Wood has great potential for uses in outdoor conditions, but it can be easily degraded due to the action of environmental factors (solar radiation, moisture, fungi, insects, etc.). The protection of wood is therefore a very actual research topic, and it is also the object of this work. The main goal of this Doctoral Thesis is to obtain a water-based alkyd paint formulation in the form of emulsion and to optimize its composition with necessary additives, in particular, with nanosized red iron oxide pigments which can protect the decorative qualities of thermally treated wood (TTW) during outdoor exposure. In the literature review, the main factors responsible for the degradation of wood and their effect on the structure and properties of wood are summarized. The chemistry of coatings for the protection of wood and the challenges that are faced in reformulation of paints, due to more stringent regulations which limit the use of organic solvents and promote greener alternatives, like water-based paint formulations, are considered. In Europe, this is stated by the Directive 2004/42/EC of the European Parliament on the limitation of emissions of volatile organic compounds (VOC) from decorative paints and varnishes. In the first part of the experimental section, the optimal composition of the alkyd emulsion and the effects of additives on the film properties have been investigated. The different chemo-physical properties of thermally treated wood compared with those of untreated wood have been also evaluated. After thermal modification, wood becomes more hydrophobic and this has been confirmed from the changes of the surface energy of thermally treated wood: the polar component of the surface energy decreases with increasing temperature of thermal modification. In the second part of the experimental section, artificial and outdoor weathering tests have been done to determine the suitable concentration of red iron oxide nanoparticles which can give better protection against photodegradation. Results show that red iron oxide pigments at a concentration of 8 % in alkyd emulsion are efficient to protect the wood surface against discoloration. During the outdoor weathering test, the performance of alkyd emulsion has been compared with that of the solvent-based formulation. Results confirm that the water-based alkyd emulsion gives better protection of the thermally treated wood surface than the solvent-based formulation, thus confirming that the replacement of organic solvent with water gives a product with equivalent or better properties for the protection of thermally treated wood in outdoor conditions.
Evaluation of wood surface coating performance using water based, solvent based and powder coating
