Fracture toughness of epoxy adhesive containing dual-capsules self-healing system

Abstract

Structural polymeric adhesive such as the two-part epoxy adhesive, offers many benefits in comparison to the more conventional joining methods, for instance welding and mechanical fastening. Due to epoxy's thermosetting nature, when polymerisation occur, a highly crosslinked material with superior mechanical properties will be produced. However, due to this crosslinked molecular structure they are also known to be brittle, and once crack initiated in the material, there will be no mechanism to slows down and inhibit their propagation. From the previous literatures, it was found that, rubbery second-phase inclusions can significantly increase the toughness of this thermosetting polymeric adhesive. In this study, second-phase inclusions in the form of dual-capsule self-healing system were dispersed into a commercially available epoxy adhesive to improve its mechanical properties. Tapered double cantilever beam (TDCB) specimens were used to access the Mode-I fracture toughness of the adhesive. And, it was found that, by incorporating these microcapsules an increment of as high as 80% of its baseline Mode-I fracture toughness (GIC) can be obtained. Apart from that, recovery of fracture toughness of up to 74% after full fracture can be achieved due to the self-healing characteristic of these microcapsules. Scanning electron microscopy (SEM) was used to analyse the fracture surface of the joints. The self-healing adhesives demonstrate recovery of both cohesion and adhesion properties with room temperature healing.