Polyaspartic ester polyurea-TiO2 nanocomposite coatings for UV protection of leading edge of wind turbine blades

Polyaspartic ester polyurea (PAEPU) supplies a promising matrix for high-durability coatings. However, its poor UV-A resistance make its usage limited. In this work, commercially available anatase TiO2 particles (0.05-10 wt %) were dispersed in PAE matrix without any modification. PAEPU/TiO2 composites were supplied by the reaction of PAE/TiO2 matrix with an aliphatic isocyanate. UV-Visible spectra of spin coated PAEPU/TiO2 composite thin films showed an exponential decrease in transmittance with increasing amount of TiO2. The optical response is dominated by UV blocking for TiO2 amounts smaller than 0.3 wt%. For above 0.5 wt% TiO2 amounts, transparency to translucency transition signifies the beginning of multiple scattering. The diameter of particles analyzed by AFM showed that particle diameter is 47 +/- 11 nm taking into account of images of the PAEPU films containing 0.3 wt% of TiO2 particles. Radial distribution function of the particle domains achieved from microscopy suggests that interparticle distance gets smaller than the wavelength of the incident light even at low the particle concentration. Accelerated weathering test were performed by applying 0.1, 0.5, 1.0, and 3.0 wt% TiO2 containing PAEPU composite films on a white primer with Doctor Blade method. 0.1 wt% PAEPU/TiO2 composites shows lower Delta E value compare to both neat and higher amounts of TiO2 containing PAEPU composite films. The results suggest that without the complexity and cost of the surface modification, the low loading of commercial TiO2 into PAE matrix may supply UV-stabilized PAEPU coatings relevant to the leading-edge protection of wind-turbine blades.