VARIATIONS IN WETTABILITY ON HEAT-TREATED WOOD SURFACES: CONTACT ANGLES AND SURFACE FREE ENERGY

The contact angles for Pinus (Pinus taeda), Erisma (Erisma uncinatum), Araucaria (Araucaria angustifolia) and Hymenaea (Hymenaea stilbocarpa) woods were obtained using four test liquids (water, diiodomethane, formamide, and ethylene glycol). The values of surface free energy were calculated for the heat-treated woods in order to analyze their changes in polar and non-polar (dispersive) components. According to the results of contact angles, surface free energies and surface polarities, the woods showed reduced wettability after heating treatment and become hydrophobic. Pinus and Araucaria were by far the most polar samples, since they presented low values of contact angle and high wettability (more hydrophilic). The approach used to calculate the surface free energy from the measurements of contact angle depends on the use of two, three or four test liquids, since different profiles were obtained for their polar and non-polar components. The surface characteristics for the wood samples were mainly defined based on polarity, which is an important parameter aiming at inferring when they are more polar (more hydrophobic), i.e. of great technological interest.