Fabrication of ZIF‐8@Polyphosphazene core‐shell structure and its efficient synergism with ammonium polyphosphate in flame‐retarding epoxy resin

A novel zeolitic imidazolate framework (ZIF‐8) nanoparticles@polyphosphazene (PZN) core‐shell architecture was synthesized, and then, ZIF‐8@PZN and ammonium polyphosphate (APP) were applied for increasing the flame retardancy and mechanical property of epoxy resin (EP) through a cooperative effect. Herein, ZIF‐8 was used as the core; the shell of PZN was coated to ZIF‐8 nanoparticles via a polycondensation method. The well‐designed ZIF‐8@PZN displayed superior fire retardancy and smoke suppression effect. The synthesized ZIF‐8@PZN observably raised the flame retardancy of EP composites, which could be demonstrated by thermogravimetric analysis (TGA) and a cone calorimeter test (CCT). The chemical structure of ZIF‐8@PZN was characterized by X‐ray diffraction (XRD), X‐ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM). Compared with pure epoxy, with the incorporation of 3 wt% ZIF‐8@PZN and 18 wt% APP into the EP, along with 80.8%, 72.6%, and 64.7% decreased in the peak heat release rate (pHRR), the peak smoke production rate (pSPR), and the peak CO production rate (pCOPR), respectively. These suggested that ZIF‐8@PZN and APP generated an intumescent char layer, and ZIF‐8@PZN can strengthen the char layer, resulting in the enhancement in the flame resistance of EP.     

Synthesis of MoO3 with different morphologies and their effects on flame retardancy and smoke suppression of polyurethane elastomer

Molybdenum trioxide (MoO₃) microrods, nanofibers, and nanoplates were synthesized via the hydrothermal method and high‐temperature calcination method, respectively. Then the MoO₃ was added into polyurethane elastomer, respectively. The flame retardancy and smoke suppression of the composites added with different MoO₃ were studied by thermal gravimetric analysis, cone calorimeter, and smoke density. The results show that the three kinds of MoO₃ with different morphologies could promote the formation of char and possess flame retardancy and smoke suppression, and MoO₃ nanofibers exhibit a higher degree of flame retardancy, and 1 wt% addition could make the peak heat release rate of polyurethane elastomer composites reduce from 881.6 kW m^?2 for a pure sample to 343.4 kW m^?2, a decrease by 61.0%. As for smoke suppression, MoO₃ nanoplates possess the best smoke suppression; 5 wt% could decrease a pure sample's smoke density by 41.3% from 361 to 212. Moreover, the char residue of composites after combustion was analyzed by Raman spectra and X‐ray photoelectron spectroscopy, and the flame retardancy and smoke suppression mechanisms of MoO₃ were discussed.     

Synthesis and application of a dual functional P/N/S‐containing microsphere with enhanced flame retardancy and mechanical strength on EP resin

A phosphazene derivative flame retardant with a highly cross‐linked microsphere structure, named poly(cyclotriphosphazene‐c‐sulfonyldiphenol) (PCPS) microspheres, were synthesized by 1‐pot reaction and then applied on flame retarded epoxy (EP) resin. The microstructure and chemical composition of PCPS microspheres were characterized using scanning electron microscopy, transmission electron microscopy, and element mapping. The thermal stability of PCPS microspheres and PCPS/EP composites was explored through thermogravimetric analysis. Thermogravimetric data showed that the PCPS microspheres have excellent thermal stability, and the char yield is about 43% at the end of 800°C. The incorporation of PCPS microspheres significantly increased the char yield of PCPS/EP composites. The flammability was investigated by limited oxygen index tests and cone calorimeter. The limited oxygen index value of PCPS/EP composite was increased to 29.8 from 26.6 when 3 wt% of PCPS microspheres was added. Compared with neat EP, the flame retardancy was greatly improved. The peak heat release rate and smoke production rate of PCPS/EP composites were reduced by 45.0% and 43.6%, respectively. The mechanical properties including tensile strength and modulus were both improved due to the enhancement of PCPS microspheres. The PCPS microspheres act as a dual function for improving both the flame resistance and mechanical strength of PCPS/EP system.     

Reduction in smoke emitted and fire hazard presented by flexible poly (vinyl chloride) through novel synthesis of SnO2 supported by activated carbon spheres

A novel catalyst consisting of SnO₂ supported by activated carbon spheres (ACS), referred to as “ACS@SnO₂,” was demonstrated as being much more efficient than either ACS or SnO₂ alone. As such, it is capable of improving the thermal stability and flame retardancy of flexible poly (vinyl chloride) (fPVC). The resulting ACS@SnO₂ composite exhibits a higher reactivity and excellent stability due to the presence of evenly dispersed SnO₂ particles attached to the ACS, as well as the high degree of graphitization of the ACS. Smoke suppression and the synergistic flame‐retardant effect of the ACS@SnO₂ on the fPVC were thoroughly investigated by performing a cone calorimeter test and thermogravimetric analysis. The cone calorimeter test data reveal that the addition of the ACS@SnO₂ greatly improved the flame retardancy of the fPVC, with 32% and 58.4% decreases in the peak heat release rate and smoke production rate, respectively. This is attributed to the formation of a continuous and compact protective layer and the synergistic effects of the ACS and SnO₂ in promoting the ability of the fPVC to isolate heat and oxygen. Furthermore, the ACS@SnO₂/fPVC composite produced greatly increased amounts of char residue, thereby attenuating the fire hazard presented by fPVC composites.     

Phosphorus‐free boron nitride/cerium oxide hybrid: A synergistic flame retardant and smoke suppressant for thermally resistant cyanate ester resin

Establishing a phosphorus‐free strategy to fabricate high‐performance thermosetting resins owning outstanding thermal resistance, good flame retardancy, and smoke suppression is important for sustainable development. Herein, a unique phosphorus‐free hybrid (BN@CeO₂) was synthesized through chemically grafting cerium oxide (CeO₂) on surface of exfoliated boron nitride (BN) nanosheet with the aids of γ‐aminopropyltriethoxysilane and polydopamine coating, which was then embedded into bisphenol A cyanate ester (BCy) resin to fabricate new BN@CeO₂/BCy composites with high thermal resistance. Compared with BCy resin, the BN@CeO₂/BCy composite with 4 wt% BN@CeO₂ not only has delayed initial ignition time by 23 seconds but also severally shows 58.1%, 23.1%, and 44.4% lower smoke produce rate, total heat release, and peak heat release rate. The study on mechanism behind outstanding flame retardancy reveals that the improved heat resistance and flame retardancy of BN@CeO₂/BCy composite are attributed to multiply effects induced by BN@CeO₂ and its interaction with BCy resin; specifically, these effects come from BN (physical barrier) and CeO₂ (free radical trapping effect and catalytic char layer formation) as well as those from the synergistic effect of BN and CeO₂. These excellent comprehensive properties of BN@CeO₂/BCy composites demonstrate that BN@CeO₂ is an environment‐friendly and synergistic modifier for developing heat‐resisting thermosetting resins with outstanding flame retardancy and smoke suppression.     

Effect of surface chemical modification for aluminum hypophosphite with hexa‐(4‐aldehyde‐phenoxy)‐cyclotriphosphazene on the fire retardancy,water resistance,and thermal properties for polyamide 6

The surface chemical modified aluminum hypophosphite (AHP) defined as MAHP was successful prepared through P–H bonds on AHP surface reacted with the aldehyde groups in hexa‐(4‐aldehyde‐phenoxy)‐cyclotriphosphazene made in our lab. The wettability of the flame retardants was evaluated by water contact angle tests, and the water contact angle of the prepared MAHP dramatically increased from 0° for AHP to 145°, which indicated the surface modification made the superhydrophilic AHP into superior hydrophobic MAHP. The prepared MAHP and AHP, respectively, incorporated into polyamide 6 (PA6) matrix to prepare flame retardant PA6 composites and the fire retardancy and thermal degradation behavior of flame retardant PA6 composites were investigated by limiting oxygen index, vertical burning test (UL‐94), cone calorimeter, and thermogravimetric analysis tests. The morphologies and chemical compositions of the char residues for PA6 composites were investigated by scanning electron microscopy and X‐ray photoelectron spectroscopy, respectively. The water resistant properties of flame retardant PA6 composites were evaluated by putting the samples into distilled water at 70°C for 168 hr, and the mechanical properties for flame retardant PA6 composites were investigated by the tensile, flexural, and Izod impact strength tests. The results demonstrated that the PA6/MAHP composites successfully passed UL‐94 V‐0 flammability rating, and the limiting oxygen index value was 27.6% when the loading amount of MAHP was 21 wt%. However, there is no rating in vertical burning tests for PA6/AHP composite with the same amount of AHP, which indicated the surface modification of AHP enhanced the flame retardancy efficiency for PA6 composites. The morphological structures and analysis of X‐ray photoelectron spectroscopy of char residues revealed that the surface modification of AHP benefited to the formation of a sufficient, flame retardant elements rich, more compact and homogeneous char layer on the materials surface during combustion, which prevented the heat transmission and diffusion, limit the production of combustible gases, inhibit the emission of smoke and then led to the reduction of the heat release rate and smoke produce rate. The mechanical properties results revealed that the surface modification of AHP enhanced the mechanical properties, especially the Izod impact strength comparing with that of PA6/AHP composites with the same amount of flame retardant. After water resistance tests, the PA6/MAHP composites remained superior flame retardancy and presented continuous and compact char layer after cone calorimeter tests; however, the fire retardancy for PA6/AHP composite obviously decreased, and the char layer was discontinuous with big hole caused by the extraction of AHP by water during water resistance tests. Copyright © 2017 John Wiley & Sons, Ltd.     

Zeolitic imidazolate frameworks‐8 modified graphene as a green flame retardant for reducing the fire risk of epoxy resin

A novel hybrid material of ZIF‐8/RGO (zeolitic imidazolate frameworks‐8 loaded the surface of graphene) was synthesised by a simple method and characterized. Then, ZIF‐8/RGO was added into epoxy resin (EP), and the flame retardancy and smoke suppression of the EP composites were studied. Compared with pure EP, the peak heat release rate and the total heat release of the EP composites were reduced remarkably, and their LOI and UL94 vertical burning rating were also improved. In addition, their smoke production rate and total smoke production were decreased drastically. The improved flame retardancy and smoke suppression were mainly attributed to the physical barrier effect of graphene. Meanwhile, the metal oxide decomposed from ZIF‐8 could contribute to the production of char residue and enhance the compactness of the char layer.     

Flame retardancy and smoke suppression of silicone foams with microcapsulated aluminum hypophosphite and zinc borate

The flame‐retardant microcapsules were successfully fabricated with an aluminum hypophosphite (AHP) core. Fourier transform infrared (FTIR) and X‐ray photoelectron spectroscopy (XPS) were used to verify that AHP was encapsulated in the microcapsules, and thermogravimetry analysis showed that microencapsulated AHP (MAHP) possessed higher thermal stability than that of AHP. Then, a flame‐retardant and smoke suppression system for silicone foams (SiFs) was obtained through a synergistic effect of MAHP and zinc borate (2ZnO·3B₂O₃·3.5H₂O). The mechanical properties, flame retardance, and smoke suppression of SiFs with MAHP and zinc borate were tested using the tensile test, limiting oxygen index (LOI) test, UL‐94 test, and cone calorimeter test. The mechanical properties indicated that the tensile strength and elongation at break of SiFs could evidently improve with the incorporation of MAHP. Compared with pure SiF, SiF8 with 4.5‐wt% MAHP and 1.5‐wt% zinc borate could achieve an LOI value of 30.7 vol% and an UL‐94 V‐0 rating, the time to ignition amplified almost six times, the peak heat release rate and total heat release were 51.10% and 46.00% less than that of pure SiF, respectively, the fire performance index increased nearly 13 times, and the fire growth index value was only 13.18% of pure SiF. Moreover, the partial substitution of zinc borate imparted a substantial improvement in both flame retardancy and smoke suppression. Especially, the peak smoke production rate and total smoke production of SiF8 were merely 38.46% and 38.84% of pure SiF.     

Synergistic effect of DOPO immobilized silica nanoparticles in the intumescent flame retarded polypropylene composites

The synergistic effect of 9,10‐dihydro‐9‐oxa‐10‐phosphaphenanthrene‐10‐oxide (DOPO) immobilized silica (SiO₂‐DOPO) nanoparticles with an intumescent flame retardant (IFR) on the flame retardancy of polypropylene (PP) was investigated by UL 94 vertical tests and limiting oxygen index (LOI) measurements. It was found that the PP/IFR composites (25 wt%) achieved the UL94 V0 grade and LOI increased to 32.1 with an incorporation of 1.0 wt% SiO₂‐DOPO nanoparticles. Based on thermogravimetric analysis, scanning electronic microscopy and rheological analysis, it is speculated that three factors are mainly contributed to the improvement of the flame retardancy. First, the thermal stability of PP/IFR composites was improved by incorporating SiO₂‐DOPO nanoparticles. Second, the presence of SiO₂‐DOPO nanoparticles could induce the formation of a continuous char skin layer during combustion. The compact char layer could effectively impede the transport of bubbles and heat. Third, rheological analysis indicated that SiO₂‐DOPO nanoparticles could increase viscosity of the PP/IFR composites, which was also benefited to increase flame retardancy. Copyright © 2013 John Wiley & Sons, Ltd.     

A novel graphene hybrid for reducing fire hazard of epoxy resin

Epoxy resin (EP) is more and more important in many fields, but its application is limited due to the inflammability in air of EP. Therefore, reducing the fire hazard of EP is necessary. In this work, a kind of hybrid flame retardant (α‐ZrP‐RGO) consisting of a 2‐dimensional inorganic reduced graphene oxide (RGO) modified with a planar‐like α‐zirconium phosphate (α‐ZrP) particles was prepared successfully via 1‐step hydrothermal method. The effects of α‐ZrP‐RGO on the thermal performance, flame retardancy, and smoke suppression of EP were investigated by preparing EP composites containing both EP and α‐ZrP‐RGO. Thermogravimetric results revealed that α‐ZrP‐RGO could improve the char yield of EP at 700°C obviously. In addition, compared with pure EP, the peak heat release rate and the total heat release of EP composites were decreased significantly, while the limited oxygen index of EP composites was increased. Meanwhile, the smoke production rate of EP composites was reduced obviously with the addition of α‐ZrP‐RGO. The enhanced flame retardancy and smoke suppression of EP composites were mainly attributed to not only the physical barrier effect of both α‐ZrP and RGO but also the catalytic effect of α‐ZrP during the combustion process of EP composites.     

Excellent flame retardancy and air stability through surface coordination of few-layer black phosphorus with TiL4 in epoxy resin

Black phosphorus (BP) has been attractive for many research groups as its promising properties. However, the poor air stability of BP has limited its practical applications. To simultaneously address this problem and improve the flame retardancy of BP in epoxy resin (EP), a surface coordination strategy was proposed. Herein, a titanium ligand (denoted as TiL₄) was designed to coordinate BP nanosheets, which can occupy the lone pair electrons of BP. The Ti–P coordination contributed to the improvement of ambient stability of BP. The serious degradation was observed from pure BP owing to the oxidation. Whereas, the surface coordination can impede the ambient degradation rate of BP by 74.07%. With the addition of 1.5 wt% TiL₄@BP, the char yield of EP nanocomposites was increased by 20.55% due to the catalytic charring effect of TiL₄@BP. The incorporation of 1.5 wt% TiL₄@BP can reduce the peak of heat release rate and total heat release values of EP by 29.41% and 23.32%. The EP/TiL₄@BP 1.5 also can pass the UL-94 V-0 rating, and its value of limiting oxygen index was enhanced by 13.60%. The improvement in the flame retardancy of BP in EP can be largely ascribed to synergistic catalytic charring effects between BP and TiL₄. The condense and compact char layer can act as a physical barrier to restrict the exchange of pyrolytic products and the transfer of heat. In addition, the free radical quenching effect of BP nanosheets also accounted for the excellent flame retardant performance of EP. This work proposed a reference for synchronically obtaining the improvement for the air stability and flame retardant performance of BP.     

Synergistic effect of bismuth oxide and mono‐component intumescent flame retardant on the flammability and smoke suppression properties of epoxy resins

A novel mono‐component intumescent flame retardant named pentaerythritol phosphate melamine salt (PPMS)‐hybrid bismuth oxide (PPMS‐Bi₂O₃) was synthesized and carefully characterized by FTIR, ¹H NMR, ³¹P NMR, SEM‐EDS, and TG analyses. Then, PPMS‐Bi₂O₃ was utilized as flame retardant for epoxy resins (EPs), and the thermal stability, flame retardancy, and smoke suppression properties of EP composites were investigated. TG results show that PPMS‐Bi₂O₃ is more conducive to enhance the thermal stability and char forming ability of EP composites compared with the same addition of PPMS or the mixture of PPMS and Bi₂O₃, and this positive effect is enhanced with the increasing Bi₂O₃ content. Cone calorimeter test reveals that the PPMS‐Bi₂O₃ can effectively reduce the heat release and smoke production in comparison with PPMS or the mixture of PPMS and Bi₂O₃ due to the formation of a more compact and intumescent char against fire, as judged by digital photographs and SEM images. EDS analysis indicates that the combination PPMS and Bi₂O₃ by hydrogen bonds promotes to generate more phosphorus‐rich and aromatization structures in the condensed phase that enhance the barrier effect and anti‐oxidation ability of the char, thus imparting higher flame retardant and smoke suppression efficiencies to EP composites.     

Synergistic effect of flame retardants and graphitic carbon nitride on flame retardancy of polylactide composites

In order to improve the flame retardant of polylactide (PLA), the synergistic effect of graphitic carbon nitride (g‐C₃N₄) with commercial‐available flame retardants melamine pyrophosphate (MPP) and 9,10‐dihydro‐9‐oxa‐10‐phosphaphenanthrene‐10‐oxide (DOPO) was investigated. The PLA composites containing 5 wt% g‐C₃N₄ and 10 wt% DOPO had a highest limited oxygen index (LOI) value of 29.5% and reached the V‐0 rating of UL‐94 test. The cone calorimeter tests exhibited that DOPO had a better synergistic effect with g‐C₃N₄ than MPP to improve flame retardancy of PLA. The peak heat release rate (pHRR) and total heat release (THR) of PLA composites containing 10 wt% DOPO could be reduced by 25.2% and 23.6%, respectively, as compared with those of pure PLA. The presence of rich phosphorus element and aromatic groups in DOPO contributed to obtain continuous compact char layer and increase the graphitization level of char residues, thereby, resulting in improving the flame retardancy of PLA together with g‐C₃N₄. In addition, the incorporation of DOPO can serve as a plasticizer to reduce the complex viscosity, improving the processability of PLA composites.     

Synthesis of a novel phosphorus‐containing curing agent and its effects on the flame retardancy,thermal degradation and moisture resistance of epoxy resins

A novel phosphorus‐containing compound diphenyl‐(1, 2‐dicarboxylethyl)‐phosphine oxide defined as DPDCEPO was synthesized and used as a flame retardant curing agent for epoxy resins (EP). The chemical structure of the prepared DPDCEPO was well characterized by Fourier transform infrared spectroscopy, and ¹H, ¹³C and ³¹P nuclear magnetic resonance. The DPDCEPO was mixed with curing agent of phthalic anhydride (PA) with various weight ratios into epoxy resins to prepare flame retardant EP thermosets. The flame retardant properties, combustion behavior and thermal analysis of the EP thermosets were respectively investigated by limiting oxygen index (LOI), vertical burning tests (UL‐94), cone calorimeter measurement, dynamic mechanical thermal analysis and thermogravimetric analysis (TGA) tests. The surface morphologies and chemical compositions of the char residues for EP thermosets were respectively investigated by scanning electron microscopy and X‐ray photoelectron spectroscopy (XPS). The water resistant properties of the cured EP were evaluated by putting the samples into distilled water at 70°C for 168 hr. The results revealed that the EP/20 wt% DPDCEPO/80 wt% PA thermosets successfully passed UL‐94 V‐0 flammability rating and the LOI value was as high as 33.2%. The cone test results revealed that the incorporation of DPDCEPO effectively reduced the combustion parameters of the epoxy resin thermosets, such as heat release rate and total heat release. The dynamic mechanical thermal analysis test demonstrated that the glass transition temperature (Tg) decreased with the increase of DPDCEPO content. The TGA results indicated that the incorporation of DPDCEPO promoted the decomposition of epoxy resin matrix ahead of time and led to a higher char yield and thermal stability at high temperatures. The surface morphological structures and analysis of the XPS of the char residues of EP thermosets revealed that the introduction of DPDCEPO benefited the formation of a sufficient, compact and homogeneous char layer with rich flame retardant elements on the epoxy resin material surface during combustion. The mechanical properties and water resistance of the cured epoxy resins were also measured. After water resistance tests, the EP/20 wt% DPDCEPO/80 wt% PA thermosets retained excellent flame retardancy, and the moisture adsorption of the EP thermosets decreased with the increase of DPDCEPO content in EP thermosets because of the existence of the P–C bonds and the rigid aromatic hydrophobic structure in DPDCEPO. Copyright © 2015 John Wiley & Sons, Ltd.     

Hierarchical MoS2/polyaniline binary hybrids with high performance for improving fire safety of epoxy resin

Here we report a facile strategy to fabricate phosphoric acid doped polyaniline/molybdenum disulfide (PANI/MoS₂) hybrids as high-performance nanofillers in epoxy (EP) resin for the first time. In situ growth of PANI on the surface of two-dimensional MoS₂ template resulted in the uniform dispersion and strong interfacial adhesion of PANI/MoS₂ hybrids within EP matrix, which can be confirmed by the obvious increase (13.5°C) in glass transition temperature (T_g) of EP composites. The MoS₂ nanosheets also acted as a critical component to generate synergistic effect with PANI on reducing the fire hazards of EP resin. It resulted in a remarkable removal of flammable decomposed products and a considerable reduction of toxic CO yield. The dramatical decreases in real-time smoke density and total smoke production, and high-graphitized char layer in condensed phase were obtained for EP composite with 5 wt% PANI/MoS₂ hybrids. The multiple synergistic effects (synergistic dispersion and synergistic char formation) are believed to be the primary source for these obvious enhancements of properties of EP composites. This facile strategy may achieve the potential application of functionalized MoS₂ in polymeric nanocomposites.     

Effect of anion of polyoxometalate based organic–inorganic hybrid material on intumescent flame retardant polypropylene

In this work, 12‐tungestocobaltic acid based organic–inorganic hybrid material, [Bmim]₆CoW₁₂O₄₀ (CoW) was synthesized and applied as a synergist in polypropylene (PP)/intumescent flame retardant (IFR) composites. The flame retardant properties were investigated by the limiting oxygen index (LOI), UL‐94 vertical burning test, thermal gravimetric analyzer (TGA), cone calorimeter and scanning electron microscopy (SEM) etc. The results showed that the PP composites with 16 wt% IFR and 1 wt% CoW achieves the UL‐94 V‐0 rating and gets a LOI value 28.0. However, only add no less than 25 wt% single IFR, can the PP composites obtain the UL‐94 V‐0 rating, which suggests that CoW has good synergistic effects on flame retardancy of PP/IFR composites. In addition, the SEM and cone calorimeter tests indicated the CoW improves the quality of char layer. The rate of char formation has been enhanced also because of the existence of CoW. It is the combination of a better char quality and a high rate of char formation promoted by CoW that results in the excellent flame retardancy of PP/IFR composites. Copyright © 2016 John Wiley & Sons, Ltd.     

Phosphorylated cellulose/Fe3+ complex: A novel flame retardant for epoxy resins

A novel flame retardant containing cellulose, phosphorus and ferrum complex (Cell‐P‐Fe) was successfully synthesized and then it was used as flame retardants in epoxy resins (EP). Due to the present of acid sources and carbon sources, the Cell‐P‐Fe exhibits improved thermal stability and flame retardant properties. The EP/Cell‐P‐Fe composites with 10 wt% of Cell‐P‐Fe show remarkably improved LOI and UL‐94 values compared with the flame retardants without ferrum. At the loading of 10.0 wt% flame retardants, the char yield for EP/Cell‐P‐Fe composites increased to 29.1 wt%, indicating the improved thermal stability at high temperature. Moreover, thermogravimetric analysis, morphology of char residues and FTIR results demonstrate that stable char layers are formed on the surface of the composites during the combustion, attributing to the catalytic carbonization effect of Fe and phosphorus and the present of cellulose as carbon source. The stable char layers, which can protect the underlying materials from heat and oxygen, play an important role in the flame retardancy enhancement.     

Synergistic flame‐retardant effect of DOPO‐based derivative and organo‐montmorillonite on glass‐fiber‐reinforced polyamide 6 T

Herein, a bridged 9,10‐dihydro‐9‐oxa‐10‐phosphaphenanthrene‐10‐oxide (DOPO) derivative (PN‐DOPO) in combination with organ‐montmorillonite (OMMT) was used to improve the flame retardancy and mechanical properties of glass‐fiber‐reinforced polyamide 6 T (GFPA6T). The flame retardancy and thermal stabilities of the cured GFPA6T composites were investigated using limiting oxygen index, vertical burning (UL‐94) test, cone calorimeter test, and thermogravimetric analysis (TGA). The morphological analysis and chemical composition of the char residues after cone calorimeter tests were characterized via scanning electron microscopy and energy dispersive spectrometry. The results indicate that 2 wt% OMMT combined with 13 wt% PN‐DOPO in GFPA6T achieved a V‐0 rating in UL‐94 test. The peak heat release rate and total smoke release remarkably decreased with the incorporation of OMMT as compared to those of GFPA6T/15 wt% PN‐DOPO. The TGA results show that the thermal stability and residual mass of the samples effectively increased with the increase in OMMT content. The morphological analysis and composition structure of the residues demonstrate that a small amount of OMMT could help form a more thermally stable and compact char layer during combustion. Also, with the incorporation of OMMT, the layers consisted of more carbon‐silicon and aluminum phosphate char in the condensed phase. Furthermore, GFPA6T/PN‐DOPO/OMMT composites exhibited excellent mechanical properties in terms of flexural modulus, flexural strength, and impact strength than the GFPA6T/PN‐DOPO system. The combination of PN‐DOPO and OMMT has improved the flame retardancy and smoke suppression of GFPA6T without compromising the mechanical properties.     

Polyaniline‐coupled graphene/nickel hydroxide nanohybrids as flame retardant and smoke suppressant for epoxy composites

Graphene‐polyaniline/nickel hydroxide ternary hybrid (RGO‐PANI/Ni(OH)₂) was synthesized and incorporated into epoxy resin (EP) to improve the fire retardant property. Thermogravimetric analysis results showed that the RGO‐PANI/Ni(OH)₂ nanohybrid could catalyze the thermal degradation of epoxy matrix that was essential to trigger the char formation. The char yield of the RGO‐PANI/Ni(OH)₂/EP composite was improved compared with that of the samples with graphene and polyaniline only. With 3.0‐wt% RGO‐PANI/Ni(OH)₂, significant reduction in peak heat release rate (40%) and peak smoke production rate (36%) was observed in the cone calorimeter tests. Thermogravimetric analysis/infrared spectrometry (TG‐IR) results indicated that the flammable volatiles of the RGO‐PANI/Ni(OH)₂/EP composite was reduced compared with those of the EP and RGO‐PANI/EP. The superior flame retardant and smoke suppressant behaviors of the RGO‐PANI/Ni(OH)₂ nanohybrid over RGO‐PANI were attributed to the combination of good barrier effect of graphene with catalytic ability of char formation of PANI and metal hydroxide.     

Flame retardancy of epoxy resin nanocomposite with a novel polymeric nanoflame retardant

A wrapped nanoflame retardant, designated as polyhedral oligomeric silsesquioxane (POSS)‐poly(4‐bromostyrene) (PBS)‐carbon nanotubes (CNTs), was synthesized via π‐π stacking interactions between the walls of multiwalled carbon nanotubes and the silicon‐bromine containing hybrid copolymer (designated as POSS‐PBS) that was copolymerized by 4‐bromostyrene and acryloyloxyisobutyl polyhedral oligomeric silsesquioxane. The POSS‐PBS‐CNTs exhibited good dispersibility in epoxy resin (EP) without obvious aggregation. Furthermore, the fire behaviors of this flame‐retardant EP (FR‐EP) nanocomposites were examined via limited oxygen index (LOI) and cone calorimeter (CONE) tests. The FR‐EP had an ideal LOI value of 35.3% and its residual char yield obtained from CONE test was significantly enhanced from 5.9% to 15.3% with the incorporation of 4 wt% POSS‐PBS‐CNTs and 1.33 wt% Sb₂O₃ into EP matrix. Additionally, the addition of 4 wt% POSS‐PBS‐CNTs or POSS‐PBS can efficiently decrease the peak heat release rate (PHRR) of EP matrix by 41.0% or 45.6%, respectively.