Chemists make degradable plastics from flies

Black soldier flies could be a renewable feedstock for making hydrogels and other degradable polymers. Texas A&M University chemistry professor Karen L. Wooley and graduate student Cassidy Tibbetts spoke about the project during talks at ACS Fall 2023 in San Francisco. Wooley spoke on Monday, in the Division of Polymeric Materials Science and Engineering, and Tibbets spoke on Tuesday, in the Division of Polymer Chemistry.

The larvae of black soldier flies have garnered attention and investment in recent years for their ability to compost food waste and as animal feed. But the adults live just a few days; they reproduce and then die. “They’re largely a waste stream right now,” Tibbetts told C&EN.

Looking to do something with this waste, chemists in Wooley’s lab discovered that they could extract the polysaccharide chitin from the flies. By stripping acetyl groups from chitin, the chemists made chitosan, an antimicrobial and antioxidant polymer that has applications in cosmetics, drug delivery, and food storage.

Hongming Guo, another graduate student in Wooley’s lab, added carboxylic acid groups to the chitosan and made the material into an emulsion. He then cross-linked the modified chitosan emulsion through amide and ester linkages by adding carbodiimide agents. The resulting hydrogel can soak up to 47 times its mass in water in about a minute. This biodegradable material, Wooley said, could be used to soak up water during flooding and then release it during periods of drought.

In addition to making chitosan, Wooley’s lab is working to break chitin into simple molecules, such as glucosamine and N-acetyl glucosamine. These could be used as feedstocks to make degradable polycarbonates.

Brett Helms, a staff scientist at Lawrence Berkeley National Laboratory who is familiar with the work, said the superabsorbent hydrogels Wooley’s team discovered are just the beginning. “We should be looking for ways to produce useful materials sustainably, which includes broadening our perspective regarding feedstocks for their design and production,” he said in an email.

“We don’t want to be competing with things that we need for food, things that we need for fuel, things that we need for construction,” Wooley told C&EN.