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Viscoelastic Behavior of Liquid Silicone Rubber (LSR)

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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.

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Viscoelastic Behavior of Liquid Silicone Rubber (LSR)

  1. 1. Viscoelastic Behavior of Liquid Silicone Rubber Time, Temperature and Vulcanization , p SIMTEC SILICONE PARTS, LLC and Polymer Engineering Center University of Wisconsin-MadisonWhere Science Meets Innovation™
  2. 2. Prof. Tim A. Osswald Prof. Juan P. Hernández Miguel Hidalgo Dr. Dr Natalie Rudolph Katerina SánchezWhere Science Meets Innovation™
  3. 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. 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. 5. Dynamic Mechanical Test (Polymer) Stress/Strain St /St i Solid LiquidComplex modulus Solid Liquid Where Science Meets Innovation™
  6. 6. Dynamic Mechanical Test (Complex Modulus)Magnitude Magnitude Solid Liquid Where Science Meets Innovation™
  7. 7. Dynamic Mechanical Test (Energy Dissipation) Stress/Strain St /St i Energy dissipation: Volume specific dissipative energy Where Science Meets Innovation™
  8. 8. Dynamic Mechanical Test (Energy Dissipation)Stress/Strain SHEAR Energy dissipation: Where Science Meets Innovation™
  9. 9. Sliding Plate Rheometer (Complex Viscosity)Stress/StrainSt /St i SHEAR Solid Liquid Complex Viscosity Dissipative term (Viscosity) Liquid Storage term (Elasticity) or Solid Where Science Meets Innovation™
  10. 10. Temperature and VulcanizationWhere Science Meets Innovation™
  11. 11. Curing Behavior of LSR Where Science Meets Innovation™
  12. 12. Curing Behavior of LSR and HCR Where Science Meets Innovation™
  13. 13. Solid-Liquid Transition (LSR) Vulcanized rubber Frequency = 1 Hz q y cg reached More viscous More elastic Where Science Meets Innovation™
  14. 14. Viscosity of Vulcanizing Elastomers (LSR) Vulcanization Heating g Shear thinning Where Science Meets Innovation™
  15. 15. Time ScaleWhere Science Meets Innovation™
  16. 16. Stress Relaxation L Stress=(t)  =/L Constant strain  Where Science Meets Innovation™
  17. 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. 18. Stress Relaxation Time –Temperature Superposition Temperature Where Science Meets Innovation™
  19. 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. 20. Dynamic Test Maxwell model Time scale Equilibrium Dynamic response Deformation Where Science Meets Innovation™
  21. 21. Time Scale and Temperature Maxwell model Constant Test Temperature (TT) TT ≈ Ts TT ≈ Tg Where Science Meets Innovation™
  22. 22. Viscoelastic Properties of Polyisobutylene TT =25oC G’’ G G’ TT ≈ Tg TT ≈ TsMarvin and Oser (1962) Where Science Meets Innovation™
  23. 23. Time Scale and Temperature Reference temperature 95°C 35°C 105°C Where Science Meets Innovation™
  24. 24. Time Scale and Temperature Time –Temperature Superposition Where Science Meets Innovation™
  25. 25. Time-Temperature Superposition Where Science Meets Innovation™
  26. 26. ConclusionsState of matter: A polymer is a solid and a liquid at all times, temperatures, and degrees of vulcanizationTemperature: Softening Temperature and cg at Tan =1Time scale: Softening Temperature and cg is time (frequency, cooling rate/heating rate) dependentPressure : Softening Temperature and cg are time dependent (another story) Where Science Meets Innovation™
  27. 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

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