Measurement of dynamic and static contact angles on wood for the determination of its surface tension and the penetration of liquids into the wood surface

Surface tensions of various species of solid wood and the penetration of liquids into the wood surface were measured by determination of contact angles with a software equipped goniometer. The contact angles were evaluated by means of the methods of Zisman and of Owens/Wendt resp., to calculate the (critical) surface tensions. It has been found that with few exceptions there is no decisive influence of the wood moisture content on the surface tensions, in spite of rather lower contact angles at surfaces of higher wood moisture content indicating better wetting conditions. Using the method of Owens/Wiendt the surface tension of earlywood with its greater roughness was distinctly higher than of the smooth latewood. No difference however could be found using the method according to Zisman. The penetration behaviour of liquids into wood surfaces depends on the different diameters of wood cells and the viscosity and molecule size of the penetrating liquids. Penetration was retarded with increasing viscosity of the liquids and the smaller cell diameters in latewood in comparison to earlywood.