Conformation order of poly(l-lactic acid) chains during the melt crystallization process: infrared and two-dimensional infrared correlation spectroscopy study

Chain conformation order of poly (l-lactic acid) (PLLA) was investigated by time-lapsed Fourier transform infrared (FTIR) spectroscopy and two-dimensional infrared correlation spectroscopy during the isothermal crystallization at 140 °C. The result showed that the PLLA formed α-crystal during the isothermal crystallization at 140 °C. According to the detailed information in the region of 1000–1500 cm−1 investigated by infrared and 2D correlation spectroscopy, it was found that the conformation of C–O–C groups changed prior to that of CH3 groups. Moreover, the formation of the initial helix chain conformation was interfered by the interchain interactions between the CH3 groups, which consequently resulted in the formation of α-crystal with the distorted 103 helix conformation.