Abstract
The handling of carbon nanotube (CNT) powders is a plausible scenario during the course of the CNT life-cycle. However, related exposure data remain limited. In this context, information about the dustiness of CNT is therefore of great interest, for example for control banding or exposure modelling. Here, we investigate the dustiness of fourteen CNT powders using the Vortex Shaker (VS) method. The central component of the VS method is a stainless steel cylindrical tube, continuously shaken in a circular orbital motion, in which a small volume (0.5 cm3) of the powder to be tested is placed. All samples were obtained through the NANoREG Nanomaterials Information and Web-Order system. The test procedure that we have developed is based on four principal components: (i) a respirable cyclone for gravimetric sampling, (ii) a CPC as a reference instrument for number concentration measurement, (iii) an MPS for collection of particles for EM observations/analysis, and (iv) an ELPI for size-resolved aerosol measurement. In this paper, the data were evaluated using two parameters: (i) the mass-based dustiness index in the respirable fraction; and (ii) the number-based dustiness index in the respirable fraction. The results indicate that the method leads to relatively accurate mass- and number-based dustiness indices. The indices obtained span wide ranges, of 2 and 3 orders of magnitude variation for mass and number respectively, suggesting a corresponding significant difference in terms of potential exposure. EM observations reveal that airborne CNTs are mostly released as bundles of different shapes ranging from a few tens of nanometers up to tens of micrometers in size.
Highlights
IntroductionDustiness is a generic term used to define the ability of a powdered material (e.g., loose, granulated, or pelletized powders) to generate an aerosol (airborne particles) during handling
Dustiness is a generic term used to define the ability of a powdered material to generate an aerosol during handling
The technique was derived from an original concept that was developed as part of a field study devoted to evaluating the release of aerosols during the handling of single-walled carbon nanotubes (SWCNT) [11]
Summary
Dustiness is a generic term used to define the ability of a powdered material (e.g., loose, granulated, or pelletized powders) to generate an aerosol (airborne particles) during handling. The dustiness of a powder is an important determinant for worker exposure and should be considered during the design and operation of many industrial or research processes [1]. Dustiness has been a required input parameter in control banding (CB) tools used to evaluate and control the risk of exposure to nanomaterials [2, 3]. Its use is increasing in risk assessment, for example for the carbon nanotube group [4].
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