Release from Composites by Mechanical and Thermal Treatment - Safety of Nanomaterials along Their Lifecycle - page 264

materials (e.g., with band-saw, rotary cutting wheel, and wet saw cutting). Wet cut-
ting and sawing are sometimes used to reduce heat.
Bello et al. (2009a) investigated airborne exposures to nanoscale particles and
fibers, which were generated during dry and wet abrasive machining of two three-
phase advanced composite systems containing CNTs, micron-diameter continuous
fibers (carbon or alumina), and thermoset polymer matrices. The schematic layout of
the research laboratory is very similar to that shown in Figure 12.11. Two methods
were applied: band-saw and a rotary cutting wheel. The band-saw blade was a dia-
mond grit (220 grit, 60 µm) specific for composite machining and used with a blade
speed of 20 m/s and a rate of advance of 0.2-0.4 cm/s. The composite cutting wheels
employed used the same kind of abrasive surface as the band-saw, but with water
to flush dust particles during machining, a speed of 15 m/s and a rate of advance of
0.4 cm/s. The cutting wheel was covered with guards on all sides, which helped to
reduce aerosol emissions.
The duration of one cut was on average 5-15 s, so several cuts were performed on
each composite to improve reliability of the data. The whole cutting cycle of 4-5 cuts
lasted 1-3 min. Measurements of airborne particles during the cutting were detected
by FMPS, APS, and CPC. Additionally, particles were collected for subsequent elec-
tron microscopy characterization.
Wet cutting, the common approach, did not significantly increase the parti-
cle number concentration above background whereas dry cutting, without any
emission controls, resulted in high airborne concentrations of nanoscale and fine
particles, as well as submicron and respirable fibers. The results showed that par-
ticle release depended on composite thickness and type, but the concentration of
nanoscale, fine particles, and fibers did not vary between composites without and
with nanofiller.
Stahlmecke et al. (2014a) investigated the sawing process of novel building insu-
lation materials. For the schematic setup of the test room see Figure 12.13. To assess
the number size distribution of the particles in the test room an FMPS, APS, and a
CPC were employed. An ESP was used for sampling and subsequent SEM analy-
sis. Sawing of the materials into smaller pieces was simulated using an electrical
jigsaw operated with 1500 strokes per minute. A piece of material with a width
of 15 cm was cut into four smaller pieces. Therefore, three lines, corresponding
to an operation time of approximately 30 s of the jigsaw, were cut during each
experiment. For an MDF-board as the comparison material and the experimental
nanomaterial composite board, a blade intended for wood was used. In the case of
the hard Rockpanel ® , a blade intended for metal had to be used. Five repetitions for
each material and each task were conducted. The results showed for all materials
significantly higher concentrations of nanoscale particles as well as micrometer-
range particles but without a difference between the materials without and with
nanoporous additive.
Even though sawing was employed and tested in several studies no single defined
method can currently be identified. Research on the test procedure, setup, and
parameters still has to be conducted to be able to suggest a reliable test method for
nanomaterial release by cutting and sawing.