Wrapping food in plastic can prolong its freshness, but with petroleum-based plastics, the freshness comes at an environmental cost.
Researchers at Georgia Tech believe they’ve created a potentially viable alternative to such plastics, one that’s not only compostable, but could keep food fresher longer.
And all it took was was some trees and some crabs.
A different kind of plastic
Described in the journal ACS Sustainable Chemistry and Engineering, the new type of materials is comprised of layers of cellulose nanocrystals from wood pulp and chitin nanofibers, which can be found in the discarded shells of crabs and shrimp.
The cellulose is the most common biopolymer in the world. The second most common? Chitin.
“The main benchmark that we compare it to is PET, or polyethylene terephthalate, one of the most common petroleum-based materials in the transparent packaging you see in vending machines and soft drink bottles,” said J. Carson Meredith, a professor at Georgia Tech’s School of Chemical and Biomolecular Engineering, said in a statement. “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.”
This new material may accomplish that feat because of its overall structure. In addition to be strong, flexible and transparent, the layers of cellulose nanocrystals better defend the food from gases, like oxygen, that can spoil it.
“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.”
The film, which you can see in the video above, is created by suspending the cellulose and chitin in water, spraying them in layers and allow them to dry. It holds together well because the cellulose is negatively charged while the chitin is positively charged. Opposites, after all, attract.
“They … form a nice interface between them,” Meredith said.
The materials needed for this plastic are readily available. Cellulose is already produced, and the process for capturing it is well-established. The shellfish food industry has plenty of chitin available, but producing the chitin in nanofiber form is still something that needs work.
Also needing work? The material itself. While it stands up to oxygen better than PET, Meredith and his team need to refine it further to block out water vapor.