Scalable upcycling of thermoplastic polyolefins into vitrimers through transesterification

Abstract

About 150 million tons of disposed plastic is accumulated each year globally. A massive challenge will be addressed even if a fraction of this amount is reclaimed as relevant feedstock for innovative materials, provided this transformation is accomplished through an affordable process with minimal resources in a high-throughput manner. Vitrimers, the dynamic networks enabled by an associative covalent bond exchange, are an emerging class of materials that combine the best of thermoplastic and thermoset characteristics. Here we report that high performance vitrimers can be produced through chemical transformation of commodity thermoplastic polyolefins (TPOs) in a simple and economical way. Polypropylene (PP) and polyethylene (PE) retrieved from recycling have been converted into permanently crosslinked networks that are rubber-elastic above the melting point, and are capable of bond exchange at a further elevated temperature. We find that the dynamically crosslinked network shows thermally triggered shape-memory behaviour with 90% recovery after multiple fixity–recovery cycles. With superior mechanical stability compared to the precursor TPO, dynamic networks can establish interfacial covalent bonding to assemble objects of complex shapes through welding. The developed method can be applied to a wide range of TPOs without prior knowledge of their precise composition. It suggests a new direction towards recovery of ‘smart’ materials for sustainable and affordable technologies from plastic recycling, using conventionally operated instruments, without the need to upgrade the infrastructure of the polymer processing industry.