via New Scientist (h/t Lucianne)
Maggie McKee - 13:26 24 August 04
The same material that makes golf balls tough may soon make bullet holes vanish in "self-healing" aircraft fuel tanks, say US navy researchers. Recently, US scientists discovered that a commercially sold polymer - used to coat bowling pins, helmets, and golf balls - displays a curious property when shot at: it can immediately "pave over" the bullet holes. Now, a team led by Christopher Coughlin, a materials engineer at the Naval Air Systems Command in Patuxent River, Maryland, is trying to understand why the polymer self-heals. He hopes one day it can be used to help aircraft fuel tanks recover quickly from enemy fire. "If you're 500 miles from your naval base - which could be an aircraft carrier in the ocean - you have to be worried. Are you going to have enough fuel to make it back?" Coughlin asks.
Pointy bullets
To test the self-healing behaviour, his team has been shooting various types of bullets at a 1.5-millimetre-thick sheet of the polymer, which is manufactured by DuPont and called Surlyn. The cleanest and quickest seals came after hits with a relatively small (5.6 mm), very pointy bullet, while larger, blunt-tipped projectiles - especially when shot from an angle - "chunked out" holes in the material. He presented the results Monday at the American Chemical Society meeting in Philadelphia, Pennsylvania. He believes the melting properties of the material may explain why it self-heals. "It's not going to self-heal if you just poke a hole in it with an ice pick," Coughlin told New Scientist. "It's not going to get hot enough to melt." He says speeding bullets heat the Surlyn to around its melting temperature. "We're trying to understand how that affects whether things get stuck back together," he says.
The melting properties appear to depend on Surlyn's polyethylene chains and methacrylic acids. These comprise a random mixture of ionic and nonionic regions that each want to stay with their kind. "It's like chains of spaghetti where parts are stuck together, which changes how the material flows [when heated]," Coughlin says. |