Changes in the Composition of the Dried Asian Lacquer (Korean Lacquer) Film Irradiated with Ultraviolet Light

Abstract

Asian lacquer is a material that has been used in Asia from ancient times to coat the surface of objects. It is a durable material, but is known to be weak to ultraviolet light (UV). Here, to understand the deterioration characteristics of Asian lacquer due to UV, the changes were analyzed using ultraviolet photometry, IR, and pyrolysis/GC/MS (pyrolysis/GC/MS), after exposing the lacquer coating film to UV (<i>λ</i>= 340 nm). In the ultraviolet photometry, the surface exposed to UV showed fluorescence. In IR analysis, the powder sample showed little change after exposure to UV, but on the surface, C = O groups increased, while C―H groups decreased significantly. Analysis with pyrolysis/GC/MS revealed that the composition of organic acid increased significantly. Carboxylic acids having 9 or less carbon atoms and dicarboxylic acids were significantly increased compared to carboxylic acid having 16 carbon atoms. In addition, urushiol with the oxidized side chain was also increased. This shows that the penetration depth of UV is the limiting factor for deterioration, and that the deterioration of lacquer due to UV proceeds with the destruction of carbon–carbon single and double bonds and the subsequent formation of carboxylic acid.