New process could turn shrimp into tough, biodegradable plastic

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Though we often fail, as a species we do make a genuine effort to use every part of the animals we consume. When it comes to shrimp, the most valuable part is the meat — but that still leaves the heads, organs, and shells. Much of this waste is ground up and used as cheap protein content in fertilizers and other substances, but we also use some of the specific components. Notably, shrimp shells are collected and treated to remove the protein chitin, one of nature’s most abundant substances, which is modified into the polymer chitosan. Chitosan is abundant and cheap, used in everything from water filtration to self-healing paints, and it’s famous for its ability to break down in the environment. Still, in spite of significant research, it could never quite hold up as a general-purpose plastic.

Now, researchers from the Wyss Institute for Biologically Inspired Engineering claim to have solved this problem with a new treatment for chitosan. It forms a tough and pliable liquid crystal that can be cast or injection-molded like a conventional plastic, but which will break down in as little as two weeks under the elements. In fact, it’s so rich in nutrients that used scraps of the material can support plant growth like fertilized soil — so the chitosan used for plastics can still be used as a fertilizer, down the road.

The breakthrough builds on the concept of Shrilk — Shrimp chitin mixed with silk proteins — but replaces the silk component with wood flour. This allowed the chitosan polymer to maintain its shape after injection without sacrificing the biodegradability. Their manufacturing process allows chitosan to assume virtually any shape, with a range of colors based on the acidity during manufacture.

Chitin in found in the shells of many insects and crustaceans, though the most abundant source today is shrimp.

Applications will likely be industrial at first — the problem with biodegradable consumer electronics is that they tend to be used in such as way that they biodegrade before the user is done with them. However, this bioplastic could still represent a huge volume of near-immortal plastics left in landfills or dumped into the ocean — not to mention the pollution associated with their manufacture. The ability to re-sell old equipment as fertilizer could provide a cost incentive to switch.

The precise physical properties of the plastic have not been released yet, but the researchers are already working to organize pilot projects for large-scale manufacturing.