Material PropertiesMelt rheology and extrudate swell of titanium (IV) oxide nanoparticle-filled isotactic polypropylene: Effects of content and surface characteristics

Melt rheology and extrudate swell of isotactic polypropylene (iPP) filled with titanium (IV) oxide (TiO2) nanoparticles of varying content (i.e., 5-30 wt.%) and surface characteristics [i.e., uncoated, silica (SiO2)-coated, and stearic acid-coated] during capillary melt-extrusion were investigated. The wall shear stress of both the iPP melt and the melts that contained nanoparticles increased in a non-linear, decreasing-rate manner with increasing apparent shear rate. The incorporation of the nanoparticles generally increased the wall shear stress of the melts, with stearic acid-coated ones exhibiting the least variation in the property values. The shear viscosity, when plotted with the real shear rate on a log-log scale, exhibited a linear, decreasing function with the real shear rate. Clearly, the iPP melts containing stearic acid-coated TiO2 nanoparticles exhibited the lowest shear viscosity values. Lastly, the extrudate swell of the iPP melt and the melts that had been filled with nanoparticles was found to increase with increasing apparent shear rate, while it was found to decrease generally with the addition and increasing amount of nanoparticles.