German researchers at the Fraunhofer Institute for Environmental, Safety and Energy Technology UMSICHT in Oberhausen have developed self-healing elastomers that can repair themselves by stopping the growth of cracks. Latex from the Hevea Brasiliensis tree is used.
Hevea latex contains capsules filled with the protein hevein. If the bark of the tree is damaged, the latex escapes and the capsules break open to release hevein, which links the rubber particles in the latex to seal the wound. The scientists are now applying this principle to elastomers.
The researchers loaded microcapsules with a one-component adhesive (polyisobutylene) and put it in elastomers made of synthetic caoutchouc to stimulate a self-healing process in plastics. If pressure is put on the capsules, they break open and separate this viscous material. Then this mixes with the polymer chains of the elastomers and closes the cracks.
A number of tests on a variety of synthetic caoutchoucs indicated self-healing properties. The restored tension expansion was 40% after a healing period of 24 hours.
Even better results were achieved by supplying elastomers with ions. Here, the caoutchouc tree also acted as the model. Hevein proteins ions link up to close cracks as if the material is damaged particles with opposite charges look for a new bonding partner to which it adheres.
Research into self-healing polymers is being conducted at Iowa State University in the US.