A Study of Concentrated Suspensions in Polyethylene Melts and the Impact on Viscosity and Polymer Processing Operations

Abstract

AbstractFilled polymer compounds can present processing challenges, including poor dispersive mixing, high screw shaft torque and energy consumption, flow instabilities, and significant increases in melt pressures and temperatures. Previous theoretical development and experimental evaluations of polymer melts filled with particulate solids showed that the viscosity can be described with a model based on percolation theory concepts. This paper describes a batch mixer characterization method developed to measure the effects of filler concentration and operating conditions on the melt viscosity and process response. Experimental results are compared with capillary rheometer measurements using several low-density polyethylene resins, calcium carbonate and titanium dioxide. The theoretical treatment of the viscosity as a particulate percolating system with power-law behavior was used to analyze and compare rheometer and batch mixer data. The effects of resin molecular weight, filler type and size on viscosity and melt processing were examined and there was good agreement between rheometer and mixer viscosity trends, and percolation model predictions. The laboratory experiments and model estimates provide quantitative information that can be used to develop and troubleshoot extrusion compounding, single screw extrusion and low-shear forming processes.