Is Silicone the Answer to Phase Out PFAS?
While many agree that removing potentially harmful per- and polyfluorinated substances (PFAS) from textiles makes sense, the question remains: How do you achieve the same level of performance without them? Particularly with oil-repellency, the search for a PFAS-free replacement has proved difficult.
A group of chemists and scholars gathered last week in Raleigh, N.C., to discuss solutions to that problem at the American Association of Textile Chemists and Colorists’ (AATCC) PFAS in Textiles Conference.
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One of the most promising solutions proposed by several presenters was silicone.
PFAS chemicals work well in repelling oil due to their long-chain structure, referring to the length of the carbon backbone in the molecule. These long-chain PFAS are commonly referred to as “forever chemicals” since it takes them so long to break down, if at all.
According to Kevin Golovin, assistant professor of mechanical engineering at the University of Toronto, those longer chain (C8 and up) PFAS work so well at repelling stains and water because their length allows them to pack tighter along the surface of a fabric, creating an impermeable barrier.
“The service science term for this is self-assembled monolayers or SAMs,” he said. “That is the way that the industry basically until today has achieved oil repellency—by forming these self-assembled poly layers where we see groups packed on the surface.”
Golovin outlined research at the University of Toronto that looked into the oleophobic properties of PFAS compared to other finishes, such as C6s, waxes and silicone. The team came up with a means of manipulating the molecular flexibility of silicone to make a new configuration called a brush.
“We have single chains of silicone sticking straight up off the surface, and the idea was if these are packed together close enough, there’s just no room for oil to get in between the chains,” Golovin said.
Golovin says the researchers have been working on this for the past six years, and have proved their hypothesis correct, with the silicone brushes repelling oil about as well as PFAS would.
“We put the silicone finish on the fabric in this very thin DWR (durable water repellent) so you can’t see it, and when you put droplets of oils on the fabric, you get the repellency,” he said.
The push to find viable alternatives to PFAS for water and oil repellency has ramped up in recent years as several states—including California, Maine, Vermont and Washington—have passed legislation regulating the use of the chemicals in consumer products.
PFAS chemicals can leech into the soil and water during production, and according to the U.S. Environmental Protection Agency (EPA), PFAS are found in the blood of people and animals all over the world and are present at low levels in a variety of food products. Of the thousands of PFAS chemicals in existence, some have been linked to harmful health effects including cancer and reproductive issues.
Many companies, from apparel makers to home textiles, have phased PFAS out of their products. And some are turning to silicone solutions to provide performance properties to fabrics. Upholstery maker Nassimi, for instance, has completely phased out PFAS from its textiles, and the company uses a silicone solution to provide liquid repellency to its Supreen performance fabric.
“We’ve learned the natural ability of silicone to repel stains, and we’ve taken that knowledge and we put it into a C zero that works as well as anything in the market—it is resistant to both water and oil,” said Debbye Lustig, vice president, Nassimi.
And while silicone can have a sticky, rubbery feel, Lustig said Nassimi runs its yarn through a proprietary purification process prior to the silicone solution bath, which helps the finish not only adhere to the fibers, but also retain a soft, natural-feeling hand.
Dow uses silicones in its DOWSIL IE-8749 emulsion, which is a sustainable silicone DWR for fashion and technical textiles, as well as its silicone hybrid DOWSIL IE-9100 emulsion, which offers a softer hand and improved logo printability. But those products are only water repellent and don’t resist oil.
To address that second need Dow is developing a durable water and oil repellent using silicones that has yet to hit the market. However, Jacob Milne of Consumer Solutions, a business unit of Dow, said current prototypes are demonstrating durable oil repellency.
“We’ve tested this material in a number of fabrics—your synthetics, nylons, polyesters, etc., as well as cottons and whatnot,” he said.
Golovin said this kind of research and development with silicone should continue, as the material has shown great promise in providing repellency on par with PFAS finishes.
“In the medium term, I think we should focus on the durability of fluorine-free silicone finishes,’ Golovin said. “We’ve been working on this, and I think it’s an important thing to do.”
As the discussion of PFAS alternatives drew to a close at the conference, Sudhakar Puvvada—a veteran of VF Corp. and co-founder of Dream Catcher Innovation Labs—urged those working on these solutions to PFAS-free DWORs to keep pushing the bounds of science and innovation.
“With these new technologies, you don’t just make one product and walk away from it,” he said. “There has to be some investment and patience to keep that innovation moving forward.”
