Factors Influencing Polymers in Electrical Applications

When selecting polymers for use as insulators, in capacitors, and other electrical applications, we must consider factors other than their interaction with electric fields. The following examples illustrate some of the other factors that we must consider. 

Our principal concern is often the polymer s mechanical properties. For instance, the requirements of the handle of an electrician s screwdriver are very different from those of wire insulation. In the former application, we are free to choose stiff polymers of many types, including glassy amorphous polymers. In contrast, wire insulation must be flexible, which limits our choice to ductile polymers. 

In storage capacitors it is important that we keep the dielectric constant to a minimum. This is not just a question of selecting the most appropriate polymer we must also ensure that contaminants that could raise the dielectric constant are kept to a minimum. Polymer manufacturers sell special grades of polypropylene (which is invariably the polymer of choice) that they describe as ultraclean . These resins are made with catalysts that are extremely active and thus leave very little residue in the polymer. Such resins typically contain little or no anti-oxidant and are extruded under conditions and using equipment that are designed to minimize oxidation. 

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