From Hydrophilicity to Hydrophobicity: A Critical Review: Part I. Wettability and Surface Behavior

Surface properties of wood are important for both wettability and hydrophobic modification. Glueability of wood is related to wettability, while durability and decay resistance are affected by physical and chemical components. This review (Part I) discusses hydrophilic characteristics of surfaces. Surface theories, calculation methods for surface tension, topography, contamination, and aging are reviewed. It was found that surface tension data were often disparate; a standardized procedure for contact angle measurement would permit reproducible measurements and comparable data for surface characterization. Surface tension of wood can be estimated using Zisman's critical surface tension, geometric-mean, harmonic-mean, and acid-base approaches. To date, however, no procedures have been developed for determining absolute values of surface tension. Few controversies exist in the literature regarding effects of surface topographic characteristics on surface tension. However, there are disputes regarding mechanisms of surface contamination and aging. Further research on surface tension of wood is warranted. Hydrophobic modifications and superhydrophobic wood are discussed in Part II