Document Type : Research Article
Authors
1
Department of Forestry and Cellulose Industry Engineering, Faculty of Natural Resources, Behbahan Khatam Alanbia University of Technology, Behbahan, Iran
2
Department of Forestry and Cellulose Industry Engineering, Faculty of Natural Resources, Behbahan Khatam Alanbia University of Technology, Behbahan, IranBehbahan, Iran
Abstract
Introduction
The disadvantages such as vulnerability to destructive factors and instability in dimensions create limitations in wood consumption. Various methods for improving wood properties using heat treatments have been utilized, with the basis being the chemical alteration of wood through heat. Treatment with hot oil can enhance undesirable wood properties by ensuring uniform heat penetration throughout the wood structure, limiting oxygen access to reduce fire risk. Environmentally friendly heat treatments use natural and renewable oils without toxic substances. This study aimed to determine changes in biological resistance, physical, and mechanical properties of beech (Fagus orientalis) wood samples subjected to hot oil treatment using a warm-cool method, comparing results with control samples.
Materials and Methods
Beech wood specimens were prepared from defect-free air-dried logs, cut to standard dimensions for physical, mechanical, and biological tests. Wood samples were treated with sunflower oil, rapeseed oil, and a mixture of both using a warm-cool method. Tests for water absorption according to ASTM D4446-05 standard, three-point bending test and modulus of elasticity per ASTM D143-94 standard, and impact resistance per ASTM D256-04 standard were conducted. Both selective and non-selective termite feeding tests were performed under controlled laboratory conditions following AWPA-E1:06 2008 standard.
Results and Discussion
Control samples showed the highest weight loss in both tests compared to treated samples, significantly attracting termites. No significant differences in termite feeding percentage were observed among samples treated with different oils. Hot oil treatment significantly increased beech wood density compared to control samples. Samples treated with sunflower oil had significantly higher density than those treated with rapeseed or mixed oils. The increase in density may be attributed to the replacement of air within the cells with oil. The key factor contributing to this phenomenon is the heating of the air inside the wood cells using hot oil, which initially saturates the wood and subsequently creates a vacuum due to cold treatment. The vacuum created and the rapid contraction of air during cold immersion enhance the suction of oil into the wood cells. A significant difference in volumetric swelling was observed between the control samples and those treated with the mixture of the two oils after two hours of immersion. After 24 hours of immersion in water, the volumetric swelling of the control samples was significantly greater compared to all treated samples. Furthermore, impact resistance decreased following the heat treatment; however, no significant differences in impact resistance reduction were observed among the samples treated with different oils in this experiment. Additionally, the heat treatment did not have a significant effect on flexural strength and modulus of elasticity.
Conclusion
Sunflower oil, rapeseed oil, and their combination significantly influenced beech wood characteristics by reducing termite feeding across all treated woods noticeably. Hot oil treatment altered wood chemistry by degrading hemicellulose and increasing cellulose crystallinity while oils acted as barriers against moisture absorption, enhancing biological resistance in wood. Oil treatment increased beech wood density significantly depending on the density and viscosity of the oils used during treatment. The absorbed oils reduced empty spaces within the wood structure affecting weight and consequently density positively. Blocking moisture reduces the amount of water entering the wood structure, improving dimensional stability. Warm oil treatment significantly affects impact resistance but shows minimal changes in properties like modulus of elasticity and flexural strength compared to control samples. Research results indicate a decrease in mechanical properties of wooden samples at higher temperatures during laboratory testing, intensifying with treatment temperature increase. High temperatures affect cell wall components, potentially damaging materials like hemicelluloses, leading to reduced mechanical strength, especially impact resistance. Lower temperatures have less effect on strength reduction. With a maximum treatment temperature of 130 degrees Celsius considered in this study, which is not high compared to other heat treatments, less significant decreases in mechanical strength were observed, showing no significant difference between control and treated samples. Based on the conducted studies, the treatment of wood with heat-treated oil from rapeseed and sunflower, as well as a mixture of both oils, significantly increases the resistance of beech wood against termite attacks. On the other hand, the results indicate that the heat treatment can control and improve certain physical properties of wood, such as the degree of swelling, while it leads to a reduction in some mechanical resistances of the wood, including impact resistance.
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