Melt Flow Index 2001 - EMA 4161C PHYSICAL PROPERTIES OF...

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EMA 4161C PHYSICAL PROPERTIES OF POLYMERS MELT FLOW INDEX LABORATORY 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 that is used to extrude a polymer melt. The cylinder is charged with polymer and held for sufficient time to ensure complete melting. A piston carrying a static weight then loads the charge from above. 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.
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