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 timetemperature 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.

Shear creep and recovery of a technical polystyrene

“…Above the glass-rubber transition, a second pronounced transition shows up, which is called network transition [5][6][7]. It was described for the same material in previous publications [3,8]. In this region the recoverable compliance rises from the rubbery level of about 5 • 10 -6 Pa -l up to a long-time-limiting value, the steady-state recoverable compliance Je of 4.7 -10 -4 Pa -1.…”

“…2. Double-logarithmic plot of the creep compliance vs. creep time in the glass-rubber transition for polystyrene of the polymer was described in more detail elsewhere [2,3]. For sample preparation the granulate was filled into a metallic mold and the material is molded in three steps in moderate vacua under a slight mechanical pressure.…”

Measuring device for precise evaluation of torsional creep and recovery data

“…105g/mol and Mw = 3.86 • 10 s g/mol. The molecular weight distribution of the polymer was described in more detail elsewhere [3,15].…”

“…They used it successfully for the determination of the shear behaviour of anionic polystyrenes and blends of anionic polystyrenes [2]. If the measurements of storage and loss modulus can be continued into the Newtonian region with sufficient accuracy, it is even possible to derive the recoverable compliance from these data by conversion [3].…”

“…For measurements up to the rubbery plateau we use the modified TNO torsional creep apparatus [1,15], for the rubbery plateau and the melt region we use a modified dynamic viscosimeter [3]. Compliances into the flow region have been measured by sample torsion between parallel plates with application of torque by torsion of a thin wire with small torsional stiffness, from which the upper moving clamp is suspended [3]. This technique yielded satisfying results of the creep compliance; it did not allow, however, the determination of the recovery behaviour.…”