聚乳酸立构复合物的结晶行为

Crystallization Behavior of Poly(Lactic Acid) Stereocomplex

采用溶液成膜法制备了不同质量比的左旋聚乳酸(PLLA)和右旋聚乳酸(PDLA)形成的立构复合物(sc)。通过差示扫描量热仪、偏光显微镜和X射线衍射仪研究了不同配比、热历史和无机粒子对聚乳酸立构复合物及其结晶行为的影响规律。结果表明,质量比为5/5和6/4的样品能够形成立构复合程度较高的PLA-sc;热历史对结晶行为有较大的影响,处理温度为220℃左右时PLA-sc的进一步完善结晶或者快速熔融结晶都有利于PLA-sc的形成和热稳定性;2种成核剂在熔融结晶过程中都能有效地提高立构复合物的结晶能力,抑制左旋或右旋聚乳酸均聚物的形成,保证了完善的立构复合程度;此外,PLA-sc晶体形貌会随着左旋和右旋的配比而发生变化,立构复合物的存在很大程度上影响到了均聚物的球晶形貌和结晶行为。

Poly( lactic acid) stereocomplex( PLA-sc) was prepared by blending poly-( L-lactic acid)( PLLA) with high molecular weight and poly( D-lactic acid)( PDLA) via solvent- mixing method. The formation and the crystallization behaviors of PLA-sc were investigated by differentical scanning calorimtery( DSC),polarizing optical microscope( POM) and X-ray diffraction( XRD). Furthermore,the influence of thermal history and nucleating agents on the PLAsc crystallization behavior was discussed. Fully stereocomplexation of PLLA /PDLA blend can be achieved from the mass ratio of 5 /5 and 6 /4 for PLLA and PDLA. when the temperature is around 220 ℃,PLA-sc was preferentially formed either by the further crystallization or enhanced crystallization rate. Two different types of nucleating agents( Lak and talc) can effectively enhance the crystallization behavior of PLA-sc,prevent the formation of PLA homopolymer( PLLA and PDLA) and keep the high thermal stability of PLA-sc. The crystal morphology can be changed with the mass ratio of PLLA and PDLA. The presence of PLA-sc also changes the crystal morphology and crystallization behavior of PLA homopolymers.