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UV Transparency of PFTE Tubing

03/18/2016 4:30 PM

A couple of year ago, manufacturers of PFTE products began removing the surfactant PFOA from their manufacturing processes (due to health and environmental concerns). This change did cause some changes in PFTE Films and membranes.

I am trying to find out in the case of PFTE tubings, if the change in surfactants could possibly cause a decrease in the amount of UV light that is able to pass through the material? I have found the name of one substitute surfactant (Gen X, made by DuPont) but no discussion or information on if this or other substitutes for PFOA have caused any changes in material behavior.

UV resistance (not causing degradation of the material under exposure to UV) is one property of PFTE materials. But in some cases, UV transmission is also a required property (and is mentioned on some vendors sites). Range of interest is in the UVB range (above 280nm).

Thank-you!

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#1

Re: UV transparency of PFTE tubing

03/18/2016 5:03 PM

It appears that even Acronym Finder has an error. This should probably be PTFE. (PolyTetraFluoroEthylene) (TeflonTM)

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#2

Re: UV transparency of PFTE tubing

03/18/2016 6:47 PM

This might help....

..."Unmodified types of plastics that are regarded as having unacceptable resistance to UV are POM (Acetal), PC, ABS and PA6/6. Other plastics such as PET, PP, HDPE, PA12, PA11, PA6, PES, PPO, PBT and PPO are regarded as fair. Note that a PC/ABS alloy is also graded as fair. Good resistance to ultraviolet rays can be achieved from polymers extruded by Zeus such as PTFE, PVDF, FEP, and PEEKTM. The only plastics found with excellent resistance are the imides, Polyimide (PI) as used in the Hubble Space Telescope and Polyetherimide (PEI).

PTFE has particularly good UV resistance because of its very strong carbon-fluorine (C-F) bond [almost 30% higher than the carbon-hydrogen (C-H) bond], which is the common side bond that surrounds the carbon (C-C) backbone in a helix and protects it. Most fluoropolymers also do not have the light absorbing chromophore impurities in their structure that can act as an initiator for photo-oxidation.

One useful interaction of UV and plastics is with fluorescent whitening agents (FWA). In natural light many polymer products can appear to have a yellow appearance. But by adding a FWA the UV light absorbed is then emitted in the blue region of visible light (400-500nm wavelength), instead of the yellow region. Compared to other additives FWAs only need to be added at small levels, typically 0.01 - 0.05 % by weight.

How to Avoid UV Degradation

There are several ways of avoiding UV degradation in plastics - by using stabilizers, absorbers or blockers. For many outdoor applications, the simple addition of carbon black at around a 2% level will provide the protection for the structure by the blocking process. Other pigments such as titanium dioxide can also be effective. Organic compounds such as benzophenones and benzotriazoles are typical absorbers which selectively absorb the UV and re-emit at a less harmful wavelength, mainly as heat. The benzotriazole type is good, as it has a low color and can be used at low dose rates below 0.5%.

The other main mechanism for protection is to add a stabilizer, the most common being a HALS (Hindered Amine Light Stabilizer). These absorb the excited groups and prevent the chemical reaction of the radicals.

In practice, the various types of additives used are in combinations or are compounded into the original polymer to be produced as a special grade for UV protection. It may be attractive to add antioxidants to some plastics to avoid photo-oxidation, but care must be taken that the antioxidant chosen does not act as an UV absorbent, which will actually enhance the degradation process."...

http://www.coleparmer.com/TechLibraryArticle/834

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#6
In reply to #2

Re: UV transparency of PFTE tubing

03/20/2016 1:28 PM

There is information on which tubing is transparent to UV. But not the % transmission, the wavelengths or if this had the potential to change with the change in processing (i.e. new surfactant).

Frankly, I do not even know that this property is tested. I know for the Teflon films, they test stretch, density and dielectric constant. At the same time, companies like Zeus do state that the tubing is used in applications where transmission is needed (water treatment). So they must have some idea...

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#8
In reply to #6

Re: UV transparency of PFTE tubing

03/20/2016 1:52 PM

No reflection on SE, but neither he, nor I are nearly as qualified as Relativity PL to speak to the subject.

Mr. Bingham is eminently qualified.

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#3

Re: UV transparency of PFTE tubing

03/18/2016 9:50 PM

gargoyle13,

You will NOT find an answer here. Trust me on this.

Testing Uv transmission of polymers is straight forward, but many variables must be considered.

Testing long term resistance to Uv degradation is another issue. That takes time.There are ways to accelerate these tests, but they still take time.

The manufacturer is the ONLY source of reliable information on these properties and they may not be willing to share this data with you. Trade secrets and all.

If there are applicable specifications, they may help in your search.

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#4

Re: UV transparency of PFTE tubing

03/19/2016 12:41 AM

"But in some cases, UV transmission is also a required property (and is mentioned on some vendors sites). Range of interest is in the UVB range (above 280nm)."

PTFE does not exhibit any absorption bands in the ultraviolet region. UV transmission decreases steadily towards the shorter wavelengths, but for longer wavelengths above 280nm, you will find that spectrophotometer results on 0.075mm specimens (0.003in) yield UV transmission approaching 80%.

Perfluorooctanoic acid (PFOA) was primarily used as a surfactant just in emulsion polymerisation (for fluoropolymers mostly destined for paste extrusion of thin-wall tubes and the manufacture of unsintered threadseal tapes). It was absent from most suspension polymerisation processes. There are good reasons for its removal from its role in emulsion polymerisation:
https://en.wikipedia.org/wiki/Perfluorooctanoic_acid

You will not find discernible changes in the UV transmission spectrum of thin-wall PTFE tubing due to the shift from PFOA to the more environmentally responsible GenX.

Mark Bingham
Relativity PL
fluoroplastics.com

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#5
In reply to #4

Re: UV transparency of PFTE tubing

03/19/2016 9:57 AM

I rescind my previous statement about OP not finding the answer here.

It would seem that you are well qualified to answer his question.

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#7
In reply to #4

Re: UV transparency of PFTE tubing

03/20/2016 1:39 PM

This has been a really confounding problem to solve. It is the UVB light that does the majority of the work in this digestion. Increasing the lamp wattage from 8W to 15W has not provided any appreciable difference. But if light output was the issue, it should have. The fixture is not a likely source of the problem as the two lamps require different ballasts and connections. One is manufactured in house; the other was purchased at a home improvement store.

The lamp vendor claims nothing has changed (a phosphor is obsolete but they have a 15 year supply of the current one), and the warehouse company lamps are purchased through believes all the lamps are made by a single manufacturer then labeled for the different vendors. But this is not, to my knowledge the common use of the lamps, so changes made to decrease cost for example may pass the vendors internal testing, but affect what we are doing with them.

Issues with Teflon film/tape following the discontinuation of PFOA in the process brought up this possibility. Does any of the surfactant get caught up in the final product? Could any of the substitute surfactants have UV absorbance? With the change in surfactant, is there any other part of the process that may have changed?

Thank-you for your detailed and helpful information, by the way!

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#9
In reply to #7

Re: UV transparency of PFTE tubing

03/20/2016 6:16 PM

Gargoyle,

I wonder if your troublesome batch of 'PTFE' tubing is in fact 'Teflon FEP' rather than 'Teflon PTFE'. The UV transmission properties of those two different fluoropolymers are dramatically different.

https://www.chemours.com/Teflon_Industrial/en_US/assets/downloads/Chemours_Teflon_FEP_Film_Tech_Bulletin_K26942.pdf

On page 8 you can see that with 'Teflon FEP' (fluorinated ethylene propylene), UV transmission is quite scatty. Look at the rapid rise in transmission as the visible spectrum region is entered. Casual use of the T-word, or a warehouse picking error, may have delivered you FEP rather than PTFE.

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#10
In reply to #9

Re: UV transparency of PFTE tubing

03/21/2016 9:29 AM

You certainly brought out a completely relevant point: Always make sure of what you are specifying and obtaining from your supplier(s) before you get it, and after you get it.
Then you will get it. Never gloss over material specification on the critical aspects of a project. No need endangering your contribution to the species by being careless! On the other hand, this certain lack of attention to detail by some "in the field" could be an assist to natural selection. The Darwin Awards must be coming up soon.

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#13
In reply to #9

Re: UV transparency of PFTE tubing

03/21/2016 10:57 AM

Thank-you this is good information!

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#11

Re: UV Transparency of PFTE Tubing

03/21/2016 9:32 AM

By the way, I have not been made aware of this new plastic (I assume it is a plastic)? This PFTE, what is the monomer, and how is it made? Who discovered it? Where can I get some? What are the gas permeability values for water, carbon dioxide, oxygen, nitrogen, argon, helium, and hydrogen?

Has it been used in outer space? Inner space. How far would a woodchuck chuck a roll of PFTE?

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#12

Re: UV Transparency of PFTE Tubing

03/21/2016 10:49 AM

Perfluorooctanoic acid, in the small amounts that remain after manufacturing (it is used as a processing aid in the manufacture of polytetrafluoroethylene), would likely have no contribution to UV transmission.

The only way to be sure is to measure samples yourself.

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#14

Re: UV Transparency of PFTE Tubing

03/21/2016 10:58 AM

PTFE, not PFTE...

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#15
In reply to #14

Re: UV Transparency of PFTE Tubing

03/21/2016 12:58 PM

You do realize I was being a bit tongue in cheek with that about "new" plastic? right?

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