United States.
A new study by the National Institute of Standards and Technology (NIST) aims to investigate the process of surface degradation and potential particle release from a commercial nano-silica/polyurethane coating under accelerated UV exposure.
Many of the coating properties, such as mechanical, electrical, and ultraviolet (UV) resistance, are greatly enhanced by the addition of nanoparticles, which can potentially increase the use of nanocoatings for many outdoor applications. However, because the polymers used in all coatings are susceptible to wear degradation, the nanoparticles in a coating can be brought to the surface and released into the environment during the life cycle of a nanocoating.
Recent research has shown that the matrix in an epoxy nanocomposite undergoes photodegradation during exposure to UV radiation, resulting in the surface accumulation of nanoparticles and the subsequent release of the compound.
In this study, specimens of a commercial polyurethane (PU) coating, to which a solution of surface-treated silica nanoparticles with 5% by mass was added, were exposed to well-controlled and accelerated UV environments. They measured surface morphological changes from nanocoating and surface accumulation of nanoparticles based on UV exposure, along with chemical change and mass loss using a variety of techniques.
The surface particles of the coating were collected using a simulated rain process developed at NIST, and the collected runoff specimens were measured using optical emission spectroscopy of inductively coupled plasma to determine the amount of silicon released from the nanocoatings.
The results showed that the added silica nanoparticle solution decreased the photodegradation rate (i.e. stabilization) of the commercial PU nanocoating. Although degradation was slower than with the previous epoxy nanosilica model system, degradation of the PU matrix resulted in the accumulation of silica nanoparticles on the nano-crawler surface and released into the environment by simulated rain.
These experimental data are valuable for the development of models to predict the long-term release of nanosilis from commercial PU nanocoatings used outdoors and are therefore essential for assessing health and environmental risks over the lifetime of outdoor PU nanocoating.
Source: Journal of Coatings Technology and Research
