Mechanical recycling and electro‐thermal welding of epoxy vitrimer nanocomposites

Abstract

Vitrimers constitute a new class of recyclable thermosets based on the incorporation of associative dynamic covalent bonds, such as disulfide bonds, into the crosslinked matrix. These reversible bonds usually require excess dynamic bonds to confer proper self‐healing and recycling capabilities to the thermoset. In that way, we manufacture epoxy resins cured with 4‐aminophenyl disulfide (AFD) in a stoichiometric ratio, and with 10 and 20 wt% of AFD excesses to analyze the effect of composition on resin properties. Beyond the neat vitrimers analysis, we manufacture nanocomposites doped with carbon nanotubes (CNT) to obtain electroactive vitrimers. These epoxy resins and nanocomposites can be mechanically recycled by milling and hot‐pressing. The recycled nanocomposites conserve partially CNT integrity and dispersion. Even more, recycled nanocomposites with AFD excesses maintain the mechanical strength of the pristine nanocomposites. Vitrimer nanocomposite samples can be also electrically welded, due to their heating by the Joule effect, through a relatively low voltage application, and therefore with low energy consumption, to obtain a monolithic specimen. In summary, the manufactured epoxy vitrimers and nanocomposites are recyclable and sustainable epoxy materials, which can be processed and reprocessed using technologies easily implementable, fast, and with low energy consumption.Highlights Electroactive and re‐processable vitrimer nanocomposites are manufactured. Nanocomposite vitrimers show conductivities similar to conventional epoxies. Bond exchanging temperatures can be reached by Joule heating. CNT addition enhances disulfide exchanges and thermo‐mechanical recyclability. Electrothermal welding of vitrimer nanocomposites is successfully tested.

Recent Trends of Recycling and Upcycling of Polymers and Composites: A Comprehensive Review

“…Electroactive vitrimers-epoxy resins nanocomposites with carbon nanotubes (CNT)-have been mechanically recycled by milling and hot-pressing, conserving partial CNT integrity and dispersion, maintaining the mechanical strength of the pristine nanocomposites, and having the ability to be electrically welded through heating by the Joule effect [109]. Moreover, chemical recycling of polycyanurate thermosets has been demonstrated by activating 'dormant' covalent bonds, and they can be recycled into the original monomers, which can be circularly reused for their original purpose [110].…”