聚乳酸/羧基化聚丙烯共混物的形态与热性能研究

以扫描电子显微镜、热重分析仪、差示扫描量热仪、热台偏光显微镜分别研究了聚乳酸/羧基化聚丙烯共混体系的相形态、热性能和结晶形态.结果显示,共混物熔体冷却时,聚乳酸和羧基化聚丙烯均形成球晶,但羧基化聚丙烯球晶较大而十字消光较暗,聚乳酸球晶尺寸较小而十字消光较亮,且聚乳酸球晶产生规则的、不连续的同心环线——裂纹,裂纹厚度约为1~2μm,且裂纹内部有微纤存在.当聚乳酸含量≤50%时,由于聚丙烯上羧基的存在而使共混体系具有较好的相容性.共混物的热分解过程分为三个阶段,热分解温度的变化是聚丙烯上的羧基、聚乳酸和聚丙烯骨架分解三种机制共同作用的结果,少量聚乳酸能够明显提高共混物中聚丙烯上羧基的热稳定性.共混物中的羧基化聚丙烯组分可以发挥稀释剂的作用,大幅度降低了聚乳酸的冷结晶温度.聚乳酸含量≥50%时,共混熔体降温时DSC谱图中聚乳酸和羧基化聚丙烯分别结晶,而聚乳酸含量<50%时,只观察到羧基化聚丙烯的结晶行为.

MORPHOLOGY AND THERMAL PROPERTIES OF THE POLY(LACTIC ACID)/CARBOXYLATED POLYPROPYLENE BLENDS

The compatibility,thermal property,crystallization behavior and crystal morphology of the poly(lactic acid)/carboxylated polypropylene(PLA/EPP) blends were investigated by using scanning electron microscopy(SEM),thermogravimetric analysis(TGA),differential scanning calorimetry(DSC) and polarizing optical microscopy(POM),respectively.The results suggest that the blends have better compatibility and thermal stability and exhibit no clear glass transition temperature when the content of the PLA component is lower than 50%.The crystal morphology of both components is spherulites,but PLA exhibits smaller and brighter Maltese crosses,while EPP shows bigger and darker Maltese crosses.Moreover, the spherulites of PLA component show regular discontinuous concentric circlelines surrounding the nuclear of the spherulite,which are cracks with a width about 1～2 μm in SEM micrograph caused by internal stress of the spherulite,and there are some microfibers within the cracks.All the blends exhibit three decomposition stages in the TG curves corresponding to the decomposition of the carboxy groups in EPP,PLA component and main chains of the EPP,respectively,and some content of PLA will improve the thermal stability of the EPP component.The DSC thermalgrams of blends exhibit three main melting peaks,while two lower-temperature melting peaks have been found for the carboxylated polypropylene,and the higher-temperature one is for the PLA.During the melt-crystallization process; the blends have two mainly crystallization peaks when the content of the PLA component is greater than 50%.The EPP component in blends acts as a diluent decreasing much of the cold-crystallization temperature of the PLA in melting process, and improves the melt-crystallization behavior of PLA in melt-cooling process.