Crystallinity and dimensional stability of biaxial oriented poly(lactic acid) films

Transparent biaxial oriented poly(lactic acid) (BOPLA) films with improved dimensional stability were successfully prepared by controlling the crystallization of poly(lactic acid) (PLA). The crystalline morphology of PLA films can be manipulated by changing certain processing parameters, such as stretch ratio, heat setting temperatures, and heat setting time. Optical and mechanical properties as well as dimensional stability of the resulting polymer films are governed by their crystallinity and crystalline morphology. Crystallization behavior and kinetics of PLA, therefore, were investigated using wide angle X-ray diffraction (WAXD), small angle X-ray scattering (SAXS), and differential scanning calorimetry (DSC) techniques. Mechanical properties and the dimensional stability of the biaxial oriented PLA films were obtained and correlated with their processing conditions. Poly(lactic acid) films prepared by melt extrusion methods have great potential for food packaging, shrink labeling and protective film applications. However, shrinkage at elevated processing temperature should be minimized to avoid puckering of the polymer film. Shrinkage of less than 2% was achieved for a BOPLA film stretched 300% in both directions at 75 °C and then annealed at 160 °C for 30 s. Fabrication, properties, and potential applications of a series of biodegradable films will be described.