Phosphorus-based Flame Retardants Research Articles

Single overall ‘H-shaped’ multifunctional compound achieves fire safety, durability, enhanced strength, and smoke suppression of cotton fabrics

Challenges currently faced by phosphorus-based flame retardants for cotton fabrics include reduced fabric strength after treatment, high smoke release during combustion, formaldehyde release from commercial phosphorus-based flame retardants and poor flame retardant durability after treatment. In the present work, a P/N/B synergistic flame retardant TBST is synthesized using phosphoric acid, cyanuric acid, boric acid, pentaerythritol, etc. The phosphorus‑nitrogen‑boron atomic ratio is 2:3:1, and it is successfully prepared on cotton fabric to prepare TBST/Cotton. When the weight gain rate is 29.8 %, the LOI value is 41.6 ± 0.3 %, indicating that TBST/Cotton has excellent flame retardant performance. At the same time, in the vertical flame test, the length of residual carbon is 5.6 cm. In addition, the THR and HRR are reduced by 58.4 % and 91.9 % respectively compared to Cotton, indicating that TBST/Cotton has excellent combustion performance. In addition, compared to the residual carbon content of Cotton at 710 °C, the residual carbon content of TBST/Cotton in nitrogen increased by 27.79 %. For a 30 % increase in weight, the increase in longitudinal mechanical strength is 23.1 %. Inferred the decomposition mechanism and flame retardant mechanism of TBST/Cotton. TBST/Cotton has the advantages of good flame retardant durability and enhanced mechanical properties, and the reinforcement mechanism of TBST has been speculated.

A novel strategy utilizing oxidation states of phosphorus for designing efficient phosphorus-containing flame retardants and its performance in epoxy resins

The oxidation state of phosphorus has a great influence on the flame retardant action of its flame retardants. In this study, a reactive phosphorus-containing flame retardant (POG-DOPO) with both low and high phosphorus oxidation states is synthesised and incorporated into epoxy resin. The results show that the part in high oxidation state act mainly in the condensed phase and the part in low oxidation state act mainly in the gas phase. Furthermore, the flame retardant exhibits a synergistic flame retardant effect, resulting in a higher flame retardant efficiency than that of flame retardants with a single phosphorus oxidation state. Compared with unmodified epoxy resin, the peak heat release rate, total heat release rate and total smoke release of POG-DOPO modified epoxy resin with only 3wt% phosphorus are reduced by 70.9%, 51.2% and 55.7%, respectively. Its LOI increases to 31.8% and vertical combustion test achieves UL-94 V-0 rating. This study provides a strategy for the structural design of efficient phosphorus-based flame retardants.

A system with efficient flame retardant and antibacterial properties for the development of exceptional durable functional cotton fabrics

Phosphorus-based flame retardants are widely employed in the study of flame retardancy for cotton fabrics due to their halogen-free nature and high efficiency. The addition of nitrogen and other elements can further enhance flame retardant properties through synergistic effects. However, the synthesis of flame-retardant multifunctional additives based on phosphoramidic ammonium salts has been scarcely reported. In this study, a halogen-free and formaldehyde-free phosphoramidite ammonium salt was synthesized as a synergistic flame retardant multifunctional additive. This compound, with phosphorus as the primary flame retardant element and a nitrogen-containing guanidine group, was used to modify cotton fabrics. The treated fabrics exhibited enhanced flame retardant and antibacterial properties. Notably, cotton fabrics treated with a 17.9 % weight gain showed a damaged length of 4 cm in the vertical flame test, and the LOI value increased to 41.5 %, remaining at 27.3 % even after 50 washing cycles. The results of the cone calorimeter test (CCT) revealed that the peak heat release rate (PHRR) and total heat release (THR) of treated cotton were 30.35 kW/m2 and 5.46 MJ/m2, respectively, representing reductions of 87.04 % and 36.07 % compared to untreated cotton. Physical performance tests indicated only a slight decrease in the strength and whiteness of the cotton fabrics, while softness increased after treatment. Moreover, the treated cotton fabric exhibited excellent antibacterial properties, with antibacterial rates of 99.26 % against E. coli and 98.54 % against S. aureus.

Pyrolysis and flammability of phosphorus based flame retardant pressure sensitive adhesives and adhesive tapes

Pressure-sensitive adhesive tapes are used in a variety of applications such as construction, aircrafts, railway vehicles, and ships, where flame retardancy is essential. Especially in these applications, phosphorus-based flame retardants are often chosen over halogenated ones due to their advantages in terms of toxicity. Although there are pressure-sensitive adhesives with phosphorus flame retardants available on the market, their flame-retardant modes of action and mechanisms are not entirely understood. This research article provides fundamental pyrolysis research of three phosphorus-based flame retardants that exhibit different mechanisms in a pressure-sensitive adhesive matrix. The flame-retardants modes of action and mechanisms of a 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) derivate, an aryl phosphate, and a self-synthesized, covalently bonded DOPO derivate (copolymerized) are investigated. The blended DOPO derivate is volatilized at rather low temperatures while the covalently bonded DOPO derivate decomposes together with the polymer matrix at the same temperature. Both DOPO derivates release PO radicals which are known for their flame inhibition. The aryl phosphate decomposes at higher temperatures, releases small amounts of aryl phosphates into the gas phase, and acts predominantly the condensed phase. The aryl phosphate acts as precursor for phosphoric acid and improves the charring of the pressure sensitive adhesive matrix. All flame retardants enhance the flammability of the adhesives depending on their individual mode of action while the covalently bonded flame retardant additionally improves the mechanical properties at elevated temperatures making it a promising future technology for pressure-sensitive adhesives.

Utilizing the oxidation defects of black phosphorus to reduce and stabilize copper(I) molybdate to achieve flame retardancy and smoke suppression in polycarbonate composites

Promising phosphorus-based flame retardants reduce thermal hazards while increasing non-thermal hazards. This work utilizes the oxidative defects of black phosphorus, which can synchronously reduce and stabilize copper(I) molybdate while introducing surface modification with sodium alginate in an environmentally friendly ball milling process to enhance dispersibility. First, the T5% and Tmax of PC/BP@CM@SA (2 wt%) increase by 9.5 °C and 8 °C, respectively, under nitrogen. Second, UL-94 V0 was achieved, and the peak heat release rate, total heat release, and total smoke release decreased by 44.0 %, 22.1 %, and 17.0 %, respectively. Compared with that of the neat sample, the height of the char layer doubled, while its graphitization degree decreased from 2.38 to 2.14. In short, this is largely attributable to the catalytic action and physical barrier effect of BP@CM@SA. This study provides a way to balance the reduction in thermal hazards and increase in non-thermal hazards of phosphorus-based flame retardants such as black phosphorus.

Phase change material microcapsules doped with phosphorus-based flame retardant filled titanium dioxide nanotubes for enhancing the energy storage and temperature regulation performance of buildings

Solar energy is not only a green alternative to fossil energy but also a candidate for future mainstream energy sources. To improve the efficiency and application range of solar energy, we investigated tris (1-chloro-2-propyl) phosphate (TCPP) modified titanium dioxide nanotubes (TNTs) doped phase change material microcapsules (p-t-MPCMs) to enhance the temperature regulation and flame retardancy of epoxy resin (EP) coatings. Transmission electron microscopy (TEM) and Fourier transform infrared (FTIR) spectroscopy determined the successful preparation of p-TNTs and p-t-MPCMs. Moreover, it was confirmed that the p-t-MPCMs had great thermal stability and reliability by the thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The p-t-MPCMs increased residual mass by 12.2 % at 600 ℃ while correcting the initial melting temperature of MPCMs by 1.0 ℃. Based on the principle of oxygen consumption, the heat release rate (HRR) of EP coatings containing the p-t-MPCMs (p-t-MPCM/EP) was reduced from 665.92 kW/m2 to 443.78 kW/m2, resulting in a total heat release reduction (THR) of 17.73 % tested by a conical calorimeter. Then the results of the miniature chamber model demonstrated that p-t-MPCM/EP had outstanding temperature control ability. In summary, the p-t-MPCMs expressed great potential in regulating building temperature timely and improving the fire safety of EP coatings.

Flame retardant polyvinyl alcohol composite with excellent comprehensive properties prepared using Cu2O/chitosan and phosphorus-based flame retardants

Flame retardant polyvinyl alcohol composite with excellent comprehensive properties prepared using Cu2O/chitosan and phosphorus-based flame retardants

Core-shell flame retardant/APP-PEI@MXene@ZIF-67: A nanomaterials self-assembly strategy towards reducing fire hazard of thermoplastic polyurethane

Ammonium polyphosphate (APP) is the most commercially valuable phosphorus-based flame retardant, but poor interaction with the polymer interface limits the flame-retardant efficiency. In this work, a new type of multi-layered nanomaterial coating APP (APP-PEI@MXene@ZIF-67) was prepared and introduced into thermoplastic polyurethane (TPU) polymers by a simple and green assembly strategy. The effects of different loading shells of modified APP on the flame retardancy of TPU composites were investigated, as well as their gas/condensed phase thermal degradation products and their flame-retardant mechanisms. The results showed that APP-PEI@MXene@ZIF-67 was more favorable for catalytic char formation than APP, and the residual char formed by its composites was denser and more continuous. Compared with the pure TPU, the pHRR, THR, pSPR, and TSP of TPU/APP-PEI@MXene@ZIF-67–2BL composites were decreased by 72.75 %, 87.25 %, 59.58 %, and 85.97 %, respectively, which significantly reduced the heat and smoke release during the combustion process. The gas-phase and condensed-phase flame retardant mechanisms synergized to construct a possible approach to address the fire risk and heat/smoke hazards of TPUs and promote the extensive application of TPU polymers.

Research on the synergistic flame retardation of epoxy resin through surface-modified aluminum diethylphosphinate in conjunction with DOPO and CFA

Surface modification of aluminum diethylphosphinate (ADP) was successfully achieved through the utilization of silane coupling agent KH-560. Simultaneously, the modified aluminum diethylphosphinate (K-ADP) served as the primary flame retardant, with 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) as the phosphorus-based flame retardant and charring‐forming agent (CFA) as the nitrogen-based synergistic flame retardant. This approach was employed to investigate the flame-retardant modification of epoxy resin. The optimal dosage of the surface modifier was investigated through moisture absorption test and viscosity measurements. Synergistic flame-retardant interactions among K-ADP, DOPO, and CFA were examined using techniques such as cone calorimetry test, thermogravimetric analysis, and residual char infrared analysis. The results indicated that the optimal dosage of KH-560 is 5%, resulting in a significant reduction in moisture absorption to 0.195%. At 80 °C, the addition of K-ADP leaded to only a 22.7% increase in system viscosity, demonstrating a notable viscosity reduction effect. When the addition of K-ADP is 14%, the Limiting Oxygen Index (LOI) value reached 30.5%, achieving a V-0 rating. Moreover, by maintaining the total addition at 14% and introducing DOPO and CFA, it is evident that most of samples meet UL-94 V-0 rating, with the LOI elevated to 32.2%. CCT results indicated a significant decrease in both average heat release rate and total smoke production, reduced by 24.1% and 7.0%, respectively. This notably enhanced the flame-retardant and smoke-suppressant properties of the EP composite material. The addition of K-ADP, DOPO, and CFA improved the mechanical performance of the EP composite material, surpassing the effectiveness of adding ADP individually.

Preparation, Cure, Characterization, and Mechanical Properties of Reactive Flame-Retardant Cyanate Ester/Epoxy Resin Blends and their Carbon Fiber Reinforced Composites

This study explores the formulation space of flame retardant thermoset polymers, specifically involving blends of epoxy and cyanate ester (EP/CE) and a reactive phosphorus-based flame retardant, poly (m-phenylene methylphosphonate) (PMP). Two CE monomers were investigated, each blended with the same epoxy monomer (DGEBA) in a 1:1 wt ratio. The impact of phosphorus concentration on the neat (neat meaning no fibers were present) resin blends was characterized using differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The flammability and mechanical characteristics were assessed using micro-combustion calorimetry (MCC) and dynamic mechanical analysis (DMA). Carbon fiber composite panels were successfully fabricated using a wet layup process and autoclave curing with a fiber volume fraction (Vf) of approximately 0.5. DMA testing of the cured composite laminates pinpointed that the average Tg of the EP/CE blend was reduced with PMP addition by up to 39 °C at a phosphorous level of 3 wt%. Cone calorimetry tests confirmed the effectiveness of the flame retardant by reducing the peak Heat Release Rate (HRR) by approximately 27 %. The integration of PMP into EP/CE only marginally reduced the 3-point flexural strength (6–15 %) and modulus (7–13 %) relative to baseline samples.

A facile strategy for synthesizing hyperbranched phosphorus-containing polyol: Toward enhancing intrinsic flame retardancy and smoke suppression of rigid polyurethane foams

Rigid polyurethane foams (RPUFs) are critically challenged by their inherent high flammability and the generation of toxic smoke. In this study, we synthesized a novel, easily manufacturable hyperbranched phosphorus-containing polyol, named HPEAP. The RPUF composites containing 50 wt% HPEAP exhibited exceptional performance, notably in reducing flammability and enhancing flame retardancy. Compared to traditional RPUF and brominated RPUF, the composites with 50 wt% HPEAP showed significant reductions in peak heat release rate (65.56 %) and total heat release (72.38 %). It is noteworthy that phosphorus-based flame retardants typically have the drawback of increasing smoke production. However, the addition of 50 wt% HPEAP significantly reduced the total smoke production of RPUF by 66.34 %, overcoming a common limitation. This performance is largely attributed to the excellent thermal stability of HPEAP and its ability to promote a super high char yield. In summary, this work presents a straightforward approach for manufacturing high-performance RPUF products with enhanced fire safety characteristics, showcasing HPEAP's potential to improve the environmental and safety profiles of polyurethane foams.

Quantitative assessment of whether phosphorus-based flame retardants are optimizing or degrading the fire hazard of aircraft carbon fiber/epoxy composites

Fire hazards are a primary concern in aircraft accidents, and controlling combustible materials is pivotal in managing cabin fire risks. This work aims to elucidate the impact of widespread measures that introduce phosphorus-based flame retardants (PFRs) on the fire safety of carbon fiber epoxy composites (CF/EP). Firstly, the hazardous indicators for flame retardant CF/EP composites exhibit two categories of optimization and degradation, which are caused by the intrinsic feature, pyrolysis characteristics and chemical valence states of PFRs. Secondly, the fire hazards of composites are assessed by fusing the analytic network process and information weights guided by Nash Equilibrium theory. The method combines the merits of subjective and objective weights from dimensions of intrinsic hazards, interrelationships and data dispersion of indicators. Finally, the assessed fire hazard rankings under 35 and 65 kW/m2 both are EP > CF/EP16%DOPO-HQ > CF/EP > CF/EP7%DPO. In conclusion, DOPO-HQ (+1) primarily increases the fire hazard of CF/EP due to gas-phase flame-retardant effects, while DPO (+3) predominantly reduces the fire hazard of CF/EP by contributing to condensed-phase effects. This work highlights the contradictory effects of PFRs on the fire safety of CF/EP composites due to structure and thermal stability. The proposed ANP and IW hybridization method provides a theoretical foundation for selecting flame retardants and assessing material fire hazards comprehensively.

Effects of iron-based metal–organic framework-MIL-53(Fe) and phosphorus-based flame retardants on the flame retardancy of high-density polyethylene

Effects of iron-based metal–organic framework-MIL-53(Fe) and phosphorus-based flame retardants on the flame retardancy of high-density polyethylene

Characteristics and Quality of Flame-Retarded Ramie Fabrics for the Development of Functional Textiles.

Cellulose fabric testing for flame-retardant studies is frequently necessary in various textile applications. Natural cellulose material from ramie (Boehmeria nivea) is being promoted as an alternative raw material for the development of fire-resistant fabrics. This research aims to optimize the coating process of ramie fabric using a phosphorus-based flame retardant (FR) to enhance its flame-retardant characteristics. The FR treatment involves bleaching the fabric with H2O2; followed by fabric finishing using a formula comprising 3% (v/v) hydroxymethyl resin; phosphoric acid (2%); and two formulations of the flammable agent Flamatic DM-3072N: 40% (v/v) and 50% (v/v), applied using the pad-dry-cure method. The flame-retardant properties of the treated fabric are evaluated through flammability testing based on the ASTM D6413-08 standard, limiting oxygen index (LOI) analysis, and micrograph surface structure analysis with SEM. The results indicate that ramie fabric treated with the FR-50% material exhibits superior fire resistance, preventing fire spread on the fabric with a char length of 15-30 mm and a LOI value of 29. These findings highlight the potential of FR-treated ramie fabrics for various industries, including the automotive and protective clothing industries.

Bio-based flame retardant for manufacturing fire safety, strong yet tough versatile epoxy resin

Bio-based flame retardants have attracted growing attention for sustainability and comparable efficiency to petroleum-based counterparts but suffer from compatibility issues with epoxy resins and the trade-off between strength and toughness. Here, a Schiff base-derived phosphorus-based flame retardant (TV-DOPO) was developed from biobased vanillin and tyramine. In the presence of the binary curing agents, nanoscale in-situ constructive phase separation induced by hierarchical thermal curing process and strong hydrogen bonding provide the composite resin with enhanced both stiffness and toughness. The flexural and impact strengths reached 159 MPa and 55.4 kJ m−2, which were increased by 36.5% and 129.6%, respectively, compared with the pristine epoxy, meanwhile excellent flame retardance was well maintained (UL-94 V-0 rating). Remarkably, these conjugated phosphaphenanthrene-containing composite resins demonstrate excellent UV-shielding capacity and optical transmittance. In this work, in-situ construction of a crosslinked network with tunable size of phase separation domains can be simply achieved by modulating the ratio of binary curing agents, to fabricate epoxy resins with all-around enhanced performance.

Self-evolutionary recycling of flame-retardant polyurethane foam enabled by controllable catalytic cleavage.

Polyurethane (PU) foams, pivotal in modern life, face challenges suh as fire hazards and environmental waste burdens. The current reliance of PU on potentially ecotoxic halogen-/phosphorus-based flame retardants impedes large-scale material recycling. Here, our demonstrated controllable catalytic cracking strategy, using cesium salts, enables self-evolving recycling of flame-retardant PU. The incorporation of cesium citrates facilitates efficient urethane bond cleavage at low temperatures (160 °C), promoting effective recycling, while encouraging pyrolytic rearrangement of isocyanates into char at high temperatures (300 °C) for enhanced PU fire safety. Even in the absence of halogen/phosphorus components, this foam exhibits a substantial increase in ignition time (+258.8%) and a significant reduction in total smoke release (-79%). This flame-retardant foam can be easily recycled into high-quality polyol under mild conditions, 60 °C lower than that for the pure foam. Notably, the trace amounts of cesium gathered in recycled polyols stimulate the regenerated PU to undergo self-evolution, improving both flame-retardancy and mechanical properties. Our controllable catalytic cracking strategy paves the way for the self-evolutionary recycling of high-performance firefighting materials.

Investigation of combustion and mechanical properties of huntite-hydromagnesite and intumescent flame retardants in polypropylene composites

Achieving high mechanical performance in a polymer composite is one of the primary concerns when using mineral-based flame retardants. Mineral-based flame retardants should be added to the matrix at 50%–70% to achieve a high level of flame retardancy. High mineral content increases the modulus of elasticity and reduces the ductility of the material. This can be disastrous in applications where flexibility is critical. To overcome this problem, minerals can be used in combination with other effective flame retardants. In this study, the combination of halogen-free mineral-based huntite/hydromagnesite (H/H) and phosphorus-nitrogen-based intumescent flame retardants was investigated to improve the flame retardancy and maintain the flexibility of polypropylene (PP). For this purpose, PP carrier composites were prepared by extrusion by decreasing the mineral concentration in the active formulations and increasing the ratio of phosphorus-based flame retardants. These composites were subjected to mechanical, morphological (SEM), color, and flammability (UL94) tests. As a result, composites with UL94 V0 flammability and 18% to 104% higher tensile strength than equivalent H/H-based flame retardants were obtained.

Preparation of Ar–P–N-structured flame retardant via Kabachnik–Fields reaction for fire safety and mechanical reinforcement of polyurethane

Fire safety of polyurethanes (PUs) has limited their further practical applications. To address this problem, we designed novel phosphorus-based flame retardants (P-FR) by incorporating aryl (Ar) groups via Kabachnik–Fields reaction, realizing π–π interaction-reinforced Ar2 and Ar5. Total heat release and peak heat release rate of PU/Ar5, whose flame-retardancy-index of 5.02 due to reduced combustion time, decreased 23.24 and 9.23 %, respectively, compared with neat PU. Moreover, UL94 rating for PU/Ar5 was improved from V-2 to V-0. These results demonstrate that Ar5 effectively generate a barrier effect that blocks oxygen, fuel, and heat. Sluggish mobility and phase transition are responsible for such enhancement due to a delay effect with the existence of π–π interactions and steric hindrance. Encouragingly, tensile strength and toughness of PU/Ar5 were greatly improved by 1345.8 and 670.3 %, respectively, compared with neat PU. We believe that this study could provide a promising method for introducing specific function to flame retardants to enhance fire safety and mechanical properties of composites.

Phosphorus-based flame retardant acrylic pressure sensitive adhesives with superior peel strength and transfer characteristics

Acrylic pressure sensitive adhesives (PSAs) are widely utilized in various fields due to their excellent thermal, weather, and oil resistance. However, due to their flammability, they are vulnerable to fire, which brings a critical challenge for their application in various industries. Here, new phosphorus-based acrylic PSAs which show excellent flame retardancy are demonstrated, without sacrificing adhesion properties. By controlling the monomer composition based on five different monomers, we synthesized seven acrylic copolymers for PSAs, and investigated the correlation between monomer composition and adhesion characteristics in terms of peel strength and transfer characteristics. Among seven polymers, A5H5 which exhibits the highest peel strength (1117 gf/in.) and superior transfer characteristics (transfer area 8.30 %) is selected for further investigation. The phosphorous-based acrylic PSAs are prepared through addition of different amounts of dimethyl methylphosphonate in A5H5 polymeric matrix, and thoroughly investigated in terms of flame retardancy and adhesion characteristics in terms of peel strength and transfer characteristics. The phosphorus-based PSA (A5H5-D30) exhibited superior flame retardancy of V-0 rating under the UL-94 characterization method. Furthermore, the A5H5-D30 present excellent film transfer characteristic showing a transfer area of 0 % and residue of 0 wt% in air without massive decrease in peel strength (991 gf/in.).

The effect of phosphorus based flame retardants on the thermal and fire retardant properties of chicken feather/thermoplastic polyurethane composites

The aim of the study was to enhance the flame-retardant properties of chicken feather (CF) reinforced thermoplastic polyurethane (TPU) composites by incorporating three different phosphorus-based flame retardants, namely aluminum hypophosphite (AHP), ammonium polyphosphate (APP), and aluminum diethyl phosphinate (AlPi), at concentrations of 5, 10, and 20 wt%. The effectiveness of the additives was evaluated through various tests, including limiting oxygen index (LOI), vertical burning test (UL 94 V), thermogravimetric analysis (TGA), and mass loss calorimeter test (MLC). The results indicated that all three additives exhibited flame retardant properties in both the condensed and gas phases, but APP and AHP performed better than AlPi due to their enhanced char formation capabilities. The flame retardant effectiveness of the additives decreased in the order of APP > AHP > AlPi.