Color Stabilization of Wood and Durability Improvement of Wood Coatings: A New UV Light-Protection Concept for Indoor and Outdoor Applications
Despite increased use of competitive materials such as metals and plastics, wood remains a highly popular material for construction and decoration purposes in applications including furniture, parquetry, timber work, joinery, cladding, and decking. To ensure long life, wood substrates are usually coated with various decorative and protective finishes such as paints, transparent stains and penetrating finishes or film-forming clear varnishes. Transparent systems that allow the natural features of wood - including color, grain and texture - to remain visible are attracting interest and demand for them has been increasing. However, the long-term instability of such transparent systems in outdoor applications has so far seriously hindered them from becoming more widespread. The main reason for this instability is the UV light transparency of the topcoats and the extreme sensitivity of certain wood components, particularly lignin, to UV light degradation. Even in indoor diffuse light conditions, naturally pale wood tends to yellow and darken with time as a result of lignin photo-oxidation.
This new HALS compound is a milestone in the development of durable color protection of natural wood substrates. It is the first additive that totally inhibits photo-oxidation of lignin and acts as an efficient color stabilizer by simple aqueous solution pretreatment of the substrate. However, durable protection against yellowing and photodegradation of wood surfaces is only achieved if the HALS is used in conjunction with a UVA. The latter is either applied in the pretreatment itself or preferably in a subsequently applied topcoat.