Synergistic Flame Retardant Effect Research Articles

A novel strategy utilizing oxidation states of phosphorus for designing efficient phosphorus-containing flame retardants and its performance in epoxy resins

The oxidation state of phosphorus has a great influence on the flame retardant action of its flame retardants. In this study, a reactive phosphorus-containing flame retardant (POG-DOPO) with both low and high phosphorus oxidation states is synthesised and incorporated into epoxy resin. The results show that the part in high oxidation state act mainly in the condensed phase and the part in low oxidation state act mainly in the gas phase. Furthermore, the flame retardant exhibits a synergistic flame retardant effect, resulting in a higher flame retardant efficiency than that of flame retardants with a single phosphorus oxidation state. Compared with unmodified epoxy resin, the peak heat release rate, total heat release rate and total smoke release of POG-DOPO modified epoxy resin with only 3wt% phosphorus are reduced by 70.9%, 51.2% and 55.7%, respectively. Its LOI increases to 31.8% and vertical combustion test achieves UL-94 V-0 rating. This study provides a strategy for the structural design of efficient phosphorus-based flame retardants.

Advanced flame-retardant melamine foam with ultra-sensitivity and prolonged fire warning, featuring smart device-integrated graphene oxide/attapulgite nano-coating

Enhancing flame retardancy and fire-warning capabilities of thermal insulation materials used in building external walls is crucial for ensuring fire safety as well as guarding people's lives and assets. Herein, we have developed an environmentally friendly nano-coating that possesses flame-retardant and early-warning properties by integrating graphene oxide (GO) and attapulgite (ATP) onto melamine foam (MF) through a layer-by-layer self-assembly method (LBL). The GO-ATP-MF composite demonstrates a rapid response to flame (<1 s) due to GO's thermally induced reduction. Additionally, ATP's synergistic flame-retardant effects on both gas and condensed phases contribute to outstanding flame retardancy, enabling an enduring fire alarm duration (>1330 s). The warning duration time of this composite surpasses the majority of GO-based fire-warning nano-coatings reported to date. Moreover, incorporating a Bluetooth wireless transmission system facilitates real-time fire information sharing among smart devices, thereby optimizing fire signal transmission efficiency. Thus, this study advances GO-based flame-retardant nano-coatings and devices with high sensitivity and prolonged fire-warning capabilities, providing an innovative idea to enhance the fire safety of MF as a thermal insulation material.

Engineering sulfonated carbon black for flame-retardant and smoke-suppressive polycarbonate with well-preserved mechanical performances

To cope with the practical demands of high-performance polycarbonate (PC) and explore the application of carbon black (CB) in flame retardant field, a sulfonated carbon black (CB-SS) was synthesized and applied to flame retardant PC in this work. Compared with PC/CB composite, PC/CB-SS composite displays better overall performances under the same flame retardant addition. The PC/3CB-SS composite with 3 wt.% of CB-SS achieves a vertical burning test (UL-94) V-0 rating with a limiting oxygen index (LOI) of 29.5%, and its peak heat release rate (PHRR) and total smoke release rate (TSR) are respectively reduced by 17% and 6% relative to those of PC/3CB with 3 wt.% of CB. The flame retardancy mechanism is proposed by analyzing the char residue obtained from cone calorimetry test, which confirms the synergistic flame-retardant effect between sodium sulfonate and CB in condensed phase. Moreover, PC/3CB-SS shows much better mechanical properties than PC/3CB, and its elongation at break is increased by 223% compared with that of PC/3CB. This is mainly due to the more even dispersion of CB-SS within PC and the stronger interfacial force between CB-SS and PC. This work provides an effective approach for the creation of fire-retardant and smoke-suppressive PC composites with well-preserved mechanical properties, contributing to expanding the industrial applications of PC.

MoS2@Fe3O4 prepared by γ-ray in situ reduction for enhancing the fire safety and mechanical properties of EVA/MCA composites

The high flammability of ethylene vinyl acetate copolymers (EVA) limits its important applications in fire safety, and the addition of highly effective flame retardants can improve this deficiency. Melamine cyanurate (MCA) has limited carbon-forming ability and therefore is often combined with other flame retardants to achieve synergistic flame retardant effects and thus improve the flame retardancy of EVA. Therefore, in this study, MoS2@Fe3O4 hybrid materials were synthesized by in-situ growth of molybdenum disulfide (MoS2) and ferric oxide (Fe3O4) and their structures were characterized using various techniques. The hybrids were blended with melamine cyanurate (MCA) into ethylene vinyl acetate copolymer (EVA) by melt blending method to reduce the fire hazard. The EVA composites with 1.0 wt% MoS2@Fe3O4 blends significantly improved the coke residue and limiting oxygen index values to 22.5 % and 23.2 %, while their peak heat release rate, total heat release, and total smoke release were reduced by 62.5 %, 11.7 %, and 35.3 %, respectively, as compared to pure EVA. The results suggest that the use of MoS2@Fe3O4 hybrids in combination with MCA is a promising strategy for the development of advanced flame-retardant materials.

Progress in Application of Silane Coupling Agent for Clay Modification to Flame Retardant Polymer.

Polymer composites are widely used in various fields of production and life, and the study of preparing environmentally friendly and flame retardant clay/polymer composites has gradually become a global research hotspot. But how to efficiently surface modify clay and apply it to the field of flame retardant polymers is still a potential challenge. One of the most commonly used surface modification methods is the modification of clay with silane coupling agents. The hydrolysable groups of the silane coupling agent first hydrolyze to generate hydroxyl groups. These hydroxyl groups then undergo a condensation reaction with the hydroxyl groups on the surface of the clay, allowing for organic functional groups to be grafted onto the clay surface. The organic functional groups and polymer matrix react to generate chemical bonds so that the composite material's interface is more closely combined. Thus, the dispersion of clay in the organic polymer material and the compatibility of the two is better, which improves the flame retardant effect of the composite material. This paper introduces the classification of a silane coupling agent and the mechanism and process of silane coupling agent-modified clay, outlines the mechanism of silane coupling agent-modified clay flame retardant polymers, reviews the research results on flame retardant polymers of various clays after surface treatment with silane coupling agents in recent years, and highlights the synergistic flame retardant effect of clay and flame retardant organized by silane coupling agents. Finally, it is found that the current research in the field of silane coupling agent-modified clay in flame retardants is focused on the modification of montmorillonite, sepiolite, attapulgite, and kaolinite by KH-550, KH-560, and KH-570, and the development trends in this field are also prospected.

Effect of different IFS (MWCNTs, BN, and ZnO) on flame retardant, thermal and mechanical properties of PA6/aluminum diisobutyl phosphinate composites

AbstractIn this paper, the effects of the synergistic flame retardation of aluminum diisobutyl phosphinate acid (APBA) with three inorganic fillers of different dimensions (multi‐walled carbon nanotubes [MWCNTs] [1‐dimensional], hexagonal boron nitride [BN] [2‐dimensional], and zinc oxide [ZnO] [3‐dimensional]), respectively, on the properties of nylon 6 (polyamide 6 [PA6]) materials were investigated. It was shown that under the same additive amount, with the increase of spatial dimension of inorganic fillers, the thermal stability and residual carbon capacity were improved. Which would catalyze the formation of more and denser carbon layers in the matrix material, effectively blocked the transfer of oxygen and heat, enhanced the cohesive‐phase flame retardancy of synergistic flame‐retardant PA6 composites, and exerted a better synergistic flame‐retardant effect with APBA. So that the flame‐retardant properties of PA6 composites were gradually improved, and the mechanical properties were also gradually increased. The comprehensive performance of three types of inorganic fillers gradually improves in the order of MWCNTs &lt; BN &lt; ZnO. When the addition amount of ZnO was 2 wt%, the vertical combustion grade (UL‐94) of PA6 composite was V‐0, and the limiting oxygen index (LOI) was as high as 36.5%. The tensile strain increased by 19.11% and impact strength increased by 20.26% compared with PA6, and PA6/APBA‐Zn can be used as a flame retardant PA6 composite material with balanced overall performance.Highlights Diisobutylaluminium hypophosphite and inorganic fillers have efficient synergistic flame retardant effects in PA6. With the increase of spatial dimension of inorganic fillers, the better the synergistic flame retardant effect in PA6. The flame retardant can degrade to release the phosphorous free radicals. Inorganic fillers can cross‐link with the PA6 substrate and promote the charring.

Effect of Organic–Inorganic Mixed Intumescent Flame Retardants on Fire-Retardant Coatings

Expandable graphite (EG) was modified with a charring agent and organic–inorganic hybridized intumescent flame retardants (MEG) were synthesized. This study uses a cone calorimeter (CCT) and a DaqPRO 5300 radiation heat flow meter (Fourtec, Tel Aviv, Israel) to evaluate the fire-resistant properties influenced by MEG on intumescent fire-retardant coatings. The impact of MEG on the thermal degradation of these coatings was investigated through the use of thermogravimetric analysis (TGA). The results obtained by CCT demonstrated that the incorporation of MEG markedly diminished the heat release rate and total heat release rate of the coating, in addition to enhancing the char residue compared to coatings with only expandable graphite (EG). Furthermore, TGA results demonstrate that adding MEG increases the weight of the char residue at elevated temperatures, suggesting improved thermal stability. Based on these findings, MEG exhibits a synergistic flame-retardant effect when combined with intumescent fire-retardant (IFR) systems. This synergy not only improves the flame-retardant properties of the coatings but also enhances their overall thermal stability, making MEG a promising additive for developing more efficient fire-retardant materials. Thus, MEG-modified coatings offer superior protection against fire hazards, highlighting their potential for practical applications in fire safety.

Alkoxysilyl derivative of carbamoylphosphonate as a flame retardant modifier of cotton fabrics

This research describes the synthesis of a silane derivative containing phosphorus and nitrogen atoms, leveraging their synergistic flame retardant effect through the incorporation of a PH bond to the isocyanate moiety. The synthesized silane featured alkoxysilyl groups, facilitating permanent bonds with the cotton fabric surface via hydrolysis. Cotton fabrics were modified using silane solutions of varying concentrations (2.5 %, 5 %, and 10 %) through a dip-coating process to determine the effect of the modifier amount on fabric properties. The modified fabrics were subjected to FT-IR, TGA, SEM, and EDS analyses, as well as microcalorimetric and LOI tests, to assess changes in flammability. FT-IR, SEM/EDS, and add-on analyses confirmed effective coverage of the cotton fabric with the flame retardant. Thermogravimetric tests indicated a significant reduction in the mass loss rate during thermal degradation. LOI analyses demonstrated a decrease in flammability (increase in LOI value), while microcalorimetric tests showed a substantial decrease in the heat release rate, correlating with increased modifier concentration on the fabric surface. Post-washing analyses revealed that, although some of the modifier was washed out, the samples still retained reduced flammability.

A bio‐based reactive P/N synergistic flame retardant for improving the fire safety and mechanical properties of epoxy resin

AbstractA high‐efficiency bio‐based P/N synergistic flame retardant (PVFD) is synthesized by combining furfurylamine and vanillin. The compound incorporates two different valence states of phosphorus as flame retardant structures, namely phenylphosphoryl dichloride (PPDC) and 9,10‐dihydro‐9‐oxa‐10‐ phosphophenyl‐10‐oxide (DOPO). PVFD and epoxy resin (EP) can cure into a cross‐linked network, thus not only improving the mechanical properties of EP but also achieving P/N synergistic flame retardant effects. Experimental results demonstrate that EP/PVFD‐5 obtained by adding 5 wt% of PVFD to EP passes the UL‐94 test and achieves V‐0 grade, whose limiting oxygen index (LOI) is up to 38.0%. EP/PVFD‐5 exhibits a decrease of 10.14% in peak heat release rate (PHRR), 16.90% in total heat release (THR), and 10.0% in total smoke release (TSP), while the residual carbon content increases by 8.5%. Additionally, the bending strength, bending modulus, tensile strength, and elongation at break of EP/PVFD‐5 increase by 3.9%, 4.9%, 45.1%, and 26.3%, respectively.Highlights The bio‐based raw materials we used are eco‐friendly and readily available. PVFD, an efficient P‐N synergistic compound, was synthesized. PVFD promotes the char formation of EP and dilutes the O2 concentration. PVFD does not cause the degradation of mechanical properties of EP.

Phosphonitrile hybrid metal-polyphenol network: An effective strategy for developing functional PVA composites with flame retardancy, antibacterial and UV resistance

The white pollution caused by non-degradable plastics poses a serious threat to human society and the environment, thus developing biodegradable material is urgent. In this work, a novel phosphonitrile hybrid metal-polyphenol network was constructed and used for the preparation of flame retardant, UV resistant and antibacterial multifunctional polyvinyl alcohol composite (PVA@HCPD-Ag). The limiting oxygen index (LOI) value of PVA@HCPD-Ag was improved to 33.5%, while the peak heat release rate (PHRR) and total heat release (THR) decreased by 35.62% and 47.76%. Besides, the ultraviolet protection factor (UPF) value of PVA@HCPD-Ag was significantly improved from 4.63 of the original PVA to 482.79, while the tensile strength was increased by 10.23%. Furthermore, the inhibition efficacy of PVA@HCPD-Ag for E. coli and S. aureus was up to 98.12% and 99.99%. This work explored the synergistic flame retardant effect of in-situ reduced Ag0 and phosphonitrile crosslinked polyphenol network and proposed an advanced strategy for developing high value-added functionalized PVA materials.

Elemental synergy flame retardant effect of Schiff base derivatives with similar chemical structure in TPU

To investigate the synergistic flame retardant effect of various elements, three flame retardants (SMAE, SDPS, SDPB) with similar chemical structure and containing different flame retardant elements were designed, synthesized, and applied to TPU. The test results showed that SMAE had a phosphorus-nitrogen synergistic effect and primarily exerted its flame retardant effect in the gaseous phase. The limiting oxygen index value of the TPU/4SMAE reached 32 % and passed UL 94 V-0 rating test. SDPB was obtained by introducing the boron, which further enhanced the flame retardant effect in the gaseous phase. The thermogravimetric combined with Fourier transform infrared spectroscopy results showed that TPU/4SDPB had the lowest intensity of gaseous phase products. With only 2 wt% SDPB, TPU can pass UL 94 V-0 test. Therefore, it also demonstrated that there was a good synergy between boron and phosphorus and nitrogen. SDPS was obtained by introducing the silicon, which can exert the flame retardant effect in the condensed phase. Scanning electron microscopy results showed that char layer of TPU/SDPS was the densest and silicon was retained as Si-O and Si-C in the char layer. However, the gaseous phase flame retardant effect of SDPS was restrained, and TPU/4SDPS only passes the V-2 rating. Hence, this work provided the direction of Schiff base derivatives flame retardants structure design in TPU.

Influence of phosphomolybdate modified with quaternary ammonium salts on enhancing the flame retardancy and antibacterial characteristics of epoxy resin/aluminum diethylphosphinate composites

In this work, we synthesized a series of compounds, denoted as xCTAB@AMP, by incorporating varying different molar fractions of cetyltrimethylammonium bromide (CTAB) into ammonium phosphomolybdate (AMP). The effects of CTAB modification on the surface characteristics, morphology and hygroscopicity of AMP were studied. Moreover, we explored the combined flame-retardant impact between xCTAB@AMP and aluminum diethylphosphinate (ADP) when incorporated into epoxy resin (EP), as well as the resulting composite's mechanical properties, thermal stability and antibacterial properties. The EP composite containing 50 molar percent CTAB-modified AMP (EP/50CTAB@AMP/ADP) demonstrated remarkable flame retardancy, achieving a UL-94 V-0 rating and increasing limiting oxygen index (LOI) to 30.0%. This formulation significantly lowered the peak heat release rate (PHRR) to 452 kW/m2, a 65% reduction to that of EP, and the total heat release (THR) to 68 MJ/m2, a 24% decrease to that of EP. Additionally, compared to EP, the peak smoke production rate (PSPR) of this composite was decreased by 30% (0.28 m2/s), the total smoke production (TSP) was reduced by 25% (30.2 m2), and peak carbon monoxide release rate (PCOP) was diminished by 34% (0.038 g/s). The combination of 50CTAB@AMP and ADP in the EP matrix exhibited an exceptional synergistic flame-retardant effect. Concurrently, the CTAB modification bolstered the interfacial interactions between AMP and the EP matrix, which enhanced the mechanical properties of EP/AMP/ADP composites. As a result, the tensile strength and elongation at break of the EP/50CTAB@AMP/ADP composite increased by 13% and 15%, respectively, compared to the EP/AMP/ADP. Moreover, the 50CTAB@AMP maintained its inherent antibacterial activity, which endowed the EP/50CTAB@AMP/ADP composite with a potent inhibitory effect against Staphylococcus aureus, a common pathogenic bacterium.

Half etching of ZIF-67 towards open hollow nanostructure with boosted absorption ability for toxic smoke and fume in epoxy composites

Metal-organic frameworks (MOFs) are favored in the field of flame retardancy due to the catalytic effect of metal nodes on char layer formation and the synergistic flame-retardant effect of organic ligands containing elements such as nitrogen and phosphorus. However, the inherent microporosity of MOFs limits their adsorption efficiency for toxic smoke and flammable gases. In this work, an organic phosphorus-modified MOF with a distinctive nanostructure of hierarchically porous (P-Co-MOF/ZIF) was successfully synthesized. In brief, an amino-functionalized zeolitic imidazolate framework (NH2-ZIF) was initially synthesized through a ligand substitution reaction with ZIF-67. Subsequently, organic phosphorus flame retardants were grafted on NH2-ZIF, and the acidic substances generated during this process were used to synchronously half etch ZIF, resulting in a ZIF with a high specific surface area and unique nanostructure. Through this simple synthetic method, the catalytic ability of transition metals in ZIF is preserved, and organic phosphorus flame retardants are incorporated into ZIF, resulting in the synergistic flame-retardant effect of phosphorus and nitrogen. Additionally, its unique hierarchically porous nanostructure can effectively enhance the adsorption of volatile products during the combustion process, thereby offering outstanding flame retardancy and smoke suppression effects for epoxy resin (EP). The results indicate that adding 2 wt% P-Co-MOF/ZIF to EP can increase the limiting oxygen index value to 29.5%. Furthermore, the peak of heat release rate, total heat release, and total smoke production of the composite material can decrease by 43.3%, 37.9%, and 38.1%, respectively, compared to EP. Therefore, this work will provide new inspiration for designing functional nanostructures and synthesizing efficient flame retardants.

Flame-retardant shape-stabilized phase change composites with superior solar-to-thermal conversion

Building thermal management is responsible for over 40 % of total energy use, of which about 20 % is directly related to the operation of heating. Materials saving energy to heat buildings would contribute substantially to sustainability. In this study, we have developed a series of flame-retardant shape-stabilized phase change composites (PCCs) by incorporating MXene@PTA and flame-retardant phytic acid dicyandiamide (PD) into a waterborne polyurethane framework using a simple vacuum impregnation technique, and their thermophysical properties, photothermal conversion, and flammable retardant performance were systematically studied. It was found that the resulting composite, termed PMWP PCCs, achieved an enthalpy efficiency and relative enthalpy efficiency of 68.66 % and 99.7 %, respectively. And it maintained excellent shape stability even after 180min at 70 °C, which demonstrates effective inhibition of leakage of phase change material. Furthermore, the maximum temperature of PCCs without modified MXene was observed to be around 37 °C, which rose to more than 45 °C after adding modified MXene, indicating higher photothermal conversion performance. Most importantly, compared to pure PEG, the peak heat release rate and total heat release value of the modified phase change composites were found to be reduced by 6.7–35.8 % and 13.2–19 %, respectively. The results suggest that the combination of MXene and PD exhibits a synergistic flame retardant effect, enhancing the flame retardancy. These outcomes underscore the promising application potential of PMWP PCCs in the fields of thermal management and energy storage.

Surface thermal-curing phosphorus-containing coated rigid polyurethane foam with highly-efficient flame retardancy and reinforced mechanical property

A phosphorous-containing HEMAP–co–GMA (HPG) prepolymer was successfully prepared by the ring-opening reaction of glycidyl methacrylate (GMA) and 2–hydroxyethyl methacrylate phosphate (HEMAP) as monomers, and flame retardant HEMAP–GMA copolymer (HPG) coating on the surface of rigid polyurethane foam (RPUF) was further fabricated by free-radical thermal-curing. The HPG coating endowed RPUF excellent flame retardancy and fire hazardous safety. The HPG coated on RPUF (HPG/RPUF) reached UL94 V–0 rating, and the limited oxygen index value of the HPG-2/RPUF improved from 19.0 % of RPUF to 27.8 %. The cone calorimetric test results showed that the total heat release and mean peak heat release rate values of the HPG-2/RPUF reduced by 79.6 % and 54.6 % compared to those of RPUF, respectively. The flame–retardant mechanism of HPG/RPUG was speculated the synergistic flame retardant effect between the barrier of the dense char layer and the inhibition of phosphorus–containing free–radicals. The three–dimensional crosslinked HPG coating not only provided HPG/RPUF excellent water resistance, but also enhanced compressive properties and heat–insulation. The highly efficient flame–retardant HPG coating has great potential in fire protection of the heat insulation foams.

Flame retardant, toughened, reinforced, transparent and long shelf-life one-component epoxy resins via a P/N/Si-containing hyperbranched polymer

One-component epoxy resins (OCEPs) cured from latent imidazole-based curing agents that exhibit high toughness, high strength, high fire safety, long shelf life, low dielectric properties and transparency are eagerly awaited in advanced manufacturing. However, existing research on latent imidazole-based curing agents/OCEPs mainly focuses on simultaneously improving their flame retardancy and shelf life, but neglects their poor toughness, strength and dielectric properties, and often compromises their transparency. Herein, a hyperbranched polymer (Si-DP) containing P/N/Si was fabricated to further improve the flame retardancy, toughness, strength and dielectric properties of EP10 (the transparent OCEPs comprising the latent imidazole-based curing agent PHI-HPP). EP10 containing Si-DP (EP10/Si-DP) boasted a shelf life longer than 81 days. The synergistic flame-retardant effect of P, N and Si elements enabled EP10/Si-DP3 to achieve a UL-94 V-0 rating with a limiting oxygen index of 33.9 %, the peak heat release rate and total smoke production of EP10/Si-DP5 were reduced by 44.4 % and 25.5 %, respectively, compared with EP10. The increased free volume and Si-O flexible bonds resulted in a 261.1 % higher impact strength of EP10/Si-DP5 than EP10. The excellent interfacial bonding of Si-DP with epoxy resins and the increased rigidity groups led to 74.0 % and 60.7 % higher tensile and flexural strengths of EP10/Si-DP5 than EP10, respectively. The intramolecular cavities and the low-polar Si-C bonds of Si-DP reduced the dielectric constant and dielectric loss of EP10/Si-DP. Meanwhile, EP10/Si-DP maintained inherent excellent transparency and high glass transition temperature (Tg). Carbon fiber epoxy composites prepared from EP10/Si-DP5 exhibited remarkable improvement in flame retardancy, smoke suppression as well as mechanical and interfacial performances. Overall, this research proposes an effective approach for preparing long shelf-life OCEPs with excellent overall performance.

Linear polyborosiloxane for improving the flame-retardancy of cyanate ester resin

The increasing demands for electronic packing materials necessitate stringent criteria for the overall properties of cyanate ester (CE) resins. In this work, a novel linear polyborosiloxane with a distinctive organic-inorganic hybrid Si–O–B backbone, featuring functional epoxy and phenyl groups (denoted as LPSi-B), was synthesized via a solvent- and catalyst-free one-pot polycondensation. Subsequently, the synthesized LPSi-B was co-crosslinked within the bisphenol A dicyanate ester (BADCy) thermoset network. The presence of abundant active epoxy groups in LPSi-B facilitated its involvement in the cyanate curing reaction, demonstrating excellent compatibility within the resin matrix. The resulting LPSi-B/BADCy composite not only exhibits outstanding mechanical properties but also demonstrates notable flame-retardant and dielectric characteristics. Specifically, the hybrid nature of LPSi-B, combining the flexibility of Si–O–B chains with the rigidity of side-chain phenyl groups, fosters intermolecular non-covalent π-π interactions directly linked to boron atoms, thus mitigating network polarization. Furthermore, the synergistic flame-retardant effect arising from boron and silicon components was harnessed to achieve halogen-free, phosphorus-free, and environmentally friendly fire safety outcomes. This innovative design ensures exceptional compatibility and interface bonding between LPSi-B and the polymer matrix, thereby endowing cyanate ester resin with superior comprehensive performance suitable for advanced applications in wave-transparent and electronic packing materials.

Real-time monitoring of charcoal layer resistance for investigating the synergistic flame retardant mechanism of zinc oxide and intumescent flame retardants in SBS

Metal oxides as synergists of intumescent flame retardant (IFR) lead to an extremely complex formation process of intumescent char layers. The lack of means to detect the evolution of the char layer in real time makes it challenging to investigate the synergistic flame retardant mechanism between metal oxides and IFR. Herein, an innovative method of detecting real-time changes in the resistance of the char layer under flame ablation is used to investigate its changes in morphology, thus assisting in revealing the synergistic flame retardant mechanism of zinc oxide (ZnO) in IFR/SBS. ZnO showed a significant synergistic flame retardant effect with IFR without MEL and no synergistic effect with MEL-containing IFR. The analysis of the char layer structure revealed that ZnO played a role in promoting gas release and char layer formation and increasing the viscosity of the molten char layer regardless of the presence or absence of MEL.The difference in the morphology of the char layer could not reveal the experimental phenomenon that there is no synergistic flame retardant effect between ZnO and MEL-containing IFR. The analysis of the real-time resistance of the charcoal layer reveals that ZnO achieves its synergistic flame retardation with the MEL-free IFR by increasing the expansion of the charcoal layer at the initial stage of its formation. For MEL-containing IFR, 0.5% ZnO inhibits the rupture of the char layer by promoting its formation in the early stages of ablation, and 1% ZnO leads to the rupture of the char layer instead, due to the promotion of gas release. Excess ZnO (2%) caused pyrolysis gases to escape from the voids of the char layer rather than allowing it to expand. The analysis of the real-time resistance of the charcoal layer can help to accurately reveal the flame retardant mechanism.

A functional phosphorus/nitrogen‐containing compound for endowing epoxy resin simultaneously with better fire safety, comparable transparency and improved toughness

AbstractCurrently, the flame retardancy of epoxy resin (EP) was achieved at the expenses of the transparency and/or toughness. In the present work, a phosphorus/nitrogen‐containing compound (FDNP) was synthesized by one‐pot method using 9,10‐dihydro‐9‐oxa‐10‐phospha‐phenanthrene‐10‐oxide, furfural and N‐phenyl‐p‐phenylenediamine as raw materials, and further adopted as a functional agent for epoxy resin. The results demonstrated that the FDNP remarkably improved the fire safety of EP. The incorporation of 4 wt% FDNP enabled EP to pass UL‐94 V‐0 rating test and achieve a limiting oxygen index value of 35.5%; meanwhile, the peak heat release rate, total heat release rate and total smoke release were significantly reduced by 41.3%, 41.6% and 72.5% as compared with the pure EP, respectively. What is more, the EP/4 wt% FDNP composite kept almost the same transparency of the pure EP, simultaneously its impact strength was more than doubled as that of the pure EP. Herein, the improved flame retardancy is contributed to a synergistic biphasic flame retardant effect including the formation of a compact protective carbon layer and the release of both non‐combustible gases and phosphorus‐containing radicals.

Characterization and Flame-Retardant Properties of Cobalt-Coordinated Cyclic Phosphonitrile in Thermoplastic Polyurethane Composites.

Halogen-free organophosphorus flame retardants have promising application prospects due to their excellent safety and environmental protection properties. A cobalt-coordinated cyclic phosphonitrile flame retardant (Co@CPA) was synthesized via a hydrothermal method using hexachlorocyclotriphosphonitrile (HCCP), 5-amino-tetrazolium (5-AT), and cobalt nitrate hexahydrate (Co(NO3)2∙6H2O) as starting materials. The structure was characterized using Fourier transform infrared (FTIR), nuclear magnetic resonance spectroscopy (1H-NMR), scanning electron microscopy (SEM), and thermogravimetric analysis (TGA). Thermoplastic polyurethane (TPU) composites were prepared by incorporating 10-(2,5-dihydroxyphenyl)-9,10-dihydro-9-oxa-10-phosphame-10-oxide (ODOPB), Co@CPA, and silicon dioxide (SiO2) via melt blending. The flame-retardant performance and thermal stability of the TPU composites were evaluated through limiting oxygen index (LOI), vertical combustion (UL-94), TG, and cone calorimetric (CCT) tests. SEM and Raman spectroscopy were used to analyze the surface morphology and structure of the residual carbon. A synergistic flame-retardant effect of ODOPB and Co@CPA was observed, with the most effective flame retardancy achieved at a TPU:ODOPB:Co@CPA:SiO2 ratio of 75:16:8:1. This composition exhibited an LOI value of 26.5% and achieved a V-0 rating in the UL-94 test. Furthermore, compared to pure TPU, the composite showed reductions in total heat release, CO production, and CO2 production by 6.6%, 39.4%, and 48.9%, respectively. Our research findings suggest that Co@CPA demonstrates outstanding performance, with potential for further expansion in application areas. Different metal-based cyclic phosphonitrile compounds are significant in enriching phosphorus-based fine chemicals.