LCR7000 & RHEOSIGHTS P/N: 974194 |
Rev: A
|
ECO: 52468
www.dynisco.com
From lab to production,
providing a window into the process
-89-
Extras
Measurement of Melt Density
To get apparent melt density of a material, its volume at test temperature and the mass of
that volume must be known. We can get the volume of material by running the rheometer
over a given distance at constant speed. The rheometer extrudes a known volume of
material and then we measure its mass. The following test for extrudate swell is suggested:
1. Pick the longest die you have. This will allow for easier cutting of the extrudate strand as
it exits the die.
2. Set the rheometer to 360 sec melt time, all rates at 12 mm/min and a melt force of 890 N,
and delay- time 120 sec. Set the start position to 6.0 inches and the first location to 8.0
inches, set all remaining positions to 8.1
3. When the rheometer reaches the start position, wipe the die clean and remove all
material directly under the die.
4. It will take four minutes to go from start position to 8.0 inches when the plunger hits 8.0
it will stop. Collect all the extrudate that has come out from the start position to the 8.0
inch position. Using a balance obtain the mass of this material. Let the material cool before
weighing as hot material can affect the balance reading.
5. The volume extruded from the rheometer is (independent of speed) 1.82 cc per inch of
stroke or 3.64 cc (cm
3
) for the test described.
6. Divide the mass of material by 3.638 to get the apparent melt density in g/cc when using
the test described above.
Note: The melt indexer has a looser piston to barrel clearance tolerance. This allows more
material to go by the plunger tip on the melt index and may cause the density obtained
using an indexer to be
slightly
less than that from the rheometer.
The Non-Newtonian Index
The Non-Newtonian Index is defined as follows:
A standard rate sweep is performed at 190
o
C at rates from 0.05 to 500 mm/min. A 2nd
order polynomial is then fit to the log shear stress vs. log shear rate data. Shear rates at the
specific stresses
σ
1
and
σ
2
are determined from the fit. (A fit of rate vs. stress can also be
done.)
