Structure Evolution of α′-Phase Poly(lactic acid)

Poly(lactic acid) films consisting of alpha'-forms were prepared and uniaxially drawn. The effects of the draw rate at temperatures above the glass transition temperature on chain conformation, degree of crystallinity, and crystalline phase transformation were investigated by a combination of vibrational spectroscopy (infrared and Raman), differential scanning calorimetry, and wide-angle X-ray diffraction (WAXD). It was established that the alpha'-crystal's phase of poly(lactic acid) films does not transform into either an alpha or beta crystals on uniaxial drawing at a fixed draw ratio of 4. However, the degree of crystallinity was significantly increased on deformation. The structural change as a function of deformation also promotes an increase in the strain-induced enthalpic relaxation endothermic peak appearing near the glass transition region. While the overall changes in physical properties can be attributed to the changes in the degree of crystallinity as a function of strain rate, polarized Raman spectra, and WAXD clearly illustrated changes and the differences in the amorphous and crystalline orientation as a function of processing conditions. (C) 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 49: 1446-1454, 2011