Effects of temperature on surface accumulation and release of silica nanoparticles in an epoxy nanocoating exposed to UV radiation

Polymer nanocoatings are increasingly used outdoors and in harsh environments. However, because most common polymers degraded by the weathering elements, nanoparticles in polymer nanocoatings may be released into the environments. Such nanoparticle release potentially poses an environmental health and safety risk. This study investigated the effects of temperature on the surface accumulation and release of nanosilica for an epoxy nanocoating exposed to ultraviolet (UV) radiation. Specimens of an amine-cured epoxy containing 5 mass % nanosilica were exposed to 295 nm to 400 nm UV radiation at three temperatures (40°C, 50°C, and 60°C). Surface accumulation and release of nanosilica as a function of UV dose were measured by atomic force microscopy and inductively-coupled plasma optical emission spectrometry, respectively. Nanosilica accumulated rapidly on specimen surface at low UV doses but the rate of accumulation slowed down at high UV doses. Further, the amount of surface accumulation increased with increasing temperature. The mass of Si release increased with increasing temperature for high UV doses; but at low doses, the trend was different: the mass of Si release was greatest at 50°C and smallest at 60°C. Kinetic parameters derived from this study are essential for developing credible models to predict the long term risks of polymer nanocoatings used outdoors.