Mechanical recycling of poly(butylene succinate)/poly(lactide) blends: Assessment of film blowing processability and film performances after multiple extrusions

Polylactic acid (PLA) and polybutylene succinate (PBS) are often blended to compensate for each other's limitations, and their blends are widely used for flexible packaging applications. While several studies in the literature address the mechanical recycling of these pure resins, few have focused on the mechanical recycling of PBS/PLA blends. Moreover, to the best of our knowledge, no research has explored the possibility to use these blends, subjected to multiple extrusions, for blown film production. In this study PBS/PLA systems were formulated with different weight ratios of the two polymers (20 %, 50 %, and 80 % PBS) and subjected up to five extrusion cycles. The obtained results evidenced that by increasing the PBS content within the blends, the re-grading/branching phenomena, experienced by this latter polymer phase as a result of recycling, prevailed on the molecular weight reduction, undergone by PLA phase. Moreover, during the mechanical recycling of the blends with higher PLA content (at 50 % and 80 %), the formation of random copolymers PBSx-PLAy has been demonstrated, positively affecting the polymer phases' compatibility. As a consequence of these structural modifications, PBS and PBS-rich blends resulted suitable for film blowing up to the fifth recycling step, showing a progressive stiffening (up to 77 %) and a moderate reduction in ductility (around 26 %) by increasing the number of extrusion cycles. On the other hand, the films at 50 % and 80 % of PLA evidenced the best barrier properties, even outperforming the neat PLA and PBS films, due to the enhanced compatibility between the component resins.