Continuous dry dispersion of multi-walled carbon nanotubes to aerosols with high concentrations of individual fibers

Barbara Katrin Simonow,Mikolaj Jandy,Carmen Thim,Daniela Wenzlaff,Asmus Meyer-Plath,Sabine Plitzko,Jana Thiel,Nico Dziurowitz

doi:10.1007/s11051-018-4262-y

Abstract

The assessment of the toxicity of airborne nanofibers is an important task. It relies on toxicological inhalation studies and validated exposure measurement techniques. Both require nanofiber-containing aerosols of known morphological composition and controlled fraction of individual fibers. Here, a dry powder dispersion method is presented that operates with mixtures of nanofibers and microscale beads. Aerosolization experiments of mixtures of multi-walled carbon nanotubes (MWCNTs) and glass beads that were continuously fed into a Venturi nozzle enabled high generation rates of aerosols composed of individual and agglomerate nanofiber structures. The aerosol process achieved good stability over more than 2 h with respect to concentration and aerodynamic size distribution. Its operation duration is limited only by the reservoir volume of the cyclone used to separate the beads from the aerosol. The aerosol concentration can be controlled by changing the mass ratio of MWCNTs and glass beads or by adapting the mass feed rate to the nozzle. For two agglomerated MWCNT materials, aerosol concentrations ranged from 1700 to 64,000 nano-objects per cm3. Comprehensive scanning electron microscope analysis of filter samples was performed to categorize and determine the morphological composition of the aerosol, its fiber content as well as fiber length and diameter distributions. High fractions of individual fibers of up to 34% were obtained, which shows the setup to be capable of dispersing also highly tangled MWCNT agglomerates effectively.

Highlights

The unique properties of carbon nanotubes (CNTs) make them a widely studied material with promising commercial applications
While highly tangled multi-walled CNTs (MWCNTs) agglomerates with granular morphology have been reported to show no fiber-toxic effect (Pauluhn 2009), inhalation exposure studies of well-dispersed MWCNTs have observed asbestos-like carcinogenicity (Oberdörster et al 2015)
To test the performance of the dry dispersion aerosolization system, mixtures were prepared of glass beads with either pristine ARIGM001 or pristine Baytubes MWCNTs in different mass ratios

Summary

Introduction

The unique properties of carbon nanotubes (CNTs) make them a widely studied material with promising commercial applications. The production capacity and use of CNTs have been reported to steadily increase (De Volder et al 2013). In accord to the fiber toxicology paradigm (Pott and Friedrichs 1972; Stanton and Wrench 1972), their fibrous morphology and biodurability have raised concerns about potential lung carcinogenicity especially for multi-walled CNTs (MWCNTs). While highly tangled MWCNT agglomerates with granular morphology have been reported to show no fiber-toxic effect (Pauluhn 2009), inhalation exposure studies of well-dispersed MWCNTs have observed asbestos-like carcinogenicity (Oberdörster et al 2015). Mercer et al (2013) have shown that individual and short MWCNT structures may translocate to secondary organs like the liver. Characteristic for asbestos, was observed for MWCNTs

Methods

Results

Conclusion