Abstract
The durability of transparent coatings applied to an oak wood exterior is relatively low due to its anatomic structure and chemical composition. Enhancement of the protection of oak wood against weathering using transparent hydrophobic coatings is presented in this study. Oak wood surfaces were modified using UV-stabilizers, hindered amine light stabilizer (HALS), and ZnO and TiO2 nanoparticles before the application of a commercial hydrophobic topcoat. A transparent oil-based coating was used as a control coating system. The artificial weathering test lasted 6 weeks and colour, gloss, and contact angle changes were regularly evaluated during this period. The changes in the microscopic structure were studied with confocal laser scanning microscopy. The results proved limited durability against weathering of both tested hydrophobic coatings. The formation of micro-cracks causing the leaching of degraded wood compounds and discolouration of oak wood were observed after 1 or 3 weeks of the weathering test. Until then, an oil-based coating film had protected the wood sufficiently, but after 6 weeks the wood was fully defoliated to its non-homogenous thickness, which was caused by the presence of large oak vessels, and by the effects of specific oak tannins. Using transparent hydrophobic coatings can prolong the service life of the exteriors of wood products by decreasing their moisture content. Without proper construction protection against rainwater, the hydrophobic coating itself cannot guarantee the preservation of the natural appearance of wood exteriors.
Highlights
Water contained in wood is a precondition allowing wood-destroying fungi and insects to prosper [1,2,3]
The potential use of two selected hydrophobic coatings protecting oak wood exposed to weathering on its exterior is discussed in this study
Even though the hydrophobic coatings partially preserve the hydrophobic characteristics during weathering, they do not prevent leaching of depolymerized lignins and extractives from wood
Summary
Water contained in wood is a precondition allowing wood-destroying fungi and insects to prosper [1,2,3]. The water synergistically interacts with solar radiation and causes atmospheric degradation of the wood surface [4,5,6], as well as dimensional changes and crack formation [7]. Modification in the form of hydrophobization can increase the natural durability of wood against biotic and abiotic damages on its exterior [8,9]. Modifications changing the properties of wood in its entire volume, such as thermal treatment or acetylation, are a frequent treatment method [10,11]. Hydrophobic coatings have the advantage of easier application and lower cost compared to thermal treatment, acetylation, or plasma treatment, and they preserve the original appearance of the wood, thereby positively influencing human perception [13]
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