Mechanisms of Aging and Release from Weathered Nanocomposites - Safety of Nanomaterials along Their Lifecycle - page 326

put the SiO 2 amounts released by simulations of real-world scenarios into context.
Nguyen and coworkers finally also screened the spontaneous release via the air-
borne phase. A polytetrafluoroethylene (PTFE) sample collector was placed below
the vertically fixed nanoSiO 2 -epoxy nanocomposite during irradiation (Nguyen
et al. 2011; Nguyen et al. 2012). Microscopic analysis (SEM) of the PTFE collec-
tor after irradiation revealed the presence of fragments, which can only have fallen
off the nanocomposite. These fragments contained Si and O elements (determined
by EDXS), allowing identification of spontaneous release, albeit with unknown
polymer/nanoiller ratio and unknown quantification.
The complementary study of induced release into the atmosphere was performed
by Stintz and coworkers, who first irradiated PU and polyacrylate coatings contain-
ing ZnO or Fe 2 O 3 nanoparticles (following EN 927-6:2006), then released by a sand-
ing process (Göhler et al. 2010). The number of aerosol particles with diameters
below 100 nm systematically increased as determined by engine exhaust particle
sizer (EEPS), typically by a factor of 2-8 compared to the nonirradiated samples.
However, the SEM and TEM analysis of morphology and EDX analyses of material
identified these airborne particles as fragments of the matrix with bound nanofillers,
not as individual nanofillers. Results of a further study confirmed these findings.
Herein, investigations on the sanding-induced particle release were performed based
on artificially weathered (ISO 11341:2004) polyacrylate coatings and PP plastics
containing different kinds of nanopigments. In contrast to the coatings, the weather-
ing-caused change in the number of released particles showed a systematic decrease
for the analyzed PP samples (Göhler et al. 2013a).
14.4 CHARACTERIZATION OF RELEASED FRAGMENTS:
DETECTION, QUANTIFICATION, IDENTIFICATION
After either spontaneous or induced release, all studies used electron microscopy,
mostly SEM, some TEM, to detect if release occurred. Sampled fragments on col-
lectors, air filters, or liquid aliquots were in many cases identified by elemental infor-
mation (EDXS, ICP-MS) or further by chemical information (TGA, XPS, FTIR).
In the airborne state, the same instruments as for release from sanding (compare
Chapter 12) were employed for quantification (often CPC), which can additionally
be coupled to classification steps to derive also size-classified quantification, with
different detection limits of fast mobility particle sizer (FMPS), EEPS, and scanning
mobility particle sizer (SMPS) (Göhler et al. 2013a). Especially for low forces and
hence low release rates, the background dominates even under clean-room condi-
tions with less than 1,000 particles/cm³, so that no size information can be extracted
without sampling and identification of released fragments against the background.
In liquids (immersion or run-off waters), several complementary methods can
quantify the released fragments: ICP-MS and ICP-OES to quantify all released
nanofillers regardless of fragment morphology, gravimetry to quantify all released
fragments together (Busquets-Fite et al. 2013), and ultracentrifugation with spec-
troscopy of supernatants to quantify free nanofillers selectively. If coupled with syn-
chronized refractive index detection, the ultracentrifugation approach (AUC-RI) has