There are few environments in which the mantra “Reduce, Reuse, Recycle” resonates more than in space. The limited supplies, constrained confines and microgravity weightlessness of vehicles on orbit only add to the logistical challenges.
NASA – the National Aeronautical & Space Administration – estimates it costs at least $10,000 for every pound of products or materials that the agency projects skyward. So it’s easy to understand why reducing volume and waste, while also lightening the payload on space missions is paramount.
A Seattle-area firm called Tethers Unlimited Inc. has been working closely with NASA for more than three years to develop an in-space plastics recycling technology – in conjunction with 3D printing – to help that cause.
“The motivating factor, initially,” noted Rachel Muhlbauer, TUI’s director of research and development, “was that powders aren’t good in the space environment, particularly in the [International Space] Station, because you can’t contain them, there’s no gravity, they don’t settle, they just float around and become part of the environment. That creates problems for both health and safety, and for electronics.”
Such factors render undesirable the typical plastics recycling method of grinding used thermoplastics into small particles for reheating and reshaping. Instead, Muhlbauer explained in a Sept. 5 telephone interview, Tethers devised a method that borrows from injection molding but has adapted it for extrusion.
“We take scrap plastic, put it in a melting chamber,” Muhlbauer said, “and a piston moves down while [the material] is at temperature and melted, and presses [it] into its material forming stage.” From there, it forms into the shape of 3D printer filament, and then it is extruded out. Tethers calls the resulting recycling process Positrusion.
The firm also has developed a 3D printer to work in conjunction with this process, and it refers to the integrated unit — recycler, spooled plastic filaments, and 3D printer — as the Refabricator.
In all, the Refabricator is roughly the size of a mini-refrigerator. Its size was predefined by the EXPRESS Rack on the Space Station, explained Dr. Allison Porter, who is both Refabricator project manager and TUI’s flight mission manager. “EXPRESS” is an acronym for “EXpedite the PRocessing of Experiments for Space Station” — multipurpose payload rack systems that store and support research aboard the space station. NASA refers to the spatial units on these racks as “lockers.” TUI began by developing its Positrusion recycling machine to fit into one locker, but then expanded that to two lockers, once they decided to integrate the 3D printer and recycler into a single unit, Muhlbauer and Porter explained.
Tethers so far is exclusively using SABIC’s Ultem™ 9085 polyetherimide material on this project.
“We chose to work with Ultem 9085 as our material for the space station mission because it’s been validated for use in space – both within the ISS [International Space Station] … as well as outside the station in the space environment, because it doesn’t degrade under vacuum like a lot of polymers do,” Muhlbauer said, noting the material has very good properties for flammability and toxicity, giving it “high utility in space.”
The recycling machine, however, itself can be adapted to any plastic, she added. It’s just a matter of changing the parameters of the temperature control. Three thermoplastic resins are currently approved for use in space with the 3D printer – Ultem 9085 plus ABS and HDPE.
Muhlbauer said TUI has already tested HDPE in-house on its recycling machine at its Bothell, Wash. headquarters, and “it worked beautifully.” Efforts continue with ABS, as well, she noted.
NASA is pushing a “common-use materials initiative.” As a result, most packaging materials now in space are a derivative of polyethylene. TUI is working with the agency to develop the optimum launch packaging materials (food packaging, baggies, etc.) that can be recycled and reused multiple times via the Refabricator.
“You don’t want to create trash in space,” Muhlbauer said; “you want to be able to reuse it.”
Porter added: “We’ve tested up to seven cycles of recycling so far, and we’ve not seen any significant degradation yet.”
Both NASA and Tethers see real possibilities for using this Positrusion process and recycling unit on Earth, as well.
“This technology and this payload design is obviously tuned for space, so there are certain design aspects that are much more rigorous than would be necessary for a commercial unit.,” Porter noted. “But it’s something that we’re exploring and we know there is interest in this.”
The Refabricator technology is fairly autonomous and would translate well to something like a submarine or a cruise ship or perhaps a ground base that is difficult to reach by land. “For the recycler itself,” Muhlbauer said, “we see a huge terrestrial market for being able to make your own 3D printing filament.” And the two components – the recycling unit and the 3D printer – easily could be separated for different uses, they noted, for example to allow 3D printing hobbyists to make and reuse their own filament.
TUI also has discovered that plastic materials recycled using their Positrusion remelting and reforming process retain their properties better than those recycled via more traditional grinding process.
“When you grind plastics up before reprocessing, you’re essentially cleaving the [polymeric] chains mechanically,” Muhlbauer explained. “You’re putting the polymers under a lot of shear, and they do not do well under shear.
“With our process, you’re avoiding that step. You’re only thermal cycling it, and we’re trying to keep the temperatures under the thermal degradation temperature of the material, so we keep the properties of the material a lot longer, through the cycles of reuse” than if it were being ground up and melted multiple times.
The TUI process has very precise thermal controls, and operates under vacuum in the melt-process stage, which also helps to pull out the water, oxygen and any contaminants that might have found their way into the used parts. This level of control aids the highly autonomous system desired in space, she said, but may be less necessary on a potential ground-based system.
Tethers is currently in the process of building a flight unit of the Refabricator, as well as an identical backup unit. “We plan on going to the flight-certification testing at Marshall [Space Flight Center in Huntsville, Ala.] this winter,” Porters said, “and then [prepare it] to be delivered to the space station late spring next year.
Tethers designed and built all the Refabricator’s components, Porter explained, to enable it to better control the operating conditions of the entire plastic process, from recycling to printing, and to provide maximum autonomy of the unit, rather than depending on the inputs of another system.
That said, Muhlbauer noted, “The Positrusion recycler we developed will work with any 3D printer … and is machine-independent.” Asked about the total investment in this project so far, she said that, between both NASA and Tethers, “we’re in the millions” of dollars.
But there are indications that this particular NASA payload may also have a big, potential payoff, in terms of waste reduction and reuse, both in space and on land.
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