Effect of tannin reinforced coatings on weathering resistance of wood

The aim of this study was to improve weathering resistance of Scots pine wood by treating the surfaces with water based transparent and opaque wood coatings containing tannins. In this study, the most effective tannin type and the lowest amount of tannin concentration were determined from 3 different tannin types and concentration levels. Valex, mimosa and Pinus brutia bark tannin at 3 different concentration levels were mixtured with the water based transparent and opaque wood coatings. Tannin containing coatings of 200 g/m2 were applied to cover all the front surface of the samples with a brush for three times. Samples coated with tannin containing coatings with various concentrations were exposed to artificial weathering for 1512 hours. Color, gloss, surface roughness and macroscopic changes were evaluated periodically during the test, and the results of coated samples were compared with controls. Visible surface degradations such as erosion, cracks and checks occurred on control samples while no crack formations were recorded for coated samples. Results showed that wood surfaces got dark color, lost the gloss and become rougher after the weathering test. Samples with tannin reinforced coatings showed better surface properties than control and reference samples.Color measurement data showed that high concentration levels were needed for the least color change on the surfaces however concentration increase of tannins in the transparent coating affected surface gloss and roughness of samples negatively. The most promising tannin types in transparent coatings against the surface degradations were determined as valex and Pinus brutia bark tannins. Opaque coating alone was found to be resistant against weathering factors and the measurements clearly showed that there is no need to corporate any UV absorbers to this coating. This study revealed that natural UV absorbers as tannins could be an alternative to expensive inorganic UV absorbers for transparent coating systems since they are cheap and environmentally frendly.