The chemistry of self-healing polymers

Composites are materials that are composed of two macroscopic phases. In the case of polymeric composites such as fibreglass, they usually comprise glass or carbon fibres for strength and a polymer phase surrounding the fibres. This polymer is usually an epoxy or polyester resin that cures to form a densely cross-linked polymeric network of covalent bonds. The cross-linking provides properties such as stiffness and strength as well as resistance to solvents or other chemicals. Polymer composites, however, are susceptible to cracking and delaminating (ie when the cured resin de-bonds from the fibres), which are difficult to detect and repair. By making this repair automatic, the materials would have extended lifetimes, thus making their products - from structural applications, through adhesives and microelectronics used in mobile phones, to medical implants - safer and more reliable.