The biocomposite films look similar to many synthetic plastics, but their structure is hierarchically reinforced, as seen in the fluorescence microscopy image at right. Image: Orlin Velev, NC State University.
The biocomposite films look similar to many synthetic plastics, but their structure is hierarchically reinforced, as seen in the fluorescence microscopy image at right. Image: Orlin Velev, NC State University.

Materials with enhanced structure derived from crustaceans and seaweed could be part of a next-generation solution to the challenge of replacing petroleum-based plastic films, according to new research from engineers at North Carolina State University (NC State).

By combining chitosan, a biopolymer that makes crab shells hard, with agarose, a biopolymer extracted from seaweed that is used to make gels, the engineers were able to create unique biopolymer composite films with enhanced strength. In addition, these films are biodegradable, have antibacterial properties, repel water and are transparent, which could eventually lead to them being used as sustainable packaging films for food and consumer goods.

“How do we find sustainable replacements for synthetic polymers?” asked Orlin Velev, professor of chemical and biomolecular engineering at NC State and corresponding author of a paper on this work in Cell Reports Physical Science. “Synthetic polymers make very good films, but we want to replace them with natural biopolymers. The question becomes how do we adjust the joint structure of these natural polymers – in our case agarose and chitosan – so we can have all the desirable properties of synthetic polymers inside a sustainable, biodegradable film?”

Simply mixing chitosan and agarose together may not be enough. According to Velev, previous efforts to produce such mixtures reported improvements in properties, but when these mixtures dried, they created gritty films that may lack the right strength.

So, Velev and his collaborators took a different approach, by reinforcing the agarose films with fibrillated colloidal-scale material – called soft dendritic colloids – made from chitosan. The strong chitosan micro- and nanoscale fibrils are hierarchically branched to add strength and stability to the agarose film where they are embedded.

“It is challenging to modify natural polymers chemically, but we can alter their morphology and use them as composites,” said Yosra Kotb, a PhD graduate at NC State and first author of the paper. “We use chitosan dendritic particles to reinforce the agarose matrix because of the compatibility of both materials, leading to good mechanical properties. Chitosan particles also have an opposite charge to agarose. When mixed, these charges are neutralized so the resulting materials also become more resistant to water.”

The biopolymer composites are about four times stronger than agarose films alone and can resist Escherichia coli, a commonly studied bacterium. The paper also showed that a sheet made from these biopolymer composite films became greatly degraded after a month underground. In contrast, a common plastic sandwich baggie remained completely intact after the same period underground.

“Interestingly, our composite is initially strongly antibacterial,” Velev said, “but because it is made from natural materials, after some time bacteria will still colonize it – so after a month underground it will biodegrade readily.”

Velev added that his lab will continue working to make improvements to the structure of the biopolymer composite films, with the goal of eventually matching the properties of synthetic polymer ones.

“If you package food, you want the package to be impermeable to oxygen and water,” he said. “But natural materials are permeable, so we will continue to work to make our films more impermeable to water and oxygen.”

Increasing the scalability of the material production process is also one of the future goals. “How do you make the polymer substitute film in a continuous process that is rapid enough to make it in large enough amounts – like papermaking?” Velev said.

This story is adapted from material from North Carolina State University, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.