Single and twin screw extruder based continuous processing techniques offer significant advantages in the processing of pastes in comparison to batch mixers. These advantages include high surface to volume ratio and hence better heat transfer characteristics, tailorable mixing behavior, and ability to work with modular elements i.e., flexible manufacturing capabilities. The extrusion technologies also offer the facility to process and compact solids, melt, mix, deaerate/devolatilize, pressurize, react and shape within the confines of a single machine. In this report the fundamentals of the processing of pastes in extruders are reviewed and elucidated using both single and twin screw extruders. The applications of the extrusion technology in various industries are further outlined by summarizing the technical journal and patent literature available.
The review also includes a methodology for proper characterization of pastes and a mechanism and framework for mathematical modeling of the processing of pastes in single and twin screw extruders. One, two and three dimensional mathematical models of the extrusion processes are covered. Important findings and experimental methods to verify the modeling results are discussed.
The review concludes that the basic failing of the available techniques, both in mathematical modeling and experimental studies, involves the inability to incorporate and characterire the microstructure of the paste as it evolves in the extruder. Future directions of research in this area are provided.