Due to black filler materials, black plastics have posed a serious challenge in ineffective sorting. Black plastic early has a 0% recycling rate, which ultimately finds its way into landfills.
While researchers have made considerable progress in sorting black plastics, the solution for black plastic recycling largely remains ineffective. In those efforts, researchers at Cornell University and Princeton University have used an additive substance to mitigate black plastic pollution.
The team used sunlight and LED to leverage carbon black additive to convert black and colored polystyrene waste into reusable materials.
“Simple, visible light irradiation holds the potential to transform the chemical recycling of plastics, using the additives already found in many commercial products,” says the lead authors.
A photothermal conversion is an emergent approach that utilizes heat to break down plastic into chemically useful materials, which are then recycled into new products. The heat in this process is derived from a helper compound.
The foremost issue before the researchers was searching for a compound that wouldn’t create more waste and easily merge with the recycling process.
Intriguingly, the researchers took advantage of already existing black polystyrene – carbon black. Researchers tried to establish the feasibility of depolymerization of polystyrene by carbon black using a model system of polystyrene–carbon black. They found that subsequent visible light irradiation enables depolymerization.
Experimenters ground a mixture of lab-made polystyrene and carbon black into a fine powder and sealed the glass vial. The vial was then placed under high-intensity white LEDs for 30 minutes. The team found that carbon black converted light into heat.
This heat broke the molecular structure of polystyrene, creating shorter one-, two-, and three-styrene units. The mixture of these three units was separated using a reaction apparatus. The team also recycled the leftover carbon black and styrene monomer into polystyrene.
Smart robots that predicts waves in real-time could cut green energy costs
“We successfully demonstrated photothermal conversion to polymerize and depolymerize polystyrene using carbon black as a photothermal conversion agent. We showcased efficient depolymerization using approximately 5 wt % carbon black loading with high-intensity white LEDs,” mentions the study.
After successfully demonstrating photothermal conversion, it was time to experiment with consumer black plastic. They used black plastic from food containers and coffee cup lids, and up to 53% of the polystyrene was converted to styrene monomer.
When the light from the LED was replaced with sunlight, researchers observed a higher reaction efficiency of up to 80%. However, plastic waste contaminated with oil or juice broke down slightly less efficiently. Similarly, sunlight displayed a higher rate of 67% compared to 45% of white LEDs when a multicolored mixture of black, yellow, and red was converted to styrene.
This enhanced efficiency is associated with the increased light intensity achieved by focused sunlight. Researchers assert that this powerful technique of breaking down polystyrene waste can make the circular economy of black plastics more achievable.
Eco-friendly recycling technology restores spent battery cathode materials
Journal Reference
- Sewon Oh, Hanning Jiang, Liat H. Kugelmass, and Erin E. Stache. Recycling of Post-Consumer Waste Polystyrene Using Commercial Plastic Additives. ACS Central Science. DOI: 10.1021/acscentsci.4c01317
