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Spotlight: The Behavior of Polymers in Our Recycled Plastics

Recycling Plastic Under the Microscope
Recycling Plastic Under the Microscope
This video shows what happens when mixed plastics melt and then crystallize during the recycling process. The various colors show the complex dance of the polymers — the building blocks of the plastic — as they line up and crystallize. When they do not align properly, the recycled plastic becomes brittle. Credit: K. Migler/NIST

Not all plastics are the same, and they don’t all blend together well during recycling. At NIST, researchers are looking for ways to make recycled plastic stronger and more valuable. It’s all about the chemistry.

Recycling plastic involves melting the material down and then molding or extracting it into new shapes. If different types of plastics are melted and mixed together, their building blocks, called polymers, may not adhere well to each other when they crystallize.

That’s exactly what this video shows. See through a microscope as polymers from mixed plastics crystallize. In the beginning, when the plastic is melted, the polymers point in all directions, and the resulting color is magenta. As the molten plastic cools, the polymers crystallize. Yellows show areas where the polymers align in one direction, while the blues show a different direction.

If the polymers do not align and adhere to each other properly, the resulting plastic can be brittle and weak.

If scientists can get the polymers from different types of plastic to have good chemistry together — so they line up nicely when they crystallize — then recycled plastics will be stronger and more valuable.  

When recycled plastic is more valuable, it’ll be seen as an important raw material rather than a waste product. That will mean more recycled plastic in our products and less plastic pollution in our oceans.  

This is the vision of the circular economy.

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Released August 10, 2021, Updated October 18, 2022