Study of factors related to performance improvement of self-healing epoxy based on dual encapsulated healant

Our earlier work developed epoxy based self-healing composites with embedded dual microcapsules, which contain unreacted epoxy as the polymerizable component and mercaptan and tertiary amine catalyst as the hardener, respectively. Self-healing was allowed to proceed rapidly, offering attractive repair effectiveness. To give full play to the healing agent, influences of a series of factors on healing chemistry of the composites were studied in this paper. It was found that strong alkality of the catalyst, high activity of mercaptan, and low viscosity of the encapsulated epoxy prepolymer ensured high healing efficiency and rate of healing. In addition, matching of the microcapsules' sizes and fractions was critical for keeping stoichiometric ratio of the components at the damage areas, as required by the mechanism of the healing reaction (i.e. addition polymerization). Homogeneous dispersion of the capsules under proper stirring speed led to timely contacts between the healant fluids flowing out of the fractured capsules. Larger microcapsules favored filling of the cracks in terms of larger amount of the released healing agent, while smaller ones facilitated mixing and interdiffusion of the ingredients. The results provided key data for optimizing the self-healing system.