Heat treatment of wood in dry medium and investigation on its effect on surface wettability and adhesion strength of coating

In this study, the effect of heat treatment of Alder (Alnus glutinosa), Poplar (Populus nigra) and Spruce (Picea abies) on adhesion strength of clear and acid catalyzed transparent coating was investigated. For this aim, wooden samples were prepared with dimension of 200×100×18 mm (longitudinal, tangential, radial) from sapwood on tangential surface. Samples were kept under heat treatment in oven with 150 and 180˚C temperatures for about 3 hours. After treatment, samples’ surfaces were sanded with 120 and 180 grit size sand paper, respectively. Contact angle of water was measured before and after treatment. Samples’ surfaces were covered with a transparent coat in two separate processes which were clear and acid catalyzed. Adhesion strength of coating measured with Pull Off method according to ASTM D-4541 standards. Results showed that the heat treatment increased contact angle. This increase continues as the heat treatment temperature goes higher and it leads to decrease in wettability of samples’ surfaces. Results also indicated that heat treated of wood had significant effect on adhesion strength of coating. Adhesion strength in control samples was more than heat treated samples. lowest coating strength was observed in samples which were heat treated in 180 ˚C.