Self-healing systems for aeronautical application

In order to extend the lifespan of materials, great interest is being turned to the development of self-healing systems. They are smart materials since they have the ability to independently trigger the repair processes by hindering the propagation of microcracks that are generated due to mechanical, chemical or thermal actions. The aviation industry is particularly interested in making composite materials with self-healing ability because they lead to the reduction of fuel costs and overcome difficulties connected to damage diagnosis and repair. Depending on the different approaches that have been investigated to integrate self-healing ability in several matrices, self-repairing systems can be classified in Extrinsic and Intrinsic. Extrinsic self-healing materials are based on the dispersion of microcapsules or vascular channels containing healing agents within the matrix of interest. When the crack occurs in the material, the microcapsules or vascular channels rupture, causing the release of the healing agent that, first, diffuses along the damaged area and, subsequently, reacts chemically in order to effectively repair the crack. The main problem of microcapsule-based extrinsic systems is that, once repair by leakage of the healing agent has occurred, a new repair cannot occur at that same site. For this reason, the scientific community has been working for a few years on replacing these systems with simpler ones based on reversible interactions, which allow for multiple rounds of repair at the same site. One of the most studied interaction for the realization of self-healing systems is hydrogen bonding. With this contribution we want to describe our composite self-healing system for aeronautical application. We synthesized copolymers based on methacrylic monomers with different percentages of urea-N-2-amino-4-hydroxy-6-methylpyrimidine-N’-(hexametylen-n-carboxyethyl methacrylate) HEMA-Upy such as 2.5, 5.0 and 7.8 wt %. By dispersing these copolymers, into the epoxy matrix selected for aviation applications, it is possible to impart self-healing ability to the resulting composite material, thanks to the quadruple hydrogen bond interactions between the polymer chains.