Rheo-Optical Studies of Low-Density Polyethylene Films in the Nonlinear Viscoelastic Region

Abstract

The time-dependent birefringence was measured simultaneously with stress relaxation for annealed low-density polyethylene films at various temperatures ranging from 15 to 80°C under relatively large strains of about 10%, at which the films showed nonlinear stress-strain and birefringence-strain curves during the tests with a constant rate of elongation.The master curves of the strain-optical coefficient at relatively large strains of about 10% were very similar to that obtained at a small strain of about 3%. The strain-optical coefficient increased with increasing time and reached an equilibrium at long time. However, the larger the strain was sustained the higher the equilibrium value became.