Self-healing rubber that binds back together after being snapped or punctured

Self-healing rubber that binds back together after being snapped or punctured could pave the way for self-healing shoes, fan belts, washing-up gloves and more.

"You can feel the material mending itself when you hold the fractured sides together," inventor Ludwik Leibler told New Scientist. "It's a very strange feeling."

When the material melds together again, it has just as much strength as it had before, says Leibler, a polymer chemist at the Industrial Physics and Chemistry Higher Educational Institution (ESPCI) in Paris, France. See the material self-healing in the video top right.

The material could eventually make it a cinch to repair holes in shoes, snapped fan belts and punctured kitchen gloves. It might also make strange new products possible – for instance bags that can be ripped open and then resealed. "You don't need a zip when you can make a resealable hole in it," Leibler says.

Regular rubber gets its strength from the fact that long chains of polymer molecules are coupled, or "crosslinked," in three different ways: through covalent, ionic, and hydrogen bonding between molecules.

Of these three bond types, only the hydrogen bonds can be remade once a material is fractured, although normally there are not enough hydrogen bonds for the rubber to re-couple in this way.

The solution devised by Leibler and colleagues is to simply get rid of the ionic and covalent bonds. They developed a transparent, yellowy-brown rubber in which crosslinking is performed only by hydrogen bonds. The new substance self-heals when its surfaces are brought together under gentle compression, at room temperature.

The material is synthesised from fatty acids and urea, which are cheap and renewable. The downside is that getting rid of covalent and ionic bonding means the material is weaker than regular rubber.

Along with the project's sponsor –French chemicals company Arkema – the ESPCI team hopes to improve the self-healing material before deciding upon its first application. They expect to create a whole spectrum of properties.

"They have done a fantastic job making this material," says Tony Ryan, a polymer expert at the University of Sheffield in the UK. "Someone is going to make a lot of money out of this – and I hope it is them. I certainly hope they have patented it."