Determining MFR and MVR for plastic pipes

Flow rate, melt index ISO 1133-1, ISO 1133-2, ASTM D1238

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Melt mass flow rate (MFR), often also referred to as melt index, describes the ease of flow of plastics at a defined temperature. This property is measured by extruding a thermoplastic polymer melt at a specified temperature, under a pressure generated by a specific weight, through a capillary tube of known dimensions. The result is the extruded mass per unit of time, expressed in g/10 min.  With a known melt density it is possible to determine MFR from the melt volume flow rate (MVR). In this test method the weighing of polymer extrudates is replaced by continuous measurement of the extrusion volume. The result for the MVR value is shown in cm³/10 min. The advantage of this test is the significantly greater level of test sequence automation, requiring no operator intervention. The test method employs a specimen size of approximately 4 to 8g. A test lasts approximately 10 to 25 minutes and requires only limited technical expenditure. 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%.  Variations in molecular distribution can be identified quickly and reliably in this simple way, particularly in the polyolefins often used for manufacturing pipes, as well as in other polymers.  This test method is usually employed in goods inwards checks by pipe manufacturers and allows them to ensure that continuous production can be maintained, even when changing batches. 

Key standards

  • ISO 1133-1 - Plastics - Determination of the melt mass-flow rate (MFR) and melt volume-flow rate (MVR) of thermoplastics - Part 1: general 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
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