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[塑料] 塑料阻燃深度总结(十三)高分散阻燃剂

发表于 2013-10-20 09:08:23 | 显示全部楼层 |阅读模式


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本帖最后由 846082533 于 2015-12-31 14:59 编辑 <br /><br />
1.3.4 高分散阻燃剂
57Flame retardants of very small particle size were always of great interest. As mentioned earlier, fumed silica, which apparently has some flame retardant action, is widely used in epoxy formulations for encapsulation of electronic elements. Another example is use of 0.1- to 2.0-μ msizeSb2O3, which helps not only with good flame retardancy but also with good pigmentation of PVC. Colloidal-size(0 . 03 μm) antimony pentoxide, which has a much lower refractive index than Sb2O3, can be used in transparent PVC applications.In transparent polycarbonate applications, very small amounts (in the range of 0.02 wt%) of halogenated sulfonate salts, also of submicron particle size, are used. Very fine particle metal oxides can also be used in the flame retardancy of polycarbonate , however, apparently this use did not find commercial application. A significant amount of melamine of micrometer and submicrometer particle size which is dispersable in the polyol is used in the flame retardancy of polyurethane foams.

58It was always thought that flame retardants of submicrometer particle size would have an essential advantage over flame retardants of regular particle size (micrometer and above) in terms of efficiency. Practice proved that this is true only to a certain extent and depends very much on the type of flame retardant and the flame retardant test used. For example, some phosphate esters and brominated flame retardants are soluble in a polymer matrix. Obviously, it is impossible to achieve better than this distribution for any solid flame retardant, and it is known that these soluble flame retardants do not show extraordinary efficiency compared to their solid counterparts dispersed in the polymers. There is a large class of flame retardants that will melt before they start interacting with the polymer and provide a flame retardant effect. It is clear that little can be achieved by using very fine particles of such flame retardants. A similar comment applies to flame retardants that decompose and totally disintegrate before interacting with the polymer.
59A number of publications have shown the advantages of using highly dispersed ATH
or MH. The average size of the particles of these specially prepared hydroxides is in the range 100 to 300 nm and the authors qualify them as nanofillers. Usually, no or very little advantage is seen with these nanoscale hydroxides in terms of the LOI and UL-94 tests, but some advantages are observed in cone calorimetry. In another study, an attempt was made to flame-retard poly(methyl methacrylate) with fumed silica. Even at relatively high
loadings of the silica, only marginal improvement in LOI values was observed. A decrease in the heat release rate measured in cone calorimetry is the commonly seen advantage of nanoscale particles, including nanoclays (discussed in detail in other chapters). Although many mechanistic studies on flame retardancy of nanocomposites are in progress, there is an often accepted point of view that because of their small size, nanoparticles can sinter and create a ceramic – carbon coke on the surface of a polymer which insulates it from heat. Because the flames are small in the LOI and UL-94 tests, they do not provide enough heat for sintering, and that effect of nanoparticles is not seen.

翻译问题:①The average size of the particles of these specially prepared hydroxides is in the range 100 to 300 nm,这里讲到的不是“平均半径”,可以翻译为“平均直径”。②“当前,有关纳米复合材料阻燃机理的研究已经取得了许多进展”,这句翻译也是错误的。正确的翻译是:“虽然目前存在很多纳米复合材料阻燃机理”,“in progress”不是进展的意思,而是“尚存在”的意思。

60There is another physical mode of action o f micro- or nanoscale particles, often
overlooked, which is related to the change in rheology of the polymer melt. Even a few percent loading can decrease melt flow significantly. This change in melt viscosity does not itself make it possible to pass the flame retardant test, but in combination with other flame retardants it can be an important tool for improving performance. For example, formulations passing the UL-94 test with a V-2 rating can be upgraded to V-1 or even V-0 with the addition of < 1 wt% of a nanofiller. The effect in the LOI test could be negative or positive. If melt flow contributes to high LOI numbers and will be suppressed by the presence of a nanofiller, the LOI value may actually decrease. This is just an example of a controversy that often appears in the literature and sometimes leads to erroneous conclusions.

人们通常忽视微米或纳米粒子的另一物理作用机理,该机理与纳米粒子对聚合物熔体流变性能有关,即极少量的纳米粒子也将大大降低聚合物的熔体流动性。纳米粒子对聚合物熔体粘度的这一影响并不能有助于材料通过阻燃性能测试,但复配其它阻燃剂协效使用则是提高阻燃性能的一个有效方法。例如添加1%的纳米填料,即可使UL94 V-2级的阻燃材料通过V-1级甚至V-0级。纳米填料对材料LOI值的影响可能是负面的也可能是正面的。熔体流动性越好,其LOI值就越高,因为添加纳米填料后材料流动性变差,相应的LOI值将降低。这是常见于相关文献的争论焦点之一,也是时常会导致得出错误结论的原因之一。

62The most publicized issue in flame retardants nowadays is the potential replacement of some brominated flame retardants with nonhalogenated flame retardants due to environmental concerns with some halogenated materials. There is also a belief, especially in Europe and the Far East, that halogen-containing flame retardant can evolve small amount of dioxins or dibenzofurans when heated and that plastics containing these flame retardants are therefore not suitable for recycling or incineration. Because of lack of alternative flame retardants, the use of halogen-containing flame retardants has been restricted in Europe and Japan. This has led some manufacturers to eliminate voluntarily the use of flame retardants: mostly because of “environmental” reasons and but because of cost saving as well. Thus, the drive to reduce cost and be more competitive while hav-ing a “green” image led to badly compromised fire safety. Considerable loss of life occurred from small ignition source s causing severe burning of non-flame-retarded TV sets. The European regulation regarding electrical and electronic device waste disposal, which requires separate treatment of halogen-containing parts, is another driver for the use of nonhalogen flame retardants or the complete avoidance of flame retardants.

63It is clear that there is a great demand for environmentally friendly (usually construed to mean halogen-free) and easily recyclable flame retardant thermoplastics. However, this requirement is in conflict with another environmental requirement, biodegradation. Normally, thermally and hydrolytically stable products, which are required for multiple recycling, tend to be persistent in nature. Therefore, for the future design of flame retardants it is important to make a distinction between one-time short-period-use products, which are biodegradable, and long-term stable products, which are subject to recycling. However, even very thermally and hydrolytically stable flame retardants should eventually be destroyed, either thermally or chemically, under controlled conditions. Newly developed flame retardants should comply with these requirements.


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