Influence of flow-type-dependent matrix rheology on droplet breakup in twin-screw extruded polymer blends

Abstract The morphology of immiscible polymer blends generated during twin-screw extrusion depends on the deformation history of the dispersed phase and on the matrix rheology. Here, this effect is investigated numerically in a two-dimensional, co-rotating, fully intermeshing batch twin-screw extruder. A Newtonian dispersed phase is considered, while the matrix is modeled as Newtonian, a Generalized Newtonian Fluid (GNF) accounting for shear thinning, and a Generalized Newtonian Fluid with Flow-Type dependence (GNFFTy), which combines shear thinning in shear-dominated regions and elongational thickening in extension-dominated regions. Velocity-gradient histories along tracer trajectories are used in a morphology model including droplet deformation, breakup, filament stretching, and coalescence. The three rheologies give similar gross flow structures but different local viscosity fields. The GNF model reduces viscosity in high shear regions, whereas GNFFTy predicts localized viscosity enhancement in extensional screw-screw gaps. These differences affect breakup, showing that shear-rate-based morphology predictions may miss topology-dependent viscosity effects.