Study On Improvement Of Bagasse Oxygen Pulping By Laccase Pretreatment

China’s pulping and papermaking industry growed rapidly in recent years, lacking of fiber raw material supply and pressure on the environment has become a bottleneck restricting the sustainable development of pulping and papermaking industry. Using environment-friendly enzyme pretreatment combined with alkali-oxygen pulping method to make full use of non-wood fiber resources has great significance for ease our country’s fiber raw material shortage and environmental pressures. Laccase was used to pretreatment bagasse which belongs to agricultural solid wastes. In this paper, the effect of laccase pretreatment on bagasse material, pretreatment waste water and subsequent alkali-oxygen pulping were studied. And the best laccase pretreatment condition was established. Moreover, the mechanism on alkali-oxygen pulping with laccase pretreatment was studied by analysis fiber surface morphology and the structure of lignin and carbohydrate in bagasse material and its alkali-oxygen pulp by using XRD, SEM, NMR, IR and other modern instrument analysis method.The results of laccase activity and stability showed that in the mesasuring process of laccase activity enzyme concentration had the greatest impact on activity, pH value had relatively light effect on activity. The optimum conditions of laccase activity mesasuring in the experimental range were 25 thousand times of the enzyme concentration, pH value 5.0. Laccase stability was affected by the environment temperature. If laccase placed at room temperature, the place time should not exceed 6 h. The laccase lost activity completely when it was heated at 94℃ (boiling) for 5 minutes.The effect of laccase pretreatment on pulping properties and physical properties was studied. The results indicated that the optimum conditions of enzyme pretreatment were laccase dosage 80 U/g pulp, temperature 50℃, liquor ratio 1:6, pH 5.0 and pretreatment time 6 h. Under above mentioned suitable conditions, the pulping properties and physical properties of bagasse alkali-oxygen pulping with laccase pretreatmented were improved. It was beneficial to the dissolution of molecules lignin in bagasse and can reduce the loss of carbohydrates in subsequent pulping, adding right amount of mediator HBT in the process of bagasse laccase pretreatment. In the case of similar Kappa number, the pulp viscosity and paper strength properties were increased.The results of hydroxyl radicals delignification selectivity with laccase pretreatment showed that the optimum conditions of hydroxyl radicals processing were H2O2 dosage:30%, H2O2 added in three portions by mass percentage of 25%:25%:50%, CoSO4 dosage:0.04%, NaOH dosage:22%, temperature:80℃, time: 4 h. The main pulping properties under optimum conditions were:pulp yield 51.01%, Kappa number 16.8, whiteness 66.1% ISO. The delignification selectivity of hydroxyl radicals processing was improved after laccase pretreatment.The mechanism of bagasse alkali-oxygen pulping with laccase pretreatment showed that:the laccase pretreatment before pulping was beneficial to the dissolution of small molecule lignin and suger in bagasse. And it made the material structure more loose, which was beneficial to improving the delignification selectivity of subsequent pulping. In the case of similar Kappa number, the pulp yield and pulp viscosity were increased. After laccase pretreatment the crystallinity of pulp was improved, at the same time the hydroxyl groups content and adhesive between fibers in the process of papermaking were increased, which may be the main reason for improving the paper strength properties.