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"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.
"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.
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A few years down the road, you may
be able to get that scratch out of your car’s bumper simply by parking
in a sunny spot. Researchers have created a polyurethane coating that
heals itself when exposed to ultraviolet light.
"This new material will have a lot of practical applications," said
study co-author Marek Urban, a chemist at the University of Southern
Mississippi. “It could coat anything that can be scratched—electronics,
aircraft, cars, you name it."
Self-healing coatings could minimize upkeep and repair on a variety of
products, saving consumers money and reducing waste.
“Your car would last for a long time, and it would look new for a long
time,” Urban said.
The new compound is not the first man-made self-healing material. In
2001, researchers at the University of Illinois embedded tiny
liquid-filled capsules in a polymer coating. When the coating cracked,
the capsules ruptured, spilling healing agents into the damaged area and
repairing it.
One of the Illinois scientists, Scott White, founded a company based on
this technology in 2005. Autonomic Materials, Inc. could have
self-healing coatings on the market in the next couple of months,
according to a recent article in the MIT Technology Review.
Other researchers have devised different methods. In 2002, scientists
from UCLA and USC created a compound that heals itself quickly when
exposed to high temperatures. The new coating is similar in that it
requires an external stimulus to work. But the stimulus—UV
radiation—should not be difficult to introduce. A few minutes in the sun
would do the trick.
“It’s a new healing chemistry for polyurethane,” said Nancy Sottos, a
materials scientist at the University of Illinois who was not involved
in the new study.
Urban and co-author Biswajit Ghosh, also of the University of Southern
Mississippi, created the compound by mixing chitosan—a derivative of
chitin, the main component of arthropod exoskeletons—into polyurethane.
They made tiny nicks in the new material, then exposed it to UV light
about as intense as that given off by the sun. The radiation set off a
series of reactions, causing damaged molecules to link up with each
other again. The cuts healed in about 30 minutes.
This repair process, described Thursday in the journal Science, is not
moisture-sensitive, meaning it should work in all climates. And making
the new coating won’t break the bank, according to Urban.
“It’s very economical,” he said. “You can get chitosan for almost
nothing.”
The mending reactions don’t seem to work a second time, so each part of
the coating can repair itself only once. But Urban doesn’t see this as
much of a drawback in the real world.
“Even if you try to hit the same spot, within a couple of microns,
statistically the chances of it happening are very small,” he said.
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