Page 35 from: Recycling Technology 2020

35
2020

Research

US army recycles plastics to
repair military equipment
The US Army Research Laboratory has found a way to convert post-consumer plastics into 3D printing materials. This allows
trained veterans to quickly create replacement parts for military vehicles, weapons and equipment.

U
sing a process called solid-state shear
pulverisation, researchers at the US
Army Research Laboratory (ARL)

were able to create composite thermoplastic
filaments. In this process, shredded waste –
mostly plastic bottles as well as some paper
and cardboard – was pulverised in a twin-
screw extruder to create a fine powder. This
powder is then melt-processed into 3D print-
er filament.

It is key that the material is first properly
cleaned and dried. If so, the tensile strength
of printed parts from recycled PET was found
to be equivalent to printed parts made from
commercial off the shelf PET pellets and com-
mercial filaments.

The new composites have ‘improved
mechanical properties’ such as improved
strength for 3D printed materials. With an
average strength of 70 Megapascal, it makes
them helpful building blocks to repair mili-
tary trucks, weapons and other important
tools.

No waiting times
Luckily, most military bases in America

have a 3D printer up and running. The down-
side is that military bases sometimes have to
wait up to a month for a new filament to be
restocked, says US Marine Corps Captain
Anthony Molnar. ‘This process will change
that,’ he notes.

‘Ideally, soldiers wouldn’t have to wait for
the next supply truck to receive vital equip-
ment,’ agrees ARL researcher Dr. Nicole
Zander. ‘Now they can 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,’ she explains.

‘As our enemies have shown us, they can
often outpace 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,’ remarks Cap-
tain Molnar.

He observes that PET plastics like water
bottles and food packaging are one of the
‘most prolific’ types of wastes found on the
battlefield. Being able to repurpose this mate-
rial on location will notably reduce the logis-
tic burden of transporting parts to different
military bases – while saving a lot of money
on waste disposal.

‘Scratching the surface’
The US Marine Corps and research spe-

cialists are now collaborating to build a mobile
recycling trailer for specially trained soldiers
to fabricate 3D printing filaments from plastic

waste. ‘We still have a lot to learn about how
to best process these materials and what kinds
of additives will improve their properties,’ Dr.
Zander points out. ‘We’re just scratching the
surface of what we can ultimately do with
these discarded plastics.’

Continued research will aim to create even
stronger filaments to realise the printing of
more durable and tougher replacement parts,
says Molnar. ‘This will further enable soldiers
to push the boundaries of expeditionary man-
ufacturing into not only larger parts, but also
other areas such as printing building materi-
als, unmanned platforms, and force protec-
tion devices.’

Author:
Kirstin Linnenkoper

www.arl.army.mil

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