Structural changes and crystallization kinetics of polylactide under CO2 investigated using high-pressure Fourier transform infrared spectroscopy

The structural changes and crystallization kinetics of polylactide (PLA) during cold crystallization under CO2 at 80 degrees C were studied using in situ high-pressure Fourier transform infrared (FTIR) spectroscopy. The FTIR spectra show that PLA can crystallize under air and CO2, and some differences are observed. In the second-derivative spectra, the 1220cm(-1) band is only found for PLA crystallized under CO2, and the tt conformer of PLA crystallized under CO2 is located at 1749cm(-1), while that of PLA crystallized under air is located at 1751cm(-1). From wide-angle X-ray diffraction, only the -crystal is observed when PLA is crystallized under air, whereas the -crystal appears when crystallized under CO2. The crystalline-sensitive bands at 921 and 1458cm(-1) were used to analyze the crystallization kinetics of PLA. When PLA crystallizes under air, the 1458cm(-1) band changes faster than the 921cm(-1) one; when it crystallizes under CO2, the result reverses. This suggests that CO2 hinders interchain interactions while promoting the helix conformation. (c) 2015 Society of Chemical Industry