PKG829 Packaging Plastics Laboratory

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PKG829 Packaging Plastics Laboratory

• Lab 2 Determination of Melt Flow Index by
  Extrusion Plastometer
• Li Xiong
• Fall 2004

2
Objectives

• To get familiar with the test procedure for
  measuring the melt flow index of plastic
  packaging materials
• To determine the melt flow index of selected
  polymer samples by the Extrusion Plastometer
  technique.

3
Some Background Info.

• Melt Flow Index (MFI)
• Definition the rate of extrusion of a
  thermoplastic material through an orifice of
  specific length and diameter under prescribed
  conditions of temperature and pressure
• V. Shah, 1984

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Significance

• Measure the flow rate of the material
• Distinguish different grades of a polymer
• Quality control
• Determine the extent of degradation
• Predict MW, MWD and molecular architecture
• Higher MW, Lower MFI
• For the same MW, narrower the MWD, lower MFI
• For the same MW/MWD, linear polymer has lower MFI

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Cautions

• Correlation of MFI and processability does not
  necessarily exist
• The effect of additives is not observed in the
  melt flow test
• The factors affecting the rheological properties
  of polymer melts might vary dramatically between
  melt flow test and large-scale processes

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EquipmentRay-Ran Melt Flow Indexer MK II Digital
Model 2 A

• The plastometer is mainly consisted of
• Cylinder
• Piston
• Heater
• Die
• See section 5 in ASTM D1238-99 for detailed
  apparatus info.

Reprint from www.msu.edu/tanprase
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Test Specimen (section 6 in ASTM D1238-99)

• any form that can be introduced into the bore of
  the cylinder
• Powder
• Granules
• Strips of film
• Molded slugs
• Pellets

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Conditioning (see section 7 in ASTM D1238-99)

• Most thermoplastic materials do not need
  conditioning process
• Exception is for those contain volatiles, are
  chemically reactive, or have special
  characteristics requiring conditioning process
• Moisture issue
• Affect reproducibility of MFI measurement
• Accelerate degradation

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Test Conditions

• See section 8.2 and table 1 in ASTM D1238-99
• Test conditions are shown as Condition __/__
• For example, Condition 190/2.16
• Temperature 190oC
• Total Load (including piston) 2.16 kg
• Suggested sample mass, testing time under
  standard test conditions
• Table 2 in ASTM D1238-99

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Test Procedure(see section 9 and 10 in ASTM
D1238-99)
In this procedure, the travel distance of piston
is pre-selected. In each measurement, the time
needed for the piston to travel that specified
distance is the measurement taken during the test.
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Procedure A (Manual) (see section 9 in ASTM
D1238-99)
Sample ID ________
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Procedure B (Automatic) (see section 10 in ASTM
D1238-99)

• Select travel distance for the piston to either
  6.35 mm (0.25 in) or 25.4 mm (1 in)
• See section 10.2.8 and table 3 in ASTM D1238-99)
• Choose 6.35 mm for material with MFI lt 10 g/10
  min or 25.4 mm for material with MFI ? 10 g/10 min

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Procedure B (cont)
Sample ID ________ Temperature ________ Piston
travel distance ________
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Calculation for Procedure B
There are two ways to calculate the density d in
the above equation, denoted by B-1 and B-2 in the
following slide
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B-1 to Calculate density d
Assume at 190oC, the difference of density of
LDPE, LLDPE and HDPE is not significant. And it
applied to T gt Tm only.

• Based on the article by Paul Zoller The pressure
  volume temperature properties of polyolefins,
  Journal of Applied Polymer Science, p.1051, vol.
  23, 1979.

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B-2 to calculate density d
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Report

• Nature and physical form of the test specimen
• Test conditions in standard form
• Test procedure used
• Original recorded data for each procedure
• Detailed MFI calculation for each procedure
• Show the detailed calculation to get the number
  426 in the equation used to calculate MFI in
  procedure B, and what is the unit of 426? Why?
  And where does number 600 come from? (see
  figure 2 Details of extrusion plastometer in
  ASTM D1238-99)

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Discussion

• The MFI values (average) found in procedure A and
  B
• Comparison of MFI values (average) found in
  procedure A and B
• Discussion of the accuracy of each procedure
  (manual procedure A, auto procedure B-1, and auto
  procedure B-2)
• A detailed discussion of the relationship between
  MFI and the MW, MWD and molecular architecture of
  the two test resins
• List at least 3 factors affecting the result of
  MFI test

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Questions?

• Lab report is due by 5pm on Oct. 12, 2004
• My office hour is 4-5pm on Monday or by
  appointment