Fire retardant polymers flammability characteristics

It is seen from Table 6.7 that, without exception, in a wide range of commercially available fire retardant polymers the incorporation of fire retardant additives into the formulation produces distinct improvements in LOI values and flammability and flame spread characteristics of the polymers listed. 

Polymers in their raw state are usually technically unsatisfactory in one respect or another, such as their stability to light or heat, or their processability, or flammability, or colour, or opacity, or antistatic characteristics, etc., and they simply could not be used in commercial applications successfully without the incorporation of one or more additives [2] to modify behaviour. The additives are often present at very low concentrations (0.1-3 parts per hundred of resin, by weight) and are called stabilizers, UV absorbers, viscosity modifiers, lubricants, fire retardants, pigments, etc. Fillers may be present at 50 or even 150 parts per hundred of resin, by weight. Thermosetting resins tend to have fewer additives of the kind... 

For some non-fire retardant grades of polymers, fire retardancy characteristics might improve when a filler is incorporated into the formulation. Thus, for epoxy resins, the incorporation of minerals, glass fibre, silica or graphite all improve flame spread, flammability and LOI from the poor category for the virgin polymer to the good... 

Apart from the decomposition temperature, the propensity for char formation is another polymer thermal characteristic of practical importance. The char-forming tendency generally shows a negative correlation with flammability a sample with the greatest char residue is also the least flammable polymer and the presence of flame retardant additives also increases char formation. In the case of fire, the amorphous crust of char material that forms on the fluid surface reduces the heat flux to the burning fluid, which in turn reduces the combustion rate. 

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