Self-emulsification synthesis of epoxy phosphate ester and its flame-retardant mechanism in flexible poly(vinyl chloride)/magnesium hydroxide composites

A trade-off dilemma exists for simultaneously improving the mechanical properties and flame resistance of flexible polyvinyl chloride (fPVC)/magnesium hydroxide (MH) composites. In this study, epoxy phosphate ester (EPE), a hydrophobic surface modifier of MH, was synthesized using a self-emulsification method. After modification, EPE was bonded to the surface of MH (MHEPE) without altering its morphology. The results of limiting oxygen index and cone calorimetry tests indicated that fPVC/MHEPE exhibited better flame retardancy and smoke suppression effects than did fPVC/MH. The peak of the heat release rate, total heat release, peak of the smoke production rate, and total smoke production of the fPVC/MHEPE composite were 206.0 kJ m⁻², 45.90 MJ m⁻², 0.0729 m² s⁻¹, and 9.88 m², which were 8.64%, 14.00%, 27.61%, and 9.02% lower than those of the fPVC/MH composite, respectively. For the fPVC/MHEPE composite, a compact and continuous char residue formed, which could inhibit heat and flammable volatile migration between the matrix and burning zones. In the gas phase, the dilution effect of H₂O vapor reduced the concentrations of O₂ and flammable volatiles. The free-radical quenching effect of ·PO and ·PO₂ also played a vital role in extinguishing flame and terminating combustion. Further, the introduction of EPE improved the tensile and impact strengths of the fPVC/MH composites because of the excellent interfacial compatibility between MHEPE and the fPVC matrix. This study provides a simple and workable solution for the trade-off dilemma, and the remarkable flame retardancy and mechanical properties of the fPVC/MHEPE composite render it a promising cable material.     

Facile preparation and flame retardancy mechanism of cyclophosphazene derivatives for highly flame-retardant silicone rubber composites

A novel and efficient flame retardant cyclophosphazene derivative Hexa (p-acetamidophenoxy) cyclotriphosphazene (HACP) was successfully prepared via a facile one-step reaction. The chemical structure of HACP was characterized and confirmed by FT-IR, ¹H and ¹³C NMR. Then the as-prepared HACP was incorporated into addition-cure liquid silicone rubber (ALSR) matrix to prepare highly flame-retardant rubber composites. It was found that the incorporation of HACP can significantly enhance the flame resistance of ALSR. Typically, the ALSR composites filled with 30 phr HACP achieved UL-94 V-0 rating and meanwhile the total heat release and total smoke release were decreased by 26.9% and 41.5%, respectively. Moreover, the flame-retardant mechanism of ALSR/HACP composites was investigated by TGA, Py-GCMS, FT-IR, SEM and EDX, confirming that HACP plays a significant role in capturing free-radicals and forming protective layers. This work designed a novel cyclophosphazene-based flame retardant to significantly enhance the flame retardancy of ALSR, which may offer some valuable inspiration for the fabrication of highly flame-retardant polymer composites.     

Synthesis of a novel char-forming agent (PEIC): Improvement in flame retardancy,thermal stability,and smoke suppression for intumescent flame-retardant polypropylene composites

A novel char-forming agent named PEIC was designed and synthesized combining pentaerythritol octahydrogen tetraphosphate (PEPA) and tris(2-hydroxyethyl) isocyanurate. PEIC was combined with the silica-gel-microencapsulated ammonium polyphosphate (OS-MCAPP), preparing intumescent flame-retardant polypropylene (PP) composites. The results of the limiting oxygen index (LOI) show that the composite containing 30 wt % IFR with OS-MCAPP:PEIC = 2:1 presents the optimal LOI of 32.7%. Meanwhile, the cone calorimeter tests show that its peak heat release rate is 432 kW m⁻², which decreases by 62.1% compared with that of pure PP, showing a high-efficient flame retardancy. The exhibited UL-94 V-0 rating for all the composites indicates that the IFR composed of PEIC and OS-MCAPP has high-efficient flame retardancy in PP. The analysis of residue char reveals that PEIC could improve the quality of char in compactness, intumescentia, and the degree of graphitization. Further, the effect of IFR on the mechanical properties of PP composites was also evaluated and discussed. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48296.     

低烟无卤阻燃HIPS的研究

采用熔融法制备包括有机蒙脱土（OMMT）、红磷（RP）和酚醛树脂（PFR）体系的阻燃高抗冲聚苯乙烯（HIPS）复合材料，用基于耗氧原理的锥形量热仪研究复合材料的阻燃性能，用扫描电子显微镜观察了复合材料燃烧残余物的微观结构形态。结果表明，与纯HIPS相比，制备的HIPS／OMMT复合阻燃材料阻燃性能有所提高，但提高幅度有限；与HIPS／OMMT复合阻燃材料相比，添加RP和PFR的阻燃RP／PFR／HIPS／OMMT复合材料的热释放速率及其峰值、质量损失速率和生烟速率等燃烧性能参数继续降低，且火灾性能指数大幅提高，表现出低烟和高效的阻燃特点。     

Study on the ablative properties of ethylene propylene diene terpolymer/silsesquioxane insulation materials

Octaphenylsilsesquioxane (OPS), polyphenylsilsesquioxane (PPSQ), and octavinylsilsesquioxane (OVP) have been incorporated into ethylene propylene diene terpolymer (EPDM) in order to study their effects on the ablative properties of the respective EPDM composites. The results show that PPSQ and OVP serve as effective ablative additives for EPDM composites. The linear ablation rates of EPDM composites with 4.4 wt % OVP or PPSQ were reduced by 21 or 16.5%, respectively, compared with the control sample. Moreover, OVP and PPSQ also improved the flame retardancy and suppressed smoke emission. The heat release rate of EPDM composite with 4.4 wt % OVP was measured as 90.6 kW m⁻², 17% lower than that of the control sample, and the same amount of PPSQ reduced the total smoke release from 1946 to 1497 m² s⁻¹. Thermogravimetric analysis results showed EPDM/OVP composite to leave a higher residual mass than the calculated value. Besides, scanning electron microscopy, cone calorimetry (CONE), and BET tests showed that the chars formed during the ablation of EPDM composites containing OVP and PPSQ had better structural stability and thermal stability owing to the fact that they were denser and more homogeneous. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48365.     

Synergistic flame retardant effects of activated carbon and molybdenum oxide in poly(vinyl chloride)

The synergistic effects of activated carbon (AC) and molybdenum oxide (MoO₃) in improving the flame retardancy of poly(vinyl chloride) (PVC) were investigated. The effects of AC, MoO₃ and their mixture with a mass ratio of 1:1 on the flame retardancy and smoke suppression properties of PVC were studied using the limiting oxygen index and cone calorimeter tests. It was found that the flame retardancy of the relatively cheaper AC was slightly weaker than that of MoO₃. In addition, the incorporation of AC and MoO₃ greatly reduced the total heat release and improved smoke suppressant property of PVC composites. When the total content of AC and MoO₃ was 10 phr, PVC/AC/MoO₃ had the lowest peak heat release rate and peak smoke production rate values of 173.80 kW m^?2 and 0.1472 m² s^?1, which represented reductions of 47.3 and 59.9%, respectively, compared with those of PVC. Furthermore, thermogravimetric analysis and gel content tests were used to analyze the flame retardant mechanism of AC and MoO₃, with results showing that AC could promote early crosslinking in PVC. Char residue left after heating at 500 °C was analyzed using scanning electron microscopy and Raman spectroscopy, and the results showed that MoO₃ produced the most compact char, with the smallest and most organized carbonaceous microstructures. © 2017 Society of Chemical Industry     

Preparation and characterization of the halogen-free,smoke suppression,organic–inorganic hybrid flame-retardant expandable polystyrene materials

Expandable polystyrene (EPS) is a plastic widely used in the field of construction, but it is flammable. This work provided a novel strategy for flame-retardant modification of EPS. A kind of polyester polyol (JZP) with the high content of phosphorus and nitrogen was synthesized. Then, intrinsic flame-retardant polyurethane (PFWPU) with the high content of phosphorus and nitrogen was synthesized by JZP acted as soft segment chain extender. Finally, a high-efficiency flame-retardant expandable polystyrene thermal insulation material (AF-EPS) was prepared by the organic–inorganic hybrid flame-retardant synergistic action of PFWPU and ammonium polyphosphate. The effects of different contents of inorganic flame retardants on flame retardancy of materials were studied by limiting oxygen index (LOI), cone calorimetry, thermogravimetric analysis/infrared spectrometry , scanning electron microscopy, and so on. The test results showed that the carbon residue rate of the modified material increased from 0 to 28.5%, the LOI increased from 17 to 35.8%, and the vertical combustion test reached the highest grade V-0. In addition, the total smoke production of AF-EPS samples decreased from 2.33 m² to 0.57 m², the time to ignition was increased to 41 s, and the peak heat release rate and the total heat release were decreased by 90.2 and 62.7%, respectively.     

Facile Synthesis of Zinc-Containing Mesoporous Silicate from Iron Tailings and Enhanced Fire Retardancy of Rigid Polyurethane Foam

Iron tailings (ITS), as solid decay absolved afterward beneficiation, are adverse to the environment. ITS to prepare zinc-containing mesoporous silicate (MAO-Zn) by a calcination-crystallization method are used. An admixture of ammonium polyphosphate (APP) and MAO-Zn can solve the problem of poor flame retardancy in rigid polyurethane foam (RPUF), giving them higher thermal stability and lower heat release. The total heat release rate and smoke factor values exhibited by RPUF-3 are 24.52 MJ m⁻² and 234.29 MW m⁻² respectively, a decrease of 38.45% and 29.60% respectively compared to pure RPUF. Lower combustible and toxic gas release intensities are in RPUF-3. Meanwhile, RPUF-3 possesses enhanced compactness char residue with higher graphitization degree, endowing RPUF-3 with excellent fire observed performance. This work demonstrates the potential of ITS in the fire retardancy field.     

Enhancement of fire safety in epoxy resin composites through incorporation of microencapsulated diatomite

Diatomite (DIA) particles are commonly employed as flame-retardant additives for polymers, yet their intrinsic inefficiency requires substantial quantities for optimal efficacy. To address this issue, we proposed a novel approach involving the microencapsulation of DIA with polyethylene glycol phosphate (PEGP) to enhance the flame retardancy of epoxy resin (EP). Characterization of the prepared DIA@PEGP utilized scanning electron microscopy with energy-dispersive x-ray spectrometry and Fourier transform infrared spectroscopy. The resulting EP composite, DIA@PEGP-4/EP, achieved a limiting oxygen index of 33.2% and achieved a V-0 level in vertical combustion tests. Compared to EP, DIA@PEGP-4/EP demonstrated significantly improved fire performance, with 38.6%, 47.8%, 25.0%, 41.3%, and 60.4% reduction in peak heat release rate, total heat release, peak smoke production rate, total smoke production, and CO yield. Furthermore, the highest FPI value of 0.080 m²·s/kW for DIA@PEGP-1/EP and the lowest FGI value of 8.734 kW/m²·s for DIA@PEGP-4/EP, indicate that the incorporation of DIA@PEGP into EP enhances its fire safety. The flame retardancy mechanism of DIA@PEGP-4 involves the formation of a phosphorus-containing aromatic carbon layer during EP char formation, capturing radicals in the gas phase during combustion.     

偶联剂表面改性对膨胀阻燃聚丙烯性能的影响

采用硅烷偶联剂、钛酸酯偶联剂、铝钛、铝硅复合偶联剂对无卤膨胀型阻燃剂（IFR）进行表面改性,对比了表面改性前后IFR堆积密度和休止角的变化,研究了表面改性对IFR阻燃聚丙烯（PP）分散性能、力学性能及阻燃性能的影响,并采用锥形量热仪对比了表面改性前后IFR阻燃PP的燃烧行为。结果表明,4种表面改性剂中铝硅复合偶联剂的改性效果最优;可显著改善IFR在PP中的分散性,提高了PP的极限氧指数和UL 94阻燃级别,材料的断裂伸长率提升了200 %,冲击强度提升了50 %;还可抑制IFR的析出,材料燃烧时的热释放速率及总量、生烟速率及总量下降幅度达到30 %左右。     

Synthesis and properties of a phosphate ester as curing agent in an epoxy resin system

Phosphate ester compounds display good flame retardancy effect in epoxy resin systems. In this paper, several novel phosphate esters, used as curing agents for epoxy resins, were synthesized based on P₂O₅, phosphoric acid, and different types of alcohol. The structures of phosphate esters were characterized by ³¹P nuclear magnetic resonance (³¹P NMR). Then, a series of flame retardant epoxy composites were prepared by curing the epoxy resins (E-44) with the phosphate esters. The flame retardancy and thermal degradation behaviors of flame retardant epoxy composites were investigated by cone calorimeter test (CCT) and thermogravimetric analysis (TGA), respectively. The results of CCT indicated that phosphate esters can significantly decrease heat release rate, total heat release (THR), and smoke production rate. The sample cured by butyl phosphate ester from phosphorus pentoxide, phosphoric acid and butanol showed the best flame retardant performance among all samples. The TGA results showed that phosphate esters could enhance char residues of flame retardant epoxy composites when compared with those of a composite using T31 as a curing agent at high temperature. It may be concluded that good flame retardant properties of flame retardant epoxy composites are related to the formation of a protective phosphorus-rich char layer. These phosphate esters have a good future on flame retardant epoxy composites.     

Superior thermal stability and smoke suppression of epoxy resin composites with graphene/LDH phosphorus-rich hybrids

In this article, graphene/LDH phosphorus-rich triple hybrid was prepared by a mild method and used to effectively improve the thermal stability and smoke suppression of epoxy resin (EP). The graphene was firstly reacted with hexamethylenediamine (HA) and followed by the treatment with the layered double hydroxide (LDH) and NaH₂PO₄ solutions. Compared to the unmodified graphene, the initial decomposition temperature of the triple hybrids increases significantly from 168.6 to 292.5°C. The residual carbon content is greatly improved and the residual mass is up to 84.1%. Elemental analysis reveals the content of phosphorus in EP composites is as high as 10 wt%. In flame retardancy tests, the peak heat release rate of the EP composite with 5 wt% graphene/LDH phosphorus-rich hybrids decreases to 786.15 KW/m², 41.19% drastic reduction compared to that of EP. These results indicate that the triple functionalization process effectively expands the interval distribution of heat release and makes the heat release process more gradual and spread flames smaller. The smoke production rate and total smoke production rate of EP composite with 5 wt% graphene/LDH phosphorus-rich hybrids are 0.32 m²/s and 40.91 m², which are significantly reduced by 65.22 and 57.83%, respectively. This gentle and efficient process provides a new approach to multi-functional design to improve the thermal stability and smoke suppression of resin-based composites.     

Preparation of novel biomass humate flame retardants and their flame retardancy in epoxy resin

Humic acid (HA), a biomass material with plentiful oxygen-containing functional groups, showed huge potential to be considered as a promising charring agent in flame retardancy. In this study, this HA was modified with four different metal ions like Fe²⁺, Mn²⁺, Al³⁺, and Cu²⁺ and finally, introduced into the epoxy resin (EP) to enhance the flame retardancy of the EP and the dispersion of these flame retardants into the EP matrix. When 10 wt% of HA-Fe and HA-Mn were incorporated into EP matrix, the limiting oxygen index (LOI) was increased from 21.2% for EP to 26.6 and 25.3% for the EP composites and the peak heat release rate (pHRR) was reduced by 36 and 35.5%, respectively. Such a significant improvement in flame retardancy was attributed to the catalytic charring of HA in the presence of metal ions, which ultimately increased the residual char formation and produced compact char layers during the combustion process to retard the transfer of heat and combustible gases between the EP composites and the flame zone. Finally, this kind of application provided a feasible way for the development of an environmentally friendly flame retardant with high efficiency, which improved the fire safety of EP matrix.     

High-value use of lignocellulosic-rich eucommia residue for promoting mechanical properties and flame retardancy of poly(butylene succinate)

Cellulose- and lignin-based fillers can significantly enhance the mechanical properties and flame retardancy of biomass polyesters, whereas complicated and high-cost processes may be necessary for the extraction. Thus, we explored the direct use of eucommia residues (ERs), a plantation waste containing rich lignocellulosic substances (ca. 18% cellulose, 13% hemicellulose, and 35% lignin), to reinforce polyesters and improve their flame retardancy. With poly(butylene succinate) (PBS) as the polyester matrix, the ER could enhance the tensile and flexural modulus of polyester-based composite by 87 and 72%, respectively, via a facile melt-mixing method with 30 wt % ER. Such enhancements, accompanying cost reduction, came from the cellulose crystallinity and rigid chemical structure of lignin, along with the strong interaction between ER and PBS. Besides, the carbon residue of PBS/ER composites in the flame-retardant study could maximally increase by 508%, benefited from the immense hex-carbon rings of cellulose and lignin in ERs. The ER also reduced the peak heat release rate and total heat release of PBS by 43 and 20%, respectively. This work reduces the pressure from waste treatment, promotes the high-value application of plantation lignocellulosic-rich wastes in package plastics and membranes, and supports sustainable material development based on biomass multicomponents resources. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48543.     

锥形量热法研究木质素基膨胀型阻燃剂对环氧树脂阻燃抑烟效果

以来自自然界储量第二的木质素作为膨胀型阻燃剂的基体,通过接枝氮、磷元素成功合成碳源、酸源、气源三位一体的木质素基膨胀型阻燃剂（Lig-T）,实现了良好的阻燃性能。将Lig?T按照不同含量添加到环氧树脂（EP）中制备EP/Lig-T复合材料,以锥形量热测试考察复合材料的热稳定性能和阻燃性能,并重点考察复合材料在接近真实火灾事故时的热释放和烟释放规律。结果表明,当Lig-T含量为20 %（质量分数,下同）时,复合材料的热释放速率峰值为1 374 kW/m²、热释放总量为41.63 MJ/m²、烟释放总量为1 634 m²/m²,与EP参比试样的数值相比,均呈现下降的趋势,燃烧结束的残炭率从4.26 %增至10.01 %。基于气相和凝聚相的协效阻燃机理,木质素作为膨胀型阻燃剂的碳源使得复合材料在高温条件下具备更好的成炭效果,在燃烧过程中形成稳定且致密的炭层结构,在实现高效阻燃的同时减少有毒烟气的释放,降低火灾的危害。     

Influence of modified fiber–MHSH hybrids on fire hazards,combustion dynamics,and mechanical properties of flame-retarded poly(butylene succinate) composites

Environmental problems caused by polymers and polymers have historically dominated both academic and industrial attention. Sustainable biodegradable wood-plastic composites (WPCs) as an optimum can solve the environmentally critical problems caused by petroleum-based polymers. However, they are flammable, prone to fire accidents, and often have a contradiction between mechanical performance and flame-retardant properties, which limits their range of applications. Here, we reported a flame-retarded poly(butylene succinate) (PBS) WPC prepared with modified natural fiber-magnesium hydroxide sulfate whisker (MHSH) hybrids and intumescent flame retardant s (IFRs). The mechanical performance, flame-retardant properties , thermal stability, and actual fire simulation parameters of composites were investigated. Owing to the unique composition characteristics of modified cassava dregs-MHSH hybrids, the mechanical properties (70P/23I/5C/2M, flexural strength was 39.2 ± 1.960/MPa, impact strength was 7.95 ± 0.3975/ [KJ/m²]), flame retardant properties (70P/23I/5C/2M, the limiting oxygen index value was 39.6%, UL-94 was V0) and thermal stability of WPC have been improved. Thereby, the balance between mechanical performance and flame retardant properties of biocomposites has been achieved in the practical engineering requirements. Furthermore, cone calorimeter data indicated that modified cassava dregs–MHSH hybrids played a role in improving the fire safety of composites. The total heat release, total smoke produce, toxic gas release, and total oxygen consumed of 70P/23I/5C/2M were lowered compared with those of 70P/25I/5C. Dynamics analysis indicated that the addition of modified cassava dregs–MHSH hybrids increased the activation energy of composites. Based on the experimental and analyses data, especially the morphological characterization of char residue analysis, it illustrated that modified cassava dregs–MHSH hybrids have a reinforcement and flame-retardant effect. The combusted residue of the incorporated modified cassava dregs–MHSH hybrids could support the three-dimensional charred layer formed by the combustion products of the IFR and the PBS. Thus, the more stable three-dimensional charred layer could not only effectively reduce thermal conductivity of composites but also hinder the propagation of heat into the interior substrate, thereby improving the flame-retardant properties of the WPC. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48490.     

四溴双酚-A阻燃体系在HIPS／OMMT复合材料中的阻燃性研究

采用熔融插层法分别制备高抗冲苯乙烯／有机蒙脱土（HIPS／OMMT）复合材料和四溴双酚-A／三氧化二锑（TBBPA—Sb2O3）体系阻燃的HIPS／OMMT复合材料,透射电镜研究表明,有机蒙脱土均匀地分散于HIPS基体当中,形成了插层复合结构,锥形量热仪和氧指数仪研究表明：与纯的HIPS相比,HIPS／OMMT复合材料的阻燃性和抑烟性有所提高,但阻燃性的提高幅度较有限：与仅添加OMMT时的HIPS／OMMT复合材料相比,添加相同量OMMT时TBBPA—Sb2O3体系阻燃的HIPS／OMMT复合材料的热释放速率（HRR）和热释放速率峰值（PHRR）均有所降低,氧指数有所增加,且随TBBPA—Sb2O3阻燃剂添加量的增加阻燃性能的提高越明显,但TBBPA—Sb2O3的加入会导致聚合物燃烧过程生烟速率和生烟量的显著增加．因此此类阻燃剂的加入量不宜过高。     

The Effect of Different Smoke Suppressants with APP for Enhancing the Flame Retardancy and Smoke Suppression on Vinyl Ester Resin

Flame retarded and smoke suppressed vinyl ester resin (VER) were prepared through ammonium polyphosphate (APP) coupled with different smoke suppressants. The flame retardancy of these composites was tested by the limiting oxygen index and UL-94 tests. The typical combustion parameters including heat release rate (HRR), peak of HRR (p-HRR), total heat release, smoke production rate, and total smoke production were detected using a cone calorimeter. The smoke suppressants CaCO₃, ZnMoO₄, Cu₂O, and Fe₂O₃ show different effect on flame retardancy and smoke suppression of VER composites when they are coupled with APP, the synergistic action of APP and CaCO₃ is more effective on decreasing the HRR and smoke release rate than several other smoke suppressants. This is attributed to the fact that CaCO₃ could promote the formation of a dense carbon layer with high thermal stability and anti-oxidation property, which could act as an effective physical barrier. The flame retardant performances and mechanisms of APP and CaCO₃ were evaluated and analyzed at length by thermogravimetric coupled with a Fourier transform infrared spectrometer (FTIR), scanning electron microscopy, FTIR, and X-ray diffraction. POLYM. ENG. SCI., 60: 314–322, 2019. © 2019 Society of Plastics Engineers     

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.     

Properties of a novel inherently flame-retardant rigid polyurethane foam composite bearing imide and oxazolidinone

A novel inherently flame-retardant rigid polyurethane (PU) foam with imide and oxazolidinone was prepared by using 3,3′,4,4′-biphenyltetracarboxylic dianhydride (PTDA) and 9,10-dihydro-9-oxa-(10-glycidoxypropylene)-10-phosphap-henanthrene-10-oxide (e-DOPO) as reactive flame retardants. The physical and mechanical properties of the prepared PU foams were investigated. The compressive strength was improved to 0.22 MPa, the thermal conductivity decreased, and the density hardly changed. Thermogravimetric (TG) analysis and TG analysis coupled with Fourier transform infrared spectroscopy indicated that the PTDA and e-DOPO showed a small improvement in thermal properties. The fire behaviors were evaluated based on the limited oxygen index (LOI), cone-calorimetry experiment, and smoke-density test. The LOI of the PU foam with PTDA and e-DOPO reached 22.4%. The peak of heat release rate and total heat release decreased to 227.50 kW m⁻² and 11.27 MJ m⁻² from 281.28 kW m⁻² and 14.05 MJ m⁻², respectively. The morphologies of the PU foam and residues after the cone-calorimetry test were characterized by scanning electron microscopy. X-ray photoelectron spectroscopy analysis indicated that PTDA and e-DOPO lead to an increase in graphite in the residue and the formation of a better barrier to prevent burning by the condensed-phase mechanism. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47943.