Biomedical Engineering Reference
In-Depth Information
Below we will summarize the results of simulated release and (workplace) exposure
scenarios as listed in Table 13.4. The simulated scenarios investigated are low energy
abrasion (Golanski et al. 2011, 2012; Schlagenhauf et al. 2012; Wohlleben et al. 2013)
and high energy abrasion (Golanski et al. 2012; Hirth et al. 2013), sanding (Cena and
Peters 2011; Huang et al. 2012; Wohlleben et al. 2013), grinding, polishing, cutting/
drilling (van Broekhuizen et al. 2011; van Landuyt et al. 2012, 2013; Methner et al.
2012; Fleury et al. 2013), and other high-energy impacts on nanocomposites (Sachse
et al. 2013; Golanski et al. 2012; Raynor et al. 2012).
With respect to CNT fragments released from machining from polymer matri-
ces, so far there is a consensus that the debris mass is dominated by micron-sized
composite fragments of matrix with bound CNTs, not by freely released CNTs, nei-
ther individually nor in bundles, for example, CNT-epoxy (Cena and Peters 2011;
Golanski et al. 2012; Huang et al. 2012, Hirth et al. 2013), CNT-polyurethane
(Schlagenhauf et al. 2012; Wohlleben et al. 2013; Hirth et al. 2013), and CNT-cement
(Hirth et al. 2013). Similar observations were made for release from nanoplatelet
composites (Raynor et al. 2012; Sachse et al. 2013), pigment composites with various
polymers (Golanski et al. 2011), and dental composites (van Landuyt et al. 2013).
In exception, Schlagenhauf et al. (2012) and Methner et al. (2012) identified free-
standing CNTs and nonagglomerated CNFs, respectively, due to machining (cutting,
grinding, and abrasion) of CNT or CNF containing composites. In addition, protru-
sions of CNTs at the composite fragments surface were observed (Cena and Peters
2011; Schlagenhauf et al. 2012; Hirth et al. 2013). Hirth et al. (2013) hypothesized
that the phenomenon of protrusion is material-depending, that is, brittle versus tough
matrix scenarios.
In general, it can be concluded that the number of particles released depends very
much on the level of input energy, for example, high shear wear by, for example,
turning speed, granular size of the sander paper, and the rigidity/hardness of the
matrix. Release of nanofiller has been associated with inhomogeneity of disper-
sion of the nanofiller in the matrix (Schlagenhauf et al. 2012; Golanski et al. 2012),
extreme high shear forces (Golanksi et al. 2012), or degradation of the matrix (Hirth
et al. 2013).
In the few cases where a shift of mode or mean diameter was observed between
nano- and non-nano control matrices, the tendency was that nano matrices shifted to
a slightly larger size mode.
13.4 DISCUSSION AND CONCLUSION
Over the last few years a tremendous progress in the area of exposure assessment
can be observed, both with respect to the development of devices and measurement
strategies, and the number of field exposure and laboratory release studies.
Recent developments underline the usefulness of tiered approaches and the use of
control banding tools based on exposure models, as first tier estimates of the poten-
tial for release. Furthermore, the usefulness of dose-estimating measurement devices
that mimic deposition curves has been identified (Fissan et al. 2007), and (a) prepro-
totypes of a wide-range size resolving personal sampler (2 nm-5 µm) up to 8 size
fractions, (b) a sampler for aerosol fraction deposited in the gas-exchange region
Search WWH ::
Custom Search