Research On The Improvement Of Paper Strength By Using Hemicelluloses

With the development of economic globalization, resource and environmental problems have become common problems in the world, and pulp and paper industry is affected seriously. Therefore, the renewable biomass resource utilization becomes the developing direction of modern industry and much attention has been paid on how to realize the integrated papermaking industry.Hemicellulose is an inexhaustible carbohydrates resource and sorely in need of development and utilization. In the pulping process, most of hemicellulose is dissolved into the waste liquor, leading to a waste of resources. Hemicellulose can be used in papermaking because of its active chemical properties. However, due to the complexity of its molecular structure, such as the degree of polymerization and monosaccharide composition, the dissolved types and degradation of hemicelluloses in papermaking waste liquor vary with the particular fiber materials and pulping processes, which limits its application in industry. This paper, therefore, focuses on hemicellulosic structure. Different hemicellulosic models were prepared and then used as wet-end additives and surface sizing agents in papermaking to investigate the influences of configuration and molecular weight of hemicelluloses on their paper-strengthening effects. Moreover, the paper-strengthening effect of hemicellulose from APMP waste liquor was also studied.Firstly, xylan, glucomannan and arabinogalactan with higher purity were extracted from woods. The structural characterization and molecular weight distribution determination were then carried out. The xylan with higher purity and yield was chosen to be treated with hydrochloric acid, and the hemicelluloses with different molecular weights were obtained.Then the hemicelluloses, obtained above, were used as wet-end additives to improve the strength of handsheets. The influences of configuration and molecular weight of hemicelluloses on their paper-strengthening effects were investigated. Results showed that xylan, glucomannan and arabinogalactan all had obvious paper-strengthening effects. Glucomannan had the best effects, followed by xylan and then arabinogalactan. Hemicelluloses with higher molecular weight had better strengthening effects.The hemicelluloses were then used as surface sizing agent coordinating with starch. Results demonstrated that xylan had the best sizing performance (paper-strengthening effect and water resistance), followed by glucomannan, and their effects were both greater than that of starch alone. Furthermore, hemicelluloses with higher molecular weights had better sizing effects.Compared with hemicelluloses obtained from raw materials, the hemicelluloses in APMP (alkaline peroxide mechanical pulp) waste liquor was degraded to a certain degree during pulping process. However, it also showed good paper-strengthening effects when used as wet-end additives and surface sizing agent.Secondly, the thin waste liquor was used to replace fresh water to prepare the surface sizing agent. By comparing the strengthening effects of sizing agents on corrugated medium, a better gelatinizing and application process of sizing agent was selected:the sizing agent with concentration of starch8%was prepared by directly using waste water for gelatinizing, and the dosage of aluminum sulfate was twice of the common dosage in surface sizing operating. Results of the application indicate that this type of surface sizing agent has approximately the same sizing effect as that of10%starch alone. This means that using this kind of surface sizing agent not only decreases the sizing cost, but also reduces the pollution on the environment.Finally, the pulping thick waste liquor of APMP was modified by cross linking, and used as surface sizing agent for corrugated medium. The results show that the strengthening effect of modified waste liquor was significantly better than that of the original waste liquor. Glyoxal was better cross-linking agent, and the optimal modification conditions were glyoxal dosage20%, reaction temperature70℃, reaction time2.5h, pH6. When the resultant product was mixed with gelatinized starch by a solid ratio of1:1for surface sizing application, the tensile strength and ring crush strength of sized corrugated paper increased by44.2%and46.0%, respectively, compared to that of the controlled sample.Overall, the results of the present study provide some theoretical references and technical support for the application of hemicelluloses in nature and pulping waste liquor to improve paper physical strength. The hemicelluloses, especially in the high yield pulping waste-liquor, can replace starch for papermaking application to some extent, which might provide a new way to alleviate the food and energy resource crisis.