Chemical Compatibility of Perfluoropolymers

Perfluoropolymers such as PTFE, PFA, and FEP are by far the most chemically resistant among thermoplastics. Few substances chemically interact with 

A few chemicals have been reported to attack perfluoropolymers at or near their upper service temperature (260°C).t They react with 80% sodium or potassium hydroxide. They also react with some strong Lewis bases including metal hydrides such as boranes (B2Hg), aluminum chloride, ammonia, and some amines (R-NH2) and imines (R=NH). Slow oxidative attacks may take place in the presence of 70% nitric acid at 250°C under pressure. It is important to test the effect of these reagents on perfluoropolymers under the specific application temperature to determine the material limitations. 

Perfluoropolymers derive their chemical resistance from an extremely strong carbon-fluorine bond and an impermeable sheath of fluorine atoms surrounding the carbon-carbon chain. Relatively high crystalline content renders these polymers insoluble in solvents. 

Another commercially significant perfluoro-pol5mier is the copolymer of tetrafluoroethylene-per-fluoromethyl vinyl ether. It has chemical resistance characteristics similar to the other perfluoropol5miers. 

Some halogenated solvents are absorbed by perfluoropolymers without any chemical interaction or degradation. The action is strictly physical and the removal of the absorbed species restores it to its original state. Too much absorption by a perfluoropoly-mer sample can be an indication of excessive porosity. A highly porous sample may appear blistered due to the expansion of vapors in the surface pores. A properly fabricated part does not exhibit blistering. 

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