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