Masood Khabazian - Polymer Engineering Group/Department of Chemical Engineering /Tarbiat Modares University,Tehran,Iran.
Nadereh Golshan Ebrahimi - Polymer Engineering Group/Department of Chemical Engineering /Tarbiat Modares University,Tehran,Iran.
Mahdi Nadali - Polymer Engineering Group/Department of Chemical Engineering /Tarbiat Modares University,Tehran,Iran.

The uniaxial elongational viscosity of polyethylene depends on its molecular structure. The presence of long chain branches in LDPE leads to the well-known strain hardening behavior. The rise in viscosity above Trouton ratio is not seen for its linear version, HDPE. Therefore, it is of great importance to make a connection between the rheological behavior of polyethylene and its molecular structure. The MSF model is a successful model to describe the uniaxial elongational viscosity of various polymers with only two nonlinear parameters, namely β and fmax. β determines the steepness of strain hardening whereas fmax shows the steady state value of viscosity.