Virgin TFE is almost universally inert as a result of the molecular structure of the resin. The molecules are closely packed together and consist of long chains of carbon atoms protected by a tightly held sheath of fluorine atoms. Components made of this material exhibit excellent impermeability to most corrosive liquids, vapors and gases, even at elevated temperatures, as well as under pressure and vacuum. They are affected only by molten alkali metals, fluorine and chlorine trifluoride at elevated temperatures and pressure.
Virgin TFE has exceptional electrical and dielectric properties, but can be somewhat limited for mechanical applications. It will creep or cold flow when a compressive load is applied. Since it is a soft material, it can also experience a high rate of wear when used in a dynamic situation.
The addition of inert fillers will increase resistance to wear, deformation and creep. It will also improve stiffness, thermal conductivity, hardness and dimensional stability. However, the fillers decrease properties such as tensile strength, elongation, and dielectric values.
Milled glass fibers are the most widely used filler for TFE. They have the least effect on chemical and electrical properties and add greatly to the mechanical properties of unfulled TFE. These compounds resist acids and oxidation but can be attacked by alkali.
This filler has better wear and creep resistance and better thermal conductivity than the glass fiber with TFE. The compound is easily machined, but has poor chemical resistance in the presence of acids and alkali.
CARBON & GRAPHITE
These fillers are used both separately and together in TFE compounds. They have good chemical resistance to corrosive environments. They also exhibit good initial wear and rubbing or sliding contact characteristics, both dry and in water. They are frequently used in piston rings to reduce cylinder wall wear by entrapping abrasive foreign particles in their relatively soft surfaces.
MOLYBDENUM DISULFIDE (MoS2*)
This filler is used, frequently in combination with others, to increase surface hardness and to reduce the coefficient of friction and steady-state wear.