Effects of organo-LDH dispersion on thermal stability, crystallinity and mechanical features of PLA

PLA-based composites were prepared by mixing the polymer in the melt with organophilic Mg/Al LDH and Mg Stearate. The obtained materials were therefore characterized in comparison with the unfilled PLA with the aim of investigating the relationships between the morphology of the polymer composites and their thermal stability, crystallinity and mechanical properties. The degradative effects induced by the presence of O-LDH and its organic component (i.e. alkyl carboxylates used as surfactant) were evaluated by analysing the samples with SEC and TGA under standard and modulated conditions, in the presence of nitrogen and air. The collected results proved that the main effects on degradation are due to inorganic reactive species and to increased interfacial surface owing to intercalated/exfoliated morphology. The main thermal transitions of the composites were studied by XRD and DSC (even in modulated conditions) before and after annealing processes at different temperatures. The results inherent to the percentage of crystallinity, the content of rigid amorphous fraction (RAF), and the main size of crystalline domains were discussed by considering the filler nature/content, its dispersion degree in polymer matrix and the annealing temperature. By crystallization at 80 °C the filler promoted both RAF and crystallites size. Unlike unfilled PLA, the composites showed an increase of the stiffness and a general loss of ductility which were tentatively ascribed to annealing at 80 °C and to the extent of interfacial interactions.