How to Test the Property of Molten Plastics?

When a polymer is chosen for certain applications, there are many parameters that is taken into consideration. Properties like melt flow index, tensile strength, compression strength are some properties that are measured. Melt flow index testing is one test that is done at the very prime level of the manufacturing. It is done on the granules which further take intended shape. In this test, we estimate the flow rate of the molten plastic. Depending upon the flow rate, its suitability for the application can be decided.

What is Melt Flow Index Tester?

Technically speaking, Melt flow index is ease of flow of the melt of a plastic. Mass of molten polymer flown in grams in 10 minutes from a die of defined circumference and length. The process sounds very simple, but actually a lot of precision required while performing this test.

Melt flow index tester has a hot barrel and a system control unit. A die called orifice made according to standards is attached at the bottom of the hot barrel along with a cutter. There are many accessories provided with it, which help in performing the test accurately and maintaining the machine in good condition.

How to perform a melt flow index test?

As it is a table top model, first, you need to check the adjust of the instrument using the plumb line. There should not be any tilt in the assembly of the instrument, else results may vary.  The temperature range of barrel may go from ambient temperature to 400°C depending upon the type of polymer you are using. Feed the granules in the barrel using a spoon. Using a spanner, you need to make sure, there is no free space left inside the barrel. Using the piston, you need to put the weight on the granules inside the barrel. You would notice that, before you begin the test, some molten liquid starts coming out of the orifice, this is because the temperature has started to rise. Before you begin the test, cut the plastic thread coming out from orifice using the manual cutter and begin the test immediately. The timer will start running. A thin plastic string will start coming out from the barrel. Once the timer completes its 10 minutes’ cycle, cut the sample string using a manual cutter and measure the output. The weight of molten plastic is the MFI of the plastic sample.  

Precautions to be taken

  • Always cut the sample before beginning the test.
  • Make sure there is no free space in the barrel while feeding the granules.
  • Always clean the barrel before changing the sample type.
  • Maintain an appropriate distance from the instrument to avoid any heat contacts.
  • Take special care of piston, it should not get deformed in any case. Any dent, chip or deformity will give inaccurate results.
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