Using sunlight to recycle black plastics

Using sunlight to recycle black plastics
by Clarence Oxford
Los Angeles CA (SPX) Nov 26, 2024

Researchers have developed a sunlight-powered technique to recycle black and colored polystyrene plastics, offering a new approach to handling materials typically sent to landfills. Black coffee lids and foam containers, often made of polystyrene, are challenging to recycle due to their color additives. A study published in 'ACS Central Science' describes a method leveraging an existing additive in black plastics - carbon black - combined with visible light to create reusable chemical building blocks.

"Simple, visible light irradiation holds the potential to transform the chemical recycling of plastics, using the additives already found in many commercial products," said Sewon Oh, Hanning Jiang, and Erin Stache, co-authors of the paper.

The process involves using light to break down plastics into reusable chemical components, but the challenge has been identifying a sustainable helper compound. Erin Stache and her team tackled this by utilizing carbon black, a common additive in black polystyrene waste.

To demonstrate, the researchers powdered a lab-made mix of polystyrene and carbon black, sealed it in a glass vial, and exposed it to high-intensity white LED light for 30 minutes. The carbon black converted the light into heat, which broke the plastic into shorter styrene molecules. These molecules, consisting of one, two, or three styrene units, were easily separated in the reaction setup. The team successfully reused the leftover carbon black and styrene monomer to make new polystyrene, highlighting the method's circularity.

When applied to post-consumer waste like food containers and coffee lids, up to 53% of the polystyrene converted to reusable styrene monomer. Efficiency dropped slightly with contaminants such as canola oil and soy sauce. However, the researchers achieved better results outdoors using focused sunlight, with 80% efficiency. Testing multicolored plastic mixtures under sunlight showed similar promise, converting 67% compared to 45% under LEDs.

The researchers attribute sunlight's higher efficiency to its greater intensity and suggest their method could establish a closed-loop recycling process for polystyrene waste.

The project received support from Cornell University, Princeton University, and the U.S. Department of Energy's Catalysis Science Early Career program.

Research Report:Recycling of Post-Consumer Waste Polystyrene Using Commercial Plastic Additives