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Posted: March 17, 2009

Coating makes scratches on cars disappear when exposed to sunlight

(Nanowerk News) Scientists have developed a polyurethane coating that heals its own scratches when exposed to sunlight, offering the promise of scratch-free cars and other products.
"We developed a polymeric material that is able to repair itself by exposure to the sun," said Marek Urban of the University of Southern Mississippi in Hattiesburg, whose study appears in the journal Science ("Self-Repairing Oxetane-Substituted Chitosan Polyurethane Networks").
"In essence, you create a scratch and that scratch will disappear upon exposure to the sun," Urban said in an interview on the Science website.
The self-healing coating uses chitosan, a substance found in the shells of crabs and shrimp. This is incorporated into traditional polymer materials, such as those used in coatings on cars to protect paint.
When a scratch damages the chemical structure, the chitosan responds to ultraviolet light by forming chemical chains that begin bonding with other materials in the substance, eventually smoothing the scratch. The process can take less than an hour.
Urban said the new coating uses readily available materials, offering an advantage over other self-repairing coatings, which he said were "fairly elaborate and economically unfeasible."
The team tested the compound's properties using a razor-blade-thin scratch. "We haven't done any of the tests to show how wide it can be," Urban said in a telephone interview.
He said the polymer can only repair itself in the same spot once, and would not work after repeated scratches.
Obviously, this is one of the drawbacks," he said, adding that the chances are low of having two scratches in exactly the same spot.
Howell Edwards, who leads the chemical and forensic sciences division of the University of Bradford in Britain, said the findings were novel.
"Clearly, there are future applications of this work in the repair of automotive components, which extensively use polyurethane polymers, that have suffered minor damage," Edwards said in a statement.
Urban said the coating could be used in packaging or furniture or anything that requires a high-performance type of coating.
"You can dream up anything you desire," he said.
Urban said his team has patents pending on the material and is considering commercialization.
Source: Reuters (Julie Steenhuysen)