The development of the electrical properties of composites as a function of the degree of mixedness of a conductive filler distributed into an insulating polymer is investigated. A wide‐angle X‐ray diffraction (WAXD)‐based quantitative phase analysis method was used to characterize the variations of the concentrations of the insulating binder and the conductive particles around their mean values as a function of mixing time in an intensive batch mixer. Increasing the time and hence, the specific energy input, during the mixing process results in a more homogeneous spatial distribution of the conductive filler in the polymeric matrix, which in turn results in a decrease of the volume conductivity of the composite. The decreasing conductivity of the composite is attributed to the better coating and hence the isolation of the conductive particles from each other, thus hindering the formation of a conductive network “percolation”. Overall, these results suggest that the control of the electrical properties of conductive composites could benefit from a good understanding and adequate control of the dynamics of the mixing process and the resulting degree of mixedness of the conductive particles in the polymer matrix.

Extrusion of filled polymer is commonly employed in diverse industries including compounding operations. The analysis of extrusion of filled polymers is complicated especially by the ubiquitous viscoplasticity and wall slip of the filled polymers. Furthermore, the role played by entrainment of air in the processor, the continuously evolving microstructure, and hence the rheological behavior of the filled polymer in the mixing volume of the extruder and the flow instabilities associated with the converging flows involving the filtration of the binder polymer present additional challenges to the analysis. Specialized techniques are also necessary to quantitatively describe the dispersive and the distributive degree of mixing of the compound. The principal tasks of this study included the collection of experimental data from twin‐screw extrusion using an instrumented and industrial‐scale co‐rotating extruder in conjunction with a well‐characterized filled polymer, which exhibits viscoplasticity and wall slip. The process allowed the adequate mixing of the ingredients and the removal of its air content. Next, the processing data were compared with the results of numerical simulation using the Finite Element Method. The predictions compared favorably with the experimental temperature and pressure distributions obtained under different sets of operating conditions. The distributive degree of mixing (spatial homogeneity) of the filled polymer upon exit from the die was also characterized employing a wide angle X‐ray diffraction technique in spite of the amorphous nature of both the filler and the binder polymer, i.e., hollow glass spheres and poly(dimethyl siloxane) polymer.

Two x-ray based techniques involving energy-dispersive analysis and diffractometry were introduced to the analyses of the degree of mixedness, i.e. the “goodness of mixing” of concentrated suspensions. A hydroxyl terminated polybutadene matrix was mixed with aluminum and ammonium sulfate. In the analysis, the ratio of the relative volume fractions of the two solid components was used as the basis of the analytical evaluation. Both characterization techniques are capable of determining the relative volume fraction of the two solid components as a representative measurement of the distributive mixing efficiency and both are sensitive to the scale of examination. The introduced techniques should be useful in the better definition of the degree of mixedness as well as in resolving differences in mixing efficiencies of various mixers used in processing of concentrated suspensions.

Samples of a concentrated suspension were systematically collected from the mixing volume of a continuous processor. The large amplitude oscillatory shear behavior of the samples was found to be significantly affected by the screw configuration employed and the location. Microstructural analyses employing nuclear magnetic resonance imaging, wide‐angle X‐ray diffraction and X‐ray radioscopy revealed substantial entrainment of air into the suspension during continuous processing. The volume fraction of the entrained air increased with geometries and operating conditions leading to partially full channels. Overall, air entrainment is identified as a dominant factor in the development of the microstructure and the rheology of concentrated suspensions and should be considered in their optimum processing.

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