Viscoelasticity and viscoplasticity of polypropylene/polyethylene blends

Observations are reported on polypropylene/polyethylene blends with various concentrations of components in uniaxial tensile tests with constant strain rates, relaxation tests, and creep tests at room temperature. A model is developed for the viscoelastic and viscoplastic responses of polymer blends at arbitrary three-dimensional deformation with small strains. Material constants in the constitutive equations are determined by fitting the experimental data. It is found that all adjustable parameters evolve with blend composition following an analog of the rule of mixture. Lifetime of blends under condition of creep rupture is evaluated by numerical simulation.