Flame-retardant textile nanofinishes

Flame-retardant textile nanofinishes

11 Flame-retardant textile nanofinishes 11.1 INTRODUCTION The desire for textiles with reduced flammability has a long recorded history beginning fro...

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Flame-retardant textile nanofinishes 11.1 INTRODUCTION The desire for textiles with reduced flammability has a long recorded history beginning from production of high-performance fibers with intrinsic flameretardant properties such as asbestos, ceramic fibers, kevlar, nomex, and polybenzimidazole to the application of chemicals with the ability to retard the tendency to ignite and burning. This provides many application areas, including home and office applications such as floor coverings, curtains, furniture, workers and firefighter’s uniforms, transportation, and military applications. Textiles with flame-retardant properties belong to a group of protective technical textiles that protect the wearers and textiles material from flame and heat. Over the past years, researchers have been looking for flame-retardant materials with higher efficiencies, minimum effect on fibers inherent properties producing through simple and cost-effective processes, and retaining the property for long time resulting in durable properties. Another important factor is the safety of the material to the environment, limiting the application of some of the introduced materials. In addition to the common halogen, phosphorous, and nitrogen-containing materials with flame-retardant properties, the field has widely progressed by recent development of nanoparticles, nanocomposites, and nanocoating. In this chapter after a brief overview of common flame-retardant compounds, their classification, and general mechanisms, we will focus on the nanoparticles currently applied to impart flame-retardant properties into textiles. Nanocoating methods, namely, layer-by-layer (LBL) assembly and sol-gel methods will also be discussed.

11.2 GENERAL CLASSIFICATION AND MECHANISM Looking up into literature, we have come up with different classification of flame-retardant materials. Most of the classifications are based on the theory of fiber combustion shown in Fig. 11.1 based on the report by Nanofinishing of Textile Materials https://doi.org/10.1016/B978-0-08-101214-7.00011-X

© 2018 Elsevier Ltd. All rights reserved.

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Gas phase Thermal oxidation (flame)

O2

Products

Dispersion

Volatile products

Heat

Thermal degradation

Char

Condensed phase

Heat from ignition

Heat

Dispersion

Thermal oxidation

Fig. 11.1 Fiber combustion theory. Reprinted with permission from Camino, G., Costa, L., Luda di Cortemiglia, M.P., 1991. Overview of fire retardant mechanisms. Polym. Degrad. Stab. 33, 131–154. Copyright 1991, Elsevier.

Camino et al. (1991). According to the classification proposed by Horrocks (1986), flame retardants can be categorized into six groups based on the mechanism of retarding the flammability as: 1. Heat removal 2. Increased decomposition temperature (pyrolysis temperature, Tp) 3. Inhibition from oxygen as a necessary compound for combustion 4. Reducing the volatile and combustible gases 5. Increased combustion temperature (Tc) 6. Interfering the flame chemistry Another classification as proposed by Schindler and Hauser (2004) is three groups of primary flame retardants based on halogens and phosphorous materials, synergistic compounds that their combination with the first group flame retardants possess sufficient flame-retardant properties such as nitrogen and antimony, and adjunctive materials working based on physical barrier. Another classification, which is currently more acceptable, has grouped the flame retardants into four categories based on their action as gas phase, condensed phase, intumescent, and heat sink flame retardants. Gas phase action of flame retardants regarded the evolution of reactive species capable of scavenging free radicals formed during combustion in

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the vapor phase. The widely known compounds working based on this mechanism are halogen-based flame retardants that produce hydrogen halides reacting with hydroxyl and hydrogen radicals interfering with the burning cycle. Phosphorous compounds with constituent of PO, HPO2, and PO2 can also work based on gas phase action. Phosphorous compounds with the ability to form acidic intermediates such as phosphoric acid are also in this group. Forming a barrier between the fibers and flame for instance by forming chars, affecting the pyrolysis reaction causing less flammable volatiles, preventing further degradation of material, and inhibiting the production of flammable degradation products is regarded as condensed phase action of flame retardants. Phosphorous compounds with the ability to form phosphorous acids can also act based on condensed phase, and one of the widely known applications is in cellulose as hydroxyl-containing polymer. Here cotton crosslinking by the produced phosphoric acid or catalyzed dehydration of cellulose as shown in Fig. 11.2 (reactions 11.1 and 11.2) prevented the production of flammable levoglucosan (reaction 11.3) (Neisius et al., 2015). Synergistic systems based on incorporation of nitrogen based

Fig. 11.2 Possible reactions for condensed phase flame-retardant phosphorous compounds on cellulose.

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materials with phosphorous compounds have been also reported as condensed phase mechanism enhancing the flame retardant properties. Nitrogen-based flame retardants can be efficient in both gas and condensed phase action, releasing ammonia diluting combustible gases. Formation of insulating barrier around fibers below the Tp, by applying boric acid and its hydrated salts is also grouped in this method, producing foam-like surface insulating the fibers from heat and oxygen. Intumescent flame retardants, which can be also grouped as condensed phase materials, are a combination of a char-forming agent (polyol, sorbitol, resorcinol, polyhydtrophenol, sugar, glucose, maltose, dextrin, and starch), dehydrating compound capable of forming acid (mono and di ammonium phosphate, melamine phosphate), foam-forming material to release nonflammable gases under combustion (urea, melamin, guanidine, chloroparaffin, dicyandiamide) and stabilizers, crosslinkers, or binders. It has been proved that the intumescent materials work based on formation of foamed char layer preventing the combustion of fibers by inhibition of oxygen and heat (Vandersall, 1971). Heat sink materials work based on heat removal by endothermic reactions, releasing nonflammable gases such as H2O and CO2. The famous flame retardants work based on this mechanism are Al2O3, Mg (OH)2, and CaCO3. Flame retardants can be also categorized based on their durability to laundry as durable, semidurable, and nondurable flame retardants. UV graft polymerization has been applied to produce durable flame-retardant properties on fibers. This includes the application of monomer with flame-retardant properties such as phosphorous-containing materials and their polymerization under UV light exposure forming graft polymerized on the surface (Neisius et al., 2015). Chemical bonding of flame-retardant monomers by crosslinking with the textile substrate has been also developed to produce durable properties. Common crosslinker that has been used in flameretardant finishing is formaldehyde and its derivatives, although many attempts have been made to replace formaldehyde due to environmental problems. In this regard, dimethylol dihydroxy ethylene urea (DMDHEU) was also developed to crosslink a hydroxyl functionalized oligomeric phosphorous compound (HFPO) on cotton fabric (Yang and Qiu, 2007). Another attempt was the application of maleic anhydride with sodium hypophosphite (SHP) forming ester crosslinking with cotton (Wu and Yang, 2008). Application of carboxylic acids such as 1,2,3,4-butane tetracarboxylic acid (BTCA) and triethanolamine as formaldehyde-free crosslinkers has been also

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reported to provide durable flame-retardant properties. In these studies, the flame-retardant material was HFPO (Yang et al., 2009; Guan et al., 2009) and the protection properties were imparted to cotton, silk, and nylon fabrics. In Table 11.1, we tried to summarize most of the reported flame retardant agents for cotton, wool, polyester, and nylon fabrics based on reports from Vandersall (1971), Schindler and Hauser (2004), and Neisius et al. (2015). As indicated in Table 11.1, most of the researches have been done to impart flame-retardant properties into cotton. Wool fibers are inherently less flammable compared with cotton, and synthetic fibers such as polyester show melt-drip behavior thus indicating vertical flame resistance due to melting away from the flame (Schindler and Hauser, 2004). In spite of many progresses in introduction of new halogen, phosphorous, and nitrogencontaining flame retardants, environmental limitations involved in halogen-based materials producing toxic gases and smoke, negative effects of some flame retardants on fabric handle and reduced tensile strength, and formaldehyde release during the application urged the researchers to propose new materials and application processes with more environmentfriendly manners. In this regard, first step was the development of silicone-based materials. Synergistic combination of phosphonate and silicone has been reported as shown in Fig. 11.3, producing durable flameretardant properties on cotton, while siloxane forms crosslinking with cotton hydroxyl groups (Zhao, 2010). The superior properties of siloxane-based agents directed researchers to the introduction of sol-gel method using hydrolysis and condensation of tetraethyl orthosilicate (Totolin et al., 2010). It has been reported that siliconcontaining flame retardants form thermal stable and protective coatings on the surface (Norouzi et al., 2015). Within the development of nanotechnology and its outstanding effects in textile finishing, use of nanoparticles, nanocomposites, and nanocoating methods have brought many advantages to the progressive trend of textile flame-retardant finishing. Combining nanoparticles with traditional flame-retardant materials has been also reported to enhance the thermal stability and mechanical strength while reducing the environmental effects. Flame-retardant nanomaterials can be applied into textiles through conventional exhaustion, pad-dry-cure, backcoating, laminating, sol-gel, and LBL self-assembly methods. Incorporation of nanoparticles and nanocoatings for flame-retardant finishing benefits from no adverse effect on color, comfort, handle, and tensile strength of the treated fabrics (Alongi et al., 2014a).

Table 11.1 Common flame retardant agents based on fiber type Fiber type Flame retardant

Maleic acid + sodium hypophosphite Phosphate acrylate monomer polymerized by UV (TGMAP) UV curable phosphate monomers Vinyl phosphonic acid + triallyl cyanurate (crosslinker) (Opwis et al., 2011) Novel compound named as PDHA with chemical structure of

Nondurable/condensed phase P/N synergism/nondurable/condensed phase Nondurable/gas phase/harsh handle/high cost Nondurable Semidurable/improved whiteness Semidurable Semidurable Stiffness/formaldehyde release/reduced tensile strength Improved handle and tensile strength (difficult reactive and direct dyeing) Eliminate the production of bis(chloromethyl) Reduced acidic tendering Final washing to phosphoric acid removal/unpleasant odor/anticrease/P-N synergism/harsh handle Anticrease and flame retardant/cellulose crosslinking

UV graft polymerization UV graft polymerization Enhanced char formation due to phenolic moiety/UV graft polymerization/Durable (Yuan et al., 2012)

Nanofinishing of Textile Materials

Ammonium sulfamate Diammonium phosphate Ammonium bromide Acid boric/borax Aluminumhydroxy phosphate (AHP) Halogen + Sb2O3/Sb2O5 Hexa bromo cyclo dedecane Tetrakis (hydroxymethyl)phosphonium chloride) (THPC) + urea Precondensated of THPC + urea +ammonia + hydrogen peroxide THPC + sulfate THPC + hydroxyl salts N-methylol dimethylphosphonopropionamide

168

Cotton

Remarks

2-acryloyloxydroxyethyl diethyl phosphate (Siriviriyanun et al., 2008)

Wool

Silk

Nylon

Covalent bonding resulting in durable properties Durable/nucleophilic substitution of chlorine by cotton hydroxyl groups Flame retardant and oil repellency Char formation/combined dyeing and finishing Yellow effect on fibers Toxic polybrominated dioxin formation Nondurable

Carcinogen

Flame retardant and antidrip, intumescent char forming/10 % tensile strength loss Lowering nylon Tm/nylon crosslinking

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Polyester

169

Copolymerization of phosphoramide monomers with acrylic acid and acrylic acid (Huang et al., 2012a,b) Dimethyl-[1,3,5-triacrylol hexahydro)triazinyl]3-oxopropyl phosphonate (Yoshioka-Tarver et al., 2012) Dimethyl phosphite + paraformaldehyde + cyanuric chloride (Nguyen et al., 2012) Fluorinated derivatives of cyclophosphazene (Zhanxiong and Liping, 2010). Hexafluoro zirconate Hexafluoro titanate salts Tetrabromophthalic anhydride (TBPA) Urea + phosphoric acid N-methyloldimethylphosphonpropionamide Hydroxyfunctional organophosphorous (HFPO) + BTCA Diethyl-2-(methacryloyloxyethyl) phosphate Tridibromopropylphosphate (Tris) Cyclic phosphate/phosphonate Hexabromocyclododecane (HBCD) Mixture of bis-phosphonic acid and ammonium sulfamate (Feng et al., 2012) 2-hydroxy propylene spirocyclic pentaerythritolbisphosphonate) (PPPBP) Condensation product of thiourea + formaldehyde + urea Back-coating with antimony trioxide + bromine donator and binder

Admicellar polymerization by sodium dodecyl sulfonate as surfactant and azobis isobutyro nitrile as radical initiator/soft handle

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Fig. 11.3 An example of phosphonate and silicon-based flame retardant.

11.3 NANOCLAY Nanoparticles of hydrous aluminum silicates with sheet structure (layer) also known as natural phyllosilicates such as montmorillonite (MMT), bentonite, kaolinite, hectorite, and halloysite that are usually organically modified to alter the surface properties improving their adsorption capacity have high surface area, high cation exchange capacity, and high modulus. Chemical structure of MMT consists of (Na, Ca)0.33(Al, Mg)2(Si4O10)(OH)2nH2O forming 2:1 type layered silicates of packets of two tetrahedral silicate layers and an octahedral with adjacent margins. Ion exchange of MMT with surfactant cations such as quaternary ammonium salts has been extensively investigated and the potential of such compounds as adsorbents and antibacterial agents has been widely reported (Sadeghian Maryan et al., 2013). Most of the research studies devoted to addition of clay nanoparticles into polymer matrix producing nanocomposite fibers through melt spinning possessing higher mechanical properties along with flame-retardant properties (Norouzi et al., 2015). Textile finishing with clay nanoparticles is mainly done by producing polymer/nanoclay composite and its application as a coating material on fabrics (Ghosh, 2011). Polyurethane resins have been combined with MMT and applied on polyester fabric through coating to develop flame-retardant properties (Devaux et al., 2002). The exact mechanism of flame-retardant properties of clay nanoparticles has not been recognized yet. Although scientists reported that while the polymer matrix is burned and gasified during combustion, the incorporated nanoclays accumulate at the surface and form a barrier for oxygen diffusion, thereby slowing down the burning process (Ghosh, 2011). It has been also speculated that clay nanoparticles act by enhanced char formation. However, thermal stability may be restricted due to nanoclay or degradation products of organic modifier, which catalyzes the degradation of polymer (Asadi and Montazer, 2013). In spite of these merits, there are no complete flame-retardant properties when clay nanoparticles are applied alone, and always combination of clay with other traditional organophosphorous compounds results in better activities (Ghosh, 2011). Incorporation of clay dispersions on textile substrates has been also developed in recent years. For this approach, surface modification of textile

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is necessary for attachment of nanoclays into surface (Carosio et al., 2011a). For instance, cotton fabrics with flame-retardant properties have been prepared by prenitrogen gas plasma treatment followed by nanoclay treatment (Shahidi and Ghoranneviss, 2014). The char yield of the treated samples increased by 12% due to the synergistic effect of N2 plasma and clay nanoparticles inhibiting the transmission of heat, energy, and O2 between flame and cotton fabrics. Synergistic effects of clay and intumescent flame retardants have also focused on the ability to provide enhanced flame-retardant properties through protective barrier, which swells and forms a stable char at the surface of the material acting as a thermal shield (Wu et al., 2014). This was achieved by preparation of electrospun nylon 6 nanocomposite nanofibers containing MMT and intumescent nonhalogenated flame-retardant additives. The ability of hollow polyester nonwoven fabric treated with nanoclay/ TiO2/polysiloxane to provide thermal stability above 400°C has been also reported (Asadi and Montazer, 2013). TG–DTA analysis showed more residual ash in presence of nanoclay and the degradation of polyester delayed at high temperatures. Layered double hydroxide (LDH), known as brucite-like compound, which is a class of anionic materials with general formulation of M1x 2 + Mx 3 + ðOHÞ2 x + Az x H2 O, where M is metallic cation (Mg2+, Ca2+, Zn2+, Al3+, Cr3+, Fe3+, Co3+) and A (Cl, CO3 2 , NO3  ) refers to the interlayer anion, has been also regarded with potential flame-retardant properties due to the increased thermal degradation temperature of fibers, insulating barrier formation over the surface and endothermic heat sink action of LDH releasing water and carbon dioxide diluting the combustible gases. The potential of LDH to suppress the smoke production rate has been also reported (Pan et al., 2016). In addition to preparation of LDH/polymer nanocomposite fibers, incorporation of LDH on textile fabrics through finishing is mainly reported by LBL assembly, which will be focused in Section 11.8. We found a recent study on the application of LDH combined with dyeing (vinyl sulfone reactive dye) providing fabrics with UV resistance and flame-retardant properties (Barik et al., 2017).

11.4 CARBON NANOTUBE Carbon nanotubes (CNTs) are also regarded as flame-retardant materials due to the formation of char layers acting as a heat barrier and thermal insulator re-emitting the radiation back to gas phase retarding the polymer

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degradation, increased thermal conductivity, and radical scavenging effect. It has been reported that due to the fibrous morphology of CNTs, their effect as a barrier needs high level of concentration compared with nanoclays. Most of the researches are focused on the application of CNTs in polymer matrix, while several studies have been also focused on addition of other fillers such as clay, graphite, or intumescent compositions into CNT/ polymer mixture. CNTs were stabilized on cotton fabrics using vinylphosphonic acid monomer as a crosslinking agent introducing UV curable flame retardants improving the thermal properties and flammability of the coated samples due to heat insulation effect and the mass transport barrier of CNTs embedded in the coating (Parvinzadeh Gashti and Almasian, 2013). Backcoating of cotton fabrics with polyurethane nanocomposite of CNTs/conventional phosphorus flame retardants such as melamine polyphosphate and ammonium polyphosphates (APPs) has been carried out indicating the synergistic effect between CNTs and phosphorous compounds reducing the flammability and improving thermal stability of the fabric (Wesolekand and Giepard, 2014). Combination of CNT with clay nanoparticles has been also developed to enhance the flame-retardant properties due to the synergistic sealing effect of CNTs between clay platelets, creating a compact protective surface layer. Electrospun nylon 6 nanofiber consisting of multiwall CNTs, nanoclay particles, and intumescent flame retardants was an example (Yin et al., 2015). CNT was coated by an exhaustion method and stabilized on cotton using BTCA as crosslinking agent and SHP as catalyst, increasing the thermal stability (Liu et al., 2008). In a very recent study, carboxylated single-walled CNTs were stabilized on cotton fabrics in presence of citric acid as a crosslinker and SHP as a catalyst. Fine dispersion of CNTs was prepared using sodium dodecyl sulfonate as a dispersing agent. The result indicated high char yield of treated fabric with durable properties (Motaghi and Shahidi, 2017). The positive effect of SHP as a phosphorous compound in enhancing the char yield and flame-retardant properties has been proved by researchers (Yazhinia and Prab, 2015).

11.5 NANO-ORGANIC-INORGANIC HYBRID Polyhedral oligomeric silsesquioxane (POSS) with general structure of silicon-oxygen cage surrounding by organic R groups, shown in Fig. 11.4,

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Fig. 11.4 POSS general structure.

has been recently developed as a promising flame-retardant material forming thermally stable silica layer under degradation reaching to the surface acting as a protective layer. It has been found that POSS treatment of cotton fabric using DMDHEU as a binder favored the carbonization of the cellulose and slow down the kinetics of thermo-oxidation in air. The main result is the formation of a carbonaceous surface char that acts as a physical barrier toward the heat and oxygen transfer to the polymer. The authors compared the potential of the treated fabrics with samples finished with conventional phosphorus-based flame retardant and indicated that the performance of nanoparticles is higher than traditional flame retardant during the combustion tests by cone calorimetry. It was speculated that nanoparticles are able to induce the carbonization of cellulose, but through a physical mechanism due to the formation of a ceramic barrier on the textile surface. However, formation of phosphoric and polyphosphoric acid at high temperatures modifies the combustion mechanism of the cellulose chemically in condensed phase (Alongi et al., 2012a). In 2015, branched polyethyleneimine (BPEI), APP, and fluorinateddecyl polyhedral silsesquioxane on cotton fabric was developed to produce multifunctional flame retardant, self-healing, self-cleaning, and superhydrophobicity (Chen et al., 2015).

11.6 SiO2 In situ formation of silica nanoparticles or silica coatings onto polyester, cotton, and their blends has shown promising thermal stability and flameretardant properties. Silica nanoparticles were prepared from waste agriculture products such as rice husk (RH-SNP), and their combination with organic borate as back coating on linen fabrics indicated the synergistic effect (Attia et al., 2017).

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Most of the reported researches concern the application of sol-gel method to promote the formation of a surface silica insulating barrier capable of enhancing the thermo-oxidative stability and flame-retardant properties. Several studies showed that the structure of precursors used in sol-gel method, namely, number and type of hydrolysable groups and presence of aromatic rings has direct effect on the obtained result. Independent from the structure of the precursors, the mechanism of flame-retardant properties is through char formation (Alongi et al., 2012b). It is reported that the thickness of the shielding layer through sol-gel treatment of textiles is very limited. Thus, combination of sol-gel treatment with other conventional flame retardants has been investigated. For instance, addition of 5 wt% phosphorous-containing materials resulted in enhanced flame-retardant properties of cotton (Alongi et al., 2012a). In addition to mixing alkoxysilane precursor with phosphoric acid compounds, it is possible to use precursors with concurrent presence of Si and P components such as diethylphosphatoethyltriethoxysilane as a monomer to prepare a hybrid phosphorous/silicon organic-inorganic flame retardant (Brancatelli et al., 2011). A comprehensive review has been published by Alongi et al. (2014a) concerning recent sol-gel treatment of textile substrates for achieving flame-retardant properties.

11.7 METAL (OXIDE/HYDROXIDE) NANOPARTICLES Aluminum oxide hydroxide nanoparticles (bohemite) act as a heat sink flame retardant through endothermic decomposition releasing water, resulting in cooling and dilution effects (Alongi et al., 2012a). Nano TiO2 particles have been also incorporated into textiles to impart flame-retardant properties. It has been reported that TiO2 promotes the dehydration of cellulose in high temperature forming a char barrier (Lam et al., 2011). Wall effect theory based on the potential of TiO2 to act as a wall absorbing heat and dissipating it in the combustion zone has been also speculated by researchers. Most of the researches concerning with the application of TiO2 are in combination with a crosslinker such as BTCA and a catalyst, namely, SHP with phosphor source being advantageous to the obtained flame-retardant properties (Hashemikia and Montazer, 2012). TiO2 nanoparticles prepared by sol-gel method were applied on cotton fabric using pad-dry-cure method in presence of BTCA/SHP and chitosan phosphate (El-Shafei et al., 2015). Flame-retardant cotton fabrics based on pad-dry-cure treatment of fabrics with SHP, maleic acid, triethanolamine, and nano TiO2 have been

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prepared by Lessan et al. (2011). The results revealed the importance of SHP in enhancing the flame-retardant properties. Triethanolamine prevented the fabric yellowing during the process. Similar to TiO2, ZnO nanoparticles have been also investigated in combination with other flame-retardant materials to provide enhanced properties (Abd El-Hady et al., 2013). N-Methylol dimethyl phosphonopropionamide in combination with melamine resin, phosphoric acid, and nano ZnO was applied on cotton fabrics (Lam et al., 2011). The authors regarded ZnO as a cocatalyst imparting higher durable flame-retardant properties with lower mechanical strength loss and formaldehyde release.

11.8 NANOCOATINGS BASED ON LBL TECHNIQUE LBL assembly, which is done through immersing the substrate into positively and negatively charged polyelectrolyte and/or nanoparticle solutions to prepare multilayer coatings, has been developed as a novel flame-retardant technology in textile nanofinishing. This method mainly contains coating deposition of textile material by positive and negative dispersions of particles, alternately. Some of the LBL coatings based on positive and negative counterparts have been summarized in Table 11.2. Creation of surface barrier and thermal insulator system promoting char formation and inhibiting the production of volatile species, thereby preventing the transmission of heat and oxygen are the general mechanisms of inorganic LBL flame-retardant properties. Intumescent coatings based on the organic or hybrid organic-inorganic LBL coatings have been also developed as more efficient flame-retardant finishing of textiles. In these systems, acid source and gas source are the layers, while in most cases cotton substrate acts as a carbon source. The mechanism is based on the action of the acid source promoting the thermal degradation of the carbon source forming a thermal insulation layer, while inert gases are produced under degradation of gas source promoting the char foam to form a porous and swollen carbon layer, improving the flame-retardant properties (Qiu et al., 2018). Poly(diallydimethylammonium chloride), poly(allylamine), poly (diallydimethylammonium chloride), and APP were LBL deposited on cotton, polyester, and their blends showing potential to create thermally stable char forming capacity not only in cotton as a carbon source substrate but also in polyester (Alongi et al., 2012a).

176

Cotton

Sodium MTT Silica Anionic Al2O3 Silica 1,3,5,7,9,11,13,15-octakis(cyloxide) hydrate POSS Ammonium polyphosphate (APP) Ammonium polyphosphate (APP) Poly(sodium phosphate) (PSP) Sodium MTT Graphene oxide Phytic acid Titanate nanotube Mg-Al layered double hydroxides (Mg-AlLDH) Laponite clay Sodium polyborate

Ramie

Poly(vinylphosphonic caid) (PVPA) Ammonium polyphosphate (APP)

Polyester

Silica α-zirconium phosphate nanoplateles

Positive counterpart

Ref.

Polyethyleneimine (PEI) Ammonium coated silica Cationic Al2O3 Branched Polyethyleneimine (BPEI) Octa-3ammoniumpropyl chloride POSS

Li et al., 2010 Laufer et al., 2011 Ug˘ur et al., 2011 Alongi et al., 2014a,b Li et al., 2011a

Ammonium coated silica Chitosan Poly(allylamine) (PAA) Amino derivative of poly (acrylic acid) Derivative of polyacrylamide Chitosan Chitosan Alginate

Carosio et al., 2012 Carosio et al., 2012 Li et al., 2011b Huang et al., 2012a Huang et al., 2012b Laufer et al., 2012 Pan et al., 2015 Pan et al., 2016

Branched Polyethyleneimine (BPEI) Polyhexamethylene guanidine phosphate (PHMGP) Branched Polyethyleneimine (BPEI) Amino functionalized multi wall carbon nanotube Ammonium coated silica Octa-3ammoniumpropyl chloride POSS

Li et al., 2009 Fang et al., 2016 Wang et al., 2014 Zhang et al., 2013 Carosio et al., 2011a,b Carosio et al., 2011b

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Table 11.2 Nanocoatings based on layer by layer technique Fiber type Negative counterpart

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Chitosan provides multiactions in LBL systems, thus has attracted researchers as a positive counterpart. The promising features of chitosan include (1) acting as a char-forming agent due to the polyhydroxy structure, (2) production of nitrogen under degradation acting as a gas source, and (3) acting as a binder providing durable properties. Moreover, chitosan is regarded as a biocompatible agent, thus providing the opportunity to produce biobased intumescent LBL coatings. In this regard, one of the examples is application of chitosan and DNA from herring sperm that contains phosphate acid source, deoxyribose (char former), and many nitrogencontaining bases (Carosio et al., 2013). A comprehensive review published by Qiu et al., 2018 provided detailed information on LBL method for achieving flame-retardant properties.

11.9 FLAME-RETARDANT EVALUATION METHODS Among various standard methods of evaluating flame-retardant properties of textiles, limiting oxygen index (LOI) and cone calorimetry have been widely used. LOI is limiting oxygen index determined according to ASTM D 2863, which is defined as the content of oxygen in an oxygen/nitrogen mixture. In this regard, fabrics with LOI index of higher than 20 will not get burnt. Cone calorimetry is based on the measurement of heat release rate during textile combustion using an oxygen consumption calorimeter. Mass loss rate, ignition time, and CO2/CO production can be also measured by this method (ASTM E 135, ISO 56.60-1). Another recent approach is development of microscale combustion calorimeter working based on pyrolysis combustion method (Neisius et al., 2015).

11.10 CONCLUSION In spite of the vast number of studies concerning with the introduction of newly emerging nanobased technologies to impart flame-retardant properties into textiles as proposed in this chapter, the efforts to commercializing these materials for replacing the common flame retardants is in the initial steps. Research on developing more durable flame-retardant properties using nanoparticles and nanocoating methods is still demanded. Reviewing the literature shows the possible focus of the future research on use of bio-nanobased materials to produce sustainable green systems inhibiting harmful effect on the environment. For instance, use of proteins such as

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casein and hydrophobins containing phosphate and disulfide groups has been regarded as potential flame retardants with char-forming effect. Introduction of flame-retardant materials with multifunctional properties imparting multifeatures such as antibacterial, superhydrophobicity, and self-healing would be of high importance directing the future studies.

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FURTHER READING Alongi, J., Colleoni, C., Rosace, G., Camino, L.C., Dicortemiglia, M.P.L., 1991. Overview of fire retardant mechanisms. Polym. Degrad. Stab. 33, 131–154. Li, Y.C., Mannen, S., Morgan, A.B., Chang, S., Yang, Y.H., Condon, B., Grunlan, J.C., 2011c. Intumescent all-polymer multilayer nanocoating capable of extinguishing flame on fabric. Adv. Mater. 23, 3926–3931.