Importance of Melt Flow Index Testing in Polymers

Polymers are used in manufacturing a wide range of products. A good quality polymer can bring profit and branding, whereas low-quality polymer can bring safety issues, sales loss, and downfall in branding. Hence, an efficient polymer test method is used by manufacturers to rank the polymer material by evaluating its melt flow properties.

Why is polymer testing required?

The use of melt flow index (MFI) test, which is also known by the name of melt flow rate (MFR) test, dates back to the preliminary time of polymer science and material categorization. This testing method may seem very basic but is the best technique to rank the polymer samples as per its test results. Many polymer processors give high importance to this evaluation based ranking. Moreover, medical device, food, and pharmaceutical packaging manufacturers have set polymer melt flow testing as their clearance criteria for suppliers. They use the test results as benchmarks to ensure that the material will match the intended behaviour during its processing, extrusion or injection moulding.

How is the test conducted?

The MFI tester is an accurate testing instrument which is used to calculate the polymer mass extruded through a capillary die at a particular temperature and applied force. The testing sample can be a virgin resin or material from a finished thermoplastic product. The specimen is loaded into the preheated barrel of the tester along with a piston. A specified amount of load is kept on the piston for the application of force. When the appropriate condition is reached the specimen starts melting and starts flowing out from the capillary die. After cooling down, the extruded polymer sample weighed. The test results are then computed, which is the weight of sample flown in 10 minutes of time.

Characteristics determination of polymer by MFI test

Distinct useful characteristics of polymers are determined by testing the flow properties of the material. The melt viscosity of a polymer during the test is inversely proportional to its flowing behavior. More the polymer is viscous, slower will be the flow. The test data can also be linked to the molecular weight of the sample. Long chain polymer requires more time to get pushed through the capillary and thus have a slow flowing nature. Data related molecular weight distribution can also be taken by performing the test at the same temperature with distinct load application. Also, the shear viscosity of a particular sample can be computed by applying an inversely proportional relationship. The reasons behind opting for an MFI test over other techniques for evaluation of these properties are its promptness and its cost-effective nature.

Maybe the melt flow index testing appears to be basic and is sometimes not opted over the complicated and latest technologies, but it can deliver highly accurate and analytic test results complying all the test requirements.

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