A big problem with biodegradable material is that moisture almost instantly destroys it. Biodegradable paper cups, for instance, will dissolve into a pulp in no time, so you’d better chug that boiling coffee as fast as you can. Plant-based plastics, while more resistant to degradation from moisture, tend to warp and weaken over time. Conventional plastics, while tough and sturdy, are often loaded with toxic chemicals and ruin the environment.
There has to be a better plastic out there, right?
A team from Singapore is proposing a new solution: biodegradable plastic made of shrimp shells that actually gets stronger when wet.
In a study published in Nature Communications, scientists from the Singapore University of Technology and Design and the Institute for Bioengineering of Catalonia report the creation of a biodegradable material that becomes nearly 50 percent stronger when submerged. Instead of fighting water, it uses it to make itself stronger.
The base ingredient is chitosan, derived from chitin, the stuff in shrimp shells and insect exoskeletons that gives them their structural integrity. Chitin, as you can imagine, is produced in overwhelming amounts all over the world. There’s an estimated 100 billion tons of it made annually, a ton of it discarded as seafood processing waste.
Plastic made from shrimp shells isn’t exactly new, as research teams have been experimenting with it for a little over a decade now, at least. But for most of that time, it’s encountered the same problem that every other biodegradable plastic alternative has yet to solve: chitosan weakens in water.
When in Doubt, Look to the Worms
The Singaporean research team claims to have not only solved that problem, but flipped it on its head. The researchers looked into the marine worm Nereis virens, which has zinc-reinforced fangs that lose strength when the metal is removed. Taking cues from the worm, the team experimented with adding trace metals to chitosan.
When tested, the resulting thin, faintly green film stood toe to toe with plastics like polypropylene under dry conditions. When submerged, however, they performed at the level of tougher plastics like polycarbonate and PETG, materials typically used in durable, long-lasting water bottles.
Water and nickel act like cables inside the material’s molecular network, pulling polymer chains closer together instead of letting them drift apart. About 87 percent of the nickel washes out during the first soak; the researchers designed a closed-loop system to reuse it. They figure that the nickel from a single AAA battery could be recycled into more than a dozen drinking cups.
The team molded cups out of this shrimp and metal biodegradable plastic. The cups held water for at least a week and produced sheets over three square meters in size. They buried some in soil to test its biodegradability. It reached its half-life in about four months, a process that can take traditional plastics centuries.
As is often the case with this early research, scaling production and confirming safety still lie ahead before you’ll be snatching up shrimp plastic cups from your local Pottery Barn, but it is a promising first step.
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