Effect of species on the hydroxyl accessibility of wood: results obtained by deuterium exchange

In this research, the hydroxyl (OH) accessibility in the beech, spruce and pine wood was measured by impregnation of the wood specimens with heavy­ water (D₂O) (deuterium exchange). After impregnation of wood specimens with heavy water and drying in a vacuum oven, the relative hydroxyl accessibility (% accessible hydroxyl groups) was determined with ATR-FTIR spectrometry by calculation of the integrated peaks for the OH and OD stretching vibrations at wavenumbers of 3500 and 2500 cm^-1, respectively. The absolute accessibility (mmol hydroxyls/g wood) was determined using an advanced dynamic vapour sorption equipment, (DVS-ET1) by measuring the increased dry mass of the sample due to deuteration after conditioning with heavy water at 95% RH. The results showed that the relative accessibility was not affected by the wood species and its extractive content and more than half of the hydroxyl groups could be accessible. The absolute accessibility in spruce was higher than that in beech. For spruce wood, the earlywood had less accessible hydroxyl groups than the latewood. The poor linear correlation between the hydroxyl accessibility and equilibrium moisture content (EMC) confirmed that the moisture absorption by wood was not controlled exclusively by the hydroxyl accessibility.