viscoelastic behavior of liquid silicone rubber (lsr)
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Viscoelastic Behavior of Liquid Silicone RubberLiquid Silicone Rubber
Time, Temperature and Vulcanization, p
SIMTEC SILICONE PARTS, LLCand
Polymer Engineering CenterPolymer Engineering Center University of Wisconsin-Madison
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Prof. Tim A. Osswald
Prof. Juan P. HernándezMiguel Hidalgo
Dr Natalie RudolphDr. Natalie RudolphKaterina Sánchez
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• When is LSR a solid or a liquid? q
• What role does temperature play?
• What role does time scale play?
• What role does vulcanization play?
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Dynamic Mechanical Test (Fixed Frequency)Strain input
El ti l t tElongational test
LIQUIDSOLID
Viscous stress response
LIQUID
Elastic stress response
SOLID
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Dynamic Mechanical Test (Polymer) St /St iStress/Strain
Complex modulusSolid Liquid
Solid Liquid
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Solid Liquid
Dynamic Mechanical Test (Complex Modulus)
Magnitude Magnitude
Solid Liquid
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Solid Liquid
Dynamic Mechanical Test (Energy Dissipation) St /St iStress/Strain
Energy dissipation:
Volume specific dissipative energy
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Dynamic Mechanical Test (Energy Dissipation)
Stress/Strain
SHEAR
Energy dissipation:Energy dissipation:
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Sliding Plate Rheometer (Complex Viscosity) St /St iStress/Strain
SHEAR
Solid Liquid
Complex Viscosity
Dissipative term (Viscosity)Dissipative term (Viscosity)
Storage term (Elasticity)
Liquid
or
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Storage term (Elasticity)Solid
or
Temperature and Vulcanization
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Curing Behavior of LSR
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Curing Behavior of LSR and HCR
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Solid-Liquid Transition (LSR)
Frequency = 1 Hz
Vulcanized rubber
q y
cg reached
More elasticMore viscous
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Viscosity of Vulcanizing Elastomers (LSR)
Heating
Vulcanization
g
Shear thinning
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Time Scale
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Stress Relaxation
LStress=(t)
=/L
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Constant strain
Stress Relaxation
100oC 25oC -50oC
100 104 108 1012 101610-410-8
3 years 30,000 years
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Stress Relaxation
Time Temperature Superposition
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Time –Temperature Superposition
Stress Relaxation
De >> 1
R)
Log(
ER
De > 1
De < 1
10-3 seconds 10-1 seconds seconds
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Dynamic Test
Maxwell model
Dynamic responseEquilibrium
Time scale
Deformation
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Time Scale and Temperature
Maxwell model Constant Test Temperature (TT)
TT ≈ TgTT ≈ Ts
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T 25 C
Viscoelastic Properties of PolyisobutyleneTT =25oC
G’
G’’
TT ≈ TgTT ≈ Ts
G
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Time Scale and Temperature
35°CReference temperature 95°C
105°C
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Time Scale and Temperature
Time –Temperature Superposition
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Time-Temperature Superposition
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Conclusions
State of matter: A polymer is a solid and a liquid at all times, temperatures, and degrees of vulcanization
Temperature: Softening Temperature and cg at Tan = 1
Time scale: Softening Temperature and c is timeTime scale: Softening Temperature and cg is time (frequency, cooling rate/heating rate) dependent
Pressure : Softening Temperature and cg are timedependent (another story)
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Biographical Note
SIMTEC Silicone Parts, LLC1902 Wright Street, Madison WI 53704, USATel: 1-608-663-4553; Email: info@simtec-silicone.com@Website: www.simtec-silicone.com
SIMTEC is a research and technology driven company exclusivelySIMTEC is a research and technology driven company exclusively focused on developing custom, high-precision Liquid Silicone Rubber
(LSR), overmolded and Two Shot parts and components for innovative companies worldwide.
Polymer Engineering Center, University of Wisconsin-Madison1513 University Avenue, Madison, WI 53706, USAT l 1 608 265 2405 W b it htt // i d /Tel: 1-608-265-2405; Website: http://pec.engr.wisc.edu/
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