Melt Volume-Flow Rate

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Melt volume-flow rate (MVR) (Author: Prof. Dr. H.-J- Radusch)

Measurement of melt-volume flow rate (MVR)

The melt-volume flow rate (MVR = melt-volume flow rate or, conversely, MVI = melt volume index) is used to characterise the flow behaviour of a thermoplastic material. Melt index testers are used to determine the melt volume flow rate, as they are also used to determine the melt mass-flow rate (MFR).

Equation for determining the MVR value

The melt-volume flow rate MVR indicates the volume extruded from the capillary in 10 minutes. The MVR value is given in cm³ (10 min)^-1 and calculated according to the equation:

$MVR={\frac {\pi \cdot r^{2}\cdot l\cdot t_{ref}}{t}}={\frac {427\cdot l}{t}}$

mit

r		piston radius
l		piston travel distance
tref		600 s
t		measurement time

The determination of the melt index is standardised in ISO 1133 [2] and ASTM D 1238 [3].

The test conditions must be specified for each characteristic value determined.

Information content and comparability of the MVR value

The melt index value represents only one value indirectly proportional to viscosity at a relatively low shear rate. Due to the simple measurement principle, there is no direct comparability with viscosity values measured on high-pressure [Capillary Rheometer|capillary rheometers]] [1]. Viscosity values measured using a melt indexing machine can differ by up to 30 % compared to corrected, actual values measured using high-pressure capillary rheometers [4].

Acknowledgement

The editors of the lexicon would like to thank Prof. Dr. Hans-Joachim Radusch, Martin-Luther-Universität Halle-Wittenberg and Polymer Service GmbH Merseburg for this guest contribution.

See also

• Melt mass-flow rate
• Moulding compound test
• Glowing hot-wire test
• Capillary rheometer

References

[1]	Radusch, H.-J.: Determining Process-Related Properties. In: Grellmann, W., Seidler, S. (Eds.): Polymer Testing. Carl Hanser, Munich (2022) 3. Edition, pp. 62–64 (ISBN 978-1-56990-806-8; e-Book 978-1-56990-807-5; see AMK-Library under A 22)
[2]	ISO 1133: Plastics – Determination of the Melt Mass-flow Rate (MFR) and Melt Volume-flow Rate (MVR) of Thermoplastics Part 1 (2022-06): Standard Method Part 2 (2011-12): Method for Materials Sensitive to Time-temperature History and/or Moisture
[3]	ASTM D 1238a (2023): Standard Test Method for Melt Flow Rates of Thermoplastics by Extrusion Plastometer
[4]	Schramm, G.: Einführung in die Rheologie und Rheometrie. Gebrüder Haake, Karlsruhe (2nd Edition 2004) (Content as pdf)