Army research unlocks process that breaks down biodegradable plastics

PLASTICCOVER
Much of the planet is swimming in discarded plastic, which is harming animal and possibly human health. Can it be cleaned up? Photo credit Army.mil

By U.S. Army DEVCOM Army Research Laboratory Public Affairs

With Army funding, scientists invented a way to make compostable plastics break down within a few weeks with just heat and water. This advance will potentially solve waste management challenges at forward operating bases and offer additional technological advances for American Soldiers.

The new process, developed by researchers a t University of California, Berkeley and the University of Massachusetts, Amherst involves embedding polyester-eating enzymes in the plastic as it's made.

When exposed to heat and water, an enzyme shrugs off its polymer shroud and starts chomping the plastic polymer into its building blocks — in the case of biodegradable plastics, which are made primarily of the polyester known as polylactic acid, or PLA, it reduces it to lactic acid that can feed the soil microbes in compost. The polymer wrapping also degrades.

The process eliminates microplastics, a byproduct of many chemical degradation processes and a pollutant in its own right. Up to 98% of the plastic made using this technique degrades into small molecules.

“These results provide a foundation for the rational design of polymeric materials that could degrade over relatively short timescales, which could provide significant advantages for Army logistics related to waste management,” said Dr. Stephanie McElhinny, program manager, Army Research Office.

Plastics are designed not to break down during normal use, but that also means they don't break down after they're discarded. Compostable plastics can take years to break down, often lasting as long as traditional plastics.

The research teams embedded nanoscale polymer-eating enzymes directly in a plastic or other material in a way that sequesters and protected them until the right conditions to unleash them. In 2018, they showed how this works in practice. The team embedded in a fiber mat an enzyme that degrades toxic organophosphate chemicals, like those in insecticides and chemical warfare agents. When the mat was immersed in the chemical, the embedded enzyme broke down the organophosphate.

The researchers said protecting the enzyme from falling apart, which proteins typically do outside of their normal environment, such as a living cell, resulted in the key innovation.

In a Nature paper, the researchers showcased a similar technique by enshrouding the enzyme in molecules they designed called random heteropolymers or RHPs, and embedding billions of these nanoparticles throughout plastic resin beads that are the starting point for all plastic manufacturing. The process is similar to embedding pigments in plastic to color them.

“This research really opens the door to a new class of biotic-abiotic hybrid materials with functions only currently found in living systems,” said Dr. Dawanne Poree, program manager, ARO.

The results showed that the RHP-shrouded enzymes did not change the character of the plastic, which could be melted and extruded into fibers like normal polyester plastic at temperatures around 170 degrees Celsius (338 degrees Fahrenheit).

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