Introduction to Polyurethane - · PDF fileWhat Are Polyurethanes? • Polyurethanes are...
Transcript of Introduction to Polyurethane - · PDF fileWhat Are Polyurethanes? • Polyurethanes are...
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Introduction to Polyurethane! Chemistry and Structure-Property Relationships
05/07/16
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Monomers and Polymers
• Monomer(mono–one;mer–part):Smallmolecules• Polymer–Cons8tutesmanymonomers.• Polymeriza8on–Processofcovalently(chemically)bondingmanymonomers
together.Canbefewhundredstothousandsmonomerunits
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Polymer types
• Polymers can be broadly classified into • Thermosets–Cannotbemeltedonceformed
• Elastomers(NaturalRubber,PU,SBRetc)• RigidThermosets(Epoxy,Vinylesteretc)
• Thermoplas8cs-Canberecycled• EngineeredPlas8cs(PC,Nylon,AlloyssuchasXenoyetc)• CommodityPlas8cs(HDPE,PPetc)
• Choice of Polymer depends on • Hardnessandotherphysicalpropertyrequirements• Environmentalfactors(Exposuretooil,water,otherfluids,Temperatureetc)• Toolingcost(Injec8onmoldsvsopencastvscompressionmolds)• Modeoffailure(Fa8gue,cutandtear,wear,compressiveloadsetc
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What Are Polyurethanes?
• Polyurethanes are organic polymers that contain the urethane group in the structure
• Typically, polyurethanes are formed via the reaction of a Polyol (-OH group) with a Isocyanate (-NCO group)
• Polyureas contain the urea group in the structure
• Compositions may be contain just urethane group or a combination of urea and urethane groups.
R
NH O
O
R R
NH
O
NH
R
UrethaneGroup UreaGroup
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Polyurethane classifications
- Linear polyurethanes - Castable polyurethanes - Millable polyurethanes - Thermoplastic polyurethanes - Cellular polyurethanes - Sprayable polyurethanes - Porometric polyurethanes - Spandex fibers
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Castable Polyurethanes
• Represent only a small portion of the overall polyurethane industry • Made by mixing several ingredients, introducing into a mold, and heat curing at
temperatures (100-130°C)
• The curing process operates by extending chains of a prepolymer made from a macro diol and a diisocyanate
• The full mechanical properties of the urethane are not realized until a posturing operation is completed
• Castable urethanes can be cured with amine or diol curatives. Special formulations may use a combination of diols and amines as curatives.
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POLYURETHANES
RUBBERS PLASTICS
RubberBand
CarTireTread
Men’sShoeHeel
MaterialHardnessComparison
GolfBall
BowlingBall
Fluo
rocarbon
s
Polyprop
ylen
e
Polystyren
e
Nylon
s
Acetals
Ulte
m
Acrylics
Phen
olics
4555657585
SHOREDDUROMETER507090100110120130140150
ROCKWELLR
203040506070809095
SHOREADUROMETER
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Polyurethane (A versatile compound)
CuredPolyurethane
DiisocyanateType1)TDI2)MDI3)PPDI
4)H12MDI5)HDI6)TODI
PolyolType1)Polyether2)Polyester
3)Polycaprolactone4)Polycarbonate
CuraVveType1)MBOCA
2)Butanediol3)TMP4)TIPA
5)DiethyltolueneDiamne
PartA,Prepolymeror“Resin”
PartB,Cura8veor“Poly”
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Diisocyanates used in Cast Urethanes
Aromatic • Toluene diisocynate (TDI) 2,4 & 2,6
• 4,4’ diphenylmethane diisocyanate (MDI)
• Paraphenylene diisocyanate (PPDI)
• 1,5-naphthalene diisocyanate (NDI)
• Reactivity: NDI> MDI> TDI
TDI
MDI
PPDI
NDI
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Diisocyanates (cont’d.)
Aliphatic • H12MDI
• 1,6 Hexamethylene diisocyanate (HDI)
• Lower reactivity
• Non-yellowing due to lack of double bonds.
• Lower volume in hot cast market
H12MDI
HDI
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Polyols used in Hot Cast Urethanes
Polyethers • PTMEG or Poly THF(C4): Excellent mechanical properties, hydrolysis resistance and very low abrasion
loss. • PPG(C3)-cheaper with lower performance. More susceptible to oxidation
Polyester • Compounds formed by polymeric reaction of an acid (adipic acid) with a glycol (ethylene glycol). Water is
the by product • Better tear, abrasion and oil resistance but lower hydrolytic stability Polycaprolactone (C6) • Subgroup of polyesters. More expensive • Hydrolysis resistance: Polyester< Polycaprolactone< PTMEG
Polycarbonate • Superior hydrolysis resistance • Excellent High Temperature properties • High viscosity polymers. Difficult processing.
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Polyols - Polyethers O
CH2 - CH - CH3
Propylene Oxide
HO - (CH - CH2 - O)n - CH2 - CH - (O - CH2 - CH)n - OH
CH3 CH3 CH3
H2C CH2
H2C CH3
O
Tetrahydrofuran
HO - (CH2 - CH2 - CH2 - CH2 - O )n - CH2 - CH2 - CH2 - CH2 - OH
Poly(oxytetramethylene) glycol (PTMG)
Polypropylene Glycol (PPG)
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Polyols - Polyesters
HO - CH2 - CH2 - OH + HO - C - CH2 - CH2 - CH2 - CH2 - C - OHEthylene Glycol Adipic Acid
HO - CH2 - CH2 - (O - C - CH2 - CH2 - CH2 - CH2 - C - O - CH2 - CH2)n - OH
Polyethylene Adipate Glycol
-H2O
O
O O
O
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H2N CH2 NH2
MBCA (4,4'-Methylene bis (2-chloroaniline)
ClCl
1,4 -Butanediol
HO - CH2 - CH 2 - CH2 - CH 2 - OH
Hydroquinone bis (beta hydroxyethyl) ether (HQEE, XA)
HO - CH2 - CH 2 - O O - CH2 - CH 2 - OH
Trimethylolpropane (TMP)CH3 - CH2 - C - CH2 OH
CH2 OH
CH2 OH
MBOCA
BDO, 1,4-BD
HQEE
TMP
Curatives
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Reactivity of Isocyanate group
• Highly reactive, affected by electronic structure
• “R” group effects the reactivity of the NCO group
• Also reactivity is driven by the compound reacting with isocyanate group
• Amines>Hydroxyls• Alipha8cAmines>Aroma8camines• PrimaryHydroxyls>SecondaryHydroxyls
R"N=C=O
!OH!NH
H"O"H
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Cast Polyurethane Types
CastPolyurethanes
Prepolymers
QuasiPrepolymers
OneShotSystems
• BestPerformance• Lessforgivingonra8o• Mostexpensive
• Highermonomercontentthatprepolymer
• Widerangeofhardnessfrom3components
• Processingcanbechallenging
• Cheapest• Lowestperformance• EH&Sissuesduetomonomer
handling• Exothermneedstobe
managed
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Formation of Prepolymer
OHHO R NCOOCN
OO
+
RNH NCOC
OR N
HOCN CO
POLYOL DIISOCYANATE
URETHANE PREPOLYMER
FurtherchainextensioncanoccurashydroxylsitesreactwithterminalNCOgroups.
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Prepolymer Curing with Chain Extender
ChainextensionwithUrethanegroup:Polyurethane
ChainextensionwithUreagroup:Poly(Urea-Urethane)
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Prepolymer Curative
Polyurethane Prepolymer Processing
Dispensing
Demold
Curing
Finishing
Post-Cure
(Melting),Warming &Degassing
Melting orWarming
(Degassing)
Metering
Molding
Mixing
Part A Part B
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Choice of Polyurethane
• Application specific performance • Ethershavebeeerhydoly8cstabilitythanesters• Estershavebeeeroilresistancethanethers• Estershavebeeercutandtearresistancethanethers• Aminecuredurethaneshavebeeerhightemperatureproper8esthandiolcured
urethanes.
• Processing • TDIsystemsareeasiertoprocessthanMDIsystems• Diols(suchas1,4BDareliquidatroomtemperature)whereascertainamines(suchas
MBOCA)needtobemelted
• Cost • MDIsystemsaregenerallycheaperthanTDIsystems• Estersaretypicallycheaperthanethers• QuasisystemsarecheaperthanPrepolymers
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Schematic of Polyurethane elastomer
• SofSegment• Hardsegment• Hydrogenbonding
• SelfreinforcingstructureofPU
• Performancecanbeachievedbychoosingrightrawmaterials
• Performanceenhancingaddi8vesrarelyneeded
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1. CONCENTRATION OF HARD SEGMENT
2. COMPOSITION OF SOFT SEGMENT
3. COMPOSITION OF HARD SEGMENT
4. SEGREGATION OF HARD SEGMENT
SoftSegment
HardSegment
What controls properties?
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Phase segregation and effect on properties
• Phasesegrega8onrequirementsareapplica8onspecific
• Aprocessorcancontrolphasesegrega8onbychoosing• Chemistry(Iso/Polyol/cura8vepackage)
• TDI/PTMEG/MOCA=Good.TDI/PTMEG/BD=Bad
• Ra8oofcura8ve• >100%theory=morelinear=beeerfa8gueresistance.• Toomuchexcesscura8ve(>120%)disruptsphasesegrega8on
• Processingcondi8ons• Highermoldtemperatures(belowdegrada8on)leadstosmallercrystalsize=lowerhardness
• Typically suppliers are able to provide application specific chemistry but a general knowledge of urethane chemistry helps in understanding why certain choices are made
• Good phase segregation leads to • Hightemperatureproper8es• Beeerdynamics(lessheatbuildunderdynamicloads)• Fa8gueproper8es• Cutandtearresistance
• Certain applications may also require “not to great” phase segregation • Deadblowhammer–cura8vepackagesinten8onallydisruptnaturalphasesegrega8on.
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Structure property relationships
ApplicaVonrequirements
Chemistry Comments
Highcutandtear Polyesterbackone Hydrogenbondingleadstocutgrowthresistance
Highrebound PTMEGbackbone Highlevelsofphasesegrega8on.Beeerrebound
Sofcompounds Triolcures Triolcuresdisruptphasesegrega8onleadingtolowerhardness
Clearcompounds Alipha8c Lowerphasesegrega8on.Saturateddoublebonds–nofreeradicalgenera8on
Morein“WhatUrethaneWhere”presenta8on
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• Reac8onsofisocyanatesareallexothermic• LiquidPrepolymerscanReactWith:
-HydroxyCompounds-Amines-Water-UreasandUrethanes-AndcanDimerize(isocyanatepolymeriza8on)
Reactions of Prepolymers
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Reaction with Water
H2N-R-NH2 + 2CO2 2 H2O+ OCN-R-NCO
• The reaction with water provides the primary source of gas for blowing in the manufacture of low density flexible foams.
• Can be an issue in hot cast where bubbles/foam is not needed • Water can be introduced while
• Drum handling • Curative handling • Processing
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R’-NCO+OCN-R’
CCO
O
R’-NN-R
Uretidinedione (dimer)
Isocyanate Polymerization Reactions
• Dimerreac8onismorecommonwithMDIprepolymerswithhighmonomercontent
• Happensatalltemperaturebutmoreprevalentathigherorlowertemperatures• Shelflifecri8calinmanycompoundswithhighmonomercontent
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~ R C O R ~ + H2O ~ R C OH + HO R ~O O
~ R NH C NH R ~ + H2O ~ NH C OH + H2N R ~O O
~ R NH C O R ~ + H2O ~ NH C OH + HO R ~O O
Ester Acid Alcohol
Urea Carbamic Acid Amine
Urethane Carbamic Acid Alcohol
Hydrolysis Reactions
• EsterhydrolysiscommonissuewhenusingPolyesterbasedPUinhotmoistenvironments(Example:TDI/Ester/AminecureinAsia)
• Diolcureslesssuscep8blethanaminecures
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Additives Plasticizers:
– Non-Reactive Diluents (Do Not Change Ratio of Curative/Prepolymer) – Benzoflex 9-88SG: 10pph Lowers Hardness 5-6 Points With Esters – Usually Preblend with Prepolymer; With Curative Sometimes – Typically used to soften or reduce cost
Fillers – No Reinforcing Action in Urethanes – Must Be Dry – Cost reduction in Conjunction with Plasticizers – 10 pph Increases Hardness About 2 Points – Not common to use fillers
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Catalysts and Other Additives
Catalysts – Amine Cures (e.g., MBCA, E 300)
• Azelaic, Adipic, Oleic Acids – 0.2% Azelaic in MBCA
Reduces Pot Life and Demold by Factor of 2
– Diol/Triol Cures (e.g., 1,4-BD, HQEE, TMP)
• Niax A-33, Fomrez C-2, SUL-4, UL-32
– Highly Active in MDI Systems
Other Additives – Degassing Aids – SAG-47
– Internal Lubricants – Graphite, MoS2 , Silicones, etc.
– Antistatic Agents – Catafor, Carbon Blacks
– Stabilizers – Stabaxol for Esters, Antioxidants, UV Stabilizers
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Ques8ons