Halogen-Free Flame-Retardant Flexible Polyurethane Foam with a Novel Nitrogen–Phosphorus Flame Retardant

Ti3C2Tx MXene-based hybrid nanocoating for flame retardant, early fire-warning and piezoresistive tension sensing smart polyester fabrics

Flammability feature of textiles is a big underlying risk causing fire disasters. The fabrication of reliable fire resistant and quick fire warning fabrics is imperative but challenging. Herein, three types of early fire-warning polyester fabrics, namely, FPP@AM-X, FPP@PM-X and FPP@AX-M1, with good flame retardant and piezoresistive sensing performance were developed by fabricating polyethyleneimine (PEI), ammonium polyphosphate (APP), phytic acid (PA) and MXenes onto phosphorus-containing flame retardant polyethylene terephthalate (FRPET) via polydopamine (PDA) mediated layer-by-layer self-assembly. Owing to the improved thermoelectric properties of MXenes, FPP@A5-M1 exhibited a maximum thermoelectric voltage of 0.59 mV at a temperature difference of 130 °C and can provide an ideal cyclic early fire warning response within 4 s. In addition, due to the synergistic flame retardant effect of MXenes and APP in the coating layer, FPP@A5-M1 could be self-extinguished within 2 s after ignition and the value of peak heat release ratio and total smoke production decreased by 41.9% and 30.4%, respectively. Besides, the MXene-based hybrid coated fabric can detect the movement of human fingers and elbows, illustrating its potential application in piezoresistive tension sensing. This work provides a new route to designing and developing multi-functional and smart fire protection fabrics.

Flame-Retardant and Smoke-Suppressant Flexible Polyurethane Foams Based on Phosphorus-Containing Polyester Diols and Expandable Graphite

A liquid-phosphorus-containing polyester diol, PPE, was prepared via condensation polymerization using commercial reactive flame retardant 9,10-dihydro-10-[2,3-di(hydroxycarbonyl)propyl]-10-phospha-phenanthrene-10-oxide, adipic acid, ethylene glycol, and 1,4-butanediol. PPE and/or expandable graphite (EG) were then incorporated into phosphorus-containing flame-retardant polyester-based flexible polyurethane foams (P-FPUFs). The structure and properties of the resultant P-FPUFs were characterized using scanning electron microscopy tensile measurements, limiting oxygen index (LOI), vertical burning tests, cone calorimeter tests, thermogravimetric analysis coupled with Fourier-transform infrared spectroscopy, X-ray photoelectron spectroscopy, and Raman spectroscopy. Unlike the FPUF prepared using regular polyester polyol (R-FPUF), PPE increased the flexibility and elongation at break of the resultant forms. More importantly, the peak heat release rate (PHRR) and total heat release (THR) of P-FPUF were reduced by 18.6% and 16.3%, respectively, via gas-phase-dominated flame-retardant mechanisms, compared with those of R-FPUF. The addition of EG further reduced the peak smoke production release (PSR) and total smoke production (TSP) of the resultant FPUFs while increasing the LOI and char formation. Interestingly, it was observed that EG noticeably improved the residual quantity of phosphorus in the char residue. When the EG loading was 15 phr, the resulting FPUF (P-FPUF/15EG) attained a high LOI value (29.2%) and exhibited good anti-dripping performance. Meanwhile, the PHRR, THR, and TSP of P-FPUF/15EG were significantly decreased by 82.7%, 40.3%, and 83.4%, respectively, compared with those of P-FPUF. This superior flame-retardant performance can be attributed to the combination of the bi-phase flame-retardant behavior of PPE and condensed-phase flame-retardant characteristics of EG.

Sunflower Oil as a Renewable Resource for Polyurethane Foams: Effects of Flame-Retardants

Currently, polyurethane (PU) manufacturers seek green alternatives for sustainable production. In this work, sunflower oil is studied as a replacement and converted to a reactive form through epoxidation and oxirane opening to produce rigid PU foams. Confirmatory tests such as Fourier-transform infrared spectroscopy (FT-IR), gel permeation chromatography (GPC), and hydroxyl value among others were performed to characterize the synthesized polyol. Despite the versatility of rigid PU foams, they are highly flammable, which makes eco-friendly flame retardants (FRs) desired. Herein, expandable graphite (EG) and dimethyl methyl phosphonate (DMMP), both non-halogenated FR, were incorporated under different concentrations to prepare rigid PU foams. Their effects on the physio-mechanical and fire-quenching properties of the sunflower oil-based PU foams were elucidated. Thermogravimetric and compression analysis showed that these foams presented appreciable compressive strength along with good thermal stability. The closed-cell contents (CCC) were around 90% for the EG-containing foams and suffered a decrease at higher concentrations of DMMP to 72%. The burning test showed a decrease in the foam's flammability as the neat foam had a burning time of 80 s whereas after the addition of 13.6 wt.% of EG and DMMP, separately, there was a decrease to 6 and 2 s, respectively. Hence, our research suggested that EG and DMMP could be a more viable alternative to halogen-based FR for PU foams. Additionally, the adoption of sunflower polyol yielded foams with results comparable to commercial ones.

Phytic Acid-Iron/Laponite Coatings for Enhanced Flame Retardancy, Antidripping and Mechanical Properties of Flexible Polyurethane Foam

The use of flexible polyurethane foam (FPUF) is severely limited due to its flammability and dripping, which can easily cause major fire hazards. Therefore, choosing an appropriate flame retardant to solve this problem is an urgent need. A coating was prepared on the FPUF surface by dipping with phytic acid (PA), Fe2(SO4)3·xH2O, and laponite (LAP). The influence of PA-Fe/LAP coating on FPUF flame-retardant performance was explored by thermal stability, flame retardancy, combustion behavior, and smoke density analysis. FPUF/PA-Fe/LAP has a good performance in the small fire test, which can pass the UL-94 V-0 rating and the limiting oxygen index reaches 24.5%. Meanwhile, the peak heat release rate values and maximum smoke density of FPUF/PA-Fe/LAP are reduced by 38.7% and 38.5% compared with those of neat FPUF. After applying PA-Fe/LAP coating, the value of fire growth rate index decreases from 10.5 kW/(m2·s) to 5.1 kW/(m2·s), dramatically reducing the fire risk. Encouragingly, the effect of PA-Fe/LAP coating on cyclic compression and permanent deformation is small, which is close to that of neat FPUF. This work provides an effective strategy for making a flame-retardant FPUF with antidripping and keeping mechanical properties.

Halogen-free instinct flame-retardant waterborne polyurethanes: composition, performance, and application

Ideal halogen-free instinct flame-retardant waterborne polyurethanes have high flame-retardant efficiency, environmental friendliness, fine compatibility, and good thermostability. Phosphorus flame-retardants are currently widely used in halogen-free instinct flame-retardant waterborne polyurethanes (HIFWPU), especially those with phosphorous-nitrogen co-structures. Phosphorous-nitrogen HIFWPU have become a hotspot because their co-structures provide higher flame-retardance as compared to waterborne polyurethanes. This review introduces three main types of HIFWPU based on composition, performance and application. HIFWPU not only have improved flame-retardance but also satisfy the various requirements for functionality. HIFWPU have been widely developed in textile, furniture, automobile, and aerospace applications.

A Phosphorous-Containing Bio-Based Furfurylamine Type Benzoxazine and Its Application in Bisphenol-A Type Benzoxazine Resins: Preparation, Thermal Properties and Flammability

Polybenzoxazine (PBa) composites based on phosphorous-containing bio-based furfurylamine type benzoxazines (D-fu) and bisphenol-A type benzoxazines (Ba) were developed for flame retardation. The structure of D-fu was analyzed by Fourier transform infrared (FTIR) spectroscopy and ¹H-NMR spectroscopy. The curing temperature of Ba/D-fu mixtures was systematically studied by differential scanning calorimetry (DSC). Thermogravimetric analysis (TGA) demonstrated the excellent char formation ability of the PBa composites with the addition of phosphorous-containing D-fu. The flame retardancy of the PBa composite materials was tested by the limited oxygen index (LOI), vertical burning test (UL-94) and cone calorimeter (CONE). The LOI and UL-94 level of PBa/PD-fu-5% reached 34 and V0 rate, respectively. Notably, the incorporation of 5% D-fu into PBa led to a decrease of 21.9% at the peak of the heat-release rate and a mass-loss reduction of 8.0%. Moreover, the fire performance index increased, which demonstrated that the introduction of D-fu can diminish fire occurrence. The role of D-fu in the condensed and gas phases for the fire-resistant mechanism of the PBa matrix was supported by SEM-EDS and TGA/infrared spectrometry (TG-FTIR), respectively. Dynamic mechanical analysis (DMA) revealed that the Tg of PBa flame-retardant composites was around 230 °C. Therefore, PBa composites are promising fire-retardant polymers that can be applied as high-performance functional materials.

Halogen-free and phosphorus-free flame retardants endow epoxy resin with high flame retardancy through crosslinking strategy

Epoxy resin (EPs) has been widely used in many fields in recent years, such as electronics, adhesives, coatings, and so on, which mainly benefiting from its excellent mechanical and chemical properties, low price and easy preparation. However, conventional EPs tend to be flammable, which significantly prevents their applications especially in high flame-resistance required areas. In this work, we introduce nitrile groups and the benzoxazine ring into the flame-retardant, followed by a simple heat treatment for a multiple cross-linking reaction in EPs. The resultant halogen/phosphorus-free and environmentally friendly network not only suppress the migration of the functional flame retardants from the substrate, but also shows much enhanced flame-retardant property, including the UL-94 rate, total heat release and reduced peak heat release rate. As a result, the thermosets can pass the UL-94 V-0 rate and reach a LOI value at 32.7% at a very low addition amount (10 wt%) of this cross-linked flame retardant.

Design of copper salt@graphene nanohybrids to accomplish excellent resilience and superior fire safety for flexible polyurethane foam

Flexible polyurethane foam (FPUF) is the most commonly used polyurethane, but its highly flammable characteristics makes it ignite easily and release a lot of heat and toxic gases. Here, the effect of different forms of copper salt modified graphene (rGO@CuO, rGO@Cu₂O and rGO@CSOH) on improving the fire protection efficiency and mechanical property of FPUF is explored. Hybrid FPUF is characterized by thermogravimetric analysis (TGA), cone calorimeter, thermogravimetric analysis/Fourier transform infrared spectroscopy (TG-IR), tension, compression, and falling ball rebound testing. Compared with pure FPUF, the FPUF/rGO@CSOH show a significant decreasement in reducing the heat release of FPUF, the PHRR and THR are reduced by 36.9% and 29.4%, respectively. While the FPUF/rGO@Cu₂O demonstrate excellent smoke and toxic gases suppression in FPUF, the PSPR and TSR are reduced by 24.6% and 51.9%, and the COP and COY are also reduced by 51.9% and 55.3%, respectively. After adding the copper salt hybrid, the buffering performance of FPUF did not change. Fortunately, the tensile and compressive strength increase obviously. The flame retardant and smoke suppression mechanism of hybrid FPUF has also been studied. This article gives a effective strategy for the preparation of FPUF with outstanding mechanical property, flame retardant and smoke suppression properties.

Use of Novel Non-Toxic Bismuth Catalyst for the Preparation of Flexible Polyurethane Foam

Foam products are one of the largest markets for polyurethane (PU) and are heavily used in many sectors. However, current PU formulations use highly toxic and environmentally unfriendly production processes. Meanwhile, the increasing environmental concerns and regulations are intensifying the research into green and non-toxic products. In this study, we synthesized flexible polyurethane foam (PUF) using different weight percentages (0.025%, 0.05% and 0.1%) of a non-toxic bismuth catalyst. The bismuth-catalyzed foams presented a well evolved cellular structure with an open cell morphology. The properties of the bismuth-catalyzed flexible PUF, such as the mechanical, morphological, kinetic and thermal behaviors, were optimized and compared with a conventional tin-catalyzed PUF. The bismuth-catalyst revealed a higher isocyanate conversion efficiency than the stannous octoate catalyst. When comparing samples with similar densities, the bismuth-catalyzed foams present better mechanical behavior than the tin-catalyzed sample with similar thermal stability. The high solubility of bismuth triflate in water, together with its high Lewis acidity, have been shown to benefit the production of PU foams.

Polybenzoxazine Resins with Cellulose Phosphide: Preparation, Flame Retardancy and Mechanisms

Phosphated cellulose (PCF) was synthesized based on urea, phosphated acid and cellulose. The structure of the PCF was confirmed by Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy coupled with the Energy Dispersive Spectrometer (SEM-EDS). Benzoxazine (Ba)/PCF hybrid materials were fabricated and thermally cured to prepare polybenzoxazine composites (PBa/PCF). The effects of PCF on the curing temperature of Ba were analyzed through differential scanning calorimetry (DSC). The thermogravimetric (TGA) results demonstrated an increased char residue of 50% for the PBa composites incorporating PCF-5% compared with the pure PBa. The peak heat release rate (PHRR) and total heat release (THR) values of the PBa/PCF-5% composites clearly decreased by 58.1% and 16.5% compared to those of the pristine PBa. The smoke released from the PBa/PCF system significantly reduced with the loading of PCF. Moreover, the limited oxygen index (LOI) and vertical burning test level (UL-94) of PBa/PCF-5% reached up to 31 and V0. The flame retardant mechanism of the PCF in the PBa matrix was investigated TG-FTIR and char residues analysis. Finally, the dynamical mechanical analysis (DMA) results demonstrated that the Tg of the PBa/PCF composites was approximately 230 °C, which does not affect further applications of PBa composites.

A Study on Circular Economy Material Using Fish Scales as a Natural Flame Retardant and the Properties of Its Composite Materials

Fish scales (FSs) are fishery wastes that can cause environmental pollution. This study aimed to solve this environmental problem. FSs were used as a flame retardant for polymer materials, making them valuable. Fish scales were combined with a commercial flame retardant, ammonium polyphosphate (APP), through synergistic effects to reduce the amount of commercial flame retardant. The use of FSs conforms to the concept of a circular economy and lowers costs by reducing the consumption of APP. Thermogravimetric analysis (TGA), integral procedural decomposition temperature (IPDT), pyrolysis kinetics, limiting oxygen index (LOI), the Underwriters Laboratories 94 (UL94) flammability test, scanning election microscopy, Raman spectroscopy, and energy-dispersive X-ray spectroscopy were used to determine the thermal properties, flame retardant properties, flame retardant mechanism, char morphology, and composition of the composites. The TGA results indicated that the addition of 40% flame retardant raised the char residue from 16.45 wt.% (pure EP) to 36.07 wt.%; IPDT from 685.6 °C (pure EP) to 1143.1°C; LOI from 21% (pure EP) to 30%; and UL94 classification from fail (pure EP) to V-0. These results suggest an increase in char residue, which indicates better protection of the polymer matrix material. The improvements in IPDT, LOI, and UL94 classification, which indicate greater thermal stability, lower flammability (from flammable to fireproof), and higher flammability rating (from fail to V-0), respectively, suggest that the composite material has favorable thermal properties and is less inflammable.

Flame Retardancy Behaviors of Flexible Polyurethane Foam Based on Reactive Dihydroxy P-N-containing Flame Retardants

Green and environment-friendly high-efficiency flame retardants (FRs) are crucial to polymer FR modification. Here, a green FR 2-((bis(2-hydroxyethyl)amino)methyl)-5,5-dimethyl-1,3,2-dioxaphosphinane 2-oxide (HAMPP) was synthesized. The HAMPP was incorporated with a cyclic phosphorus structure, which will readily carbonize to inhibit or prevent further combustion. Moreover, the HAMPP contains dihydroxy reactive groups that can be used as a monomer in the polymerization reaction to obtain the main chain containing phosphorus polymer. Research studies on FRs were based on flexible polyurethane foam (PU-HAMPPs). The limiting oxygen index value of PU foam with 10% HAMPP could reach 23.7%, passing a UL-94 V-0 rating together. With the addition of HAMPP, the peak heat release rate of PU foam decreased significantly, the decomposition temperature increased, the heat release capacity reduced by 31%, and the char yield increased by 42%. The chemical composition and morphology of the char residual have been studied and analyzed thoroughly. We find that HAMPP forms a molten viscous protective layer uniformly on the material surface and releases some incombustible gases. These indicated that the FR exploited both condensed-phase and gas-phase flame retardancy mechanisms. Besides, the addition of FRs improved the mechanical properties.

Effect of tris(1-chloro-2-propyl)phosphate in combination with aluminum hypophosphite and melamine polyphosphate on flame retardancy and thermal decomposition of rigid polyurethane foams

RPUF with tris(1-chloro-2-propyl)phosphate (TCPP), melamine polyphosphate (MPP) and aluminum hypophosphite (AHP) alone, as well as their binary and ternary blends, were prepared via a one-step process. The effect of TCPP in combination with AHP and MPP on flame retardancy and thermal decomposition in the RPUF has been investigated. The results show that adding TCPP, MPP and AHP into RPUF simultaneously can significantly ensure the uniform cell structure, enhance the compressive strength, thermal stability and fire resistance of RPUF, decrease the thermal conductivity, the release of toxic HCN at high temperature. TGA results indicate that partial substitution of TCPP with MPP and AHP could improve the char residue. When the content of TCPP is 10 wt%, the optimal ratio of MPP and DPER was 1/2, the TCPP10/MPP3.3/AHP6.7/RPUF sample reached a V1 rating in vertical UL-94 test with a limiting oxygen index of 27.4%. The compressive strength and specific compressive strength (compressive strength/density) for TCPP10/MPP3.3/AHP6.7/RPUF sample increased about 82.6% and 44.3% compared to that of pure RPUF, respectively. The cone calorimeter test results showed that adding EG, MPP and AHP into RPUF simultaneously can significantly decrease the heat release rate (HRR), total heat release (THR) and smoke emission behavior of RPUF sample. Based on these facts, a potential flame-retardant mechanism was proposed.

The optical shielding performances and mechanisms of green flame-retardant two-component matte films under various application conditions

Herein, we meticulously investigated the optical shielding performances and mechanisms of green flame-retardant two-component waterborne polyurethane matte films based on a previous study. The relevant performances were evaluated by changing various environmental factors including nanoparticle content, pH, temperature and storage-time. Specifically, upon combination with TiO₂, the ultraviolet-light transmittance was reduced to 1.9% and the 60° glossiness decreased by 63%. When the pH was 8.0, the shielding efficiency and transmittance of ultraviolet light were 100% and 0%, respectively. The 60° glossiness of spin-films increased with an increase in storage time. Besides, TiO₂ nanoparticles were beneficial for delaying the thermal decomposition via synergistic flame retardance.

Herein, we meticulously investigated the optical shielding performances and mechanisms of green flame-retardant two-component waterborne polyurethane matte films based on a previous study.

Effects of Expanded Graphite, Aluminum Hydroxide, and Kaolin on Flame Retardancy and Smoke Suppression of Polyurethane Composites

Polyurethane is a widely used polymer that has good abrasion resistance and low-temperature resistance. However, polyurethane composite materials are highly inflammable and thus require the use of flame retardants. This study selected green and environment-friendly flame retardants such as expanded graphite, aluminum hydroxide, and kaolin to be used as individual or paired retardants to produce polyurethane composites. By analyzing the potential and mechanical properties of the polyurethane composites, it was found that the composite material with the flame retardant composed of graphite and modified kaolin had better flame retardancy, smoke suppression performance, and high thermal stability.

Flame retardant and smoke-suppressant rigid polyurethane foam based on sodium alginate and aluminum diethylphosphite

In order to improve the flame-retardant effect and thermal behaviour of rigid polyurethane foam (RPUF), the flame retardancy of sodium alginate (SA), aluminium diethyl phosphite (ADPO₂) and expandable graphite (EG) were proposed. First, the structures of RPUF with or without flame retardancy were confirmed by scanning electron microscopy (SEM). Additionally, the combustion behaviours and thermal performance of the flame-retardant polyurethane were evaluated through thermogravimetric analysis (TGA), limiting oxygen index (LOI) tests, and UL-94 tests. Finally, the cone calorimeter results reveled the RPUF/5ADPO₂/7.5SA/7.5EG exhibit excellent thermodynamic properties. The results of the heat release rate (HRR), total heat release (THR), total smoke production (TSP), and smoke production rate (SPR) could demonstrate the smoke-suppressant and flame-retardant of polyurethane. The system of RPUF/ADPO₂/SA/EG showed excellent flame-retardant in polyurethane.

Reinforcing Condensed Phase Flame Retardancy through Surface Migration of Brucite@Zinc Borate-Incorporated Systems

An efficient brucite@zinc borate (3ZnO·3B₂O₃·3.5H₂O) composite flame retardant (CFR), consisting of an incorporated nanostructure, is designed and synthesized via a simple and facile electrostatic adsorption route. It has been demonstrated that this incorporated system can enhance the interfacial interaction and improve the mechanical properties when used in ethylene-vinyl acetate (EVA) composites. Meanwhile, in the process of burning, the CFR particles can successively migrate and accumulate to the surface of the burning zone, increasing the local concentration and rapidly generating a compact barrier layer through a condensed phase reinforcement mechanism even at a lower loading value. Especially, compared with the EVA/physical mixture (PM, with the same proportion of brucite and zinc borate), the heat release rate (HRR), the peak of the heat release rate (PHRR), the total heat released (THR), the smoke production rate (SPR), and mass loss are considerably reduced. According to this study, controlling the nanostructure of flame-retardant particles, to improve the condensed phase char layer, gives a new approach for the design of green flame retardants.

Synthesis of multielement phosphazene derivative and the study on flame-retardant properties of epoxy resin

Herein, we have successfully synthesized phosphorus/nitrogen/silicon tri-elements compound phosphazene derivative hexa-[4-( N-(3-(triethoxysilyl)propyl)acetamide)phenoxy]cyclotriphosphazene (HNTPC) from hexachlorotriphosphazenitrile, methyl 4-hydroxybenzoate, and 3-triethoxysilylpropylamine, and it was used as an additive flame retardant in epoxy resin (EP). Then, the thermal stability and flame retardancy of the composite (HNTPC/EP) were tested. Thermogravimetric analysis showed that the presence of HNTPC made EP matrix decompose at a relatively low temperature, thus promoted the formation of a stable coke layer and protected the matrix from fire. Therefore, the amount of carbon residue was markedly increased at 800°C, indicating an outstanding condensed phase flame-retardant effect. Furthermore, various combustion test data manifested that the addition of HNTPC could significantly improve the flame-retardant performance of EP. In addition, the sample could pass the vertical burning tests (UL-94) V-1 grade when the addition amount was 10% and the limiting oxygen index value was 32.6%, the peak heat release rate and total heat release rate decreased by 40.0% and 21.5%, respectively. Besides, the results of scanning electron microscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy also showed that HNTPC can promote the formation of carbon layer and improved the flame-retardant property of EP. Finally, the condensed phase and gas phase synergistic flame-retardant mechanism of HNTPC was proposed.

Novel approach towards the synthesis of highly efficient flame retardant electrode and oil/organic solvent absorber

We have developed a facile one pot process to synthesize an ultra-light functionalized spongy graphene (FSG). This is the first approach to use carbon based flame retardant spongy material as an electrode to build completely flame retardant supercapacitor (FRS) also as an oil/organic solvent absorber. The fully FRS concept has created by the compilation of as-prepared FSG with flame retardant separator and electrolyte. As-prepared FSG contained high amount of phosphorus and nitrogen functional groups, which makes it potent flame retardant electrochemical material, to use it as an efficient FR electrode. Flame test of FSG revealed that it doesn't catch fire for ∼1500 s. Also, FSG was able to sustain flame retardancy at a temperature as high as 1500 °C for continuous exposure of ∼300 s. FSG used as an electrode for symmetric capacitor possessing maximum specific capacitance of 494.3 F g^-1 at a current density 1 A g^-1. Corresponding high energy density and power density values are 55.6 Wh kg^-1 and 1799 W kg^-1. It shows cycling stability of 86.1% after 5000 cycles at current density of 10 A g^-1. The electrochemical property of FSG was also confirmed using three electrode system. Flame retardant FSG material was also used for the absorption and recovery of oil and organic solvents. FSG has high oil and organic solvent sorption capacity in the range of 40-70 g/g, also can be reused for minimum 10 cycles. Such approach has great significance for multifunctional graphene based nanocomposites will open the new window for large-scale applications.

Novel MoS2-DOPO Hybrid for Effective Enhancements on Flame Retardancy and Smoke Suppression of Flexible Polyurethane Foams

A novel MoS₂-DOPO hybrid has been successfully synthesized through the grafting of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) on the surface of MoS₂ nanosheets using allyl mercaptan as an intermediate. MoS₂-DOPO was used as a flame retardant additive to prepare flame-retardant flexible polyurethane foam (FPUF). The influence of MoS₂-DOPO on the mechanical, thermal stability, and flame retardancy properties of FPUF composites were systematically investigated. The incorporation of MoS₂-DOPO could not deteriorate greatly the tensile strength and 50% compression set of FPUF composites, but effectively improves the char residue. The cone calorimeter and smoke density tests results revealed that the peak heat release rate, total heat release, and the maximum smoke density of the MoS₂-DOPO/FPUF composite were reduced by 41.3, 27.7, and 40.5%, respectively, compared with those of pure FPUF. Furthermore, the char residue after cone calorimeter tests and pyrolysis gaseous products of the MoS₂-DOPO/FPUF composite were analyzed by scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction, and thermogravimetric analysis/infrared spectrometry. The results suggested that the MoS₂-DOPO hybrid played a synergistic flame retardant effect of gas and condensed bi-phase action. In addition, a possible flame retardancy and smoke suppression mechanism of the MoS₂-DOPO/FPUF composite were proposed. This study provides a facile and promising strategy for the fabrication of polymer materials with excellent flame retardancy and smoke suppression properties.

Layer-by-layer modified low density cellulose fiber networks: A sustainable and fireproof alternative to petroleum based foams

Wood-based cellulose fibers were used to prepare porous, low density and wet-stable fiber networks (FN). Multilayer coatings consisting of chitosan (CH), sodium hexametaphosphate (SHMP) and inorganic nanoparticles comprising of either sodium montmorillonite (MMT), sepiolite (SEP) or colloidal silica (SNP) were deposited by the layer-by-layer (LbL) technique onto FNs in an effort to impart flame-retardancy. A simulated fire scenario measured by cone calorimetry showed that five quadlayers (QL) of CH/SHMP/CH/MMT, CH/SHMP/CH/SEP and CH/SHMP/CH/SNP can produce significant reduction in peak heat release rate (pkHRR). In detail, the coating containing SEP showed the largest reduction of the pkHRR by 47% relative to the uncoated FN. MMT and SEP coated FNs were also able to self-extinguish fire and to retain their shapes after direct exposure to a methane flame. This study hence shows that the LbL assembly is a highly effective way to impart flame-retardant properties to this new type of porous FN.

Investigation of the Flame-Retardant and Mechanical Properties of Bamboo Fiber-Reinforced Polypropylene Composites with Melamine Pyrophosphate and Aluminum Hypophosphite Addition

To improve the flame-retardant performance of bamboo fiber (BF) reinforced polypropylene (PP) composites, melamine pyrophosphate (MPP) and aluminum hypophosphite (AP) at a constant mass ratio of 2:1 were added. The influence of the MPP/AP mass fraction on the mechanical and flame-retardant properties of the BF reinforced PP composites were evaluated by mechanical testing, limiting oxygen index (LOI) and cone calorimetry. Mechanical tests demonstrate that tensile properties of BF/PP decreased with the increase of MPP/AP mass fraction, while flexural properties of composites exhibited very different tendencies. Both flexural strength and modulus increased slightly with the addition of MPP/AP at first, and then decreased significantly after a relatively high content of MPP/AP was loaded. This was due to the poor interfacial compatibility between PP and MPP/AP. The flame retardancy of BF/PP composites has been greatly improved. When 30% MPP/AP was loaded into the composites, the LOI increased to 27.2%, which was 42.4% higher than that of the composite without flame retardant addition. Cone calorimetry results indicated that MPP/AP worked in both gas and condensed phases during the combustion process. Peak heat release rate, total smoke production and mass loss of the composites were significantly reduced because of the addition of MPP/AP.

Highly Effective Flame-Retardant Rigid Polyurethane Foams: Fabrication and Applications in Inhibition of Coal Combustion

The extemporaneous combustion of coal remains a major threat to safety in coal mines because such fire accidents result in casualties and significant property loss, as well as serious environmental pollution. This work proposed the fabrication of flame-retardant rigid polyurethane foam (RPUF) containing expandable graphite as char expander/sealant with melamine phosphosphate and 2-carboxyethyl (phenyl)phosphinic acid as char inducer and radical trapping agents. The as-prepared RPUF successfully inhibited coal combustion by forming thermally stable high graphitic content expandable intumescent char sealing over the coal. The RPUF achieved UL-94 V-0 rating in addition to significant reductions in peak heat release, total heat release, and CO and CO₂ yields. The external and the internal residual char structure was studied by X-ray photoelectron spectra, Raman spectroscopy, and real-time Fourier transform infrared spectra techniques, and a flame-retardant mode of action has been proposed. This work provides important insight into a facile fabrication of highly efficient and economical flame-retardant RPUF to inhibit the spontaneous combustion of coal.

A Review of a Class of Emerging Contaminants: The Classification, Distribution, Intensity of Consumption, Synthesis Routes, Environmental Effects and Expectation of Pollution Abatement to Organophosphate Flame Retardants (OPFRs)

Organophosphate flame retardants (OPFRs) have been detected in various environmental matrices and have been identified as emerging contaminants (EC). Given the adverse influence of OPFRs, many researchers have focused on the absorption, bioaccumulation, metabolism, and internal exposure processes of OPFRs in animals and humans. This paper first reviews the evolution of various types of flame retardants (FRs) and the environmental pollution of OPFRs, the different absorption pathways of OPFRs by animals and humans (such as inhalation, ingestion, skin absorption and absorption), and then summarizes the environmental impacts of OPFRs, including their biological toxicity, bioaccumulation, persistence, migration, endocrine disruption and carcinogenicity. Based on limited available data and results, this study also summarizes the bioaccumulation and biomagnification potential of OPFRs in different types of biological and food nets. In addition, a new governance idea for the replacement of existing OPFRs from the source is proposed, seeking environmentally friendly alternatives to OPFRs in order to provide new ideas and theoretical guidance for the removal of OPFRs.