Exposure to nanoscale particles and fibers during machining of hybrid advanced composites containing carbon nanotubes
This study investigated airborne exposures to nanoscale particles and fibers generated during dry and wet abrasive machining of two three-phase advanced composite systems containing carbon nanotubes (CNTs), micron-diameter continuous fibers (carbon or alumina), and thermoset polymer matrices. Exposures were evaluated with a suite of complementary instruments, including real-time particle number concentration and size distribution (0.005–20 μm), electron microscopy, and integrated sampling for fibers and respirable particulate at the source and breathing zone of the operator. Wet cutting, the usual procedure for such composites, did not produce exposures significantly different than background whereas dry cutting, without any emissions controls, provided a worst-case exposure and this article focuses here. Overall particle release levels, peaks in the size distribution of the particles, and surface area of released particles (including size distribution) were not significantly different for composites with and without CNTs. The majority of released particle surface area originated from the respirable (1–10 μm) fraction, whereas the nano fraction contributed ~10% of the surface area. CNTs, either individual or in bundles, were not observed in extensive electron microscopy of collected samples. The mean number concentration of peaks for dry cutting was composite dependent and varied over an order of magnitude with highest values for thicker laminates at the source being >1 × 106 particles cm−3. Concentration of respirable fibers for dry cutting at the source ranged from 2 to 4 fibers cm−3 depending on the composite type. Further investigation is required and underway to determine the effects of various exposure determinants, such as specimen and tool geometry, on particle release and effectiveness of controls.
KeywordsNanoparticle Nanocomposite Fiber CNTs Airborne exposures Occupational health Nanotechnology EHS
This work was supported under the Nanoscale Science and Engineering Centers Program of the National Science Foundation (Award # NSF-0425826) and by Airbus S.A.S., Boeing, Embraer, Lockheed Martin, Saab AB, Spirit AeroSystems, and Textron Inc. through MIT’s Nano-engineered composite aerospace structures (NECST) Consortium. Namiko Yamamoto acknowledges support from the Linda and Richard (1958) Hardy Fellowship. Authors would like to thank Dr. Arthur Miller of NIOSH for his generous offering of the prototype electrostatic precipitator and C. Santeufemio and Dr. Earl Ada of the UML Materials Characterization Lab for their technical assistance with EM analysis.
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