Direct metathesis deconstruction to recycle poly(dicyclopentadiene) composites.

Abstract

The permanent cross-links that give thermosets their strength and durability also make them difficult to recycle. Here, we present a green, scalable strategy for the chemical deconstruction of poly(dicyclopentadiene) (pDCPD) thermosets and composites using metathesis-based chemical recycling. Key findings include the identification of cyclopentyl methyl ether as a "green" processing solvent for mild deconstruction and an understanding of the catalytic fragmentation mechanism wherein both ring-closing metathesis and chain transfer pathways are present. The deconstruction protocol is shown to be effective for a variety of pDCPD samples produced via distinct ring-opening metathesis polymerization (ROMP) curing methods, including frontal-ROMP, photoROMP, and thermal ROMP, as well as with commercial thermoset formulations and fiber-reinforced composites. As a proof of concept for future translatability, embedded electronics, glass fibers, pristine carbon fibers, and >90% recovery of polymer fragments are demonstrated. Last, a detailed life cycle analysis indicates that this approach offers a viable (high credit) alternative to contemporary thermoset disposal and incineration, opening a path toward closed-loop recycling of high-performance pDCPD materials.