Polymer researchers probe self-healing fuel tanks

On the atomic scale, shooting particles at stuff to see what happens is a long established scientific principle. But a group of US scientists which applied the idea on a macro scale found that a commercial polymer has a very interesting property: when it is shot at, it immediately "repairs" the bullet holes.

The polymer is currently used to coat golf balls, bowling pins and helmets, but the researchers think it could eventually be used to create self-healing fuel tanks for military aircraft, New Scientist reports.

At the moment, bullet-proofing fuel tanks is a heavy business involving a layer of rubber sandwiched in several layers of shielding. When it is pierced, the rubber swells to fill the hole.

Christopher Coughlin, a materials engineer at the Naval Air Systems Command in Patuxent River, Maryland is leading the research. His team has shot a variety of bullets at 1.5mm thick sheets of the polymer and determined that large, blunt-tipped bullets would tear holes in the material, but holes produced by smaller projectiles with pointy tips healed over very quickly.

The key to the material's behaviour probably lies in its melting point. Coughlin explains that the bullets speeding through the polymer - known commercially as Surlyn - heat it to its melting point allowing it to stick itself back together. "It's not going to self-heal if you just poke a hole in it with an ice pick," he remarked.

The team is now working to better understand exactly how the material sticks itself back together again. They also need to find a way round the polymer's irritating habit of disintegrating on contact with jet fuel.

However, if a fuel resistant variety of the polymer can be found, or if the research team can find a way to bond it to another fuel resistant material, it would offer a lightweight way to protect planes' fuel tanks. And as Coughlin points out, anything that saves weight on a plane is a real bonus. ®

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