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.

1. Viscoelastic Behavior of
Liquid Silicone Rubber
Time, Temperature and Vulcanization
, p
SIMTEC SILICONE PARTS, LLC
and
Polymer Engineering Center
University of Wisconsin-Madison
Where Science Meets Innovation™

2. Prof. Tim A. Osswald
Prof. Juan P. Hernández
Miguel Hidalgo
Dr.
Dr Natalie Rudolph
Katerina Sánchez
Where Science Meets Innovation™

3. • 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?
Where Science Meets Innovation™

4. Dynamic Mechanical Test (Fixed Frequency)
Strain input
Elongational t t
El ti l test
SOLID LIQUID
Elastic stress response Viscous stress response
Where Science Meets Innovation™

5. Dynamic Mechanical Test (Polymer)
Stress/Strain
St /St i
Solid Liquid
Complex modulus
Solid Liquid
Where Science Meets Innovation™

6. Dynamic Mechanical Test (Complex Modulus)
Magnitude Magnitude
Solid Liquid
Where Science Meets Innovation™

7. Dynamic Mechanical Test (Energy Dissipation)
Stress/Strain
St /St i
Energy dissipation:
Volume specific dissipative energy
Where Science Meets Innovation™

8. Dynamic Mechanical Test (Energy Dissipation)
Stress/Strain
SHEAR
Energy dissipation:
Where Science Meets Innovation™

9. Sliding Plate Rheometer (Complex Viscosity)
Stress/Strain
St /St i
SHEAR
Solid Liquid
Complex Viscosity
Dissipative term (Viscosity)
Liquid
Storage term (Elasticity) or
Solid
Where Science Meets Innovation™

10. Temperature and Vulcanization
Where Science Meets Innovation™

11. Curing Behavior of LSR
Where Science Meets Innovation™

12. Curing Behavior of LSR and HCR
Where Science Meets Innovation™

13. Solid-Liquid Transition (LSR)
Vulcanized rubber
Frequency = 1 Hz
q y
cg reached
More viscous More elastic
Where Science Meets Innovation™

14. Viscosity of Vulcanizing Elastomers (LSR)
Vulcanization
Heating
g
Shear thinning
Where Science Meets Innovation™

15. Time Scale
Where Science Meets Innovation™

16. Stress Relaxation
L
Stress=(t)

=/L
Constant strain 
Where Science Meets Innovation™

17. Stress Relaxation
100 o C 25 o C -50o C
10 -8 10 -4 10 0 10 4 10 8 10 12 10 16
3 years 30,000 years
Where Science Meets Innovation™

18. Stress Relaxation
Time –Temperature Superposition
Temperature
Where Science Meets Innovation™

19. Stress Relaxation
De >> 1
Log(ER) De > 1
De < 1

10-3 seconds 10 -1 seconds seconds
Log(time)
Where Science Meets Innovation™

20. Dynamic Test
Maxwell model Time scale
Equilibrium Dynamic response
Deformation
Where Science Meets Innovation™

21. Time Scale and Temperature
Maxwell model Constant Test Temperature (TT)
TT ≈ Ts TT ≈ Tg
Where Science Meets Innovation™

22. Viscoelastic Properties of Polyisobutylene
TT =25oC
G’’
G
G’
TT ≈ Tg
TT ≈ Ts
Marvin and Oser (1962)
Where Science Meets Innovation™

23. Time Scale and Temperature
Reference temperature 95°C 35°C
105°C
Where Science Meets Innovation™

24. Time Scale and Temperature
Time –Temperature Superposition
Where Science Meets Innovation™

25. Time-Temperature Superposition
Where Science Meets Innovation™

26. 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 cg is time
(frequency, cooling rate/heating rate)
dependent
Pressure : Softening Temperature and cg are time
dependent (another story)
Where Science Meets Innovation™

27. Biographical Note
SIMTEC Silicone Parts, LLC
1902 Wright Street, Madison WI 53704, USA
Tel: 1-608-663-4553; Email: info@simtec-silicone.com
@
Website: www.simtec-silicone.com
SIMTEC 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-Madison
1513 University Avenue, Madison, WI 53706, USA
Tel: 1 608 265 2405 Website: http://pec.engr.wisc.edu/
T l 1-608-265-2405; W b it htt // i d /
Where Science Meets Innovation™ ©Simtec Silicone Parts, LLC