The Modification And Application Of Cross Linked Starches In Corrugating Medium Surface Sizing

At present, paper mills always use starch surface sizing to enhance ring crush strength of corrugating medium. But because most of the papers are derived from the waste paper pulping, so that paper properties are not very good. Paper properties will lose very fast so far as to gone especially when paper is put in moist environment. Since nowadays most of our country’s paper mills are located in the Yangtze river delta and the pearl river delta. The climate there is very humid, especially in the summer which has a high temperature and a high humid environment, so that the strength of corrugated medium will lose fast.Multiple hydroxyl groups exsit in starch, the hydroxyl peculiar has a chemical property of alcoholic hydroxyl. When those hydroxyl react with chemical reagent with two or more functional groups, different starch molecules hydroxy crosslink together, the resulting derivative is called crosslinking starch. When corn starch was oxidized the long chains which exised in starch wound be ruptured, which wound expose more hydroxyl groups that made it more suitable for crosslinking.How to enhance the strength and improve the water resistance of corrugated medium was studied in this paper.When glyoxal or sodium trimetaphosphate and oxidized starch crosslinking reacts, first gelatinize oxidized starch and then add glyoxal or sodium trimetaphosphate will be better compared with mixed them up and heated pasting togather, so that the starch’s viscosity was more suitable for surface sizing. Crosslinking reaction occured when oxidized starch paste mixed glyoxal at 95℃ as well as in the drying process which pasted corrugated base paper was put in 105℃ oven. By experiment, sizing quantity controlled less than 4g·m-2, the sizing liquid temperature was 95℃ so that the papers had better properties. When glyoxal was used as crosslinking agent, the optimal solution was that, 40%glyoxal addition was 1.5%(relative to starch), the density of oxidized starch was 10%, sizing liquid p H was 5. Compared with the oxidized starch sizing, the paper’s ring crush index increased by 12.35%, the tensile index increased by 23.45%, Cobb water absorption value reduced by 67%. When sodium trimetaphosphate was used as crosslinking agent, the optimum solution is that, sodium trimetaphosphate addition was 6%(relative to starch), the density of oxidized starch was 10%, sizing liquid p H was 5. Compared with the oxidized starch sizing, the paper’s ring crush index increased by 18.5%, tensile index increased by 7.2%, Cobb water absorption value reduced by 56.26%.In the process of oxidation reaction when used original starch, also crosslinking reaction occured at the same time. Glyoxal, ammonium persulphate and corn starch crosslinking reacted, ammonium persulphate oxidized corn starch, glyoxal used as crosslinking agent.By experiment, when the system reacted for 30 min and the system was p H7 which was preferred. When not added aluminium sulfate, the best solution was that reaction system was 85℃, 40%glyoxal addition was 1.5%(relative to starch), ammonium persulfate addition was 0.8%(relative to starch) for reaction. After adding aluminium sulphate 5%(relative to starch), the best solution was that the reaction system was 95℃, 40%glyoxal addition was 1.5%(relative to starch), and ammonium persulfate addition was 0.8%(relative to starch). Compared to the corrugating medium which was painted by 10% oxidized starch, ring crush index increased by 22.08%, tensile index increased by 17.11% at most, Cobb water absorption value reduced by 71.80%.