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Properties of thermally modified woods by a Brazilian process
* 1 , 2 , 3 , 3 , 3
1  Department of Forest Engineering, Agrarian and Environmental Sciences Sector, Midwestern State University, Professora Maria Roza Zanon de Almeida Street, Irati 84505-677, PR, Brazil
2  Federal University of Mato Grosso
3  Federal University of Paraná
Academic Editor: Miha Humar


Thermal modification processes are strategies to improve properties of wood with environmental liability when no chemicals is used. The VAP HolzSysteme®, developed in Brazil, promotes the thermal modification of wood in an atmosphere saturated with water vapor ensuring low oxygen content. In this process, the heat is directly transferred from the water vapor to the wood, providing conditions for thermal changes at low temperatures. To evaluate this process, samples of Pinus taeda and Eucalyptus grandis woods, used for decking, were treated in an industrial autoclave at a final temperature of 160ºC. The treated woods were evaluated through the characterization of the anatomical, physical properties, chemicalm mechanical properties, and thermal properties of the woods. The anatomical characteristics were maintained, allowing the identification of the wood after the term modification, however, reduction of the cell wall and cracks in the ray cells were observed in both species. The heat treatment promoted lower equilibrium moisture, reducing the hygroscopicity and improving the dimensional stability, however, the effect on the basic density of the wood was different, in the P. taeda wood there was a reduction, while in the wood of E. grandis there was an increase. Considering the chemical composition of the wood, the total lignin content and total extractives increased, while the hemicellulose content decreased in both woods. The heat-treated woods showed a reduction in static flexural strength and radial hardness, but the longitudinal hardness of P. taeda increased while its tangential hardness reduced, whereas the wood of E. grandis showed the opposite behavior. With heat treatment, the resistance to thermal degradation of wood increases, with a significant decrease in the curve in the range associated with the degradation of hemicelluloses, from 200 to 260°C. The heat treatment improved the wood stability, on the other hand it can impair mechanical properties.

Keywords: Pinus taeda; Eucalyptus grandis; wood modification