Melt Flow Index (MFI) or Melt Flow Rate (MFR) is a measurement of a given polymer's flow characteristics, or its rheological properties, in molten condition at a known pressure. The MFI as well known as the melt Mass-Flow Rate or MFR has been used since the earliest days of polymer science and materials characterization. The melt-flow index test, also known as the melt-flow rate (MFR), measures the rate at which melt polymers are pushed through capillaries of specific diameters and lengths.

Why is it used?

Melt Flow Index values for individual materials of varying gravimetric weights may be used to measure the molecular weight distribution of the polymer being tested. Typically, MFI of a polymer resin is inversely proportional to its molecular weight, meaning that higher the molecular weight, lower will be the melting rate of the polymer.

In general, higher MFI indicates lower viscosity of a material, whereas, comparing polymers in the same class, lower melt flow rates are associated with higher molecular weights and/or lower branches.

Significant variations in the melt flow rate lead to practical problems, such as nozzle jamming, thread breaking, porous structures, uneven heating, and so forth. Therefore, studies on melt flow rates and filament thermal and mechanical strengths are desired in polymer composites. The influence of different grain sizes combinations on melt flow, mechanical, and morphological properties of composite filaments has yet to be investigated.

The melt viscosity at test temperatures is directly related to MFI, since a sample with higher viscosity will flow slower. Processing conditions can be precisely optimized using capillary rheometers that measure polymer melt viscosity in relation to temperature and strain rate.

To get better, more appropriate, viscosity data...it is best to conduct rheological tests using either capillary or parallel plate rheometers. Capillary rheometry, which is a controlled-shear-rate test, can provide a true measure of viscosity, or flow resistance.

In that respect, it is different from capillary rheometer, which is a device measuring viscosity, which can adjust and vary the test flow rate while measuring the forces required to achieve this flow rate.

A flow-rate melt test moves the molten material through at a single flow rate, thus at a single shear rate, and cannot capture the entire range of behavior of a material with respect to changing shear rates. Those instructing industrial professionals in the process are quick to point out that a materials melt flow rate (MFR) value is a single point on a curve describing viscosity as a function of shear rate.

Conclusion

The melt flow rate can be used to predict different properties of the material, such as the behavior of the processing, long-term viscoelastic behavior, stability in the final application, etc. Therefore, it is a significant quality-control parameter for many polymers and plastics materials. The melt flow index test is one of those procedures which provides a wide range of insights into chemical as well as physical properties of the plastic materials used by various industries.

The Melt flow Index Testing Machine offered by Pacorr testing Instruments is an extremely effective test tool which is used by most of the plastic manufacturers for the determination of the material melt flow index with utmost precision and to assure the best quality of products.