Quantitative rates of release from weathered nanocomposites are determined across 5 orders of magnitude by the matrix, modulated by the embedded nanomaterial

Abstract

Major uses of nanomaterials are as functional fillers embedded in a solid matrix, such as plastics, tires, and coatings. Degradation of the solid matrix during the use phase can lead to a release of the nanomaterial and of fragments which might further degrade and release nanomaterials or smaller fragments in secondary processes. Here we focus on release induced by weathering, and specifically on quantitative rates of the mass of fragments released in the size range between 2nm and 10μm. We combine data from several experimental campaigns and 27 materials, using identical aging and sampling intensities, and identical analysis technique. The protocol specifies ISO4892 conditions of UV aging, optionally with rain, then immersed sonication, then size-selective quantification. All of these are elements of the protocol that was developed and pre-validated in a pilot international interlab comparison by the NanoRelease initiative. We rescaled releases for UV dose and immersion volumes, and find that the resulting release rates in units of mg release per MJ photons are determined across 5 orders of magnitude by the matrix (PE, PU, PA, POM, epoxy, cement), with less than a factor 10 up- or down-modulation by the embedded metal-oxide, carbonaceous, or organic nanomaterials. Variations of the aging and sampling conditions or a restriction of quantification to the size range from 2nm to 150nm do not affect this conclusion. Our results enable more realistic mass flow modeling and suggest limits in which release rates of nanocomposite materials can be estimated from rates measured on the neat matrix.