propagation. The main advantage of using FRs is that they limit the release of toxic
gases and noxious smoke; further, they can eliminate polymer dripping during
burning and spreading of fire. FRs are broadly classified into halogenated and
non-halogenated FRs.
Over the years, halogenated FRs (HFRs) are the most commonly used FRs in the
plastic industry. HFRs are said to act in the vapor phase that means they actually
interfere with the chemistry of the flame. Chlorinated and brominated are both used
in this role, but brominated FRs have been the most effective and the most common
one is hexabromocyclododecane. However, HFRs generate a large amount of toxic
gases and smoke. Moreover, HFRs can cause environmental pollution as they
release large amounts of smoke and toxic corrosive gases. Therefore, environmental
concerns and governmental regulations restrain the use of HFRs in several countries. Thus, it is necessary to develop novel environment-friendly and efficient FRs
to achieve a balance between FR performance and environmental issues.
There are several factors that affect polymer flammability, but the most important and crucial factor is the chemical structure of the polymer. From literature, it is
clear that aromatic, hetero aromatic, and non-burning hetero atoms, such as N-, P-,
S-, Si-, and B-containing derivative compounds, when incorporated into the
polymer main chain or copolymerized, efficiently reduced flammability [7–12]. The
thermal stability of a polymer also plays an important role in controlling its FR
activity. Moreover, the inherent mechanical properties, melt viscosity, melting
temperature (T m ), and glass transition temperature (T g ) of a polymer are also
important in determining its FR activity [13, 14]. It has been found that polymers
with superior mechanical, thermal, and rheological properties show excellent FR
activity. Generally, to improve the inherent properties of polymeric materials,
different types of nanofillers are incorporated in polymer matrices to prepare
polymer nanocomposites (PNCs) [15, 16]. However, to improve the FR activity,
these nanofillers are surface-modified with P- and/or N-containing surfactants in
order to improve their compatibility with polymeric matrices as well as to improve
their FR activity [17–20]. Heat release and toxic gas inhalation are the main reasons
for death in fire accidents; in fact, the number of such deaths is higher than that of
deaths occurring due to fire burns. Therefore, it is necessary to develop strong
fire-toxicant inhibitors; in the past few decades, immense research efforts have been
carried out in the area of polymeric FRs and smoke suppressants. The findings of
these studies revealed that graphene and nanoclay-functionalized metal oxides
exhibit excellent smoke toxicity and heat-release inhibition compared to pristine
metal oxides owing to their synergetic action [21–24]. C, N, and Si-based inorganic
network substituents exhibited flame retardant activity due to increasing char formation and reduction in the heat-release rate.
In this monograph, we critically review the main results of the academic and
industrial research on halogen-free FRs such as P-, N-, and P, N-based salts and
surface-modified nanofillers containing different types of P, N-based organic
compounds with respect to their synthesis, FR activity, and FR mechanism. In
particular, toxicant evolution and inhibition, FR mechanisms, synergetic effects,
2
1 Introduction
gases and noxious smoke; further, they can eliminate polymer dripping during
burning and spreading of fire. FRs are broadly classified into halogenated and
non-halogenated FRs.
Over the years, halogenated FRs (HFRs) are the most commonly used FRs in the
plastic industry. HFRs are said to act in the vapor phase that means they actually
interfere with the chemistry of the flame. Chlorinated and brominated are both used
in this role, but brominated FRs have been the most effective and the most common
one is hexabromocyclododecane. However, HFRs generate a large amount of toxic
gases and smoke. Moreover, HFRs can cause environmental pollution as they
release large amounts of smoke and toxic corrosive gases. Therefore, environmental
concerns and governmental regulations restrain the use of HFRs in several countries. Thus, it is necessary to develop novel environment-friendly and efficient FRs
to achieve a balance between FR performance and environmental issues.
There are several factors that affect polymer flammability, but the most important and crucial factor is the chemical structure of the polymer. From literature, it is
clear that aromatic, hetero aromatic, and non-burning hetero atoms, such as N-, P-,
S-, Si-, and B-containing derivative compounds, when incorporated into the
polymer main chain or copolymerized, efficiently reduced flammability [7–12]. The
thermal stability of a polymer also plays an important role in controlling its FR
activity. Moreover, the inherent mechanical properties, melt viscosity, melting
temperature (T m ), and glass transition temperature (T g ) of a polymer are also
important in determining its FR activity [13, 14]. It has been found that polymers
with superior mechanical, thermal, and rheological properties show excellent FR
activity. Generally, to improve the inherent properties of polymeric materials,
different types of nanofillers are incorporated in polymer matrices to prepare
polymer nanocomposites (PNCs) [15, 16]. However, to improve the FR activity,
these nanofillers are surface-modified with P- and/or N-containing surfactants in
order to improve their compatibility with polymeric matrices as well as to improve
their FR activity [17–20]. Heat release and toxic gas inhalation are the main reasons
for death in fire accidents; in fact, the number of such deaths is higher than that of
deaths occurring due to fire burns. Therefore, it is necessary to develop strong
fire-toxicant inhibitors; in the past few decades, immense research efforts have been
carried out in the area of polymeric FRs and smoke suppressants. The findings of
these studies revealed that graphene and nanoclay-functionalized metal oxides
exhibit excellent smoke toxicity and heat-release inhibition compared to pristine
metal oxides owing to their synergetic action [21–24]. C, N, and Si-based inorganic
network substituents exhibited flame retardant activity due to increasing char formation and reduction in the heat-release rate.
In this monograph, we critically review the main results of the academic and
industrial research on halogen-free FRs such as P-, N-, and P, N-based salts and
surface-modified nanofillers containing different types of P, N-based organic
compounds with respect to their synthesis, FR activity, and FR mechanism. In
particular, toxicant evolution and inhibition, FR mechanisms, synergetic effects,
2
1 Introduction