Thermodynamic characteristics of surface densified solid Scots pine wood

Wetting phenomena of surface densified solid wood and its surface energetic behavior were investigated. The specimens of three different initial thicknesses (22 mm, 20 mm, and 18 mm) were surface densified to a target thickness of 15 mm in order to obtain three different degrees of surface densification. After surface densification one third of the specimens was heat treated at 200 °C in the presence of steam, and one third of the specimens was oil treated with linseed oil. The sessile drop technique was used to estimate the apparent contact angle of water, diiodomethane, and formamide on control and surface densified wood. The contact angle data were used to determine the surface free energies of the control and surface densified wood by the Owens Wendt Rabel and Kaelble (OWRK) method. The results of contact angle measurements revealed that surface densification process affects surface wettability. The apparent contact angles of test liquids were higher in the case of surface densified wood compared to the control undensified wood. Heat treatment and oil treatment of the surface densified wood additionally increased the contact angle of tested liquids. Furthermore, a larger reduction in the void spaces of the wood due to higher degree of densification did not affect the apparent contact angles of tested liquids and consequently the surface free energy. The surface densification process lowered the surface energetics and the polarity of wood. Furthermore, heat treatment and oil treatment additionally increased the hydrophobic character of the examined surfaces and lowered the dispersive and polar components of surface free energy.