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[塑料] 塑料阻燃深度总结(十一)协效作用

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发表于 2013-10-20 09:13:28 | 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 />1.3.2.7 协效作用
The concept of synergism is very often used in the optimization of flame retardant formulations; however, synergism is sometimes misinterpreted. By definition, synergism means enhanced performance of the mixture of two or more components compared to the simple additive performance of the components at the same concentration.
协效作用常用于优化设计阻燃配方,然而其概念却常被人们所曲解。按照定义,“协效作用”是指在相同添加量时,由两种或两种以上组分构成体系的性能提高优于有两种组分各自单一作用的性能提高之和。
The two mostly common examples of synergism, halogens with antimony and phosphorus with nitrogen, were discussed earlier. Apart from Sb2O3, halogen-containing flame retardants are synergistic with other metal oxides, including Bi2O3,SnO2, MoO3, Fe2O3, and ZnO. In some formulations these metal oxides can substitute for Sb2O3 partially or completely. Zinc borates or zinc sulfide can be used in the same role of partial substitution of
Sb2O3. In many instances these metal oxides also provide additional advantages of smoke suppression.
卤-锑与磷-氮阻燃协效体系是两个最为常见协效作用体系。研究表明,卤系阻燃剂也可与除Sb2O3之外的Bi2O3、SnO2、MoO3、Fe2O3及ZnO等其它金属氧化物产生协效作用;在一些配方中,这些金属氧化物可以部分或全部替代Sb2O3协效剂。此外,ZB或硫酸锌也可部分替代Sb2O3。有研究发现,这些金属氧化物也可发挥一定的抑烟作用。
A very sharp synergistic effect between ammonium polyphosphate (APP) and some inorganic minerals, salts, and oxides in a narrow concentration range was discovered independently by Levchik et al. and by Lewinetal. Later, similar effects were noted in systems containing ammonium polyphosphate and zeolite. Although different speculative mechanisms of catalysis of charring (e.g., by zeolites), or thermal oxidative promotion of charring by manganese dioxide were proposed, these mechanisms probably play a minor role. The principal mechanism appears to be interaction of polyphosphoric acid formed during thermal decomposition of APP and metal -containing compounds. Since only divalent and higher valency metals show this effect, it is reasonable to assume that metal cations help to crosslink polyphosphoric acid and increase its viscosity. This, in turn, helps to create a more thermally insulative char structure. If the mineral compound is added in large quantities, solid crystalline phosphates are formed, and this results in cracking of the char and the loss of insulating properties. This also explains why this synergistic effect is observed in a very narrow concentration range.
Levchik等研究发现,特定配比时APP与无机矿物、盐类及氧化物间存在高效的协同作用。随后,Levin等发现APP与沸石之间也存在高效的协效作用。有学者曾提出过两种理论机理,分别为催化成炭(如沸石)或热氧化成炭作用(如二氧化锰),但实际上,这两种机理都作用甚微。该协效体系主要的作用机理是APP热分解生成的聚磷酸与金属化合物之间的作用。因为只有两价与高价的金属氧化物具备上述协效性,故有理由相信是金属阳离子促进了聚磷酸的交联而提高了后者的粘度,从而形成了隔热性更佳的类炭层结构。如添加大量的金属氧化物,可形成结晶磷酸盐,这将导致形成炭层裂缝以及隔热性的降低。这同时也是该协效体系只能在特定配比时才能发挥协效作用的原因。
54Because of increased attention to halogen-free systems in recent years, there
has also been a significant effort to enhance the fire retardant performance of aluminum hydroxide (ATH) and magnesium hydroxide (MH), because these additives are used at very high loading levels. It is interesting that just a simple combination of ATH and MH can be synergistic. This probably relates to the extension of the temperature interval for the elimination of water. Combinations of MH and zinc borate were found to be synergistic in poly(ethylene-co-vinyl acetate), (EVA) according to a cone calorimeter study. It was found that zinc borate catalyzes dehydration of MH. In addition, zinc borate helps to sinter particles of MgO together, which, in turn, leads to better retention of combustible
polymer in the condensed phase and eventual charring. Further addition to MH and zinc borate to nanoclay and low-melting glass allowed achievement of a V-0 rating in the UL-94 test.
近年来,人们对于无卤阻燃系统的关注度在逐渐升温,同时也在致力于改善ATH与MH需极大添加量才能发挥阻燃作用的现状。有趣的是,ATH与MH简单混合即可发挥协同作用,这可能与复合物脱水温度范围的延长有关。Cone研究表明,乙烯-乙烯醋酸共聚物(EVA)中,MH与ZB可发挥协效阻燃作用,ZB可催化MH脱水。此外在凝聚相中,ZB可促进MgO微粒结块形成隔热层并最终成炭。在纳米粘土和低熔玻纤改性的EVA中,添加MH与ZB协效阻燃体系可使材料达到UL94V-0级。


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