| The research uses the 5 years old Populus xeuramericana CL. 'Zhonglin46'from HeZe as rawmertarial, analying the chemical constituents and fiber morphology, study on the effect of different conditions and cooking additives on the pulping of this aspens. At the same time study the bleaching ability by different bleaching processes and the biobleaching mechanism. Conclusions were as follows:(1) Populus×euramericana CL. 'Zhonglin46'from HeZe contains 81.34% holcellulose,20.62% lignin and 1.78% bezene-ethanol extraction. The length of fiber is 1.03mm, the width of fiber is 23.89μm, and L/W is 43.(2) The optimized condition for Populus×euramericana CL. 'Zhonglin46'cooking was:Alkaline sodium hydroxide sulphite pulping, sodium hydroxide dosage(by Na2O) 23%, sulfitity 40%, anthraquinone dosage 0.08%, liquor ratiol:4.5, maximum temperature 165℃, the first cooking time 90min to 140℃and keep 140℃for 60min(start from 80℃), then spend 40min rising the temperature to 165℃and keep 165℃for 50min.Under this condition, the coarse pulp yield is 52.7%, the kappa number is 19.4, the viscosity is 1312 mL·g-1, the residual alkali of Black Liquor is 8.1g·L-1.(3) The result shows that the use of cooking additives is suitable for the pulping and papermaking of Populus×euramericana CL. 'Zhonglin46'. The optimal effect comes when using dosage of green oxygen 0.5% instand of anthraquinone with dosage of cooking accelerator Almy 0.05%, the screened pulp yield is 48.2%, the kappa number is 10.8, the viscosity is 1309 mL·g-1, the residual alkali of Black Liquor is 7.9g·L-1.(4) An optimum process of biobleaching treatment could be the dosage of xylanse(EC.3.2.1.8) 151U/g, treating time of 120min, treating temperature of 55℃, pH 6.0, pulp consistency of 10%. The Populus×euramericana CL. 'Zhonglin46'pulp was bleached in this condition with the enzyme, the brightness of biobleached pulp is 66.0%ISO, increased by 4.8% than the pulp bleached with oxygen delignification lignin, and the viscosity was increased to 1131mL/g. The biobleaching by xylanse can impove the pulp bleaching ability and increase its strength in some degree.(5) Study on the mechanism of biobleaching by xylanse, compared to the contrast pulp, the content of pentosan reduced 2.28%, the content of klason lignin reduced 0.1%.According to X-ray, the crystallinity of the biobleached pulp increased 1.82%. Xylanase pretreatment released the lignin of amorphous zone, increase of the hydrogen bond between the fibers, and improve the crystallinity of the pulp and fiber strength..According to SEM, the surface of the unbiobleaching fiber is smooth, and the surface of the biobleaching fiber is not smooth and become porous and permeable.According to IR, biobleach can increase free hydroxide radical, and increase hydrogen bond. At the same time, biobleach can also degradation the pentosan, and dissolve out some lignin.(6) Brightness of oxygen delignification lignin is 63.0%ISO, viscosity is 1060mL·g-1, kappa number is 9.3. In the general O-D1-E-D2 bleaching process, time has little effect on the results of the bleaching.Using the time of 60min in D1, D2 processes and 30min in E process. O-D1-E-D2 bleaching result is:brightness is 87.1%ISO, viscosity is 805 mL·g-1.(7) Treated with following bleaching processes after xylanase pretreatment, brightness and viscosity are on the rise. When dosage of chlorine 0.9%, O-X-D-E-P bleaching result is:brightness is 87.9%ISO, viscosity is 949 mL·g-1.In O-X-Mn-P bleaching process, the brightness of pulp is 81.2%ISO, and viscosity can above 900 mL·g-1 when the dosage of KMnO4 0.4%.In light or super light ECF bleaching process, O-X-D1-Ep-D2 is better than other method, when dosage of chlorine 0.6%, the brightness of pulp can above 88%ISO,and the viscosity reached 961 mL·g-1. In the same brightness, O-X-D1-Ep-D2 can save 60% ClO2 than O-D1-EP-D2.After acid treatment, in the same amount of total chlorine, the brightness of the pulp is almost in the same degree, and viscosity of suspensions decreased in varying degrees, down about 7%-8%. |
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