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.