Pilot Inter-Laboratory Studies for Evaluating Weathering-Induced Release of Carbon Nanotubes from Solid Matrices

R. Zepp, D. Bouchard, E. Sahle-Demessie, W. Wohlleben, S. Vazquez-Campos, J. Carter, C. Kingston, R. Canady, B. Acrey, C-Y. Chen
U.S. EPA, NERL,
United States

Keywords: weathering, release, solid matrices, interlaboratory, carbon nanotubes, testing, polyamide, epoxy

Summary:

Nanomaterials are increasingly being used in polymer composites to enhance the properties of these materials. Here we present results of a pilot inter-laboratory study to simulate the effects of weathering on the potential release of multiwalled carbon nanotubes (MWCNT) from their composites with two polymers. In this study, wafers of MWCNT in epoxy and polyamide nanocomposites were exposed in four laboratories in the US and Europe under carefully controlled conditions including cycles of simulated sunlight and rainfall over a 2000-hour period. Based on the conditions specified by ISO 4892-2 for the standardized, widely established weathering simulation equipment, such period is equivalent to outdoor weathering of up to ≈ 2 years in mid-latitude U.S. Wafers with no added MWCNT were exposed under the same conditions. The weathered samples from all four aging labs were redistributed and analyzed in the U.S. and Canada for released MWCNT by SEM imagery and EDXS spectroscopy. Weathered surfaces of wipe samples were examined by SEM imagery for possible detachment of fragments and/or CNTs. Simultaneously, and again on samples from all four aging labs, two labs in the U.S. and Europe performed analyses of samples derived from immersion in a standardized leaching medium. Four methods were used for leachate analyses including TEM, UV-visible spectroscopy, ICP-MS and AUC or FFF (for particle size characterization). Results of these studies and their interlaboratory reproducibility will be discussed. This research contributes to the science and tools needed to evaluate transformation, potential exposure, and impacts of engineered nanomaterials across their life cycles. The results highlight the importance of developing standard test guidelines that improve data quality and reduce the potential for inter‐laboratory variability. Further results on the potential use of the NanoRelease testing materials as Benchmark Materials for release phenomena and the transfer of NanoRelease protocols to further materials will be presented in the twin talk by Wohlleben et al.