MFR or MVR: Correctly Distinguish Melt Mass-Flow Rate and Melt Volume-Flow Rate

→ Product: Dynisco LMI6000 Melt Flow Indexer

 

A polypropylene is specified with an MFR of 12 g/10 min, while the test instrument reports an MVR of 15 cm³/10 min for another batch. Are the two materials therefore comparable? And can one value simply be converted into the other?

This is exactly where confusion often arises in practice. MFR and MVR both describe the flow behavior of a thermoplastic melt under defined test conditions. However, they use different reference quantities: MFR considers the mass extruded within a certain period of time, whereas MVR considers the corresponding volume.

Although there is a direct relationship between the two quantities, the density of the polymer melt at the actual test temperature must be known. The solid-state density from a material data sheet is generally not suitable for this purpose. In addition, MFR and MVR values can only be meaningfully compared if, among other things, the test temperature, test load, material condition and test method are identical.

A melt flow value without information on temperature and test load is therefore incomplete from a metrological perspective. MFR and MVR must always be evaluated together with the specified test conditions.

For standardized characterization of thermoplastic materials, ICS Schneider offers, among other products, the Dynisco LMI6000 Melt Flow Indexer and the Dynisco LMI5000. Further solutions for plastics processing, material testing and melt pressure measurement can be found under Dynisco Products at ICS Schneider.

What does the melt flow index describe?

The so-called melt flow index is an empirical characteristic used to characterize the flow behavior of thermoplastic materials under precisely defined conditions.

The basic principle is simple:

A defined quantity of polymer is placed in a heated test barrel and brought to a specified temperature. A piston applies a defined mass to the melt. The material is thereby forced through a standardized capillary die.

The amount of material flowing through the die within a defined period of time is then determined.

Two different quantities can be considered

MFR = mass-based melt flow

or:

MVR = volume-based melt flow

Both describe the same material under the same test conditions from different perspectives.

The commonly used term MFI

stands for:

Melt Flow Index

and is frequently used in practice as a general term for melt flow testing.

For clear technical documentation, however, it should be specified whenever possible whether the actual quantity is:

• MFR or
• MVR.

What does MFR mean?

MFR stands for:

Melt Mass-Flow Rate

.

The typical unit is:

g/10 min

MFR indicates

the mass of polymer melt that theoretically flows through the test die within ten minutes under defined test conditions.

In simplified form:

MFR = mass of extrudate / time

normalized to:

10 minutes

Example

A material has the following value under the specified test conditions:

MFR = 8 g/10 min

This does not necessarily mean that material is actually collected for exactly ten minutes during the test.

The mass determined within a defined period of time is converted to:

g/10 min

.

What does MVR mean?

MVR stands for:

Melt Volume-Flow Rate

.

The typical unit is:

cm³/10 min

With MVR, the mass of the extrudate is not required

Instead, the volume of polymer melt displaced through the die within a certain period of time is determined.

For this purpose, the movement of the piston in the test barrel can be measured at high resolution.

The volumetric flow rate is calculated from:

• piston cross-sectional area,
• distance traveled by the piston,
• required time.

An important practical advantage

is that for a pure MVR determination, it is not necessary to manually cut off and subsequently weigh each extrudate section.

This can simplify the test procedure and reduce operator influence, especially for recurring quality tests.

MFR and MVR in direct comparison

Property	MFR	MVR
Designation	Melt Mass-Flow Rate	Melt Volume-Flow Rate
Reference quantity	Mass	Volume
Typical unit	g/10 min	cm³/10 min
Measuring principle	Determine mass of extrudate	Determine volume displacement via piston movement
Scale required	yes for gravimetric determination	not required for pure MVR determination
Melt density required	no for direct gravimetric MFR	no for MVR itself
Melt density required for conversion MVR → MFR	–	yes
Dependent on temperature and test weight	yes	yes

A numerical value of 10 g/10 min and a numerical value of 10 cm³/10 min therefore do not mean the same thing.

Relationship between MFR, MVR and melt density

Mass, volume and density are fundamentally related by:

m = ρ × V

For MFR and MVR, this gives:

MFR = MVR × ρmelt

or:

MVR = MFR / ρmelt

Where:

• MFR is in g/10 min,
• MVR is in cm³/10 min,
• ρmelt is in g/cm³.

Example

With:

MVR = 12 cm³/10 min

and:

ρ = 0.75 g/cm³

the result is:

MFR = 12 × 0.75

MFR = 9 g/10 min

However, this simple mathematical conversion only works if a melt density suitable for the specific test is used.

Why melt density is decisive

Density provides the link between the volume-based MVR and the mass-based MFR.

This is also where one of the most common conversion errors occurs.

Not just any material density is required

The relevant value is the density of the polymer melt under the respective test conditions.

Dynisco refers to the value determined for this conversion as:

apparent melt density

.

It can be determined by performing a combined MFR/MVR test on the Melt Flow Indexer being used.

Melt density can be influenced by

• temperature,
• polymer grade,
• fillers,
• reinforcing materials,
• additives,
• material composition.

A density value determined once should therefore not be transferred uncritically to every other material batch or formulation.

Why solid-state density should not simply be used

Material data sheets frequently specify density at room temperature.

For example:

ρ = 0.90 g/cm³

However, this value describes the solid plastic and not necessarily the polymer density at a test temperature such as:

190 °C

or:

230 °C

.

The specific volume changes when the material is heated

As a result, the density also changes.

Simply inserting the solid-state density into:

MFR = MVR × ρ

can therefore lead to a systematic deviation.

For a reliable conversion, the apparent melt density should be determined for the specific material and actual test temperature or obtained using a method intended for this purpose.

Influence of test temperature

The test temperature is one of the most important parameters of a melt flow test.

As temperature increases, the viscosity of many polymer melts decreases significantly.

The material can therefore flow through the die more quickly.

An MFR value is therefore always temperature-dependent

A result of:

10 g/10 min at temperature A

must not automatically be considered equivalent to:

10 g/10 min at temperature B

.

MVR measurement is also temperature-dependent

This is because temperature simultaneously influences:

• flow behavior,
• viscosity,
• melt volume,
• melt density.

A different test temperature can therefore change both the directly measured value and the relationship between MFR and MVR.

Influence of test weight and test load

In addition to temperature, the load acting on the test piston has a major influence on the flow rate.

A larger load generates greater pressure on the polymer melt.

This typically increases material throughput through the capillary die.

The test load is therefore an essential part of the result

A value such as:

MFR = 15 g/10 min

has only limited significance without knowledge of the test conditions.

For a reproducible material assessment, the following, for example, must be clearly defined:

• material,
• test temperature,
• test weight or total load,
• test method used.

A higher test weight does not simply mean a better measurement

The test weight is not freely selected merely to produce an easily measurable value.

It must correspond to the:

• material,
• standard,
• material specification,
• comparison data set.

When are two melt flow values comparable?

Two MFR or MVR values can only be meaningfully compared if the essential test conditions are the same.

At a minimum, the following should be checked

• same material or comparable material grade,
• same test temperature,
• same test load,
• same result quantity, MFR or MVR,
• comparable test method,
• correct material preparation,
• comparable conditioning,
• valid instrument condition and test setup.

Typical error

Data sheet A specifies:

MFR = 8 g/10 min

Data sheet B:

MFR = 12 g/10 min

It is then concluded that material B clearly flows more easily.

However, if different:

• temperatures or
• test weights

were used, this direct comparison is not valid.

Consider material batch and material condition

Melt flow testing is frequently used for quality control of different material batches.

If the MFR or MVR changes between two batches, this may indicate a change in the rheological behavior of the material.

Possible causes include

• different average molecular weight,
• changed molecular weight distribution,
• polymer degradation,
• crosslinking,
• different additive concentration,
• change in filler content,
• moisture,
• material mixing,
• recycled material content.

The melt flow value initially only indicates that the flow behavior under the defined test conditions has changed.

The specific chemical or structural cause cannot be determined unequivocally from the MFR or MVR alone.

Moisture and material preparation

A reproducible melt flow test begins before the test barrel is filled.

Depending on the polymer, moisture can have a significant influence on the test result.

With moisture-sensitive or hydrolysis-sensitive plastics

water can promote polymer degradation at high temperatures.

This can cause changes in:

• molecular weight,
• viscosity,
• MFR,
• MVR

during the test.

The specified conditioning requirements must therefore be followed

Depending on the material, this may include defined drying conditions.

For batch comparisons, it is also advisable to document:

• material condition,
• drying conditions,
• storage conditions,
• time between drying and testing.

Gravimetric determination of MFR

With the gravimetric test principle, the polymer exiting the die is cut off at defined time intervals.

The individual extrudate sections are then weighed.

In simplified form

MFR = m × 600 / t

Where:

• m = mass of collected extrudate in g,
• t = collection time in s,
• 600 = conversion factor to 10 minutes.

Example

Within:

60 s

the following mass is collected:

1.2 g

of extrudate.

Then:

MFR = 1.2 × 600 / 60

MFR = 12 g/10 min

The advantage

MFR is determined directly from the actual measured mass of the extrudate.

The practical effort

primarily involves:

• cleanly cutting the extrudate,
• correct timing,
• weighing,
• handling the samples.

Volumetric determination of MVR

With the volumetric method, the movement of the piston over a defined distance is recorded.

Because the cross-sectional area of the test barrel is known, a certain piston movement corresponds to a defined displaced melt volume.

In simplified form

the displaced volume is calculated from:

piston cross-sectional area × piston travel

.

From volume and time:

MVR in cm³/10 min

is calculated.

With Dynisco Melt Flow Indexers

a digital encoder can be used to measure the piston movement.

The Dynisco LMI6000 supports this type of volumetric measurement with the corresponding test methods.

An advantage in routine operation

is that the time-consuming sequence:

cutting → collecting → weighing

can be omitted for pure MVR determination.

Determine MFR and melt density using a combined test

A combined test in which gravimetric and volumetric information are recorded simultaneously is particularly useful.

For the same material sample, both:

• mass of the extrudate and
• corresponding volume displacement

are then available.

This allows the apparent melt density to be determined

In simplified form:

ρmelt = MFR / MVR

This material-specific value can subsequently be used to calculate an equivalent MFR from the MVR in later volumetric tests.

Important

The determined apparent melt density does not automatically apply:

• at other temperatures,
• to other material types,
• to significantly changed formulations,
• to arbitrary material batches.

Dynisco explicitly points out that apparent melt density is temperature-dependent and can be influenced by fillers or reinforcing materials, for example.

Convert MVR to MFR

If the appropriate apparent melt density is known, an MVR value can be converted into an MFR value.

The basic equation is:

MFR = MVR × ρ

Example

Measured:

MVR = 20 cm³/10 min

Determined apparent melt density:

ρ = 0.72 g/cm³

Then:

MFR = 20 × 0.72

MFR = 14.4 g/10 min

Conversely

MVR can be determined from MFR and density:

MVR = MFR / ρ

With:

MFR = 14.4 g/10 min

and:

ρ = 0.72 g/cm³

the result is again:

MVR = 20 cm³/10 min

Calculation example: MFR from MVR and melt density

During a quality test, the following is measured under defined conditions:

MVR = 18 cm³/10 min

From a previous combined test, the following is known for the material at the same test temperature:

ρ = 0.76 g/cm³

Calculation

MFR = 18 × 0.76

MFR = 13.68 g/10 min

The result can be rounded to

MFR ≈ 13.7 g/10 min

However:

If a solid-state density of, for example:

0.90 g/cm³

were accidentally used, the result would be:

MFR = 18 × 0.90 = 16.2 g/10 min

The unsuitable density assumption alone would therefore create a significant deviation.

What does the melt flow index reveal about the polymer?

MFR and MVR are sensitive to changes in the rheological properties of a plastic.

For many unbranched thermoplastics, there is a relationship between:

• molecular weight,
• melt viscosity,
• melt flow.

In simplified terms, the following often applies

higher molecular weight → higher viscosity → lower MFR

and:

lower molecular weight → lower viscosity → higher MFR

However, this relationship is not universal

This is because flow behavior also depends on:

• molecular weight distribution,
• chain branching,
• additives,
• fillers,
• moisture,
• thermal history,
• shear history.

MFR should therefore not be interpreted as a direct measurement of a single molecular parameter.

MFR is not a direct viscosity measurement

A common mistake is to equate MFR with viscosity.

A high MFR often means that the material flows more easily under the test conditions used.

However, MFR is not a conventional viscosity with the unit:

Pa·s

Polymer melts are also typically non-Newtonian

Their apparent viscosity depends, among other things, on the shear rate.

A single MFR test therefore only represents one defined loading point of the material’s flow behavior.

For more comprehensive rheological characterization

capillary rheometers, for example, can be used.

These allow investigations across different:

• shear rates,
• shear stresses,
• temperatures.

An overview of corresponding solutions can also be found under Dynisco Products at ICS Schneider.

Distinguish between melt flow index and production process

MFR and MVR testing is performed under standardized laboratory conditions.

An extrusion line, on the other hand, operates under completely different rheological conditions.

In the actual process, factors include

• higher and changing shear rates,
• different pressure profiles,
• temperature gradients,
• screw geometry,
• shear heating,
• residence time,
• die resistance.

An MFR value can therefore be very useful for:

• material approval,
• batch control,
• incoming inspection,
• trend evaluation.

However, it does not directly describe the actual pressure or actual viscosity at every point in an extruder.

Relationship with melt pressure and extrusion

If the flow behavior of a polymer changes, this may also affect the melt pressure in the production process.

Under otherwise comparable process conditions, a material with a higher viscosity can, for example, cause a higher pressure drop across:

• screen packs,
• melt filters,
• adapters,
• dies.

Melt pressure therefore provides additional process information

It is measured directly in the production line and can identify changes caused, for example, by:

• clogged screens,
• changed material viscosity,
• changes in throughput,
• temperature changes.

For such applications, ICS Schneider offers, among other products, Dynisco melt pressure sensors and combined pressure/temperature sensors. One example is the Dynisco TPT463 Melt Pressure Transducer, which combines pressure and temperature measurement at the measuring point.

MFR or MVR from the laboratory and melt pressure from the production line therefore complement each other, but measure different quantities.

ISO 1133 and ASTM D1238

MFR and MVR are determined using standardized test methods.

One key standard is:

ISO 1133-1

for determining the melt mass-flow rate MFR and melt volume-flow rate MVR of thermoplastics.

Another internationally widespread standard is:

ASTM D1238

Why the standard is important

It does not merely define how the result is calculated.

For reproducible results, specifications or defined procedures for the following are important, among other things:

• test instrument,
• test barrel,
• piston,
• die,
• temperature,
• load,
• preheating time,
• test procedure,
• evaluation.

Two results are therefore not automatically comparable simply because both test reports state “MFR”.

The test standard and specific test conditions must also match or be permissible for the respective material specification.

Factors influencing repeatability

At first glance, a melt flow test appears mechanically simple.

In reality, numerous details can influence repeatability.

Typical influencing factors include

• temperature stability in the test barrel,
• correct test weight,
• material quantity,
• material compaction,
• air inclusions,
• preheating time,
• condition of the die,
• cleanliness of barrel and piston,
• timing of extrudate cutting,
• scale resolution,
• piston travel measurement,
• material moisture,
• thermal aging of the material during the test.

Automation can reduce operator influence

The Dynisco LMI6000 features, among other things, automated weight handling and supports different test methods depending on its configuration.

A digital encoder enables volumetric measurement of piston movement, while an automatic cutting unit can produce reproducible extrudate sections for the corresponding test methods.

Typical errors in MFR and MVR testing

Observation	Possible cause	Recommended check
MFR values from two data sheets differ significantly	different temperature or test weight	compare complete test conditions
MFR and MVR have similar numerical values and are assumed to be identical	mass and volume have been confused	check units g/10 min and cm³/10 min
MFR calculated from MVR does not match gravimetric MFR	unsuitable melt density used	determine apparent melt density under test conditions
Conversion systematically gives an excessively high value	solid-state density used instead of melt density	check density basis
Measured value increases during repeated testing of the same sample	possible thermal or hydrolytic degradation	check drying, residence time and temperature
Large scatter between repeated measurements	different material compaction or air inclusions	check filling and compaction procedure
MFR unexpectedly high	material degradation, lower viscosity or incorrect test load possible	check material condition, temperature and weight
MFR unexpectedly low	higher viscosity, incorrect temperature or contaminated die	check temperature and test die
Several batches cannot be compared reproducibly	different conditioning	standardize drying and material preparation
MVR changes although the material is nominally the same	batch difference or changed melt density	perform combined MFR/MVR test
Laboratory value is stable but extrusion pressure still changes	process-related cause rather than material characteristic	check temperature, screen condition, throughput and die
Production pressure is stable but MFR is outside specification	process compensates for material change	evaluate laboratory value and process parameters separately

Practical example: incoming inspection of two batches

The supply agreement for a granulate specifies:

MFR = 10 ± 1 g/10 min

at a defined test temperature and test load.

Batch A

produces:

10.3 g/10 min

Batch B

produces:

13.1 g/10 min

Under identical, standardized test conditions, the second batch therefore indicates a change in flow behavior.

However, this does not automatically mean

that the cause is known.

Possible reasons may include:

• material degradation,
• different molecular weight distribution,
• formulation change,
• material mixing.

Here, MFR serves as a quick quality characteristic rather than a complete material analysis.

Practical example: MFR and MVR appear contradictory

A material is measured with:

MFR = 11.0 g/10 min

and:

MVR = 14.5 cm³/10 min

At first glance, these appear to be two different melt flow values.

Calculation of apparent melt density

ρ = MFR / MVR

ρ = 11.0 / 14.5

ρ ≈ 0.759 g/cm³

Therefore:

14.5 cm³/10 min × 0.759 g/cm³ ≈ 11.0 g/10 min

Result

The two values do not contradict each other.

They describe the same material flow once as:

mass per time

and once as:

volume per time

.

Practical example: temperature not taken into account

Laboratory A reports for a material:

MFR = 7 g/10 min

Laboratory B:

MFR = 11 g/10 min

An instrument error is initially suspected.

However, examination of the test records reveals

that different test temperatures were used.

The two results are therefore not directly comparable.

For a comparative test, the following must therefore be used

• identical temperature,
• identical load,
• comparable material condition,
• the same relevant test standard.

The test conditions therefore always form an integral part of the MFR or MVR value.

Systematically prepare a melt flow test

1. Clearly identify the material: Document polymer type, material designation and batch.
2. Determine the test specification: Define the material standard, customer specification or test standard.
3. Select the measured quantity: Define MFR, MVR or combined MFR/MVR determination.
4. Specify the test temperature: Do not choose it freely; use the value specified by the applicable test requirement.
5. Determine the test load: Use the specified weight or total load.
6. Condition the material: Follow the required drying and storage conditions.
7. Clean the test instrument: Check barrel, piston and die for residues.
8. Stabilize the temperature: Allow the specified test conditions to be fully reached.
9. Fill the correct amount of material: Ensure uniform filling.
10. Minimize air inclusions: Compact the material according to the specified procedure.
11. Observe the preheating time: Do not expose the material to heat for too short or unnecessarily long a period.
12. Perform the test: Apply the gravimetric, volumetric or combined method according to the specification.
13. For MFR, weigh the extrudate correctly: Check the scale and cutting intervals.
14. For MVR, record piston travel correctly: Check the encoder or displacement measurement.
15. Use melt density for conversions: Do not use an unverified solid-state density.
16. Evaluate repeated measurements: Check scatter and plausibility.
17. Fully document the result: Specify MFR/MVR, unit, temperature, test weight, standard, material and batch.

Suitable Dynisco testing equipment at ICS Schneider

Dynisco LMI6000

The Dynisco LMI6000 is an automated melt flow indexer for laboratory, quality control and production-related material testing.

ICS Schneider specifies, among other things:

• support for test methods A, A/B, B, C and D depending on the version,
• compliance or performance in accordance with ASTM D1238, ASTM D3364, ISO 1133-1 and other test standards,
• electromechanical Auto-Lift system for automated weight handling,
• digital encoder for volumetric measurement of piston movement,
• automatic sample cutting,
• temperature control of ±0.1 °C,
• operating temperature up to 400 °C,
• weights from 0.325 to 31.6 kg,
• 10.2″ touchscreen,
• connection of external scales,
• USB, network and data functions.

Particularly for recurring quality tests

automated weight handling can reduce operator influence and standardize the testing procedure for series measurements.

Dynisco LMI5000

The Dynisco LMI5000 is also designed for the characterization of plastics and polymer materials.

ICS Schneider specifies, among other things:

• determination of melt flow index and melt flow,
• determination of apparent melt density,
• support for international standards such as ASTM D1238 and ISO 1133,
• temperature range up to 500 °C,
• temperature control ±0.1 °C,
• digital encoder as an option for volumetric testing,
• weights from 0.325 to 31.6 kg,
• USB and scale interface.

Dynisco melt pressure sensor technology for the production process

While LMI test instruments determine material characteristics under defined laboratory conditions, additional process variables are required in extrusion lines.

Under Dynisco Products, you will therefore also find:

• melt pressure sensors,
• melt pressure transmitters,
• melt temperature sensors,
• indicators and controllers,
• capillary rheometers.

This allows laboratory testing and actual process monitoring to complement each other effectively from a technical perspective.

Conclusion

MFR and MVR are among the most important characteristics for quickly evaluating the flow behavior of thermoplastic materials. Both quantities are based on the same fundamental melt flow test but consider material throughput from different perspectives.

MFR describes mass per unit of time

MFR is specified in:

g/10 min

.

MVR describes volume per unit of time

MVR is specified in:

cm³/10 min

.

Melt density links the two values

Under identical test conditions:

MFR = MVR × ρmelt

An appropriate apparent melt density at the actual test temperature must be used for the conversion.

Temperature and test weight are part of the measurement result

An MFR or MVR value without knowledge of the test conditions has only limited significance for a technical comparison.

The material condition also matters

Batch, moisture, thermal history, fillers and material degradation can change the flow behavior.

The melt flow index does not replace complete rheological characterization

MFR and MVR provide a defined comparative value. They do not describe the complete flow behavior of a polymer across different shear rates and process conditions.

Laboratory values and the production process should be considered together

MFR and MVR can be used, for example, for incoming inspection and batch control. Melt pressure, temperature and other process variables, on the other hand, indicate what is actually happening in the extrusion line.

For practical applications

Identify material and batch → define the test standard → select MFR or MVR → apply the specified temperature and test load → condition the material correctly → clean and stabilize the test instrument → fill the sample reproducibly → determine MFR gravimetrically or MVR volumetrically → use the apparent melt density at the test temperature for conversions → check repeatability → always document the result together with temperature, load, standard and material information.

FAQ: Correctly Evaluate MFR, MVR and Melt Flow Index

What does MFR mean?

MFR stands for Melt Mass-Flow Rate and describes the mass of a polymer melt that flows through a test die under defined test conditions within a period normalized to ten minutes.

In which unit is MFR specified?

Typically in g/10 min.

What does MVR mean?

MVR stands for Melt Volume-Flow Rate and describes the volume of polymer melt that flows through the test die under defined test conditions within a period normalized to ten minutes.

In which unit is MVR specified?

Typically in cm³/10 min.

What is the difference between MFR and MVR?

MFR is mass-based, while MVR is volume-based. Both values describe the flow behavior of the same polymer melt from different perspectives.

Is MFI the same as MFR?

MFI is frequently used as a general or historical term for the melt flow index. For an unambiguous technical specification, however, a distinction should be made between MFR and MVR.

Can I compare MFR and MVR directly?

Not simply as numerical values because they use different units. Both quantities can be related to each other under identical test conditions using the melt density.

What is the relationship between MFR and MVR?

In simplified form, MFR = MVR × ρmelt.

How do I calculate MVR from MFR?

Using MVR = MFR / ρmelt.

Which density is required for the conversion?

An appropriate apparent melt density of the material at the respective test temperature is required.

Can I use the density from the material data sheet?

A solid-state density specified at room temperature should not be used without verification because the density of the polymer changes in the molten state and with temperature.

Why does density change when heated?

The specific volume of the polymer changes with temperature. This also changes its density.

Is melt density constant for every polymer?

No. It depends, among other things, on temperature, polymer grade, additives, fillers and material composition.

Why is the test temperature important for MFR?

The temperature influences the viscosity of the polymer melt and therefore directly affects the flow rate through the test die.

Can I compare MFR values measured at different temperatures?

Not directly. The specified test conditions must be taken into account for a reliable comparison.

Why is the test weight important?

The weight applies a load to the piston and therefore pressure to the melt. A different test load typically results in a different flow rate.

Can I simply use a larger test weight?

No. The test load must be selected in accordance with the relevant standard or material specification.

What information should be specified together with the MFR value?

For an unambiguous technical assessment, the material, test temperature, test load and applied test specification or standard should in particular be known.

When are two MFR values comparable?

When they have been determined under comparable or identical test conditions specified for the material.

Does the material batch affect MFR?

Yes. Differences in molecular structure, additives, fillers, material degradation or composition can result in a changed MFR.

Can moisture affect MFR?

Yes. Particularly with hydrolysis-sensitive polymers, moisture can cause polymer degradation during heating and thereby alter the flow behavior.

Does plastic need to be dried before an MFR test?

This depends on the material and the specified test conditions. Required conditioning and drying conditions must be observed.

What does a high MFR mean?

Under identical test conditions, a higher MFR means that more material mass flows through the test die. This often corresponds to a lower-viscosity melt, although the precise interpretation depends on the polymer.

What does a low MFR mean?

Under identical test conditions, less material flows through the test die. This may, for example, be associated with higher melt viscosity.

Can I directly determine molecular weight from MFR?

Not in general. MFR can correlate with molecular weight but is additionally influenced by molecular weight distribution, branching, additives and other material properties.

Is MFR a viscosity?

No. MFR is an empirical flow characteristic in g/10 min and not a viscosity in Pa·s.

Why is an MFR value insufficient for complete rheological characterization?

Polymer melts exhibit shear-rate-dependent behavior. An MFR test only captures behavior under one defined combination of temperature, load and test die geometry.

What is apparent melt density?

It is the density or correlation quantity determined under the specific test conditions for the relationship between volumetric and gravimetric melt flow.

How can apparent melt density be determined?

It can be determined using a combined test in which MFR and volumetric piston movement are recorded for the same material sample.

Can a melt density determined once always be reused?

Only if the material and test conditions remain sufficiently comparable. Changes in temperature or material formulation in particular must be taken into account.

What is the gravimetric test method?

The extrudate is collected at defined intervals and weighed. MFR in g/10 min is then calculated from this mass.

What is the volumetric test method?

The piston movement is measured and used to determine the displaced melt volume per unit of time. The result is MVR in cm³/10 min.

Why can MVR be useful in routine testing?

Volumetric measurement can be performed without manually cutting and weighing each extrudate section, thereby reducing operator influence.

Which standard applies to MFR and MVR?

A key international standard is ISO 1133-1 for determining the melt mass-flow rate MFR and melt volume-flow rate MVR of thermoplastics. ASTM D1238 is also widely used.

Are ISO 1133 and ASTM D1238 identical?

No. Both cover melt flow testing, but the specific requirements and procedures must be considered according to the standard applicable in each case.

Why do my repeated MFR measurements fluctuate?

Possible causes include temperature deviations, different material compaction, air inclusions, cutting errors, scale effects, moisture, contamination or thermal changes to the sample.

Why must the test die be clean?

Residues alter the effective flow geometry and can therefore affect material flow and the test result.

Why must the test barrel be clean?

Material residues can affect friction, piston movement, contamination and the thermal conditions of the next test.

Can MFR be used for incoming inspection?

Yes. Under defined test conditions, it is very suitable for comparing material batches against a specified requirement.

Can MFR detect contamination?

Contamination or material mixing can change the MFR. However, MFR alone does not unequivocally identify the cause of the change.

What does MFR have to do with melt pressure in an extruder?

Both quantities respond to the flow behavior of the polymer but are measured under completely different conditions. Melt pressure is an actual process variable, while MFR and MVR are standardized laboratory characteristics.

Can a stable MFR guarantee a stable extrusion process?

No. The process is additionally influenced by temperature, throughput, screw condition, screen pack, die, pressure and many other parameters.

What is a melt pressure sensor used for?

It measures the actual pressure of the polymer melt in the extruder, adapter, filter or die and is therefore used for process monitoring or control.

What is the Dynisco LMI6000?

The LMI6000 is an automated melt flow indexer for characterizing polymer materials and, depending on the version, supports different gravimetric and volumetric test methods.

Can the LMI6000 determine MVR?

Yes. A digital encoder enables volumetric measurement of piston movement with the corresponding test methods.

What temperature range does the LMI6000 have?

ICS Schneider specifies an operating range from ambient temperature up to 400 °C.

What temperature control does the LMI6000 provide?

ICS Schneider specifies temperature control of ±0.1 °C.

Which test weights are available for the LMI6000?

ICS Schneider specifies a weight range from 0.325 to 31.6 kg.

Which standards does the LMI6000 support?

ICS Schneider specifies, among others, ASTM D1238, ASTM D3364 and ISO 1133-1 as well as additional international standards.

What is the Dynisco LMI5000?

The LMI5000 is a melt flow indexer for determining melt flow and additional material properties of plastics.

Can the LMI5000 determine apparent melt density?

Yes. Depending on its configuration, the instrument can be used for combined MFR/MVR testing and for determining apparent melt density.

Where can I find the Dynisco LMI6000 at ICS Schneider?

Further information is available under Dynisco LMI6000 at ICS Schneider.

Where can I find the Dynisco LMI5000 at ICS Schneider?

Further information is available under Dynisco LMI5000 at ICS Schneider.

Where can I find Dynisco melt pressure sensors?

An overview of the available sensor and testing technology can be found under Dynisco Products at ICS Schneider.