Birefringence and orientation of polyethylene zone-drawn under various thermomechanical conditions

Abstract

In this paper, the influence of deformation and thermomechanical drawing conditions on the development of birefringence and orientation in high-density polyethylene during zone drawing is described. The orientation process of the crystalline phase does not proceed uniformly with deformation and is complete at lower draw ratios, while orientation of the amorphous phase increases continuously up to the highest draw ratios. The maximum birefringence considerably exceeds that of a polyethylene crystal (as high as 0.081) and the amorphous orientation almost approaches that of the crystalline phase. This indicates that the zone-drawing technique is highly effective in producing orientation. The birefringence is affected simultaneously by drawing stress and temperature; at higher temperatures and lower stresses, softening effects predominate, while in the opposite case stiffening effects become operative. The occurrence of both factors is regulated by the time of thermal exposure in the heating zone.