Research on the aging properties of exterior wood coatings

Coatings can protect exterior wood from air and water damage. Exterior wood coatings tend to accumulate and age under various environmental factors such as ultraviolet radiation, temperature, and humidity. This study investigated the influence of different aging factors on four kinds of exterior wood coatings for beech, including polyurethane coating, alkyd resin coating, polyurethane coating with alkyd resin coating composite and polyurethane coating with phenolic resin coating composite. The results showed that the weight, size, chromatic aberration, luster loss, and hardness of the four coatings achieved stability at the second stage after a certain period of aging and that the changes were small at this stage. At the first aging stage, the water content in the substrates generally presented a “one-way” motion, that is, the quantity of water penetrated into the substrates from painting films was less than the quantity of water leakage. The results further indicated that chromatic aberration of composite coating was less obvious than that of the single coating. Moreover, because the luster loss of phenolic resin coating underwent severe loss, it may not be suitable for exterior wood coating in the high requirements of the occasion. Compared with alkyd resin coating, polyurethane coating had lower water permeability and can maintain high adhesion longer. Further comparisons indicated that the aging performance of polyurethane coating and the alkyd resin coating composite was the best. This paper could provide an understanding of the use of exterior wood painting for protection and adornment and enrich research in the area of design and study of exterior wood painting.