Caracterização reológica do compósito polipropileno-atapulgita por reometria capilar.

Abstract

In this work, the system PP, Attapulgite was studied by capillary rheolog>' at 5- 25% filler content and temperatures of 180, 200 and 220°C at shearing rates compatible to those involved in injection and extrusion processes, i.e., 11,64 to 2327,12 s'1. Shear stress and shear rates experimentally obtained for ali composites as well as those of straight polypropylene were correlated to the Ostwald de Waele model. The same was done for the experimentaly determined apparent viscosity and corrected shear rate. The influence of attapulgite concentracion, shear rate and temperature on the processability of the composite's and of the matrix were investigated by observing the flow curves, power index, consistency index and apparent viscosity. Our results show that the rheological model of Ostwald de Waele successfully described the flow behavior of PP and PP/attapulgite system under the experimental shearing conditions employed. The study shows that pseudoplasticity increased with temperature up to 15% w/w attapulgite content becaming insensitive to both concentracion and temperature at higher filler contents. The consistency index (K) increased with attapulgite concentracion and decreased with temperature increments. Apparent viscosity increased with filler content, and decreased with increasing temperature and shear rates, which characterize pseudoplastic behavior. At higher temperature and shear rates the apparent viscosity of ali composites teaded to a single value which shows that although attapulgite addition doe increase PP viscosity it does was change its processabillity at shear rates above 3000 s*1 at temperatures of 200 and 220°C.