Plastic recycling is already not nearly as efficient or widespread as it should be. Part of that is because some plastics aren't easily recycled. Black plastic, for example, generally can't be sorted at recycling facilities, so it often goes right into landfills.
That could be changing, however.
Researchers at Cornell University and Princeton University have figured out a way to use sunlight to alter the chemical composition of black plastics to make them more recyclable. They announced their results in a study published in ACS Central Science in November.
This is a huge step forward that has the potential to mitigate a serious plastic waste problem.
The recycling problem isn't so much with black plastic itself, but with how sorting systems at recycling facilities work. Usually, facilities shine infrared or near-infrared lights on plastic recyclables to sort them by color. But since black absorbs infrared, the machines can't "see" the black plastic, so it gets sent off to a landfill or incinerator. According to Beyond Plastics, the "vast majority" of black plastic is not recycled.
This new method to recycle plastic makes it much easier to recycle all colored plastic, however.
A Cornell release on the study explained researchers were looking at ways to break down plastics into reusable starter materials for more plastic. They realized the agent in black plastic that turns the material black, a compound called carbon black, was the key.
Carbon black releases a tremendous amount of heat when it absorbs light. When researchers beamed LED light at a black plastic powder, it heated up and broke down the polymer chains in the plastic into monomers, the building block of plastic products.
They next tried the same process but with sunlight, rather than LED light. The result was a significant increase in efficiency. The team then converted the monomers into plastic, demonstrating the circular potential of this new recycling method.
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"Carbon black or similar black pigments are prevalent in our society, commonly found in tires, plastics, and inks. It has been known for many years that these black additives absorb light and release heat," said Sewon Oh, a lead author of the study, per the Cornell report. "However, we had not taken advantage of this already incorporated carbon black to generate an immense amount of heat to recycle plastic back to monomer, a starting ingredient for plastics."
The study's co-authors also said: "Simple, visible light irradiation holds the potential to transform the chemical recycling of plastics, using the additives already found in many commercial products."
Anything we can do to make plastic recycling easier, more efficient, and more complete is crucial as we look to move past the scourge of plastic pollution and the carbon emissions required to make virgin plastic.
Using the sun is a pretty smart, clean way to do it.
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