Particle emissions and respiratory exposure to hazardous chemical substances associated with binder jetting additive manufacturing utilizing poly methyl methacrylate

Background

During industrial scale binder jetting utilising poly methyl methacrylate (PMMA) hazardous chemical substances (HCSs) such as PMMA powder particles, methyl methacrylate (MMA) and acetone may be emitted and potentially inhaled by Additive Manufacturing (AM) operators.

Methods

Physical and chemical characterisation of virgin and used PMMA powder samples were characterised in terms of their size, shape and chemical composition. Direct reading particle counting instruments were used to determine particle emissions and emission rates (ER). Internationally recognised methods were used to monitor HCSs in the ambient workplace environment and personal respiratory exposure of the AM operators.

Results

There were no differences between the median powder size distributions of virgin and used PMMA powders. Scanning Electron Microscopy images indicated the presence of <10 µm and <4 µm sized particles in virgin and used powders. Particle ERs as high as 3.33 × 10⁶ particles/min for 0.01 - ∼1.00 µm sized particles were measured during the post-processing phase. Inhalable and respirable particles, acetone, pentane and toluene were detected in ambient air and AM operators were exposed to quantifiable concentrations of these HCSs.

Conclusions

Particles sized 0.01 - ∼1.00 µm were the most prevalent particles emitted, with a maximum ER of 3.33×10⁶ particles/min. Eight-hour Time Weighted Average personal exposures were below their respective Occupational Exposure Limit (OELs), with the exception of inhalable particles (mean >50% of the South African OEL). Recommendations were made to reduce exposure to inhalable particles, which could be applied to other AM facilities.