抄録
The stationary viscoelastic properties of general purpose polystyrene (GPPS) and high impact polystyrene (HIPS) melts were measured by means of a screwless extruder. Since the cone rim pressure was not equal to the atmospheric pressure, some theoretical considerations were necessary to derive an approximate relation for calculating the first normal stress difference from the profile of Weissenberg's pressure and the value of pressure at the cone rim.
Measurements of Weissenberg's pressure were performed in a stationary state which occurred at 7∼10min after the starting of the rotor and continued for about 5min. The first normal stress difference observed for low density polyethylene (M.I.=2.0, 190°C) showed a fairly good agreement with the literature values. The first normal stress difference for GPPS was slightly greater than that for HIPS at the same shear rate.
Some flow properties were measured with an extruder-type rheometer according to both Bagley's and the pressure gradient methods, which gave the same results. The apparent viscosity of HIPS was somewhat greater than that of GPPS at the same shear rate. The rigidity, calculated from the first normal stress difference and the apparent viscosity for HIPS, was considerably higher than that for GPPS at the same shear rate. The correlation between the Weissenberg effect data and the exit pressure data was also examined.
