Melt rheological, extrudate swell and melt fracture behavior of calcium carbonate and titanium (IV) dioxide nanoparticle-reinforced polypropylene composites

Abstract

Melt rheology, extrudate swell and melt fracture of isotactic polypropylene (iPP) filled with CaCO3 or TiO2 nanoparticles in various amounts (i.e., from 0 to 30 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 the apparent shear rate. The stearic acid - treated nanoparticles exhibited the hydrophobic characteristic that resulted in a significant reduction in the wall shear stress when the amount of the fillers increased when comparing with the nanoparticles having a hydrophilic surface. The percentage of extrudate swell was found to increase with increasing the apparent shear rate in a non-linear manner, while it was found to increase linearly with increasing the wall shear stress. The extrudate swell decreased with increasing the amount of the fillers. Lastly, T he serverity of the melt fracture was found to increase with increasing the apparent shear rate. The maximum TiO2 content of 30 wt.% showed no evidence of the melt fracture. With increasing the L/D ratio, the critical shear rate at which the melt fracture was observed and shifted toward a higher value, possibly a result of the partial molecular relaxation during the flow through a longer die.