毛细管流变仪

毛细管流变仪第1页/共138页1Introduction

Polymersareusedbecause:TheyarecheaptoformintoshapeinmoltenstateTherefore,Weneedtounderstandhowtheyflowwhenmoltenalsoimportantin:foodprocessing,pharmaceuticals,paints,inks,pastes,slurriesetc...

VeryimportantinPolymerProcessing第2页/共138页But,moltenpolymersarecomplicatedsystems...TemperaturedependentRatedependentTimedependentWorkdependent(andthat’sbeforeweaddlubricants,fillers,plasticisers,foamingagentsetc…!)Inbetweenaliquidandasolid第3页/共138页

InfluencesonViscosity

molecularstructureofsampletemperaturepressuretimeshearrate(T,p,t,g)

=g..第4页/共138页Shearviscositydefinitiong-shearrate.

t-shearstress

=g.

-shearviscosityViscosityisameasureofresistanceofafluidagainsttheappliedshearforce.ShearviscosityisonlyonepartofRheology.

Itisthedominanteffectforpressureinextruders,injectionmouldingmachinesanddies.第5页/共138页TypicalprocessshearratesRelaxationCoatingFreesurfaceMixingExtrusionInjectionmoulding第6页/共138页Whydoweneedahigh-pressurecapillaryrheometer?Theapplicationisimportantlog/s-1DMAOsc./Rot.rheometerHighpressurecapillaryrheometerViscosities:(low-),middle-tohigh-viscousQuantities:Shear-andextensionalviscosity,wallslip

relaxation,PVT,Flowinstabilities10-110-3Levelling104101Extrusion,InjectionMoulding100102Mixing103106RollCoating,SprayingViscosities:lowviscoustosolid-likeQuantities:Shearviscosity,yield,viscoelasticproperties,relaxationetc.Non-destructiveOscillaroryshearrot.rheometer:structural/lowshearmeasurements–

high-pressurecapillary:processingflowbehaviour第7页/共138页2.Structure2.16kg

Singlepointtest(generatesonenumber)MFIdie(2.095mmdiameter)

Definedbystandards(ISO1133)

Simple

Cheap

Easytouse

PressuredrivenMeltFlowIndexer(MFI)第8页/共138页MeltFlowIndexer(MFI)

Singlepointtest

Doesnotgenerateengineeringunits-(gramsper10minutes)

Mainlyashearflowmeasurement-neglectsextension

Verylowshearratetest (app=2.4MFI)But,第9页/共138页TypicalprocessshearratesRelaxationCoatingFreesurfaceMixingExtrusionInjectionmouldingMFItest第10页/共138页CapillaryRheometerMeasure:PressuredropPistonCapillarydiePressuretransducerPolymermeltSet:PistonspeedDieDim’s第11页/共138页CapillaryrheometryWeset:Temperature,pistonspeed,diegeometryWemeasure:Meltpressure(long&shortdies)Givingus:Shearstress(atarangeorrates)Extensionalstress(atarangeorrates)第12页/共138页CapillaryrheometryLongdie:shearShortdie:extension第13页/共138页3Shearviscosity完全发展区剪切应力的计算管壁处第14页/共138页3Shearviscosity不可压缩性流体剪切速率的计算第15页/共138页L2R3ShearviscosityGivenquantity:pistonspeedwallshearrateMeasuredquantity:pressuredropwallshearstressEntrancepressuredropShearpressuredropvMeasuredpressuredrop=+PLBARRELPLPlPwENTRANCELENGTH

FULLYDEVELOPEDFLOWREGION0Z0LsmallramextruderMeasuringPrinciple第16页/共138页Pressuredropthroughacapillary/slitdie第17页/共138页Newtonianfluid

shearrate,

=4Q/r3

shearstress,

=Pr/2Lshearviscosity,

=/

ShearFlowAnalysis

g.g.(g).g.g.第18页/共138页CalculationofEntrancePressureDrops1.HistoricalBagley-MethodaccordingtoDIN11443

full

10203040HighshearrateLowshearrateL/DPges(L/D=0)=EntrancePressureDrop

••••°°°°Principle:

MeasurementoftheFullPressureDropatconstantShearrateanddifferentL/DratioLinearextrapolationtoL/D=0E.B.Bagley,J.Appl.Physics28(1957),624

第19页/共138页CalculationofEntrancePressureDrops2.PracticalDifficultieswithHistoricalBagleyMethodfull10203040L/DnegativeEntrancePressureDrop!

••••?Problems:linearextrapolationcanleadtophysicallyimpossibleresultsExtrapolationshowsverylargestandarddeviation第20页/共138页CalculationofEntrancePressureDrops3.ReasonsfortheErrorsinExtrapolationReasons:

atsmallL/D-valuesnon-linearitiesoccurforallsamplesatthemomentthereisnotheoreticalapproachathighL/D-valuesnon-linearitiesduetowallslip,compressibility...(theoreticalprediction)full

24681012L/DNon-linearitiesatsmallL/DHistoricalBagleyTruecurve•

••••••••Kelly,Coates,Dobbie,Fleming,Plastics,RubberandCompositesProcessingandApplications1996,vol.25,No.7,313.Datasnottruetoscale.第21页/共138页CalculationofEntrancePressureDrops4.Solution:Doublecapillarysystemfull

5101520L/DInnovation:

Measurement-noExtrapolationneeded!SimultaneousmeasurementoffullpressuredropalongcapillarydieandentrancepressuredroponorificediePshear=Pfull-PoOrificedie(pinholewithneglectableL/D-ratio)CapillarydiewithL/D=16第22页/共138页TheRosandDoubleCapillarySystemwithorificedieMeasurethedieentrancepressuredropdirectlyL2RvpentrancepshearPfullPfull=Pshear+Pentrancevpentranceleft:Capillarydie right:Orificedie第23页/共138页RabinowitschCorrection

第24页/共138页Fornon-NewtonianflowprofileRabinowitschCorrectionn=d(log)d(log).Correctedshearflow(polymermelts)Ifn=0.5,=1.25*c.4QR3Apparentshearrate(Newtonianmaterial)a=.polyethylene 0.3to0.6polypropylene 0.3to0.4PVC 0.2to0.5polyamide 0.6to0.9.

a.4QR33n+14nc=.Optional,buttrytokeepconsistency!第25页/共138页WallSlipcorrection第26页/共138页WallSlipAfundamentalassumptioninmostrheologyisvelocityatthemetalwall=0SlipiswellknowntooccurinPVC,HDPEandmetallocenecatalysedpolymers

Difficulttomeasure-canbeapproximatedusingcapillaryrheometrySlipisaffectedbyfillersandlubricants

第27页/共138页Evidenceofwallslip

第28页/共138页WallSlipCorrection4VsWallSlipNoWallSlipapp1/RResult:Dependencyofwallslipvelocityonshearstress(trueshearrate)slipshearfullQQQ+=Rv4sliptrueapp+g=g..2slip3true3appRv4R4Rp×+p×g=p×g..

Mooney,M.,J.Rheology

2,210(1931)第29页/共138页WallSlipMeasurement

Slipcomponentofflowrate,

Q=R2v

[Vs]mm/s[w]kPaPE

Vs=1.50(w/100)3.20

w

90kPaPVC

Vs=9.5(w/100)2.28

SometypicalslipvelocitiesManymaterialsonlyslipaboveacriticalstress,typically0.1MPa第30页/共138页ExtensionalFlowAnalysis第31页/共138页4ExtensionalFlowAnalysis第32页/共138页4ExtensionalFlowAnalysis第33页/共138页4ExtensionalFlowAnalysis第34页/共138页4ExtensionalFlowAnalysis第35页/共138页第36页/共138页第37页/共138页拉伸黏度是在实际纺丝过程即非稳态拉伸流中的黏度。表观拉伸黏度定义为：

第38页/共138页采用摄影的方法，对稳态的丝条拍照，从照片量取纤维直径沿轴向的变化数据第39页/共138页第40页/共138页ExtensionalFlowAnalysis第41页/共138页5meltfracture第42页/共138页第43页/共138页第44页/共138页第45页/共138页第46页/共138页第47页/共138页第48页/共138页第49页/共138页第50页/共138页第51页/共138页第52页/共138页第53页/共138页第54页/共138页第55页/共138页第56页/共138页第57页/共138页实际成型加工及流变测量中，物料流动状态受诸多因素影响，常常出现不稳定流动情形。许多情况下，流场边界条件存在一个临界值。一旦超越该临界值，就会发生从层流到湍流，从平整到波动，从管壁无滑移到有滑移的转变，破坏了事先假定的稳定流动条件。研究这类熔体流动不稳定性及壁滑现象是从“否定”意义上讨论高分子的流变性质，具有重要意义。该问题的工程学意义是，当工艺过程条件不合适，会造成制品外观、规格尺寸及材质均一性严重受损，直接影响产品的质量和产率，严重时甚至使生产无法进行。高分子流动不稳定性主要表现为挤出过程中的熔体破裂现象、拉伸过程（纤维纺丝和薄膜拉伸成型）中的拉伸共振现象及辊筒加工过程中的物料断裂现象等。熔体在管壁发生滑移与此类现象密切相关。可以肯定地说，这些现象与高分子液体的非线性粘弹行为，尤其是弹性行为有关，是高分子液体弹性湍流的表现。第58页/共138页熔体的挤出破裂行为：在挤出过程中，当熔体剪切速率超过某一临界剪切速率时，挤出物表面开始出现畸变的现象。表现为：最初表面粗糙，而后随剪切速率（或切应力）的增大，分别出现波浪型、鲨鱼皮型、竹节型、螺旋型畸变，直至无规破裂。

第59页/共138页从现象上分，挤出破裂行为可归为两类：一类称LDPE（低密度聚乙烯）型。破裂特征是先呈现粗糙表面，当挤出超过临界剪切速率发生熔体破裂时，呈现无规破裂状。属于此类的材料多为带支链或大侧基的聚合物，如聚苯乙烯、丁苯橡胶、支化的聚二甲基硅氧烷等。第60页/共138页一类称HDPE（高密度聚乙烯）型。熔体破裂的特征是先呈现粗糙表面，而后随着剪切速率的提高逐步出现有规则畸变，如竹节状、螺旋型畸变等。很高时，出现无规破裂。属于此类的材料多为线型分子聚合物，如聚丁二烯、乙烯-丙烯共聚物，线型的聚二甲基硅氧烷、聚四氟乙烯等。这种分类不够严格，有些材料的熔体破裂行为不具有这种典型性第61页/共138页流变曲线的差别：属于LDPE型的熔体，其流变曲线上可明确标出临界剪切速率或临界剪切力位置，曲线在临界剪切速率之前为光滑曲线，之后出现波动，但基本为一连续曲线属于HDPE型的熔体，其流变曲线在达到临界剪切速率后变得复杂。随着剪切速率的提高，流变曲线出现大幅度压力振荡或剪切速率突变，曲线不连续，有时使流变测量不能进行第62页/共138页造成熔体破裂现象的机理十分复杂，肯定地说，它与熔体的非线性粘弹性、与分子链在剪切流场中的取向和解取向（构象变化及分子链松弛的滞后性）、缠结和解缠结及外部工艺条件诸因素有关。从形变能的观点看，高分子液体的弹性是有限的，其弹性贮能本领也是有限的。当外力作用速率很大，外界赋予液体的形变能远远超出液体可承受的极限时，多余能量将以其它形式表现出来，其中产生新表面、消耗表面能是一种形式，即发生熔体破裂。第63页/共138页ElongationalviscosityinfluenceConvergenceintoaflatentrydieLDPEHDPEAlsoimportantinanyconvergentordivergentpartofaprocess第64页/共138页Tordella的流动双折射实验对LDPE型熔体，其应力主要集中在口模入口区，且入口区的流线呈典型的喇叭型收缩，在口模死角处存在环流或涡流。当剪切速率较低时，流动是稳定的，死角处的涡流也是稳定的，对挤出物不产生影响。但当剪切速率后，入口区出现强烈的拉伸流，其造成的拉伸形变超过熔体所能承受的弹性形变极限，强烈的应力集中效应使主流道内的流线断裂，使死角区的环流或涡流乘机进入主流道而混入口模。主流线断裂后，应力局部下降，又会恢复稳定流动，然后再一次集中弹性形变能，再一次流线断裂。这样交替轮换，主流道和环流区的流体将轮番进入口模。这是两种形变历史和携带能量完全不同的流体，可以预见，它们挤出时的弹性松弛行为也完全不同，由此造成口模出口处挤出物的无规畸变。第65页/共138页对HDPE型熔体，其流动时的应力集中效应主要不在口模入口区，而是发生在口模内壁附近，口模入口区不存在死角环流。低剪切速率时，熔体流过口模壁，在壁上无滑移，挤出过程正常。当剪切速率增高到一定程度，由于模壁附近的应力集中效应突出，此处的流线会发生断裂（后面将说明，流线断裂的一个原因是由于分子链解缠结造成的）。又因为应力集中使熔体贮能大大增加，当能量累积到超过熔体与模壁之间的摩擦力所能承受的极限时，将造成熔体沿模壁滑移，熔体突然增速（柱塞上压力下降），同时释放出能量。释能后的熔体又会再次与模壁粘着，从而再集中能量，再发生滑移。第66页/共138页这种过程周而复始，将造成聚合物熔体在模壁附近“时滑时粘”，表现在挤出物上呈现出竹节状或套锥形的有规畸变。当剪切速率再增大时，熔体在模壁附近会出现“全滑动”，这时反而能得到表面光滑的挤出物，即所谓第二光滑挤出区。此时应力集中效应将转到口模入口区。在极高的剪切速率下，熔体流线在入口区就发生扰乱，这时的挤出物必然呈无规破裂状。第67页/共138页1．3影响熔体挤出破裂行为的因素一切能够影响熔体弹性的因素，都将影响聚合物熔体的挤出破裂行为。这些因素大致可分为三类：一是口模的形状和尺寸；二是挤出成型过程的工艺条件；三是挤出物料的性质。第68页/共138页1．3．1口模形状、尺寸的影响口模的入口角对LDPE型熔体的挤出破裂行为影响很大。实验发现，当入口区为平口型（入口角）时，挤出破裂现象严重。而适当改造入口区，将入口角减小变为喇叭口型时，挤出物外观有明显改善；且开始发生熔体破裂的临界剪切速率（或临界剪切应力）增高。口模的定型长度L对熔体破裂行为也有明显影响。对于LDPE型熔体，已知造成熔体破裂现象的根源在于入口区的流线扰动。这种扰动会因聚合物熔体的松弛行为而减轻，因而定型长度L越长，弹性能松弛越多，熔体破裂程度就越轻，对于HDPE型流体，熔体破裂现象的原因在于模壁处的应力集中效应，因而定型长度越长，挤出物外观反而不好。第69页/共138页1．3．2挤出工艺条件和物料性质的影响给出低密度聚乙烯在不同挤出速度（不同剪切速率）下通过同一个口模时，测得的压力波动沿口模轴向的分布图。已知低密度聚乙烯通过口模时，其弹性形变主要发生在入口区。，挤出速度越小，材料发生的弹性形变小，且形变得以松弛的时间较长，因此熔体内的压力波动幅度较小。适当升高熔体温度是另一个典型例子。熔体温度升高，粘度下降，会使松弛时间缩短，从而使挤出物外观得以改善。因此在工厂中，升高料温（特别是口模区温度）是解决熔体破裂的快速补救办法。第70页/共138页从材料角度看，平均分子量大的物料，最大松弛时间较长，容易发生熔体破裂。而在平均分子量相等的条件下，分子量分布较宽（较大）的物料的挤出行为较好，发生熔体破裂的临界剪切速率较高，这可能与宽分布试样中低分子量级分的增塑作用有关。填料的作用。无论填加填充补强剂还是软化增塑剂，都有减轻熔体破裂程度的作用。这一是因为某些软化剂的增塑作用；二是填料本身无熵弹性，填入后使能够发生破裂的熔体比例减少。第71页/共138页AdeeperlookinsideWhathappensintheentrancezoneofacapillarydie?

achangeincross-sectionleadstoaentrance-pressure-dropbecauseof:ElasticstringingAccelerationsecondaryflow

Extensional,viscousflowPressuretransducerCapillarydie第72页/共138页ComparisonofTypicalShearData第73页/共138页ComparisonofTypicalExtensionData第74页/共138页TypicalPolymerProcessingTemperatures1.Polyolefins:~190°CPolyethylene(HDPE,LDPE,LLDPE)Polypropylene(PP)2.PVC:~165-180UPVCandplasticised3.EngineeringPolymers:~240-300°C

Nylon,PET,ABS4.Rubbers:~80-100°C

第75页/共138页Cogswell:EntrancePressureDropExtensionalViscosityShearviscositycurve1101001000110100100010000100000Correctedshearrate[1/s]Shearviscosity[Pas]sample1sample2Extensionalviscositycurve10100110100100010000Extensionalrate[1/s]Extensionalviscosity[kPas]Differencesonlyinextension(Structuresensitivity)BenefitsofCapillaryRheometry第76页/共138页ComparisonofDatafromCapillary&RotationalRheometersPolypropyleneMeasuredat190C

第77页/共138页Lowviscositysamplescanbeinvestigatedunder

processingconditions

ComparisonofDatafromCapillary&RotationalRheometers第78页/共138页AnalysisofFlowCurvesOnline-pressuredrophomogeneityofyoursampleimportantfactorforquality(influenceofMixing,pre-shearetc.)homogeneous:inhomogeneous:g.tPrinciple:Rampinsteps第79页/共138页AnalysisofinhomogeneitiesPressuredeviationsgivesapprox.averagelengthscaleEquilibriumDtDtDVmainlyusedforpolymerblends,suspensions...第80页/共138页3commoncorrectionsin

capillaryrheometry1.Bagley(entrancepressurelosses)2.Rabinowitsch(non-Newtonianflow)3.WallSlip(non-zerovelocityatdiewall)第81页/共138页FlowcurvesMeasurementSequenceofshearstepsmeasurement:DvttStepRatepapp=g.htappApparentvalues-datahastobecorrected.第82页/共138页AdvantagesofCapillaryRheometryPressuredrivenMimicstheprocess(flowthroughadie/nozzle)SimpletouseRobustSimpletointerpretAccuratedrivesystemAccuratetemperaturecontrol*engineer’spointofview第83页/共138页AdvantagesofCapillaryRheometryWideshearraterange,from0.1->100,000/sShearandextensionAbsoluteData(Bagley,Rabinowitsch,wallslip)Density,compressibilityDieswell&ElasticityUniaxialextension*rheologist’spointofview第84页/共138页RangeoftestsonRosandRheometers第85页/共138页TestProcedureI1.Selectthetypeoftest2.Selectthecapillarydie(s)3.Selectthepressuretransducer(s)4.Setmachinetemperature5.Setmachineparameters

-overloadlimits,equilibriumdetermination6.Runtest第86页/共138页TestProcedureII1.Chargethebarrel2.Manualcompression3.Starttest4.Pre-teststages

-compression(2)atsetspeed

-pre-heat(2)totaltime:9mins*5.Teststages*dependsonborediameter第87页/共138页Rheometersoftware第88页/共138页Rheometersoftware

resultsanalysis第89页/共138页1.SteadyshearTest:Dataobtained:Uses:RangeofconstantshearratesLongdieandoptionalshortdieShearstressandshearviscosityatarangeofshearratesDiedesign,extruderdesign,pressuredropprediction,flowmodelling,qualitycontrol,development第90页/共138页1.SteadyShear第91页/共138页1.SteadyShearCapillarywallshearrateisonlydependentupondiediameter,forasetpistonspeed.Typicalshearrates:*0.5mmØdies:50-100,000s-11mmØdies: 10-15,000s-12mmØdies: 1-1,500s-1StandardSpeedmachine第92页/共138页SteadyShear-testpressures第93页/共138页SteadyShear-typicalresults第94页/共138页SteadyShear-typicalresults第95页/共138页2.ExtensionalViscosityTest:Dataobtained:Uses:RangeofconstantshearratesLongdieandshortdieExtensionalstressandextensionalviscosityatarangeofshearratesDiedesign,pressuredropprediction,flowmodelling,qualitycontrol,development,filmblowing,fibrespinning第96页/共138页2.Shear/extension-typicalresultse=9(n+1)2(Dpe)2322.第97页/共138页Extension-typicalresults第98页/共138页3.MeltFractureTest:Dataobtained:Uses:Examinesareasofmeltinstability Longdieand/orshortdie,or2materialsAccuratedeterminationoftheconditionswhereinstabilityoccursDiedesign,profileextrusion,troubleshooting,injectionmouldingHDPE,PVC,heavilyfilled第99页/共138页3.MeltFracture第100页/共138页3.Evidenceofmeltfracture第101页/共138页4.MaterialdegradationTest:Dataobtained:Uses:RangeofshearrateswithwaitstagesLongdieand/orshortdieShearandextensionvaryingwithtimeatarangeofshearratesTimedependentmaterialsMoisturedependentmaterialsResidencetimedesignTroubleshooting第102页/共138页4.Materialdegradation第103页/共138页5.LowspeeddegradationTest:Dataobtained:Uses:ConstantlowshearrateLongdieand/orshortdieShearandextensionvaryingwithtimeataconstantshearrateTimedependentmaterialsMoisturedependentmaterialsResidencetimedesignTroubleshooting第104页/共138页5.Lowspeeddegradation第105页/共138页6.StressrelaxationTest:Dataobtained:Uses:PressuredecayfromconstantrateLongdieand/orshortdieDecayinpressureovertime-indicativeofelasticbehaviourTimedependentmaterialsHighlyelasticmaterialsQualitycontrolThermoforming第106页/共138页6.Stressrelaxation第107页/共138页6.Stressrelaxationresults

LDPEwithMg(OH)2filler第108页/共138页7.Flow/NoflowTest:Dataobtained:Uses:Constantshearrateastemperaturedecreases,singledieMinimumflowtemperatureProcessdesignMaterialspecification第109页/共138页7.Flow/Noflow第110页/共138页8.ManualtestTest:Dataobtained:Uses:Afterinitialheat-up,takeovermanualcontrol&takedatapointswheneverShear/extensionaldata,testpressuresInitialinvestigationEstablishconditionsbeforetesting第111页/共138页9.LowlevelscriptTest:Dataobtained:Uses:ProgramtestyourselfWhateveryouwantNon-standardtestse.g.crosslinking*needadetailedunderstandingofhowthemachineworks第112页/共138页10.WallslipTest:Dataobtained:Uses:Steadyshearusing3dieswithsameL:Dratio,differentdiametersSlipvelocityvs.shearstressDiedesignProcessdesignTroubleshootingFillereffects第113页/共138页10.Wallslip第114页/共138页10.Wallslip第115页/共138页11.PVT/DensitytestTest:Dataobtained:Uses:CompressesmeltSpecialplugdie&pistontipMeltcompressibility(versuspressure)Meltdensity(5%)FlowsimulationFiller&additiveinvestigationMaterialspecificationTroubleshooting第116页/共138页11.PVT/Densitytest第117页/共138页11.PVT/densitytest第118页/共138页11.PVT/densitytestresults

LDPEat200°C第119页/共138页12.FibrespinningtestTest:Dataobtained:Uses:Specialhaul-offmotor&scalesHaul-offspeedrampedupForcevshaul-offspeedBreakingpoint,tensileforceUniaxialextensionIndicationofbiaxialextensionEmpiricaldeterminationoftensilestrength第120页/共138页12.FibrespinningtestPracticalmeasurementF,vpUni-axialextension(HaulOff):Extensionalpropertiesatsmallextensionrates第121页/共138页HaulOff:ExampleLDPEatdifferenttemperatures

Maininterestisruptureforceundernon-isothermalconditionsLaun,Schuch.:J.Rheol.33(1989),119第122页/共138页13.DieSwellTestTest:Dataobtained:Uses:Lasergaugediametermeasurementofextrudateafterexitingdie

Extrudatediametervs.shearrateIndicationofelasticity(highshearrates)Profileextrusion,thermoforming,shrinkfilmetc.第123页/共138页13.DieSwellTest1.Die-SwellI(Laser-Die-Swell)Properties:Mono-orbiaxiallaser-systemMelt&DieCuttersallowmeasurementwithdefinedmelttensionResolution0.01mmCalculationofGandEaccordingtoCogswell第124页/共138页13.DieSwellTest2.Die-SwellI(Video-Die-Swell)

Properties:

higherresolution(0.01mm)twodimensionalmeasurementdetectionofthedieswelldynamics

第125页/共138页DieSwell:ExamplePP1hashigh-moleculartailinMwDcomparedtoPP2

Viscositycurvesnearly