Search

In this study the viscosity behavior of the polymer-based drug delivery system (Soluplus-Fenofibrate) at high shear rates was investigated using (i) Computational Fluid Dynamics (CFD) methods and (ii) experimental data acquired with a high-pressure capillary rheometer. The barrel and capillary were rebuilt in the virtual domain by means of finite-volume methods and used for fluid dynamic simulations. Our primary focus was on validating the Carreau-Winter and Yasuda material models in the Open Field Operation and Manipulation program (OpenFOAM) and investigating their usefulness in this type of simulation. First, the models were fitted to experimental data from a well-known system – polystyrene type (145D, BASF). The results showed that the Yasuda model fit must be applied to obtain the correct material properties when simulating a non-Newtonian melt flow in a wide range of shear rates. The Carreau-Winter model was found to be valid only in the zero shear-rate viscosity region. On the basis of these findings, the Soluplus-Fenofibrate system was subsequently characterized and simulated. We observed that Fenofibrate (lipid-regulating agent) acts as a plasticizer in this polymer system and decreases system viscosity at lower shear rates compared to pure the Soluplus (polyvinyl caprolactam-polyvinyl acetate-polyethylene glycol graft copolymer) at the same temperatures. Our results show that the viscosity models can be implemented accurately even for processes with high shear rates, which also involve high temperatures.

We developed novel non-invasive ultrasound based systems for the measurement of temperature distributions in the screw-ante chamber, the detection of unmelted granules and for the monitoring of the plasticizing process along the screw channel. The temperature of the polymer melt stored in the screw ante-chamber after the plasticization should be homogeneous. However, in reality the polymer melt in the screw ante-chamber is not homogeneous. Due to the fact the sound velocity in a polymer melt is temperature depending, we developed a tomography system using the measured transit times of ultrasonic pulses along different sound paths for calculating the temperature distribution in radial direction of a polymer melt in the screw ante-chamber of an injection moulding machine. For the detection of unmelted granules in the polymer melt we implemented an ultrasound transmission measurement. By analyzing the attenuation of the received pulses it is possible to detect unwanted inclusions. For the monitoring of the plasticizing process in the channels of the screw an ultrasonic pulse is transmitted into the barrel. By analyzing the reflected pulses it is possible to estimate solid bed and melt regions in the screw channel. The proposed systems were tested for accuracy and validity by simulations and test measurements.

In injection molding investigations on mixing efficiency and thermal homogeneity of the melt in the screw chamber are of great interest as the directly effect the quality of the molded parts. For most injection molding applications mixing is performed in the single screw plasticizing unit of the injection molding machine. In this work, a CFD approach with two coupled fluid domains is used in order to describe the plasticizing process in an injection molding machine. One domain rotates and translates in axial direction (screw), the other one increases its length (chamber). On basis of the calculated pressure, velocity and temperature field of the polymer melt the thermal melt homogeneity is investigated. To analyze the optical-mechanical homogeneity of the melt a Euler-Lagrangian method is used to calculate the distribution of tracer particles within the screw chamber.