Abstract
AbstractSpheronization of cylindrical extrudates on a rotating friction plate involves breakage and rounding. Little attention has been given to the breakage stage and quantitative modeling of this process is scarce. Two simple models are compared with experimental data obtained for the early stages of spheronization of microcrystalline cellulose/water extrudates. Tests were conducted for different times (t), rotational speeds (ω), initial loadings, and on pyramidal friction plates with different dimensions. The first model, describing the number of pellets, validated ω3t as a characteristic time scale for the breakage stage. The kinetic parameters obtained by fitting showed a systematic dependence on plate dimensions expressed as a scaled gap width. The second model, a simple population balance, described the evolution of the number and length of pellets. The pseudo rate constants provided insights into the kinetics: extrudates tended to break near the middle, while breakage of smaller pellets was slowed down by more pellet–pellet collisions.
Highlights
Spheronization is a widely used granulation technique in the pharmaceutical sector,[1] which can produce smooth, relatively spherical pellets with a narrow size distribution from a fine powder
Lau et al[6] found that ω3t was a characteristic time scale for rounding of pellets. Applying this to the data sets here collapse them to a common trend, indicating that this time scaling holds for the extrudate breakage process
One initial extrudate length was considered in this work and there is a need for other lengths to be considered, as industrial operations feature a mixture of extrudate lengths in the initial batch
Summary
Spheronization ( known as marumerization) is a widely used granulation technique in the pharmaceutical sector,[1] which can produce smooth, relatively spherical pellets with a narrow size distribution from a fine powder. It is a two-stage process: in the first stage, the material is mixed with a binder to form a wet mass (a soft solid termed the “dough” or “paste” in different communities) and extruded through a mesh or die plate to generate extrudates of approximately equal diameter.[2] These are fed into a cylindrical bowl with its axis vertical whose base (the friction plate) rotates at high speed (Figure 1A). Collisions with the wall and with other extrudates cause them to break into shorter sections, which travel around the edge of the plate in a “rope” (a toroidal bed: see References 3 and 4), dragged by the protuberances on the plate.
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