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Oscillating Flow Extrusion Disclosure Number: IPCOM000018634D
Publication Date: 2003-Jul-29

Publishing Venue

The Prior Art Database


Significantly improved mixing of non-compatible, semi-compatible and compatible polymers, polymer blends and alloys, fillers and additives can be carried out by using a novel extrusion screw design. This new screw design consists of a series of sections, with each of these sections consisting of forward conveying elements and reverse conveying elements. Such sections ensure multiple compression and expansion cycles (oscillations) are imposed upon on the material as it is being transported through the extrusion system. Continuous effective mixing is achieved as each section creates internal friction throughout the whole volume of the flowing polymer. This design eliminates the need for high shear stress kneading block sections thereby decreasing degradation of the polymer and energy input. As a result of these oscillations, multiple repeated mixing cycles provide excellent mixing. The degree of mixing can be controlled by the design of the oscillating units. For example, the number of units, the pitch, the length-to-diameter all can vary within the unit and between the units. This concept can be implemented all types of extrusion systems, including, but not limited to single screw extruders, co-rotating and counter-rotating, intermeshing and non-intermeshing twin-screw extruders and continuous mixers. The process was demonstrated with an impact polypropylene copolymer polymerized via the gas phase process. A conventional and an improved screw were compared in a twin screw extruder. The conventional screw had conveying elements in the feeding zone, kneading blocks in the melting zone and conveying elements in the pressurization zone. The new screw was set up with seven alternating units each consisting of six forward elements and one reverse element. The pitch of the forward elements decreased from 1.4 L/D to 0.5 L/D. The rubber phase dispersion was measured by an optical method using a digital camera and computer count of the rubber gels. The rubber gels of size greater than 100 micron decreased 2 to 6 times with the new screw compared to the conventional design. Similar improvement was observed with equal number of forward and reverse elements; i.e., a symmetrical arrangement.