Effect of Shear Rate and Nanoclay Content onthe Die Swell of Polypropylene NanocompositesExtruded Under Capillary Flow

摘要

Die swell is an important parameter of polymeric materials during extrusion. It plays a significant role in governing the final dimensions of the extrudate and hence is of utmost importance for die design and process control during extrusion. In present study, effect of shear rate and nanoclay content on die swell behavior during extrusion of polypropylene clay nanocomposites with different percentage (I and 2%) of nanoclay loading was measured by means of Rosand RH7 Capillary Rheometer at 200°C. The results emphasize that there is no significant change in shear viscosity and shear stress with addition of nanoclay at different shear rates (50 to 10000 sec~(-1)). However, the power law index (n) indicates that the polymer melt becomes less shear thinning with increasing nanoclay loading. Also at lower shear rates up to 1000 sec~(-1), PP with 1% nanoclay showed higher die swell in comparison to pure PP, whereas at shear rates beyond 1000 sec~(-1) the same blend showed lower die swell compared to pure PP. The die swell of PP with 2% nanoclay is lower than PP with 1% nanoclay at low shear rates till 600 sec~(-1) which is reversed as the shear rate is increased beyond 2000 sec~(-1). So we observed in this study that by controlling the shear rate we can control the die swell behavior of PP nanoclay nanocomposites.