Potential Endothermic Flame Retardant Fillers

Despite these reservations, the presently available data suggests that, with the possible exception of nesquehonite, none of the candidate materials is a significantly more effective flame retardant than aluminium hydroxide (also known as alumina trihydrate or ATH), although as will be shown later, magnesium hydroxide may have some advantages in terms of smoke production. 

ATH also comes closest to meeting all of the criteria mentioned previously, and this explains its current pre-eminence. It owes its relatively low cost and wide availability to its production on a vast scale as an intermediate in alumina manufacture. The main limitation of ATH is 

Candidate material (common names and formula) Approximate onset of decomposition i°C) Approximate enthalpy of decomposition (kj kg-i) Volatile content % w/w  

Calcium sulfate dihydrate, Gypsum CaS04.2H20 60-130 Not available 21 0 21 

Basic magnesium carbonate. Hydromagnesite 4.MgC03.Mg(0H)2.4H30 220-240 1,300 19 38 57 

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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. 

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