Fraunhofer Institute for Structural Durability and System Reliability LBF
Fraunhofer Institute for Structural Durability and System Reliability LBF

Electrical Conductivity

Most polymers have pronounced insulation properties. One possibility to make plastics conductive is by adding conductive filler particles or additives into the polymer matrix. When exceeding the limiting concentration (percolation threshold) a sudden rise in electrical conductivity sets in, increasing with rising concentration of conductive filler particles.

We offer our support in topics and examinations such as:

  • Direct Current (DC) conductivity at high and low impedances
  • Frequency dependent conductivity (AC)
  • Inline conductivity measurements in polymer processing
  • Rheo-electrical measurements
  • Complex dielectric permittivity
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Polymers are normally good electric insulators, this meaning; they have an extremely low electric conductivity. Electrical charges absorbed from the environment can stay in the material for a long period of time without draining off, the material becomes electrically charged. The surface of the material, which is in direct contact with its surrounding, and for example, might be subject to humidity, will have a considerably different electric conductivity within the material. For this reason a distinction must be made between the surface and volume conductivity. Trace amounts of impurities such as fingerprints can change the order of magnitude of the conductivity. Therefore measurement, sample preparation and control of the measurement environment must be carried out with great diligence. Furthermore, highly sensitive instruments are a requirement for reliable measurements.

Our expertise allows us to carry out:

 

  • Measurements of direct current conductivity according to ASTM D257
  • Four-point measurement for high conductivities
  • Tailor-made measurements for different test specimens and sample geometries

 

 

Instrument parameters:

Temperature:   Roomtemperature (Standard climate)

Measurement rage of conductivity:   10-16 S/cm to 10-7 S/cm

The dielectric properties of a substance are linked with the induced polarization, the orientational polarization and charge carrier mobility within the electrical field. In polymers the orientation of molecular dipoles in the electric alternating current field (or after switching on and off) are determined by the molecular mobility of the chain molecules and polymer groups. Beside the examination of relaxation processes, dielectric spectroscopy can offer information on the mobility of charge carriers and polarization processes at the interface. Measurement parameters are the real- and imaginary parts of the complex dielectric function or the complex AC conductivity.

  • Temperature and frequency dependent measurements of the real and imaginary part of the dielectric function or the AC conductivity ( or the loss-angle)
  • Isothermal measurements of the real and imaginary parts of the dielectric function (for hardening reactions/processes, for example)
  • Measurement of permittivity and the loss angle

 

 

Instrument parameters:

Frequency range:        10-4 Hz to 107 Hz

Temperature range:    -150 °C to 400 °C

Pre-selected control parameters of the product stream can be monitored in real-time and continuously with inline- or online process control. For online arrangements, a small portion of the main material flow is diverted for the measurement. This diverted side flow is then either discarded or joined back into the main flow. With the inline measurement technique, the measurement takes place in the main material flow.

We have developed tailor-made DC and AC measurement methods for process control in compounding and injection molding.

A measurement nozzle with internal electrodes is available for extruding and compounding. For the material- and process optimization in injection molding processes an injection form, with electrodes across the test sample in different spacing’s, for standard test bars is available.

We can develop custom-made electrode geometries for your polymer processing.

 

Instrument Parameters:

Temperature:    up to 450°C

Pressure:            up to 1500 bar

Conductivity:   > 10-10 S/cm

For the examination of the influence of the thermo-mechanical history of polymer melts or reactive resins with conductive fillers on the electric conductivity, measurements are carried out in a rheometer.

This requires special measurement geometries that create mechanical shearing as well as allow the measurement of the electric conductivity.

 

 

 

 

Instrument Parameters:

Temperature range:    -150°C to 300°C

Frequency range:        0.001 Hz to 30 Hz

Conductivity:              > 10-10 S/m

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