Melt flow index (MFI)
The melt flow rate is determined in accordance with DIN EN ISO 1133 and is characteristic of the flow behavior or viscosity of a thermoplastic material. The melt viscosity is determined by means of melt index testing under specified, material-specific loads and temperatures. For this purpose, the granular sample is melted in a heatable cylinder. After a preheating phase of five minutes, the melt is forced through a nozzle of defined diameter via a piston supported by a weight. The amount of melt that thus flows through the nozzle within a certain time gives the MVR or MFI value. Depending on the test method, either the volume per time (MVR) or the mass per time (MFI) is determined. Both values can be converted into each other using the melt density at the test temperature used and taking into account the test pressure. Due to its ease of use, this method is frequently used in quality assurance.