Evaluation of heat-treated wood swelling by differential scanning calorimetry in relation to chemical composition

Retification is a heat treatment that decreases the swelling of wood and increases its resistance to fungal attack. In this study, differential scanning calorimetry (DSC) was applied in order to determine the fibre saturation point (FSP) of natural and retified wood. FSP values were used to determine the total swelling of natural and heat-treated wood. The DSC method was compared to the volumetric shrinkage approach. The influence of heat treatment temperature and duration on the swelling of wood was investigated. Relationships between chemical changes and the reduction of swelling were analysed thoroughly. The equivalence of the DSC method and the volumetric shrinkage method is shown. FSP in association with anhydrous density is a good indicator for the evaluation of the overall swelling of heat-treated wood. Reduction of wood swelling with increasing temperature and duration of thermal treatment is often attributed to hemicellulose destruction. This study shows that the reduction of beech wood swelling cannot only be attributed to the disappearance of adsorption sites that goes with hemicellulose destruction. It is suggested that other phenomena such as structural modifications and chemical changes of lignin also play an important role.