A quantitative study of nanoparticle release from nanocoatings exposed to UV radiation

Nanoparticles are increasingly used in polymer coatings (i.e., nanocoatings) to improve multiple properties including the mechanical, electrical, gas barrier, and ultraviolet (UV) resistance of traditional coatings. These high performance nanocoatings are often used in outdoor environments. However, because polymers are susceptible to degradation by weathering elements, nanoparticles in a nanocoating may be released into the environment during its life cycle, which potentially poses an environmental health and safety concern and may hinder application of these advanced coatings. This study presents protocols and experimental technique to quantify the release of nanosilica from epoxy nanocoating as a function of UV exposure. Specimens of an epoxy coating containing 5% untreated nanosilica in specially designed holders were exposed to UV radiation (295–400 nm) in a well-controlled high-intensity UV chamber. Exposed specimens were removed at specified UV dose intervals for measurements of coating chemical degradation, mass loss, nanosilica accumulation on specimen surface, and nanosilica release as a function of UV dose. Measurement of nanosilica release was accomplished by (a) periodically spraying UV-exposed specimens with water, (b) collecting runoff water/released particles, and (c) analyzing collected solutions by inductively coupled plasma-optical emission spectrometry using a National Institute of Standards and Technology (NIST)-developed protocol. Results demonstrated that the amount of nanosilica release was substantial and increased rapidly with UV dose. Mass loss, chemical degradation, and silica accumulation on specimen surface also increased with UV dose.