Basic study of the rheological properties of particle filled polymer melts

Basic rheological studies in steady shear and elongational flow were carried out for small particle filled molten state polymer compounds.

Polystyrene has been chosen as a matrix polymer. Polystyrene is one of the most widely used polymers and exhibits little thermal and mechanical degradation. Calcium carbonate particles having average particle diameters of 17 µm to 0.07 µm were used as fillers both in the untreated and stearic acid surface treated states. Carbon black with basic particle diameters of 0.045 µm was also used for comparison.

The influences of particle size, surface treatment and loading level were discussed. The yield stresses of these systems were estimated graphically both in steady shear and elongational flow experiments. It was found that the yield stresses of the systems decrease roughly inversely with increasing average particle diameter. The stearic acid surface coating was observed to substantially reduce the yield stress and viscosity in both shear and elongational flow. The addition of untreated calcium carbonate and carbon black particles makes the shear stress or viscosity overshoot phenomenon more striking in the transient state of steady shear flow. Stearic acid surface coating reduces the overshoot phenomenon.

A phenomenological plastic viscoelastic constitutive equation was applied to filled systems with time dependent yield values. Theoretical predictions give satisfactory agreement with experimental data. Comparison was made for both transient and steady state shear and elongational flow.