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 (T-d) 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, X-c = 1% and 11%, were prepared by cold crystallization at 80 degrees C. Whatever X, 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 T-d = 60 or 70 degrees C but crystalline at 80 degrees C. Also, the molecular orientation of both the amorphous and ordered phases increased with draw strain. Whatever X-c, the orientation of the ordered phases was insensitive to T-d, whereas higher orientation in the amorphous phase was achieved at lower T-d, and the trend was more significant for X-c = 1% compared with 11%. (C) 2014 Elsevier Ltd. All rights reserved.