transform infrared spectroscopy (FTIR) or TGA-mass spectrometry (MS).
TGA-MS provides information on evolved gas fragment ions with their m/z values
and intensities. Meanwhile, TGA-FTIR provides information on the functional
groups in the decomposed components; further, any rearranged reaction intermediate compounds can also be analyzed. In general, PUs exhibit good physical
properties, such as durability, abrasion resistance, chemical resistance, and
self-lubrication and hence are considered industrially attractive polymers.
Therefore, it is necessary to know the properties of the produced smoke and toxic
gases when PUs are exposed to flame. Chlorinated phosphate esters are widely used
in the preparation of FR PU foams but their disadvantage is that their usage may
lead to high smoke and toxic corrosive gas content. Hence, it is necessary to study
the FR mechanism of PUs in the presence of various additives and FRs, which can
inhibit or decrease smoke and toxic gas evolution. Some additives effectively trap
the volatile isocyanates evolved during the combustion of PU foams, which
decreases smoke and toxic gas content. Price et al. [76] reported that smoke and
toxic gas evolution from PU foams can be reduced using melamine. At high
temperatures, melamine can react with the released isocyanates and suppresses
smoke and toxic gas evolution [77]. McKenna and Hull et al. [78] systematically
analyzed the release of toxic components from PU foams during combustion as well
as the methods employed to assess their flame toxicity. They further studied the
decomposition of PUs; at temperatures greater than 600 °C, volatile fragments of
PUs release nitrogen-rich “yellow smoke,” which contains volatile nitrogen compounds, non-volatile polyols, polymerized isocyanates, and isocyanate droplets.
The yellow smoke further decomposes into small volatile components, such as
HCN, CH 4 , CO 2 , CO, and NO 2 [78, 79]. From the practical viewpoint, a consideration of the associated fire hazards is important because they affect both human
lives and property. PUs are highly flammable and release large amounts of smoke,
heat, and toxic combustible gases; oxygen depletion, which occurs during burning
threatens human lives. The two main causes of fire-related deaths are inhalation of
toxic smoke and burns [80, 81]. Smoke development in flames is highly dependent
on the structure of the gases, which act as the fuel, and the ratio of fuel to oxidant.
Liu et al. [69] evaluated the thermal decomposition and smoke and toxic component
evolution from PU materials (Fig. 5.1). They also studied the factors affecting
smoke and toxic gas suppressants. Polymers consisting of only aliphatic structural
units generate relatively less smoke compared to polymers containing aromatic
groups in their backbone, but aliphatic polymers are more flammable than aromatic
compounds. To understand smoke and toxic gas generation, one must know the
chemical structure of the polymer and its thermal degradation characteristics.
The FR activity mechanism of a polymer can be either gas-phase or
condensed-phase, which can be determined using TG-FTIR and gas chromatography–mass spectrometry (GC–MS) [82]; these techniques can also be used to
determine rearranged reaction intermediates and mechanisms [83, 84]. On the basis
of the obtained results, it may possible to reduce smoke and toxic gas formation
during polymer burning. A number of reports are available on smoke and toxic gas
5.1 Thermal Degradation and Evolution of Components During PU …
51
TGA-MS provides information on evolved gas fragment ions with their m/z values
and intensities. Meanwhile, TGA-FTIR provides information on the functional
groups in the decomposed components; further, any rearranged reaction intermediate compounds can also be analyzed. In general, PUs exhibit good physical
properties, such as durability, abrasion resistance, chemical resistance, and
self-lubrication and hence are considered industrially attractive polymers.
Therefore, it is necessary to know the properties of the produced smoke and toxic
gases when PUs are exposed to flame. Chlorinated phosphate esters are widely used
in the preparation of FR PU foams but their disadvantage is that their usage may
lead to high smoke and toxic corrosive gas content. Hence, it is necessary to study
the FR mechanism of PUs in the presence of various additives and FRs, which can
inhibit or decrease smoke and toxic gas evolution. Some additives effectively trap
the volatile isocyanates evolved during the combustion of PU foams, which
decreases smoke and toxic gas content. Price et al. [76] reported that smoke and
toxic gas evolution from PU foams can be reduced using melamine. At high
temperatures, melamine can react with the released isocyanates and suppresses
smoke and toxic gas evolution [77]. McKenna and Hull et al. [78] systematically
analyzed the release of toxic components from PU foams during combustion as well
as the methods employed to assess their flame toxicity. They further studied the
decomposition of PUs; at temperatures greater than 600 °C, volatile fragments of
PUs release nitrogen-rich “yellow smoke,” which contains volatile nitrogen compounds, non-volatile polyols, polymerized isocyanates, and isocyanate droplets.
The yellow smoke further decomposes into small volatile components, such as
HCN, CH 4 , CO 2 , CO, and NO 2 [78, 79]. From the practical viewpoint, a consideration of the associated fire hazards is important because they affect both human
lives and property. PUs are highly flammable and release large amounts of smoke,
heat, and toxic combustible gases; oxygen depletion, which occurs during burning
threatens human lives. The two main causes of fire-related deaths are inhalation of
toxic smoke and burns [80, 81]. Smoke development in flames is highly dependent
on the structure of the gases, which act as the fuel, and the ratio of fuel to oxidant.
Liu et al. [69] evaluated the thermal decomposition and smoke and toxic component
evolution from PU materials (Fig. 5.1). They also studied the factors affecting
smoke and toxic gas suppressants. Polymers consisting of only aliphatic structural
units generate relatively less smoke compared to polymers containing aromatic
groups in their backbone, but aliphatic polymers are more flammable than aromatic
compounds. To understand smoke and toxic gas generation, one must know the
chemical structure of the polymer and its thermal degradation characteristics.
The FR activity mechanism of a polymer can be either gas-phase or
condensed-phase, which can be determined using TG-FTIR and gas chromatography–mass spectrometry (GC–MS) [82]; these techniques can also be used to
determine rearranged reaction intermediates and mechanisms [83, 84]. On the basis
of the obtained results, it may possible to reduce smoke and toxic gas formation
during polymer burning. A number of reports are available on smoke and toxic gas
5.1 Thermal Degradation and Evolution of Components During PU …
51