Superficial micro-scratches in the car body or on other high-gloss surfaces are harmless, but annoying. A new paint by researchers from Saarbrücken, Germany, is now to remedy the situation: Made of maize starch, the paint is able to repair small scratches by itself due to the special arrangement of its molecules. The cross-linking via ring-shaped molecules makes the material movable, so that it compensates for the scratches and these disappear again. The new coating was developed by INM experts together with scientists from Saarland University. The net-like structure of the coatings is achieved by using ring-shaped derivatives of corn starch, so-called cyclodextrins. These were threaded like pearls onto long-chain plastic molecules. In the polyrotaxanes produced in this way, the cyclodextrins on the plastic thread can move freely on certain sections of the line and are prevented from unthreading by bulky stopper molecules. The pearl chains are cross-linked by a chemical reaction.
The resulting network is flexible and elastic like a stocking. When exposed to heat, the cyclodextrin beads migrate back along the plastic threads into the area of the surface scratch, thus compensating for the gap formed by the scratch. The composition of the polyrotaxanes was changed by adding further ingredients such as heteropolysiloxanes and inorganic nanoparticles to produce a functional coating with higher mechanical stability and weather resistance. Thus, the original repair time was reduced from several hours to only a few minutes. The scientists are currently working on transferring the production of the coating from the laboratory scale to the pilot plant scale.