Melt rheology and extrudate swell of organobentonite-filled polypropylene nanocomposites

Melt rheological properties and extrudate swell of organobentonite-filled polypropylene nanocomposites were studied by using a capillary rheometer in a shear rate range of 50-8000s(-1) and a temperature range of 190-210 degrees C. The nanocomposites exhibited shear-thinning behavior and the viscosity was well-described by the power law in this shear rate region. The addition of organobentonite enhanced the pseudoplasticity, i.e. increased the shear thinning behavior. With increasing organobentonite concentration, the shear stress/viscosity increased, while the power law index (n) decreased, and this effect is more significant at higher filler concentrations (> 3wt%). The dependence of shear viscosity on temperature obeyed the Arrhenius-Eyring expression, and the activation energy (Ea) decreased with increasing shear rate. Extrudate swell is a non-linear function of shear rate, while it is a linear function of shear stress or temperature. With increasing organobentonite concentration (> 3 wt%), the extrudate swell clearly decreased, which is attributed to the limitation of the elastic recovery of the polymer chains by oriented silicate layers. (C) 2008 Elsevier Ltd. All rights reserved.