FACTORY TESTING AND CONTROL OF NATURAL RUBBER AND

PaperNo.4FACTORYTESTINGANDCONTROLOFNATURALRUBBERANDMIXEDBATCHESUSINGTHERUBBERPROCESSANALYZERBy:JohnS.Dick,*AlphaTechnologies,Akron,OHandChrisStevens,AlphaTechnologies,Swindon,UKPresentedatameetingoftheRubberDivision,AmericanChemicalSocietyOrlando,FloridaSeptember21-24,1999*SpeakerNoticeWhilethisinformationispresentedingoodfaithandbelievedtobeaccurate,AlphaTechnologiesdoesnotguaranteesatisfactoryresultsfromrelianceuponsuchinformationanddisclaimsallliabilityforanylossordamagearisingoutofitsuse.ExceptforthelimitedwarrantysetforthinAlphaTechnologies'standardsalescontractforitsrubbertestinginstrumentsandequipment,ALPHATECHNOLOGIESMAKESNOEXPRESSORIMPLIEDREPRESENTATIONSORWARRANTIESASTOTHEFITNESS,MERCHANTABILITY,ORANYOTHERMATTERWITHRESPECTTOTHEINFORMATIONCONTAINEDINTHISPAPER,ORANYPRODUCT,EQUIPMENTORSYSTEMSREFERREDTOHEREIN.Nothingcontainedhereinistobeconstruedasarecommendationtouseanyproduct,equipment,systemorprocessinconflictwithanypatent.Thedatafromwhichfiguresarederivedarebasedonsamplestestedandarenotguaranteedforallsamplesorapplications.2FactoryTestingandControlofRawNaturalRubberandMixedBatchesUsingtheRubberProcessAnalyzerBy:JohnS.Dick,AlphaTechnologiesChrisStevens,AlphaTechnologiesAbstractBecauseofitsnaturalorigin,itisgenerallyrecognizedthatroutineshipmentsofrawnaturalrubberarepotentiallyoneofthemostvariablerawmaterialswhichcanbeusedinthetireproductionprocess.TheRPA2000RubberProcessAnalyzerisbeingusedbysometoquantifythisvariabilityinordertoimplementchangestoimprovetireuniformity.ThisstudyresultedfromsuchanRPAtireplantfactoryinvestigationofnaturalrubbervariation.Arapid2-minutetestprogrammedontheAutoRPAwasfoundtobeveryeffectiveandpracticalfortestingthequalityofbothrawnaturalrubberbalesandfactorymixedstocks.Inthisstudy,theRPAquantifiedthe%RangeofVariationtobeashighas24%forwithinbalevariation,andashighas42%forvariabilitybetweenbalesandsources.Significantimprovementsinstatisticaltestsensitivity(signal-to-noise)wereobservedfortheRPAwhenhigherstraintestconditionswereemployedinthisnaturalrubbertesting.Alsoitwasobservedthatnaturalrubbervariationisduemoretochangesinitselasticqualityandtoalesserextentduetoviscositydifferences.Inaddition,itwasfoundthatthisnaturalrubbervariabilitysignificantlycontributestobatch-to-batchvariationoffactorymixedstocks,eventhoughthemagnitudeofthisvariationissomewhatreducedbyadditional“passes”(increasedworkhistoryfrommultiplepassmixing).Lastly,theRPAdynamicpropertiesoftherawnaturalrubberwerestatisticallyrelatedtothequalityofmix.3INTRODUCTIONTheRubberindustryconsumesmorenaturalrubberthananyothersinglesyntheticelastomer.Howeverthequalityofthisnaturalrubbercanvarygreatlybecauseofitsnaturalorigins.Examplesofsomeofthesourcesofthisvariationaregivenbelow.•TreeClone•AgeofTree•SoilConditions•ClimateConditions•MannerofLatexCoagulation•ProcessingHistory•StorageHistory.Forexample,theHeveatreeclonecanproducebimodalorunimodalmolecularweightdistributions1,2(referenceFigure1).Alsoithasbeenreportedthatthemagnitudeofmolecularweightdistribution(MWD)canvarygreatlywiththeMW/MNratiobetween2.5to10forallgradesofNR.3Moreover,thereportedgelcontentfornaturalrubber(believedtobecausedbyfreeradicalcrosslinking4orreactionofaldehydegroupswithfreeaminoacidsorproteinmolecules5)canvaryfrom5to50%.Thesequalityvariationsareverysignificantandarearesultofthedifferentconditionsgivenabove.Itisgenerallyrecognizedthatnaturalrubberisquitevariable.Thepurposeofthisstudywastoquantifytheextentofthatvariationasitrelatestoviscoelasticpropertiesandwhateffectthisvariationhasonthetiremanufacturingprocess.EXPERIMENTALFactoryMixingConditionsInordertomeasurethevariationofrawnaturalrubberandtoquantifythevariationsbeingimpartedtothemixingstudies,anRPA2000Auto®waslinkedtothefactorymixingofatirewirecoatcompound.Thiswirecoatformulationwasbasedon100phrnaturalrubber(SIR20).TheAutoRPAwasappliedtomixingofthemasterbatches,theremills,andthefinalbatchesforthewirecoatstock.Allbatchesweredumpedata4specifiedtemperatureandthetimeandpoweratdumpwereautomaticallymeasuredforeverybatch.Aspecifiedconstantrotorspeedwasusedthroughouteachmix.TheRPAtestingwasappliedtotwoseparatemixingcampaigns(orruns)aboutfourdaysapart.Thefirstcampaignincluded63batcheswhilethesecondconsistedof76batches.TheRPAwasconfiguredtoperformatestofshortduration(2minutes,7seconds)inordertocompleteeachtestwithinthemixcycletimeandkeepupwithproduction.(Thefastestmixcyclerecordedforthiscompoundwas2.5minutes).TestConditionsAnRPA2000Autowasusedforallfactorytesting.Figure2showsthisinstrument.ThisautomatedunitwasconfiguredwithPETpolyester(27μmthickness)filmfortheupperlayerand51μmthickNylon6,6filmforthelowerlayer.(Throughthiscombinationoffilms,anappliedstrainof100%canbeappliedtothesampleswithouttearingthefilm.OnlyoneRPAtestconfigurationwasusedthroughoutthisstudy.Itconsistedofashortoneminuteconditioningat0.5Hz,1%strain,and100°C,followedbyasimplestrainsweepat1Hz.and100°C.Thisstrainsweepconsistedof1,10,30,and100%strain.Thetotallapsetesttimeis2minutesand7seconds.Inordertokeepthesetestsshort,nolowfrequencieswereapplied