Peroxide Crosslinking of Elastomers

International Latex Conference

August 11, 2015

Peter Dluzneski

Outline

- Polymer Applications for Organic Peroxides

- Classes of Organic Peroxides

- Crosslinking Mechanisms of Sulfur and Organic Peroxides

- Advantages of Organic Peroxides in Crosslinking

- Kinetic Considerations in Peroxide Decomposition

Organic Peroxides

ROOR’RO:OR’

- When Heated, the Peroxide Bond Cleaves

Homolytically to Yield Two

Radicals.

RO• •OR’

- These Radicals are Highly Reactive

(Electrons Don’t Like to be Unpaired)

RO• •OR’

- Peroxides have O-O Bond

Organic Peroxides Uses

Monomers

Polymer

Modified

Polymer

Final

Polymer

Product

Organic Peroxides Uses

Monomers

Polymer

Modified

Polymer

Final

Polymer

Product

Polymerization

Initiation

C CR•

C C•R C C

C CR C C•

C CC C

C C•C CC

C CC C•

C CCC C

C C•

6

Monomers

Polymer

Modified

Polymer

Final

Polymer

Product

Polymerization

Initiation

C CR C C•C

C CC C•

CC C

C C•

Organic Peroxides Uses

7

H

Monomers

Polymer

Modified

Polymer

Final

Polymer

Product

Polymerization

Initiation

Grafting

RO•

ROH•ROH •ROH

X

•

X

•

X•

•

Organic Peroxides Uses

8

•

Monomers

Polymer

Modified

Polymer

Final

Polymer

Product

Polymerization

Initiation

Grafting

Visbreaking

RO• HROH•ROH ••••

Organic Peroxides Uses

9

Monomers

Polymer

Modified

Polymer

Final

Polymer

Product

Polymerization

Initiation

Grafting

Visbreaking

ROH

•

•

Cross-Linking

ROORRO• •OR

HH ROHHOR•• ROHHOR

Organic Peroxides Uses

10

Monomers

Polymer

Modified

Polymer

Final

Polymer

Product

Polymerization

Initiation

Grafting

Visbreaking

Cross-Linking

••

Organic Peroxides Uses

11

Hydroperoxides

1hr Half-Life

Temp (°C)Typical

Structure

Example

Products

Primary

Applications

180 to 200 R-OOH Luperox® CU-80

Luperox® DIBHP

Ketone Peroxides N/A R2-C(OOH)2

et al

Luperox® DDM-9

Luperox® 224

Dialkyl Peroxides 137 to 152 R-OO-R’ Di-Cup®

Vul-Cup®

Luperox® 101

Luperox® D16

Crosslinking

Polymer Modification

Polymer Initiation

Composite Cure

Peroxyketals 112 to 134 Luperox® 230

Luperox® 231

Luperox® 331

Luperox® 531

Peroxyesters 56 to 125 Luperox® P

Luperox® 10

Crosslinking

Polymer Initiation

Composite CureRC-OOR’

O

Monoperoxy

Carbonates

117 to 121 Luperox® TAEC

Luperox® TBECROC-OOR’

O

Diacyl Peroxides 81 to 92 Luperox® A

Luperox® DEC

Luperox® LP

Crosslinking

Polymer Initiation

Composite CureRC-OOCR’

O O

R-C-R’

OO-R

OO-R

Peroxy

Dicarbonates

66 to 69 Luperox® 221

Luperox® 223

Luperox® 225ROC-OOCOR’

O O

Polymer Initiation

Composite Cure

Polymer Initiation

Composite Cure

Crosslinking

Polymer Initiation

Composite Cure

Crosslinking

Polymer Modification

Polymer Initiation

Composite Cure

Polymer Initiation

Composite Cure

Organic Peroxides Uses

Crosslinking Involves the Formation of Covalent Bonds Between Polymer Chains

● Improves High and Low Temperature Properties

● Higher Tensile Strength, Lower Elongation

● Better Fluid Resistance

● Lower Compression Set

● Better Fluid Resistance

● Improved Resistance to Stress Cracking

Polymer Crosslinking

Sulfur vs. Peroxide Cure Mechanisms

Polymer Crosslinking

Sulfur Peroxide

H H H H

S S

S

S

S

S

S S

R O O R’S S

S

S

S

S

S S

S SS

S

S

S

S S

S SS

S

S

S

S S

S SSSS S

S S

S SSSS

S S SH HS SSSS S S SH HS S

SSS

SS SS

S

SS

S

S

SS

S S

SS

S

S

S

S

Sulfur vs. Peroxide Cure Mechanisms

Polymer Crosslinking

S S

SS

S

S

S

S

Sulfur

H H

R O O R’R O• •O R’R O•

•O R’R O•

•O R’R O••O R’ R O••O R’ R OHHO R’• •

Peroxide

Sulfur vs. Peroxide Cure Mechanisms

Polymer Crosslinking

S S

SS

S

S

S

S

Sulfur Peroxide

• •• •• •• •••

- Sulfur becomes the cross-link - The peroxide induces a direct C-C cross-link

- Relatively weak S-S bonding that can

break and re-form.

- Direct C-C bonding that is much more

difficult to break.

Sulfur vs. Peroxide Cure Mechanisms

Polymer Crosslinking

Sulfur Peroxide

S S

SS

S

S

S

S

- Sulfur becomes the cross-link - The peroxide induces a direct C-C cross-link

- Relatively weak S-S bonding that can

break and re-form.

- Direct C-C bonding that is much more

difficult to break.

- Simple Formulation

- Cure kinetics controlled by peroxide selection

and other ingredients (e.g. coagents

and anti-scorch agents)

- Requires activator and accelerator

- Cure kinetics controlled by accelerators

- Not inhibited by open-air curing

Comparison of Cure Properties

Sulfur vs. Peroxide Cure Mechanisms

Polymer Crosslinking

Sulfur Peroxide

S S

SS

S

S

S

S

- Simple Formulation

- Cure kinetics controlled by peroxide selection

and other ingredients (e.g. coagents

and anti-scorch agents)

- Requires activator and accelerator

- Cure kinetics controlled by accelerators

- Not inhibited by open-air curing

Comparison of Cure Properties- Better Heat Aging/Compression Set

- No Discoloration

- Better Clarity

- Able to Co-vulcanize Saturated and Unsaturated

Elastomers

- Better Abrasion Resistance

- Better Hot Tear Resistance

Comparison of Vulcanizate Properties

Polymers that can be Crosslinked with Peroxides

Polymer Crosslinking

Sulfur can only be used to cross-link polymers

that contain unsaturation.

Fully saturated polymers can only be cross-linked by

Peroxides.

Sulfur Peroxide

Other

BR – Polybutadiene

SBR – Styrene Butadiene

NBR – Nitrile- Butadiene

IR - Polyisoprene

NR – Natural Rubber

CR - Polychloroprene

EVA – Ethylene Vinyl Acetate

EPM (“EPR”) – Ethylene-Propylene

EPDM – Ethylene-Propylene-Diene

IIR (“Butyl”) – Butylene-Isoprene

HNBR – Hydrogenated Nitrile- Butadiene

PE – Polyethylene

CM (“CPE”) – Chlorinated Polyethylene

CSM – Chlorosulfonated Polyethylene

ACM – Polyacrylate

MQ – Silicone

ECO – Polyepichlorohydrin

FKM – Fluoroelastomers

BRSBR

NBR IR

NR

EPDM

EPM

EVA

HNBR

PE

IIR

CSM

CM

CR

MQ

ACMFKM

ECO

Some polymers contain additional functionality which

Allows them to be cross-linked by other chemical agents.

Overall, peroxides are the most universal cross-linking agent.

Polymer Crosslinking – Heat Aging

Properties of NBR Compound after Heat Aging (70 hrs at 257°F)

Sulfur Cured Peroxide Cured

Before After Before After

Tensile strength (MPa) 19.3 13.7 21.4 23.1

Elongation, % 380 80 395 215

Compression Set (%) Sulfur Cured Peroxide Cured

70 hrs at 212°F (100°C) 66 20

70 hrs at 257°F (125°C) 82 30

Organic Peroxide Decomposition is a First Order Reaction

● The Rate of Decomposition is Dependent on Temperature

● The Extent of Decomposition is Dependent on Both Time and Temperature

● The Half Life is the Time Required for Half of the Peroxide Groups to Decompose at a Given Temperature

Organic Peroxide Decomposition

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

0 1 2 3 4 5 6 7 8

Per

cen

t R

emai

nin

g P

ero

xid

e

Number of Half Lives

Percent of Peroxide Remaining with Subsequent Half Lives

50%

25%

12.5%

6.25%3.13% 1.6% 0.8% 0.4%

Organic Peroxide Decomposition is a First Order Reaction

● The Rate of Decomposition is Dependent on Temperature

● The Extent of Decomposition is Dependent on Both Time and Temperature

● The Half Life is the Time Required for Half of the Peroxide Groups to Decompose at a Given Temperature.

Organic Peroxide Decomposition

Half-Life of Di-Cup® DiCumylPeroxide at Various Temperatures

Temperature

Half-Life Time(°C) (°F)

25 77 ~2500 years

40 104 ~140 years

50 122 ~22 years

100 212 ~ 4 days

150 302 ~15 minutes

200 392 ~ 9 seconds

k=A • e -Ea/RT

Arrhenius Rate Equation

Organic Peroxide Decomposition

50°

60°

70°

80°

90°

100°

110°

120°

130°

140°

150°

160°

170°

180°

190°

250°

150°

350°

200°

300°

°C °F

Luperox® 610

Luperox® 10

Luperox® 11

Luperox® DEC

Luperox® A98

Luperox® 231

Luperox® P

Di-Cup® RVul-Cup® R

Luperox® D-16Luperox® DI

Luperox® CU80

1 Hour Half Life

Temperature

The Stability of the Organic Peroxides Varies Greatly

● The Temperature Required for Half of the Peroxide to

Decompose in One Hour is Referred to as the

“1 Hour Half Life Temperature”

● This Provides an Indication of the Stability of the Peroxide

and Can Be Used as a Guide to Select the Proper Peroxide

for an Application.

Temperatures Required for Full Cure in 30 minutes

°C °F

Luperox® 225 90 194

Luperox® LP 100 212

Luperox® 575 110 230

Luperox® 231 135 275

Luperox® TBEC 145 293

Vul-Cup® R 160 320

Summary

Organic Peroxides are Used in Many Industries to Manufacture, Modify, and

Crosslink Polymers.

The Organic Peroxide Crosslink Mechanism Differs Greatly from that of Sulfur

and Offers Many Advantages Over Other Vulcanization Techniques.

The Stability of Organic Peroxides Vary Greatly Depending on the Molecular

Structure.

The Wide Range of Organic Peroxide Stabilities Enables the Selection of an

Appropriate Peroxide for Virtually Every Application.

Disclaimer

The statements, technical information and recommendations contained herein are believed to be accurate as of the date hereof. Since the

conditions and methods of use of the product and of the information referred to herein are beyond our control, Arkema expressly disclaims any

and all liability as to any results obtained or arising from any use of the product or reliance on such information; NO WARRANTY OF FITNESS

FOR ANY PARTICULAR PURPOSE, WARRANTY OF MERCHANTABILITY, OR ANY OTHER WARRANTY, EXPRESS OR IMPLIED, IS MADE

CONCERNING THE GOODS DESCRIBED OR THE INFORMATION PROVIDED HEREIN. The information provided herein relates only to the

specific product designated and may not be applicable when such product is used in combination with other materials or in any process. The user

should thoroughly test any application before commercialization. Nothing contained herein constitutes a license to practice under any patent and

it should not be construed as an inducement to infringe any patent, and the user is advised to take appropriate steps to be sure that any proposed

use of the product will not result in patent infringement.

© 2011 Arkema Inc.

Di-Cup® is a Registered Trademark of Arkema Inc.

Vul-Cup® is a Registered Trademark of Arkema Inc.

Luperox® is a Registered Trademark of Arkema Inc.

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