塑料阻燃性深度总结.doc

塑料阻燃性深度总结原著：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, andheat 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 assemble d product. Tests can be small, intermediate, orfull 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 than10s after any flame application. The mean combustion time for the five specimens tested (10 flame applications) should not exceed5s, 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 drips should be observed. The sample is classified V-2 if it satisfies the combustion time criteria 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 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 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 100mm in area and up to 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100mm100mm、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、 Ignitability depends to a large extent onhow quicklythe 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 canor , removing heat from the 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 ofextinguishinga polymer flame depends on the mechanism ofthermal decompositionof the polymer. Whereas ignition of a polymer correlates primarily with theinitial temperature of decomposition,steady combustionis 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 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-linking.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 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 scissionanddepolymerizationpolymers are usuallymore flammablethan polymers that crosslink or remove pendant groups.Cross-linkingleads to precursors of char and as a result, tolower 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，聚合物主链随机断裂为链段碎片；链端断裂，聚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）；聚丙烯腈（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 witharomatic or heterocyclic groups in the main chainare less combustible than polymers with an aliphatic backbone. Polymers with shortflexible linkagesbetween aromatic rings tend tocrosslink and char. These polymers are thermally stable and show relatively good flame retardancy. For example, bisphenol A based polycarbonate, 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 polymers 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、PU、双酚A型环氧树脂。10、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 performance 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 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 precursors of graphite. These pregraphitic domains are embedded in the amorphous char. This type of char, called turbostratic char , is usually formed at 600 to 900, temperatures typically found on the surface of burning polymers. Char that contains more pregraphitic domains is more stable to thermal 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 diffu sion of combustible materials to the flame. The best-performing char would be amorphous uncracked 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600-900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 一般阻燃作用机理12、Although flame 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 distinguishesgas-phase-activeandcondensed-phase-activeflame retardants. Gas-phase-activeflame retardants act primarily throughscavenging free radicals responsible for the branching of radical chainreactionsin the flame. This is thechemical mechanism of action in the gas phase. Other flame retardants generate large amounts of noncombustible gases, whichdiluteflammable gases, sometimesdissociate endothermically,and decrease the temperature byabsorbing 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通过捕捉燃烧的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, charring 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、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 always 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。多种阻燃机理配合发挥作用，称之为协效阻燃。 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 halogenin the form of radical or halogen halideat thesame temperaturerange orbelow the temperature 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 hydrogen 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 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、溴、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，氟或碘比溴或氯价格昂贵，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 chlorine 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 properties, 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 brominated 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 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 resistance 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。很多溴系阻燃剂都是可工业化应用的。溴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和环氧树脂。在这方面，研究重点是芳香族卤系阻燃剂。尽管溴系脂肪族阻燃剂通常比溴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。溴系阻燃剂结构相近时，含溴量越高其热稳定性越好。完全溴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。溴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。许多溴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溴系阻燃剂。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 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? radicals. 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 reducesthe concentration of H? ，OH? and HCO? radicals, whereas there is an increase in the content of the diradicals Cand soot. As the concentration of inhibitor is increased, the flame temperature decreases. Small additions of halogen inhibitors (on the order of a few mol%) can reduce the rate of flame propagation up to 10-fold and have a marked effect on the ignition limits. On the other hand, halogens accelerate the formation of soot in the flame.在一些其它反应中，活性较强的自由基(H? ，OH? ，CH3)可被活性较弱的自由基Br?取代，而Br?又可与其它分子中的H?中心生成HBr。光谱学研究表明，添加卤系阻燃剂可明显降低火焰中H? ，OH? 和HCO?自由基的数量，但却增加了C2（碳双自由基）和烟炱的数量。火焰温度降随阻燃剂的添加量增大而降低，添加少量的卤系阻燃剂即可使材料的火焰传播速度降至原来的1/10，并有效降低易燃性，但卤系阻燃剂的不足之处是提高了烟炱的量。21、It is well established that Sb2 O3 is synergistic with halogen-containing flame retardants because it facilitates delivery of halogen atoms in the gas phase and prolongs residence of the halogens in the flame zone so that more “hot” radicalscan be scavenged. It is also well established that Sb2 O 3 catalyses dehalogenation of the flame retardant, so halogens can be moved into the flame at a lower temperature. In the flame, antimony trihalide (e.g., SbBr3)is reduced step by step to metallic antimony , which could be further oxidized by the oxygen or hydroxyl radical.研究表明，Sb2O3可与卤系阻燃剂产生协同作用，因其可以促进气相中卤自由基生成，并可延长其在火焰中的作用时间，从而可使其捕获更多燃烧所需要的活性自由基。研究表明，Sb2O3还可催化卤系阻燃剂脱卤，使卤素自由基在较低温度下即可参与阻燃。22、Interference with the antimony halogen reaction will affect the flame retardancy of the polymer. For example, metal cations from color pigments or an inert filler such as calcium carbonate or talc may lead to the formation of stable metal halides, rendering the halogen unavailable for reaction with antimony oxide. The result is that neither the halogen nor the antimony is transported into the vapor zone. Silicones have also been shown to interfere with the flame retardant action of halogenated flame retardants.妨碍卤-锑反应将影响聚合物的阻燃性。例如，着色剂或惰性填料（如碳酸钙或滑石粉）中的金属离子可与卤素离子形成稳定的金属卤化物，妨碍卤素与锑氧化物的反应，结果导致卤和锑不能进入气相发挥阻燃作用。另外，含硅化合物对卤素阻燃剂的阻燃作用也存在负面影响。23、It is also believed that the large heat capacity of hydrogen halides and their dilution of the flame results in a decrease in the mass concentration of com-bustible gases and the temperature of the flame.人们认为，卤化氢较大的热容和对火焰的稀释作用可有效降低可燃气体的浓度与火焰温度。24、As mentioned earlier, the halogen radicals evolved from the flame retardant inthe condensed phase abstract the hydrogen from the polymer and produce unsaturation. The double bonds are known to be precursors of char formation through either cross-linking or aromatization. If hydrogen abstracted from the aromatic ring, this ring has a chance to couple with another ring and start forming polyaromatic structures, which are precursors of graphitic domains in the char. This char formation is an important condensed-phase contribution of halogen-based flame retardants, which is often overlooked.如前所述，在凝聚相中卤系阻燃剂释放的卤自由基与聚合物中的氢原子反应生成卤化氢，并形成不饱和键，不饱和键可通过交联或芳构化成炭。如果卤自由基与芳环上的氢原子发生反应，所形成的不饱和芳环就可与其它芳环形成多芳环结构，这就是炭层中重要的石墨化前体的来源。该成炭作用是常被人们所忽视的卤系阻燃剂在凝聚相中的阻燃作用。25、There is another condensed-phase mode of action that is specific for aliphatic bromine, and it is the opposite of char formation. Bromine radicals generated thermally at low temperature in the polymer melt can cause chain scission at tertiary C atoms. Examples of polymers where this mechanism is operational are polystyrene (foams) and polypropylene ( preferably thin parts, films, or fibers). The decreased molecular weight causes fast dripping of the hot polymer, which cools the flame and eventually extinguishes it.脂肪族溴系阻燃剂具备一种特有的凝聚相作用方式，该作用与成炭作用原理相反。较低温度时，聚合物熔体中的溴自由基可诱发碳链上叔碳原子处的链断裂；此机理适用的聚合物基体包括PS和PP（尤其为片材、薄膜及纤维）。分子量大的降低导致热聚合物快速的熔融滴落，降低了火焰的温度并可致其自熄。26、Poly(tetrafluoroethylene) (PTFE) is used at a very low level (0.01 to 0.5 wt%) in combination with other flame retardants to suppress flaming drips. The flame retardant action of PTFE is not relate d to any chemical reaction of fluorine or halogen fluoride. During polymer processing at 200 to 300?C, PTFE particles soften, the shear force of extrusion elongates the particles up to 500%, and microfibrils are formed. Upon combustion the microfibrils shrink back when the polymer melts and a network that prevents dripping is formed. This flame retardant action of PTFE is a physical phenomenon.极少量（0.01 to 0.5 wt%)的PTFE复配其它阻