Testing the MFR and MVR of Plastics
The melt flow test (also referred to as melt index test or melt flow index test) is a test method used to determine the flow properties of thermoplastic materials. The test measures how much material flows through a standardized die while subjected to a specified load and temperature. The result is expressed as melt index (MI) or melt flow index (MFI), which by using various different test methods, delivers standard characteristic values such as MFR (melt mass-flow rate) and MVR (melt volume-flow rate).
The MFR and MVR tests are used to evaluate the processability of plastics and to ensure that the quality and properties of the produced plastic material meets the specified requirements. The test is commonly implemented by plastic manufacturers and processors who are tasked with guaranteeing that the plastic materials being tested are suitable for their intended application.
The melt flow test also plays an important role in the quality assurance of plastic products. Through regular melt index tests, deviations in the production chain can be detected and corrected at an early stage of the process.
Term definitions Standards Comparison of test methods Test conditions according to standard Downloads Request a consultation
Term definitions related to the MFR and MVR test
| Normative term | Characteristic value | Unit | Normative reference | Synonyms | Meaning |
|---|---|---|---|---|---|
Melt mass-flow rate | MFR | g/10min | Melt Index Melt flow index Mass-flow rate MFI value | Mass of a thermoplastic material passing through a die of specified dimensions and properties at a specified temperature and under a known load within a time period of 10 minutes. | |
Melt volume-flow rate | MVR | cm3/10 min | ISO 1133-1 | Volume-flow rate MVI value | Volume of a thermoplastic material passing through a die of specified dimensions and properties at a specified temperature and under a known load within a time period of 10 minutes. |
Flow rate ratio | FRR | ISO 1133-1 | Quotient of two melt mass-flow rates measured under different standardized loads and thus representing different points on a viscosity curve. | ||
Density of the plastic melt at test temperature | ρ | g/cm3 | ISO 1133-1 ASTM D1238 | Melt density | MFR / MVR quotient. The value can be determined by simultaneously measuring the melt mass-flow rate and melt volume-flow rate in an extrusion plastometer. |
Apparent shear rate | γ ̇ (gamma point) | 1/s | ISO 11443 | Apparent shear rate Apparent shear rate | Shear rate resulting from the uncorrected calculation of the flow of a non-Newtonian fluid. |
Apparent shear stress | τ (tau) | Pa | ISO 11443 | Apparent shear stress | Shear stress calculated for a die with a small orifice ratio (L/D < 100) without applying a correction for a drop in pressure. |
Apparent viscosity | η (eta) | Pa s | ISO 11443 | Apparent viscosity | Viscosity calculated from the quotient of the apparent shear stress and apparent shear rate. |
Standards for MFR and MVR tests on plastics
- ISO 1133-1 - Plastics – Determination of the melt mass-flow rate (MFR) and melt volume-flow rate (MVR) of thermoplastics – Part 1: Standard 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
- ASTM D3364 Standard Test Method for Flow Rates for Poly (Vinyl Chloride) with Molecular Structural Implications
In addition, the specification standards of the individual molding materials must be observed, in which the test temperatures, the nominal loads, and if necessary, other special material-specific conditions to be used for MFR and MVR tests are standardized. These may deviate from the ISO 1133 and ASTM D1238 standard specifications.
ISO vs. ASTM in MFR and MVR measurements
The procedures for MFR, MVR and FRR measurements on thermoplastics are equivalent but not identical according to ISO 1133 and ASTM D1238, since they differ in some respects, especially in the test procedure and test conditions:
- For some polymers, the test temperatures and test weights are specified differently in ISO and ASTM.
- The recommended volume of polymer to be used is slightly different.
- The duration of the preheating phase is set to at least 5 minutes in ISO 1133-1, but can also be significantly longer. In ASTM D1238, the duration of the preheating phase is standardized at 7 minutes with a strict tolerance of ±0.5 minutes.
- According to the ISO standard, the starting point of the test is at a piston position of 50 mm above the die, while ASTM sets this point at 46±2 mm.
- Testing of sensitive polymer types with respect to time- or temperature-dependent history and/or moisture (e.g., PBT, PET, or PA) are described in the separate ISO 1133-2 standard, while ASTM D1238 specifies a narrowly tolerated time sequence of testing for all polymer types.
- ISO 1133-1 leaves it largely up to the operator to determine suitable section or measurement intervals for the measurement procedure, while ASTM D1238 specifies very precisely over what piston travel distance or at which section interval measurements are to be made at which MFR or MVR value.
Overview of the test methods according to ISO 1133 and ASTM D1238
ISO 1133 and ASTM D1238 describe the test methods for MFR and MVR determination in a similar manner and can therefore be categorized as technically equivalent standards, although there are significant differences in the application of the test requirements, which in some cases do not allow for reproducibility of the results between standards.
| Test methods | Test results | Typical measurement range | Level of test sequence automation | Applications | Related extrusion plastometer |
|---|---|---|---|---|---|
Method A - MFR | Melt mass-flow rates, MFR in g/10 min | Min: approx. 0.2 g/10 min Max: approx. 75 g/10 min | Low level of automation
| Incoming goods inspection Teaching and training Tests on filled polymers with variable density distribution | |
Method A - MFR | Melt mass-flow rates, MFR in g/10 min | Min: approx. 0.2 g/10 min Max: approx. 75 g/10 min | Improved level of automation
| Incoming goods inspection Teaching and training Tests on filled polymers with variable density distribution |
|
Method B - MVR | Melt volume-flow rates, MVR in cm³/10 min By simultaneously weighing the extrudate sections, the melt density at test temperature can be determined. | Min: approx. 0.1 g/10 min Max: approx. 2000 g/10 min | High level of automation
| Incoming goods inspections Teaching and training Production control Research and development | |
Method C - half-die | Melt volume-flow rates, MVR in cm³/10 min By simultaneously weighing the extrudate sections, the melt density at test temperature can be determined. | Min: approx. 0.1 g/10 min Max: approx. 2000 g/10 min | High level of automation
| For polyolefins with high flow rates Incoming goods inspections | |
Method D - multi-weight test, FRR | Melt mass-flow rates, MFR Apparent shear rate | Min: approx. 0.1 g/10 min Max: approx. 900 g/10 min | High level of automation
| Incoming goods inspection Teaching and training Production control Research and development Shift work with changing operators |
Method A - MFR test
In method A, the extrudate is cut off at constant time intervals and its mass is determined with an analytical balance. The test result is the extruded mass per unit of time (melt mass-flow rate MFR), which is indicated in g/10 min.
Method A can be used for all filled or unfilled thermoplastic polymers.
Method B - MVR test
In method B, instead of the mass of an extrudate cut in regular intervals, the extruded volume of the polymer melt is determined. For this, the extrusion plastometer must be equipped with a piston displacement transducer. The MVR (melt volume-flow rate) is the extruded material volume per unit of time and is indicated in cm3/10 min. It is calculated from the distance the piston travels per unit of time.
A significant advantage of method B is the elimination of mechanical cutting. With good synchronization of the displacement/time measurement value, this method can achieve a high level of accuracy within short measurement times and piston displacements. Thus, depending on the material, accuracy requirement and MVR result, it is possible to carry out more than 30 individual measurements with a single extrusion barrel filling.
The MVR value can be used for material specification purposes according to ISO 10350-1. However, In the case of filled molding materials, the simple conversion to an MFR value is usually not possible because of fluctuations in the density of the plastic melt.
Method C - MVR test with half-die
Method C refers to an MVR test variation of method B.
For thermoplastics with an MFR value greater than 75 g/10 min, in addition to being able to reduce the nominal load, both ISO 1133 and ASTM D1238 support the use of a die with half the height and half the diameter of the orifice. However, direct reproducibility of results that are determined using the standard die is not possible.
Method D, multi-weight test – FRR
With some polyolefins it is common to state the MVR value for different load levels and determine the flow rate ratio (FRR). When using simple extrusion plastometers, this requires measurements from several fillings. Extrusion plastometers, such as the Aflow extrusion plastometer from ZwickRoell, which is equipped with an automatic load changing device can measure multiple load levels from a single filling.
Test conditions for melt flow rate measurements
| Polymer | ISO | ASTM D1238 | |||||
| IUPAC codes | Standard | Drying | Temp. [°C] | Weight [kg] | Temp. [°C] | Weight [kg] | |
| Polyolefins | PU | ISO 17855-1 ISO 4427-1 ISO 4437-1 ISO 15494 ISO 22391 | (no) | 190 190 190 | 2.16 21.6 5 | 125 125 190 190 190 190 190 250 310 | 0.325 2.16 0.325 2.16 5 10 21.6 1.2 12.5 |
| UHMW-PE | ISO 21304-2 | 190 230 | 21.6 21.6 | ||||
| PP | ISO 19069-2 ISO 15494 ISO 15874-2 | (no) | 190 230 | 5 2.16 | 230 | 2.16 | |
| PE & PP | ISO 18263-2 | 230 | 2.16 | ||||
| Styrene | PS | ISO 24022-2 | (no) | 200 | 5 | 190 200 230 230 | 5 5 1.2 3.8 |
| PS-I | ISO 19063-2 | (no) | 200 | 5 | |||
| SAN | ISO 19064-2 | (no) | 220 | 10 | 220 230 230 | 10 3.8 10 | |
| ABS | ISO 19062-2 | (no) | 220 240 265 | 10 10 10 | 200 220 230 | 5 10 3.8 | |
| ABS/PC blends | (no) | 230 250 265 265 | 3.8 1.2 3.8 5 | ||||
| MABS | ISO 19066-2 | (no) | 220 240 265 | 10 10 10 | |||
| ASA, ACS, AEDPS | ISO 19065-2 | (no) | 220 | 10 | 230 230 | 1.2 3.8 | |
| ASA, ACS, AEDPS (high-heat grades) | ISO 19065-2 | (no) | 240 265 | 10 10 | |||
| Acrylic | PMMA | ISO 24026-2 | (no) | 230 | 3.8 | 230 230 | 1.2 3.8 |
| Polyester | PC homopolymer PC copolymer | ISO 21305-2 | < 0.02 % | 300 330 | 1.2 2.16 | 300 | 1.2 |
| PBT, PBTP | ISO 20028-2 | <0.02% (PBT) | 2301 2501 2651 | 1.2 2.16 5 10 21.6 | |||
| PET | ISO 20028-2 | < 0.02 % | 2701 | 1.2 2.16 5 10 | 250 285 | 2.16 2.16 | |
| High viscosity PET | ISO 20028-2 ISO 12418-2 | 2801 | 1.2 2.16 5 10 | ||||
| PET and PBT | ISO 20029-2 | 1901 2301 2501 | 2.16 5 10 | ||||
| Cellulose ester | CA,CH, CN, CP, CAB | (no) | 190 190 190 210 | 0.325 2.16 21.6 2.16 | |||
| Vinyl | PVC-P PVC-U | ISO 24023-2 ISO 21306-2 | (no) | 1752 | 20.0 | ||
| PVC | 190 | 21.6 | |||||
| PVAC | (no) | 150 | 21.6 | ||||
| EVAC | ISO 21301-1 | (no) | 190 | 2.16 | |||
| PVDF | 230 230 | 5 21.6 | |||||
| Other polymers | PB-1 | ISO 21302-1 ISO 15876-3 ISO 15494 | (no) | 190 190 | 2.16 5 | ||
| POM | ISO 29988-2 | (no) | 190 | 2.16 | 190 190 | 1.05 2.16 | |
| PA | ISO 16396-2 | < 0.02 % | 2251 2501 2751 3001 | 1.2 2.16 5 10 21.6 | 235 235 235 275 275 | 1 2.16 5 0.325 5 | |
| PCL | (no) | 80 125 | 2.16 2.16 | ||||
| EVOH | ISO 21309-2 | 210 | 2.16 | ||||
| Polyphenyls | PPE + PS, unfilled PPE + PP PPE + PS, filled PPE + PA PPE + PPS | ISO 20557-2 | 250 250 300 280 300 | 10 10 5 5 10 | |||
| PPS | ISO 20558-2 | 315 315 315 | 1.2 2.16 5 | 315 | 5 | ||
| Fluoropolymer | FEP (PFEP) | ISO 20568-2 | (no) | 372 372 | 2.16 5 | 372 | 2.16 |
| PFA | ISO 20568-2 | (no) | 372 | 5 | 372 | 5 | |
| ETFE | ISO 20568-2 | (no) | 297 | 5 | 297 | 5 | |
| EFEP | ISO 20568-2 | 265 | 5 | ||||
| PVDF | ISO 20568-2 | (no) | 230 230 | 5 21.6 | 120 120 230 230 | 5 21.6 2.16 5 | |
| VDF/CTFE | ISO 20568-2 | 230 230 | 2.16 5 | ||||
| VDF/HFP | ISO 20568-2 | 230 230 | 2.16 5 | ||||
| VDF/TFE | ISO 20568-2 | 297 | 5 | ||||
| VDF/TFE/HFP | ISO 20568-2 | 265 | 5 | ||||
| PCTFE | ISO 20568-2 | (no) | 265 265 | 21.6 31.6 | 265 265 265 | 12.5 21.6 31.6 | |
| CPT | ISO 20568-2 | 297 | 5 | ||||
| ECTFE | ISO 20568-2 | (no) | 271.5 | 2.16 | 271.5 271.5 | 2.16 5 | |
| PVDF | 230 230 | 5 21.6 | |||||
| Polysulfone | PPSU | ISO 24025-2 | (no) | 365 | 5 | 365 380 | 5 2.16 |
| PSU | ISO 24025-2 | (no) | 343 | 2.16 | 343 360 | 2.16 10 | |
| PESU | ISO 24025-2 | 350 | 2.16 | 360 380 | 10 2.16 | ||
| Alternatively | ISO 24025-2 | 360 | 10 | ||||
| Thermoplastic elastomer | TPU | ISO 16365-2 | (< 0.03%) | Tmelt + 10°C | 2.16 5 10 21.6 | ||
| TPE | 190 200 220 230 240 250 | 2.16 5 2.16 2.16 2.16 2.16 | |||||
| TEO | 230 | 2.16 | |||||
| Ketones | PEEK | ISO 23153-2 | 400 400 | 2.16 10 | 400 | 2.16 | |
| PK | ISO 21970-1 | 240 | 2.16 | ||||
Values in brackets [ ... ] are used in practice, however no standard-based reason is known.
- Any weight and temperature combination is acceptable
- To ASTM D3364
Frequently asked questions related to the MFR measurement and MVR measurement
Polyolefins, such as PE or PP, are generally quite easy to test and place only minor demands on the conditioning of the test specimen. The framework requirements for temperature and test weight are defined in ISO 17855-1, ISO 22391 and in ISO 19069-2. The test standard used is ISO 1133-1 or ASTM D1238. The MFR and MVR measurement is normally performed under method A (plastic MFR) or method B (plastic MVR). When the flow rate ratio FRR is to be determined, method D is used.
Polyesters are among the moisture-sensitive polymers and must be dried to a very low residual moisture level before testing. This is expediently achieved by means of a vacuum furnace with nitrogen purging and subsequently checked by moisture determination using Karl Fischer titration. The polymer is transported to the testing instrument under exclusion of air and measured in method A (MFR) or B (MVR) directly after it has been quickly filled into the extrusion plastometer. The temperature and test weight parameters for PET and PBT are specified in ISO 20028-2. For PET it is also common to provide the intrinsic viscosity, which is determined using a Ubbelohde viscometer according to IS 1628-1. In addition to this relatively complex procedure, it is common in the production sector to determine the IV value via a correlation calculation from the MFR value, which is much faster to measure.
Since testing instruments according to ISO and ASTM standards are very similar in design and the metrologically relevant components such as the die, piston and extrusion barrel are identical, you can assume an almost identical value level of MFR and MVR values, provided that the same test load and same test temperature are used for the respective polymer.
The main difference in the methods for MVR and MFR determination on thermoplastics according to ISO 1133 and ASTM D1238 lies in the test procedure and the test conditions:
- Test temperatures and test weights are different for some polymers.
- The recommended volume of polymer to be used is slightly different.
- Preaheating phase: ISO 1133-1: more than 5 minutes; ASTM D1238: 7±0.5 minutes.
- Starting point of the test: ISO standards at a piston position of 50 mm above the die; ASTM standard piston position 46±2 mm.
- Testing of moisture-sensitive and rapidly thermally degrading plastics: separate ISO standard 1133-2; ASTM D1238 for all polymer types
- Section or measurement intervals: in ISO, this is largely left up to the operator; ASTM D1238 specifies very precisely over what piston travel distance or at what section interval measurements are to be made at which MFR value or MVR value.
Downloads
- Industry Brochure: Plastics & Rubber PDF 9 MB
- Product Brochure: Extrusion plastometers PDF 3 MB
- Product Information: Aflow Extrusion Plastometer PDF 90 KB
- Product Information: Mflow Extrusion Plastometer PDF 127 KB
- Product Information: Cflow Extrusion Plastometer PDF 221 KB