Material formed from crab shells and trees could replace flexible plastic packaging

Described in the journal ACS Sustainable Chemistry and Engineering, the material is made by spraying multiple layers of chitin from crab shells and cellulose from trees to form a flexible film similar to plastic packaging film. Cellulose is the planet's most common natural biopolymer, followed by chitin, which is found in shellfish, insects and fungi.

The team devised a method to create a film by suspending cellulose and chitin nanofibres in water and spraying them onto a surface in alternating layers. Once fully dried, the material is flexible, strong, transparent and compostable.

Prof J Carson Meredith, who led the research, said that the material could offer advantages over polyethylene terephthalate (PET), one of the most commonly used transparent packaging materials. "Our material showed up to a 67 per cent reduction in oxygen permeability over some forms of PET, which means it could in theory keep foods fresher longer," he said.

The team had been looking into chitin for an unrelated reason when they wondered if it might have use in food packaging. "We recognised that because the chitin nanofibres are positively charged, and the cellulose nanocrystals are negatively charged, they might work well as alternating layers in coatings because they would form a nice interface between them," Meredith said.

Part of the reason the new material improves upon conventional plastic packaging as a gas barrier is because of the crystalline structure of the film. "It's difficult for a gas molecule to penetrate a solid crystal, because it has to disrupt the crystal structure," Meredith said. "Something like PET on the other hand has a significant amount of amorphous or non-crystalline content, so there are more paths easier for a small gas molecule to find its way through."

With the amount of cellulose already produced and a ready supply of chitin-rich by-products left over from the shellfish food industry, Meredith claimed that there's enough material available to make the new films a viable flexible-packaging alternative.

The group is now working on improving the material’s ability to block water, as well as exploring the development of manufacturing processes that could eventually enable the materials to be produced commercially.

This is not the first time that researchers have explored the use of naturally occurring chitin to replace plastic materials. Last year, The Engineer reported on a Nottingham University led effort to make biodegradable shopping bags from discarded shrimp shells.