Characterization of aerosols released during handling or processing operations of MWCNTs

Abstract : The goal of this study was to characterize the release at the source and potential for exposure to multi-walled carbon nanotubes (MWCNTs) in an industrial pilot plant. Various operations had been investigated: cleaning of the gas phase reactor, filling bins with MWCNTs powder, hot compounding of MWCNT-containing polymer composites and dry cutting of the composites into mm-sized pellets. In addition, manual transferring and sieving of MWCNTs have been examined with the intention of investigating a worst case potential exposure scenario. The activities were operated in normal conditions, with the exception of the simulation of the worst case scenario of manual transferring and weighing for which extreme precautionary principles were adopted. Background conditions were determined in parallel. Overall particle concentration levels, size distributions were not significantly different for the reactor cleanout and filling bins operations from the background aerosol that could be attributed to the outside air that fed the workplace atmosphere. The hot compounding and dry cutting processes resulted in particle concentration levels and size distributions significantly different from the background. Besides polymer fragments and carbonaceous aggregates, few possible polymer fragments containing MWCNTs were observed on EM micrographs of aerosol samples collected close to the source. The results obtained during the manual transferring and sieving as a worst case potential exposure scenario demonstrate an association between the activity and the increase of the particle concentration and the modification of the size distribution. EM micrographs indicated that MWCNTs existed mainly as bundles whose size ranged from approximately a few 100 nm to 10 µm.