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1、塑料阻燃机理最精辟之总结编辑廖家志原著：SERGEI V L EVCHIK1.1引言1.2聚合物燃烧与测试1.2.1可燃性的实验室测试1、Flammability of polymers is assessed primarily through ignitability, flame spread, and heat release。聚合物的燃烧性主要从易燃性、火焰传播性、释热性三个方面进行评估。2、Numerous flammability tests are known and are performed either on representative samples or on an
2、 assemble d product. Tests can be small, intermediate, or full scale 。许多可燃性测试可用试样或最终产品进行，在规模上分为小型、中型及大型测试。3、A V-0 classification is given to material that is extinguished in less than 10 s after any flame application.The mean combustion time for the five specimens tested (10 flame applications) shou
3、ld not exceed 5 s, and no combustible drips can be observed. A V-1 classification is received by a sample with maximum combustion time 50 s and mean combustion time for five specimens 25 s. No combustible dripsshould be observed. The sample is classified V-2 if it satisfies the combustion time crite
4、ria of V-1 but flammable drips igniting the cotton are allowed。UL94V0级评定标准：每次点燃后10s内即发生自熄，5个试样(10次点燃)的平均燃烧时间不超过5s，无具 有引燃性的熔融滴落。V-1级评定标准：试样最长的燃烧时间小于30s，平均燃烧时间小于25s，无具有引燃性 的熔融滴落。V-2级评定标准：符合V-1级标准的燃烧时间限制，允许具有引燃性的熔融滴落。4、The LOI test does not represent a real fire scenario, but it is good as a screening
5、tool because it gives a numerical value instead of a discrete classification (e.g., V-0, V-1, V-2).虽然LOI法仅能测试实验室条件而非真实火情下材料的易燃性，但其可提供较详实的数据而非不连贯的等级划 分(例如，V-0, V-1, V-2)。5、The cone calorimeter test is a bench-scale (medium-sized) test developed at NIST which quickly gained popularity in the academic
6、community as well as for standardization purposes (e.g., ISO 5660-1, ASTM E-1354). It is also used as a tool for fire protection engineering because it allows prediction of large-scale test results. A cone calorimeter measures consumption of oxygen from a burning sample 100 x 100 mm in area and up t
7、o 50 mm thick. The heat release is calculated from the oxygen consumption data.锥形量热仪测试法是美国国家标准及技术研究院(NIST)制定与规范的一个中等规模实验室测试法，它很快得 到了学术界的普遍认可，并为其制定了相关标准(例如ISO 5660-1, ASTM E-1354)。因该法所得数据与大规模测 试所得数据具有一定的相关性，故它也是研究火安全防护工程的重要方法。Cone法可测试面积为100mm x100mm、厚度不超过50mm试样的燃烧耗氧量，并由耗氧量计得样品的释热量。1.2.2聚合物的燃烧6、Ignita
8、bility depends to a large extent on how quickly the surface can be raised to the ignition temperature. Special consideration has to be given to polymers that melt before thermal decomposition. Usually, at a low heat exposure, melting precedes ignition and the polymer can or , removing heat from the
9、surface.This phenomenon is beneficial for flame retardancy of uncharrable polymers. On the other hand, at a higher heat exposure, ignition may occur before the surface is heated to sufficient depth for the melted material to flow, and such polymers may ignite relatively easy.材料的易燃性在很大程度上取决于材料表面温度上升到
10、燃点的速度。人们异常关注熔融温度低于热降解温度 的聚合物。通常暴露于较小热源时，如果材料在被点燃之前为熔融态，则可通过 流动和 熔滴来降低表面热 量。这十分有益于非成炭类聚合物的阻燃。相反，暴露于较大热源时，材料在可为熔融流动态之前即被点燃，该 类聚合物则相对易燃。7、The possibility of extinguishing a polymer flame depends on the mechanism of thermal decomposition of the polymer. Whereas ignition of a polymer correlates primarily
11、 with the initial temperature of decomposition, steady combustion is related to the tendency of the polymer to yield a char, which is produced at the expense of combustible volatile fragments.聚合物的自熄性取决于其热降解机理，其易燃性则相关于其热降解的初始温度，稳定燃烧则与其成炭性相关，成 炭性越好，可燃性挥发物则越少。8、Four general mechanisms are important for
12、 thermal decomposition of polymers:(1) random chain scission, in which the polymer backbone is randomly split into smaller fragments: (2) chain-end scission, in which the polymer depolymerizes from the chain ends; (3) elimination of pendant groups without breaking of the backbone: and (4) cross-link
13、ing. Only a few polymers decompose pre-dominantly through one mechanism： in many cases a combination of two ormore mechanisms is in effect. For example, polyethylene and polypropylene tend primarily to decompose via random chain scission, which in the case of polyethylene is also accompanied by some
14、 cross-linking. Poly(methyl methacrylate) and polystyrene tend to depolymerize, poly(vinyl chloride) primarily undergoes elimination of pendant groups (dehydrochlorination), and polyacrylonitrile crosslinks. In terms of flammability, random scission and depolymerization polymers are usually more fla
15、mmable than polymers that crosslink or remove pendant groups. Cross-linking leads to precursors of char and as a result, to lower flammability. Elimination of pendant groups results in double bonds, which can also give crosslinks or lead to aromatization.对于聚合物而言，以下四个机理十分重要：无规断链，聚合物上链随机断裂为链段碎片；链端断裂，聚
16、合物 从链端开始裂解：无主链破坏的端基消除：交联。大多数情况下，聚合物的热降解遵循两种或两种以上上述 机理，极少数只遵循其中单个机理。比如，PE和PP主要通过无规断链的方式裂解，但PE的裂解还伴随一些 交联反应的发生；PMMA和PS受热时将发生解聚反应；PVC主要发生端基消除反应(脱HCl)；聚丙烯月青(PAN) 热分解时则发生交联。对可燃性而言，热分解时发生无规断链和解聚的聚合物通常比发生交联或端基消除的聚合 物更加易燃。交联可促进成炭，从而降低可燃性。端基消除导致形成双键，可促进发生交联或芳构化。9、In general, polymers with aromatic or heteroc
17、yclic groups in the main chain are less combustible than polymers with an aliphatic backbone. Polymers with short flexible linkages between aromatic rings tend to crosslink and char. These polymers are thermally stable and show relatively good flame retardancy. For example, bisphenol A - based polyc
18、arbonate, phenol formaldehyde resins, and polyimides are self-extinguishing and show either a V-2 or V-1 rating in the UL-94 test. On the other hand, polymers with relatively long flexible (aliphatic) linkages are still relatively combustible despite aromatics in the backbone. Examples of these poly
19、mers are poly(ethylene terephthalate), poly(butylene terephthalate), polyurethanes, and bisphenol A - based epoxy resin.一般而言，主链上含芳环或杂环基团的聚合物比脂肪族聚合物更为难燃。芳环间较短的柔性键可发生交联并成炭， 此类聚合物具有较好的热稳定性和阻燃性。例如在UL94测试中，双酚A型聚碳酸酯、苯酚甲醛树脂、聚酰亚胺 都可以自熄并达到V-2或V-1级。但是，含有较长柔性键（脂肪链）的聚合物的聚合物，虽主链上有芳环却仍相对 易燃；例如PET、PBT、？顷双酚A型环氧树脂。1
20、0、Charring of polymers proceeds through various stages: (1) cross-linking, (2)aromatization, (3) fusion of aromatics, and (4) graphitization. The ability of a polymer to perform in one or several of these stages leading to char formation depends primarily on the polymer structure. However, this perf
21、ormance can be improved significantly by the use of flame retardants. Although many polymers tend to cross-link at early stages of thermal decomposition, this does not necessarily result in char formation. Char is formed only if the cross-linked polymer contains aromatic fragments and/or conjugated
22、double bonds and is prone to aromatization during thermal decomposition.聚合物的成炭分为多个步骤，依次为：交联；芳构化；芳族稠环化；石墨化。聚合物的成炭性主要取决 于其结构，但是同时也可以通过使用阻燃剂来获得提高。尽管多种聚合物在热分解初始阶段就趋于交联，但这并 不足以导致成炭。炭层的形成条件是：热分解过程中，交联聚合物含有芳环碎片及或共轭双键，并趋于芳构化。11、Fused aromatic rings in the char tend to assemble into small stacks, which are p
23、recursors of graphite. These pregraphitic domains are embedded in the amorphous char. This type of char, called turbostratic char ,is usually formed at 600 to 900C, temperatures typically found on the surface of burning polymers. Char that contains more pregraphitic domains is more stable to thermal
24、 oxidation and therefore less likely to burn away and expose the polymer surface to the heat of the flame. On the other hand, highly graphitized chars are rigid and may have cracks, which do not retard diffusion of combustible materials to the flame. The best-performing char would be amorphous uncra
25、cked char with a requisite pregraphitic domain content.炭层中的芳香族稠环趋于形成小型堆叠结构，称为石墨化前体。这些前体镶嵌于无定形化炭层中形成无规炭层”， 该结构通常于聚合物表面温度为600-900C间时形成。炭层中含有的石墨前体越多，其热稳定性就越好，因此似 乎也较难燃尽，并降低聚合物表面暴露于火焰热流中的概率。但另一方面，高度石墨化的炭层十分坚硬且可能存 在裂缝，导致无法有效阻止可燃材料暴露于火焰。因此，性能最为优异的炭层应是含有适量石墨化前体的无定形 无裂缝炭层。1.3阻燃1.3.1 般阻燃作用机理12、Although flame
26、 retardants may differ from one another in terms of chemical structure, certain general mechanisms of action are applicable to various classes of flame retardants. The first line of separation normally distinguishes gas-phase-active and condensed-phase-active flame retardants. Gas-phase-active flame
27、 retardants act primarily through scavenging free radicals responsible for the branching of radical chain reactions in the flame. This is the chemical mechanism of action in the gas phase. Other flame retardants generate large amounts of noncombustible gases, which dilute flammable gases, sometimes
28、dissociate endothermically, and decrease the temperature by absorbing heat. This slows combustion and may eventually result in extinguishment of the flame. This is the physical mechanism of action in the gas phase.尽管各种阻燃剂的化学结构不同，但通用的作用机理是可适用于多种阻燃剂的。通常根据作用机理，可将其分为 气相作用阻燃剂和凝聚相作用阻燃剂两大类。气相作用阻燃剂主要诵过捕捉燃烧的
29、链支化反应所需的活性自由基 发挥作用，这是其化学作用的机理。另一类阻燃剂可产生大量的不可燃气体以稀释可燃气体，有时也可以通过吸 热来降低材料表面温度。这有效降低了材料的可燃性，也可致其自熄。这是阻燃剂于气相中的物理作用机理。13、Condensed-phase mechanisms of action are more numerous than the gas-phase mechanisms. Charring, discussed briefly above, is the most common condensed-phase mode of action. Again, charri
30、ng could be promoted either by chemical interaction of the flame retardant and the polymer or by physical retention of the polymer in the condensed phase. Charring could also be promoted by catalysis or oxidative dehydrogenation.凝聚相作用机理比气相作用机理更为常见。前面简要讨论过的成炭是最为常见的凝聚相作用机理。提高材料的成 炭性有多种途径：聚合物和阻燃剂的反应型成炭
31、、聚合物在凝聚相滞留成炭或氧化脱氢成炭。14、Some flame retardants show almost exclusively a physical mode of action. Examples are aluminum hydroxide and magnesium hydroxide. On the other hand, there is no single flame retardant that will operate exclusively through a chemical mode of action. Chemical mechanisms are alwa
32、ys accompanied by one or several physical mechanisms, most commonly endothermic dissociation or dilution of fuel. Combinations of several mechanisms can often be synergistic.有些阻燃剂几乎是通过单一的物理作用机理阻燃的，例如氢氧化铝（ATH）和氢氧化镁（MH）.然而，没有一种 阻燃剂是通过单一的化学作用机理而阻燃的。化学作用机理通常伴随一种或多种物理机理（如分解导致的吸收热 量或稀释可燃气体）发挥阻燃作用。多种阻燃机理配合
33、发挥作用，称之为协效阻燃。1.3.2各类阻燃机理1.3.2.1卤系阻燃剂15、Halogen-containing flame retardants represent the most diversified class of retardants. To be effective, halogen-containing flame retardants need to release halogen in the form of radical or halogen halide at the same temperature range or below the temperature
34、of decomposition of the polymer. Theoretically, four classes of chemical compounds can be used as halogenated flame retardants: those containing fluorine, chlorine, bromine, or iodine. Fluorinated organics are normally more stable than any other polymers and do not release fluorine radicals or hydro
35、gen fluoride. Nevertheless, there are a few examples of the commercial use of fluorinated flame retardants operating differently from all other halogenated flame retardants, and they will be discussed later. By contrast, iodinated organics have very low thermal stability and cannot be processed with
36、 most commercial polymers. In addition, fluorine and iodine are more expensive than chlorine or bromine, which also limits development of flame retardants based on these two halogens.卤系阻燃剂代表品种繁多的一类阻燃剂。简言之，卤系阻燃剂即是可在聚合物分解温度范围内或低于降解温度时 释放出卤素自由基或卤化物的阻燃剂。理论上，含氟、氯、漠、或碘的化合物都可以作为卤素阻燃剂使用。含氟 有机物通常比任何聚合物都稳定，极难
37、释放出氟自由基或氟化氢。不过，现已有一些与所有其它卤系阻燃剂的作 用机理截然不同的工业化氟系阻燃剂。与氟化物不同的是，含碘有机物的热稳定性极差，不能与大多数工业聚合 物一起加工。再者，氟或碘比漠或氯价格昂贵，这也极大限制了氟系与碘系阻燃剂的发展。16、Chlorinated aromatic products are relatively stable and therefore not very efficient, but chlorinated aliphatic and c ycloaliphatic flame retardants are well known. The chlor
38、ine content in some chlorinated paraffins can reach 70%, and some improved grades can be used in polyolefins and in high-impact polystyrene （HIPS）. A broad range of brominated flame retardants are commercially avail-able. Brominated flame retardants help maintain a good balance of physical propertie
39、s, such as good impact and tensile strength and a high heat distor-tion temperature. These flame retardants are generally suitable for many plastics; however, their principal use is in engineering plastics and epoxy resins. In this case the emphasis is on aromatic products. Although aliphatic bromin
40、ated flame retardants are often more efficient than aromatics, their use has been limited to certain polymers. For similar structures there is usually a correlation between degree of bromination and thermal stability. Fully brominated aromatics have low volatility and are used in engineering resins
41、with a relatively high processing temperature. Polymeric and oligomeric brominated aromatic flame retardants are also widely used. In addition to good thermal stability, they show better physical properties. One of the main disadvantages of many brominated aromatic flame retardants is their low resi
42、stance to ultraviolet （UV） light; how-ever, there are specially designed commercial flame retardants that show good UV stability.氯系芳香族化合物的热稳定性相对较好，因此并不十分高效，但氯系脂肪族和脂环族阻燃剂则是效果相对较好的 两种阻燃剂。一些氯化石蜡的含氯量达70%，可用于聚烯烃和HIPS的阻燃。很多漠系阻燃剂都是可工业化应用 的。漠系阻燃剂可保持材料较好的物理性能，例如良好的抗冲击性、拉伸强度与较高的热变形温度。这些阻燃剂 通常可用于许多塑料，现主要用于工程塑料
43、和环氧树脂。在这方面，研究重点是芳香族卤系阻燃剂。尽管漠系脂 肪族阻燃剂通常比漠系芳香族阻燃剂更为高效，但是它们仅适用于特定的聚合物。漠系阻燃剂结构相近时，含漠 量越高其热稳定性越好。完全漠化的芳环化合物具有较好的热稳定性，可用于加工温度相对较高的工程塑料。漠 系芳香族低聚物阻燃剂也应用广泛，除具备优良的热稳定性外，还表现出良好的物理性能。许多漠系芳香族阻燃 剂的缺点是抗紫外性能较差，不过现在已经开发出了经特殊设计的抗紫外线性能优良的工业化漠系阻燃剂。17、It is generally accepted that the main mechanism of flame retardant a
44、ction of halogenated flame retardants is in the gas phase, and it is primarily the chemical mode of action. The reaction begins with the abstraction of halogen radical from the flame retardant. This halogen immediately abstracts hydrogen from either the flame retardant additive or the polymer.人们普遍认为
45、，卤系阻燃剂的主要作用方式为气相作用，且主要为化学作用。首先，作用始于阻燃剂受热分解放 出卤自由基，自由基可迅速捕获阻燃剂或聚合物热分解放出的H自由基。18、In the absence of a synergist, hydrogen h alides volatilize and enter the flame. Hydrogen halides will quickly react with hydrogen or hydroxyl radicals and regenerate the halogen. Examples of such reactions with HBr are s
46、hown below in reactions (1.4) and (1.5). Further bromine radicals will react with hydrocarbons in the gas phase and regenerate HBr as shown in reaction (1.6), with the process repeating until bromine leaves the flame.若不添加协效剂，HX (卤化氢)将挥发至火焰中，并迅速与H自由基或OH自由基反应重新生成卤素自由基X。 此后，在气相中，卤素自由基X将与烯烃类聚合物反应生成HX，该反
47、应循环往复地进行，直至耗尽火焰中的X 自由基。19、Atomic hydrogen and hydroxyl radicals are very important for sustaining combustion. The hydrogen radical is responsible for the chain-branching free-radical reactions in the flame, whereas the hydroxyl radical is responsible for the oxidation of CO to CO2, which is a highly
48、 exothermic reaction and is responsible for the larger part of the heat generation in the flame.H自由基与OH自由基对维持燃烧起至关重要的作用。研究表明，H自由基主导了火焰中的链支化自由基反应； 而OH自由基则可氧化CO生成CO2,这是一个放热量极大的反应，燃烧产生的大部分热即来源于此。20、In some other reactions, the more reactive radicals (H ，OH，CH3 )are replaced by the less active Br radica
49、ls. If Br meets H in the presence of a neutral molecule (third body), HBr is regenerated. It has been found by spectroscopy that the introduction of halogen-containing inhibitors into the flame clearly reduces the concentration of H，OH and HCO radicals, whereas there is an increase in the content of the diradicals C2 and soot. As the concentration of inhibitor is increased, the flame temperature decreases. Small additions of halogen inhibitors (on t
