Reprocessable Vitrimers From Post-Consumer Polyolefin Blends: Elucidating Phase-Selective Dynamic Networks

Reprocessable and recyclable polyolefin (PO) vitrimers can be used as alternatives to conventional non-recyclable thermosets. While recent studies have successfully demonstrated dynamic network formation in virgin POs, the application of dynamic covalent chemistry in post-consumer mixed POs remains unexplored. Herein, we report the first reactive melt extrusion approach that utilizes nitroxide-mediated silyl ether chemistry to produce post-consumer high-density polyethylene (HDPE) and polypropylene (PP) blended vitrimers. Key findings show that the fully formulated 75:25 wt./wt. HDPE/PP vitrimer creates a covalently crosslinked network with a storage modulus of >1 MPa at 220°C. Thermomechanical benchmarking against a permanent epoxy-ester thermoset reveals that the upcycled vitrimer combines thermoset-like dimensional stability above 180°C with dynamic melt-reprocessability, albeit with a modulus above its melting transition that is lower than the permanent network. For the first time, 2D wideline separation (2D WISE) solid-state NMR was used to qualitatively validate highly phase-selective crosslinking. This is the first study that establishes vitrimer formation from mixed post-consumer PO blends, thus providing a scalable upcycling pathway for municipal solid waste.