Study On Effect Of Biologic Pretreatment On The Pulpability Of Straw And Mechanism

Current research on biopulping in papermaking focus on biomechanical pulping. In order to reduce the environmental impact of pulping and energy consumption, improve the conventional pulping ways and take full advantage of straw, the optimum conditions of laccase ,White rot fungi and xylanase pretreatment straw material; the comparison of pretreatment process between Laccase/carbon sources system(LCS) and laccase/mediator system(LMS);the effect of the biologic pretreatment on NaOH -AQ cooking of rice straw and wheat straw were investigated thoroughly as well as the probing of pretreatment mechanisms with analyses of chemical composition, screen classification, X-diffraction, infrared spectrum and SEM pictures. The key results are listed below in sequence: 1. The optimum conditions of xylanase pretreatment rice straw and wheat straw were very close: pH value 4.5, pretreatment temperature 45°C, liquor to straw ratio 5:1 (6:1 for wheat straw) pretreatment time 4h,enzyme dosage 20IU ? g"1, The optimum conditions of laccase pretreatment rice straw and wheat straw were pH value 5.0, pretreatment temperature 45°C(40 °C for wheat straw), liquor to straw ratio 7:1 (6:1 for wheat straw), pretreatment time 4h,enzyme dosage 30IU ? g"1. wheat straw pretreated with White rot fungi Phellinus Pini showed that the optimum time was 15 days . 2. Laccase/carbon sources system (LCS) can completely replace the expensive laccase/mediator system (IMS) for degradation of lignin in rice straw. 3. Pretreatments of straw with xylanase , laccase and white rot fungi prior to NaOH-AQ cooking decreased kappa number, improved the pulpability of straw, enhanced brightness and physical properties of the resultant pulp, alkali charge was saved as well. 4. By analysis of crystalline rate, chemical composition, screen classification, infrared spectrum and SEM pictures it was learned that laccase pretreatment had the best selectivity and fiber length; many pores emerged in the surface and cell wall of wheat straw after wheat straw was pretreated with white rot fungi and enzyme, which were beneficial in cooking.