Effect of Index on Curing Kinetics

1
Effect of Index on Curing Kinetics Viscoelastic
Properties of PU gels
Lifeng Wu
HUNTSMAN POLYURETHANES
TRFA 2006 Annual Meeting September 11, 2006
2
Gel

• Gel a colloidal system consisting of a liquid
  which is dispersed in a solid polymeric matrix
  resulting in a soft, gelly, material.
• Applications
• Adhesives
• Energy absorbers, dampers

3
PU Gels

• Hydrogel
• Poly(ethylene oxide) network swelled with water
• Plasticizer gel
• PU network plasticized with phthalates
• Polyol gel
• PU network with excess multifunctional polyol
• Monol gel
• Polyol mixture of diol and monol crosslinked with
  multifunctional isocyanates

US6908979 and US6914117 (Huntsman patents)
4
Polyol Gel

• Materials
• Rubinate? 1209 prepolymer based on MDI (NCO
  21.5)
• Jeffol G31-55 polyether triol (OHv 55)
• Jeffcat TD-33A tertiary amine catalyst

Cat.

• Index
• r ? NCO0/OH0
• r 0.5 1.0
• Conversion
• p ? (NCO0 NCO)/NCO0

5
Rheology

• Rheology study of the flow and deformation of
  matter.

AR 2000 Rheometer
G storage modulus G loss modulus ? phase
angle tan-1(G/G)
6
Curing Rheology (r 0.5, 0.6)
Gel Point G G
7
Curing Rheology (r 0.7, 0.8)

• Similar behavior to r 0.6.

8
Curing Rheology (r 0.9, 1.0)

• G shows 2nd stage growth .

High crosslink density
9
Curing kinetics
Gel Point

• Molecular weight Mw(r,p)
• Crosslink density ?(r,p)
• Macosko and Miller, 1976

10
Viscosity at Initial Stage

• Viscosity ?0 G/? (? 1 rad/s)

11
Initial Growth of Molecular Weight
?0 Mw2

• ?0 Mw for unentangled polymers
• ?0 Mw3.4 for entangled polymers

12
Crosslink Density ?
13
Viscoelastic Properties (r 0.5,0.6)
G ?0 (low ?),G ?0.5
G G ?0.5 (critical gel)
14
Viscoelastic Properties (r 0.7,0.8)
G ?0, G ?0.5
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Viscoelastic Properties (r 0.9,1.0)
G ?0, G ?0 0.5
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Plateau Modulus G0
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Curing Rheology at High Indices
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Relaxation Behavior During Curing
G ?0.5
G ?0
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Mechanism Dangling Chains

• Before transition

? lt 0.4 mol/L ? dangling chains gt 50
G ?0.5

• After transition

? gt 0.6 mol/L ? dangling chains lt 25
G ?0
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Conclusion

• Before gel point
• Initial ? and Mw growth is nearly independent of
  index
• log(?) t
• After gel point
• index r ? ? crosslink density ? ? ? dangling
  chain ? ? G(?), G(?)
• r 0.5 G G ?0.5 (critical gel)
• r 0.6 0.8 G ???0, G ?0.5
• r 0.9, 1.0 G ???0, G ?0 0.5 (2nd stage
  growth)

21
Effect of Conversion on Mw and ?

• Macosko and Miller, 1976