Effect of Mechanical Recycling on the Crystallization of PA 11 and PA 11 LDPE Blends.

Abstract

This study investigates the effect of mechanical recycling on the thermal crystallization of virgin polyamide (PA 11) and a post-consumer PA 11 - low-density polyethylene (LDPE) blend (90/10) over ten reprocessing cycles. Isothermal, non-isothermal, and successive self-nucleation and annealing (SSA) methods are used. Isothermal analysis revealed accelerated crystallization kinetics with increasing reprocessing cycles, as shown by an increase in the inverse of the half-crystallization time (1/τ_1/2exp) and a decrease in the crystallization energy barrier (K_g), likely due to enhanced chain mobility and molecular weight reduction from thermal degradation. SSA analysis revealed differences in lamellar structures. After three cycles, virgin PA 11 presented a shoulder in the SSA profile, indicating the formation of thinner lamellae. In contrast, post-consumer PA 11 showed a progressive increase in its main melting peak, suggesting the development of thicker lamellae with a more uniform molecular population. Thermogravimetric analysis showed reduced thermal stability, as indicated by lower activation energy (E_a). Despite these changes, their effect is not significant to limit reprocessing, confirming their recyclability for at least ten cycles. To further assess their long-term viability; structural, rheological, and mechanical properties will be presented in a subsequent study.