D.E. Gorka, J.M. Gorham
National Institute of Standards and Technology,
Keywords: silver nanomaterials, textiles, surface chemical characterization, chemical transformations
Summary:Nanomaterials have been increasingly used in consumer products and silver nanomaterials (AgNMs) especially have been used for their antibacterial properties. Increased use of AgNMs in consumer products will result in their increased disposal and entrance into the environment. To better understand what materials are entering the environment, work needs to be performed to determine the chemical and physical properties of AgNM-containing consumer products throughout their lifecycle. The aim of this work is to evaluate the chemical and physical transformations that AgNM-containing textiles undergo during modeled human and environmental exposure. A lab-synthesized AgNM-containing cotton fabric (prepared following NIST Special Publication 1200-08) and a commercially available AgNM-containing wound dressing were studied. To model these textiles during use, both materials were exposed to simulated wound fluid or synthetic sweat for a time period of up to 7 days. After exposure, textiles were extracted and stored under vacuum to minimize extraneous transformations. Both pristine and exposed materials were analyzed quantitatively and qualitatively using a variety analytical techniques including scanning electron microscopy (SEM) with energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), inductively coupled plasma mass spectrometry (ICP-MS), UV-visible spectroscopy (UV-vis), and dynamic light scattering (DLS). Electron microscopy revealed the formation of micron sized silver chloride structures on the surface of the commercial wound dressing after sweat exposure. XPS showed surface transformation from silver/silver oxide to silver chloride, while XRD found the bulk material was a mixture of silver and silver chloride suggesting the commercial wound dressing still contained zero-valent silver even after 7 days of exposure. Interestingly, the transformation to silver chloride was not found when the textiles were exposed to simulated wound fluid. Both XPS and XRD found the commercial wound dressing remained as metallic silver. Study of the wound fluid solution by ICP-MS after exposure found a soluble silver fraction suggesting the presence of protein in the simulated wound fluid allowed the silver to remain soluble. In contrast, the ICP-MS results from sweat and the commercial wound dressing showed minimal enhancement of soluble silver, suggesting that any dissolution that occurred promptly complexed and reprecipitated as AgCl. Lastly, we will discuss work that we are doing on modelling after use phases of the textiles. Both textiles were exposure to either artificial landfill leachate or the moderately hard water (MHW). Additionally, both the lab-synthesized textile and the commercial wound dressing were exposed to the modeled human exposure media followed by the modeled environmental media to create a more realistic exposure scenario. A better understanding of the chemical and physical transformation of AgNMs in consumer products will help manufacturers and regulators to make more informed decisions on product design and use.