The melt mass-flow rate, MFR, often also designated as melt index, describes the flow properties of plastics at a defined temperature.
This property is measured by extruding a thermoplastic polymer melt through a capillary of known dimensions at a defined temperature and under a pressure determined by a weight. The result is the mass extruded per time unit, expressed in g/10 min.
If the melt density is known, it is possible to determine the MFR from the melt volume flow rate, MVR. In this measurement procedure the weighing of polymer sections is replaced by a continuous measurement of the extrusion volume. The result of the MVR value is expressed in cm³/10 min. The advantage of this measurement is the much more automated measuring procedure, which does not require operator intervention.
The test method works with a specimen size of approx. 4 to 8 g. A test takes approx. 10 to 25 minutes and is performed with limited technical effort. Moisture-sensitive polymers such as polyamide 6 or polyamide 66 must first be dried at temperatures below 80°C to a moisture content of less than 0.08%.
Especially with the polyolefins often used for pipe production, but also with other polymers, fluctuations in the molecular distribution can be easily and reliably detected in this simple way.
The measurement procedure is usually used in the incoming goods inspection of a pipe manufacturer. This ensures that production can continue in an uninterrupted manner, even after a batch change.
- ISO 1133-1 - Plastics — Determination of the melt mass-flow rate (MFR) and melt volume-flow rate (MVR) of thermoplastics — Part 1: General test method
- ISO 1133-2 - Plastics — Determination of the melt mass-flow rate (MFR) and melt volume-flow rate (MVR) of thermoplastics — Part 2: Method for materials sensitive to time-temperature history and/or moisture
- ASTM D1238 - Standard Test Method for Melt Flow Rates of Thermoplastics by Extrusion Plastometer