(754g) Modified Application of Johanson's Model towards Roller Compaction

Modified
Application of Johanson's Model Towards Roller Compaction

Jasmine Rowe, John
Crison

Roller
compaction (RC) is a continuous dry granulation process commonly used in the
pharmaceutical industry to improve powder flow and blend uniformity via powder
densification.  RC has gained substantial attention over the last couple of
decades because neither moisture nor heat is required for granulation (as is
the case for wet granulation and hot melt extrusion, respectively).  The
process by which densification is achieved is through powder being fed between
two rolls that are rotating in opposite directions of each other.  This
counter-rotating motion of the rolls and friction between the powder and the
roll surface draw the powder through the rolls and maximum compaction
(densification) occurs when the separation between the rolls is at its
minimum.  The resultant compact, or briquette, may then be milled to achieve
the desired granule size.

While the RC mechanical process appears to
be simple, efforts to quantitatively model this process have proven challenging
because of complex material behavior in the feeding and compaction zones. 
Consequently, a trial-and-error approach has typically been adopted towards RC
process design, which is both time- and resource-intensive.  In response to the
need for a more efficient approach towards RC processing, Johanson developed
one of the most widely-used models for RC simulation, a powder mechanics model
based on Jenike's steady state flow theory that predicts the physical
properties of the final compact based on material and process parameters [Johanson, J. R. (1965).
A rolling theory for granular solids. ASME, Journal of Applied Mechanics Series
E, 32(4), 842?848]. 
However, practical application of Johanson's model to experimental work has
been limited because one of the model input parameters, the pressure being
applied to the feed powder as it enters the rolls (P₀), is difficult
to obtain experimentally without sophisticated pressure sensor-instrumented
equipment.

In this work, an alternative approach has
been established, which expands upon Johanson's model to enable its
incorporation into a daily work flow.  This new method requires only standard,
routinely-measured, process parameters as inputs and is capable of solving for P₀
a priori to extensive experimentation.  An excellent correlation between simulated
and experimental results has been achieved for both placebo and active blends. 
Additionally, a dimensionless relationship between key process input parameters
and final compact properties has been elucidated, which provides valuable
information for efficient scale-up procedures.