Thursday 8 October 2020

Design Properties for Engineers: Electrical and Dielectric Properties of High Performance Polymers


Electrical and Dielectric Properties of High Performance Polymers

In today’s post, we discuss the electrical and dielectric properties of different high performance polymers which can support you during the material selection process

Volume resistivity and surface resistivity

We start with the electrical properties of volume resistivity and surface resistivity. Volume resistivity tells us if the selected polymer allows electric conductivity through the part. Surface resistivity shows us if the polymer has an electric isolating behavior. In general, high performance polymers show a volume resistivity higher than 1014 Ω x cm and a surface resistivity higher than 1013 Ω. Both values indicate that high performance polymers are excellent electrical isolators. However, the isolation behavior is influenced by temperature and humidity. The higher the temperature, the more the chains start to move and this in turn lowers the isolation performance. Influence of humidity on the electrical performance plays a key role with hygroscopic polymers such as the polyimides (PAI, PBI, and PI) and PPA. 

Dielectric strength

Next electrical property is the dielectric strength. This value is estimated on a 1 mm thick polymer plate on which the current (measured in kV) will be increased till it breaks through the wall. For high performance polymers this value ranges between 20 to 30 kV / mm. PTFE has with 50 kV / mm the highest dielectric strength. 

Dielectric constant and dissipation factor

Among the dielectric properties, we discuss the dielectric constant and the dissipation factor. The dielectric constant tells us the isolation behavior: the lower this value is, the better the electric isolation behavior. Polar polymers such as PVDF have a higher dielectric constant compared to nonpolar polymers.  The dissipation factor shows the transformation of electrical energy into heat. A high dissipation factor results in a high transformation into heat. PTFE has here again the lowest values. 

To conclude: high performance polymers behave similar in their electrical performance compared to engineering and commodity plastics. There are variations within the high performance polymers caused by the different additives. 

Thank you for reading and #findoutaboutplastics


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