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[塑料] 塑料阻燃深度总结(十三)高分散阻燃剂

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塑料阻燃深度总结(十三)高分散阻燃剂
  
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.

学者们通常对较小粒径的阻燃剂十分感兴趣。如前所述,具备阻燃作用的气相二氧化硅已广泛应用于环氧树脂(如电子元器件封装材料)。此外,粒径为0.1μm-0.2μm的Sb2O3,不仅可以提高PVC的阻燃性,还可以使其具有较好的着色性。而Sb2O5胶粒(0.03μm)相对于Sb2O3有极低的折射率,因此可用于透明PVC。在透明PC中,通常以极少量(0.02%左右)的亚微米级卤系磺酸盐作为阻燃剂。极细的金属氧化物微粒也可以用于阻燃PC,但至今尚未工业化。对阻燃PU发泡材料,可采用分散于多元醇的大量微米和亚微米级MA。
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.
就阻燃剂效率而言,长期以来人们认为亚微米级阻燃剂要高于普通阻燃剂(微米及微米以上)。实践证明,该“规律”只在某些条件下适用,这主要取决于阻燃剂的类型与所选用的阻燃性测试法。例如,一些磷酸酯和溴系阻燃剂可以很均匀地分散于聚合物基体,对任何固体阻燃剂而言,如此良好的分散是不可能达到的,然而前者良好的分散却未必后者表现出更高的阻燃效率。事实上,许多阻燃剂在与聚合物发生作用而发挥阻燃效用之前为熔融态。很明显,该类超细阻燃剂并不十分高效,同样现象在与聚合物作用之前即发生热分解甚至全部裂解的阻燃剂中可见。
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.

大量文献表明,高分散ATH、MH的阻燃性优异。通过特殊方法这些氢氧化物纳米填料,其平均半径为100nm-300nm。通常,这些纳米填料在LOI与UL94测试中表现平平,但在cone测试中却表现突出。在一项实用气相二氧化硅阻燃PMMA的研究中,即使添加量相当高,LOI却仅稍微提高。而通常在Cone测试中,纳米填料(包括纳米粘土)可有效降低材料的HRR。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,一个人们普遍认同的观点是:由于纳米填料的“小尺寸效应”,纳米微粒可在聚合物表面结块形成一个有效的隔热层,即类陶瓷-碳焦化层。由于LOI和UL94测试都为小型火焰,不能为纳米微粒的结块提供足够的热量,因此在小型火测试中纳米微粒很难发生结块。
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.

近年来,阻燃学术界最为热门的话题就是一些含卤材料引发的环境问题,以及为卤素阻燃剂寻找替代品。在欧洲和远东地区有学者认为,燃烧时卤系阻燃剂将释放少量的二噁英或二苯并呋喃,这同时也是含卤系阻燃剂的塑料无法回收或销毁的重要原因。由于目前还缺乏卤系阻燃剂的替代品,且欧洲和日本已全面禁用卤系阻燃剂。这导致一些生产商处于对“环境问题”和成本问题的考虑,已停止使用阻燃剂。因此,生产商这种为降低成本与“响应环保法规”的做法已经导致严重的火安全隐患。这使得极小的点火源即可引起为阻燃电视机的火烧不止,这已导致多人丧生。随后,欧洲颁布了有关电子电器设备废物的处理规范,规定卤系废物需进行特殊处理,这一方面推广了无卤阻燃剂的使用,但同时也可能成为对阻燃剂的全面禁令。
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.

现在,大力发展环境友好型(无卤)与易回收的阻燃塑料势在必行。然而,这却与另一环保主题背道而驰,这就是材料的生物降解性。一般情况下,热稳定性和抗水解性优异的材料都需进行多步回收,它们在自然条件下极其稳定。因此,就阻燃剂的设计方向而言,严格区分一次性短期使用的生物降解材料与长期使用的稳定性优异的可回收材料是十分重要的。然而,无论热稳定性和抗水解性多么优异的阻燃剂,采用可控的高温分解或化学降解法都必须是可破坏的。新开发的阻燃剂应达到这些要求。
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