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EMA 4666C POLYMER PROCESSING LABORATORY EXPERIMENT 3 - MELT FLOW INDEX PURPOSE: To familiarize the student with the operation of an extrusion plastometer, and demonstrate the relationship between the melt flow index (MFI) and molar mass. OVERVIEW: The extrusion plastometer is a simple form of capillary rheometer, which is commonly used to compare different grades of the same polymer type. The plastometer itself is simply a heated cylinder which is used to extrude a polymer melt. The cylinder is charged with polymer and held for sufficient time to ensure complete melting. The charge is then loaded from above by a piston carrying a static weight. As the load on the piston drives the melt through a die at the bottom of the cylinder, sections of the extrudate are cut-off at measured time intervals. By definition, the MFI is the mass of extrudate driven through the die in a 10 minute interval. Therefore, the index is an indirect measure of viscosity at specified load/temperature combinations. The principal difference between grades of the same polymer that is reflected in the MFI is molar mass. Because of the inverse proportionality between the MFI and viscosity, in general, polymer grades with a higher melt flow index possess lower molar mass. However, the presence of additives,
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This note was uploaded on 09/18/2011 for the course EMA 4666c taught by Professor Brennan during the Spring '08 term at University of Florida.

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