Researchers develop self-healing, biodegradable plastic

Researchers at the University of Konstanz have developed mineral plastics with numerous positive properties, including microbiological degradability. Their work has been published in the journal Small Methods.

Back in 2016, Konstanz chemists created a mineral plastic that was hard, non-flammable, self-healing and could be produced at room temperature in water, which is very energy-efficient and does not require toxic solvents. Before hardening, it could be shaped in any way the user desired — like chewing gum — and by adding water, it could be converted back to its ‘chewing gum’ form to be reshaped and thus recycled.

But even though this plastic, with its novel manufacturing process and outstanding material properties, has since attracted great interest from industry, it still had a crucial shortcoming: due to its chemical composition, it was difficult to biodegrade.

“Previously, we used polyacrylic acid to produce our mineral plastic,” said Konstanz chemist Helmut Cölfen. “Chemically, this acid has the same backbone as polyethylene, which is known to cause major problems in the environment because it is hardly biodegradable.”

A research team led by Cölfen and Ilesha Avasthi, a postdoc in Cölfen’s lab, set to work looking for an alternative basic building block to develop an environmentally compatible mineral plastic that retains the intriguing properties of the original material. Now, the chemists have presented the next generation of their mineral plastic.

Instead of petroleum-based ingredients such as polyacrylic acid, they now use polyglutamic acid. This natural biopolymer is readily available in large quantities and can even be obtained sustainably; for example, from biotechnological production using microorganisms. A variety of microorganisms that already exist in the environment can degrade polyglutamic acid.

“Our new mineral plastic has the same positive properties as the previous one, but has the decisive advantage that its basic building block — polyglutamic acid — can be produced with the help of microorganisms and is completely biodegradable,” Cölfen said.

In order to prove that this biodegradability applies to the mineral plastic itself and not just to its individual components, the chemists enlisted the support of David Schleheck and postdoc Harry Lerner from the Department of Biology at the University of Konstanz. Their task was to make the plastic disappear, with the help of microorganisms.

In degradation experiments, the biologists were able to show that microorganisms found in forest soils, for example, began metabolising the mineral plastic after just a few days. After only 32 days, the microorganisms had completely degraded the plastic. The researchers have thus succeeded in making mineral plastic, with all its positive material properties, that is also sustainable and biodegradable.

Image courtesy University of Konstanz.