UV-induced polymerization of urushiol. II: Effects of hydrogenation degree of urushiol on surface morphology

There are a large number of lacquer-coated, excavated cultural treasures in China, e.g. Qin Terracotta Army. The lacquer film is formed via the laccase-catalyzed polymerization and a coupling reaction on the long aliphatic unsaturated side chain, which requires a long drying period and specific conditions. The protection and restoration of these archaeological findings and the development of new lacquer wares should find a facile way urgently to dry raw lacquer rapidly. Furthermore, to keep lacquer wares’ excellent brilliance, the surface morphology is of much importance. Urushiol, the basis of lacquer, can be cured under UV irradiation within 2 min in the absence of a photoinitiator, which dramatically shortens the drying time. The wrinkled coating with lusterless surfaces, however, was obtained. In this paper, a facile approach was developed to prepare cured urushiol films with glossy smooth surfaces using a high-pressure mercury lamp as a UV source. The CC bonds in the long aliphatic unsaturated side chain of urushiol were hydrogenated for different times, and the effects of hydrogenation degree of urushiol on surface morphology of the UV cured films were investigated by scanning electron microscopy (SEM). The results showed that when hydrogenated for 3 h or more, the percentage of hydrogen element was over 10.43 wt%, the morphology of the UV cured films was transformed from lusterless wrinkling to glossy smooth, and that the UV cured films of urushiol acetate also gave glossy smooth surface.