Rethinking nylon recycling: A novel chemical approach for sustainable polyamide valorization

This study focuses on the sustainability of plastics and presents the first report on the recycling of polyamide (PA) using a dicarboxylic acid (DA) in a process known as acidolysis. PA was depolymerized with adipic acid as the cleavage agent, and the impact of reaction conditions on the characteristics of the recycled products (RP) was evaluated. It was observed that harsher conditions increased the depolymerization yield and based on extensive characterization, a mechanism for PA depolymerization was proposed. Subsequently, the RP obtained under the conditions of 190 °C, a ratio of 0.5, and a reaction time of 5 h was selected to partially substitute PA up to 30% of adipoyl chloride in the synthesis of new PA. From the results, no differences in the chemical or crystalline structure were observed upon incorporation of the RP, as evidenced by Fourier-transform infrared spectroscopy (FTIR), nuclear magnetic resonance (NMR), and X-ray diffraction (XRD) analyses. Finally, Life cycle assessment (LCA) showed that acidolysis recycling of PA has lower environmental impacts than hydrolysis across all categories, with reductions from 13% in global warming potential (GW) to 68% in marine ecotoxicity (ME), and slightly better performance than virgin PA6 despite minor increases in GW (+2%) and ozone formation–human health (OF-HH, +11%) due to adipic acid. Virgin caprolactam production and end-of-life (EoL) waste treatment remain the main hotspots, highlighting the potential benefits of replacing adipic acid and scaling up acidolysis recycling. Overall, this work demonstrates for the first time the potential of DA-based PA depolymerization as a means to enhance plastic sustainability. • First report on polyamide recycling via dicarboxylic acid acidolysis. • Adipic acid efficiently depolymerizes PA under mild reaction conditions. • Reaction conditions affect yield and properties of recycled polyamide products. • Recycled PA used up to 30% in new PA synthesis without structural changes. • LCA shows acidolysis recycling has lower environmental impact than hydrolysis.