An upcycling strategy for polyamide 6: preparing thermoplastic polyamide elastomers from glycolysates produced by controlled degradation

Abstract

Polyamides (PAs) represent a class of polymers conducive to chemical recycling, where the amide group acts as a reactive site for degradation agents. However, the inherent stability of the amide group means that chemical recycling of PAs often necessitates stringent conditions, such as high temperatures and pressures, significantly hindering advancements in PA chemical recycling. Moreover, the effectiveness of chemically recycling polyamides into monomers or oligomers—essential components for subsequent polymer synthesis—has not been conclusively verified through comprehensive research. Here, we present the first demonstration of a method for the upcycling of PA6 into high-performance PA derivatives. In the proposed method, PA6 is first degraded into oligomers with reactive end groups via glycolysis, with the reactivity of the resulting glycolysates subsequently verified. This oligomer acts as an intermediate in thermoplastic polyamide elastomer (TPAE) synthesis, facilitating direct integration with flexible polyethylene glycol oligomers into TPAE without requiring further degradation to monomers. The mechanical properties of the resultant TPAEs are commensurate with those previously reported for PA6-based TPAEs. By fine-tuning the reaction time and catalyst concentration, it is possible to control the molecular weight of the PA6 glycolysates, thus adjusting the TPAE's mechanical properties. This study presents an innovative approach that seamlessly combines the degradation process of PA6 with the synthesis pathway of TPAE, thus achieving the cost-effective upcycling of PA6 into TPAE.