Reducing the Size of Polystyrene with an Impact

    Polystyrene is one of the most commonly used forms of plastics used in everyday materials in three predominant forms, traditional polystyrene that is typically used for impact resistance applications, polystyrene film used in packaging applications and polystyrene foam predominantly used in everyday items. Polystyrene foam has impacted the environment the most of these three since it tends to be used in single use applications where it becomes immediately thrown away once used. The reason for this is due to the fact there are no current ways of breaking down polystyrene that are competitive in costs compared to the production of new polystyrene. As of this year though a few scientists at Ames Laboratory, in partnership with Clemson University, may have found a cost effective and environmentally friendly way of breaking down polystyrene.

    The process uses a mechanochemical process in the form of ball-milling to deconstruct polystyrene in a single step that can be performed at room temperature in ambient air as well as in the absence of harmful solvents. Ball-milling is the process by which metal ball bearings and material are agitated in an enclosed volume allowing for the collision between these ball bearings and material initializing a chemical reaction. The initial testing process was conducted with loading commercial polystyrene into a shaker mill along with milling ball sets that were either manufactured from hardened steel, tungsten carbide , or silicon nitride. The ball-to-material weight ratio was kept between 10:1 to 13:1 and the run time was kept to 12 an hour run time. The size of these ball bearings is much larger than that of the polystyrene chains which means when a polystyrene chain becomes sandwiched in between two colliding bearings, the collision creates an energetic than chemical reaction that breaks down these long chains into smaller chains of styrene. With a long period of time these smaller chains will eventually break down into single monomers of styrene. The batch which was processed in air showed that the ambient oxygen and metal bearings acted as co-catalysts to enable extraction of the monomeric styrene later on. Throughout the whole milling process the maximum temperature reached was 60℃ therefore confirming that thermal decomposition was not the reason for the breakdown of the polystyrene since polystyrene tends to break down at 325℃.

    The fragmented material has the possibility to be recycled in the form of new polystyrene material which would reduce the total carbon emissions released into the environment from the production of new polystyrene. This process has yet to be proven at a large scale which would be needed in order for this practice to be adopted in the commercial field determining whether this process is feasible for a real world recycling method of polystyrene. 

Sources:

1. Mraz, Stephen J. “Please Enable Cookies.” StackPath, 23 Mar. 2021, www.machinedesign.com/leaders/materials/article/21158993/a-new-way-to-break-down-polystyrene-and-clean-up-the-environment.

2. “Scientists Discover Ways to Break down Polystyrene Waste.” Yahoo!, Yahoo!, 20 Mar. 2021, in.style.yahoo.com/scientists-discover-ways-break-down-120715259.html. 

3. Balema, Viktor P, et al. “Depolymerization of Polystyrene Under Ambient Conditions.” New Journal of Chemistry, vol. 45, no. 6, 2021, pp. 2935–2938., doi:10.1039/D0NJ05984F.