The development of polythene as a high-frequency dielectric

The paper is mainly concerned with the power factor of polythene (the high polymer of ethylene), which, being normally of the order of 0.00015-0.0003, renders the material highly suitable as a high-frequency dielectric. It has been found, however, that oxidation may occur during the processing of the material in the manufacture of cables and mouldings, and that this increases the power factor and may also lead to difficulties in extrusion. These effects may be virtually eliminated, however, by the use of small amounts of anti-oxidants. The measurable, albeit low, power factor of pure polythene is hardly concordant with the supposedly non-polar nature of the substance, and a number of possible explanations of the small basic power factor have been investigated. Measurements of power factor over wide frequency and temperature ranges show that its variation for pure polythene is extremely sluggish, but that oxidation causes the appearance of marked peaks; these observations are examined in the light of present theories of dipole loss. A brief account is given of the structure of polythene, and of its main physical and mechanical properties.