Mechanism of Extrinsic and Intrinsic Self-healing in Polymer Systems

Self-healing materials, which can increase the lifespan of various types of products, have been researched quite intensively in recent decades. In general, self-healing polymers and composites are classified based on their mechanisms of action. While extrinsic systems depend on an external healing agent, the process takes place through reversible bonds or supramolecular interactions in intrinsic systems. In this chapter, the main mechanisms of self-healing epoxy systems, involving extrinsic and intrinsic approaches, autonomous and non-autonomous, are presented and discussed. Since the development of the first extrinsic self-healing epoxy systems, based on microcapsules and vascular networks, which are still the most studied approaches for coatings and composites, many new possibilities have been researched, especially systems involving intrinsic mechanisms. Among them, mechanisms of dynamic covalent networks based on thermally activated reversible Diels–Alder reactions and disulfide bonds, and photoreversible cross-linking have been considered. Furthermore, new trends in self-healing processes concerning vitrimers, non-covalent supramolecular systems, shape memory-assisted self-healing, and bio-based epoxy materials are introduced, looking forward to a wider range of possible applications.