| Wetting phenomena refer to macroscopic manifestations of intermolecular forces acting across a solid-liquid interface. The purpose of this work is to achieve a better understanding of wetting phenomena on wood which also may guide us to improve the interaction between e.g. wo od and adhesives.
A modified Wilhelmy method has been developed for the measurement of wetting forces on wood. In addition, wetting and surface characterization techniques based on column wicking and inverse gas chromatography (IGC), respectively, have been applied to spruce wood particles. The wetting measurements by the Wilhelmy method were performed on extracted and non-extracted, fresh and aged pine wood veneers. The results show that a severe contamination of the probe liquids may occur during the measurements. The contamination is caused by dissolution or by the presence of extractives at the wood-liquid interface, and it generally results in a distinct decrease in the liquid surface tension. It is also observed that wicking of the liquid occurs into voids of wood and along its irregular and rough surface. The Wilhelmy method may however provide an efficient means of recording and controlling such contamination and wicking effects.
The measured wetting forces permit an apparent contact angle to be estimated.
Based on the van Oss-Chaudhury-Good approach, (Lewis) acid-base properties of the wood veneers were determined. The results indicate that the acid and base components of the surface free energy of the wood increase and decrease, respectively, with aging time, probably due to reorientation of functional groups, and due to oxidation, at the wood/extractives- air interface.
The surface characterization of spruce particles by IGC indicated that wood without extractives shows a greater Lewis acidic and less Lewis basic character than wood containing extractives. The wetting measurements on spruce particles by the column wicking were in general influenced by sorption of the probe liquids in the wood substance, i.e. bulk sorption. Temperature measurements during the wetting process also indicate that sorption of probe liquid vapor may occur in advance of the moving liquid front.
By more suitable methods for measurements of the wetting properties of wood, valuable technical information about the capacity of wood to interact with adhesives and co atings may be generated. | 