The present study investigates the feasibility of utilizing polylactic acid (PLA) and PLA-based natural fiber-reinforced composites (NFRCs) in mechanical recycling. A conical twin screw extrusion (CTSE) process was utilized to recycle PLA and PLA-based NFRCs consisting of 90 wt.% PLA and a 10 wt.% proportion of either basalt fibers (BFs) or halloysite nanotubes (HNTs) for up to six recycling steps. The recycled material was then injection molded to produce standard test specimens for impact strength and tensile property analysis. The mechanical recycling of virgin PLA led to significant discoloration of the polymer, indicating degradation during the thermal processing of the polymer due to the formation of chromatophores in the structure. Differential scanning calorimetry (DSC) analysis revealed an increase in glass transition temperature (T_g) with respect to increased recycling steps, indicating an increased content of crystallinity in the PLA. Impact strength testing showed no significant detrimental effects on the NFRCs’ impact strength up to six recycling steps. Tensile testing of PLA/HNT NFRCs likewise did not show major decreases in values when tested. However, PLA/BF NFRCs exhibited a significant decrease in tensile properties after three recycling steps, likely due to a reduction in fiber length beyond the critical fiber length. Scanning electron microscopy (SEM) of the fracture surface of impact specimens revealed a decrease in fiber length with respect to increased recycling steps, as well as poor interfacial adhesion between BF and PLA. This study presents a promising initial view into the mechanical recyclability of PLA-based composites.

The burgeoning crisis of plastic waste accumulation necessitates innovative approaches towards sustainable packaging solutions. Polylactic acid (PLA), a leading biopolymer, emerges as a promising candidate in this realm, especially for environmentally friendly packaging. PLA is renowned for its compostable properties, offering a strategic avenue to mitigate plastic waste. However, its dependency on specific industrial composting conditions, characterized by elevated temperatures, humidity, and thermophilic microbes, limits its utility for household composting. This study aims to bridge the research gap in PLA’s recyclability and explore its feasibility in mechanical recycling processes. The research focuses on assessing the mechanical characteristics of PLA and PLA-based composites post-recycling. Specifically, we examined the effects of two extrusion methods—conical and parallel—on PLA and its composites containing 20 wt.% basalt fibers (BF). The recycling process encompassed repeated cycles of hot melt extrusion (HME), followed by mechanical grinding to produce granules. These granules were then subjected to injection moulding (IM) after 1, 3 and 5 recycling cycles. The tensile properties of the resulting IM-produced bars provided insights into the material’s durability and stability. The findings reveal that both PLA and PLA/BF composites retain their mechanical integrity through up to 5 cycles of mechanical recycling. This resilience underscores PLA’s potential for integration into existing recycling streams, addressing the dual challenges of environmental sustainability and waste management. The study contributes to the broader understanding of PLA’s lifecycle and opens new possibilities for its application in eco-friendly packaging, beyond the limits of composting. The implications of these findings extend towards enhancing the circularity of biopolymers and reducing the environmental footprint of plastic packaging.