Importance of melt index testing in polymers

Polymers are used in the manufacture of a wide variety of products. A good quality polymer can bring profit and branding, while low quality polymer can cause safety problems, loss of sales and ruin in branding. Therefore, an efficient polymer test method is used by manufacturers to rank the polymer material by evaluating melt flow properties.

Why are polymer tests required?

The use of the melt flow index (MFI) test, also known as the melt flow rate (MFR) test, dates back to the preliminary days of polymer science and materials categorization. This test method may seem very basic, but it is the best technique to rank the polymer samples based on the test results. Many polymer processors place great importance on this evaluation-based ranking. In addition, medical device, food and pharmaceutical packaging manufacturers have instituted polymer melt flow testing as their supplier approval criteria. They use the test results as benchmarks to ensure that the material matches the intended behavior during processing, extrusion or injection molding.

How is the test performed?

The MFI tester is an accurate testing instrument used to calculate the polymer mass extruded through a capillary die at a certain temperature and applied force. The test sample may be a virgin resin or a finished thermoplastic material. The sample is loaded into the preheated cylinder of the tester along with a piston. A certain amount of load is held on the piston for the purpose of applying force. When the correct condition is reached, the sample begins to melt and begin to flow out of the capillary die. After cooling, the extruded polymer sample was weighed. The test results are then calculated, which is the weight of the sample flown in 10 minutes.

Characteristic determination of polymer by MFI test

Various useful properties of polymers are determined by testing the flow properties of the material. The melt viscosity of a polymer during the test is inversely related to its flow behavior. The more viscous the polymer, the slower the flow will be. The test data can also be linked to the molecular weight of the sample. Long chain polymers take longer to push through the capillary and thus have a slow flowing character. Data related molecular weight distribution can also be determined by running the test at the same temperature with a clear load application. Also, the shear viscosity of a particular sample can be calculated by applying an inverse relationship. The reasons for choosing an MFI test over other techniques to evaluate these properties are its speed and cost-effective nature.

Melt flow index testing may seem simple and sometimes avoid the complicated and latest technologies, but it can provide highly accurate and analytical test results that meet all testing requirements.