Preparation Of Acetate Grade Dissolving Pulp And Its Application For Acetylation

In this thesis, birch was applied to obtain the acetate grade dissolving pulp with high brightness (≥90%ISO), high a-cellulose content (≥96%), and high polymerization of degree (≥900) by establishing the optimum conditions of alkaline pre-impregnated kraft pulping, elemental chlorine free bleaching (D-E-D) and total chlorine free bleaching (dimethyldioxirane), bacteaial xylanase cooperated with alkaline purification. And the optimum condition of acetylation was established. SEM, FT-IR, X-ray, and TGA were used to analyze the properties of birch pulp and cellulose acetate. And it can be concluded that all the properties of birch pulp could achieve the standard of acetate grade pulp. TGA analysis revealed that the existence of acetyl could enhance the thermal stability of cellulose acetate.In the investigation of alkaline pre-extraction, extraction with high liquor to wood ratio and low alkali concentration favored the removal of hemicelluloses, while using the same alkali charge; the hemicellulose dissolution rate of alkaline-extracted birch chips was higher than that of alkaline-pretreated eucalypt and Chinese oak chips.The DMD was both selective and effective as a delignifying agent, and the selectivity of delignification was better than that of oxygen delignification. The H2O2 bleaching pretreated with DMD will improve the delignification efficiency and brightness. In the long sequence for the bleaching of dissolving pulp, acid treatment can be used in two approaches:to remove the metal ions without washing before the chelation stage, and to reduce hemicellulose and ash in the final stage.The a-cellulose content of pulp purified with alkaline was higher than that of xylanase treated pulp. Xylanase cooperated with alkaline treatment will contribute to promote the content of a-cellulose and brightness, and it is better to apply the xylanase treatment prior to the process of bleaching.As compared to xylan of birch pulps, the xylan of bamboo pulps was more easier to be removed with bacterial xylanase cooperated with alkaline treatment.