Can the water industry survive without PVDF membranes? Should it be forced to lose its preferred material? I decided to write this blog as a follow up to an interview for last week’s Water Desalination Report article, ‘All PFAS are not created equal’. PFAS compounds are incredibly useful and woven through all aspects of products ‘essential’ for our daily lives. In the membrane industry, the most common material used is PVDF. This could itself be classed as a PFAS compound or is certainly made from PFAS monomers.
In recent years, PFAS restrictions have been greeted with enthusiasm in some quarters of the membrane industry, since they provide a new target contaminant and therefore a new opportunity. However, others are worried that the membrane itself may fall foul of the restrictions. The initial concern was that membranes, particularly PVDF, may leach components or may breakdown thereby contributing to the problem of PFAS contamination of the environment.
The US Environmental Protection Agency (EPA) has issued a family tree describing the compounds included in the PFAS definition. Some commentators are more selective in their PFAS definition, but the tree shows that PFAS covers a broad range of compounds including polymers used for membranes.
While EPA has focused on the effect of PFAS chemicals on health and the environment, the EU has decided to flex its muscles and try to tackle the cause of the problem. In 2006, the EU introduced REACH regulations, (Registration, Evaluation, Authorisation and Restriction of Chemicals) which covered all aspects of the use of chemicals within EU member states. At that time, these regulations posed a threat to membrane manufacture in Europe due to restriction or control of the use of aprotic solvents such as NMP. It took a decade before the regulation had teeth, but in the end, EU manufacturers were able to accommodate and comply with the solvent restrictions. The worst that could be said for membrane manufacturing in Europe is that new entrants faced greater barriers in setting up new facilities than in the past.
Some fluorinated chemicals were also restricted under the original proposals and from a revision in 2017, but the effects were limited. However, there has now been a dramatic new development in the chemicals covered by REACH to include all PFAS compounds. A proposed extension of REACH regulations is now out for consultation, and this is likely to have far-reaching consequences. The proposal would ban the manufacture and use of PFAS and if adopted in full, this would mark the beginning of the end for membranes such as PVDF made from fluorinated polymers. Derogations may be granted for some PFAS chemicals in cases where there is deemed to be no alternative, but these derogations would be time limited. Of course, it is possible that there will be pushback which would allow PVDF membrane manufacture to continue under close scrutiny, but the direction of travel seems clear, eg see All news – ECHA (europa.eu), PFAS Guide – Find PFAS chemicals in your products (chemsec.org).
In my view, it seems like a case of ‘Over-Reach’ setting targets which are ‘Out of Reach’. Does the threat from stable polymers such as the PVDF used in membranes justify such draconian control? Two thirds of the current membrane filtration market for water uses PVDF. There are alternatives but there are also reasons why PVDF is the market leader. I find it very concerning that in the future, membrane selection may not be determined by the normal evolutionary pressures of the marketplace but by an administrator’s pen.
Are PVDF membranes really that bad? Let’s have a quick look at the issues. The PVDF polymer is made from a fluorinated monomer. The resulting polymer is made into a membrane. The membrane gradually degrades during its life in terms of its mechanical strength, but according to leaching tests used for drinking water approval, it does not leach monomers or fragments injurious to health (except potentially as micro-plastics, but this is a different issue). At the end of its life, the membrane is disposed of through incineration or landfill.
In terms of affecting the environment, there appears to be the potential for manufacturing risk, but this takes place in a series of controlled environments. In use, risk is negligible since the membranes are chemically stable. At the end of life, disposal is a more serious problem since recycling has always been limited due to fears of cross-contamination and disposal methods do impact the environment. Constraints on these practices will increase due to new regulations. Perhaps the consequence for PVDF membranes is that manufacturing and disposal will be effectively off-shored, ie moved outside of the EU (and probably US), while ‘use’ may continue to be permitted, at least for a time. Eventually though, the use of PVDF membranes will probably cease entirely within the EU and other jurisdictions may well adopt similar restrictions.
PVDF membranes are clearly facing an existential threat and I fear that we could be in danger of throwing the baby out with the bath water. PES could be a short term beneficiary, and it now seems highly likely that the recent trend towards ceramics will accelerate. There is no doubt that one way or another we are in for a decade of fundamental change for the membrane filtration industry. I would be interested in the thoughts of others on this important issue.
Dear Graeme,
I’m afraid that I do not see a relationship between PFAS and PVDF, other than that both are fluorinated. Therefore, I do not see the chemical foundation for the statement [The proposal would ban the manufacture and use of PFAS and if adopted in full, this would mark the beginning of the end for membranes such as PVDF made from fluorinated polymers.]
PVDF is made by polymerizing vinyl fluoride a.k.a. 1,2-difluoroethylene.
PFAS means “perfluorinated alkyl sulfonates”
PVDF is not a PFAS as it is not perfluorinated nor is it a sulfonate. Neither vinyl fluoride nor PVDF are perfluorinated materials. “Perfluorinated” means that every “H” is replaced with an “F”. Clearly that is not the case, for PVDF.
PVDF is a very stable polymer thanks to the strength of the carbon-fluoride bond and its resistance to breakdown by micro-organisms. In this regard it is similar to its ‘cousin’, PVC.
Perhaps you would care to elaborate? References to the original regulatory sources that mention a potential ban or restriction action of PVDF would be helpful.
I agree with your concerns and this is why I wrote the post. The EU states the definition of PFAS as Per- and polyfluoroalkyl substances (PFASs) defined as: Any substance that contains at least one fully fluorinated methyl (CF3-) or methylene (-CF2-) carbon atom (without any H/Cl/Br/I attached to it). The PVDF repeat unit is [-CH2-CF2-]n and currently appears to fall within the EU proposed restrictions, though some polymerised substances are excluded depending on the linkages. Where the CF repeat unit is linked on either side to a methylene unit, the polymer does not appear to be excluded. The explanation on restrictions is A substance that only contains the following structural elements is excluded from the scope of the proposed restriction:
CF3-X or X-CF2-X’, where X = -OR or -NRR’ and X’ = methyl (-CH3), methylene (-CH2-), an aromatic group, a carbonyl group (-C(O)-), -OR’’, -SR’’ or –NR’’R’’’, and where R/R’/R’’/R’’’ is a hydrogen (-H), methyl (-CH3), methylene (-CH2-), an aromatic group or a carbonyl group (-C(O)-).
Since PVDF has two X linkages rather than an X and an X’, it appears to me that it is included as a PFAS.
The diagram I used at the top of the blog from the US EPA is explicit in listing PVDF as a PFAS. The EU has a consultation on its proposals until Sept 2023, https://echa.europa.eu/restrictions-under-consideration/-/substance-rev/72301/term.
If you think my interpretation is incorrect, pls let me know
Graeme, can you point to the interview that you reference from WDR (“All PFAS are not created equal”) above? I can’t seem to find it on their website. Thanks.
Dear Graeme,
Thank you for your reply and I have been reading more on the subject. The definition of PFAS has broadened significantly over time, since it all began with PFOS and PFOA from 3M, roughly half a century ago now. ECHA seems to have gone over-reached a bit by including PVDF as a PFAS. But it’s all a matter of definition, of course. I learned that the perfluoro surfactants are used in the synthesis of PVDF. However, there are ways to make PVDF without using them (ARKEMA). I don’t know what the alternatives are, that they use. I think that the biggest issue that PVDF and all other, stable halogenated polymers share is the lack of a sustainable end-of-life treatment option. But, coming back to the main focus of the proposed regulation, I think it’s inappropriate to include the stable fluoropolymers here. The US EPA’s definition of “polymer of low concern” could be used to help distinguish between polymers that should be included (because they could break down into smaller fluorinated fragments in the environment) and others that should not be.
There is the bigger question of halogenated organic materials in general and whether we should continue to rely on this chemistry for various purposes. Much will depend on whether viable alternatives can be found for the end-of-life. Personally, I believe that viable alternatives will be discovered. There will be a way to incinerate them safely, or a way to recycle them – perhaps at the molecular level – if not both. This chemistry is tremendously useful, therefore the incentive to search for solutions is very high, which makes it probable that solutions will be found.
Hi Els, thanks for your comment. I agree with your sentiment, but as things stand, PVDF is defined by ECHA as a PFAS regardless of how it is made. The industry needs to convince the EU committee that benefits outweigh risks and seek a derogation. The EU starts from the position that the material is in the class of potentially harmful compounds and will only be allowed if it can be proven that risks are low and benefits outweigh those risks. I certainly agree that this class of compounds is useful and indeed may turn out in some cases’ to be irreplaceable. I am particularly concerned in the membrane world for the fate of MBR which relies on PVDF almost completely.