Xylanase In Pulp Bleaching Application Research
Xylanase is the degradation of xylan hemicellulose general term for a group of enzymes
, enzyme composition of the complex, which mainly acts on the main chain, a 1,4-endo-p xylanase and xylosidase In general, the role of the former from the main chain within the chain in xylosidase can randomly xylan main chain degradation into short chain xylo-oligosaccharides; while the latter acting on the short-chain XOS, from the non-reducing end of the release of xylose. Xylanase in the pulp and paper industry has a wide application, it can be used in bio-pulping, pulp bleaching, waste paper recycling of secondary fiber, deinking waste paper processing and paper surface treatment, especially in Biological bleaching of pulp potential application has already aroused great concern peers.
Study found that both hardwood or softwood kraft pulp and other chemical pulp, whether traditional chlorine bleaching sequence with or with advanced non-chlorine bleaching sequence matching, using xylan enzyme treatments can promote the degradation of residual lignin in pulp and solubility of lignin extraction, not only can improve the pulp brightness and whiteness stability, improve water treatment and papermaking fiber properties, and can significantly reduce the follow-up drift order the amount of chemical reagents, thus reducing the pulp bleaching on the environment pollution. Many micro-organisms to wood fiber as the carbon source will also produce xylanase and cellulase. Xylanase in the use of bio-bleaching, which more or less a certain amount of cellulose, cellulose include endoglucanase, exo-glucanase and cellobiase, cellulase enzyme degradation of cellulose, resulting in decreased pulp strength, yield reduction, but the existence of a small amount of cellulase activity, not only more efficient removal of lignin, but also to improve the treatment of pulp and brittle. Xylanase and cellulase components in the effect on pulp and pulp strength will be different. The paper systematically reviewed the structure of the enzyme xylanase pulp properties, and help xylanase bleaching mechanism.
1 in the semi-cellulose pulp Semi-cellulose pulp fiber morphology and paper physical properties play an important role, the right to retain half of cellulose can not only improve the pulp yield, but also can enhance the strength of pulp. Despite the semi-natural wood cellulose fiber distribution throughout the cell wall, but in the semi-kraft pulp cellulose microfibril outer focus, therefore, hemicellulose on the fiber, water and chemicals between the pulp chemical reaction plays an important role in the decision. In the pulping process, the structure of hemicellulose changed greatly. In the Kraft pulping process, sodium hydroxide and sodium sulfide by boiling wood chips, semi-acetyl cellulose was completely eliminated, the number of glucuronic acid group were also significantly reduced.
Sulfate in the conventional cooking process, softwood than hardwood xylan xylanase showed greater resistance to the main base because of arabinose, arabinose in the stripping reaction from the base easily eliminate the main chain, while the first generation of partial change sugar to acid end group, thereby further resist stripping reaction occurs, so that the main chain stability. The heating process in sulfate cooking stage, relatively high alkali concentration, part of the xylan dissolved in the slurry, as the cooking progresses, the concentration of alkali kept down, when dropped to the critical point, one or more short chain xylan or less to form crystalline microfibril deposition to the surface, it is clear arabinose and glucuronic acid-base in the 1,4-xylopyranosyl chain a prominent, prevented the formation of crystals in the cooking process to remove them to improve the crystallization of xylanase trend. Xylose-based configuration of xylan and cellulose allow close contact between, this may be because some of xylan removed after the substitution tend to occur with the slurry of crystalline cellulose, absorbed in the fiber surface, although part of the xylan in the cooking process does not dissolve, but a considerable portion of xylan adsorption and deposition by way of re-exist in the Pulp. In sulfate cooking process, the deposition of xylan and lignin deposition at the same time, these deposits connected by chemical bonds of polymers, some of softwood glucomannan also dissolved in the alkaline solution, but its instability, at 130 degrees Celsius for a short period of time when it will be completely degraded, therefore, whether softwood or hardwood, pulp glucomannan Portugal is lower than xylan, however, there the fiber in the glucomannan is very stable, they do not dissolve. In conventional pine kraft pulp, the xylan about 1 / 2 is the deposition of xylan; in birch kraft pulp, the xylan deposition accounts for about 3% of plasma volume, is the pulp xylan in all 5% -10%, xylan adsorption of those molecules seem to prefer low-sugar acid base dissolved xylan. In sulfite cooking process more thoroughly dissolved hemicellulose into simple sugars and oligosaccharides, no deposition phenomenon, therefore, residual hemicellulose distribution in the whole cell fibers, sulfite pulp Kraft has more than E low soluble sugar content and more hemicellulose components. In sulfite cooking process, remove the base as arabinose, coniferous wood in the O-methyl glucuronic acid arabinoxylan into 4 1 O 1-methyl-glucuronic acid, xylan, acid sulfite Kraft pulp has more than glucomannan.
Xylanase In Pulp Bleaching Application Research
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