Views:11 Author:Site Editor Publish Time: 2017-08-15 Origin:Site
This chapter will describe the design and functionality of co-rotating and counter rotating twin screw extruders for pharmaceutical applications. Screw and process design to facilitate effective mixing are addressed. Control parameters and the associated interactions (i.e., Screw rpm versus feed rate) to achieve a quality product are proffered. Staging of unit operations in a twin Screw extruder and downstream system functionalities are described. Case studies are also presented to provide insight into how melt extrusion is being applied today. Finally, potential future growth areas are identified for melt extrusion.
The use of twin screw extruders to create sophisticated dosage forms is expanding because the continuous melt extrusion (ME) process has been proven to be a consistent and repeatable way to make high-quality products. twin screw extruders are continuous small mass continuous mixers that are the plastics industry preferred manufacturing methodology for compounding and devolatilization. It is without question that pharmaceutical companies have reaped the benefit of over half a century of technological developments and process refinement in plastics. It is only in the last decade or so that extrusion has emerged as a viable platform for pharmaceutical development.
Extrusion is the process of changing the physical properties of the substance by forcing it through an orifice or die under controlled conditions. The extrusion equipment is classified into three main categories: ram, radial screen, and roll and screw extruders. Among these, the screw extruders are the most important in the pharmaceutical industry because the screw extruders continuously convert feed material to the finished form such as a rod, tube, or film. The rotating screws force the feed material forward towards the die, and the material is softened by the frictional heat developed through the barrel wall. The feed reaches the end of the screw in a viscous state that can then be forced through an orifice (or die) and molded into the desired shape.
Pharmaceutical screw extruders are designed based on the desired extrudate and are required to meet the current regulatory standards for the manufacture of dosage forms. They are classified as single-screw extruders, twin-screw extruders, multi-screw extruders.