Moisture sorption properties of hardwoods as affected by their extraneous substances, wood density, and interlocked grain

Abstract

Wood samples of nine tropical hardwoods from Peru and sugar maple from Quebec were selected for moisture sorption 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. Wood extractives, interlocked grain, equilibrium moisture content (EMC), and hygroscopic stability were highly variable within and among wood species. Sequential extraction with organic solvents was the most suitable method for evaluating the effect of extractives on sorption behavior in tropical hardwoods. Cyclohexane extractives had a little influence on EMC. The acetone fraction was the most significant variable affecting EMC and hygroscopic stability of tropical hardwoods, while the methanol fraction had a negligible effect on the sorption behavior of these species. In general, EMC decreased and hygroscopic stability increased as the concentration of acetone extractives increased. The influence of these acetone-soluble compounds on EMC decreased as relative humidity increased. However, the acetone fraction of copaiba ( Copaifera sp.), and probably caoba ( Swietenia sp.), appeared to play a hydrophilic role in controlling the EMC of wood. Finally, EMC also decreased as wood density and interlocked grain increased.