Mechanochemical recycling converts polystyrene to a commodity chemical

A solvent-free ball-milling process can break down waste polystyrene into benzene and aliphatic hydrocarbons in as little as 15 min (Angew. Chem., Int. Ed. 2025, DOI: 10.1002/anie.202512687). By also including benzoic anhydride in the reaction vessel, Junpeng Wang and his team at the University of Akron converted the freshly generated benzene directly to benzophenone, creating a one-pot method to valorize consumer waste into a useful chemical feedstock.Polystyrene is one of the most recognizable and widely used plastics, with applications as diverse as packaging, construction, and medical equipment. However, the high cost of current recycling processes, combined with the low value of recovered material, means polystyrene is also one of the world’s least recycled plastics. In Spain, for example, 80% ends up in landfills and the remainder is incinerated.Meanwhile, mechanochemistry, which drives chemical reactions by stimulating reactants via mechanical forces, is an inherently cost- and energy-efficient method. This simple process has already attracted interest as a strategy to handle plastic waste, including per- and polyfluoroalkyl substances (PFAS) and polyethylene. But rather than destroying or depolymerizing the plastic, Wang’s team focused on degrading polystyrene into simple benzene units, which they upcycled into valuable commodity chemicals.The researchers began by grinding plastic pellets with an aluminum trichloride catalyst in a six-ball mill, driving a reaction known as a Friedel-Crafts dealkylation to form benzene and long-chain aliphatic hydrocarbons. Within 15 min, the reaction had degraded more than 90% of the starting polystyrene, a substantial time and energy savings compared with previous recycling methods.With a route