2. Outline
• Definitions
• Basic Equipment
• Viscosity vs. Shear Rate Curves
• What they tell us
• How we can use them
• Melt Index: “What is it?”
• Moisture?
4. Rheology is:
• Science of material flow behavior
• Uses very complicated and difficult
to understand mathematical
background (tensors, co-rotational
or co-deformation curved space,
etc.)
• Can be presented in very
complicated way which is hard to
understand for non-specialists
5. Mathematics is complicated
∂ xi
∂ τij
∂ xj
-
∂ p
= 0
∂ vj
∂ xj
= 0
τij + K(τij) = 2 η eij
.δ τij
δ t
τij = τji
τij
∫= K1(CI,CI
-1
) CI + K-1(CI,CI
-1
)CI
-1
)( )e-(t-t’)
dt’
t
-∞
∂ T
∂ xj
( ∂ T
∂ xj
λ )+ ρ Cp
∂ T
∂ xj
vj = 2 η eij eij
. .
6. Explanation of Rheology
• Mathematics is overemphasized
Complicated mathematical
background leads sometimes to
“scientific exhibitionism” of the
presenter
• Such an approach is useful for
scientific people and conferences
but usually useless for practical
people
7. Explanation of Rheology
• Understanding of the physics is emphasized
– the mathematics is avoided as much as
possible
– the explanation is based on physical
understanding what is happening
• Such an approach cannot be used for
development in rheology but may be useful for
understanding material behavior
8. AIR
10 0
105
10 10
10 15
10 20
10 - 5
Viscosity [ Pa s ]
WATER
ENGINE
OIL
polymer melts
GLASS
Glass
Windows of the Cathedral of
Chartres in France have “Flowed”
since they were Produced 600
years ago.
3 mm
600
YEARS
Paper
Thin
Glass behaves like Fluids !!!
IF YOU WAIT LONG ENOUGH
9. Tim’s Definition of Rheology
• The flow characteristic of a polymer at
various shear and temperature conditions.
10.
11. Crystallinity (semi-crystalline)
Definition: A state of molecular structure in
some resins attributed to the existence of
solid crystal with a definite geometric form.
Such structures are characterized by
uniformity and compactness.
Semi-Crystalline Resins:
• LDPE,HDPE, PP, FEP, Nylon, PET, PU
12. Amorphous (non-Crystalline)
Definition: Devoid of crystallinity or
stratification. Most plastics are amorphous
at processing temperatures, many retaining
this state under all normal conditions
Amorphous Resin:
• PS, PVC, ABS, PC, PMMA
14. Viscosity
• A measure of the internal friction resulting
when one layer of fluid is caused to move
in relationship to another layer.
• Example:
The flow characteristic of 50 wt. motor oil at
50°F in the winter versus its flow characteristic
when it is drained out of the oil pan after the
motor has been warmed up to 200°F
22. Melt Density using a
Capillary Rheometer
• Definition: The density of a polymer when
it is in a molten state. The melt density is
totally dependent to the temperature at
which is it measure or processed.
• ei, HDPE typically has a solid density of
about .96 gm/cc but in the molten/process
range it has a density of .75 gm/cc
23. Melt Index(MI, MFR, MFI)
The terms “melt index” (MI), “melt flow rate”
(MFR) and “melt flow index” (MFI) refer to the
same test. MFR was introduced to replace MFI.
The term MFI is used to refer to the flow rate of
PE obtained under Condition 190/2.16 (formally
know as Condition E). The use of such terms is
not encouraged for other materials. It is
suggested, by ASTM D 1238 that the term melt
flow rate (MFR) be used for other plastic
materials.
25. What does MFI mean?
Not Much!VISCOSITY
SHEAR RATE
γapp = 2.4 MFI
.
0 sec-1
10 sec-1
26. Hygroscopic
• Definition: Having the tendency to absorb
moisture from the air. Some resins are
hygroscopic, thus requiring drying prior to
processing.
• “Wet” resin will decrease the physical
properties of the resin, typically
embrittlement will occur.
27. Moisture Content
• Definition: The amount of moisture in a
material determined under prescribed
conditions and expressed as a percentage of
the weight of the moist specimen, that is, the
original weight comprising the dry substance
plus any moisture present.
• Hygroscopic Resins
– HIPS, ABS, Nylon, PET, PETG
• In some processes, HDPE is dried.
28. Moisture Analyzer
• Moisture Analyzer is used to measure the moisture content of a
hygroscopic material
• Moisture content of resins can range from .005% to .18% measured in
parts per million depending on the resin being processed
