Surface degradation and nanoparticle release of a commercial nanosilica/polyurethane coating under UV exposure

Abstract

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

Novel Attribute of Organic–Inorganic Hybrid Coatings for Protection and Preservation of Materials (Stone and Wood) Belonging to Cultural Heritage

“…Silicon dioxide nano-particles (from 0.1% to 8%) have been added to polymer based on silanes/siloxanes [37][38][39], fluoropolymers [40,41], polyurethanes [42,43], polyurethane-acrylate [44], methacrylic resins [45,46], unsaturated polyester resin [47], DGEBA-amine epoxy resins [48,49]. In these hybrids, silica nano-particles usually have dimensions around 7-14 nm in mean diameter [37,38].…”

“…After the nano-particles' addition, the mixture with polymer(s) can be subjected to sonication [42,48,50,51] or vigorous stirring in order to prepare an optimal and homogeneous dispersion [37,47,52]. However, sometime the stirring procedure did not ensure nano-particles homogeneously dispersed in the polymer film; SEM (scanning electron microscopy) observations highlighted aggregates with average diameters dependent on the nano-particles concentration [38,52].…”

“…With regard to the durability of these hybrid coatings, release of nano-material by matrix degradation in outdoor uses is a topic of great concern because the polymer binder in a nano-coating can be prone to degradation under the UV radiation of sunlight. Due to the matrix degradation, the nano-particles could be exposed on the coating surface and become more likely susceptible to be released into the environment [42], for example by rain action [49]. The rate of chemical degradation of the hybrid polymer can be lower than for the neat polymer, indicating that the nanosilica particles are able to photostabilize the matrix.…”

Protocol for collecting and quantifying release from weathered epoxy-nanosilica coatings: using a simulated rain method and inductively coupled plasma-optical emission spectrometry

“…Nanomaterial accumulation at the nanocoating surface is a common observation from the polymer nanocoating degradation processes [15][16][17][18][19]. The primary objective of this SP is to provide a specific protocol for collecting and quantifying the amount of nanomaterial that is released after a combination of accelerated weathering and simulated rain spray.…”

“…In the study that serves as the example for this protocol [17], the atomizer was operated at an air flow of 16 L/min and a pressure of 83 kPa, but select parameters appropriate for the case at hand.…”