Plastic Researchers Develop a Sustainable Alternative to Polystyrene

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Polystyrene is one of the most important plastics worldwide, but has so far been considered not very sustainable. A research team at the Helmholtz Center Hereon (Germany) has now developed an alternative polystyrene that contains renewable raw materials, can be produced energy-efficiently, and is biodegradable.

It’s found in protective packaging for televisions and electronic devices, in decorative moldings and baseboards for interior home construction, and even in Petri dishes. Polystyrene is one of the world’s most important plastics. Nearly 20 million metric tons of it are produced annually. The material is primarily made from crude oil and is virtually non-recyclable—brand-new polystyrene is cheaper, so used products are usually incinerated or landfilled. Like other plastics, polystyrene is hardly biodegradable in nature.
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 recyclability represent a major step forward,” says Ph.D. candidate Phannaro Nhem, who is currently working on his dissertation under Prof. Francesca Toma, director of the Hereon Institute for Functional Materials for Sustainability. Researchers from the Brandenburg University of Technology Cottbus-Senftenberg (BTU) (Germany), the Free University of Berlin (Germany), and Helmut Schmidt University in Hamburg (Germany) were also involved.

50 Percent Renewable Raw Materials

Commercially available polystyrene is produced by allowing styrene molecules to react with one another 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 to occur. The team supplemented the styrene molecules with the chemical compound itaconic anhydride. This can be produced through fermentation from plant-based carbohydrates such as sugar. The polystyrene then contains about 50 percent of this bio-based raw material.
The manufacturing process also became more energy-efficient: Instead of heated reaction vessels, the researchers used microwave radiation as a heat source. “It’s just like in a home kitchen. Heating food on the stove takes a long time and consumes 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. “Our results show that it could establish itself as a more energy-efficient alternative for controlled polymerization processes.”

The new polymer was developed based on the principle of "design for degradation"—controlled degradation at the end of its life cycle—thereby paving the way for polystyrene to become part of closed-loop material cycles and the circular economy. 

Francesca Toma

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 later on. “Unlike conventional polystyrene, our variant breaks down into small fragments as a result,” says Nhem. Bacteria are also able to process the small polystyrene fragments—unlike conventional, tightly cross-linked polystyrene. “The new polymer was developed based on the principle of ‘design for degradation,’ which involves controlled degradation at the end of its lifespan,” adds Francesca Toma, “thereby opening the way for polystyrene as a material toward closed-loop material cycles and the circular economy.”
Initial tests show that the material can be processed on injection molding machines. Using the current laboratory setup, the team initially produced mini Petri dishes the size of a 1-euro coin. However, many applications are conceivable in the future. Initial studies with human stem cells also suggest that the material is highly biocompatible and is just as suitable for cell cultures as commercially available polystyrene.

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