Assessment of the Degree of Mixedness of Filled Polymers

For a given compounding application the selection of the type of processing equipment, the geometry and the operating conditions is always an important challenge. The outcome of this selection process significantly affects the economics of the process, as well as the microstructural distributions and hence the ultimate properties of the compound. Here mixing indices, defined on the basis of the statistics of the distributions of the concentrations of a plasticized elastomeric binder and graphite filler, were used to quantitatively characterize and compare the degree of mixedness of products of batch mixing, co-rotating and counter-rotating fully-intermeshing twin screw extrusion processes. Two separate experimental methods, involving the wide-angle x-ray diffraction and thermo gravimetric analyses, were used for the characterization of the mixing indices at two different scales of examination. The mixing indices were sensitive to changes in geometry and operating conditions. The resulting electrical properties of the conductive composite samples, mixed with either the batch or continuous, i. e., using either co-rotating or counter-rotating twin screw extrusion, correlated with their degree of mixedness. The presented methodologies should facilitate more accurate comparisons of the performances of different types of processors and better tailoring of the structure and ultimate properties of filled polymers.