Distributive mixing in a single-screw extruder - Evaluation in the flow direction

This study investigates distributive mixing in the flow direction for a single-screw extruder. With a custom-designed transparent extruder, an Image Analysis System, and a newly defined parameter, i.e., distribution index, the distribution mechanism is thoroughly examined with respect to various processing conditions or screw designs. Experimental results indicate that the longitudinal distribution can be enhanced with an increasing RPM, a longer metering section, or a decreasing diameter of the die. However, a plateau region occurs when an optimum condition exists for the RPM and the length of the metering section. In addition, an extruder modified with a barrier, pin-elements, or high helix angle performs better in the longitudinal mixing than the conventional one. Our results further demonstrate that leakage flow significantly enhances mixing in the flow direction.