# Modeling Shear-Thinning Flow in Twin-Screw Extrusion Processes

## TL;DR

This paper presents a model to characterize screw element behavior in twin-screw extrusion for both Newtonian and shear-thinning materials.

## Contribution

A novel model with six parameters and an evaluation framework for shear-thinning flow in extrusion processes.

## Key findings

- The model aligns with literature for Newtonian fluids using the Pawlowski approach.
- Screw speed's impact on pressure and power was quantified for shear-thinning materials.
- Confidence intervals for screw parameters were determined to differentiate element types.

## Abstract

Background/Objective: Hot-melt extrusion has been established as a formulation strategy for various pharmaceutical applications. However, tailoring the screw configuration is a major challenge where 1D modeling is utilized. This usually requires specific screw parameters, which are rarely noted in the literature, especially when dealing with shear-thinning formulations. Methods: Therefore, a custom-made test rig was used to assess the behavior of various conveying and kneading elements using Newtonian silicon oil and shear-thinning silicon rubber. The pressure and the power were measured as a function of volume flow. A model was proposed characterizing the screw element behavior by six individual parameters A1, A2, A3, B1, B2, B3. Results: The experimental results regarding the behavior with respect to Newtonian fluids were in good agreement with the literature and were modeled in accordance with the Pawlowski approach. In terms of shear-thinning fluids, the influence of screw speed on pressure and power was quantified. An evaluation framework was proposed to assess this effect using two additional parameters. Based on a high number of repetitive measurements, a confidence interval for the individual screw parameters was determined that is suitable to highlight the differences between element types. Conclusions: Finally, geometrical screw parameters for Newtonian and shear-thinning flow were assessed and modeled, with three conveying and three kneading elements characterized.