Non destructive ways to differienciate between Neoprene and EPDM

[iboivin]

Hi all,

We had a problem with diaphragms for vacuum pumps. It used to be made of Neoprene and all of a sudden the supplier used EPDM. For our application, we really need Neoprene. Since we don't really know when the supplier started to use EPDM, we want to be able to test the diaphragm to identify the material without having to destruct the part. Any easy way?

Thanks

IB

 

[CoryPad]

How about density difference? EPDM can be < 1 [&middot;] 10[sup]3[/sup] kg m[sup]-3[/sup], while Neoprene can be 20% to 30% higher. A simple test is to see if parts float in water.

Regards,

Cory

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[iboivin]

Thanks Cory for the idea. I tried it, but it didn't work. Both sank :-(

We are still looking.

IB

 

[patprimmer]

Try weighing them, even though they both sink, there will still most probably be a different part weight.

If it is a multi cavity mould, make sure you weigh each cavity, as they may vary from cavity to cavity.

Regards
pat pprimmer@acay.com.au
eng-tips, by professional engineers for professional engineers
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[iboivin]

Hi Pat,

Thanks for the tip, even though it didn't work. It's very difficult to see the difference between the two parts since they are the same color, same shape and same weight. There is a metal disk inside the part that I think is interfering with the test we try to do.

We keep on looking!

IB

 

[swall]

I know you asked for a non destructive test. But, if you put a drop of stoddard solvent or similar petroleum substance on the diaphragm and let it sit overnight, the neoprene will be unchanged but there be some swelling on the EPDM. This will ruin the EPDM diaphragm, but you can't use EPDM anyway, right?

 

[patprimmer]

Another destructive way is to burn a small piece and smell the smoke. You might notice a difference. You might be able to trim a piece from a non critical area.

This will be time consuming and probably unreliable, and may also have health issues if done as a process rather than a once off test.

Regards
pat pprimmer@acay.com.au
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[gambro]

Most petroleum-based products (such as hydraulic oil used in injection molding machines) will cause EPDM rubber to swell or dissolve. Chloroprene Rubber (Neoprene) on the other hand is generally resistant to most oils, fats and greases.

 

[swall]

Actually, if you're going to burn a small sample, there is a good test.You take a piece of copper wire and heat it red hot in a bunsen burner, then melt some of the rubber on to it. Stick the wire and rubber into the bunsen burner and you will get a green flame because of the chlorine. It's called the biostein test or something like that.

 

[iboivin]

Thanks to all of you!
We will try to use the petroleum-based products. We will do some tests. We want to be able to use the test on site where technicians will need to change the part.

IB

 

[RichGeoffroy]

Iboivin:

The best way to absolutely identify the difference between Neoprene (polychloroprene) and EPDM is by Infrared Spectrophotometry. Infrared analysis yields a “fingerprint” of the chemical composition of the polymer, and can easily differentiate between both polymers.

Most labs can perform infrared analysis. Usually the analysis is somewhat destructive --- a small sample is taken and dissolved or ground up or a thin cross-section taken for the analysis. However, if the part is not too large and has a reasonably flat surface, the lab can perform ATR (Attenuated Total Reflectance). This IR technique will identify what polymer was used to make the diaphragm.

Sounds expensive, but it really isn’t. This equipment is a staple for most labs. An IR spectrum will generally run around $200.



Rich Geoffroy
Polymer Services Group
polyserv@cox.net