The melt flow index (MFI) or melt flow rate (melt volume ratio, MFR) is a measure of the flow properties of a given polymer, also known as rheological properties, in the melt state under a known applied pressure. The MFI value indicates the amount of polymer extruded from a known specific die, expressed as the amount in g/10 minutes or the melt volume velocity in cm3/10 minutes.
-testleri.jpg "MFI and MVR (Melting Flow Index and Melt Volume Ratio) Tests")
Since polymers consist of polymer molecular chains of varying lengths, the length of the chain determines the flow properties. Because it is difficult to control the exact chain length during polymerization, the resulting mixture or distribution of chain lengths, also known as the molecular weight distribution, affects the resulting flow properties. This molecular weight distribution also makes an important contribution to the physical and mechanical properties of the resulting polymer, among other factors.
The basic principle of the melt flow index is simple. The polymer resin, flakes or powders are fed into a heated barrel, the bottom of which is a mold with a known hole diameter. The standard hole die size is 2.095 mm in diameter. When the polymer granules are introduced into the mold, it is important to ensure that all trapped air is removed by tampering with the granules, as any air entrapment will produce erroneous results. When the mold is full, a piston with a known dead weight is placed in the barrel. Extruded samples are cut and weighed to calculate the melt flow index.
Changes in the melt flow index value on incoming material can have detrimental effects on productivity and quality. Therefore, it is very important to test the material to ensure that the quality standards are met.
The melt flow index is the volume of extrudate expressed in g/10 minutes and the melt flow rate in cm3/10 minutes.
There are two common international standards referenced for MFI and MVR testing:
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