How does a melt flow index tester measure the melt flow properties of a polymer?

Reviewed by Anurag Mishra (Sr. Technical Consultant)

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The measurement of melt flow properties is a critical aspect in the characterization of polymers, providing valuable insights into their processing behaviour and end-use applications. 

At the forefront of this analysis is the melt flow index (MFI) tester, a high-quality lab testing instrument designed to quantify the flow ability of molten polymers under specific conditions. 

This MFI tester operates on a principle that involves extruding a standardized amount of polymer through a precisely calibrated capillary under controlled temperature and pressure conditions. In this blog, we will focus on how you can easily measure the melt flow properties of polymers. So, let us get started!

Introduction to Melt Flow Index Testing

Melt flow index (MFI) testing is a widely embraced technique within the plastics industry, serving as a crucial method for assessing the viscosity and flow properties of polymer melts. 

This pivotal test holds significance in enabling manufacturers to gain comprehensive insights into the behaviour of their plastic materials throughout the processing stage and in their ultimate performance in end-use applications. The primary objective of conducting melt flow index testing is to precisely quantify the fluidity and viscosity characteristics inherent in polymers. 

This information becomes instrumental for manufacturers in evaluating the suitability of their materials for specific manufacturing processes and verifying compliance with stringent quality standards. 

Notably, different manufacturing processes may necessitate materials with varying melt flow indexes, thereby emphasizing the versatility of this testing methodology. Additionally, by scrutinizing the melt flow index of plastic resins before their transformation into final products, manufacturers can uphold a consistent and high-quality production process.

What is a Polymer and why are Melt Flow Properties Important?

In the realm of plastics and materials science, the term "polymer" is frequently encountered, but what exactly does it signify? In straightforward terms, a polymer constitutes a large molecule constructed from recurring units known as monomers. These monomers intricately link together, forming extended chains and giving rise to the structure of a polymer.

Polymers manifest in diverse forms, spanning the realms of both natural and synthetic materials. Examples of natural polymers encompass rubber, silk, and cellulose, while synthetic polymers, such as those found in everyday items like plastic bottles, bags, and packaging materials, are crafted through human ingenuity.

Having defined the nature of polymers, it's pertinent to explore the significance of melt flow properties in comprehending these materials. Melt flow properties elucidate a polymer's ability to flow when subjected to heat, a critical attribute that profoundly influences the quality and uniformity of products manufactured from these materials.

The widely employed melt flow index (MFI) test serves as a key method for gauging this property. The process involves the controlled heating of a small quantity of polymer resin until it reaches its melting point, followed by its passage through a standardized orifice under constant pressure. The ensuing measurement of the molten polymer's flow rate through the orifice is recorded as its melt flow rate (MFR) or melt index (MI).

Now, let us discuss some easy-to-follow steps to measure the melt flow properties of polymers.

How to measure the melt flow properties of polymers with an MFI tester?

You can easily measure the MFI properties of polymers by following the steps mentioned below:

  • Turn the machine ON and set the SV value on the PID controller.

  • After setting the temperature and timer, turn the heater on by pressing the heater on the switch.
  • Wait for the reading in the PV display in the PID controller to reach the value of the SV display.
  • After the required temperature for the test has been attained, fil the barrel of the machine with the plastic granules you want to test.

  • Poke the granules with the plunger after they are inserted into the barrel. This will ensure close packing of the granules and eliminate the air between the granules.
  • When the granules are inserted in the barrel, there will be a slight decrease in the PV value on the PID monitor. Wait for this value to again reach the SV value. We also need to preheat the granules before starting the test.
  • Once the PV and SV values are the same, place the plunger provided with the machine along with the dead weight on it into the barrel.
  • After placement of the plunger, there will be extrudate coming out of the die/orifice placed in the lower end of the barrel.

  • When the time cycle on the digital timer is complete, the cutter will automatically cut the extrudate from the barrel. This can also be done manually, if the machine is set on the manual operation.
  • Weigh the extrudate cut from the barrel using a digital balance. This weight will be used for calculating the Melt Flow Index of the sample.

Calculate the MFI using the formula:

MFI = Weight of sample in gm/ 10 min.

In this way, you can easily conduct melt flow index tests on the materials and ensure that accurate products will be delivered to the customers. If you want to know more about this testing instrument, then you can give us a call at +91 9313 140 140 or email us at Our team of experts will consult you regarding all your needs and queries.

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