Change in wood material properties
When the drying process begins, the temperature increases, and then the internal
vapour pressure and volume change arise. If the mc exceeds the fibre saturation
point, the water in the cells will be forced out from the wood because of the
increasing interior water and vapour pressure during the heating process.
Furthermore, as the temperature rises, the water in the cells, bounded or free,
starts to vaporize, and the mixture of water and gas will be forced out from the
wood. Hence, when the mc decreases below the fibre saturation point, the
remaining water consists of bound water in the wood cell walls and will be forced
out of the wood in the form of vapour. If the internal pressure exceeds the strength
value in the wood tissue, it causes internal checks in the wood structure, which in
turn affect the wood properties. Another phenomenon that might appear if the
process is uncontrolled is thermal runway