Effect of the unidirectional drawing on the thermal and mechanical properties of PLA films with different L -isomer content

Abstract

This work simulates the thermoforming process of two different L-isomer content PLA grades (95.6 and 98%), studying the influence on the induced morphology and the variation in the thermal and tensile properties. The thermoforming process was simulated with uniaxial tensile tests performed at different temperatures and strain rates, reporting the tensile behavior before, dur-ing, and after the test. The resulting structural changes were analyzed by wide-angle X-ray scattering and Fourier transformed infrared spectroscopy. Thermal characterization was carried out with differential scanning calorimetry and dynamomechanical thermal analy-sis. The results showed that, regardless the L-isomer content, drawing at 70 C produced a stable mesomorphic phase that showed greater tensile properties than the original films. This mesomorphic phase, indeed, could be reordered into a crystalline structure under mild annealing conditions (5 min/75C), if compared with those needed for similar amorphous PLA specimens (60 min/120C), thus providing a processing opportunity for obtaining thermally stable PLA products at temperatures above 100C.