Improvement of Photoprotection of Wood Coatings by Using Inorganic Nanoparticles as Ultraviolet Absorbers

Abstract

Ultraviolet (UV) light is high-energy radiation that induces degradation of organic compounds, such as wood. To prevent UV damage, several strategies have been used, including creating a UV light barrier at the wood surface. The most common strategy is to apply a coating to the wood surface. However, coating alone may not be effective enough to protect wood exposed outdoors. For example, clear coatings often contain additives to protect the material from UV radiation (hindered amine light stabilizers, quenchers, UV absorbers). This article reports work on the photostability of wood surfaces coated with waterborne nanocomposite urethane-acrylate systems in outdoor conditions. The wood color variation of sugar maple (Acer saccharum Marsh) was measured following accelerated aging. Different types of nanoparticles (ZnO, CuO) were used in water in predispersed and powder forms. Once cured, the nanoparticle dispersions were characterized by transmission electron microscopy. The best photoprotection was obtained with ZnO predispersed in water. Our major conclusion is that ZnO nanoparticles are better than CuO nanoparticles as additives intended to reduce the discoloration of clear-coated wood exposed outdoors. The highest increase in gloss was achieved with the mixture of inorganic and organic UV absorbers, which appear to show synergistic behavior.

The Search for Durable Exterior Clear Coatings for Wood

“…Similarly, Cristea and Riedl showed that zinc oxide and titanium dioxide nanoparticles improved the durability of clear coatings on black spruce wood exposed to accelerated weathering [66]. Auclair and co-workers compared the ability of different inorganic (zinc or copper oxide nanoparticles) and organic photostabilizers (UVA/HALS) to prevent the discolouration of clear-coated sugar maple panels exposed to accelerated weathering [67]. The best photoprotection was obtained with zinc oxide nanoparticles (2% w/w) [67].…”

“…Auclair and co-workers compared the ability of different inorganic (zinc or copper oxide nanoparticles) and organic photostabilizers (UVA/HALS) to prevent the discolouration of clear-coated sugar maple panels exposed to accelerated weathering [67]. The best photoprotection was obtained with zinc oxide nanoparticles (2% w/w) [67]. The combination of inorganic and organic UV absorbers was also effective and showed synergistic effects on the gloss of the coatings [67].…”

“…The best photoprotection was obtained with zinc oxide nanoparticles (2% w/w) [67]. The combination of inorganic and organic UV absorbers was also effective and showed synergistic effects on the gloss of the coatings [67]. Schaller and co-workers also compared the ability of different organic and inorganic photostabilizers to prevent the deterioration of clear-coated pine panels exposed to accelerated weathering [68].…”

UV-protection of wood surfaces by controlled morphology fine-tuning of ZnO nanostructures

“…A few studies report wood surface coatings based on inorganic nanoparticles acting as UV absorbers (Rao et al 2016). Generally, these nanoparticles are semiconductor materials which absorb UV light via electron transition between conduction band and valence band but are transparent to visible light (Aloui et al 2007;Auclair et al 2011;Fu et al 2015). For instance, southern pine specimens were vacuum impregnated by nano-ZnO dispersions for UV protection (Clausen et al 2010).…”

“…The main drawback of such treatments is the leaching of added particles over time, lowering the protection efficiency, and necessitating regular application of new layers. Facing this challenge, a mixture of inorganic UV absorbers in a transparent organic coating to obtain highly durable and efficient UV protection coatings was reported recently (Auclair et al 2011). ZnO-based acrylate coatings were applied to impregnate wood to reduce yellowing under UV exposure (Weichelt et al 2010).…”