Granule Deformability

Power dissipation can lead to temperature increases of up to 40°C in the mass. Note that evaporation of liquid as a result of this increase needs to be accounted for in determining liquid requirements for granulation. Liquid should be added through an atomizing nozzle to aid uniform hquid distribution in many cases. In addition, power intensity (kW/kg) has been used with some success to judge granulation end point and for scale-up, primarily due to its relationship to granule deformation [Holm loc. cit.]. Swept volume ratio is a preliminary estimate of expected power intensity. 

Most of the densification occurs in Stage II. Granule deformation is the predominant mechanism of densification. The compact density, Dcompact, may be approximated in this stage as... 

FIG. 20-70 The influence of moisture as a percentage of sample saturation S on granule deformability. Here, deformation strain (AZVL) is measured as a function of applied stress, with the peak stress and strain denoted by tensile strength and critical strain AL/L)c of the material. Dicalcium phosphate with a 15 wt % binding solution of PVP/PVA Kollidon VA64. [Holm et cd.. Powder Tech., 43, 213 (1985).] With kind permission from Elsevier Science SA, Lausanne, Switzerland. 

FIG. 21-114 Interparticle forces and granule deformability. Interparticle forces include capillary forces, viscous lubrication forces, and friction forces. Reprinted from Design and Optimization of Granulation and Compaction Processes for Enhanced Product Performance, Ennis, 2006, with permission of E[Pg.2335]

The important contributions of binder viscosity and friction to granule deformability are illustrated by fractions of energy dissipated during computer simulations of granule collisions, as depicted in Fig. 21-116. 

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