Summary In the present work, an attempt is made to study the Lewis acid-base properties of wood by contact angle analysis. Using contact angle data for extracted, non-extracted, fresh and aged pine wood veneer samples, the Lewis acid-base contribution to the work of adhesion ( W a AB ) and the Lewis acid-base components of the surface free energy of the wood samples were determined by basic wetting theory, and by the so-called van Oss-Chaudhury-Good (vOCG) model. Results show, on the one hand, that W a AB between water and the non-extracted wood decreases with increasing aging time. This indicates that extractives migrate from the interior of wood to its exterior surface during the aging, creating a hydrophobic wood surface. On the other hand, W a AB between the non-extracted wood and ethylene glycol tends to increase with longer aging times. No such trends are observed for extracted samples. If water is considered to be predominantly Lewis acidic, and ethylene glycol predominantly Lewis basic, the changes in W a AB with longer aging times, indicate that the acidity and the basicity of non-extracted wood in these cases increases and decreases, respectively. This is presumably due to the presence of the extractives, and to reorientation of functional groups and oxidation at the wood/extractives-air interface. The acid-base characterization by the vOCG model also indicates that the acidity and the basicity of the non-extracted wood increases and decreases, respectively, with increasing aging time. However, there seems to be a similar trend even for extracted wood, presumably due to reorientation of functional groups at the wood-air interface. In the vOCG model, considerably higher base/acid ratios are obtained when using probe liquid parameters according to van Oss compared to those obtained by using liquid parameters according to Della Volpe and Siboni.
There is an increasing demand for engineered wood products in modern structures. Birch plywood is promising in structural applications, due to the combined advantages of its superior mechanical properties and the cross lamination configuration. However, the off-axis mechanical properties of birch plywood have not been thoroughly investigated. The aim of this paper is to establish a comprehensive experimental dataset that could serve as the input in the analytical or numerical models to design birch plywood under various load conditions. Specifically, tensile, compressive and shear tests were conducted under five different angles to the face grain, i.e., from 0° (parallel) to 90° (perpendicular) to the face grain, with an interval of 22.5°. The stress-strain relationships, failure modes, strength and elastic properties of birch plywood are highly dependent on the load-to-face-grain angle. The strength and the elastic properties are also predicted by various analytical and empirical models. Parametric analyses are performed to study the influence of the interaction coefficient [[EQUATION]] in Tsai-Wu failure criterion and the Poisson’s ratio [[EQUATION]] in the transformation model on the predicted strength and modulus respectively. Lastly, the possibilities of predicting the on-axis shear modulus based on the off-axis uniaxial tests are discussed in this paper.
Abstract The effect of extractives removal on liquid sorption, swelling and surface energy properties of unmodified wood (UW) and thermally modified Scots pine heartwood (hW) (TMW) was studied. The extraction was performed by a Soxtec procedure with a series of solvents and the results were observed by the multicycle Wilhelmy plate method, inverse gas chromatography (IGC) and Fourier transform infrared (FTIR) spectroscopy. A significantly lower rate of water uptake was found for the extracted UW, compared with the unextracted one. This is due to a contamination effect in the latter case from water-soluble extractives increasing the capillary flow into the wood voids, proven by the decreased water surface tension. The swelling in water increased after extraction 1.7 and 3 times in the cases of UW and TMW, respectively. The dispersive part of the surface energy was lower for the extracted TMW compared to the other sample groups, indicating an almost complete removal of the extractives. The FTIR spectra of the extracts showed the presence of phenolic compounds but also resin acids and aliphatic compounds.
The objective of this work was to study surface energetics of thermally modified wood particles exposed to dry-humid cycling. This information can give insight in the adhesion properties between the modified wood and composite matrices, adhesives or coatings. The surface energy characterization as well as the dry-humid cycling was performed using inverse gas chromatography (IGC). Duplicates of thermally modified and unmodified spruce particles with size 0-0.125 mm were investigated and conditioned in dry-humid cycles at 0-75 % RH and 0‑25 % RH. The BET specific surface area as well as the dispersive surface energy heterogeneity (or distribution) at different surface coverage was determined. The results showed similar trends for the different cycles in the dry and humid states, respectively. The difference in dispersive surface energy distribution between the dry and humid state was more pronounced at the lower surface coverage.
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