Fluorine helps make PET plastic waste easier to recycle

by | Apr 17, 2024

Pre-activation of plastics with fluorine-containing molecules disrupts their stability, making them easier to break down and upcycle.
A shiny, iridescent plastic material.

Using simple, one-pot protocol, researchers have combined the power of fluorine and hydrogen bonding to upcycle PET bottles into different types of polyester plastics, creating a closed-loop system for recycling plastic waste.

Polyester plastics constitute over 10% of total plastic production and find extensive application in packaging, fiber production, and single-use beverage bottles. With global plastic production doubling since the beginning of the century to almost 400 million metric tons per year in 2021, plastic waste has become an environmental scourge and one of the greatest challenges facing our planet.

“Basically everywhere we look now, we find plastic,” said Jenna Jambeck, a professor at the University of Georgia’s College of Engineering who researches plastic waste and who was not involved in the current study. “It’s all around us, and we know it’s in the air and in different food products. But we don’t really know yet what the impacts are on human health.” 

The inherent challenge in upcycling PET plastics

Plastics are so prevalent because they’re practical and cheap to produce. The (perhaps unfortunate) reality is it’s unlikely we’ll stop using them altogether, even with major policy changes. However, researchers led by Xuefeng Jiang at East China Normal University have proposed a way to reduce excessive production by upcycling the plastic items we already have.

“Depolymerization [the chemical breakdown of plastics into their components] for polyester is in great demand with an energy-efficient process and diverse high-value-added monomer recovery for environmentally friendly recycling,” wrote the team in their paper, recently published in Advanced Science.

Despite ongoing research aimed at finding sustainable solutions to upcycle plastic waste, breaking down plastic polymers into their monomer units and linking them back together conventionally requires high temperatures, pressures, or metal additives.

But Jiang and his colleagues reasoned that a simpler approach could be taken using polyfluorinated organic acids — a class of organic compounds that contain multiple fluorine atoms attached to a carbon backbone.

“Our study commenced with […] fluorinated additives, disrupting the intermolecular forces between PET chains,” wrote the team. “After an extensive screening, the results revealed a significant advantage of fluorinated acids over other[s].”

The key is the small atomic radius and chemical properties of the fluorine atoms, which interact strongly with the polyester chains, disrupting their stability and making them more susceptible to chemical degradation.

A promising start, but there is a catch

Using a variety of techniques to elucidate the mechanism, from scanning electron microscopy to X-ray analysis and computational simulations, the team determined that reversible bonds formed between the fluorine molecules and components in the PET polymer backbone. This leads to “pre-activation involving swelling and decrystallization” of the plastic, lowering the energetic barrier required to break down the long polymer chain into its constituent components.

The scientists showcased the effectiveness of their approach across various types of polyester plastics, including common items like disposable beverage bottles, fibers, sheets, and more complex blends.

They achieved impressive yields of over 90% in recovering diverse monomers, which could potentially be used to create new polymer chains. However, further investigation is needed to confirm the suitability of these monomers for producing new plastics. Moreover, the successful demonstration of this method on a kilogram scale is promising, achieving a remarkable 96% yield. Yet, whether this can be scaled up to industrial plastic recycling remains uncertain.

While these findings open doors to innovative plastic recycling methods, there are crucial aspects to address. Aside from scalability concerns, there’s a need for rigorous evaluation of the environmental impact, particularly regarding the use of perfluorinated acids.

These chemicals, known as “forever chemicals,” have raised alarms due to their potential health risks and persistence in nature. Their inclusion in the process could hinder its widespread adoption, highlighting the importance of thoroughly assessing the ecological consequences of any proposed solution to plastic waste.

Reference: Xuefeng Jiang, et al., From Polyester Plastics to Diverse Monomers via Low-Energy Upcycling, Advanced Science (2024). DOI: 10.1002/advs.202403002

Feature image credit: Emily Bernal on Unsplash

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