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THE FUNDAMENTALS OF
RHEOLOGY
Rheological tests can be very helpful tools for polymer
processing and development. This presentation is
designed to be an informative introduction and guide to
rheological tests, and finding correlations between
equipment and processing techniques.
CAPILLARY RHEOLOGY
• Provides more information than melt
flow testing
• How does the material behave when
melted?
• What are the correlations between flow
parameters and mechanical properties?
• Polymers are non-Newtonian materials,
consequently their flow is not
proportional to the pressure applied
“the flow and shear properties of
materials up to high pressures”
WHY CAPILLARY
RHEOLOGY?
• Determine the optimal working
parameters for materials processing
(injection molding, blow molding,
extrusion, etc.)
• Investigate processing issues in a
faster and non-disruptive manner
• Find which materials will work best for
complex parts or long flow lengths
• Replicate manufacturing parameters
for design, troubleshooting, and
simulations
TYPES OF RHEOMETERS
Extensional CapillaryRotational
ROTATIONAL
RHEOMETERS
For viscoelastic properties
Rotary motion
Plate geometry: most common
for thermoplastic melts
EXTENSIONAL
RHEOMETERS
For elongational viscosity (high
viscosity materials)
Rotating drum
Extensional flows: very
sensitive to crystallinity &
polymer long-chain branching
CAPILLARY
RHEOMETERS
For viscous properties
Capillary action
Capillary flow: Flow through a narrow
space. Different piston speeds (shear
rates) applied. Viscosity changes
tracked relative to shear rates.
SHEAR FLOW
Flow between two parallel plates of area A
Moving with constant velocity V
θ
s
A
D
F
SHEAR FLOW
Flow between two parallel plates of area A
Moving with constant velocity V
Shear Rate
Shear Stress
Viscosity
POLYMER RHEOLOGICAL BEHAVIOR
WATER
POLYMERSP1
1
P2
1 2
P3
1 2 3
Pressure
Flow
WATER
POLYMERS
Polymer flow is not proportional to the applied pressure Flow curve
MECHANICAL & RHEOLOGICAL PROPERTIES
Vs. MOLECULAR WEIGHT
A polymer’s structure influences all its mechanical,
chemical, and rheological properties
MOLECULAR WEIGHT
LOW MEDIUM HIGH ULTRA-HIGH
Young’s
Modulus
Impact
Strength
Melt
Viscoscity
-2.000
-1.000
0.000
1.000
2.000
3.000
4.000
-2.00 -1.00 0.00 1.00 2.00 3.00 4.00 5.00
log(Viscosity)
log (shear rate)
Viscosity Vs. Shear Rate
M = 50000
M = 75000
M = 100000
RHEOLOGICAL PROPERTIES
Vs. MOLECULAR WEIGHT
-2.000
-1.000
0.000
1.000
2.000
3.000
4.000
-2.00 -1.00 0.00 1.00 2.00 3.00 4.00 5.00
log(viscosity)
log (shear rate)
Viscosity Vs. Shear rate
M = 75000 MWD broad
M = 75000 MWD narrow
Rheological curve at different MW
(monodisperse polymers)
Rheological curve at different MWD
(monodisperse and polydisperse polymer)
With the same average MW, polydisperse polymers can
be processed better than monodisperse polymers
High-molecular weight leads to:
1) Higher Strength: due to higher inter-chain forces, more
entanglements
2) Higher Impact Strength: due to lower degree of
crystallization at higher chain length, more
entanglements
3) Higher Chemical Resistance: due to higher inter-chain
forces
4) Reduction of the “fluidity” (inverse of viscosity) of the
polymer in the melted status: due to the presence of
more entanglements
MECHANICAL & RHEOLOGICAL PROPERTIES
Vs. MOLECULAR WEIGHT
POLYMERS & PROCESSES
MATERIAL
Polycarbonate
(PC)
Polyethylene
Terephthalate
(PET)
Polyvinyl chloride
(PVC)
Process • Injection molding • Blow molding • Extrusion
Application
(Examples)
• Spotlights • Plastic bottles • Electrical wires
Advantages
• Transparency
• High-optical clarity
• Acts as a barrier
• High impact
resistance
• Chemically resistant
• Recyclable
• Insulator
• Lightweight
• Durable
• Mechanical damage
resistance
CAPILLARY RHEOLOGY
• Many polymer processing
techniques can be simulated
using a capillary rheometer
• This allows users to experiment
with new parameters for
various polymer processing
equipment without having to
stop operation and waste a
batch of material
• Plastic extrusion, injection
molding, blow molding, film
blowing, co-extrusion...
PLASTIC EXTRUSION
• Pellets are added into the feeder
• A constant temperature is maintained
• Screw is rotating continuously
• Polymer melts at a constant temperature
• Polymer is pushed through breaker plate into the die
Polymer
Granules
Feeder
Heaters
Polymer MeltExtrudate Die Screw/Barrel
Water
tank
Pull
Roller
Feeder
Heater
Polymer
Granules
Extrudate
Die
Screw/Barrel
Mold Cavity
Molded Part
PLASTIC INJECTION MOLDING (IM)
• Pellets are added into the feeder
• Screw is rotating (not continuously)
• Different temperature for different zones
• Screw moves along the barrel as a piston
• Polymer is injected into a mold
• The part is molded and ejected
Extrudate
drops
Extrudate fits to
the mold
Mold closes
& air blows
Air Hose
Residue is
trimmed
Cutter
PLASTIC BLOW MOLDING
• Extrusion or injection blow molding
• Molten material (parison) drops in the mold
• Mold is closed
• Air is blown through an air hose
• Molded part is ejected
Polymer Melt Extrudate
Mold
opens,
part
drops
PLASTIC FILM BLOWING
• Molten material is extruded through a circular die (usually vertically)
• Air is introduced in the center of the die
• “Bubble–like” expansion
• The tube of film passes through nip rolls
Extrudate
Air
Nip Rolls
Product
• Two or more materials fed into
co-extrusion dies
• Constant temperature is
maintained in the die
• Film is extruded
• Layer thickness controlled by
relative speeds and sizes of
extruders
Example Application: food packaging
PLASTIC CO-EXTRUSION
Adhesive Polymer Resin Polymer Resin
Co-Extrusion Dies
Rollers
Co-Extruded Tape
Winding
Feeder 1
Feeder 2
)(Log
)(Log-1 0 1 2 3 4 5
f (T, P, material)
INJECTION MOLDINGEXTRUSION
MELT FLOW
CAPILLARY
RHEOMETRY
ROTATIONAL RHEOMETRY
PROCESSING & FLOW CURVE OF POLYMERS
CAPILLARY RHEOMETERS
MEASURE LOAD
OR PRESSURE
SET DIE GEOMETRY
AND PISTON SPEED
Shear Rate=
Speed of Deformation
Viscosity =
Resistance to the Flow
Shear Stress
Pressure
Transducer
Motor-Driven
Piston
h
V

A
F






Capillary
Die (L/D)
Force (Load Cell)
RAW DATA:
Constant shear rate steps with
pressure reaching the equilibrium
after a transient stage
RHEOLOGICAL CURVES:
Viscosity (Pa· s) as a function of
shear rates (s-1)
Shear stress (Pa) vs shear rate
(s-1)
RHEOLOGICAL DATA
PP @ 230°C
Filled PP @ 230°C
RHEOLOGICAL DATA
Virgin PP:
Non–Newtonian
shear thinning behavior
η = 241 – 34 Pa·s
max P ≅ 8 MPa
Filled PP (50% wt flax):
Non–Newtonian
shear thinning behavior
η = 1061 – 81 Pa·s
max P ≅ 20 MPa
EXTRUSION/IM & THE CAPILLARY RHEOMETER
Polymer Granules
Feeding
Extrudate Die Barrel
CO-EXTRUSION & SQC ANALYSIS
Die Swell Accessory
EXTRUSION & SR DIE SWELL ACCESSORY
Extrudate Die
Swelling of the Polymer
EXTRUSION/IM & MELT FRACTURE
Unstable flow Polymer GranulesBarrel
Production Rate
Output
Smooth Shark
Skin
Spurt Fracture
Unstable flow
Direction
of flow
Increasing
Flow rate
Melt
Instability
IM MOLD FILLING & SR PVT ACCESSORY
Partial Filling Complete Filling
Simulations for Mold Filling Phase
PVT Test
Mold Cavity
Molded Part
Complete Mold Filling is Critical to the Process
IM MOLD FILLING& SR TC ACCESSORY
TC Test
Mold Cavity
Molded Part
Heat Conduction through the material is
critical to get a perfectly molded part
BLOW MOLDING/FILM BLOWING & SR STRETCHING UNIT
Polymer Melt Extrudate
Air Hose
Stretching
THANK YOU FOR YOUR TIME!

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The Fundamentals of Rheology

  • 2. Rheological tests can be very helpful tools for polymer processing and development. This presentation is designed to be an informative introduction and guide to rheological tests, and finding correlations between equipment and processing techniques.
  • 3. CAPILLARY RHEOLOGY • Provides more information than melt flow testing • How does the material behave when melted? • What are the correlations between flow parameters and mechanical properties? • Polymers are non-Newtonian materials, consequently their flow is not proportional to the pressure applied “the flow and shear properties of materials up to high pressures”
  • 4. WHY CAPILLARY RHEOLOGY? • Determine the optimal working parameters for materials processing (injection molding, blow molding, extrusion, etc.) • Investigate processing issues in a faster and non-disruptive manner • Find which materials will work best for complex parts or long flow lengths • Replicate manufacturing parameters for design, troubleshooting, and simulations
  • 5. TYPES OF RHEOMETERS Extensional CapillaryRotational ROTATIONAL RHEOMETERS For viscoelastic properties Rotary motion Plate geometry: most common for thermoplastic melts EXTENSIONAL RHEOMETERS For elongational viscosity (high viscosity materials) Rotating drum Extensional flows: very sensitive to crystallinity & polymer long-chain branching CAPILLARY RHEOMETERS For viscous properties Capillary action Capillary flow: Flow through a narrow space. Different piston speeds (shear rates) applied. Viscosity changes tracked relative to shear rates.
  • 6. SHEAR FLOW Flow between two parallel plates of area A Moving with constant velocity V θ s A D F
  • 7. SHEAR FLOW Flow between two parallel plates of area A Moving with constant velocity V Shear Rate Shear Stress Viscosity
  • 8. POLYMER RHEOLOGICAL BEHAVIOR WATER POLYMERSP1 1 P2 1 2 P3 1 2 3 Pressure Flow WATER POLYMERS Polymer flow is not proportional to the applied pressure Flow curve
  • 9. MECHANICAL & RHEOLOGICAL PROPERTIES Vs. MOLECULAR WEIGHT A polymer’s structure influences all its mechanical, chemical, and rheological properties MOLECULAR WEIGHT LOW MEDIUM HIGH ULTRA-HIGH Young’s Modulus Impact Strength Melt Viscoscity
  • 10. -2.000 -1.000 0.000 1.000 2.000 3.000 4.000 -2.00 -1.00 0.00 1.00 2.00 3.00 4.00 5.00 log(Viscosity) log (shear rate) Viscosity Vs. Shear Rate M = 50000 M = 75000 M = 100000 RHEOLOGICAL PROPERTIES Vs. MOLECULAR WEIGHT -2.000 -1.000 0.000 1.000 2.000 3.000 4.000 -2.00 -1.00 0.00 1.00 2.00 3.00 4.00 5.00 log(viscosity) log (shear rate) Viscosity Vs. Shear rate M = 75000 MWD broad M = 75000 MWD narrow Rheological curve at different MW (monodisperse polymers) Rheological curve at different MWD (monodisperse and polydisperse polymer) With the same average MW, polydisperse polymers can be processed better than monodisperse polymers
  • 11. High-molecular weight leads to: 1) Higher Strength: due to higher inter-chain forces, more entanglements 2) Higher Impact Strength: due to lower degree of crystallization at higher chain length, more entanglements 3) Higher Chemical Resistance: due to higher inter-chain forces 4) Reduction of the “fluidity” (inverse of viscosity) of the polymer in the melted status: due to the presence of more entanglements MECHANICAL & RHEOLOGICAL PROPERTIES Vs. MOLECULAR WEIGHT
  • 12. POLYMERS & PROCESSES MATERIAL Polycarbonate (PC) Polyethylene Terephthalate (PET) Polyvinyl chloride (PVC) Process • Injection molding • Blow molding • Extrusion Application (Examples) • Spotlights • Plastic bottles • Electrical wires Advantages • Transparency • High-optical clarity • Acts as a barrier • High impact resistance • Chemically resistant • Recyclable • Insulator • Lightweight • Durable • Mechanical damage resistance
  • 13. CAPILLARY RHEOLOGY • Many polymer processing techniques can be simulated using a capillary rheometer • This allows users to experiment with new parameters for various polymer processing equipment without having to stop operation and waste a batch of material • Plastic extrusion, injection molding, blow molding, film blowing, co-extrusion...
  • 14. PLASTIC EXTRUSION • Pellets are added into the feeder • A constant temperature is maintained • Screw is rotating continuously • Polymer melts at a constant temperature • Polymer is pushed through breaker plate into the die Polymer Granules Feeder Heaters Polymer MeltExtrudate Die Screw/Barrel Water tank Pull Roller
  • 15. Feeder Heater Polymer Granules Extrudate Die Screw/Barrel Mold Cavity Molded Part PLASTIC INJECTION MOLDING (IM) • Pellets are added into the feeder • Screw is rotating (not continuously) • Different temperature for different zones • Screw moves along the barrel as a piston • Polymer is injected into a mold • The part is molded and ejected
  • 16. Extrudate drops Extrudate fits to the mold Mold closes & air blows Air Hose Residue is trimmed Cutter PLASTIC BLOW MOLDING • Extrusion or injection blow molding • Molten material (parison) drops in the mold • Mold is closed • Air is blown through an air hose • Molded part is ejected Polymer Melt Extrudate Mold opens, part drops
  • 17. PLASTIC FILM BLOWING • Molten material is extruded through a circular die (usually vertically) • Air is introduced in the center of the die • “Bubble–like” expansion • The tube of film passes through nip rolls Extrudate Air Nip Rolls Product
  • 18. • Two or more materials fed into co-extrusion dies • Constant temperature is maintained in the die • Film is extruded • Layer thickness controlled by relative speeds and sizes of extruders Example Application: food packaging PLASTIC CO-EXTRUSION Adhesive Polymer Resin Polymer Resin Co-Extrusion Dies Rollers Co-Extruded Tape Winding Feeder 1 Feeder 2
  • 19. )(Log )(Log-1 0 1 2 3 4 5 f (T, P, material) INJECTION MOLDINGEXTRUSION MELT FLOW CAPILLARY RHEOMETRY ROTATIONAL RHEOMETRY PROCESSING & FLOW CURVE OF POLYMERS
  • 20. CAPILLARY RHEOMETERS MEASURE LOAD OR PRESSURE SET DIE GEOMETRY AND PISTON SPEED Shear Rate= Speed of Deformation Viscosity = Resistance to the Flow Shear Stress Pressure Transducer Motor-Driven Piston h V  A F       Capillary Die (L/D) Force (Load Cell)
  • 21. RAW DATA: Constant shear rate steps with pressure reaching the equilibrium after a transient stage RHEOLOGICAL CURVES: Viscosity (Pa· s) as a function of shear rates (s-1) Shear stress (Pa) vs shear rate (s-1) RHEOLOGICAL DATA
  • 22. PP @ 230°C Filled PP @ 230°C RHEOLOGICAL DATA Virgin PP: Non–Newtonian shear thinning behavior η = 241 – 34 Pa·s max P ≅ 8 MPa Filled PP (50% wt flax): Non–Newtonian shear thinning behavior η = 1061 – 81 Pa·s max P ≅ 20 MPa
  • 23. EXTRUSION/IM & THE CAPILLARY RHEOMETER Polymer Granules Feeding Extrudate Die Barrel
  • 24. CO-EXTRUSION & SQC ANALYSIS
  • 25. Die Swell Accessory EXTRUSION & SR DIE SWELL ACCESSORY Extrudate Die Swelling of the Polymer
  • 26. EXTRUSION/IM & MELT FRACTURE Unstable flow Polymer GranulesBarrel Production Rate Output Smooth Shark Skin Spurt Fracture Unstable flow Direction of flow Increasing Flow rate Melt Instability
  • 27. IM MOLD FILLING & SR PVT ACCESSORY Partial Filling Complete Filling Simulations for Mold Filling Phase PVT Test Mold Cavity Molded Part Complete Mold Filling is Critical to the Process
  • 28. IM MOLD FILLING& SR TC ACCESSORY TC Test Mold Cavity Molded Part Heat Conduction through the material is critical to get a perfectly molded part
  • 29. BLOW MOLDING/FILM BLOWING & SR STRETCHING UNIT Polymer Melt Extrudate Air Hose Stretching
  • 30. THANK YOU FOR YOUR TIME!