Workers' Exposure Assessment during the Production of Graphene Nanoplatelets in R&D Laboratory

Abstract

Widespread production and use of engineered nanomaterials in industrial and research settings raise concerns about their health impact in the workplace. In the last years, graphene-based nanomaterials have gained particular interest in many application fields. Among them, graphene nanoplatelets (GNPs) showed superior electrical, optical and thermal properties, low-cost and availability. Few and conflicting results have been reported about toxicity and potential effects on workers' health, during the production and handling of these nanostructures. Due to this lack of knowledge, systematic approaches are needed to assess risks and quantify workers' exposure to GNPs. This work applies a multi-metric approach to assess workers' exposure during the production of GNPs, based on the Organization for Economic Cooperation and Development (OECD) methodology by integrating real-time measurements and personal sampling. In particular, we analyzed the particle number concentration, the average diameter and the lung deposited surface area of airborne nanoparticles during the production process conducted by thermal exfoliation in two different ways, compared to the background. These results have been integrated by electron microscopic and spectroscopic analysis on the filters sampled by personal impactors. The study identifies the process phases potentially at risk for workers and reports quantitative information about the parameters that may influence the exposure in order to propose recommendations for a safer design of GNPs production process.

Keywords: 2D nanostructures; exposure assessment; graphene nanoplatelets; nanotechnologies; occupational safety and health; risk mitigation.

Figure A1

UF3—PNC calibration (a) and UF4—PNC calibration (b).

Figure A2

UF3—D_avg and LDSA calibration by means Idiff (a) and Ifilter (b) parameters.

Figure A3

UF3—PNC calibration (a), UF5—PNC calibration (b), UF4—PNC calibration (c).

Figure A3

UF3—PNC calibration (a), UF5—PNC calibration (b), UF4—PNC calibration (c).

Figure A4

UF5—D_avg and LDSA calibration (a,b), UF5—D_avg and LDSA calibration, UF4—D_avg and LDSA calibration (c,d).

Figure 1

SEM images of the graphite intercalated compound (a), the worm-like expanded graphite (b) and graphene nanoplatelets’ (GNPs’) morphology (c,d) and STEM images of GNPs morphology (e,f).

Figure 2

Atomic force microscopy (AFM) morphology of a GNP (a) and height profile along three different sections (b).

Figure 3

Scheme of the GNPs production process.

Figure 4

Schematic layout of the production labs.

Figure 5

Time series of particle number concentration (PNC; a), lung deposited surface area (LDSA; c) and modal average diameter (D_avg; e) referred to the thermal expansion at 1150 °C (phase 1A) and time series of PNC (b), LDSA (d) and D_avg (f) referred to the liquid exfoliation (phase 1B).

Figure 6

Time series of PNC (a), LDSA (c) and D_avg (e) referred to the thermal expansion at 1050 °C (phase 2A) and time series of PNC (b), LDSA (d) and D_avg (f) referred to the liquid exfoliation (phase 2B).

Figure 6

Time series of PNC (a), LDSA (c) and D_avg (e) referred to the thermal expansion at 1050 °C (phase 2A) and time series of PNC (b), LDSA (d) and D_avg (f) referred to the liquid exfoliation (phase 2B).

Figure 7

EDS spectrum of the material collected during the thermal expansion process by the Sioutas on the backup filter (a–c), two magnifications of a SEM image of the material collected on the backup filter (d,e) and a SEM image of the filter C (f) with “worm-like” expanded graphites (WEGs) highlighted in the red circle.

Figure 8

Residual curve of phase 1A (a) and phase 2A (b) as the difference between the PNC time series of the personal and the environmental instrument.