Clear coatings containing UV absorbers (UVAs), hindered amine light stabilizers (HALS) and biocides can substantially slow down the weathering process of wood and maintain its natural color for a period of time.1 However, there are few commercially available coatings that can push refinishing intervals past two or three years. Currently, wood in exterior applications with translucent coatings requires frequent refinishing and maintenance,2 which limits competitiveness with alternative materials. One cause of the frequent maintenance is the premature photodegradation of additives in coatings. The additives currently used in clear coatings to protect wood against ultraviolet (UV) radiation and black-stain are mostly organic and are often vulnerable to photodegradation, which, along with volatilization and leaching, reduce their long-term efficacy. As additive efficiency decreases, coatings and wood will break down, creating micro-cracks or small perforations that facilitate fungal colonization.3 All of this results in the loss of wood’s aesthetic properties.
One approach to improve the coating and wood photostabilization is to replace organic UVAs with inorganic metal oxide nanoparticles such as ZnO, TiO2 and CeO2.3,4 Several studies have investigated this approach in wood coating applications. Weichelt et al. (2010)5 and Auclair et al. (2011)6 report the effectiveness of ZnO nanoparticles in slowing down wood discoloration and delamination of UV-cured coatings. Similar results are presented by Cristea et al. (2011)7 where the addition of ZnO and TiO2 nanoparticles in an acrylic stain slows down photodegradation. However, these studies also reported that nanoparticles tend to aggregate and sediment, leading to adhesion problems. Since the performance of nanocomposites can be greatly influenced by the dispersion, there is a need to improve nanoparticle dispersion in coatings.
Our September issue features articles and news about wood coatings, intumescent technology for sustainable buildings, tips for outsourcing coatings manufacturing, and an article on a liquid EPDM for waterborne coatings, which was the winner of the PCI Award for Technical Excellence at the Waterborne Symposium earlier this year.