Can crab shells and trees replace plastics?

An eco-friendly material made from crab shells and trees could replace plastic food packaging, according to US researchers. The material – made by spraying alternating layers of crab-shell chitin and tree cellulose onto a surface – is described in a paper in ACS Sustainable Chemistry and Engineering.

Like plastic, when dried the material is tough, malleable and transparent. Unlike plastic, it is also biodegradable.

Cellulose fibres are complex polysaccharides (undigestible sugar molecules) that give plants structural support. They are the earth’s most abundant natural biopolymer. Chitin, found in shellfish, insects and fungi, is the next most abundant.

The researchers, led by J. Carson Meredith of the Georgia Institute of Technology, had been investigating cellulose for its renewable plastic potential. They were exploring chitin for a different reason when it dawned on them that chitin’s nanofibres might complement the cellulose nanocrystals.

“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 form a nice interface.”

The team suspended the cellulose and chitin nanofibres in water before spraying them onto a surface to create the material. As a bonus, its crystalline structure is harder for gas molecules to penetrate than plastic derived from the petroleum-based polyethylene terephthalate (PET).

Meredith says “Our material showed up to a 67 percent reduction in oxygen permeability over some forms of PET, which means it could in theory keep foods fresher longer.”

More than 322 million tonnes of plastic is produced each year around the world, much of which ends up in the oceans where it has increasingly serious impacts on marine life.

Biodegradable alternatives such as the chitin-cellulose composite may be part of a solution to the pollution problem, but more work is needed. The researchers note that it will take further research to improve the material’s ability to block moisture and find ways to produce it economically at scale.

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