Orientation and structural development of semicrystalline poly(lactic acid) under uniaxial drawing assessed by infrared spectroscopy and X-ray diffraction

The effects of drawing temperature (Td) and draw strain on the orientation and structure of semicrystalline poly(lactic acid) (PLA) films were investigated by wide angle X-ray diffraction and polarized Fourier transform infrared spectroscopy. Semicrystalline PLA samples with two initial levels of crystallinity, Xc = 1% and 11%, were prepared by cold crystallization at 80 °C. Whatever Xc and Td, the total amount of the ordered phases (i.e. crystalline + mesophase) increased with draw strain, which could be ascribed to the formation of strain-induced mesophase at Td = 60 or 70 °C but crystalline at 80 °C. Also, the molecular orientation of both the amorphous and ordered phases increased with draw strain. Whatever Xc, the orientation of the ordered phases was insensitive to Td, whereas higher orientation in the amorphous phase was achieved at lower Td, and the trend was more significant for Xc = 1% compared with 11%.