Investigation Of Effects Of Two Flame Retardants On The Fire Characterisit Ics Of Flexible Poly Ether Foam

2.2    Flame Retardants
Flame retardants are materials that inhibit or resist the spread of fire. They are materials capable of increasing fire resistance, especially by reducing the ease with which a polymer burns[14]. They usually contain one of these elements; phosphorus, boron, halogen or antimony. These flame retardants may be physically blended with or chemically bonded to the host polymer. They generally either lower ignition susceptibility or lower flame spread once ignition has occurred.
2.2.1    Historical development of flame retardants.
The use of flame    retardants    has been practiced in the ancient time since about the year 450 BC [15] when alum was    used    to        reduce    the    flammability    of    wood    by    the E gyptians. In about the year 200 BC the Romans used the mixture of clay and gypsum as flame retardants on wood. Mixture of alum and vinegar as flame retardant was used to reduce flammability of theatre curtains, at about 1638. In 1735, alum was mixed with ferrous sulphate and borax to reduce flammability in wood and textiles by Wyld in Britain. In the year 1783, alum was used to retard flammability in balloons. In 1821, Gay -Lussac reported a mixture of Tri ammonium        orthophosphate        [(NH 4)3PO4],        Ammonium chloride [NH4Cl] and borax to be  effective on linen and hemp. In 1912 Perkin described a flame -retardant treatment for cotton using a mixture of sodium st annate and ammonium sulphate [(NH 4)2SO4].
In the early 19th century, with advent of synthetic polymers, modern developments were concentrated on the development of polymer compatible flame retardants. With the outbreak of the Second World War in 1945, flame-proof canvas for outdoor use by the military was produced. These were treated with chlorinated parafins, and an insoluble metal oxide, mostly antimony oxide as a glow inhibitor, plus a binder resin [15]. After the war, there was an increase in use of thermoplastics and thermosets on a large s cale for applications in building, transportation, electrical engineering and electronics, new flame retardant systems were developed. These, mainly consists of inorgan ic and organic compounds based o n bromine, chlorine, phosphorus, nitrogen, boron, and metallic oxides and hydroxides.
2.2.2    Types of flame retardants
Flame retardants can be distincted into reactive and additive flame retardants [16]. Reactive flame retardants are reactive components chemically buil t into a polymer molecule. Additive flame retardants are incorporated into the polymer either prior to, during or (most frequently) following polymerization.
Flame-retardant chemicals are divided into four families [17- 22]. These are inorganic, halogenate d, organophosphorus and nitrogen-based flame retardants.
Classification of flame retardants
•    Flame retardants are classified based on different conditions which include durability, nature of the compounds and methods of incorporation to the host polymer.
•    Classification of flame retardants based on durability