chapter  4
24 Pages

Twin-Screw Extrusion and Screw Design

ByWilliam Thiele

For those unacquainted with twin-screw extruders (TSEs), there is cause for cautious optimism in knowing that the use of this well-proven and versatile tool is within grasp to make a better, more repeatable, "good-manufacturing-practice" (GMP) product. However, given the peculiar nature of pharmaceutical-grade materials and processes, potential users should also exercise caution about importing solutions that worked for plastics and rubber, which served as the preamble for most of this work. This chapter deals with the most basic properties of the key process elements for a twin-screw extruder, namely, the barrels, the screw elements, and the shafts on which they are staged and driven. Pharmaceutical processes may also involve solids reduction, phase separations, precision distributions, reaction and purification operations, and validated reproducibility in a way more stringent manner than the world of plastics and food processing common to twin-screw extruders. The basic model for distributive mixing is dividing and recombining material without disturbing the individual morphological components.