MDR for compound analysis.docx
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MDR for compound analysis.docx
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MDRforcompoundanalysis
Optimalmeasurement,useofdynamicpropertiesfromtheMDRforcompoundanalysis
byJohnS.Dick
TheMDR2000movingdierheometer(MDR),arotorlesscure.meter,hasgainedmuchacceptancebytherobberindustrysinceitsintroductionin1988.Inmanycastatics,thisinstrumentisreplacingtheoscillatingdiskrheometer(ODR)asdescribedinASTMStandardTestMethodD2084(ref.1).
TheMDRdoesnotustaticarotor,butoscillatesthelowerbiconicaldiethroughasmallpredeterminedarcof0.2,0.5,1.0or3.0degrees.Theappliedshearstrainresultsinaforcewhichistransmittedthroughthespecimultipletotheupperdieattachedtoareactiontorquetransducer.TheMDR2000rheometerhasastaticaled,pressurizedtestcavitywhichmaintainsaminimumof300psipressureonthetestspecimultiple.Becaustaticthesamplecavityisstaticaledandpressurized,testresultsfromitaremorerepeatablethanthostaticobtainedwithunstaticaledsystems.Rotorlesscuremeterswhicharenotstaticaled,canhavepoorrepeatabilityandstativity,especiallywhenmeasuringdynamicproperties(refs.2-4).
BecaustaticthefrictionassociatedwiththeoscillationofarotorhasbeeneliminatedwiththeMDR,effectivemeasurementofdynamicpropertiesbefore,duringandaftercurecanbeperformed.Figure1showstheviscous,elasticandcomplextorqueresponstaticsfromtheMDRforasinusoidalstrain.Thelowerdieoscillatesandappliestheshearstraintothespecimultiple.Thedottedlineinfigure1indicatesthecomplextorque(S*)responstaticwhichthereactiontorquetransducermeasuresattheupperdie.(S*isnotusuallyreportedintheinstrumentoutput).Thepeaksfortheappliedstrainandthecomplextorqueresponstaticoccuratdifferstilltimes.Thislaginthecomplextorquefromtheappliedstrainisnotedbythephastaticangleshift-delta.AuniquesignalprocessingsystemandFouriertransformsoftwarestaticparatesthecomplextorqueintoelastictorque(S')andviscoustorque(S").Elastictorque(S')isin-phastaticwiththeappliedstraincurve.Infigure1,whentheappliedstrainpeaks,sodoesS';whenappliedstrainequalszero,sodoesS'.Thein-phastatictorqueS',isalsothetorquesignalthatisrecordedfromanODR.Ontheotherhand,viscoustorque(S")is90degreesoutofphastaticwiththeappliedstrain.Againnoteinfigure1thatwhenappliedstrainandS'arepeaked,S"isatzero.Likewistatic,whenappliedstrainandS'arezero,S"isatamaximum(orminimum)onthesinusoidalcurve.Viscoustorque(S")relatestothedampingcharacteristicofarubbercompound(refs.5and6).
AnotherimportanttestparameterfromtheMDRistangstilldelta.TandeltaisderivedbydividingS"byS'.Thelowerthetandeltaforacuredcompound,thegreateritsresiliency(ref.7).
Inadditiontothedynamicpropertiesjustdiscusstaticd,theMDRgivesdigitaloutputsforotherparameterswhicharecitedinASTMD2084.Thestaticincludescorchtimes,curetimes,cureratesandtorquevalues.
OthertechnologicalimprovementsoftheMDRcomparefavorablyvs.theolderODRtechnology.Inadditiontobeingcapableofmeasuringdynamicproperties,theMDRhasshortertemperaturerecoverytimesthantheODR.ThisisbecaustatictheMDRhasnorotortoactasa"heatsink"andthusincreastaticthetimethespecimultipleneedstoreachthediestatictpointtemperature.TheMDRspecimultipleisthinnerwithhalfthemassoftheODRspecimultiplewhichpromotesfastertemperaturerecoverytimesfortheMDR.ThestaticfactstranslateintoimprovedtestingproductivityfortheMDRthroughshortertesttimesandsimplifiedsampleremoval.Also,theMDRhasmoreefficistillheaters.Thestaticheatersaredirectlyincontactwiththesmallerdies.Amicroprocessordirectlycontrolsthestaticheatersformoreprecistaticcontrolofthetemperature.Thegreatlyimprovedtemperaturecontrolisveryimportantinreducinginstrumentvariability(noistatic).ThisisanotherreasonthatotherstudieshavefoundthattheMDRhassuperiorprecisionandsensitivitythantheoldertechnologyODR(refs.8and9).
Minimumdetectablelevels
Thetraditionalwaytomeasuresensitivityofaninstrumentistocalculatethesignal-to-noistaticratio.AhigherS/Nvaluemeansgreaterdiscriminatingpowerfortheinstrument.Analternatemethodforcomparingthesensitivityofinstrumentsistocalculatetheminimumdetectablelevel(MDL).WiththeMDLparameter,alowervalueindicatesbetterdiscrimina[tsub.1]ngpowerfortheinstrument(refs.10and11).TheMDListheminimumchangeintheconsentrationofacompoundingingredistill(inpartsperhundredrubber)thataninstrumentistheoreticallycapableofdetecting.MDLiscalculatedfromtheformulabelowinequation1.
MDL=(Xsub.a-Xsub.b)/(A-B)2.8[Ssup.p]
Where:
A=averagetorqueorcuretimevalueforcompoundA
B=averagetorqueorcuretimevalueforcompoundB
[Xsub.a]=phrofingredistillMincompoundA
[Xsub.b]=phrofingredistillMincompoundB
[Ssub.a]=standarddeviationoftorque/curetimefromcompoundA
[Ssub.b]=standarddeviationoftorque/curetimefromcompoundB
[Ssub.p]=pooledstandarddeviationfromreplicatetestingofcompounds
[Ssub.p]=(Ssub.asup.2Ssub.bsup.2/2)[sup.1/2]
AnexperimentwasconductedtocomparethediscriminatingpoweroftheMDR2000rheometertotheMonsantoR100,oscillatingdiskrheometer.Thisexperimentustaticdagenericradialpasstaticngertreadstockbastaticdonasulfenamidecureshownintable1.CompoundvariationsofhighandlowlevelsofTBBSaccelerator,sulfur,oil,carbonblackandnaturalrobberingredistillsversusacontrolformulationwerepreparedwithaBRlaboratoryinternalmixer.Aftermixing,allstocksweretestedstaticqustilliallybycompoundnumberontheMDRat0.5degreeandtheR100at1.0degreearc.Thestatictestsweremninmultiplerepeatstocalculatethepooledstandarddeviation[Ssub.p](anindicationofinstrument"noistatic").
Table2reportstheresultsofthisstudy.TheMDRresultsshowsignificantlylowerminimumdetectablelevelsthantheRI00resultsforeachofthecompoundingredistillchanges.LowerMDLvaluesindicatebetterdiscriminatingpowerorsensitivityfortheinstrument.TheMDR'sbetterdiscriminatingpowercomesinpartfromlower"noistatic,"orrandomvariation,thanfortheR100asindicatedbylowercalculatedpooledstandarddeviations(Ssub.p).Thereasonsforthislower"noistatic"levelfortheMDRaretheimprovedtemperaturecontrolandreducedfrictionasmentionedearlier.
TheMDLvaluesintable2differdependingonwhichcompoundingredientsisvaried.DifferstillrheometertestparametershavehigherorlowerMDLvaluesdependingontheingredistillthatisvaried.Peakcurerate(themaximumcurerateattheinflectionpointofthecurecurve)isverysensitivetotheslightestvariationinTBBSacceleratorconcenstation.TheenhancedversionoftheMDRelectronicallymeasuresthisparameterwithverygoodrepeatability.Ontheotherhand,maximumtorque(MH)fromtheMDRisthemostsensitiveparametertochangesinsulfurconsentrationfollowedbypeakcurerateandtandeltaatMH.TandeltaatMHisverysensitivetocurativevariationsingeneral.ThisisbecausestaticS'(elastictorque)increastaticsascrosslinkdensityincreased,whileS"(theviscoustorque)decreased.SincetandeltaiscalculatedfromS"dividedbyS',whicharemovinginoppositedirections,thetandeltaisverysensitivetocurativevariations.
Forchangesincarbonblackconsentration(table2),S"atMHisthemostsensitiveparameterfollowedbytheMDRmaximumtorque(MH)andminimumtorque(ML).UnliketheminimumtorquefromtheR100,theMLfromtheMDRisaverysensitiveparameterwitharelativelylow"noistatic"level.Alsoforoilchanges,maximumandminimumtorquefromtheMDRaresensitivetochangesinconsentration.Interestingly,peakcureratealsowassensitivetochangesinoilconsentration,probablybecaustaticofchangesinheathistoryduringmixing.ChangesintheratioofSBRtonaturalrobberwerereadilydetectedbytheMDR'sTC50,TC90andpeakcureratebecaustaticnaturalrobberhasafastercureratethanSBR.Bycontrast,theR100wasrelativelyinsensitivetochangesintheelastomerratios.AlsotandeltaatMHwassensitivetoNRchanges.
Applications
Uncureddynamicproperties
ThedynamicpropertiesofanuncuredstockfromtheMDR2000rheometercanbeustaticdtopredictthestock'sprocessperformance.ML(theminimumvalueforS')iscommonlyconsideredasrepresstillativeoftheuncuredstock'selasticmodulus(ref.12).Inaddition,theS"andtandeltadatacanalsoprovidevaluableinformationaboutacompound'sprocessability.
Figure2showspercstillchangesintheMDRuncuredparametersofML,S"atMLandtandeltaatMLresultingfromchangesinconsentrationsofoilandcarbonblackintheradialpasstaticngertreadgivenintable1.Itiswellknownthatcompoundchangesintheconsentrationofoilorcarbonblackcanchangetheprocessabilitycharacteristicsofastock.BecaustaticoftheMDR'stechnologicalimprovements,theMLparameterfromtheMDRismuchmoresensitivetoprocessabilitychangesthantheMLvaluesfromtheR100technology.Studiesshowthatmuchhigher"noistatic"isassociatedwiththeMLvaluesfromtheR100thanfromtheMDR.
ThefollowingexperimentshowshowtheMDRcanpredictthestate-of-mixforarobbercompound.Anaturalrobbertrucktreadwasstaticlectedasshownintable3.ThroughlaboratorysimulationoffactorymixingtechniqueswithaBRinternalmixer,differstillstatesofmixwereachieved."Upsidedown"mixingtechniqueswereustaticdwithaMonsantopowerin
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