Optimized composition of alkyd emulsion with nanoparticles of iron oxide for enhancing protection of thermally modified wood
E Sansonetti, D Cīrule, I Andersone, B Andersons, E Kuka
Thermal treatment is acknowledged as an environmentally friendly method to improve durability of wood and some of its properties, such as biological resistance, dimensional stability, reduced hygroscopy. Despite these improvements, when used outdoors, also thermally treated wood is subjected to the action of environmental factors, like solar radiation, moisture, precipitations, temperature, etc., giving place to a series of chemical and structural transformations, defined as “weathering”, which negatively affect its service life. In this research an alkyd emulsion containing red transparent iron oxide pigments was obtained, whose composition is optimized to protect the decorative properties of thermally treated wood during outdoor exposure. In particular, attention was dedicated to the selection of surfactants for the emulsification of resins and to the investigation of oxidative properties of alternative metal primary driers, which could replace the cobalt.
Initially the surface wetting properties of thermally treated wood were investigated and considered for the optimization of the alkyd emulsion formulation. The determination of the surface energy of wood, by means of contact angle, before and after thermal treatment shows that the polar component of the surface energy decreases with increasing temperature of thermal treatment. This explains the more hydrophobic character of thermally treated wood, which must be considered for the formulation of suitable paints and the selection of appropriate additives.
In the second part of the research, artificial weathering test was carried out to determine the suitable concentration of red transparent iron oxide pigments, which can give better protection against photodegradation and minimize the color changes of wood surface. The obtained results show that a concentration of 8 % for red transparent iron oxide pigments in alkyd emulsion is necessary to ensure protection of the thermally treated wood surface. Another important conclusion from the obtained results is that the replacement of organic solvent with water is possible and paint with comparable or even better efficiency can be obtained.