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.     

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.     

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 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     

用于环氧树脂不饱和聚酯的聚合物型磷系阻燃剂

研究了1种新型富芳香结构的含磷聚合物阻燃剂聚苯基磷酸(9,10-二氢-9-氧杂-10-膦酰杂菲)苯撑酯(PDPPP)的合成及其对环氧树脂(ER)、不饱和聚酯树脂(USPE)的阻燃性能的影响。这种阻燃剂是由2-(6-氧-6氢-膦酰杂菲)1,4-对苯二酚(ODOPB)与苯膦酰二氯通过熔融缩聚获得。将磷含量为13.8%的PDPPP添加到环氧树脂、不饱和树脂中,结果表明该聚合物对环氧树脂、不饱和树脂具有良好的阻燃性能,PDPPP含量只需达到2%即磷含量只需达到0.28%时氧指数LOI可达28,阻燃性UL-94可达到V0级。     

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.     

新型含磷环氧树脂的研究进展

有机和无机磷化物是新一代无卤、环保和绿色新型阻燃改性单体,可合成具有优异热稳定性、阻燃特性和物理机械性能的新型含磷环氧树脂。综述了DOPO的结构性能和化学反应性,以及以DOPO和氧氯化磷为原料合成新型含磷中间体和环氧树脂的结构、合成方法及性能等。     

新型含氮环氧树脂研究进展

氮系阻燃剂具有高效、低毒(包括其分解产物)等优点,故已成为当今阻燃剂的发展方向。综述了氮系阻燃剂的特点及其阻燃机理,以及目前国内外对含氮环氧树脂(EP)和含氮阻燃固化剂的最新研究进展,并对其发展前景作了展望。     

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。     

Synergistic action of expandable graphite on fire safety of a self-intumescent flame retardant epoxy resin

Previously, it was reported that epoxy resin (EP) filled with ammonium polyphosphate (APP) and copper (I) oxide (Cu₂O) at a mass ratio of 8/2 (APP8-Cu₂O2) as a self-intumescent system demonstrated promising fire retardancy. To further improve the flame retardant efficiency, the possibility of expandable graphite (EG) as an effective synergist for the self-intumescent EP system was revealed by limiting oxygen index (LOI) test. The results showed that the incorporation of EG increased the LOI value of EP/APP8-Cu₂O2 obviously. The highest LOI value was obtained at the EG/APP8-Cu₂O2 mass ratio of 3/7, indicating the optimal synergistic effect being achieved. Furthermore, UL-94 test results showed that the excellent synergistic effect resulted in the addition of 13 wt% EG/APP8-Cu₂O2 of 3/7 not only endowed EP a relatively high LOI value of 34.3%, but also made it pass UL-94 V-0 rating. Moreover, the main fire hazard parameters obtained from cone calorimeter tests, such as peak heat release rate, total smoke production, and peak CO production were reduced 40.3%, 30.3%, and 46.2%, respectively by the combination effect of EG/APP8-Cu₂O2 with mass ratio of 3/7, suggesting the excellent improvement in the fire safety of EP significantly. Finally, a possible action mode, which would be beneficial for developing other flame retardant polymers with high fire safety, was proposed.     

Thermal degradation behaviors and flame retardancy of epoxy resins with novel silicon‐containing flame retardant

A novel macromolecular silicon‐containing intumescent flame retardants (Si‐IFR) was synthesized, and its structure was a caged bicyclic macromolecule containing phosphorus‐silicon characterized by IR. Epoxy resins (EP) were modified with Si‐IFR to get the flame retardant EP, whose flammability and burning behavior were characterized by UL 94 and limiting oxygen index (LOI). Twenty percentage of weight of Si‐IFR was doped into EP to get 27.5% of LOI and UL 94 V‐0. The degradation behavior of the flame retardant EP was studied by thermogravimetry, differential thermogravimetry, scanning electron microscopy, and X‐ray photoelectron spectroscopy analysis. The experimental results exhibited that when EP/Si‐IFR was heated, the phosphorus‐containing groups firstly decompose to hydrate the char source‐containing groups to form a continuous and protective carbonaceous char, which changed into heat‐resistant swollen char by gaseous products from the nitrogen‐containing groups. Meanwhile, SiO₂ reacts with phosphate to yield silicophosphate, which stabilizes the swollen char. The barrier properties and thermal stability of the swollen char are most effective in resisting the transport of heat and mass to improve the flame retardancy and thermal stability of EP. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

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.     

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.     

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     

Aryl phosphinate anhydride curing for flame retardant epoxy networks

An aryl phosphinate anhydride (9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide)-methyl succinic anhydride (DMSA), with a pendent phosphorus group was synthesized and used as a reactive type flame retardant. The structure of DMSA was confirmed by FTIR, mass, elemental analysis, ¹H and ³¹P NMR spectroscopies. The aryl phosphinate anhydride was successfully used to cure some commercial epoxides, such as bisphenol A diglycidyl ether (DGEBA) and epoxy-novolac. The epoxy networks obtained were characterized by dynamic mechanical analysis (DMA), thermogravimetric analysis (TGA), and the limiting oxygen index (LOI) test. Epoxy resins cured with DMSA exhibit higher LOI values and char yields compared with those cured by commercial anhydrides, such as phthalic anhydride (PA) and hexahydrophthalic anhydride (HHPA). Furthermore, the LOI value and the char yield of the epoxy-resin composites increase with increasing phosphorus content. The flame retardancies of the epoxy-resin composites were significantly improved by using aryl phosphinate anhydride. © 1998 Society of Chemical Industry.     

Flame retardant epoxy polymers using phosphorus‐containing polyalkylene amines as curing agents

Two series of novel phosphorus‐containing poly(alkylene) amines with or without aromatic groups were synthesized via reacting phosphoryl chloride derivatives with commercially available polyetheramines, ethylenediamine and N‐phenyl‐1,4‐phenylenediamine, respectively. Chemical structures of the amines were characterized with FTIR, NMR, P (phosphorus) content measurement, and amine content titration. These amines were then utilized as curing agents to react with diglycidyl ether of bisphenol A for preparing phosphorus containing epoxy polymers. The introduction of soft ? P? O? linkage, polyalkyene, and hard aromatic group into the backbones of the synthesized phosphorus‐containing amine (PCA) provides epoxy resins with tunable flexibility. Thermal analysis of differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) reveals that these resulted epoxy resins possess moderate T_g's and thermal stability. Furthermore, high char yields in TGA and high limited oxygen index (LOI) values indicate that these phosphorus‐containing epoxy (PCE) resins are capable of exhibiting excellent flame retardant properties. These polymers can be potentially utilized in flame retardant epoxy coatings and other applications. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 3526–3538, 2001     

Novel flame retardant thermosets from nitrogen‐containing and phosphorus‐containing epoxy resins cured with dicyandiamide

A novel phosphorus‐containing epoxy resin (EPN‐D) was prepared by addition reaction of 9,10‐dihydro‐9‐oxa‐10‐phosphaphenanthrene 10‐oxide (DOPO) and epoxy phenol‐ formaldehyde novolac resin (EPN). The reaction was monitored by epoxide equivalent weight (EEW) titration, and its structure was confirmed by FTIR and NMR spectra. Halogen‐free epoxy resins containing EPN‐D resin and a nitrogen‐containing epoxy resin (XT resin) were cured with dicyandiamide (DICY) to give new halogen‐free epoxy thermosets. Thermal properties of these thermosets were studied by differential scanning calorimeter (DSC), dynamic mechanical analysis (DMA), thermal mechanical analyzer (TMA) and thermal‐gravimetric analysis (TGA). They exhibited very high glass transition temperatures (T_gs, 139–175°C from DSC, 138–155°C from TMA and 159–193°C from DMA), high thermal stability with T_{d,5 wt %} over 300°C when the weight ratio of XT/EPN‐D is ≥1. The flame‐retardancy of these thermosets was evaluated by limiting oxygen index (LOI) and UL‐94 vertical test. The thermosets containing isocyanurate and DOPO moieties showed high LOI (32.7–43.7) and could achieve UL‐94 V‐0/V‐1 grade. Isocyanurate and DOPO moieties had an obvious synergistic effect on the improvement of the flame retardancy. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

浅色水滑石/红磷复合阻燃剂的制备及性能

采用白磷插层进入水滑石层间后再转化为红磷的方法制得红磷插层水滑石,从而得到了用于环氧树脂体系的浅色水滑石/红磷复合阻燃剂。考察了白磷和水滑石配比对转化率的影响及红磷含量对丙氨酸交换量的影响,并研究了白磷插层水滑石阻燃剂用于环氧树脂的阻燃性能。结果表明转化后红磷在水滑石中的含量与转化前白磷与水滑石的配比之间符合一定的线性关系,即y=-8.44373+0.72491x;丙氨酸的交换量随着红磷含量的增大而减小;以插层水滑石为阻燃剂,阻燃效果优于水滑石/红磷混合物,且颜色较浅,亨特白度为30.13,大于直接混合的23.93;当水滑石、红磷质量分数分别为5%、1.48%时,环氧树脂的阻燃性能就达到FV-0级。     

含磷阻燃剂阻燃环氧树脂热降解动力学

以2-二苯基膦酰基-1,4-苯二酚(DPO-HQ)为阻燃剂制备了阻燃环氧树脂,利用动态热重分析法(TGA)研究了纯环氧树脂(EP)和阻燃环氧树脂(FR-EP)在不同升温速率下的热稳定性,建立了EP和FR-EP体系的动力学模型和非模型动力学(MFK),并对比分析了模型动力学和非模型动力学对于描述EP体系和FR-EP体系的适用性.结果表明:阻燃剂的引入降低了环氧树脂初始降解温度,但增加了残炭率.由Flynn-Wall-Ozawa方法和Coats-Redfern方法建立的模型动力学表征EP和FR-EP体系高温降解过程中误差较大,而非模型动力学能更准确地预测和描述EP和FR-EP体系的高温降解行为.     

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。