Dual Role of Magnetic Ionic Liquids as Curing Agents of Epoxy Resin and Microwave-Absorbing Additives

The dual role of phosphonium- and imidazolium-based ionic liquids (ILs) combined with FeCl4 counteranions as hardeners for epoxy resin (ER) and additives for improving the microwave-absorbing properties was investigated. The influence of the chemical nature of the cation on the curing process of ER was evaluated by rheometric and differential scanning calorimetry (DSC) analysis. No significant curing process was observed for the ER-based systems until 7 days of storage at room temperature. DSC analysis under the dynamic mode was carried out at different heating rates to evaluate the best curing protocol and the kinetic parameters. Phosphonium-based ILs promoted faster curing rate and lower activation energy of the epoxy system, higher cross-link density observed by dynamic mechanical analysis, and better thermal stability. Moreover, ER cured with phosphonium ILs presented good microwave-absorbing properties, with minimum reflection loss values of −13.5 dB (at 9.5 GHz) and −11.5 dB (at 14.5 GHz), corresponding to more than 90% of electromagnetic attenuation. These results indicate that ER cured with these magnetic ILs can be used as promising microwave-absorbing materials in both X-band (8–12 GHz) and Ku-band (12–18 GHz).