Effect of xylanase pretreatment of wood chips on fiber separation in the CTMP refining process
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The effect of xylanase treatment of eucalyptus wood chips on chip refining and fiber properties was investigated. The fiber separation region and fiber surface structure were observed with SEM, TEM, and AFM. The fiber length and fines were analyzed with a Bauer-McNett classifier and optical image analysis of flowing suspensions (FQA). The results showed that xylanase degraded and hydrolyzed some xylan in the fiber wall, thus loosening the fiber wall structure. Therefore, in the subsequent refining process, fiber separation occurred in the secondary wall. This resulted in fibers with less lignin and extractives on the surface, which will benefit the interfiber bonding.Keywords:
Refining (metallurgy)
Enzymatic Hydrolysis
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Bleaching kraft pulp with chlorine can result in toxic chlorinated species in bleach plant effluent. Removing lignin from kraft pulp with xylanase reduces chlorine required for bleaching, which, in turn, reduces toxic species in bleach plant effluent. Kraft pulp mills using xylanase pretreatment have reduced chlorine requirement for bleaching by 20 to 25% for hardwood pulp but only 10 to 15% for softwood pulp. The work reported here demonostrates that xylanase molecular size and pulp pore structure determine the amount of lignin that xylanase can remove from pulp. Using softwood pulp, xylanases wilh molecular weights of 20,000 Da, 39,000 Da, and 67,000 Da removed 48%, 39%, and 30% of lignin respectively. Mild cellulase pre-treatment of softwood pulp increased the apparent median pore size from 37Å to 67Å which enabled xylanase to reduce chlorine requirement for softwood pulp bleaching by 31%. The same process applied to hardwood pulp eliminated 41.8% of chlorine required for bleaching.
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The ability of xylanase to enhance the bleaching of kraft pulp has been successfully implemented at the industrial scale to provide an economically competitive option for the reduction of chlorine use. It is not clear how this enzymic process works because the carbohydrate-degrading enzyme is not expected to act directly on the residual lignin in pulp. The elucidation of the mechanisms of xylanase aided bleaching has been difficult due to the variable responses of different pulping and bleaching parameters. Two patterns have nevertheless been demonstrated, bleach boosting where there are substantial savings in bleaching chemicals after xylanase pretreatment and direct brightening where there is a small but significant increase in pulp brightness immediately after a xylanase treatment. The former is commonly observed in chlorine based bleaching while the latter seems to occur in partially bleached pulps. To determine the target substrates responsible for these apparently different phenomena, carefully designed experiments will be required so that the effects dependent on pulping and bleaching conditions, pulp washing, and the type of wood and enzyme are taken into account.
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The xylanase from Leveking was used in the experiment of bleached Soda-AQ pulp of fast-growing poplar. The suitable conditions of the xylanase from Leveking were obtained in the pretreatment of the Soda-AQ pulp of fast-growing poplar that temperature was 58°C, pH was 8.5, time was 120min and the dosage of the xylanase was 8IU/g. The pulp brightness was increased by 3.7%ISO when compared XDPQ and DPQ bleaching pulp under identical conditions. The pulp brightness was increased by 4.1%ISO when compared XDED and DED bleaching pulp under identical conditions. The untreated and pretreated Soda-AQ pulp of fast-growing poplar by the xylanase of two-dimensional and three dimensional figure of fiber surface under AFM were analyzed to explain the xylanase effect in the pulp bleaching theoretically.
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Abstract Blends of poly(butylene terephthalate) and high density polyethylene at a ratio of 80:20 wt% were reinforced with short glass fibers varying from 10 to 30 wt% to enhance mechanical properties. Considerable fiber damage occurred during injection molding, reducing the number average fiber length from the starting value of 4.5 mm to < 1 mm. This value decreased with increasing fiber content, which is also responsible for lowering the reinforcement efficiency. The variation in mechanical properties has been explained on the basis of fiber concertration. The effect of an ionomer, which was used to compatibilize the blends, on properties of corresponding composites has also been studied.
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Xylanase treatment is used to enhance the bleaching of kraft pulp. This technology is used in 15 mills in North America and enables the mills to bleach pulp while using 10% to 20% less chlorine dioxide or other oxidative chemicals. Xylanase treatment is carried out on brownstock prior to the bleach plant. This treatment location is satisfactory for most mills, but there is an interest in improving the benefits a mill can obtain from xylanase and in treating pulp in mills not amenable to brownstock treatments. This paper describes the xylanase treatment of pulp after the first chlorine dioxide (Do) bleaching stage. Such treatments can take place in neutral wash stages or in the first alkaline extraction stages. There is significant opportunity using xylanase treatments in these stages to obtain a greater benefit than in conventional xylanase treatments of brownstock.
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This research used poplar sulfate pulp as material to improve traditional three stages bleaching by using xylanase and exploit a new pulping method fitted to poplar sulfate pulp. We did this in order to find in what pretreatment condition it could be best . The xylanase AU-3's best pH is 8 in the condition of 70℃ and 10 IU·g-1 pulp. In this case its whiteness could increase 2%ISO than blank pulp not pretreated by xylanase. The biological bleaching with the xylanase could reduce the amount of effectively chlorine we used,and also be good to the environment.
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