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Melt Flow Index Testing Procedure

Melt flow rate is an indirect measure of molecular weight, with high melt flow rate corresponding to low molecular weight. At the same time, melt flow rate is a measure of the ability of the material's melt to flow under pressure. The machine which is designed to test MFR is Melt Flow Indexer（MFI）.Melt flow rate is inversely proportional to viscosity of the melt at the conditions of the test, though it should be borne in mind that the viscosity for any such material depends on the applied force. Ratios between two melt flow rate values for one material at different gravimetric weights are often used as a measure for the broadness of the molecular weight distribution.
ISO 1133  specifies two procedures for the determination of the melt mass-flow rate (MFR) and the melt volume-flow rate (MVR) of thermoplastic materials under specified conditions of temperature and load. One is a mass-measurement method. The other is a displacement-measurement method. Normally, the test conditions for measurement of melt flow rate are specified in the material standard with a reference to ISO 1133. 
The procedure for determining MFI  is as follows:
A small amount of the polymer sample (around 4 to 5 grams) is taken in the specially designed MFI apparatus. A die with an opening of typically around 2 mm diameter is inserted into the apparatus.
The material is packed properly inside the barrel to avoid formation of air pockets.
A piston is introduced which acts as the medium that causes extrusion of the molten polymer.
The sample is preheated for a specified amount of time: 5 min at 190 °C for polyethylene and 6 min at 230 °C for polypropylene.
After the preheating a specified weight is introduced onto the piston. Examples of standard weights are 2.16 kg, 5 kg, etc.
The weight exerts a force on the molten polymer and it immediately starts flowing through the die.
A sample of the melt is taken after the desired period of time and is weighed accurately.
MFI is expressed in grams of polymer per 10 minutes of duration of the test.
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