Scaling up the graphene production from R&D to the pilot plant stage. Implications for workers' exposure to airborne nano-objects

Given the exceptional thermal, electrical, and mechanical properties of graphene, the interest is now shifting from scientific and technological application to industrial deployment, testified by the significant increase in demand for graphene-based products. Consequently, it is paramount that occupational safety and health (OSH) research now places utmost importance on ensuring the well-being of workers at every stage of graphene production. The present study evaluates workers' exposure potential during the production cycle of few-layer graphene (FLG) by liquid-phase exfoliation, incorporating the Prevention-through-Design approach in the transition from the laboratory scale to the pilot plant production. A measurement campaign was conducted according to the multi-metric approach proposed by the Organization for Economic Cooperation and Development and European Committee for Standardization guidelines. Multi-metric real-time instruments were used to determine particle number concentration (PNC), particle size distribution and lung deposited surface area (LDSA) along with time-integrated instrumentation to collect airborne ultrafine dust for off-line gravimetric analysis and chemical and morphological characterization. The obtained data indicate that the FLG powders storage, including the cleaning of equipment and surfaces, is the most critical step for exposed workers, with higher levels of PNC and LDSA compared to the other production phases. Recommendations for OSH risk mitigation strategies in the scaling up of the FLG production process have been proposed according to OSH principles for nano and advanced materials development. In particular, production and storage of FLG in liquid suspension or bound to a solid matrix should be preferred rather than in powder form. When not possible, a closed system with local exhaust ventilation is recommended. Finally, if the particles transport towards other areas of the plant is not properly mitigated, the sole use of personal protective equipment during the powder handling phases will be not sufficient for protecting workers from the potential exposure.