Car coating made from crab shell material heals scratches automatically

Direct sunlight might be bad for you, but it can do wonders to your car. US scientists at the University of Southern Mississippi have developed a new polyurethane material that heals its own scratches in less than an hour when exposed to sunlight.

The material’s secret lies in using molecules made from chitosan – a carbohydrate derived from the shells of crabs and other crustaceans.

Tiny scratches to the surface of the material close up in only a few minutes when the material is exposed to the ultraviolet (UV) light in sunlight.

According to Marek Urban, who led the study, the material could make a good topcoat for an automobile.

The scientist and his team combined polyurethane with a molecule made up of chitosan. They then modified this chitosan slightly with the addition of the structures composed of four carbon atoms called oxetane rings.

“It is the oxetane rings that give the material its ability to heal,” Urban reported in the journal Science.

When a scratch is made, some of the rings are broken, leaving chemically reactive free ends. The chitosan then 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, beginning at the bottom of a scratch, and pulling it closed like a zipper.
Urban says scratches about 10 micrometres wide and 50 deep heal over after 30 minutes of exposure to UV light.

However, 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.

According to the expert, the material could be useful for a number of applications, including vehicles and furniture, or electronic devices like cellphones.

“If you scratch it, let it sit under the Sun for some time and it’s cured,” he said.

Urban said his team has patents pending on the material and is considering commercialisation.



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