Dynamic mechanical and calorimetric analysis of compression‐molded PLLA of different molecular weights: Effect of thermal treatments

The effect of thermal treatment on compression‐molded poly(L‐lactic acid) (PLLA) has been investigated by means of viscosimetric molecular weight ( {article}{empty}{document}Mwᵥ{document} ) determination, differential scanning calorimetry (DSC), and dynamic mechanical thermal analysis (DMTA). Starting from two initial molecular weight PLLAs, amorphous samples with different {article}{empty}{document}Mwᵥ{document} have been obtained due to degradation occurring during the molding. The crystallization capability of the materials after different thermal treatments has been determined as a function of the molecular weight, and their dynamic mechanical properties have been measured. Initially fully amorphous PLLA matrices attained very high degrees of crystallinity (up to 90%) following different annealing processes. Concomitantly, PLLA degrades due to thermal cleavage of the chains. This is an unavoidable effect that must be taken into consideration when defining the material processing and annealing conditions. Crystallization phenomena occurring in the material during the treatment are clearly documented by DMTA.