10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
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A New Risk Grouping Concept for High Aspect Ratio Materials - The Fibre Dustiness Test by Vibro-Fluidization
ELISABETH HEUNISCH, Dirk Broßell, Volker Bachmann, Nico Dziurowitz, Carmen Thim, Daniela Wenzlaff, John Schumann, Kerstin Kämpf, Asmus Meyer-Plath, Sabine Plitzko, Federal Institute for Occupational Safety and Health (BAuA)
Abstract Number: 471 Working Group: Aerosols and Health - Connecting the Dots
Abstract Introduction High aspect ratio materials (HARM) like carbon nanotubes (CNT) exhibit material properties that enable innovative applications but also raised concerns about potentially harmful effects to humans due to their asbestos-like morphology. Control banding by grouping of HARM by hazard- and exposure-related properties is a promising approach to risk assessment and risk mitigation for a large family of materials. Such grouping requires identifying dust release quantifying properties that enable a differentiation of HARM with low, moderate or high dustiness together with information on dust morphology.
Methods We have developed a dustiness test for powdery HARM and studied it for a broad range of CNT materials. Fibre dustiness testing was performed by vibro-fluidization that passes a low-volume airflow through a vertically vibrating powder column. Vibration allows overcoming adhesive forces between powdery agglomerates that would otherwise hinder fluidization. The vibro-fluidization method allows controlling airflow, vibration amplitude and frequency. The released aerosol was monitored and collected downstream to study the dust generation process and to determine process and material-related parameters. All collected samples were analysed by means of scanning electron microscopy (SEM) to obtain detailed information on the dust composition and its morphology.
Results and Discussion We performed dustiness tests on 15 different types of MWCNTs. The results allowed to develop a material ranking scheme based on the emission propensity for different morphological dust classes and to define distinct emission bands for low, moderate and high dustiness. SEM-based morphological analysis, of more than 500 emitted objects per material, enabled us to rank HARM according to their propensity to emit fibres in individual or agglomerated form. We also measured pair-wise distributions of diameter and length to identify and quantify potentially rigid fibres and those matching the WHO definition for potentially hazardous fibre geometry with a self-developed software. The obtained results form the basis of our proposed new grouping strategy for control banding that classifies HARM using a risk matrix. The matrix considers both intrinsic material and process-related properties such as bio-durability, toxicity as well as dustiness, grade of agglomeration and presence of hazardous WHO-fibres.