Commonly synthesized NPs include Ag, Au, Cu, Pd, Pt, Re, Ru, Zn, Co, Al, Cd,
Pb, Fe, and Ni; among them Fe and Ni are highly reactive and explosive. Further,
metal NPs can also include the category of bimetallic NPs (i.e., Pt–Pd, Cu–Ni),
which often exist as core–shell and alloy structures. Bimetallic NPs have better
properties or efficiency than their single-metal NP counterparts [15]. Metal NPs are
produced in the form of colloidal solutions or solid particles by simple techniques,
such as bio-assisted synthesis, hydrothermal synthesis, microwave-assisted synthesis. They have shown interesting characteristics, such as localized surface
plasmon resonance (LSPR), high reactivity, and broad absorption in the electromagnetic spectrum. Due to their advanced optical, optoelectrical, catalytic,
anti-microbial/-cancer/-viral properties, metal NPs are highly interesting materials
for numerous practical applications.
Metal oxides are considered one of the most stable naturally occurring compounds. They are formed by reaction between electronegative oxygen and electropositive metal. They have polar surfaces due to presence of anionic oxygen and
are insoluble in most organic solvents due to strong bonding between the metal and
oxygen. The formation of metal oxides is the lowest free energy states for the
metals in the oxidative nature of Earth and among other compounds of periodic
table. Presently, they are widely used nanomaterials due to their high natural
abundance, high chemical stability, tunable bandgap/band edge positions, and
excellent thermal/electrical conductivity. Their applications include semiconductors, superconductors, and even insulators. With growing industrial interest, various
types of versatile metal oxides, such as Al 2 O 3 , TiO 2 , Fe 3 O 4 , Fe 2 O 3 , SiO 2 , ZnO, and
CeO 2 have been synthesized for application in the water purification, cosmetics,
bio-medical, energy, and environmental remediation fields. These metal oxides can
be easily modified by doping, resulting in hetero-structures and mixed oxides, to
further meet the stringent demands of excellent properties and efficiency. (Layered)
metal hydroxides are an interesting category of inorganic nanomaterials with
flexible properties achieved by tailoring the structure and composition. These
materials occur in two forms: (1) hydroxides with neutral layers, without intercalated molecules (i.e., b-Ni(OH) 2 and b-Cu(OH) 2 ); (2) hydroxides with a cationic
layer and with intercalated molecules (i.e., a-Ni(OH) 2 and a-Cu(OH) 2 ) [16]. Due to
their high surface area, high thermal stability, and excellent ion exchange capability, these materials have attracted attention for catalysis, supercapacitors, fuel
cells, flame retardants, sensors, and pollutant removal.
To improve the FR activity of polymers, various metal oxide NPs, such as Cu 2 O,
MoO 3 , Sb 2 O 3 , Bi 2 O 3 , Co 3 O 4 , and SnO 2 have been used to prepare polymer
nanocomposites [17–19]. These metal oxides can catalyze the formation of char
residue and strengthen it during polymer combustion. It has been reported Cu dust
and Cu 2 O are excellent smoke suppressants for all polymers, especially for PU
polymers [20–22]. In the initial stages, Cu 2 O nanoparticles catalyze the formation
of poly phosphoric acid from EDA-APP, subsequent dehydration of EP, and
accelerate the formation of intumescent char as shown in Fig. 7.1. This char layer
acts as a barrier to heat and O 2 transfer. Further, it limits the supply of flammable
gases to the flame zone, resulting in a reduced smoke and toxic gas evolution. Due
84
7 Polymer Nanocomposites for Fire Retardant Applications
Pb, Fe, and Ni; among them Fe and Ni are highly reactive and explosive. Further,
metal NPs can also include the category of bimetallic NPs (i.e., Pt–Pd, Cu–Ni),
which often exist as core–shell and alloy structures. Bimetallic NPs have better
properties or efficiency than their single-metal NP counterparts [15]. Metal NPs are
produced in the form of colloidal solutions or solid particles by simple techniques,
such as bio-assisted synthesis, hydrothermal synthesis, microwave-assisted synthesis. They have shown interesting characteristics, such as localized surface
plasmon resonance (LSPR), high reactivity, and broad absorption in the electromagnetic spectrum. Due to their advanced optical, optoelectrical, catalytic,
anti-microbial/-cancer/-viral properties, metal NPs are highly interesting materials
for numerous practical applications.
Metal oxides are considered one of the most stable naturally occurring compounds. They are formed by reaction between electronegative oxygen and electropositive metal. They have polar surfaces due to presence of anionic oxygen and
are insoluble in most organic solvents due to strong bonding between the metal and
oxygen. The formation of metal oxides is the lowest free energy states for the
metals in the oxidative nature of Earth and among other compounds of periodic
table. Presently, they are widely used nanomaterials due to their high natural
abundance, high chemical stability, tunable bandgap/band edge positions, and
excellent thermal/electrical conductivity. Their applications include semiconductors, superconductors, and even insulators. With growing industrial interest, various
types of versatile metal oxides, such as Al 2 O 3 , TiO 2 , Fe 3 O 4 , Fe 2 O 3 , SiO 2 , ZnO, and
CeO 2 have been synthesized for application in the water purification, cosmetics,
bio-medical, energy, and environmental remediation fields. These metal oxides can
be easily modified by doping, resulting in hetero-structures and mixed oxides, to
further meet the stringent demands of excellent properties and efficiency. (Layered)
metal hydroxides are an interesting category of inorganic nanomaterials with
flexible properties achieved by tailoring the structure and composition. These
materials occur in two forms: (1) hydroxides with neutral layers, without intercalated molecules (i.e., b-Ni(OH) 2 and b-Cu(OH) 2 ); (2) hydroxides with a cationic
layer and with intercalated molecules (i.e., a-Ni(OH) 2 and a-Cu(OH) 2 ) [16]. Due to
their high surface area, high thermal stability, and excellent ion exchange capability, these materials have attracted attention for catalysis, supercapacitors, fuel
cells, flame retardants, sensors, and pollutant removal.
To improve the FR activity of polymers, various metal oxide NPs, such as Cu 2 O,
MoO 3 , Sb 2 O 3 , Bi 2 O 3 , Co 3 O 4 , and SnO 2 have been used to prepare polymer
nanocomposites [17–19]. These metal oxides can catalyze the formation of char
residue and strengthen it during polymer combustion. It has been reported Cu dust
and Cu 2 O are excellent smoke suppressants for all polymers, especially for PU
polymers [20–22]. In the initial stages, Cu 2 O nanoparticles catalyze the formation
of poly phosphoric acid from EDA-APP, subsequent dehydration of EP, and
accelerate the formation of intumescent char as shown in Fig. 7.1. This char layer
acts as a barrier to heat and O 2 transfer. Further, it limits the supply of flammable
gases to the flame zone, resulting in a reduced smoke and toxic gas evolution. Due
84
7 Polymer Nanocomposites for Fire Retardant Applications