Direct evidence of amine-metal reaction in epoxy systems: An in situ calorimetry study of the interphase formation

Epoxy resins are ubiquitously encountered in industrial applications as in adhesives and composites. The properties of epoxy-amine networks are directly impacted by the presence of metal (hydr-oxidized) surfaces, leading to a modification of their glass transition temperature T-g. We propose here an innovative experimental approach, investigating the interaction of DETA amine and DGEBA epoxy with Al and Cu powder substrates (partially (hydr)oxidized). We explored for the first time the formation of the amine-metal interphase by in situ mixing calorimetry to evaluate the energetics of interaction. While DGEBA interacted only slightly with Al-based surface, the reaction with DETA was associated with a high exothermic enthalpy of reaction. The enhancing role of surface hydroxylation was also evidenced by comparing boehmited Al to a simply oxidized counterpart. An even larger exothermic effect was measured with copper, which was related to the high chelating power of Cu compared to Al. The possible underlying mechanism of amine-metal interphase formation was discussed with a generalized schematic.