Abstract
Wet granulation is a complex process with several competing physical phenomena occurring in the granulator, which ultimately leads to the formation of the granules. These phenomena are divided into three groups of rate processes: (1) wetting, nucleation, and binder distribution, (2) consolidation and growth, and (3) attrition and breakage. The physical phenomena that control these processes are the same, independent of the type of granulation used. Granule size, size distribution, and porosity, as well as many other key product attributes are controlled by the balance of the rate processes that occur in the granulator. This chapter examines the underlying physics behind each rate process, defines the controlling formulation properties and process parameters for each rate process, uses regime maps to establish the operating regime for the granulator; and provides quantitative relationships to predict the effect of changing operating parameters and formulation properties. This chapter focuses on developments in the past decade where substantial advances in quantitative understanding of granulation rate processes have been made with an emphasis on work done by our group at The University of Queensland and The University of Newcastle. The philosophy of this chapter is to characterize process parameters in generic terms that are equipment independent (collision velocity, powder surface flux, etc.).