Characterization Of S7-xyn Xylanase And Its Application In The Bleaching Of Wheat Straw Pulp

Paper industry is one of the most important industries of our national economy, and it is becoming one of China's most serious sources of industrial pollution. In the traditional chlorine bleaching process, dioxin as the representative of the strong carcinogenic substances in bleaching wastewater cause serious environmental pollution, and brings great difficulties for the treatment of bleaching wastewater. Therefore, looking for small degree pollution or pollution-free alternatives has become an urgent task for pulp and paper industry. Use of xylanase treatment on pulp can reduce bleaching chemical consumption, increase physical strength and brightness of pulp. As high temperature and high alkaline bleaching process, heat, alkali and low cellulase activity of xylanase is the first choice of xylanases for biobleaching .In this study, S7-xyn xylanase characterization was investigated, applied in the ECF and TCF bleaching of wheat straw pulp, and compared the bleaching effect with two commercial xylanases. The main results are as follows:The recombinant Pichia pastoris producing S7-xyn xylanase was cultured in a 10L fermentor ,and the highest xylanase activity reached 371IU/mL; S7-xyn xylanase liquid was obtained after treatment on the broth, and S7-xyn xylanase characterization was investigated. The optimum catalytic temperature of S7-xyn xylanase is 70℃, and maintains high activity from 60℃to 80℃. The thermal stability at 65℃is good; The optimal reaction pH of S7-xyn xylanase ranges from 6.0 to 10.0; the optimum pH is 9.0, and is stable from pH 3.0 to pH 12.0; S7-xyn xylanase activity is activated by Na⁺, Mg²⁺ and K⁺, especially K⁺. Cu²⁺, Al³⁺ and Fe ³⁺ have strong inhibition on the S7-xyn xylanase activity; The optimum substrate of S7-xyn xylanase is oat xylan, and it dose not have cellulase activity.The optimal condition for S7-xyn xylanase treatment on wheat straw is 10IU / g, 70℃, pH 9.0, 1.5h. S7-xyn xylanase treatment on wheat straw is conducive to the following DEPP bleaching, and the final pulp brightness and physical performance is better than the control. The effect of S7-xyn xylanase treatment is the best to reduce the use of chlorine dioxide; After S7-xyn xylanase treatment on wheat straw, the following OP bleaching effect was not obvious. The use of S7-xyn xylanas treatment on pulp after oxygen delignification is conducive the hydrogen peroxide bleaching, and improves the final pulp brightness and physical properties, The effect of S7-xyn xylanase treatment on wheat straw pulp is the best among the three xylanases, and it reduces approximate 10% hydrogen peroxide charges. In this paper, S7-xyn xylanase successfully applied to the bleaching of wheat straw pulp, and experimental data is provided for the development of biobleaching, which provides a new idea to energy saving and emission reduction for the paper industry...