The Basical Research About The Enzymatic Removal Of Cottonseed Coat On Cotton Fibre

The application of enzymes in the textile industry has developed rapidly over the last decade. As opposed to chemical methods, using enzymatic methods leads to processes requiring lower temperatures, less rinsing water consumption and a lower pollution load. Cellulases, hemicellulases and pectinases acting on native cellulosic fibres have become the target enzymes in bioprocessing. Removal of the lignin-containing cottonseed coat fragments is the greatest obstacle for the commercialization of cotton biopreparation. On account of the tangled structure and diverse components their removal requires more concentrated chemical solutions, longer steaming periods and higher temperature in the traditional chemical processes.In the study, the structure and components of the nature cottonseed coat were characterized, and also the main constituent hemicelluloses. In order to understand the enzymatic removal of the cottonseed coat, the adsorption of xylanase on cottonseed coat was researched. Then the hydrolysis of hemicelloses by xylanase was discussed and also the hydrosis of cottonseed coat by cellulase.The sectional view showed the structure of the nature cottonseed coat. The color of the slipe was distinct gradation which was related to the different compositions in seven different cell tiers. It was found that only 2-3 cell tiers of the nature cottonseed coat would stay on the fibers. This part was compact of different kinds of cells and the cells were smaller than other tiers.Then the components of the cottonseed coat were collected. Hemicelluloses (36.5%), lignin (30.3%) and cellulose (23.1%) are the major constituents of cottonseed coat. Twelve hemicellulosic fractions were obtained by sequential treatment of cottonseed coats'holocellulose with different concentration NaOH at 25℃for 12 h under continuous agitation. The yields of the water soluble hemicellulosic fractions were similar with the water insoluble ones. Characterized by GC, GPC, FT-IR and NMR, the hemicellulosic fractions were mainly low-branchedβ-(1, 4)-xylans and partially 4-O-methyl-glucuronoxylans. In comparison, the water insoluble hemicellulosic fractions were more linear and stabler than the water soluble ones. The hemicellulosic fractions from cottonseed coats had larger molecular weights (Mw, up to 1 453 000 g mol-1).The kinetic, equilibrium and thermodynamic models in association with model parameters would be helpful to understand more about the enzymic hydrolysis of the cottonseed coat.The adsorption of xylanase on cottonseed coat was investigated using a bath-adsorption technique at 283,298,310 K. The experimental data were modelled using adsorption isotherms, kinetic equations and intraparticle diffusion kinetics. In addition the adsorption thermodynamic parameters were also measured. The results of kinetic model showed that the process followed the pseudo-second-order rate expression. It was found that the Freundlich model and also Dubinin-Radushkevich isotherm were suitable to describe the equilibrium isotherms.ΔG0,ΔH0 andΔS0 were calculated by thermodynamic study as-3.17 kJ mol-1 (298 K),-6.29 kJ mol-1 and-10.73 J mol-1 K-1, respectively. The negativeΔH0 value showed that, in nature, the adsorption is exothermic which corresponded with the decreasing adsorption capacity with an increasing temperature. The negativeΔG0 indicated the feasibility and spontaneity of the adsorption process.Some preliminar researches about the enzymatic hydrolysis of the cottonseed coat were practiced. The hemicelluloses separated from the cottonseed coat were degraded with Pulpzyme HC. The digestion degree value was calculated by the equation depended on the release of reducing sugars concentration which was determined from DNS fitting curve equation. The optimum enzyme reaction temperature was 60℃and pH was 5.5. The duration of 80 min was chose as the most suitable enzymolysis time. The degradation degree value was 57.5%when 0.24 ml pure Pulpzyme HC was added with one milligramme hemicelluloses powder. The K+content substrate (0.5 mmol L-1) enhanced the enzymic degradation of hemicelluloses. The other metal ions were found to be some inhibitors of Pulpzyme HC. The effects of chelating agent (EDTA) were complex and no trend was observed.It was found that more than 80% of nature cottonseed coat could be degraded by cellolase under 30℃, pH=6.0 for 80 min with the liquid-solid ratio as 0.075 ml mg-1. The results of the orthogonal system showed that the liquid-solid ratio was the most important factor for the hydrolysis, then the pH of the solution and the duration of the process; the tempetrature was the least one. All the findings of the present work would have significant implications for the research about the xylanase on cotton pretreatment.