智数汽车大数据麦克恒通汽车轻量化在线
查看: 844|回复: 0
收起左侧

[塑料] s塑料阻燃深度总结(四)---卤系阻燃剂

[复制链接]
发表于 2013-10-20 09:30:09 | 显示全部楼层 |阅读模式
<

亲,赶快注册吧,有更多精彩内容分享!

您需要 登录 才可以下载或查看,没有帐号?立即注册

x
本帖最后由 846082533 于 2015-12-31 14:59 编辑 <br /><br />
1.3.2 各类阻燃机理
1.3.2.1 卤系阻燃剂

   
17It is generally accepted that the main mechanism of flame retardant action 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,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。
18In 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 shown 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 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 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 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 O 3 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” radicals  can 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。
23It 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。

24As mentioned earlier, the halogen radicals evolved from the flame retardant in
the 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。
26Poly(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复配其它阻燃剂可以有效抑制聚合物的熔融滴落。PTFE的阻燃作用机理与氟或氟卤化物的所有化学作用都无关。在聚合物加工温度(200℃~300℃)下,PTFE微粒会发生软化,挤出成型时的熔体中的微纤维将发生回缩,形成一个可抑制熔融滴落的类网络结构。PTFE的这种阻燃作用为物理作用机理。
27Potassium perfluorobutanesulfonate is added to polycarbonate at a low loading
of 0.05 to 0.2 wt% which allows preservation of transparency and clarity of the polymer. Even at such a low concentration, perfluorobutanesulfonate provides a V-0 rating to the polycarbonate. In this case the sulfonate group is primarily responsible for the flame retardant effect of the product, whereas the perfluorobutane group, due to its strong electron-withdrawing effect, increases the acidity of the sulfonate group. No contribution o f hydrogen fluoride is known for potassium perfluorobutanesulfonate
聚碳酸酯(PC)中添加少量(0.05-0.2%)全氟丁基磺酸钾时,材料仍可保持良好的透明性,并可使PC的阻燃性达到UL94V-0级。磺酸盐发挥了主要的阻燃作用,电负性较强的全氟丁基基团可增强磺酸盐的酸性。对全氟丁基磺酸钾而言,氟化氢并没有参与阻燃作用。

[size=+0]
[size=+0]
[size=+0]

[size=+0]

您需要登录后才可以回帖 登录 | 立即注册

本版积分规则