Effect of mechanical reprocessing on PA6/carbon nanotube nanocomposites

As demand for sustainable materials intensifies, understanding how mechanical recycling affects the performance of engineering polymers and their nanocomposites is critical. This research investigates how repeated reprocessing affects the structural, thermal, rheological, morphological and mechanical characteristics of polyamide 6 (PA6), and its nanocomposites reinforced with multi-walled carbon nanotubes (MWCNTs). Both pure PA6 and PA6/MWCNT nanocomposites were subjected to mechanical recycling, through repeated grinding and injection molding (up to three cycles). Repeated reprocessing did not significantly alter the overall crystalline structure of neat PA6 and PA6/MWCNT nanocomposites, with the α crystalline phase remaining predominant and only slight variations in diffraction peak shape observed. FTIR confirmed chemical stability of the polymer. The glass transition temperature (Tg) was found to decrease with recycling, indicating chain scission, though SEM revealed that filler morphology remained largely unchanged. Crystallinity increased in neat PA6, whereas in the nanocomposites remained constant after the initial recycling cycle. The nanocomposites exhibited greater viscosity and more pronounced shear-thinning behavior, attributed to the interactions between the nanotubes and the polymer matrix. Water uptake was lower in recycled PA6 due to the increased crystallinity, while addition of MWCNTs consistently enhanced the long-term moisture resistance. The specific modulus and specific strength of recycled PA6 increased compared to the virgin material. Conversely, the nanocomposites demonstrated no significant variation in specific modulus and strength following reprocessing. The key challenge of this research lies in disentangling the relationship between structural degradation, polymer crystallinity, and nanofiller interactions during repeated reprocessing, and how these factors influence the nanocomposite properties.