Ion liquid selective depolymerization of epoxy resin insulation materials from electric power industry in a polar aprotic solvent system

Growing interest has been shown in environmentally friendly, cost-effective methods for recovering and reusing glass fiber-reinforced epoxy resin composites. An efficient strategy was developed for chemical recycling of cured epoxy resin from retired composite insulator mandrel using 1-ethyl-3-methylimidazole acetate ([Emim][OAc])/dimethyl sulfoxide (DMSO) as the depolymerization system. Epoxy resin with chain structure could be recovered with water as precipitant. The process became more affordable and sustainable by eliminating water and then reusing reaction solvent. The resin products' fourier transform infrared spectroscopy (FTIR) and hydrogen nuclear magnetic resonance (HNMR) analysis before and following the decomposition process revealed that the cured crosslink segments (ester group) of epoxy resins could be selectively destroyed. The density functional theory (DFT) illustrated that the solvation effect of DMSO weakened the electrostatic interaction between [OAc]⁻ and [Emim]⁺, which was significantly more conducive to the nucleophilic addition of imidazole cation. Furthermore, it was proposed to control the selective breaking process of the epoxy resin cured crosslinked ester group by nitrogen heterocyclic carbene reaction, and further esterification to obtain regenerated resin containing ester carbonyl. This recovery process opened up a sustainable path with high atom economy. Retaining of epoxy chain structure was conducive to subsequent secondary curing recovery, and the reaction system could be reused many times.