Continuous Powder Blending inside Twin Screw Extruder
Authors: Daniel Mateo-Ortiz1, Dana Alhasson1, Sean Garner2, William Ketterhagen2, Nandkishor Nere2, Bei Chen1, Michael Dennis1
1. Drug Products, Science and Technology, AbbVie 2. Global Pharmaceutical R&D, AbbVie
Purpose: Our study aimed to develop fundamental understanding of powder blending at the early stages of twin screw extrusion as function of material properties (non-cohesive and cohesive powders) and process conditions using Discrete Element Method (DEM) and experimentation. Previous work in the pharmaceutical and food industry has focused on mixing when materials are melted, or homogeneity at the output of the extruder.
Methods: DEM models were developed to study powder flow/mixing inside the extruder. The simulations were performed using EDEMTM and the Hertz–Mindlin contact model. The geometry and dimensions of the extruder were based on the ZSK-18 Coperion Twin Screw Extruder. Experiments were subsequently conducted in the ZSK-18 to characterize powder mixing efficiency. Near-infrared (NIR) spectroscopy was used to evaluate blend uniformity. A clear extruder was built to experimentally visualize powder mixing inside the extruder. The experimental and DEM simulation factorial designs included screw configuration, screw speed and powder feed rate. For the DEM models, the materials properties (inputs to the simulation) and process conditions were defined based on experimental data. In addition, residence time distribution was studied experimentally and using DEM.
Results: Experimental results show higher blend uniformity variability at high screw speed and high feed rate. The RTD profiles when using a screw configuration with only conveying screw elements are similar to an ideal plug flow reactor (PFR) while the profiles when using kneading elements are more similar to an ideal continuous stirred tank reactor (CSTR). Similar RTD profiles for both experimental and computational experiments were observed. DEM simulations show good axial mixing for all the screw configurations studied while good cross mixing was only observed for screw configurations with kneading elements.
Conclusion: It was demonstrated that the twin screw extruder can provide acceptable powder mixing based on a unit dose scale, therefore, enabling continuous powder mixing in the extruder. Screw configuration using 90 degree kneading elements improved blend uniformity by providing better cross mixing. DEM computational models provided a better understanding of mixing patterns inside the extruder at particle scale.
Daniel Mateo, Senior Scientist II, AbbVie, Inc.
Daniel Mateo joined AbbVie in 2015. He received his B.S. and Ph.D. from University of Puerto Rico Mayaguez Campus, both in chemical engineering. Dr. Mateo has gained experience in various areas of product development, including process development, technology transfer, process validation, commercial manufacturing and continuous improvements. He has strong technical expertise in the areas of powder technology and computational modeling (i.e. CFD, DEM). He has published multiple papers related to powder flow and is a member of the American Institute of Chemical Engineers (AIChE).