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Approaches to evaluating weathering effects on release of engineered nanomaterials from solid matrices
Citation:
Zepp, R., W. Wohlleben, E. Sahle-Demessie, C. Kingston, D. Bouchard, B. Acrey, A. Commodore, O. Okungbowa, AND E. Walton. Approaches to evaluating weathering effects on release of engineered nanomaterials from solid matrices. ACS Fall 2017 National Meeting, Washington, DC, August 20 - 24, 2017.
Impact/Purpose:
Presented at the ACS Fall 2017 National Meeting.
Description:
Increased production and use of engineered nanomaterials (ENMs) over the past decade has increased the potential for the transport and release of these materials into the environment. Here we present results of two separate studies designed to simulate the effects of weathering on the potential release of multiwalled carbon nanotubes (MWCNTs) from polyamide or epoxy composites, and nanosilica from composites with low-density polyethylene (LOPE) with added pro-oxidant. With these weathering-resistant ENMs, the release was primarily driven by degradation of the polymer matrix. The MWCNT-polymer composites were investigated in a pilot inter-laboratory study to simulate the effects of weathering on the potential release of multiwalled carbon nanotubes (MWCNTs) from their composites with two polymers. Wafers of MWCNTs in epoxy and polyamide nanocomposi tes were exposed in four laboratories in the US and Europe under carefully controlled conditions to cycles of simulated sunlight and rainfall over a 2000-hour period. Particles released upon submersion of the weathered wafers in the leaching fluid described in EPA Method 1311 were analyzed by Transmission Electron Microscopy (TEM), Inductively Coupled Plasma- Mass Spectrometry (ICP-MS), and Ultraviolet-Visible Spectroscopy (UV-Vis). Rates ofrelease of MWCNTS determined by ICP-MS (Co associatedwith MWCNTS) and UY-Vis agreed within a factor of two. Other weathering studies of nanosilica-LDPE composites were conducted using simulated sunlight under dry conditions. The nanocomposites were modified by addition of a pro-oxidant to stimulate degradation of the polymer matrix. Polymer degradation was followed by Fourier-transform-infrared spectroscopy (FTIR) and changes in tensile mechanical properties were followed using the ASTM 882 protocol. Addition of the pro-oxidant accelerated deterioration of mechanical strength by an order of magnitude compared to controls. Atomic force microscopy was used to characterize changes in the shape of the weathered composites. Wavelength studies demonstrated that the short-wavelength component of simulated sunlight was most effective in inducing photodegradation of the matrix with added pro-oxidant. Action spectra based on these wavelength studies are used to evaluate the effects of sunlight over space and time on photodegradation of the nanocomposites.
