Melt flow index

The melt volume-flow rate ( English MVR = M elt V olume-flow R ate or formerly and still often colloquially as M elt V olume R ate or MVI = M elt V olume I ndex hereinafter) is used to characterize the fluidity (molding composition testing) of a Thermoplastics under certain pressure and temperature conditions . The melt mass flow rate is determined in the same way as the melt volume flow rate and differs in the measurement result from the melt density. It is a measure of the viscosity of a plastic melt . This allows conclusions to be drawn about the degree of polymerization , i.e. the average number of monomer units in a molecule.

The MVR / MFR according to ISO 1133 is determined by means of a capillary rheometer , whereby the material (granulate or powder) is melted in a heatable cylinder and pressed through a defined nozzle (capillary) under a pressure created by the applied load . The emerging volume or mass of the polymer melt (the so-called extrudate) is determined as a function of time . A major advantage of the melt volume flow rate is the simple measurement of the piston travel with a known piston diameter to determine the melt volume that has escaped. In contrast to this, with the melt mass flow rate, the tapped melt strands have to be weighed and there is additional effort for handling.

${\ displaystyle MVR = {\ frac {volume} {10 \, \ mathrm {min}}}}$

or

${\ displaystyle MFR = {\ frac {Mass} {10 \, \ mathrm {min}}}}$

The unit for the MVR is cm³ / 10 min, for the MFR g / 10 min.

Example: MFR / 190/5 (test temperature 190 ° C, mass 5 kg) from Hostalen GM5010T2 ( polyethylene ) = 0.4 - 0.7 g / 10 min

If a plastic is damaged - for example by chemical attack or radiation - in such a way that chain degradation begins, its melt viscosity decreases and the melt volume flow rate increases. Material contamination or errors during processing can also negatively affect the MVR / MFR. The MVR / MFR only indirectly says something about the flow properties of plastics, rather it is a value that is used in quality assurance.

Main areas of application of the melt volume flow rate / melt mass flow rate

Production control
Incoming goods inspection
Damage analysis / customer complaint

Typical test conditions for some plastics

	Test load / kg
Test temperature / ° C	0.325	1.2	2.16	3.8	5	10	21.6
125	EVA
150			EVA
190			PE EVA POM		PE PP		PE WPC
200					PS
220						ABS SAN ASA
230			PP	PMMA	PP PVDF
235			PA -12 PA -11		PA -12 PA -11	PA -11
250			PBT
260			PBT		PMP	PMMI
275					PA
280		PPE / PS	PET PPE / PS	PPE / PS	PPE / PS
300		Pc	PPE / PS		PA -GF PPE / PS	PPE / PS
315					PPS
330			Pc			PA6T
340			Pc			PEI
343			PSU
360						PES PPSU PSU
400			PES PPSU PEEK

Sources: DIN Pocket Book Thermoplastic Molding Compounds , CAMPUS database , manufacturer material data sheets

Measurement uncertainty

To melt flow rate (MFR) are collaborative study data are available. The comparative standard deviation s _R is linearly dependent on the MFR over a wide range. Their relative value - s _{R, rel} - is usually between 3 and 8% , depending on the material . However, significantly higher s _{R, rel} values are observed for most polycondensates if the sample is not pretreated in accordance with ISO 1133-2. Round-robin test data based on polycondensates with suitable sample pretreatment are not yet available. s _R is a good estimate of the standard uncertainty u .

literature

Otto Schwarz: Kunststoffkunde , Würzburg: Vogel Verlag, 2005, ISBN 3-8023-1987-7
Walter Hellerich; Günther Harsch; Siegfried Haenle: Material guide for plastics: properties, tests, characteristics , Hanser Fachbuchverlag Munich, 2004, ISBN 3-446-22559-5
ISO 1133 (DIN EN ISO 1133) Determination of the melt mass flow rate (MFR) and the melt volume flow rate (MVR) of thermoplastics
ISO 1133-2 (DIN EN ISO 1133-2) Plastics - Determination of the melt mass flow rate (MFR) and the melt volume flow rate (MVR) of thermoplastics - Part 2: Method for materials that are sensitive to a time or temperature-dependent history and / or moisture

Individual evidence

↑ Bruno Wampfler, Samuel Affolter, Axel Ritter, Manfred Schmid: Measurement uncertainty in plastics analysis - determination with round robin test data . Hanser, Munich 2017, ISBN 978-3-446-45286-2 , pp. 83-84 .

[1] Bruno Wampfler, Samuel Affolter, Axel Ritter, Manfred Schmid: Measurement uncertainty in plastics analysis - determination with round robin test data . Hanser, Munich 2017, ISBN 978-3-446-45286-2 , pp. 83-84 .