How to Measure Melt Flow Index: Methods, Machines, and Standards

The Melt Flow Index (MFI) is one of the most important parameters for understanding the flow characteristics of thermoplastic polymers. Whether you are working in plastics manufacturing, quality control, or polymer research, measuring the melt flow index accurately ensures consistency, process efficiency, and product quality. In this guide, we will explore how to measure melt flow index, the machines used, standard methods, and essential formulas.

What is Melt Flow Index?

The Melt Flow Index (MFI), sometimes called Melt Flow Rate (MFR), measures the ease of flow of melted thermoplastic polymers through a standardized die under controlled temperature and load. It reflects the molecular weight, viscosity, and processability of the plastic material.

A higher MFI indicates that the plastic melts and flows easily, making it suitable for injection molding, while a lower MFI implies higher viscosity and better mechanical strength.

Why Measuring Melt Flow Index is Important

• Quality Control: Ensures consistency between batches of plastic materials.
• Process Optimization: Helps determine suitable processing temperatures for extrusion and molding.
• Material Comparison: Assists in selecting polymers with desired flow properties for specific applications.
• Compliance: Meets industrial standards like ASTM D1238 and ISO 1133.

Without accurate MFI measurement, manufacturers risk producing inconsistent products that may fail in applications like packaging, automotive parts, or consumer goods.

Methods of Measuring Melt Flow Index

The Melt Flow Index Test is a standardized procedure, and the method depends on the type of polymer and equipment used. The primary methods include:

1. Gravimetric Method

This is the most common method for measuring MFI.

• A specific weight is applied to the polymer melt inside the barrel of the plastic melt flow index tester.
• The polymer is extruded through a standardized die at a controlled temperature.
• The extrudate is collected for a fixed time (usually 10 minutes) and weighed.
• MFI Formula:

MFI (g/10 min) = Weight of extrudate (g) ÷ Time (10 min)

This method provides the flow rate in grams per 10 minutes, which is widely used in laboratories and production lines.

2. Volumetric Method

• Instead of weighing, this method measures the volume of polymer extruded in a specific time.
• Suitable for polymers with very low or high flow properties where weighing may be difficult.

3. Capillary Rheometer Method

• A more advanced method where a melt flow index machine applies varying pressures and temperatures.
• Provides detailed flow curves and viscosity data, which is helpful for high-performance polymers.

Equipment Used: Melt Flow Index Machine

A Melt Flow Index Tester is the standard instrument used for measuring MFI. Key components include:

• Barrel: Heats the polymer to its melting temperature.
• Piston/Plunger: Applies a constant load to push the polymer through the die.
• Die: Standardized orifice for measuring flow.
• Collector: Collects extrudate for weighing or volume measurement.
• Digital Display: Shows MFI readings (for modern digital models).

Types of MFI Testers

1. Manual Melt Flow Index Tester: Affordable and suitable for small labs.
2. Semi-Automatic Tester: Reduces human error in timing and weighing.
3. Automatic/Digital Tester: High precision, programmable temperature, and load control.

Choosing a Melt Flow Index Tester Manufacturer

When selecting a melt flow index tester manufacturer, consider:

• Compliance with ASTM D1238 and ISO 1133 standards
• Digital or automatic features for accurate readings
• Local service support and spare parts availability
• Affordable melt flow index tester price
• Proven track record in polymer testing solutions

Reputable manufacturers provide both equipment and calibration services, ensuring reliable and repeatable measurements.

Steps to Measure Melt Flow Index

1. Sample Preparation: Dry the polymer pellets to remove moisture.
2. Set Temperature: Adjust the barrel to the polymer’s recommended melting point.
3. Load Sample: Place the polymer into the heated barrel.
4. Apply Weight: Use the specified load (weight) on the piston.
5. Extrusion: Allow polymer to flow through the die.
6. Collection: Collect extrudate for a set time and weigh it.
7. Calculate MFI: Use the MFI formula to get the value in g/10 min.

Repeat the test at least three times for accuracy and consistency.

Standards for Melt Flow Index Testing

• ASTM D1238: Standard Test Method for Melt Flow Rates of Thermoplastics by Extrusion Plastometer.
• ISO 1133: Specifies the method for determining melt mass-flow rate and melt volume-flow rate of thermoplastics.
• GB/T 3682: Chinese standard equivalent.

Following these standards ensures reproducibility and comparability across laboratories and industries.

Factors Affecting Melt Flow Index

1. Temperature: Higher temperature reduces viscosity and increases MFI.
2. Load/Weight: Increasing weight increases flow rate.
3. Polymer Type: Molecular weight and additives affect melt behavior.
4. Moisture Content: Wet polymers can reduce accuracy and cause degradation.

Careful control of these factors ensures reliable results.

Melt Flow Index Tester Price

The price of a melt flow index tester depends on type, features, and manufacturer:

Investing in a reliable tester is crucial, as inaccurate measurements can lead to production issues and quality failures.

Conclusion

Measuring Melt Flow Index is a fundamental step in plastic quality control. Using the right plastic melt flow index tester, following standard methods, and understanding the MFI formula ensures accurate, consistent results. By partnering with a reliable melt flow index tester manufacturer, companies can optimize polymer processing, maintain product consistency, and meet industry standards.

For purchasing high-quality melt flow index machines or consulting about tester price, you can contact industry experts and authorized suppliers. 📞 +91 9210 903 903 📧 info@prestogroup.com