Directional Depolymerization of Nylon 6 to Caprolactam Monomer With Ionic Liquids as Solvent and Catalyst

Nylon 6 (polyamide 6, PA6) is an important high-performance polymer, which is widely used in various industrial and daily-life fields. Notably, it serves as the predominant material for fishing nets, and discarded fishing nets have become a major source of marine plastic pollution, making the resource recovery of waste PA6 extremely significant. Chemical recycling to monomers is the optimal route for closed-loop recycling of PA6. However, factors such as the high melting point and stability of amide bonds in PA6 make its depolymerization challenging. In this work, a series of functionalized ionic liquids were prepared and employed as both solvents and catalysts for the depolymerization of PA6. The ionic liquids reduce reaction system viscosity to improve mass and heat transfer and efficiently activate the amide bonds of PA6. Therefore, directional depolymerization of PA6 toward caprolactam (CPL) monomers was achieved, with high depolymerization conversion and selectivity. Furthermore, the ionic liquid exhibited excellent applicability to practical waste PA6 such as fishing nets and good reusability. This study provides a green approach for the closed-loop recycling of waste PA6.