Flame Retardant Mechanism Research Articles

Polyurethane Materials for Fire Retardancy: Synthesis, Structure, Properties, and Applications

As the demand for high-performance polymers broadens, polyurethane (PU) polymers with various chemical modifications have attracted attention. This review explores the chemical structure and functional variations of PUs. PUs are used in a variety of fields, ranging from aerospace engineering to daily necessities, and show remarkable safety adaptability through designable synthesis processes. This study is divided into four main parts: (1) synthesis and structure, covering the synthesis of PU base and modification of additive compounds; (2) performance, studying physical properties and thermal degradation processes; (3) application, evaluating the commercial potential of PU polymers; and (4) flame retardancy, analyzing five established flame-retardant mechanisms. The last part discusses how PUs can meet sustainable development goals by replacing petroleum-based materials with green materials. By emphasizing non-petroleum resources and novel, sustainable modification strategies, this review conducts guidance for the safe and environmentally friendly application of PUs in the future.

Impact of phosphonate and phosphoramidate in Si/P/triazine hybrid flame retardants on cotton flammability

Phosphorus and nitrogen-containing flame retardants are well-known for their high efficacy when used in combination, either as separate compounds or within the same molecule. However, a detailed examination of the chemical bonding of phosphorus is needed to understand the flame behavior. To this end, two different scenarios were examined and compared with a phosphorus-free benchmark. Both scenarios contain a triazine ring and a silane-based precursor. The first scenario involves a direct bond between phosphorus and triazine (phosphonate), while the second involves a bridging of phosphorus and triazine via nitrogen (phosphoramidate). This allowed to investigate the structural effect of phosphoramidate and phosphonate of triazine derivatives on the thermal and flame retardant behavior. The flame-retardant performance and mechanism of the treated samples were investigated by means of the vertical flame test (DIN EN ISO 15025), thermogravimetric analysis and microscale combustion calorimetry, amongst others. Our research shows that triazine-based phosphonate has a better flame retarding effect on cotton than phosphoramidate at the same phosphorus concentration. Self-extinguishing characteristics was observed at a low add-on value of 0.23 mmol/g for phosphonate-based flame retardant, while a higher add-one value of 0.24 mmol/g was required in the case of phosphoramidate. The comprehensive analysis demonstrated that both flame retardants undergo mechanisms in both the gas phase and condensed phase by releasing incombustible gases and promoting the carbonization of cotton fabrics.

Research on the flame retardancy properties and mechanism of modified epoxy resin with graphene‐based hybrid

AbstractThe inherent disadvantage of epoxy resin (EP) is that it is easy to burn, and a large number of toxic and harmful gases are generated in the combustion process, and there is a huge fire hazard. Graphene, a two‐dimensional‐layered material with physical barrier effects, is used by many researchers to enhance the fire safety of EP, but because of its easy aggregation, it is difficult to prepare high‐performance flame retardants. In our work, a high‐performance graphene flame retardant was prepared by grafting a hollow zirconium organic frame material onto the surface of graphene. First, zirconium‐based organic frame material (UiO66‐NH2) with different particle sizes was prepared by adjusting acetic acid, the hollow organic frame material was etched with sodium tungstate under acidic conditions, and then reacted with organophosphorus and graphene oxide, thus W‐UiO66‐DOPO‐RGO were obtained. The results show that the W‐UiO66‐3‐DOPO‐RGO/EP has enhanced smoke suppression and flame retardancy, the LOI value up to 33.5%, vertical combustion class up to UL‐94V‐0, PHRR and TSP reduced by up to 58% and 42%, respectively. Through the characterization of the condensed and gas phase of EP composites, the relevant flame retardancy mechanism was clarified, which were mainly the synergistic flame retardancy and smoke suppression mechanism among the adsorption of fractional pores of hollow bimetallic MOFs, catalytic carbonization of metals, condensed phase and gas phase interaction of phosphorus elements, and physical shielding of RGO.Highlights A high‐performance graphene‐based flame retardants were proposed. 3 wt% of W‐UiO66‐3‐DOPO‐RGO endows EP with excellent flame retardancy. The fire safety mechanism of W‐UiO66‐DOPO‐RGO/EP was proposed.

Layered Double Hydroxide Nanosheets Incorporated Hierarchical Hydrogen Bonding Polymer Networks for Transparent and Fire-Proof Ceramizable Coatings

In recent decades, annual urban fire incidents, including those involving ancient wooden buildings burned, transportation, and solar panels, have increased, leading to significant loss of human life and property. Addressing this issue without altering the surface morphology or interfering with optical behavior of flammable materials poses a substantial challenge. Herein, we present a transparent, low thickness, ceramifiable nanosystem coating composed of a highly adhesive base (poly(SSS1-co-HEMA1)), nanoscale layered double hydroxide sheets as ceramic precursors, and supramolecular melamine di-borate as an accelerator. We demonstrate that this hybrid coating can transform into a porous, fire-resistant protective layer with a highly thermostable vitreous phase upon exposure to flame/heat source. A nanosystem coating of just ~ 100 μm thickness can significantly increase the limiting oxygen index of wood (Pine) to 37.3%, dramatically reduce total heat release by 78.6%, and maintain low smoke toxicity (CITG = 0.016). Detailed molecular force analysis, combined with a comprehensive examination of the underlying flame-retardant mechanisms, underscores the effectiveness of this coating. This work offers a strategy for creating efficient, environmentally friendly coatings with fire safety applications across various industries.

Flame retardancy and durability of cotton fabric modified with high-efficiency diboraspiro rings groups flame retardant.

The synthesis of highly efficient and environmentally friendly flame retardants through the synergistic interaction of boron, phosphorus and nitrogen is becoming a new research direction. In this study, N-DBSPA, a flame retardant with high flame retardancy, high thermal stability and high efficiency, was prepared by the reaction between pentaerythritol borate and amino trimethylene phosphate, and the limiting oxygen index (LOI) of the modified cotton fabric increased from 18 % to 44.7 % at a weight gain (WG) of 20.4 %. After 50 wash cycles (LCs), it still reached 34.2 % and passed the Vertical Flame Test (VFT), indicating good flame retardancy and wash resistance. Cone Calorimetry Test (CCT) showed a 90.2 % reduction in Peak Heat Release Rate (PHRR) and a 32.9 % reduction in Total Heat Release (THR). The thermogravimetric test (TG) showed an increase in the charring residue of cotton fabrics from 10.9 % to 36.2 % at 750 °C in a nitrogen atmosphere. Finally, the flame retardant mechanism of the modified cotton fibers was speculated from the condensed phase and gas phase, respectively.

Effect of dimethylamine pyrophosphate on the mechanical, thermal decomposition and flame-retardant properties of rigid polyurethane foams

To solve the problem of the insufficient flame retardancy of rigid polyurethane (RPUF), a new flame retardant, dimethylamine pyrophosphate (DMPY), was introduced into rigid polyurethane foam, and one-step foaming technology was used to prepare RPUF/DMPY composites. Furthermore, the thermal stability, flame retardancy, combustion characteristics, and gas-phase products were analyzed via thermogravimetric analysis (TGA), limiting oxygen index (LOI), cone calorimetry (CCT), and thermogravimetric infrared spectroscopy (TG-FTIR). The flame-retardant measurements revealed that when the DMPY amount exceeded 20 parts, the LOI of the RPUF/DMPY composites increased to above 23%, and all the samples reached the UL-94 V-0 level. In addition, the peak heat release rate and total heat release values of the RPUF-3 composites prepared with RPUF/DMPY were 192.6 kW/m2 and 19.98 MJ/m2, respectively, which were 35.0% and 29.1% lower than those of the pure RPUF, respectively, and significantly reduced the heat release of the RPUF composites. The analysis of char residue revealed that DMPY can effectively improve the density and graphitization degree of char residue during the combustion process of RPUF/DMPY composites, thereby endowing them with excellent flame-retardant properties. On this basis, the flame-retardant mechanism of the DMPY-based flame retardant RPUF composite material is proposed. This work provides new ideas for the development of new flame retardant PPUF composites.

Comparative Study on Cyclic Phosphazene-Based Flame Retardants for Ether Electrolytes in Li-S Batteries: Flame Retardancy and Performance Analysis

Abstract This study presents a systematic investigation of three cyclic phosphazene-based flame retardant additives, hexachlorocyclotriphosphazene (HCCP), hexafluorocyclotriphosphazene (HFPN), and ethoxy-pentafluorocyclotriphosphazene (EtPFPN), for ether-based electrolytes in lithium-sulfur batteries. Through comprehensive analysis of molecular orbital calculations, self-extinguishing time measurements, and electrochemical characterization, we reveal distinct structure-dependent flame retardancy mechanisms and their impact on battery performance. HCCP demonstrates superior flame suppression through P-Cl bond decomposition but exhibits electrochemical instability above 15 wt%. HFPN functions primarily as a co-solvent, achieving significant flame retardancy above 20 wt% while maintaining stable electrochemical performance. EtPFPN emerges as the most promising candidate, effectively integrating into the electrolyte solvation structure to provide optimal flame retardancy, though requiring higher concentrations for complete suppression. Notably, synergistic effects between LiNO3 and the flame-retardant additives enhance both safety and electrochemical stability. These findings provide critical insights for the molecular design of flame-retardant electrolytes in high-performance Li-S batteries, demonstrating the importance of balancing safety enhancement with electrochemical stability through strategic additive selection and concentration optimization.

One-step green synthesis durable flame-retardant, antibacterial and dyeable cellulose fabrics with a recyclable deep eutectic solvent.

The development of cellulose fabrics with good flame retardancy and durability has been a primary concern for in firefighting clothing. A recyclable ternary deep eutectic solvent (TDES) was used to prepare surface ammonium phosphate-modified cellulose fabrics (SACF). The incorporation of ammonium phosphate groups notably enhanced the durable flame retardancy of cellulose fabrics. The limiting oxygen index (LOI) of SACF could reach 48 %, and remain at 33.5 % even after 50 laundering cycles (LCs). And the TDES can be recovered and reused for 5 cycles and the SACF still remains flame retardancy. It also exhibited excellent antibacterial properties (with an antibacterial rate of 99.79 % against E. coli) and dyeability with cationic dyes. Moreover, the flame-retardant of the SACF did not decrease after dyed and showed both condensed-phase and gas-phase flame-retardant mechanisms during combustion. This method for producing flame-retardant cellulose fabrics with recyclable TDES effectively reduces the use of chemical reagents and holds promise for application in eco-friendly manufacturing and firefighting garments.

Preparation and flame retardancy of an Al2O3 infiltration layer on polycarbonate surface

Abstract In this study, the surface flame retardancy of polycarbonate (PC) was improved and the impact of flame retardants on the substrate were minimized by pre-mixing Al2O3 particles with dichloromethane, an infiltration promoter, to form a suspension, and then treating PC with the suspension to form an Al2O3 infiltration layer. For this layer, its structure and composition were characterized, its flame retardancy was evaluated, and its flame retardancy mechanism was investigated. The characterization results confirmed that an Al2O3 infiltration layer was successfully prepared on the PC surface under the aid of dichloromethane and that the involvement of dichloromethane induced certain microscopic pores and voids in the PC, with some dichloromethane remaining within the surface infiltration layer. The surface Al2O3 infiltration layer mainly served as a condensed-phase flame retardant. The infiltration layer prepared using a suspension with a dichloromethane-to-Al2O3 mass ratio of 24:1 not only exhibited a good overall performance but also achieved the best improvement in the PC flame retardancy, such as an increase in the vertical burning rating from HB to V-0, as well as the LOI increased from 24 to 31.3, and a 35% reduction in the peak heat release rate compared to those of pure PC.

Bio-based molecules with ionically bonded phosphorus toward ultra-high flame-retardant efficiency of PLA plastics.

The fire safety of polymer plastics has become a global consensus, and creating a more efficient flame-retardant network is in line with the trend. Here, a direct strategy for low usage of flame retardants and fire-resistant PLA plastics was proposed. The bio-based flame-retardant PDT, which was formed by ionic bonding of phytic acid and organic amine molecules, had high flame-retardant efficiency for PLA. PLA/PDT composite demonstrated excellent flame-retardant performance during service, achieving UL-94V-0 grade with only 2wt% of addition and a LOI of 29.3%, significantly better than previous work. In cone calorimeter test, heat release, CO2 production, and av-EHC were inhibited. And the flame-retardant mechanism was analyzed in detail through SEM, XPS, Raman, and TG-IR. Besides, the thermal stability and crystallinity of PLA composites were enhanced. It was expected that this work will provide a new approach for the development of sustainable flame-retardant PLA plastics.

Ethanol-induced ammonium polyphosphate-silver gel paint: breaking the trade-off between conductivity, flame retardancy and adhesion in single-layer functional coatings.

Electrical fires pose significant threats to the lives and property safety of people. Although utilizing coatings to impart conductivity and flame retardancy to materials is convenient and reliable, traditional layer-by-layer preparation methods have the limitations of cost, convenience and scalability. Therefore, a single-layer coating that simultaneously imparts excellent conductivity and flame retardancy to materials presents broader application prospects. And good adhesion of the coating is another essential aspect. However, the trade-off between conductivity, flame retardancy, and adhesion creates huge challenges in the development of such coatings. Here, we report an ethanol-induced ammonium polyphosphate-silver (APP-Ag) gel paint to completely address the above issues. High molecular weight APP served as both a flame retardant and an adhesive, while the coordinating action of phosphate groups ensured the effective dispersion of nanosilver, and the nitrogen-containing carbon layer formed from triethanolamine and ascorbic acid at high temperature significantly enhanced the conductivity of the coating by connecting the silver nanoparticles. The coated materials could exhibit an electrical conductivity of over 200 S m-1, with the limiting oxygen index (LOI) exceeding 60%. Meanwhile, the peak heat release rate (PHRR) and total heat release (THR) decreased by more than 30% compared to those of the untreated materials. Additionally, we utilized this gel paint to fabricate electric heating fabrics, motion sensors, and fire alarm devices. Finally, we have thoroughly explored the potential mechanisms of conductivity, flame retardancy, and adhesion of the gel coatings.

Facial functionalization carbon fiber with MnO2 nanosheets for high‐performance epoxy composites with excellent flame retardancy and mechanical properties

AbstractThe carbon fiber (CF) reinforced epoxy composites possess exceptional and distinctive properties as advanced composite materials. However, the flammability of epoxy resin and inadequate interfacial bonding between the resin and CF often impose limitations on their broader application. Herein, in order to enhance the flame retardancy of EP composites effectively, a hierarchical reinforcement was developed by facilely growing MnO2 nanosheets onto CF surface through an in situ process. Owing to their synergistic effects of physical barrier and chemical catalytic behavior, the presence of MnO2 nanosheets can effectively retard the combustion process by facilitating charring formation and suppressing heat and smoke release. Specifically, compared to the Untreated CF, the modified fiber reinforced composites exhibited significantly improved fire safety with reduction of 76.23%, 51.5% and 23.1% in peak heat release rate, total heat release and peak smoke production rate, respectively. Additionally, incorporating MnO2 nanosheets significantly enhanced mechanical properties of the composites, leading to remarkable enhancements of 41.8% in flexural strength and 28.14% in interlaminar shear strength. This study proposes an effective strategy for achieving outstanding flame retardancy and mechanical performance, thereby introducing an innovative concept for the production of high‐performance CF reinforced polymer composites.Highlights Growth of MnO2 nanoparticles enhanced the mechanical properties of the CF/EP composites. The CF‐MnO2/EP composites showed excellent flame retardancy. The flame retardant mechanism of CF‐MnO2/EP composites were analyzed. Highlight the potential application of MnO2 in the field of flame retardancy.

Temperature-sensitive intelligent gel to prevent coal spontaneous combustion: Large-scale simulation fire extinguishing experimental study

Coal spontaneous combustion seriously endangers mine safety production. In this study, a temperature-sensitive intelligent gel was synthesised from methylcellulose (MC), polyethene glycol (PEG) and sodium chloride (NaCl). The flow characteristics of temperature-sensitive intelligent gel (abbreviated as TSIG) under different conditions were analyzed by viscosity test. An infrared spectrometer also analyzed the microscopic flame retardant mechanism of temperature-sensitive intelligent gel. A large-scale simulation fire extinguishing test bench was designed at the coal mine site to analyze the flame retardant effect of the temperature-sensitive intelligent gel on coal oxidation reaction at different injection temperatures. The results show that the temperature-sensitive intelligent gel undergoes a liquid–solid phase transition at a temperature higher than 60 °C. When MC: PEG: NaCl = 1: 6: 5, the temperature-sensitive intelligent gel showed the best flow characteristics. The large-scale simulation fire extinguishing experiments show that the CO concentration is significantly reduced after the temperature-sensitive intelligent gel is injected at the coal temperature of 300–900 ℃, and both show excellent fire extinguishing effects. The addition of temperature-sensitive intelligent gel can inhibit the number of free radicals in the process of coal oxidation, block the chain reaction of coal spontaneous combustion, and comprehensively inhibit the process of coal spontaneous combustion. The research results provided theoretical support for the application of temperature-sensitive intelligent gel in coal spontaneous combustion areas. Additionally, they guided the design of temperature-sensitive intelligent gel to prevent coal spontaneous combustion technology.

Synthesis of nitrogen and phosphorus-doped chitosan derivatives for enhanced flame retardancy, smoke suppression, and mechanical properties in epoxy resin composites.

Biomass-based flame retardants have attracted significant academic interest due to their environmental benefits and sustainability. Nevertheless, devising straightforward, eco-friendly, and mild methodologies to synthesize flame retardants of epoxy resins (EP) remains a formidable challenge. This paper reports the successful synthesis of a novel nitrogen and phosphorus-doped chitosan derivatives flame retardant (MMCA) utilizing phytic acid, chitosan, and melamine cyanurate via electrostatic self-assembly and physical encapsulation in an acidic aqueous solution. The incorporation of 5wt% MMCA into the EP readily achieved a UL-94V-0 rating. This improvement can be primarily attributed to the early formation of a continuous, dense, robust, and expanded char layer during combustion, coupled with the synergistic flame retardant mechanisms of radical scavenging and the dilution of non-combustible gases. Compared to pristine EP, EP/5MMCA exhibited significant reductions of 23.7%, 29.2%, and 24% in total smoke production rate, peak heat release rate, and peak smoke production rate, respectively. Moreover, the strategic introduction of MMCA also enhanced the glass transition temperature, storage modulus, and crosslinking density of EP, improving its tensile, compressive and impact properties. This study proposes a simple, viable, and environmentally sustainable strategy for the fabrication of biomass-based flame retardants, resulting in notable improvements the flame retardancy, smoke suppression, fire safety, and mechanical robustness of EP.

An innovative method for preparing durable flame-retardant cotton fabrics using tetrakis(hydroxymethyl)phosphonium sulfate without specialized equipment.

In this study, two phosphorus-based flame retardants diethylenetriamine trimethyl diphosphonate lysine (APTA) and a tetrakis(hydroxymethyl)phosphonium sulfate prepolymer with urea (DUPT) were synthesized. The structures of these compounds were characterized via nuclear magnetic resonance (NMR) and Fourier-transform infrared spectroscopy (FTIR). FTIR and scanning electron microscopy (SEM) analyses revealed that DUPT crosslinked APTA onto cellulose, which was pre-processed with diethylenetriamine dipropylene oxide (NAED) to introduce NH groups through PCN bonds. The APTA/DUPT-30 cotton exhibited a limiting oxygen index (LOI) of 36.4 % and a damaged length of 4.8 cm. After 50 washing cycles, the treated cotton maintained an LOI of 30.5 % and a damaged length of 5.4 cm. These results indicate the exceptional flame retardancy and washing resistance of the treated cotton fabrics. Moreover, the thermogravimetry (TG) curves indicated that APTA/DUPT altered the degradation process of the cotton fabrics. The TG-FTIR data and residue analysis from the vertical flame-retardant test confirmed that the treated cotton utilized a condensed-phase flame-retardant mechanism. Overall, this approach effectively imparts excellent durable flame retardancy to cotton fabrics through stable PCN bonds, eliminating the need for specialized equipment.

Effects of two phosphonamide flame retardants derived from biomass pyridine on flame retardancy and flame-retardant mechanism of Polyamide 6

Achieving favorable flame retardancy in polyamide 6 (PA6) without compromising its mechanical performance remains a challenge, with a notable gap in understanding the influence of flame-retardant structure on PA6 properties and mechanisms. In this study, two biomass-derived phosphonamide flame retardants, P,P-diphenyl-N-(pyridin-3-yl) phosphonamide (DPDA) and P,P-Diphenoxy-N-(pyridin-3-yl) phosphonamide (DPPA), were synthesized and incorporated into PA6 to develop flame retardant composites. Results demonstrated that the PA6-9DPDA, containing a P-C bond, achieved a UL-94 V-0 rating with a Limiting Oxygen Index (LOI) of 27.9 %, while PA6-9DPPA, containing a P-O-C bond, maintained the UL-94 V-2 rating of pure PA6 but with an increased LOI of 29.4 %. DPPA exhibited a more favorable impact than DPDA on enhancing the tensile performance of PA6. Mechanisms indicated that DPDA primarily operates through vapor phase flame retardancy, whereas DPPA utilizes condensed phase flame retardancy. Overall, this study proposes a sustainable approach for fabricating PA6 composites with enhanced comprehensive performance.

Improvement of fame retardancy and thermal stability of epoxy composites by modifying salen-based polyphosphazene microspheres with Co-based metal organic frameworks

A functionalized cross-linked polyphosphazenes microsphere (Salen-PZN-Ni@Co-MOF) was fabricated by enveloping Salen-Ni-based polyphosphazenes (Salen-PZN-Ni) with a type of hybrid flame retardant (Co-MOF) to enhance the flame retardant, smoke suppression properties and mechanical properties of epoxy (EP) composites. Thermogravimetric analysis indicated that the incorporation of Salen-PZN-Ni@Co-MOF significantly enhanced the thermal stability of the EP composites. The existence of Salen-PZN-Ni@Co-MOF enhanced both the vertical burning rating and resulted in a higher limiting oxygen index. The addition of 5 wt% Salen-PZN-Ni@Co-MOF conspicuously improved the fire safety of EP, as evidenced by the results of the cone calorimeter. For instance, the peak heat release rate and total heat release rate of the EP composites were decreased by 25.3% and 44.97%, respectively. In addition, the incorporation of Salen-PZN-Ni@Co-MOF significantly inhibited the generation of toxic carbon monoxide and other volatile compounds. Furthermore, a synergistic effect between Salen-PZN-Ni and Co-MOF was observed. The proposed flame retardant mechanism of Salen-PZN-Ni@Co-MOF is attributed to the synergistic catalytic carbonization effect and the formation of thermally stable components. Consequently, enhanced fire safety in EP composites is achieved through the synergistic interaction among various components (nickel and Co-MOF) with polyphosphazene microspheres. Meanwhile, the excellent compatibility between Salen-PZN-Ni@Co-MOF and EP enhances the mechanical properties of EP composites.

Preparation of eugenol-based flame retardant epoxy resin with an ultrahigh glass transition temperature via a dual-curing mechanism

Eugenol epoxy resin, as one of the most promising biobased epoxy resins, still faces problems of insufficient heat resistance, high flammability, and complicated synthesis processes. Based on the principles of the Diels–Alder (D-A) addition reaction and epoxy-amine open-loop crosslinking, the EUEP epoxy monomer (EUEP) was synthesized, and ternary cocuring (EUEP-BDM-DDS) was performed with bismaleimide (BDM) and the high-temperature curing agent 4,4′-diamino-diphenyl sulfone (DDS). The resulting system exhibited an exceptional glass transition temperature (Tg) of 306 °C, surpassing other eugenol epoxies and commercial bisphenol A epoxies. EUEP-BDM-DDS demonstrated superior mechanical properties with high moduli (up to 4.14 GPa for tensile and 4.10 GPa for flexural). Its processing characteristics were also favorable, featuring a long pot-life, low viscosity, and suitable for all operating processes of traditional DGEBA-DDS systems. In addition, the formation of rigid six-membered rings during curing and the higher cross-linking density gave the resin system excellent flame retardant properties, with a limit oxygen index of 33.5 % and passing the V-0 class test of UL-94. The system exhibited significantly lower peak heat release and smoke release rates compared to DGEBA-DDS, indicating enhanced fire safety. And the analysis revealed a coacervated flame retardant mechanism. Moreover, the composite material derived from EUEP-BDM-DDS displayed improved interlaminar shear strength, flexural strength, and high-temperature mechanical properties, outperforming the DGEBA-DDS system. This study paves the way for utilizing biobased eugenol epoxy resins in advanced composite materials, offering enhanced performance and fire safety. It holds significant implications for promoting the application of biobased materials in high-performance composites.

Phytic acid/cellulose nanofibers modified layered double hydroxides flame retardants: Synthesis, properties and applications

Layered double hydroxides (LDHs) tend to agglomerate and primarily exhibit a single condensed phase flame-retardant mechanism, limiting their application as flame retardants (FRs) for wood. In this paper, we prepared a composite FR by intercalating phytic acid (PA) into the LDH layers through anion exchange. Additionally, cellulose nanofibers (CNF) were incorporated to interact with the hydroxyl groups on the LDH surface, improving the dispersion and stability of LDH. LDH-PA-CNF exhibited excellent flame-retardant performance and good dispersibility, which was suitable for flame-retardant modification of wood. After impregnating the wood with LDH-PA-CNF, the total heat release (THR) and total smoke release (TSR) of Wood@LDH-PA-CNF decreased by 21.2 % and 56 %, respectively, compared with the untreated wood. The limited oxygen index (LOI) value of Wood@LDH-PA-CNF has been significantly improved from 21 % to 75.4 %. Based on the analysis of the composition and chemical structure of the residues and gases produced during the combustion of Wood@LDH-PA-CNF, the synergistic flame-retardant mechanism in both condensed and gas phases of LDH-PA-CNF was proposed. This study provides novel insights into the design of high-performance FRs and offers valuable clues for enhancing the homogeneous dispersion and synergistic effects of inorganic FRs.

A high-molecular-weight flame retardant derived from bis[tetrakis(hydroxymethyl)phosphonium] sulfate for cotton fabrics

A high-molecular-weight flame retardant, bis[tetrakis(hydroxymethyl)phosphonium] (THPS)-urean-(PO3)(NH4)2, was synthesized for cotton fabrics. Fourier-transform infrared spectroscopy, nuclear magnetic spectroscopy, scanning electron microscopy, and X-ray photoelectron spectroscopy analyses confirmed that (THPS-urea)n-(PO3)(NH4)2 effectively infiltrated the fibers and grafted onto cellulose through N–P(=O)–O–C covalent bonds. The fabric treated with 30 wt% of (THPS-urea)n-(PO3)(NH4)2 (C30) had a limiting oxygen index of 46.8 %. Even after 50 laundering cycles according to the AATCC 61-2013 3A standard, C30 maintained a limiting oxygen index of 39.8 %. Thermogravimetric-Fourier-transform infrared spectrometry, thermogravimetry, and cone calorimetry tests revealed that C30 exhibited excellent flame retardancy. Upon exposure to flame, C30 formed a stable char layer, which prevented the spread of heat and combustible gases. Additionally, C30 was free of formaldehyde, making it suitable for producing infant textiles. After grafting with the flame retardant, C30 retained its mechanical properties. The high-molecular-weight flame retardant enhanced the flame resistance and durability of cotton materials owing to its numerous N–P(=O) (ONH4)2 groups, which facilitated a condensed-phase flame retardancy mechanism.