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

Abstract

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.

PLA based biocomposites reinforced with Arundo donax fillers

“…The dispersion of the ADF inside the polymer matrix was estimated by calculating the mixing index (MI) according to the procedure described by Kalyon et al [22,23] and applied in our previous work [24]. This parameter can help in assessing the actual degree of dispersion of the filler, taking into account the actual filler concentration in a number of randomly chosen samples and comparing this with the average concentration.…”

Co-rotating twin-screw extruders: Detailed analysis of conveying elements based on smoothed particle hydrodynamics. Part 1: Hydrodynamics

“…FEM was also used to simulate complex fluids in extruders including wall slip phenomena, (e.g., Kalyon et al, 1999;Lawal et al, 1999;Malik et al, 2014). However, simulating free-surface flows in partially filled screw sections remains extremely challenging.…”

Numerical simulation of reactive extrusion processes for activated anionic polymerization

“…And in the reactor, the fluid flows forward by means of the drag of screws and the pressure. Therefore, the abovementioned complexity makes it very difficult to perform the numerical simulation of reactive extrusion processes based on the real reactor model (David et al, 2000;Goffart et al, 1996;Van Der Wal et al, 1996;Kalyon et al, 1999), and the equivalent reactor model should be constructed. At present, one-dimensional equivalent reactor models are adopted in many investigations.…”