3D printing supplies from plastic waste

Materials World magazine
24 Sep 2018

Waste plastics, like water bottles, found at military bases could be used to 3D-print essential supplies, reducing waiting times and improving safety. Idha Valeur reports.

On the battlefield it can take weeks for supplies and replacement parts to reach personnel. Researchers, led by Dr Nicole Zander from the Army Research Laboratory (ARL), USA, have made it possible for soldiers themselves to make the required parts on site, in a matter of hours, using materials found on their own base as feedstock.

Supplying troops with essentials such as food, fuel and ammunition requires thousands of support staff, contractors and manufacturers. Most of the items are not stocked at front-line locations, meaning occasional shortages occur. To fill the resource gap, the military often relies on conventional feedstock like commercially available plastic filaments to feed the 3D printers they have available at base to create the parts needed. However, these must also be requisitioned and can take days, weeks or sometimes months to arrive.

Zander, US Marine Corps Captain Anthony Molnar and colleagues have now found a solution to combat the long process by using polyethylene terephthalate (PET), commonly used for water and soft drink bottles, as base material for the printer.

During testing, the team created a vehicle radio bracket using 10 water bottles. It took approximately two hours from starting the process to producing a complete bracket.

Zander explained to Materials World that ‘PET is one of the most abundant plastics on the battlefield because most soldiers prefer to drink bottled water. It is also an engineering grade plastic and makes a good filament for 3D printing. I mostly work in the polymers area, but I also do work recycling metals through sand casting such as cartridge brass. ARL has a few projects in metals recycling.’

In the beginning of the research process, the scientists decided that other plastics such as polypropylene (PP) and polystyrene (PS) used for yoghurt pots and plastic utensils, were unsuitable for 3D-printing. Nevertheless, when strengthening PP with other materials, like wood fibres, cardboard and cellulose waste materials, all easily accessible on base to create composite filaments, the process worked. Brittle PS plastic was mixed with PP, which generated a strong yet flexible filament.

‘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 tool, parts and other gadgets,’ said Zander.

Solid-state pulverisation (SSSP), the process used to generate composite PP/cellulose filaments, helped the team conclude that the new composite had improved mechanical properties fit for making strong 3D-printed materials. ‘The SSSP process uses high shear and compressive forces to effectively disperse nano and micro fillers throughout the polymer matrix. In addition, SSSP can be used to extract microcrystalline cellulose (MCC) and disperse low-cost, cellulose-rich waste materials such as corrugated cardboard or waste paper. We are able to use the same extruder that we use in the melt processing for SSSP to make the polymer/MCC powder and then melt process the powder to make the composite filament,’ Zander explained.

Process ahead

The team is currently building a recycling trailer where trained soldiers can create 3D-printed filaments from waste. In addition, Zander is exploring methods to print materials from plastic pellets instead of filaments. If successful, this would mean that soldiers would be able to quickly produce larger 3D-printed parts and machinery.

‘We need to automate this process as much as possible so that it will be easier for deployed soldiers without any specific polymer science training to be able to make filament.’ Zander said.

Zander foresees further developments in plastic waste creations. ‘We still have a lot to learn about how to best prove these materials and what kinds of additives will improve their properties. She said, ‘We’re just scratching the surface of what we can ultimately do with these discarded plastics.’

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