Question

What does MFI mean? And what are your values for this parameter?

Answer 1

The  MFI Mean "melt flow index"

The  MFI is a measure of the ease of flow of the melt of a thermoplastic polymer.

It is defined as the mass of polymer, in grams, flowing in ten minutes through a capillary of a specific diameter and length by a pressure applied via prescribed alternative gravimetric weights for alternative prescribed temperatures

Measurement

1. 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.
2. The material is packed properly inside the barrel to avoid formation of air pockets.
3. A piston is introduced which acts as the medium that causes extrusion of the molten polymer.
4. 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.
5. After the preheating a specified weight is introduced onto the piston. Examples of standard weights are 2.16 kg, 5 kg, etc.
6. The weight exerts a force on the molten polymer and it immediately starts flowing through the die.
7. A sample of the melt is taken after the desired period of time and is weighed accurately.
8. MFI is expressed in grams of polymer per 10 minutes of duration of the test.

The concept of obtaining activation energy from MFI can be extended to copolymers as well wherein there exists an anomalous temperature dependence of melt viscosity leading to the existence of two distinct values of activation energies for each copolymer.

MFI (In Grams) = Weight of Melted samples in 10 minutes