We investigated the drying kinetics of sawn wood of invasive wood species, black locust, American maple, and European horse chestnut. Specimens of 22 mm, 28 mm and 46 mm thick were dried in a laboratory convective kiln drier at 40 °C and 60 °C. Dynamic mechanical properties were analysed during drying by the frequency response in the longitudinal and flexural vibrations of 490 mm long specimens. We also determined gravimetrically in short periods the average moisture content (MC) and moisture content gradient, as well as the transverse shrinkage of wood. Drying was faster at higher temperatures, where the thickness of the specimens had a negative effect on the drying rate. The lowest longitudinal (EL) and bending modulus of elasticity (EB), were confirmed in the green state for all wood species and drying conditions. During drying, the reduction of MC of wood first caused an increase of the longitudinal modulus of elasticity. The changes appeared even at an average moisture content above the fibre saturation point (FSP), before shrinking of wood. The change was greater in thicker boards where a higher MC-gradient was present. The EB was always lower than the EL. The bending modulus of elasticity did not change significantly above FSP, but began to increase with the reduction of MC of wood in the hygroscopic range.
|
