Recycling of PLA-based bioplastics: The role of chain-extenders in twin-screw extrusion compounding and cast extrusion of sheets

Poly (lactic acid) polymers (PLA) belong to the bioplastic family of polymers entirely derived from renewable resources. Among biopolymers, PLA is one of the most technologically interesting materials, thanks to its good mechanical properties and to its moderate thermal stability. There are many fields of application in which the use of PLA seems to be promising, including cast extrusion and thermoforming. However, the strong tendency of PLA to degrade compromises the possibility of recovering the so-called post-process material (i.e., process waste), making PLA and most bioplastics difficult to use in production processes that require a physiological reuse of post-process material, such as the thermoforming process, where huge amounts of scrap material is naturally produced during the trimming phase. In this context, the present study examines the effect of three successive compounding processes by twin-screw reactive extrusion on the rheological and thermal properties of two formulations of compostable bioplastic materials based on PLA, in the presence of a chain extender additive. Subsequently, virgin compounds and post-process material were mixed and cast extruded into slabs. The slabs were then characterized to evaluate their rheological, thermal, and mechanical properties. Finally, the effect of the chain extender was evaluated by adding the additive directly during the cast extrusion of slabs made with 100% post-process material. The results showed that the twin-screw compounding process induces a lower degradation in the material compared to the cast extrusion process. Furthermore, experimental findings show that adding the chain extender during the cast extrusion process of the slabs proved to be an effective post-process material recovery strategy.