Viscoelastic properties of carbon mixes

Abstract

The critical stress in the extrusion of polymers above which the extrudate becomes irregular is known to be a function of the rubberlike elastic modulus. In this paper the validity of this relation is put to test for carbon mixes. A parallel plate apparatus is used for determining the viscoelastic properties of the carbon mixes. The rubberlike modulus and the viscosity are calculated from the plot of generalized strain vs. time for constant load assuming a suitable rheological model. The viscosity of the mixes in general shows a yield stress and exhibits some non-Newtonian behaviour. The stress calculated using the rubberlike elastic modulus does not agree with the critical stress as obtained in actual extrusion of the core mix. The dependence of viscoelastic properties on the nature and particle size of the filler as well as the nature of binder is reported.