Molecular Insights into Hydrolysis, Alcoholysis, Ammonolysis, and Acidolysis of Polyamide 6

Recycling emerges as a pivotal strategy to mitigate plastic waste, particularly for polyamides. This study delves into the chemical recycling of polyamide 6 (PA6) using quantum chemistry calculations. We investigate the molecular mechanisms of hydrolysis, alcoholysis, and ammonolysis as well as acidolysis with acetic acid. Our findings elucidate a two-step process in PA6 recycling: depolymerization and cyclization. PA6 is degraded to 6-aminocaproic acid and its derivatives in the depolymerization step, and these intermediates are then turned into ε-caprolactam in the cyclization step. Each step has several reaction pathways with different energy profiles. In pure solvents, depolymerization is identified as the rate-limiting step. The introduction of acetic acid changes the rate-limiting step and effectively lowers the energy barrier, enhancing the recycling process. Computational results align with prior experimental data and offer a plausible molecular explanation of polyamide recycling. These insights are vital for devising more efficient and sustainable chemical recycling methods for polyamides.