Melt Flow Index Tester: ISO 1133 Principle, Testing Method & Applications

Introduction

A Melt Flow Index Tester is a laboratory instrument used to measure the flow features of molten thermoplastic materials under specified temperature and load conditions. It measures how much polymer passes through a standard die within a defined period, helping manufacturers test raw material stability, processability and quality. The test is especially important in plastic manufacturing, injection moulding, extrusion and polymer quality control.

The internationally recognised ISO 1133 standard describes methods for finding Melt Mass Flow Rate (MFR) and Melt Volume Flow Rate (MVR). ASTM D1238 is another widely used standard for measuring the melt flow properties of thermoplastic materials. These tests help plastic processors compare material batches and identify differences that can affect manufacturing performance.

What is the Principle of a Melt Flow Index Tester?

The working principle of a Melt Flow Index Tester is based on extruding molten polymer through a standard capillary die using a controlled temperature and already set load.

The instrument includes a heated barrel, piston, standard die and calibrated weights. A measured quantity of plastic granules is put into the heated barrel, where the material melts and becomes suitable for extrusion. A piston applies pressure through the selected test load, forcing the molten polymer through the die.

The amount of material extruded over a specified time is measured to show its melt flow rate.

A higher flow rate generally shows lower melt thickness under the specified test conditions, while a lower flow rate shows greater resistance to flow. This information helps manufacturers check thermoplastic flow behaviour and maintain stability between production batches.

How Does ISO 1133 Melt Flow Index Testing Work?

ISO 1133 provides a standardized approach to test the melt flow properties of thermoplastics.

The current ISO 1133-1:2022 standard specifies two measurement procedures:

• Procedure A (Mass Measurement): The extruded polymer is collected over set time intervals, cut into portions and weighed. The measured mass is used to calculate MFR in grams per 10 minutes.

• Procedure B (Displacement Measurement): The movement of the piston over a specified time is measured with MVR in cubic centimetres per 10 minutes.

ISO 1133-2 helps in finding materials whose flow behaviour is greatly affected by moisture or time temperature history. The suitable standard and procedure should be selected according to the polymer being tested.

What Is the Melt Flow Index Testing Procedure?

A reliable MFI test requires controlled preparation, temperature stabilisation and continuous measurement conditions. The general testing sequence involves:

1. Sample preparation: Take a representative polymer sample and prepare it according to the material specification. Moisture sensitive materials may require proper drying.

2. Temperature setting: Set the barrel temperature according to the prescribed polymer testing conditions.

3. Sample loading: Introduce the required quantity of polymer into the heated barrel.

4. Preheating: Allow the sample to reach the specified thermal condition while following the specified preheating time.

5. Load application: Position the piston and apply the specified test weight.

6. Extrusion: Allow the molten polymer to pass through the standard die.

7. Measurement: Collect and weigh the extruded material for Procedure A, or record piston displacement for Procedure B.

8. Result calculation: Calculate and report the MFR or MVR along with the test temperature and applied load.

Following the specified procedure is important because differences in temperature, sample moisture, preheating time and applied load can affect the final result.

How Is Melt Flow Index Calculated?

For Procedure A, the melt mass flow rate is calculated using:

MFR = (m × 600) / t

Where:

• MFR = Melt Mass-Flow Rate (g/10 min)

• m = Average mass of extruded polymer (g)

• t = Cutting time interval (seconds)

• 600 = Conversion factor for 10 minutes

For example, if 0.25 grams of polymer is collected in 30 seconds:

MFR = (0.25 × 600) / 30 = 5 g/10 min

The result should always be reported with its test temperature and load, as the same polymer can produce different flow values under different testing conditions.

For Procedure B, MVR is calculated from the piston displacement and the cross sectional area of the barrel over the specified time.

What Is the Difference Between MFI, MFR and MVR?

MFI is the commonly used industry term for melt flow index, while MFR and MVR are the specific measurement terms used in ISO 1133.

• MFI: Commonly used to describe the melt flow characteristics of a thermoplastic material.

• MFR: Measures the mass of molten polymer extruded over 10 minutes, expressed in g/10 min.

• MVR: Measures the volume of molten polymer extruded over 10 minutes, expressed in cm³/10 min.

MFR and MVR are related, but they are not interchangeable without thinkin of the polymer's melt density at the test temperature. MVR can be especially useful when comparing filled and unfilled polymers.

Which Plastic Materials Can Be Tested Using an MFI Tester?

A suitable Melt Flow Index Tester can test a wide range of thermoplastic materials, provided the instrument setup and testing conditions are suitable.

Common materials include:

• Polypropylene (PP)

• High-Density Polyethylene (HDPE)

• Low-Density Polyethylene (LDPE)

• Linear Low-Density Polyethylene (LLDPE)

• Other polyethylene grades and suitable thermoplastic resins

MFI testing of polypropylene and polyethylene is commonly used in raw material inspection. It is also related to plastic granule testing and recycled plastic quality testing, where changes in flow behaviour can show differences in material behaviour or processing history.

Why Is Melt Flow Index Testing Important in Plastic Manufacturing?

Melt flow testing supports quality control throughout the polymer processing industry. Injection moulding manufacturers use MFI results to check if incoming resin has suitable flow properties for their production requirements. Extrusion manufacturers use these measurements to monitor material stability and find changes between batches.

Other important uses include:

• Incoming inspection of plastic raw materials.

• Comparing polymer grades from different suppliers.

• Monitoring recycled plastic material consistency.

• Test possible polymer degradation.

• Supporting thermoplastic processing and quality assurance.

However, MFI is a standardised quality control measurement, not a complete rheological analysis. Actual processing behaviour also depends on shear rate, temperature, equipment design and other material properties.

What Should You Check Before Selecting a Melt Flow Index Tester?

When selecting polymer testing equipment, check its measurement capability and compatibility with the suitable standard.

Important factors include temperature range and accuracy, barrel and piston dimensions, standard die dimensions, available test weights, measurement resolution and temperature control.

Perfect Group India offers Melt Flow Index Testing Equipment for laboratories and plastic manufacturing quality control use.

Its PMFIT-07 Melt Flow Index Tester features a temperature range of ambient to 400°C, temperature accuracy of ±1°C and a least count of 0.1°C. The listed configuration includes standard test weights and a die measuring 2.095 mm × 8 mm.

Choose the Right Melt Flow Index Tester for Your Laboratory

Continued polymer testing starts with reliable measurement conditions and suitable testing equipment. A Melt Flow Index Tester helps manufacturers test thermoplastic flow characteristics, compare raw material batches and strengthen quality control processes.

Explore the Melt Flow Index Tester by Perfect Group India for your plastic and polymer testing requirements. Contact our team to discuss instrument specifications, available features setup and your laboratory's testing needs.