ANALYSIS OF THE INFLUENCE OF POLYMER MELT VISCOELASTIC PROPERTIES ON THE MIXING QUALITY IN A DISK EXTRUDER CALCULATION

Abstract

The amount of virgin plastic produced is increasing every year. At the same time, to meet modern requirements, polymers are modified with various additives forming composite polymer materials. The production of this type of materials requires the use of equipment capable of ensuring high-quality mixing of components within a wide range of properties. One way to meet these requirements is to use cascade extrusion systems, in which a screw-disk extruder is used as a melter and homogenizer [1–2]. The article discusses the influence of the viscoelastic properties of polymer melt in modeling the mixing process in disc extruders, which is key to achieving homogeneous and isotropic composite materials. A Newtonian fluid model, which ignores the viscoelastic properties of the material, can be used to determine velocity fields and productivity during extrusion. However, its limitations lead to inaccurate predictions in cases where the material exhibits viscoelastic properties. To overcome these shortcomings, a second-order rheological model can be used, which describes both the viscous and elastic properties of the material. Using numerical modeling, a comparison was made between the results obtained using the Newtonian fluid model and the modified second-order rheological equation in the Rivlin-Ericksen formulation. The results showed that when viscoelastic effects are taken into account, the radial flow velocity increases, and the value of the shear strain caused by this component decreases. The values of the shear strain caused by the tangential velocity do not depend on the magnitude of the radial velocity. The total shear strain when using different fluid models remained virtually unchanged: 1719,2 units for the Newtonian fluid model and 1695 units for the second-order model. Thus, the difference between the calculation results is 1,38 %, which is not significant for this indicator.