the release of non-flammable gases and radicals, such as –Cl, –Br, and –OH,
which interrupt flame propagation. In the condensed-phase FR mechanism, acid
compounds, such as phosphorus and sulfur-containing acids are formed; they
dehydrate the polymer and form a char layer on the surface of the polymer. This char
layer can prevent heat and oxygen from coming into contact with the polymer and
thus its flammability is reduced. Based on these phenomena, FR activity is classified
into various categories, which will be discussed in the following sections.
2.1 FR Polymers
Since the end of the last decade, different types of FRs have been used for the
synthesis of FR polymers either as chain extenders or monomers. When a FR
polymer is exposed to flame, it inhibits or suppresses the initial stages of flame by
releasing non-flammable gases or by forming char during burning. Hence, the
synthesis of easy-to-use FR polymers is extremely important for different applications. The synthesis of FR materials gained much attention in the USA during
World War II; in particular, FR military clothing and aerospace coatings were
considered to be of paramount importance. A FR does not burn but prevents or
delays the flammability of the material in which it is incorporated. Overall, the best
FRs are expected to exhibit three key properties, viz (i) increasing the limiting
oxygen index (LOI) value, (ii) decreasing the peak HRR, and (iii) suppress smoke.
The basic FR mechanism varies depending on the type of FR used, chemical
Fig. 2.1 Schematic representation of a polymer combustion cycle
6
2 Polymer Combustion and Flame Retardancy
which interrupt flame propagation. In the condensed-phase FR mechanism, acid
compounds, such as phosphorus and sulfur-containing acids are formed; they
dehydrate the polymer and form a char layer on the surface of the polymer. This char
layer can prevent heat and oxygen from coming into contact with the polymer and
thus its flammability is reduced. Based on these phenomena, FR activity is classified
into various categories, which will be discussed in the following sections.
2.1 FR Polymers
Since the end of the last decade, different types of FRs have been used for the
synthesis of FR polymers either as chain extenders or monomers. When a FR
polymer is exposed to flame, it inhibits or suppresses the initial stages of flame by
releasing non-flammable gases or by forming char during burning. Hence, the
synthesis of easy-to-use FR polymers is extremely important for different applications. The synthesis of FR materials gained much attention in the USA during
World War II; in particular, FR military clothing and aerospace coatings were
considered to be of paramount importance. A FR does not burn but prevents or
delays the flammability of the material in which it is incorporated. Overall, the best
FRs are expected to exhibit three key properties, viz (i) increasing the limiting
oxygen index (LOI) value, (ii) decreasing the peak HRR, and (iii) suppress smoke.
The basic FR mechanism varies depending on the type of FR used, chemical
Fig. 2.1 Schematic representation of a polymer combustion cycle
6
2 Polymer Combustion and Flame Retardancy