| Cationic starch ether is a chemical modified starch which can be achieved by reacting with the agent (tertiary amine compounds, quaternary amine compounds and imino compounds) in alkaline catalyst condition. Due to the high charge of cationic starch with high degree of substitution (HCS), it can be used in the wet-end papermaking to strongly adsorb filler, fiber and other anionic substances. The reaction can increase the fine fiber and filler retention rate, and improve the strength of paper. When HCS used in paper coating, it can strongly bind the negative charge between pigments and pigments, pigments and paper fibers to improve the color depth and fix colors.Firstly, HCS were prepared with NaOH as alkali catalyst,3-chloro-2-hydroxypropyl trimethyl ammonium chloride (CHPTAC) as a cationic reagent, in the presence of a small amount of water, using the improved process to get different degree of substitution of cationic starch. The amount of NaOH and CTA, reaction temperature, reaction time, water content were fully discussed. Then, the orthogonal experimental method was used to optimize the conditions of preparing HCS. Single factor experiments results were abtained:water content was 30%, CTA/AGU was 1.0(the mol ratio of CHPTAC with unit glucose), NaOH/CTA was 1.2(the mol ratio of NaOH with CTA), the reaction temperature was 65℃, the reaction time was 4h. Orthogonal optimum conditions obtained as follows:water content was 25%, CTA/AGU was 1.0, NaOH/CTA was 1.4, reaction temperature was 60℃, reaction time was 5h.Then the prepared HCS were used in high-yield pulp. The influences of different degree of substitution of cationic starch and its concentration on pulp retention and enhancement of strenth were discussd. The different slurry pH value on the use of the performance of HCS, the impact of HCS react with slurry in different time were taked into account. PDMDAAC (Poly diallyldimethyl ammoniumchloride), cationic starch with low degree of substitution were compared with HCS in order to research the effect that HCS used in high-yield pulp. The results were found that the degree of substitution of 0.64 HCS showed the best effect in paper folding and the tensile strength, the optimum dosage is 0.6%～0.8%. In the condition of pH7.2, the reaction time of 5～10min, that the cationic starch with high degree substitution of 0.64 obtained the best effect. The results that compared to the application of two other kinds of additives showed that the HCS with high degree of substitution of 0.64 revealed the best application. The tensile strength values of paper was far more than the low degree of substitution of cationic starch and PDMDAAC.Moreover, the orthogonal experiment was used to optimize the coating formulation of surface layer, then the HCS were used in the optimized coating formulations. The rheological behaviors of coating were researched and the printing effects of coating paper were tested. It was found that:The amount of cationic starch greatly impact the viscosity of coating, and with the increase of degree of substitution, the coating liquid viscosity will increase as well, and the best dosage was 2%～4%. With the increase of degree of substitution, the paper whiteness reduced. When used the cationic starch that the degree of substitution are more than 0.4, the color density values of paper were significant higher than that of less than 0.4 degree of substitution of cationic starch. HCS with DS of 0.849 was contrasted with another cationic additive PDMDAAC (self-made), it was found that:self-made cationic starch in some areas had been better than PDMDAAC, and the satisfactory print density results was achieved. Finally, orthogonal experiment was used to optimize the best formula that the HCS used as a fixing agent in paper coating, the results were obtained as follows:PVA40%, HCS3%, PCC:SiO2=70:30, CMC1%, dispersing agent 0.6%, defoamer 0.05%～0.1%.
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