机械活化对木薯淀粉醋酸酯化反应的强化作用

采用搅拌球磨机对木薯淀粉进行机械活化，以不同活化时间的木薯淀粉为原料，以醋酸酐为酯化试剂、甲磺酸为催化剂制备淀粉醋酸酯，并以取代度为评价指标，分别研究了机械活化时间、反应时间、反应温度、催化剂用量及醋酸酐用量对木薯淀粉醋酸酯化反应的影响. 结果表明，机械活化对木薯淀粉酯化反应有显著的强化作用，活化时间越长，取代度越高. 主要原因是机械活化使木薯淀粉紧密的颗粒表面和结晶结构受到破坏，降低了结晶度，酯化试剂更容易渗透到颗粒内部使淀粉醋酸酯化. 其他因素对淀粉酯化反应的影响规律受活化时间的制约，活化时间越长，酯化反应对反应温度、催化剂及醋酸酐浓度的依赖性越低. 并利用红外光谱对木薯淀粉、活化淀粉及高取代度淀粉醋酸酯的结构进行了表征.

Enhancement Effects of Mechanical Activation on Esterification of Cassava Starch

Cassava starch was mechanically activated by a stirring-type ball mill.Using acetic anhydride as esterification agent and methanesulfonic acid as catalyst,starch acetate was synthesized from cassava starch with different activation times.The effects of mechanical activation time,reaction time,reaction temperature,catalyst amount and acetic anhydride amount on esterification of cassava starch were investigated respectively by using degree of substitution(DS) of starch acetate as evaluating parameter.The results indicated that mechanical activation considerably enhanced the esterification of cassava starch,the DS increased with increasing activation time.The reasons are due to that the crystal structure and compact granule surface of cassava starch were destroyed by mechanical activation,the crystallinity decreased and reagents were easier to diffuse into starch intra-molecules.Moreover,it was also found that other affecting factors had a certain influence upon esterification and were closely related to the activation time of cassava starch,and the effects of reaction temperature,catalyst and acetic anhydride concentrations on esterification were reduced with increasing activation time.Furthermore,the structures of native starch,activated starch and high DS starch acetate were further characterized by using FT-IR.