Lasures en base agua para madera en exterior aditivados con nanopartículas

Wood is an easily degradable material in an outdoor environment. Its deterioration can lead to some serious structural damages, with economic and historical losses. Surface protection with coatings with specific technical performances for outdoor use is one of the methods to increase its durability. From the existing technology for wood coating, opaque finishing processes consisting of several products applied on several layers are those that offer greater protection to wood for exterior use, but market is demanding transparent colorless finishing systems that let see the wood aspect, with few solids and low dry film thickness that provides a natural appearance, easy to apply and maintain. Transparent pigmented lasurs fulfil these requirements, but colorless ones, due to the state of the UV organic filters technology, with insufficient efficiency for this type of coatings, have a limited durability. The use of metallic oxides with nanometric size with capacity to filter UV radiation focuses on the current research to obtain transparent and colorless finishes with greater efficiency and durability. In this thesis different blends of a base lasur of pure acrylic binders with nanoparticles additives of CeO2, ZnO and TiO2 in dispersion have been studied. The analysis by electronic microscopy, SEM and TEM, indicates that no agglomerates of nanoparticles are formed, although they tend to cluster, maybe due to a greater affinity for one of the binders used. These groupings cause that nanoparticles distribution is not completely homogeneous, being this effect much more pronounced in the case of the nanoparticles of ZnO and TiO2. The blends have been applied in a single layer of low dry film thickness directly on the wood, Scots pine, iroko and ipe, without applying primers previously. As reference, formulations with the same base but with organic additives and transparent iron oxide pigments applied in the same way have been used. Different artificial ageing tests have been carried out, in Xenotest and in QUV, with different temperature, humidity and radiation conditions in order to know the defects that could appear under extreme exposure conditions. Furthermore, natural ageing tests have been done to know the behavior of the different formulations in real conditions although only in a geographical location. The monitoring of these tests have been carried out by appearance assessment, color and gloss measurements, and FT-IR spectroscopy. Depending on the wood specie, final results are different due to the influence of the microstructure and chemical composition of wood, but also incompatibilities with some wood species can appear due to their chemical composition, for instance between ipe and ZnO. None of the colorless blends with nanoparticles have improved the behavior of the formulation with conventional organic additives. Only the blend with CeO2 could be compared with the mixture with organic additives but without improving it.