The military researchers presented their work this week at the 256th National Meeting & Exposition of the American Chemical Society.
“Ideally, soldiers wouldn’t have to wait for the next supply truck to receive vital equipment,” said Nicole Zander, PhD. “Instead, they could basically go into the cafeteria, gather discarded water bottles, milk jugs, cardboard boxes and other recyclable items, then use those materials as feedstocks for 3D printers to make tools, parts and other gadgets.”
According to the US Government Accountability Office, the Department of Defense has an inventory of 5 million items distributed through eight supply chains in order to keep military personnel supplied with food, fuel, ammunition and spare parts. Few of these items are stockpiled at front-line locations, however, meaning that shortages can occur at critical times. Many of these front-line locations do have 3D printers, but they often have to wait an extended period of time for feedstock to be replenished.Zander, along with Marine Corps Captain Anthony Molnar and colleagues at the US Army Research Laboratory, has been investigating recycling PET plastic, which is commonly found in water and soda bottles. They determined that filament produced from recycled PET was just as strong as commercially available 3D printer filament. The team used the recycled PET filament to 3D print a vehicle radio bracket, which normally has a long lead time. The process required about 10 water bottles and took about two hours to 3D print.
Originally, the researchers found that other types of plastic, like polypropylene (PP), which is found in yogurt and cottage cheese containers, and polystyrene (PS), used in plastic utensils, were not practical for 3D printing, but some tinkering made them more useful. They strengthened the PP by mixing it with cardboard, wood fibers and other cellulose waste materials, and they also blended PS with PP to make a strong and flexible filament.
The team used a process called solid-state shear pulverization to create composite PP/cellulose materials. Shredded plastic and paper, cardboard or wood flour was pulverized in a twin-screw extruder to generate a fine powder, which was then melted and processed into filament. The researchers tested the new composites and discovered that they had improved mechanical properties that could be used to 3D print strong objects.
Zander and her team are building a mobile recycling center that will allow trained soldiers to make 3D printing filaments out of plastic waste. They are also looking into ways to 3D print from plastic pellets instead of filament, which could allow for the printing of larger objects.
“We still have a lot to learn about how to best process these materials and what kinds of additives will improve their properties,” Zander said. “We’re just scratching the surface of what we can ultimately do with these discarded plastics.”
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