Researchers at the University of Tennessee, Knoxville, are studying microplastics and nanoplastics to determine how they form in the environment—and how to reduce or even prevent their formation.

Approximately 75% of all plastic used is either landfilled or cast into the environment, leading to fragmentation into particles smaller than the eye can see that are penetrating cell membranes and accumulating within organisms, potentially harming aquatic life, plants, and humans.

“The presence of plastics after their end of life is problematic for a number of reasons, including their impact on human health and the environment,” said Mark Dadmun, the Paul and Wilma Ziegler Professor of Chemistry who specializes in polymer science. “The polymer science community has been at the forefront of wrestling with the complexity of microplastics and finding solutions.”

Furthermore, microplastics (sizes between 1 micrometer and 5 millimeters) and nanoplastics (sizes between 10 nanometers and 1 micrometer) can also be formed by mechanical abrasion, such as everyday processes like washing laundry or driving, which creates friction between tires and roads.

Dadmun and his students, including Shelby Watson-Sanders, have provided insight into the formation of these nanoplastics. In a paper published this spring in Nature Communications, Dadmun and Watson-Sanders, with collaborators from several other institutions, built on earlier research on polymer recycling to explore what is triggering the polymer chains to break down into nanoplastic fragments that persist in the environment.

“Polymers are like a bowl of spaghetti in that they’re very loosely entangled,” Dadmun explained. “Some polymer chains in a given plastic piece can line up in small sections to form crystalline portions that offer stronger material properties.”

These properties allow us to create products like milk cartons, water bottles, and pill bottles. However, it’s these strong, organized crystallines that do not degrade easily and thus break off into nanoplastics. Approximately 70% of the materials we use commercially are developed with this crystalline structure.

The team specifically studied different grades of polypropylene, poly(ethylene terephthalate) (PET), and polystyrene (PS), which are the second, fourth, and fifth most-produced polymers worldwide. Researchers degraded the polymers under various conditions and were able to validate the correlation between the crystalline parts of the polymer that fail to degrade with their fragmentation and the creation of nanoplastics.

“This information tells us where the nanoplastics are coming from so we can design the next generation of plastics to produce less of them,” Dadmun said.