The Filled grades of PTFE can be compounded & customized for specific service conditions & applications. Filled PTFE grades have specific properties improvement based on filler, type of filler & percentage of filler.
Mechanical properties
The compressive creep behaviour of filled PTFE is one of the most significant properties to the designer and user.
In comparison with unfilled PTFE the compressive modulus of filled PTFE is greater and hence, for the same stress, a lower deformation will occur. This difference diminishes, however, as temperatures rise and the compressive performance of unfilled and filled PTFE draws close together at 200°C (392°F). The reason is almost certainly that the general reduction in the compressive modulus of the PTFE matrix overrides the support given by the random distribution of filler particles.
Electrical properties
The addition of fillers does have a marked effect on the electrical properties as well. In particular, graphite – and carbon filled compounds may have a relatively high conductivity, which can assist the dissipation of static charges in applications where these are a problem.
Filled PTFE is a mixture of materials, and voids – no matter how small – are always present: as with all porous materials, the properties are dependent on the nature of the environment and of any inadvertent contamination. The electrical properties are no exception and are markedly dependent on the environmental humidity.
Thermal properties
The thermal expansion of most fillers is less than that of PTFE and since the expansion of the composite will be somewhere between that of the two constituents, filled PTFE compounds expand less than unfilled PTFE. During fabrication certain fillers, notably fibres and platelets, become preferentially oriented (as do the particles of PTFE to a much lesser degree). The result is that some compounds have a markedly different expansion in the directions parallel and perpendicular to the direction of moulding.
The thermal conductivity of PTFE is very low, making it a good thermal insulating material. Many fillers, notably metals and metal oxides, have high thermal conductivity, but in general they are effectively encapsulated by PTFE so that the conductivity of the compounds is still relatively low.
Post time: Feb-10-2018