TGA研究酚醛树脂的分解动力学

Pyrolysiskineticsofphenol–formaldehyderesinbynon-isothermalthermogravimetryHaiyunJianga,b,JigangWanga,*,ShenqingWua,BaoshengWangb,ZhangzhongWangbaJiangsuKeyLaboratoryofAdvancedMetallicMaterials,SchoolofMaterialsScienceandEngineering,SoutheastUniversity,Nanjing211189,ChinabSchoolofMaterialsScienceandEngineering,NanjingInstituteofTechnology,Nanjing211167,ChinaARTICLEINFOArticlehistory:Received18June2009Accepted8September2009Availableonline12September2009ABSTRACTThepotentialdamageduringthepyrolysisofphenol–formaldehyde(PF)resinintheman-ufacturingofcarbon/carboncomponentsisserious.Accuratelymodelingthekineticsofthepyrolysisreactioncanleadtoimprovementsinprocessing.Tostudythepyrolysiskinet-icsofPFresin,non-isothermalpyrolysiskineticsisinvestigatedusingthermogravimetricanalysis(NGA)atcontrolledheatingrates.Theresearchindicatesthatthepyrolysisprocessconsistsofthreeconsecutiveandoverlappingstages.PEAKFITwasemployedtoseparateoverlappingregions,andthenpyrolysiskinetictripletofPFresiniscalculated.Withthedeterminedapparentactivationenergies,themostprobablemechanismfunctionsandthecorrespondingpre-exponentialfactor,themodelagreeswellwiththeexperimentaldata.2009ElsevierLtd.Allrightsreserved.1.IntroductionBecauseofexcellentfrictionresistance,flameretardantheatresistanceandmechanicalproperties,phenol–formaldehyde(PF)resinisoftenpyrolyzedtomanufacturecarbon/carboncomposites[1–3].However,thepyrolysisprocessinghasapo-tentialdamageonthestructureandpropertiesofcarbon/car-bonmaterials[1].Duringthepyrolysisprocess,PFresinisconvertedintoamorphouscarbonaccompaniedbythere-leaseofmanygaseousproducts.Atthesametime,thermalstressaswellasotherfactorsmaydeterioratethestructureofcomposites.Therefore,itisnecessarytodecreasethedestructionofcompositesthroughunderstandingthepyroly-sismechanismofPFresinaccuratelyandoptimizingthepyrolysisprocedureparameters.Inrecentdecades,manyre-searcheshavebeendonetorevealthethermalbehaviorofPFresin[1–7].TypicallyOuchiproposedamechanismofpyro-lysisconsistingofthreestages.Firstlyadditionalcrosslinkswereformedastheresultofcondensationreactionsbetweenfunctionalgroupsofthecuredphenolic.Thenthecrosslinkswerebroken,resultingintheevolutionofmethane,hydrogenandcarbonmonoxide.Finallyhydrogenatomswerestrippedfromtheringstructureandhydrogengaswasevolved.Simi-larlyTrickandSaliba[2]suggestedamechanismdescribedtheresinpyrolysisreactionasoccurringinthreemajorreac-tionregions:formationofadditionalcrosslinks,breakingofthecrosslinks,andstrippingofthearomaticrings.Despiteofthediscrepancyofdifferentpyrolysismechanisms,thereisextensiveviewpointdividingthepyrolysisprocessofPFre-sinintothreeregions.Eachoftheseregionsdoesnotrepre-sentanelementaryreactionbutratherarelativelycomplicatedsetofreactionsandismodeledbyanapparentoverallkineticexpression.Onthebaseofthis,thepyrolysiskineticsofPFresinwasinvestigated[1,4,8].BishopandMinkowycz[8]putforwardamodeloffourone-orderreac-tionstosimulatethepyrolysismechanismbyisothermal0008-6223/$-seefrontmatter2009ElsevierLtd.Allrightsreserved.doi:10.1016/j.carbon.2009.09.036*Correspondingauthor:Address:JiangsuKeyLaboratoryofAdvancedMetallicMaterials,SchoolofMaterialsScienceandEngineering,SoutheastUniversity,Nanjing211189,China.Fax:[phone].E-mailaddress:[e-mail](J.Wang).CARBON48(2010)352–358availableat[4].Inthiswork,thekineticsofpyrolysisreactionofPFresinwasstudiedbythethermo-gravimetricanalysis(TGA)technique.Differentialofthermo-gravimetry(DNG)curvewasseparatedintothreemajorpeaks.Andthenthekineticparametersofthermaldecompositionwerecalculatedbyemployingmode-freemethodsandthereactionmodelsweredeterminedbymeansoflinearregres-sion.Especially,36commonmechanismfunctionswereof-feredtoestimatetheprobablemechanisminordertodecreasetheerrorderivedfromthechoiceofreactionmodel.2.ExperimentalThePFresinwiththermosettingpropertywasprovidedbyTianjinDayingResinCompany,anditstradenumberis213#.Theviscosityoftheresinis0.8–1.53Pas,whichisdeter-minedbyrotaryviscosimeterat293K.Thecontentoffreephenolwaslessthan21%.Andthesolidcontentwas80±3%.ThePFresinwasgelledat370K,andthentheSam-plesabout10mgmasswereloadedrespectivelyintoacruci-bleprotectedbynitrogenwithaflowof25cm3min1.TGAcurveswererecordedinaderivatographsystemSDTQ600(TAInc.,USA)ataconstantlinearheatingrateof5,7,10,15and20Kmin1from363to1100K.BasedontheresultofTGA,thedifferentialofthermogravimetric(DTG)curveswereplottedusingoriginsoftware.3.Theoreticalbackground3.1.ThekineticparametersThekineticanalysisfromtheTGAwascarriedoutusingtheconversionrateaaccordingtotheformula:a¼mimsmimf;ð1Þwheremi,mfandmsarethemassatintial,finalandmoments,respectively.Generally,thepyrolysisprocesscanbeas-sumedasfollows[9–14]:da=dt¼kðTÞfðaÞ:ð2ÞAccordingtotheArrheniusequation,thetemperaturedependenceoftherateconstantkfortheprocessiswrit