Polyurethane nanocomposite films containing nano-cerium oxide as UV absorber; Part 2: Structural and mechanical studies upon UV exposure

Degradation of a water-based polyurethane clear coat containing nano-sized cerium oxide was investigated. Nanoparticles at different concentrations were dispersed in a water-reducible polyol polyacrylate dispersion resin, followed by mixing with polyisocayanate hardener from which wet films of 90 μm thick were prepared. Samples were exposed to 700 h of accelerated artificial weathering (QUV).Their performances were then accessed by DMTA and ATR–FTIR spectroscopy. It was revealed that the glass transition temperature (Tg) of films systematically increased with increase in nano ceria content. Due to UV absorption and decrease in photo-oxidation and chain scission reactions, the storage moduli of clear coats containing nano ceria were shown higher than that of the blank polyurethane after UV exposure. Tg for both pure blank polyurethane and nano-ceria embedded clear coats increased with increase in degradation time. Most of variations in Tgs occurred in the first 150 h of exposure. ATR–FTIR spectra also proved these results by showing depreciation in intensities of CH and NH peaks. It was seen that the surface of the clear coats as analyzed by ATR–FTIR was polyurea-rich and contained urea functionality at least as much as polyurethane. During weathering, the photo-oxidation of CH groups to carbonyl groups occurred.