Melt flow index

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.

Melt flow rate is very commonly used for polyolefins, polyethylene being measured at 190 °C and polypropylene at 230 °C.

FRR is commonly used as an indication of the way in which rheological behavior is influenced by the molecular weight distribution of the material.

MFI additionally does not take account of long chain branching[7] nor the differences between shear and elongational rheology.

[10] The activation energies developed from MFI values has the advantage of simplicity and easy availability.

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.