Js. Ramaker et al., SCALE-DOWN OF A HIGH-SHEAR PELLETIZATION PROCESS - FLOW PROFILE AND GROWTH-KINETICS, International journal of pharmaceutics, 166(1), 1998, pp. 89-97
For the predictive modelling of the high-shear pelletisation process i
t is necessary to have a better understanding of the underlying mechan
isms. Therefore, pelletisation experiments were carried out with micro
crystalline cellulose and lactose in a coffee grinder (small-scale) an
d in a Gral 10 ('large'-scale). A toroidal flow-pattern was observed a
nd described for both apparatus. There was no effect of increased impe
ller speed on the velocity of pellets in the torus; only a change in a
ngle with the tangential direction was observed. Moreover, the size of
pellets decreased rapidly to a new value. This size increased again w
hen the impeller speed was reduced to the initial (low) value. This su
ggested the existence of fast break-up and growth, resulting in a dyna
mic equilibrium depending on the impeller speed. Tracer experiments we
re used to investigate the turnover limes of different sieve fractions
. First order conversion rate constants for the pellets of different s
ieve fractions, calculated from colour concentrations at several proce
ssing times, were equal for both apparatus when plotted against the di
mensionless diameter of the pellets (d/d(50)). These results are a str
ong indication for the usefulness of small-scale experiments to retrie
ve a rapid insight into relevant mechanisms of growth of high-shear pe
lletisation. (C) 1998 Elsevier Science B.V. All rights reserved.