Abstract
This paper compares the resistance of 20 commercial transparent and semi-transparent coatings applied to European and Siberian larch during artificial weathering in Xenotest. The change in gloss, colour, contact angle of wetting, resistance to Aspergillus niger and Penicillium brevicompactum moulds was evaluated, and visual changes at the top surface of treated wood species were measured. Overall, the durability of coatings on European larch was higher than that on Siberian larch. The most durable of the tested coatings was a thin-film, i.e., semi-transparent oil-based film containing TiO2 pigment and propiconazole fungicide. Of the transparent coatings, the most stable was a thick acrylic coating. Conversely, penetrating transparent oil systems had low colour stability and overall lifespan. Artificial weathering of all of the coatings resulted in a marked decrease in their resistance to moulds.
Highlights
Like all natural materials, wood used in building applications is subject to natural weathering—a combination of chemical, mechanical and energy factors acting on its surface
Our results focus on the evaluation of changes in colour (Figures 3–5), gloss (Table 3), visual defects (Figures 6 and 7) and changes in the hydrophobicity of coatings (Figure 8) after artificial accelerated weathering
Considering the finding that that ∆E* < 3 is a colour difference of wood surfaces that cannot be distinguished by a subjective observer [50], none of the coating systems were able to restrict colour changes during weathering
Summary
Wood used in building applications is subject to natural weathering—a combination of chemical, mechanical and energy factors acting on its surface. Weathering causes loss of gloss and colour and leads to cracks and change in chemical composition, erosion and roughening of wood surfaces [1,2]. Due to this fact, the appearance of wood changes over the course of several months, with bacteria, moulds and wood-colouring fungi [3,4] contributing to the overall change in colour. Natural weathering can be partially reproduced via artificially accelerated weathering in UV chambers equipped with water spray In such chambers, high-intensity UV radiation combined with rapid fluctuations in moisture kill bacteria and other microorganisms that are involved in natural weathering [5]. The protective function of wood coatings is defined by their thickness [12], water and vapour permeability [13,14], hydrophobicity [15]
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