Physical recycling of bio-based polyester nanocomposites

Abstract This study investigates the physical recyclability of polylactic acid (PLA) and poly(butylene succinate) (PBS) nanocomposites containing organo-modified montmorillonite (OMMT) or multi-walled carbon nanotubes (MWCNTs). Degradation was evaluated by changes in intrinsic viscosity (IV) and mass-flow rate (MFR), indicating that injection moulding caused more pronounced molecular chain scission than extrusion and that PLA was more susceptible to degradation during reprocessing than PBS. Dynamic mechanical analysis (DMA) measurements revealed that the storage and loss moduli of the polymers are strongly influenced by the type and dispersion of nanofillers, with OMMT increasing and MWCNTs slightly decreasing the stiffness. The effect of reinforcement depends on the polymer phase state, remaining nearly constant for PLA in its glassy region but decreasing for PBS in its rubbery state. Differential scanning calorimetry (DSC) measurements at different cooling rates revealed that MWCNTs act as effective nucleating agents for both PLA and PBS, significantly enhancing crystallinity, especially in PLA, due to improved nanoparticle dispersion, as observed in scanning electron microscopy (SEM-EDS) elemental mapping images. In conclusion, physical recycling could potentially serve as a sustainable alternative to composting for biopolymer-based nanocomposites by extending their lifecycle.