Recent Advances for Flame Retardancy of Textiles Based ...

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This paper aims at updating the progress on the phosphorus-based flame retardants specifically designed and developed for fibers and fabrics (particularly referring to cotton, polyester and their blends) over the last five years. Indeed, as clearly depicted by Horrocks in a recent review, the world of flame retardants for textiles is still experiencing some changes that are focused on topics like the improvement of its effectiveness and the replacement of toxic chemical products with counterparts that have low environmental impact and, hence, are more sustainable. In this context, phosphorus-based compounds play a key role and may lead, possibly in combination with silicon- or nitrogen-containing structures, to the design of new, efficient flame retardants for fibers and fabrics. Therefore, this review thoroughly describes the advances and the potentialities offered by the phosphorus-based products recently developed at a lab-scale, highlighting the current limitations, open challenges and some perspectives toward their possible exploitation at a larger scale.

In this context, the present paper aims at providing an overview of the recent advances in the design of phosphorus-based FRs, also in combination with nitrogen- or silicon-containing structures, for different fibers and fabrics: in particular, the evolution from chemical to low environmental impact products will be thoroughly described, highlighting the current achievements and limitations, as well as the open challenges and perspectives.

Nowadays, the approach adopted by the scientific community is being slightly changed: indeed, the durability of any new flame retardant is still needed, but the novel processes and methods developed in last five years seem to be more addressed to the design of low impact and eco-friendly systems.

Any new flame retardant should not cause any alteration in the hue of the dye and/or dyeability of the fibers/fabrics.

Air permeability of the treated textiles should be maintained, irrespective of the possible high amounts of chemicals needed to provide flame retardant features.

Any new flame retardant should possess an overall comparable cost-effectiveness to the already existing chemicals and preferably be less costly.

Despite the efficiency of such commercially available treatments, both academic and industrial researchers are still seeking worthy alternatives, also taking into account the requirements that have to be fulfilled by the new products. In particular, with respect to the already existing FRs:

Conversely, the chemistry behind Pyrovatex ® is based on a conventional pad-dry-cure process in the presence of a methylolated crosslinking agent, which is responsible for the formation of covalent bonds with the hydroxyl groups of the cellulosic substrate. Nonetheless, about 50% of Pyrovatex ® FR treatment has been reported to be lost during the first laundry occurrence, because of the extraction of unreacted products, though it remains stably linked thereafter.

The chemistry of the Proban ® process exploits a tetrakis(hydroxymethyl) phosphonium–urea condensate, which, after padding, is crosslinked by ammonia gas in a dedicated plant and then subjected to peroxide oxidation for stabilizing the resulting polymeric matrix [ 11 ]. The washing fastness of this treatment is due to the deposition of the chemical within the fibers by a construction of a polymer network during the heating process: as a consequence, Proban ® is not linked to the fibers but is mechanically retained within the fiber interstices. One of its major disadvantages refers to the possible release of formaldehyde during the fabric use [ 12 ].

In this context, some new products have been designed and nowadays are commercially available. In particular, Trevira CS ® , which is based on the use of a phosphorus-containing comonomer (in the form of propionylmethylphosphinate), has been exploited for conferring flame retardant properties to polyester fibers and fabrics [ 9 , 10 ]. Regarding cotton and cellulosic-rich substrates, the present focus is either on the synthesis of effective non-halogenated additives for coatings and back-coated fabrics or on the utilization of hydroxymethylphosphonium salts (Proban ® ) or N-methylol phosphonopropionamide derivatives (Pyrovatex ® ).

The aforementioned disadvantages stimulated the scientific community toward the design and development of phosphorus-based compounds, which seem less toxic and may represent a suitable alternative to their halogen-based counterparts. Though it is not a general case that all phosphorus compounds are non-toxic, the development of new flame retardants based on phosphorus compounds has shown that they have lower toxicity profiles as compared to halogen-based counterparts [ 7 , 8 ]. In general, the development of any new flame retardant should involve a complete assessment of its performance in material as well as its toxicity.

However, according to the very stringent directives recently promoted by the EU community and USA, some of the halogenated compounds (such as brominated diphenyl derivatives) have been banned, as they have clearly shown a high toxicity for both animals and humans [ 6 ].

Specifically referring to the textile field, FRs can also be classified according to their “laundry durability”: indeed, a non-durable FR is washed off immediately when soaked in water, but may resist dry cleaning. Conversely, semi-durable FRs are able to resist water-soaking and possibly a few washes, while durable FRs endure some 50 or 100 washing cycles.

2000 onward: Several efforts were carried out in the design of char-former flame retardant additives, possibly containing phosphorus-based products. Another goal was the investigation into the possibility of replacing bromine derivatives with other less toxic and efficient products. Furthermore, during this period, nanotechnology was demonstrated to show outstanding potential for conferring flame retardant features to fibers and fabrics, through the use of nanoparticles having different aspect ratios. In particular, the exploitation of both top-down (using preformed nanoparticle suspensions) and bottom-up (exploiting the generation of single nanoparticles or nanoparticle assemblies—even hybrid organic-inorganic structures) was successfully considered [ 4 5 ].

1950–1980: The “golden period” of flame retardant research, involving the appearance of the first patents on FRs based on organophosphorus compounds for cellulosic textiles (i.e., cotton). During this period, inherently FR synthetic fibers bearing aromatic structures were also developed.

A review published in 2011 succeeded in summarizing the state of the art for the different commercially available flame retardants for textile materials, which were classified according to the following periods [ 3 ]:

Favor the formation of a char or an intumescent protective layer when the textile interacts with a flame or a heat source.

Modify the pyrolysis process to lower the quantity of flammable volatiles developed, favoring, at the same time, the creation the char, i.e., a carbonaceous residue that also limits the heat and mass transfer between the textile material and the flame.

Lower the developed heat to below that necessary to carry on the combustion process.

From an overall point of view, the self-sustaining combustion cycle of can be broken in the presence of FR additives, thus achieving the extinction of the flame or reducing the burn rate. In particular, they can:

On the basis of the chemical composition and their thermal and fire characteristics, if they are not inherently flame retarded, fibers and fabrics have to be treated with additives that may contain halogen, nitrogen, phosphorus, sulphur, boron, metals, etc., hence becoming flame retarded. The aforementioned additives can be added during spinning processes performed on synthetic fibers, or deposited on the synthetic or natural fiber/fabric surface, hence creating a protective layer/coating. Both finishing and coating methods can be exploited: concerning the former, the fiber/fabric is impregnated with a solution or a stable suspension that contains the FR additive. Conversely, the coating method involves the application of a continuous or discontinuous layer/film on both surfaces of the textile.

From an overall point of view, combustion in the presence of flames is a gas-phase process exploiting the oxygen taken from the surroundings. As a consequence, before the occurrence of the combustion process, the textile undergoes degradation: some of the so-obtained degradation products turn into combustible volatile species that, in combination with oxygen, fuel the flame. If the heat generated in the combustion is sufficient, it can be easily transferred to the textile substrate, hence giving rise to further degradation phenomena and supporting a self-sustaining combustion cycle ( ).

In this context, the ease of flammability of textiles has been faced by designing and synthesizing suitable flame retardants (FRs), i.e., additives that are able to suppress or delay the appearance of a flame and/or reducing the flame-spread rate (flame retardants) or delaying ignition or reducing the rate of combustion when needed (fire retardants) [ 2 ].

Textiles play an important role in everyday life: one of their main drawbacks refers to their structure, as they are mainly made of organic polymers, which conversely, if not inherently flame-retarded (such as polyaramides and polyphosphonate fibers), are flammable and potentially dangerous species. Specifically referring to fibers and fabrics, the annual UK fire statistics have clearly demonstrated that most of fire incidents occur in houses, involving upholstering furniture, bedding and nightwear [ 1 ].

The micro-combustion calorimeter (MCC) has recently been standardized (ASTM D7309-13) and exploited for evaluating the flammability of polymers [ 16 , 17 ]. In this process, a small specimen (about 2–10 mg) undergoes pyrolysis through a fast heating up in inert atmosphere (with a heating rate below 1 °C/s). The obtained pyrolysed products are then mixed with O 2 /N 2 mixture to expedite combustion. The oxygen concentration and flow rates of the combustion gases are evaluated, and the amount of generated heat is calculated on the basis of oxygen consumption calorimetry.

Although not specifically designed for fabrics, cone calorimetry tests (according to ISO 5660) have become a standard bench scale model of early flaming [ 14 , 15 ]. In particular, the cone calorimeter mimics the penetrative burning seen as fire burning into a specimen. It evaluates the heat release rate and the effective heat of combustion from a burning material exposed to a controlled radiant heat source (ISO 5660 part 1). Usually, such parameters as Time To Ignition (TTI), Total Heat Release (THR), Heat Release Rate and corresponding peak (pkHRR), Effective Heat of Combustion (EHC), Mass Loss (ML) and Mass Loss rate (MLR) can be evaluated. The cone calorimeter can also be utilized to evaluate smoke generation (ISO 5660 part 2): in this case, the measured parameters include the determination of CO and CO 2 concentrations, as well as the assessment of smoke density (Specific Extinction Area–SEA, Total Smoke Production–TSP, etc.).

Flame spread (UL-94, which contains EN 60695 11-10, ASTM D 635-03 and D 3801-00) is a bench-scale test which measures the rate of flame spread usually calculated as the ratio of the distance to the time taken of the advancing flame front to reach defined distances marked on the fabric specimen. The upward fire spread is far faster than downward and horizontal flame spread and, hence, adopted as a better means of assessing the fire hazard of a fabric.

Simple ignition tests (used in many standards, such as BS 5438 and EN ISO 6941) represent another usual approach for assessing the flammability of a textile material: more specifically, a standard gas flame is applied to the face or lower edge of a vertically oriented fabric sample; ignition is examined by visual observations and the time needed to ignite the specimen is recorded. The textile does not pass the test when, after the removal of ignition source, the flame achieves any end of the sample. If the flame reaches extinction, the char length, dimension of holes, afterglow, and type of any wreckage (molten drops, etc.) are thoroughly evaluated.

The obtained LOI values may be affected by several fabric structural parameters, when measured for the same fiber type: this makes LOI values relative and not absolute data. In addition, the textile material is ignited at the top and thus it burns vertically downward (i.e., in candle-like manner) which is opposite to the burning of any material freely suspended.

Limiting oxygen index (LOI), also called oxygen index (OI), is one of the most popular scientific methods, used in many standards, such as ISO 4589 and ASTM D2863. LOI denotes the minimum concentration (vol %) of O 2 in a mixture of O 2 and N 2 that will just sustain flaming combustion of a material in a candle-like manner. Textile materials burn rapidly when they exhibit LOI values up to 21 vol %, while they burn slowly when LOI is in between 21 vol % and 25 vol %. LOI values beyond 26 vol % indicate some flame retardant features [ 13 ].

The measurement of textile flammability involves either scientific (i.e., research) test or the standard test methods. The former provide information suitable for assessing the burning behavior and are exploited for the design of new FRs or fire-retardant treatments.

Generally speaking, ignition occurs when a small flame is applied to flammable fabrics for no more than 12 s and the textile continues to burn after the removal of the flame. Therefore, most of the work on flammable fabrics focuses on the evaluation of the facility of ignition, the rate and extent of flame spread, the duration of flame propagation, the heat release and heat of combustion. All these parameters are merged with a quantitative portrayal of burning wreckages, such as melt dripping. It is very difficult to find a single test method able to measure all the aforementioned parameters. Concerning the fabrics that show self-extinction, such as flame-retarded fabrics, tests comprise the evaluation of time of afterflame and afterglow and extent of fire damage (specifically referring to char length, dimension of holes, or damaged sample length).

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This section summarizes the current methods that allow assessing the reaction of a textile toward the exposure to a flame or a heat flux. All the developed methods take into account that, for textiles, the high fiber surface to mass ratio favors their easy ignition; in fact, these materials burn faster than other bulk polymers.

The condensed or gas phase activity of phosphorus compounds significantly depends on their structure, as well as on the polymer substrate. For example, in case of natural polymers like cellulose and wool, the phosphorus compounds primarily exhibit condensed phase activity where dehydration of the polymer, leading to the formation of a thermally stable char, is the predominant mechanism. Referring to synthetic polymers containing oxygen and nitrogen atoms in their structure, catalytic hydrolysis of the ester or amide groups by phosphorus acids promotes an enhanced melt dripping and fast shrinkage from flame. As far as olefin-based polymers are considered, the phosphorus compounds mainly act in the gas phase by recombining the key fuel species such as H and OH radicals and preventing their oxidation. Some minor physical effects due to volatilization of phosphorus compounds and dilution of the fuel can also occur.

The efficiency of phosphorus compounds to change the decomposition and combustion characteristics of polymers makes their fire suppressant use imperative. Depending on the substrate and their chemistry, there could be chemical interactions in the condensed phase at elevated temperatures, which lead to changes in the decomposition pathway of the polymer and possible formation of carbonaceous char residues on the surface of decomposing polymer, hence preventing its further oxidation. In other instances, the phosphorus compounds and some of their decomposed products preferably volatilize from the polymer substrate when heated. These phosphorus species further decompose to release reactive phosphorus species, which then interact with the combustion intermediates in the gas phase as inhibitors. In most cases, such interactions lead to recombination of the H and OH radicals and prevent their oxidation.

In some cases, the de-polymerization of thermoplastic polymer chains in the presence of a heat source reduces the viscosity of the system and enables it to retreat from the fire without producing any residue.

An additive is considered to be active in condensed phase if it alters the thermal decomposition characteristics of the polymer by a chemical reaction. Hydrolysis, dehydration, chain scission or de-polymerization are some of the main chemical reactions occurring in condensed phase activity. This activity is usually characterized by a reduction in the decomposition temperature of the polymer and increased formation of char residue at elevated temperatures [ 19 ].

Phosphorus-based flame retardants are quite versatile in their flame retardant action. Phosphorus compounds often exhibit both condensed and gas phase activity [ 18 ]. A simplified scheme of various flame retardant actions of phosphorus is presented in .

4. Chemical Phosphorus-Based FRs for Textiles

The following paragraphs will describe the recent advances concerning the use of phosphorus-based chemical products, suitable for conferring flame retardant properties to different fibers and fabrics. In general, summarizes the recent findings of P-based flame retardants and their performance on textile fabrics.

Table 1

Type of P-based FRTextile materialHighlightsDurability (washing fastness)Ref.Dioxaphosphorinane derivativesPETNew oligomers were synthesized and their burning behavior was compared to Antiblaze 19®.
The new oligomers showed higher thermal stability and more char residue comparing to Antiblaze 19®.
The thermal stability and flame retardant properties were studied only on the oligomeric derivatives.
Treated PETs with these oligomers were not investigated.ND *[20]UV-curable flame retardantsCottonCotton fabric was treated with UV-curable flame retardants and cured under UV-lamp in presence of photoinitiator.
LOI values increased with increasing the FR content.
MCC showed a decrease in HRC and HRR and THC with increasing the FR content.
As increasing the monomer concentration and UV exposure time, the coating yield increased.
Relatively small monomers were not suitable for UV-curing as they might evaporate during curing process.Yes[21,22,23]Cotton and Cotton/polyester blendAllyl-functionalized polyphosphazene additive was investigated, avoiding the disadvantage of small molecules.
The treated fabrics showed good flame retardancy with char formation.
The additive acts in the condensed phase mode of actionYes[24]Polyester/Polyamide blendUV-curable epoxy based oligomer formulation.
Vinyl phosphonic acid (VPA) was incorporated in the formula.
The thermal stability, char formation and LOI values of the treated fabrics increased with increasing the concentration of the VPA acid
The peel strength values increased gradually up to 50.8 N/cm with increasing VPA.ND[25]Triazine-based flame retardantsCottonThe triazine-based flame retardants are derivatives of cyanuric chloride.
These additives are considered as active flame retardants, forming ether bond by replacement the chlorine atoms with the hydroxyl groups pf cellulose.
The fabrics were treated with flame retardants by impregnation.
Thermal analysis showed a char formation which proves the condensed phase mode of action.
LOI values increased with increasing the add-on of flame retardants.
With increasing the flame retardant concentration, the treated fabrics did not show any afterglow, which can be considered as self-extinction.Yes[26,27,28,29,30,31,32,33]Hybrid organic-inorganic flame retardantsCottonThe fabrics were treated with flame retardants using the sol-gel technique.
Increasing the sol-gel precursors on treated fabrics, showed a decrease of the HRC, PHRR and TGA onset and an increase of the char residue.
Increasing the solid dry add-on increased relatively the after flame with no afterglow.
Increasing the solid dry add-on increased the LOI value and decrease of the THR and HRC.Yes[34,35,36,37,38,39,40,41]PA6The PA6 samples were treated with different concentrations of equimolar mixtures of the flame retardant and TEOS.
Combination of P- and Si-based additives improved the thermos-oxidative stability and combustion behavior by increasing the char residue and reducing the HRC and PHRR of treated samples, respectively.ND[38]Polymeric flame retardant additivesCottonThe cotton fabrics were treated by dipping/soaking in a solution of the polymeric flame retardants.
Binders or crosslinkers were used when needed to bind the polymer permanently onto fabrics.
LOI values of the treated fabrics showed an increase with increasing the add-on.
The vertical burning test of the treated fabrics showed a reduction of the afterglow time and char length.
Cone calorimetry showed a decrease of HRR THR and CO2/CO ratio with increasing the add-on.Partially studied[42,43,44,45,46,47,48,49]Nylon fabricsThe nylon fabrics were dip-treated in a solution containing FR and crosslinker.
MCC analyses showed a decrease of HRR, THR and HRC.Yes[49]Phosphoramidate derivativesCottonLOI values of the treated fabrics increased with increasing the phosphorus content.
The treated fabrics with add-on beyond 5 wt % were found self-extinction.
The thermal stability and the flame retardancy performance of phosphoramidates are influenced by the nature of chemical substituents and type of cotton fabrics.Partially studied[50,51,52,53,54,55,56,57]Nylon and polyesterThe vertical flame test showed better flame retardancy of treated nylon fibers.ND[56]Open in a separate window

4.1. Dioxaphosphorinane Derivatives for PET Fibers

These new flame retardants were designed to exhibit similar performances in their activity to Antiblaze 19®, i.e., a trimethylolpropane methylphosphonate oligomer obtained from the reaction of trimethylolpropane phosphite with dimethyl methylphosphonate [54], employed for poly(ethyleneterephtalate) (PET) fibers. In particular, Negrell-Guirao and co-workers [20] synthesized 2,5-ethyl-5-(allyloxymethyl)-2-oxo-1,3,2-dioxaphosphorinane (1), 2-butyl-5-ethyl-5-(allyloxymethyl)-2-oxo-1,3,2-dioxaphosphorinane (2) and 2-benzyl-5-ethyl-5(allyloxymethyl)-2-oxo-1,3,2-dioxaphosphorinane (3) ( ).

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Due to the two pseudo-asymmetric centers for dioxaphosphorinane monomers, compounds (1), (2) and (3) exist as diasterioisomers. However, the radical polymerization of dioxaphosphorinane monomers shows the influence of the presence of a chain transfer agent (CTA) on the efficiency of the radical polymerization reaction. Moreover, dimethyl phosphite can play a role by enhancing the fire retardant efficacy of dioxaphosphorinane derivatives. As the CTA concentration increases, the monomer conversion increases as well and the degree of polymerization decreases ( ).

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The products of the polymerization reaction were isolated as mono- and di-adduct, rather than high MW polymers. Furthermore, the flame retardancy of these dioxaphosphorinane derivatives was not assessed: therefore, it was not possible to make a real comparison with Antiblaze 19®.

4.4. Hybrid Organic-Inorganic Flame Retardants

Hybrid organic-inorganic flame retardants are materials that usually favor the formation of a carbonaceous layer upon exposure to a heat source [34]. Among the different strategies that can be successfully exploited, the sol-gel technique is one of many techniques developed for incorporation of these hybrid organic-inorganic flame retardants onto textiles [35].

In this context, several phosphorus-based silicon containing flame retardants have been developed. Hu and co-workers [36] exploited the reaction of isophorone diisocyanate with (3-aminopropyl)triethoxysilane and 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO), obtaining oligomer 24 of .

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After the hydrolysis of the product in acidic media, a sol-gel solution was obtained and used for treating cotton fabrics by dipping. The treated samples were then dried in the oven at 80 °C and then 130 °C. TG analyses showed a decreased onset temperature and an increased char with increases in the concentration of the sol-gel precursor on cotton fabrics: these findings were attributed to the acid environment promoted by the degradation of the organophosphorus part and to the thermal stability of Si–O bonds that exerted a protection on the underlying fabric. A similar trend was found in MCC tests: PHRR and HRC values showed a decrease with increases in the concentration of the precursor. All these results proved that the sol-gel precursor acts in the condensed phase by increasing the char formation of the treated cotton samples, which reduces the heat release.

Quite recently, Vasiljević and co-workers [37] exploited an addition reaction of DOPO to vinyltrimethoxysilane in the presence of Azobisisobutyronitrile (AIBN) as initiator, giving rise to the formation of the flame retardant (25) shown in .

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Different concentrations of the obtained flame retardant were prepared in ethanol and were hydrolyzed using HCl. The cotton fabrics were then treated by the pad-dry-cure method at 20 °C, subsequently dried at 120 °C and then cured at 150 °C. TG analyses showed a decrease of the thermal stability and an increase of the char formation with increases in the amount of dry solid on the treated cotton fabrics. In addition, the flame retardant performance of treated cotton fabrics was investigated using vertical flame spread tests: by increasing the solid dry add-on, an increased flaming combustion after the removal of the flame was found; conversely, LOI values were improved.

Pursuing this research, the same group exploited the combination of the sol-gel precursor (25) and tetraethoxysilane (TEOS), which was utilized as a sol-gel finishing for polyamide 6 (PA6) fabrics [38]. The obtained hybrid system decreased the Total Heat Release values of the treated fabrics, increasing, at the same time, the char yield with respect to the use of precursor (25) alone, hence proving the synergistic behavior of the combined hybrid system.

Yang et al. [39] reacted (3-aminopropyl)trimethoxysilane with diphenylphosphinic acid in order to prepare the flame retardant precursor (26) shown in .

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The obtained precursor was dissolved in aqueous/ethanol solutions at different concentrations and applied as a hybrid organic-inorganic flame retardant for cotton fabrics. After treatment, the fabrics were dried at 140 °C. The thermal stability and the flammability behavior of the treated fabrics were assessed; furthermore, the washing fastness was evaluated. TG measurements showed an increase of char formation of the treated cotton fabrics at 500 °C. Vertical flame spread tests revealed char formation quickly after ignition and the specimens achieved self-extinction after the removal of the flame. In addition, the treated fabrics did not lose their flame retardancy after several laundry cycles, thus proving the durability of the proposed flame retardant treatment.

Very recently, Liu et al. exploited a similar synthetic approach for obtaining hybrid organic-inorganic 3-aminopropyl triethoxysilane derivatives on cotton fabrics [40]. To this aim, a nucleophilic substitution was carried out ( ). A 10 wt % solution of the hybrid precursor (27) was prepared and then the cotton fabrics were immersed for different times before a subsequent thermal treatment.

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In a similar way, Wang and co-workers synthesized the precursor (27) shown in , which was applied onto cotton fabrics at different concentrations [41]. TG data of the fabrics treated with precursor (27) showed an increase of the thermal stability with increases of final dry add-on. Conversely, the cotton fabrics treated with precursor (28) exhibited a lower thermal stability as compared to the other hybrid system. However, both flame retardants showed an increase of the char residue with increases in the add-on on the treated fabrics. A similar trend was found when the treated fabrics were subjected to vertical flammability tests. Therefore, from an overall point of view, the designed hybrid coating systems were able to provide improved fire retardancy to cotton, exploiting the formation of a thermally stable char that prevents the underlying substrate from ignition and limits the release of flammable gases during the thermal degradation process. Finally, the washing fastness of the flame retardant was assessed: in particular, the specimens treated with the sol-gel precursor (28) did not exhibit any change of the phosphorus content after the first washing cycle.

4.7. Miscellaneous and Potential Phosphorus-Based Flame Retardants for Textile Applications

In addition to the list of chemical structures and chemical classifications that are mentioned earlier, it is worth listing some miscellaneous and promising flame retardants based on their chemical structure and behavior ( ).

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Table 2

Chemical structureTextile materialHighlightsRef.cottonThe FR monomer was grafted onto cotton fabrics using gamma chamber.
TG analysis of the treated fabrics showed a decrease of the onset decomposition temperature and increase of char formation.
The burning test showed that treated fabrics burnt much slower than untreated fabrics.[58]Viscose fiber fabricThe FR was applied to viscose fiber fabric through grafting polymerization.
LOI values increased by increasing the grafting percentage.
LOI values were almost unchanged after many washing cycles which showed the durability of the covalent bond.
Cone calorimetry data of treated fabric showed a significant decrease of PHRR and THR compared to untreated fabric.[59]cottonThe FR was used as sol-gel precursor.
It was hydrolyzed with 3-aminopropyltriethoxysilane (APTES) in deionized water in presence of HCl followed by the addition of a crosslinker.
The fabrics were treated by impregnation in solutions and cured at 150 °C after processing.
The burning test showed that all treated cotton fabrics burned completely with significant reduction of burning time and burning rate compared to untreated fabrics.
The FR exhibited condensed phase mode of action as TG analysis showed an increase of char formation.[60]cottonThe cotton fabrics were treated by soaking in finishing baths of FR, each at different concentrations but all at pH = 5.
The FR can react with cellulose without using other crosslinkers.
LOI values of treated fabrics increased by increasing the FR concentration.
The treated fabrics were found durable up to 50 washing cycles as no change had been noticed on the LOI values or the physical performance of the treated fabrics.[61]cottonThe cotton fabrics were treated by impregnation in an aqueous solution of FR, binder, crosslinker and pyrovatex.
LOI values of the treated fabrics with different binders and crosslinkers were below 21 which means they can ignite easily and burn rapidly.[44]cottonThe fabrics were treated by immersion in an aqueous solution of the FR in the presence of a buffer and shrinking agent.
LOI measurements showed an increase in LOI values with increases in the FR concentration.
The treated fabrics showed durability up to 30 laundry cycles which was considered as semi-durable flame-resistant.
The vertical burning test showed no afterflame or afterglow and a decrease in the char length with an increase in the FR concentration.[62]cottonThe fabrics were treated by immersion in an aqueous solution of the FR in the presence of a shrinking agent
The treated fabrics showed durability up to 30 laundry cycles which was considered as semi-durable flame-resistant
The vertical burning test showed no afterflame or afterglow and a decrease in the char length with an increase in the FR concentration.[63]PA6 fibersMeltable flame retardant which facilitates the compounding process.
Rheological measurements showed that this FR behaves as a plasticizer for PA6.
TG analysis showed higher char formation of formulated PA6 with the FR compared to neat PA6, while PCFC showed a predominant action in the gas-phase mode.
UL-94 test showed a V0 rating with 15 wt % of FR in PA6.[64]PET and PBT fibersThe UL-94 test for the formulated PET and PBT fibers with FR showing a V0 rating.[65]Open in a separate window