Self-healing elastic polymers developed with the help of a tree


March 7, 2011

The healing process demonstrated in the caoutchouc tree-inspired elastomer (Photo: Fraunhofer)

The healing process demonstrated in the caoutchouc tree-inspired elastomer (Photo: Fraunhofer)

When the caoutchouc tree is damaged, liquid latex containing capsules of the protein hevein escapes from inside of it. Those capsules rupture, releasing the hevein, which links the latex particles together and ultimately closes up the wound. The whole bursting/sealing-microcapsules thing is obviously a pretty good idea, as it has been put to use in human technology such as self-healing concrete, electronics, paint and aircraft epoxy resin. Now, German researchers have copied the caoutchouc tree's modus operandi to create a self-sealing elastic polymer.

Scientists from the Fraunhofer Institute for Environmental, Safety and Energy Technology loaded microcapsules with the adhesive polyisobutylene, then put those capsules into synthetic caoutchouc sap elastomers. The idea was that when pressure was put on the elastomers to the point of cracking, the capsules would rupture and mix with the elastomers' polymer chains, thus sealing the cracks.

As it turned out, the capsules didn't cooperate. When the polyisobutylene was added in an uncapsulized form, however, a self-healing effect did occur – the elastomers' tension expansion was restored by 40 percent after a 24-hour healing period.

The scientists further copied the caoutchouc tree, by charging the elastomer with ions. In the case of the tree, the hevein proteins link up with one another (and in the process, with the latex) via ionic bonding. By charging the synthetic elastomer, a similar effect could be achieved with the polyisobutylene.

Fraunhofer will have a self-healing muffler made from the experimental material on display at the Hannover Fair from April 4th to 8th. A self-healing biorenewable polymer is also being developed at Iowa State University.

About the Author
Ben Coxworth An experienced freelance writer, videographer and television producer, Ben's interest in all forms of innovation is particularly fanatical when it comes to human-powered transportation, film-making gear, environmentally-friendly technologies and anything that's designed to go underwater. He lives in Edmonton, Alberta, where he spends a lot of time going over the handlebars of his mountain bike, hanging out in off-leash parks, and wishing the Pacific Ocean wasn't so far away. All articles by Ben Coxworth

There is a lot of talk about self healing polymers and self healing concrete. The simple fact is are expensive and relatively weak. It seems to me that making a stronger substance is more important then one that fixes itself. Am I wrong?

On a side note what are the environmental impacts of such a substance? Is it less recyclable. I definitely could see a funny SNL skit where an employee has to recycle a pile of bottles and as hard as he tries to shred them they keep turning back into bottles. All while a musical score similar to that of fantasia plays in the back ground.

Michael Mantion

another use would be as a coating to drain pipes like you find under a kitchen sink . . . the coating would make them just about 100% leak-proof . . . I hope you pursue this as a practical application . . .

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