Preparation and investigation of flame‐retardant epoxy resin modified with a novel halogen‐free flame retardant containing phosphaphenanthrene,triazine‐trione,and organoboron units

In this article, a novel flame retardant (coded as BNP) was successfully synthesized through the addition reaction between triglycidyl isocyanurate, 9,10‐dihydro‐9‐oxa‐10‐phosphaphenanthrene‐10‐oxide and phenylboronic acid. BNP was blended with diglycidyl ether of bisphenol‐A to prepare flame‐retardant epoxy resin (EP). Thermal properties, flame retardancy, and combustion behavior of the cured EP were studied by thermogravimetric analysis, limited oxygen index (LOI) measurement, UL94 vertical burning test, and cone calorimeter test. The results indicated that the flame retardancy and smoke suppressing properties of EP/BNP thermosets were significantly enhanced. The LOI value of EP/BNP‐3 thermoset was increased to 32.5% and the sample achieved UL94 V‐0 rating. Compared with the neat EP sample, the peak of heat release rate, average of heat release rate, total heat release, and total smoke production of EP/BNP thermosets were decreased by 58.2%–66.9%, 27.1%–37.9%, 25.8%–41.8%, and 21.3%–41.7%, respectively. The char yields of EP/BNP thermosets were increased by 46.8%–88.4%. The BNP decomposed to produce free radicals with quenching effect and enhanced the charring ability of EP matrix. The multifunctional groups of BNP with flame retardant effects in both gaseous and condensed phases were responsible for the excellent flame retardancy of the EP/BNP thermosets. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45291.     

Synthesis of phosphaphenanthrene derivatives as flame retardants and their properties in epoxy resin composites

In order to further improve the flame-retardant properties of epoxy resins (EPs), two hydroxyl-containing phospha-phenanthrene derivatives, DOPO-PHBA and DOPS-PHBA, were prepared from the molecular structure design by using 9,10-dihydro-9-oxa-10-phospha-phenanthrene-10-oxide (DOPO), 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-sulfide (DOPS), and 4-hydroxybenzaldehyde (PHBA) as the raw materials. These composites of DOPO-PHBA/EP and DOPS-PHBA/EP were prepared by melt blending. The results showed that UL-94 V-0 was achieved with an LOI of 31.9% when just 7.5% DOPS-PHBA was added to EP, while a limited oxygen index of 35.2% was achieved with 10% DOPO-PHBA/EP. Moreover, in comparison with 7.5% DOPO-PHBA/EP, 7.5% DOPS-PHBA/EP has the lower peak of heat release rates, total heat release values, and fire growth rate, demonstrating that the flame-retardant DOPS-PHBA is more effective at reducing heat release, enhancing the material's flame retardancy, and lessening the intensity of EP burning. The Thermogravimetric-infraredspectrometry (TG-IR) results showed that the phosphorus-containing radicals generated by DOPS-PHBA/EP pyrolysis trapped the free radicals, such as H˙, O˙, or HO˙, thus providing free radical quenching. Furthermore, combining the macro and micro Scanning electron microscopy (SEM) test results, DOPS-PHBA/EP has a better char formation ability and a denser char layer, which can play a better role in heat and oxygen insulation.     

A DOPO Derivative Constructed by Sulfaguanidine and Thiophene toward Enhancing Fire Safety,Smoke Suppression,and Mechanical Properties of Epoxy Resin

In order to eliminate the negative effect of traditional 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) -based flame retardants on heat resistance, mechanical properties, and curing process of epoxy resin (EP), a DOPO derivative (DST) constructed by sulfaguanidine and thiophene is designed and used as co-cured agent for EP. Compared with EP, the maximum decrease of glass transition temperature (T_g) in all EP/DST samples is less than 5%, indicating EP modified by DST maintains good heat resistance. Encouragingly, DST shows satisfactory flame-retardant efficiency and excellent smoke suppressing effects. EP containing barely 5 wt% of DST (P content: 0.37 wt%) achieves a UL-94 V-0 rating and 32.8% limited oxygen index (LOI) value. Its peak heat release rate (PHRR), total heat release (THR), and total smoke production (TSP) are also decreased by 31.2%, 18.8%, and 30.2% . Further, DST significantly improves mechanical properties of the EP/DDM/DST system. The tensile strength and modulus increase by 37.2% and 14.6%, respectively, as DST content is 7.5 wt%. It is revealed that DST has positive quenching and diluting effects in the gas phase, as well as promoting the formation of a compact char layer in the condensed phase.     

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.     

Transparent low‐flammability epoxy resins with improved mechanical properties using tryptamine‐based DOPO derivative

A novel flame‐retardant hsaltryptamine phosphaphenanthrene (HTD) was successfully synthesized and characterized by Fourier transform infrared spectrometry and nuclear magnetic resonance. HTD was used to improve flame retardancy of epoxy resin (EP). When the addition content of HTD reached 4 wt%, the EP/HTD thermoset passed a UL‐94 V‐1 rating and had limited oxygen index value of 29.2%. Compared to neat EP, the release of heat and smoke decreased significantly due to the gaseous‐phase and condensed‐phase flame‐retardant mechanism of HTD. The char residue after cone calorimeter test was analyzed and the results showed that the char residue of EP/8%HTD thermoset exhibited homogeneously crosslinked char layer, which acted as a good barrier for the release of heat and oxygen. The transmittance and mechanical properties of EP/HTD thermosets had been tested. EP/HTD thermoset possessed high transparency and good mechanical properties. In comparison to neat EP, tensile strength, flexural strength, and Izod unnotched impact strength of EP with 8% loading of HTD was improved by 21.9%, 20.5%, and 17.4%, respectively. POLYM. ENG. SCI., 59:2008–2015, 2019. © 2019 Society of Plastics Engineers     

聚甲基亚膦酸双酚A酯阻燃剂的合成及其应用

以甲基二氯膦和双酚A为单体,通过熔融缩聚合成了聚甲基亚膦酸双酚A酯(PMPBE)。通过傅里叶变换红外光谱(FTIR)、核磁共振谱仪、热失重分析仪(TGA)、差示扫描量热仪(DSC)、垂直燃烧仪、极限氧指数仪及微型量热仪表征了PMPBE及环氧树脂(EP)/PMPBE共混物的结构和性能。结果表明,随着PMPBE添加量的增加,复合材料的极限氧指数逐渐提高,最大放热速率和放热量逐渐降低,EP在700 ℃的残炭率明显提高。当添加20份PMPBE时,EP的极限氧指数从19.0 %提高到27.6 %,达到V-0级,最大放热速率与放热量均下降了27 %;说明该阻燃剂是良好的本征型阻燃剂。     

Synthesis of a novel,multifunctional inorganic curing agent and its effect on the flame‐retardant and mechanical properties of intrinsically flame retardant epoxy resin

Traditional curing agents have only a single property, while traditional synthetic organic flame‐retardant hardeners often show poor tolerance to oxidants, strongly acidic or alkaline reagents, and organic solvents and have toxicity problems. Here, a novel and multifunctional flame‐retardant curing agent of the inorganic substrate multifunctional curing agent of the inorganic substrate (FCIN) was proposed first and successfully prepared, and then an intrinsically flame‐retardant epoxy resin (EP) was prepared by covalently incorporating FCIN nanoparticles (FCINs) into the EP. The curing behavior of the FCINs was investigated, showing that FCIN/EP expresses a higher global activation energy than tetraethylenepentamine (TEPA)/EP and that the FCINs had strong interfacial adhesion to the EP matrix. Additionally, the FCINs were well dispersed and provided a remarkable improvement in mechanical and flame‐retardant properties of the intrinsically flame‐retardant EP. With the incorporation of 9 wt % FCINs into the EP, dramatic enhancements in the strength, modulus under bending, and toughness (～36%, ～109%, and ～586%, respectively) were observed, along with 85.2%, 46.4%, 98.3%, and 77.26% decreases in the peak heat release rate, total heat release, smoke production rate peak, and total smoke production, respectively, with respect to that of TEPA/EP. The mechanisms of its flame‐retardant, smoke‐suppression, and failure behaviors were investigated. The development of this unconventional, multifunctional flame‐retardant curing agent based on an inorganic substrate showed promise for enabling the preparation of a variety of new high‐performance materials (such as intrinsically flame‐retardant EP and functional modified polyesters). © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46410.     

Cross-linked Salen-based polyphosphazenes (Salen-PZNs) enhancing the fire resistance of epoxy resin composites

In this work, two cross-linked Salen-based polyphosphazenes (Salen-PZNs: Salen-PZN-1 microspheres and layered Salen-PZN-2), which contains Salen-Schiff base and phosphazene components, were synthesized. The results showed that the peak heat release rate and total smoke production of 3% Salen-PZN-1/epoxy resin (EP) (3 wt% addition) were reduced by 23.8% and 87.3%, respectively. Meanwhile, after introducing the layered Salen-PZN-2 into EP, efficient flame resistance was obtained. The results of thermogravimetric analysis/infrared spectrometry proved that the harmful gasses of 5% Salen-PZN-1/EP composites were reduced during the combustion. The possible flame retardancy mechanism was considered to be the synergy of phosphate group catalysis, release of nitrogen-containing noncombustible gasses and gas phase quenching. Therefore, this work provides a method for preparing polymers with highly efficient flame-retardant properties.     

Preparation,mechanical properties,and thermal degradation of flame retarded epoxy resins with an organophosphorus oligomer

An organophosphorus oligomer, poly(DOPO-substituted hydroxyphenyl methanol pentaerythritol diphosphonate) (PFR), was synthesized from the dehydrohalogenation polycondensation of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide substituted hydroxyphenyl methanol (DOPO-HBA) with 3,9-bis(chloro)-2,4,8,10-tetraoxa-3,9-diphosphaspiro [5.5]undecane-3,9-dioxide (SPDPC). The structure of PFR was confirmed by FTIR, ¹H NMR, and ³¹P NMR. Advanced flame retardant epoxy resins (FREP) were obtained by incorporating PFR into EP, cured by 4,4′-diaminodiphenylmethane (DDM). Effects of PFR on thermal, dynamic mechanical properties, and flame retardant properties of the epoxy resins were investigated. The dynamic mechanical analysis (DMA) results showed that EP/PFR exhibited higher glass transition temperature than that of neat EP. Moreover, incorporation of PFR significantly enhanced the char yield at higher temperatures. The addition of PFR into epoxy resins significantly improved their flame retardancy, due to the reduction of peak heat release rate, total heat release as well as the mass loss rate.     

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 organophosphorus flame retardant for transparency,low-flammability,and mechanical reinforcement epoxy resin

To maintain transparency and improve flame retardancy and mechanical properties of epoxy resin, a reactive organophosphorus flame retardant (DPDDM) was designed and synthesized, which was derived from 3,4-dihydroxybenzaldehyde, 4, 4′- diamino diphenylmethane and 9,10-dihydro-9-oxa –10- phosphaphenanthrene-10-oxidein two steps. Compared with neat epoxy resin (EP), the tensile strength and flexural strength of the EP with 5% DPDDM increased by 28.6% and 42.8%, respectively, indicating that DPDDM can significantly improve the mechanical properties of EP materials. Meanwhile, the DPDDM modified EP materials have good transparency and the EP with 5% DPDDM passed the V-0 rating and had the limiting oxygen index as high as 34%. Cone calorimeter test results showed that the heat release and smoke generation of the modified materials were significantly lower than the unmodified materials, which were reduced by 32.6% and 64.6%, respectively, indicating that the modified materials can greatly improve the safety of fire prevention. This work provides a new approach to prepare transparent epoxy resin with good mechanical properties and excellent flame retardancy.     

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.     

Flame retardancy and pyrolysis behavior of an epoxy resin composite flame-retarded by diphenylphosphinyl-POSS

To reduce the flammability of epoxy resin (EP), a flame retardant (designated as D-POSS) containing diphenylphosphinyl and polyhedral oligomeric silsesquioxane (POSS) was constructed by aminopropyl-isobutyl POSS and diphenylphosphinyl chloride. The chemical structure of D-POSS was fully characterized, then it was used to enhance the flame retardancy of EP. When the flame-retardant EP composite contained 4 wt% D-POSS, its limiting oxygen index value was 29.0% and it achieved UL 94 V-1 rating. Also, its peak of heat release rate (pk-HRR), total heat release (THR) and total smoke production were decreased by 35.3%, 30.3%, and 38.3%, respectively. Moreover, the results from cone calorimeter disclosed that diphenylphosphinyl group and POSS group in D-POSS showed a strong synergistic effect in inhibiting pk-HRR, THR, and smoke production, promoting the charring formation of EP material, and forming an intumescent char layer. Additionally, the theoretical THR reduction of flame-retardant EP composite was calculated by the equation deduced from the standard, and it was almost same with the practical THR reduction. Notably, some silicon oxide enriched on the residue's surface. The phenomenon led to form a double-layer residue that consisted of white yarn-like outer char and normal intumescent inner char. This double-layer residue was contributed to enhance EP composite's flame retardancy.     

An intrinsic flame retardant epoxy resin with high transparency and strengthened mechanical property

In order to search for multifunctional epoxy thermosets (EP) with low flammability, high transparency and satisfied mechanical performance, DOPO-based phosphonate ammonium salt (DOA) was synthesized from 10-hydroxy-9,10-dihydro-9-oza-10-phosphaphenanthrene-10-oxide (DOPO-OH) and 2-amino-2-methyl-1,3-propanediol (AMPD). Under the influence of DOA, the flame-retardant and mechanical performances of the resulting EP were obviously improved. On account of the enhanced interaction and the incorporated flexible fragments in epoxy macromolecular chains, the tensile strength, elongation at break, and impact toughness of EP/5.0 wt% DOA significantly increased from 65.4 ± 1.2 MPa, 6.7 ± 0.6%, and 12.1 ± 1.3 kJ m⁻² of EP to 81.4 ± 2.8 MPa, 10.6 ± 0.5%, and 18.0 ± 1.1 kJ m⁻², respectively. In the presence of DOA, the limiting oxygen index (LOI) value of EP/5.0 wt% DOA increased to 35.5% and it passed the underwriter laboratories-94 vertical burning tests (UL-94 V) and got a V-1 rating. Moreover, the peak value of heat release rate (PHRR) was decreased by 38.0%. The analyses of char residues and volatile products showed that the activities of DOA on reducing the flammability of EP were ascribed to the protective effect of the char, the release of incombustible gases, and the radical-capture action of phosphorus-containing free radicals. Moreover, the modified epoxy thermosets still retained a high transparency.     

Flame retardant and mechanical properties of epoxy composites containing APP−PSt core−shell microspheres

Ammonium polyphosphate (APP)–polystyrene (PSt) core–shell microspheres (CSPs) were synthesized via in situ radical polymerization. The core–shell structure was confirmed by transmission electron microscope (TEM). The results of optical contact angle measurements demonstrated a significant improvement in hydrophobicity of the modified APP. The obtained APP–PSt CSPs were added into epoxy (EP) system with various loadings. Effects of CSP on flame retardancy, thermal properties, heat release rate (HRR), smoke production, and mechanical properties of EP/CSP composites were investigated by limiting oxygen index (LOI), UL‐94 tests, thermogravimetric analysis (TGA), cone calorimeter, and tensile test. LOI and UL‐94 indicated that CSP remarkably improved the flame retardancy of EP composites. TGA showed that the initial decomposition temperature and the maximum‐rate decomposition temperature decreased, whereas residue yields at high temperature increased with the incorporation of microspheres. Cone calorimetry gave evidence that HRR, peak release rate, average HRR, and smoke production rate of EP/CSP composites decreased significantly. The morphology of char residues suggested that CSP could effectively promote EP to form high‐quality char layer with compact outer surface and swollen inner structure. Tensile strength of EP was enhanced with the addition of CSP. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40218.     

Melamine poly(metal phosphates) as flame retardant in epoxy resin: Performance,modes of action,and synergy

Melamine poly(metal phosphates) (MPMeP) are halogen‐free flame retardants commercialized under the brand name Safire. Melamine poly(aluminum phosphate) (MPAlP), melamine poly(zinc phosphate) (MPZnP), and melamine poly(magnesium phosphate) (MPMgP) were compared in an epoxy resin (EP). The thermal decomposition, flammability, burning behavior, and glass transition temperature were investigated using thermogravimetric analysis, pyrolysis combustion flow calorimeter, UL 94 testing, cone calorimeter, and differential scanning calorimetry. While the materials exhibited similarities in their pyrolysis, EP + MPZnP and EP + MPMgP showed better fire behavior than EP + MPAlP due to superior protective properties of the fire residues. Maintaining the 20 wt % loading, MPZnP was combined with various other flame retardants. A synergistic effect was evident for melamine polyphosphate (MPP), boehmite, and a derivative of 6H‐Dibenzo[c,e][1,2]oxaphosphinine‐6‐oxide. The best overall performance was observed for EP + (MPZnP + MPP) because of the best protection effectiveness of the fire residue. EP + (MPZnP + MPP) achieved V1/V0 in UL 94, and an 80% reduction in the peak heat release rate. This study evaluates the efficiency of MPMeP in EP, alone and in combination with other flame retardants. MPMeP is a suitable flame retardant for epoxy resin, depending on its kind and synergists. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43549.     

Layer-by-layer assembled bagasse to enhance the fire safety of epoxy resin: A renewable environmental friendly flame retardant

In an effort to make rational use of resources, wasted bagasse were collected, and then fabricated by layer-by-layer (LbL) assembly to prepare an environmentally benign flame retardant for epoxy resin (EP). Six chitosan/ammonum polyphosphate bilayers were successfully deposited on the surface of bagasse, which endows EP/6BL@BF composites with a limiting oxygen index value of 24.1% and V-1 rating in UL-94 test. Compared with untreated bagasse, cone calorimetry test reveals that the incorporation of 6BL@BF reduces the peak heat release rate and total heat release by 64.6% and 13.2%, respectively. Besides, expandable graphite (EG) was combined with 6BL@BF to further enhance the fire safety and thermal stability of EP composites. Furthermore, the gas and condensed phase analysis of EP/6BL@BF/EG-3 composite was investigated by TG-IR, scanning electronic microscopy, Laser Raman spectroscopy, and X-ray photoelectron spectroscopy, and the flame retardant mechanism of 6BL@BF/EG was proposed. Finally, the mechanical properties of EP composites were investigated systematically.     

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.     

Flame retardant,mechanical, and hot air aging properties of ethylene-propylene-diene monomer/ammonium polyphosphate/nano-silic composite rubber

In this work, effect of the ratio of nonhalogenated flame retardants (ammonium polyphosphate [APP] and nano-silica [nano-SiO₂]) on the mechanical, thermal, and flame retardant properties of ethylene-propylene-diene monomer (EPDM) composite rubber were investigated. Vulcanization characteristics, high temperature compression permanent deformation, thermal oxygen aging, dynamic thermodynamic analysis, thermal stability, cone calorimetry, limiting oxygen index (LOI), horizontal vertical combustion (UL-94), and scanning electron microscopy were carried out. The experimental results showed that the mechanical properties of the composite rubber decreased with the addition of APP. However, the addition of nano-SiO₂ was found to significantly improve the mechanical properties of the composite rubber when it was incorporated. In terms of flame retardant properties of EPDM composite rubber, the combination of APP and nano-SiO₂ has a synergistic flame retardant effect in comparison to the use of single APP flame retardant. The heat release rate of EPDM composite rubber decreased by 34%, the total heat release decreased by 19%, the LOI increased by 76%, and the flame retardant grade of EPDM composite rubber reached V-0. The EPDM composite rubber fabricated in the present study showed excellent fire resistance and desirable mechanical properties, which are of practical significance for further expanding the application ranges of EPDM rubbers.     

A high-efficiency DOPO-based reactive flame retardant with bi-hydroxyl for low-flammability epoxy resin

A high-efficiency DOPO-based reactive flame retardant (DPE) with bi-hydroxyl was successfully synthesized via reacting DOPO with imine obtained from the condensation of ethanolamine and 1,4-phthalaldehyde, and used as co-curing agent to improve the fire safety of epoxy resin (EP). Its chemical structure was characterized by Fourier transform infrared (FTIR) spectra, ¹H, ³¹P nuclear magnetic resonance (NMR) spectra and elemental analysis. The curing behavior, thermal properties, flame-retardant properties of EP/DPE systems were investigated. The results revealed that DPE slightly decreased the glass transition temperature (T_g), but accelerated the curing cross-linking reaction of EP. Furthermore, DPE decreased thermal degradation rate of epoxy matrix and promoted the formation of residual char at high temperature. After adding DPE, the flame retardant of epoxy thermosets was greatly improved. Especially, the thermoset modified with 5 wt% DPE achieved limiting oxygen index (LOI) value of 33.6% and V-0 rating in UL-94 test, demonstrating the highly efficient flame retardancy. While its peak heat release rate (PHRR), total heat release (THR) and total smoke production (TSP) were respectively decreased by 32.6%, 17.8%, and 13.9% compared with neat EP. Moreover, the research on flame retardant mechanism disclosed that DPE played dual flame-retardant effect in the gaseous and condensed phases.