Repeated Thermomechanical Reprocessing of PA6/Graphene Nanoplatelets Nanocomposites

Abstract

Repeated thermomechanical processing of engineering thermoplastics such as polyamide-6 (PA6), as encountered during mechanical recycling, is often accompanied by progressive losses in mechanical and structural performance. Here, we show that graphene nanoplatelets (GNPs) can mitigate these effects and improve the durability of PA6 during repeated thermomechanical reprocessing. PA6/GNP composites were prepared by twin-screw extrusion and subjected to three thermomechanical reprocessing cycles (repeated injection molding and grinding) to assess structure−property evolution. Reprocessing does not significantly alter the crystalline structure of either neat or GNP-filled PA6; the α-phase remains dominant with only minor variations. DSC reveals that repeated reprocessing increases the degree of crystallinity by up to 33%, depending on GNP loading, while the melting temperature remains essentially unchanged. FT-IR indicates negligible chemical degradation. Rheological analysis also shows that GNPs increase melt viscosity and induce shear-thinning behavior, consistent with restricted chain mobility arising from filler−matrix interactions. SEM analysis confirms stable dispersion at low GNP loadings, although some agglomeration is observed at 10 wt %. Mechanically, GNP incorporation improves stiffness retention during repeated reprocessing, whereas tensile strength exhibits only minor changes across the investigated GNP loadings. Water uptake decreases in neat PA6 with repeated reprocessing, whereas GNP-filled systems show minimal change, reflecting the combined influence of crystallinity and filler morphology. Overall, this study provides a systematic multicycle evaluation of PA6/GNP composites, demonstrating how GNPs influence crystallization, rheology, and mechanical performance during repeated thermomechanical reprocessing. The findings highlight the potential of graphene-modified PA6 for applications requiring improved performance stability under repeated processing, thereby supporting circular-economy strategies.