Curing behaviour of epoxy resin/graphite composites containing ionic liquid

Abstract

By adopting the isoconversional method, subtle changes in the curing activation energy (Eα) among epoxy resin/graphite composites by the inclusion of expanded graphite (EG), ionic liquid of 1-butyl-3-methyl-imidazolium hexafluorophosphate ([BMIm]PF6) or their combination are shown in the whole conversion range. At lower concentrations (1 phr) of EG, compared with the Eα of the neat epoxy resin, the composite with EG has a lower Eα before the gelation, and a higher Eα after the gelation. At higher concentrations of EG, however, in the whole conversion range, the composite with EG shows a higher Eα compared with the neat epoxy resin. As the curing proceeded, a peculiar increase in Eα is found in systems containing [BMIm]PF6. Due to the formation of hydrogen bonding between [BMIm]PF6 and the hardener (Jeffamine), the reactivity of Jeffamine is considerably decreased, leading to a much higher Eα in [BMIm]PF6-containing systems, especially at higher conversion. In systems containing a combination of [BMIm]PF6 and EG, due to the interactions between EG and [BMIm]PF6, the shielding effect provided by the well-dispersed EG sheets constrains the formation of the hydrogen bonding between [BMIm]PF6 and Jeffamine, leading to lowered Eα compared with that for the system containing [BMIm]PF6 only.