MFI (Melt Flow Index), along with its subcategories MFR (Melt Mass-Flow Rate) and MVR (Melt Volume-Flow Rate), is one of the key indicators in understanding the behavior of thermoplastic materials. This data gives us insight into how well the material flows in the molten state – which is extremely important in its industrial processing.
So if you mold, inject or extrude plastic, then knowing MFI will save you a lot of time and trouble.
1. What is MFI and what does it tell us?
MFI represents the amount of material that flows out of a heated device under a specific force in a certain time. It is measured in grams per 10 minutes (g/10 min), which means how much mass of molten plastic flows through the capillary.
A higher MFI means a more fluid mass (lower viscosity), while a lower MFI means a denser, more difficult-to-flow material.
2. How is MFI measured?
The measurement is performed in a device called a plastometer. A heated polymer sample is placed in it, and a weight (e.g. 2.16 kg) is placed above it, which presses on it via a piston. Below a temperature adapted to the material, the molten mass begins to be extruded through a narrow capillary.
Process A involves weighing the amount of extruded material every few seconds, while Process B involves monitoring the piston movement. Based on this data, the MFR or MVR is calculated.
3. Why is MFI important?
Because it affects the choice of processing technology! If you are using injection molding to produce thin walls or complex shapes, you will want a material with a higher MFI. On the other hand, extruding pipes or profiles requires more viscous masses with a lower MFI.
MFI is also a great indicator of quality between different batches of material – if the value varies too much, something is wrong.
4. Factors affecting MFI
– Molecular weight: Higher means a denser mass and lower MFI.
– Temperature: Higher temperature reduces viscosity and increases MFI.
– Presence of additives: Fillers, stabilizers and recycled components can change the flow of the mass.
5. MFI Measurement Equipment
Simple but very accurate equipment is used to measure MFI:
– Heated barrel
– Piston and weight (standard weights, e.g. 2.16 kg)
– Capillary (die), usually 8 mm long and 2.1 mm wide
– Thermometer or PRT sensor for precise temperature
– Unit of measurement for mass or displacement
All together, it allows you to simulate how the material will behave in real production.
6. Conclusion
MFI is not just a number – it is the key to stable production, correct material selection and better product quality. By understanding this property, you can solve problems faster and improve the efficiency of the entire plastics processing process.
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