DEVELOPMENT OF POLYMER BLEND MORPHOLOGY DURING COMPOUNDING IN A TWIN-SCREW EXTRUDER .4. A NEW COMPUTATIONAL MODEL WITH COALESCENCE

In Part II of this series of publications, the first generation model of morphology evolution during polymer blending in a twin-screw extrud er was presented. The model was based on a simplified flow analysis, a nd an assumption that dispersion occurs via drop fibrillation followed by disintegration. In the present Part TV, several modifications of t he model are discussed. (i) The flow analysis was refined by computing the pressure profiles. (ii) The flow paths and strain history of the dispersed droplets within the screw elements are computed directly, wh ich makes it possible to determine the drop susceptibility to deformat ion and break. (iii) Besides the fibrillation mechanism, a drop-splitt ing mechanism for low supercritical capillary numbers is incorporated. (iv) The choice of breakup mechanism is based on micro-theological cr iteria. (v) The coalescence effects are taken into account. (vi) The t heoretical model is self-consistent, without adjustable parameters. Th e validity of theoretical assumptions was evaluated by comparing the m odel predictions with the experimental droplet diameters at different positions in the twin-screw extruder.