Relationship of wood surface energy to surface composition

The wood cell wall is composed of cellulose, lignin, hemicelluloses, and extractives. Thus, the surface energy of the wood material must be some combination of the surface energies of these components. The influence of extractives on wood surface chemistry can be important in diverse industrial applications, such as coating, pulping, and wood-based composites. In this study, pine wood meal was subjected to heating, washing with toluene, and extraction with acetone/water, dichloromethane, and ethanol/benzene. The surface properties and composition were then determined by Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and inverse gas chromatography (IGC). The dispersive component of the surface free energy, the enthalpy, the entropy, and the acid/base interactions were calculated from IGC measurements and compared to the surface composition as revealed by XPS. Heating and washing with toluene altered surface properties only slightly. Extraction of wood meals with acetone/water, dichloromethane, and ethanol/benzene appeared to partially and selectively remove most extractives from the wood, resulting in an increased dispersive component of the surface energy, increased acidity, and increased basicity. The surface energy appeared to be related to the distribution of surface oxygen-containing functional groups.