Micromechanical Analysis of Pharmaceutical Granules using Advanced Experimental Imaging Methodologies

Fundamental level understandings on the processing behaviours of materials in granular and powder form is of high interest to number of engineering industries for example, mining, mineral, pharmaceutical, geotechnical and for advanced material processing applications. Handling and processing of pharmaceutical powders through confined geometries have very important role in pharmaceutical industry and many related powder process engineering sectors. Smooth flow of powders and granules mixtures from the feeding hopper to the compression chamber plays a very crucial role to achieve the integrity and quality of the final product. In this context, establishing clear understandings on the flow and compaction characteristics of particulates is vital. The mechanical behaviour of particulate materials such as powders and grains are different from the conventional states of matter. Depending on the loading levels and geometrical conditions, often they display combined features of solid, liquid and gaseous states. Though an extensive amount of studies are reported in the existing literatures on their mechanical response to loading, there are still a number of challenges to address: (i) Sensing stress distribution in particulate systems is not yet established especially when the size of the particulates are less than a millimetre (ii) Understanding is lacking on whether the stress distribution in initial static filling would influence the dynamic flow trajectories of the particulates when they are allowed to flow from the static state (iii) Micromechanical behaviour of particulates under low levels of external loading is still lacking and (iv) Interaction characteristics of stress and velocity distributions in particulate systems as a function of grain-scale properties and geometrical arrangements are still lacking. The present thesis addresses all of these important challenges in a systematic manner. The research is primarily based on the application of sensing stresses and displacements in particulates using advanced photo stress analysis tomography (PSAT), qualitative velocimetry using colour coding technique (CCT) and quantitative digital particle image velocimetry (DPIV). The required grain-scale properties are characterised comprehensively using a number of standard experimental methods. Where possible, experimental results on the stress and velocity distribution for particulate systems are compared with simulations using discrete element method (DEM) and analytical equations respectively, though the primary focus is on the experimental approaches. A number of outcomes from this research shed new lights and provide fundamental level understandings on the micromechanical properties of particulate systems with relevance to pharmaceutical granules processes.