| Cationic starch (CS) is one of the most important derivatives of starch. It is widely used inpapermaking industry. Especially the good properties of quaternary ammonium based cationicstarch which can be used under wide pH range have caught the attention of more and morepaperworkers and researchers.Now the degree of substitution (DS) of cationic starch used in wet-end of papermaking isgenerally in the range of 0.01 to 0.07, and the DS of this kind of starch is low. In order to makebetter use of cationic starch and to develop cost-effective paper additives preparation ofcationic starch by wet process was intensively studied. Through investigation of the relevantinfluencing factors, the preparation procedure was optimized. Also the preparation proceduresof different DS(0.01～0.05) based cationic starch products were optimized by the same method.By analyzing the synthesis conditions, a repeatable and cost-effective procedure was developed.Then, the synthetic products were used as strength aids in the wet-end of papermaking, and thestrengthening effects were investigated and discussed.In the first part of the research work, the preparation procedure of low substituted ofcationic starch was studied. By wet process, the influending factors including reactiontemperature, alkaline dosage, reaction time were intensively studied. And the relationshipbetween these factors and DS of cationic starch was discussed. The synthesis procedure ofstarch with DS of 0.05 was initially optimized. By changing the dosage of quaternaryammonium salt (3-chloro-2-hydroxypropy-trimethyl-ammonium chloride,CHPTMA), thereaction conditions with the corresponding DS of 0.05, 0.033, 0.022 and 0.01 were optimizedaccording to orthogonal experimental analysis. By intensive comparisons of the relevantprocedures,the optimum conditions were obtained as follows: temperature of 55℃～60℃,reaction time of 6～7, addition amount of water(quality to starch) of 1.2:1, and NaOH/CHPTof 1.94～2.12.Secondly, the application of low substituted CS in wet-end of papermaking was studied.The strengthening effect of cationic starch on bleached softwood pulp, bleached hardwoodpulp, unbleached softwood pulp and the mixture of bleached softwood pulp and bleachedhardwood pulp was discussed. Then the CS was applied in sack paper as strengthening agent.The experimental results show that: striking strengthening effect can be achieved. Amongdifferent products of cationic starch, the product with DS of 0.022. can give the most strikingstrengthening effect. Then the application condition and procedure of CS was preliminaryoptimized. Subsequently, the application of the starch product with DS of 0.022 in sack paperwas further studied, the results show that: when furnish pH, starch dosage, mixing time of starch and furnish are 8.0～9.0, 1.0%～1.5% and 10min, and when filler loading level, is lessthan 15%, optimum effect can be obtained (the drainage and retention of paper was well,≥93%).Also, the synthetic products were compared with the commercial products, the resultsshow that the strengthening effect of the synthetic product is better.The synthetic products were finally characterized by Fourier transform infraredspectroscopy (FTIR) and scanning electron microscope (SEM).The mechanism of the productsused as paper strengthening agents was studied theoretically. The interaction between CS andfiber was also elucidated.
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