Mathematical modeling and experimental studies of twin-screw extrusion of filled polymers

Extrusion of filled polymers is commonly employed in diverse industries inc luding 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 r heological behavior of the filled polymer in the mixing volume of the extru der and the flow instabilities associated with the converging flows involvi ng the filtration of the binder polymer present additional challenges to th e analysis. Specialized techniques are also necessary to quantitatively des cribe 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 c orotating extruder in conjunction with a well-characterized filled polymer, which exhibits viscoplasticity and wall slip. The process allowed the adeq uate mixing of the ingredients and the removal of its air content. Next, th e processing data were compared with the results of numerical simulation us ing the Finite Element Method. The predictions compared favorably with the experimental temperature and pressure distributions obtained under differen t sets of operating conditions. The distributive degree of mixing (spatial homogeneity) of the filled polymer upon exit from the die was also characte rized employing a wide angle X-ray diffraction technique in spite of the am orphous nature of both the filler and the binder polymer, i.e., hollow glas s spheres and poly(dimethyl siloxane) polymer.