A Circular Thermoplastic Vulcanizate (TPV) Comprising Biobased EPDM and Recycled Polypropylene: Introducing Vitrimer Chemistry

The advancement of high-performance thermoplastic vulcanizates (TPVs), featuring recyclability and reprocessability, has gained considerable interest in the quest for a sustainable and circular economy. This research introduces a novel TPV-vitrimer utilizing bioderived ethylene-propylene-diene rubber (EPDM) and recycled polypropylene (r-PP) to facilitate associative covalent adaptable networks (CANs). We have chemically modified EPDM to epoxidized EPDM (e-EPDM) and subsequently grafted maleic anhydride (MA) onto r-PP to produce MA-grafted r-PP. During the dynamic vulcanization process in an internal mixer, β-hydroxy ester linkages have been formed between the epoxy group of e-EPDM and the grafted maleic anhydride of r-PP. The transesterification catalyst (Zn(Ac)2) enhances the bond-exchange capacity of β-hydroxy ester linkages at elevated temperatures, enabling reprocessability while preserving thermo-mechanical stability. A comparative study with a traditional thermoplastic elastomer (TPE) and TPV demonstrates the benefits of the TPV-vitrimer system regarding mechanical properties, cross-link density, and rheological characteristics. The TPV-vitrimer sample also exhibits enhanced recyclability along with shape memory capability, which is unattainable in TPE and TPV. This research highlights that vitrimer-based TPV utilizing biobased and recycled feedstock could be a feasible substitute for conventional materials, thereby improving the circularity of the material economy.