Researchers from ISU's Polymer and Food Protection Consortium wanted to track where chemicals found in polypropylene — known as No. 5 plastic — ended up after the plastic was washed for recycling.
Recycling facilities can use several different methods to wash their plastics, so researchers mimicked those techniques with untreated water to see how each one affected the chemicals.
In particular, the study looked at phthalates, a class of plastic additives that serve a functional purpose in plastic manufacturing but may affect cancer risks, as well as hormones and child development, according to the Centers for Disease Control and Prevention and Environmental Protection Agency.
“We wanted to understand if the recycling process can remove any of these kinds of chemicals of concern from the final product,” said ISU food science professor Greg Curtzwiler, who led the study.
One method they tested used an industrial soap. The plastic material was ground up into small flakes — about 1 millimeter wide. Ultrasonic vibration and sodium hydroxide were used with the soap to clean the material. They found that using the soap did reduce the phthalates in the plastic but transferred them into the wash water.
Different batches of material were tested through several wash cycles, and the chemicals built up through each one.
But, Curtzwiler said, this is a good thing for repurposed plastic.
“We’re seeing that these processes could potentially remove some of these other chemicals from its second life,” he said.
Even though the water was contaminated, Curtzwiler said this process isolates the chemicals into the water where they can be treated and removed from the process entirely. He said researchers at ISU's Polymer and Food Protection Consortium are studying this, too.
“There are some other techniques that we’re in the process of optimizing to further remove some of these other chemicals that are a little bit more challenging to remove,” Curtzwiler said.
He added that some recycling facilities already treat their water, and some don’t use water at all to wash their materials.
A long-term goal, Curtzwiler said, is to find a way to use less plastic entirely, while still having products that function the way they need to.
