281826 The Design of Particulate Delivery Forms Via Single Drop Granule Formation Mechanisms

Sunday, October 28, 2012
Hall B (Convention Center )
Heather N. Emady, School of Chemical Engineering, Purdue University, West Lafayette, IN

The overall goal of my future research program is to apply the engineering design approaches I have learned in my Ph.D. to industrially relevant particulate processing problems.  My research interests lie in the broad realm of particle technology, with specific interests in single drop granule formation and the fundamentals of powder/liquid interactions.

Many industries, including pharmaceuticals, food, agricultural chemicals, and detergents utilize particulate processes to produce varying granular products.  Wet granulation is one of these processes, where a liquid binder is added to a fine powder in order to get larger granules for improved particle properties.  In typical granulation equipment, many of the granulation rate processes (wetting and nucleation, consolidation and growth, and breakage and attrition) occur simultaneously, making it notoriously difficult to control and predict product properties, such as size and shape. 

Recently, a new granulation approach, regime separated granulation, has been proposed as a way to physically separate the different rate processes to get dramatically better control of the product granule attributes.  The first and most important stage in any regime separated granulation process is nucleation, where new granules are formed by the addition of liquid to the powder bed.  Drop controlled nucleation, where one drop forms one granule, is the most desirable operating regime.  In order to apply regime separated granulation in practice, more knowledge is necessary regarding the mechanisms by which granules are formed from drop impact and penetration into a static powder bed. 

In my doctoral work, I conducted single drop granule experiments with a syringe and a dish filled with powder to simulate drop controlled nucleation in static beds.  From high speed camera videos of drop impact and penetration, I identified three different granule formation mechanisms:  Tunneling, Spreading, and Crater Formation.  Each mechanism produced distinctly different granule shapes.  To quantify the conditions under which each mechanism will occur, I performed dimensional analysis and created a new regime map that plots the powder bed porosity (ε) against the modified granular Bond number (Bog*), which is a ratio of the capillary force acting on a particle to the gravitational force acting on a particle.  Subsequently, I derived a mechanistic model based on a force balance for the Tunneling mechanism and compared it to the regime map.  This new knowledge about granule formation mechanisms opens up opportunities for designing processes and altering formulations to produce a given granule formation mechanism that leads to a particular granule shape and structure.

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