(656a) In-Line Evaluation of Powder Properties during Mixing Processes Using a Drag Force Flow Sensor

The mixing time required for a dry powder blend to reach homogeneity is highly dependent on many factors, including numerous process parameters and physical properties of the component particles, such as their relative size, shape and density. In order to optimise the efficiency of a mixing operation, it is important for the process to be stopped quickly following the attainment of a homogeneous blend, this can also minimise the effects of over-processing such as particle attrition.

In-line Process Analytical Technology (PAT) tools can generate and display real-time data, enabling the user to accurately monitor and control the physical properties of a blend without the interruptions required to conduct off-line analytical techniques. As a result, important process decisions, such as when the mixing time is sufficient and the process can cease, can be accurately and rapidly made despite novel and modified process conditions and formulations being trialled.

The application of a Drag Force Flow (DFF) sensor overcomes many limitations associated with PAT tools which use spectrographic and particle size analysis techniques. This highly sensitive, in-line measurement tool provides robust and high (temporal) resolution measurements of the forces exerted by the flow of powder within a process. The DFF sensor uses optical technology, with the probe itself containing two Fiber Bragg Grating (FBG) optical strain gauges. As particles impact the probe, the optical strain gauges are stretched or compressed by these minor deflections. The degree of stretching or compression is detected by an optical interrogator which is calibrated to measure DFF and Force Pulse Magnitude (FPM) values are calculated which correspond to changes in the fundamental bulk properties of the particulate flow. The thin, cylindrical shape of a DFF sensor means that it provides minimal intrusion to flow and is therefore appropriate for use across a diverse range of applications, including mixing and blending.

In this study, the suitability of the DFF sensor is evaluated, focusing on assessing its ability to follow the physical changes of powder blends during mixing. The mixing processes of two different formulations within a vertical twin-shaft mixer were monitored using this in-line measurement technique. Repeatable FPM data was generated between repeat measurements of the same formulation and a clear plateau in the FPM data was displayed, associated with the achievement of an even dispersion of components. Agreement between the mixing time required to reach homogeneity was observed between the real-time DFF data and potentiometric titration data conducted on extracted aliquots.

The DFF sensor was demonstrated to be a highly sensitive instrument for routine monitoring and control during mixing, its ability to identify suitable timeframes for a blend to reach homogeneity has vast potential to improve the efficiency of such processes.