Sunlight-Based Recycling for Black Plastic
Published 14 January 2025
Black plastic is notoriously difficult to recycle on account of its colour: easily missed by waste sorting systems, it commonly ends up as residue in landfill. A team of researchers in the US is working to overcome this issue with a new recycling method that uses white LEDs or the power of sunlight.
Carbon black is one of the most prevalent additives in both commercial- and industrial-grade plastics, used to improve the material’s performance, in addition to being a colour pigment. But while it’s a hindrance to the current recycling process (it’s undetectable by the near-infrared scanners that sort plastic waste), researchers at Cornell and Princeton universities are actually leveraging the substance for their new recycling system.
The team is building on an emerging strategy for plastic recycling that employs light to break down plastics into chemically useful materials, ready for new products. The process requires a ‘helper’ compound to convert light into heat (thus breaking polymer bonds apart). In this case, it’s carbon black.
When recycling black polystyrene, for instance, the material (which contains carbon black) is ground into a fine powder before being placed in a sealed vial under high-intensity white LEDs for 30 minutes. The carbon black converts the LED light into heat, which breaks down the plastic into its separate molecular components. These units, along with the carbon black, can then be recycled into new polystyrene.
Aiming to achieve a closed-loop recycling process, the team is testing other coloured plastics and scenarios. For example, focused sunlight as the heating agent yields higher conversion rates, while foodstuff contaminants (like soya sauce and orange juice) result in slightly less efficient results.
See our One-Minute Explainer: Circular Design for more context about closed-loop systems and Materials Evolution A/W 26/27 for other approaches to plastic waste.
