Viscoelasticity of melts of polyethylene blends. 2

Abstract

1. The activation energies of viscoelastic relaxation and viscous flow of melts of LDPE/HDPE blends of the same composition are the same. 2. The viscosity of melts of blends of linear and branched polyethylenes with low shear stresses is higher and corresponds to the value predicted by the rule of logarithmic additivity for high shear stresses. 3. The shear rate corresponding to the appearance of elastic turbulence increases exponentially with an increase in the proportion of HDPE in the polyethylene blend. 4. The equilibrium shear modulus of the melt can be regulated within broader limits by mixing HDPE and LDPE than by altering the molecular characteristics of the polymer. 5. The Havriliak-Negami equation in principle cannot describe the ratio of the rates of accumulation and dissipation of energy in steady-state shear flow whenPw/2ġgη0 > 0.5 (not the experimentally observed viscosity superanomaly is predicted, i.e.,dσ12/dġg < 0). 6. The first difference of normal stresses in shear flow, calculated with the die swell with the Bagley equation, is close to the experimental results for HDPE melts and HDPE/LDPE blends if the concentration of HDPE > 60%; for LDPE melts and blends containing HDPE < 60%, the best agreement of the predicted and experimental values is attained in calculations with the Tanner dependence.