Condensed Phase Flame Retardant Research Articles

A polysulfides adsorption strategy through cation-anion interactions for achieving high-safety lithium-sulfur batteries in multiple scenarios

The widespread application of lithium-sulfur batteries (LSBs) is hindered by challenges such as the shuttle effect of polysulfides (LiPSs), slow reaction kinetics, and fire safety concerns. In this study, surface-functionalized boron nitride nanosheets (ChBN) are prepared and employed as functional separator coatings, enabling multiple application scenarios of LSBs. Specifically, a creative strategy of cation-anion interactions is constructed through the strong chemisorption of N+ on the ChBN surface to Sn- in LiPSs. In addition, the boron nitride and N+ showed synergistic effects on adsorption-catalysis, further facilitating the rapid and sufficient deposition of Li2S. The prepared LSBs with ChBN + SP/PP separators exhibit excellent cycle stability (an ultralow capacity degradation of 0.034 % per cycle over 500 cycles at 2C). These LSBs are available over a wide temperature range of −20 to 60 °C, offering a capacity of 1208 mA h/g at 60 °C and 919 mA h/g at −20 °C. Furthermore, the presence of ChBN effectively improves the fire-safety of pouch batteries through the condensed-phase flame retardant mechanism. This simple fabrication process of ChBN is effective and favorable for large-scale manufacturing, which provides a feasible method for the development of high-safety LSBs.

A high-efficiency and durable flame retardant for cotton fabrics: Ammonium ethyl acryloylphosphoramidate

The ammonium ethyl acryloylphosphoramidate (AEA) was synthesized by acrylamide, ethanolamine, and phosphorus oxychloride; the nuclear magnetic resonance (NMR) and Fourier transform infrared spectroscopy (FTIR) were applied to analyze the structure of AEA molecule. Using the dip-cure process to treat raw cotton (RC) with AEA flame retardant, the finished fabric had excellent flame retardancy. The cone calorimeter, thermogravimetric, FTIR, and vertical flame tests illustrated finished fabrics underwent synergistic and condensed-phase flame retardation. The finished fabric also had excellent durability, and the higher the sealing degree of phosphorus atoms, the higher the durability. The limiting oxygen index (LOI) of RC-AEA3-20 (raw cotton finished with 20 wt% AEA3) reached 45.4 %. However, the LOI only dropped to 34.9 % after 50 laundering cycles under the AATCC 61–2013 3 A standard. The excellent durability and FTIR analyses of finished fabrics suggested that the –N–P(=O)–O–C– covalent bond was formed between flame retardant and cellulose. This covalent bond exhibited a p–π conjugation effect, enhancing the stability of –N–P(=O)–O–C– bond, improving the durability of finished fabrics. In conclusion, adding reactive groups into flame retardants, like CH2=CH– and –N–P(=O)–O−NH4+, could increase the durability of finished cotton fabrics.

Self-crosslinking phosphorus-containing durable flame retardants for cotton fabrics

The phosphorus-containing flame retardant that can enter the interior of cotton fiber and has self-crosslinking ability was designed and synthesized. The flame retardant contains two components, 2-(1-(dimethoxy phosphoryl)-2,5, 8-Triazectridecyl) phosphonate starch (PTPS) and 4-(hydroxymethyl)-10-((3-((5-(hydroxymethyl)-10-((3-((tris(hydroxymethyl)phosphonio)methyl)ureido)methyl)-2,6,8,12,14,18-hexaaza-4,10,16-Triphosphanonadecane (BPTP). The structure of PTPS and BPTP were detected by NMR and FTIR, and the results showed that the synthesis of PTPS and BPTP was successful. During the treatment, cellulose was first endowed with -NH groups. Then PTPS molecule and BPTP molecule were grafted onto cellulose through the reaction of P-CH2OH groups and -NH groups. After 50 laundering cycles (NFPA2112–2012 standard), the limiting oxygen indexes (LOIs) of the fabrics treated with 35 wt% CFN-PB and 30 wt% CFN-PB were 28.80% and 27.30%, respectively, and passed the vertical flame test (VFT). Compared with the raw cotton, the peak heat release rate (PHRR), the total heat rate (THR) and the flame growth rate (FGR) of the CNF-PB treatment fabric were reduced by 62.90 %, 29.43 % and 62.91 % respectively. These indicate that the flame retardant PB could be firmly fixed on the fibers and show good flame retardancy durability. In the VFT, and cone calorimetry test, the CFN-PB treated fabric showed the condensed phase flame retardant mechanism.

Enhanced Fire Safety of Energy-Saving Foam by Self-Cleavage CO2 Pre-Combustion and Phosphorus Release Post-Combustion.

Rigid polyurethane foam (RPUF) is widely utilized in construction and rail transportation due to its lightweight properties and low thermal conductivity, contributing to energy conservation and emission reduction. However, the inherent flammability of RPUF presents significant challenges. Delaying the time to ignition and preventing flame spread post-combustion is crucial for ensuring sufficient evacuation time in the event of a fire. Based on this principle, this study explores the efficacy of using potassium salts as a catalyst to promote the self-cleavage of RPUF, generating substantial amounts of CO2, thereby reducing the local oxygen concentration and delaying ignition. Additionally, the inclusion of a reactive flame retardant (DFD) facilitates the release of phosphorus-oxygen free radicals during combustion, disrupting the combustion chain reaction and thus mitigating flame propagation. Moreover, potassium salt-induced catalytic carbonization and phosphorus derivative cross-linking enhance the condensed phase flame retardancy. Consequently, the combined application of potassium salts and DFD increases the limiting oxygen index (LOI) and reduces both peak heat release rate (PHRR) and total heat release (THR). Importantly, the incorporation of these additives does not compromise the compressive strength or thermal insulation performance of RPUF. This integrated approach offers a new and effective strategy for the development of flame retardant RPUF.

Fabrication of nickel phytate modified bio-based polyol rigid polyurethane foam with enhanced compression-resistant and improved flame-retardant

A bio-based flame retardant nickel phytate (PA-Ni) was synthesized and combined with soybean oil-based polyol (SO) to create a green rigid polyurethane foam (RPUF) with enhanced compressive strength, good thermal stability and flame retardant. The results showed that the RPUF-SO2/Ni3 with 3 wt% PA-Ni had the highest initial and termination temperature, maximum thermal decomposition rate temperature and carbon residue, and better thermal stability. Its limiting oxygen index was increased by 2.6% compared with RPUF-SO2 without PA-Ni added, and the peak heat release rate (PHRR) and total heat release rate (THR) were reduced by 14.92% and 19.92%, respectively. In addition, RPUF-SO2/Ni3 had the lowest Ds under the conditions of flame (18.90) and flameless (22.41), and had the best smoke suppression effect. And the compressive strength of RPUF-SO/Ni3 was significantly enhanced by the addition of PA-Ni. The results show that the improvement of flame retardancy of RPUF is mainly the result of the combined effect of gas-phase and condensed-phase flame retardancy, among which the flame retardancy of RPUF-SO/Ni3 was the best. The current findings offer a practical way to produce green and low-carbon RPUF as well as promising prospects for the material's safe application.

Microcapsule Modification Strategy Empowering Separator Multifunctionality to Enhance Safety of Lithium-Metal Batteries.

The uncontrollable growth of lithium dendrites and the flammability of electrolytes are the direct impediments to the commercial application of high-energy-density lithium metal batteries (LMBs). Herein, this study presents a novel approach that combines microencapsulation and electrospinning technologies to develop a multifunctional composite separator (P@AS) for improving the electrochemical performance and safety performance of LMBs. The P@AS separator forms a dense charcoal layer through the condensed-phase flame retardant mechanism causing the internal separator to suffocate from lack of oxygen. Furthermore, it incorporates a triple strategy promoting the uniform flow of lithium ions, facilitating the formation of a highly ion-conducting solid electrolyte interface (SEI), and encouraging flattened lithium deposition with active SiO2 seed points, considerably suppressing lithium dendrites growth. The high Coulombic efficiency of 95.27% is achieved in Li-Cu cells with additive-free carbonate electrolyte. Additionally, stable cycling performance is also maintained with a capacity retention rate of 93.56% after 300 cycles in LFP//Li cells. Importantly, utilizing P@AS separator delays the ignition of pouch batteries under continuous external heating by 138s, causing a remarkable reduction in peak heat release rate and total heat release by 23.85% and 27.61%, respectively, substantially improving the fire safety of LMBs.

Eco-friendly, efficient and durable flame retardant lyocell fabrics prepared via a feasible grafting of taurine

Inspired by alkaline oxidative degradation of cellulose, a novel eco-friendly scenario for preparation of flame retardant lyocell fabrics was developed by the chemical grafting of biomass taurine. FTIR and XPS results verified the establishment of a covalent bond between taurine and lyocell fabric. Thermogravimetric analysis and vertical combustion test proved the improved char-forming ability and flame resistance of the grafted fabric. The THR and pHRR of the finished fabric were successfully reduced by 67.3 % and 89.9 % respectively after modification. In addition, after 50 wash cycles, the LOI value of the grafted fabric was maintained at 29.5 %. The gas-phase and condensed-phase flame retardant mechanisms were proposed from the analyses of pyrolysis gaseous products and char residue of the modified fabrics. The modification process is simple to operate and provides a feasible green flame retardant strategy for flammable lyocell fabrics.

Comparative study on the flame retardancy, pyrolysis behavior, and flame retardant pathways of black phosphorus in polyurethane and polypropylene

Black phosphorus nanosheets (BPns) have gained widespread attention in the field of flame retardancy due to their highly efficient flame-retardant properties achieved with a low addition rate (e.g., 0.4%). However, the pyrolysis pathways of BP in polymers have not yet been elucidated. This work systematically studies the flame retardancy and pyrolysis behavior of BP in oxygen-containing (polyurethane, PU) and oxygen-free (polypropylene, PP) polymers, distinguishing between the gas-phase and the condensed-phase flame retardant effect of BP. Through slow heating and staged heating methods, the condensed phase and gas phase pyrolysis products of BP in PU and PP at different temperatures are compared in detail. The distinct flame retardant pathways of BP in PU and PP are revealed. The results indicate that the oxidation of BP commences with its reaction with atmospheric oxygen, implying that the condensed-phase flame-retardant effect of BP primarily occurs at the polymer surface. In PP, BP mainly functions as a gas-phase flame retardant. In the condensed phase, BP generates phosphate derivatives that cover the substrate surface, providing solely a physical barrier effect. In PU, while BP demonstrates an outstanding gas-phase flame-retardant effect, it also accelerates the early dehydration carbonization of alcohols within the substrate, resulting in the formation of phosphate ester compounds (P–O–C structure) to bolster the thermal stability of residual carbon. Additionally, the side reactions of BP during catalytic carbonization will decrease the thermal stability of ester bonds in PU. This work lays a theoretical foundation for the development and application of BP-based flame retardant systems.

Hybrid sol-gel coatings doped with phytic acid-urea salt for fire protection of polyester/cotton blend fabrics

It is highly desirable to construct a sustainable hybrid silica coating to enhance the flame retardant (FR) properties of polyester/cotton (T/C) blend fabrics. In this study, a novel urea phytate salt was synthesized and used to prepare a phosphorus/nitrogen-doped hybrid silica sol system. The hybrid silica coating was then applied to the T/C fabric to develop a highly efficient FR-coated T/C fabric with improved washing durability. The surface morphology, size distribution, and condensation degree of the hybrid silica sol particles were characterized. The thermal stability, heat release, flame retardancy, and mode of action of the coated T/C fabrics were also investigated. The coated T/C fabrics exhibited self-extinguishing performance, with the damaged length decreasing from 30 cm to 8.5 cm and the LOI increasing from 17.1% to 30%. The desirable flame retardancy of the coated T/C fabric was well maintained even after 10 washing cycles. The remarkably inhibited heat release ability suggested a decreased fire hazard. A potential condensed-phase flame retardancy mechanism was proposed based on TG and char residue analyses. This study presents an eco-friendly and efficient hybrid silica coating that effectively reduces the fire hazard of T/C fabrics.

Core-shell flame retardant/APP-PEI@MXene@ZIF-67: A nanomaterials self-assembly strategy towards reducing fire hazard of thermoplastic polyurethane

Ammonium polyphosphate (APP) is the most commercially valuable phosphorus-based flame retardant, but poor interaction with the polymer interface limits the flame-retardant efficiency. In this work, a new type of multi-layered nanomaterial coating APP (APP-PEI@MXene@ZIF-67) was prepared and introduced into thermoplastic polyurethane (TPU) polymers by a simple and green assembly strategy. The effects of different loading shells of modified APP on the flame retardancy of TPU composites were investigated, as well as their gas/condensed phase thermal degradation products and their flame-retardant mechanisms. The results showed that APP-PEI@MXene@ZIF-67 was more favorable for catalytic char formation than APP, and the residual char formed by its composites was denser and more continuous. Compared with the pure TPU, the pHRR, THR, pSPR, and TSP of TPU/APP-PEI@MXene@ZIF-67–2BL composites were decreased by 72.75 %, 87.25 %, 59.58 %, and 85.97 %, respectively, which significantly reduced the heat and smoke release during the combustion process. The gas-phase and condensed-phase flame retardant mechanisms synergized to construct a possible approach to address the fire risk and heat/smoke hazards of TPUs and promote the extensive application of TPU polymers.

Flame retardant polyurethane microbubble elastomer based on ionic liquid/ammonium polyphosphate/aluminum hypophosphite ternary flame retardant system

AbstractTo develop a highly efficient flame retardant system for polyurethane microbubble elastomer (PME), a phosphate‐based ionic liquid (IL) 1‐methyl‐3‐(dioxyphosphoryl)‐propyl imidazole bromide was synthesized, and then combined with ammonium polyphosphate (APP) and aluminum hypophosphate (ALHP) to form a ternary flame retardant system, which shows excellent synergistic flame retardancy and plays an important role in both gas phase and condensed phase flame retardancy. Compared with pure PME, the limiting oxygen index of flame retardant PME with 6 wt% IL and 15 wt% APP/ALHP increased from 20.25% to 29.25%, the char yields is increased by 13 times, and the heat release rate, total heat release rate, mass loss rate, and smoke production rate are reduced by 74%, 19%, 67%, and 22%, respectively. Ignition time increased from 9 s to 19 s, and extinguishing time increased from 295 s to 573 s. At the same time, the addition of IL promoted the dispersion and compatibility of APP/ALHP in the PME matrix and improved the mechanical properties. In addition, IL also shows potential in antistatic modification, providing the possibility for materials to meet both flame retardant and antistatic requirements.

Rubber-based phosphaphenanthrene grafted polymer and its application to fabricate flame retardant polycarbonate blend with satisfied comprehensive mechanical properties

Grafting flame retardant groups onto common polymer molecule can be a good strategy to constructing superior flame retardant macromolecules, which provides a promising direction to fabricate fire safety polymer materials with satisfied comprehensive mechanical properties. In this thesis, a rubber-based phosphaphenanthrene grafted polymeric molecule (P-SBS) was synthesized via the grafting reaction of 9, 10-dihydro-9-oxa-10-phenanthrene-10-oxide (DOPO) with thermoplastic styrene-butadiene-styrene copolymer (SBS), and then applied to melt blending with polycarbonate (PC) to form P-SBS/PC blend with sea-island structure. The incorporated P-SBS not only brought PC much higher comprehensive flame retardancy, including higher limited oxygen index, shorter self-extinguishing time, less heat release during burning process, higher-quality char layer structure, and fewer amount of flammable volatile emission; but also endowed it with more satisfied comprehensive mechanical properties, including larger elongation at break, better anti-impact, higher flexural strength, and maintained tensile strength. By analysing burning residue, tracking thermal decomposition volatile emission, and inferring the pyrolysis route of P-SBS, the gas- and condensed-phase flame retardant mechanisms of P-SBS in suppressing the flammability of PC matrix were disclosed. The morphology analysis on the matrix fracture section and the embeded P-SBS particles before and after mechanical fracture, revealed the behavioral mechanism of P-SBS particles in improving the ductility, toughness, and stiffness of PC matrix. This study provides a beneficial reference to superior flame retardant molecule constructing and advanced flame retardant polymer material manufacturing.

Bismuth trioxide replaced diantimony trioxide to obtain polyvinyl chloride leather with high flame retardancy and low flame propagation rate

Diantimony trioxide (Sb2O3) has been widely used in polyvinyl chloride leather (PVCL, PVC powder: plasticizer = 50 phr: 50 phr). However, the EU and the IARC have included it in the list of restricted substances. In response to these restrictions on Sb2O3, this work developed a high flame retardant PVCL with reduced or no Sb2O3 content by introducing bismuth trioxide (Bi2O3). The results showed that the horizontal burning rate of 1Bi2O3/3Sb2O3/PVCL decreased by 51.2% compared to that of 4Sb2O3/PVCL. When the addition amount of Bi2O3 reached 6 phr, the horizontal burning rate of 6Bi2O3/PVCL decreased by 20.5% compared to that of 4Sb2O3/PVCL, which can achieve complete replacement of Sb2O3. The improved flame retardancy can be primarily attributed to the flame retardant effect of Bi2O3 in PVCL foam layer. During combustion, Bi2O3 facilitated crosslinking and charring in the PVCL foam layer matrix, contributing to condensed phase flame retardancy. Additionally, it promoted the decomposition of the PVCL foam layer matrix, generating more HCl (g), thereby enhancing gas phase flame retardancy. This study has developed a high flame retardant PVCL through a simple method, which was expected to meet the application needs of the automotive interior materials.

A cationic, durable, P/N-containing starch-based flame retardant for cotton fabrics

A cationic, durable flame retardant for cotton fabrics, 6-(2-(dimethoxy phosphoryl)-2-(trimethyl ammonium)) methoxy-2-methoxy-polysaccharide ammonium phosphate (DTPAP), was synthesized. Its structure was verified by NMR and FTIR spectroscopy. According to the FTIR spectra and X-ray photoelectron spectroscopy (XPS), DTPAP formed P(=O)-O-C bonds with cellulose molecules and firmly grafted to cotton fabrics, giving the fabric a high durability. DTPAP-25-treated fabrics passed the vertical flame test (VFT), and the limiting oxygen index (LOI) was 43.9 %. After 50 laundering cycles (LCs), the DTPAP-25-treated fabrics had an LOI of 29.9 %, passed the VFT, and retained their flame retardancy. EDS data showed that, compared with engrafted cationic ammonium phosphate flame retardants, the DTPAP-treated fabrics contained fewer metal ions. Cone calorimetry data showed that DTPAP-25-treated fabrics did not display concentrated heat release. The results suggested that DTPAP exhibited a condensed-phase flame retardant mechanism, and the introduction of cations into the ammonium phosphate flame retardant reduced ion exchange, which improved the durability.

Bioinspired phosphorus-free and halogen-free biomass coatings for durable flame retardant modification of regenerated cellulose fibers

Inspired by mussel adhesion and intrinsic flame retardant alginate fibers, a biomass flame retardant (PPCA) containing adhesive catechol and sodium carboxylate structure (-COO−Na+) based on biomass amino acids and protocatechualdehyde was designed to prepare flame retardant Lyocell fibers (Lyocell@PPCA@Na). Furthermore, through the substitution and chelation of metal ions by PPCA in the cellulose molecular chain, flame retardant Lyocell fibers chelating copper and iron ions (Lyocell@PPCA@Cu, Lyocell@PPCA@Fe) were prepared. Compared with the original sample, the peak heat release rate (PHRR) and total heat release (THR) for modified Lyocell fibers were significantly reduced. In addition, the modified sample exhibited a certain flame retardant durability. TG-FTIR analysis showed that the release of flammable gaseous substances was inhibited. The introduction of Schiff bases and aromatic structures in PPCA, as well as the decomposition of carboxylic metal salts were beneficial for the formation of char residue containing metal carbonates and metal oxides to play the condensed phase flame retardant effect. This work develops a new idea for the preparation of eco-friendly flame retardant Lyocell fibers without the traditional flame retardant elements such as P, Cl, and Br.

Formaldehyde-free and durable phosphorus-containing cotton flame retardant with -N=P-(N)3- and reactive ammonium phosphoric acid groups

A flame retardant (FR) hexachlorocyclotriphosphazene diethylenetriamine ammonium phosphoric acid (HDAPA) was synthesized. Vertical flammability test and limiting oxygen index (LOI) results showed that cotton samples finished with HDAPA solutions (15 % and 20 %) could pass vertical flame retardancy test, and LOIs reached 30.1 % and 35.4 % even after 50 laundering cycles according to AATCC 61-2013 3A washing standard (3A), performing flame retardancy and washing durability. Meanwhile, Fourier transform infrared and X-ray photoelectron spectroscopy analyses suggested that HDAPA was grafted on cotton fibers through -P(=O)-O-C covalent bond. Total heat release (1.98 MJ/m2) and char residue (16.2 %) of HDAPA treated cotton were much lower than those (4.26 MJ/m2, 3.2 %) of untreated cotton. Thermogravimetry results showed HDAPA changed thermal decomposition pathway of cotton fabric, which was further supported by thermogravimetric-Fourier infrared spectrometer results, revealing HDAPA performed a condensed phase flame retardancy mechanism. Scanning electron microscopy implied HDAPA entered amorphous region of cotton fibers to react with cellulose. Mechanical properties of HDAPA treated cotton decreased a little. Although the synthesis process used formaldehyde but no free formaldehyde released. In consequence, the aforementioned results indicated that the introduction of -N=P-(N)3- and -P(=O)(O−NH4+)2 groups to FR was an viable method to improve flame retardancy and durability.

Phosphorus-containing reactive compounds to prepare fire-resistant vinyl resin for composites: Effects of flame retardant structures on properties and mechanisms

The traditional flame-retardant method for carbon fiber reinforced vinyl ester resin composites is to add a large amount of solid flame retardants, which not only leads to the deterioration of the material's mechanical properties, but also increases the resin viscosity and affects the molding process of composites. In addressing this issue, this work adopts a liquid reactive flame retardant strategy and synthesizes six novel liquid phosphorus-containing reactive compounds as flame retardants. A comparative study is conducted on the effects of the structure of compounds (valence and group of phosphorus and number of reaction groups) on the properties of materials. The results demonstrate significantly improved flame retardancy and toughness, as well as unaffected viscosity and strength of the resin. When the phosphorus content does not exceed 3 wt%, the limiting oxygen index (LOI) of the resin can reach over 30% and UL-94 passes the V-0 rating. The structure of compounds significantly affects their flame retardancy mechanism. Especially, compounds rich in P-O-C structure have more outstanding condensed phase flame retardancy (promoting charring) and are more favorable for improving the LOI; Compounds rich in P-Ph and P-C structures have higher thermal stability and mainly exert gas phase flame retardancy, which is more beneficial for improving the self-extinguishing properties of materials. Furthermore, a synergistic flame retardant effect is observed between carbon fiber and compounds rich in P-Ph.

Gas Phase-Heat Absorption-Condensate Phase Stepwise Flame Retardant Strategy to Prepare Coal Tar Pitch-Based Porous Carbon for Supercapacitor.

Porous carbon is widely used in energy storage-conversion systems, and the question of how to explore an efficient strategy for preparation is very significant. Herein, the flame retardant capability of (NH4 )2 SO4 /Mg(OH)2 that contains gas phase-heat absorption-condensate phase components is assisted to carbonize coal tar pitch in air and obtain the porous carbon. The mechanism of stepwise inflaming retarding is systematically investigated. In the carbonization process in a muffle furnace, (NH4 )2 SO4 decomposes releasing gases at below 400°C to act as the role of gas phase flame retardant. Mg(OH)2 starts to decompose at ≥ 400°C, and it has the effect of heat absorption and condensed phase flame retardation (MgSO4 and MgO). What's more, the flame retardant also serves as an N, S source and template. The obtained porous carbon possesses an ultrahigh carbon yield of 56.9wt.%, hierarchical pore structure, and multi-heteroatoms doping. It can still reach up to 244.7Fg-1 even loaded 20mg of active material. In addition, the (NH4 )2 SO4 /agar gel electrolyte is synthesized, and the fabricated flexible ammonium ion capacitor exhibits a superior energy density of 40.8Whkg-1 . This work uncovers a new way to construct porous carbon, which is expected to synthesize more carbon materials using other carbon sources.

Investigation of the synergistic effect of red phosphorus and magnesium hydroxide on the thermal degradation behavior and flame resistance of the intumescent fire‐retardant polypropylene system

AbstractHigh fire‐resistance polypropylene (PP) composites were prepared by using environment‐friendly flame retardants including expandable graphite (EG), red phosphorus (RP), and magnesium hydroxide (MH). Synergism between EG, RP, and MH on the thermo‐oxidation behavior and flame resistance of PP was found. The incorporation of MH and RP formed highly thermally stable mixtures of magnesium phosphates consisting of Mg3(PO4)2, Mg(PO3)2, and α‐Mg2P2O7 at both amorphous and crystalline phases in the burning process. The mixture not only covered the surface of burning materials but also could reinforce the char structure of the PP/EG composites, thereby significantly enhancing the condensed phase flame retardant mechanism of the composites. Mass ratios of the flame retardants were also optimized to obtain the composite with the highest flame retardant efficiency. The result revealed that the combination of EG, RP, and MH in PP at MH/RP mass ratio of 3/2 with only a total additive content of 18 wt.% could make its limiting oxygen index (LOI) increase from 16.8% to 27.2% and the UL‐94 rating was improved from none to V‐0. In addition, the mechanical properties of the composites were improved via the surface treatment of MH and RP with calcium stearate and silicone oil, respectively.

Synthesis of solid reactive organophosphorus‐nitrogen flame retardant and its application in epoxy resin

AbstractA solid reactive organophosphorus‐nitrogen flame retardant 4N‐BDP was devised and synthesized in order to address the flaws of the widely used organophosphorus flame retardants BDP as well as the issue of flame retardant modification of epoxy resin (EP). A series of flame‐retardant EP composites were prepared by adding 4N‐BDP and BDP to EP in a specific proportion. The flame‐retardant properties of the two were compared, and the flame‐retardant mechanism of 4N‐BDP was deeply analyzed. The results of the UL‐94 test revealed that sample 4N‐BDP‐6 obtained the greatest V‐0 level, while BDP‐6 had no level, when the addition ratio of flame retardant was 8.03%. In the cone calorimeter test, the peak smoke production rate (pSPR) and total smoke production (TSP) of BDP‐6 were not significantly different from those of pure EP. In contrast, TSP and pSPR of 4N‐BDP‐6 decreased by 39.50% and 50.00% respectively compared with EP. Compared with BDP, 4N‐BDP shows better flame retardancy and smoke suppression performance, which can significantly improve the fire resistance of EP. The flame‐retardant mechanism of 4N‐BDP was resolved by scanning electron microscopy, XPS, and thermogravimetric analysis/infrared spectrometry. 4N‐BDP can increase the residual carbon rate of the composites, improve the residual carbon strength, play an excellent condensed phase flame retardant effect, and avoid further decomposition of the materials. In the gas phase, the decomposition of 4N‐BDP produces PO·, PO2· and NH3, which play a good quenching effect and dilution effect. The escape of NH3 will leave bubbles in the residual carbon, making the residual carbon more fluffy, further improving the ability of heat insulation and oxygen insulation, and enhancing the flame retardant effect of the condensed phase. In general, the flame‐retardant mechanism of 4N‐BDP is a synergistic combination of condensed phase and gas phase flame retardant mechanism. This work provides a new approach to improve the defects of organophosphorus flame retardant BDP commonly used in the market and enhance the fire resistance of EP.