Aerosol Emission Monitoring and Assessment of Potential Exposure to Multi-walled Carbon Nanotubes in the Manufacture of Polymer Nanocomposites

Abstract

Recent animal studies have shown that carbon nanotubes (CNTs) may pose a significant health risk to those exposed in the workplace. To further understand this potential risk, effort must be taken to measure the occupational exposure to CNTs. Results from an assessment of potential exposure to multi-walled carbon nanotubes (MWCNTs) conducted at an industrial facility where polymer nanocomposites were manufactured by an extrusion process are presented. Exposure to MWCNTs was quantified by the thermal-optical analysis for elemental carbon (EC) of respirable dust collected by personal sampling. All personal respirable samples collected (n = 8) had estimated 8-h time weighted average (TWA) EC concentrations below the limit of detection for the analysis which was about one-half of the recommended exposure limit for CNTs, 1 µg EC/m 3 as an 8-h TWA respirable mass concentration. Potential exposure sources were identified and characterized by direct-reading instruments and area sampling. Area samples analyzed for EC yielded quantifiable mass concentrations inside an enclosure where unbound MWCNTs were handled and near a pelletizer where nanocomposite was cut, while those analyzed by electron microscopy detected the presence of MWCNTs at six locations throughout the facility. Through size selective area sampling it was identified that the airborne MWCNTs present in the workplace were in the form of large agglomerates. This was confirmed by electron microscopy where most of the MWCNT structures observed were in the form of micrometer-sized ropey agglomerates. However, a small fraction of single, free MWCNTs was also observed. It was found that the high number concentrations of nanoparticles, ~200 000 particles/ cm 3 , present in the manufacturing facility were likely attributable to polymer fumes produced in the extrusion process.

Airborne engineered nanomaterials in the workplace—a review of release and worker exposure during nanomaterial production and handling processes

“…Handling nanopowders in an exhaust hood [31]; transferring from storage container to a balance [7]; weighing inside a fume hood [41]; mixing nanofibers with solvents [41]. mixing CNTs powders with polymer melt in an extrusion process [42] or during injection moulding [43,44] Machining & abrasion…”

“…Weighing, transferring & mixing* Metal/metal oxides: TiO2 [6,24,35], Al2O3 [14,35], CuO [6], SiO2 [21], ZnO [9], MgO/Y2O3/CaO/FeO [35], CeO2 [58], Ag [6,14], Si [19], indium tin oxide [9]; Carbonaceous: MWCNT [6,7,28,36,42,52], CNTs [43,44], carbon black [7], nanofibers [31], carbon nanofibers [6,41], fullerenes [6,7], carbon nanodiscs/carbon nanocones [28]; Others: ceramic powders [31].…”

“…Additionally, a rotarytype oil vacuum pump was identified as a source of 300 nm particles [36]. Polymer fume condensate can release nanoparticles during nanocomposite manufacturing by extrusion processes [42,44,71]. The studies were able to distinguish these secondary releases of nanoscale particles by comparing the aerosol profiles (size and concentration) obtained with and without their potential sources.…”

“…Figure 4. Near-source airborne ENM particle concentrations (left) and sizes (right) (modal size or estimation from transmission electron microscopy analysis) in workplaces, ranked by production and handling activities (data source: In most of the cases, released airborne ENMs were agglomerates or aggregates, often resulting in complex particle morphologies, such as loose, porous clusters of metal oxides particles [6], densely packed Ag particles [72], entangled CNFs [31,69], chain-like structures of CNTs [68] or in certain cases combining with other background particulate matters [42,47]. Only one study reported individual Ag vapor condensate particles [73].…”

Elucidating the Potential Biological Impact of Cellulose Nanocrystals

“…During these latter stages of the life-cycle, the risk of exposure can mostly be attributed towards the possible abrasion of the product, which could result in the release of individual CNCs, small CNC aggregates, or nanocellulose-polymer composite (nano)particles, which could be subsequently inhaled or penetrate through the skin upon contact. Recent research on this matter has again focused upon CNTs [51][52][53]. From these initial studies it has been postulated that the release of CNTs, at least in their bare form and also combined with polymer matrix is relatively low.…”