| The study uses Populus×euramericana AS-AQ Pulp as raw material, discuss measure of decrease of ClO2and H2O2in bleaching, optimum condition of various additive, condition and theory of alkaline xylanase, and improved effect from using bleaching additive and xylanase. The main conclusions are as follows:1) Compared with84.5%ISO traditional five periods bleaching, in the use of chlorine amount to1.8%, brightness is amount to85.6%ISO under the way of adding ClO2splitting and controlling pH in Do.Compared with D0E1D1E2D2traditional five periods bleaching, the (D0RE1P)(D1E2P)(D2E3P) D3save chlorine amount to1.2%. The bleaching cancels washing unit between D and E periods, adds alkaline extraction by H2O2strengthening. In the use of chlorine amount to2.2%, brightness is amount to84.7%ISO.All kinds of additives optimum dosage are:0.6%H2O2,1.0%DMSO,1.0%SA,1.0%glucose. These can save chlorine dosage are:0.2%,0.6%,0.6%,0.1%. The two best effects are H2O2and SA, but the worst is DMSO.2) One period bleaching of2.0%H2O2-2.0%SPB, brightness is amount to73.6%ISO.It higher than traditional bleaching’s0.6%ISO in use of4.0%H2O2, and decreases2.0%H2O2.The optimum condition of H2O2-TAED activation system:TAED and H2O2the molar ratio of0.6:1, NaOH3.0%, MgSO40.05%, Na2SiO33.0%,10%pulp consistency,70℃,90min. The optimum H2O2dosage of activation system is3.0%. Brightness is amount to78.0%ISO, higher than traditional bleaching’s3.6%ISO in use of5.0%H2O2, and decreases2.0%H2O2with reducing temperature, shortening time.3) The optimum pretreatment condition of alkaline xylanase:0.40IU/g dosage, pH=8.5,50℃, 60min,8%pulp consistency. The brightness is to56.0%ISO under this condition, higher than contrasted pulp without xylanase pretreatment3.0%ISO.According to SEM, the surface of the biobleaching fiber is more coarse and soft than unbiobleaching fiber. The tail of fiber becomes porous and permeable.According to X-ray, the crystallinity of the biobleached pulp increased a little compared with contrast pulp. It is illustrated that alkaline xylanase attacks amorphous zone primarily without destroying crystalline region.According to IR, free hydroxide radical is turn on after xylanase pretreatment. Xylanase can make carbonyl group and lignin oxidative degradative.4) For the improvement of DED, the brightness of OXD1PED2P with xylanase pretreatment and adding H2O2in D stage amount to82.1%ISO, and the consumption of chlorine can be decreased from1.8%to1.4%. Similarly, the brightness of OXD1SAED2SA adding SA amount to82.6%ISO. The consumption of chlorine can be saved0.4%.For the improvement of DEPP, the brightness of OXDPEPP with xylanase pretreatment and adding H2O2in D stage amount to80.2%ISO, and the consumption of chlorine can be saved0.3%compared with traditional bleaching. In the same way, the brightness of OXDSAEPP adding SA amount to83.0%ISO. The consumption of chlorine can be saved0.3%.It could be improved by xylanase pretreatment, adding KMnO4bleaching stage and SPB replacing H2O2about OP bleaching. The brightness of OXMnPSPB amount to80.3%ISO.in the use of3.0%H2O2. Likewise, the brightness of OXMnPTAED amount to82.4%ISO.For the ODP, achieving85.0%ISO needs1.0%H2O2and1.0%SPB. The consumption of H2O2can be reduced by2.0%. The brightness attains to85.0%ISO by means of TAED activation and1.0%H2O2. However,84.7%ISO brightness of traditional ODP bleaching requires3.0%H2O2.For the DED, DEPP and ODP bleaching, take measures of alkaline xylanase pretreatment before blraching, adding H2O2and SA in D stage, or adding SPB and TAED assisting P stage Bleaching, can not only reduce consumption of chlorine, but also maintain physical property of paper. Tensile index and folding strength are enhanced. |
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