Upcycling of polymer waste to closed-loop recyclable polymers

Abstract

This study presents a novel approach aimed at developing the reclamation of waste plastics and the utilization of bio-based resources to develop sustainable and closed-loop recyclable polymers. Specifically, it focuses on the integration the diol monomer bis(2-(2-hydroxyethoxy)ethyl)terephthalamide (BHEETA), derived from the chemical recycling of waste polyethylene terephthalate (PET), with a renewable fatty acid-derived diester to produce a long hydrocarbon bearing poly(ester-amide). A series of polymers was prepared under solvent-free conditions via the melt transesterification of BHEETA with dimethyl esters of varying chain lengths, specifically ranging from fourteen to eighteen backbone carbon atoms. The properties of these polymers, including crystallinity and melting temperature, were regulated based on the diester chain length. The polymers exhibited excellent thermal stability high melting and crystallisation temperatures owing to the presence of the long hydrocarbon chain. Finally, to achieve closed-loop circular economy, the polymer was chemically degraded to its monomers. The monomers were easily separated and purified to recover in high yield (>90%). The recovered monomers were used to regenerate the polymer with near-identical material properties. This report presents a strategy to upcycle a waste polymer and to utilize bio-derived feedstocks towards the development of sustainable polymers. To the best of our knowledge, this is the first study to detail the closed-loop recycling of poly(ester-amide) derived from PET waste and long-chain fatty acids.