Dynamic shear properties of a technical polystyrene melt

Abstract

A dynamic viscometer of the Couette type is described which permits the determination of storage and loss shear modulus of polymer melts with high accuracy. For a technical polystyrene, results of measurements of storage and loss moduli are reported in the temperature interval between the rubbery plateau and degradation. From these data, the courses of storage and loss compliances and the course of the time-dependent shear compliance are derived and compared with the results of creep measurements.

The frequency dependence of the storage compliance shows clearly the presence of the so-called network transition between the end of the glass transition and the onset of flow. The time-temperature shifting laws for the flow process and for the network transition are shown to obey the WLF shift equation, but with different sets of parameter values. Consequently, the complete data do not obey the time-temperature superposition law.

Comparison with non-Newtonian viscosities, measured by means of a slit and a capillary viscometer attached to an extruder, shows the excellent validity of the Cox-Merz rule, provided either the absolute dynamic viscosity or the stressing viscosity are used for this comparison.