MOISTURE ADSORPTION ISOTHERMS OF ACACIA MANGIUM AND ENDOSPERMUM MALACCENSE USING DYNAMIC VAPOUR SORPTION

Two Malaysian hardwoods, namely, acacia (Acacia mangium) and sesenduk (Endospermum malaccense) were studied to determine their moisture sorption behaviour using a dynamic vapour sorption (DVS) apparatus. For comparison, two temperate softwoods, Sitka spruce (Picea sitchensis) and radiata pine (Pinus radiata), and one commercially modified wood, Accoya (radiata pine that is chemically modified with acetic anhydride), were tested with the same DVS. The sigmoid isotherm plot for each of the wood tested showed differences in the adsorption and desorption plots. At 90% relative humidity (RH), acacia and sesenduk had lower hygroscopicity (16.2 and 17.9% respectively) compared with radiata pine (18%) and Sitka spruce (20.1%). The modified Accoya had the lowest hygroscopicity (7.5%) due to bulking of the cell wall with acetyl. Hysteresis of Accoya also exhibited the lowest value between the adsorption and desorption isotherms. Data were analysed using the Hailwood–Horrobin (HH) model for isotherm fitting and determination of monolayer and polylayer moisture content. The OH group concentration in the HH monolayer did not correspond to the total accessible OH group derived by calculation based on the chemical composition of each of the wood species.