Rheological properties and model for particle-filled polymer melts

An experimental and theoretical study of the rheology of particle filled polymer melts was carried out. The systematic experimental study focuses on three different material systems--rubber compounds (SBR/N11O, PTT), filled thermoplastics (PS/CaCO;A three dimensional viscoelastic-plastic phenomenological model for flow of particle filled polymers has been formulated. The simplified Leonov model is employed in the approach to describe the viscoelastic behavior of the polymer matrix. A structure function is introduced to express the stress generated by the flow of dispersed phase, under the assumption that the material obeys the von Mises yield criterion. The model has been applied to a variety of filled polymers. The study shows that the model fits well the steady shear viscosity data over a large shear rate range. Most of the predictions of transient shear flow behavior are found to be in reasonable agreement with the experimental data. The discrepancies in comparison of the prediction with the experimental data in transient start-up shear flow and stress relaxation mainly lies in the improper yield value and relaxation time obtained from the curve fitting of the steady shear viscosity data, since these values are test condition dependent. The model is further expanded by combining both a phenomenological and a structure kinetics approach without yield criterion. The structure kinetics is introduced through a structure function which is a combination of an internal and an external structure functions characterizing the thixotropic behavior of the particle phase. The theory has been used to predict the experimental results in several shear flow situations. The predictions by the phenomenological model with von Mises yield criterion are improved by the inclusion of the structure kinetics in the development of the rheological model. Fairly good agreement can be achieved in transient start-up shear flow, sequential rest-start-up shear flow, and some of the results in stress relaxation.