Melt rheology and extrudate swell of calcium carbonate nanoparticle-filled isotactic polypropylene

Melt rheology and extrudate swell of isotactic polypropylene (iPP) filled uncoated and stearic acid-coated CaCO3 nanoparticles in various amounts of filler (i.e. from 5 to 25 wt%) during capillary melt-extrusion were investigated. The wall shear stress for both neat iPP and iPP compounds increased in a non-linear manner with increasing apparent shear rate. The apparent shear viscosity for all of the samples investigated was found to decrease in a non-linear manner with increasing apparent shear rate. Addition of uncoated CaCO3 nanoparticles was responsible for increasing the apparent shear viscosity of the compounds, while stearic acid-coated ones did not affect the apparent shear viscosity of the iPP matrix as much. The percentage of extrudate swell was found to increase with increasing apparent shear rate in a non-linear manner, while it was found to increase linearly with increasing wall shear stress. Lastly, the percentage of extrudate swell was found to be a decreasing function of the filler loading. (C) 2004 Elsevier Ltd. All rights reserved.