改性淀粉与聚乳酸共混物的结构与性能

Structures and Properties of the Blends of Modified Starches and Poly(lactic acid)

可生物降解的聚乳酸(PLA)可用于替代化石燃料基聚合物,可再生淀粉改性PLA有利于其推广应用。采用湿法工艺制备了3种马来酸酐(MAH)改性玉米淀粉(CSM),与PLA共混制备了PLA/CSM的共混物,对改性淀粉和PLA与不同淀粉的共混物进行了结构与性能研究。红外分析表明,MAH可通过酯化接枝至淀粉上,MAH水溶液滴入淀粉水分散液中的淀粉酯化程度高于MAH直接加入淀粉水分散液接枝而得的,冷冻干燥得到的MAH改性淀粉由粒度仪测得的粒径小于热干燥的改性淀粉。差示扫描量热分析(DSC)和X射线衍射(XRD)分析表明,PLA中混入淀粉后易于结晶,结晶度也提高了,冷冻干燥的改性淀粉与PLA共混膜的结晶度高于热干燥改性淀粉共混的PLA膜,玻璃化转变温度有所下降,但仍高于52℃;扫描电镜(SEM)可观察到改性淀粉与PLA共混有较好的界面相容性,热失重分析(TG)表明PLA与改性淀粉共混后热稳定性降低,但5%热失重温度仍高于220℃,600℃残炭率有3%以上。湿法工艺可用于淀粉接枝MAH,改性后淀粉可用于PLA的共混改性以降低成本。

The biodegradable poly(lactic acid)(PLA)is a candidate for substituting the fossil-fuel-based polymers.The renewable starch-modified PLA is conducive to its widespread use.Three maleic anhydride(MAH)modified corn starches(CSM)were prepared by the wet process.PLA/CSM blends were prepared by mixing PLA and CSM.The structures and properties of CSM,the blends of PLA and various starches were studied.Infrared analysis shows that MAH could be grafted onto the starch granules by esterification.The degree of esterification for the corn starches modified by the addition of MAH solution is higher than that modified by the addition of MAH particles.The particle size analysis displays that the particle sizes of CSM dried by the lyophilization are smaller than these of CSM dried by heat.The results of differential scanning calorimetry(DSC)and X-ray diffraction(XRD)show that the blends of PLA with starches are easy to crystallize and have higher crystallinity.The crystallinity of the PLA film blended with the lyophilized modified starches is greater than that blended with hot-dried modified starches.However,the glass transition temperature of PLA decreases with the addition of starches,but it is still higher than 52℃.The results of scanning electron microscopy(SEM)show that there is a good interface compatibility between PLA and the modified starches.The results of thermogravimetry analysis(TG)indicate that the thermal stability of PLA drops with the addition of CMS,but the temperature of 5%weight loss is still over 220℃,and the char yield at 600℃is over 3%.The wet process for MAH-grafted starches is practical.The modified starches could be used for blending modification of PLA to reduce the cost.