Effects of Diels–Alder Adduct and Lass Transition on the Repeated Self‐Healing of Aliphatic Amine‐Cured Epoxy Resin

Abstract

AbstractA thermally reversible Diels–Alder (DA) adduct is incorporated via solution mixing in an aliphatic amine‐curable bifunctional epoxy resin in order to trigger and support self‐healing. The DA adduct is a reaction product of furan‐functionalized benzoxazine (G‐f) and N‐phenylmaleimide (PMI). Epoxy formulations containing stoichiometric amount of hexamethylene diamine without (EM) and with additional DA (EMDA) are cured at 70 °C. To investigate the chemical pathway, epoxies containing G‐f (EMGf ) and PMI (EMM) only are also produced and tested. Mechanical and thermal properties of the epoxy systems are studied by dynamical mechanical analysis and differential scanning calorimetry, respectively. For the repeated self‐healing tests compact tension (CT) specimens with an arrest hole are used. Healing is achieved by a thermal cycle covering both the retro DA (140 °C) and DA formation temperature ranges (70 °C). Improved self‐healing is detected when healing is supported by the reversible DA reaction superimposed to the T g‐assisted one. Very high self‐healing efficiency is found for the EMDA when the cracked CT specimens are healed at temperatures just above the T g, that is, omitting the retro DA reaction required temperature step.