Thanks to the built-in predetermined breaking point Researchers Develop Biodegradable Polystyrene

Polystyrene is one of the most important plastics in the world, but has so far been considered unsustainable. A research team has now developed an alternative polystyrene that contains renewable raw materials, can be produced energy-efficiently, and is biodegradable. 

It is found in protective packaging for televisions and electronic devices, in decorative moldings and baseboards used in home interiors, and even in Petri dishes: Polystyrene is one of the world’s most important plastics. Nearly 20 million metric tons of it are produced. To date, the material has been manufactured primarily from crude oil and is hardly recyclable.

According to its own statement, a research team led by the Helmholtz Center Hereon has now developed a more sustainable polystyrene. “The factors of biodegradable raw materials, energy consumption, and recycling represent a major step forward,” says Ph.D. candidate Phannaro Nhem.  Researchers from the Brandenburg University of Technology Cottbus-Senftenberg (BTU), the Free University of Berlin, and Helmut Schmidt University in Hamburg were also involved.

50 percent renewable raw materials

Commercially available polystyrene is produced by allowing styrene molecules to react with each other to form plastic. In this process, the styrene molecules link together to form a stable chain. The container in which the reaction takes place must be heated for this purpose. 

The team supplemented the styrene molecules with the chemical compound itaconic acid anhydride. It can be produced through fermentation from plant-based carbohydrates such as sugar. The polystyrene then contains about 50 percent of that bio-based raw material. Instead of heated reaction vessels, the researchers used microwave radiation as a heat source. 

“It’s just like in your kitchen at home. Heating food on the stove takes a long time and uses a lot of energy. Microwaves are faster,” says Phannaro Nhem. “So far, microwave technology has not yet become widely established in polymer synthesis,” says Francesca Toma, director of the Hereon Institute for Functional Materials for Sustainability. However, the results suggest that it could establish itself as a more energy-efficient alternative for controlled polymerization processes.

Predetermined breaking point for recycling

In addition, the team used dibenzo[c,e]oxepane-5-thione (DOT) as a monomer, thereby incorporating thioester groups into the material. These building blocks act as strategically incorporated predetermined breaking points within the polymer network. This allows the material to be chemically broken down into smaller fragments at a later stage. 

“Unlike conventional polystyrene, our version breaks down into small fragments as a result,” explains Nhem. Bacteria are also able to break down these small polystyrene fragments—but not conventional, tightly cross-linked polystyrene.