Self-healing of nanofiber-based composites in the course of stretching

Here we aim to elucidate the self-healing mechanisms in composites with embedded solution-blown nanofibers containing separate reservoirs of epoxy resin and hardener in their cores. In tensile tests of such composite materials with the resin- and hardener-containing solution-blown nanofibers embedded in a polymer matrix, it is shown that the fibers can be ruptured by stretching, thereby releasing the epoxy resin and hardener. Given a resting (or holding) period of 1–2 h, such materials can experience a restoration or even enhancement of stiffness in subsequent stretching, thereby displaying self-healing properties. In two model macroscopic experiments with a single crack tip, conducted in the Appendix with the aim to elucidate the self-healing mechanism, the epoxy resin and hardener released into the tip are shown to react with each other, resulting in a cured and hardened epoxy that heals the crack tip.