Catalyst-free reprocessable, degradable and intrinsically flame-retardant epoxy vitrimer for carbon fiber reinforced composites

Fire risk and waste disposal are two major conundrums for carbon fiber reinforced composites (CFRCs), particularly for the thermoset-based ones; and it is beset with difficulties to solve them simultaneously. In this work, a phosphorus-containing diol with tertiary amine structure named 2-(bis(2-hydroxyethyl)amino)ethyl diphenylphosphinate (DPEA) was synthesized and successfully used as a transesterification modifier in an epoxy-anhydride curing system to construct epoxy vitrimers with dynamic ester networks, which further served as matrix for CFRCs. The phosphinate structure in DPEA was covalently bonded into the epoxy, endowing the vitrimers and CFRCs with intrinsic flame retardancy. With 0.30 mol% DPEA, both achieved a UL-94 V-0 rating with enhanced LOI value and reduced heat release. Meanwhile, thanks to the self-catalytic tertiary amine and highly reactive primary hydroxyls from DPEA, the transesterification within the dynamic ester networks was accelerated, endowing reprocessibility of the vitrimers as well as healing and recycling capacity of the relevant CFRCs. Killing two birds with one stone, this work provided a promising and feasible way to make sustainable and flame-retardant CFRCs with comprehensive properties.