Computation of the morphological changes of a polymer blend along a twin-screw extruder

The control of the morphology of an immiscible polymer melt is of vital importance for the mastering of the final properties of the product. As polymer blends are produced using corotating twin-screw extruders, understanding and modeling the changes experienced by the blend during this process is of great interest. In the present study, starting from Ludovic software, developed for computing flow parameters in the twin-screw extrusion process, we present a computation of the droplet morphology development, based on the basic mechanisms of break-up and coalescence. Depending on the value of a local capillary number and on local flow conditions, different changes may occur: affine deformation, drop splitting, break-up by capillary instability, and coalescence. It is thus possible to follow, all along the screws, the changes in morphology, either for a single particle or for a particle distribution. Examples of these different computations are presented and compared with experimental results. Generally speaking, orders of magnitude of droplet size and tendencies when modifying processing conditions are correctly described, but the model still suffers from the abscence of description of the melting process.