Effect of crystalline forms (α′ and α) of poly(lactic acid) on its mechanical, thermo-mechanical, heat deflection temperature and creep properties

In this paper the effect of crystallinity and crystalline forms (ratio of the less ordered alpha' and the more ordered alpha crystalline forms) of injection moulded Poly(Lactic Acid) (PLA) was analysed on the mechanical, thermo-mechanical, Heat Deflection Temperature (HDT) and creep properties. The injection moulded PLA specimens were post-production annealed in a heat chamber at 80 degrees C crystallization temperature (T-c) for 0-60 min to develop various crystallinity as well as at 80-140 degrees C T-c for one hour to develop various ratios of alpha' and alpha crystal forms with the possible maximum crystallinity. It was demonstrated that not only crystallinity, but also the ratio of the crystalline forms of alpha' and alpha significantly influences the application-wise properties like storage modulus and thus HDT as well as tensile, flexural, impact properties and finally creep characteristics. In most cases better properties (higher HDT, storage modulus, mechanical properties, and creep resistance) could be reached by increasing the a to a' crystalline form ratio in the PLA specimens. (C) 2016 Elsevier Ltd. All rights reserved.