Inspired by biological systems in which damage triggers an autonomic healing response, a polymer composite material that can heal itself when cracked has been developed. In this paper we summarize the self-healing concept for polymeric composite materials and we investigate fracture mechanics issues consequential to the development and optimization of this new class of material. The self-healing material under investigation is an epoxy matrix composite, which incorporates a microencapsulated healing agent that is released upon crack intrusion. Polymerization of the healing agent is triggered by contact with an embedded catalyst. The effects of size and concentration of the catalyst and microcapsules on fracture toughness and healing efficiency are investigated. In all cases, the addition of microcapsules significantly toughens the neat epoxy. Once healed, the self-healing polymer exhibits the ability to recover as much as 90 percent of its virgin fracture toughness.

Self-healing protective films of 1,2-bis(triethoxysilyl)ethane (C2H5O)3Si(CH2)2Si(OC2H5)3 (abbreviated to BTESE) polymer containing sodium silicate Na2Si2O5 (water glass) and cerium(III) nitrate Ce(NO3)3 were prepared on a zinc electrode previously treated in a 1×10−3 M Ce(NO3)3 solution at 30 °C for 30 min. After the surface of coated electrode was crosswise scratched with a knife edge, the electrode was immersed in an aerated 0.5 M NaCl solution at 30 °C for many hours and polarization measurements of the scratched electrode were carried out for estimating the self-healing effects of the films on zinc corrosion at the scratches. The optimal quantities of Na2Si2O5, Ce(NO3)3 and BTESE in the films were determined by polarization measurements and observation of pit formation at the scratches. No pitting corrosion occurred at the scratches on the zinc electrode covered with a film composed of their optimal quantities after immersion in the solution for 72 h.

A highly protective and self-healing film of 1,2-bis(triethoxysilyl)ethane (C2H5O)3Si(CH2)2Si(OC2H5)3 polymer containing sodium silicate (water glass) Na2Si2O5 and cerium(III) nitrate Ce(NO3)3 was prepared on a zinc electrode previously treated in a Ce(NO3)3 solution. The film was examined by polarization measurement of the electrode in an aerated 0.5 M NaCl solution after the electrode was scratched and immersed in the solution for 4–72 h. Self-healing mechanism of the film was investigated by X-ray photoelectron spectroscopy and electron-probe microanalysis for the coated electrode surface after scratched and immersed in the NaCl solution. A passive film composed of Zn(OH)2, ZnSi2O5 and Ce3+–Si2O52− salt or complex was formed on the scratched surface and preferential deposition of Si2O52− compounds occurred at a defect of the passive film where Cl− accumulated, resulting in suppression of pitting corrosion at the scratch.