On the coarsening of the phase morphology of PP/EVA blends during compounding in a twin screw extruder

The coarsening of the phase morphology of polypropylene (PP) blends, containing 20 wt% of the copolymer ethylene vinyl acetate (EVA) as the dispersed phase, during compounding in a co-rotating twin screw extruder (Co-TSE) was investigated. Blending was performed by applying a fixed screw profile, temperature and screw rotation speed, with various flow rates, which allowed identification of the effect of the residence time on the blend morphology. The average EVA particle size increased linearly with the mean extrusion residence time. From this relationship, the coarsening kinetics, including the minimum droplet size that would be obtained and the coarsening rate due to the domination of coalescence over droplet breakup during extrusion, was quantified. The data reported herein provide greater insight into Wu's theory for the prediction of the droplet size in polymer blends compounded in a Co-TSE.