A photochemical method for improvement of color stability at polymer-wood biointerfaces

Abstract

The possibility of photochemical improvement of color stability by UV-irradiation treatment at coating-wood biointerfaces was investigated. The surface of beech wood was partially delignified by exposure to UV-irradiation by passing of samples under UV lamps: a mercury (Hg) lamp with a peak wavelength of 366 nm, a gallium (Ga) lamp with peak wavelengths at 410 and 420 nm and a combination of a mercury and a gallium (Hg + Ga) lamp. After UV-irradiation, the samples were coated with a UV-curable acrylic coating. The number of passes under the lamps was varied to determine the optimum combination of the number of passes and the lamp type that produces the smallest change in color of the coated wood in an indoor environment. The coated samples that had been UV-irradiated by passing 15 times under both an Hg lamp and a Ga lamp showed the smallest change in color (decrease in the Delta E by 23.23% compared to the untreated coated samples) after 72 h of accelerated artificial sunlight exposure. Microscope images of the same samples showed deformation of the cells in wood surface layer and a roughening of the "wood-coating line", which could be related to a partial removal of lignin. These findings suggest that delignification of wood leads to more photo-stable polymer-wood interfaces in terms of color.