Effect of different heat treatment applications on the layer properties of some wood varnishes

In this study, the effect of heat treatments applied under different atmospheric conditions and at different temperature levels on the layer properties of some varnishes was investigated. Beech (Fagus Sylvatica L.) and Scots pine (Pinus Silvestris L.) wood samples were subjected to heat treatment at 170 °C, 190 °C and 210 °C by hot air, oil treatment and ThermoWood methods. Then, the surfaces of the samples were coated with water-based, polyurethane and synthetic varnishes according to industrial applications. Surface hardness, surface gloss, varnish adhesion strength and color change tests were performed on the prepared samples. According to the results of the study, for both wood species, both surface hardness and varnish adhesion strength were found to be similar for samples heat-treated with ThermoWood and hot-air methods. Hardness and adhesion strength were generally lower in oil heat-treated samples. The total color change after varnish applications was higher in hot air method for Scotch pine samples and in oil heat treatment method for beech samples. The effect of heat treatment method on gloss was insignificant. In addition, varnish adhesion resistance and gloss values decreased and total color change increased with increasing heat treatment temperature. Heat treatment temperature had no significant effect on hardness values. On the other hand, higher hardness values were determined in polyurethane and water-based varnishes compared to synthetic varnish. However, the highest adhesion strength was obtained in synthetic varnish for all heat-treated samples. In addition, the least discoloration of the heat-treated samples was determined after water-based varnish applications and the highest gloss values were determined after polyurethane varnish applications. As a result, it can be said that heat treatment temperature is more effective on adhesion strength, color change and gloss, and heat treatment method is more effective on surface hardness in yellow pine and beech samples coated with different varnishes. Keywords: Wood material, Heat treatment method, Gloss, Color change, Hardness, Varnish, Adhesion strength.