Th Melt Flow Index, MFI, is take under pressures and shear rates which do not represent the actual conditions the material will see during processing. As a result, the MFI is not a good representation of the material processing characteristics. For these reasons, many people completely ignore this data, yet it can be helpful for scheduling and the anticipating potential changes.

For example, if you are processing a lot of material which has a MFI of 5, and you have to decide whether to change to a lot with an MFI of 6 or a lot with an MFI of 10… it is more likely that the lot with a 6 MFI is more likely to process similar to the lot currently processing.

Additionally, if you have to change from a lot with an MFI of 5 to a lot with an MFI of 10, the technician can be warned that the next lot is likely to have a lower viscosity.

I have found MFI data to be a moderately helpful tool when no other rheological data is available. Whenever possible, it is helpful to have more relevant rheological data such as that from a spiral flow, capillary rheometer, or a dual plate rheometer.

-Andy