NBR & ETHYL ALCOHOL SWELL

[TallOne1113]

Need to get more swell out of a peroxide cured NBR compound for a gasket application. Best I've gotten is approx 2% change in thickness after 72 hr immersion at room temp in ethyl alcohol. Anything I can add to the compound to get more swell? I need about 4 to 6%. Thanks very much.

 

[Shylanel]

Are you trying to formulate a compound that will swell 4-6% in EtOH or want to find something that will swell the compound 4-6%?

Lower the degree of crosslinking either through the peroxide level or cure conditions to get more swell. Increasing the free volume of the base resin with more branching will also help. This can also be done with plasticizers but they can leach out if in contact with a compatible solvent. Be careful.

Acetone or MEK will swell what you have more than EtOH.

 

[TallOne1113]

I'm trying to get the compound to swell more in ethyl alcohol per customer request. I will certainly look at decreasing the crosslink density. Thanks very much.

 

[stancom]

I agree with Shylanel that reducing the crosslink density is a straightforward option - provided other properties such as resistance to stress relaxation are not impaired. An alternative is to reduce the loading of any fillers in the compound. If all else fails a more extreme solution might be to add a small amount (ca 5-10%) of a polyacrylate rubber because it has a comparatively low resistance to alcohols.

Assuming the test sample is unrestrained the 2% thickness increase equates to a volume swell of ca 6% and the target will be equivalent to a 15% swell. The difference seems significant but please review the test conditions and measurements to ensure reproducibility is not a contributory factor, something I can speak about from experience. I take it the 'room temperature' is a standard lab temperature such as 23 C.