1、北京理工大學(xué)第2章 聚合物燃燒與成炭2.1 聚合物熱降解過程及機(jī)理2.2 聚合物燃燒化學(xué)反應(yīng)及控制2.3 聚合物燃燒模式和特點(diǎn)2.4 聚合物熱分解成炭2.5 聚合物燃燒性能分類2.6 促進(jìn)聚合物成炭的途徑2.7 熱行為研究及炭的表征2.8 煙的形成及抑制精選課件北京理工大學(xué)為什么要了解聚合物的熱降解過程與機(jī)理？The Importance of Thermal Degradation of Polymers Polymer degradation during heating or combustion is of considerable importance on understandin

2、g and possibly prediction fuel production and fire behavior. The efficiency of matching 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 aspe

3、ct of the modification in the fire retardancy.2.1 聚合物熱降解過程及機(jī)理 了解聚合物燃燒行為及產(chǎn)物；阻燃劑的選擇及配方設(shè)計(jì)；指導(dǎo)新型阻燃材料的研究.精選課件北京理工大學(xué)2.1 聚合物熱降解過程及機(jī)理參考文獻(xiàn)：Jang B N, Costache M, Wilkie C A. The relationship between thermal degradation behavior of polymer and the fire retardancy of polymer/clay naocomposites J. Polymer, 2005,4

4、6: 10678-10687. The changes in degradation pathway of these polymers have elucidated and the common factor is that inter-chain reactions, such as intermolecular aminolysis/acidolysis, radical recombination and hydrogen abstraction, become significant in the presence of clay. It was suggested that th

5、e number of degradation pathways of the polymer is one of the factor that can affect the fire retardancy of polymer/clay nanocomposites. 精選課件Thermal decomposition： a process of extensive chemical species change caused by heatThermal degradation： a process whereby the action of heat or elevated tempe

6、rature on a material, product, or assembly causes a loss of physical, mechanical, or electrical properties2.1 聚合物熱分解過程及機(jī)理北京理工大學(xué)精選課件Classification of Thermal Degradation Reactions Depolymerisation Reactions (radical and non-radical) Fragmentation (monomer, chain fragments) Substituent Reactions Elimi

7、nation, Cyclization北京理工大學(xué)2.1 聚合物熱分解過程及機(jī)理Structural defectsReactive impurities“Special” structures (e.g. chain end, etc.）“Weak links”精選課件Depolymerisation Reactions (radical and non-radical) breaking of the main polymer chain backbone at any intermediate stage the products are similar to the parent ma

8、terial (the monomer units) the ultimate product may be monomer or volatile chain fragments北京理工大學(xué)2.1 聚合物熱分解過程及機(jī)理精選課件Substituent Reactions 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 int

9、act volatile products, if they are produced, will be quite unlike monomer北京理工大學(xué)2.1 聚合物熱分解過程及機(jī)理精選課件（1）Polyolefins Of the polyolefins, low-density polyethylene, high-density polyethylene, and polypropylene are of the greatest commercial importance because of their volume. Their uses are too numerous t

10、o mention, but fire properties are critical when used for electrical wire and cable-coating applications. Upon thermal decomposition, very little monomer formation is observed for any of these polymers; they form a large number of different small molecules, mostly hydrocarbons. Thermal stability of

11、polyolefins is strongly affected by branching, with linear polyethylene most stable and polymers with branching less stable.Thermal Degradation Behavior of Some Polymers 北京理工大學(xué)2.1 聚合物熱分解過程及機(jī)理精選課件 Polyethylene（Random-chain scission）PE begins to decompose at 292(inert atmosphere, reductions in molecul

12、ar 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.北京理工大學(xué)2.1 聚合物熱分解過程及機(jī)理精選課件Fig. Intramolecular transfer proc

13、esses北京理工大學(xué)2.1 聚合物熱分解過程及機(jī)理精選課件 Polypropylene （Random-chain scission）PP ：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: penta

14、ne (24%), 2methyl-1-pentene (15%), and 2-4 dimethyl-1-heptene (19%).北京理工大學(xué)2.1 聚合物熱分解過程及機(jī)理精選課件 Polystyrene （End-chain scission, R） Monomer (approximately 40%) is the principal volatile product with very much smaller amounts of benzene and toluene.北京理工大學(xué)2.1 聚合物熱分解過程及機(jī)理精選課件 PS shows no appreciable weig

15、ht loss below 302 although there is a decrease in molecular weight due to scission of “weak” links. Above this temperature, the products are principally monomer with decreasing amounts of dimmer, trimer, tetramer and pentamer. These oligomers are formed in intramolecular transfer reactions, which ar

16、e in direct competition with the monomer- producing depolymerisation process.北京理工大學(xué)2.1 聚合物熱分解過程及機(jī)理精選課件 Polymethyl methacrylate（End-chain scission） PMMA is a favorite material for use in fire research because it decomposes almost solely to monomer and burns at a very steady rate. Methyl groups effect

17、ively block intramolecular hydrogen transfer, leading to a high monomer yield. It has been shown that depolymerisation is a radical chain reaction and that degradation in the region of 300-400 is associated with initiation by both end-chain and random-chain initiation processes. 北京理工大學(xué)2.1 聚合物熱分解過程及機(jī)

18、理精選課件Fig. Thermal degradation mechanism of PMMA 北京理工大學(xué)2.1 聚合物熱分解過程及機(jī)理精選課件Poly(vinyl chloride)（chain stripping, substituent elimination） The radical mechanisms: Initiation involves liberation of chorine atom from a labile centre.北京理工大學(xué)2.1 聚合物熱分解過程及機(jī)理精選課件 Molecular elimination of HCl is proceeded by a

19、 cyclic transition state 北京理工大學(xué)2.1 聚合物熱分解過程及機(jī)理精選課件 The thermal degradation of PVC involves the elimination of HCl and leads to the formation of macromolecular residues with polyene sequences. The latter then rearrange and decompose to yield sizeable amounts of aromatic hydrocarbons (toluene, methyln

20、aphthalene, etc.) Aromatic compounds (benzene, naphthalene, anthracene) are produced simultaneously with HCl in the first decomposition stage.北京理工大學(xué)2.1 聚合物熱分解過程及機(jī)理精選課件引發(fā)聚合物燃燒有三個必要環(huán)節(jié)： 加熱 分解/裂解 被點(diǎn)燃 北京理工大學(xué)2.2 聚合物燃燒化學(xué)反應(yīng)及控制精選課件北京理工大學(xué)2.2 聚合物燃燒化學(xué)反應(yīng)及控制發(fā)精選課件 By preventing fire outbreak or By delaying ignitio

21、n and flame spread in the developing fire By interrupting the combustion process北京理工大學(xué)2.2 聚合物燃燒化學(xué)反應(yīng)及控制精選課件Ignition temperature: The lowest temperature of a combustible material at which sustained combustion can be initiated, i.e. heat lost heat gainedFlashover: The rapid transition to a state of tot

22、al surface involvement in a fire of combustible materials within an enclosure 北京理工大學(xué)2.2 聚合物燃燒化學(xué)反應(yīng)及控制精選課件What Happens When Something Burns?The simplest example of a combustion process is the burning of methane. CH4 + O2 CO2 + H2OBut even this simple combustion involves many free-radical production st

23、eps: 北京理工大學(xué)2.2 聚合物燃燒化學(xué)反應(yīng)及控制精選課件 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北京理工大學(xué)2.2 聚合物燃燒化學(xué)反應(yīng)及控制精選課件 Chain-branching steps produce two free radicals, accelerati

24、ng 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. The flame-carrying radicals H , HO , O , occu

25、r in all flames, whether in methane or in polymers. 北京理工大學(xué)2.2 聚合物燃燒化學(xué)反應(yīng)及控制精選課件Two ways to interrupt the cycle: Solid phase inhibition involves changes in the polymer substrate. Systems that promote extensive cross-linking at the surface, form a carbonaceous char upon heating. Char insulate the under

26、lying 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.北京理工大學(xué)2.2 聚合物燃燒化學(xué)反應(yīng)及控制精選課件 Vapor gas inhibition involves changes in the con

27、centration of free radical HOand H. Reactive species are built into the polymer which are transformed into volatile free-radical 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 fla

28、me and the cycle is interrupted. Of course, for many materials both solid and vapor phase inhibition are involved. 北京理工大學(xué)2.2 聚合物燃燒化學(xué)反應(yīng)及控制精選課件Combustion Modes Flaming Mode Non-flaming Mode Chemical reaction Chemical reactionin gases phase in condensed phase Smouldering combustion and Glowing combusti

29、on北京理工大學(xué)2.3 聚合物燃燒模式和特點(diǎn)精選課件Smouldering combustion statistics in real fire about 75%, lethal rate 50%; being able to cause burning through smoke; can occur at the beginning of burning; a big volume of CO produced converted further to burning. 北京理工大學(xué)2.3 聚合物燃燒模式和特點(diǎn)精選課件Glowing combustion taking place aft

30、er the formation of char; taking place at the surface /interface; accompanied by light colour; in the presence 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. 北京理工大學(xué)2.3 聚合物燃燒模式和特點(diǎn)精選課

31、件Intrinsically Flame Retardant Less Flame RetardantFlammable Polytetrafluoroethylene Silicones Polystyrene Aromatic polyethersulfone Polycarbonates Polyacetal All-aromatic polyimidesPolysulfone Acrylics All-aromatic polyamides Wool Polyethylene terephthalate All-aromatic polyesters Polyolefins All-a

32、romatic polyethers Cellulose (wood, cotton, paper) Polyvinylidene dichloride Polyurethanes Table 2-1 Polymers and Flammability Classification北京理工大學(xué)2.4 聚合物燃燒性能分類精選課件2.4 聚合物燃燒性能分類 The first group consists of relatively flame retardant structures containing either high halogen, or aromatic groups that

33、confer high thermal stability as well as the ability to form char on burning. Second are the less flame retardant materials, many of which can be made more flame retardant by appropriate chemistry. The third class consists of quite flammable polymers which are more difficult to make flame retardant

34、because they decompose readily, forming large quantities of fuel, but these can be made appropriately flame retardant for particular applications by the addition of additives.北京理工大學(xué)精選課件High temperature materials are intrinsically flame retardant;There are three general types of structures: (1) linea

35、r single-strand polymer; (2) ladder polymers consisting of an uninterrupted sequence of cyclic aromatic or heterocyclic structures;(3) and spiro polymers in which one carbon is common to two rings. Polymer with high aromatic character and very strong connecting linkages between rings produce more ch

36、ar on heating, retaining most of the potential fuel of the original polymer as residue; In practice, the choice of a polymer depends on cost and on the importance of flame retardancy in relation to its final use.北京理工大學(xué)2.4 聚合物燃燒性能分類精選課件2.5 聚合物分解成炭Formation of Char 燃燒的聚合物表面溫度接近300-600時，強(qiáng)烈的熱降解發(fā)生。該溫度也是炭

37、層底部靠近聚合物表面的溫度。而炭層的外表面與火焰接觸，其溫度可達(dá)1500。因此，炭形成的溫度是在300-1500之間。北京理工大學(xué)精選課件 A polymer passes through several steps in the formation of char: 交聯(lián)（cross-linking） 芳香化（aromatization） 稠環(huán)芳香化（fusion of aromatics） 渦流層狀炭（turbostratic char formation） 石墨化（graphitization） 北京理工大學(xué)2.5 聚合物分解成炭精選課件The Role of Char Char for

38、mation may limit the amount of fuel available. When an adherent and insulating layer of char is built up on the surface of a polymer, this layer may insulate the underlying polymer from the flame and ,thus, make further degradation more difficult.北京理工大學(xué)2.5 聚合物分解成炭精選課件什么是炭？ 聚合物燃燒表面所產(chǎn)生的炭，其化學(xué)及物理結(jié)構(gòu)決定了炭的

39、阻燃作用。炭是復(fù)雜的不溶混合物，是由許多芳香-脂肪化合物及雜原子（O、N、P）組成。從微觀形貌看，炭有結(jié)晶和非晶區(qū)。炭具有一些物理性質(zhì)，如熱傳導(dǎo)、導(dǎo)電性、對輻射的反射和吸收等；炭也有一些機(jī)械性能，如完整性、硬度、塑性等。 北京理工大學(xué)2.5 聚合物分解成炭精選課件Non-charable or charablepolymers that undergo chain scission and volatilize with, at most, a negligible amount of the char formation, e.g., PE, PP, PS, PMMA; polymers t

40、hat undergo chain stripping reactions, producing unsaturation in the main chain with loss of hydrogen atoms and the pendant groups and give a moderate amount of char, e.g. PVC, PVA, PAN; polymers that contain aromatic rings that can cross-link simultaneously with chain scission reactions and produce

41、 moderate to high amounts of char, e.g., aromatic polyamides, polyesters, polycarbonates, polyimides.北京理工大學(xué)2.5 聚合物分解成炭精選課件 Char-forming polymers Bisphenol A-polycarbonate 北京理工大學(xué)2.5 聚合物分解成炭精選課件北京理工大學(xué)2.5 聚合物分解成炭CO2精選課件 Bisphenol A-polycarbonate 450開始熱降解；25%殘?zhí)糠€(wěn)定到650； TGA曲線形狀由以下過程構(gòu)成： polymervolatiles po

42、lymercross-linkingchar charvolatilesMain Products of Degradation: 35% carbon dioxide, bisphenol A and phenol北京理工大學(xué)2.5 聚合物分解成炭精選課件 PA6、PA66（Do yourself）Pieter Gijsman et al. Differences in the flame retardant mechanism of melamine cyanurate in polyamide 6 and polyamide 66 J. Polymer Degradation and S

43、tability， 2002, 78: 219-224.北京理工大學(xué)2.5 聚合物分解成炭精選課件Polymers that naturally Produce Char 在一定條件下，甚至脂肪烴的碳?xì)渚酆衔锒寄軌虍a(chǎn)生一些炭。碳?xì)渚酆衔镏蠧-C鍵離解能（dissociation energy）為65-90 kcal/mol，而C-H鍵的離解能為90-105 kcal/mol。兩者能量接近，因此高溫下隨著鏈的斷裂可以脫氫：北京理工大學(xué)2.6 促進(jìn)聚合物成炭的途徑精選課件 烯丙基鏈端上的H是活潑的，其C-H鍵離解能為85 kcal/mol，因此可以導(dǎo)致脫氫，形成共軛雙烯（conjugated di

44、enes）。雙烯可與活潑雙鍵反應(yīng)并進(jìn)一步形成芳環(huán)： 北京理工大學(xué)2.6 促進(jìn)聚合物成炭的途徑精選課件雙烯還可進(jìn)一步脫氫形成三烯進(jìn)而環(huán)化：北京理工大學(xué)2.6 促進(jìn)聚合物成炭的途徑精選課件 Polyacrylonitrile PAN在迅速加熱的條件下，如燃燒條件下，產(chǎn)生碎片及揮發(fā)產(chǎn)物。放慢加熱速度，250-350下側(cè)基分子內(nèi)反應(yīng)發(fā)生，導(dǎo)致環(huán)狀多胺（polyamine）結(jié)構(gòu)生成。這種環(huán)狀多胺結(jié)構(gòu)對于較高溫度下的成炭是十分有利的。北京理工大學(xué)2.6 促進(jìn)聚合物成炭的途徑精選課件 接枝促進(jìn)聚合物熱降解成炭 參考文獻(xiàn)：電子束輻射接枝EVA共聚物薄膜阻燃性能的研究與表征 J，科學(xué)通報, 1997, 42（2

45、0): 2167-2171 氧化還原反應(yīng)促進(jìn)成炭 Cu2O和MoO3對PVC阻燃抑煙的作用北京理工大學(xué)2.6 促進(jìn)聚合物成炭的途徑精選課件 添加劑促進(jìn)成炭（Additives that promote char formation）APB (Ammonium pentaborate NH4B5O84H2O) is an effective char promoter in PU thermoplastics. As in the case of cellulose, both physical and chemical factors help to increase char in poly

46、urethanes (e.g., boric acid, which evolves upon thermal decomposition of APB, react with alcohols producing borate esters or with isocyanurates producing borate amides). Both the esters and amides serve as highly cross-linked char precursors. APB is also found to be somewhat effective in natural rub

47、ber, polyester resin, PVC, and polyamide-66. The following figure illustrates the char-promoting tendency of APB in PA-66. The addition of 25 parts per hundred of PA-66 leads to the conversion of 28% of PA-66 into nonvolatile residue. 北京理工大學(xué)2.6 促進(jìn)聚合物成炭的途徑精選課件北京理工大學(xué)2.6 促進(jìn)聚合物成炭的途徑精選課件熱行為研究手段： 熱失重分析（TG

48、A，Thermogravimetric Analysis） 微分熱失重分析（DTG，Differential Thermogravimetric Analysis） 差熱分析（DTA，Differential Thermal Analysis） 差熱掃描量熱分析（DSC，Differential Scanning Calorimetry） 熱機(jī)械分析（TMA，Thermomechanical Analysis） 熱揮發(fā)分析（TVA，Thermal Volatilization Analysis） 裂解氣相色譜（PGC，Pyrolysis Gas Chromatography） 色質(zhì)聯(lián)用（GC-

49、MS，Gas Chromatography-Mass Spectrometry）北京理工大學(xué)2.7 熱行為研究及炭的表征精選課件炭的結(jié)構(gòu)表征 傅立葉紅外光譜法 拉曼光譜法 核磁共振波譜法 X-射線光電子能譜法 元素分析 掃描電鏡等北京理工大學(xué)2.7 熱行為研究及炭的表征精選課件（1）一些聚合物燃燒發(fā)煙的數(shù)據(jù) 聚合物燃燒過程中生煙量是不同的 聚合物發(fā)煙來自于不完全燃燒； 聚合物的產(chǎn)煙量除與結(jié)構(gòu)因素有關(guān)外， 還與燃燒模式（無焰燃燒還是有焰燃燒） 樣品尺寸、樣品位置、通風(fēng)與否、熱通量等有關(guān)。 文獻(xiàn)報導(dǎo)的煙的數(shù)據(jù)應(yīng)客觀看待，因數(shù)據(jù)出自不同的標(biāo)準(zhǔn)和不同的測試設(shè)備。北京理工大學(xué)2.8 煙的形成及抑制精選課

50、件Materials Smoke density, Dm MaterialsSmoke density, Dm Acetal 0Polyethylene terephthalate 390Nylon 6 1Polycarbonate 427Polymethyl methacrylate 2Polystyrene 494PE Low density High density 1339 Acrylonitrile-butadiene-styrene 720Polypropylene 41Polyvinyl chloride 720Polyvinylidene chloride 98Table.2-

51、2 Smoke Chamber Results for Various Materials （Rohm & Haas XP-2 Chamber（ASTM D-2843） 北京理工大學(xué)2.8 煙的形成及抑制精選課件Table 2-3 Some examples taken from Hilado book（ASTM E-662）Materials Dm (non-flaming) Dm (flaming) PE-1486150 PE-2719387PP-1 780110PP-2456110 PU rigid-1 272112PU rigid-2363161PU flex.-1 7758PU fl

52、ex.-230041PS-1 395780PS-2372660ABS-1 76660PC-148324PC-23375北京理工大學(xué)2.8 煙的形成及抑制精選課件（2） 煙的組成Consisting of a dispersion of solid (carbon flakes, soot beads, ash, sublimed pyrolysis products, oxides of inorganic compounds) or liquid (sublimed pyrolysis products) particles in a carrier gas (combustion gas

53、and air). Varying in diameter from 0.002-0.5m.北京理工大學(xué)2.8 煙的形成及抑制精選課件Fig. Polymer pyrolysis, burning and smoke evolution北京理工大學(xué)2.8 煙的形成及抑制精選課件（3） 煙的產(chǎn)生 Pasternak et al (Combustion Science and Technology, 1982, 28: 263-270) consider smoke generation during the combustion of polypropylene to follow a step

54、wise ring-growth mechanism consists of three phases:北京理工大學(xué)2.8 煙的形成及抑制精選課件 thermalPhase 1: polymer simple fuel (polymer fragments and degradation pyrolysis products)Phase 2: simple fuel reactive aromatic smoke nuclei intermediates stable polycyclic aromatic hydrocarbons particulate growthPhase 3: smo

55、ke nuclei smoke particles coagulation and agglomeration北京理工大學(xué)2.8 煙的形成及抑制精選課件 （a）Ideal char structure (b) Poor char structure Aliphatic fuels are cracked to smaller alkyl radicals which in the absence of oxygen grow to form conjugated polyenes or polybenzenoids which may be radical, ionic, or neutral

56、. Aromatic fuels are thought to proceed directly to polybenzenoid intermediates.北京理工大學(xué)2.8 煙的形成及抑制精選課件（4）聚合物結(jié)構(gòu)對產(chǎn)煙的影響聚合物結(jié)構(gòu)不僅影響其燃燒行為，同樣也影響其煙的形成。下列一些結(jié)構(gòu)因素影響聚合物的產(chǎn)煙量： 芳香及多烯聚合物較脂肪與含氧聚合物有較大的產(chǎn)煙趨勢； 單元主鏈有芳環(huán)的聚合物較側(cè)基有芳環(huán)的聚合物產(chǎn)煙量要低； 低鹵或中等水平含鹵聚合物產(chǎn)煙量有增加的趨勢，但高鹵聚合物產(chǎn)煙量有降低的趨勢； 產(chǎn)煙量與降解生成的燃料類型有關(guān)，與聚合物的熱穩(wěn)定性有關(guān)。北京理工大學(xué)2.8 煙的形成及抑制精

57、選課件（5）抑煙機(jī)理 無機(jī)金屬氫氧化物的抑煙機(jī)理無機(jī)氫氧化物能夠顯著降低燃燒聚合物材料的產(chǎn)煙量。這一現(xiàn)象與氧化物殘?jiān)砻嫖胶嘉镔|(zhì)，繼而將其氧化為CO2有關(guān)。北京理工大學(xué)2.8 煙的形成及抑制精選課件For example:- An EVA copolymer containing 63% of either ATH or magnesium hydroxideThese samples were exposed to smoldering conditions at 440 and the relative quantities of CO and CO2 evolved were mea

58、sured. The results showed that the inorganic hydroxide containing formulations generate more CO2 and less CO than the copolymer itself on combustion. The process is related to the efficiency of the residual alumina and magnesia as carbon oxidation catalysts.北京理工大學(xué)2.8 煙的形成及抑制精選課件 過渡金屬對PVC的抑煙機(jī)理 (a) Le

59、wis Acid Mechanism（路易斯酸機(jī)理）The Bell Laboratories Edelson and Starnes propose that during dehydrochlorination of PVC, the MoO3 acts as a Lewis acid isomerization (異構(gòu)化) catalyst to favor the formation of trans-alkene (反式烯烴) segments. These trans-polyenes（反式多烯）, which cannot undergo intramolecular cycli

60、zation to form benzene, are stable to higher temperatures where different mechanisms ensue to give aliphatic (less smoky) products.北京理工大學(xué)2.8 煙的形成及抑制精選課件北京理工大學(xué)2.8 煙的形成及抑制(a)(b)(c)(d)精選課件 The Bell reports consider two possibilities for trans-polyene formation. One is the straightforward Lewis acid iso