Structural, thermal, rheological and optical properties of poly(lactic acid) films prepared through solvent casting and melt processing techniques

Abstract

Abstract In this study, structural, thermal, rheological and optical properties of poly(lactic acid) (PLA) films prepared by solvent casting and melt processing were observed and compared, in order to gain a better understanding of processing methods on the properties of the polymer. The structural study revealed that the solvent cast PLA film had a comparatively rough surface when fractured, with longer fibrils and produced strong X-ray diffraction peaks, which suggested different crystalline structures within the film. The melt processed film, on the other hand, appeared to be smooth when fractured and had a broad amorphous X-ray diffraction pattern. Thermal analysis indicated that the solvent cast films tended to form crystalline structure because the cold crystallization temperature was higher for the films prepared by solvent cast method. Both films demonstrated a Newtonian plateau at lower frequency with a zero-shear rate viscosity above 1000 Pa s, and showed a shear thinning behaviour at a higher frequency, with the shear thinning of the solvent cast PLA film being stronger than that of melt processed film. In addition, the structural and molecular changes due to the difference in processing conditions were investigated using polarized light microscopy and synchrotron-FTIR microspectroscopy.