The Physical changes of timber.
Timber has properties to absorb moisture from the nature and the area (bending) also to release it’s moisture content in dry conditions (swelling). Therefore, the loss of stability in wood occurs. The reason is a physical phenomenon, the OH (hydroxyl) groups which are bounded to the cell wall, consistently gathers H2O (free water) into the wood.
When the air becomes dry, the water in the wood evaporates and thisconditions cause the wood bending and cracking.
Thermal modified timber is a final product, with a minimum 180°C heat treatment. This physical modification takes place in 4 stages.
First of all, free water (H2O) which is contained in the wood is removed by using the regular kiln drying process, this process nearly takes 3 days and removes the free waters from the cells. During the first stage the moisture content of the timber becomes 9%.
At the second stage, the OH groups are removed from the cell wall with a temprerature of 105°C-212°C. With a temperature reached in the chamber of 160°C and above the Thermal Modification is getting finalized. This process takes around 6 hours approximately.
The process at this stage gives the following results; decomposing of the hemicelluloses to fulfural and carboxylic acid, reducing of pH value, crystallization of the cellulose, caramelizing of lignin, removal of the resin and other extractive substances. The most obvious effect is that the Hydroxyl groups are removed from the cell walls.
At the last stage; Wood is passed through the cooling process and is harmonized to the ambient temperature (about 18 hours).