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

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

Polystyrene is part of a larger global problem with plastic waste. Hundreds of millions of tons of polymers are produced each year, most of which are discarded after use. Due to the chemical stability and durability of industrial polymers, plastic waste does not break down easily at landfills and is often incinerated, producing carbon dioxide and other hazardous gases. To stop the growing flood of polymer waste and reduce carbon dioxide emissions, plastics need to be recycled or converted into new value-added products.

At present, recycling of the vast majority of plastics is not economically feasible; they sort and separate are time and labor intensive, while chemical processing and remanufacturing require significant energy input and toxic solvents. Reprocessed polymers often exhibit inferior performance to those of newly manufactured “manufactured” materials.

A team of scientists from the Ames laboratory used ball-forming 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 that places materials in a scale vial with metal ball bearings, which is then stirred until a desired chemical reaction takes place. This experimental approach is called mechanochemistry and has numerous applications in the synthesis of new materials and attractive properties regarding plastic recycling.

The deconstruction of polystyrene proceeds through a series of chemical events involving mechanical cutting of the macromolecules, which generates free radicals that are observable in the ground material, even after prolonged exposure to air. The metal bearings used for grinding and the oxygen in the environment serve as co-catalysts that allow the extraction of the monomeric styrene from the formed oligomeric radical drag. The experiments showed that the temperature rise in the material during grinding is not responsible for the observed phenomenon, since the temperature in the ground powder does not exceed 50oC, while the thermal decomposition of polystyrene in the air starts at about 325oC. The Clemson Group confirms the extensive deconstruction of the original polymer into smaller fragments, oligomeric materials, suitable for further processing into new value-added products.

“This method is an important breakthrough that enables the disassembly of a polymer at the same time as its degradation under environmental conditions, i.e. ~ 300 C below the thermal decomposition temperature of the pristine material,” said Viktor Balema, senior scientist at Ames, said. “We think this proof of concept is an exciting opportunity for the development of new recycling technologies for all types of plastics, and it will contribute to the creation of the circular economy.”

His partner at Clemson University, Kentwool Distinguished Professor Igor Luzinov, further noted that “this discovery offers new ways for low temperature recovery of monomers from multicomponent polymer-based systems such as compositions and laminates. Our technology will also allow the monomer to be extracted from crosslinked materials. which contain 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 carbon-centered species in polystyrene ground in the air. This is a surprising result because free radicals normally is very reactive.The presence of the radicals also gives direct evidence that the grinding directly causes tearing of the polymer chains.We expect that the reactive sites associated with the free radicals can be used to function the processed polymers to add new value acquired products added. “

The research is further discussed in the paper “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; appears on the front page of the New Journal of Chemistry.