Non-linear shear modulus for a linear low density polyethylene.

The response of a polydisperse (M(w)/M(n) = 8.45) linear low density polyethylene to imposed step shear strains up to strains of 10 are measured with the Rheometrics System IV. The measured stress is factorable into a product of a time-dependent term, which is just the linear relaxation modulus, and a strain-dependent term, the damping function, except at short times and large strains. This damping function is, at high strains, only slightly less in magnitude than the corresponding values for branched polyethylene of broad molecular weight distribution (MWD), but much greater than values obtained with unbranched polystyrenes of narrow MWD, suggesting that the observed damping function may be as much or more controlled by polydispersity than by long chain branching.