Relation between MFI and spiral flow 
Author Message
 Relation between MFI and spiral flow

Hello,

I'm looking for information that describes the relation between the
Melt Flow Index and the spiral flow value of a polymer. I need to
determine the MFI of the biopolymer that my company produces, but it
is not possible to perform the standard MFI test. The only way to say
something about the flow properties is to perform spiral flow tests.
Ideally, I would like to "translate" spiral flow values to MFI.

I don't have access to libraries of universities, so I'm stuck with
the Internet and I haven't found anything besides formal definitions
of these properties. I don't know if there are any (empirical)
relations between the properties, but I hope someone can give me some
pointers.

Thanks in advance,

Jaap van Heemst
-----
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Sun, 12 Dec 2004 16:10:02 GMT
 Relation between MFI and spiral flow
I doubt that you will ever find a general or universal formula that correlates MFI and spiral flow, because the spiral flow test results depend on so many variables which you do not consider when you run MFI, like: spiral tool design (melt cooling conditions or tool venting) or molding machine design & size and molding conditions etc.! MFI does not use any tool, just a die!

You might be able to establish for yourself some kind of an empirical correlation between MFI and spiral flow for a very specific set of MFI and spiral flow tests, but only when you stick to well defined test conditions ...


Quote:
> Hello,

> I'm looking for information that describes the relation between the
> Melt Flow Index and the spiral flow value of a polymer. I need to
> determine the MFI of the biopolymer that my company produces, but it
> is not possible to perform the standard MFI test. The only way to say
> something about the flow properties is to perform spiral flow tests.
> Ideally, I would like to "translate" spiral flow values to MFI.

> I don't have access to libraries of universities, so I'm stuck with
> the Internet and I haven't found anything besides formal definitions
> of these properties. I don't know if there are any (empirical)
> relations between the properties, but I hope someone can give me some
> pointers.

> Thanks in advance,

> Jaap van Heemst
> -----
> Spamblock in effect; remove the obvious for valid email address.



Sun, 12 Dec 2004 16:49:17 GMT
 Relation between MFI and spiral flow
On Wed, 26 Jun 2002 10:49:17 +0200, "Rolf Wissmann"

Quote:
>I doubt that you will ever find a general or universal formula that
>correlates MFI and spiral flow, because the spiral flow test results
>depend on so many variables which you do not consider when you run MFI,
>like: spiral tool design (melt cooling conditions or tool venting) or
>molding machine design & size and molding conditions etc.! MFI does not
>use any tool, just a die!

>You might be able to establish for yourself some kind of an empirical
>correlation between MFI and spiral flow for a very specific set of MFI
>and spiral flow tests, but only when you stick to well defined test
>conditions ...

Initially, the spiral flow tests are intended to compare the flow
properties different grades of our material among themselves, so in
that respect a conversion to MFI is not needed. Unfortunately, our
customers (i.e. injection molders) frequently ask for a MFI-value
(that, obviously, I can't provide).

I'm aware of the large differences in test methods originating from
the differences in equipment and conditions, so indeed I do not expect
to find a generally applicable formula. I was kind of hoping, however
unlikely, that someone once tried to establish an empirical
correlation for any   plastic (with a defined MFI) showing what spiral
flow values can be measured as a function of molding conditions and
use that as a stepping stone.

Thanks for your reply.

Jaap van Heemst
-----
Spamblock in effect; remove the obvious for valid email address.



Sun, 12 Dec 2004 23:35:24 GMT
 Relation between MFI and spiral flow
I'm afraid, if your customer is asking for an MFI value you may have no other choise then getting it measured for your specific resin. Even though, for an injection molder, spiral flow data are probably more usefull than MFI values, because the spiral flow test "is closer to real conditions during injection molding" than MFI is, resin suppliers normally prefer to deliever MFI test data, because MFI is kind of standardized and easier & faster to do than a spiral flow test, which as far as I know is not standardized and therefor not very often done ...


Quote:
> On Wed, 26 Jun 2002 10:49:17 +0200, "Rolf Wissmann"

> >I doubt that you will ever find a general or universal formula that
> >correlates MFI and spiral flow, because the spiral flow test results
> >depend on so many variables which you do not consider when you run MFI,
> >like: spiral tool design (melt cooling conditions or tool venting) or
> >molding machine design & size and molding conditions etc.! MFI does not
> >use any tool, just a die!

> >You might be able to establish for yourself some kind of an empirical
> >correlation between MFI and spiral flow for a very specific set of MFI
> >and spiral flow tests, but only when you stick to well defined test
> >conditions ...

> Initially, the spiral flow tests are intended to compare the flow
> properties different grades of our material among themselves, so in
> that respect a conversion to MFI is not needed. Unfortunately, our
> customers (i.e. injection molders) frequently ask for a MFI-value
> (that, obviously, I can't provide).

> I'm aware of the large differences in test methods originating from
> the differences in equipment and conditions, so indeed I do not expect
> to find a generally applicable formula. I was kind of hoping, however
> unlikely, that someone once tried to establish an empirical
> correlation for any   plastic (with a defined MFI) showing what spiral
> flow values can be measured as a function of molding conditions and
> use that as a stepping stone.

> Thanks for your reply.

> Jaap van Heemst
> -----
> Spamblock in effect; remove the obvious for valid email address.



Mon, 13 Dec 2004 00:05:38 GMT
 Relation between MFI and spiral flow

Quote:

> Unfortunately, our
> customers (i.e. injection molders) frequently ask for a MFI-value
> (that, obviously, I can't provide).

Why not?


Mon, 13 Dec 2004 04:08:32 GMT
 Relation between MFI and spiral flow
On Wed, 26 Jun 2002 18:05:38 +0200, "Rolf Wissmann"

Quote:
>I'm afraid, if your customer is asking for an MFI value you may have no =
>other choise then getting it measured for your specific resin. Even =
>though, for an injection molder, spiral flow data are probably more =
>usefull than MFI values, because the spiral flow test "is closer to real =
>conditions during injection molding" than MFI is, resin suppliers =
>normally prefer to deliever MFI test data, because MFI is kind of =
>standardized and easier & faster to do than a spiral flow test, which as =
>far as I know is not standardized and therefor not very often done ...

I agree with you that spiral flow tests are more usefull to obtain
data about the flow properties because I would perform spiral flow
tests using the same molding conditions as I would with molding of
real products (except for applying holding pressure of course).

To answer Thomas Koenig's question as well: obtaining a MFI is very
difficult (if not impossible) for two reasons.
First, our material is a starch-based biopolymer. Starch starts to
degrade around 190 C (the same temperature at which a MFI is measured)
and this will certainly happen during the 10 minutes that a MFI test
lasts. Testing at this temperature will defeat its purpose because I
would be measuring partly degraded and caramalized starch.
Second, starch plastics don't exhibit the same melting behavior as
regular thermomplastics. Heating the material only (as happens in a
MFI test) will not melt it (completely). To get from granulate to a
truely viscous melt you need shear forces introduced by the rotational
movement of a{*filter*}(obviously, lacking in a MFI test). Admitted, pure
starch has some sort of melting temperature but that lies beyond the
degradation temperature.

I guess I'll be stuck with explaining this whenever I tell an
injection molder that I can't give a MFI but only a spiral flow value
at processing conditions.

Jaap van Heemst
-----
Spamblock in effect; remove the obvious for valid email address.



Mon, 13 Dec 2004 16:14:35 GMT
 Relation between MFI and spiral flow
... this means your molder has to mold your polymer very gently in
order not to degrade it and you have to make sure that the hold-up
time during injection molding will be kept to a minimum ...

Typically one expects from a robust polymer, that it does not start
to degrade very significantly up to a hold-up time in an injection
molding machine of 20-30 minutes! That used to be the goal when I
developed polymers. For that reason we helt the molten polymer
for up to 30 min in the MFI device before running the MFI test ...

Are you using any kind of stabilizers ?


Quote:
> On Wed, 26 Jun 2002 18:05:38 +0200, "Rolf Wissmann"

> >I'm afraid, if your customer is asking for an MFI value you may have no =
> >other choise then getting it measured for your specific resin. Even =
> >though, for an injection molder, spiral flow data are probably more =
> >usefull than MFI values, because the spiral flow test "is closer to real =
> >conditions during injection molding" than MFI is, resin suppliers =
> >normally prefer to deliever MFI test data, because MFI is kind of =
> >standardized and easier & faster to do than a spiral flow test, which as =
> >far as I know is not standardized and therefor not very often done ...

> I agree with you that spiral flow tests are more usefull to obtain
> data about the flow properties because I would perform spiral flow
> tests using the same molding conditions as I would with molding of
> real products (except for applying holding pressure of course).

> To answer Thomas Koenig's question as well: obtaining a MFI is very
> difficult (if not impossible) for two reasons.
> First, our material is a starch-based biopolymer. Starch starts to
> degrade around 190 C (the same temperature at which a MFI is measured)
> and this will certainly happen during the 10 minutes that a MFI test
> lasts. Testing at this temperature will defeat its purpose because I
> would be measuring partly degraded and caramalized starch.
> Second, starch plastics don't exhibit the same melting behavior as
> regular thermomplastics. Heating the material only (as happens in a
> MFI test) will not melt it (completely). To get from granulate to a
> truely viscous melt you need shear forces introduced by the rotational
> movement of a{*filter*}(obviously, lacking in a MFI test). Admitted, pure
> starch has some sort of melting temperature but that lies beyond the
> degradation temperature.

> I guess I'll be stuck with explaining this whenever I tell an
> injection molder that I can't give a MFI but only a spiral flow value
> at processing conditions.

> Jaap van Heemst
> -----
> Spamblock in effect; remove the obvious for valid email address.



Mon, 13 Dec 2004 18:21:10 GMT
 Relation between MFI and spiral flow

Quote:

> To answer Thomas Koenig's question as well: obtaining a MFI is very
> difficult (if not impossible) for two reasons.
> First, our material is a starch-based biopolymer. Starch starts to
> degrade around 190 C (the same temperature at which a MFI is measured)

For different polymers, MFI values are done at different
temperatures.  If you wanted to measure an MFI of polycarbonate
at 190C, you'd have quite a lot of zeros :-)  You could define
a different temperature for your MFI, so the problem wouldn't
be there.

Quote:
> Second, starch plastics don't exhibit the same melting behavior as
> regular thermomplastics. Heating the material only (as happens in a
> MFI test) will not melt it (completely). To get from granulate to a
> truely viscous melt you need shear forces introduced by the rotational
> movement of a{*filter*}(obviously, lacking in a MFI test).

You could melt your polymer in an extruder and measure its viscosity
function in an online rheometer, at different temperatures.
Fit the data to Carreau-WLF, and you have quite a lot of information.

Some people (online rheometer vendors) also offer the computation of
an MFI value from rheologcal data, using some correlation or other.
If you do that consistently (i.e. using the same formula for every
polymer grade you make), then your customers will get used to the
way that MFI values correspond to processing behaviour.

A single number, such as an MFI, is never enough to characterize
a polymer fully, anyway.  It is entirely possible two polymers
with identical chemical composition and identical MFI which have
widely differing processing characteristics if these polymer
differ in molecular weight distribution or branching structure.



Tue, 14 Dec 2004 02:24:54 GMT
 
 [ 8 post ] 

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