NanoRelease Weathering Protocol interlab-tested on CNT in 2 matrices, intralab-applied to 27 NM-matrix combinations: Matrix matters most

W. Wohlleben, R.G. Zepp, E. Sahle-Demessie, S. Vázquez-Campos, J. Carter, C. Kingston, R. Canady, B. Acrey, C-Y Chen
BASF SE,
Germany

Keywords: lifecycle, release, weathering, CNT, metal oxides, organic pigments

Summary:

Release assessment regards the detachment of a fragment from a larger whole, such as a consumer product during use, and includes the release mechanism, form of the released entity, release scenario, probability of release, and lifecycle simulation, if relevant (Harper et al., 2015). In the case of nanocomposite matrix with embedded nanomaterials,(Stark et al., 2015) a release event might encompass an emission of the nanomaterial. We speculated that the matrix should strongly impact release rates, and extrapolated from the known photodegradation susceptibility that weathering release rates should rank highest for epoxy composites, less for polyurethane (PU), polyamide (PA) and polycarbonate (PC) and least from polyethylene (PE) composites (Kingston et al., 2014). We weathered CNT-epoxy and CNT-PA composites in four aging labs in the US and Europe, and analyzed the bulk aging and the fragments sampled into leaching media by shaking and sonication, in analysis labs in the US, Canada and Europe. The results confirm that weathered CNT-epoxy is prone to release fragments that can be identified, compared and quantified by established methodology. It might thus serve as positive control Benchmark Material in release studies, as it also clearly differentiates from CNT-PA in released entity and probability of release. Beyond NanoRelease, market-relevant nanocomposites were investigated by the SUN and MARINA projects and BASF. We selected datasets that are compliant with the NanoRelease protocol and re-analyzed these datasets “orthogonally” to the original design of the campaigns: We compare not only different nanomaterials in the same matrix, but compare different matrices with same or different nanomaterials, and compare neat matrices with no fillers at all. Released fragments from in total 27 materials are analyzed by size-selective quantification of all fragments below 150nm diameter. Rescaled for immersion volumes, the release rates in units of mg/m² per MJ/m² photons rank primarily by the matrix, with less than a factor 10 up- or down-modulation by the embedded metal-oxide, carbonaceous, or organic nanomaterials. We experimentally confirm the working hypothesis of Kingston et al. (2014) that release phenomena can be extrapolated from the susceptibility of the matrix – in fact this holds true across 5 orders of magnitude of release rates. Further, we confirm their prediction that PE would result in lowest release rates of nanomaterials, epoxy and cement among the highest release rates, with PA and PU at intermediate rates. The work was partially funded by the SUN and MARINA projects, which receive funding from the European Union FP7 (grant agreements n° 604305 and n° 236215). Kingston, C., et al. (2014). Release Characteristics of Selected Carbon Nanotube Polymer Composites. Carbon, 68, 33-57. Harper, S., et al. (2015). Measuring Nanomaterial Release from Carbon Nanotube Composites: Review of the State of the Science. J. Phys: Conf Series, 617(1), 012026. Wohlleben, W. and Neubauer, N. (2016) Quantitative rates of release from weathered nanocomposites are determined across 5 orders of magnitude by the matrix, modulated by the embedded nanomaterial. NanoImpact, submitted. Stark, W. J., et al. (2015). Industrial applications of nanoparticles. Chem Soc Rev. doi:10.1039/C4CS00362D