Fluorinated Rubber (FKM)
Common chemical composition:
Common monomer: Vinylidene fluoride
Fluorinated rubber includes copolymers and terpolymers of hydrocarbon monomers, more or less fully fluorinated.
- Copolymers of vinylidene fluoride – hexafluoropropylene: the rigidity of the polyvinylidene fluoride chain is decreased. This type of FKM is worked with great difficulty due to strong nerve. It also features very poor “tack”. It produces vulcanizates that are very resistant to heat, ozone, oils, aliphatic, aromatic and chlorinated hydrocarbons. It is not very resistant to steam and low temperatures. It has rather weak mechanical properties;
- Terpolymers with tetrafluoroethylene: exhibits even poorer tack compared to the previous, which can cause great difficulties in moulds. However, it is better resistant to heat;
- Tetrafluoroethylene-propylene copolymers: at the moment, only “Aflas 150” is sold. It is cross-linked with peroxides and can be integrated by small amounts of carbon black. It produces vulcanizates that can be used continuously at up to 230°C. It shows lower resistance to hydrocarbons, much worse to chlorinated hydrocarbons, but better to steam. It is not very resistant to carbonyl solvents but exhibits good resistance to acids.
- Tetrafluoroethylene – propylene – vinyl glycidyl ether terpolymers : they represent the evolution of Aflas. They are not sold yet and are being studied to increase the versatility of use of Aflas compared to vulcanizing systems. These terpolymers can also be cross-linked with metal ions, amines and phenols. They possess the same properties as the copolymers and, in addition, offer the possibility of cross-linking at room temperature.
Kalrez: it is produced by DuPont and defined as perfluorinated. The chemical composition has not been disclosed, but it is known to be composed of carbon and fluorine atoms. It has exceptional chemical inertness and shows resistance to: polar and non-polar solvents, organic acids, strong oxidizing agents, steam, hydrazine, acidic oil mixtures and hydraulic fluids. It is suitable for items that can be used continuously at up to 288°C. It has an advantage over other fluorine elastomers in terms of resistance to higher temperatures. It is only supplied in the form of finished items.
Fields of Application:
Terpolymers with tetrafluoroethylene are mainly used for O-rings, hoses, gaskets, expansion joints, shaft seals, rubberized fabrics.
Tetrafluoroethylene – propylene – vinyl glycidyl ether terpolymers have not been used yet. However, they can be used in self-vulcanizing paint, possessing properties of resistance to heat, steam and acids.