Further insight on amine-metal reaction in epoxy systems
Résumé
Among thermosetting polymers, epoxy resins are major components of adhesives, sealants, paints and composites. Polymerization is often achieved by reaction of epoxy monomers like DGEBA with amine hardeners such as DETA. Previous works showed that polyamines interact with metal (hydr/oxide) substrates leading to the formation of an interphase involving the chelation of surface metal ions. In this work, we further explored the interaction between DETA and aluminum (hydr)oxide, denoted Al, via a combined experimental and modeling approach. We inspected in depth by DSC the modifications of glass transition temperature Tg and change in heat capacity ΔCp after curing, allowing us quantifying the impact of Al amount on DGEBA/DETA degree of cure α. A new parameter, the “percentage of inhibition of cure” denoted , was defined reaching up to ~4 % in our experimental conditions. In parallel, in situ mixing calorimetry confirmed the exothermic character of DETA interaction with Al with various degrees of division. DFT calculations were carried out to examine DETA/Al3+ chelates. Among plausible chelate configurations, one was associated with a lower conformational energy and shorted Al-N bond lengths, suggesting greater stability. Calculated and experimental Raman spectra were additionally investigated, allowing us to discuss further about the DETA/Al3+ chelates at play.
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