Methods for analyzing wall slip in the die of a capillary rheometer

Wall slip in the die of a capillary rheometer was investigated. Corn meal and water were mixed to a moisture content of 35% wet basis. Oil was then added at 0%, 2.5%, and 5% of the total mass. A capillary rheometer was used to extrude the mixture at 100C. Three die diameters were studied: 2mm, 4mm, and 8mm. Two length to diameter ratios were studied: L/D=4 and L/D=8. Pressure and flow rate in grams per 30 seconds were collected from the capillary rheometer to perform the Bagley correction, determine the flow behavior index, and correct for slip using the Mooney slip analysis method. Several slip analysis methods were considered prior to the selection of the Mooney method. Overall, the Bagley correction was successful for all die diameters except 2mm. The Mooney method was successful for the 5% added oil content samples. An increase slip velocity was observed as shear stress increased. Mooney plots for 0% and 2.5% resulted in negative shear rate values. An empirical model was developed to predict apparent viscosity of the mixture as a function of total oil content.