Effects of extensional flow and nanofiller incorporation on dispersed phase size in the blending of high-viscosity-ratio immiscible vinyl polymers

The influence of extensional strain and strain rate on dispersed phase size during blending of a dilute mixture of vinyl polymers, high-density polyethylene in polystyrene, was examined; the viscosity ratio was substantially larger than four so that shearing was not expected to contribute to drop breakup. Coarse blends were formulated by employing an internal mixer, and these blends were processed through different converging dies attached to the outlet of a capillary viscometer. Variables included the die geometry and the volumetric flow rate. Average dispersed phase sizes were determined by analyzing scanning electron micrographs of sections of strands leaving the viscometer, and it was found that extensional flow was very effective in reducing the dispersed phase size. Coarse blends were also formulated by separately incorporating nanoparticles of hydrophobic fumed silica as well as hydrophilic fumed silica in the blends at a 4 wt% nanofiller level. This resulted in a significant reduction in drop size compared to the previous value; this was likely the result of lowered drop coalescence. These nanoparticle-containing blends were also subjected to extensional flow, and this resulted in a further reduction in the average dispersed phase size. However, the final result was only slightly better than that obtained previously with the help of extensional flow alone. This suggests the use of nanoparticle incorporation along with employing extensional flow when the presence of nanoparticles provides multifunctionality to the resulting blend.