Document Type : Research Paper
Authors
1 Associate Prof. Wood and Forest Products Science Research Division, Research Institute of Forests and Rangelands, Agricultural Research Education and Extension Organization (AREEO) P.O. Box 13185-116, Tehran, Iran
2 Assistant Prof., Research Institute of Forests and Rangelands, Agricultural Research Education and Extension Organization (AREEO), Tehran, Iran
3 Wood and forest products division, Research Institute of Forests and Rangelands, Agricultural Research Education and Extension Organization (AREEO), Tehran, Iran
Abstract
Background and objectives: The purpose of this study was to investigate the effect of heat treatment on bio-durability and some physical and mechanical properties of two wood species (Fraxinus Sp. and Picea Sp.). So, thermo-wood samples were prepared from Fraxinus Sp. and Picea Sp. based on thermo-D process. Heat-treated and untreated wood specimens were evaluated after exposing to white rot fungus for 16 weeks. The laccase activity and its effect on mass loss and wood density were also investigated. Moreover, some mechanical properties include impact strength and compression parallel to grain of both wood specimens was measured before and after exposing to fungus. The results showed that thermally modification improves the bio-durability of both wood species. The results also revealed reduction of mechanical properties due to heat treatment except compression parallel to grain.
Materials and methods: In current study, the wood specimens were prepared from Ash and spruce woods. First, the prepared specimens were heat treated based on thermo-D process. Then, to investigate the biological resistance as well as physical and mechanical properties measurements, several specimens were prepared from heat treated and untreated wood. White rot fungus (Trametes versicolor) was used to evaluate the biological resistance of wood samples. Malt extract agar was also used as a culture medium. After preparing the white rot fungus, they were initially transferred on the culture medium in kolle dishes and then were placed inside the germinator to cover the surface of culture medium. Afterwards, the heat treated and untreated wood samples were exposed to the fungus and finally kolle dishes containing wood and fungus samples were transferred to the germinator. After 16 weeks, all specimens were taken from the germinator out and evaluated their physical and mechanical properties as well as biological resistance. The experiments included measurement of laccase activity, mass loss, density, impact strength and compression parallel to grain. The applied standards for physical, mechanical, and biological resistance experiments included EN113, ASTM D143-09, and ASTM D256. Eventually, the obtained results were statistically analyzed based on ANOVA method by SPSS software.
Results: The results showed that the white rot fungus has been more efficiency on untreated specimens compared to thermo-wood in both wood species (Fraxinus Sp. and Picea Sp.). Therefor heat treatment improved the biological resistance, and also causes some changes in physical and mechanical properties of Ash and Spruce wood. The results also showed that thermal modification at high temperatures not only reduces the density of both woods, but also inhibited the reduction effect on density due to white rot fungus activity. Moreover, the results revealed that the compression parallel to grain of specimens was increased by heat treatment. On the other hand, reduction of this mechanical property due to the white rot fungus activity in thermo-wood samples was less than the controls. Evaluation of impact strength of specimens showed negative effect of heat treatment on this mechanical property. In addition, reduction of impact strength after exposure to the white rot fungus in heat treated specimens was higher than untreated.
Conclusion: Based on the results, thermal modification can generally causes improvement of biological resistance, reduction of some physical and mechanical properties as well as more stability of applied properties of Ash and Spruce wood which is exposed to the white rot fungus.
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