prospective in industrial application.The improment of bleaching performance by the xylanase pretreatment is attributed to the hemicelluloses,hexenuronic acid and part of lignin removal from the pulp.