A pilot interlaboratory comparison of protocols that simulate aging of nanocomposites and detect released fragments
Wendel Wohlleben, Deborah S. Jacobs, Justin M. Gorham, Li Piin Sung, Tinh Nguyen
The safe use of nanocomposites depends, in part, on a good understanding of the fate of nanofillers throughout the nanocomposites lifecycle. Various modifications of ISO weathering protocols have been proposed to assess what is released and at which rate from the aging of nanocomposites. Here we investigated the variations of the nanoparticle release phenomenon in polymer nanocomposites by a pilot interlaboratory comparative aging study of a polyamide composite containing 4 mass % of silica nanoparticles (nanosilica). Both induced release by mechanical shear after dry weathering at different UV intensities and spontaneous release during wet weathering were studied. We observed that, although it did not influence the rate of polyamide degradation, nanosilica was enriched both on the remaining surface and in the released fragments. We also found that the characteristics of released fragments - which is the essential input for fate, transport and (eco-)toxicological testing were reproducible between different aging and analysis protocols. The released fragments were a polydisperse mixture of predominantly composite pieces from nanometer up to several micrometer in diameter and clustered or individual silica nanoparticles. The fraction of individual nanosilica was microscopically observed but could not be quantified. Simplified ultraviolet (UV) + immersion protocols can partially replace, complement, or extend accelerated weathering apparatus with run-off collection. A combined protocol is proposed for measuring the quantity of release fragments from polymer nanocomposites aged in different accelerated weathering apparatuses.