Thermo-vacuum modification of spruce (Picea abies Karst.) and fir (Abies alba Mill.) wood

Abstract

The study presents results of the characterization of Norway spruce (Picea abies Karst.) and fir (Abies alba Mill.) wood thermally modified by TERMOVUOTO® technology at temperatures in the range of 160 to 220°C in vacuum conditions. Sixteen thermo-vacuum treatment tests were carried out using a pilot laboratory unit on 30-mm-thick spruce and fir boards in various combinations of the process parameters, i.e. temperature ( T ), duration ( t), and pressure ( p ). The treated material was characterized to reveal the changes of the physical-mechanical properties including color and durability. The treated wood showed an improved performance with relation to the dimensional stability and durability. The measured mechanical properties did not show any significant decrease. Analytical models, based on the existing correlations between wood properties and process parameters, were assessed, thus allowing the control of the process.

Effect of Thermo-Vacuum Treatment on the Color and Chemistry of Larch Wood

“…Compared with the untreated samples, the lightness values (L*) decreased by 13.2%, 22.4%, 22.5%, 28.2%, and 43.8% with increasing temperature of heat treatment, respectively. Similar results have been reported by Allegretti et al (2012) for spruce and fir wood by thermo-vacuum treatment. Both a* and b* values gradually increased as the increasing treatment temperature.…”

“…Although the study of heat treatment was started by Stamm (1946), it has been systematically studied and industrialized only in the last dozen years. There are several different industrial heat treatment processes: "Thermowood" in Finland by the use of steam (Viitanen et al 1994), Plato wood in the Netherlands with a combination of steam and heated air (Tjeerdsma et al 1998), retification or bois perdure in France (Dirol and Guyonnet 1993), oil heat treatment in Germany (Rapp 2001), and the Termovuolo process by applying vacuum (Allegretti et al 2012;Ferrari et al 2013). Changes in color and surface chemistry caused by heat treatment have been intensely investigated (Bryne et al 2010;Matsuo et al 2011;Tuong and Li 2011).…”

“…In order to meet the needs of customers, heat treatment has been used as a way to make wood darken and redden (Bekhta and Niemz 2003;Esteves and Pereira et al 2009). Thermo-vacuum treatment has been reported as a method of darkening the wood color by some researchers (Allegretti et al 2012;Ferrari et al 2013). The color of alder birch wood is darkened by thermo-vacuum treatment and the discoloration mechanisms are analyzed using wet chemical analysis and FTIR (Yang et al 2015).…”

Dimensional stability and equilibrium moisture content of thermally modified hardwoods

“…One of the methods that is currently being used in the market is modification in a vacuum atmosphere. Thermo-vacuum treatment is classified as dry/wet, close/open thermal treatment, and its detailed specification can be found in selected publications (Esteves et al 2008;Allegretti et al 2012;Sandak et al 2015). The dry, open process uses wood with a 12% moisture content, which slowly increases the temperature until it reaches the temperature of 200 to 240 °C in a vacuum atmosphere, and the modification residues are removed from the tank during the process.…”

Comparison of EMC and durability of heat treated wood from high versus low water vapour pressure reactor systems

“…Several of the heating techniques and processes used in scientific studies were improved and developed into commercial thermal wood modification plants. The majority of these processes are known to operate at relatively low water vapour pressure conditions (0-0?1 MPa) on wood in its oven dried state, such as in the Thermowood processes in steam (Viitaniemi 1997), the OHT process in hot oil (Rapp and Sailer 2000), the NOW-Process in nitrogen (Dirol and Guyonnet 1993) and vacuum heating processes (Allegretti et al 2012). Others operate at a high water vapour pressure (0?5-0?8 MPa), sufficient to retain wood moisture at high temperature, such as in the FWD processes (Burmester 1973;Giebeler 1983), the PLATO process (Boonstra et al 1998) and the FirmoLin process (Willems 2009).…”