[lhohenstreet]

I had a question regarding acetone coming into prolonged contact with fluorocarbon o-rings. I know that the o-rings begin to come apart, but my question is what exactly is happening to cause this? Are they dissolving into the acetone or is the acetone causing the o-rings to become brittle and fall apart? Or is it something else entirely?

Thank you!

[marquis]

It can be a number of things that cause oring to degrade.
First, all polymers are poor in some solvents.  It's just which solvents.  So identify the solvent your fluoropolymer is "bad" in and adjust as needed.  Second, state of cure can have a lot to do with it.  If the oring is over cured, that's part of the problem.  And then there are the fillers that can cause problems. 

Probably the easiest solution is to get a number of different kinds of Orings and soak them in acetone to see which ones work best. 

[wildfyr]

Two things could be happening. One is that acetone might be extracting plasticizers which changes the mechanical properties of the o-rings, making them brittle. Plasticizers are put into polymers to make them more pliable.

The other things that could happen is that the fluoropolymers could be "swelling" with acetone. Swelling with solvent is something really only polymers do. A material isn't dissolving, but a solvent is penetrating the polymer matrix. This too can greatly modify the mechanical properties of the o-rings, and it also can really change the volume they take up if they swell enough, causes whatever the rest of the seal is to abrade them.