Mechanisms of twin screw melt granulation

Twin screw melt granulation is a new alternative method for granulation that offers several advantages over wet and dry granulation methods. Twin screw melt granulation has been rapidly gaining interest over recent years in the pharmaceutical industry. Since it operates in steady state with controlled thermal and mixing history, twin screw melt granulation produces granules with more consistent and uniform quality than batch processes. This article reviews the recent progresses in investigating how the granulation formation mechanisms and granule properties are impacted by twin screw extruder parameters (machine parameters and process parameters) and system parameters (degree of fill, specific mechanical energy, and residence time) during twin screw melt granulation. Because of the unique mixing and melting mechanisms of twin screw extruder, thermoplastic binders with high melt viscosity could be applied in twin screw melt granulation. The effects of binder properties and drug-binder interactions on the granulation mechanisms and granule properties are also discussed.