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 TiO 2 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.

Colour changes and associated wood degradation in exterior and interior applications influenced by ultraviolet (UV) and visible radiation (VIS) decreases the aesthetic value of the products and shortens the overall life of transparent coatings. The aim of the paper is to achieve colour stabilization of oak, larch, Douglas fir and spruce heartwood via surface treatment with UV stabilizers, hindered amine light stabilizers (HALS), nanoparticles TiO2, ZnO, and mixtures thereof, during exposure to UV and VIS radiation. Colour changes were evaluated during accelerated artificial ageing testing in Xenotest. The distinctly individual character of colour changes in surface treatments due to the underlying wood species was confirmed. A synergistic effect was found when using a combination of active substances compared to substances used individually. The mixture of benzotriazoles with HALS (Tinuvin 5151) in combination with TiO2 and ZnO nanoparticles was confirmed as one of the most effective treatments for colour stabilization of wood due to UV and VIS spectrums.

The effect of the initial modification of beech and spruce wood using a solution of caffeine and of a commercial product FN-NANO® FN-1 containing a water dispersion of TiO2 nanoparticles for increasing the service life of a transparent oil and acrylate coatings during 6 weeks of artificial accelerated weathering was tested. Changes in colour, gloss, and the contact angle of water were monitored. Degradation of the coating film was also evaluated visually and microscopically. The resistance of the coatings to mould growth was also subsequently tested. Based on the results, it is possible to recommend the initial treatment of spruce and beech wood with a 2% caffeine solution or 15% solution of FN-NANO® dispersion to increase the overall life of a transparent acrylic coating in exterior applications. No positive effect of the applied treatments was observed with the oil coating. In addition, lower concentrations of FN-NANO® did not have a sufficient effect, and the synergistic effect of using FN-NANO® in a mixture with a 1% caffeine solution was also not confirmed.

No abstract

Bonding processes play a significant role in the wood and furniture industry. They allow for the creation of fixed joining of construction elements, creation of new materials and, last but not least, aesthetic appreciation of parts. However, the quality of bonded joints is affected by many factors, one of which is the moisture of the bonded materialwood. The main objective of this research was to determine the influence of wood moisture on the strength of bonded joints formed by polyvinyl acetate (PVAc) and polyurethane (PUR) adhesives. In current practice these adhesives are being increasingly used for their properties and zero formaldehyde content. The procedure for determining the bond strength (tensile shear strength of lap joints) corresponded to standard EN 205. It was ascertained that in addition to actual moisture of bonded wood, the quality of the joint is also affected by the environment to which the glued joint is subsequently subjected. In a normal environment, the strength of the tested joint PVAc adhesive decreases with increasing wood moisture, but it still meets the requirement of the standard. In a humid environment, the strength falls below the limit of the standardized value. In a normal environment the joint strength bonded with PUR adhesive is similar, but the decrease in strength is lower. In a humid environment it shows the highest strength at 20% wood moisture and meets the specified standard minimum strength (4 MPa). Graphs were created from the measured values that clearly show the influence of wood moisture on the final bond strength of a joint.