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Can 3-D Printing Go Green? OPEN ACCESS

3-D Printing's Downsides Include Hazardous Chemicals, Plastic Waste and Prodigious Energy Consumption. Following Nature's Blueprints Could Make it Cleaner

[+] Author Notes

R.P. Siegel is a technology writer based in Rochester, N.Y.

Mechanical Engineering 138(10), 42-47 (Oct 01, 2016) (6 pages) Paper No: ME-16-OCT3; doi: 10.1115/1.2016-Oct-3

This article explores various advantages and disadvantages of 3D printing. As 3D printers have become smaller, less expensive, and easier to use, they have become increasingly popular. Additive manufacturing could make manufacturing more sustainable because it creates far less waste than traditional subtractive methods and because making products locally would shorten supply chains, reducing fuel use and carbon pollution from shipping. The researchers believe that 3D printing could ‘accelerate consumerism of nonbiodegradable throwaway plastic objects.’ Students have found that 3D printers use six common resin types: acrylates, thiols, alkenes, vinyl ethers, epoxides, and oxetanes. Acrylates, which the Ember printer uses, are the most common because they work well in a 3D printer and are considered safest for creating solid objects from liquids.

Two years ago the design software giant Autodesk made an unconventional move.

The company's CAD software, which once could assemble only blocky, geometric shapes, had evolved to let engineers design new kinds of intricate micron-scale geometries. These could only be fabricated using 3-D printing. The company wanted to understand its customers’ needs and the additive manufacturing workflow as intimately as possible. “The best way to understand this was to make our own hardware,” said Shalom Ormsby, a designer at Autodesk.

The company took the leap and built its first production-quality 3-D printer, the Ember.

But building this 3-D printer was not enough. Autodesk prides itself on its sustainability efforts. It has ramped up recycling; it uses only renewable energy to run its business; and it maintains a website with examples of sustainable solutions for buildings, manufacturing, and infrastructure. It has embedded ecological intelligence, including life cycle analysis—a cradle-to-grave analysis of a product's impact—directly into its software to help designers make sustainable choices regarding energy, materials, and water.

3-D printers can create an endless variety of intricate plastic parts, but where will those parts go when it's time to dispose of them?

Grahic Jump Location3-D printers can create an endless variety of intricate plastic parts, but where will those parts go when it's time to dispose of them?

Autodesk recognized that 3-D printing posed an opportunity, but also a problem.

As 3-D printers have become smaller, less expensive, and easier to use, they’ve become increasingly popular. A growing maker movement, including online groups and meetups at local maker spaces, has enthusiastically adopted the technology. Commercial applications are taking off. Soon, proponents say, everyone will be able to manufacture just about anything, anywhere.

Additive manufacturing could make manufacturing more sustainable because it creates far less waste than traditional subtractive methods and because making products locally would shorten supply chains, reducing fuel use and carbon pollution from shipping. But additive manufacturing could also cause new problems.

3-D printing could “accelerate consumerism of nonbiodegradable throwaway plastic objects,” Janine Benyus, author of the landmark book Biomimicry and founder of the Biomimicry Institute, has written. Because 3-D printers work at high temperatures, they consume a lot of energy: a home 3-D printer uses about as much power as a desktop computer. This could have major implications for local energy grids. What's more, toxins in the 3-D printing supply chain, including the chemicals in polymer resins, could jeopardize both human health and the environment, she said.

When Autodesk released the Ember in 2014, the company therefore found itself producing a device designed to produce plastic objects that could be implanted in hips, knees, or hearts, make their way into the hands or mouths of toddlers, or get discarded in ditches bordering streams.

Autodesk's Dawn Danby aims to develop nontoxic printer-resin chemicals.

Photo: Blue Bergen

Grahic Jump LocationAutodesk's Dawn Danby aims to develop nontoxic printer-resin chemicals.Photo: Blue Bergen

“As we began to invest a lot in the world of additive manufacturing, lots of questions came up about how we might support that industry in being more sustainable, especially at this early stage.”

— Dawn Danby, Autodesk sustainable design program

“As we began to invest a lot in the world of additive manufacturing, lots of questions came up about how we might support that industry in being more sustainable, especially at this early stage,” Dawn Danby, who manages Autodesk's sustainable design program, recalled.

Could Autodesk really make 3-D printing more sustainable—and in time to keep plastic waste and toxic material from proliferating?

Danby and her colleagues decided to try.

Autodesk had staff who knew how to help cut its 3-D printer's energy consumption and reduce its packaging to prevent waste. But it lacked the expertise in chemistry and toxicology to properly evaluate and improve the various resins the printer might use as feedstocks.

For help, Danby reached out to Tom McKeag, who directs the Berkeley Center for Green Chemistry (BCGC). McKeag is a landscape architect by training and considers himself neither a scientist nor an engineer. But he's managed to train himself in product design and manufacturing, and he has become an expert and strong proponent of bioinspired design, in which designers use nature as a model when coming up with solutions.

Since 2008, McKeag has taught courses in bioinspired design and other topics at University of California, Berkeley, where the center is based. He served for three years on the board of the Biomimicry Institute, and edits Zygote Quarterly, a bioinspired design magazine.

By 2015, McKeag was co-teaching an interdisciplinary, project-oriented class called Greener Solutions, which trains students to draw from chemistry, engineering, and environmental health science to come up with sustainable solutions for real-world problems. Each year the class, co-taught by Megan Schwartzman of U.C. Berkeley's School of Public Health, addresses a problem presented by a sponsoring company. General Coatings has tapped the class to find safer formulations for spray foam insulation; Seventh Generation requested improved preservatives for personal care products; and Levi's asked them to investigate cleaner alternatives to the finishing process for wrinkle-free Dockers.

Autodesk was “trying to inspire more innovation around materials while setting a higher bar for safety and sustainability,” Danby said. “We want a greener resin, but what exactly does that mean?”

McKeag had some ideas, and he knew who else could help. He contacted Beth Rattner, executive director of the Biomimicry Institute.

Founded in 1998 by Janine Benyus, the Biomimicry Institute works on the premise that life has evolved for billions of years while solving myriad problems associated with thriving on this planet, and Benyus believed we could learn a great deal by studying what nature does and how its processes work.

In particular, nature often employs clever mechanisms, some of which designers have adapted to fashion new technologies. For instance, John Dabiri and his team at Stanford found a way to pack wind turbines more tightly together while improving performance. They did it by studying the way that schools of fish use leading vortices—the whirlpool-like masses of fluid along the leading edge of a moving object—to propel themselves. A company called EvoLogics mimicked the acoustics of dolphins’ signature whistles in an underwater modem that detect signals from sea-floor pressure sensors to provide warnings of a tsunami. Many other examples exist.

“[Biomimicry] is not really technology or biology; it's the technology of biology,” Benyus has written. “It's making a fiber like a spider, or lassoing the sun's energy like a leaf.”

At Berkeley, McKeag was already collaborating with Rattner, who advises the Greener Solutions classes on chemistry and the relevant biological literature. The Biomimicry Institute was also helping fund the class and paying a graduate student named Justin Bours, who had previously taken the course, to develop criteria for a “green” 3-D printing resin.

McKeag kicked off the work by teaming up with Bours and Marty Mulvihill, a chemist and former director of BCGC. They searched the scientific literature to learn how a biomimetic approach could improve printer resins, and they produced a report in April 2015 that identified 11 bioinspired design principles to guide the class's investigation.

McKeag then challenged the Greener Solutions students to develop a framework to assess safety and sustainability. The class came up with four criteria.

“Biomimicry is not really technology or biology; it's the technology of biology.”

— Janine Benyus, Founder of the Biomimicry Institute

First, the students asked if the ingredients could be sourced locally and if they could be grown. In nature, plants and animals grow on a small number of readily available nutrients, all drawn from their diet or the surrounding environment. For example, songbirds in the woods display a dazzling variety of colors. Unlike today's manufacturers, who obtain raw materials from multiple points worldwide, most birds use nutrients to synthesize a single material, which they assemble to build nanostructures that scatter specific wavelengths of light, producing the species’ characteristic colors.

Second, they considered whether the material uses structure, including nanostructure, to impart function. Consider the Humboldt squid. Its rubbery body transitions smoothly to a beak whose tip is the hardest non-mineral material known to man, yet both the body and the tip are made of the same chemical components, but in different proportions. If a single resin material could take on different properties based on how it was applied and cured by the printer, this could pose a significant opportunity for 3-D printing.

“If [the 3-D printer] still requires petroleum-based inputs and still creates products that, at the end of their usable life, are not recyclable, then it has not lived up to its potential.”

— Dawn Danby

The class also considered whether resin was drawn from a small set of ingredients. In nature, a mere 20 amino acids combine to make more than 100,000 different proteins in the body. Was there a way to follow nature's lead and come up with a small set of safe chemical building blocks called monomers that could combine to produce a range of different materials or material properties? To find out, the Berkeley student researchers explored options such as “multi-tasking monomers,” which would be programmed to produce different materials under different processing conditions.

Finally, the class considered whether 3-D printed products could be recycled, the way nature converts waste from one organism or biological process into food or feedstock for another. As Dawn Danby said, “if it still requires petroleum-based inputs and still creates products that, at the end of their usable life, are not recyclable, then it has not lived up to its potential.”

Next, the class performed a hazard assessment on current 3-D printing materials, operating on the guiding principle that the chemistry used should be benign for both human health and the environment.

The students found that 3-D printers use six common resin types: acrylates, thiols, alkenes, vinyl ethers, epoxides, and oxetanes. Acrylates, which the Ember printer uses, are the most common because they work well in a 3-D printer and are considered safest for creating solid objects from liquids. Yet acrylates are far from perfect. The monomers and oligomers that make the resin solidify into plastic are highly reactive by design, which means that uncured acrylates can be hazardous in the environment, much like liquid paint. SLA printers tend to leave 20-30 percent of the resin uncured.

The class broke into groups. Different groups recommended replacing the photoinitiator, modifying the base resin, or using a different initiation mechanism. They considered only the materials, suggesting no changes to the printer itself.

The photoinitiator, a chemical called TPO, responds to light by catalyzing acrylate monomers and oligomers to form the polymer, or plastic. But it's also a reactive chemical that's known to harm animal reproduction and the freshwater environment. For that reason, the class followed a principle that McKeag, Mulvihill, and Bours had called the optimal activator, which meant using light or another environmental factor, rather than a chemical, to catalyze the reaction.

They suggested using a blend of curcumin, the principal component of turmeric, the pungent spice used to help flavor curry, and riboflavin, otherwise known as vitamin B2. The literature the class surveyed described their use as photoinitiators in polymerization reactions. Since both are edible, they’ll likely be considerably safer than the current photoinitiator.

Another group of Greener Solutions students proposed a different bioinspired approach to initiate the reaction: exposing the resin to a change in acidity. Oysters and mussels use this approach to enable the watersoluble adhesives they secrete that solidify and attach them to rocks under water. The process, known as calcium carbonate mineralization, is already used in two-dimensional lithography, so there was a sound basis for it.

Tom McKeag (center), who directs the Berkeley Center for Green Chemistry, watches students in the 2015 Greener Solutions class do a teambuilding exercise.

Grahic Jump LocationTom McKeag (center), who directs the Berkeley Center for Green Chemistry, watches students in the 2015 Greener Solutions class do a teambuilding exercise.

Since nature also grows its own ingredients, one group in the class proposed replacing the acrylate resin with triglycerides (fats) derived from castor oil. Another group recommended chitosan, the material insects and crustaceans use to build their shells. Earlier research had shown that these replacements were both effective and safe, with the triglycerides likely to produce softer materials.

In the end, Autodesk decided to pursue several of the class's suggestions. These included developing a turmeric-based photoinitiator, a pH-based photoinitiator derived from oysters and mussels, and a chitosan-based resin, said Chris Venter, an Autodesk senior research scientist who leads the biomaterials development for printers like Ember and the yet-to-be-released Escher, which will use multiple robotic print heads for high-volume production. The company even hired Bours as a full-time chemist to continue developing the new resin components.

Between Autodesk, the Greener Solutions class, and other researchers, “we should get to benign feedstocks fairly quickly,” said the Biomimicry Institute's Rattner.

Doing so will mitigate the degree of harm from 3-D printing as more people become involved in design and creation. But it's clear that far more can be achieved. “How do we get to where we can operate these at ambient temperature, like your body does?” Rattner asks. “Your body makes some pretty great ceramics, namely your teeth, without a kiln or a furnace, so why can’t we get a 3D printer to do that?”

Meanwhile, at Autodesk, Bours is developing an online database of 3-D printing materials to help manufacturers, designers, and developers make sound materials choices.

Autodesk will eventually stop selling resin, but will make public what they’ve learned about developing safe, nontoxic resins, Venter said. The company hopes that the safer resins they develop will be cheaper than today's and will encourage more people to try 3-D printing. Down the road, the resins could be made from “simple, common ingredients that are purchased locally—perhaps even at the grocery store,” Venter said.

That's a long way from the toxic resins and plastic trash 3-D printers are poised to generate today. But for 3-D printing and many other products and endeavors, “nature has already solved so many of those other dimensions of the problem,” giving us renewable, non-toxic, biodegradable technologies that require less energy, water and time to make, Rattner said.

Indeed, that's what can happen when you follow nature's lead.

Copyright © 2016 by ASME
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