protect the substrate from oxygen attack. Intumescent FR research was started in the
19th century using organic polymers. In 1821, Gay-Lussac started his research on
FR cellulosic materials and he recommended the use of ammonium phosphate to
improve the FR properties of polymeric materials. Later on, Tramm et al. described
an intumescent coating and patented it in 1930. Intumescent coatings have attracted
much attention due to their anti-dripping property, halogen-free composition, low
smoke emission, and low amount of toxic gases. Presently, intumescent FRs are
used commercially in many surface-coating applications, for example on wood,
plastics, and metals, to provide fire protection. Most N-based salts and N,P-based
salts show intumescent flame retardant (IFR) activity. Some metal oxides containing graphene and clay also exhibit IFR activity. Intumescent FRs lead to the
formation of a dense char layer; therefore, char-forming agents, such as ammonium
polyphosphates (APP) and melamine polyphosphate (MPP), are introduced into
polymers to prepare such FRs. Currently, research is focused on the development of
FR PUs due to their multitude of applications in various domains, such as furniture,
electronic devices, vehicles, surface coatings, and foams [4, 10]. However, all
commercially available PUs using for various applications are flammable.
Therefore, a number of FRs are introducing into PUs through chemical reactions.
If FR compounds are part of the monomer or polymer, the corresponding polymer
is inherently flame retardant. There are two commonly used methods to achieve
flame retardancy in polymers, namely additive-type and reactive-type methods.
2.1.4.1 Additive Method
In this method, FR polymers are prepared via physical mixing. Additive FRs are
incorporated in the polymer matrix without any chemical bonding between the
additives and polymer. The FR additives are dispersed evenly throughout the
polymer matrix via physical interactions, such as H-bonding, van der Waals forces,
and ionic interactions. Most additive FRs are not compatible with polymers and
may experience phase separation and leaching. As there are no covalent bonds
between the polymers and additive FRs, this method is not effective in improving
the FR properties of polymers. Therefore, in order to increase the FR activity, large
quantities of FR additives should be incorporated, which adversely affects the
mechanical properties of the polymers.
2.1.4.2 Reactive Method
Using this method, FR polymers are synthesized via the introduction of reactive FR
additives into the polymer in the form of a monomer or polymer precursor.
Consequently, reactive FRs are more effective in improving the FR activity of
polymers compared to additive-type FRs owing to the presence of covalent bonds
between the FR compounds and polymers; under such conditions, the FR additives
are neither phase-separated nor leached out. However, they do not increase the
8
2 Polymer Combustion and Flame Retardancy
19th century using organic polymers. In 1821, Gay-Lussac started his research on
FR cellulosic materials and he recommended the use of ammonium phosphate to
improve the FR properties of polymeric materials. Later on, Tramm et al. described
an intumescent coating and patented it in 1930. Intumescent coatings have attracted
much attention due to their anti-dripping property, halogen-free composition, low
smoke emission, and low amount of toxic gases. Presently, intumescent FRs are
used commercially in many surface-coating applications, for example on wood,
plastics, and metals, to provide fire protection. Most N-based salts and N,P-based
salts show intumescent flame retardant (IFR) activity. Some metal oxides containing graphene and clay also exhibit IFR activity. Intumescent FRs lead to the
formation of a dense char layer; therefore, char-forming agents, such as ammonium
polyphosphates (APP) and melamine polyphosphate (MPP), are introduced into
polymers to prepare such FRs. Currently, research is focused on the development of
FR PUs due to their multitude of applications in various domains, such as furniture,
electronic devices, vehicles, surface coatings, and foams [4, 10]. However, all
commercially available PUs using for various applications are flammable.
Therefore, a number of FRs are introducing into PUs through chemical reactions.
If FR compounds are part of the monomer or polymer, the corresponding polymer
is inherently flame retardant. There are two commonly used methods to achieve
flame retardancy in polymers, namely additive-type and reactive-type methods.
2.1.4.1 Additive Method
In this method, FR polymers are prepared via physical mixing. Additive FRs are
incorporated in the polymer matrix without any chemical bonding between the
additives and polymer. The FR additives are dispersed evenly throughout the
polymer matrix via physical interactions, such as H-bonding, van der Waals forces,
and ionic interactions. Most additive FRs are not compatible with polymers and
may experience phase separation and leaching. As there are no covalent bonds
between the polymers and additive FRs, this method is not effective in improving
the FR properties of polymers. Therefore, in order to increase the FR activity, large
quantities of FR additives should be incorporated, which adversely affects the
mechanical properties of the polymers.
2.1.4.2 Reactive Method
Using this method, FR polymers are synthesized via the introduction of reactive FR
additives into the polymer in the form of a monomer or polymer precursor.
Consequently, reactive FRs are more effective in improving the FR activity of
polymers compared to additive-type FRs owing to the presence of covalent bonds
between the FR compounds and polymers; under such conditions, the FR additives
are neither phase-separated nor leached out. However, they do not increase the
8
2 Polymer Combustion and Flame Retardancy