Swelling Properties of Hardwoods as Affected by their Extraneous Substances, Wood Density, and Interlocked Grain

Samples of nine tropical hardwoods from Peru and sugar maple wood from Quebec were selected to perform moisture sorption tests associated with swelling tests using a multiple step procedure at 25°C. Cold-water and hot-water extractives, sequential cyclohexane, acetone, and methanol extracts, ash content, wood density, and interlocked grain also were evaluated on matched samples. Swelling properties were highly variable within and among wood species. The wood density corrected for the extraneous substances was the most significant variable positively affecting the transverse and volumetric swelling of tropical hardwoods. Sequential extraction with organic solvents was the most suitable method for evaluating the effect of extractives on swelling properties of tropical hardwoods. The extractives soluble in cyclohexane were the more accessible, but they virtually did not contribute to wood swelling. The substances dissolved in acetone appeared to be located within cell walls. After wood density, these compounds were the most significant variable negatively affecting the radial swelling. The substances dissolved in methanol were located within cell walls. After wood density, this extracted fraction was the most significant variable negatively affecting the tangential swelling. The acetone and methanol extracted fractions positively affected the dimensional stability of tropical hardwoods. Finally, the effect of the interlocked grain on swelling was only indirect given that this grain pattern reduces the equilibrium moisture content