Surface checking of wood is increased by photodegradation caused by ultraviolet and visible light
The aim of this research was to test the hypothesis that exposure to solar radiation increases the checking of wood exposed to the weather, and to examine the causes and spectral dependency of such an effect. Lodgepole pine decking samples were exposed outdoors under filters, which blocked selected regions of the solar spectrum while allowing other weathering factors to act on samples. Surface checking in samples was quantified after 12, 24 and 36 weeks of exposure, and the chemical and micro-structural changes occurring at weathered wood surfaces were examined. Check numbers and dimensions were greater in samples exposed under a filter to the full solar spectrum than in samples exposed under filters that blocked the transmission of UV, visible or infrared radiation. Samples that were shielded from more energetic wavelengths developed less checking and also showed less delignification at the exposed wood surfaces. Checks developed at the margins of rays and propagated at the interface between adjacent tracheids, close to the middle lamella. We conclude that exposure to UV and visible light increases the tendency of wood to check during exterior exposure. Our findings point to a link between changes in cell micro-structure as a result of photodegradation of lignin and the development of visible checks in wood exposed outdoors.
The effect of plasma treatment on mechanical properties, surface roughness and durability of plywood treated with copper-based wood preservatives
The effect of plasma treatment on strength properties of wood-based composites was studied. Veneers were obtained from beech logs (Fagus orientalis L.) and treated with 3 % of Tanalith E and Celcure AC-500. Two types of gasses (O2 and N2) were tested for plasma treatment. The effect of plasma treatment on bonding shear strength, bending strength and modulus of elasticity of plywood panels were determined according to EN 314-1 and EN 310, respectively. Surface roughness, leaching, decay test against white (Trametes versicolor) and brown rot [Postia placenta (FPRL 280)] and ground contact test of plywood samples were evaluated after plasma treatment. Results showed that plasma treatment with O2 increased the bonding strength of plywood compared to control and treated groups. However, plasma treatment slightly increased the mass losses caused by white rot, but decreased mass losses caused by brown rot in some groups. Regarding leaching test, plasma treatment slightly increased the leaching rate of copper in some groups. Ground contact test revealed that there was no delamination in bonding line on the plasma-treated samples.
Effect of weathering of new wood on the subsequent performance of semitransparent stains
To quantify the effect of weathering of new wood surfaces on subsequent coating performance, uncoated planed western redcedar beveled siding and roughsawn Douglas-fir plywood panels were exposed outdoors for 1 to 16 weeks. Following this preweathering, the specimens were coated with an oil-based semitransparent stain and placed outdoors again for 5 years. The stained specimens were evaluated annually to determine the effect of preweathering on finish performance. Evaluations based on visual techniques were compared with those using image analysis instrumentation.