Improvements on weathering resistance of wood by tannin and nano metal oxides

The aim of this study was to improve UV resistance of Scots pine wood in outdoors by coating the surfaces with a water based stain reinforced with 3 different concentration levels of valex, mimosa and Pinus brutia bark tannins, and zinc and cerium oxide nano particles. For this purpose, samples coated with tannin + nano metal oxide reinforced stain were exposed to accelerated weathering for 1512 hours. Commercially available nano coating was used as a reference chemical. Color, gloss, surface roughness and macroscopic changes were evaluated periodically during the test, and the results of coated samples were compared with controls. Results showed that wood surfaces got dark color, lost the gloss and become rougher after the weathering test. Samples with tannin and nano metal oxide reinforced stains showed better surface properties than control and reference samples. Color parameters and surface roughness values clearly showed low tannin concentrations gave better results in tannin and nano zinc oxide combinations. Cerium oxide was found to be more efficient on protection of wood surfaces in comparison to zinc oxide. Cracks were observed in control and reference samples after 48 hours of weathering period while there was not any crack formation on the test samples. General condition of samples seemed to be better for mimosa and pine tannins for zinc oxide combinations, and valex and pine tannins for cerium oxide combinations after the weathering test. Results of such a combination system clearly showed amount of expensive inorganic nanoparticles could be reduced with the addition of natural antioxidants into transparent coatings.