NanoRelease: Pilot interlaboratory comparison of a weathering protocol applied to resilient and labile polymers with and without embedded carbon nanotubes

Abstract

A major use of multi-walled carbon nanotubes (MWCNTs) is as functional fillers embedded in a solid matrix, such as plastics or coatings. Weathering and abrasion of the solid matrix during use can lead to environmental releases of the MWCNTs. Here we focus on a protocol to identify and quantify the primary release induced by weathering, and assess reproducibility, transferability, and sensitivity towards different materials and uses. We prepared 132 specimens of two polymer-MWCNT composites containing the same grade of MWCNTs used in earlier OECD hazard assessments but without UV stabilizer. We report on a pilot inter-laboratory comparison (ILC) with four labs (two US and two EU) aging by UV and rain, then shipping for analysis. Two labs (one US and one EU) conducted the release sampling and analysis by Transmission Electron Microscopy (TEM), Inductively Coupled Plasma- Mass Spectrometry (ICP-MS), UltravioleteVisible Spectroscopy (UVeVis), Analytical Ultracentrifugation (AUC), and Asymmetric Flow Field Flow Fractionation (AF4). We compare results between aging labs, between analysis labs and between materials. Surprisingly, we found quantitative agreement between analysis labs for TEM, ICP-MS, UVeVis; low variation between aging labs by all methods; and consistent rankings of release between TEM, ICP-MS, UVeVis, AUC. Significant disagreement was related primarily to differences in aging, but even these cases remained within a factor of two.

Environmental Impacts by Fragments Released from Nanoenabled Products: A Multiassay, Multimaterial Exploration by the SUN Approach

“…Additionally to PP, the CNT was integrated in three complementary matrices: polyoxymethylene ("POM") nanocomposite identical to the FP used in a human tox study, 19 cement ("cement") nanocomposite identical to the FP used in a human tox study, 19 and epoxy ("epoxy") nanocomposites identical to those applied in the NanoRelease interlab testing (Table SI_2). 20 Comparative testing of environmental weathering releases was performed on the identical nanocomposites, finding release rates that increase across 5 orders of magnitude in the order of polyolefin−POM−epoxy−cement. 21 NEP Fragmentation, Use Phase.…”

“…The Al and Co content is known from earlier release investigations on the same batch of CNT_epoxy. 20 FP Surface Chemistry Analysis (X-ray Photoelectron Spectroscopy Plus Hydrophobicity). Surface composition was investigated by XPS to determine element concentrations and content of ENM at the fragments' surface.…”

Methods evaluation for assessing release of manufactured nanomaterials from polymers, consistent with the NanoGRID framework : Advanced and Additive Materials : Sustainability for Army Acquisitions

“…The second general release paradigm is degradation of the composite matrix (Duncan 2015). This is an area that has been extensively evaluated as part of the NanoRelease project (Froggett et al 2014;Kingston et al 2014;Wohlleben et al 2017;Wohlleben and Neubauer 2016), particularly in the context of MWCNT embedded in composites. This earlier work has identified several key degradation mechanisms, and has included a number of studies that have specifically measured release via these various mechanisms.…”

Impact of UV irradiation on multiwall carbon nanotubes in nanocomposites: Formation of entangled surface layer and mechanisms of release resistance

“…MWCNTs are one nanofiller of concern for potential environmental and/or human health effects due to its high aspect ratio [7, 19–24]. There have been a number of studies conducted to date on release of MWCNTs due to mechanical stresses (e.g., abrasion, sanding, polishing) [1, 23, 25–35], yet fewer on the fate and release caused by environmental stresses [14, 17, 23, 31, 32, 36]. Recent studies on the potential toxicological effects of materials released from MWCNT nanocomposites have not shown increased toxicity compared to particles released from the polymer matrix under the environmental conditions tested [14, 23, 32, 33].…”