In this study, the characteristics of airborne particles generated during injection molding and grinding processes of carbon nanotube reinforced polycarbonate composites (CNT-PC) were investigated. Particle number concentration, size distribution, and morphology of particles emitted from the processes were determined using real-time particle sizers and transmission electron microscopy. The air samples near the operator’s breathing zone were collected on filters and analyzed using scanning electron microscope for particle morphology and respirable fiber count. Processing and grinding during recycling of CNT-PC released airborne nanoparticles (NPs) with a geometric mean (GM) particle concentration from 4.7 × 103 to 1.7 × 106 particles/cm3. The ratios of the GM particle concentration measured during the injection molding process with exhaust ventilation relative to background were up to 1.3 (loading), 1.9 (melting), and 1.4 (molding), and 101.4 for grinding process without exhaust ventilation, suggesting substantial NP exposures during these processes. The estimated mass concentration was in the range of 1.6–95.2 μg/m3. Diverse particle morphologies, including NPs, NP agglomerates, particles with embedded or protruding CNTs and fibers, were observed. No free CNTs were found during any of the investigated processes. The breathing zone respirable fiber concentration during the grinding process ranged from non-detectable to 0.13 fiber/cm3. No evidence was found that the emissions were affected by the number of recycling cycles. Institution of exposure controls is recommended during these processes to limit exposures to airborne NPs and CNT-containing fibers.
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This research was supported by the NSF Grants 120329 and 0425826 and in part by a seed grant from the UC Center for Laboratory Safety. We are grateful to Dr. Earl Ada for his assistance with TEM and SEM analysis, and Dr. Rebecca Gore for her advice with statistical analysis. We also would like to sincerely thank Dr. Eileen Birch of NIOSH for her efforts to analyze CNT-PC and airborne samples for their CNT content and Dr. Martin Shafer of the University of Wisconsin for his assistance with the SF-ICP-MS analysis of the airborne dust.
The authors declare no conflict of interest.
Supplementary Information accompanies the paper on the Journal of Exposure Science and Environmental Epidemiology website
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