Scope:

Melt Flow Rate (MFR) is measured by ASTM D1238 and is helpful in estimating the extruder rate (using an extrusion plastometer) of thermoplastic resins through an orifice at a specified temperature and load. Melt flow rate indicates the ease with which melted plastics can flow. Due to the reduced molecular weight, the degraded materials will normally flow more, and might have diminished physical characteristics as well. So, it can be used for differentiating grades of polyethylene or determine the extent of plastic deterioration caused by molding. The flow rates of a component and the resin on which it is molded are evaluated and finally the percentage difference is calculated. 

Test Procedure:

ASTM D1238 uses an extrusion plastometer that consists of an extrusion barrel heated exactly to a specified temperature. A die of standardized diameter, and a piston with weight are applied to its upper end. The barrel of extrusion should be loaded into the barrel of the melt flow apparatus with the test sample which is approximately 7 grams. The material is placed on a plunger with a fixed weight and the molten material is forced through the die. The extrudate is collected at uniform time intervals and the weight is measured. The melt flow rate data are evaluated from the extruded mass (g) per 10 minutes.

Specimen size:

About 14 grams of material is required. 

Data:

Flow rate = 600t*weight of extrudate

where

 t = time of extrudate in seconds and melt flow rate = grams per 10 minutes.

Conclusion:

ASTM D1238 is a standard test method which is used to determine the melt flow index (MFI) of thermoplastic polymers.