A new method for recycling black polystyrene plastics, such as coffee lids and food containers, could help divert these materials from landfills. The approach, reported in ACS Central Science, uses sunlight or white LED light to transform black and colored polystyrene waste into reusable chemical components.
Black plastics are notoriously difficult to recycle due to the color additives complicating sorting processes. Researchers at Cornell University and Princeton University, led by Sewon Oh, Hanning Jiang, and Erin Stache, have developed a technique that uses carbon black, a common additive in these plastics, to initiate a recycling process using light. “Simple, visible light irradiation holds the potential to transform the chemical recycling of plastics, using the additives already found in many commercial products,” the authors stated.
The method involves grinding polystyrene mixed with carbon black into a fine powder, which is then sealed in a glass vial. Exposing the vial to high-intensity white LED light for 30 minutes causes the carbon black to absorb the light and convert it into heat. The heat breaks the polystyrene’s molecular structure, yielding smaller chemical components — mainly one-, two-, and three-styrene units. These byproducts were effectively separated during the process, and both the carbon black and styrene monomer were recycled to create new polystyrene, demonstrating the potential for a circular recycling system.
When applied to post-consumer black plastic items such as coffee lids and food containers, the method converted polystyrene into styrene monomer at a rate of up to 53%. The process was slightly less efficient for plastics contaminated with substances like soy sauce or canola oil. However, switching from LED light to focused sunlight significantly improved efficiency, achieving conversion rates as high as 80%.
The technique was also tested on a multicolored mixture of polystyrene waste, including black, yellow, red, and colorless materials. Under sunlight, the conversion rate reached 67%, compared to 45% under LED light. The researchers attribute the improved results to the higher light intensity sunlight provides.
The study highlights the potential for a closed-loop recycling process for polystyrene waste, mainly using natural sunlight as a more sustainable energy source. By focusing on a commonly used additive like carbon black, the researchers aim to reduce the need for additional chemicals in recycling.
Cornell University, Princeton University, and the U.S. Department of Energy’s Catalysis Science Early Career program funded the research.
Bravo, I have long awaited this find.