Melt Flow Index is a measure of how many grams of polymer are melted within 10 minutes. The test of MFI is done with a certain temperature depending on the type of plastic being tested. A sample is loaded into the preheated barrel of the instrument, together with a piston and weight is placed on the piston to apply force. The melted plastic of the system is then cooled and measured by weight. This MFI test is described in more detail on the ASTM D1238 document.
The MFI test, also called Melt mass-flow rate or MFR, has been used since the beginning of the polymer to emerge. Although the instruments used to perform the tests are still not perfect, but this method can present data to compare samples quickly. Some factories still use MFI data specification reference that made in 1940 and 1950 for some types of polymers. The MFI of this polymer is an important specification for estimating how the material will behave when extruded and injected in a molding machine.
One other application of MFI is used for failure analysis. Samples of failed products can be tested and compared to the specifications of the product. The MFI analysis will easily identify whether the part has been produced with the wrong type of polymer, the analytical data can also provide an understanding of the other properties of the section. Commercial plastic parts typically contain filler, additive, and colorant materials together with polymer blends. Imbalances in the recipe may affect the mechanical properties and yields of the melt stream.
While Melt Flow Index testing may be imperfect and often lose out with more complex and modern testing techniques, it can still provide exceptional analytical value depending on test requirements. MFI testing should not be ignored as a first step – or perhaps the only step – of a testing protocol. Furthermore, while this testing technique is not expensive and relatively easy, it should still be done with a well-qualified testing lab with appropriate qualifications, resulting in reliable results and used as actionable data.