A CONSTITUTIVE ANALYSIS OF UNIAXIAL, EQUIBIAXIAL AND PLANAR EXTENSIONOF A COMMERCIAL LINEAR HIGH-DENSITY POLYETHYLENE MELT

From constant strain-rate experiments in extensional flows, nonlinear strain measures and effective damping functions are derived for a line ar high-density polyethylene melt. Experimental results are compared w ith predictions of two molecular theories, the Doi-Edwards model and t he molecular stress function approach of Wagner and Schaeffer. Orienta tion (but not stretch) of macromolecules at small and large strains is well represented by the Doi-Edwards orientation tenser. Stretch of ma cromolecules is found to be isotropic as predicted by the molecular st ress function model, which is in excellent agreement with the data. Fo r the latter model, a novel strain energy function is presented. (C) 1 998 The Society of Rheology.