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

The dispersion of an elastomeric phase (blend of two miscible copolyme rs: ethylene-vinyl acetate and ethylene-methyl acrylate) in a polyprop ylene matrix along a corotating twin-screw extruder was studied experi mentally. A sliding barrel allowed a direct access to the screws and t hus permitted a rapid cooling and sampling. The dispersion of the elas tomeric phase was controlled by scanning electron microscopy and the s ize distribution was obtained by image analysis. The particle size dis tribution was measured at different locations along the screws in orde r to quantify the evolution of the morphology. Complementary studies w ere carried out on a pre-shearing rheometer (Rheoplast) in order to st udy 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 exp eriments enhance the importance of the melting mechanism and put in ev idence that the final morphology of the blend is controlled by the opp osite mechanisms of break up and coalescence.