Filled PTFE stock shapes from Modern Plastics are used in a very large number of fields. Some of PTFE’s properties can be improved and/or modified by adding suitable fillers, allowing the use of PTFE in fields otherwise precluded to this polymer. The fillers most commonly used are: glass fiber, carbon, bronze or graphite, in the form of powder intimately mixed with the PTFE.
The addition of fillers to the PTFE improves or modifies its properties depending upon the nature and quantity of filler:
- remarkable increase in wear resistance
- decrease of deformation under load and of creep
- reduction of thermal expansion
- some types of filler increase the thermal and electric conductivity
PTFE is reinforced with glass fibers. The added glass fiber improves the wear properties and, to a minor degree, also the deformation strength under load while leaving substantially unchanged the electrical and chemical characteristics. Glass itself has a rather poor resistance against alkalis and is easily attacked by hydrofluoric acid. The coefficient of friction is slightly increased, and for this reason, graphite is sometimes added to compensate this side effect.
Carbon is added to the PTFE, along with small percentage of graphite. Also, the carbon tends to improve wear and deformation strength to a considerable degree while leaving the chemical resistance practically unchanged but substantially modifying the electrical properties.