聚合物燃烧与成炭

,北京理工大学,第2章聚合物燃烧与成炭,2.1聚合物热降解过程及机理2.2聚合物燃烧化学反应及控制2.3聚合物燃烧模式和特点2.4聚合物热分解成炭2.5聚合物燃烧性能分类2.6促进聚合物成炭的途径2.7热行为研究及炭的表征2.8烟的形成及抑制,北京理工大学,为什么要了解聚合物的热降解过程与机理？,TheImportanceofThermalDegradationofPolymersPolymerdegradationduringheatingorcombustionisofconsiderableimportanceonunderstandingandpossiblypredictionfuelproductionandfirebehavior.TheefficiencyofmatchingthedecompositiontemperatureoftheflammablesubstrateandtheFRsisoneofthemainkeystogoodflameretardancy.ThechangesindegradationpathwayofthepolymersinthepresenceofFRsisaimportantaspectofthemodificationinthefireretardancy.,2.1聚合物热降解过程及机理,了解聚合物燃烧行为及产物；阻燃剂的选择及配方设计；指导新型阻燃材料的研究.,北京理工大学,2.1聚合物热降解过程及机理,参考文献：JangBN,CostacheM,WilkieCA.Therelationshipbetweenthermaldegradationbehaviorofpolymerandthefireretardancyofpolymer/claynaocompositesJ.Polymer,2005,46:10678-10687.Thechangesindegradationpathwayofthesepolymershaveelucidatedandthecommonfactoristhatinter-chainreactions,suchasintermolecularaminolysis/acidolysis,radicalrecombinationandhydrogenabstraction,becomesignificantinthepresenceofclay.Itwassuggestedthatthenumberofdegradationpathwaysofthepolymerisoneofthefactorthatcanaffectthefireretardancyofpolymer/claynanocomposites.,Thermaldecomposition：aprocessofextensivechemicalspecieschangecausedbyheatThermaldegradation：aprocesswherebytheactionofheatorelevatedtemperatureonamaterial,product,orassemblycausesalossofphysical,mechanical,orelectricalproperties,2.1聚合物热分解过程及机理,北京理工大学,ClassificationofThermalDegradationReactionsDepolymerisationReactions(radicalandnon-radical)Fragmentation(monomer,chainfragments)SubstituentReactionsElimination,Cyclization,北京理工大学,2.1聚合物热分解过程及机理,StructuraldefectsReactiveimpurities“Special”structures(e.g.chainend,etc.）“Weaklinks”,DepolymerisationReactions(radicalandnon-radical)breakingofthemainpolymerchainbackboneatanyintermediatestagetheproductsaresimilartotheparentmaterial(themonomerunits)theultimateproductmaybemonomerorvolatilechainfragments,北京理工大学,2.1聚合物热分解过程及机理,SubstituentReactionsthesubstituentsattachedtothebackboneofthepolymerareinvolvedthechemicalnatureoftherepeatunitischangedalthoughthechainstructuremayremainintactvolatileproducts,iftheyareproduced,willbequiteunlikemonomer,北京理工大学,2.1聚合物热分解过程及机理,（1）PolyolefinsOfthepolyolefins,low-densitypolyethylene,high-densitypolyethylene,andpolypropyleneareofthegreatestcommercialimportancebecauseoftheirvolume.Theirusesaretoonumeroustomention,butfirepropertiesarecriticalwhenusedforelectricalwireandcable-coatingapplications.Uponthermaldecomposition,verylittlemonomerformationisobservedforanyofthesepolymers;theyformalargenumberofdifferentsmallmolecules,mostlyhydrocarbons.Thermalstabilityofpolyolefinsisstronglyaffectedbybranching,withlinearpolyethylenemoststableandpolymerswithbranchinglessstable.,ThermalDegradationBehaviorofSomePolymers,北京理工大学,2.1聚合物热分解过程及机理,Polyethylene（Random-chainscission）PEbeginstodecomposeat292(inertatmosphere,reductionsinmolecularweight),althoughextensiveweightlossisnotobservedbelow372.PilotedignitionofPEduetoradiativeheatinghasbeenobservedatasurfacetemperatureof367.Products:propane,propene,ethane,ethene,butane,butene-1andhexane-1.,北京理工大学,2.1聚合物热分解过程及机理,Fig.Intramoleculartransferprocesses,北京理工大学,2.1聚合物热分解过程及机理,Polypropylene（Random-chainscission）PP：reductionsinmolecularweightarefirstobservedat227to247andvolatilizationbecomessignificantabove302.PilotedignitionofPPduetoradiativeheatinghasbeenobservedatasurfacetemperatureof337.Products:pentane(24%),2methyl-1-pentene(15%),and2-4dimethyl-1-heptene(19%).,北京理工大学,2.1聚合物热分解过程及机理,Polystyrene（End-chainscission,R）Monomer(approximately40%)istheprincipalvolatileproductwithverymuchsmalleramountsofbenzeneandtoluene.,北京理工大学,2.1聚合物热分解过程及机理,PSshowsnoappreciableweightlossbelow302althoughthereisadecreaseinmolecularweightduetoscissionof“weak”links.Abovethistemperature,theproductsareprincipallymonomerwithdecreasingamountsofdimmer,trimer,tetramerandpentamer.Theseoligomersareformedinintramoleculartransferreactions,whichareindirectcompetitionwiththemonomer-producingdepolymerisationprocess.,北京理工大学,2.1聚合物热分解过程及机理,Polymethylmethacrylate（End-chainscission）PMMAisafavoritematerialforuseinfireresearchbecauseitdecomposesalmostsolelytomonomerandburnsataverysteadyrate.Methylgroupseffectivelyblockintramolecularhydrogentransfer,leadingtoahighmonomeryield.Ithasbeenshownthatdepolymerisationisaradicalchainreactionandthatdegradationintheregionof300-400isassociatedwithinitiationbybothend-chainandrandom-chaininitiationprocesses.,北京理工大学,2.1聚合物热分解过程及机理,Fig.ThermaldegradationmechanismofPMMA,北京理工大学,2.1聚合物热分解过程及机理,Poly(vinylchloride)（chainstripping,substituentelimination）Theradicalmechanisms:Initiationinvolvesliberationofchorineatomfromalabilecentre.,北京理工大学,2.1聚合物热分解过程及机理,MoleculareliminationofHClisproceededbyacyclictransitionstate,北京理工大学,2.1聚合物热分解过程及机理,ThethermaldegradationofPVCinvolvestheeliminationofHClandleadstotheformationofmacromolecularresidueswithpolyenesequences.Thelatterthenrearrangeanddecomposetoyieldsizeableamountsofaromatichydrocarbons(toluene,methylnaphthalene,etc.)Aromaticcompounds(benzene,naphthalene,anthracene)areproducedsimultaneouslywithHClinthefirstdecompositionstage.,北京理工大学,2.1聚合物热分解过程及机理,引发聚合物燃烧有三个必要环节：加热分解/裂解被点燃,北京理工大学,2.2聚合物燃烧化学反应及控制,北京理工大学,2.2聚合物燃烧化学反应及控制,发,BypreventingfireoutbreakorBydelayingignitionandflamespreadinthedevelopingfireByinterruptingthecombustionprocess,北京理工大学,2.2聚合物燃烧化学反应及控制,Ignitiontemperature:Thelowesttemperatureofacombustiblematerialatwhichsustainedcombustioncanbeinitiated,i.e.heatlostheatgainedFlashover:Therapidtransitiontoastateoftotalsurfaceinvolvementinafireofcombustiblematerialswithinanenclosure,北京理工大学,2.2聚合物燃烧化学反应及控制,WhatHappensWhenSomethingBurns?Thesimplestexampleofacombustionprocessistheburningofmethane.CH4+O2CO2+H2OButeventhissimplecombustioninvolvesmanyfree-radicalproductionsteps:,北京理工大学,2.2聚合物燃烧化学反应及控制,Propagationstepsthatproducefreeradicalskeeptheburninggoing;CH4+HOCH3+H2OCH4+HCH3+H2CH3+OCH2O+HCH2O+HOCHO+H2OCH2O+HCHO+H2CHOCO+HCO+HOCO2+H,北京理工大学,2.2聚合物燃烧化学反应及控制,Chain-branchingstepsproducetwofreeradicals,acceleratingthereactionwithexplosiveforce;H+O2HO+OTerminationstepsoccurwhenradicalsareremoved,quenchingcombustion.H+R+MRH+MWhereRisanyorganicradicalandMisanysurface.Heatistransferredtothesurface,producinghigherenergyM.Theflame-carryingradicalsH,HO,O,occurinallflames,whetherinmethaneorinpolymers.,北京理工大学,2.2聚合物燃烧化学反应及控制,Twowaystointerruptthecycle:Solidphaseinhibitioninvolveschangesinthepolymersubstrate.Systemsthatpromoteextensivecross-linkingatthesurface,formacarbonaceouscharuponheating.Charinsulatetheunderlyingpolymerfromtheheatoftheflame,preventingproductionofnewfuelandfurtherburning.Othersystemsevolvewaterduringheating,coolingthesurfaceandincreasingtheamountofenergyneededtomaintaintheflame.,北京理工大学,2.2聚合物燃烧化学反应及控制,VaporgasinhibitioninvolveschangesintheconcentrationoffreeradicalHOandH.Reactivespeciesarebuiltintothepolymerwhicharetransformedintovolatilefree-radicalinhibitorsduringburning.Thesematerialsdiffuseintotheflameandinhibitthebranchingradicalreaction.Asaresult,increasedenergyisrequiredtomaintaintheflameandthecycleisinterrupted.Ofcourse,formanymaterialsbothsolidandvaporphaseinhibitionareinvolved.,北京理工大学,2.2聚合物燃烧化学反应及控制,CombustionModesFlamingModeNon-flamingModeChemicalreactionChemicalreactioningasesphaseincondensedphaseSmoulderingcombustionandGlowingcombustion,北京理工大学,2.3聚合物燃烧模式和特点,Smoulderingcombustionstatisticsinrealfireabout75%,lethalrate50%;beingabletocauseburningthroughsmoke;canoccuratthebeginningofburning;abigvolumeofCOproducedconvertedfurthertoburning.,北京理工大学,2.3聚合物燃烧模式和特点,Glowingcombustiontakingplaceaftertheformationofchar;takingplaceatthesurface/interface;accompaniedbylightcolour;inthepresenceofmetallic,non-metallicelements(Mg,Al,Li,Na,K,Ti,Zr,U,Pu,Zn,P,B,etc.)Thecombustiontemperaturedisplayshigherthanthecombustiblegasesandliquid.,北京理工大学,2.3聚合物燃烧模式和特点,Table2-1PolymersandFlammabilityClassification,北京理工大学,2.4聚合物燃烧性能分类,2.4聚合物燃烧性能分类,Thefirstgroupconsistsofrelativelyflameretardantstructurescontainingeitherhighhalogen,oraromaticgroupsthatconferhighthermalstabilityaswellastheabilitytoformcharonburning.Secondarethelessflameretardantmaterials,manyofwhichcanbemademoreflameretardantbyappropriatechemistry.Thethirdclassconsistsofquiteflammablepolymerswhicharemoredifficulttomakeflameretardantbecausetheydecomposereadily,forminglargequantitiesoffuel,butthesecanbemadeappropriatelyflameretardantforparticularapplicationsbytheadditionofadditives.,北京理工大学,Hightemperaturematerialsareintrinsicallyflameretardant;Therearethreegeneraltypesofstructures:(1)linearsingle-strandpolymer;(2)ladderpolymersconsistingofanuninterruptedsequenceofcyclicaromaticorheterocyclicstructures;(3)andspiropolymersinwhichonecarboniscommontotworings.Polymerwithhigharomaticcharacterandverystrongconnectinglinkagesbetweenringsproducemorecharonheating,retainingmostofthepotentialfueloftheoriginalpolymerasresidue;Inpractice,thechoiceofapolymerdependsoncostandontheimportanceofflameretardancyinrelationtoitsfinaluse.,北京理工大学,2.4聚合物燃烧性能分类,2.5聚合物分解成炭,FormationofChar燃烧的聚合物表面温度接近300-600时，强烈的热降解发生。该温度也是炭层底部靠近聚合物表面的温度。而炭层的外表面与火焰接触，其温度可达1500。因此，炭形成的温度是在300-1500之间。,北京理工大学,Apolymerpassesthroughseveralstepsintheformationofchar:交联（cross-linking）芳香化（aromatization）稠环芳香化（fusionofaromatics）涡流层状炭（turbostraticcharformation）石墨化（graphitization）,北京理工大学,2.5聚合物分解成炭,TheRoleofCharCharformationmaylimittheamountoffuelavailable.Whenanadherentandinsulatinglayerofcharisbuiltuponthesurfaceofapolymer,thislayermayinsulatetheunderlyingpolymerfromtheflameand,thus,makefurtherdegradationmoredifficult.,北京理工大学,2.5聚合物分解成炭,什么是炭？聚合物燃烧表面所产生的炭，其化学及物理结构决定了炭的阻燃作用。炭是复杂的不溶混合物，是由许多芳香-脂肪化合物及杂原子（O、N、P）组成。从微观形貌看，炭有结晶和非晶区。炭具有一些物理性质，如热传导、导电性、对辐射的反射和吸收等；炭也有一些机械性能，如完整性、硬度、塑性等。,北京理工大学,2.5聚合物分解成炭,Non-charableorcharablepolymersthatundergochainscissionandvolatilizewith,atmost,anegligibleamountofthecharformation,e.g.,PE,PP,PS,PMMA;polymersthatundergochainstrippingreactions,producingunsaturationinthemainchainwithlossofhydrogenatomsandthependantgroupsandgiveamoderateamountofchar,e.g.PVC,PVA,PAN;polymersthatcontainaromaticringsthatcancross-linksimultaneouslywithchainscissionreactionsandproducemoderatetohighamountsofchar,e.g.,aromaticpolyamides,polyesters,polycarbonates,polyimides.,北京理工大学,2.5聚合物分解成炭,Char-formingpolymersBisphenolA-polycarbonate,北京理工大学,2.5聚合物分解成炭,北京理工大学,2.5聚合物分解成炭,CO2,BisphenolA-polycarbonate450开始热降解；25%残炭稳定到650；TGA曲线形状由以下过程构成：polymervolatilespolymercross-linkingcharcharvolatilesMainProductsofDegradation:35%carbondioxide,bisphenolAandphenol,北京理工大学,2.5聚合物分解成炭,PA6、PA66（Doyourself）PieterGijsmanetal.Differencesintheflameretardantmechanismofmelaminecyanurateinpolyamide6andpolyamide66J.PolymerDegradationandStability，2002,78:219-224.,北京理工大学,2.5聚合物分解成炭,PolymersthatnaturallyProduceChar在一定条件下，甚至脂肪烃的碳氢聚合物都能够产生一些炭。碳氢聚合物中C-C键离解能（dissociationenergy）为65-90kcal/mol，而C-H键的离解能为90-105kcal/mol。两者能量接近，因此高温下随着链的断裂可以脱氢：,北京理工大学,2.6促进聚合物成炭的途径,烯丙基链端上的H是活泼的，其C-H键离解能为85kcal/mol，因此可以导致脱氢，形成共轭双烯（conjugateddienes）。双烯可与活泼双键反应并进一步形成芳环：,北京理工大学,2.6促进聚合物成炭的途径,双烯还可进一步脱氢形成三烯进而环化：,北京理工大学,2.6促进聚合物成炭的途径,PolyacrylonitrilePAN在迅速加热的条件下，如燃烧条件下，产生碎片及挥发产物。放慢加热速度，250-350下侧基分子内反应发生，导致环状多胺（polyamine）结构生成。这种环状多胺结构对于较高温度下的成炭是十分有利的。,北京理工大学,2.6促进聚合物成炭的途径,接枝促进聚合物热降解成炭参考文献：电子束辐射接枝EVA共聚物薄膜阻燃性能的研究与表征J，科学通报,1997,42（20):2167-2171氧化还原反应促进成炭Cu2O和MoO3对PVC阻燃抑烟的作用,北京理工大学,2.6促进聚合物成炭的途径,添加剂促进成炭（Additivesthatpromotecharformation）APB(AmmoniumpentaborateNH4B5O84H2O)isaneffectivecharpromoterinPUthermoplastics.Asinthecaseofcellulose,bothphysicalandchemicalfactorshelptoincreasecharinpolyurethanes(e.g.,boricacid,whichevolvesuponthermaldecompositionofAPB,reactwithalcoholsproducingborateestersorwithisocyanuratesproducingborateamides).Boththeestersandamidesserveashighlycross-linkedcharprecursors.APBisalsofoundtobesomewhateffectiveinnaturalrubber,polyesterresin,PVC,andpolyamide-66.Thefollowingfigureillustratesthechar-promotingtendencyofAPBinPA-66.Theadditionof25partsperhundredofPA-66leadstotheconversionof28%ofPA-66intononvolatileresidue.,北京理工大学,2.6促进聚合物成炭的途径,北京理工大学,2.6促进聚合物成炭的途径,热行为研究手段：热失重分析（TGA，ThermogravimetricAnalysis）微分热失重分析（DTG，DifferentialThermogravimetricAnalysis）差热分析（DTA，DifferentialThermalAnalysis）差热扫描量热分析（DSC，DifferentialScanningCalorimetry）热机械分析（TMA，ThermomechanicalAnalysis）热挥发分析（TVA，ThermalVolatilizationAnalysis）裂解气相色谱（PGC，PyrolysisGasChromatography）色质联用（GC-MS，GasChromatography-MassSpectrometry）,北京理工大学,2.7热行为研究及炭的表征,炭的结构表征傅立叶红外光谱法拉曼光谱法核磁共振波谱法X-射线光电子能谱法元素分析扫描电镜等,北京理工大学,2.7热行为研究及炭的表征,（1）一些聚合物燃烧发烟的数据聚合物燃烧过程中生烟量是不同的聚合物发烟来自于不完全燃烧；聚合物的产烟量除与结构因素有关外，还与燃烧模式（无焰燃烧还是有焰燃烧）样品尺寸、样品位置、通风与否、热通量等有关。文献报导的烟的数据应客观看待，因数据出自不同的标准和不同的测试设备。,北京理工大学,2.8烟的形成及抑制,Table.2-2SmokeChamberResultsforVariousMaterials（Rohm&HaasXP-2Chamber（ASTMD-2843）,北京理工大学,2.8烟的形成及抑制,Table2-3SomeexamplestakenfromHiladobook（ASTME-662）,北京理工大学,2.8烟的形成及抑制,（2）烟的组成Consistingofadispersionofsolid(carbonflakes,sootbeads,ash,sublimedpyrolysisproducts,oxidesofinorganiccompounds)orliquid(sublimedpyrolysisproducts)particlesinacarriergas(combustiongasandair).Varyingindiameterfrom0.002-0.5m.,北京理工大学,2.8烟的形成及抑制,Fig.Polymerpyrolysis,burningandsmokeevolution,北京理工大学,2.8烟的形成及抑制,（3）烟的产生Pasternaketal(CombustionScienceandTechnology,1982,28:263-270)considersmokegenerationduringthecombustionofpolypropylenetofollowastepwisering-growthmechanismconsistsofthreephases:,北京理工大学,2.8烟的形成及抑制,thermalPhase1:polymersimplefuel(polymerfragmentsanddegradationpyrolysisproducts)Phase2:simplefuelreactivearomaticsmokenucleiintermediatesstablepolycyclicaromatichydrocarbonsparticulategrowthPhase3:smokenucleismokeparticlescoagulationandagglomeration,北京理工大学,2.8烟的形成及抑制,（a）Idealcharstructure(b)Poorcharstructure,Aliphaticfuelsarecrackedtosmalleralkylradicalswhichintheabsenceofoxygengrowtoformconjugatedpolyenesorpolybenzenoidswhichmayberadical,ionic,orneutral.Aromaticfuelsarethoughttoproceeddirectlytopolybenzenoidintermediates.,北京理工大学,2.8烟的形成及抑制,（4）聚合物结构对产烟的影响聚合物结构不仅影响其燃烧行为，同样也影响其烟的形成。下列一些结构因素影响聚合物的产烟量：芳香及多烯聚合物较脂肪与含氧聚合物有较大的产烟趋势；单元主链有芳环的聚合物较侧基有芳环的聚合物产烟量要低；低卤或中等水平含卤聚合物产烟量有增加的趋势，但高卤聚合物产烟量有降低的趋势；产烟量与降解生成的燃料类型有关，与聚合物的热稳定性有关。,北京理工大学,2.8烟的形成及抑制,（5）抑烟机理无机金属氢氧化物的抑烟机理无机氢氧化物能够显著降低燃烧聚合物材料的产烟量。这一现象与氧化物残渣表面吸附含碳物质，继而将其氧化为CO2有关。,北京理工大学,2.8烟的形成及抑制,Forexample:-AnEVAcopolymercontaining63%ofeitherATHormagnesiumhydroxideThesesampleswereexposedtosmolderingconditionsat440andtherelativequantitiesofCOandCO2evolvedweremeasured.TheresultsshowedthattheinorganichydroxidecontainingformulationsgeneratemoreCO2andlessCOthanthecopolymeritselfoncombustion.Theprocessisrelatedtotheefficiencyoftheresidualaluminaandmagnesiaascarbonoxidationcatalysts.,北京理工大学,2.8烟的形成及抑制,过渡金属对PVC的抑烟机理(a)LewisAcidMechanism（路易斯酸机理）TheBellLaboratoriesEdelsonandStarnesproposethatduringdehydrochlorinationofPVC,theMoO3actsasaLewisacidisomerization(异构化)catalysttofavortheformationoftrans-alkene(反式烯烃)segments.Thesetrans-polyenes（反式多烯）,whichcannotundergointramolecularcyclizationtoformbenzene,arestabletohighertemperatureswheredifferentmechanismsensuetogivealiphatic(lesssmoky)products.,北京理工大学,2.8烟的形成及抑制,北京理工大学,2.8烟的形成及抑制,(a),(b),(c),(d),TheBellreportsconsidertwopossibilitiesfortrans-polyeneformation.OneisthestraightforwardLewisacidisomerizationofcis-alkenes（顺式烯烃）intotrans-alkenes.TheotherhastheMoO3actingasaLewisacidwhichinte