Investigation of solution-based healing of furan-functionalized epoxy-amine thermoset

A healable system based on the Diels-Alder reaction was obtained by furan functionalization of conventional epoxy-amine thermosets and by using solutions containing multifunctional maleimide molecules for healing. The properties of this system were investigated. Particularly the coupled reaction and diffusion phenomena were studied and the role of the healing agent's properties on healing efficiency was evaluated. In addition, numerical analysis was performed to elucidate the temporal behavior and spatial distribution of maleimide and furan moieties within the thermoset. Reaction and diffusion phenomena were investigated by measuring diffusion coefficients. Using previously obtained reaction rate constants the Damköhler number (Da) was calculated for the systems investigated. The value of Da obtained for the typical 1.6 mm-radius sphere was 0.72, which indicates that the system was neither diffusion nor reaction limited. The influence of healing agent on healing efficacy of the system was investigated by performing compact tension (CT) tests. Healing time, multimaleimide structure, maleimide concentration, and solvent selection were variables investigated. DMF and toluene were found to be viable solvents for multimaleimides. Better healing performance was observed for DMF-based healing agents as a result of higher multimaleimide solubility, and the greater swelling capacity of DMF resulting in improved contact between surfaces. However, toluene-based healing agents showed more efficient use of maleimde reaction as a result of reduced penetration and higher surface reaction. Numerical analysis showed that the depth of maleimide penetration was four times greater in DMF based systems compared to toluene based systems.