Enhancing weathering durability of pre-protected and unprotected wood by using bark extracts as natural UV absorbers in waterborne acrylic coating

Abstract

One of the crucial problems for wooden garden furniture is fading with the effect of UV rays. The color changes as a result of weathering have affected the usage of furniture. In this study, waterborne acrylic coatings containing bark extracts were evaluated as an environment-friendly wood surface preservative to improve the service life of wood in outdoor conditions. For this purpose, waterborne acrylic coatings were produced using extracts from the bark of 10 tree species applied on two different wood surfaces (scots pine and beech). The natural weathering test was conducted to determine the changes in the physical, mechanical and chemical structures of the coatings and wooden surfaces. It was observed that the color changes and surface roughness values were similar to the control samples for the heat-treated wood while they were the lowest for the impregnated scots pine. The color change of the test coatings applied on the unprotected scots pine surfaces provided similar results to the control coatings. The ATR-FTIR spectroscopy analysis revealed changes in the chemical structure, which explained why color changes occurred. The pre-protection methods affected the penetration of coatings and adhesion strength. The differences in the chemical structure of barks also influenced the viscosity of the coatings. After the weathering test, the change in the dry film thickness and adhesion strength of the acrylic coatings containing bark extract was similar to the control coatings for the heat-treated wood. The change in the adhesion strength values in the test coatings on the pine surfaces was similar to the control coatings. The macroscopic evaluation also showed the effectiveness of the bark extracts against weathering conditions. It is thought that it may be possible to use tree bark extracts with high UV absorbability instead of commercial UV absorbers in waterborne acrylic coatings used in outdoor conditions.