223
Flammability and the Flame Retardants
Flammability is a process that involves various steps before a substance is completely destroyed by the fire. These steps include (a) preheating of the material, (b)
decomposition, (c) ignition, and (d) combustion and propagation. When an external
source heats the materials, it results in an increase in the temperature of the material
at a rate dependent upon the intensity of the ignition source, thermal conductivity of
the material, specific heat of the material, and latent heat of fusion and vaporization
of the material. An extreme rise in a material’s temperature can cause decomposition of the materials and the weak bonds of materials start to break down the material into gaseous compounds. An increasing concentration of the decomposed
gaseous compounds allows for sustained oxidation in the presence of an ignition
source and the available oxygen-rich environment makes the material ignite without
the need of the ignition source, leading to the self-propagating combustion of the
material [7]. However, decreasing the rate of heating, ignition, and combustion by
the addition of specific chemicals that can physically or chemically hinder the flammability process can significantly retard the flammability and such chemicals are
dubbed as FRs.
FRs have the ability to constrain, minimize, or delay the spread of fire by quashing
the chemical reaction in the fire. They may also work by creating an external protective layer on a material [8], thereby serving as an insulation coating to reduce the
chances of catching fire by decreasing the rate of heating. FRs have found their use
in various daily-life products, for example plastics, textiles, electronics, construction
materials, and furnishing foams to reduce fire hazards [9], thus the market share of
FRs is worth billions of dollars. In 2016, an estimated worldwide consumption was
2.3 million metric tons with an annual increase in production by 3% globally [10].
Based on their method of incorporation in polymers, FRs are either additive or
reactive [11]. Additive FRs are usually mixed or dissolved within the polymeric
materials, while reactive type retardants are chemically attached with the polymeric
materials through covalent bonds [1, 11]. Most of the additive FRs are volatile and
may leach out in the environment easily, whereas reactive mixtures tend to leach out
far less than the additive counterpart does. Due to their increasing use, widespread
exposure within the environment with FRs is inevitable and many documented evidences show the presence of FRs in various environmental media, including indoor
and outdoor air [12], water (surface or groundwater) [13], oceans [14] and even in
human milk [15]. Thus, FRs present serious health risks to humans and wildlife [16].
Based on their activity, FRs work either in their vapor phase or the condensed
phase, as depicted in Fig. 14.1. Furthermore, they differ from each other by their
mechanism of action and FRs may act through chemical or physical mechanisms to
impede the combustion process during preheating, decomposition, ignition, and
flame propagation [17, 18]. Overall, more than 175 different types of FRs are known,
which are generally classified under five major categories that include halogenated,
organophosphate, nitrogenous, inorganic, and intumescent coatings [19]. Here, we
have briefly discussed various FRs.
14 Role of Flame-Retardants as EDCs in Metabolic Disorders
Flammability and the Flame Retardants
Flammability is a process that involves various steps before a substance is completely destroyed by the fire. These steps include (a) preheating of the material, (b)
decomposition, (c) ignition, and (d) combustion and propagation. When an external
source heats the materials, it results in an increase in the temperature of the material
at a rate dependent upon the intensity of the ignition source, thermal conductivity of
the material, specific heat of the material, and latent heat of fusion and vaporization
of the material. An extreme rise in a material’s temperature can cause decomposition of the materials and the weak bonds of materials start to break down the material into gaseous compounds. An increasing concentration of the decomposed
gaseous compounds allows for sustained oxidation in the presence of an ignition
source and the available oxygen-rich environment makes the material ignite without
the need of the ignition source, leading to the self-propagating combustion of the
material [7]. However, decreasing the rate of heating, ignition, and combustion by
the addition of specific chemicals that can physically or chemically hinder the flammability process can significantly retard the flammability and such chemicals are
dubbed as FRs.
FRs have the ability to constrain, minimize, or delay the spread of fire by quashing
the chemical reaction in the fire. They may also work by creating an external protective layer on a material [8], thereby serving as an insulation coating to reduce the
chances of catching fire by decreasing the rate of heating. FRs have found their use
in various daily-life products, for example plastics, textiles, electronics, construction
materials, and furnishing foams to reduce fire hazards [9], thus the market share of
FRs is worth billions of dollars. In 2016, an estimated worldwide consumption was
2.3 million metric tons with an annual increase in production by 3% globally [10].
Based on their method of incorporation in polymers, FRs are either additive or
reactive [11]. Additive FRs are usually mixed or dissolved within the polymeric
materials, while reactive type retardants are chemically attached with the polymeric
materials through covalent bonds [1, 11]. Most of the additive FRs are volatile and
may leach out in the environment easily, whereas reactive mixtures tend to leach out
far less than the additive counterpart does. Due to their increasing use, widespread
exposure within the environment with FRs is inevitable and many documented evidences show the presence of FRs in various environmental media, including indoor
and outdoor air [12], water (surface or groundwater) [13], oceans [14] and even in
human milk [15]. Thus, FRs present serious health risks to humans and wildlife [16].
Based on their activity, FRs work either in their vapor phase or the condensed
phase, as depicted in Fig. 14.1. Furthermore, they differ from each other by their
mechanism of action and FRs may act through chemical or physical mechanisms to
impede the combustion process during preheating, decomposition, ignition, and
flame propagation [17, 18]. Overall, more than 175 different types of FRs are known,
which are generally classified under five major categories that include halogenated,
organophosphate, nitrogenous, inorganic, and intumescent coatings [19]. Here, we
have briefly discussed various FRs.
14 Role of Flame-Retardants as EDCs in Metabolic Disorders