The Chemistry of Polyurethane Elastomers Robert Czeiszperger Anderson Development Company

History of PU O • Poly – Urethane C H2N • Poly = Many • Urethane a.k.a. Ethyl Carbamate

O

CH2

CH3

– Historically used as a cancer fighting drug, but found to cause cancer itself – Found in beverages made by fermentation such as beer and wine

Chemical Reactions H

H N

C

O

+

O

Isocyanate

N

R R

R

Hydroxyl

O C O

Urethane

R

Chemical Reactions H

H N

C

O

R

+

N

N

R

H

O C

R

N H

Isocyanate

Amine

Urea

R

Chemical Reactions H N

C

+

O

R

Isocyanate

N

O H

O

H

C

R

O

H

Carbamic Acid

Water

O

C

O

CO2 gas evolves

H

H

O N

N

C

R

N R

Urea

H

C

O

+

N R

H

R

2nd Isocyanate

Amine

Polyurethane Application Overview • Flexible Foam – Furniture and Bedding – Automotive Seating

• Rigid Foam – Dow Great Stuff®

• Coatings – Truck Bedliners (Polyurea, technically)

• Adhesives – Gorilla® glue

• Sealants – Caulk like you’d get a Lowe’s or Home Depot

• Elastomers – “Cast” Urethane

PU Elastomer Applications • • • • •

Oilfield parts Mining Industrial rolls and wheels Fork truck tires Recreation – inline skate wheels – Golf balls

• Everything else imaginable

Diphenylmethane Diisocyanate (MDI) 4,4’-MDI “pure MDI”

C

O

N

N

C

O

N

2,4’-MDI Gives liquidity

C O

4 position is 3x reactive than the 2 position

N C O

2,2’-MDI N C O

N C O

Toluene Diisocyanate (TDI) CH3

CH3

N C

N

O

N

C

C

O

O

N C O

2,4-TDI

2,6-TDI

Available as 100% 2,4, 80/20, and 65/35

Ultra-High Performance Diisocyanates

N

C

O H3C

O

C N

O

O

C

CH3

N C O C

N

N

N

1,5-Naphthalene Diisocyanate (NDI)

1,4-Phenylene Diisocyanate (PPDI)

Very Symmetric

o-Tolidine Diisocyanate (TODI)

C

O

Aliphatic Diisocyanates O

O C

O C

C N

N

Hexamethylene Diisocyanate (HDI) CH3

N C O

N H3C

Slower to react

C O

Dicyclohexylmethane Diisocyanate (H12MDI) Heat and Light Stable

N N

C

O

CH3

Isophorone Diisocyanate (IPDI)

Polyether Polyols H

H

H

O

CH2

x

O CH

CH2 n

CH2

CH3

Polypropylene Glycol (PPG)

O

CH2

CH2

O

O CH2 O H CH n CH3

Hydroxyethyl capped Polypropylene Glycol (EO capped PPG)

CH2 CH2 CH2 CH2 O

H n

Polytetramethylene Ether Glycol (PTMEG)

H O

x

Polyether Polyols

O O

O

CH3 Ethylene Oxide

Propylene Oxide

THF

Polyester Polyols O

Polyethylene Adipate

O

O H

H

O

O

x

O

O

Polybutylene Adipate

O

O H

H

O

O O

O O H

O x

H

O

O O

Polycaprolactone (1,4-BDO initiated)

x

x

Polyester Polyols O R

C

+

OH

Acid

O HO

R

Alcohol

1

R

C

O

Ester

O O

O O

Caprolactone

R

1

+

H2O

“MDI” Chain Extenders - Diols CH2 CH2 OH HO CH2 CH2

CH2 O CH2 HO CH2 CH2 OH

1,4-Butanediol (BDO)

Diethylene Glycol (DEG)

O HO

O OH

O

HO O

Hydroxyethyl Resorcinol (HER)

Hydroquinone dihydroxylethyl Ether (HQEE)

OH

“TDI” Chain Extenders – Aromatic Diamines Cl

Cl

H2N

Cl

Cl

H3C

NH2

4,4’ Methylenebis (2-orthochloroaniline) (MBOCA or MOCA)

CH3

H2N

NH2

H3C

CH3

Methylenebis (3-chloro-2,6-diethylaniline) (MCDEA) CH3

CH3 NH2

H3C

S NH2

H2N

S

S

CH3

CH3

NH2

S

O

CH3

O O

H2N

O NH2

3,5-Dimethylthio-2,4(or 6)-toluenediamine Trimethylene glycol di-p-aminobenzoate (2,4-DMTDA and 2,6-DMTDA) (TGDBA)

“Aliphatic” (Isocyanate) Chain Extenders – Aromatic Diamines H2N

NH2

Methylenedianiline (MDA) CH3

CH3

NH2 H3C

H2N

NH2

H3C

NH2

CH3

Diethyltoluenediamine (2,4-DETDA and 2,6-DETDA)

CH3

Triol Crosslinkers OH

HO

HO

H3C

OH

N

CH3

HO

CH3

CH3

OH

Trimethylolpropane (TMP)

Triisopropanolamine (TIPA)

O HO O

OH

O OH CH3

Hydroxyethyl Capped TMP (93 equiv. wt EO-capped TMP)

Elastomer Structure (Morphology) • Three Basic Components – Diisocyanate – Chain Extender (Curative or short chain diol) – Polyol

• These three components react together and form two phases. – Hard-segment phase – Diisocyanate + Chain Extender – Soft-segment phase - Polyol

Elastomer Structure (Morphology) • Two Types of Hard-Segment Phases – Symmetrical Diisocyanates (MDI, H12MDI, NDI,PPDI, TODI) reacted with symmetrical diol curatives. • Phase separation driven by order or crystallinity. • Results in “macro” phase separation with larger hard segments

– Unsymmetrical Diisocyanates (TDI, IPDI) need aromatic diamine curatives (resulting in urea linkages) to form a good elastomer. • Phase separation driven by hydrogen bonding of urea linkage • Results in “micro” phase separation with smaller hard segments

Urethane and Urea Linkage: Hydrogen-Bonding O

H N R

H

O N

C O

R

C

R

N

R

H

Urethane (One H-Bond)

Urea (Two H-Bonds)

Elastomer Structure (Morphology)

Elastomer DMA Curve

Stoichiometry • Stoichiometry: Ratio of components on a molecule basis – For urethanes, ratio of Curative reactive groups to unreacted isocyanate groups in prepolymer – 0.95 = 95 curative reactive sites to 100 isocyanates – MDI systems use the inverse of stoichiometry • Isocyanate to curative groups

Stoichiometry Effect on Polymer MW

STOICHIOMETRY EFFECT 500 450 400 350 300 250 200 150 100 50 0 0.800

Split Tear vs. Stoichiometry

0.900

1.000

1.100

1.200

STOICHIOMETRY EFFECT Compression Set vs. Stoichiometry 70 60 50 40 30 20 10 0 0.800

0.900

1.000

1.100

1.200

Stoic. Effect on Properties • Hardness – Stable; minor change 85 to 105

• Modulus – Stable; minor change 85 to 105

• Tensile – Max @ 95 to 100; slight decrease outside

• Tear Strength – Max @ 100 to 105; significant decrease below this range

• Elongation – Max @ 100 to 105; minor decrease below this range

Stoic. Effect on Properties • Compression Set – Decreases from 105 to 90

• Abrasion – Increases from 90 to 105

• Hysteresis – 90 to 95 is optimum

• Flex Life – 100 to 105 is optimum

• Resilience – Max @ 85 to 90; slight decrease above this range

Polyurethane Additives • Catalysts – Used to increase reaction rate and decrease demold time. • Metal catalysts – NCO:OH reaction – Tin (dibutyltin dilaurate, stannous octoate) – Bismuth (bismuth neodecanoate) – Zinc

• Amine catalysts (33LV) – NCO:OH and NCO:Water • Organic acids (oleic acid, adipic acid, azaleic acid) – NCO:NH2 reaction.

Polyurethane Additives • Plasticizers – – – – –

Ester or Ether – Benzoflex® 9-88SG, Santicizer® 160 Ester – DBP Ether – DOP, DOA Used to lower elastomer hardness Typically lower mechanical properties by the percentage used.

• Degassing agents – Used to prevent severe foaming during the degassing step. – Sag 47, X-Air

Polyurethane Additives • Pigments and Dyes – Used to color the elastomer – Diluted in a plasticizer or polyol typically

• Fillers – Calcium carbonate, talc, silica – Used to lower cost – Difficult to process due to increased viscosity

• Slip Aids – Surface modified UHMW-PE, Teflon, Moly, Silicone compounds – Used to lower coefficient of friction and improve abrasion

Polyurethane Additives • Antioxidants – Used to protect against polyether backbone degradation due to heat and oxygen

• UV Stabilizers – Used to prevent or delay polyether backbone degradation and/or discoloration due to UV light

• Anti-Static Agents – Used to eliminate or reduce the static electric charge on the elastomer surface

Polyurethane Additives • Flame Retardants – Halogenated or phosphorus containing compounds used to reduce the tendency of elastomers to burn.

• Antimicrobial Agents – Used to prevent microbial or fungal attack of polyesters

• Antihydrolysis Agents – Used to delay hydrolysis of polyesters –Staboxyl®