influence of different curing systems on the physico ... of different curing systems on the...

417Polymers & Polymer Composites, Vol. 18, No. 8, 2010

Influence of Different Curing Systems on the Physico-Mechanical and Rheological Properties of CSM Rubber

*Correspondingauthor:[email protected]

©SmithersRapraTechnology,2010

INTRODUCTION

Improvement in the properties of polymers can be obtained by chemically modifying the polymer backbone, by introducing structuralirregularities or by grafting onto the polymerchain.Bychlorosulfonationofpolyethylene in solution the structural regularity is destroyed by changing the thermoplastic material into a rubbery material, which is described asCSM rubber according toASTMD14181.Itcontains25%to43%byweightofchlorineand1.0%to1.5%by weight of sulfur as SO2Cl units.Depending on chlorine contents, itsflexibilityalsovaries.Suchchlorine-containing polymers are commonly used as insulators or sheath materials in nuclear environments because of their well-known radiation resistance2-4.

Compared tounsaturatedelastomersthey have superior resistance to the

deterioratingeffectsofozone,oxygen,weather, heat, chemicals and oil. Polar rubbers interact with their active functional groups via condensation or substitution reactions.

ThehighreactivityofCSMrubberisdue to -SO2Clgroups,whichprovidescrosslinkingsitesallowingwidechoiceof practical curing systems. Two types of curing processes are available for CSMrubber(a)Ioniccure(b)Covalentcure5. In ionic curing systems, normally ionic crosslinking occurs which isaccelerated by moisture and this is possible only when the acid acceptor is adivalentmetaloxide.Inthecovalentcure system, covalent crosslinkingoccurs,andmostapplicationsforCSMrubbermakeuseofthistypeofcuring5.

The properties and performance of a rubber product depend on many factors including the chemical nature of the rubber, the amount andkinds

of ingredients incorporated into the rubber compound, processing and vulcanizing conditions, design of the product and service conditions. Physico-mechanical properties of different curing systems vary due to the difference in their efficiencyof crosslinking. In order to obtain adesirable combination of properties andservicelifeachemicalcrosslinkingsystemhavinghigherefficiencyshouldbe considered. Proper judgmentcan be obtained from accelerated aging behaviour, as the crosslinkingsystem has marked influence onthe degradation characteristics of elastomers6-10.

Studies of CSM rubber compoundshave not received much attention even though they possess good weather resistance, electrical properties and agingresistance.FewresearchworksdealingwithCSMrubberhavebeenreported in the literature11-13. The effect of β irradiation on structural changes ofCSM rubber has been studiedbyFoucault et al.14.Chailanet al.15 have investigated the effect of thermal

InfluenceofDifferentCuringSystemsonthePhysico-MechanicalandRheologicalPropertiesofCSMRubber

MadhuriNandaandDebaKumarTripathy*RubberTechnologyCentre,IndianInstituteofTechnology,Kharagpur721302,India

Received:23July2009,Accepted:8June2010

SUMMARYCuringsystemsplayavitalroleindesigningrubbercompoundsforvariousindustrialapplications.Keepingthisinview,acomparativestudyoftheeffectsoffourdifferentcuringsystemssuchassulfur,dicumylperoxide(DCP),metaloxide(PbO)andepoxyresinonthecuringcharacteristics,physico-mechanical,andrheologicalpropertiesofchlorosulfonatedpolyethylenerubber(CSM)hasbeencarriedout.Thehighestvaluesofmaximumrheometrictorqueandscorchsafetywereobservedintheperoxide-curedsystem,whereassulfur-curedCSMrubber compounds possessed superior mechanical and rheological properties compared to those of the other curedsystems.Itisinterestingtonotethatallcuringsystemsexhibitedincreasesintensilestrength,hardness,tearstrengthandcrosslinkdensityafteraging. Thismaybeduetopostvulcanization.UnlikeuncuredCSMcompound,incuredCSMcompoundthelosstangentincreasedwithfrequency,whichmaybeduetotheinsufficienttimeavailableformolecularrelaxation.ProbablecrosslinkedstructuresfordifferentcuringsystemshavebeenproposedbasedontheobservationsofattenuatedtotalreflectanceFouriertransforminfraredspectroscopy.

418 Polymers & Polymer Composites, Vol. 18, No. 8, 2010

Madhuri Nanda and Deba Kumar Tripathy

degradation on the viscoelastic and dielectric properties of metal oxidecured CSM compounds. Recentlyphysical and electrical properties of sulfurcuredcarbonblackfilledCSMrubber compound has been reported by Tripathy et al.16,17.NofurtherstudyontheeffectofcuringsystemsonCSMrubber has been reported so far.

In the present study an attempt has beenmade to explore the details ofphysico-mechanical and dynamic rheologicalbehaviourofCSMrubbercured by four different curing systems with a view to select the most suitable curing system for industrial use. The influence of curing system on heatagingpropertiesofCSMrubberhasalso been studied. Surface analysis has been studied using attenuated total reflectanceFouriertransforminfrared(ATR-FTIR)spectroscopy.

EXPERIMENTAL

Materials Details of the compositions of themixesaregiveninTable 1.CSMrubber[(Hypalon-40),35%chlorinecontent,Mooney viscosity ML1+4at100°C=56)] manufactured by DuPont DowElastomers was used. Magnesium oxideusedwasofanalyticalgradewithspecificgravity3.8,andwassuppliedbyE.MerckLimited,Bombay,India.

Sulfur of chemically-pure grade with aspecificgravityof1.9,wassuppliedbyM/SNice chemicalsPvtCochin,India.Curativessuchasdibenzothiazyldisulfide(MBTS),diphenylguanidine(DPG)anddipentamethylenethiuramtetrasulfide(Tetrone-A)weresuppliedby M/S ICI limited, Hoogly, India.Triallyl cyanurate used in a stabilized form (40%) was manufactured byDegussa,Germany.Dicumylperoxide(DCP) with a purity of 40% wasprocured from M/S ICI limited,Hoogly,India.Leadmonoxide(PbO)wassuppliedbyLobaChemiePvtLtd,Mumbai. Toluene was of analytical gradewithBP110.6 °C,whichwasprocured from Ranbaxy Chemicals,NewDelhi,India.Epoxyresin,gradeAraldite LY553, was obtained fromCibatulLimited,Bombay.Stearicacidof chemically-pure grade was procured locally.

Sample Preparation Mixingwascarriedoutinalaboratorysize tworollmixingmill (325mm×150mm)atafrictionratioof1:1.25according to ASTM D3182 withcareful control of temperature, nip gap,mixingtimeanduniformcuttingoperation. The curing characteristics of the compounds were determined withaMonsantoRheometer(R−100)accordingtoASTMD2084andASTMD5289procedures.Mouldingwasdone

in an electrically heated hydraulic press having 300 mm × 300 mm platensat 160 °C (Peroxide) and 150 °C(Epoxy,metaloxide,andsulfur)atapressure of 4.0 MPa. Vulcanizationwas done to optimum cure (90%ofthe maximum cure) using differentmoulding conditions determined from torquedataobtainedfromMonsantoRheometer. The test specimens were punched out from moulded sheets.

TESTINGPROCEDURE

Physical Test MethodsThe cure characteristics of the compounds were determined with the help of an oscillating disc rheometer with an arc of oscillation of 3°. The chemistry of peroxidevulcanization explainsthatanoxygen-oxygen bond present in peroxideundergoes homolytic cleavage at high temperature. The rheometric characteristics of CSM compoundfortheperoxidesystemandforotherthree curing systems were studied at 160and150°Crespectively.TensileStrength, modulus and elongation at breakweredeterminedbyaHounsfield1145 universal testing machineaccordingtoASTMD412-80at25°Cusing dumb-bell shaped specimens. Tear strength was also determined using Hounsfield 1145 accordingto ASTM method D−624 using adie C specimen. Shore-A hardnessof the vulcanizates was determined according to ASTM D2240-81.Compression setwasdeterminedbycompressingthespecimento25%ofitsoriginal thicknessfor22hoursat70 °C. The specimen was removedandallowed30minrecovery,andthenthe permanent set was measured as a percentage of the original thicknessaccordingtoASTMD395-85.Mouldedsheetswereheat-agedat100 °C for72hoursinanelectricallyheatedairoven for the aging study.

Chemical Test MethodsThe resistance to solvent was determined by a swelling test. The

Table1.CompositionsofunfilledCSMvulcanizatesinphr(partsperhundredrubber)Mix No / Curing System

Epoxy(G1) Metal oxide (G2)

Peroxide (G3)

Sulfur (G4)

CSM 100 100 100 100MgO - 5 4 4Stearic acid - 2 - -MBTS 0.5 0.5 - 0.5DPG 0.5 - - 0.5TETRONEA 0.75 0.5 2 0.75TAC - - 5 -DCP - - 6 -EpoxyResin 10 - - -PbO - 10 - -Sulfur 1 - - 1



volume fraction of rubber (Vr) in the vulcanizate was determined by equilibrium swelling in toluene,using the method reported by Ellis andWelding18. The relationship used for calculating Vr is represented by equation(1):

Vr =D −FT( )ρr−1

D −FT( )ρr−1 +A0ρs−1

(1)

where T is the weight of the test specimen, F is the weight fraction of the insoluble components in the sample, D is the de-swollen weightofthetestspecimen,A0 is the weight of absorbed solvent, corrected for swelling increment, ρr is the density of the rubber and ρs is the density of the solvent. The number of effective network chains per unit volumeof rubber is denoted as υ, which was calculated using Flory–Rehner equation(equation(2))19,20

υ=−1Vs×ln 1−Vr( )+Vr +µVr2

Vr1/3 −Vr / 2 (2)

Whereυ is the number of effective network chains per unit volume ofrubber, Vs is the molar volume of the solvent and μ is the polymer-solventinteractionparameter(Flory-Huggins’s interaction parameter),whichwasfoundtobe0.40121.

FTIR–ATRMeasurementsFourier-transform infrared spectra (FTIR) were recorded on a Nexus870spectrometerwithanattenuatedtotal reflection (ATR) attachment.Aminimum of 32 scans were signal-averaged at a resolution of 4 cm-1. For FTIR-ATR measurements, the

spectrometer was equipped with aDTGSdetector.Theinternalreflectionelement(IRE)chosenwasa45degreeZnSecrystal.

RheologicalMeasurementsFor measurement of dynamic viscoelastic properties, Rubber Process Analyzer (RPA2000, AlphaTechnologies,Akron,USA)wasused.TheRPAwasaparallelplaterheometer,capable of measuring the complexmodulus of rubber compounds under dynamic shear deformation. It helped in measuring the rheological, rheometric, and dynamic viscoelastic properties of the polymers over a wide range of conditions.Thefrequencysweeptestwas performed, in which the oscillating frequencychangewasprogrammedinstepsfrom0.13to30Hzataconstantstrain amplitude of 2.9% and underconstant temperature conditions (110°C).

RESULTSANDDISCUSSION

Curing CharacteristicsThe cure characteristics of the samples obtained from the Monsanto Rheographs are summarized in Table 2.Thehighestvalueofmaximumrheometric torque (MH) was shown bytheperoxidesystem,whereasthelowest value was shown by the metal oxide system. This is due to highcrosslink density of peroxide curedCSM compounds22. Among all thesystems, the peroxide one showedthe highest scorch safety. The highest valueofminimumrheometrictorque(ML) was shown by the sulfur system, whereas the lowest value was shown by the peroxide system. The effectof different curing systems on the

optimum curing time (T90) and cure rate of CSM compoundswas foundto be marginal.

Physico-Mechanical PropertiesThe physico-mechanical properties of CSM vulcanizates cured by fourdifferent curing systems both before and after aging are presented in Table 3. Depending on the vulcanizationsystem,differentcrosslinkstructuresare obtained. In sulfur and epoxycuredCSMrubberC-S-Ccrosslinksareformed,whileperoxideyieldsC-Ccrosslinks.Inthemetaloxidesystem,ioniccrosslinksareformed.Thefreemobility of the chain segments of the macromolecules depends on their relative distance, and therefore on the length of the crosslinks. Therefore,the type of crosslink structureinfluences the property spectrum ofthe vulcanizate23-25. From this table, it can be observed that the tensile strength for sulfur-cured vulcanizates has been found to be higher than those of the other three systems. This may be due to the formation of sulfidiccrosslinks in the CSM vulcanizates.In the metal oxide and epoxy curesystems, comparable tensile strength wasobserved.Anintermediatevalueof tensile strength was observed for theperoxidecuresystem.Sulfur-curedCSM vulcanizates showed highermodulus values. The DCP curedsystemshaverigidC-Clinkages,whichcanbebrokeneasilyunderanappliedstress, whereas in sulfur cured systems, flexibleC-SandS-Slinkagesexistandtheyrequiremorestresstobreakthebonds.Howeverhighertearstrengthwasobservedinthemetaloxidecuresystem, which may be due to the ionic crosslinkedstructure.

Table2.RheometriccharacteristicsofunfilledCSMvulcanizatesMix no Initial viscosity

d N-mMinimum torque

(ML),dN-mMaximum torque

(MH),dN-mScorch time

(min)Optimum cure time (T90),min

Cure rate (min-1)

G1 28 9 52 3 15 8.3G2 30 10 48.5 2.75 17.5 6.77G3 34 7 61 3.5 16 8G4 35 12 49 2.5 15 8



The crosslinking systems that leadto covalent bonds, such as sulfur and dicumyl peroxide systems exhibitedbetter compression set response. The best set properties were achieved with the organic peroxide system, whichforms strong –C–C– links betweenthepolymericchains.Thecrosslinkingefficiency of CSM vulcanizates ismeasured in termsof their crosslinkdensity. A higher crosslink densityvaluewasobservedfor theperoxideand epoxy curing systems. In theperoxide curing system, triallylcyanurate was used as a coagent, which improved the cure rate, giving higher crosslinkdensity.Intermediatevaluesofcrosslinkdensitywereobservedinthe case of the sulfur curing system. In metaloxidecuredCSMvulcanizates,the crosslink density value wascomparatively low, which may be due to an ionic crosslink network beingformed between the polymeric chains.

CSM rubber having no unsaturationsitespossessesexcellentresistancetoheat, weather, ozone and chemicals. Changing the curing systems had amarginal effect on the aging behaviour ofCSMvulcanizates.Increasesinthetensile strength and tear strength after aging were observed in all systems, which may be due to post-vulcanization. Elongation at break decreased afteragingforallsamples.Heatagingstudiesalso showed marginal effects on the hardnessandcrosslinkdensity.

FourierTransformInfrared/Attenuated TotalReflectance (FTIR–ATR) SpectroscopyInfrared spectra of the compounds wereobtained for bothCSM rubberand vulcanized compounds. Special attention was paid to the spectral region of the -SO2Clgroupstoestablishthe existence of variations betweenthe raw and the crosslinked states.The assignments of the principal bands for raw rubber are presented in Table 4. Similar findings have alsobeen reported26. Figure1 represents the FTIR-ATR spectra of CSMrubber(spectruma)andepoxycuredCSM vulcanizate (spectrum b). IRanalysis provided a confirmation ofthe assumption that such specific bonds were formed. It appeared that thecharacteristicbandofC-SO2Cl(at1366cm-1)inthespectrumofpureCSM

was less intense in the spectrum of the vulcanizate. The absorption bands at 829and1246cm-1 may be due to the C-O-C stretching vibrations of theepoxyring.Thebandat1654cm-1 is due totheC=Cstretchingfrequencywhichis observed as a result of decomposition of the SO2Cl group present in pureCSMrubber. Thebandat1183cm-1

is due to C-S-Cstretchingvibrations,which further supports the formation of a crosslinked network in CSMvulcanizates as shown in Scheme 11. Additionally,thevulcanizatespectrumrevealed the presence of a broad yet weakbandat3386cm-1which may be attributed to the stretching vibrations of–OH(H-bonded)groups,obtainedduetoringopeningoftheepoxyresin(Scheme 1).

Figure 2 represents the FTIR-ATRspectraofCSMrubber (spectruma)

Table3.Physico-mechanicalpropertiesofunfilledCSMvulcanizatesProperties Epoxy(G1) Metaloxide(G2) DCP(G3) Sulfur(G4)

Beforeaging

After aging

Beforeaging

After aging

Beforeaging

After aging

Beforeaging

After aging

Tensile strength, MPa 21.8 22.3 20.3 21.2 25 26.3 27.9 28.2M100%,MPa 0.9 1 1 1.1 1.2 1.3 1.3 1.4M200%,MPa 1.2 1.4 1.5 1.7 1.6 1.9 2.2 2.7M300%,MPa 1.7 2.3 1.9 2.3 2.4 3 3.3 3.7Elongationatbreak(%) 806 693 969 863 935 765 874 770Tearstrength(N/mm) 20.4 21.3 29.3 33.4 23.6 24.1 25.7 26.3HardnessIRHD 38 41.5 45 48 41 44 50 51Compressionset22hrsat100°C,% 6 6 11.1 8.7 4.9 3.4 6.7 4.9Crosslinkdensity(υ×103), mol/cc 2.1 2.4 1.8 2 2.5 2.7 2 2.3

Table 4. Assignment of infrared bands of chlorosulfonated polyethyleneWavenumber (cm-1) Group Assignment2928 CH3-,-CH2-,>CH- υ(C-H)2855 CH3-,-CH2-,>CH- υ(C-H)1457 -CH2 δ(C-H)1366 -SO2Cl υ(SO2)asym

1253 -CH2- γ(CH2)1161 -SO2Cl υ(SO2)Sym

1016 Unknown Unknown723 -CH2- γ

γ(CH2)

665 -CHCl- υ(C-Cl)



and metal oxide (PbO) cured CSMvulcanizate (spectrum b). In the caseof ionomericCSM, thepeakat1606cm-1withashoulderat1581cm-1 is probably due to the asymmetric –COO- stretching of magnesium stearate.Thebandat1016cm-1 with ashoulderat1040cm-1 is believed to be due to the symmetric stretching of sulfonate groups present as lead sulfonate as shown in Scheme 21. The characteristic band of C-SO2Cl(at1366cm-1) in the spectrum of pure CSMwasfoundtobelessintenseinthespectrumoftheCSMvulcanizate,which further supports the hydrolysis of the sulfochloride group present in thepolymer(Scheme 2).

Figure 3 represents the FTIR-ATRspectraofCSMrubber(spectruma)andDCPcuredCSMvulcanizate(spectrumb).Bands at 1695 cm-1 may be due to N–(C=O)–N from crosslinkingassociated with TAC domains. Thebandat1611cm-1 can be attributed to thequadrantstretchingofTACpresentas a part of the CSM crosslinkeddomain. Formation of cumyl alcohol through dissociation of DCP duringcuring reactions can also account for thebroadyetweakbandat3400cm-1

(Scheme 3).Thebandat1099cm-1is

duetoN-CH2stretching vibrations that arise from TAC domains associatedwithcrosslinks27(Scheme 3).

Figure 4 represents the FTIR-ATRspectraofCSMrubber(spectruma)andsulfurcuredCSMvulcanizate(spectrumb).Thebandat1657cm-1 is due to the

Figure1.FTIR–ATRspectraofrawCSMrubberandepoxycuredCSMvulcanizate

Scheme 1. Probable network structure of chlorosulfonated polyethylene crosslinked by epoxy system

C=C stretching frequency, which isobtained as a result of decomposition of the SO2ClgrouppresentinthepureCSM rubber. Thebandat 1183 cm-1

is due to C-S-Cstretchingvibrations,which further supports the formation of crosslinked network in CSMvulcanizates as shown in Scheme 41.



Figure3.FTIR–ATRspectraofrawCSMrubberandDCPcured CSM vulcanizate

Figure2.FTIR–ATRspectraofrawCSMrubberandmetaloxide cured CSM vulcanizate

Scheme 2. Probable network structure of chlorosulfonated polyethylene crosslinked by metal oxide system



The characteristic band of C-SO2Cl(at 1366 cm-1) in the spectrum of the vulcanizate was found to be less intensive. This drop in intensity of the sulfochloridegroup(SO2Cl)absorptionclearly indicated the participation in the crosslinkingofCSMrubberbydifferentvulcanizing systems.

RheologicalPropertiesFrequency SweepFigure 5 reveals the processibility of uncured compound via complexviscosity (η*) as a function of frequency. All samples show shearthinning effect, i.e. a decrease in η*

withincreasingfrequency.Compoundsobtained from sulfur cure formulation were more viscous than those of the other systems. Figure 6 shows the elasticmodulus(G’)asafunctionoffrequencyfortheuncuredcompound.It is apparent from the figure thatthe different curing systems had a

Scheme3.ProbablenetworkstructureofchlorosulfonatedpolyethylenecrosslinkedbyDCPsystem



remarkableeffecton the rheologicalbehaviour even at high frequency.Storage modulus increased with frequency; however, the rate ofincrease decreased with increase in the test frequency, which may beduetotheinsufficienttimeavailablefor molecular relaxation. In otherwords,thehigherthetestfrequency,the higher the elasticity. At lowfrequency, the influence of differentcuring systems on storage modulus was more pronounced. Sulfur-cured CSMcompoundsshowedthehigheststorage modulus. Figure7 shows the loss tangent (tanδ) as a function of frequencyfortheuncuredcompound,which decreased sharply at lower frequency,whileathigherfrequencythe rate of decrease was slow, so that the curves are nearly parallel to the horizontalaxis.Intheentirerangeoffrequencystudied,tanδfortheepoxycuring system was higher than those of the other three curing systems. This may be due to the predominantly viscous response of epoxy cureCSMcompoundwith relatively lowmolecular entanglement.

Cured CompoundsFigure8showsthecomplexviscosity(n*)asafunctionoffrequencyofcuredcompounds. It is clearly observed from the plot that the viscosity of cured compounds increased for all curing systems compared to those of uncured compounds. This is due to the formation of three dimensional crosslinked networks in the CSMvulcanizates.Allsamplesshowaverystrong shear-thinning effect. Figure9 shows the plots of the storage modulus

Figure4.FTIR–ATRspectraofrawCSMrubberandsulfurcuredCSMvulcanizate

Scheme 4. Probable network structure of chlorosulfonated polyethylene crosslinked by sulfur cure system

Figure5.ComplexviscosityasafunctionoffrequencyinuncuredCSMcompounds



G’versusfrequencyfordifferentcuringsystems of the CSM vulcanizates.It is clearly observed from Figure9 that storagemodulusexhibitsnearlyfrequency-independence, supportingthe crosslinking of polymeric phaseinthepolymermatrix.Duetonetworkformation between the polymeric chains inCSMvulcanizates there isno molecular slippage taking placewithinthisrangeoffrequency.Storagemodulus increased after curing for all cure system, which may be due to increaseinelastomericphaseinCSMvulcanizates.

Thefrequencydependencelosstangentfor CSM vulcanizates is displayedin Figure 10. Unlike the uncuredcompound loss tangent increased with increase in frequency for all curingsystems. This was attributed to the fact that, at higher frequencies, thepolymerchaindidnothavesufficienttimeformolecularrelaxation.Sulfur-curedCSMvulcanizateshowedhigherloss tangent values compared to those of other curing systems. This may be due to high elastic modulus value of sulfur-cured vulcanizate.

CONCLUSIONS

The effect of different curing systems on curing characteristics, physico-mechanical and rheological properties ofCSMvulcanizateswasinvestigated.From rheometric studies of CSMcompounds it was observed that the peroxide system exhibited themaximum rheometric torque andmaximum scorch safety while themetaloxidesystemshowedminimumrheometric torque. It was evidentthat the sulfur-cured system showed higher tensile strength and hardness values,whereasthemetaloxidesystemshowed higher tear strength. Increase in tensile strength, tear strength, and decreaseinelongationatbreakwereobserved after aging for all curing systems studied. This may be due post-vulcanization. Better physicalproperties supported by good aging resistance make CSM vulcanizates

Figure6.ElasticmodulusasafunctionoffrequencyinuncuredCSMcompounds

Figure7.Dampingfactor(tanδ) as a function of frequency in uncured CSM compounds

Figure8.ComplexviscosityasafunctionoffrequencyincuredCSMcompounds



Figure9.ElasticmodulusasafunctionoffrequencyincuredCSMcompounds

Figure10.Dampingfactor(tanδ) as a function of frequency in cured CSM compounds

suitable for industrial applications such as conveyor belt linings or cable and conductor insulators. -SO2Clgroups participated in a different way duringthecrosslinkingprocess,whichdependedonthecrosslinkagentused.A probable crosslink structure hasbeen proposed for all curing systems, which has been supported by ATRstudies. Higher viscosity valueshave been observed for the sulfur cure system in frequency-dependentviscosity plot for both uncured and curedCSMcompound.Theviscosity

increase was accompanied by an increaseinthestoragemodulus(G’).In the case of the cured compounds, thefrequencyindependencenatureofstorage modulus has been observed. This can be explained on the basisof formation of three dimensional crosslinked network structures inCSMvulcanizates.UnliketheuncuredCSMcompounds,inthecuredCSMcompound the loss tangent increased with frequency. This was attributedto the insufficient time available formolecular relaxation. Based on the

physico-mechanical and rheological studies, both peroxide and sulfursystemexhibitedbetterpropertiesthantheepoxyandmetaloxidesystems.Thepresent investigation also revealed that thenegativeeffectofmetaloxideasacuringsystemduetoitstoxicnaturecan be successfully overcome by sulfur andperoxidecuringsystemsinthecaseofCSMrubber.

REFERENCES1. BrydsonJ.A.,RubberChemistry,

Appliedscience,London(1978).2. GillenK.T.andCloughR.L.,

Radiation-thermal degradation of PE andPVC:Mechanismofsynergismand dose rate effects, Radiation Physics and Chemistry, 18(1981)661-669.

3. CloughR.L.,Radiation-resistantpolymers, in ‘Encyclopedia of PolymerScienceandEngineering’(eds.:KroschwitzJ.)Wiley,NewYork,667–708(1988).

4. ChaianyaS.S.,MahendraJ.P.,ManishR.D.andMadhavV.P.,High-energy radiation-resistant elastomeric vulcanizates.I.Chlorosulfonatedpolyethylene, Journal of Applied Polymer Science, 51(1994)1505-1513.

5. MortonM.,RubberTechnology.VanNostrandReinhold,NewYork,365-366(1973).

6. BevilacquaE.M.,ThermalStabilityofPolymers,MarcelDekker,NewYork(1970).

7. CappsR.,Effectofcuresystemsandreinforcingfillersondynamicmechanical properties of chlorobutyl elastomers for potential vibration-control applications, Rubber Chemistry and Technology, 59(1986)103-122.

8. SheltonJ.R., Stabilization fundamentalsinthermalautoxidationof polymers, in ‘Stabilization and DegradationofPolymers’,(eds.:AllaraD.L.,HawkinsW.L.)Wiley-Interscience,NewYork,215-225(1978).

9. SahaDeuriA.andBhowmickA.K.,AgeingofrocketinsulatorcompoundbasedonEPDM,Polymer Degradation and Stability, 16(1986)221-239.



10.SahaDeuriA.,andBhowmickA.K.,Influenceofageingonstrength properties and morphology offracturesurfaceofhydroxyterminated polybutadiene rubber, Materials Chemistry and Physics, 18 (1987)35-48.

11.OwczarekM.andZaborskiM.,Chlorosulfonatedpolyethylenecross-linkedwithaminosilanes,Kautschuk Gummi Kunststoffe, 58(2005)432-437.

12.NersasianA.,KingK.F.andJohnsonP.R.,Novelcuringsystemsforchlorosulfonated polyethylene, Journal of Applied Polymer Science, 8(1964)337-354.

13.MaynardJ.T.andJohnsonP.R.,Ioniccrosslinkingofchlorosulfonatedpolyethylenes, Journal of Applied Polymer Science, 7(1963)1943-1950.

14.FoucaultF.,EsnoufS.,LeMoelA.,Irradiation/temperaturesynergyeffects on degradation and ageing of chlorosulfonated polyethylene, Nuclear Instruments and Methods in Physics Research B, 185(2001)311-317.

15. ChailanJ.F.,BoiteuxG.,ChauchardJ.,PinelB.andSeytreG.,Effectsof thermal degradation on the viscoelastic and dielectric properties of chlorosulphonated polyethylene (CSPE)compounds,Polymer Degradation and Stability, 48(1995)61-65.

16.NandaM.andTripathyD.K.,Physico-mechanical and electrical properties of conductive carbon blackreinforcedchlorosulfonatedpolyethylene vulcanizates, eXPRESS Polymer Letter, 2(2008)855-865.

17.NandaM.,ChaudharyR.N.P.andTripathyD.K.,Dielectricrelaxationofconductivecarbonblackreinforcedchlorosulfonatedpolyethylene vulcanizates, Polymer Composite (onlinepublished).

18.EllisB.andWeldingG.N.,Estimation, from swelling, of the structural contribution of chemical reactions to the vulcanization ofnaturalrubberPartI.Generalmethod, Rubber Chemistry and Technology,37(1964)563-570.

19.FloryP.J.,PrinciplesofPolymerChemistry,CornellUniversityPress,Ithaca,NY(1953).

20.FloryP.J.andRehenerJ.,Statisticalmechanicsofcross-linkedpolymernetworksΠ.Swelling,Journal of Chemical Physics, 11(1943)521-526.

21.BratonA.F.M.,HandbookofSolubility Parameters and Other CohesionParameters.CRCPress,BocaRaton,USA.(1983).

22. Abdel-AzizM.M.,MoftiS.andBasfarA.A.,Influenceofdifferentcuring systems on the physico-mechanical properties and stability ofSBRandNRrubbers,Radiation Physics and Chemistry, 63(2002)81-87.

23.SacriniE.,FontanelliR.andFontanaA.,Neworganicperoxidesandtheiruse in elastomer curing, Kautschuk Gummi Kunststoffe, 37(1984)312-313.

24.BrazierD.W.andSchwarzN.N.,Thecureofelastomersbydicumylperoxideasobservedindifferential scanning calorimetry, Thermochimica Acta, 39(1980)7–20.

25.CaplaM.andBarsigE.,Simultaneous degradation and crosslinkingeffectofdicumylperoxideonethylene–propylenecopolymers, European Polymer Journal, 16 (1980)611.

26.RoychoudhuryA.andDeP.P.,Studies on chemical interactions betweenChlorosulfonatedpolyethyleneandCarboxylatednitrile rubber, Journal of Applied Polymer Science, 63(1997)1761-1768.

27.MitraS.,Ghanbari-SiahkaliA.,KingshottP.,RehmeierH.K.,AbildgaardH.andAlmdalK.,Chemicaldegradationofcrosslinkedethylene-propylene-diene rubber in an acidic environment. Part II. Effectofperoxidecrosslinkinginthe presence of a coagent, Polymer Degradation and Stability,91(2006)81-83.

influence of different curing systems on the physico ... of different curing systems on the...

Documents