Retardant fillers smoke formation

One of the emerging technologies that is showing great promise is the use of hydrated mineral fillers such as aluminium and magnesium hydroxides, as such materials can provide high levels of flame retardancy without the formation of smoke or corrosive and potentially toxic fumes. The use of fillers as flame retardants has recently been reviewed by Rothon [23]. Essentially the key features are an endothermic decomposition to reduce the temperature, the release of an inert gas to dilute the combustion gases and the formation of an oxide layer to insulate the polymer and to trap and oxidise soot precursors. 

Fire retardant fillers affect smoke formation. " Table 12.5 gives some data on the specific extinction area. The data show that, with the exceptions of A1(OH)3 and Mg(OH)2, fillers have a small effect on smoke suppression. 

Major results General fillers do not affect smoke formation by any means other than simple dilution. Fire retardant fillers such as Mg(0H)2 decrease smoke formation only at high concentrations." Materials which are known catalysts of degradation (e.g., copper) increase smoke formation. ... 

Combined filler and flame retardant functions Does not require halogens Does not produce toxic gases Suppresses smoke formation Non-volatile and unaffected by water Low cost Non-toxic Requires high loadings Affects physical properties and processing behaviour Relatively low decomposition temperature... 

Zinc borate is an inorganic flame retardant which can be used by itself or in combination with aluminum hydroxide or magnesium hydroxide with which it forms synergistic mixtures of high performance flame retardants. It is frequently used as a surface coating on these two fillers. It reduces smoke emission and promotes char formation. 

Joseph Storey has introduced a zinc hydroxystannate flame retardant, which it found to be the closest non-toxic alternative to antimony trioxide in halogenated systems. The new material also has excellent smoke suppression properties. In halogen-free systems, tin char formation occurs, leading to reductions in filler loadings and improved physical properties. 

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