How Does a Melt Flow Index Tester Measure the Flow Properties of Thermoplastics?

The test is commonly used for:

• Incoming raw material inspection
• Batch-to-batch quality control
• Polymer comparison
• Research and development
• Process monitoring
• Material selection
• Checking compliance with applicable specifications

For manufacturers working with thermoplastics, regular MFI testing can therefore become an important part of maintaining consistent production quality.

How Does a Melt Flow Index Tester Work?

The working principle of a Melt Flow Index Tester is relatively straightforward. The instrument consists mainly of a heated barrel, piston, standard die, and a system for applying a specified load.

First, the barrel is heated to the required test temperature. The selected thermoplastic sample is then introduced into the barrel.

The material is allowed to melt under controlled conditions. Once the sample has reached the required temperature and is ready for testing, a specified load is applied to the piston.

The pressure created by the load pushes the molten polymer through the small die positioned at the bottom of the barrel.

As the polymer exits the die, the extruded material is collected and measured over a specified time. Depending on the testing procedure, the extrudate may be cut at defined intervals and weighed.

The amount of polymer that flows through the die during the specified period is then used to determine the Melt Flow Rate.

Understanding the Test Result

The MFI value gives manufacturers a simple way to compare the flow behaviour of different thermoplastic materials.