Polymers have a complex rheological behavior such as melt viscosity, flow behavior, or viscoelastic properties. This must be taken into account when using these materials. The viscosity of a polymer is an important parameter for the design of plastic processing processes.
Rheological investigations are used to optimize the properties of the polymers so that they can meet all requirements.
Rheological properties can be determined by the deformation of larger quantities of material by means of mechanical rheometers, or on a very small scale by means of microcapillary rheometers or optical technologies such as microrheology.
The melt flow index (MFI) is used to characterize the flow behavior of thermoplastics and is a measure for the viscosity of a polymer melt. Material impurities and processing errors can be detected by comparative measurements of the MFI. Therefore, the melt flow index is used as a standard in quality assurance or fault analysis. The MFI allows conclusions on the degree of polymerization, therefore the average number of monomer units in one molecule.
The melt flow index is determined under defined, material-specific loads and temperatures. Depending on the test method, either the volume per time (MVR) or the mass per time (MFI) is determined.
Standards: DIN EN ISO 1133