Could plants and crab shells replace plastic?

A biodegradable "plastic" wrapping made from crab shells and plant waste has been developed by scientists in the US.

In 2016, about 335 million tonnes of plastic were produced globally, and roughly 50% of that plastic was only for single use, and thrown away afterwards. Just over half of plastic thrown in the bin comes from plastic packaging, such as plastic wrap for food. But rather than using plastic to preserve our food, what if we could use food waste and other natural sources to make that wrapping in the first place?

Now a study published in ACS Sustainable Chemistry and Engineering proposes a way to do just this. Carson Meredith and his team at Georgia Tech have developed a "plastic" wrap based on chitin, the rigid material in the shells of crustaceans like crabs as well as insect exoskepetons and fungi, and cellulose, the woody material in plant stems. “We found out that chitin could make interesting and transparent, flexible films, and we thought wouldn’t it be cool if we could make packaging from this?,” says Meredith.

Their sources mean that chitin and cellulose are among the most abundant polymers found in nature, and can be extracted from food waste that would otherwise be discarded. Better yet, when they are combined, they have impressive characteristics.

“The chitin nanofibres are positively charged, and the cellulose nanocrystals are negatively charged,” explains Meredith. “They work well as alternating layers in coatings because they have excellent adhesion and create nice barrier films.”

These barrier films created by the combination of chitin and cellulose have similar properties to that of plastic packaging, which is quite promising.  They form very dense and transparent films, and are robust. “Most importantly, they are high crystalline materials,” adds Meredith.

High crystallinity means that this new material is made up of neatly packed molecules, forming a lattice, or a net-like structure that slows air from getting through the film. For food wrapping, blocking air from reaching the food is critical in preventing decomposition and microbial growth.

Although this new material shows potential to replace plastic wrap, Meredith and his team must overcome challenges such as the humidity and condensation that comes with food storage; their current material in development does not protect food from water. Nonetheless, this discovery is a huge milestone in the effort to reduce platic.

“You’re taking plant waste material and food waste material, making food packaging for food out of them, and then the packaging can be composted with food waste. Ultimately, this makes a circular and renewable manufacturing strategy,” concludes Meredith.