Photostabilization of rubberwood using cerium oxide nanoparticles. Part 1: Characterization and colour changes

Light induced darkening and deterioration of wood used outdoors is undesirable. Photoprotection of wood could be achieved by using additives that reflect or absorb harmful radiation responsible for degradation. Nano metal oxides have strong absorption in the UV range of solar radiation and good transparency in the visible region. They offer unique benefits in protecting coatings and coated substrates from being degraded by UV radiation. However, to exploit the properties of nanoparticles, homogenous dispersion without agglomeration is necessary. In the present work, the photostabilization of rubberwood surfaces coated with cerium oxide (CeO2) was studied. The nanoparticles were surface functionalized with an organic alkoxy silane (3-glycidyloxypropyltrimethoxy silane) to improve the homogenous distribution in coatings, and the modified nanoparticles were dispersed in isopropanol and polyurethane (PU) coating. Rubberwood surfaces coated with dispersed nanoparticles (concentration 0.5 % to 6 % w/v) were exposed to a fluorescent UVA light source (λ=340 nm) at 60 °C in an accelerated weathering tester for 500 h and 1000 h. Colour changes due to UV light exposure were monitored using a spectrocolourimeter. Dispersion of CeO2 nanoparticles in PU coatings (concentration >2 %) restricted the photoyellowing of wood polymers.