Can you imagine eco-friendly wood that can be applied in an extremely harsh environment, like a bathroom, a swimming pool deck, house siding or roofing, and last perfectly without any treatment with chemicals? Even today the idea of having an environmentally friendly material with such characteristics seems unreal. But it does exist!
What is thermally modified wood?
So, this material is named thermally modified wood. This is wood that was thermally treated by the temperature of 185-230 degrees Celsius without adding any chemical substances. In the course of time thermally modified wood doesn’t change its geometry: it doesn’t contract, expand, cast or crack. It doesn’t rot even in water and doesn’t require any chemical treatment. It’s absolutely firm to influence of micro-organisms and corrosion. It has denser structure and holds the heat in winter and coolness in summer 30% better than other sawn timber types. To crown it all, even the cheapest species of wood obtain saturated noble dark tints of fine wood and become full-thickness-colorized after thermal treatment.
Thereby, thermally modified wood combines eco-friendliness of natural wood and valuable physical and mechanical properties.
How it works?
Thorough research of both theoretical and practical aspects of heat treatment of wood was held in the 1990s by several European countries: France, Finland and the Netherlands. Eventually, VTT Technical Research Centre of Finland devised the following technology.
The first and the longest phase is desiccation. This way the moisture content in wood is lowered to almost 0%. The processing time depends on the initial moisture content, type of of wood and thickness of timber.
The next stage is thermal modification per se. This procedure is held in a closed chamber by the temperature of 185-215 degrees Celsius in the absence of oxygen. The role of the protective environment is played by steam: it both prevents wood from firing up and gets involved into chemical modification processes that wood goes through.
After heat treatment, wood is hardened off within 5-15 hours. It is being cooled off until the moisture content is decreased to 5-7%. The latter condition is carefully monitored, since too dry wood is not so easily worked up.
The change that you can see with the naked eye is the change of wood grain. It becomes more visible and gets a dark, saturated noble hue, uniform over the entire cross section. Even the cheapest types of wood look rich and exotic after heat treatment. Hereafter any type of processing is allowed, including brushing, varnishing and painting.
As a consequence of thermal destruction of hemicelluloses in wood, it is unlikely to expand or contract; the equilibrium moisture and acidity level decrease. At the same time the material remains absolutely eco-friendly.
Resistance of thermally modified wood to expansion or contraction due to temperature and moisture changes is 10-15 times as high as that of non-treated wood. Besides, such wood becomes corrosion resistant.
The moisture content is 4-6 times less than after conventional industrial drying, and the level of moisture absorption is decreased by 80%; thermally modified wood won’t rot even in water.
Resistance to biological effects is increased 25 times, without any disinfectant treatment.