Viscoelastic Behavior of Liquid Silicone Rubber (LSR)
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Viscoelastic Behavior of Liquid Silicone Rubber Liquid Silicone Rubber Time, Temperature and Vulcanization SIMTEC SILICONE PARTS, LLC and Polymer Engineering Center Polymer Engineering Center University of Wisconsin-Madison Where Science Meets Innovation™
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Presentation by Professor Tim Osswald, Director of SIMTEC Silicone Parts Technical Advisory Board for Silicone Elastomers US 2011. ABSTRACT: Polymers are both solid and liquid at the same time, regardless of the temperature. However, during processing and usage they appear to be either in the liquid or solid state. This is due to the density and the mobility of the molecule chains of the polymer. Silicone rubber has particularly good properties for applications that require both absorption as well as transmission of vibrations. This paper presents the fundamental behavior of liquid silicone rubber, addressing the time-temperature dependence of storage and loss moduli, as well as their development during cure. The whole range between viscous and perfectly elastic behavior, and their interaction is demonstrated with measurements and simple models.
Transcript of Viscoelastic Behavior of Liquid Silicone Rubber (LSR)
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: [email protected]@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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