Construction of a fluorine-free anti-smudge waterborne polyurethane coating

A fluorine-free anti-smudge waterborne polyurethane coating was constructed via the dispersion of hexamethylene diisocyanate trimer into organosilicon-grafted waterborne polyurethane. In the film-forming process, the interaction among carboxyl, hydroxyl and isocyanate groups blocked the hydrophilic groups and improved the density of the coating, thereby preventing contaminants from penetrating into it. Furthermore, the organosilicon side chain migrated onto the coating surface to form a low surface energy amphiphobic layer, which endowed the coating with superior anti-graffiti performance. The surface energy of the as-constructed coating was 24 mN m−1. The water, diiodomethane and hexadecane contact angles were 95°, 70° and 36°, respectively, with corresponding sliding angles of 35°, 10° and 1°, thereby showing that the coating had no affinity to oil- and water-based ink graffiti. More strikingly, the anti-graffiti performance remained after 400 abrasion cycles under a pressure of 110 kPa and under harsh chemical treatment (strong acids, bases and salts). The constructed coating also showed an optical transparency as high as 93 % due to the high crosslinking degree.