Particle and fiber exposures during processing of hybrid carbon-nanotube advanced composites

Particle and fiber exposures, especially those at the nanoscale with as yet unknown toxicological effects, are a major concern in any manufacturing environment. In this study, airborne exposures to nano- and micro-scale particles and fibers generated during CNT synthesis, handling, and abrasive machining of advanced laminated composites containing carbon nanotubes (CNTs) are studied. Particle release during wet and dry machining is studied for two three-phase nanoengineered advanced composite systems comprised of micron-diameter advanced fibers and nanometer-diameter CNTs embedded in thermoset polymer matrices. CNTs in the study have high aspect ratio being ∼10 nm in diameter and range in length from 50-100 microns. Exposures were monitored with a suite of complementary instruments, including real time particle number concentration and size distribution. Transmission electron microscopy with EDX is utilized to characterize morphology and elemental composition of particles, fibers and CNTs. CNTs, either individual or in bundles, were not observed in collected samples including during abrasive machining. However, significant amounts of particles as well as nanoscale and respirable fibers were generated in such processes as expected. The common practice of wet cutting was shown to be highly effective in keeping overall exposures consistently at background levels. Further investigation is required to determine the effects of numerous variables on particle release including specimen and tool geometry, CNT synthesis variables, cutting rates, and polymer systems and processes.