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16-05-2019 | Materials Technology | News | Article

Self-restoring Corn Starch Coating

Nadine Winkelmann

Due to the special arrangement of its molecules, a new coating made of corn starch is able to repair small scratches by itself through heat. The net-like structure of the coating makes the material moveable, so that it can even out scratches and make them disappear.

Superficial micro-scratches that occur on car bodies or other high-gloss surfaces are harmless, but annoying. In collaboration with experts from the Leibniz Institute for New Materials (INM), scientists from Saarland University have developed a new coating that is able to repair small scratches on its own due to its special molecular arrangement. The fact that it is cross-linked via ring-shaped molecules makes the material intrinsically 'stretchy', which means it can compensate for scratches and make them disappear again. Ring-shaped derivatives of maize starch, so-called cyclodextrins, were used to achieve the net-like structure. These were threaded – like pearls – onto plastic molecules with long synthetic chains to form structures known as polyrotaxanes. The cyclodextrins on the plastic thread can move freely on certain sections and are prevented from unthreading by bulky stopper molecules. These 'pearl chains' are cross-linked via a chemical reaction. 

Heat as a trigger

The network that this creates is as moveable and flexible as a stocking. When exposed to heat, the cyclodextrin beads migrate back along the plastic threads into the area of the scratch on the surface and compensate for the gap that was formed there. To provide the functional coating with higher mechanical stability and weather resistance, the composition of the polyrotaxanes was changed by adding further constituents such as heteropolysiloxanes and inorganic nanoparticles. This reduced the original repair time from several hours to just a few minutes. The scientists are currently working on scaling up production of the coating from laboratory to pilot.

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