´a,2Sofı´aVazquez-Rodriguez,2RodolfoCruz-Silva,1JorgeRomero-Garcı
´nchez2JoseLuisAngulo-Sa
1´nenIngenierı´ayCienciasAplicadas,UAEM.Av.Universidad1001,CentrodeInvestigacio
´xicoCol.Chamilpa,CP62210,Cuernavaca,Morelos,Me
2´´CentrodeInvestigacionenQuımicaAplicada,Saltillo,Coah.Blvd.EnriqueReynaNo.140,
´xicoCP25100Saltillo,Coahuila,Me
Received12June2006;accepted14November2006
DOI10.1002/app.26026
Publishedonline8May2007inWileyInterScience(www.interscience.wiley.com).ABSTRACT:ShortglassfiberTypeEwascoatedwithelectricallyconductingpolyaniline(PAn)byinsituchemicalpolymerization.TheresultingPAncoatedglassfiber,withsurfaceconductivityof3.3Â10À1S/cm,wasmelt-com-poundedwithisotacticpolypropylene(iPP).Polypropylenegraftedwithmaleicanhydridewasinvestigatedasanadhe-sionpromoterforthesecomposites.Differentialscanningcalo-rimeterandpolarizedlightmicroscopyindicatesthatthePAncoatedglassfiberhasastrongnucleatingactivitytowardsiPP.Scanningelectronmicroscopyshowedtheimprovementinthewettinganddispersionofthefiberswhentheadhesionpromoterwasadded,althoughthisalsoledtofiberencap-sulationandloweringtheelectricalconductivityofthecom-posites.TheadhesionpromotergreatlyimprovedtheYoung’smodulusofthecomposites,andareactionbetweenthemaleicanhydridegroupsoftheadhesionpromoterandthePAnwasproposed.Compositeswithanelectricalcon-ductivitygreaterthan10À9S/cmwereachievedusinga30wt%ofPAncoatedglassfiber.Ó2007WileyPeriodicals,
Inc.JApplPolymSci105:2387–2395,2007
Keywords:electricallyconductivecomposites;reinforcedcomposites;nucleatingagent;adhesionpromotor;maleicanhydridecopolymer
INTRODUCTION
Polyaniline(PAn),anintrinsicallyconductivepoly-mer,hasbeenincreasinglyemployedintheprepara-tionofthermoplastic-basedcompositesforantistaticorelectromagneticshieldingapplicationsinthelastyears.1–7Thegreatpotentialofthispolymerintheaforesaidapplicationsisduetoitsenvironmentalstability,relativelyhighelectricalconductivityandlow-costsyntheticroute.8Comparedwithtraditionalelectricallyconductivemetallicfillers,PAnhasadvantagessuchaslowerweight,lowercost,andhighercorrosionresistance.However,PAnisinfusi-ble,anddirectblendingofPAnpowderwithther-moplasticsbymeltprocessingtechniquesresultsin
Correspondenceto:R.Cruz-Silva(rcruzsilva@uaem.mx).Contractgrantsponsor:CONACYT;contractgrantnumber:46046.
Contractgrantsponsor:PROMEP;contractgrantnumber:UAEMOR-PTC-151.
JournalofAppliedPolymerScience,Vol.105,2387–2395(2007)C2007WileyPeriodicals,Inc.V
ThisarticleisdedicatedtothememoryofProf.JoseLuisAngulo-Sanchez.incompletedispersionleadingtocompositeswithpoormechanicalproperties.Sincetheintroductionofcounter-ioninducedprocessability,9blendsofPAnandawiderangeofthermoplasticshavebeenpre-paredbyextrusionorinjectiontechniques,1–7,10butlowinterfacialadhesionhasledtoadecreaseinthemechanicalpropertiesoftheblends.Forthisreason,incorporationofreinforcementsoradhesionpro-moterstoPAn-thermoplasticblendsisexpectedtoimprovetheoverallmechanicalperformanceoftheresultingcomposites.
Theelectricalconductivityofcompositesofinsulat-ingandconductingphasesiswelldescribedbythepercolationtheory.11Whenacertainamountofcon-ductivefillerisgraduallyaddedtoaninsulatingma-trix,theconductivityofthecompositeremainsclosetothatofthematrix,butwhentheamountofconduc-tivefillerishighenoughtoformacontinuumnet-work,adrasticincreaseintheelectricalconductivityisachieved.Thefractionofconductivefilleratthispointiscalledpercolationthreshold.Furtheradditionoftheconductivefillerhasalessdramaticimpactonelectricalconductivity.Notonlytheconcentrationbutalsotheshapeandaggregationbehavioroftheparticlesoftheconductivefillerhavestronginfluencetolowerthepercolationthreshold.12,13Theoretical
2388andexperimentalstudieshaveshownthatparticleswithaggregationbehaviororhighaspectratio,suchasfiberorflakes,achievethe13,14percolationthresholdatlowervolumeconcentrations.ItisexpectedthatPAn-coatedfiberscanachievethepercolationthresholdatrelativelylowconcentra-tionnotonlybecauseofitshighaspectratiobutalsoduetoaphenomenoncalleddoublepercolation,com-monincompositeswheretheconductingphase15,16islocatedbetweentwononconductingphases.Forinstance,Taipalusetal.1foundthatinternarycompo-sitesofpolypropylene(PP)/glassfiber/PAn,locationofPAnattheinterfacebetweenthefibersandthematrixloweredthepercolationthresholdduetoadoublepercolationmechanism.Nevertheless,uponPAnincorporation,adecreaseinthemechanicalpropertieswasobserved.Whenconductingcarbonfiberwasemployedinsteadofglassfiber,animprovementinelectricalconductivitywasachieved.4Inthiscase,thePAnphasebehavedasa‘‘bridge’’toconnectthecarbonfibers.Asimilarbehaviorwasobservedincompositesofnickelflakescoatedwithconductivepolypyrrole.17Recently,glassfiber2andmica6coatedwithPAnwereusedtopreparecompo-siteswithepoxyresin.Inthesecases,thePAn-coatedparticleshelptodevelopaconductivenetworkwithinthecomposite.Howeverbothcompositeswerepre-paredinliquidmediaandthepolymerizationtookplaceaftermixing.Inmeltprocessing,itispossiblethatadhesionofphysicallyadsorbedPAnonrein-forcementswouldnotbestrongenoughtoresistthehighshearduringprocessing.
SincetheworkdonebyGregoryetal.,18thesur-facemodificationofawiderangeoffiberswithPAnhasbeenextensivelystudied.19–22Geethaetal.23studieddifferentsulfonicacidinthesurfacemodifi-cationofglassfibersbyinsituchemicalpolymeriza-tion.However,graftingofPAntosilicondioxidesurfacesusingsilanecouplingagentsbearinganilinemoietieswasfirstproposedbyWuetal.24,25toimprovetheadhesionbetweentheinorganicsub-strateandthePAn.Usingasimilarapproach,LiandRuckensteinsuccessfullygraftedPAnonsurfacetreatedglassfiber.26However,thismaterialhasnotbeenusedtopreparefiberreinforcedcompositesbymeltprocessingtechniques,andoptimizationofthesurfacemodificationprocesswouldbeinter-esting.
Theaimofthisworkwastoinvestigatetheme-chanical,thermalandelectricpropertiesofisotacticpolypropylene(iPP)/PAn-coatedshortglassfiber(SGF)composites.Therelationbetweenthemorphol-ogyandboththemechanicalandelectricalproper-tieswasinvestigated.APP–maleicanhydridecopoly-mer,awidelyusedadhesionpromoterinPP/SGFcomposites,27wasincorporatedtothecompositestoimprovetheirmechanicalproperties.Inaddition,a
JournalofAppliedPolymerScienceDOI10.1002/app
CRUZ-SILVAETAL.
novelreactordesignforPAncoatingofSGFbyinsitupolymerizationispresented.
EXPERIMENTAL
Materials
AnilinewasacquiredfromBaker(Xalostoc,Mexico)anddistilledunderreducedpressurebeforeuse.SGFTypeEwasacquiredfromVitroGroup(Monterrey,Mexico).N-phenyl-g-aminopropyltrimethoxysilanewasacommercialproductfromSylquest(Y-9669TM).Polypropylenegraftedmaleicanhydridecopolymer(PP-gMA)wasacquiredfromUniroyalChemicalunderthetradenameofPolybond3200.Themaleicanhydridecontentwasof1.0%asdeterminedbyFTIRspectroscopy.28iPPwithaMFIof3.8andden-sityof0.9g/cm3,wasacquiredfromIndelpro,Basell.Allotherreagentswereofanalyticalgradeandusedasreceived.Fibermodification
SGFwascalcinatedinafurnaceat5008Cfor3htoeliminatethesizingandcouplingagents,thenwashedwithwaterandtreatedwith10wt%hydro-chloricacidsolutionfor3hat608Ctoincreasethesilanolgroupsconcentrationonthesurface.After-wards,thefiberwasthoroughlywashedwithdis-tilledwater.Afterdrying,silanizationwasdonebyimmersionina0.025wt%N-phenyl-g-aminopropyl-trimethoxysilanesolutioninmethanolduring24h.Then,thefiberswererinsedwithmethanol,driedundernitrogenflow,andfinallyinavacuumovenfor3hat1008C.
ModificationofsilanizedSGFbyinsitupolymer-izationofanilinewasdoneina5-Ljacketedreactor(Fig.1),where1.5kgofSGFwaspacked,and4LofHCl1.0Nand20mLofanilinewereadded.Nitro-genwasbubbledtroughthepackedfiberduring2handmaintainedduringthepolymerization.Thereac-tionwasinitiatedbyadding56.4gofammoniumpersulfatedissolvedin250mLofdegassed1.0Nhy-drochloricacid.Thereactionmediawasunstirred;howevertheliquidwasrecirculatedthroughthepackedfiberusingaperistalticpumpatapproxi-mately180mL/min.Temperaturewaskeptcloseto08Cbyrecirculatingcoolingfluidbythejacket.ThreehoursafterthereactionwasinitiateddeepgreenPAn-coatedSGFwasobtained.Thesefibersweretreatedina2.0wt%solutionofsodiumcar-bonateandwashedthoroughlywithdeionizedwater.Thebluecolorofthefiberatthisstagewasindicativeofdedoping.ThePAn-coatedSGFwasredopedwithp-toluenesulfonicacid,whichunlikechlorine,hasbeenreportedtobethermallystableupto2008Casdopingagent.29Afterwardsthefiberwas
driedinaconvectionovenat708C.ThisprocedureaffordedPAn-coatedSGF,withafractionalPAnweightof4%,asdeterminedbythermogravimetry.ThisvalueindicatesthattheorganiccoatingisratheracomplexofPAnandtoluenesulfonicacidinexcess;howeveritwillbereferredsolelyasPAn.Preparationofcomposites
Priortomixing,PAn-coatedSGFwasdriedinavac-uumovenfor4hat608CwhereastheiPPandPP-gMAweredriedinavacuumovenfor12hat908C.BlendingwasperformedinaBanburyTypeMixerat2008CusingCAMrotors.iPPwasfirstmeltedat25rpmfor5min,PP-gMAwasaddedatthispointinsomeformulations.Then,thePAn-coatedSGFwasaddedgraduallyovera3-minperiodandmixedforanadditional4-minperiod.Thentheblendswereremovedfromthemixer,cooledtoroomtem-perature,andcrushedusingamillequippedwithasieve.Finally,thecompositeswerepressmoldedunder2.45MPainasteelmoldobtainingsquarecompositesof20cmÂ20cmand2.6mmwide.Characterization
Differentialscanningcalorimetry
Adifferentialscanningcalorimeter(MDSCTAInstru-ments2920)wasusedforthermalanalyses.Samplesofabout12mgwereloadedinaluminumsealed
pansandheatedatarateof108C/minfrom20to2008C,heldinthistemperaturefor3mintoerasepre-viousthermalhistory,andcooledtoroomtempera-tureatthesamerateandheldfor3min.Then,asec-ondheatingscanwasperformedfrom20to2008C.Thetemperaturesatthemaximumofthecrystalliza-tionexothermandthemeltingendotherminthesec-ondheatingscanweretakenasthemelting(Tm)andcrystallizationtemperatures(Tc),respectively.Calcula-tionsofthecrystallinefractionofthepolymericphaseweredoneusingaheatoffusionof209J/g.30Opticalandpolarizedlightmicroscopy
OpticalandpolarizedlightmicroscopyobservationsofthecompositesweredoneinaOlympusBX90microscopeusingsmallsamplesmeltedandpressedtoformafilm.Forpolarizedlightmicroscopyobser-vation,modelcompositeswerepreparedmixingindividualfibersofPAn-coatedSGFwithmeltiPPorPP/PP-gMAblendsandobservedusingaMetler-ToledoFP90heatingstage.Sampleswereheatedto2008Candheldinthistemperaturefor3minandthencooledtoroomtemperatureat58C/min.
Mechanicalproperties
Young’smodulus,elongationatbreak,andtensilestrengthofthecompositeswereacquiredusinganInstronuniversalmachine,accordingtoASTMD638.Allsampleswerecutintodogbonessamplesandconditionedfor48hat51%R.H.and228C.Thetestwasrunata5.08mm/mindeformationrate.
X-raydiffractionpattern
ASiemensD-5000X-raydiffractometerwasusedtoacquirethewide-angleX-raydiffractionpatterns(WAXD)ofthepress-moldedcomposites.Dataacquisi-tionwasdoneinthe2ymodeusingaCuKaradiationsource(intensity25mA,35kVaccelerationvoltage).Electricalresistancemeasurements
Single-fiberelectricalconductivitymeasurementsweredoneusingaKeithley2400sourcemeter.Indi-vidualfiberswereplacedbetweentwosilverpaintelectrodesoveraglassslide.Thegapbetweentheelectrodeswasmeasuredbyopticalmicroscopy.Theelectricalresistanceofthecompositeswasmea-suredusingaKeithley6517Aelectrometer/highresist-ancemeter.Samplesof2cmÂ2cmÂ0.26cmwerecutfromthecompressionmoldedcomposites,andtheinsulatingskinlayerofthecompositeswascarefullyremoved.Oppositesidesofthesamplewerecoatedwithsilverpainttoreducethecontactresistance.2390Theelectricalresistancewasmeasuredparallelandacrosstheplaneofcompression.Eachvalueistheaverageofthreemeasurements.Scanningelectronmicroscopy
SEMobservationsweredoneinaTopCom510equip-ment.CompositessamplesandPAn-coatedSGFwerefracturedunderliquidnitrogenandcoatedwithathinlayerofAu/Pd.
RESULTSANDDISCUSSION
SGFmodificationandcompositesformulationInFigure2(a)isshownaphotoofthePAn-coatedSGFafterbeingscratched.Thisimagerevealsthatthecoatingisdebondedasafree-standingthinfilm.Theinsetshowsanopticalmicroscopyimageofasinglefiberthathasauniformcoating,asindicated
FigureSGF)2(a)SEMimageofPAncoatedSGF(PAn-coatedobservedaftercroscopynextbeingtothescratched.fiber.TheAinsetdebondedshowsanthinopticalfilmmi-isPAn-coatedimageSGF.
ofasinglefiber.(b)SEMimageoftheJournalofAppliedPolymerScienceDOI10.1002/app
CRUZ-SILVAETAL.
Figureobtained3(a)coated10wtfromOpticalSGF.
%ofiPP/PAn-coatedmicroscopyimagesofthinfilmsPAn-coatedSGFSGFandcomposites(b)30wt%containingofPAn-bythehomogeneousgreencolorofthefiber.InFig-ure2(b),aSEMimageofthePAn-coatedSGFasobtainedafterthefibermodificationisshown.ThemorphologyofthePAncoatingconsistsofathinfilmwithparticlesadheredontoitssurface.Thethinfilmismostprobablygrownfromadsorbedanilineonthefibers,whereastheparticlesaregrownintheliquidphaseandlateradheredonthegrowingPAnfilm,inagreementwiththegrowthmechanismofPAn31filmspreparedbyinsituchemicalpolymeriza-tion.Theconductivityofthefiber(3.3Â10À1S/cm)issimilar26tothatreportedbyLiandRucken-stein,andishighenoughtobeobservedwithoutmetalliccoatingbyscanningelectronmicroscopy.Single-fiberconductivitymeasurementsalsopro-videdinformationonthehomogeneityofthecoat-ing.Electricalconductivityofseveralfibersfromabundlefluctuateslessthanoneorderofmagnitude,andlessthantwoordersofmagnitudefromfibersfromadifferentbundle.ByusingdensitiesofbothmaterialsandthegravimetricresultswewereabletocalculatetheaveragePAncoatingthickness($300nm)andtheelectricalconductivityofthebulk
PP/PAnCOATEDSHORTGLASSFIBERCOMPOSITESPAnofthecoating($3.6S/cmÀ1).Opticalmicros-copyimagesrevealedthatmostoftheSGFkeptthePAncoatingaftermeltprocessingat10wt%withiPP[Fig.3(a)];however,somePAnparticleswerealsopresentbecauseofdebondingofthecoating.IncreasingtheamountofPAn-coatedSGFledtoahigherdegreeofdebonding,duetofiberabrasionduringcompounding,butevenat30wt%offillerload[Fig.3(b)]alargenumberoffibersremaincoatedwithPAn.
EffectiPP/PP-ofgMAthePAn-coatedcrystallization
SGFoniPPandTheeffectofthePAn-coatedSGFonthethermalpropertiesofiPPandiPP/PP-gMAblendswasstud-iedbyDSC.InTableI,thecrystallizationtempera-turesofthecompositesareshown.TheTcofiPPis1128Cbutaftertheadditionof10wt%ofPAn-coatedSGFtheTcincrementsto124.28C.Thisnucle-atingactivityofPAn-coatedSGFtowardsiPPwaspreviouslyreported.32Thethermalpropertiesinpresenceoftheadhesionpromoterwerealsostud-ied.Theadditionof5.0wt%ofPP-gMAtopureiPPincreasedthecrystallizationtemperatureto115.78C.ThisisattributedtothepresenceofC¼¼OgroupsfromthemaleicanhydridemoietiesthatbehaveasnucleatingpointsinthenonpolariPPmatrix.33Theadditionof10wt%ofPAn-coatedSGFtotheiPP/PP-gMAblendincrementstheTcto121.58C,indicat-ingthatthenucleatingactivityofthePAnismain-tainedinthepresenceofPP-gMA,contrastingwithpreviousstudiesonnucleatingfibers,wherethenucleatingactivityissuppressedafterPP-gMAaddi-tiontothecompositeduetofiberencapsulation.34FurtheradditionofPAn-coatedSGFtothecompo-sitescausesonlyaslightincrementintheTc,sug-gestingthat10wt%providesenoughsurfacetothepolymermatrixtonucleate,andconsequentlythecrystalgrowthratebecomeslimitedabovethatcon-centrationofPAn-coatedSGF.ThedevelopmentoftranscrystallinezonesaroundPAn-coatedSGFincomposites,withandwithoutPP-gMA,isshownin
CompositionandThermalTABLEPropertiesI
oftheComposites
Composition(wt%)
PAn-coated
SampleiPPPP-gMA
SGF
TcXcTmPP000010000112.20.45164.8PP001090010122.40.47164.9PP002080020123.60.49165.1PP003070030123.90.51164.6PP05009550115.70.46164.1PP051085510121.50.47164.7PP052075520123.50.49164.9PP0530
65
5
30
124.6
0.48
164.3
2391
Figureogy(b)dediPP/PP-of4singlePolarizedgMAPAn-coatedopticalblend.AsingleSGFmicroscopyuncoatedembeddedshowingmorphol-glassinfiber(a)iPPandparison.
iniPPduringcrystallizationisshownin(c)forembed-com-Figure4(a,b),respectively.Aspreviouslyreported,notranscrystallizationisinducedbythebareglassfiber,32,33whichisshowinFigure4(c).Thewidthofthecrystallizationexothermslightlysharpensinallcompositesformulations[Fig.5(a,b)],ascomparedtothematrix,mostlikelyduetothenucleatingeffectofthePAn-coatedSGF.Thecrystallinefraction(TableI)slightlyincrementsforthecompositesasthecontentofPAn-coatedSGFdoes,indicatingthattranscrystallizationpropagatetothematrix.
SurfacetreatmentofSGFandsomepolymericfiberscaninducetranscrystallinezonesofdifferentcrystaltype,suchasthegorbform.35,36Forthisrea-son,wecarriedoutastudyofthecompositesbywideangleX-raydiffraction,shownintheFigure6.Nevertheless,theiPPandiPP/PP-gMAblend(Fig.6,curvesaandb,respectively),aswellasthecompo-sites,showedonlythecharacteristicpeaksofa-typePP.Thesepeaksappearat2yof14.18,16.98,18.58,21.18,and21.88,andcorrespondtothe(110),(040),
JournalofAppliedPolymerScienceDOI10.1002/app
(130),(111),andtheoverlapped(131)and(041)reflectionsoftheaphaseofiPP.37However,afteradditionofthePAn-coatedSGF,theratiobetweenthepeakscorrespondingtothe(110)and(040)reflec-tionplaneschange,asshownforcompositesofiPPandiPP/PP-gMAcontaining30wt%ofPAn-coatedSGF(Fig.6,curvescandd,respectively).Thischangecanbeattributedtodifferentorientationofthe38polymerchainsnearthesurfaceofthecompos-ite,whichmayhavebeeninducedbythepressmoldingprocessinpresenceofthePAn-coatedSGF.Morphologyandmechanicalproperties
TheSEMmicrographofthefracturesurfaceofthecompositeofiPPwith30%ofPAn-coatedSGFisshowninFigure7(a).ThelargenumberofdebondedfibersevidencestheweakinteractionbetweenthefibersandtheiPP.Duringthefracture,pulloutof
thefibersoccurs,indicatingthatthestressisnottransferredtothereinforcingfibers.Howevermostofthefibersarestillcoated,mostprobablywithPAn,becauseiPPhaspooradhesiontoglassfibersandthefractureofiPP/glassfibercompositesshowsmainlycleanpulled-outglassfibers.1IntheFigure7(b),thesurfacefractureoftheiPP/PP-gMAsamplecontaining30wt%ofPAn-coatedSGFisshown.BoththewettinganddispersionofthefibersimproveddrasticallyuponadditionofthePP-gMA,inpartduetothelowermeltviscosityofPP-gMA.Ontheotherhand,thehigherpolarnatureofthead-hesionpromotermakesthematrixmorecompatiblewithPAncomparedtoiPP,resultinginanincreaseintheadhesionbetweenthefiberandthematrixiniPP/PP-gMAcomposites.Inconsequence,thefrac-turemechanismnowinvolvesfiberbreakage,indi-catingthatthestresswasefficientlytransferredtothereinforcement.
TheYoung’smoduliofthecompositesareshowninFigure8(a).AlinearincrementuponadditionofthePAn-coatedSGFisdisplayedforbothtypesofcomposites.Wecalculatedtheefficiencyfactorval-ues39forbothsetofcompositesusingtheKrenchel’slaw,whereVisthevolumefractionandEthemodulus,andthesubscriptsfandmrefertothefiberandthepolymermatrix,respectively,andZistheKrenchel’sefficiencyfactor.
E¼ZEfVfþEmVm
(1)
Figurecomposites:7Typical(b)iPP/PP-g(a)MAiPPfractureblendwithwith30surfacesofcompressionmolded30wtwt%%ofofPAn-coatedPAn-coatedSGFSGF.
andTheefficiencyfactordependsonthefiberlengthandorientationandfiber-matrixinterfacialadhesion,butsincetheadditionofthePP-gMAaffectsmainlythislastparameter;thuswecanascribethechangeoftheefficiencyfactortothepresenceoftheadhesionpro-moter.Theefficiencyfactorcalculatedusingtheeq.(1)foriPP/PAn-coatedSGFcompositeswas0.16andfortheiPP/PP-gMA/PAn-coatedSGFcompo-siteswas0.33.ThetwofoldincrementwhenPP-gMAwasusedindicatestheimprovementofthefiber-ma-trixinterfacialadhesion,increasingthemodulusfrom1.9to4.5GPaat30wt%ofPAn-coatedSGF.ThetensilestrengthinbothsetofcompositesshowedareductionafteradditionofthePAn-coatedSGFduetotheeffectofinterfacialflaws[Fig.8(b)].Thisisbecausetensilestrengthismeasuredafterirreversibledeformationofthesampleandfiber-matrixvoidformation,andthusislesssensitivetoreinforcementascomparedtoYoung’smodulus.
WhereasinteractionbetweenPAn-coatedSGFandiPPismainlymechanicalbecauseofthehighrough-nessofthefiber[Fig.2(b)],severalchemicalinterac-
tionscouldarisebetweenthePAn-coatedSGFandthePP-gMA.Theaminoend-groupsofthePAncanreactwiththemaleicanhydridegroupsofthePP-gMA,producinganamidethatunderhightem-peraturecanfurtherreactbycondensation,originat-inganimidegroup,40asshowninFigure9.ThiscovalentbondingbetweenthePAnandthepolymermatrixwouldexplaininsomeextenttheincrementoftheinterfacialadhesion.Inaddition,duetopartialdebondingofthePAn-coatedSGFduetoabrasionorshearstressduringmeltprocessing,thePP-gMAcanreacteitherwiththesilanolgroups27(producedbytheacidtreatmentofthefiber)orwiththesec-ondaryaminegroupsofthesilaneontheexposedsurfaceoftheglassfiber.Electricalproperties
PP-g-MAwasaneffectiveadhesionpromoterimprovingtheYoung’smoduleofcompositesofiPP
withPAn-coatedSGF;howeveritseffectonelectricalconductivityshouldbeanalyzed.TheconductivityofthecompositesversustheamountofPAn-coatedSGFisshowninFigure10.ThecompositeofiPPwithPAn-coatedSGFincrementsitselectricalcon-ductivitybythreeordersastheamountoffiberisincreasedfrom20to30wt%,indicatingapercola-tionphenomena,whereasthecompositecontainingPP-gMAshowsonlyaslightincrement.ThisisduetoPAn-coatedSGFencapsulationafteradditionoftheadhesionpromoter,andissupportedbySEMobservations[Fig.7(b)].Similarelectricalconductiv-itybehaviorhas41beenobtainedinPP–stainlesssteelfibercompositesandethylenevinylacetate42copoly-mer/copoliamide/PAnternaryblendswhenadhe-sionpromoterswereadded.AllthecompositesÀhavesimilarelectricalconductivityvalues,inthe1013to10À12S/cmorder,regardlessofthemeasuringdirec-tion,exceptforthecompositeofiPPwith30wt%ofPAn-coatedSGF,thathasaconductivitythreeordersofmagnitudehigherwhenmeasuredperpendiculartothecompressiondirection.Thisisbecausefiberorientationisinducednearthesurfacebythecom-pressionmolding,helpingtoachievethepercolation
alongtheplaneofcompression,producingananiso-tropicelectricallyconductivecompositeatlowercon-centrationthatthosecontainingrandomorientedfibers.12Additionofmorethan30wt%ofPAn-coatedSGFnotnecessarilywouldleadtoanincreaseofelectricalconductivitybecauseoftheincreaseoffiberbreakageandabrasion.Compositesofelectri-callyconductivemetallicfibersandthermoplasticsoftenachievethepercolationat6%to10%volumefraction,13,41butinourcase,theresultingelectricalconductivityoftheiPP/PAn-coatedSGFislowerthantheexpected,indicatingthatpartialdebondingofthePAncoatingtookplaceduringprocessing.Thisisfurthersupportedbyopticalmicroscopyimages[Fig.3(b)].Nevertheless,theelectricalcon-ductivityreachedat30wt%ofloadingwasintherangeofelectrostaticdischargeapplicationsusingaverylowamountofPAninthecomposite($1.2wt%ofPAn).Tofurtherimprovethiscomposite,theadditionoflow-viscositymelt-processablePAncom-plexmayincreasetheelectricalconductivitybyact-ingasabridgebetweentheelectricallyconductivesegmentsoftheindividualfibers,asitdoesincar-bonfiber/melt-processablePAncomposites,4andbyreducingthedebondingofthePAn-coatedSGF.ThisworkdemonstratesthatPAn-coatedSGFisapoten-tialapplicationofthisconductivepolymer;howevertheprocessingconditionsmaybeoptimizedtoreducethecoatingdebondingoftheglassfiberdur-ingmeltprocessingandtoimprovetheelectricalandmechanicalpropertiesofthecomposite.
CONCLUSIONS
PAn-coatedSGFwaspreparedinanovelunstirredreactorthatovercomesproblemswithlargeunstirredanilinepolymerizations,suchasautoaccelerationandincreaseofthereactionmediatemperature.Ahighfiber/liquorweightratio(1:3)wasachieved,whilebreakageofglassfiberandabrasionofthecoatingwasavoidedbecauseoffiberimmobilization.PAn-coatedSGFshowedastrongnucleatingactivitytowardsiPP,resultinginashiftofthecrystallizationtemperatureupto128C.PolarizedlightmicroscopyshowedtheformationoftranscrystallinezonesonthePAn-coatedSGFvicinity,andX-raydiffractionpatternsindicatesthatthecrystallinephaseofboth
PP/PAnCOATEDSHORTGLASSFIBERCOMPOSITESmatrixandtranscrystallinezonesarea-type.Addi-tionofPAn-coatedSGFincrementedtheYoung’smodulusofthecomposites.MaleatedPPprovedtobeaneffectiveadhesionpromoter,increasingbothdispersionandwettingofthefibers,butaffectednegativelytheelectricalconductivityofthecompo-sitesduetofiberencapsulation.AreactionbetweenthemaleicgroupsoftheadhesionpromoterandtheterminalaminogroupsofPAnwasproposedtoexplaintheimprovementininterfacialadhesion.Theelectricalconductivityreachedwithaverylowfrac-tionofPAn(30wt%ofPAn-coatedSGF,equivalentto1.2wt%ofPAn)andisintherangeofelectro-staticdischargeapplications.
BlancaHuerta,SandraPeregrina,andEsmeraldaSaucedoareacknowledgedforthermalanalyses,mechanicalprop-ertiesevaluation,andSEMimages,respectively.EdgarAmaroisacknowledgedforelectricalconductivitymeas-urementsandR.Cruz-SilvathanksProf.FelipeAvalosforhelpfuldiscussion.
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