Melt Flow Index
One of the properties most often quoted for both natural polymers
and masterbatches is Melt Flow Index (MFI).
What is MFI and why is it significant ?
Melt Flow Index is the output rate (flow) in grammes that occurs in
10 minutes through a standard die of 2.0955 ± 0.0051 mm diameter
and 8.000 ± 0.025mm in length when a fixed pressure is applied to
the melt via a piston and a load of total mass of 2.16 kg at a
temperature of 190°C (some polymers are measured at a higher
temperature, some use different weights and some even different
orifice sizes).
Melt Flow Index is an assessment of average molecular mass and
is an inverse measure of the melt viscosity; in other words, the higher
a MFI, the more polymer flows under test conditions. Knowing the
MFI of a polymer is vital to anticipating and controlling its
processing. Generally, higher MFI polymers are used in injection
moulding, and lower MFI polymers are used with blow moulding or
extrusion processes.
What affects the melt flow properties of polymers ?
Many factors affect polymers" flow properties. Molecular weight
distribution, the presence of co-monomers, the degree of chain
branching and crystallinity influence a polymer"s MFI as well as
heat transfer in polymer processing.
How is MFI important to masterbatches ?
In addition to its importance to natural polymers, the MFI of a
masterbatch is also important because the MFI indicates the
relative ease with which a masterbatch can be distributed during
a compounding operation or in injection moulding machines,
film extruders, etc.