Westwood technology and
Thermo-treatment of wood worldwide
Six Main Thermo-Modification Technologies in the World
All the thermo-treatment processes have in common the treatment of sawn wood at elevated temperatures in the range between 160 °C and 260 °C (320 – 450 °F) in an oxygen-free environment. The main differences between the processes are to be seen in the process conditions (process steps, steam or nitrogen, wet or dry process, use of oils, steering schedules, etc.) and published in several patents. As the processes are different, the cost and result of thermo-treatment are also different. Westwood is the latest technology of the new generation implementing the 3-D heat control, which is especially important to treat hardwoods.
Here are six main thermo-treatment processes in the world:
Plato-Process (The Netherlands)
Retification process (France)
Bois perdure (France)
OHT oil-heat treatment (Germany)
ThermoWood process (Finland)
Plato-Process (PLATO BV - The Netherlands)
The PLATO process uses different steps of treatment and combines a hydrothermolysis step with a dry curing step. The impact of the hydrothermolysis in the PLATO-treatment results in the occurrence of different chemical transformations. One goal of this 2-step process is the use of the presence of abundant moisture in the woody cell walls during the hydrothermolysis. This provokes an increased reactivity of the cell wall components under relatively low temperatures. In order to reach a selective degree of depolymerisation of the hemicellulose during the hydrothermolysis, relative mild conditions can be applied to limit unwanted side reactions. The process time is depending on the wood species used, the thickness, shape of wood etc., and uses a thermolysis step (4-5 hours ) followed by an intermediate drying step (3-5 days ) and a final curing step (14-16 hours). In some cases, a conditioning step (2-3 days) is needed. The heating medium can be steam or heated air.
Retification process (NOW New Option Wood - France)
The process starts with relatively dry wood (approx. 12 %) and heats up the material up to 200°C - 240°C in a nitrogen atmosphere (below 2 % oxygen). There are different production sites in France.
Bois perdure (BCI-MBS - France)
The process starts with fresh wood, subsequently a fast drying process and heating up to 200°C - 240°C under a steam atmosphere. The first step of the process consists of artificial drying in the oven. Then the wood is heated under a steam atmosphere (steam generated from the water of the wood).
OHT Process (oil-heat treatment) (Menz Holz - Germany)
The process is performed in a closed process vessel. After loading the process vessel with wood, the hot oil is pumped from the stock vessel into the process vessel where the hot oil is kept at high temperatures circulating around the wood. Before unloading the process vessel the hot oil is pumped back into the stock vessel.
For different degrees of upgrading, different temperatures are used. To obtain maximum durability and a minimum oil consumption the process is operated at 220°C. However, to obtain maximum durability at acceptable strength reductions, temperatures between 180°C and 200°C are used. It proved to be necessary to keep the desired process temperature (for example 220°C) for 2-4 hours in the middle of the wooden pieces to be treated. Additional time for heating up and cooling down is necessary, depending on the dimension of the wood. The heating medium is crude vegetable oil. The oil serves for a fast and equal transfer of heat to the wood, providing the same heat conditions all over the vessel and furthermore limiting the oxygen in the vessel. Linseed oil proved to be a good medium though the smell that develops during the heat treatment may be a drawback. The smoke point and the tendency to polymerization are also important for the drying of the oil in the wood and for the stability of the respective oil batch. The ability of the oil to withstand heating to a minimum temperature of 230°C is a prerequisite. The consistency and color of the oil change during heat treatment. The oil becomes thicker because volatile components evaporate, the products arising from the decomposition of the wood accumulate in the oil and change its composition.
This leads to an improved setting of the oils.
Thermo Wood process (Stora, Finnforest, Stellac, Jartek - Finland)
Since the 1990th comprehensive research on heat treatment had led to commercialized processes in Finland. An industrial-scale wood heat treatment process, under the trade name of ThermoWood, has been developed at the Finnish Research Center VTT together with the Finnish industry. Today the process is licensed to the members of the Finnish ThermoWood Association. The ThermoWood process can be divided into three main phases: Phase 1 - The kiln temperature is raised at a rapid speed using heat and steam to a level of around 100ºC. Phase 2 - Once the high temperature kiln drying has taken place, the temperature inside the kiln is increased to a level between 185ºC and 230ºC. Phase 3 - The final stage is to lower the temperature by using water spray systems. Then once the temperature has reached 80-90ºC, re-moisturizing and conditioning take place to bring the wood moisture content to a useable level of over 4%.
Westwood process (Westwood - USA)
Westwood developed its process in 2003 in Europe and then was the first company in the US to start its thermo-treatment plant in 2007. Westwood technology in opposite to the other European processes has been developed to treat hardwoods as the most complicated (hardwoods while heated start thermo-chemical reactions to heat themselves, which need to be carefully controlled). Also, Westwood created a way to remain thermo-treated lumber absolutely flat after the process, which significantly reduces the waste factor.
Westwood technology is completely atomized. We use a completely new way to control reactions inside of wood during our thermo-treatment process. The computer analyzes and manages over 20 parameters every 5 seconds to control a 3-dimensional heatwave inside of our chambers. As a result, the Westwood process is optimizing by itself, being non-dependable on the different chemical compositions of lumber (even within one species), and its initial moisture content, the way of stacking lumber, thickness, which allows making any hardwood, softwood, or exotic specie in predictable color with no waste factors. Westwood is the only technology that is able to control the temperature of thermo-chemical reactions inside of the chambers in a 3-D chamber's space. Our process is also based on the latest European research, which showed that achieving a color during the thermo-treatment process is not necessary making wood so durable as needed. The right process is the combination of time and temperature to occur all natural reactions inside of wood. Westwood uses the process which gives enough time for all necessary reactions inside of wood for essential durability and in the same time saves enough strength of the treated wood.