Dynisco LMFI 5500 Series - Calculating PET Intrinsic Viscosity (I.V.) from the Melt Indexer; The Amount of Sample

From lab to production,
providing a window into the process
Any inaccuracies in the melt density will be propagated proportionally along to the MFR values. Thus a 1% error in
the melt density means a 1% accuracy error in the MFR the value.
Calculating PET Intrinsic Viscosity (I.V.) from the Melt Indexer
This feature allows the Melt Indexer to correlate Melt Flow Rate (g/10 min.) to Intrinsic Viscosity (dl/g). Intrinsic
Viscosity (IV, ASTM D3835) is a “wet chemistry” technique used to assess the specific volume of an isolated
polymer chain, when dissolved in a good solvent. This value is directly related to the molecular weight of the
polymer. Melt viscosity or MFI measurement is another, empirical (non-absolute like I.V.), way to assess molecular
weight. Melt Viscosity and Intrinsic Viscosity are related in such a way that IV can be directly calculated from Melt
Index values. This is described in greater detail in the applications brief, “Correlating Melt Rheology of PET to
Solution Intrinsic Viscosity” by J. Reilly and P. Limbach, available from DYNISCO POLYMER TEST on request.
The Amount of Sample
ASTM gives a recommendation of how much material to put in the barrel to perform a test. However, by
determining the proper charge and controlling it from run to run. Testing can be made easier and more
reproducible. The distance from the top of the die to the piston’s first scribe mark is about 5 cm. Filling the
barrel up to the first scribe mark is the minimum charge needed to run a test. During the recommended 6-minute
melt time, some material flows out of the die so a larger charge is needed. The best situation would be to add just
enough material, so that, during the melt time, the plunger slowly falls and is just above the first scribe mark when
the 6-minute melt time has expired. In this way, the required 6-minute melt time is satisfied and there is no
excessive waiting before the first cut is made (or timing flag starts in timed tests). A conservative estimate for
charge weight can be calculated if an approximate melt flow rate and melt density for the material are known by
using the following formula:
Charge Mass = 3.6ρ+0.6*MFR
P/N:974179 Rev: 0918 ECO: 49667
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