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PFAS have an Achilles’ heel

Debates about durable water repellency (DWR) will not die down. It is no surprise that it featured on the Textile Discovery Summit that the American Association of Textile Chemists and Colorists (AATCC) organized in Charlotte, North Carolina, at the start of October. Dr Kiarash Arangdad, the director of emerging chemistries at Elevate Textiles, spoke at the event to explain the difference between fluorinated and non­fluorinated DWR and talk delegates through the direction that compliance requirements are moving in for bringing “forever chemicals” to market. Naturally, per­ and polyfluoroalkyl substances (PFAS) were part of his focus. 

PFAS also featured prominently in comments that Professor William Dichtel of Northwestern University in Evanston, Illinois, made to the world’s media earlier this year. The professor was announcing the results of a study he and his team had carried out. 

“PFAS has become a major societal problem,” says Professor Dichtel. “Even a tiny amount causes negative health effects, and will not break down. We can’t just wait out this problem.” He and his team confirmed that fire cannot incinerate PFAS, including the perfluorooctanoic acid (PFOA) that has been present in many of the DWR treatments used in outdoor clothing for years, and water cannot dilute them.

He adds: “We wanted to use chemistry to address this problem and create a solution that the world can use; it’s exciting because of how simple our solution is.” More of his team’s exciting and simple solution to the problem later.

Demand for protection
Four hikers walking over a hill

If the professor’s assessment of PFAS is fair, it is perhaps no surprise that most announcements about DWR technology in recent years have made considerable play of new solutions being free of perfluorinated chemicals (PFCs). Nevertheless, DWR innovations keep coming because demand for high­performance weather protection and stain resistance remains strong.

Singapore ­based chemicals developer Huntsman Textile Effects is a case in point. It introduced new DWR technology, PHOBOTEX® R­ACE, in the middle of this year, making it clear from the outset that it was PFC­free. Global marketing manager for finishing chemicals, Kerim Oner, says there are indications of ongoing demand for DWR technology in most surveys in which outdoor enthusiasts are invited to say what qualities matter most to them when it comes to choosing apparel. “Not getting wet at the summit of a mountain comes near the top of most of the lists,” he explains. “Fit is always important, too, of course, but not getting wet is a priority.” He says companies including Huntsman have no concerns about continuing to meet that need as they progress along the road to non­fluorinated (C­zero) chemistries and adds that “this is the story behind PHOBOTEX® R­ACE”.

He observes that earlier attempts to achieve “sustainable repellency” with non­fluorinated chemistries led to some fabric developers using larger volumes of chemicals to achieve an acceptable level of protection. In contrast, he describes PHOBOTEX® R­ACE as something of a hybrid, saying: “You can achieve very good repellency with lower amounts, and have much less chemical add­on on the fabric.”

Balancing act

Achieving this balance is the key, in Mr Oner’s opinion. This must take into account what he describes as “the ecological profile” that the user companies want to portray, but it also must be in keeping with the performance criteria that a brand or a mill wants to set and choosing technology that is suitable for the end use the brand has in mind for the fabric. “The chemistry you are choosing must be suitable for that end use, and you have to be sure it won’t impair the fabric quality,” he explains. “It must also be compatible with the other finishes you are going to use, perhaps in a coating or in some kind of lamination. Not all chemicals will be suitable for that.”

There is also the important issue of compliance with manufacturing restricted substance lists (MRSL), which used to change from year to year and now seem to change from month to month, he warns. Huntsman has been sharing updates with mills and brands to help keep them up­to­date with these developments. And, naturally in a competitive market like textile chemicals, all of this needs to take place while keeping a close eye on price as well.

Cellulosic fiber challenge
A woman holding and examining a garment from a rack

We know of Huntsman innovation in high performance non­fluorinated DWR treatments from many years ago. What links other recent technologies such as ZelanTM R3 or PHOBOTEX® RSY to the latest innovation is that each has been part of an ongoing effort to address all of these needs. Of PHOBOTEX® R­ACE, the company has said it will work on all types of fibers and blends, while also offering compatibility with resin finishing to ensure “unmatchable performance on cellulosic fibers”. There are particular challenges in incorporating effective DWR technology into cellulosic fibers, Kerim Oner explains, because these fibers, including cotton of course, contain fats, come from the soil and need washing and pre­treatment before dyeing. A lot depends on how well you do that and on what dyestuffs you use and how well you wash the dye off. “They do not come in a completely uniform state,” he says. Also in the case of cotton, its hydrophilic properties can make it absorb rather than repel moisture. All of this makes the treatment of cellulosic challenging.

Returning to the subject of PFAS, Mr Oner says Huntsman sees “an accelerated shift” away from them in the next couple of years. It is not only mills and chemical suppliers that are driving this change, he explains. National governments, the state of California, the US Environmental Protection Agency, the European Chemicals Agency, Bluesign, GOTS and others are taking steps to encourage the phasing out of PFAS from non­essential use, and most apparel, in his view, would come into the non­essential use category. “There will still be a need for some use of PFAS in technical textiles applications,” he continues, “situations in which it might be risky to change what is in place too quickly. Examples include workwear for environments such as oil rigs. Companies will want workwear that does not absorb solvents, for example, because of the risk of fire and other health hazards. These customers may be reluctant to switch to a different system.”

He says PHOBOTEX® R­ACE has made a positive early impression on mills, with trials under way in almost all regions, and that commercialization will follow soon. Something else that has pleased him is a series of approaches from research institutes as well. They want to try the technology out on different fibers and fabrics to see if they, too, can “come up with something exciting”.

PFOA falls apart

If the writing is on the wall for PFAS, there is the possibility that the solution Professor Dichtel and the team at Northwestern University have found, no matter how brilliant, has come several years too late to save the practice of using those chemicals in DWR for textiles. But perhaps not.

Here is what the team has come up with. Using low temperatures and what they have described as inexpensive, common reagents, they have succeeded in developing a process that causes at least two major classes of PFAS compounds, including PFOA, “to fall apart, leaving behind only benign products”.

Scientist looking through a microscope

The secret to PFAS’s seeming indestructibility, the Northwestern team has said, lies in its chemical bonds. PFAS contains many carbon­fluorine bonds, the strongest in organic chemistry. As the most electronegative element in the periodic table, fluorine wants electrons. Carbon, on the other hand, is more willing to give up its electrons. “When you have that kind of difference between two atoms that are roughly the same size, which carbon and fluorine are, that’s the recipe for a really strong bond,” Professor Dichtel explains.

The safest form of fluorine

But the professor’s team found a weakness. PFAS contains a long tail of these unyielding carbon­fluorine bonds. At one end of the molecule, there is a group that often contains charged oxygen atoms. The team identified this as the Achilles’ heel of PFAS and targeted this head group by heating the PFAS in dimethyl sulfoxide with sodium hydroxide, a common reagent. The process decapitated the head group, and triggered this reaction in what remained of the compound. “It started spitting out fluorine atoms to form fluoride,” the professor says, “which is the safest form of fluorine.”

He points out that this will not apply to all types of PFAS, and there are thousands of them, but the fact that it does apply to PFOA is significant in the context of discussions about DWR and outdoor apparel. Plus, the professor is convinced that other PFAS will have their own Achilles’ heel. If, for argument’s sake, clothing manufacturers continue to use PFOA in the durable water repellency finishes they apply to workwear, the Dichtel method of destroying it to leave behind only benign substances could make the ongoing use of these substances much more viable. And if this works in workwear, PFAS could yet have a sustainable future in protecting outdoor enthusiasts from wet conditions.

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Kerim Oner, Global Marketing Manager – Finishing, Huntsman Textile Effects