The Study On ECF Bleaching Property And Mechanism By Thermostable And Alkaline Tolerant Xylanase Pretreatment

The thermostable and alkaline tolerant (TAT) xylanases are quite important for paper industry to reduce the energy, pollution and cost in the pulping and papermaking processes. The effect of the TAT xylanase X pretreatment on hardwood and softwood pulp bleaching properties was studied. The improvement bleaching mechanism was studied systematically by various physical and chemical methods. The main results are as follows:TAT xylanase X can be used under flexible technical conditions. A good assistant bleaching effect can be obtained by the pretreatment at temperature 70-80℃, pH 8.0-9.5, enzyme dosage 4 IU/g for softwood pulp and 2 IU/g for hardwood pulp,10.0% consistency for 2 hr.The xylanase X has a good selectivity for the pretreatment. The final brightness of the bleached pulps by the xylanase X pretreatment was 1%ISO higher than that of the bleached unpretreatment pulps (89 %ISO) while the viscosities and yield of pulps were not reduced basically. The total bleaching ClO2 dosage could be saved from 15 to 17% when the pulps were pretreated by the xylanase X under the same bleaching conditions as regular bleaching. The modification effect of xylanase X pretreatment on hardwood pulp bleaching is much better than that on softwood pulp.The effect of buffer solution treatment on the lignin removal in the pulps is more than that of the xylanase X treatment while the effect of xylanase X treatment on the hexenuronic acid removal in the pulps is more than that of the buffer solution.It is shown that the xylanase X pretreatment can hydrolyze the xylan in the pulps and LCC specifically and result in the swelling and porosity inside pulp fibers and outside partly which allow the low molecular weight xylan, lignin and LCC could be dissolved to some content.The bleaching chemicals can easily penetrate inside the pulp fibers because of their porosity increase by the xylanase X pretreatment. As the same reason, the products from the reaction of the chemicals with lignin etc. can be easily dissolved in the bleaching. The combination improve the bleachability by the the xylanase X pretreatment.The IR, nitrobenze oxidation and ozonation etc prove that the xylanase X pretreatment do not change the lignin structure in the pulp and LCC to given content.