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28 January 2018 Tablets & Capsules W Granule growth occurs through primary particle layering on a granule's surface and through coalescence of two or more granules (Figure 1b). This step generally also densifies the granules. Granule breakage occurs when the stresses in the granulator (either shear stresses or normal stress from impact with the impeller or chopper blades or granulator wall) exceed the granules' strength, and the granules fail (Figure 1c). Changing each of the operating parameters listed above may change the rate and regime of each granulation mechanism, and therefore change the granule properties. Below are some suggestions and comments on how to approach each operating parameter. Granulator geometry In many industries and applications, you may have no control over the granulator geometry. However, if you have a role in purchasing or designing new granulation equipment, it's generally best to select or design a While high-shear granulation is very commonly used, it's notoriously difficult to design and scale up, whether it be scaling up from a lab- or pilot-size machine to a production machine or from an existing production machine to one with a larger capacity. This is mainly because of the many operating parameters and competing mechanisms occurring in the granulator. et high-shear mixer granulation is a particle size enlargement process in which fine powder is combined with a liquid binder. As the binder is sprayed into the process bowl, the granulator's impeller and chopper blades shear the powder. The resulting granules have spe- cific desirable properties, including, for example, particle size, granule strength, bulk density, dissolution time, compressibility, and content uniformity. To achieve the desired granule properties, you can modify several operating parameters, including granulator geometry and size, impeller speed, chopper speed (if any), binder-addition method and flow rate, and granulation time. The traditional approach to scaling up high-shear granulation has been to increase the process size by small increments and troubleshoot at each new scale. The reality is that changing granulator scale affects all of the granulation mechanisms in different ways, and no set of scale-up rules will encompass all the changes. You must consider the effect of scale on each of these mechanisms if you want to increase batch size while retaining similar attributes in the final granules. These days, we usually think of granulation as occur- ring through three simultaneous and, at times, competing mechanisms: nucleation, growth and consolidation, and breakage [1]. Nucleation can be considered the first step in the process and involves the initial formation of gran- ules, called nuclei . In the case of high-shear granulation, nuclei are formed when liquid first hits the powder bed and interacts with the particles, as shown in Figure 1a. Scaling up wet high-shear mixer granulation Rachel Smith University of Sheffield granulation Figure 1 Agglomeration mechanisms b. Growth and consolidation a. Nucleation c. Breakage