Autonomic healing of polymer composites

Structural polymers are susceptible to damage in the form of cracks, which form deep within the structure where detection is difficult and repair is a lmost impossible. Cracking leads to mechanical degradation(1-3) of fibre-re inforced polymer composites; in microelectronic polymeric components it can also lead to electrical failure(4). Microcracking induced by thermal and m echanical fatigue is also a long-standing problem in polymer adhesives(5). Regardless of the application, once cracks have formed within polymeric mat erials, the integrity of the structure is significantly compromised. Experi ments exploring the concept of self-repair have been previously reported(6- 8), but the only successful crack-healing methods that have been reported s o far require some form of manual intervention(10-18). Here we report a str uctural polymeric material with the ability to autonomically heal cracks. T he material incorporates a microencapsulated healing agent that is released upon crack intrusion. Polymerization of the healing agent is then triggere d by contact with an embedded catalyst, bonding the crack faces. Our fractu re experiments yield as much as 75% recovery in toughness, and we expect th at our approach will be applicable to other brittle materials systems (incl uding ceramics and glasses).