From the depths of the oceans to stomachs of whales waste plastics are out of control. Now there is a new entry in the quest for an alternative that won't require us to get more responsible about littering, although vegetarians may have very mixed feelings.
Plastic waste is a classic tragedy of the commons problem. Even if we were able to get 90% of the people who currently dump products without thinking to mend their ways, the rest would still end up destroying marine life the rest of us love, just a little more slowly.
Twenty years ago there were hopes that starch or cellulose-based plastics would solve the problem. Since bacteria have had hundreds of millions of years to work out how to break these down they've got pretty good at it. But the products on the market have proven less than ideal. Some don't break down properly or do so only under certain circumstances, and they can cause problems for recyclers.
So the Harvard Wyss Institute for Biologically Inspired Engineering went looking for a different bioplastic base. Chitin was an obvious answer. Most famously the main ingredient in crustacean shells, it also appears in the wings and armor of many insects and the cell walls of fungi, making it, according to the Institute, the second most common organic material on Earth. It can be thought of as the invertebrate version of keratin, which mammals use to make fur, claws and fingernails.
When treated with sodium hydroxide chitin turns to chitosan, a polysaccharide used medically, for water filtration and to enhance plant growth. Somewhat ironically it has also been shown to help plants fight fungal infections. Despite its variety of uses commercial consumption of chitosan does not get close to matching the available supply of chitin from waste shrimp shells.
The Institute's substitute for plastic bags is a product made by combining chitosan with a protein from silk, which has been named Shrilk. In Macromolecular Materials and Engineering the Institute's Dr Javier Fernandez and Dr Donald Ingber describe their process for producing Shrilk and 3D printing the product into a chess set. "You can make virtually any 3D form with impressive precision from this type of chitosan," says Fernandez
"Our scalable manufacturing method shows that chitosan, which is readily available and inexpensive, can serve as a viable bioplastic that could potentially be used instead of conventional plastics for numerous industrial applications." says Ingber.
Subtle differences in the manufacturing process can leave the Shrilk too brittle for most uses, but with experimentation Fernandez and Inber were able to detail a reliable method for what they wanted. Adding wood flour removed the problem of shrinkage which would have ruled their product out for some purposes.
Most importantly, the pair claim Shrilk breaks down within two weeks in the environment, and even serves as an effective stimulant for plant growth, a assertion they support with the below video of a blackeye pea in soil with Shrilk added.
