Dispersed Phase Size During the Blending of Relatively-Inelastic Polymer Melts

The influence of simultaneous drop breakup and drop coalescence on polymer-morphology was studied during the blending of polymer melts in a commercial counter-rotating twin-screw extruder. The polymers employed were PET and nylon 66, and these were chosen to minimize fluid elasticity and drop coalescence effects. Each material was dispersed in the other, and the dispersed phase size was determined using scanning electron microscopy. Variables examined included dispersed phase concentration, shear rate, residence time in the extruder and the addition of a compatibilizer. As has been the experience of others, it was found that coalescence was significant at all concentrations examined, and it increased with increasing dispersed phase concentration. However, coalescence could be drastically reduced with the help of a compatibilizer. It appeared that there were no elastic effects, and the measured drop size seemed to approach the Taylor limit as the dispersed phase concentration was lowered. An unexpected finding was that an increase in shear rate resulted in an increase in droplet size, especially at high concentrations.