Structure and Time-Dependent Mechanical Behavior of Highly Oriented Polyethylene

The structures of polyethylene films and film fibers, having different orientation degrees and prepared by orientational crystallization and orientational drawing, have been investigated by electron microscopy and X-ray diffraction and specific features of the supermolecular structures and differences in the mechanical properties of the samples obtained by these methods have been discovered. Thermomechanical tests have also shown that samples prepared by the two techniques demonstrate different behavior on heating. The time-dependent behavior of the mechanical properties - tensile strength and elastic modulus - have been studied. The phenomenon of slow relaxation of the elastic modulus has been observed for the samples obtained by orientational drawing. It is shown that a long-term decrease in the elastic modulus can be attributed to the presence of structural elements capable of relaxation due to a weak connection between them, their small sizes, and the inhomogeneity of the sample deformation during orientational drawing.