Impact of mechanical reprocessing on degradation and performance of PA11 and PA 11-LDPE blends

Abstract

This study examines the mechanical recycling of a virgin PA 11 and a post-consumer PA 11–low density polyethylene (LDPE) (90/10) blend over ten reprocessing cycles. Fourier transform infrared spectroscopy (FTIR) and proton nuclear magnetic resonance (¹H NMR) analyses revealed changes in the intensity and position of specific absorption bands and proton signals, indicating progressive chain scission and molecular rearrangements. A carbonyl band was identified in the virgin PA 11 after reprocessing, a confirmation of thermo-oxidative degradation. Mechanical testing showed gradual reductions in elastic modulus, stress at break, and impact strength, with significant deterioration from the third cycle onward. Rheological analysis revealed consistent decreases in storage modulus (G′), loss modulus (G″), complex viscosity (η*), and changes in damping factor (tan δ), reflecting lower molecular weight and altered viscoelastic behavior. This was further confirmed via Cole–Cole and van Gurp–Palmen plots. In the post-consumer blend, scanning electron microscopy (SEM) showed progressive coalescence of LDPE droplets, contributing to reduced interfacial area and decreased impact resistance. In general, the results showed that virgin PA 11 retains acceptable performance up to three cycles, while the post-consumer blend exhibits faster and more pronounced degradation driven by both chemical and morphological changes particularly due to droplet coalescence and loss of interfacial area.