Melting characteristics of polyethylenes. A comparative study of low‐pressure and irradiated polyethylenes

Abstract

Dilatometers of simple design were used to determine the relationship between specific volume and temperature for several different kinds of polyethylene: samples with densities of approximately 0.91 and 0.96 made at high and low pressures, respectively, and samples of low‐density material which had been irradiated with 10⁶−10⁸ roentgens supplied by 800‐kv. electrons. It was found that polyethylene made at low pressures is not only more crystalline than that made at high pressures, but also that it melts much more sharply. Despite the fact that irradiation raises the softening temperature of polyethylene, we have shown that the melting point of the crystalline regions of polyethylene is not thereby increased. It was found that in highly irradiated polyethylenes, the volume change with temperature deviates from linearity at 150°C. and rises rapidly at 170°C.