The extensional properties of M1 obtained from the Carri-Med elongational viscometer

Abstract

The extensional flow properties of the “round robin” fluid M1 were examined using the Carri-Med elongational viscometer at 20 ° C. With this particular fluid, use of a spinneret caused flow of a pulsating nature or a distortion of the filament, or both. Consequently, flow of the fluid was directly out of the tube. The filament was stretched using the rotating drum operating at various speeds. The amount of die swell observed depended upon the take-up speed. The measured diameter profile and the calculated strain rate curve showed distinct differences from those obtained with most other polymer solutions previously examined. The apparent extensional viscosities were determined, and showed Trouton ratios in the range 300–10 000. As a function of total strain, the fluid appeared to strain harden up to a strain of about 2.5, and then pass through a maximum, before strain thinning slightly. Average values of stress and strain rate were also determined using a two-point method. The results from this showed the apparent extensional viscosity to increase as a power law function of strain rate, although the value of the power law index did depend upon the choice of the two points selected. The particular collection of flow characteristics observed in this fluid are, if not unique, then certainly unusual in a number of aspects. Overall, the material is undoubtedly strain hardening, although the exact form which this takes, particularly at low strains, would appear to be a direct consequence of the relaxation time of the fluid.