Polyamide Depolymerization: Unlocking Polymer Dissolution with Dicarboxylic Acids

Abstract

Polyamides (PAs) are widely used due to their high performance and versatility. However, this resistance goes with a counterpart: challenging recycling in harsh conditions, generally above the melting point, preventing the recovery of valuable compounds. Circular approaches by depolymerization are mainly limited by low chain mobility, hindered by a high crystallinity and strong hydrogen bonding. In this study, we demonstrate that polyamide (PA6) can be depolymerized below 200 °C by disrupting hydrogen bonding in the presence of an adequate solvent. A weak difunctional acid was used both as dissolution-promoter and depolymerization agent, enabling the complete depolymerization of PA6 into water-soluble products -monomers and short oligomers-within 2 hours. A plausible reaction mechanism for this depolymerization process was proposed based on model reactions and density functional theory (DFT) calculations. Furthermore, the system demonstrates high efficiency and selectivity to isolate PA6 from mixtures with other polymers. A PA6 depolymerization extent ranging from 94 to 96 % and almost complete recovery of the mixed polymer (> 90 %) was reached. These results open promising opportunities in the recycling of complex real waste.