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Melt Flow Index

Melt Flow Rates of Thermoplastics by Extrusion Plastometer (ASTM D1238)


To determine the rate of extrusion of molten resins through a die of specified length and diameter under prescribed conditions of temperature and load. 

 This test is particularly useful for quality control tests on thermoplastics.  It indicates the uniformity of the flow rate of the polymer as made by an individual process, and may indicate uniformity of other properties. 

 The flow rate as measured by the extrusion Plastometer is not a fundamental polymer property; it is an empirically defined parameter influenced by the physical properties and molecular structure of the polymer and by the conditions of the measurement.  Test results may not correlate directly with processing behavior. 


Formulated pellets are preheated in the MFI apparatus for 6-8 minutes at temperatures specified for the given polymer.  After preheat, a mass specified for the given polymer is placed on top of the piston and extruded material is collected for a specified time interval.

After the extruded sample is weighed after cooling and the melt flow index (g/10 minutes) is calculated.