A simple improved mathematical model for polytetrafluoroethylene (PTFE) paste extrusion

摘要

The rheology of non-melt processable polytetrafluoroethylene (PTFE) pastes has been studied using three capillary rheometers having barrels of different diameters equipped with capillary dies of various designs. The pressure drop is measured as a function of apparent shear rate (flow rate), reduction ratio (cross sectional area of barrel to that of die), contraction angle, length-to-diameter ratio, and diameter of the barrel (scale-up). To describe the effects of die design for scale-up purposes, a simple phenomenological mathematical model has been developed. The model takes into account the elastic-plastic (strain hardening) and viscous nature of the material in its non-melt state, due to the creation of fibrils and the presence of lubricant, respectively. In addition, it takes into account the slip condition at the paste/wall interface. The model predictions are found to be consistent with experimental results obtained from macroscopic pressure drop measurements and it can be used for scale-up purposes.