Cure Reactivity - A Route to Improved Performance in Halobutyl Applications TI

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TITLE:

Cure Reactivity - a Route to Improved Performance inHalobutyl Applications

TEXT:Summary

The halogenation of butyl rubber with eitherchlorine or bromine significantly increasescure reactivity, provides compatibility withunsaturated polymers, and enhancesadhesion as compared to regular butylrubber.

The differences in cure reactivity ofchlorinated and brominated butyl and theirversatility in responding to a wide range ofcuring systems are illustrated. Significantimprovements in heat, ozone, flex fatigueresistance and compression set can beachieved through the selection ofappropriate curing systems.

The versatility and properties of halobutylrubber have led to significant growth in theuses of butyl type polymers in a diverserange of tire and non-tire applications whichare described in this Technical Information.

Introduction

The halogenation of polymers has beenstudied extensively since Roxborough firstchlorinated natural rubber in 1801 (1). Thepotential commercial utility of such a productwas not recognized until 1930 when smallquantities were produced for use inprotective coatings, inks, and adhesives.Attempts were made to produce chlorinatedemulsion polyisoprene during World War IIand patents were issued to Bartovics (2) andDIanni (3). The chemistry of the chlorinationof natural rubber was extensively studied byBloomfield (4).

Extensive early references on the subject ofhalogenation of isoprene polymers and otherrubbers were published by Davis and Blake(5), and Whitby (6). Halogenation of butylrubbers was first studied by R.T. Morrisseyand co-workers at B.F. Goodrich Companyin the late 1940s (7). Their research led to

the commercialization of a brominated butylrubber, HYCAR 2202. The Goodrich workwas of great importance in demonstratingthe practical value of bromination; the abilityto form strong adhesive bonds betweenbutyl rubber and highly unsaturated rubber,as well as the ability to obtain goodvulcanizate properties in blends, which wasunattainable prior to this work, had beendemonstrated for the first time.

The early types of brominated butyl rubberwere made by a batch process in whichregular butyl rubber was mixed in internalmixers with a brominating agent and astabilizer. Despite its useful properties, thepolymer did not achieve widespreadindustrial use and was subsequentlywithdrawn from the market because of thevery high production costs and difficulties inachieving consistency and stability.

The chlorination of butyl rubber wasemphasized by Exxon workers (8) in the1950s and the first commercial product wasintroduced in 1960. This was made in acontinuous process by reacting chlorine withbutyl rubber and was less costly to producethan brominated butyl made by the earlybatch process.

Despite its early limitations, brominatedrubber offered some potential advantagesover chlorinated butyl rubber in cure rate,adhesion and vulcanizate aging. Hence, theinterest in brominating butyl persisted in therubber industry, particularly among tiremanufacturers seeking the highestperformance standards in radial tire innerliners. This interest led to the developmentby Polysar Limited (now part of Bayer AG) ofa continuous solution process by which ahighly stable and uniform brominated butylrubber could be manufactured on a largescale (9).




The development and commercialization ofbrominated and chlorinated butyl rubber hasled to significant growth in the use of butyltype polymers.

Fundamentals of Butyl and HalobutylRubber

Butyl rubbers are copolymers of isobutyleneand isoprene, the isoprene being present atlevels between 0.5 - 2.5 mole % . They arevery impermeable to air, exhibit highdamping, and are reasonably flexible at lowtemperatures, having a Tg of 72 C. Thiscombination of properties is unique. Otherpolymers exhibiting low permeability and lowresilience, such as nitrile rubber, haverelatively high Tgs and exhibit poorer lowtemperature flexibility, while polymers withlow Tgs, such as polybutadiene andpolyisoprene exhibit very high permeabilityto air.

The impermeability of butyl rubber is largelyattributable to the isobutylene chains ofwhich it is primarily composed. Two methylside groups on every other carbon atom inthe backbone cause steric hindrance. Thechains, therefore, move relatively slowly sothat they block the passage of gasmolecules rather than moving aside andletting them pass.

The bulky methyl groups also prevent thechains taking up a regular configuration andcrystallizing, while at the same time theyhave only small dipole movements which donot give rise to strong interchain attractions.Because of this structure, butyl rubbers havegood low temperature flexibility and highdamping characteristics.

The low level of isoprene units in butylrubber results in slower cure rates comparedto unsaturated polymers such as NR andSBR, making it impractical to obtain goodvulcanizate properties in blends with theseand other highly unsaturated elastomers.

Achievement of interfacial cured adhesion ofbutyl to unsaturated rubber compounds isalso impossible. These covulcanization and

adhesion deficiencies of regular butylrubbers are overcome by halogenation. Thedouble bonds provided by the isoprene inbutyl rubber will react with the halogens,bromine or chlorine, to give the bromobutyland chlorobutyl modifications of butyl rubberwhich are much more reactive than theparent polymer.

Halogenation of Butyl Rubber

As has been so often the case throughoutthe history of the rubber industry, practicaldevelopments in the applications forhalogenated butyl rubber have run ahead ofthe fundamental knowledge of the chemistry.In early patents, it was assumed thatbromination led predominantly to theaddition product, while it was understood ata relatively early stage that substitutionproducts predominated in the chlorinationreaction, but methods for precise analysiswere not available until more recently. Workby Poutsma (10) and others describe thechlorination reactions of various types ofalkenes, and these reactions are now wellunderstood.

Using model compounds, Vulkovsinvestigation of the halogenation behavior ofbutyl rubber brought about a betterunderstanding of these systems (11). Due tosteric hindrance imposed by the methylgroups, the products of chlorination andbromination differ from patterns typical ofother tri-substituted alkenes. In chlorobutylthere are no observable addition productsacross the double bonds, while inbromobutyl, substitution products notnormally observed in reactions of other tri-substituted alkenes, are predominant.

In the bromination and chlorinationprocesses, the reaction is believed toproceed by an ionic mechanism as shown inFigure 1.




+

CH2 C

CH3

CH2 + X2 CH2 C C CH2

X

HCH3

CH2 C C CH2

X

HCH2

- H+ CH2 C C CH2X

CH3 H

+

Fig. 1: Halogenation with molecularbromine / chlorine

A halogen ion is formed; a proton iseliminated; and substitution takes place.NMR (nuclear magnetic resonance) studiesindicate that up to 90 percent of the halogenis allylic to the double bond. Most of theunsaturation is retained although it is largelyisomerized

Curing Chemistry and Cure Systems

The introduction of bromine or chlorine intothe position allylic to the double bonds of theisoprenic unit converts butyl rubber into amore reactive, faster curing and moreversatile polymer. The CBr bond, beingweaker than the CCl bond, results in fastercure rates and greater inherent reactivity forbromobutyl compared to chlorobutyl. Thisgreater reactivity in bromobutyl leads to amore versatile curing chemistry andnecessitates a higher level of stabilizer in theraw polymer. Conversely, chlorobutyl,having the lower reactivity, requires higherlevels of allylic halide for a satisfactory curerate and state of cure in commercialpolymers.

Sulfur Cure

Figure 2 shows that both bromobutyl andchlorobutyl will cure with zinc oxide, but onlybromobutyl will cure with sulfur alone, nozinc oxide or accelerator being necessary.

Fig. 2: Cure response

This unique sulfur cure of bromobutyl wasfirst described by Feniak et al (12) whoshowed that either poly or disulfidecrosslinks are formed (Figure 3) and thatwhile the vulcanizates revert on heat aging,the additional of any one of a number ofbases (e.g. ZnO) improved the agingcharacteristics as well as increasing thestate of cure. Levels of sulfur as low as0.5 phr will give a rapid and reasonabledegree of cure.

~C CHBr

+ Sx ~ ~

~ ~

~ ~C CHBr

+ SxBr2 ~ ~

~ ~

~ C CH

CH2

Sy + S2Br2

CH2

C CH

C

S

CH2Br

Br

CH

Br

CH

S

C

CH2Br

Fig. 3: Proposed mechanism for sulfur cureof bromobutyl




In blends containing bromobutyl and naturalrubber with sulfur as the sole curative, thenatural rubber portion of the blend alsocures, which suggests that an intermediate,such as sulfur bromide, is formed andmigrates from the bromobutyl into thenatural rubber phase causing rapidcrosslinking of the latter.

The difference in the cure response to sulfurbetween bromobutyl and chlorobutyl is ofpractical importance as well as theoreticallysignificant.

Zinc Oxide

Zinc oxide plays an important role in curinghalobutyl rubbers. Both polymers will cure inthe presence of zinc oxide alone, the higherallylic halide content in chlorobutyl resulting

in a higher state of cure than is achieved inbromobutyl. The latter exhibits a betterbalance of scorch and cure behavior.Studies made of the mechanism of zincoxide curing of halobutyl using modelcompounds (13) show two competingprocesses occurring. The major onegenerates a zinc halide which acts as acatalyst for the crosslinking reaction.Crosslinking proceeds in a mannerdescribed by Baldwin (14) resulting in CCbond formation. The elimination of hydrogenhalide causes the formation of conjugateddiene groups which do not participate in thezinc oxide crosslinking reaction. The dienegroups form more readily in chlorobutyl thanin bromobutyl, resulting in a reduction incrosslinking efficiency (based on originalhalide content) (15). (Figure 4)




ZnO

+ ZnX2

+ ZnX3-

Initiation- Loss of HX- Formation of ZnX3

PropagationCatalysed withzinc halide

Terminationreaction

ZnX2

+

Continuation of crosslinking

D

X

X

X

Fig. 4: Mechanism of zinc oxide crosslinking




Effect of Accelerators on ZnO/S Systems

The effects of adding three differentaccelerators MBTS, TMTD or alkyl phenoldisulfide (Vultac) to zinc oxide/sulfur curesystems are shown in Figure 5. Inbromobutyl, TMTD and alkyl phenol disulfideexhibit the fastest cure rate and higheststate of cure, whereas MBTS depresses thecure rate and state of cure. MBTS isextremely useful for adjusting scorch time soas to increase scorch time and processingsafety, particularly if added early in themixing cycle. Similar effects are observedwhen using chlorobutyl, but higher states ofcure are observed when using either TMTDor alkyl phenol disulfide. MBTS is lesseffective in increasing scorch time inchlorobutyl than in bromobutyl.

Fig. 5: 100 % BB2030 / CB1240

Significantly higher levels of adhesion tonatural rubber and to itself are achieved withbromobutyl, compared to chlorobutyl, in allcure systems studied (Figure 6).

While the ZnO/S/MBTS cure system had thehighest self-adhesion, zinc oxide, whenused as the sole curative, had the highestadhesion to natural rubber. Sulfur alonegave the lowest adhesion. Similar trendswere observed in chlorobutyl but all systemsresulted in significantly lower adhesionrelative to bromobutyl. Physical propertiesfor bromobutyl and chlorobutyl are similar,the modulus of vulcanizates beinginfluenced by the cure systems.

0

5

10

15

20

25

Zn

O S

Zn

O/S

Zn

O/S

/MB

TS

Zn

O S

Zn

O/S

Zn

O/S

/MB

TS

Cure System

kNm

at 1

00C

BB 2030 / SelfBB 2030 / NRCB 1240 / SelfCB 1240 / Natural

Fig. 6: Inner liner - hot adhesion

Other accelerators commonly used to modifythe zinc oxide/sulfur cure systems includesulfenamides which, like MBTS, initially actas retarders, but ultimately produce highstates of cure; thiuram sulfides, TMTD;TMTM and DPTT in small amounts can beused as secondary accelerators and areused extensively for faster curingcompounds in industrial rubber products;morpholine disulfides, dimorpholinyl disulfide(Sulphasan R) and 4-morpholinyl-2-benzothiazole disulfide (Morfax) provideexcellent scorch safety. These may be usedeither as the sole source of sulfur inconjunction with elemental sulfur, or withsecondary accelerators such as TMTD, orguanidines. They also impart good aging,adhesion and flex properties.

Dithiocarbamates, such as ZDC, can beused in small quantities (0.25 to 0.75 phr) toaccelerate zinc oxide cures used in heatresistant applications and to improvecompression set. They impart very fast curerates and can be useful in low-temperaturevulcanization processes but are notrecommended for open steam cures. Suchcompounds are susceptible to scorch, hencethe accelerator level should be kept to aminimum.

Because of the differences in cure reactivity,lower levels and simpler cure systems areeffective in bromobutyl. The cure systems




effective in chlorobutyl tend to reduce scorchsafety in bromobutyl. Therefore, whensubstituting one halobutyl for another, anadjustment to the cure systems used isgenerally required.

Other Curatives

The introduction of bromine or chlorine intothe position allylic to the double bondenables these polymers to be cured by avery wide range of curatives, some of thembeing unconventional. This versatility is anadvantage in that control over propertiessuch as heat resistance, compression setand dynamic and static ozone resistance ispossible. As a result, a wide variety ofspecific requirements can be met for highperformance applications.

The cure reactivity of bromobutyl andchlorobutyl in response to amines,peroxides, dienophiles and phenolic resinsrelative to the sulfur and zinc oxide curesystems is illustrated in Figure 7.

0

10

20

30

40

50

60

70

DIA

K

DiC

up

Zn

O S

SP

104

5

HV

A+D

iCu

p

HV

A

Curatives

To

rqu

e in

crea

se

BB 2030 CB 1240

Fig. 7: Effect of curative on torque increasewithout zinc oxide

As would be expected, bromobutyl exhibitsgreater versatility and response to thesecure systems in the absence of zinc oxide.Zinc oxide acts synergistically with all thecuratives in both polymers and enhancesthe state of cure. The torque increase asmeasured at 166 C is higher for chlorobutyl

in all cures except for the sulfur curepreviously described. (Figure 8).

These cure systems are not only oftheoretical interest from a mechanisticviewpoint, but are of practical significance inproducing high performance vulcanizateswhich exhibit excellent ozone resistance, lowcompression set and exceptional stabilitytoward high temperature oxidation.

0

10

20

30

40

50

60

70

DIA

K

DiC

up

Zn

O S

SP

104

5

HV

A+D

iCu

p

HV

A

Curatives

To

rqu

e in

crea

se (

dN

.m)

BB 2030 CB 1240

Fig. 8: Effect of curatives on torque increasewith zinc oxide

Peroxide Curing

While butyl rubbers based on copolymers ofisobutylene and isoprene degrade rapidlywhen heated in the presence of organicperoxides, (16) bromobutyl can be curedwith peroxides in conjunction with a coagent.Vulcanizates with an unusually lowcompression set, high heat resistance andexcellent ozone resistance are produced(17).

The free-radical curing of bromobutyl isprobably initiated by homolytic scission ofthe carbon bromine bond since the IR bandattributed to the exomethylene structuredisappears at about the same rate as cureproceeds.

C CH

Br

~ ~

CH2

At the same time a band appears which maybe due to




C CH~ ~

CH2

with no bromine allylic to the double bond.This suggests that curing proceeds viascission of the CBr bond but does not ruleout curing through the double bond as well.

The heat resistance and compression set ofvulcanizates cured with peroxide,peroxide + N, N m-phenylenedimaleimide(HVA#2), and HVA#2 alone are compared tothe zinc oxide cured bromobutyl in Table I.

Table 1: Comparison of cure systems in black compounds

Test Recipe *

Bayer Bromobutyl X2 100.0 100.0 100.0 100.0 100.0 100.0 100.0

N774 black 50.0 50.0 50.0 50.0 50.0 50.0 50.0

Zinc oxide 5.0 -- -- -- -- -- --

Stearic acid 1.0 -- -- -- -- -- --

Dicup 40C -- 1.5 1.5 1.5 1.5 1.5 --

HVA#2 -- -- 0.25 0.5 1.0 1.5 1.5

Compound properties

Viscosity ML 1+4 (100 C) 83 88 88 88 87 87 89

Scorch time at 135 C(min) 16 12 12 14 17 19 16

Physical properties

*Cure time at 180 C (min) 15 3 3 4 4 4 20

Hardness, Shore A 48 40 51 54 54 56 58

Modulus at 100 % elongation (MPa) 0.9 0.5 0.9 0.12 0.12 0.15 0.19

Modulus at 300 % elongation (MPa) 5.2 1.8 6.8 9.5 10.0 - 10.2

Tensile strength (MPa) 12.4 8.9 9.9 10.5 10.0 10.0 13.6

Ultimate elongation(%) 580 680 420 325 300 265 360

Compression set,70 h at 150 C (%) 58 53 40 28 20 17 13

Aged in air, 168 h at 150 C (change)

Hardness (points) +3 +3 -2 +4 +1 +1 -1

Modulus at 100 % elongation (%) +10 -5 -15 -10 -2 -5 -12

Tensile strength(%) -40 -60 -35 -25 -10 -30 -45

Ultimate elongation(%) -35 +20 +20 +7 -10 -10 -8

*For details of Test Methods throughout the text see Appendix I - Test Procedures




Continuous and intermittent stress relaxationmeasurements on the vulcanizates(Figures 9 and 10) indicate the superiorthermo-oxidative and network stability ofperoxide + HVA#2 and of HVA#2 used alonecompared to the zinc oxide cure system, theformer being more stable in the long term.

Fig. 9: Continuous stress relaxation

Fig. 10: Intermittent stress relaxation

Bromobutyl compounds cured with peroxideand HVA#2 alone and in combination,produce vulcanizates with extraordinaryozone resistance - much better thanobtained with most other cure systems.(Table 2)

Table 2: Ozone resistance

Test Recipe*

Bayer Bromobutyl X2 100.0 100.0 100.0 100.0 100.0 100.0

N774 black 50.0 50.0 50.0 50.0 50.0 50.0

Zinc oxide 5.0 - - - - -

Sulfur - 1.5 - - - -

Calcium hydroxide - 3.0 - - - -

Dicup 40C - - 1.5 1.5 1.5 -

HVA#2 - - - 1.0 - -

SP-1055 resin - - - - - 1.75

Ozone resistance rating 3 3 2 0 0 5

Appearance slightcracking

slightcracking

very slightcracking

no cracks no cracks specimenbroke




Dienophile Cure Systems

The mechanisms of crosslinking bydimaleimides in the presence of peroxidehave been described by Kovacic and Hein(18) and the uses of dimaleimides havebeen described as curatives in variouselastomers.

While N, N m-phenylene-dimaleimide alonewill cure halobutyl rubbers to producevulcanizates having low compression set,significantly higher states of cure can beachieved when used in conjunction with zincoxide.

The unaged and aged properties ofhalobutyl vulcanizates, containing mono andbis dienophiles, are compared in Tables 3

and 4. They exhibit very good heat andozone resistance combined with lowcompression set.

Wilson and Vulkov proposed the respectivemechanisms for zinc oxide and mono andbis maleimides (19). The formation ofconjugated diene groups which form onheating with zinc oxide is followed by aDiels-Alder type reaction. Using m-phenylene bis maleimide (m-PBM), athreefold increase in crosslink density isachieved in the case of bromobutyl rubber,and a five to sixfold increase in the case ofchlorobutyl rubber. By using a mixture ofmono and bis maleimide it is possible toadjust the crosslink density. (SeeAppendix III).




Table 3: Effect of dienophile cure systems

Test Recipe*

Bayer Chlorobutyl 1255 100.0 100.0 100.0 100.0

Stearic acid 1.0 1.0 1.0 1.0

N550 black 55.0 55.0 55.0 55.0

Paraffinic oil 10.0 10.0 10.0 10.0

Zinc oxide 5.0 5.0 5.0 5.0

Cure System

N, phenyl maleimide - - 1.6 4.0

N,N'-phenylene bismaleimide - 3.0 2.0 -

Compound properties

Viscosity ML 1+4 (100 C) 61 64 66 64

Mooney scorch time (min at 125 C) 14 7 12 6

Monsanto rheometer at 166 C(3 arc, 100 cpm, 0 preheat)Tc 90 (min) 7 4 7 4

Physical properties

Hardness, Shore A 52 60 60 58

Modulus at 100 % elongation(MPa)

1.4 2.8 2.4 1.4


6.5 8.5 8.3 4.7

Tensile strength (MPa) 11.8 10.6 11.9 10.8

Ultimate elongation (%) 510 390 480 730

Compression set (%)

70 h at 100 C 22 14 16 38

70 h at 150 C 57 18 31 51




Table 4: Effect of dienophile cure system on ozone resistance and heat aging

Cure System

NPM - - 1.6 4.0

NMPB - 3.0 2.0 -

Zinc oxide 5.0 5.0 5.0 5.0

Static ozone resistance, 50 pphm, 40 C, 168 h

20 % strain (rating) 3 0 0 3

50 % strain (rating) 4 0 0 3

Dynamic ozone resistance, 50 pphm, 40 C, 168 h

0-25 % strain (rating) 3 0 0 3

Aged in air, 168 h at 150 C - change

Hardness (points) -4 -1 -4 -1

Modulus at 100 % elongation (%) -30 -12 -30 -21

Tensile strength (%) -86 -60 -86 -73

Ultimate elongation (%) -22 -12 -22 -26

Amine Cures

Substituted paraphenylene diamine anti-oxidants have been used to advantage toimprove the heat resistance of zinc oxidecures in chlorobutyl and bromobutyl, (20)and published work by Timar and Edwardscontain examples of this (21). The additionof amine type antioxidants have also beenobserved to increase cure rate, reducescorch time and induce poor shelf life inuncured compounds, particularly in the caseof bromobutyl.

Polyfunctional amines, such ashexamethylene diamine carbamate (DiakNo.1), have been used in sulfurless and zincoxide free bromobutyl compounds forpharmaceutical stoppers required to passvery stringent tests for chemical inertness(reducing substances). These cure systemsare not effective in chlorobutyl. Studies byEdwards (20) have shown that certain typesof aromatic amines interact synergisticallywith zinc oxide in halobutyl elastomers toprovide a rapid and highly efficient type ofcrosslinking system. The vulcanizates

exhibit good ozone resistance and areexceptionally stable towards hightemperature oxidation, combined with lowcompression set.

The hypothesis underlying this workproposed three principal curing mechanismsfor halobutyl compounds using zinc oxidesand difunctional amine antioxidants:

- cationic cross linking due to zinc oxide asproposed by Baldwin et al (9) andsupported by Vulkov (14) in more recentstudies using model compounds.

- Hofmann type reactions in which only theamine and the halide sites are involvedand,

- a synergistic process whereby both zincoxide and amine antioxidant mechanismproceeds by Friedel-Crafts alkylation ofthe antioxidant molecules at more thanone site.

This third type of process is most rapid atcuring temperatures and capable of formingthermally and oxidatively stable crosslinks.




The properties of compounds containingADPA 86 (reaction product of diphenylamineand acetone - Aminox, supplied by UniroyalIncorporated) with, and without, zinc oxide,

and DNPD (di-beta-naphthyldiphenylamine -Agerite White, supplied by R.T. Vanderbilt)in conjunction with zinc oxide, are illustratedin Table 5.

Table 5: Zinc oxide/amine cures in bromobutyl

Test Recipe*

Bayer Bromobutyl X2 100 100 100 100

N550 black 55 55 55 55

Paraffinic oil 10 10 10 10

Cure system

Zinc oxide 5.0 - 5.0 5.0

ADPA 86 - 4.0 4.0 -

DNPD - - - 3.0

Compound properties

Mooney viscosity ML 1+4 (100 C)

Unaged 61 64 63 60

Aged 60 days at RT 62 75 97 68

Mooney scorch, t5 at 125 C (min) 30 14 12 11

Unaged properties


Modulus at 100 % elongation (MPa) 1.4 1.6 3.8 3.8




Compression set, 70 h at 150 C (%) 77 100 47 28

Aged properties, 7 days at 175 C



Modulus at 300 % elongation (MPa) - - - -






The synergistic effect of the ZnO/aminesystem results in very good heat resistanceafter aging at 175 C and low compressionset observed after 70 hours at 150 C. Thecure rates shown in Figure 11 also illustratethis synergistic effect. Of the systemsstudied, DNPD plus zinc oxide in bromobutylcompounds exhibited good scorch safety,storage stability, and fast cure rate.

Fig. 11: Monsanto Rheometer cure curves166 C/1 arc

These systems are both economical andeffective in producing high performancecompounds useful for demandingapplications involving high temperaturescombined ozone resistance, chemicalinertness, low permeability, and lowtemperature flexibility.

Resin Cures

Resin curing of regular butyl providesexcellent heat resistance. In halobutyl, lowerlevels of resin (2 3 phr) are effective, nohalide activation for the resin, as used incuring butyl, being necessary.

Halobutyl can be used to activate resincures in regular butyl (Table 6). While thedry heat resistance of resin cured halobutylis excellent, aging in high pressure steam isnot as good as that obtained when usingregular butyl cured with methylol resins.




Table 6: Resin cures *

Bayer Bromobutyl X2 100 -- 10

Bayer Butyl 301 -- 95 90

CR - Type W -- 5 --

Stearic acid 1 1 1

N339 black 50 50 50

Aromatic oil 6 6 6

Zinc oxide 5 5 5

SP-1045 resin 1.75 7 7

Compound properties

Viscosity ML 1+4' (100 C) 67 70 70

Mooney scorch time t5 at 125 C (min) 16 30 30

Monsanto rheometer, 165 C, 1 arc, t90

Max. torque (N.m) 2.0 2.3 2.1

Optimum cure (min) 15 50 43

Vulcanizate properties

Hardness, Shore A 57 62 60

Modulus at 100 % elongation (MPa) 1.8 1.7 1.6


Tensile strength (MPa) 15.2 13.9 14.8

Ultimate elongation (%) 450 740 680

Tear resistance, Die C (kN/m) 30 48 39

Aged in steam, 72 h at 195 C



Modulus at 300 % elongation (MPa) - 8.3 7.0

Tensile strength (MPa) 5.8 14 14


Tear, Die C (kN/m) 25 41 40

Volume swell (%) 47 7 4




Antioxidants

The degradation of halobutyl vulcanizatescured with zinc oxide and sulfur donoraccelerators and exposed to hightemperatures has been shown to be dueprimarily to oxidation. Aging in nitrogenshows that the networks formed by suchcuratives are thermally stable. Evaluation ofantioxidants in such compounds has shownthat while many have little or no benefit inimproving resistance to high temperature hotair aging, substituted para-phenylene-diamine types, particularly when used inconjunction with mercaptobenzimidazole,are highly effective in improving heatresistance in such compounds. Moreover,they increase the state of cure and reducescorch times significantly, particularly whenused in compounds based on bromobutyl.(21)

While this effect of amine antioxidants oncure rate and cure state subsequently led tothe study of amines as curatives (20), theuse of ADPA 86 and mercapto-benzimidazole (MBI) to improve heatresistance in zinc oxide/TMTD curedhalobutyl compounds has proved to be ofpractical benefit in a range of applications,including retreading envelopes, hose andgaskets which are exposed to hightemperatures.

The relative heat resistance compared tozinc oxide/TMTD and zinc oxide alone isshown in Figures 12 and 13 and their effecton compression set and ozone resistance,relative to peroxide and dienophile curesystems, is illustrated in Figures 14 and 15.

0

10

20

30

40

50

60

70

80

90

CIIR BIIR CIIR BIIR CIIR BIIR

Ret

ain

ed (

%)

168h 150C

24h 175C

72h 175C

24h 200C

--------- ZnO ---------TMTD

Aminox + MBI

--------- ZnO ---------TMTD

---------- ZnO ----------

Fig. 12 : Hot air aging - tensile effect of curesystem

0

20

40

60

80

CIIR BIIR CIIR BIIR CIIR BIIR

Ret

ain

ed (

%)

168h 150C

24h 175C

72h 175C

24h 200C

--------- ZnO ---------TMTD

Aminox + MBI

--------- ZnO ---------TMTD

---------- ZnO ----------

Fig. 13: Hot air aging - elongation effect ofcure system

0

10

20

30

40

50

60

70

ZnO

Zn

O/T

MT

D

Zn

O/A

DP

A86

Zn

O/T

MT

D/

AD

PA

86/M

BI

Per

oxi

de

Per

oxi

de/

HV

A #

2

Hva

#2

Set

(%

)

Brombutyl X2

Fig. 14: Effect of cure system oncompression set, 70 h at 150 C




Fig. 15: Effect of cure system on ozoneresistance (50 pphm at 40 C)

The compounds and their properties areshown in Appendices III and IV.

Blends Chemistry

Halobutyl rubber can be co-cured or co-vulcanized with a wide variety of saturatedand unsaturated polymers including naturalrubber, polybutadiene, SBR, NBR, EPR,polychloroprene, and propylene oxide for awide range of tire and non-tire applications.(22/23)

An important characteristic of elastomerblends is the extend of interfacial bondingachieved, particularly if the polymers havedifferent solubility parameters and differentreactivity. Zapp (24) has demonstrated theinfluence of cure systems in chlorobutyl/BRblends by using differential swellingtechniques with various solvents, whileBauer et al (25) showed the influence ondynamic behavior of such blends usingdifferent cure systems to achieve interphasecrosslinking. These factors are important inhalobutyl blends both regarding adhesion toother polymers and blends with more fullyunsaturated rubbers (e.g. natural rubber).

Figure 16 shows the effect of adding NR tothe halobutyls in a S/ZnO/MBTS system. Itindicates that higher states of cure thaneither of the individual components can beachieved.

Fig. 16: MH-ML data for HIIR/NR with TMTDand MBTS

This is related to the cure system beingoptimized solely for 100 % halobutyl with theNR providing more crosslinking sites. Theseresults suggest a greater degree of co-vulcanization for bromobutyl compared tochlorobutyl. In both accelerator systems100 % chlorobutyl has an equal or greaterdegree of crosslinking as measured by deltatorque. As the XIIR content decreases inboth systems there is a crossover and at lowlevels of XIIR the BIIR blends have higherdelta torque than CIIR blends. It appearsthat in CIIR blends the curative package isused predominantly by the NR while in BIIRblends curing occurs more homogeneouslygiving a greater degree of curing betweenthe two rubber phases present. A possibleexplanation for this observation is the abilityof bromobutyl to cure with sulfur alone,possibly via formation of S2Br2 (12) whichcould diffuse between NR and BIIRboundaries. This is also a possibleexplanation for the higher adhesion ofbromobutyl compared to chlorobutyl,especially to NR.

The ability of halobutyl rubbers to co-cure inblends and adhere to unsaturated rubbers,combined with their response to a widerange of curatives, to produce vulcanizateshaving the combined properties of heatresistance, ozone and chemical resistanceand low compression set, with very lowpermeability and high damping, makes themextremely versatile polymers suitable for arange of diverse applications.




Applications

The major uses for halobutyl have beeninfluenced by technological changes in tires,particularly the widespread adoption oftubeless and tubed-type steel radial plyconstruction. (26) For such tires, halobutylinner liners, having low permeability to airand moisture, combined with good heataging and flex fatigue resistance, contributeto improved tire durability and integrity andto the maintenance of low rolling resistance.

The service conditions for inner liners forpassenger and truck tires, described inTable VII, require inner liner compounds tohave excellent resistance to heat (80 C to100 C) and to flex cracking under airpressures of 30 to 120 psi (210 kPa 840 kPa) and good adhesion to carcasscompounds. The service life can be as longas eight years for passenger and five yearsfor radical truck tires.

Table 7: Service conditions - tire inner liner

Severity

Medium to high High to very high

Type of tires (radial) Passenger Truck

Total tire life (km) 90,000 400,000

Incl. no. of retreads 1 2

Typical service speed (km/h) 140 - 100 100 - 80

Average service time (riding) > 1,000 h > 4,000 h

Number of years of service(riding - parking)

Up to 8 Up to 5

Tire temperature at service speed(contained air, C)

80 - 90 90 - 100

Number of flexes when tire passes foot print

in total tire life > 40 Million > 120 Million

per second 19 9

Typical inflation pressure (bar) 2.0 8.0

Inner liner compounds must also be highlyimpermeable to air and water vapor toprevent belt edge separation caused byintra-carcass pressure build-up from airmigration into the carcass, or rusting of steelcords due to moisture vapor transmission.Low permeability of inner liners is alsoessential to maintain the correct inflationpressure in order to maximize treaddurability, and to ensure that low rollingresistance and handling traction ismaintained. A drop in 4 psi (28 kPa) cancause a ten percent rise in rolling resistance.

These market demands have broughtsignificant changes in inner linercompositions (Table 8), away from blends ofhalobutyl/natural rubber to the adoption oflow Mooney, easy processing bromobutylrubber (100 phr) in compounds having littleor no oil so as to ensure a minimum of bothair loss and moisture permeability. Thedeleterious effects on permeability andadhesion, when using blends of NR andhalobutyl compared to halobutyl alone, andthe superiority of bromobutyl compared tochlorobutyl, were described by von Hellens(27) and Walker (28).




Table 8

The results are illustrated in Figures 17 and18. The benefits in reducing oil content inbromobutyl compounds to further reducepermeability are illustrated in Figure 19.

0

5

10

15

20

25

30

35

40

45

BIIR

:NR

100

:0

BIIR

:NR

80:

20

BIIR

:NR

60:

40

BIIR

:NR

40:

60

BIIR

:NR

20:

80

BIIR

:NR

0:1

00

Q x

108

95C65C25C

Fig. 17: Bayer Bromobutyl 2030;air permeability vs. test temperatures

Fig. 18: Cured adhesion to NR compounds- BIIR vs. CIIR in blends

Fig. 19. Effect of oil content on inner linerpermeability

TechnologyPush

Technological ChangeInner Liners

MarketPull

Bromobutyl (100 phr)

Easier processing

Lower Mooney

Low oil/No oil

Reduced permeability

Electron beam

Quality/Consistency

Trend to tubeless radial

Minimum air loss

Higher pressure toreduce rolling resistance

Reduce corrosion(steel belt)

Improve durability

Quality

Processing efficiency




Sidewalls

Another important application for halobutyl isin the sidewalls of radial tires, where there isa requirement for long life and outstandingflex fatigue resistance.

Chlorobutyl, in particular, is used incompounds for white sidewall letters andcoverstrips used in radial ply passengertires.

EPDM rubber, used in blends with SBR, NRor BR to improve ozone cracking andweathering, lowers adhesion, and limitsmechanical properties. Adding chlorobutyl towhite sidewall compounds providesimproved adhesion combined with improveddynamic ozone and flex resistance, whilemaintaining good mechanical properties.The development of white sidewall andcoverstrip compounds and their propertieswere described by Blackshaw (24) andHerzlich (29). Examples of compounds andtheir properties are illustrated in Tables 9and 10.

Table 9: Tire white sidewall *

Formulation (parts by weight

Bayer Chlorobutyl 1240 60.0

Buna EP T 3950 * 7.5

NR (pale crepe) 32.5

Titanium dioxide 30.0

Nu-Cap 200 (aluminum silicate) 60.0

Stearic acid 1.0

Escorez 1102 3.0

Sunolite 240 wax 1.0

Ultramarine blue 0.2

Zinc oxide 5.0

Sulfur 0.5

Vultac 5 1.2

MBTS 0.7

Compound Properties

Viscosity ML 1+4 (100 C) 53

Mooney scorch time - large rotort5 at 125 C (min)t5 at 138 C (min)

12.97.1

Mill shrinkage (%) 29

Tel-Tak (kPa)to selfto stainless steeltrue tack

31076234

Garvey Die extrusion(# Royle, 120 C, 70 rpm)

Rate (cm/min)Die Swell (%)Appearance

89109A6

Monsanto rheometer, 165 C, 3 arc,1.7 Hz (100 cpm)

MH (dN.m)ML (dN.m)MH-ML (dN.m)t10 (min)t50 (min)t50-t10 (min)

43.011.032.02.85.93.1




Table 10: Tire white sidewall


Cured 30 min at 166 C

Hardness, Shore A 49


1.7


6.1

Tensile strength (MPa) 10.8

Ultimate elongation (%) 510

Static peel adhesionat 25 C (kN/m)to 100 % NR carcass 5.8

Static ozone resistance,50 pphm ozone,25 % extension, 40 C

time to first cracks (h) > 336

Dynamic ozone resistance,50 pphm ozone,0 to 25 % extension37 cycles/min, 40 C

time to first cracks (h) > 336

De Mattia flexto 600 % cut growth (kc)

> 250

Treads

Since the energy crisis of the early 1970s,and as a consequence of the CAFE -Corporate Average Fuel Economy regulation- emphasis has been placed on reducedrolling resistance of tires. Significantimprovements have been achieved throughtire design, new polymers and compounding.These have been reviewed by Chang andShackleton (30) in their paper An Overviewof Rolling Resistance, and Schuring (31) inhis paper The Rolling Loss of PneumaticTires. The factors influencing rollingresistance, traction and wear are illustratedin Figure 20.

Fig. 20: Parameters effecting treadperformance

There is a body of option today that believesthat the emphasis is changing towardsimprovements in traction and handlingwithout sacrifices in resistance or treadwear.High performance tires with improvedhandling and traction characteristics, as wellas good high speed performance anddurability, are the main focus. Halobutylrubbers have been used in blends withgeneral purpose rubber in tread compoundsto improve wet traction but their use hasbeen limited to specialty tires because oftheir adverse effect on abrasion resistanceand rolling resistance.

There has been a renewal of research inwhich the emphasis is to take advantage ofthe good traction imparted by halobutylblends, and overcome the past deficienciesof higher abrasion loss and rollingresistance. Tyurina and Shuarts (32) notedin their work using various ratios ofpolybutadiene and chlorobutyl that thecoefficient of friction on wet concrete wasconsiderably higher than the additive values.




Hirakawa et al (33), in their patent, claimedthat reduced rolling resistance, improvedskid properties and acceptable wearresistance were obtained using blends ofgeneral purpose rubbers. In another patent,Hirakawa (34) also demonstrated that areduction in rolling resistance without loss ofwet traction was possible when some of theblend or all of the halobutyl was added latein the mixing cycle. The effects of mixing onthe improvement in rolling resistance,observed by Hirakawa, have also beenobserved and reported by Briggs and Wei(35), and by Hess (36). By preparing blackpolymer masterbatches containing differentamounts of carbon black and then blendingin a second stage mixing process, theydemonstrated that rolling resistance wasreduced when compared to polymer blendsmixed with carbon black in a single-stageprocess. This work suggests that, whenusing halobutyl in tread compounds withgeneral purpose rubber, improvements inrolling resistance without loss of traction canbe influenced by the mixing method, inparticular by preparing masterbatchescontaining different levels of carbon black.The effect of cure systems on the dynamicproperties of blends of halobutyl andpolybutadiene have been demonstrated byBauer (25) through interphase crosslinkingbetween the heterogeneous polymerphases.

The dynamic behavior of such blends isshown in Figure 21 and their abrasionresistance in Table 11. The data suggestthat by increasing the level of high cispolybutadiene in a blend of SBR/BR/BIIR,abrasion resistance can be improved whileimproving wet traction and rolling resistance.

65 SBR 35 BR

25 SBR 65 BR 15 BIIR

50 SBR 35 BR 15 BIIR

Fig. 21: Dynamic response SBR-BR-BIIRratios

The balance of traction rolling resistanceand tread wear for high performance radialtires could be improved. This could beachieved by compound research on the useof halobutyl in treads, involving methods ofmixing to control the phase distribution ofcarbon black in polymer blends, increasingthe polybutadiene content and identifyingcure systems to induce interphasecrosslinking.

Table 11: SBR/BR/BIIR, abrasion loss/tan delta

SBR 75 65 50 25

BR 25 35 35 60

BIIR - - 15 15

Abrasion

Akron 15 152 152 124 174

Akron 20 122 126 109 137

DIN (vol. loss) 114 98 118 84

Rheovibron tan ? (100 Hz)

-8 C to +8 C 0.329 0.294 0.371 0.310

+48 C to 64 C 0.185 0.184 0.186 0.165




Inner Tubes

While regular butyl meets the needs for themajority of inner tube applications, innertubes based on halobutyl provide the sameexcellent air retention plus improved heatresistance, splice durability and resistance togrowth and softening (Table 12). Inner tubesbased on halobutyl are a premium productused under conditions of high severity whengood heat resistance is essential. Halobutylis also used where the incompatibility ofregular butyl with other rubbers cannot betolerated, or when a faster cure rate makesa major contribution to increasedproductivity.

The general properties of bromobutyl andchlorobutyl based compounds are shown inAppendix V.

The ability of halobutyl to co-cure withnatural rubber is used in specialcircumstances to improve the air retentionand heat aging of natural rubber inner tubes.This ability can also be utilized to assist inthe handling of heavy weight, uncured giant-size tubes where the green strength ofregular butyl may be inadequate. Theaddition of natural rubber will improve theuncured green strength.

Table 12: Tire inner tube - heavy duty

Compound Properties Bromobutyl X2 Chlorobutyl 1255

Viscosity ML 1+4 (100 C) 52 57

Mooney scorch t5 at 135 C (min) 8 5

Garvey die extrusion#1 Royle, 104 C, 30 rpm

Rate (mm/min)Die swell (%)Appearance rating

120022A9

108030A9

Cure time at 166 C (min) 3.5 5.0

Physical Properties Original Aged(10 days,125 C)

Original Aged(10 days,100 C)



Ultimate elongation % 570 310 540 300


Splice Endurance

Unaged % of tensile 63 35

Aged (10 days, 100 C) 47 43

Cycles to Dynamic Failure

Unaged 4,960 620

Aged (10 days, 100 C) 870 100




Curing Envelopes

Compounds based on regular butyl havinglow modulus and permanent set have beenused for many years for envelopes used incuring precured treads for retreading tires.The better heat resistance and lower setcharacteristics imparted by halobutylincrease the life of curing envelopes andconsequently improve the economics of theprocess. (See Appendix II)

Non-Tire Applications

Halobutyl rubbers are used in numerousapplications, the principal ones being shownin Table 13. These applications takeadvantage of one or more of the desirablecharacteristics, such as low permeability,energy absorption, heat and chemicalresistance. They offer advantages in fastercure rates, cure versatility and the ability tovulcanize in blends with other rubbers.Bromobutyl is used in preference tochlorobutyl whenever faster curing and/orhigher adhesive strength can be used toadvantage.

Table 13: Halobutyl non-tire applications

SoleElastomers Blends

Ball bladders

Chemical plantlining

Protective clothing

Gas masks

Pharmaceuticalclosures

Mounts

Rollers

Hose

Conveyor belts(heat resistant andfood)

Sealants

Extruded sponge

Gaskets (solid andcork)




Blends

The rubbers that can be covulcanized withhalobutyl include NR, SBR, BR, C, NBR,CSM, EPDM and CO (epichlorohydrin). Thefollowing three practical examples illustratethe value of blends:

Natural Rubber/BIIR for engine mounts. NBR/BIIR for printing rolls. EPDM/BIIR for CV extruded sponge.

Mounts

Natural rubber has been used successfullyfor many years in automotive enginemounts, suspension bushings, steeringcouplings and a variety of other dynamicapplications, while butyl rubber has beenused in high damping applications such asbody mounts.

The higher operating temperaturesprevailing in engine compartments ofpassenger cars has introduced increaseddemands for improved heat resistance formounts. Improvements in heat resistance,flex cracking and permanent set can beachieved in blends of halobutyl and naturalrubber.(37)

The addition of bromobutyl to natural rubbercompounds produces little effect on dynamicvalues when measured at low frequencies(3 5 Hz) but under high frequencies(110 Hz) dynamic modulus increases withthe bromobutyl level (Figure 22). Resistanceto flex cracking, compression set, and heataging improve as the level of bromobutyl isincreased.

Depending upon the frequency responserequired and the service temperaturesinvolved, such blends have been put topractical use as described (38) in a numberof patents.

Fig. 22: BIIR/NR blends - dynamic modulus(Rheovibron Testing)

Solvent Resistant Rollers

Some printing rollers require resistance tosolvents containing ketones which is difficultto achieve with polar rubbers such as nitrileor polychloroprene.

Excellent resistance to solvents, such asMEK, can be obtained by using blends ofNBR and bromobutyl. These blends alsoexhibit improved resistance to ozonecracking compared to nitrile rubber. (SeeTable 14)

Other applications for which these blendsappear suited include milking inflations toimprove resistance to animal fats or ozone,and molded goods for combined resistanceto chemicals and oils.

Table 14: Ozone and solvent resistanceof bromobutyl

Bayer Bromobutyl X2 100 50 --

Krynac 34.50 -- 50 100

Ozone resistance(h to cracking) 168 120 24

Volume swell in TCP (%) 0 17 54

Volume swell in MEK (%) 14 62 160

Volume swell inASTM Oil #3 (%) 180 46 9




Extruded EPDM

The usefulness of blends containinghalobutyl and EPDM in tires has beendescribed. The addition of bromobutyl to softcellular extruded EPDM compoundsprovides excellent skin formation, while insolid EPDM extrusions the fast cure rate ofbromobutyl can be used to advantage forjointing extruded profiles using shot moldingtechniques. (See Appendix VI)

Other applications for EPDM blends withhalobutyl include tank lining to improveadhesion and any application where areduction in water vapor transmission isdesirable. For example, a 50/50 blend inplace of 100 % EPDM reduces the watervapor transmission rate nearly threefold.(Figure 23)

0

1

2

3

4

100/0 75/25 50/50 25/75 0/100

Bromobutyl X2 / EPDM Ratio

g/m

Water Vapour- Transmission Rate -

Fig. 23: Bromobutyl X2/Buna EP T 2460blends

Sole Elastomer Applications

The fast cure rates of halobutyl combinedwith low permeability, and chemicalinertness have been used in a variety ofapplications in compounds when they areused as the sole elastomer. Three practicalexamples are:

pharmaceutical closures tank lining sports ball bladders

Pharmaceutical Closures

Halobutyl rubbers are widely used inpharmaceutical rubber products, such asclosures, which play an important part inpackaging and medical administrationsystems for pharmaceutical products. Theyoffer the manufacturer the possibility ofmeeting the stringent requirements imposedby this sophisticated sector of the rubberindustry.

In many cases, pharmaceutical closurescome into direct contact with pharmaceuticalproducts, either dissolved or in other forms.Therefore they must comply with existingstandards and regulations regarding thecontact of vulcanized rubbers withpharmaceuticals.

The most common pharmaceuticalapplications are listed in Table 15. Halobutylrubbers are generally preferred becausethey provide adequate protection of sterilepharmaceutical products against externalcontamination during storage and use.However, there are many otherrequirements which vulcanized rubberclosures must meet. (Table 16)

The diversity of requirements and stringentspecifications severely restrict the choice ofcompounding ingredients. Taking theserestrictions into account Harmsworth andDolezal have described the effects ofcompounding ingredients, includingaccelerators, on the physio-chemicalproperties of halobutyl rubbers for use inthese applications.

The choice of cure system depends uponthe type of halobutyl used. Factors whichmust be avoided in curing systems forpharmaceutical applications are:

Toxicity Odor Blooming Reactivity with the pharmaceutical

preparation Extrudability by the pharmaceutical

preparation Too low cure rate




Table 15: Applications of Bayer halobutylrubbers in pharmaceutical products

Closures for infusion containers

Closures for injectable vials

Closures for freeze-dried products

Lyophilisation closures

Plungers for prefilled syringes

Plungers for empty, disposable syringes

Dropper bulbs

Pipette assemblies

Closures for insulin containers

Baby teats

Sealing rings

Table 16: Performance requirements ofvulcanized rubbers in pharmaceuticalapplications

Non toxicity

High resistance to - and compatibilitywith - pharmaceutical products

Good physical properties

Excellent chemical properties

Low fragmentation/coring

Good sealing properties

Good resealing after puncturing

Sterilisability by standard (steam) aswell as non-standard (radiation)procedures

Good color retention

Excellent resistance to aging, vapor,and gas transmission, water andvegetable oils

Curable by low extraction cure systems

Examples of typical halobutyl compounds,and the effect of zinc oxide, resin and aminecures, are illustrated in Table 17




.Table 17: Effect of cure systems in pharmaceutical compounds *

Curing systems ZnO/ZDMC ZnO/Resin DIAK No.1

Bayer Bromobutyl 2030 100 -- -- 100 -- -- 100 --

Bayer Bromobutyl X2 -- 100 -- -- 100 -- -- 100

Bayer Chlorobutyl 1240 -- -- 100 -- -- 100 -- --

Calcined clay 100 100 -- 100 100 -- 100 100

Whitetex, No.2 -- -- 100 -- -- 100 -- --

Polyethylene AC-617 2 2 2 2 2 2 2 2

Paraffin wax 2 2 2 2 2 2 2 2

Zinc oxide 3 3 3 3 3 3 -- --

ZDMC 0.2 0.2 0.4 -- -- -- -- --

Schenectady 1045 -- -- -- 2.5 2.5 -- -- --

Schenectady 1055 -- -- -- -- -- 2.5 -- --

DIAK No.1 -- -- -- -- -- -- 0.5 0.5

Compound properties

Mooney viscosityML 1+4 (100 C) 66 81 82 61 78 75 67.5 86

Mooney scorch,t5 , 125 C (min) 13.9 11.2 9 25 25 8.0 7.6 6


Cure time at 170 C, min 7 7 12 10 10 20 8 8

Hardness, Shore A,0 sec3 sec

5042

5348

5245

5348

5350

5652

4739

5043

Modulus at 100 % elong (MPa) 0.8 1.1 1.1 1.0 1.5 1.2 0.7 1.0

Modulus at 300 % elong (MPa) 1.5 2.0 2.2 2.2 2.7 3.6 1.3 2.2

Tensile strength, (MPa) 5.6 6.2 6.0 5.9 7.8 6.5 4.5 5.3

Ultimate elongation, (%) 960 830 890 870 820 730 980 840

Tear strength, die C, (kn/m) 20 25 25 25 27 31 18.5 24.5

Chemical properties

Japanese pharmacopoeia

Reducing substances,ml 0.01 N Na2S2O3 2.0 1.8 0.5 1.9 1.7 0.8 0.8 0.8

U.V. light absorption at 410 nm 0.003 0.006 0.008 0.002 0.005 0.004 0.004 0.005

pH change -0.1 -0.3 -0.5 +0.3 +0.3 +0.4 -0.5 +0.1




Tank Lining

Excellent chemical resistance combined withcuring versatility have made halobutylrubbers, particularly bromobutyl rubber, thepreferred rubber for chemical resistant liningapplications. They offer superior cure ratesand ease of bonding compared with regularbutyl and EPDM rubbers.

A range of low temperature cure systemssuitable for on site or factory applicationshas been developed for low temperaturecuring in steam, water or hot air. Thereplacement of zinc oxide, used in dispersedform for health and safety reasons, willreduce water swell (Figure 24).

Fig. 24: Volume swell of bromobutyl liningformulation in water at 100 C

Typical cure systems are shown in Table 18.

High loadings of carbon black and inertfillers, such as barytes and talc, used in lowMooney halobutyl polymers, impart ease ofcalendering for a lining compound asillustrated in Table 19.

Table 18: Cure systems for chemicalplant lining

BIIR CIIR

Cure System 1 2 3

Zinc oxide 5.0 5.0 5.0

Sulfur 1.0 2.0 2.0

MBTS 1.0 -- 1.0

DPG -- -- 0.5

HVA-2 2.0 -- --

Tetrone A -- 2.5 --

TMTD -- 1.0 --

Vulcanization time (90 % t90)

at 145 C (min) 30-40 15 40-45

at 100 C (h) 16-24 8-12 16-24

at 80 C (h) 30-48 20-24 48

Table 19: Chemical plant lining compound *

Bayer Bromobutyl 2030 100

N550 black 40

Barytes 75

Platy talc 50

Paraffinic oil 10

Petrolatum 8

Pb3O4 (50 % dispersion) 10

Vulkacit 576 2

ETU 2

297

Vulcanization time - 12 h in steam at 100 C




Sports Ball Bladders

Regular butyl rubber has been the preferredelastomer for sports ball bladders becauseits low permeability maintains air pressure.The faster cure rates of halobutyl and goodsplicing characteristics, particularly ofbromobutyl, help significantly increaseproductivity. This application (Table 20) nowrepresents a significant proportion of theglobal non-tire usage of halobutyl. (39)When higher green strength is required,natural rubber (25 phr) is used in blends withhalobutyl. (See Appendix II)

These examples illustrate some of thediverse range of non-tire applications forhalobutyl used alone or in blends with otherrubbers. Both types of halobutyl are used,but bromobutyl is preferred whenever fastercuring is desirable, and/or its higheradhesive strength is an advantage.

Table 20: Sports ball bladder *

Formulation (parts by weight)

Bayer Bromobutyl X2 100

Stearic acid 1

N327 black 50

N990 black 20

Amberol ST 149 4

Silene D 10

Sunpar 115 10

Indopol H-100 10

Zinc oxide 5

Sulfur 0.5

MBTS 1.5

TMTD 0.5

Compound viscosityML 1+4(100 C)

59

Mooney scorch time(min at 125 C)

14

Cured 10 min at 166 CHardness, Shore A

53

Tensile strength (MPa) 11.5

Ultimate elongation (%) 560




Conclusions

While both chlorobutyl and bromobutyl willrespond to a wide range of curatives andcure systems, bromobutyl is more versatilein its response. Bromobutyl can be curedwith sulfur alone or peroxides (i.e. withoutzinc oxide or other accelerators present) andexhibits greater curing efficiency when zincoxide is used as the sole curative.

Vulcanizates having excellent resistance toheat, ozone and compression set can beachieved when the zinc oxide cure ismodified by the addition of thiurams plusparaphenylene diamines, and mercapto-benzimidazole; zinc oxide in combinationwith other diphenylamines act synergisticallyto yield fast curing and thermally stablecrosslinks, and the vulcanizates have goodozone resistance and compression set.Dienophiles can be used alone or inconjunction with peroxides or zinc oxide toproduce vulcanizates having extremeresistance to ozone, and very lowcompression set at high temperatures.

Bromobutyl is significantly superior tochlorobutyl as regards adhesion to naturalrubber and is faster curing in mostcompounds. Both polymers will vulcanize inblends with natural or other unsaturatedrubbers.

The major uses for these polymers havebeen identified, tire inner liners being thelargest. To obtain optimum tire performance,air and moisture permeability through theinner liner must be minimal. The mostpractical and cost effective way to achievethis is to use inner liner compounds basedon halobutyl alone. Advantages in adhesionand the overall balance of properties favorbromobutyl for high performance. Theunique balance of low temperature flexibility,high damping characteristics and cureversatility of halobutyl rubbers offerspotential for tread compounds in blends withgeneral purpose rubbers. Their weatherresistance, adhesive strength, and curecompatibility with EPDM and NR, are usedto advantage in tire sidewalls andcoverstrips. A wide variety of non-tireapplications also take advantage of theproperties of chlorobutyl and bromobutyl.




Appendix I: Test procedures

Monsanto Rheometer ASTM D 2084-81

Permeability to air Bayer Test. Q = Volume of gas (cc at N.T.P.)passing, per second, through a specimen of1 cm2 area and 1 cm thickness when thepressure difference across the specimen isone atmosphere.

Static peel adhesion Test specimen - 2 cm strips died from apress-cured laminate cured to 100 % NRcarcass stock. Specimens lined top andbottom with rubberized nylon fabric.

NR Carcass Formulation

SMR-5 CVN550Circosol 4240Zinc oxideStearic acidSantocure NSSulfur

100.030.05.05.01.50.52.4

Monsanto fatigue to failure Cam 24, not adjusted for set. Test resultsreported as the geometric mean of 12specimens.

Hardness ASTM D 2240-85

Compression set ASTM D 395-84

Stress strain ASTM D 412-83

Mooney viscosity ASTM D 1646

Abrasion resistance Bayer Procedure 01.06.442.76DIN 53 516 Jan. 77

Tel Tak Bayer Procedure 01.04.095.78

Mill shrinkage ASTM D 1917-87

Garvey Die extrusion ASTM D 2230-83

Ozone resistance (static) ASTM D 1149

Ozone resistance (dynamic) Bayer Procedure 01.04.461.761.27 cm (0.5 in) wide specimens cut from testsheets, lightly buffed and extended acrossthe grain. OREC Ozonator, 50 pphm O3 ,60 C/140 F, 0-25 % extension, 32 cpm,168 hours. Rating : 0 - zero cracks; 1 - visiblecracks under 10 X magnification; 2 - visiblecracks, naked eye; 3 - cracks easily visible;4 - severe cracking, sample intact;5 - separation.




Appendix I (Contd)

Hot air aging ASTM D 573-81.

Fluid aging ASTM D 471-79.

Spice strength(inner tubes)

Tensile strength measured across the spliceof an inner tube and calculated as apercentage of the tensile strength of the innertube.

Dynamic splice fatigue(inner tubes)

Determined as kc to failure using a standardtensile dumbbell specimen taken across thesplice.

Tensile set ASTM D 412-68




Appendix II: Formulations *

Solvent resistant rollers

Bayer Bromobutyl X2Krynac 34.50N550 blackN990 blackDOPParaplex G-62Paraffin waxPetrolatumZinc oxideMC sulfurDPTTVulkanox BKF

100--5030552

1.55

1.251.01.0

50505030--52

1.55

1.251.01.0

--1005030--52

1.55

1.251.01.0

Sports ball bladder

Bayer Bromobutyl X2Natural rubberMBTSN660 blackPrecipitated calcium carbonateParaffinic oilStearic acidTMTDZinc oxideSulfur

75250.5503010113

0.3

Mounts

Natural rubberBayer Bromobutyl X2Stearic acidZinc oxideN330 blackNaphthenic oilMC sulfurTMTDCBS

60.040.01.03.030.015.00.20.53.0

Inner Liner

HalobutylNatural rubberN660 blackParaffinic oilStearic acidZinc oxideSulfurAccelerator

100.0 to 40.040.0 to 60.0

60.07.01.03.00.5

Varied

Curing Envelopes

Bayer Chlorobutyl 1240Stearic acidN660 blackADPA 86MBIMaglite D (MgO)Paraffinic oilZinc oxide

100.01.055.01.01.00.412.05.0

Test recipe for cure systems

HalobutylStearic acidN550 blackNaphthenic oilZinc oxideSulfurAccelerators

100.01.055.010.0

0.0 to 5.00.0 to 0.5

Varied




Appendix III: Effect of cure systems in chlorobutyl on compression set, and heat andozone resistance

Test Recipe *(Appendix III)

Bayer Chlorobutyl 1255 100

Stearic acid 1

N550 black 55

Paraffinic oil 10

Zinc oxide 5

Compound Ref. 84-EV 20 21 22 23

Maglite D 1 - - -

Aminox 1 - - -

MBI 1 - - -

TMTD 0.5 0.5 - -

HVA #2 - - - 1.6

N-phenyl maleimide - - - 2.0

Compound viscosityML 1+4 (100 C) 73 71 69 66

Scorch time(min at 125C) 28.8 8.7 14 12.2

Monsanto rheometer at166 C (3 arc, 100 cpm,0 preheat)

Min. torqueMax. torquet2 (min)tc 90 (min)

1562.53.6

14.2

14.5481.66.0

15362.07.0

13.5541.66.8

Cure, min at 166 C 14 6 7 7



3.3 1.8 1.4 2.4


10.0 7.9 6.5 8.3


Ultimate elongation 400 540 510 480

Compression set (%)70 h at 100 C70 h at 150 C

1838

1242

2257

1631




Appendix III (Contd)

Ozone resistance 50 pphm at 40 C

Static, 168 h, 20 % strain 1 3 3 0

Static, 168 h, 50 % strain 2 3 4 0

Dynamic, 168 h, 0-25 % strain 0 2 3 0

Aged in air, 168 h/150 C - change

Hardness (pts) +5 -5 -4 +1

Modulus at 100 % elongation +39 -46 -30 -4



TE (f) 0.52 0.09 0.11 0.25


Hardness (pts) +2 -6 -7 +1

Modulus at 100 % elongation -3 -39 -44 -17



TE (f) 0.48 0.17 0.14 0.26


Hardness (pts) -1 -9 -9 -




TE (f) 0.27 0.04 0.04 0.08


Hardness (pts) -6 -16 -16 -8



Ultimate elongation (%) -40 -11 +12 -23

TE (f) 0.15 0.12 0.19 0.21




Appendix IV: Effect of cure systems in bromobutyl on compression set, and heat andozone resistance

Test Recipe *(Appendix IV)

Bayer Bromobutyl X2 100

Stearic acid 1

N550 black 55

Paraffinic oil 10

Zinc oxide 5

Compound Ref. 84-EV 20 21 22 23

Maglite D 1 - - -

Aminox 1 - - -

MBI 1 - - -

TMTD 0.3 0.3 - -

HVA #2 - - - 1.6

N-phenyl maleimide - - - 2.0

Compound viscosityML 1+4 (100 C) 74 70 72 66

Scorch time(min at 125 C) 7 11.6 30 24.4

Monsanto rheometer at166 C (3 arc, 100 cpm,0 preheat)

Min. torqueMax. torquet2 (min)tc 90 (min)

1762.51.85.6

14432.04.8

1335.54.07.8

12.5543.216

Cure, min at 166 C 6 5 8 16



3.0 1.7 1.3 2.3


8.3 7.9 7.2 8.4



Compression set (%)70 h at 100 C70 h at 150 C

1945

--

4468

1534




Appendix IV (Contd)

Ozone resistance - 50 pphm at 40 C

Static, 168 h, 20 % strain 0 3 3 0

Static, 168 h, 50 % strain 0 3 3 0

Dynamic, 168 h, 0-25 % strain 0 3/4 4 0


Hardness (pts) +5 +5 +7 +2

Modulus at 100 % elongation +37 +29 +62 +52



TE (f) 0.57 0.24 0.32 0.55


Hardness (pts) +1 +1 +2 +1

Modulus at 100% elongation +13 -29 -15 +13

Tensile strength (%) +12 -69 -69 -33


TE (f) 0.54 0.25 0.28 0.40


Hardness (pts) -2 -1 NIL -3

Modulus at 100% elongation +43 -51 -15 -17



TE (f) 0.46 0.05 0.1 0.15


Hardness (pts) -5 -5 -5 -1

Modulus at 100% elongation -30 -65 -55 -22


Ultimate elongation (%) -32 +20 +36 -37

TE (f) 0.32 0.17 0.15 0.24




Appendix V: Inner tube compounds *Comparison of bromobutyl with butyl and chlorobutyl

Butyl Bromobutyl Chlorobutyl

Bayer Butyl 301 100.0 - -

Bayer Bromobutyl X2 - 100.0 -

Bayer Chlorobutyl 1255 - - 100.0

Stearic acid 1.0 1.0 1.0

N650 black 70.0 70.0 70.0

Circo light oil 25.0 25.0 25.0

Zinc oxide 5.0 3.0 5.0

MBT 0.5 - -

MBTS - 0.5 0.5

TMTD 1.0 - -

ZMDC - 0.1 0.7

Sulfur 1.5 0.5 0.5

Monsanto rheometerOptimum cure time at 166 Ctc 90 (min)Minimum cure time at 166 Ctc 65 (min)

16

7.75

5

4

8

5.5

Scorch time (min at 125 C) 20.5 15.5 9

Cured Properties (Cured to tc 90)




Tensile strength (MPa) 9.2 10.6 9.7


Tensile set (%) 10 6 5

Aged in air oven, 240 h at 125 C

Change in properties

Hardness (pts) +17 +20 +22

Tensile strength (%) -56 0 -17

Ultimate elongation (%) -34 -57 -45




Appendix V (Contd)

Final property values


Tensile strength (MPa) 4.0 0 -17


Splice properties

Tensile (1 % of tube strength)

Unaged 85 88 83

Aged - 48 h at 121 C 68 74 74

Dynamic fatigue(kc to failure, 0-100 % extension)

Unaged 10 59 42

Aged - 48 h at 121 C 2 27 16




Appendix VI: Supersoft CV sponge weatherstrip * - salt bath process

Buna EP T 4969 160.0

Bayer Bromobutyl 2030 20.0

N650 black 100.0

Whiting 70.0

Paraffinic oil 60.0

Zinc oxide 5.0

Stearic acid 1.0

Desical P 5.0

TE 80 2.0

Celogen AZ 130 5.0

Carboxwax 4000 1.0

TMTD 0.8

MBT 1.5

TEDC 0.8

DPTT 0.8

Sulfur 2.0

Total weight 434.9

Specific gravity (unexpanded) 1.207

Expanded density (g/cc)/ (lb/cu.ft) 0.56/ 35.1

Water absorption, 70h at 20 C 1.7 %

Cure time at 205 C 3 min




Appendix VII: Characteristics of cure systems in halobutyl

Cure Systems

Hea

t R

esis

tan

ce

Co

mp

ress

ion

S

et

Ozo

ne

Res

ista

nce

Fle

x R

esis

tan

ce

Ad

hes

ion

Wat

er

Res

ista

nce

Sco

rch

Saf

ety

Cu

re R

ate

Miscellaneous

ZnO Low extractablesZnO + TMTD Also for blendsZnO + TCBQZnO + ZDCZnO + MBRS Also for blendsZnO + TMTD + ADPA + MBIZn + ADPAZnO + MDBPeroxide Blends with EPR & EDPMPeroxide + HVA Blends with NBR, EPR and

EPFMHVAZnO + Phenolic Fast cure - high modulusPbO + Phenolic Low water absorptionPbO + TCBQ Water resistanceZnO + DIAK Pharmaceuticals

Excellent Very Good Good Good Blank - Acceptable




Appendix VIII: Effect of blending halobutyl with natural rubber

Test Recipe *(Appendix VIII)

Halobutyl/NR 100.0

N660 black 60.0

Paraffinic oil 7.0

Pentalyn A 4.0

Stearic acid 1.0

Zinc oxide 3.0

MBTS 1.25

Sulfur 0.5

Halobutyl (phr) 100 80 60 40

BIIR CIIR BIIR CIIR BIIR CIIR BIIR CIIR

Unaged

Modulus at 300 % (MPa) 4.2 3.7 5.7 5.1 7.1 5.7 8.9 4.3

Tensile strength (MPa) 9.3 9.9 10.9 10.7 12.8 10.3 14.7 9.7

Ultimate elongation (%) 740 770 620 620 560 560 490 580

Aged in air, 168 h at100 C

Modulus at 300 % (MPa) 6.8 5.5 7.6 7.9 8.4 7.7 6.7 3.6


Ultimate elongation (%) 550 640 420 465 320 365 370 475

Permeability to air, 50 psi at65 C (Qx108) 2.9 2.9 5.4 5.7 9.2 7.5 13.8 13.2

Adhesion at 100 C

to self (kNm) 16.8 4.4 14.7 4.7 15.2 9.1 15.4 5.2

to NR (kNm) 7.5 1.3 6.2 1.3 14.7 1.9 20.8 2.9

Flex fatigue, air aged

168 h at 120 C

Cam #24 (kcy) 61.8 72.7 23.6 3.9 0.3 0.1 0.0 0.0




Appendix IX: Effect of cure systems on BIIR and CIIR

Test Recipe *(Appendix IX)

Halobutyl 100.0

N660 black 60.0

Paraffinic oil 7.0

Stearic acid 1.0

Resin (Pentalyn A) 4.0

Cure system varied

ZnOSulfur

3.00.5

ZnOSulfurMBTS

3.00.5

1.25

ZnOSulfurVultac

3.00.51.0

ZnOSulfurTMTD

3.00.51.0

CompoundProperties

CIIR BIIR CIIR BIIR CIIR BIIR CIIR BIIR

Mooney viscosityML 1+4 (100 C) 60 60 63 60 67 58 68 55

Mooney scorcht5 at 125 C (min) 10 13.4 15.7 28 8 12.9 9.0 10.8

Monsanto rheometer(3 arc, 166 C)MH (dNm)ML (dNm)tc90 (min)

39.211.910.2

37.811.27.0

31.811.217.5

28.29.08.8

51.712.36.6

42.89.87.2

5.512.34.1

42.810.43.7

Cured at 166 C (min) 10 7 18 9 7 7 - 4

Modulus at 100 %elongation (MPa)

1.2 1.6 1.0 1.3 1.7 1.9 1.7 1.3


5.6 6.6 3.7 4.2 6.8 7.5 6.1 4.6


Ultimate elongation(%)

560 550 770 740 550 560 620 700

Hardness, Shore A 51 60 52 62 56 60 57 53




Appendix IX (Contd)

Aged 168 h at 100 C


1.6 2.6 1.4 2.2 2.2 3.0 2.2 2.2


6.6 8.6 5.5 6.8 8.2 9.2 7.5 6.6


Ultimate elongation(%)

530 430 640 550 475 420 390 530

Hardness, Shore A 54 66 57 65 58 65 62 66

Adhesion

To self (kNm) 2.7 13.3 4.4 16.8 7.6 17.2 2.4 11.1

To NR (kNm) 1.2 14.8 1.3 10.3 2.0 6.2 1.0 9.8

Monsanto flex

Aged 168 h/102 C

Cam 24 (Kcy) 26 16.2 72 61.8 12.3 13.5 19.9 12.8

Registered Trademarks of Bayer AG:

BunaKrynacVulkacitVulkanox

Bibliography:(1) Dawson, T.R., Shidrowitz, P., RAPRA

1937.(2) Bartovics, A., (Firestone), U.S. Patent

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1955.

(8) Baldwin, F.P., Buckley, D.J., Kuntz, I.,Robinson, S. B., Rubber & PlasticsAge, 500, 1961.

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(29) Herzlich, H., et al, ACS Rubber Div.,Miami Beach, April 1971.

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(32) Tyurina, V.S., Shuarts, A.G., Int. Pol.Science & Tech., 3, (1), K76/01/32,1976.

(33) Pat., 4,323,485, Yokohama, April 1982.(34) Pat., 4,321,168, March 1982.(35) Briggs, G.J., Wei, J.K., Plastics &

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Kumbhani, K.J., Edwards, S., PolysarLimited, Non-Tire Applications ofBromobutyl.

Author(s):

HopkinsWalkerSumner (revised August 2000)

The above formulation is intended solely as a guide for our business partners and others interested in our products. As the conditions of use andapplication of the suggested formulation are beyond our control, it is imperative that it be tested to determine, to your satisfaction, whether it is suitable foryour intended use(s) and application(s). This application-specific analysis at least must include testing to determine suitability from a technical, as well ashealth, safety and environmental standpoints. Further, although the ingredients, quantities thereof and properties of compounds or finished goodsmentioned herein reflect our recommendation at the time of publication, this guide may not be subject to continuous review and/or updating, and you agreethat use is undertaken at your sole risk. All information is given without warranty or guarantee, and it is expressly understood and agreed that you assume,and hereby expressly release us from, all liability, in tort, contract or otherwise, incurred in connection with the use of this guide.

This information and our technical advice - whether verbal, in writing or by way of trials - are given in good faith but without warranty, and this also applieswhere proprietary rights of third parties are involved. Our advice does not release you from the obligation to check its validity and to test our products as totheir suitability for the intended processes and uses. The application, use and processing of our products and the products manufactured by you on thebasis of our technical advice are beyond our control and, therefore, entirely your own responsibility. Our products are sold in accordance with the currentversion of our General Conditions of Sale and Delivery.__________________________________________________________________________________________________________________________Bayer AG, D-51368 LeverkusenRubber Business GroupResearch and Development

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Cure Reactivity - A Route to Improved Performance in Halobutyl Applications TI