Dustiness of graphene and graphite.

Abstract

Graphene is among the most utilized nanoscale materials in the United States. It is a single-layer carbonaceous nanoscale material with a hexagonal structure. Subtractive synthesis from graphite is common in high-volume manufacturing, with graphene and graphite often present within the same workplace. There is little worker exposure data available to inform risk assessments, particularly for graphene. Dustiness determinations using EN15051-2 Workplace Exposure-Measurement of the Dustiness of Bulk Materials. Part 2: Rotating Drum Method were conducted for two graphene nanoplatelets, two graphene oxides, one few-layered graphene, one furnace carbon black, three natural and five synthetic graphites, and two coals. All 16 test materials were composed mostly of carbon. Dustiness determinations were compared to established thresholds for the inhalable, thoracic, and respirable particle size fractions. Measurements of specific surface area, moisture content, and unconsolidated bulk density were further obtained. Particles were imaged through scanning electron microscopy. The EN15051-2 test is a gentle gravity-induced procedure where the test material falls a limited distance. Dustiness determinations resulted in 2.2% or less of the test material collected in the inhalable size fraction, 0.89% or less in the thoracic, and 0.37% or less in the respirable subfraction. The thoracic fraction constituted ∼31% of the inhalable fraction overall. The masses of four of five graphenes were below the gravimetric limit of detection of 0.57 µg in the respirable size fraction. Contributing factors were the gentle nature of the test and low unconsolidated bulk densities (5.9 to 174 kg/m³) for the nanoscale materials, resulting in 0.21 to 6.1 g loaded masses. Modest enhancements to the testing protocol could potentially improve quantification for low-density materials. All test materials and quantifiable size fractions were classified as moderate or high dustiness on a mg/kg basis. The carbonaceous materials in this study have a moderate to high propensity of becoming airborne when subjected to a gentle gravity-induced stimulus. Without adequate controls to prevent dust emissions, handling could result in inhalation, dermal, and mucous membrane exposures as well as present slip, electrical, fire, and dust explosion hazards.