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 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.     

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。     

Intercalated kaolinite with ammonium dihydrogen phosphate as an effective flame retardant to enhance the flame retardance and smoke suppression of epoxy resins

To improve the compatibility and flame retardance of kaolinite (Kaol) in polymeric materials, ammonium dihydrogen phosphate (ADP) was intercalated into kaolinite to obtain a novel intercalated kaolinite (K-ADP) for enhancing thermal stability, flame retardance, smoke suppression, and mechanical performance of epoxy resins (EPs). The results show that the presence of K-ADP exerts a more positive effect on reducing the heat release and smoke generation of EPs than the same addition of Kaol. Condensed phase analysis shows that EP/K-ADP composite generates more aromatic cross-links in the condensed phase to reinforce the compactness and intumescence of char compared to EP/Kaol composite. Especially, 5 wt% K-ADP confers a 43.7% reduction in peak heat release rate value and a 36.3% reduction in peak smoke production rate value to EP. Toxic gases analysis shows that K-ADP conduces to inhibiting the release of combustible gases including isocyanates and aromatic volatiles, and generating incombustible gases including ammonia and carbon dioxide to reduce the intensity of EP combustion. The mechanical test shows that K-ADP imparts less adverse impact on mechanical behavior to EP composites than Kaol due to the good dispersion and compatibility between K-ADP with EP matrix.     

卡拉胶包覆APP/MnO2增强水性环氧树脂阻燃抑烟性能

用反相乳液法，以卡拉胶（KC）为壳材，聚磷酸铵（APP）和二氧化锰（MnO2）为芯材，制备了KC包覆APP/MnO2阻燃剂（KC-FR）。通过FTIR、 XRD、 SEM和 EDS对KC-FR进行了表征。结果表明：卡拉胶已成功包覆APP和MnO2，合成的样品具有微胶囊结构。将KC-FR应用于水性环氧树脂（EP）中，考察KC、APP、MnO2 三者质量比对EP阻燃、抑烟性能的影响。用极限氧指数（LOI）、垂直燃烧（UL-94）和锥形量热（CCT）测试了涂层的阻燃、抑烟性能。结果发现，当KC/APP/MnO2的质量比为2∶1∶1，并且在EP中添加量为20%时，制备的阻燃涂层EP2的LOI达到29.1%，UL-94达到V-0级，表现出较好的阻燃性能。EP2相比于其它涂层热释放峰值（pHRR）、热释放总量（THR）和烟释放总量（TSP）最低，相比于EP0分别下降了42%、37%和46%，表现出较好的抑烟性能。另外，热重分析（TGA）测试结果显示EP2在800℃残炭量（W800）为33%，表明KC-FR具有促进EP成炭的功能。通过SEM对残炭表面分析发现，EP2表面炭层更加致密，这表明KC-FR对促进形成稳定并且致密的炭层起到至关重要的作用。     

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.     

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.     

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.     

Property of intrinsic flame retardant epoxy resin cured by functional magnesium organic composite salt and diethylenetriamine

An efficient intrinsic flame retardants composite was prepared by curing epoxy resin with a functional magnesium organic composite salt (FMOCS, 0.685 ± 0.3 nm) and diethylenetriamine (DETA). Curing behavior, thermal and flame‐retardant properties of the cured epoxy resins were systematically investigated by infrared spectrum (FTIR), thermogravimetric analysis (TGA), vertical burning test (UL‐94) and limited oxygen index (LOI) measurement. It was found that flame retardancy and mechanical properties of the cured composite are significantly enhanced compared with DETA/EP. The LOI of the EP reached to 33%, which is much higher than the DETA/EP (19%) or its IFR composite (31%) in the optimal addition of ammonium polyphosphate (APP, 18.69 wt %), pentaerythritol (PER, 6.21 wt %) and FMOCS (3.50 wt %). Furthermore, the mechanical properties of the composite material measurement results to imply that it can enhance tensile strength (150%) and bending strength (88%) rather than DETA/EP, which were tested by impact testing machine and microcomputer control electron universal testing machines. Copyright © 2016 John Wiley & Sons, Ltd.     

Biobased epoxy resin derived from eugenol with excellent integrated performance and high renewable carbon content

Developing biobased epoxy resin with high renewable carbon content and outstanding integrated performance is beneficial for both sustainable development and applications in cutting‐edge fields. Herein, a biobased epoxy monomer (TEUP‐EP) with high renewable carbon content (100%) was synthesized from renewable eugenol with a sustainable process; TEUP‐EP was then blended with 4,4′‐diaminodiphenylmethane (DDM) to develop a new biobased epoxy resin (TEUP‐EP/DDM). The integrated performance of TEUP‐EP/DDM resin was studied and compared with that of petroleum‐based diglycidyl ether of bisphenol A (DGEBA)/DDM resin. Compared with DGEBA/DDM resin, TEUP‐EP/DDM resin has much better integrated performance and not only exhibits a glass transition temperature about 26 °C higher and a 24.4% or 57% increased flexural strength or modulus, but also shows outstanding flame retardancy. Specifically, the limiting oxygen index increases from 26.5% to 31.4% and the UL‐94 grade improves from no rating to the V‐0 level; moreover, the peak heat release rate and total heat release decreased by 63.1% and 57.4%, respectively. All these results fully prove that TEUP‐EP/DDM is a novel biobased high performance epoxy resin. The mechanism behind these attractive integrated performances is discussed intensively. © 2018 Society of Chemical Industry     

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。     

Flame retardant epoxy resin for electrical and electronic applications

Amine‐cured epoxy resins were prepared at 2% by weight phosphorus content using four halogen‐free flame retardants; poly(m‐phenylene methyl phosphonate) (Fyrol PMP); 9,10‐dihydro‐9‐oxa‐10‐phosphaphenanthrene‐10‐oxide; red phosphorus; and aluminum diethylphosphinate (OP1230). The effect of these additives on the properties of cured epoxy, including glass transition temperature, thermal stability, and fire retardancy (cone calorimetry), were studied and were compared with the conventionally used flame retardant, tetrabromobisphenol‐A (TBBA). All properties are improved for the non‐halogenated materials compared with TBBA. Further, the stoichiometric amounts of Fyrol PMP and TBBA (without an external curing agent) were reacted with epoxy to determine if they could be used as a flame retardant and as a curing agent; Fyrol PMP effectively acts as a flame retardant and as a curing agent. Evolved gas analysis is also discussed through thermogravimetric analysis/Fourier transform infrared spectroscopy. Copyright © 2013 John Wiley & Sons, Ltd.     

Synthesis of modified graphene oxide and its improvement on flame retardancy of epoxy resin

In this work, the small molecule with double-phosphaphenanthrene structure was successfully grafted on the surface of graphene oxide (GO), which is called functionalized graphene oxide (FGO). The introduction of FGO improved the poor interfacial compatibility between graphene and epoxy matrix. And FGO could be used as the highly effective flame retardant. The thermogravimetric analysis results showed a significant improvement in the char yield of cured FGO/EP. When the content of FGO was 3 wt %, the limiting oxygen index value reached 30.4%. At the same time, the three-point bending and thermomechanical tests confirmed that the mechanical properties of the epoxy resin composites were improved. Based on the char analyses of SEM images and Raman spectroscopy, the flame retardant could promote the formation of a stable carbon layer. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 47710.     

Ionic liquid modified graphene oxide for enhanced flame retardancy and mechanical properties of epoxy resin

In this work, to improve its dispersion and flame retardancy, graphene oxide (GO) was functionalized by silane coupling agent KH550 and 1-butyl-3-methylimidazole hexafluorophosphate (PF₆-ILs), and characteristics of the PF₆-ILs@GO was obtained by transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and thermogravimetric analysis (TGA). Then, the synergistic flame retardant of GO or PF₆-ILs@GO and melamine pyrophosphate (MPP) were applied for epoxy resin (EP) materials. Specifically, the limiting oxygen index (LOI) value of EP with 0.1 wt% PF₆-ILs@GO was increased to 29.2% from 27.5% of EP/MPP composites, and the UL-94 test reached the V-0 rating. The CCT results showed that the total heat release (THR) and total smoke release (TSP) of EP/MPP/PF₆-ILs@GO composites were significantly 24.4% and 53.4% lower than that of EP/MPP composites. Besides, the thermal behavior investigated by TGA indicated that the char-forming effect of GO and PF₆-ILs@GO was great, the residual char of EP/MPP/PF₆-ILs@GO composites was as high as 19.5% at 700°C, and its thermal stability was higher than that of EP/MPP composites. On the other hand, the tensile strength of EP/MPP/GO and EP/MPP/PF₆-ILs@GO composites were increased by 15.6% and 28.3% compared with EP/MPP composites. According to SEM analysis, the EP/MPP/GO composites formed a good protective char layer, which can effectively improve flame retardancy of EP. This research represents a new method of flame retardant modified GO to improve the flame retardancy and mechanical properties of polymers.     

Phosphorus-containing Salen-Ni metal complexes enhancing the flame retardancy and smoke suppression of epoxy resin composites

Two novel Salen-DPCPs metal complexes (Salen-DPCP-1 and Salen-DPCP-2), containing both Salen-Schiff base (Salen), phenyl phosphate structures (DPCP) and nickel component, were prepared to reduce fire hazards of epoxy resin (EP). The results showed that 5 wt % addition of Salen-DPCP-1 brought a higher flame-retardant efficiency to the EP, where the V-0 rating in UL-94 burning test and 31.5% of limiting oxygen index (LOI) were achieved. Meanwhile, total heat release, total smoke production, and total CO yield dramatically decreased by 28.1, 23.6, and 21.4%. In addition, these results basically reappeared when Salen-DPCP-2 were introduced into EP to obtain Salen-DPCP-2/EP composites. Chemical structure and morphology characterization of the carbon residue confirmed that Salen-DPCPs improved the catalytic charring ability and the noncombustible gas releasing ability by the Fourier transform infrared, X-ray photoelectron spectroscopy, and Scanning electron microscopy technology. Therefore, it is an efficient strategy to develop novel Salen composites modified by flame-retardant groups to improve the fire rating of polymers. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48734.     

单分子阻燃剂MPP的合成及其对醇酸树脂的阻燃抑烟

用多聚磷酸、季戊四醇和三聚氰胺合成单分子磷-氮系膨胀型阻燃剂——季戊四醇多聚磷酸酯蜜胺盐(MPP),采用傅里叶变换红外光谱仪表征了其分子结构,采用锥形量热仪和烟密度测定仪评价了MPP对醇酸树脂的阻燃和抑烟特性。结果表明:MPP对醇酸树脂的阻燃性能优于聚磷酸铵、季戊四醇、三聚氰胺构成的传统三组分膨胀型阻燃剂(IFR),有机蒙脱土(OMMT)以及IFR/OMMT复合阻燃剂。w(MPP)为30%时,醇酸树脂的热释放速率峰值从839.65 k W/m2降至251.89 k W/m2,总热释放速率从50.98 MJ/m2降至25.19 MJ/m2,动态生烟速率和有焰燃烧条件下的静态生烟速率降低,无焰燃烧条件下的静态生烟速率增大。     

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。     

Synthesis of aluminum methylcyclohexylphosphinate and its use as flame retardant for epoxy resin

A novel aluminum phosphinate—aluminum methylcyclohexylphosphinate (Al(MHP))—was synthesized by reacting n‐butyl methylphosphonite with cyclohexene, followed by reacting with anhydrous AlCl₃. The products were characterized with gas chromatography, Fourier transform infrared spectroscopy, hydrogen nuclear magnetic resonance, phosphorus nuclear magnetic resonance, X‐ray fluorescent spectroscopy, and thermogravimetric (TG) analyses. After blending with epoxy resin (EP), flame retardancy was estimated with the use of limited oxygen index (LOI) and UL‐94 test, and thermal stability was investigated using TG analysis. The morphologies and composition of the char obtained after being heated at 300 °C for 20 min followed by 500 °C for 3 min in the muffle furnace were characterized by scanning electron microscopy (SEM) with energy‐dispersive X‐ray (EDX) analysis. Results showed that Al(MHP) is an efficient flame retardant for EP, and Al(MHP)/EP can pass UL‐94V‐0 rating with an LOI of 28.8% by adding 15 wt.% of Al(MHP). TG results showed that the presence of Al(MHP) in EP increases the char yield and depresses the thermal decomposition. SEM‐EDX analysis showed that the char obtained at 300 °C is coherent and consists of P‐rich components; at higher temperature (500 °C), the char becomes tiny and loose and phosphorus element is released into gas. Compared with neat EP, composites have lower water absorption. Copyright © 2012 John Wiley & Sons, Ltd.     

Preparation of DOPO-derived magnesium phosphate whisker and its synergistic effect with ammonium polyphosphate on the flame retardancy and mechanical property of epoxy resin

In this study, a magnesium phosphate whisker (DPM-H) was synthesized by the acid–base neutralization reaction between magnesium hydroxide and 10-hydroxy-9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO-OH) at 120°C. A new synergistic intumescent flame retardant (IFR) for epoxy resin (EP), which was composed of DPM-H and ammonium polyphosphate (APP) was thoroughly studied. When the IFR loading was 8%, with the DPM-H to APP weight ratio at 1:7, the prepared flame-retardant EP (EPDA-2) passed the vertical burning tests (UL-94) V-0 rating and obtained the limiting oxygen index (LOI) value of 29.3%. Microscale combustion calorimetry (MCC) results showed that the total heat release (THR) of EPDA-2 reduced by 32.1% compared with pure EP. Meanwhile, the addition of DPM-H can partially solve the problem of the decrease of the EP mechanical property caused by the addition of APP. Compared with the flame-retardant EP with the 8% loading of APP, the impact strength of EPDA-2 increased 152.3%.