Analysis of Flow Properties in Relation to Molecular Parameters for Polymer Melts

Reported data on polystyrene, polyethylene, and polydimethylsiloxanes are contradictory with respect to the shear rate at which the transition from Newtonian to non-Newtonian flow occurs. Some data implies that the transition occurs at the same lower limiting shear rate and is independent of molecular weight above a critical molecular weight. On the other hand, other data shows that above a critical molecular weight the transition occurs at lower rates of shear as the molecular weight increases. The considerations of Bueche for melt polymer flow confirm the latter type of transition behavior. It is proposed that the discrepancies are due to molecular weight distribution, temperature effects, and methods of obtaining zero shear viscosities. Data are presented to support these views.