Particle emissions and respiratory exposure to hazardous chemical substances associated with additive manufacturing utilising poly methyl methacrylate
Van der Walt, Sylvia
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Background: There is limited but growing information available regarding the health hazards associated with additive manufacturing (AM). The study presented in this mini-dissertation is significant considering that no other studies have explored particle emissions or the personal exposure of AM operators to hazardous chemical substances (HCS), such as poly methyl methacrylate (PMMA) powder particles, acetone and methyl methacrylate (MMA), during binder jetting utilising PMMA and acetone. Aims and objectives: To determine the physical characteristics and chemical composition of PMMA powder. Assess particle emissions associated with binder jetting utilising PMMA powder. Evaluate ambient workplace concentrations as well as personal respiratory exposure concentrations of the AM operator, for particles and volatile organic compounds (VOCs) (such as acetone and MMA) when PMMA powder is utilised during binder jetting AM. Methods: Physical and chemical characterisation of virgin and used PMMA powder samples included particle size distribution (PSD), particle shape analysis, scanning electron microscopy (SEM), X-ray diffraction (XRD) as well as X-ray fluorescence (XRF). Direct reading particle counting instruments were used to measure particle emissions and emission rates during each phase of the binder jetting process. Internationally recognised methods were used to monitor HCSs in the ambient workplace environment and personal respiratory exposure of the AM operator, during the entire binder jetting process. Results: There were no noteworthy size differences found between median of the PSD of virgin (58.32 ± 0.52 μm) and used (58.40 ± 0.11 μm) PMMA. From SEM images, the presence of < 10 μm, and a few < 4 μm, sized particles were observed in both the virgin and used powders. PMMA powders comprised mainly of amorphous elements (> 99.23% for virgin powder). In the presence of high background ambient particle number concentrations particle emission rates as high as 3.33 × 1012 particles/min for 0.01 ~ 1.00 μm sized particles were measured during the processing phase. However, no significant differences between the AM phases were observed. Ambient 8-hour Time Weighted Average (TWA) concentrations were measured at 3.83 ± 2.12 mg/m3 for inhalable particles, 0.77 ± 0.20 mg/m3 for respirable particles, 15.32 ± 2.62 mg/m3 for acetone, 0.19 ± 0.08 mg/m3 for pentane and 0.30 ± 0.03 mg/m3 for toluene. Personal TWA concentrations were measured at 6.22 ± 4.72 mg/m3 for inhalable particles, 1.15 ± 0.33 mg/m3 for respirable particles, 2.02 ± 0.58 mg/m3 for acetone, 0.16 ± 0.07 mg/m3 for pentane and 0.16 ± 0.05 mg/m3 for toluene. Conclusions: In this study, a comprehensive analysis was performed in order to determine the particle emissions and respiratory hazards, and the extent thereof, to which AM operators of PMMA binder jetting are exposed. Particles sized 0.01 ~ 1.00 μm were the most prevalent sizes emitted. Inhalable, and respirable particles, acetone, pentane and toluene were detected in the workplace atmosphere. All 8-hour TWA personal exposures were below the respective TWA Occupational Exposure Limit Recommended Limit (TWA-OEL-RL), with the exception of exposure to inhalable particles, where exposure exceeded the 10 mg/m3 TWA-OEL-RL once and averaged above 50% of the OEL. Recommendations for elimination, substitution, engineering, administrative and personal protective equipment control measures were made to reduce exposure to inhalable particles, which could also be applied to other AM facilities making use of the same AM technology and PMMA powders. Study limitations and future studies were also discussed.
- Health Sciences