Determination of Melt Mass Flow Rate (MFR) and Melt Volume Flow Rate (MVR)

Special precautions must be taken for tests performed on these materials (for example, PBT, PET, or PA). First, these materials must be sufficiently dried and must be dry when poured into the extrusion barrel. An optional nitrogen blanket at the extrusion barrel prevents direct contact by the material with the ambient air. The test is run in defined time sequences and they are recorded by the software. The extrusion plastometers must meet specific conditions for this purpose in terms of spatial and temporal temperature distribution in the extrusion barrel.

Correlation of IV measurements for the MFR value for linear PET

The molecular weight of polyethylene terephthalate (PET) is usually described in terms of intrinsic viscosity. This is the IV value in dl/g. The longer the polymer chains, the higher this characteristic value. This makes it possible to demonstrate molecular chains and how they can occur when moisture that is too high during the melting process.

The disadvantages of this method are that recyclers of PET in particular, are often not equipped to handle corrosive or toxic solvents. Furthermore, the fact that the test lasts a long time poses a practical problem. Therefore, measurement of the melt mass flow rate (MFR) has been used since the early 1990s in this area as well.

Using testXpert III to control the Mflow and Aflow extrusion plastometers makes it possible to determine the correlation between IV values and the MFR by means of premeasurements, which can then be applied to other measurements.