【作者】 钱维金；

【导师】 黄祖强；

【作者基本信息】 广西大学 ， 化学工艺， 2007， 硕士

【摘要】 淀粉是一种来源广泛、价格低廉、可完全降解的天然高分子物质。原淀粉由于力学性能差，低温时分散性能不好，渗透力差等缺点使应用受到限制，淀粉经过物理或化学方法引发，与丙烯腈、丙烯酰胺和丙烯酸等单体进行接枝共聚反应，形成淀粉接枝共聚物，从而可以制得不同性能的产品，它们在高分子絮凝剂、高吸水材料、造纸工业助剂、油田化学材料，可降解地膜以及塑料等多方面的实际应用中具有优异的性能。然而由于原淀粉具有半结晶的颗粒结构，结晶区的存在使得接枝反应只能在淀粉表面进行，导致难以制备高接枝率（G）和高接枝效率（GE）的产物。因此，研究如何通过减少淀粉结晶区的方法来提高淀粉的反应活性已成为一项极其重要的研究课题。本文采用自制的搅拌磨对淀粉进行机械活化，然后将机械活化淀粉用于淀粉接枝共聚反应，采用过硫酸铵和亚硫酸氢钠为复合引发剂、丙烯酰胺为单体进行接枝共聚反应，以G和GE为评价指标，考察了机械活化时间、反应时间、淀粉浓度、引发剂浓度、单体浓度、反应温度对其接枝反应的影响；并以接枝量（G_m）为评价指标，研究了不同活化时间机械活化淀粉的接枝共聚反应动力学；采用红外光谱（FTIR）、差示扫描（DSC）、X-射线衍射（XRD）和扫描电镜（SEM）对接枝产物进行了表征。根据实验结果和理论分析，得到如下主要结论：（1）在同样实验条件下，玉米原淀粉（糊化）及活化30、60min的淀粉的接枝反应G分别为93.68、108.60和143.71％，GE分别为58.93、62.67和86.27％；木薯原淀粉（糊化）及活化30、60min的淀粉的G分别为84.90、134.01和111.94％，GE分别48.36、82.61和71.36％，由此可见，玉米与木薯淀粉经过机械活化预处理后其反应活性明显提高；但木薯淀粉活化时间过长，G和GE略有下降，这是由于机械活化过度降解所造成。（2）在实验条件下，玉米原淀粉及活化30、60min淀粉接枝反应的表观活化能（E_g）分别为34.92、31.26、17.38kJ·mol^-1，淀粉反应级数分别为0.49、0.44、0.40，单体反应级数分别为1.05、0.99、0.87，引发剂反应级数分别为0.50、0.46、0.39；木薯原淀粉及活化30、60min淀粉接枝反应的E_g分别为36.33、22.86、24.61kJ·mol^-1，淀粉反应级数分别为0.50、0.44、0.46，单体反应级数分别为1.00、0.94、0.96，引发剂反应级数分别为0.50、0.45、0.47，与原淀粉（糊化）进行比较，机械活化淀粉的反应级数与活化能显著降低。表明机械活化对木薯、玉米淀粉的接枝反应有显著的强化作用，接枝反应对反应温度、单体浓度、引发剂浓度等依赖性降低，反应活性显著增强。（3）红外光谱（FTIR）分析表明丙烯酰胺已成功参与了淀粉的接枝共聚反应；差示扫描（DSC）测试表明，随着G的增加，淀粉接枝物的热稳定性显著提高，结晶度降低；X-射线衍射（XRD）和扫描电镜（SEM）研究表明接枝反应不仅发生在无定形区，而且也发生在结晶区，接枝反应对淀粉颗粒结晶结构影响显著。更多还原

【Abstract】 Starch is a sort of natural polymer materials with wide source and low priceand can be completely degraded. Due to its poor mechanical performance, poordispersion property at low temperature and weak seepage force, native starchcan only find limited applications. After being initiated by physical or chemicalmethods, starch could be grafted with monomers such as acrylonitrile,acrylamide and acrylic acid and form graft copolymers with different properties,which may have potential applications in polymeric flocculants, super absorbentmaterials, paper manufacturing, petroleum chemical materials, degradable films,plastics and etc. However, starch granule usually has a semicrystalline structureand the graft reaction can only occur on the granule surface due to the hindranceof crystalline region, which makes it very difficult to prepare copolymer withhigh grafting ratio （G） and high grafting efficiency （GE）. Therefore, how todecrease the ratio of crystalline region in starch granule and improve thereaction activity of starch, has become an important and hot research topic. In this thesis, maize and cassava starch were mechanically activated by astirring-type ball mill. Then the activated starches were used to fabricate graftcopolymer in the presence of monomer of acrylamide and combined initiators ofammonium persulfate and sodium bisulfate. Using G and GE as evaluatingparameters, the influences of activation time, reaction time, starch concentration,initiator concentration, monomer concentration and reaction temperature on thegraft reaction were investigated. Using grafted mass （G_m） as an evaluatingparameter, the kinetics of graft copolymerization was also studied. The graftcopolymers were characterized by Fourier transform infrared （FTIR）spectroscopy, differential scanning calorimeter （DSC）, X-ray diffraction （XRD）and scanning electron microscopy （SEM）. It was found that:（1） For the maize starch, the G values of the non-activated （aftergelatinization） starch, activated starch with activation time of 0.5h and 1.0h are93.68%, 108.60% and 143.71%, respectively; while the GE values are 58.93%,62.67% and 86.27%, respectively. For the cassava starch, the non-activated（after gelatinization） starch, activated starch with activation time of 0.5h and1.0h have G values of 84.90%, 134.01%, 111.94% and GE values of 48.36%,82.61%, 71.36%, respectively. It can be seen that the mechanical activationpretreatment could obviously enhance the starch graft reactivity. However, whenthe cassava starch is over-activated, the G and GE decrease slightly due to itsexcessive degradation.（2） For the graft copolymerization of maize starch, the native starch and activated starch with activation time of 0.5h and 1.0h have apparent activityenergies （E_g） of 34.92, 31.26, 17.38 kJ.mol^-1, reaction orders of 0.49, 0.44, 0.40,monomer reaction orders of 1.05, 0.99, 0.87 and initiator reaction orders of 0.50,0.46, 0.39, respectively. For the graft copolymerization of cassava starch, thenative starch and activated starch with activation time of 0.5h and 1.0h have E_gof 36.33, 22.86, 24.61 kJ.mol^-1, reaction orders of 0.50, 0.44, 0.46, monomerreaction orders of 1.00, 0.94, 0.96 and initiator reaction orders of 0.50, 0.45,0.47, respectively. These results clearly indicate that the mechanical activationprocessing could obviously decrease the reaction orders and activity energy, andtherefore enhance the starch graft copolymerization. The mechanical activationprocessing also weakens the dependence of the graft copolymerization on thereaction temperature, initiator concentration and monomer concentration.（3）The acrylamide is successfully involved in the starch graftcopolymerization, as is verified by the FTIR analysis. DSC results demonstratethat the thermal stability of the graft copolymers improves with the increase ofG and the crystallinity of the product decreases. XRD and SEM analysis revealsthat the graft reaction occurs not only in the amorphous region, but also in thecrystalline region of the starch. And the graft reaction has notable influence onthe crystal structure of the starch granule.更多还原