第2章-聚合物燃烧与成炭.ppt

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1、第第2章章-聚合物燃烧与聚合物燃烧与成炭成炭北京理工大学北京理工大学第2章 聚合物燃烧与成炭1、聚合物燃烧的必要条件？2、隔间内材料燃烧的过程？3、理解点燃、点燃温度、点燃时间、轰燃、火焰传播等与燃烧有关的概念。4、为什么要了解聚合物的热分解机理？5、学习利用聚合物热分解机理解释聚合物或阻燃聚合物的燃烧行为。6、聚合物燃烧的模式？7、影响聚合物产烟量的因素有哪些？8、常见聚合物烟密度大小的规律如何？9、抑制聚合物燃烧产烟的途径有哪些？10、如何促进燃烧条件下聚合物材料表面炭层的形成？北京理工大学北京理工大学2.1 概概 论论 By preventing fire outbreak or By

2、delaying ignition and flame spread in the developing fire By interrupting the combustion processFire Scenario北京理工大学北京理工大学2.1 概概 论论北京理工大学北京理工大学2.1 概概 论论点燃（点燃（ignition）：）：燃烧作用开始（亦称引燃）。燃烧作用开始（亦称引燃）。点燃温度（点燃温度（ignition temperature）：）：使材料使材料 能开始持续燃烧的最低温度。能开始持续燃烧的最低温度。点燃时间（点燃时间（ignition time）：）：点燃材料，并使材料能开

3、始持续燃烧的最短时间。点燃材料，并使材料能开始持续燃烧的最短时间。轰燃（轰燃（flashover）：）：一隔间内的可燃材料发生火灾时，所有可燃物表面全部卷入一隔间内的可燃材料发生火灾时，所有可燃物表面全部卷入的迅变状态。的迅变状态。北京理工大学北京理工大学2.1 概概 论论Ignition When a material surface is exposed to heat flux from its own flame and/or from internal or external heat sources,vapors are generated,the process being de

4、fined as pyrolysis.The vapors combine with air to form a flammable vapor-air mixture.The mixture may auto-ignite or be ignited by heat sources that may be present,such as a pilot flame,spark,hot objects,and others.The process is defined as ignition.Fire propagation and fire propagation rate As a res

5、ult of the heat flux exposure,the pyrolysis boundary or front is formed and moves across the surface of the material.The movement of the pyrolysis front across the surface is defined as fire propagation and its rate as the fire propagation rate.北京理工大学北京理工大学2.1 概概 论论为什么要了解燃烧及其过程？为什么要了解燃烧及其过程？Combusti

6、on Exothermic reaction of a substance with an oxidizer,generally accompanied by flames and/or glowing and/or emission of smoke.Fire a)A process of combustion characterized by the emission of heat accompanied by smoke and/or flame b)Rapid combustion spreading uncontrolled in time and space.Fire behav

7、iour All the physical and/or chemical changes that take place when a material,product and/or structure is exposed to an uncontrolled fire.北京理工大学北京理工大学2.1 概概 论论 加热 分解/裂解 被点燃 引发可燃材料燃烧有三个必要环节：北京理工大学北京理工大学2.1 概概 论论燃料燃料氧气氧气热量热量火三角火三角 火的出现需要燃料、氧气和热，以及热的反馈。燃料、火的出现需要燃料、氧气和热，以及热的反馈。燃料、氧气和热氧气和热（三要素）形成了火三角（三要素

8、）形成了火三角（Fire Triangle）。）。per unit floor area.Fire load density:the amount of combustible material in heat content Oxygen in the air is controlled by the volume of space,window areas and ventilation arrangements Heat initially has to come from sources such as gas cooker,electrical fault,lit cigarette

9、,etc.北京理工大学北京理工大学2.1 概概 论论北京理工大学北京理工大学为什么要了解聚合物的热降解过程与机理？为什么要了解聚合物的热降解过程与机理？The Importance of Thermal Degradation of Polymers Polymer degradation during heating or combustion is of considerable importance on understanding and possibly prediction fuel production and fire behavior.The efficiency of ma

10、tching the decomposition temperature of the flammable substrate and the FRs is one of the main keys to good flame retardancy.The changes in degradation pathway of the polymers in the presence of FRs is a important aspect of the modification in the fire retardancy.2.2 聚合物热降解过程及机理聚合物热降解过程及机理 了解聚合物燃烧行为

11、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.Thermal decomposition：a process of extensive chemical species change caused by heatThermal degradation：a process whereby the action of heat or elevated temperature on a material,product,or assembly causes a loss of physical,mechanical,or electrical properties2.2 聚合物热分解过程及

12、机理聚合物热分解过程及机理北京理工大学北京理工大学What have differences between thermal decomposition and thermal degradation?北京理工大学北京理工大学热分解反应分类：热分解反应分类：（1）随机断裂随机断裂（2）链端断裂）链端断裂（3）消除反应）消除反应（4）环化反应）环化反应（5）交联反应）交联反应DepolymerizationSubstituent reactionsIn which bonds are created between polymer chains 2.2 聚合物热分解过程及机理聚合物热分解过程及机

13、理北京理工大学北京理工大学2.2 聚合物热分解过程及机理聚合物热分解过程及机理 Breaking of the main polymer chain backbone At any intermediate stage the products are similar to the parent material(the monomer units)The ultimate product may be monomer or volatile chain fragments 随机断裂随机断裂：Pn Rr+Rn-r (randon-chain scission)链端断裂链端断裂：Pn Rn+RE

14、 (end-chain scission)Depolymerization北京理工大学北京理工大学2.2 聚合物热分解过程及机理聚合物热分解过程及机理（1）Polyethylene（Random-chain scission）Very little monomer formation A large number of different small molecules,mostly hydrocarbons Propene and 1-hexene are the most abundantFig.Intramolecular transfer processes PE begins to

15、decompose at 292(inert atmosphere,reductions in molecular weight),although extensive weight loss is not observed below 372.Piloted ignition of PE due to radiative heating has been observed at a surface temperature of 367.Products:propane,propene,ethane,ethene,butane,butene-1 and hexane-1.北京理工大学北京理工大

16、学2.1 聚合物热分解过程及机理聚合物热分解过程及机理（2）Polypropylene（Random-chain scission）Reductions in molecular weight are first observed at 227 to 247 and volatilization becomes significant above 302.Piloted ignition of PP due to radiative heating has been observed at a surface temperature of 337.Products:pentane(24%),2

17、methyl-1-pentene(15%),and 2-4 dimethyl-1-heptene(19%).北京理工大学北京理工大学2.2 聚合物热分解过程及机理聚合物热分解过程及机理北京理工大学北京理工大学2.2 聚合物热分解过程及机理聚合物热分解过程及机理PP,PP/IFR 和PP/IFR/sepiolite(1%)样品的热失重曲线TG curves of the PP,PP/IFR,and PP/IFR/sepiolite(1%)compositesPP在氮气、空气气氛中热分解行为如何？在氮气、空气气氛中热分解行为如何？北京理工大学北京理工大学2.2 聚合物热分解过程及机理聚合物热分解过

18、程及机理（3）Polystyrene（End/Random-chain scission）monomer(approximately 40%)smaller amounts of benzene and toluenedimer,trimer,tetramer and pentamerFig.Intramolecular transfer processes PSPS较较PE,PPPE,PP燃烧时的产烟量大燃烧时的产烟量大,为什么为什么?北京理工大学北京理工大学2.2 聚合物热分解过程及机理聚合物热分解过程及机理Fig.Thermal degradation mechanism of PMMA

19、（4）Poly(methyl methacrylate)（End-chain scission）monomer is the only product北京理工大学北京理工大学2.2 聚合物热分解过程及机理聚合物热分解过程及机理 the substituents attached to the backbone of the polymer are involved the chemical nature of the repeat unit is changed although the chain structure may remain intact volatile products,i

20、f they are produced,will be quite unlike monomerSubstituent Reactions北京理工大学北京理工大学2.2 聚合物热分解过程及机理聚合物热分解过程及机理Fig.The radical mechanisms（5）Poly(vinyl chloride)（chain stripping,substituent elimination）北京理工大学北京理工大学2.2 聚合物热分解过程及机理聚合物热分解过程及机理 Fig.Molecular elimination-a cyclic transition state 北京理工大学北京理工大学

21、2.2 聚合物热分解过程及机理聚合物热分解过程及机理Fig.Cyclization reactions of PAN small amounts of ammonia,hydrogen cyanidecyclization reactions involving the creation of linkages between nitrogen and carbon on adjacent side groups（6）PolyacrylonitrileCyclization reactions北京理工大学北京理工大学2.2 聚合物热降解过程及机理聚合物热降解过程及机理AbstractThe c

22、hange in the degradation pathway of a polymer by incorporation of clay has a significant effect on the fire retardancy of polymer/clay nanocomposites.Since the clay layers act as a barrier to mass transport and lead to superheated conditions in the condensed phase,extensive random scission of the pr

23、oducts formed by radical recombination is an additional degradation pathway of polymers in the presence of clay.The polymers that show good fire retardancy upon nanocomposite formation exhibitRef:Jang B N,Costache M,Wilkie C A.Polymer,2005,46:10678-10687.The relationship between thermal degradation

24、behavior of polymer and the fire retardancy of polymer/clay nanocompositesExample-1北京理工大学北京理工大学2.2 聚合物热降解过程及机理聚合物热降解过程及机理significant intermolecular reactions,such as inter-chainaminolysis/acidolysis,radical recombination and hydrogen abstraction.In the case of the polymers that degrade through a rad

25、ical pathway,the relative stability of the radical is the most important factor for the prediction of the effect that nanocomposite formation has on the reduction in the peak heat release rate.The more stable is the radical produced by the polymer,the better is the fire retardancy,as measured by the

26、 reduction in the peak heat release rate,of the polymer/clay nanocomposite.北京理工大学北京理工大学2.2 聚合物热降解过程及机理聚合物热降解过程及机理For polyamide 6(PA6),polystyrene(PS)andpoly(ethylene-co-vinyl acetate)(EVA)nanocomposites,alarge reduction in peak heat release rate,about 60%,is obtained.In the cases of poly(styrene-co-

27、acrylonitrile)(SAN)andacrylonitrile-butadiene-styrene terpolymer(ABS),the claynanocomposites show a moderate reduction in PHRR(around40%).On the other hand,poly(methyl methacrylate)(PMMA)/clay nanocomposites do not exhibit any changes in the evolvedproducts upon incorporation of clay,and the fireret

28、ardancy of PMMA/clay nanocomposites is not significantlyimproved.北京理工大学北京理工大学材料科学与工程学院材料科学与工程学院2.2 聚合物热分解过程及机理聚合物热分解过程及机理Thermal degradation of some polymer and polymer clay nanocomposite and resulting reduction in peak heat release rate北京理工大学北京理工大学材料科学与工程学院材料科学与工程学院2.2 聚合物热分解过程及机理聚合物热分解过程及机理Listing

29、 of the polymer,radical produced from the polymer,bond dissociation energies(kJ/mol)and stabilization energies of the radicalsa CC BDE is carboncarbon bond dissociation energy,CH BDE is carbonhydrogen bond dissociation energy and SE is stabilization energy of radical.北京理工大学北京理工大学Ref:S V Levchik,L Co

30、ata,G Camino.Effect of Ammonium Polyphosphate on Combustion and Thermal Degradation of Aliphatic Polyamides.Makromol.Chem.,Macromol.Symp.1993,74:95-99 Polyamide（Intra-aminolysis/acidolysis,random scission）Example-22.2 聚合物热分解过程及机理聚合物热分解过程及机理北京理工大学北京理工大学 APP添加质量分数对各种脂肪聚酰胺LOI的影响 PA66,PA11,PA12,PA610,PA

31、6 为什么为什么PA66的的LOI更高？更高？为什么为什么10%质量分数的质量分数的APP可使可使PA66的的LOI有显著上升？有显著上升？PA6需要添加需要添加30%质量分数质量分数的的APP，LOI才有明显的上升才有明显的上升？LOI显著增加时所需APP添加量的顺序：PA66(10%APP)PA11(20%APP),PA12(20%APP),PA610(20%APP)PA6(30%APP)2.2 聚合物热分解过程及机理聚合物热分解过程及机理北京理工大学北京理工大学PA6，PA66的热失重数据聚合物聚合物T5%/T10%/DTG峰峰值值/T max/(%/)/C.R.550/%PA63834

32、07-/4552.6PA664014211.90/4606.6注：T5%，T10%：材料失重5%，10%时的温度，将T5%定义为分解温度；T max：峰值对应的温度；C.R.550：550时材料的固体残余百分比。PA66的TGA/DTG曲线2.2 聚合物热分解过程及机理聚合物热分解过程及机理北京理工大学北京理工大学 脂肪聚酰胺在氮气保护下加热（脂肪聚酰胺在氮气保护下加热（10/min），在），在300 500范围内分解。范围内分解。PA66较其他较其他PA存在更强烈的分子内氢键，主要是通过互变存在更强烈的分子内氢键，主要是通过互变异构按异构按方式方式2进行热分解，导致有覆盖作用的进行热分解，导

33、致有覆盖作用的CO2及及碳化二亚胺碳化二亚胺产生，而碳化二亚胺可通过三聚形成耐热的三嗪环。产生，而碳化二亚胺可通过三聚形成耐热的三嗪环。PA6倾向于按倾向于按方式方式1进行热分解，产物以进行热分解，产物以己内酰胺己内酰胺为主。因为主。因此，此，PA66较较PA6和其他和其他PA的基础的基础LOI要高。同时也将强烈影响要高。同时也将强烈影响阻燃阻燃PA的效果及机理。的效果及机理。2.2 聚合物热分解过程及机理聚合物热分解过程及机理北京理工大学北京理工大学The major effect of APP was shown to be the decrease of temperature of t

34、hermal decomposition of APA(aliphatic polyamides).Thus the fire retardant action of APP might be the combined result of a lower temperature on the surface of the burning polymer and of the formation of viscous intumescent layer of polyphosphoric acid on it.The higher oxygen index of PA66 in comparis

35、on with the other APA might be related to its additional specific route of degradation through scission of CH2-C(=O)-bond.Evolution of blanketing CO2 and formation of thermal resistant carbodiimide structures2.2 聚合物热分解过程及机理聚合物热分解过程及机理北京理工大学北京理工大学which are the peculiarities of this route may reduce t

36、he flammability of PA66.The larger fire retardant effect of APP on PA66,as compared to the other APA,could be due to its ability to shift the competition between degradation reactions of PA66 towards this same route.The larger yield of carbodiimde structures leads to the formation of even more therm

37、al stable triazine rings.2.2 聚合物热分解过程及机理聚合物热分解过程及机理北京理工大学北京理工大学2.2 聚合物热分解过程及机理聚合物热分解过程及机理 The apparent activation energy decreases considerably(120-160 kJ/mol,0.5)in the presence of APP,indicating that an ionic or molecular mechanism of degradation is likely to be activated by APP.Relatively high ap

38、parent activation energies which are generally observed for the major degradation step of the APA(E=160-220 kJ/mol,0.5)are in favour of a free radical mechanism for their thermal degradation.北京理工大学北京理工大学2.2 聚合物热分解过程及机理聚合物热分解过程及机理The activation energy calculated from TG data using Ozawa method on the

39、 degree of decomposition,=(W0-W)/(W0-W550)where W is the actual weight,W0 is the initial weight,W550 is the residual weight at 550.Ref:T Ozawa,Bull.Chem.Soc.Jap.38,1881(1965)What Happens When Something Burns?The simplest example of a combustion process is the burning of methane.CH4+O2 CO2+H2OBut eve

40、n this simple combustion involves many free-radical production steps:北京理工大学北京理工大学2.3 聚合物燃烧的化学反应聚合物燃烧的化学反应 Propagation steps that produce free radicals keep the burning going;CH4+HO CH3+H2O CH4+H CH3+H2 CH3+O CH2O+H CH2O+HO CHO+H2O CH2O+H CHO+H2 CHO CO+H CO+HO CO2+H北京理工大学北京理工大学2.3 聚合物燃烧的化学反应聚合物燃烧的化学反

41、应 Chain-branching steps produce two free radicals,accelerating the reaction with explosive force;H+O2 HO+O Termination steps occur when radicals are removed,quenching combustion.H+R+M RH+MWhere R is any organic radical and M is any surface.Heat is transferred to the surface,producing higher energy M

42、.The flame-carrying radicals H,HO,O,occur in all flames,whether in methane or in polymers.北京理工大学北京理工大学2.3 聚合物燃烧的化学反应聚合物燃烧的化学反应北京理工大学北京理工大学2.3 聚合物燃烧的化学反应聚合物燃烧的化学反应 Solid phase inhibition involves changes in the polymer substrate.Systems that promote extensive cross-linking at the surface,form a carbo

43、naceous char upon heating.Char insulate the underlying polymer from the heat of the flame,preventing production of new fuel and further burning.Other systems evolve water during heating,cooling the surface and increasing the amount of energy needed to maintain the flame.燃烧反应的控制燃烧反应的控制北京理工大学北京理工大学2.3

44、 聚合物燃烧的化学反应聚合物燃烧的化学反应举例：举例：PP+IFR（APP-based additive）+TiO2TiOTiO2 2对对PP/APPPP/APP复合膨胀阻燃体系固相交联成炭的影响复合膨胀阻燃体系固相交联成炭的影响北京理工大学北京理工大学2.3 聚合物燃烧的化学反应聚合物燃烧的化学反应CONECONE测试测试TPPTPP阻燃阻燃PC/ABSPC/ABS（8:18:1质量比）体系膨胀炭层照片质量比）体系膨胀炭层照片 TPPTPP阻燃阻燃PC/ABSPC/ABS（8:18:1质量比）体系质量比）体系锥型量热仪（锥型量热仪（CONECONE）测试）测试 膨胀炭层高度达到膨胀炭层高度达

45、到10.2cm10.2cm，有效阻隔了热、火焰及空气的进，有效阻隔了热、火焰及空气的进入，火焰很快自熄，有效地保护了下面的聚合物基材。入，火焰很快自熄，有效地保护了下面的聚合物基材。北京理工大学北京理工大学2.3 聚合物燃烧的化学反应聚合物燃烧的化学反应 Vapor gas inhibition involves changes in the concentration of free radical HO and H Reactive species are built into the polymer which are transformed into volatile free-rad

46、ical inhibitors during burning.These materials diffuse into the flame and inhibit the branching radical reaction.As a result,increased energy is required to maintain the flame and the cycle is interrupted.Of course,for many materials both solid and vapor phase inhibition are involved.北京理工大学北京理工大学 Fl

47、aming Mode Non-flaming Mode Chemical reaction Chemical reactionin gases phase in condensed phase Smouldering combustion and Glowing combustion2.4 聚合物燃烧模式和特点聚合物燃烧模式和特点Combustion Modes北京理工大学北京理工大学2.4 聚合物燃烧模式和特点聚合物燃烧模式和特点Smouldering combustion statistics in real fire about 75%,lethal rate 50%;being abl

48、e to cause burning through smoke;can occur at the beginning of burning;a big volume of CO produced converted further to burning.北京理工大学北京理工大学2.4 聚合物燃烧模式和特点聚合物燃烧模式和特点Glowing combustion taking place after the formation of char;taking place at the surface/interface;accompanied by light colour;in the pre

49、sence of metallic,non-metallic elements(Mg,Al,Li,Na,K,Ti,Zr,U,Pu,Zn,P,B,etc.)The combustion temperature displays higher than the combustible gases and liquid.北京理工大学北京理工大学2.5 烟的形成及抑制烟的形成及抑制 Consisting of a dispersion of solid(carbon flakes,soot beads,ash,sublimed pyrolysis products,oxides of inorgani

50、c compounds)or liquid(sublimed pyrolysis products)particles in a carrier gas(combustion gas and air)Varying in diameter from 0.0020.5m What is Somke？北京理工大学北京理工大学 thermalPhase 1:polymer simple fuel(polymer fragments and degradation pyrolysis products)Phase 2:simple fuel reactive aromatic smoke nuclei