potable water EPDM 3

[Elastomatt]

Guys,

I am on here seeking some advice, I have just got a project to source/develop an EPDM compound to pass BS6920 (odour/flavour and MDOD in particular).The part we are looking at developing will come into contact with drinking water before and potentially after the stopcock and apparently we must pass these tests as a minimum (tested independently).

I am focussing more on the raw materials and considering what might be promoting the growth, at present I am 'fixed' on the carbon black as it is molasses bound. Am I going the wrong way, is polymer more important and/or the cure system?

Another alternative I am considering is coating the part after moulding (not sure what with yet), the lab tell me they can submit parts but usually they submit a sheet of varying thickness. Apparently the thinner the better?

All input gratefully received!!

Cheers

Elastomatt

 

[GrahamBennett]

Boy, oh, boy, are you going to have some fun - not - with this project.

First of all, the independent tests will be expensive and can only be carried out by certain laboratories. Even if you pass the tests first time, any subsequent testing may (or may not) fail causing you to have to start all over again.

Obtaining approval for parts used in the potable water industry is very expensive and fraught with regular taste testing failures (up to 90% failure rate). The taste test is a subjective and qualitative test. Possible reasons for failing include:

A bitter (astringent) rubber taste usually caused by sulphur curing systems.
A chemical taste usually caused by peroxide curing systems, inadequate post cure and some plasticisers.
A burning taste, which is caused by surfactant residues from mould release agents and inadequate washing of cured parts.

Even when compounds and parts made from them have previously qualified, later retests can show failure and approvals will be withdrawn. Once past the “taste test”, further quantitative biological (bacteriological, algal and fungal) testing is carried out.

It is important, therefore, that a compound should contain only the minimum amounts of ingredients necessary to meet the physical property requirements. Do not use plasticisers, oils, softeners, waxes and stearic acid if possible. Avoid using carbon black pelletised with molasses. All equipment, including the mixer, must be clean and contaminant free. Use only minimal amounts of very dilute silicone oil-based release agents.

The formula below has been known to pass all potable water testing:
100phr Chlorobutyl
40phr FEF N550 (remember not to use molasses pelletised black)
5phr zinc oxide
0.5phr ZDEC

 

[Elastomatt]

Graham,

Useful reply as usual and more info. to go on then I had from an hour of searching on the net!! Sounds like it is going to be a fun project.....I now understand why they gave it to me!!

My gut feel on the molasses was that it gives the microbes something to thrive on, but the other points you have highlighted (re cure system and failure) are useful. At present I am working with a 50-60A EPDM with a sulphur cure system...... As the part will form a seal the 2 physicals I am most concerned with is comp set (70°C 24h 25% comp. 20% max.) and hardness. Although we have other elements to meet we will only need minimal values.

I will need to research the test methods a bit more, thanks for the pointers. Do you know of any literature that might be relevant? Is Chlorobutyl very expensive/difficult to source......(I am assuming it must be)?

Elastomatt

 

[GrahamBennett]

CIIR isn't difficult to get hold of and it used to be the same price as straight butyl rubber. Exxon and Lanxess are two suppliers that spring readily to mind.

http://www.materialstesting.co.uk

is a useful site. More information can be found in a Bayer publication Polynotes G7, "Rubber Compounds for Contact with Water" by N. Harmsworth (I based my reply above on information gleaned from this).

DSM Elastomers Europe has also published information on this subject. The paper is titled "Potable Water Applications: compounding and legislative issues", written by M. H. Koch, NL-Geleen.

Both of these papers are at least 15yrs old so you might have a problem getting hold of copies.

 

[Metten]

DSM is now part of Lanxess and I am not certain if Mr. Koch still works there. Pieter Segers is my current contact at Lanxess for EPDM. If you can't find the article, I could ask Pieter.

 

[Elastomatt]

Hi Metten,

If you could ask your contact at DSM about the paper I would be grateful. I have been in contact with Bayer and I am awaitng their reply.

Many Thanks

Elastomatt

 

[GrahamBennett]

Lanxess and Bayer are the same company regarding polymers.

 

[tom1953]

Graham, is it possible to post the paper on the forum, so it can be downloaded by anybody (including me)?
Thanks,
tom

 

[GrahamBennett]

The whole file, which contains both papers + other stuff related to food, drug and potable water contact, is nearly 4Mb in all. If you use my handle in lower case letters, add the numbers 033 on the end of it and send me an email to gmail.com, I'll send you a copy of my file.

 

[Metten]

In attachment the file I received from Mr. Koch's colleagues.

 

[Elastomatt]

Thanks Metten,

I received a copy of that report last week that was issued in 1999, so it will be interesting to see what is different!