[Image: DOD]

Every branch of the US military has been exploring 3D printing for a number of applications, finding it to be a useful technology for everything from day to day uses to battlefield operations.

Now the Marine Corps and the US Army Research Laboratory (ARL) are working together to improve both self-reliance and sustainability through 3D printing. The research team is examining the recycling of waste plastic, such as that from water bottles, milk jugs and yogurt containers, to make 3D printer filament.

“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.

Dr. Zander and Marine Corps Captain Anthony Molnar have been working to create 100 percent recycled filament from PET, using bottles and other plastics without any chemical modification or additives. They’re also working on creating filament from other recycled plastics and reinforced filaments.

While PET is widely used for many applications, it isn’t frequently used for 3D printing because of its high melting temperature, water absorption and issues with crystallinity. According to Dr. Zander, however, the recycled PET is a viable new feedstock for 3D printing. The mechanical properties of the parts 3D printed with the material were comparable to those printed with commercial filament. Small parts were 3D printed for evaluation, as well as several larger long lead item military parts.

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

Mechanical tests were conducted in the laboratory, including uniaxial tensile and three point bending experiments. In these tests, the tensile strength of the recycled PET was compared to commercial filaments and found to have similar strength. A custom fixture was also made to test a 3D printed radio bracket, a long lead military item. Brackets made from recycled PET failed at a similar load to brackets 3D printed from commercial ABS filament. The recycled PET has shown itself to be a viable replacement for commercial filament in a range of applications.

In addition to mechanical testing, the recycled plastic underwent other testing such as chemical analysis and thermal stability.

“Recycled polymers have a variety of different additives, fillers and dyes and may have experienced different processing conditions – even for the same polymer type,” said Dr. Zander.

According to Molnar, a project officer with the mobility and counter mobility team in Quantico, Virginia, PET plastics like water bottles and packaging are one of the most prolific wastes found on the battlefield. Both US and coalition forces produce large volumes of PET, and recycling it on location will reduce the logistic burden of transporting parts to forward operating bases as well as the costs of disposing of the material.

“Nikki’s groundbreaking research will provide U.S. forces with the ability to 3-D print replacement parts on demand,” Molnar said. “This will not only increase readiness of equipment but also provide troops with the ability to manufacture mission specific gadgets in the field. As our enemies have shown us, they can often out pace our ability to react to their new tactics and equipment. This new technology will enable the warfighter to more rapidly develop tools necessary to defeat an ever changing enemy technology. With Nikki’s continued research in incorporating additives, stronger filaments will continue to increase the capability to print stronger replacement parts. This will further enable Soldiers to push the boundaries of expeditionary manufacturing into not only larger parts, but also other areas such as printing building materials, unmanned platforms, and force protection devices.”

A major purpose behind the work is to enhance warfighter capability and readiness by enabling repairs during deployment and to reduce dependence on the logistical supply chain, a key and growing focus for the armed forces.

“While each unit carries large stockpiles of spare parts for emergencies, this is costly and increases the risk to warfighters during the convoy of those assets,” said Dr. Zander. “It is also difficult to predict the failure and lifecycle of these parts.”

Dr. Nicole Zander, ARL, demonstrates equipment for Capt. Anthony Molnar, U.S. Marine Corps. [Image: Jhi Scott/US Army]

She and Molnar are building a mobile recycling facility (MRF) so that soldiers can turn waste plastic into filament in the field.

“The MRF will be a plastic processing laboratory housed in a 20 foot ISO container, with all equipment and tools needed to fabricate 3-D printing filament from plastic waste,” said Dr. Zander.

She also said that the mechanical properties of the recycled PET could be further improved by blending it with other plastics or adding fillers such as reinforcing or toughening agents.

“Ultimately, we’d like to produce the best possible feedstock we can from recycled plastics and waste materials,” Dr. 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.”

The equipment used by the Army to produce the recycled filament was made by Thermo Fisher.

“The Army really thought out of the box on this application, turning a troublesome waste product into a valuable resource,” said Steve Post, Business Development Manager for Thermo Fisher.

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