MORPHOLOGICAL-CHANGES OF A POLYMER BLEND INTO A TWIN-SCREW EXTRUDER

The dispersion of an elastomeric phase (blend of two miscible copolymers: ethylene-vinyl acetate and ethylene-methyl acrylate) in a polypropylene matrix along a corotating twin-screw extruder was studied experimentally. A sliding barrel allowed a direct access to the screws and thus permitted a rapid cooling and sampling. The dispersion of the elastomeric phase was controlled by scanning electron microscopy and the size distribution was obtained by image analysis. The particle size distribution was measured at different locations along the screws in order to quantify the evolution of the morphology. Complementary studies were carried out on a pre-shearing rheometer (Rheoplast) in order to study the influence of the mechanical treatment upon particle size. The dispersion of the elastomeric phase was observed at the capillary exit by the above mentioned techniques. The results of these different experiments enhance the importance of the melting mechanism and put in evidence that the final morphology of the blend is controlled by the opposite mechanisms of break up and coalescence.