Rheological Implications of the Exit Pressure and Die Swell in Steady Capillary Flow of Polymer Melts. II. The Secondary Normal Stress Difference

Abstract

An equation relating the secondary normal stress difference to the “exit pressure” has been derived and used to calculate secondary normal stress difference for polyethylene and polypropylene melts. The results of these calculations indicate that the secondary normal stress difference for these fluids at shear rates of from 200 sec −1 to 800 sec −1 and at a temperature of 180°C is greater than the primary normal stress difference. This apparently unexpected result is discussed in terms of what is currently known regarding the behavior of polymer solutions.