Re: fatty acid emulsifiers for ABS

On May 4, 4:56 pm, jorge <jorge...@xxxxxxxxx> wrote:

The Melt Flow Index is a good measure when you apply the correct
instrumentation,
actually is a very good tool to identify potential problems with
different batches.


I would beg to differ. MFI is just plain a bad test. First, the
ratio of the die length to diameter is only about 4, even though a L/D
of about 20 is needed to establish the fully developed flow profile
free from any entrance effects. As a result, you are not simply
measuring the "viscosity" at a given shear rate, but are measuring the
"viscosity" combined with the entrance flow. Secondly, it is well
known and widely established that viscosity depends strongly on shear
and that the dependence is nonlinear. As I said above, you are
looking at just one point on a curve and making a guess about the rest
of the curve.

It doesn't even make a good QC test. Yes, two different MFI values
tells you that two lots are different, but two identical MFI values do
not mean that the two lots are the same for the two reasons that I
mentioned above. First, the combination of entrance effects and
"viscosity" may be such that they combine to give the same MFI. Or the
lots may have the same MFI values at that same point on their
viscosity curves, but may have completely different MFI values at
different points (assuming that you could run the MFI at those
different points).

The test is easy to run which is why it has such staying power, but it
still causes incalculable amounts of pain and suffering.

John
Aspen Research, - www.aspenresearch.com
"Turning Questions into Answers"

Opinions expressed herein are my own and may not represent those of my
employer.

.

Relevant Pages

  • Re: Neo-Aether and the Medium of Space
    ... importance of inertia to viscosity. ... the flow is inviscid. ... but I have never advocated a 'simple gas'. ... way to attain the fluid condition of Continuum Mechanics. ...
    (sci.physics)
  • Re: Science Disproves Evolution
    ... A tall pile of tar will slowly flow downhill, ... "creeps" in this way, although rocks deform very, very slowly. ... that it ignores the extreme temperature dependence of viscosity on ...
    (talk.origins)
  • Re: Challenge to the behaviourists, #1
    ... >>don't label or refer to any reasons for flowing slowly. ... Granted there are many reasons a fluid will flow faster or slower, ... the context of "viscosity" as an explanation slower rates of flow should ... same flow rate, they have different viscosities. ...
    (sci.cognitive)
  • Re: Challenge to the behaviourists, #1
    ... There are lots of reasons for flowing slowly ... >Granted there are many reasons a fluid will flow faster or slower, ... If one says that viscous flow in liquid is caused by viscosity, ... Regards - Lester ...
    (sci.cognitive)
  • Re: Gearbox oil supplier
    ... The first is the MAXIMUM viscosity (minimum flow ... while the box oil gets to its max, say 100 for arguments sake, ...
    (uk.rec.cars.maintenance)