Sometimes 3D printing may seem to be almost too good to be true, offering what can sometimes be astounding benefits in affordability, production of speed, self-sustainability, and savings in materials and labor. The downsides are few, but as with the use of any machinery, the topic of safety should always present. And although physical hazards may be few in 3D printing, toxicity to humans has been in question for years—in connection with both the materials being used and particle emissions.
As Qian Zhang, a PhD student at Georgia Institute of Technology, asserts in her recent dissertation, ‘Particle Emissions from Consumer Level 3D Printers,’ concerns continue regarding 3D printing emissions in closed environments (which would be the norm in most cases) such as the workplace, classroom, and home. Zhang’s research was comprehensive, focusing on ABS and PLA in terms of particle emissions and their dangers to the public.
Overall, as Zhang points out, ABS and PLA are the most common forms of materials used with 3D printing although many other alternative sources are beginning to gain traction too, from metal to wood—and a growing multitude of other options. ABS is used due to affordability, good strength, stiffness, and more, while PLA (although less stable and not as strong) is thought of as being more environmentally friendly due to its plant-based origins, allowing for more recycling options. Zhang considered these materials specifically, along with FDM 3D printers at the desktop level that may emit particles and volatile organic compounds (VOCs or total volatile organic compounds, TVOCs) into the air, along with gas phase pollutants.
Previous studies showed that ABS usually emitted more particles; in fact, perhaps as much as ‘one to two orders of magnitude higher’ than PLA. As the researcher points out, particle emissions can vary due to other reasons such as:
- Types of environment
- Air mixing and air rate
- Measurement instrumentation
- Calculation methods regarding particles
Carbon and oxygen were the ‘most abundant elements’ found in particle emissions, along with small amounts of metals. ABS filaments were also known to emit styrene and ethylbenzene, while PLA filaments have been known to emit lactide, lactic acid and methyl-methacrylate. The research shows that overall, VOC concentrations may be above normal limits in offices, but environmental variables such as heating, and air-conditioning, may be responsible for lowering levels of toxins substantially. Ultrafine particles are extremely mobile and may cover a large surface area, and in humans can affect the entire respiratory tract, as well as organs and cells, via transportation through the bloodstream.
“The existing results revealed the potential health effects for 3D printer emissions, while more toxicity assessments using multiple methods need to be applied and compared in order to have a broader understanding of the particle emission toxicity,” states Zhang.
Testing included an examination of the following:
- Printer operating conditions
- Printer brands
- Filament materials
- Brands and colors
- Extrusion and build plate temperatures
“Applying an existing test method to 3D printers gives insight for development of a standard test method for 3D printers and provides a database for assessing emission limits. Furthermore, it might provide insights for 3D printer and filament manufacturers to produce low emitting products and develop effective mitigation methods,” says Zhang.
Particle emissions tend to be greater as a 3D printing job begins, mainly comprised of ultrafine particles and nanoparticles.
“For shorter print jobs, these aerosol dynamic processes may never reach steady state before printing ends, whereas for longer jobs, concentrations of various sizes can remain relatively constant after about 1 hour of printing (for this condition), indicating the processes of particle formation, vapor-condensational growth, coagulation and loss reach a steady state,” states Zhang.
“Compared to number concentration profiles, the surface area and mass concentrations both take longer to reach a maximum. The large number of newly formed particles contributes little to surface area or mass, but as printing continues to supply vapors, particle growth by condensation of vapors leads to a rise in surface area and mass concentrations.”
Printer brands and filaments especially did make a big difference when using ABS, while in terms of PLA the 3D printer used had the most effect. ABS numbers turned out to be up to 3 to 104 times that of PLA yields, but Zhang points out that variations differ regarding 3D printer brands, and mass basis of particles should be taken into account also.
“A consistency among various methods showed that PLA emitted particles induced similar levels of responses at much lower doses than ABS-emitted particles, indicating PLA emitted particles are more toxic on a particle mass basis. However, calculations for the overall exposure showed ABS filaments may be more harmful due to their much higher emissions. Overall, 3D printers are sources of high levels of ultrafine particles, which are potentially harmful for their users. Therefore, the emissions should be regulated and mitigate,” concluded the research.
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[Source / Images: Particle Emissions from Consumer Level 3D Printers]