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淀粉基接枝共聚物的合成及反应动力学研究

Study on the Synthesis and Kinetics of Starch-based Graft Copolymer

【作者】 王百军

【导师】 谢晖;

【作者基本信息】 南京工业大学 , 化学工程, 2003, 硕士

【摘要】 淀粉作为一种天然高分子化合物用于工业生产各个领域已有很长的历史。由于天然淀粉虽具亲水性,但不溶于水;随着温度升高膨胀糊化;粘度高;流动性差等自然属性,其使用受到很大的限制。淀粉与乙烯基单体接枝共聚是淀粉化学改性的重要方法。接枝淀粉是通过化学或高能射线辐射方法活化淀粉大分子,使所希望的低聚物成为一个“支链状”接枝到淀粉大分子上。由于接枝淀粉是由天然淀粉与应用性能优越的具有一定聚合度的合成聚合物结合在一起,两者取长补短,从而提高了天然高聚物的使用价值及扩大了应用范围。常用的接枝单体有醋酸乙烯酯,丙烯酸甲酯,甲基丙烯酸甲酯,甲基丙烯酸乙酯,甲基丙烯酸羟乙酯,甲基丙烯酸羟甲酯,丙烯腈,甲基丙烯腈,丙烯酰胺,丁二烯,苯乙烯和马来酸酐和它们中的混合物。淀粉接枝共聚物的用途十分广泛,在高吸水材料、生物降解塑料、造纸工业添加剂、环境废水处理、石油工业、医药工业及粘合剂制造诸方面都有其一席之地。本论文通过对淀粉进行接枝共聚改性,制得的接枝共聚物具有淀粉和单体的双重优良性能,使其能够应用于水性的柔性凹版印刷油墨中做连结料。根据所查文献,采用乳液聚合的方法,以过硫酸铵为引发剂,以十二烷基硫酸钠为乳化剂,考察了淀粉与苯乙烯/丙烯酸丁酯的接枝共聚反应中引发剂浓度、单体浓度,反应温度,反应时间等条件对接枝率、接枝效率以及接枝反应速率的影响。最后,根据实验数据,对该接枝共聚反应的机理进行探讨,得出反应初期的动力学模型。主要结论:1 过硫酸铵是可溶性淀粉与苯乙烯/丙烯酸丁酯二元单体接枝共聚的有效引发剂。接枝率最高可达250.5%,接枝效率可达73.8%,单体转化率可达95.8%。2 淀粉预糊化对接枝反应有重要影响。不同糊化程度下对接枝效率进行比较,发现在75℃下预糊化30min接枝效率良好。3 在固含量为30%不变的情况下,当淀粉与单体重量比为1:4时,接枝效率最好。研究单体的比例发现,苯乙烯与丙烯酸丁酯的比例为2:1时接枝效率最好。4 最佳引发剂浓度为6.0×10-3mol/L,以此浓度的过硫酸铵引发接枝效果好,引发剂浓度过高,产物中的均聚物增加。乳化剂十二烷基硫酸钠的浓度控制在0.0208mol.L-1<WP=4>左右较为合适。5 最佳反应温度为53℃,接枝反应的时间控制在3.5小时左右为宜。温度过高,时间过长,均聚物含量增加。6 红外光谱图表明已合成出淀粉-g-PSt/BA共聚物。SEM照片发现接枝物中淀粉以团粒形状存在,即接枝反应发生在淀粉团粒表面。7 由动力学数据可以关联出在低引发剂浓度下,反应初期的接枝反应速度与反应物浓度之间的关系为:

【Abstract】 There had a long history that starch was used in industrial production for using as a kind of preferred crude macromolecule compound. There also had a limitation in its application as a result of its character of hydrophilicity, gelatinization, and glutinosity.The graft copolymerization of vinyl monomers onto starch was an important method for the chemical modification of starch. Grafted starch could be synthesized through chemical initiator or high-energy ray activated starch in order that low-grade polymer was grafted onto starch as a branched chain. As grafted starch was copolymer of starch and monomers, it had wide application area.Preferred monomers included vinyl acetate, methyl acrylate, methyl methacrylate, ethyl methacrylate, hydroxyethyl methacrylate, hydroxymethyl methacrylate, acrylonitrile, methacrylonitrile, acrylamide, butadiene, styrene and maleic anhydride and mixtures thereof.Starch graft copolymers had extensive application. It could be used in super-absorbent, biodegradable plastics, paper-making industry additive, environment effluent disposal, petroleum industry, medical and pesticide industry, and adhesives industry.The soluble starch was modified by means of graft copolymerization in experiment, in order to prepare grafted copolymer which possessed both favorable qualities of starch and monomers, and to be used as a new kind of binder in printing ink. Based on literatures, a study on graft emulsion copolymerization of styrene/butyl acrylate onto starch was carried out by using ammonium persulfate as initiator and sodium dodecyl sulfate as emulsifier. The influence of initiator concentration, monomer concentration, reaction temperature, and reaction time on grafting parameters of starch graft copolymers was investigated. Finally, the reaction mechanism was also discussed, the possible kinetic model was supposed according the results of experiment. The model agreed well with the experimental results. The main conclusions as below:1 Ammonium persulfate was a quite effective initiator in graft copolymerization of styrene/butyl acrylate with soluble starch. It was found that grafting degree approached 250.5%, grafting efficiency approached 73.8%, and the maximum monomer percent<WP=6>conversion approached 95.8%.2 The pre-gelatinization of starch had important influence on graft copolymerization. Compared grafting efficiency in different gelatinization conditions, the experiment showed that the grafting efficiency was preferable if the starch was gelatinized under 75℃ for 30 minutes.3 If the solid content of polymer emulsion was 30%, the perfect grafting efficiency was obtained when the weight ratio of starch and monomers was 1:4. On the condition of weight ratio between styrene and butyl acrylate was 2:1, grafting efficiency was also perfect.4 The preferred initiator consistency was 6.0×10-3mol/L. The homopolymer in the product was increased if the initiator consistency was over 6.0×10-3mol/L. It was preferable that the emulsifying agent consistency was 0.0208mol/L.5 The optimal reaction temperature was 53℃. The optimal reaction time was 3.5 hours. If the reaction temperature was above 53℃ or the reaction time was above 3.5 hours, the homopolymer content of the product would increase.6 The evidence of graft copolymer had been researched by means of infra-red spectrogram. The graft was occurred on the surface of starch grain through the testing result of SEM photograph.7 The expression of graft polymerization rate at the beginning of reaction was obtained from experiment was expressed as:

  • 【分类号】O631
  • 【被引频次】10
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