2. Melt Flow Index (MFI)
O Definition
O Importance of MFI
O Formula
O MFI Tester
O Test Procedure
O Standard Operating Procedure
O Test Standard
O Test Condition
3. Definition
O “Melt Flow Index (MFI) is a measure of
how many grams of a polymer flow
through the die in ten minutes. ”
O The test is performed at a given
temperature depending on the plastic.
O The force used to push
the plastic through the system is supplied
by a weight which sits on top of a ram.
O Unit:- gram/10 min.
4. Importance of MFI
O Melt Flow Index is a very valuable test for
quality assurance.
O Identification of Raw material.
O Comparison of "good" and "bad" samples
O Grade differentiation of materials
O Batch to batch comparisons
O Processing control parameters of the
plastic material before putting into
production.
O Verify Incoming Raw Material.
5. Formula of MFI
O MFI = 600 Sec x Weight of extrudate
t
T = Time of extrudate in seconds.
Unit – g / 10 min.
8. The MFI testing methods to be followed to
ensure accuracy in the process:
The sample should be in granulated form. No
other form or final product can be tested.
The granules (4 to 5 grams) are charged in the
hot barrel. It has to be made sure that there is
no space within the granules in the barrel.
Using a piston, dead weight is applied on the
granules to create a pressure and to make the
flow of the granules non-stop.
Test Procedure
9.
10. As the temperature of the barrel starts to increase,
the sample starts to melt.
This molten plastic starts to come out from the orifice
(Diameter of orifice 2 mm). There is an automatic
cutter incorporated into the machine to cut the string
of the plastic that is coming out from the orifice.
This cutter runs twice. One, before starting the test
and once after 10 minutes, which is the standard test
time.
This molten plastic is taken and weighed. The weight
in grams is divided by 10 minutes to get the actual
MFI value.
Test Procedure
11. Standard operating Procedure
O 1. First of all turn the machine on by plugging the
mains socket of the machine into a 3 pin 15 amp
socket.
O 2. Set the SV value on the PID controller and the
test duration timing on the digital timer.
O 3. Switch on the toggle switches from the control
panel for automatic cutting of sample.
O 4. After setting the temperature and timer, turn
the heater on by pressing the heater on the
switch.
O 5. Wait for the reading in the PV display in the
PID controller to reach the value of the SV
display
12. Standard operating Procedure
O 6. After the required temperature for the test has been
attained, fill the barrel of the machine with the plastic
granules you want to test.
O 7. Poke the granules with the plunger after they are
inserted into the barrel to ensure close packing of the
granules and eliminate the air between the granules.
O 8. When the granules are inserted in the barrel, there will
be a slight decrease in the PV value on PID monitor. Wait
for this value to again reach the SV value.
O 9. Once the PV and SV value are the same, place the
plunger provided with the machine along with the dead
weight on it into the barrel.
O 10. After placement of plunger, melted plastic comes out
of the barrel.
13. Standard operating Procedure
O 11. When the time cycle on the digital timer
completes, the cutter will automatically cut the
sample from the barrel.
O 12. Weight the melted sample using a digital
balance. This weight will be used for calculating
the Melt Flow Index of the sample.
14. O There are two major MFI test standards:
O ASTM D1238: Standard Test Method for
Melt Flow Rates of Thermoplastics by
Extrusion Plastometer.
O ISO1133: Determination of the Melt Mass-
Flow Rate (MFR) and Melt Volume-Flow
Rate (MVR) of Thermoplastics.
Test Standard
