Graphene oxide as a catalyst for ring opening reactions in amine crosslinking of epoxy resins

The influence of different graphite-based nanofillers on epoxide ring opening reactions, as induced by amines for diglycidyl ether of bisphenol A (DGEBA), is studied. Direct kinetic studies, with full chemical characterization and quantitative evaluation of the low molecular mass products, for reactions of DGEBA with primary and secondary monoamines as well with alcohols, are conducted. Moreover, the kinetic behavior of a commercial epoxy resin based on DGEBA and a diamine, leading to crosslinked insoluble networks, is studied by indirect methods, such as differential scanning calorimetry (DSC) and rheometry. The reported results show a relevant catalytic activity of graphene oxide on epoxy resin crosslinking by amines. For instance, for a graphene oxide content of 3 wt%, the exothermic crosslinking DSC peak is shifted (upon heating at 10 °C min-1) from 113 °C down to 96 °C, while the gel time at 50 °C is reduced by a factor of 2.5. This behavior is due to the ability of graphene oxide to catalyze primary amine-epoxy, secondary amine-epoxy and mainly hydroxyl-epoxy additions.