Polystyrene waste is everywhere and it is not biodegradable. Scientists have just found a way to break it down.

Scientists at the U.S. Department of Energy’s Ames Laboratory and their Clemson University partners have discovered a green, energy-efficient process to break down polystyrene, a type of plastic widely used in foam packaging materials, disposable food containers, cutlery, and many other applications .

Polystyrene is part of a much larger global plastic waste problem. Hundreds of millions of tons of polymers are produced every year, most of which is discarded after use. Due to the chemical stability and durability of industrial polymers, plastic waste does not easily degrade in landfills and is often incinerated, releasing carbon dioxide and other hazardous gases. To halt the growing stream of polymer waste and reduce carbon dioxide emissions, plastics must be recycled or converted into new value-added products.

Recycling the vast majority of plastics is currently not economically feasible; sorting and separating them is time and labor intensive, while chemical processing and remanufacturing requires significant energy input and toxic solvents. Reprocessed polymers often exhibit worse performance than that of freshly made “from scratch” materials.

A team of scientists at Ames Laboratory used ball mill processing to deconstruct commercial polystyrene in a single step, at room temperature, in an ambient atmosphere in the absence of harmful solvents. Ball milling is a technique where materials are placed in a milling bottle with metal ball bearings and then agitated until a desired chemical reaction occurs. This experimental approach, called mechanochemistry, has numerous applications in the synthesis of new materials and attractive properties in the recycling of plastics.

Polystyrene deconstruction proceeds through a series of chemical events in which the macromolecules are mechanically cut out, generating free radicals that are detectable in the ground material even after prolonged exposure to air. The metal bearings used for milling and the ambient oxygen act as cocatalysts that allow extraction of the monomeric styrene from the formed oligomeric radical bearing species. The experiments showed that the temperature rise in the material during grinding is not responsible for the observed phenomenon as the temperature in the ground powder does not exceed 50 ° C while the thermal decomposition of polystyrene in air starts at about 325 ° C The Clemson group confirmed the extensive deconstruction of the original polymer into smaller fragments, oligomeric materials, suitable for further processing into new value-added products.

“This method represents a major breakthrough that allows a polymer to be dismantled and degraded at the same time under ambient conditions, ie ~ 300 ° C below the thermal decomposition temperature of the pristine material,” said Viktor Balema, senior scientist at Ames Laboratory. “We believe this proof of concept is an exciting opportunity to develop new recycling technologies for all kinds of plastics, and that will help shape the circular economy.”

His Clemson University partner, Kentwool Distinguished Professor Igor Luzinov, further noted that “this discovery opens new avenues for the low-temperature recovery of monomers from multicomponent polymer-based systems such as composites and laminates. In addition, our technology will enable the monomer to be recovered. extractable from cross-linked materials with styrene units in their structures. “

Alfred P. Sloan Foundation Research Fellow, Professor Aaron Rossini of Iowa State University, further noted that “electron paramagnetic resonance spectroscopy shows large concentrations of free radical-centered species in air-ground polystyrene. This is a surprising result because free radicals are normally very reactive. Also the presence of the radicals gives direct evidence that the milling directly causes the cleavage of the polymer chains. We expect that the reactive sites associated with the free radicals can be used to functionalize the processed polymers to obtain new value. added products. “

The research is further discussed in the article “Depolymerization of Polystyrene Under Environmental Conditions” written by Viktor P. Balema, Ihor Z. Hlova, Scott L. Carnahan, Mastooreh Seyedi, Oleksandr Dolotko, Aaron J. Rossini and Igor Luzinov; listed on the front of the New Journal of Chemistry