| Mixing is crucial in most polymer processing operations towards obtaining high-quality products (e.g. tubing, tire treads and wire coverings). Material type, screw design, and processing conditions all affect mixing profoundly. Different types of mixing elements have been developed to improve mixing in the single screw extruder; however, the selection of these mixing elements is not trivial. In this work, our purpose is to provide quantitative tools to select the best mixing element.;The RTD experiments showed that the mean residence time is highest in the Saxton mixer and the lowest in the single flight element. Also, the RTD was broadest in the Saxton mixer and narrowest in the single flight mixer. This means that the polymer in the Saxton mixer experiences the widest range of strains and gets mixed more thoroughly. These results were confirmed by image analysis, which showed that polymers mixed in the Saxton mixer were more homogenously mixed compared to the two other mixing elements.;Residence time distribution (RTD) and image analysis were used to compare mixing in three different mixing elements: single flight, Maddox, and Saxton. Residence time distributions were used to indirectly grasp an insight about the strain distribution inside the extruder. Experimental RTD data were derived from silica tracer studies and compared to various mixer models. A model based on a plug flow mixer in series with two continuous stirred tanks best fit the experimental data in all three different mixing elements. For the image analysis method the degree of mixing was determined. Mixtures of polyethylene resins with carbon black were extruded and sliced. Subsequently, sliced samples were scanned to provide images showing the distribution of the carbon black in the resin. |
