Nanoparticles are added to many plastics. These are particles smaller than 100 nanometers (or billionths of a meter), and they are commonly made from silicon or metals like silver. While nanoparticles enhance the properties of plastics, what is the effect of these upon the environment when plastics degrade?
This is the question posed by scientists from the U. S., National Institute of Standards and Technology. To test this, the research group took a commercial nanoparticle-infused coating and subjected it to accelerated weathering, by creating artificial sun and rain. This was achieved through the use of ultraviolet radiation and simulated washings of rainwater.
The study involved exposing multiple samples of a commercially available polyurethane coating containing silicon dioxide nanoparticles to intense ultraviolet radiation (to simulate sunlight) for a period of 100 days. This was carried out in a special device called the Simulated Photodegradation via High-Energy Radiant Exposure sphere. The accelerated conditions meant that one day in the sphere was equivalent to up to 15 days under normal environmental conditions.
In addition, some of the material was subject to continually dry conditions and some material subject to very humid conditions (75 percent humidity.) The material was also subjected to simulated rainfall, through water being directed at periods using water under a very high pressure.
At the end of the study chemical analysis took place to assess the level of released silicone, in the form of released nanoparticles. The coatings were also assessed using atomic force microscopy and scanning electron microscopy.
The experimental outcomes were that humidity and exposure time are the key factors affecting the rate of nanoparticle release.
While the study results are interesting, further experiments will need to be run to assess the full effect of weather exposure on different types of plastics. Following on from this, the consequences of nanoparticle release also requires study to assess what this means in terms of ecological impact, and the effect on human health.
The research has been published in the Journal of Coatings Technology and Research. The research is headed “Surface degradation and nanoparticle release of a commercial nanosilica/polyurethane coating under UV exposure.”