Rheo-Optical Studies of High Polymers. XX. Time and Temperature Dependences of Crystalline and Amorphous Orientation in Low-Density Polyethylene

Abstract

The time and temperature dependences of the infrared dichroism for some crystalline and amorphous bands of low-density polyethylene were measured during stress relaxation tests in a temperature range from 25 to 70°C. From the dichroic ratios, the crystalline and amorphous orientation functions were determined. The time and temperature dependences of the strain-optical coefficient are very similar to those of the crystalline orientation functions, but those of the amorphous orientation functions are quite different. It was found that time-temperature superposition could be applied to the time-dependence curves of the crystalline orientation functions, and that the rheo-optical shift factor oT determined in the course of the superposition gave the same activation energy as had been reported for the α1 dispersion process.The intrinsic birefringence for the crystalline and amorphous phases was evaluated from the experimental results, and the contributions of the crystalline and amorphous phases to the total strain-optical coefficient were separated. The contribution of the amorphous phase is larger than that of the crystalline phase, and the two contributions show quite different dependences on time.