Effect of Initial Particle Size and Initial Distribution Shape (Unimodal and Bimodal) on the Growth Kinetics and Mechanism of Wet Granulation in a Laboratory-Scale High Shear Mixer by Means of Image Processing and Analysis
Alvaro Realpe and Carlos Velázquez. Chemical Engineering, University of Puerto Rico, Miradero, Road 108, Km 3.0, Mayaguez, PR 00680
The effect of initial particle size and initial distribution shape, unimodal or bimodal, on the growth kinetics and mechanism of wet granulation were evaluated. Wet granulation of pharmaceutical powders with initial bimodal particle size distribution (PSD) presented growth kinetics of two stages. The first stage of granule growth is fast, similar to a non-inertial regime found by Adetayo et al. (1997) for material with wide PSD, this stage is controlled by binder amount and high probability of coalescence by collision of small and large particles that increase the growth rate as indicated by coalescence kernel published in literature. The second stage is characterized by slow agglomeration for powder mixtures with water content 13.6 %v/w, and slow breakage for powder mixtures with water content of 9.9 and 11.7 %v/w. Wet granulation of pharmaceutical powders with initial unimodal PSD presented slow growth kinetics of one stage by high concentration of particles of similar size decreasing the probability of granule coalescence as compared to the high coalescence probability by collision of small and large particles. The experimental results were also described by population balance equation using coalescence kernel that increases growth rate by collision between small and large particles. The variation of three factors are consistent with the viscous Stokes' number developed by Ennis et al. (1991), it can be seen that the probability for a successful collision, and as a consequence the granules growth rate, is increased by a smaller particle size, a higher binder viscosity, and higher binder content.