Property Retention in Hybrid GNP/MWCNT-Reinforced Polyamide-6 Nanocomposites during Repeated Mechanical Reprocessing

As interest in circular material use continues to grow, understanding the performance of polyamide-6 (PA6) during repeated mechanical reprocessing is important for assessing its potential for extended material use. This study investigates the effects of repeated mechanical reprocessing on the structural, thermal, rheological, barrier, and mechanical properties of neat PA6 and hybrid PA6 nanocomposites reinforced with multi-walled carbon nanotubes (MWCNTs) and graphene nanoplatelets (GNPs). Their performance is compared with that of PA6 nanocomposites containing individual nanofillers. The reprocessed materials were characterised using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), rheological measurements, water absorption, and tensile testing. XRD showed that the predominant α-crystalline phase was retained in neat PA6 and the nanocomposites over the investigated reprocessing cycles. FT-IR showed no substantial detectable spectral changes, while SEM revealed generally similar fracture morphologies before and after reprocessing. Neat PA6 exhibited a greater reduction in glass transition temperature than the hybrid nanocomposite, while changes in crystallinity varied among the investigated compositions. The hybrid PA6/MWCNT/GNP nanocomposite exhibited higher viscosity than the investigated single-filler systems and showed relatively consistent barrier and mechanical properties over the three reprocessing cycles. Overall, the results demonstrate the retention of several structural, thermal, barrier, and mechanical properties of the hybrid nanocomposite over the three investigated reprocessing cycles.