Measurement of Wood Wettability by the Wilhelmy Method. Part 1. Contamination of Probe Liquids by Extractives

Summary This work focuses on the influence of extractives during wetting measurements on wood. Fresh and aged veneers of extracted and non-extracted heart- and sapwood of pine were prepared, and the Wilhelmy method was used to study the wettability of these veneers. In this method, the force acting on the veneers was measured during immersion in and withdrawal from a series of probe liquids. The results suggest that some of the probe liquids become severely contaminated by extractives during the measurements on the non-extracted veneers, and that this strongly affects the wood wetting measurements. The contamination is effectively detected as a distinct decrease in the surface tension of the liquids caused by dissolution or presence of wood extractives at the wood-liquid interface. It is important to note that such contamination may also occur during wetting studies on wood using other contact angle measurement techniques. The most obvious contamination occurred in the case of measurements on non-extracted veneers immersed in water and formamide. Generally, no contamination was detected in the case of measurements on extracted wood veneers. The Wilhelmy method may provide an efficient means for recording and control of any contamination of the probe liquids that may arise during wetting studies on wood.