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The Many Faces of Buna N (Nitrile)

The Many Faces of Buna N (Nitrile)

The Many Faces of Buna N (Nitrile)

(OP)
I have been searching for a specification for Buna N that will insure me that the material does not grow in Jet Fuel.  

I've ordered the stuff in about 4 different specs and some batches grow and others do not.  The suppliers keep telling me that it is the same material... however, obviously the elastomer industry does not have a handle on their processes.  

Is there any specification that I could buy this material to, that will give me consistent material props. ?

RE: The Many Faces of Buna N (Nitrile)

acrylonitrile-butadiene rubber (NBR) is a thermoset elastomer principally composed of acrylonitrile and butadiene, with the acrylonitrile content varying from ~ 18% to ~ 50%.  The higher the percentage of acrylonitrile in the rubber, the greater the resistance to swelling.  Increasing the acrylonitrile content causes a deterioration in compression set, reduces elasticity/cold flexibility, and also reduces the permeability of gases.  These factors must be balanced in order to produce the desired properties.

With regards to specification, I suggest the following:

1. Start with applicable aerospace standards like SAE AMS 3212, 3213, 3214, 3215, or 3224.  These standards specify fuel-resistant NBR in various durometers.

If you have already done this, and still have excessive variation, then you should

2. Exactly specify the requirements using ASTM D 471 Standard Test Method for Rubber Property-Effect of Liquids.  In this standard, you specify the temperature range (85 + 2 C, 100 + 2 C, etc.), the duration (22, 46, 70, 166, 670, 1006, 2998, or 4990 hours), the fluid (standard fuels ranging from 100% isooctane to 100% toluene, or your specific grade), and the acceptance criteria (minimum and maximum change in mass and/or volume-- see sections 9-14).

RE: The Many Faces of Buna N (Nitrile)

(OP)
Thank you for the information.  I will consult the supplier on the availability of high acrylonitrile NBR.  The problem that I am having is that the application necessitates a very cheap material otherwise I would have just used Viton and called it a day.  

Would it be a safe assumption that if I were to order the NBR with a higher Shore A that it would contain more acrylonitrile?  

The properties are essentially a non issue since the rubber is being used as a seal for shipping purposes.  (mostly room temp and disposable)

 

RE: The Many Faces of Buna N (Nitrile)

No, a higher Shore A durometer does not mean that it will have more acrylonitrile.

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