Effects of adding TiO2 nanoparticles to a water-based varnish for wood applied to nine tropical woods of Costa Rica exposed to natural and accelerated weathering

The addition of titanium dioxide nanoparticles (TiO2 nanoparticles) to a water-based varnish used for finishing tropical woods was studied. Three different concentrations of TiO2 nanoparticles (0%, 1.0%, and 1.5%) were evaluated. The nanoparticles were characterized by means of the transmission electron microscopy and an X-ray diffractometer. The varnish prepared was evaluated for its viscosity, adhesion of the film to the wood, water absorption, and the effects of natural weathering on the color and quality of the varnish. It was found that viscosity decreases as the concentration of TiO2 nanoparticles increases, while no variation was found in the thickness of the film. Except for Gmelina arborea and Tectona grandis, the adhesion was not statistically affected. It was found that, in the 9 species tested, incorporation of TiO2 nanoparticles decreased the values of water absorption. The evaluation of natural weathering showed that the varnish with no added TiO2 nanoparticles degraded completely after 1 year of weathering exposure, while the modified varnish film endured. Less color change was observed in lumber treated with the varnish containing TiO2 nanoparticles. The best performance of the varnish in the nine tropical woods used was observed when TiO2 nanoparticles were added at 1.5% concentration.