The team has focused their attention on the use of photopolymers, materials that are commonly found in consumer goods, adhesives and dental fillings, but are increasingly being used as epoxy resins for rapid prototyping using stereolithographic (SLA) 3D printing.
The problem is that photopolymers are made via a chemical reaction that uses a toxic heavy metal called antimony, and printed items based on the material can contain up to 100 times the levels of the heavy metal found in other polymers such as polyethylene terephthalate (PETE) which is often found in food packaging.
Researchers from Robert Morris University in Pennsylvania found that a commercially available photopolymers contained up to 10 percent by weight antimony compounds. When subjected to a battery of tests they found that up to 3 percent of the antimony content leeched out of the samples over a 20-hour period. The amount of photopolymer used in prototyping is of course relatively small, but the researchers are however concerned that the rapid projected growth in 3D printing – and as a result escalating use and disposal of materials containing antimony – could create a hazard.
There is already research suggesting antinomy levels in the environment are on the increase, the scientists report in the recently-launched journal 3D Printing and Additive Manufacturing.
“Photopolymers used in 3D printing are becoming a significant source of antimony to landfills, incinerators, and the global environment,” they write, adding that the heavy metal can also be released in the workplace when the printed material is ground or sanded.
The consequences of rising antimony levels in the environment could be severe, particularly if the heavy metal found its way into aquifers that provide drinking water. Exposure to antimony can cause arsenic-like side effects, including damage to the heart.
“With the projected growth in the 3D printing industry, the health and safety aspects associated with antimony-containing photopolymers and the safe disposal of 3D-printed models is a concern,” they conclude.
The bigger picture
Of course, leeching toxins is just one facet of a much larger debate about the environmental impact of additive versus traditional manufacturing. On the one hand, 3D printing is often portrayed as a clear environmental win, doing away with the waste that accompanies traditional manufacturing approaches such as injection molding. That is clearly true when printing some materials, such as metals, but arguably less so for materials printed using other technologies such as inkjet. And of course not all waste materials can be recycled.
Experts also diverge on how efficient 3D printing may be with regards to energy use when compared to traditional subtractive manufacturing, particularly when scaled up to meet a population-wide demand. While local production can do away with the environmental impact caused by shipping end-products to consumers, the raw materials still need to be transported to the machines, and there is a host of other variables to consider, such as greenhouse emissions, release of pollutants and the end-of-life disposal of machines.
So how green is 3D printing? The answer to the question seems to be – for now – it depends. Different printing technologies, materials and individual machines will all have a different environmental footprint, and change depending on the quantities being produced.
It does seem probable however that – with the continual refinement of the technologies deployed in additive manufacturing and the materials used – things are only going to get greener. After all, identifying an issue like antimony leeching is the first stage in coming up with a more environmentally-friendly material that bypasses the problem. Already, despite being at a very early stage of 3D printing’s technological progression, we are seeing new more friendly materials being used. Let us know your opinion on this subject in the 3D printing environment forum thread at 3DPB.com.
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