EXPLOITING ACCURATE SPINLINE MEASUREMENTS FOR ELONGATIONAL MATERIAL CHARACTERIZATION

We have constructed an apparatus which provides enhanced resolution in the measurement of the free surface profile and the axial force exiti ng the die during spinning of a liquid filament. In this paper we demo nstrate how this information can be exploited to give quantitative inf ormation about rheological material properties in isothermal elongatio nal flows. The fiber spinning experiments are coupled with mathematica l models that serve as inverse problems to deduce material properties when the fiber profile and upstream axial force are experimentally kno wn. We first develop integral and differential forms of the fiber spin ning momentum balance which describe how stress varies down the length of the filament for an incompressible material, independent of theolo gy. These forms are then combined with experiments to deduce the evolu tion of the elongational viscosity along the spinline and verify the a ccuracy of free surface measurements. A fiber spinning model specializ ed to the Giesekus constitutive equation is then combined with spinlin e measurements to determine material constants within the Giesekus con stitutive assumption. In particular; our technique is used to characte rize the elongational rheology of a Boger test fluid. We obtain signif icantly different values for the relaxation time and mobility paramete r than we obtain via shear rheometry; the solvent and polymer viscosit ies deduced from our spinline and shear experiments are essentially th e same. (C) 1997 The Society of Rheology.