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[塑料] 塑料阻燃深度总结(十)硅系阻燃剂

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发表于 2013-10-20 09:15:32 | 显示全部楼层 |阅读模式
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1.3.2.6硅系阻燃剂
48、Under the heading here we include any chemical compound containing Si. For a long time silicons were considered as useful coadditives in flame retardant systems, but recent developments, especially with polycarbonates have again drawn significant attention to silicon.

此处是指所有的含硅化合物。长期以来,含硅化合物被认为是一种有效的阻燃协效剂,但尤其是近期将其用于PC阻燃的研究使含硅化合物作为阻燃剂而备受人们关注。
49Talc is a naturally occurring magnesium silicate which is finding broad application as a filler in polyolefins. Apparently, it provides a moderate flame retardant effect, but because talc is inexpensive, it is used as a partial substitute for more expensive flame retardants. Fumed silica is used as a filler in epoxy resins for the encapsulation of electronic devices at a relatively high loading, up to 80 to 90 wt%. Because of the relatively small amount of combustible resin, this composition can be flame retarded by the addition of a very small amount of a conventional flame retardant. It is not clear if the silica contributes to the flame retardancy by any mechanism other than heat dispersion. Nanodispersed clay, which is one of the main topics of this book, is an aluminosilicate. The mechanism of its flame retardant action is discussed in other chapters of the book.

滑石粉是一种天然的硅酸镁盐类,作为聚烯烃的填料已有着广泛的应用。实际上,滑石粉的阻燃效果一般,但因其价格低廉而可作为价格较贵阻燃剂的部分替代品使用。对用于电子设备封装的环氧树脂,需添加高达80%-90%的气相二氧化硅填料。因该体系仅含较少量的可燃性树脂,故再添加少量传统阻燃剂即可达到阻燃要求。二氧化硅是否具有除热稀释以外的其它阻燃作用机理尚无定论。本书所讨论的主题—纳米分散粘土是一种铝硅酸盐,其阻燃作用机理将在其它章节进行讨论。
Octaphenylcyclotetrasiloxane in combination with potassium of sulfonated diphenylsulfone is used commercially in polycarbonate, where clarity of the polymer is important. Recently, some specific branched methylphenylsiloxanes were found particularly effective in pol ycarbonate (PC) and in PC/acrylonitrile – butadrene – styrene (ABS) blends with a low (ABS) content. It is believed that due to the inclusion of aromatic groups in the siloxane, it becomes significantly more soluble and more easily dispersed in PC than straight polydimethylsiloxane. It was shown that these siloxanes tend to migrate from the inside of the PC resin to the surface during combustion and accumulate quickly on the surface. Such movement resulted from differences in viscosity and solubility between the siloxane and the PC at high temperatures. The branched methylphenylsiloxanes showed a higher thermal stability than that of linear dimethylsiloxanes and a greater tendency to induce charring. In contrast, Nishihara et al. showed that linear polysiloxanes are more advantageous flame retardants in PC than are branched polysiloxanes because of higher mobility in the molten plastic.

磺化二苯基砜钾复配八苯基环四硅氧烷阻燃剂已工业应用于PC,而对PC而言制品的透明性是十分重要的。近来,研究发现一些支化甲基苯基硅氧烷系阻燃剂用于PC及PC/ABS合金(低含量ABS)时十分高效。人们认为,由于硅氧烷中存在芳环基团,使其与PC的相容性比聚二甲基硅氧烷更好而易于分散。研究表明,聚合物燃烧时硅氧烷可从PC内部迁移到表面并很快聚集,这是由高温时硅氧烷与PC的粘度差与浓度差引起的。支化甲基苯基硅氧烷比线性二甲基硅氧烷具备更加优异的热稳定性和成炭性。相反,Nihihala等研究发现,在PC中线性聚硅氧烷比支化聚硅氧烷具备更优异的阻燃性,因前者在聚合物熔体中具有更好的流动性。


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