Effect of Bleach Pretreatment on Surface Discoloration of Dyed Wood Veneer Exposed to Artificial Light Irradiation

To investigate the effect of bleach pretreatment on the surface photo-discoloration of dyed wood, two kinds of bleached and unbleached dyed wood veneers were irradiated in a xenon light source accelerated aging tester. The exposed surfaces' color, spectral reflectivity, chemical functional groups, and microstructure were characterized. Bleach pretreatment improved the dyeing effect of the wood veneers. However, it decreased the light fastness of the samples, and as adsorption between the dyes and wood components was reduced, some chromophoric chemical structures of the wood lignin and dyes were degraded, and some extractives (which can function as antioxidants to protect wood surfaces from discoloration) were removed. After light irradiation, the reflectance curves of dyed wood veneers was shifted toward longer wavelengths and noticeable yellowing was observed. Some parenchyma tissue, such as pit membranes in wood cell walls, suffered serious deterioration, as indicated by SEM.