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Cellulose-chitin Nanofiber Could Replace Plastic Packaging

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According to an article this past week by Physics World (Bristol, U.K.) reporter Belle Dumé, researchers at the Georgia Institute of Technology have developed a material from two naturally-occurring polymers that could offer an environmentally-friendly alternative to traditional plastic packaging for food and consumer goods. The material is made by layering cellulose the most abundant biopolymer on Earth with chitin, which is widely found in shellfish, insects and fungi.

Cellulose is a linear homopolymer of glucose, while chitin is a linear homopolymer of N-acetyl glucosamine. Both biopolymers are found in the hierarchical structures of plant cells and crustacean exoskeletons, respectively, from which nanocrystals and nanofibres can be extracted. Cellulose nanocrystals and nanofibres, and chitin nanowhiskers and nanofibres, have a high Young’s modulus and tensile strength as well as being good barriers to many gases, including oxygen.

The research team, led by Carson Meredith, created films from the two biopolymers by suspending cellulose nanocrystals (CNCs) and chitin nanofibres (ChNFs) which are negatively and positively charged, respectively in water, and then spraying them onto a compostable substrate in alternating layers. The processing technique is compatible with roll-to-roll coating.

Meredith and colleagues found that the material shows up to what is reported as a 67% reduction in oxygen permeability compared to some forms of polyethylene (PET), which is one of the most common plastics employed in transparent food packaging today. This improvement comes from the crystalline structure of the nanofibers and means that it could, in theory, keep foods fresher for longer, according to the researchers. The most impermeable composites were the ones that were made of three alternating layers of ChNF-CNC-ChNF).

"It’s difficult for a gas molecule to penetrate a solid crystal, because it has to disrupt the crystal structure," says Meredith. "Something like PET on the other hand has a significant amount of amorphous or non-crystalline content, so there are more paths and it is easier for a small gas molecule to find its way through."

Researchers reportedly said that they now need to develop a scaled-up manufacturing process so that their film is cost competitive with traditional packaging materials.

"What is more, while industrial processes to mass produce cellulose are mature, methods to produce chitin are still in their infancy," explained Meredith. "And, more research is also needed to improve the material’s ability to block water vapour.

Another important point: "Ground, coarse powders, of cellulose and chitin have a generally-recognized as safe (GRAS) status with the US Food and Drug Administration (FDA) and can be used as food additives," he told Physics World, and also further noted that any shellfish allergy response was unlikely but still needed to be addressed.

The spray-coated multilayer CNC-ChNF nanofiber film is detailed in ACS Sustainable Chemistry and Engineering.

More information is also available in this video summary and in this report from the Georgia Tech (Atlanta, Ga., USA) online news center as well as in this article about the new material being fully biodegradable.

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