Case Study Paints and Lacquers with Silica Nanoparticles - Safety of Nanomaterials along Their Lifecycle - page 385

indoor (Indoor acryl), outdoor acrylic (Outdoor acryl) paint and UV hard coat lacquer
(Lacquer), and a binder (Binder). Sanding was performed using a handheld electri-
cally powered orbital sander (Metabo Model FSR 200 Intec) mounted with grit 240
sanding paper. The airborne dust was drawn from the sanded surface through the
sander fan and collected at 100 m 3 /h from the in-built filter chamber in the sander
(Koponen et al. 2011). The dust was then passed through a 0.03 m 3 mixing chamber
where it was monitored using a TSI Fast Mobility Particle Sizer (FMPS) Model 3091
and a TSI Aerodynamic Particle Sizer Model 3321 mounted with a TSI Diluter Model
3302A and finally collected in a modified commercial electrostatic precipitator. The
sampled dust was used for subsequent characterization and toxicological studies
(Saber et al. 2012b; Saber et al. 2012c). The work was performed in a HEPA-filtered
exposure chamber and the mixing air was additionally HEPA filtered to reduce the
risk of contamination from the chamber air during sampling.
It was found that all the airborne sanding dust was complex and had a wide size
distribution, which could be described in five size modes (Figures 17.1c, 17.1d, and
17.2). The two finest size modes occurred at ca. 10 and 12-23 nm and were domi-
nated by emissions from the electrically powered sander. The third size mode was
0.05 µm in lacquer and 0.13-0.18 µm for paints. The two coarser size modes were
located at 0.9-1.2 µm and 1.6-2.0 µm, respectively, again with lacquer dust at the
lower ranges. The three upper size modes were highly dominated by paint- and lac-
quer-generated sanding dust. It appeared that these three dust size modes were spe-
cific for each product and that they generally only changed to a minor degree after
addition of nanofillers, whereas the number of particles in each size mode usually
increased (Koponen et al. 2011).
In the specific experiments with the nanosilica-doped acrylic paint (ca. 10 wt%
Bindzil CC30) and UV hard coat lacquer (ca. 5 wt% Nanocryl), the three sanding
dust size modes were also practically unchanged. However, the addition of nanosilica
appeared to have opposite effects on the number concentrations of the sanding dust. In
the case of the acrylic paint, the number of mode 3 particles significantly increased after
addition of Bindzil 30CC (Figure 17.2a). In the case of UV hard coat lacquer the number
of particles significantly decreased in all three sanding dust size modes (3, 4, and 5)
after addition of Nanocryl (Figure 17.2a). However, normalized to the total number con-
centrations in each of the sanding dust size spectra, a ca. 1.4 increase was observed for
mode 3 particle concentration of the acryl paint dust and a major decrease in the coarser
size modes 4 and 5, after addition of Bindzil 30CC (Figure 17.2b). As before, the relative
changes in the UV hard coat dust are different with negligible to minor change in the
normalized concentrations of mode 3 and mode 5 particles, and an almost doubling of
size mode 4 particles (1.8 times) after addition of Nanocryl (Figure 17.2b). This demon-
strates highly different consequences in the emission characteristics, which may be due
to both the type of matrix and the type and amount of nanofiller added.
17.4 HUMAN SAFETY
The scientific literature on toxicological tests of silica nanoparticles intended for use in
nanomaterial-based paints and lacquers appears to be rather scarce. Similarly, only a few
studies have looked into the potential hazards of dusts generated by sanding paints and