Abstract
Thermal modified wood has some advantages over natural wood, including decreased hygroscopicity, increased dimensional stability, and enhanced durability. In this study, European species of Scots pine (Pinus sylvestris), spruce (Picea orientalis), ash (Fraxinus spp.), and tropical species of tali (Erythrophleum ivorense), and iroko (Chlorophora excelsa) were thermally treated at 180 °C and 210 °C for 1,5 and 2 h, respectively. We evaluated the resistances of the untreated and thermally treated samples to decay induced by the white rot fungus, Trametes versicolor and two brown rot fungi, Coniophora puteana and Postia placenta. In addition, the samples were exposed to the termite Reticulitermes grassei and the longhorn beetle species Hylotrupes bajulus to evaluate their resistance to damage by the insects. During the heat treatment, the mass loss of the samples generally was between 9 and 14%. After the heat treatment, experiments were conducted to determine the effects of white and brown rot fungi on samples of Scots pine and tali, the effect of C. puteana on spruce, and the effects of C. puteana and P. placenta on ash and iroko. In all experiments, the mass loss due to damage from the various fungi was less than 1% for the samples that had been heat treated at 210 °C. The untreated and heat-treated tropical species exhibited higher durability with very low mass loss and 100% mortality of the insects when attacked by termites, whereas the other wood species had moderate attack. In addition, Hylotrupes bajulus exposure by two standart methods (EN 46 and 47) resulted in similar performances in most cases, although EN 47 treated samples at 210 °C showed improved durability for Scots pine (Pinus sylvestris) and spruce (Picea orientalis).
Highlights
Heat treatment is one of the alternative treatments for the protection of wood
mass losses (ML) was found to be similar for all wood species, about 9 to 11%, for heat treatment at 180 °C
ML for ash increased from 10,6% to 17,6% when the heat treatment temperature was 210 °C
Summary
Heat treatment is one of the alternative treatments for the protection of wood. The aim of heat treatment is to increase the dimensional stability of the wood and its biological resistance to destructive organisms. The heat treatment leads to significant changes in the chemical structure of the wood cell wall components such as cellulose, hemicellulose and lignin. The results are that the mechanical properties of the wood decrease, and dimensional stability and biological resistance of the wood increase (Tjeerdsma et al 1998, Jamsa and Vitainemi 2001, Yildiz 2002, Petrissans et al 2003, Gündüz et al 2008, Can et al 2010). The reason of increasing in the biological resistance of wood by heat treatment was expressed as follow; 1) the decrease in the polysaccharide content, 2) the decrease in the moisture content, and 3) the loss of OH- groups from the walls of the cells. The normal enzymatic attack does not occur as quickly as it does with untreated wood (Stamm 1956, Hill 2006)
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