Curable fluoroelastomers having low swelling tendency

A method for sealing off at least two media from each other, of which at least one is acidic, the method comprising:

• providing a curable fluoroelastomer in an amount of 40% wt to 95% wt, wherein the curable fluoroelastomer is classified as FKM in ASTM-D 1418;
• providing a nitrogen-containing polymer selected from polyamide, polyimide, mixtures and/or copolymers thereof, the nitrogen-containing polymer being present in particle form having an average particle size in the range from 0.1 to 70 μm and/or in fiber form having an average fiber diameter in the range from 0.1 to 70 μm, wherein the nitrogen-containing polymer has a melting temperature determined according to ASTM D3418-08 or a decomposition temperature of greater than 180° C.;
• mixing the curable fluoroelastomer with the nitrogen-containing polymer at a temperature lower than whichever is the lower of melting temperature and decomposition temperature of the nitrogen-containing polymer to form a polymer mixture that has curable fluoroelastomer and 0.1 wt % to 30 wt % nitrogen-containing polymer based on the total weight of fluoroelastomer and nitrogen-containing polymer;
• adding a curing system to the polymer mixture at a temperature lower than the lower of melting temperature and decomposition temperature of the nitrogen-containing polymer to form a curable fluoroelastomer composition, wherein an amount of metal oxide functioning as an acid acceptor in the curable fluoroelastomer composition is less than 1.5 wt %, and/or an amount of metal salt functioning as an acid acceptor in the curable fluoroelastomer composition is less than 5 wt %;
• providing a filler in an amount of 1 wt % to 70 wt % of a total weight of the curable fluoroelastomer composition;
• curing the curable fluoroelastomer composition so as to produce a seal;
• and
• disposing the seal between the at least two media, wherein at least one of the at least two media is acidic.