High-performance thermosets derive many of their desirable properties (e.g., chemical and
thermal stability, stiffness, and durability) from their permanently crosslinked network structures;
however, these robust crosslinks introduce a challenge to materials' circularity. Contributing ~65 million tonnes of waste to landfills annually, and comprising ~20% of plastics produced worldwide, it is imperative to develop industrially compatible and readily adoptable strategies for thermoset recycling.

In 2020, our group reported a drop-in strategy for the deconstruction of industrially relevant thermoset polydicyclopentadiene (pDCPD) using cleavable bifunctional silyl ether (BSE) comonomers, and showed that deconstruction fragments could be reintroduced into a second generation, non-deconstructable material. Although this presents an extension to the lifecycle of the pDCPD resin, it is limited to a singular reprocessing segment.

In hopes of accessing multiple generations of the material and hence further extending its lifetime, we recently investigated the behaviour of fragments reincorporated into n^thgeneration deconstructable pDCPD networks doped with a bifunctional silyl ether cleavable comonomer (iPrSi8). Indeed, we find that we are able to access second and third generations of deconstructable pDCPD networks through batch cures and frontal ring opening metathesis polymerization (FROMP), containing up to 30 mass% of degradation fragments, variable mol% of iPrSi8, virgin DCPD and initiator. Further, we propose an alternate method for BSE-deconstruction, using FeCl₃ in methanol as an economic, chemically abundant alternative to previously reported deconstruction conditions. Finally, we are leveraging the multiple-generations to assess the impact of fragment inclusion in carbon-fibre reinforced laminates, to access fully circular composite systems with the ability to recycle both the resin, and the reclaimed continuous carbon fibres.

Hayden Fowler

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