The aim of this study was to measure the concentrations of gaseous and particulate contaminants originated from additive manufacturing operations and post-processes in an occupational setting when A c c e p t e d M a n u s c r i p t plastics were used as feedstock materials. Secondary aims were to evaluate the concentration levels based on proposed exposure limits and target values and to propose means to reduce exposure to contaminants released in additive manufacturing processes. Volatile organic compounds were sampled with Tenax® TA adsorption tubes and analyzed with thermo desorption gas chromatography-mass spectrometry instrument. Carbonyl compounds were sampled with DNPH-Silica cartridges and analyzed with high-performance liquid chromatography device. Particles were measured with P-Trak instrument and indoor air quality was sampled with IAQ-Calc instrument. Dust mass concentrations were measured simultaneously with DustTrak DRX instrument and IOM-samplers. Particle concentrations were at highest (2070-81 890 #/cm 3 mean) during manufacturing with methods where plastics were thermally processed. Total volatile organic compounds concentrations, in contrast, were low (113-317 µg/m 3 mean) during manufacturing with such methods, and vat photopolymerization method. However, total volatile organic compounds concentrations of material jetting and multi jet fusion methods were higher (1114-2496 µg/m 3 mean), perhaps because of material and binder spraying, where part of the spray can become aerosolized. Chemical treatment of manufactured objects was found to be a severe volatile organic compounds source as well. Formaldehyde was detected in low concentrations (3-40 µg/m 3) in all methods except for material jetting method, in addition to several other carbonyl compounds. Notable dust concentrations (1.4-9.1 mg/m 3) were detected only during post-processing of powder bed fusion and multi jet fusion manufactured objects. Indoor air quality parameters were not found to be notably impacted by manufacturing operations. Only low concentrations (below 2 ppm) of CO were detected during several manufacturing processes. All studied additive manufacturing operations emitted potentially harmful contaminants into their environments, which should be considered in occupational additive manufacturing and workplace design. According to the measured contaminant levels it is possible that adverse additive manufacturing related health effects may occur amongst exposed workers.

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The alterations in volatile organic compound (VOC) and ultrafine particulate (UFP) matter emission profiles following thermal reprocessing of multiple materials were examined. Additionally, mechanical performance of the materials was studied. The VOCs were identified by collecting air samples with Tenax® TA tubes and analyzing them with a GC–MS system. UFP concentrations were monitored with a portable ultrafine particle counter. Total VOC emissions of all materials were reduced by 28–68% after 5 thermal cycles (TCs). However, slight accumulation of 1,4-dioxane was observed with poly(lactic acid) materials. UFP emissions were reduced by 45–88% for 3D printing grade materials over 5 TCs but increased by 62% in the case of a waste plastic material over 3 TCs. The mechanical performance of the materials was investigated by measuring their tensile strengths (TSs) and elastic moduli (EM) with an axial-torsion testing system. The reprocessed materials expressed fluctuations in their 3D printing qualities and mechanical performances. The mechanical performances were observed to reduce only slightly after 5 TCs, and the trend was observable only after the data was mass-normalized. The TSs of the samples were reduced by 10–24%, while the EM were reduced by 1–9% after 5 TCs. The TS and EM of one material were increased by 14 and 33%, respectively. In conclusion, recycled polymers are plausible 3D printing feedstock alternatives as they possess acceptable mechanical performance and low emittance according to this study. Furthermore, non-3D printing grade polymers may be applied in a 3D printer with caution.

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