Are ionic liquids effective curing agents for preparing epoxy adhesives?

This work compares for the first time the efficacy of using different ionic liquids (ILs) as epoxy hardeners in epoxy-based adhesives. Several phosphonium and imidazolium-based ionic liquids were tested as epoxy hardeners, and the thermal and mechanical properties and the lap shear strength of the cured epoxy resins were studied at different IL concentrations. Both the chemical structure and the concentration of ILs were found to impact the final properties of the epoxy resin, but among the ten different ILs studied, three of them cured the epoxy resin effectively and produced similar and even better mechanical properties and lap shear strength than those obtained with traditional amine-based curing agents. These results constitute an important step towards sustainability thanks to the non-volatility of ILs and the significantly lower amount needed for effectively curing epoxy resins.