RECENT DEVELOPMENTS IN POLYETHYLENE INSULATING MATERIALS

The commercial importance of polyethylene was first recognized during the war in wire and cable applications where it was employed as an outstanding flexible dielectric. For once a material was available which combined excellent dielectric properties, chemical, oil, moisture and oxidation resistance with low temperature flexibility, high tensile strength, and elongation. This excellent reputation has been based mainly on one class of polyethylene polymers which has been varied to a slight degree in crystallinity and molecular weight. Since such advances were made with one polymer type it was natural to investigate the possibilities of property variation through more extensive polymer changes. It was realized, however, that more rigid polymers would not supplant presently available polymers in the majority of applications, but rather would result in an overall expanded use of polyethylene in many industries. An example may be seen in wire and cable applications. Where thin-walled insulations of high strength are required, new polymers which have high rigidity will be of particular value. On the other hand, in large cable applications where a thick-walled jacket is required, the new polymers would have limited use due to this rigidity. Annual Wire and Cable Symposium (4th), Asbury Park, N. J., December 1955.