Interpretation of the rheological properties of carbon black reinforced polymer melts

Highly filled systems exhibit yield values. This is seen in the dynamic experiments and in the shear and elongational viscosities. Viscosity does not level off at finite values with decreasing deformation rate but continues to increase approximately inversely proportional to the deformation rate. This corresponds to yield values of order 5 x 10⁵ dynes/cm².

The storage modulus also does not tend to zero at low frequencies. The dynamic properties and stress relaxation results suggest high material memories for the highly filled systems. The extrudate swell values are small, however, and these systems exhibit very little delayed recovery.

The implications of these experimental results are interpreted in terms of a generalized "Schwedoff body," a single integral constitutive model with a yield value. The Von Mises yield criterion is used and alternative criteria are considered. Parameters of the model are evaluated and a unified constitutive model is found to describe the results observed from the diverse experiments. Extensions of the theory into transient phenomena are discussed.