Novel Research On Improving Paper Strength With Starch Gel And Its Mechanism

Beating pulp or using additives is the traditional method to improve paper strength, but their effects are limited currently with only 30% maximum increase. It could be worse for raw material having bad quality. In this paper, two novel technologies for improving paper strength, treating mechanical pulp with oxidized starch, were studied. Using chemical and physical methods, oxidized starch, mainly utilizing its glutinosity, could enwrap partially or even wholly on the surface of fiber, by which the combining of pulp fiber and starch retention could be improved.The technology of cooking the mixed mechanical pulp and oxidized starch was discussed. This mixture, after cooked by using stream under some fiber concentration, was squeezed to remove most water and improve the adhesive ability of starch. Result showed that oxidized starch could arrive at the top of glue ability when fiber concentration was 15% and paper strength could be improved by 133.28% with 97.6% retention rate of starch.On the basis of the technology mentioned above, the process was simplified resulting in the other method for improving paper strength which means the cooked starch was mixed with pulp and then this mixture was squeezed under some pressure to have better paper strength and starch retention. The study showed that after treated with this method, starch retention rate could arrive at 94% with paper strength increasing 141.18% at most. In addition, the second technology was much simpler and easier to be operated for large-scale application.The performance of pulp fiber after treated was tested by the two technologies. Zeta potential (minus) of the treated fiber was lower than the one of untreated, which indicated that oxidized starch formed some gel-layer with covering partially negative charge on the surface of fiber. Moreover, drain ability of the treated fiber was improved obviously.The digital-optical microscope and SEM pictures of the treated pulp fiber with these two technologies above showed that the shape of starch on the surface of fiber was flat with bigger amount. It was considered that the oxidized starch could adhere to the surface of fiber partially or wholly to form some starch gel layer with flat shape, which had good influence on the combination of fiber by improving bonding force and bridging area between fibers.