X-Ray Studies of Polyethylene under High Pressure

Abstract

The phase diagram, growth processes of extended-chain crystal and high pressure phase, and the temperature dependency of lattice parameter in polyethylene have been studied under high pressure up to 6000 kg/cm2 using a new high pressure X-ray diffraction apparatus. The high pressure phase diagram obtained by micro-DTA measurement agrees with that by X-ray measurement. The crystallization process of the high pressure phase seems to be a homogeneous and diffusion controlled two dimensional growth. The growth process of the extended-chain crystal is very rapid, and the direct formation of the extended-chain crystal without passing through the high pressure phase is clarified. The temperature dependency of the lattice parameters of the extended-chain crystal and the high pressure phase at 5000 kg/cm2 were obtained, and the shrinkage of the c-axis in the high pressure phase which shows only a sharp (100) diffraction pattern is discussed with the aid of dilatometric data.