**4. Polymers - a fire safety perspective**

Polymers of varying compositional structures are wide spread in many everyday items [39] both in synthetic and to a lesser extent in biomaterials are a probable source of toxic inhalation during decomposition in fires. Most constitute a fire risk in many household appliances, furniture and wearable materials as the elements of polymer combustion drive fire propagation from the point of ignition. A growing body of evidence suggests that the reinforcement of polymers show a strong correlation with fire resistance while reducing the need for excessive use of fire retardant as single component materials in goods. The physical and chemical relationships between polymer behavior and fire progression has a unique place in engineering with the potential to offer new flame retardants that are both safe and effective. The complexity in the development of effective flame retardants is depicted in **Figure 7** [40] and empathizes the potential for multi-levels of combustibility that lie between the condensed (liquid) and expanded (gaseous) interfaces. As pointed out by Huiqing [40], the combustion cycle of polymer materials subject to a pyrolytic state pass through an [1] initial heating phase, reaching the [2] decomposition phase followed by the [3] ignition phase. Lastly, the combustion phase is triggered by the volatility of the liquid or gaseous products of decomposition at the ignition temperature and the excess heat generated via combustion in the presence of O2 is utilized at the polymer surface to release more combustible products. This cycle contributes to increasing the free radical population and further increased chain branch reactions as described earlier in **Figure 4** accelerating the cycle of flame growth. Knowledge of the molecular properties of parameters that can be controlled is (shown in the orange box in **Figure 8**) can be applied and incorporated as design features in flame retardants to enable more effective fire suppression. Important targets in flame retardant design are effective suppressors of combustible compounds and their rate of evolution in keeping ignition temperatures below combustible thresholds. Some strategies that have been described include water formation through the use of brominated flame retardants [41] to contain temperature elevation via free radicals operating as inhibitors of flame propagation elements. Other forms of flame resistance includes charring [42] or partial burning

**17**

**Figure 7.**

**Figure 8.**

*Modified with permission from [40].*

persisting temperatures (**Figure 9**).

*Nanoscale Configuration of Clay-Interlayer Chemistry: A Precursor to Enhancing Flame…*

*Low-dimensional materials with multifunctional properties to combat fire hazards on multi-levels.*

which reduces polymers to black carbon essentially removing oxygen and hydrogen and effectively masking polymer surfaces (as assessed by measuring the limiting oxygen indexes or LOI's) [43] from further combustion through oxygen fuelling and volatile vapor mixing. In the oxidized form, char forms nitrogen oxide and heterocyclic compounds providing a basis for chemical fuel production at higher temperatures. Using two coal types as a carbon based combustion model, peak heat release correlated with the time to ignition showed the char content to decrease or increase with particle size increase [44] of the coal type investigated. Char forming chemistry has been investigated [45] and viewed as a useful alternative to halogen free retardants for polymers exhibiting fire resistance. The widespread application of organic and synthetic polymers in the manufacturing sector and related technologies increases the potential for toxic gas release by decomposition in case of fire demands safer designs of manufacturing protocols and newly improved fire resistant coating materials to replace existing ones. While char formation shows good potential to act as a shield preventing oxygen from mixing with polymers, char chemistry still remains a potential source for flammable gas release under

*A schematic showing a general role of polymer pyrolysis in combustion at the gas, liquid and solid interface and the potential for introducing key design features in flame retardants guided by key controllable properties.* 

*DOI: http://dx.doi.org/10.5772/intechopen.95788*

*Nanoscale Configuration of Clay-Interlayer Chemistry: A Precursor to Enhancing Flame… DOI: http://dx.doi.org/10.5772/intechopen.95788*

#### **Figure 7.**

*Flame Retardant and Thermally Insulating Polymers*

role of nanoclays hold much promise in this direction.

**4. Polymers - a fire safety perspective**

sufficiently contain fire progression and toxic smoke. The current problems focus not only on the material chemistry but emphasize a shift towards the intrinsic nature of the material itself. Since flame retardants conventionally operate on the principle of delaying fire progression, current objectives require using new material properties for the implementation of multi-functional flame retardants with design features better suited to the thermal properties of particular polymers. This is emphasized in **Figure 6** which seeks to manufacture a 'new generation' of materials effectively suppressing fuels that contribute to flame production such as oxygen, allow carbon dioxide permeability to reach sites to extinguish the birth of new flames and slow combustion, allow the capture and containment of toxic fumes, reduce the population of high energy radicals through quenching mechanisms and lower temperatures below the ignition phase. Health concerns must also be balanced with the dynamics of environmental issues, performance and costings making flame retardants more easily and economically available. The most attractive direction being pursued are low-dimensional materials that act as fillers for polymers bearing the ability to physically and chemically modify the thermal progression of polymers and other materials and to alter critical factors pertinent to fire control more advantageously with minimal damage to the surrounding environment. The additive or synergistic

Polymers of varying compositional structures are wide spread in many everyday

items [39] both in synthetic and to a lesser extent in biomaterials are a probable source of toxic inhalation during decomposition in fires. Most constitute a fire risk in many household appliances, furniture and wearable materials as the elements of polymer combustion drive fire propagation from the point of ignition. A growing body of evidence suggests that the reinforcement of polymers show a strong correlation with fire resistance while reducing the need for excessive use of fire retardant as single component materials in goods. The physical and chemical relationships between polymer behavior and fire progression has a unique place in engineering with the potential to offer new flame retardants that are both safe and effective. The complexity in the development of effective flame retardants is depicted in **Figure 7** [40] and empathizes the potential for multi-levels of combustibility that lie between the condensed (liquid) and expanded (gaseous) interfaces. As pointed out by Huiqing [40], the combustion cycle of polymer materials subject to a pyrolytic state pass through an [1] initial heating phase, reaching the [2] decomposition phase followed by the [3] ignition phase. Lastly, the combustion phase is triggered by the volatility of the liquid or gaseous products of decomposition at the ignition temperature and the excess heat generated via combustion in the presence of O2 is utilized at the polymer surface to release more combustible products. This cycle contributes to increasing the free radical population and further increased chain branch reactions as described earlier in **Figure 4** accelerating the cycle of flame growth. Knowledge of the molecular properties of parameters that can be controlled is (shown in the orange box in **Figure 8**) can be applied and incorporated as design features in flame retardants to enable more effective fire suppression. Important targets in flame retardant design are effective suppressors of combustible compounds and their rate of evolution in keeping ignition temperatures below combustible thresholds. Some strategies that have been described include water formation through the use of brominated flame retardants [41] to contain temperature elevation via free radicals operating as inhibitors of flame propagation elements. Other forms of flame resistance includes charring [42] or partial burning

**16**

*Low-dimensional materials with multifunctional properties to combat fire hazards on multi-levels.*

#### **Figure 8.**

*A schematic showing a general role of polymer pyrolysis in combustion at the gas, liquid and solid interface and the potential for introducing key design features in flame retardants guided by key controllable properties. Modified with permission from [40].*

which reduces polymers to black carbon essentially removing oxygen and hydrogen and effectively masking polymer surfaces (as assessed by measuring the limiting oxygen indexes or LOI's) [43] from further combustion through oxygen fuelling and volatile vapor mixing. In the oxidized form, char forms nitrogen oxide and heterocyclic compounds providing a basis for chemical fuel production at higher temperatures. Using two coal types as a carbon based combustion model, peak heat release correlated with the time to ignition showed the char content to decrease or increase with particle size increase [44] of the coal type investigated. Char forming chemistry has been investigated [45] and viewed as a useful alternative to halogen free retardants for polymers exhibiting fire resistance. The widespread application of organic and synthetic polymers in the manufacturing sector and related technologies increases the potential for toxic gas release by decomposition in case of fire demands safer designs of manufacturing protocols and newly improved fire resistant coating materials to replace existing ones. While char formation shows good potential to act as a shield preventing oxygen from mixing with polymers, char chemistry still remains a potential source for flammable gas release under persisting temperatures (**Figure 9**).

**Figure 9.**

*(a) Likely compositional elements of char (coal) representing (b) possible sources of volatile chemical fuels at ignition temperatures. Reproduced with permission from [46] and modified from [47].*

The hazards associated with fire retardant materials arise as a result of fire and the onset of flammable products released could be abated by slowing the decomposition rate of temperature polymer disintegration. Re-tuning the thermal behavioral properties of the primary polymer with other materials as additives that intervene with key elements that regulate combustion related properties to scale-down flame propagation is an important objective. In this direction, compositional integration with nanofillers can provide both structural and functional elements to alter the thermal properties of polymers and opportunities to consider more palatable flame retardants or to introduce new mechanisms to control and limit the harmful effects of existing ones currently in use. The progression of knowledge of the mechanical effects of particles on polymer stability at the nanoscale in terms of the structural harmony between filler-polymer interactions have important implications but have rarely been discussed in the context of polymer matrix, the nanoscale filler and the interfacial region [48]. This is highlighted to be particularly crucial in view of the ability of nanoparticle networks to diminish the combustibility of polymers [49].

Reinforcement of polymer strength and rigidity through stiffening uni-dimensionally or multi-dimensionally by pushing the chemical equilibrium towards char formation and increasing the barrier properties of chars could lead to new methods for fire retardancy. Hence, efforts have been directed for enabling mechanical stiffening of polymers [50] in a variety of ways that affect the flammability properties [51] closely coupled to ignitability [52] leading to a more controlled combustion arrest phase. For example, addition of co-monomers such as acrylonitrile, butadiene, and methyl methacrylate to the pyrolytic properties of polystyrene and styrene [53] and 2D-MoS2 nanosheet-containing polyurethane [54] have been fabricated. However, more recently Varol et al. [55] determined that nanoparticle nanofiller quantity and not size determine the strain hardening in polymer nanocomposites (**Figure 10**). Although this study signifies mechanical strength in the context of load bearing application of polymers, tuning strain hardening behavior with nanofillers with a reinforcement magnitude that allows the decomposition of polymers to be critically restrained at high temperatures has much value for tailoring flame retardants. Replacing the characteristics of brittlement of polymeric materials with heat resistant materials [56] by enhancing higher temperature performance in nanocomposites has meritable arguments for the flame retardant industry. A key challenge in the development of environmentally acceptable and low-to-no health risk flame retardant additives for use with conventional anti-fire hazard materials has accelerated in recent years. In line with the growing importance of nanomaterial

**19**

**Figure 10.**

*permission from [55].*

*Nanoscale Configuration of Clay-Interlayer Chemistry: A Precursor to Enhancing Flame…*

components for use in flame retardant formulations, the focus of interest has increasingly shifted towards clay based-minerals as nanofillers [57] to address some of the key challenges discussed. Multi-layering of flame retardants in nanocomposites could be an attractive structural feature to allow other additives to interact with flammable constituents that may persist even after part thermal stabilization of polymers with nanoclays. In addition, intercalation between polymer and nanoclay layers offer a level of intervention at the molecular nanoscale scale that may operate synergistically with the polymer and flame retardant chemicals. The possibility of introducing barrier properties, mechanical strength of polymers and hence diminishing volatile decompositions and support flame retardant properties cooperatively.

*(Top panel) Transmission electron microscopy images of the volume fraction (*Φ*) of SiO2 derived nanocomposites particle size with respect to particle size. (Bottom panel) Plot of the true stress (*σ*) as a function of the extension ratio (*λ*) for particles exhibiting different filler volumes and size. Modified with* 

**5. Nanoclays composites: challenging the role of conventional flame** 

Nanoclays form a class of inorganic clay based nanomaterials (**Figure 11**) with chemical and structural attributes that enable their integration with diverse materials as clay nanocomposites including polymers [59]. They exist as silicate/ aluminum-silicate structures in the form of montmorillonite, bentonite, kaolinite, hectorite, and halloysite. Nanoclays comprise layers of 1 nm thickness separated by interlayer distances between 70 to 150 nm modifiable as nanocomposites through intercalation with guest structures. While compositional mergers of nanoclay result in superior mechanical and tensile strength, properties aligned to reduce gas permeability [60] is achieved through the deposition of thin coated layers, alterations in glass temperature (temperature distortion) of nanocomposites and changes in modulus occur proportionally with increasing amounts of nanoclays and significantly alter material characteristics. Further nanoclays could be attractive additives as anti- combustion materials due to the differential permeability

**retardant mode of action**

*DOI: http://dx.doi.org/10.5772/intechopen.95788*

*Nanoscale Configuration of Clay-Interlayer Chemistry: A Precursor to Enhancing Flame… DOI: http://dx.doi.org/10.5772/intechopen.95788*

#### **Figure 10.**

*Flame Retardant and Thermally Insulating Polymers*

The hazards associated with fire retardant materials arise as a result of fire and the onset of flammable products released could be abated by slowing the decomposition rate of temperature polymer disintegration. Re-tuning the thermal behavioral properties of the primary polymer with other materials as additives that intervene with key elements that regulate combustion related properties to scale-down flame propagation is an important objective. In this direction, compositional integration with nanofillers can provide both structural and functional elements to alter the thermal properties of polymers and opportunities to consider more palatable flame retardants or to introduce new mechanisms to control and limit the harmful effects of existing ones currently in use. The progression of knowledge of the mechanical effects of particles on polymer stability at the nanoscale in terms of the structural harmony between filler-polymer interactions have important implications but have rarely been discussed in the context of polymer matrix, the nanoscale filler and the interfacial region [48]. This is highlighted to be particularly crucial in view of the ability of nanoparticle networks to diminish the combustibility of polymers [49]. Reinforcement of polymer strength and rigidity through stiffening uni-dimensionally or multi-dimensionally by pushing the chemical equilibrium towards char formation and increasing the barrier properties of chars could lead to new methods for fire retardancy. Hence, efforts have been directed for enabling mechanical stiffening of polymers [50] in a variety of ways that affect the flammability properties [51] closely coupled to ignitability [52] leading to a more controlled combustion arrest phase. For example, addition of co-monomers such as acrylonitrile, butadiene, and methyl methacrylate to the pyrolytic properties of polystyrene and styrene [53] and 2D-MoS2 nanosheet-containing polyurethane [54] have been fabricated. However, more recently Varol et al. [55] determined that nanoparticle nanofiller quantity and not size determine the strain hardening in polymer nanocomposites (**Figure 10**). Although this study signifies mechanical strength in the context of load bearing application of polymers, tuning strain hardening behavior with nanofillers with a reinforcement magnitude that allows the decomposition of polymers to be critically restrained at high temperatures has much value for tailoring flame retardants. Replacing the characteristics of brittlement of polymeric materials with heat resistant materials [56] by enhancing higher temperature performance in nanocomposites has meritable arguments for the flame retardant industry. A key challenge in the development of environmentally acceptable and low-to-no health risk flame retardant additives for use with conventional anti-fire hazard materials has accelerated in recent years. In line with the growing importance of nanomaterial

*(a) Likely compositional elements of char (coal) representing (b) possible sources of volatile chemical fuels at* 

*ignition temperatures. Reproduced with permission from [46] and modified from [47].*

**18**

**Figure 9.**

*(Top panel) Transmission electron microscopy images of the volume fraction (*Φ*) of SiO2 derived nanocomposites particle size with respect to particle size. (Bottom panel) Plot of the true stress (*σ*) as a function of the extension ratio (*λ*) for particles exhibiting different filler volumes and size. Modified with permission from [55].*

components for use in flame retardant formulations, the focus of interest has increasingly shifted towards clay based-minerals as nanofillers [57] to address some of the key challenges discussed. Multi-layering of flame retardants in nanocomposites could be an attractive structural feature to allow other additives to interact with flammable constituents that may persist even after part thermal stabilization of polymers with nanoclays. In addition, intercalation between polymer and nanoclay layers offer a level of intervention at the molecular nanoscale scale that may operate synergistically with the polymer and flame retardant chemicals. The possibility of introducing barrier properties, mechanical strength of polymers and hence diminishing volatile decompositions and support flame retardant properties cooperatively.
