Thermotreated wood is manufactured under controlled heating conditions at temperatures of 170…230 degrees C. The degree of heat depends on what type of wood is being processed and what type of characteristics are desired. The process involves no chemicals or addatives. Since the only outside agent used is moisture, we can proudly claim this to be natural product. During the thermotreatment process, the cellular structure changes. The hemicellulose starts to break down and pitch in coniferous woods evaporate.
During the thermo treatment, the following changes occur:
- Colour changes from light to dark brown
- Deformation due to moisture variations decreases by 50-90%
- Equilibrium moisture content lowers
- Thermal conductivity decreases by 0-30%
- Overall heat-transfer coefficient k improves
- Bending strength decreases by 0-30%
- Elasticity decreases, but rigidity increases
- Wear resistance improves
- Wood becomes lighter in weight
- Biological durability improves
- Pitch evaporates
- Dead knots fall out
- Cellular structure changes- wood „ages“ structurally
As it appears from above, thermotreatment offers a quite good opportunity e.g. for the carpentry industry to produce environment-friendly wood products of a new kind of structure.