Contribution of Thermal Degradation Products to the Hydroxyl Accessiblity and Hygroscopicity of Thermally Modified Wood

Abstract

The moisture exclusion efficiency of thermally modified wood is usually attributed to both reversible and irreversible effects. The purpose of this study was to find whether hydroxyl accessibility contributes to the reversible effects of thermal modification on the hygroscopicity of wood. First, untreated and modified Norway spruce wood specimens were successively extracted with acetone/ethanol (2:1 v/v), hot water, and N, Ndimethylformamide (DMF). Then, the hygroscopic characteristics (i.e., fiber saturation point (FSP), equilibrium moisture content (EMC), moisture sorption isotherms), and hydroxyl accessibility were measured. The hydroxyl accessibility (mmol hydroxyls/g wood) was accurately determined by the deuterium exchange technique. We found that the cell wall bulking caused by the thermal degradation products has no significant impact on the hydroxyl accessibility, but it reduces the hygroscopic nature.