热塑性木薯淀粉回生过程的结构与性能研究

摘要

Thermoplastic cassava starch materials was prepared with cassava starch as raw material and glycerin as plasticizer by melting mixing in a torque rheometer. The structures and properties of thermoplastic cassava starch were investigated by differential scanning calorimeter (DSC), polarizing microscope (PLM),Fourier transform infrared spectrometr (FTIR), X ray diffraction (XRD) and thermal gravimetric analysis (TG) during retrogradation process. The results indicated that the melting enthalpy of thermoplastic cassava starch material first increased then decreased over time. It had a highest melting enthalpy when the retrogradation time reached 7d, the number of starch spherulites reached the highest degree and the polarization cross was formed. Through FTIR, when the retrogradation played a main role, infrared absorption peaks had a blue-shift meanwhile hydrogen bonding action were weakened. When the degradation played a main, infrared absorption peaks had a red-shift and hydrogen bonding actions were strengthened. In addition, the crystal type turn from A+V to V in the retrogradation process of thermoplastic cassava starch, and the crystallinity was 40.44% by the calculation of TOPAS. The hydrogen bonding was take place between starch molecules, and made the thermal stability of starch material decreased in the retrogradation process.%以木薯淀粉为原料、甘油为增塑剂，通过转矩流变仪熔融共混制备热塑性木薯淀粉，利用差示扫描量热法（DSC）、偏光显微镜（PLM）、傅立叶红外（FTIR）、X射线衍射（XRD）和热重分析（TG）研究热塑性木薯淀粉材料在回生过程中的结构与性能变化。结果表明，随着回生时间的增加，热塑性木薯淀粉材料的回生焓先增大后减小，当回生时间为7d时达最高；木薯淀粉球晶出现且球晶的数目最多，偏光十字最规整，回生达最大程度。FTIR分析发现，当回生作用占主导地位，氢键作用力减弱，红外吸收峰发生蓝移；当回生时间进一步增加，淀粉降解作用占主导地位，氢键作用力增强，红外吸收峰发生红移。热塑性木薯淀粉回生过程中，晶型从（A+V）型转变成V型，通过TOPAS计算木薯淀粉结晶度最大达40.44%。甘油中的羟基与淀粉形成氢键，削弱淀粉分子间氢键的强作用力，使淀粉材料的热稳定性下降。