Dynisco LMFI 5000, Руководство пользователя

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M0726(2):LMFI Series 5000 Lab Melt Flow Indexer
26
English 02/2014
Calculations: Method B
Method B is an assessment of a material's flow characteristics based on the volumetric
displacement rather than weight of extrudate with time as in Method A. Unlike Method A, no
cutting and weighing of the extrudate is required to perform a Method B test. Results from
Method B test can be expressed directly as Melt Volumetric Flow Rate (MVR) in ml/10 min. To
relate the results of a Method B test to Method A, the apparent melt density must be known.
The determination of the apparent density is illustrated in the previous section using Method
A/B. Without the apparent melt density MFR cannot be calculated using Method B. Some
laboratories use MVR directly without ever determining MFR.
The piston’s downward travel time is determined from a counter initiated by a digital encoder.
The encoder senses distance travelled by following the bottom of the test weight(s) which are at
the top of the piston. With all Dynisco Polymer Test Systems flags, Method A and B start in the
same place. Flags may be any length desired and a test can have any number as long as the
total distance of flags is not longer than the distance from the start point and where the piston
would land on the top of the die (
≈
25.4mm). Recently, Method B has become the more common
test because it is simpler to run (hands free after material load) and more precise for routine
analysis. In addition, the encoder system makes it possible to get more from one run.
Calculations for the Method B test are as follows:
MVRρ = MFR = πR2Lρ 600
T
Where R= radius piston (cm), T (sec)
is time to traverse the distance L, L= length of flag (mm), ρ =
apparent melt density of polymer (g/cc).
You should determine the melt densities for your material using your melt indexer. Variations in
technique and difference in material grades can cause differences from user to user. The
following table of melt densities can be used as a general guide if you get values which differ by
more than 10% from these, most likely, something is being done incorrectly. Fillers, reinforcing
agents etc. tend to increase the melt density of the material. Notice that apparent melt density is
a function of temperature.
In general the solid state density is a very poor estimate of the
melt density and should not be used .
Some typical Melt Densities
Temperature(ºC) LDPE HDPE Polybutene-1 polypropylene
120 .797 - .806 .880
130 .791 - .800 .872
140 .785 - .794 .864
150 .780 .780 .787 .852
160 .777 .777 .780 .840
170 .770 .770 .774 .819
180 .765 .765 .767 .758
190 .760 .760 .760 .754
200 .755 .755 .754 .750
210 .748 .748 .746 .746
220 .744 .738 .740 .742
230 .738 .738 .733 .738
240 .733 .733 .726 .734
250 .737 .727 .719 .730