Polyamide depolymerization: unlocking polymer dissolution with dicarboxylic acids

Abstract

Polyamides (PAs) are widely used due to their strong performance and versatility. Yet, this robustness comes at a cost: their recycling is challenging, requiring harsh conditions that cause polymer degradation and diminish the material's value. Chemical approaches using depolymerization are limited mainly by low chain mobility, hindered by high crystallinity and strong hydrogen bonding in the structure. In this study, we demonstrate that dicarboxylic acids can effectively dissolve polyamide 6 (PA6), disrupting hydrogen bonding and enabling depolymerization at 200 °C within 2 hours. The reaction results in the formation of new functional water-soluble products, whose structures vary with the diacid chain length, following an upcycling approach. A plausible reaction mechanism for this depolymerization process was proposed based on model reactions and density functional theory (DFT) calculations. Furthermore, the system exhibits high efficiency and selectivity to isolate PA6 from mixtures with other polymers. The PA6 depolymerization extent ranges from 94 to 96% and almost complete recovery of the mixed polymer (>90%) was reached. These results open promising opportunities in the recycling of PAs and especially complex waste.