MODELLING OF POLYMER FLOW INSTABILITIES WITH APPLICATION TO 3D PRINTING

Abstract

Complex flow instabilities including wall slip and shear banding occur in many industrial applications, such as in polymer extrusion processes, thus affecting the throughput and the quality of the final product. The modelling of rheological data is a key point when studying different polymeric flows. The present survey incorporates three different ways to model the shear stress of shear thinning polymers as nonlinear functions of shear stress: generalized Newtonian model (Carreau-Yasuda model), wall shear slipping and banding with yield (Herschel–Bulkley model). Based on these models, the flow in the nozzle tube of a 3D printer is analyzed by a numerical model and two analytical models: the classical Weissenberg–Rabinowitsch–Mooney (WRM) model with slip; a simple model in three different regions in the tube (including yield, parabolic and band, which match their boundaries). The real data of measured shear stress by a plate–plate rheometer for three nanocomposites is used to compare the three models. The experimentally measured flow rates during the extrusion of the same nanocomposites are used to give insight into the corresponding flow structures in the nozzle tube.