3 May 2013

What chemicals can silicone withstand?

Questions come in from time to time chemical resistance for silicone, in the sense that silicone and in particular silicone rubber can be in contact with certain chemicals without being destroyed in whole or in part.

The most common answer is "It depends, can you describe more".

And it actually depends. Parameters such as the concentration of the chemical in question, exposure time and pressure, ambient temperature and exposure area can all cause the impact to be anywhere from zero to very large. Above all, there is a big difference if, e.g. a silicone adhesive joint must be able to be completely submerged in a chemical liquid, or if it only gets a few drops on it during operation. For example, you can seal a gearbox with a standard silicone sealant as long as the seal is not completely submerged in the gearbox oil, which is rarely the case.

But to give a little more guidance you can look in the table below. It shows what happens if a standard grade piece of hardened silicone rubber (ie silicone adhesives, sealants or silicone gaskets, etc.) is completely submerged in a number of chemicals and left to sit there for a week, at room temperature.

The most common effect is that the silicone rubber absorbs the chemical and swells, sometimes quite a lot. In some situations the change in volume matters, in other situations it doesn't matter. Double circle in the table means that the volume change is less than 10 %, which should be acceptable in most cases.
Resistance chemicals silicone table
An increase in volume means that several properties of the material change. The elasticity can increase, but the strength usually decreases and so does the hardness. This may degrade the performance of the application.

As the table shows, standard grade silicone is not suitable for sealing gasoline, diesel and strong solvents. There you should instead use fluorosilicone, which I wrote about here. If you need good resistance to mineral oils, you can also use silicone adhesives that are specially formulated to handle it, e.g. RTV1473.

Do you need help with this? Feel free to contact Tribotec to discuss the issue. We can give tips on which materials work where, and how to test the chemical resistance if you are unsure.

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