New Polymer Coating Heals Itself with Exposure to Sunlight

[via nytimes]

Skin is spectacular stuff. Nick it with a razor or scrape it on the sidewalk and it heals itself quickly.

Synthetic materials are another story, although it’s not for lack of effort on the part of scientists. Chemists have been trying for years to develop self-healing polymer coatings for use on cars, furniture and other objects. Some recent efforts use microspheres containing bonding chemicals. These tiny capsules are embedded in the coating. When a crack or scratch occurs, the spheres break and the chemicals flow into the void, patching it.

Biswajit Ghosh and Marek W. Urban of the University of Southern Mississippi have come up with another approach, which they describe in a paper in Science. With their method, what breaks is not a sphere, but a ring-shaped chemical, oxetane, that is incorporated in the polyurethane polymer. Another compound in the polymer, chitosan, forms cross-links at the places where the oxetane breaks, healing the scratch.

What makes the method potentially very useful is what causes the cross-links to form: exposure to ultraviolet light. That means that a damaged coating could heal itself in a matter of minutes or hours by being exposed to sunlight, which contains plenty of UV rays. If your car picks up a scratch at the parking garage, for instance, it might disappear by the time you arrive home.

Another potential advantage is that the coating does not require space-age materials. Chitosan is a derivative of chitin, which is what gives structure to the shells of shrimp, lobster and other crustaceans. So there’s plenty of it around.

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