The viscous flow of molten polystyrene. II

Abstract

The capillary flow of polystyrene has been studied in some detail. An empirical equation relating apparent fluidity to capillary wall shearing stress has been suggested which fits experimental flow curves well. This equation has the advantage of containing only two material constants: the Newtonian viscosity, η o , and a constant, k, characterizing the degree of departure from Newtonian behavior. The influence of temperature, polymer molecular weight, and solvent content on η o were discussed and suitable data presented. The dependence of the activation energy of viscous flow upon solvent content was illustrated by data on the system polystyrene-isopropylbenzene over the entire concentration range. It was shown that the constant k is relatively independent of temperature and polymer molecular weight. However, as the solvent content increases, k increases, finally assuming a more or less constant value over the range 5–20% solvent. A critical capillary wall shearing stress was observed, above which the extruded filament buckles into a spiral. This spiral inception point was shown to be an isoelongated state defined by ā = 3. The wall shearing stress at the spiral point was found to vary inversely with the molecular weight. It was relatively independent of temperature and decreased as the solvent content increased. These observations were in accord with the tentative explanation put forth for the phenomenon of spiraling.