Viscoelastic Behavior of Semicrystalline polymers at Elevated Temperatures on the Basis of A Two-Process Model for Stress Relaxation

摘要

Viscoelastic behavior at elevated temperatures of high-density polyethyl-ene and isotactic polypropylene was investigated by using the stress relaxation met.hod. The results are interpreted from the view of an established two-process model for stress relaxation in semicrystalline polymers. This model ~s based on the assumption that the stress relaxation can be represented as a superposition of two thermally activated processes acting in parallel. Each process is associated either with the crystal or amorphous phase of a polymer sample. It was found that the temperature dependence of viscosity coefficients and elastic moduli of these two fractions are similar in the two materials. The experimental data was correlated with literature data of a and ~ processes in polyethylene and polypropylene obtained from dynamic mechanical ther-mal analysis.