I would like to know why there is a big difference in die-swell of L-
LDPE which is produced by metallocene catalyst.
In fact, we polymerized m-PE and tested die-swell with other company's
We got 2.5 times higher die-swell values in our m-PE than other's.
They have similar Mw and density, comonomer(Hexene-1) content(about
Would you please explain this situation?
I am looking forward to your helps.
Unless you used the exact same metallocene cataylyst (and cocatalyst
and...) and thereby infringed on your competitor's patents, I would
not be surprised that there are differences. These would show up in
NMR analysis (the diads, triads, ...).
As for why these differences show up as differences in die swell, I
don't know. Die swell can be related to the memory of the material
(i.e., it was in a larger diameter prior to entering the die and this
state is remembered) but that does not explain all. Die swell
decrease is the die length increases, but it never reaches zero. In
addition, if the flow is shut off for a longer time than the
relaxation time of the polymer and then restarted, die swell is
immediately observed. I've never read of anything that related die
swell (or for that matter, normal forces) to any fundamental
properties of a polymer, but I certainly do not claim complete
knowledge of the literature.
Aspen Research, -
"Turning Questions into Answers"
Opinions expressed herein are my own and may not represent those of my
You said "They have similar Mw". What do you mean by Mw: Mn or Mw, or
something else? What are the molecular weight distributions of the two
How did you measure Mw?
Compare melt viscosities at very low, and very high shear rates.
Die Swell of m-PE. The answer to your question needs to assume first
that you have done the same testing on the same equippment under the
same conditions of shear, temperature;etc. This being said as John at
Aspen Research points out the conditions for this measurement are
fixed variables. Those factors that affect die swell of polymers
include molecular weight distribution and the higher Mz avg. , and how
stable the polymer is during processing so the additives have a
profound factor on keeping Mw in check especially the use of more
powerful secondary antioxidants and lastly degree of branching of the
PE. Branching is not a factor in PP. The rheology of metallocenes is
predicated on the secondary antioxidant levels used and their
compatabilty. Density determines compatability in this case.
Traditional phosphites are less compatible than phosphonites and
therefore limit the levels necessary to provide proper stability of Mw
and IV or Melt flow of the resin. As this changes so does die swell.
Some metallocene resins are more susceptible to degradation than
others and only a few techniques are sensitive enough to differentiate
Thank you Ernie
Mw mean weight of molecular weight(Mw) measured by PL-220GPC at 160¡É.
These polymers have 2.7 of molecular weight distribution.
Thank you again.
Assuming that the two resins were processed under identical conditions,
die-swell implies the presence of a high Mw fraction. Compare the high Mw
ends of the GPC plots. Does the resin with die-swell have a higher Mw tail,
perhaps as little as 1%?
Is there a insoluble high Mw (cross-linked?) fraction in the resin with
die-swell? If it is not soluble, it will not be detected by GPC.
You may also want to run GPC on the extrudate; did the Mw increase, or
cross-link during extrusion?
Is there a "melt lubricant" that reduces die-swell in the other resin?
it looks like for short chain branching (SCB) H1- & C13-NRM, on the basis of
model compounds, are most prefered. For analyzing long chain branching (LCB)
it requires a combination of H1- & C13-NRM and GPC and rheology.
The following pdf-documents ought to give you some info on the subject:
>> Have you compared the degree of molecular branching between the