Biodegradable plastics are typically produced during the chemical synthesis of natural products such as glucose obtained from sugar cane or corn. However, scientists from Wooley’s laboratory at Texas A&M University in the United States came up with a slightly different and unusual idea… In an ongoing research project, they use insects as a source of chemicals needed to produce plastics that can later biodegrade. At the annual conference of the American Chemical Society (ACS), they described their progress so far – including isolating and purifying insect-derived chemicals and how to turn them into functional bioplastics.
“For 20 years, my group has been developing methods to convert natural products – such as glucose obtained from sugar cane or trees – into biodegradable, digestible polymers that do not persist in the environment,” says Dr Karen Wooley, principal investigator of the project. “But these natural products are harvested from resources that are also used for food, fuel, construction and transportation.” So Wooley began to look for alternative sources that would not be based on plants. Her colleague, Dr. Jeffery Tomberlin, suggested that she could use the waste left over from breeding black flies (Hermetia illucens).
The larvae of these flies contain many proteins and other nutrients, so the immature insects are raised for animal feed and waste to be consumed. However, the adults have a short lifespan after the breeding days are over and are then discarded. At Tomberlin’s suggestion, adult flies became the new starting material for Wooley’s syndrome. “We’re taking something that’s literally waste and making something useful out of it,” says Cassidy Tibbetts, a PhD student working on the project.
When Tibbetts examined the dead flies, she found that their main ingredient was chitin. This non-toxic, biodegradable sugar-based polymer strengthens the shell or exoskeleton of insects and crustaceans. Industrial shellfish farmers are already extracting chitin from shrimp and crab shells for a variety of uses, and Tibbetts uses similar techniques, using ethanol scrubbing, acid demineralization, alkaline deproteinization and bleach decolorization to extract and clean insect carcasses.
Its fly-sourced chitin powder is probably purer as it lacks the yellowish color and lumpy texture. He also notes that extracting chitin from flies may avoid possible concerns about some seafood allergies. Other researchers are isolating chitin or proteins from fly larvae, but Wooley says her team is the first to use chitin from discarded adult flies, which, unlike larvae, are not used as food.
While Tibbetts continues to refine his extraction techniques, Hongming Guo, another PhD student in Wooley’s lab, is converting purified fly chitin into a similar polymer known as chitosan. It does this by removing the acetyl groups of chitin. This exposes chemically reactive amino groups that can be functionalized and then cross-linked. These steps convert the chitosan into useful bioplastics, such as superabsorbent hydrogels, which are 3D polymer networks that absorb water.
Guo has produced a hydrogel that can absorb 47 times its weight in water in just one minute. This product could potentially be used in farmland soil to capture flood water and then slowly release moisture during subsequent droughts, says Wooley. “Here in Texas, we’re always dealing with flooding or drought,” she explains, “so I was trying to figure out how to create a super-absorbent hydrogel that could deal with that.” And because the hydrogel is biodegradable, he says it should gradually release its molecular components as nutrients for crops.
This summer, the team is launching a project to break down chitin into its monomeric glucosamines. These small sugar molecules will then be used to produce bioplastics such as polycarbonates or polyurethanes, which are traditionally made from petrochemicals. Black flies also contain many other useful compounds that the group plans to use as starting materials, including proteins, DNA, fatty acids, lipids and vitamins.
Products made from these chemical building blocks are meant to be biodegradable or digested by bacteria and insects when discarded, so they won’t contribute to the current problem of plastic pollution. Wooley’s vision for the process would align it with the concept of a sustainable circular economy: “Ultimately, we’d like insects to eat plastic waste as a source of food, and then harvest it again and harvest its components to make new plastics,” he says. So insects would not only be a source but also consume discarded plastics.”
Source: www.acs.org
Photos: www.pixabay.com & www.wikipedia.org