Synthesis of aluminum ethylphenylphosphinate flame retardant and its application in epoxy resin

A novel flame retardant additive, aluminum ethylphenylphosphinate (AEPP), was synthesized from diethyl phenylphosphonite and aluminum chloride hexahydrate, and characterized by FTIR, ¹H NMR, and ³¹P NMR. AEPP was added into diglycidyl ether of bisphenol A epoxy resin (EP) cured by bisphenol A‐formaldehyde novolac resin. The flame retardancy of the cured EP was investigated by limited oxygen index, UL 94 test, and cone calorimeter test. The results revealed that the EP composite containing 15% AEPP had a limited oxygen index value of 28.2% with a UL 94 V‐0 rating. The incorporation of AEPP effectively decreased the peak heat release rate and the total heat release in cone calorimeter test analysis. Scanning electron microscopy results showed that the introduction of AEPP benefited to the formation of a smooth and continuous char layer during combustion of the flame retarded EP. The thermogravimetric analysis results indicated that the incorporation of AEPP promoted the initial decomposition of EP matrix, but AEPP/EP composites had a higher char yield at high temperatures. Moreover, the flexural properties of the flame retarded EP composites were studied.     

Novel flame‐retardant epoxy based on zinc methylethyl phosphinate

A novel flame retardant zinc methylethylphosphinate (Zn(MEP)) was used to fill epoxy resins (EPs). The structure of Zn(MEP) was conformed with Fourier transform infrared, hydrogen nuclear magnetic resonance and phosphorus nuclear magnetic resonance, and X‐ray fluorescent and X‐ray diffraction. The flammability, decomposition behavior, and glass transition temperature (T_g) of cured EP/Zn(MEP) were investigated. Zn(MEP) is stable below 406°C. EP containing 20 phr of Zn(MEP) achieves 27.5% of limiting oxygen index and UL‐94 V0 rating. Scanning electron microscopy‐energy‐dispersive X‐ray and Fourier transform infrared spectroscopy investigations show that a condensed char layer with carbon‐rich and phosphorus‐rich components was formed during heating Zn(MEP)/EP, the atomic ratio of P to Zn on the surface of the char is reduced compared with the initial sample. The P‐rich components and lower atomic ratio of P/Zn on the char surface implies that the Zn(MEP) acts in both condensed phase and gas phase. TGA investigation shows that there are interactions between Zn(MEP) and EP when they are copyrolyzed. The interactions lead to a modification in degradation process and promote the char forming. Compared with aluminum diethylphosphinate Zn(MEP) filled EP shows lower limiting oxygen index but higher T_g. In addition, the interactions between polymer and additive are different when aluminum diethylphosphinate instead of Zn(MEP) is added into EP. Copyright © 2013 John Wiley & Sons, Ltd.     

环氧树脂体系阻燃技术的发展

阐述了改善热固性环氧树脂体系阻燃性能的目的和意义，介绍了环氧树脂体系的阻燃方法。以气相机理和凝聚相机理为基础，讨论了几种常用阻燃剂的阻燃机理。分析了环氧树脂体系阻燃技术的研究现状，指出环氧树脂阻燃技术将向着安全化、复合功能化、新技术化和研究系统化的趋势发展。     

新型磷／氮协同阻燃环氧树脂的合成与性能

以双酚A环氧树脂E－51与DOPO（9,10-dihydrooxa-20－phosph henanthrene－10-oxide）合成含磷环氧树脂（ED）,以三聚氰胺与苯酚反应制备含氮的酚醛固化剂MFP。采用红外光谱对产物进行分析表征,采用热失重分析和UL94V垂直燃烧测试考查树脂的热性能和阻燃性能,同时探讨了阻燃环氧树脂的力学性能。结果表明,随着含磷量的增加,环氧树脂的热稳定性和阻燃性能得到改善,当含磷量为3％时,环氧树脂的初始分解温度高达330℃以上,在700℃下的残炭率达到30％以上,阻燃性能均达到了UL－94 V—0级。而试样的力学性能则随含磷量的增加而降低。     

改性三聚氰胺氰尿酸盐阻燃环氧树脂研究

采用分子复合技术合成了改性MCA(M-MCA)阻燃环氧树脂,采用UL94垂直燃烧测试及微型量热分析对其性能进行了研究,同时采用热失重分析方法研究其降解历程和阻燃机理。结果表明,该材料实现了阻燃剂粒子在环氧溶液及基材中超细及均匀分散,解决了常规MCA阻燃剂在环氧树脂胶液中分散困难、易团聚等问题,改性MCA阻燃树脂比传统MCA具有更佳阻燃效果,该体系阻燃机理以气相阻燃为主。     

Synthesis of bio-based reactive N/P flame retardant and its curing and flame retarding behavior in epoxy resins

In this study, a pioneering bio-based nitrogen–phosphorus flame retardant and curing accelerator named oxime-phosphazene hexakis [(4-(hydroxyimino) 2-methoxy) phenoxy] cyclotriphosphazene (HAPV) was successfully synthesized using hexachlorocyclotriphosphazene and vanillin. When 5 wt % HAPV was added into epoxy, the limiting oxygen index increased from 22% to 27% and passed UL-94 V-0 (UL is defined as Underwriters Laboratories) rating. Meanwhile, with the addition 5 wt% HAPV, the apparent activation energy (E_a) of HAPV/EP decreased from 20.22 to 67.15 kJ/mol, and the pHRR value was suppressed from 581.21 to 330.18 kW/m². It was due to that the HAPV quenched the combustion chain reaction through the gas phase and condensed phase, forming a dense char layer for blocking the heat transfer. Overall, the study provides an environmentally friendly epoxy flame retardant curing accelerator that shows great potential in epoxy flame retardant applications.     

A P/N-containing flame retardant constructed by phosphaphenanthrene,phosphonate, and triazole and its flame retardant mechanism in reducing fire hazards of epoxy resin

A P/N-containing flame retardant (PPT) constructed by phosphaphenanthrene, phosphonate, and triazole groups was successfully synthesized and used as a reactive co-curing agent for epoxy resin (EP). The curing behavior, thermal property, combustion behavior, and flame retardant mechanism of EP thermosets were comprehensively investigated. According to the analysis of DSC and TGA, PPT accelerated the crosslinking reaction and enhanced the charring ability for EP thermosets at high temperature. The results of combustion test indicated that PPT endowed epoxy thermoset with outstanding flame retardancy. When the phosphorus content was 0.71 wt%, EP/DDS/PPT-2 achieved a LOI value of 33.2% and passed V-0 rating in UL-94 test, and its peak heat release rate and total heat release were decreased by 63.7 and 30.5%, respectively, relative to EP/DDS. Moreover, the FIGRA of EP/DDS/PPT-2 was reduced from 9.7 to 3.5 kW m⁻² s⁻¹, manifesting the significantly improved fire safety of EP thermoset. The flame retardant mechanism was summarized as two parts: (a) the barrier effect of continuous phosphorus-rich char layers in condensed phase, (b) the quenching effect of phosphorous radicals and diluting effect of nonflammable gases in gaseous phase.     

Phosphaphenanthrene‐containing borate ester as a latent hardener and flame retardant for epoxy resin

Borate ester containing the phosphaphenanthrene group with N → B coordination structure (PBN) was synthesized by transesterification of tributyl borate, 2‐(6‐oxido‐6H‐dibenz?c,e??1,2?oxaphos‐phorin‐6‐yl) methanol and N,N‐dimethylethanolamine. A thermally latent curing utility for diglycidyl ether of bisphenol A epoxy resin (E51) was confirmed by differential scanning calorimetry. Additionally, its flame‐retarding function in the cured epoxy was demonstrated in terms of the limiting oxygen index (LOI) and vertical burning test. The cured epoxy with 100:20 mass ratio of E51 to PBN passed UL94 V‐0 rating with 34.3% of LOI. The flame retardation mode and thermal and mechanical properties of the cured epoxy were carefully evaluated. The results of this work suggest that application of PBN would permit the formulation of environmentally friendly one‐pot flame‐retardant epoxy resin. © 2015 Society of Chemical Industry     

环氧树脂纳米阻燃材料研究进展

综述了目前环氧树脂纳米阻燃材料的制备方法,介绍了环氧树脂/层状硅酸盐纳米阻燃材料和环氧树脂/SiO2纳米阻燃材料的优异性能并展望了环氧树脂阻燃材料的应用前景。     

Reactive cyclic phosphonamide flame retardant for epoxy resins

To take the advantage of reactivity of five-membered cyclic phosphorus compounds, 1,2,3-tri-phenyl-1,3,2-diazaphospholidine-2-oxide (TPDPO) was explored as a reactive flame retardant for epoxy resins (EPs). Through model compounds, it has been established that TPDPO selectively reacts with the secondary hydroxyl group and is inert toward both aryl amino groups and epoxide groups. The result of Soxhlet extraction supports that TPDPO is permanently bonded to the cured EPs. At a loading of only 8 wt % (0.74 wt % phosphorus), TPDPO enables the cured epoxy to achieve a UL-94 V0 rating. The thermogravimetric analysis–Fourier transform infrared analyses of the gaseous products suggest that the excellent flame retardancy of EP–TPDPO is partly due to the enhanced dehydration process of the epoxy. Also an increased char yield and the formation of a coherent char layer contribute to the good fire performance of EP–TPDPO. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 47411.     

A DOPO-based reactive flame retardant containing benzimidazole groups: Synthesis and its flame-retardation on epoxy resin

DOPO based flame retardants demonstrate exceptional flame retardancy efficiency when applied to epoxy resins. However, the crosslinking degree of epoxy resin may decrease due to the addition of DOPO, leading to a deterioration in flame retardancy and mechanical properties. Herein, a reactive DOPO derivative flame retardant 6-((1H-benzo[d]imidazol-2-yl) amino) dibenzo oxaphosphinine 6-oxide (BADO) was successfully synthesized, which contains multiple reactive sites, thus ensuring a higher degree of crosslinking in the system. As a result, the modified epoxy resin exhibits excellent flame retardancy. The limiting oxygen index value of the modified epoxy resins increased from 19.8% to 29.7% by adding 7.5 wt% BADO, and its UL-94 test passed V-0. Flame retardancy mechanism analysis reveals that BADO exhibits both gas-phase and condensed-phase flame retardant effects. In particular, the formation of a porous inside-char layer is a significant factor in reducing smoke release. The 7.5% BADO/EP composite exhibited a 43.2% reduction in total smoke production and a 43.6% reduction in total smoke rate compared to neat epoxy resins (EP). Furthermore, the addition of BADO slightly deteriorates the mechanical properties of the modified epoxy resin.     

In situ synthesized and dispersed melamine polyphosphate flame retardant epoxy resin composites

The dispersion of flame retardants in polymer matrix has significant impact on the final properties of the final materials. Homogenous dispersion for additive type flame retardant powder in polymer melt or solution with high viscosity is a challenge all the time. In the present research, melamine polyphosphate (MPP) is employed to flame-retard the epoxy resin (EP). Different from direct addition of MPP powder in viscous EP glue like conventional means, MPP is firstly synthesized by melamine and polyphosphoric acid in a good solvent for EP. Keeping fine and even dispersion of the produced MPP particles, EP prepolymer is added into the MPP containing solution. By this way, perfect dispersion of the flame retardant can be achieved both in the glue and the cured resin. A series of tests such as the particle size analysis, flammability evaluation, and mechanical properties tests are conducted to compare the MPP flame retardant EP obtained by this method and the conventional one. It shows that the in situ synthesis and compounding method can endow the MPP incorporated EP glue system with better homogeneity and stability, hence leading to higher flame retardancy and obviously improved mechanical performance of the final composite. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47194.     

Synthesis of a novel cross‐linked organophosphorus‐nitrogen containing polymer and its application in flame retardant epoxy resins

A novel cross‐linked organophosphorus–nitrogen polymetric flame retardant additive poly(urea tetramethylene phosphonium sulfate) defined as PUTMPS was synthesized by the condensation polymerization between urea and tetrahydroxymethyl phosphonium sulfate. Its chemical structure was well characterized by Fourier transform infrared (FTIR) spectroscopy, ¹³C and ³¹P solid‐state nuclear magnetic resonance. The synthesized PUTMPS and curing agent m‐phenylenediamine were blended into epoxy resins to prepare flame retardant epoxy resin thermosets. The effects of PUTMPS on fire retardancy and thermal degradation behavior of EP/PUTMPS thermosets were investigated by limiting oxygen index (LOI), vertical burning test (UL‐94), cone calorimeter measurement, and thermalgravimetric analysis (TGA) tests. The surface morphologies and chemical compositions of char residues for cured epoxy resins were investigated by scanning electron microscopy and X‐ray photoelectron spectroscopy (XPS), respectively. Water resistant properties of epoxy resin thermosets were evaluated by putting the samples into distilled water at 70°C for 168 h. The results demonstrated that the EP/12 wt% PUTMPS thermosets successfully passed UL‐94 V‐0 flammability rating and the LOI value reached 31.3%. The TGA results indicated that the incorporation of PUTMPS promoted epoxy resin matrix decomposed and char forming ahead of time, which led to a higher char yield and thermal stability for epoxy resin thermosets at high temperature. The morphological structures and analysis of XPS for the char residues of the epoxy resin thermosets shown that PUTMPS benefited to the formation of a sufficient, more compact, and homogeneous char layer with rich flame retardant elements on the materials surface during burning, which prevented the heat transmission and diffusion, limited the production of combustible gases, inhibited the emission of smoke, and then led to the reduction of the heat release rate and smoke produce rate. After water resistance tests, EP/12 wt% PUTMPS thermosets still remained excellent flame retardancy. Copyright © 2015 John Wiley & Sons, Ltd.     

Synthesis and characterization of a new phosphorus‐containing furan‐based epoxy curing agent as a flame retardant

In this study, 5‐hydroxymethyl‐2‐furfural (HMF) was used as a renewable resource for preparing an epoxy curing agent (furan‐based flame retardant, FBF), and a phosphorus‐containing functional group was also incorporated to enhance the flame retardancy of FBF. FBF was easily synthesized, and the total yield was 83%. 2‐Methyl imidazole was chosen as an accelerant to reduce the activation energy for the reaction of FBF with diglycidyl ether of bisphenol A (DGEBA). The DGEBA cured with FBF showed a low glass transition temperature and cross‐linking density compared with those of DGEBA cured with isophorondiamine (IPDA) and 4,4′‐diaminodiphenylmethane (DDM). However, the FBF‐cured DGEBA exhibited a comparable tensile strength with that of the DGEBA‐IPDA and DGEBA‐DDM systems (81.96 MPa) and a significantly higher tensile modulus (1721 MPa) owing to the H‐bonding via oxygens of the phosphorus group of FBF in the network structure. The DGEBA cured with FBF showed a high char yield and a high limitation of oxygen index value (29.7%) compared with those of the IPDA‐ and DDM‐cured ones. The cone calorimeter measurement also showed that the DGEBA‐FBF system had a low heat release rate, total heat release, and smoke production rate, indicating the improved flame retardancy mediated by FBF.     

Synthesis of polysiloxane‐type multifunctional flame retardant and its application in epoxy systems

Polymethyl(3‐glycidyloxypropyl)siloxane (PMGS) was synthesized as a flame‐retardant additive, which were cocured with diglycidyl ether of bisphenol‐A (DGEBA) using 4,4′‐diaminodiphenylsulfone as a curing agent. The structure of PMGS was confirmed through Fourier transform infrared and ¹H‐NMR spectra. The cured products were characterized with dynamic mechanical thermal analysis, thermogravimetric analysis, and oxygen index analyzer. With PMGS incorporated, the cured epoxy resin showed better thermal stability, higher limited oxygen index, and higher char yield. At moderate loading of PMGS, the storage modulus and glass transition temperature of the cured epoxy resin based on neat DGEBA were obviously improved. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

HKUST-1@APP环氧树脂阻燃复合材料的合成与性能

使用溶剂热法将HKUST-1〔Cu3(BTC)2, BTC为1,3,5-苯三甲酸〕负载到聚磷酸铵（APP）的表面制得HKUST-1@APP,然后将不同量的HKUST-1@APP与环氧树脂（EP）混合后固化制备HKUST-1@APP / EP阻燃复合材料。通过水平垂直燃烧测定仪、氧指数测定仪、电子拉力机等对EP复合材料进行了阻燃和力学性能分析。结果表明,当HKUST-1@APP的添加量为总体系的5%时,复合材料EAC-5的极限氧指数为27.5 %,垂直燃烧测试（UL-94）通过V-1级。添加HKUST-1@APP后,样品残炭的AD/AG(拉曼光谱中无定形碳的碳原子与晶体碳中SP2杂化的碳原子振动分别形成的D峰与G峰的峰面积比)降低到0.043,而添加总质量5%APP的EA-5的AD/AG为0.3161,说明HKUST-1@APP还可以改善环氧树脂燃烧过程中产生的炭层,使炭层更连续、石墨化程度更高。     

The synthesis of biphenyl ether/vanillin-based flame retardants for enhancing both the flame retardant properties and mechanical performance of epoxy resin

Imparting good flame retardancy and mechanical properties to epoxy resin (EP), while pursuing the sustainable and safe application of EP, we synthesized a novel reactive phosphorus/nitrogen flame retardant for biomass through nucleophilic addition reaction, which contains flexible ether bonds and rigid aromatic ring structure (DVD). Owing to the cooperative effect of aryl ether diamine, phosphorus phenanthrene, and biomass vanillin, the DVD exhibited excellent flame retardancy. EP/DVD-1 (0.4 wt% phosphorus content) achieved UL-94 V-0 rating, with an improvement in limiting oxygen index value from 26.5% (pure EP) to 32.5%. In the CCT, the modified DVD EP showed a 44.5% reduction in peak peak of heat release rate (PHRR) and a 38.0% reduction in total heat release compared to pure EPs. And flame retardant epoxy resin (FREP) still had good transparency after the addition of DVD, which indicated the nice compatibility between DVD andEP. What was noteworthiness was that at high levels of addition, the mechanical properties of modified EP for DVD was still improved compared to pure EP. These results demonstrate that DVD is an excellent and multifunctional bio-based flame retardant with broad application prospects in the field of EP material modification.     

Synthesis and properties of phosphorus and nitrogen containing intumescent flame-retardant curing agent for epoxy resin

A kind of intumescent ?ame-retardant curing agent (PCDSPB) was synthesised by using pentaerythritol, phosphorus oxycholoride, cyclohexane-1,3-diyldimethanamine (1,3- BAC) as raw materials and the structure was characterised by FTIR and MS. The composite materials were investigated by using TG, TG-FTIR, LOI, UL-94, SEM, and CCT. The results show that the ?lling of PCDSPB can improve the ?ame resistance of EP composites. When the phosphorus content of the composite system was 1.74 wt-%, the initial weight loss temperature was 299°C and the char yield was 26.3% at 600°C. Tensile strength was 35.4 MPa, impact strength was4.3 kJ m?2, LOI was 27.9, and the UL94 passed V-0 level. In the CCT, the peak heat release rate reduced to 276.0 kW m?2(EP-2) from 622.8 kW m?2 (EP-0), the total heat release decreased from 121.8 MJ m?2 (EP-0) to 89.5 MJ m?2 (EP-2). Therefore, the PCDSPB is a good intumescent ?ame-retardant curing agent for EP.     

Effect of Ni2+ chelated to the surface of PBFA on the charring flame retardant and smoke suppression properties of epoxy resin

Here, a phosphazene-based flame retardant (PBFA) containing active amine groups was synthesized by hexachlorocyclotriphosphazene and N-aminoethylpiperazine and nickel ion (Ni²⁺) was chelated to the surface of PBFA (named as PBFA-Ni²⁺). Incorporation into epoxy resin (EP) with a loading of 6 wt% (named as EP/PBFA-Ni²⁺-6.0), enabled the composite to pass the vertical burning test (UL-94) V 0 rating. Peak heat release rate and the total smoke release of EP/PBFA-Ni²⁺-6.0 were decreased by 41.02% and 22.74% as measured by cone calorimeter tests. The production rate of CO was inhibited when PBFA-Ni²⁺ was incorporated into EP.     

A novel flame retardant of spirocyclic pentaerythritol bisphosphorate for epoxy resins

A novel flame retardant for epoxy resins, bisdiglycol spirocyclic pentaerythritol bisphosphorate (BDSPBP) was synthesized from the reaction of diglycol with spirocyclic pentaerythritol bisphosphorate diphosphoryl chloride, which was obtained from the reaction of phosphoryl chloride with pentaerythritol. Flammability of the cured epoxy resin systems consisted of diglycidyl ether of bisphenol A (DGEBA), low‐molecular‐weight polyamide and BDSPBP are investigated by vertical burning test (UL‐94) and limiting oxygen index test (LOI). The results indicate that BDSPBP has good flame retardance on epoxy. The thermogravimetric analysis (TGA) shows that the epoxy resin containing BDSPBP has a high yield of residual char at high temperatures, indicating that BDSPBP is an effective charring agent. From the SEM observations of the residues of the flame retardant systems burned, the compact charred layers can be seen, which form protective shields to protect effectively internal structure, and inhibit the transmission of heat and heat diffusion during contacting fire. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 4978–4982, 2006