Aug 22, 2018 | By Thomas

Soldiers on the battlefield or at remote bases often have to wait weeks for replacement parts when a key piece of equipment breaks down. Now researchers from the U.S. Army Research Laboratory and the U.S. Marine Corps have found a way to fabricate these parts within hours using waste plastics, such as water bottles, cardboard and other recyclable materials found on base as starting materials for 3D printing.

3D printed vehicle radio bracket. Credit: Nicole Zander/U.S. Army Research Laboratory

The researchers presented their work at the 256th National Meeting & Exposition of the American Chemical Society (ACS) yesterday.

"The potential applications for additive manufacturing technologies are extensive—everything from pre-production models and temporary parts to end-use aircraft parts and medical implants," said ARL researcher Dr. Nicole Zander.

Supplying combat troops with food, fuel, ammunition and repair parts is a monumental task, requiring thousands of support staff, contractors and manufacturers. In all, the U.S. Department of Defense has an inventory of 5 million items distributed through eight distinct supply chains, according to the U.S. Government Accountability Office. However, few of these items are stockpiled at front-line locations, meaning that troops in those areas can experience occasional shortages of important materials. Many of these units have 3D printers that can produce spare parts and other equipment, but they rely on conventional feedstocks, such as commercially available plastic filaments, that must be requisitioned, and they can take days, weeks or even months to arrive.

The research by Zander and co-collaborator Capt. Anthony Molnar from the U.S. Marine Corps, generated 3D printing filament from recycled polyethylene terephthalate, or PET, from bottles and plastics without any chemical modifications or additives. PET plastics, found in water and soda bottles, are common waste materials found around bases. While PET is widely used in many applications, it is not widely used as a feedstock for FFF 3D printing due to its high melting temperature, water absorption and issues with crystallinity.

The researchers used a process called solid-state shear pulverization to generate composite PP/cellulose filaments. In this process, shredded plastic and paper, cardboard or wood flour was pulverized in a twin-screw extruder to generate a fine powder that was then melt-processed into 3D printing filaments.

Researchers performed mechanical testing on filaments of PET plastics, and their work shows that recycled PET filaments are as strong and flexible as commercially available filaments for 3D printers. In tests, the team used recycled PET filaments to print a vehicle radio bracket, a long-lead-time military item. This process required about 10 water bottles and took about two hours to complete.

Zander explained, "In terms of mechanical properties, most polymers used in FFF have bulk strengths between 30 and 100 MPa. Recycled PET has an average strength of 70 MPa, and thus may be a suitable 3D printing feedstock."

Dr. Nicole Zander, ARL demonstrates equipment for Capt. Anthony Molnar, U.S. Marine Corps. (U.S. Army photo by Jhi Scott)

The team also explored 3D printing with other types of plastics, such as polypropylene (PP), used in yogurt or cottage cheese containers, or polystyrene (PS), used for plastic utensils. On their own, these plastics don't work well, but the team found that by mixing them with other plastics, or the addition of fillers such as reinforcing or toughening agents, it is possible to generate strong and flexible filaments.

Researchers said the driving force for this work is to enhance warfighter capability and readiness by enabling repairs while deployed and to reduce dependence of the logistical supply chain.

Zander's team is building a mobile recycling trailer that will enable soldiers to repurpose plastics into feedstocks for 3D printing. She is also exploring ways to print materials from plastic pellets instead of filaments, which could help soldiers quickly produce larger 3D-printed parts and machinery.

"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. "Future work will involve testing select 3-D printed long-lead parts against original parts to determine if they can be a suitable long-term or at least a temporary replacement."



Posted in 3D Printing Application



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