New approaches in wood coating stabilization

A major drawback in the use of wood materials for construction and decorative applications is its sensitivity to light. Numerous researchers have shown that the ultraviolet (UV) as well as fractions of the visible (VIS) spectrum of solar radiation cause most of the chemical modification and mechanical breakdown of exposed wood. To insure the long life of wood substrates, they are usually coated with various decorative and protective finishes. The protection effect depends strongly on the opacity, i.e., the degree of pigmentation of the coatings. However, the use of UV absorbers (UVA) and hindered amine light stabilizers (HALS) both in the coating system and also in a direct wood impregnation step can improve the light stability considerably. Here the knowledge of the light sensitivity of wood is crucial for an optimal photoprotection concept for coatings and the wood substrate. This paper highlights findings of a systematic investigation of the light sensitivity of pine wood (Pinus radiata). Furthermore, it describes the correlation between quantity and type of organic UVA and HALS as well as the lignin stabilizer concept and the degree of pigmentation of the coating. These findings are of great importance for an efficient and economic use of light stabilizers in film-forming wood coating systems for pale wood species and allow a cost-effective stabilization. Presented at the 5th International Woodcoatings Congress: Enhancing Service Life, organized by the Paint Research Association (PRA), in Prague, Czech Republic, October 17–18, 2006.