Effect of tree age, thickness and depth of black poplar timbers on color change and wettability of wood after accelerated weathering

 In this study, black poplar (Populus nigra) cut from Zanjan province was used in two age groups of 18 and 38- year-old. Timbers with thicknesses of 4, 5 and 6 cm were prepared from each age group. The prepared timbers were modified during the heat treatment process (Thermowood) at a constant temperature of 212 °C. Experimental samples were obtained from the surface and middle depth of heat-treated timbers. Heat-treated and control wood samples were subjected to accelerated weathering for 150 hours. Color lightness (L*), color difference (ΔΕ*) and water droplet contact angle were measured for heat-treated and control samples before and after weathering. In order to investigation of the wettability content, the method of measuring the contact angle of the water drop - static according to the ASTM D 5946 standard was used. In general, before weathering, the brightness of the heat-treated samples decreased compared to the control sample, but after weathering, the color lightness of the control samples decreased and the color lightness of the heat-treated samples increased. Also, the content of color difference of samples after weathering compared to before weathering showed a significant decrease statistically. Heat treatment increased the contact angle of water droplets of the samples 60.31% and the contact angle of water droplets of the heat-treated and control samples increased significantly after weathering compared to before weathering.