New dispersive mixing technology for extruders and mixing devices (1, 2) is based on creating strong elongational flow to achieve efficient dispersive mixing. These mixers are designed so that all fluid elements pass through the high stress regions several times. One version of the new mixer, CRD-4, was tested on a modular 45 mm extruder using a dryblend of polyethylene and polystyrene. The CRD-4 mixer was tested against a Leroy/Maddock mixer and a Maillefer mixer. The mixing capability was studied by microscopic analysis of the domain sizes of cross sections of extruded strands. The mixer performance was also analyzed with respect to pressure profiles, characteristic curves, and melt temperature distribution. It was found that the CRD-4 mixer achieves a fine level of dispersion under most circumstances. The Leroy/Maddock mixer has limited dispersive mixing capability at low screw speed; however, its dispersive mixing capability is better at high screw speed. The CRD-4 mixer is designed with forward pumping capability. As a result, the output-pressure characteristic of a screw with a 6D CRD-4 mixer is essentially identical to the same screw with the mixer replaced by a conveying section.
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