Biomedical Engineering Reference
In-Depth Information
The most commonly reported size modes are between 20 and 80 nm. Koivisto et al.
(2011) reported in the area of a laminar flow reactor a GMD of 80 nm (1.8), and
D
AED
GMD of 120 nm (1.7). During liquid flame spraying synthesis a
D
mob
GMD of 14 nm
(1.8) was reported by Koivisto et al. (2012b).
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Powder handling activities are related to the actual production of nanomaterials,
for example, collection and harvesting during (gas-phase) synthesis and packing,
for example, bagging, as well as to downstream processes using nanomaterials for
the manufacturing of nano-enabled products, for example, bag dumping, weighing,
scoping and so on, and low energy dispersion into composites. A substantial number
of workplace studies reported the resulting (combined) exposure from several activi-
ties (Table 13.2).
Especially in the assessment of powder handling scenario, it has been observed
that exposure mostly results from agglomerates and aggregates, which contribute to
relatively high mass concentrations, whereas their contribution to the elevation of
particle number concentration is very limited. Curwin and Bertke (2011) and Tsai
et al. (2011) reported MMAD of 4 µm and larger. Several authors, for example,
Koivisto et al. (2012a) and Dahm et al. (2013), propose for these scenarios to focus
on mass concentration or include PSD up to 10,000 nm in the measurement setup.
Dahm et al. (2013) clearly demonstrated that activity-based measurements by direct
reading instruments (DRIs) have limited value with respect to quantification of expo-
sure. In their workplace study on exposure to CNTs and CNFs, they used both per-
sonal and workplace sampling followed by off-line detection of elemental carbon
(EC) and CNT structure counts by TEM and DRIs. They observed no correlation
between the results from sampling and off-line analysis and time-weighted averages
of DRI results for corresponding processes. This is partly due to the high correlation
of time series, as has been reported earlier by Klein Entink et al. (2011).
In general, clear indications on which powder handling scenario will result in the
highest exposure concentrations cannot be extracted from these studies. Recently
published results of a survey amongst 19 workplaces revealed increased particle
number concentrations in the size range between 10 and 100 nm, compared to bag-
ging of powders; however, the opposite was observed for particles with size ranges
above 100 nm (Brouwer et al. 2013). Currently, data are lacking that confirm that
amount of powder handled and level of energy, for example, fall-height, are major
modifying factors of exposure.
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A number of (experimental) studies have been published (Table 13.3) that report the
dispersion of nano-enabled products for personal care or surface coating by spray
cans or hand pumps (Nørgaard et al. 2009; Chen et al. 2010; Lorenz et al. 2011;
Nazarenko et al. 2011; Quadros and Marr 2011; Bekker et al. 2013). The use of
nanosprays is relevant for both consumers, personal care (hair, facial, and antiperspi-
rant spray), and professional use (hair products, leather impregnation, disinfections,
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