VeritasC&E
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Quick and Efficient PTFE Testing
What are quick and efficient methods to test for the quality / authenticity of a piece of PTFE (tubing for instance)?
Something that wouldn't require testing its MP / decomposition temperature (emitting toxic fumes) would be great.
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BromicAcid
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Are you specifically interested in PTFE or are you asking about fluoropolymers in general like FEP, PVDF, and PFA? Teflon tubing does exist of course
but it's very rigid, quite a few people I work with say Teflon tubing as a generic term for fluoropolymer tubing but if I handed them real Teflon
tubing they'd be like "What the heck is this?".
Analytically ATR would be useful to differentiate between some of the fluoropolymers and non-fluoropolymers but being able to differentiate between
each fluoropolymer in general is going to be difficult.
If you just want to know if it's fluoropolymer though then density might be useful. One of the properties that is looked at for polymers is also
swelling, you could determine a battery of solvents and place pieces of tubing in them, fluoropolymer being resistant to most everything is going to
have the least/no swelling.
Generally though I can pick up a piece of tubing and know immediately what it's made of, not sure if that's 17 years of chemical handling experience
at work or just due to the fact that we only have a few different kinds of tubing at work and they're all pretty distinct.
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Herr Haber
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Dip it in hot RFNA 
As BromicAcid said, PTFE tubing is quite rigid and distinct from other tubing.
Go for Viton if you need it to be flexible. My gas vent tubes are Viton, have seen NOx, Chlorine etc and seem pretty much intact. I would still use
the PTFE ones if I were to liquify chlorine though.
The spirit of adventure was upon me. Having nitric acid and copper, I had only to learn what the words 'act upon' meant. - Ira Remsen
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Organikum
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Is fake PTFE out there? That could get interesting in some applications.
Otherwise the main difference in quality is density, the denser, say the more pressure and repetitions when sintering the better the mechanical and
chemical properties, but the mechanical properties are always lousy. Makes a big difference in permeability though.
There are special scales for measuring density.
Some of the PTFE from China is made from recycled PTFE, it is often off-white to yellow but the properties are the same, in some applications recycled
PTFE even beats virgin PTFE. I think they use it now mostly for carbon filled PTFE as people were quite unwilling to buy it and everybody wanted the
virgin one.
Also pure PTFE has a change of crystal structure at 230°C (?) and this should be easily discernible and is also still far off from decomposition.
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VeritasC&E
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Thank you for your inputs.
I asked because I've seen wide variations in pricing of PTFE stuff. Also some pieces I've seen have this "soft/smooth/silky" feeling when touched (I
guessed it was because of it's water repellent properties), and some like the tubing feel more sleek.
I've found an awesome pdf which I think may be useful to forum members but I can't manage to post it. It's titled "PLASTICS AND ELASTOMERS
IDENTIFICATION CHART" and may be openly found on the web.
For the case of PTFE for instance: Drop a small sample in water > See if it sinks > If yes, proceed and burn a small corner of the sample (in
fumes hood or otherwise evading exposure to the fumes) > Does it produce a flame? > If it doesn't produce a flame (as opposed to sustained
burning or self-extinguishing burning with a flame), then proceed and observe if upon sufficient heating it drips > If it doesn't drip and passed
all the previous steps, then you are dealing with either PTFE or PVF > I don'y recommend the last step to distinguish between the two, however it
is listed as burnt PTFE fumes smelling burnt hair vs burnt PVF fumes having an acidic smell.
I hope this description and document will be useful to some of you!
[Edited on 27-8-2022 by VeritasC&E]
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BromicAcid
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I remember one arm of our company using hydrophilic PTFE tubing, it definitely had a different feel from the usual stuff- I think they treat it with
ozone to make it hydrophilic.
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VeritasC&E
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Quote: Originally posted by BromicAcid  | | I remember one arm of our company using hydrophilic PTFE tubing, it definitely had a different feel from the usual stuff- I think they treat it with
ozone to make it hydrophilic. |
That may explain the different feelings I experienced.
Is this something we can do in the lab? Like taking a hydrophobic PTFE membrane/filter and turning it hydrophilic with a small ozone generator?
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Organikum
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Making PTFE hydrophilic would probably require treatment similar to the one used to make it possible to glue the PTFE to something and can be done
with quite a lot chemicals, all of them horrible nasty ones. I think sodium metal dissolved in some solvent or sodium amalgam, molten sodium,
Thionylchloride (not sure about this) and much worse.
Can it be done in the lab? Technically yes but I would say only small style, a few square centimeters yes, half a square meter - better not.
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VeritasC&E
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| Quote: Originally posted by Organikum | Making PTFE hydrophilic would probably require treatment similar to the one used to make it possible to glue the PTFE to something and can be done
with quite a lot chemicals, all of them horrible nasty ones. I think sodium metal dissolved in some solvent or sodium amalgam, molten sodium,
Thionylchloride (not sure about this) and much worse.
Can it be done in the lab? Technically yes but I would say only small style, a few square centimeters yes, half a square meter - better not.
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These indeed are nasty. But if ozone works, would the most convenient not be to use one of those small ozone generators? (I'm inquiring since I have
no experience with them and know nothing about them other than their existence)
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Texium
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Thread Moved
30-11-2023 at 10:41 |
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