A comparison of different methods to calculate the surface free energy of wood using contact angle measurements

A number of controversies concerning the correctness of the different appro aches to determine the wood surface free energy and its components from con tact angle measurement arose in the past, and it is not clear which approac h one should follow. In this work the advancing contact angles of pure liqu ids on microtomed spruce surface were used to determine the surface free en ergy of wood. The most widely applied approaches for the surface energy of wood: the Zisman approach, the equation of state, the harmonic mean equatio n, the geometric mean equation and the acid-base approach were compared and the usefulness of this approaches referring to wood as material were discu ssed. It was found that the acid-base approach delivers a maximum of inform ation about chemical composition of the natural polymer wood, which consist s mainly of cellulose, lignin and a variety of hemicelluloses. Therefore, t he acid-base approach is most suitable to explain the coating properties (a dhesion) of wood surfaces. Furthermore, it is possible to improve the accur acy of the determination of the surface free energy of wood by increasing t he number of different liquids applied. A computerized method for the calcu lation of surface energy parameters from all five liquids used to obtain an approximate solution for disperse, acid and base components of surface fre e energy greatly facilitated this task. (C) 2001 Elsevier Science B.V. All rights reserved.