Chemical Recycling of End-of-Life Polyamide 6 via Ring Closing Depolymerization

Abstract

The chemical recycling of end-of-life polymers, a sequence of depolymerization and polymerization reactions, enables the conserving of fossil resources and can add some value to the circular economy. In this study, a process for the depolymerization of end-of-life Nylon 6 via ring-closing reactions to produce as building block N-acetylcaprolactam have been set up. In detail, a combination of acetic anhydride as depolymerization reagent and catalytic amounts of 4-dimethylaminopyridine allows under microwave irradiation and within short times (15 min) the conversion of end-of-life Nylon 6 to N-acetylcaprolactam under solvent-less conditions. Applying optimized conditions a sequence of Nylon 6 goods was transformed in good yields. The product N-acetylcaprolactam was converted to ϵ-caprolactam by transfer of the acetyl functionality to 2-aminoethanol to give N-(hydroxyethyl)acetamide a precursor for poly(N-vinylacetamide). The generated ϵ-caprolactam can be used as monomer for the synthesis of new Nylon 6, therefore a chemical recycling of the monomeric unit of Nylon 6 is feasible.