A Safer Nonstick Coating without the PFAS

“Forever chemicals,” especially polyfluoroalkyl substances (PFAS), are highly popular in cookware coatings due to their ability to repel water, oil, and grease. Teflon, created in the 1930s, is part of this group and remains popular today, despite its toxic PFAS levels.

Recent studies have linked PFAS to certain types of cancer, birth defects, and other health issues. Their chemical inertness also causes PFAS to resist the normal processes that break down organic molecules over time, thus earning them the moniker, “forever chemicals.” 

To solve the PFAS problem, researchers from the University of Toronto’s Department of Mechanical and Industrial Engineering are studying alternative materials that have promising non-stick properties without the PFAS content. Led by assistant professor Kevin Golovin, the team centered its focus on polydimethylsiloxane (PDMS). 

A safer surface

PDMS is often sold as silicone. It can be very biocompatible and even implanted safely into the body. However, in their first experiments, Golovin and his team could not get the PDMS material to be as non-sticky as PFAS-based materials.

As they continued to manipulate the structure and chemistry of PDMS to further test its properties, the breakthrough came when doctoral student Samuel Au discovered that a very short burst of oxygen plasma could add multiple CF3 reactive groups. These consist of one carbon with three fluorines—a single PFAS molecule to the ends of the silicone chains, rather than just a single CF3. The team eventually determined that seven CF3 reactive groups provided the maximum liquid repellent and nonstick properties with minimum fluorination. 

“Spectroscopy confirmed that the seven CF3 groups decorate the very tips of the silicone chains, much like the fletched feathers on the end of an arrow,” Golovin said. “We called this modification process nanoscale fletching.” 

The researchers bonded short PDMS chains to a base material, creating a surface lined with PDMS-like bristles. They then attached seven of the smallest PFAS molecules to enhance the material’s oil-repelling properties.

As a test, the team coated a piece of fabric with the new material and placed drops of various oils on it to see how well it could repel them. On a scale developed by the American Association of Textile Chemists and Colorists, the new coating achieved a grade of 6, placing it on par with many standard PFAS-based coatings being used today.  

Although PFAS molecules are part of this process, the team used the shortest possible molecule (CF3), which does not bioaccumulate. The new substance repels both water and grease, as well as standard non-stick coatings, and contains lower amounts of PFAS, making it significantly safer.

“There has always been a presumed linkage between the chain length of PFAS, its toxicity, and its liquid repellent or nonstick properties,” Golovin said.  

“Over the past few years, my lab has been disproving this, using shorter and shorter chains of PFAS or other inert polymer chains. Our ‘Eureka!’ moment came when we figured out that even single CF3 groups—the shortest possible PFAS and by some definitions not even a PFAS—could perform similarly to longer-chain PFAS, with far less health risk,” he said. 

By attaching about seven CF3 groups to the end of a silicone chain tethered to a surface, liquid-repellent properties with short-chain PFAS are possible, such as a low coefficient of friction, dropwise condensation of low surface tension fluids, and the ability to repel a wide range of liquids like solvents, oils, alcohols, and surfactant-laden aqueous solutions.  

“Exciting surface properties are possible because the CF3 groups are able to migrate to the upper-most surface of the silicone layer—a wholly different mechanism than the inertness of materials like Teflon and PFAS-treated surfaces,” Golovin mentioned. 
 

Scaling potential

Golovin hopes to collaborate with manufacturers of non-stick coatings that might wish to scale up and commercialize the process. However, nanoscale fletching requires oxygen plasma activation of the surface, which is not the most scalable industrial process.  

“Our next step is to transition this process to a wet chemistry activation, such that surfaces could be sprayed or dipped in-line,” Golovin said. “This then makes the technology feasible on a larger scale—for example, on nonstick cookware or water-repellent fabrics.” 

PFAS are used in many industries and academic fields. For example, fuel cells utilize PFAS in gas diffusion layers, and batteries utilize PFAS in their anode and/or cathode materials. 

“While our new coating technology will obviously not find use in every application, in theory, anywhere PFAS are currently being used to protect a surface from liquid impregnation, our coating can potentially offer a sustainable and non-toxic solution,” Golovin explained. 

Although the team’s new technology has substantially less fluorinated compound than comparable PFAS technologies, more work is needed to ensure all potential byproducts of the coating after degradation remain nontoxic.

“The ultimate goal will be to completely eliminate every single C-F bond from this type of coating technology, and current efforts are ongoing to make such materials,” Golovin said. 

 Mark Crawford is a technology writer in Corrales, N.M.