Argonne finds a way to recycle 'plastic No. 2' not just two or three times but infinitely
Chemists at Argonne National Laboratory in DuPage County have worked out a new way to recycle certain plastics infinitely, a discovery that could change the way we recycle containers like those used for milk and laundry detergents.
In the current process for recycling these high-density polyethylene, or HDPE, plastics, much of the material's properties are lost, so recycling can be repeated only two or three times. Argonne's novel method, developed in March, converts used HDPE into material that can be recycled many more times over.
It's a process that has been widely used in the case of plastic No. 1, commonly known as PET. Most frequently used in water and beverages bottles, plastic No. 1 is infinitely recyclable. Researchers have tried to mimic that result with HDPE, or plastic No. 2, but have faced difficulties as this material has a completely different chemical structure.
"As a proof of concept, we showed that we can take an HDPE water jug, do some chemistry and insert some particular groups that are similar to polyethylene terephthalate -- that is plastic No. 1 -- and construct and deconstruct the HDPE an infinite number of times, but maintaining the mechanical and thermal properties of the original material," said Argonne chemist Massimiliano Delferro, who leads the Catalysis Science Program in the lab's Chemical Sciences and Engineering Division.
Through the process, the recycled HDPE also became potentially biodegradable: The chemists inserted a functional group into the plastic's polymer chain that would allow bacterial enzymes to attach to the chain and begin to naturally break it down.
Delferro and his team worked in collaboration with Cornell University for four years to develop this process, but they still face one big challenge. It requires extremely rare, extremely expensive elements to be successful.
Their next step is to go back to the drawing board and find a way to scale up the process so it can be brought to market.
"We used very expensive, very exotic catalysts that we already know we cannot use at scale. But we have to consider the amount of plastic waste that we have on Earth," Delferro said. "We really need to discover or adapt other catalysts that can do the same reaction that we did with these critical elements to something that is ready to be deployed. This is what we're trying to do right now."
With most plastics, including HDPE, being made from fossil fuels, the goal is not only to reduce plastic waste but reduce carbon emissions and pollution associated with HDPE while conserving oil -- roughly 8% of the world's annual petroleum usage goes toward creating new plastic, the majority of which is discarded after it's used once.
Delferro added that the issue of plastic recycling has become all the more pressing since 2018, when the main receivers of U.S. recycling, including China and Turkey, became more stringent and stopped accepting mixed paper scraps and most plastics.
The change threw a giant wrench in the nation's recycling system, resulting in a reduction in the recycling rate from 8.7% in 2018 to 5%-6% in 2021, according to a 2022 report from environmental groups Last Beach Clean Up and Beyond Plastics, a project out of Bennington College in Vermont.
In Illinois, the number is comparable, with a statewide plastic recycling rate of 8.1%, according to a 2015 state-commissioned waste report.
"Now that we don't send anything to China -- almost zero -- that means we need to deal with our own trash, and that means we need to discover and develop technology to really deal with plastics," Delferro said.
• Jenny Whidden is a climate change and environment writer working with the Daily Herald through a partnership with Report For America supported by The Nature Conservancy. To help support her work with a tax-deductible donation, see dailyherald.com/rfa.