Effect of tall oil pretreatment on physical and mechanical properties of heat treated fir and beech

Abstract

Thermal treatment is an environmentally friendly process and effective to improve biological resistance as well as enhance dimensional stability of wood material. However, the mechanical properties of the wood are decreased by heat treatment, since the temperature is applied between 180 °C and 260 °C which affect the wood cell wall components. Tall oil is a major byproduct from pulp and paper industry running according to Kraft process. The water repellent and decay resistance properties of tall oil make it a valuable product in the field of wood protection. In this study, fir and beech samples treated with tall oil at concentration of 10 % alone, also heat treated at 190 and 212 °C respectively. In addition, the combination of both tall oil and heat treatment was applied on fir and beech samples. Water uptake and tangential swelling of untreated and treated samples was measured during two weeks. From the mechanical properties, bending strength and modulus of elasticity were determined on the samples of untreated, tall oil treated, heat treated and combination of both treatments. The lowest water uptake was obtained with the fir samples treated with tall oil and heat treated in the temperature of 212 °C. Minimum tangential swelling was found to be 3.36 % in the samples of fir treated with 10 % tall oil and heat treated at 212 °C, while the control samples exhibited the maximum as 6.59 %. In the beech samples, the best result in terms of water uptake was achieved by heat treatment at 212 °C when compared to other treatments. Tall oil treated samples improved the tangential swelling in beech samples when they were exposed to heating at 190 °C as a second treatment. ASE was improved by the combination of tall oil and heat treatment at 190 °C and 212 °C in fir and beech samples. Tall oil increased the bending strength (MOR) to the fir and beech woods when combined with heat treatment at 212 °C in comparison to heat treatment alone.