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How to Assess Properties of Plastics?

As a raw material, plastic is used widely. In packaging, storing, casings, stationary, plumbing, toys, etc.; plastic has endless uses. The reason behind its popularity is its flexible properties. It is available in many forms and can be easily moulded into any shape. But how can you decide which plastic to use for particular application? Melt flow index is one such property of plastic which decides the suitability of plastic for different applications.


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What is Melt Flow Index?

It is the measure of the flow of the molten plastic. A Melt flow index tester is used to determine the volume of molten plastic that flows through a specific die at a specific pressure. This test is very simple but a lot of precision is required to get accurate results.

In this test, the polymer granules are fed into the hot barrel of the device. A piston is placed on the barrel to apply pressure on the granules. As the temperature rises, the molten plastic starts to come out of the small die which is also called orifice. How much plastic comes out of the barrel in 10 minutes is defined as the melt flow index rate of the sample.

Precautions to be taken while performing Melt Flow Index Test 


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  1. The alignment of the machines has to be exactly level. If there is any discrepancy in the levelling, the results may vary. A plumb line is provided with the machine to check the levelling. It is a pendulum-like string attached with weight. This plumb line should not tilt in either direction, if it is tilting, the surface needs to be adjusted. The plumb line is inserted from the barrel opening and comes out from the orifice. In reference to the alignment of the orifice, the levelling can be assessed.
  1. Clean the barrel before testing the sample. This is a very important step which is often ignored by the operator. If the barrel is not cleaned first, it will result in adulteration of the sample with the previous sample that was tested. The temperature of the machine is raised above the standard melting point of the plastic, if you don’t have the idea about the melting point of the previous Once the temperature is achieved, the leftover particles will start detaching from the barrel wall and comes out through orifice. Flat and threaded tools are provided with the machine to do the cleaning job easily.
  2. Take special care of piston. This piston is used to apply pressure on the granules in the barrel. If the piston chips off or has a dent, it may not be able to apply the perfect pressure. This may affect the test result.

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