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A wood surface, which is exposed to a high temperature condition, can experience inactivation. Surface inactivation reflects physical and chemical modifications of the wood surface. Consequently, these changes result in reduced ability of an adhesive to properly wet, flow, penetrate, and cure. Thus, an inactivated wood surface does not bond well with adhesives.The changes in surface chemistry, wettability, and adhesion of inactivated wood surfaces, including heartwood of yellow-poplar (Liriodendron tulipifera) and southern pine (Pinus taeda), were studied. Wood samples were dried from the green moisture content condition in a convection oven at five different temperature levels ranging from 50 to 200°C. The comparative characterization of the surface was done by X-ray photoelectron spectroscopy (XPS), sessile drop wettability, and fracture testing of adhesive bonds. Additionally, several chemical treatments were utilized to improve wettability and adhesion of inactivated wood surfaces.The comparative analysis helped elucidate clear relationships between surface chemistry, wettability, and bond performance in regard to surface inactivation. XPS results showed that wood drying caused modification in wood surface chemistry. The oxygen to carbon ratio (O/C) decreased and the C1/C2 ratio increased with drying temperature. The C1 component is related to carbon-carbon or carbon-hydrogen bonds, and the C2 component represents single carbonoxygen bond. A low O/C ratio and a high C1/C2 ratio reflected a high concentration of non-polar wood components (extractives/VOCs) on the wood surface, which modified the wood surface from hydrophilic to more hydrophobic. A hydrophobic wood surface repelled water and wettability of this surface was low (i.e., a high contact angle). Wettability was directly related to the O/C ratio and inversely related to the C1/C2 ratio.iii Contact angle decreased with time and increased with the temperature of exposure. A dependence of wood species was evident. Southern pine had a lower wettability than yellowpoplar, which was due to a greater concentration of non-polar hydrocarbon-type extractives and heat-generated volatiles on the surface. Solvent extraction prior to drying did not improved wettability, whereas, extraction after drying improved wettability. A contribution of extractives migration and pyrolysis products deposition played a significant role in the heat-induced inactivation process of southern pine.The maximum strain energy release rate (G max ) obtained by fracture testing showed that surface inactivation was insignificant for yellow-poplar when exposed to drying temperatures < 187°C. The southern pine was most susceptible to inactivation particularly when bonded with phenol-formaldehyde (PF) adhesive. A typical surface inactivation for southern pine occurred at drying temperatures > 156°C.Chemical treatments improved the wettability of inactivated wood surfaces, but an improvement in adhesion was not evident for specimens bonded with polyvinyl-acetate (PVA) adhesive. Of the chemica...

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A review of water interaction in cellulosic-systems, particularly wood, is presented.Discussed are the different states of water in these systems according to Nuclear Magnetic Resonance results, the BET, Dent, and Hailwood and Horrobin sorption isotherm models. The discussion includes details of water structure, and, conformational analysis of cellulose crystals and amorphous cellulose. The water cluster theory is used to more adequately explain the sigrnoid curve of the wood isotherm.

A novel wood-based composite has been developed for use in structural applications. The process was designed to utilize rapidly-grown, low density, wood species. Plantation grown radiata pine is particularly well suited to this process. This is a laminated composite, where the lamina may be comprised of various materials, some of which have been treated with the viscoelastic thermal compression (VTC) process. The VTC process increases the density of wood, without causing fractures in the cell wall, thus increasing strength and stiffness of the wood material. The process may be applied to veneer, sawn wood, or strand composites. The VTC lamina is then bonded to other lamina to produce the final product. The strength and stiffness of this VTC composite exceeds any wood-based composite that is currently on the market. For example, modulus of elasticity in bending of over 20 GPa is easily obtainable.

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