Researchers have developed an innovative method to recycle black and colored polystyrene waste using sunlight or white LEDs, which could significantly enhance plastic recycling efforts.

Traditional recycling methods for polystyrene are often costly and inefficient, requiring high temperatures over 572°F (300°C) in oxygen-free environments to break down molecular bonds.

Black polystyrene, commonly found in food containers and packaging, poses a recycling challenge due to color additives that hinder sorting by optical scanners.

The new process involves grinding black plastic into powder and exposing it to intense light, allowing carbon black to convert light into heat, effectively breaking down the plastic's molecular structure.

This discovery transforms the perception of carbon black from a recycling obstacle to a catalyst for breakdown, promoting closed-loop recycling systems.

When testing post-consumer black plastics, such as food containers and coffee cup lids, researchers achieved up to 53% conversion of polystyrene into styrene monomer, with efficiency increasing to 80% under focused sunlight.

The method demonstrated improved efficiency with natural sunlight, achieving a 67% breakdown rate for a mixture of colored polystyrene pieces, compared to 45% with LED light.

While the method showed slightly less efficiency with contaminated waste samples, it performed better under natural sunlight, indicating its potential for outdoor applications.

The process is effective on real-world waste, including plastics contaminated with food residues, although slightly lower conversion rates were noted.

The researchers achieved a closed-loop recycling system, converting up to 53% of consumer waste back into styrene, with an impressive 80% efficiency using concentrated sunlight.

The simplicity of utilizing sunlight, an abundant energy source, suggests that this recycling technology could be widely adopted.

This research was supported by funding from Cornell University, Princeton University, and the U.S. Department of Energy's Catalysis Science Early Career award.