Modelling of hot melt extrusion for the enhancement of pharmaceutical oral solid soage performance
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Date
2023-03-08
Authors
Movsesian, Fiona
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Abstract
This research deals with the modelling of a twin-screw extruder that will be used for the enhance-ment of pharmaceutical oral solid dosage performance. Hot melt extrusion (HME) has been widely used as a forming technique for industrial products since the 19th century. It is a thermomechanical manufacturing process where solid materials are transformed into a uniform product making use of the rotation of screws. HME was first used in the plastic and food industries, however it has recently been embraced as a production method in the pharmaceutical industry.
This thesis consists of three parts corresponding to the following three chapters. In Chapter 1, the principles of HME and the two types of extruders, the single-screw and the twin-screw extruders, are introduced. Moreover, the choice of TSE in the pharmaceutical industry instead of SSE becomes clear and the advantages and disadvantages of HME as a drug delivery technology are analyzed. Chapter 1 ends with a review of two HME modelling approaches, a classical PDE model commonly used in the polymers industry, which primarily focuses on the description of transfer phenomena within a zone called the melt zone, and the Residence Time Distribution (RTD) model, where the extrusion process is simulated by ideal reactors such as CSTR, PFR and LFR.
In Chapter 2, another modelling approach is presented, where the process focuses on both the sol-id and the liquid state of the material. After the twin-screw extruder is divided into two zones, the equations using basic material and energy balances are derived. When using this approach, there is a time-varying interface between the two zones, complicating the PDEs solution, rendering the use of a transformation necessary. Finally, the problem is discretized, using the finite difference method (FDM) and the modelling approach is implemented in MATLAB.
The equations describing the model in Chapter 2 were derived without considering the dispersion, thus, in Chapter 3, using the same approach, with the addition of the dispersion factor to the material balance, new results are obtained. There is an important subchapter about the Peclet number, which appears in the material balance after putting this equation into dimensionless form. The Peclet num-ber is an important parameter that measures the extent of axial dispersion; when low, there is large dispersion while when the Peclet number tends to infinity the dispersion is negligible.
Finally, the last chapter, Chapter 4, summarizes the main conclusions of this thesis and suggestions for future research are presented.
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Keywords
Twin-screw extruders, Finite difference method (FDM), Peclet number