Self-healing epoxy composites – Preparation and effect of the healant consisting of microencapsulated epoxy and latent curing agent

To provide epoxy based composites with self-healing ability, two-component healing system consisting of urea–formaldehyde microcapsules containing epoxy (30–70 μm in diameter) and CuBr2(2-MeIm)4 (the complex of CuBr2 and 2-methylimidazole) latent hardener was synthesized. When cracks were initiated or propagated in the composites, the neighbor microencapsulated epoxy healing agent would be damaged and released. As the latent hardener is soluble in epoxy, it can be well dispersed in epoxy composites during composites manufacturing, and hence activate the released epoxy wherever it is. As a result, repair of the cracked sites is completed through curing of the released epoxy. The present paper studied the preparation of epoxy microcapsules by amino resins, and the influencing factors as well. On the basis of this work, mechanical properties of the epoxy filled with the healing system were evaluated. It was found that incorporation of the two-component healing system nearly did not change the fracture toughness of the neat epoxy, as indicated by the single-edge notched bending test. In the case of 10 wt% microcapsules and 2 wt% latent hardener, the self-healing epoxy exhibited a 111% recovery of its original fracture toughness. Besides, the preliminary result of double-cantilever beam testing showed that the plain weave glass fabric laminates using the above self-healing epoxy as the matrix received a healing efficiency of 68%.