Melt Flow Index Standards (FAQ)


ISO 1133-1: Determination of melt flow rate (MFR) and melt volume rate (MVR) of thermoplastics, part 1: general procedure

ISO 1133-2: Determination of melt flow rate (MFR) and melt volume rate (MVR) of thermoplastics, part 2: procedure for materials which have a sensitive time or temperature history and / or moisture

Procedure A: Strand cutting at a constant time intervals and determination of mass; result: MFR (Melt Flow Rate) in g/10 min

Procedure B: Determination of volume at constant time intervals; result: MVR (Melt Volume Rate) in cm³/10 min

Procedure C: Usage of a half die with dimensions L/D=4/1,05;
for low viscosity materials with MFR >75g/10min or MVR > cm³/10min.

Procedure D: Multi load measurement; automatic weight selection allows tests with different test weights with one barrel filling, as descripted in ASTM D1238 procedure D as Flow Rate Ratio (FRR)

Normally ISO 1133-1 or ASTM D1238 is used, as these are usually not sensitive to moisture. However, it is important to note that in any case a corrosion resistant steel grade is selected for the test barrel and piston. Standard steels can already be damaged by corrosion during a single measurement due to the acids released.

In procedure A, the strand is cut off every few seconds and the melt flow rate (MFR) is determined directly. The operator must remain with the machine during the measurement to collect the strand sections and to evaluate the result. Especially during cutting, errors can occur if the sections do not separate cleanly from the knife.

In procedure B, the melt volume rate (MVR) is calculated from the piston speed. In this procedure, the data-acquisition runs fully automatically and is therefore more convenient and less prone to errors. The determined MVR can be converted into the MFR using the melt density.

Due to the higher ease of operation and the lower error rate, we generally recommend the use of procedure B. All our melt index testers are equipped as standard with the necessary sensor for measuring the piston speed.

The direct result of a measurement with procedure B is the melt volume rate MVR. According to the standards both values MFR and MVR are equivalent. Some materials are also specified with an MVR value. However, if a MFR-value is absolutely required, the melt density is necessary for conversion.

It is important to use a melt density at test temperature and not the solid density, which is often found on material data sheets!

For unfilled and unmixed polymers, the melt density can typically be taken from the literature (e.g: PE @ 190°C ρ = 0.7636 g/ccm and PP @ 230°C ρ = 0.7386 g/ccm according to ASTM D1238). If your GÖTTFERT Melt Flow Indexer is equipped with a cutting device, the melt density can also be determined during the test according to procedure B using a balance.

Due to the higher automation and fewer sources of error, procedure B is generally preferred and more accurate. With method A, material loss during cutting or incorrect weighing is a common mistake.

Yes, such a capillary or die can be ordered from us together with the necessary piston. The half-die with L4D1.05 mm may be used according to ISO 1133 from a MFR > 75 g/10 min or MVR > 75 ccm/10 min (measured with normal capillary!). According to ISO 1133, the half die can be used with both procedure A and procedure B.

In ASTM D1238, the half-die measurement is described as Procedure C, and is presented as an alternative for materials with an MFR > 75 g/10 min. Procedure C is similar to Procedure B (path length measurement).

The result is determined in the same way as with the standard capillary and the numerical value is typically smaller by a factor of approximately 8. The result is always reported and marked with a small sub-script "h", e. g.: MFRh (190°C/2.16 kg) = 20 g/10 min

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