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Do extractive compounds of thermally modified woods play an important role in the decay and termites resistances of these modified materials? A preliminary study

Candelier K., Thévenon M.F., Collet R., Gerardin P., Dumarçay S.. 2017. In : Tondi Gianluca (ed.), Posavcevic Marko (ed.), Kutnar Andreja (ed.), Wimmer Rupert (ed.). Book of abstracts of the 3rd COST Action FP 1407 - Conference: ¿Wood modification research and applications¿. Kuchl : Salzburg University of Applied Sciences, p. 122-123. COST Action FP 1407 : Conference: ¿Wood modification research and applications¿. 3, 2017-09-14/2017-09-15, Kuchl (Autriche).

Thermal modification processes have been developed to increase the biological durability and dimensional stability of wood. However, the reasons of the decay resistance improvement of heat treated wood are still not very well known. This durability improvement of heat treated wood can be explain by several reasons, as the high hydrophobic behaviour (Weiland and Guyonnet, 2003), the polymer chemical composition modifications (Vallet et al., 2001), the hemicelluloses degradation (Hakkou et al., 2006) and the generation of new extractive substances (Lekounougou et al., 2009). The aim of this paper was to evaluate the anti-fungal and anti-termite activities of extractives compounds from heat treated ash woods according the modification process intensity. All of the tests were carried out in the laboratory with two different complementary research materials. The main research material consisted of ash (Fraxinus excelsior L.) wood thermally modified during 2 hours, at temperatures of 170, 200, 215 and 228 °C, under ThermoWood® Process. The reference material was untreated ash wood for decay and termite resistance screening tests. Each treated and untreated wood sample were extracted with water or acetone. The extractives contents were determined for each treated and control wood sample. One part of the obtained extracts was blended with malt agar block test [1200 µL? C= 2.5%m/m in acetone, in 10 mL of Malt-Agar medium] in order to investigate their anti-fungal properties. To determine the inhibition effectiveness of extractives, two different fungi were selected: Coriolus versicolor (white rot) and Poria placenta (brown rot). Fungal activity was carefully observed for the duration of seven days. The other part of extractives was impregnated within Whatman papers [70 microL, C= 2.5 % m/m in acetone, on a Cellulose paper of 2.5 cm-diameter] and expose to termite attacks. Finally, extractives were analysed by GC-MS and their number of chemical components and their respective quantity are related to their anti-termite and antifungal activity levels. First results show that anti-fungal activity of heat treated ash wood extracts vary according to heat treatment intensity and the solvent used during the extraction process ( Figure 1). It appears clearly that untreated and treated ash wood extracts are more efficient against brown rot than white rot growing.

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