基于工程化设备通过调控纺丝温度提高中间相沥青炭纤维力学和导热性能.pdf

Cite this:NewCarbonMaterials,2024,39(2):334-344DOI:10.1016/S1872-5805(24)60826-7Improving the mechanical properties and thermal conductivity ofmesophase-pitch-based carbon fibers by controlling thetemperature in industrial spinning equipmentYEGao-ming1,SHIKui1,WUHuang1,HUANGDong1,2,YEChong1,2,4,*,OUYANGTing1,ZHUShi-peng3,*,FANZhen3,LIUHong-bo1,LIUJin-shui1,2,4,*（1.College of Materials Science and Engineering,Hunan Province Key Laboratory for Advanced Carbon Materials andApplied Technology,Hunan University,Changsha 410082,China;2.Hunan Province Engineering Research Center for High Performance Pitch-based Carbon Materials,Hunan Toyi CarbonMaterial Technology Co.,Ltd.,Changsha 410000,China;3.Key Laboratory of Advanced Functional Composite Materials,Aerospace Research Institute ofMaterials and Processing Technology,Beijing 100076,China;4.State Key Laboratory of Advanced Design and Manufacturing for vehicle body,Hunan University,Changsha 410082,China）Abstract：Mesophase-pitch-basedcarbonfibers(MPCFs)werepreparedusingindustrialequipmentwithaconstantextrusionrateofpitchwhilecontrollingthespinningtemperature.Theinfluenceofspinningtemperatureontheirmicrostructures,mechanicalprop-ertiesandthermalconductivitieswasinvestigated.SEMimagesofthefracturedsurfaceofMPCFsshowthatthegraphitelayershavearadiatingstructureatallspinningtemperatures,butchangefromthefine-and-foldedtothelarge-and-flatmorphologywhenincreas-ingthespinningtemperaturefrom309to320oC.AtthesametimethethermalconductivityandtensilestrengthoftheMPCFsre-spectivelyincreasefrom704Wm1K1and2.16GPaat309oCto1078Wm1K1and3.23GPaat320oC.Thelowerviscosityandtheweakerdie-swelleffectofmesophasepitchattheoutletsofthespinneretsatthehigherspinningtemperaturecontributetotheimprovedorientationofmesophasepitchmoleculesinthepitchfibers,whichimprovesthecrystallitesizeandorientationoftheMPCFs.Key words:Mesophasepitch；Spinningtemperature；Carbonfiber；Highthermalconductivity；Mechanicalproperties1IntroductionMesophase-pitch-based carbon fibers(MPCFs)havebeenwidelyusedinthefieldsofaerospace,elec-tronic products,nuclear industry and industrialrobots15 owing to their high thermal conductivityand high modulus.These excellent properties areascribed to their highly oriented large-size graphitemicrocrystalstructurewhichwasderivedfromtheori-entatedstructureofthediscoidnematicliquidcrystalmolecules formed in spinneret channels fromthemesophase pitch.It is generally believed that themesophasepitchmoleculararrangementformedinthemelt-spinning process plays a decisive role in thestructuresandpropertiesoftheresultantMPCFs.Incomparison,the subsequent oxidative stabilization,carbonizationandgraphitizationprovidejustafurthermodificationandimprovement6.Therefore,itisne-cessarytoinvestigatesystematicallytheeffectofthespinningconditionsonthemicrostructuresandprop-ertiesoftheMPCFs.TailoringmicrostructuresandpropertiesofMP-CFsareimmenselycomplicatedbynumerousinfluen-cingfactorssuchasrawmaterial,spinningtemperat-ure,pressure,windingspeed,meshstructureandspin-neretshape712.Atpresent,researchershaveinvestig-Received date：2023-08-21；Revised date：2023-11-03Corresponding author：YEChong,PH.D,Professor.E-mail:;ZHUShi-peng,Ph.D,Professor.E-mail:;LIUJin-shui,Ph.D,Professor.E-mail:JAuthor introduction：YEGao-mingandSHIKuicontributedequallytothiswork.Supplementarydataassociatedwiththisarticlecanbefoundintheonlineversion.Homepage:http:/ the effect of melt-spinning temperature on themicrostructures and properties of MPCFs,but thesestudiesaremainlybasedonthemelt-spinningprocessof the pneumatic single-hole spinning equipment.For example,Yamada et al.13 found that the crosssection structure of MPCFs changed from onion-skinshapetorandomshapeandthentoradialshapewiththedecreasingofthespinningtemperature,eventuallyreachingaradial-splitshapeatthelow-est spinning temperature.However,White andBuechler et al.14 concluded that high viscosity ofpitchmeltwasnotconducivetotheformationoftheradial structure in their experiments.Mochida andYoonetal.1517preparedtheradialstructureandonion-skinstructureMPCFsatlowandhighspin-ning temperatures,respectively.Nevertheless,Ogaleet al.18 obtained the circular radial structure andradial-splitstructureathighandlowspinningtem-peratures,respectively.Recently,Liuetal.19studiedtheeffectofspinningtemperatureonthestructureandproperties of MPCFs by using a nitrogen pressure-driven single-hole equipment,and found that thestructureofMPCFschangedfromirregularshapetoonionskinwiththeincreaseofspinningtemperature.Insummary,differentresearcherscometodifferentoreven contradictory conclusions using a pneumaticsingle-holespinningequipmentbecauseofthecom-plicatedinteraction of extrusion pressure and extru-sionquantity20.Consequently,itisnecessarytoprobetheinfluenceofspinningtemperatureonthemicro-structureandpropertiesoftheMPCFsunderacon-stantextrusionamountofpitchmelt,whichismorevaluableforindustrialization.Inthispaper,theeffectofspinningtemperatureon the microstructure,mechanical properties andthermalconductivityoftheMPCFswasinvestigatedunderaconstantextrusionquantityusinganindustri-altwin-screwextruder.Theflowdeformationbehavi-orofthemesophasepitchwasadjustedbycontrollingthespinningtemperature.Meanwhile,themicrostruc-tural formation mechanism of the resultant MPCFswaselucidated.Thisresearchoffersastraightforwardandviablemethodforenhancingthemechanicalprop-ertiesandthermalconductivityofMPCFs,whichisvaluableforindustrialapplications.2Experimental 2.1 Mesophase pitchIn this study,the petroleum-based mesophasepitch(labelledasTYSHP)providedbyHunanTOYICarbon Material Technology Co.,Ltd.,exhibited aflow texture with 100%optical anisotropy,whosesizesarefrom0.5to4mm.ThebasicpropertiesofmesophasepitchareshowninTable1.Thesofteningpoint(SP)ofthepitchwasdeterminedbyaMettlerToledoDP70withaheatingrateof2C/minunderN2atmosphere.Tolueneinsoluble(TI)andquinolinein-soluble(QI)componentsweretestedusingaSoxhletextractor.TheopticaltextureandanisotropycontentofthepitchwereexaminedbyanOLYMPUSBX-53Ppolarizingmicroscope.TheH/CratiowasdetectedbyanElementarelementanalysisinstrument.Rheologic-alexperimentswereconductedundernitrogenusingan Anton Paar MCR102 rheometer fitted with aheatedconvectionhood.Viscositydatawereobtainedin a temperature-controlled pot at a shear rate of10s1.ThermaldecompositionbehaviorofpitchwasevaluatedusingaTAInstrumentsSDT650simultan-eous thermal analyzer from room temperature to600Cataheatingrateof2C/minunderN2atmo-sphere.2.2 Preparation of the MPCFsThe spinning equipment(homemade,HunanTOYI Carbon Material Technology Co.,Ltd.)wascomposedofafeedingdevice,twin-screwextruder,meteringpump,spinningpack,spinneretplates,col-lectionoilingandwinder(Fig.1).ThespinneretplatesTable 1 The basic properties of mesophase pitchSP/CTI/%QI/%Ashcontent/0.1106Cokingvalue/%H/CAC/%286.475.852.619.190.70.54100Note:SP,softeningpoint.TI,tolueneinsoluble.QI,quinolineinsoluble.H/C,moleratioofhydrogentocarbonatoms.AC,anisotropiccontent.第2期YEGao-mingetal:Improvingthemechanicalpropertiesandthermalconductivityof335have2000holes,andtheshapeofspinneretholeisshown in Fig.1(b),and the length/diameter ratio(L/D)ofthespinneretis11.Thepitchfiberswerespun at different spinning temperatures(309,310,311,313,314,316,318and321C)underacon-stant extrusion flow rate of 2.9 kg/h.The windingspeedwas170m/min.ThepreparedgreenpitchfiberswerelabeledasMPF-XX,wheretheXXcorrespondstothespinningtemperature.The pitch fibers prepared at different spinningtemperaturesweresubsequentlyoxidized,carbonizedand graphitized to obtain MPCFs.The pitch fiberswereoxidizedat290Cfor30mininairwithaheat-ingrateof0.5C/minfromroomtemperature.Sub-sequently,theywerecarbonizedat1500Cfor5minandfurthergraphitizedat3000Cfor5minunderar-gonatmosphere.TheobtainedsampleswerenamedasMPCF-YY,where the YY corresponds to the spin-ningtemperature.2.3 CharacterizationThediffractionpeaksandtheorientationangles(Z)ofthesampleswereobtainedbyequatorial,me-ridianandazimuthscanningsonaD/MAX-2550PCX-ray diffractometer with Cu as a target21.Mean-while,thelayerspacing(d002)andstackingheight(Lc)ofthegraphitecrystallitesofsampleswerecalculatedaccordingtothepeak(002)oftheequatorialscanningimages.Thegraphitecrystallitewidth(La)alongthefiberaxiswascalculatedfromthepeak(100)inthemeridianscanningimages.Zwasusuallyusedtochar-acterizetheorientationdegreeofgraphitelayerplanealongfiberaxis22,andthehalfwidthathalfheight(FWHM)ofthe(002)peakwasdeterminedfromtheazimuthscanning.RamanspectraofMPCFswereob-tainedusing a Thermo Fisher Scientific DXR2 Ra-manspectrometer(power5mW,wavelength532nm).Microstructure of samples was characterized by aTESCAN MAIA3 field emission scanning electronmicroscope(SEM).Thetensilestrengthofmonofilamentwastestedby an XQ-1C fiber tensiometer manufactured byShanghai Xinxian Instrument Co.,LTD,equippedwiththemaximumtensileforceof300cN,thetensilespeedof2mm/min,andthesamplespanof20mm.Thecross-section morphology of samples was ob-servedbySEM,andthecross-sectionareawascalcu-latedbytheImage-ProPlusprocessingsoftware.Fi-nally,thetensilestrengthofmonofilamentwassuc-cessfullyacquired.Theelectricalresistivity()ofMPCFswasmeas-uredbyaBritishAIM-TTIBS407micro-ohmmeter.Andthethermalconductivitywascalculatedbytheempirical formula=1261/23.Generally,the num-berofmonofilamentstestedwasmorethaneight,andtheiraveragevaluewastakenasthefinalthermalcon-ductivityofMPCFs.3Resultsanddiscussion 3.1 Rheological and thermal decomposition beha-vior of mesophase pitchFig.2 shows the rheological properties of themesophasepitch.ItcanbeseenfromFig.2athattheviscosity of mesophase pitch decreases sharply firstandthengraduallylevelsoffwithincreasingtemper-ature.That is because mesophase pitch is a typicaltemperature-sensitivesubstance,andthetemperatureplaysanimportantroleinspinning.InFig.2b,Gisthestoragemodulus,Gisthelossmodulusandtanisthelosscoefficient.AsshowninFig.2b,thestor-agemodulusandlossmodulusreflectthepropertiesofpolymerelasticityandviscosity.ThestoragemodulusGrepresentstheabilityofthepolymertostoreex-(a)Mesophase pitch pelletsMetering pumpTwin-screw extruderSpinneretPitch fiberBundling(b)Winding0.126060300.1Fig.1Schematicdiagramsof(a)thespinningequipmentand(b)thespinneret336新型炭材料（中英文）第39卷ternal energy during deformation reversibly.Thepolymerdeformationcanreturntotheinitialpositionwiththereleaseofenergy,thatis,thestoragemodu-lusrepresentstheelasticpartoftheviscoelasticbeha-vior.ThelossmodulusGisusedtocharacterizetheexternalenergydissipationcapacityduringdeforma-tion,that is,deformation leads to obvious displace-mentbetweenmolecules,andthedeformationcannotberestored,resultinginenergydissipation.Thelossmodulusrepresentstheviscouspartoftheviscoelast-icbehavior.Thelosscoefficientistheratiooflossmodulustostoragemodulus.Thelosscoefficientisalsoknownasthedampingfactororlossfactorofamaterial,reflectingthedeformationcharacteristicsofthematerial.Whenthelosscoefficientislarge,thatis,thelossmodulusismuchlargerthanthestoragemod-ulus,theflowdampingofthematerialisgreat2425.InFig.2b,withthedecreaseoftemperature,GandGincrease,and the increasing trend of loss modulus(G)ismuchlargerthanthatofstoragemodulus(G),resulting in the increase of loss coefficient(tan).Therefore,atlowertemperature,mesophasepitchhaslargerflowdampingandpoorerfluidity,makingitun-suitableforspinning.Soitisimportanttochooseasuitable spinning temperature range.As depicted inFig.2a,inthetemperaturerangeof310350C,themeltviscositytendstobestableasthetemperaturein-creases,resemblingthebehaviortoNewtonianfluid.Thermogravimetric curve(Fig.2c)shows that thestartingdecompositiontemperatureisabout321C,indicatingthatthereisnosignificantdecompositionanddenaturationofmesophasepitchbelow321C.Therefore,thetemperaturerangeof309320.5Cwasselectedasthespinningtemperature,andthecorres-ponding viscosity range was 13.56.5 Pas.In thistemperaturerange,theeffectofthespinningtemperat-ureonthemicrostructure,mechanicalpropertiesandthermalconductivityoftheMPCFswasinvestigated.3.2 MicrostructureTheXRDpatternsofthesamplesareshowninFig.3.According to the equatorial and meridionalscanningpatterns(Figs.3a,b),the(004)and(101)diffractionpeakscannotbeobservedsignificantlyinthe XRD patterns of the MPFs,indicating that the200 m(d)(a)2602702802903003103203303403501000100200300400500600700Viscosity/(Pas)Temperature/C(b)2803003203403600.1110100100010000100000GGG，G/PaTemperature/C0510152025tantan0100200300400500600707580859095100105Weight/%Temperature/C320.5 C(c)300 305 310 315 320 325 330 335 34002468101214161820222426Viscosity/(Pas)Temperature/CFig.2Rheologicalpropertiesofmesophasepitch:(a)viscosity-temperaturecurve,(b)variationcurvesofstoragemodulus(G),lossmodulus(G),andlosscoefficient(tan)withtemperature,(c)thermaldecompositionbehaviorand(d)polarizedmicroscopeimages第2期YEGao-mingetal:Improvingthemechanicalpropertiesandthermalconductivityof337crystallitesizeoftheMPFsissmall.TheLaandLcare0.481.92 nm and 2.222.66 nm,respectively(Table 2).The azimuth scanning patterns(Fig.3c)showthattheorientationangleoftheMPFsdecreasesfrom40.6to28.7asthespinningtemperaturein-creasesfrom309to320.5C.Itcanbeconcludedthatthe increasing spinning temperature promotes thepreferred orientation of the discoid nematic liquidcrystal molecules of the mesophase pitch along thefiberaxis.The equatorial scanning patterns of MPCFs(Fig.3d)display2differentpeaks(002).Theweak(002)T peak at the smaller 2 angleis usually con-sidered to be derived from the turbostratic fraction,andthe(002)Gpeakatthelarger2anglehasahighintensitywithanarrowandsharppeakshapederivedfrom the ordered graphite fraction6.With the in-creaseofspinningtemperature,the(002)Gpeakbe-comesnarrowerandsharper,andLcbecomeslarger(Table2).The(004)diffractionpeakintheequatorialscan of MPCF indicates a large graphite crystallinesize.As the spinning temperature increases,the in-tensity of(004)diffraction peak increases and thestackingofgraphitecrystallinebecomesmoreorderly.Itcanbeseenfromthemeridionalscanningpatternsthatboth(100)and(101)diffractionpeaksarefound1020304050602/()2/()/()1020304050602/()MPF-316.0(a)(004)Intensity/(a.u.)Intensity/(a.u.)Intensity/(a.u.)Intensity/(a.u.)Intensity/(a.u.)Intensity/(a.u.)(002)G(002)TMPF-320.5MPF-318.0MPF-314.5MPF-312.5MPF-311.0MPF-310.0MPF-309.0(d)(002)T(002)G(004)MPCF-320.5MPCF-318.0MPCF-316.0MPCF-314.5MPCF-312.5MPCF-311.0MPCF-310.0MPCF-309.0(e)(100)(101)MPCF-320.5MPCF-318.0MPCF-316.0MPCF-314.5MPCF-312.5MPCF-311.0MPCF-310.0MPCF-309.020304050602/()2030405060(b)(100)(101)MPF-320.5MPF-318.0MPF-316.0MPF-314.5MPF-312.5MPF-311.0MPF-310.0MPF-309.0MPF-320.5MPF-318.0MPF-316.0MPF-314.5MPF-312.5MPF-311.0MPF-310.0MPF-309.0MPF-320.5MPF-318.0MPF-316.0MPF-314.5MPF-312.5MPF-311.0MPF-310.0MPF-309.09060300306090/()9060300306090(c)(f)Fig.3XRDpatternsofsampleswith(a)theequatorialscanofMPFs,(b)themeridianscanofMPFs,(c)theazimuthalscanon(002)crystalfaceofMPFs,(d)theequatorialscanofMPCFs,(e)themeridionalscanofMPCFsand(f)theazimuthalscanonthe(002)crystalfaceofMPCFs338新型炭材料（中英文）第39卷in MPCFs(Fig.3e),indicating a three-dimensionalorderedstructure21,23.Asthespinningtemperaturein-creases,the(100)peakbecomessh