Executive Summary
The general objective of our IFPRI project was to develop various methods and apparati to probe the rheological behavior and microstructural characteristics of concentrated suspensions (“dense suspensions”) for which the solid concentration approaches the maximum packing fraction of the solid phase, and the mathematical modeling of the extrusion process for such dense suspensions. The validation of the numerical analysis results generated using FEM through experimental studies (carried-out on industrial-scale and well-instrumented extruders) and development of methods and materials to simulate the interrelationships between the processing history and the microstructure on one hand and the ultimate properties of the suspensions on the other hand were additional objectives.
The major accomplishments of the investigation include:
1. Development of comprehensive mathematical models of the single and twin screw extrusion processes which incorporate the specific flow and deformation behavior of dense pastes including their complicated wall slip and viscoplasticity. The mathematical models numerically solved the three dimensional conservation equations without the necessity to simplify the geometry of the extruder and dies which are attached to the extruder.
2. Retrofitting of a 50.8 mm twin screw extruder with a programmable logic controller, multiple sensors for pressure and temperature, an Inframetrics thermal-imaging camera, an x-ray system and an adjustable gap in-line rheometer for validation of the predictions of the mathematical model.
3. Rheological characterization of a series of polymers and suspensions and the mathematical modeling of their single and twin screw extrusion behavior and comparisons with the experimental results from our well-instrumented experimental systems.
4. Development of a specific conductive composite paste to facilitate the linking of the rheological behavior and the electrical conductivity of the paste to the specific energy input during the mixing process and the degree of mixedness of the suspension ingredients as characterized by wide-angle x-ray diffraction.
5. Development and application of a wide-angle x-ray diffraction technique to the determination of the degree of mixedness of the conductive composite quantitatively.
6. Upon receiving information from the sponsors that the wet systems (systems which contain water) are of interest setting up a shear roll mill extruder which allowed the recording of the thermal history of the wet cellulosic system being processed and the development of preliminary mathematical models of the processing of a wet system (outside of the initial scope of the project) to determine what is important in the processing of such systems and what the challenges are. Experimental and theoretical results are included here to aid IFPRI’s future research in this area.