Spectroscopy Study On Crystalline Behavior Of PLA Stereocomplex

In this study we use time/temperature resolution FTIR, synchronous radiation Xray scattering, Raman mapping as the main characteristic methods to peroform our experiment. Crystalline behavior, lamellar structure as well as the distribution of stereocomplex and PLA homo-crystal were investigated. Two kinds of sample were chosen in our study: PLLA-PDLA stereo di-block copolymer and PLLA/PDLA asymmetric blend.PLLA and PDLA segments are linked together by chemical bond for PLLA-PDLA block copolymer therefore the chiral phase separation are constrained. FTIR result reveals that at the early stage of crystallization bands associated with stereo selective interaction and helix con Figureuration could be observed which illustrated the issue that stereo selective interaction is the driven force of crystallization of SC. In addition because PLLA and PDLA segments are linked together through chrmical bonds during the crystallization process it is impossible to exclude amorphous domain from the crystalline domain which lead to the low melting point of block copolymer when compared with the blend sample.Isothermal crystallization process of asymmetry blend illustrated that blend ratio have a big influence on the crystalline rate of both HC and SC however the lamellar structure of HC and SC are the same for all three samples. Combining with our DSC result we proposed that if HC and SC formation at the same time from amorphous state the crystallization speed of both phases will constrained by each other. However if SC already exists in the sample the restriction will disappear.When observing the crystallization process of PLLA/PDLA 4:1 blend sample by insitu POM at 100℃ there are two kinds of spherulite exist in the sample: the small ones appear first and then the big ones. Raman mapping experiment illustrated that small spherulites is composed by SC only and both SC and HC signal could be obtain from those big ones.