Influence of accelerator type on properties of NR-

POLYMERTESTINGPolymerTesting26(2007)1062–1067MaterialPropertiesInfluenceofacceleratortypeonpropertiesofNR/EPDMblendsPongdhornSae-ouia,b,,ChakritSirisinhab,c,UthaiThepsuwana,PhuchongThapthongaaNationalMetalandMaterialsTechnologyCenter,114ThailandSciencePark,PaholyothinRoad,Klong1,KlongLuang,Pathumthani12120,ThailandbRubberResearchUnit,FacultyofScience,MahidolUniversity,SalayaCampus,Phutthamonthon4Road,Salaya,Nakornprathom73170,ThailandcDepartmentofChemistry,FacultyofScience,MahidolUniversity,Rama6Road,Rajdhevee,Bangkok10400,ThailandReceived4June2007;accepted16July2007AbstractTheeffectofacceleratortypeonprocessabilityandmechanicalpropertiesof60/40naturalrubber/ethylenepropylenedienemonomer(NR/EPDM)blendwasinvestigated.Threegroupsofcommercialacceleratorswereselected,i.e.,sulfenamidegroup(Santocure-TBBS),thiuramgroup(Perkacit-TMTD)andmercaptogroup(Perkacit-MBTandPerkacit-MBTS).Theresultsrevealthattheacceleratortypenotonlyaffectsthecurecharacteristics,butalsohasgreatinfluenceoncompoundviscosity.Amongtheacceleratorsstudied,TBBSgivesthebestprocessingsafetytogetherwitharelativelyhighstateofcure.Inaddition,TBBSalsoprovidesgoodcurecompatibilitybetweentheNRandEPDMphases,givingrisetosuperiormechanicalproperties.AlthoughTMTDcouldgiveahighstateofcure,itcausesseverecureincompatibility,leadingtopoortensilestrength.Duetotheirlowerreactivity,thetwomercaptoacceleratorsgivearelativelylowstateofcure.Therefore,thevulcanizatesobtainedpossesslowmodulusandhardnessaswellasdegreeofelasticity.Surprisingly,itisfoundthatthetensilestrengthoftheMBTS-curedblendisrelativelyhigh.GoodcurecompatibilitygivenbyMBTScouldbeusedtoexplaintheresults.r2007ElsevierLtd.Allrightsreserved.Keywords:Naturalrubber;Ethylenepropylenedienerubber;Blend;Accelerator;Mechanicalproperty1.IntroductionRubberblendshavebeenwidelyusedinmanyapplicationsduetotheircompromisedproperties.Blendsofnaturalrubber(NR)andethylene-propylenedienemonomer(EPDM)havegainedmuchattentionoverthepastthreedecadesbecauseitisthoughtthat,whenproperlyblended,theNR/EPDMblendcouldpossessgoodphysicalproper-tieswithadequatelyhighagingandozoneresistance[1–4].EventhoughgoodozoneresistancecouldbeachievedeasilyinNR/EPDMblends,satisfactoryphysicalpropertiesaredifficulttoattainduetothecureincompatibilitybetweenNRandEPDM[5].AsNRishighlyunsaturated,itischemicallyreactive.ARTICLEINPRESSwww.elsevier.com/locate/polytest0142-9418/$-seefrontmatterr2007ElsevierLtd.Allrightsreserved.doi:10.1016/j.polymertesting.2007.07.004Correspondingauthor.NationalMetalandMaterialsTech-nologyCenter,114ThailandSciencePark,PaholyothinRoad,Klong1,KlongLuang,Pathumthani12120,Thailand.Tel./fax:[phone]x1159.E-mailaddresses:[e-mail](P.Sae-oui),[e-mail](C.Sirisinha),[e-mail](U.Thepsuwan),[e-mail](P.Thapthong).EPDM,ontheotherhand,ishighlysaturatedandthusnon-reactive.Duetosuchdifferenceinchemicalreactivity,duringvulcanization,NRpos-sessesahighercrosslinkingrateandthecurativeshavegreatpotentialtodiffusetowardtheNRphase[6,7].ThelowersolubilityofmanycurativesintheEPDMphase,comparedtoNR,isanotherfactorthatcouldfurtherreducethepropensitytowardcrosslinkformationintheEPDMphase[7,8].Thesefactorscombinetogiveablendhavingunevencuredistribution,i.e.,theNRphaseishighlycrosslinkedwhiletheEPDMphaseispoorlycrosslinked.Toimprovecurecompatibility,manyattemptshavebeendonesuchashalogenationofEPDMinsolution,modificationofEPDMwithreactivechemicals,e.g.,maleicanhydrideorotheraccel-eratorspecies,etc.[1,2,9–12].Mastromatteoetal.[8]alsoreportedthattheuseofacceleratorswithgreatersolubilityintheEPDMphasecouldimprovethecurecompatibilityoftheblend.TheyfoundthatacceleratorshavinglongalkylsubstitutioncouldimprovethepropertiesoftheblendscontainingEPDM.However,fewoftheseacceleratorshavebeencommercialized.Asaconsequence,itistheaimofthisstudytoinvestigatetheeffectofvarioustypesofcommercializedacceleratorontheproper-tiesofNR/EPDMblends.2.Experimental2.1.MaterialsAllmixingingredientswereusedasreceived.NR(STR5L)andEPDM(Nordel4640,40-ML(1+4)@1251Cwith4.9%ENBcontent)weremanufac-turedbyUnionRubberProductCorporationCo.,Ltd.andDuPontDowElastomersCo.,Ltd.,respectively.Stearicacid,zincoxide(ZnO,whiteseal)andsulfur(S8)wereobtainedfromKijPaiboonChemicalLtd.(Thailand).AllacceleratorsemployedinthisstudyweresuppliedbyRelianceTechnochem(Flexsys)Co.,Ltd.TheseincludedN-tert-butyl-2-benzothiazolesulfenamide(Santo-cure-TBBS),tetramethylthiuramdisulfide(PerkacitTMTD),2-mercaptobenzothiazole(Perkacit-MBT)and2,20-dithiobis(benzothiazole)(Perkacit-MBTS).2.2.PreparationandtestingofrubbercompoundsThecompoundformulationusedinthepresentstudyisgiveninTable1.Themixingprocesswascarriedoutusingalaboratory-sizedinternalmixer(HaakeRheomix3000p).Themixingconditionsweresetasfollows:fillfactor¼0.7,initialchambertemperature¼601C,rotorspeed¼40rpmandmixingtime¼9min.Aftermixing,thecompoundsweresheetedoutonatwo-rollmill(LabtechLRM150).MeasurementofMooneyviscosity(ML1+4@1251C)wascarriedoutaccordingtoISO289usingaMooneyviscometer(TechProviscTECH+).Thecurecharacteristics,e.g.