Simulation Of The Mixing Of Highly Filled Suspensions In The Co-Rotating Twin Screw Extrusion Process

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ABSTRACT Currently, the selection of elements and operating conditions in the mixing of various materials in a co-rotating twin screw extruder is an art which requires previous experimental studies. In this report, we outline various experimental and theoretical tools developed to investigate the mixing process in a fully intermeshing co-rotating twin screw extruder. The thermo-raechanical history of mixing is simulated employing the finite element method. To verify the numerical findings, experimental techniques were developed to investigate the goodness of mixing of samples collected from a 50.8 mm, clam shell design, Baker-Perkins twin screw extruder. 1.INTRODUCTION Mixing of various ingredients is an important task in all basic technologies. Among many mixing operations, the mixing of highly viscous and elastic polymeric resins with other resins (blending), and various additives including fillers and reinforcements (compounding) present special challenges and necessitate specialized batch or continuous mixers. The continuous mixers include single screw and twin screw extruders, single shaft kneaders and co-rotating disc extruders (1).The nature of the mixing step may be extensive (distributive) or intensive (dispersive) in character. In extensive mixing two or more starting components are interspersed in space with one another. On the other hand intensive (dispersive) mixing describes the multitute of processes in which some intrinsic change takes place in the physical character of one or more components during processing.Extensive mixing generates composition uniformity by the imposition of large strains through various types of deformation i.e., shear, squeezing and extension, which induce an increase in the interfacial area between components (2-4). The initial orientation of the phases and subsequent orientation of the interface are critical for achieving efficient extensive mixing (3). Extensional flows improve the efficiency of extensive mixing processes (5). On the other hand, intensive (dispersive) mixing generally involves the rupture of agglomerates of solid particulates and the further separation of closely packed particles after rupture (6,7). Both types of mixing are necessary and are incorporated into various continuous mixers.Among the available continuous mixers fully intermeshing, co-rotating twin screw extruders deserve special attention. These mixers operate on the building block principle, whereby the screw elements are selected and assembled depending on the requirements of the mixing task at hand. Reviews of the operational principles and comparisons to expecially the counter-rotating twin screw extruders are available (8-12).In our study we have applied various numerical and experimental studies to gain a fundamental understanding of the dynamics of the mixing process in co-rotating twin screw extruders. The following will summarize the tools that were developed to investigate the