Three-dimensional printer emissions and employee exposures to ultrafine particles during the printing of thermoplastic filaments containing carbon nanotubes or carbon nanofibers

Recent studies have reported emission rates of up to 1012 ultrafine particles/min from fused filament fabrication three-dimensional printers when operated in unventilated or minimally ventilated test chambers. However, in these studies, there are no data to relate this rate to airborne concentrations in a manufacturing environment. An assessment of particle exposures of workers was conducted at a three-dimensional printing shop using multiple fused filament printers with unfilled and carbon nanotube and/or carbon nanofiber-infused polyetheletherketone filaments. The study simultaneously evaluated emissions in two environments: (1) in a field portable test chamber with one three-dimensional printer and (2) in the manufacturing area with multiple printers in use. Emission rates were calculated for a variety of filaments and ranged from 1.21 to 33.5 × 1011 particles/min, with geometric mean diameters ranging from 11.4 to 33.3 nm. The emission rates estimated by a scanning mobility particle sizer were much lower than from the fast mobility particle sizer due to differences in the lower size resolution. Samples collected in the chamber and manufacturing area by thermophoretic sampling included free (no polymer) carbon nanotubes and nanofibers and their bundles. The company reportedly never handled free carbon nanotubes or nanofibers, and prior research has indicated that the release of free nanomaterials through three-dimensional printing or mechanical action is highly unlikely. This presents the possibility that these materials are being released from the matrix during use or that these materials were brought into the facility through the supply chain, or by other means.