Thermal modification of wood is a high technology process. The thermally modified wood is treated by the heat that changes its chemical structure and also its mechanical and chemical properties. The method has been known since the 1930s when a group of German researchers started the analyses that were continued in the 1940s in the USA. After that other scientists deepened the investigation of different aspects up to the 1990s when the method was improved and used for industrial purposes.
Process of manufacture
The wood is thermally modified by means of high-temperature drying cycle between 165 °С and 240 °С under controlled-atmosphere without oxygen. The conditions of wood treatment beginning from temperature to process time can vary greatly, and as a result, lead to the products with different properties.
The wood is modified under high temperature stress that leads to the damages of its component, which is the most sensitive to the water (hemicellulose): the less place is available for binding of water molecules, the less water can bind to the wood, which exchanges with the ambient through such phenomena as absorption and desorption, and as a result, the less shrinkage and swelling are possible. In other words, the sizes are stable that makes the wood less sensitive to the deformation under the different environmental conditions.
The direct impact reflects on the space density and has a tendency to decrease ranging from 5% to 10% and as a result, the wood becomes easier and the stability of size increases. The color, which is getting dark, changes, and the smell, which is like the smell of roasted coffee, as a rule, disappears in time. The small and relative changes of the reaction to the fire are noticed: The beginning of burning is slow because of the wood slightly contains some volatile organic compounds.
There is also a positive influence on the durability that increases significantly during the heat treatment. A high-temperature treatment leads to the sterilization of material and degradation of substances such as starches that can allow the xylophagy inroads. The lower wood hygroscopicity reduces the water content and as a result the possibility of mold attacks that can be possible only if the material moisture content is more than 20%.
It can be exposed to the simple physical change.