Chapter 2
Polymer Combustion and Flame
Retardancy
Most polymers are derived from petroleum hydrocarbon sources and hence are
extremely flammable. However, for any material to catch fire, oxygen, heat, and
external energy are essential. During combustion, polymer particles become airborne; when a polymer is exposed to high heat energy, a significant amount of
degradation occurs. During this process, airborne particles are evolved along with
combustible volatile substances and mix with atmospheric oxygen. If the ambient
temperature is close to or above the ignition temperature (flash point temperature),
then these airborne particles will ignite. Some of the heat is fed back to the polymer
for further degradation, as shown in Fig. 2.1; in a similar way, volatile substrates
and flames will spread in a cyclic process until the polymer completely burns to
produce pyrolytic components containing heat, smoke, fumes, and toxic gases, as
depicted in Fig. 2.1. This scheme helps us to understand the process of polymer
combustion; based on this concept, different types of fire retardants (FRs) have been
designed and developed by various researchers to decrease or delay the flammability of polymers. These FRs are used to synthesize FR polymers; hence, in the
presence of a FR, the flammability of polymers is decreased. Moreover, the flame
toxicity is reduced.
In the last two decades, literally hundreds of test methods have been developed
to assess the response of plastic materials to fire and quantify flame retardance. The
cone calorimeter test is one of the most extensively used bench-scale methods for
studying the fire-retardant properties of polymeric materials. Fire-relevant properties such as the heat release rate (HRR), peak HRR, smoke production, and carbon
dioxide yield are vital to the evaluation of the fire safety of materials.
HRR is one parameter to assess the FR activity of polymers because in the
presence of heat, polymer degradation is accelerated, resulting in an increase in the
amount of airborne components, which are responsible for flame propagation. When
exposed to flame, a FR releases flame inhibitors either in the form of radicals or acidic
components. FR polymers are synthesized using FR additives and these additives
adopt various chemical pathways (such as condensed-phase and gas-phase mechanisms) to exhibit FR activity. In the gas-phase mechanism, FR activity is attributed to
© Springer Nature Switzerland AG 2020
S. Sinha Ray and M. Kuruma, Halogen-Free Flame-Retardant
Polymers, Springer Series in Materials Science 294,
https://doi.org/10.1007/978-3-030-35491-6_2
5
Polymer Combustion and Flame
Retardancy
Most polymers are derived from petroleum hydrocarbon sources and hence are
extremely flammable. However, for any material to catch fire, oxygen, heat, and
external energy are essential. During combustion, polymer particles become airborne; when a polymer is exposed to high heat energy, a significant amount of
degradation occurs. During this process, airborne particles are evolved along with
combustible volatile substances and mix with atmospheric oxygen. If the ambient
temperature is close to or above the ignition temperature (flash point temperature),
then these airborne particles will ignite. Some of the heat is fed back to the polymer
for further degradation, as shown in Fig. 2.1; in a similar way, volatile substrates
and flames will spread in a cyclic process until the polymer completely burns to
produce pyrolytic components containing heat, smoke, fumes, and toxic gases, as
depicted in Fig. 2.1. This scheme helps us to understand the process of polymer
combustion; based on this concept, different types of fire retardants (FRs) have been
designed and developed by various researchers to decrease or delay the flammability of polymers. These FRs are used to synthesize FR polymers; hence, in the
presence of a FR, the flammability of polymers is decreased. Moreover, the flame
toxicity is reduced.
In the last two decades, literally hundreds of test methods have been developed
to assess the response of plastic materials to fire and quantify flame retardance. The
cone calorimeter test is one of the most extensively used bench-scale methods for
studying the fire-retardant properties of polymeric materials. Fire-relevant properties such as the heat release rate (HRR), peak HRR, smoke production, and carbon
dioxide yield are vital to the evaluation of the fire safety of materials.
HRR is one parameter to assess the FR activity of polymers because in the
presence of heat, polymer degradation is accelerated, resulting in an increase in the
amount of airborne components, which are responsible for flame propagation. When
exposed to flame, a FR releases flame inhibitors either in the form of radicals or acidic
components. FR polymers are synthesized using FR additives and these additives
adopt various chemical pathways (such as condensed-phase and gas-phase mechanisms) to exhibit FR activity. In the gas-phase mechanism, FR activity is attributed to
© Springer Nature Switzerland AG 2020
S. Sinha Ray and M. Kuruma, Halogen-Free Flame-Retardant
Polymers, Springer Series in Materials Science 294,
https://doi.org/10.1007/978-3-030-35491-6_2
5