Abstract
AbstractA viscoelastic material when extruded rapidly through a short capillary or spinneret may exhibit an effective viscosity which is smaller than the usual or zero shear rate viscosity by a factor of several hundred. An equation is derived which expresses the effective viscosity as a function of the time the material spends in the spinneret (transit time) and the distribution function of Maxwellian relaxation times. It is assumed that the mechanical properties of the material may be represented by a generalized Maxwell model. Effective viscosities observed when a 25% cellulose acetate solution in a 96:4 (by weight) acetone:water solvent is extruded through a spinneret with radius 0.006 cm. and effective length 0.0186 cm. are given. The relaxation distribution function for the cellulose acetate solution is calculated from the dynamic viscosity data of Philippoff. From the distribution function and values of the transit time, effective viscosities are calculated and found to differ from the experimental values by −26 to 60%. In view of the fact that the effective viscosities are smaller than the zero shear rate viscosity by factors ranging from 145 to 10.8, the agreement between calculated and experimental values is quite satisfactory.
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