The proliferation of global plastic waste continues to be a growing problem for the world. Hundreds of millions of tons of plastics are produced each year and most of it is used once and then discarded. The properties that make plastics so attractive – durability and chemical stability – make it difficult to do anything with discarded plastics other than deposit them in landfills – where they don’t easily degrade over time – or burn them, which dumps carbon dioxide and various hazardous gases into the atmosphere.
Polystyrene is one of the most widely used plastics. It is found in foam packaging materials, disposable food containers, plastic cutlery, storage containers, and many other places.
Recycling plastics like polystyrene is generally not economically feasible. Sorting plastics by type is time and labor intensive and the chemical processes required to break down plastics into usable precursor materials require significant energy input and the use of toxic solvents.
Recently, a team of scientists at Ames Laboratory in Iowa has developed a process based on ball-milling that deconstructs commercial polystyrene in a single step, at room temperature, in ambient atmosphere, and in the absence of harmful solvents.
Ball-milling is a technique that places materials in a milling vial with metal ball bearings which is then agitated to initiate a chemical reaction. This approach is known as mechanochemistry.
The method represents an important breakthrough that enables dismantling of a polymer that includes its chemical breakdown without requiring solvents or the high temperatures generally needed to thermally decompose it. This discovery opens up new avenues for low-temperature recovery of monomers from polymer-based systems that include composites and laminates. It could be a very useful weapon in the battle against plastic waste.
Photo, posted December 11, 2010, courtesy of Warrenski via Flickr.