Extensional viscosity of model polymer melts

Uniaxial extensional viscosity is one of the key properties which determine the processability and the performance of a plastic material. First, researchers developed the tube model to predict the extensional viscosity of polymers in slow flow. After that, they tried to extend this model to faster flow by introducing new mechanisms such as chain stretch or convective constraint release. Although these adaptations allowed to explain quantitatively the behavior of the polymeric solutions, severe discrepancies with the theoretical predictions were observed for molten polymers. In this work, we focus on two hypothesis that could explain this apparent difference of behavior : the Stretch-Orientation induced Reduction in Friction (SORF) and the multimode stretching model. The objective of this work is to critically assess the validity of these two models. For this purpose, the extensional viscosity of polymeric solutions and bidisperse blends were measured with a filament streching rheometer. The results obtained are in agreement with the SORF theory and dispel the fact that the environment does not play any role. We do not fully reject the multimode stretching model neither. Finally, this thesis also contributes to the very small pool of extensional viscosity data of entangled polymeric systems present in the literature.