Flame Retardancy Behavior Research Articles

Highly efficient flame retardancy and fire spread behavior of rigid polyurethane foams with extremely low content of flame retardant

In recent years, flame-retardant rigid polyurethane foam (RPUF) has once again captured the scholars’ attention due to the growing the growing demands in the field of building energy efficiency. However, the inherent flammability of RPUF is high and the complexities of its flame-retardant mechanisms remain inadequately understood. In this study, a modified biomass material, amino starch phosphate ester was successfully synthesized which was then combined with expandable graphite (EG) and incorporated into RPUF. The research delved into the optimal ratio and minimal flame-retardant additive required to achieve the stringent UL-94 V-0 rating, while also thoroughly investigating the flame retardancy and thermal properties of the composite system. The findings revealed that with just 6 wt.% of flame retardants, the RPUF achieved the UL-94 V-0 rating, with a 41.1 % reduction in peak heat release rate (pHRR) and a 23.7 % decrease in total heat release (THR). Additionally, it diminishes the flame's size and width, leading to quicker extinction, while also lowering the internal combustion temperature of the polyurethane, thereby delaying both preheating and combustion times. The synergistic interaction between amino starch phosphate ester and EG during combustion results in the formation of a dense, continuous char layer, effectively inhibiting the pyrolysis and combustion of RPUF. This study provides a theoretical foundation for the development of efficient flame-retardant systems for RPUF.

Impact of Different Substituents on Thermal Curing and Flame‐Retardant Behaviors of 2,2′‐Methylenebis(4‐nitrophenol)‐Based (Poly)benzoxazines

AbstractPolymerization of benzoxazine at low temperatures is important because the high‐temperature polymerization restricts its utilization in a wide range of applications, though the polybenzoxazines possess excellent properties. The effect of nitro functionality and various substituents on the thermal curing of benzoxazine and the flame‐retardant behavior are mainly focused in this study. In the present work, 2,2′‐methylenebis(4‐nitrophenol) (NBP) was synthesized from 4‐nitrophenol and is used for the synthesis of benzoxazine derivatives with five structurally different aromatic amines. As the synthesized benzoxazine contains nitro‐groups in the phenolic part and various substituted functional groups in different positions of the amine part, the curing temperatures significantly varied among each other. The effect of different substituents on the thermal ring‐opening polymerization (ROP) of benzoxazine was studied with exotherms of the DSC thermogram. The 4‐fluoroaniline and 2‐aminobenzotrifluoride‐based benzoxazines show the highest and lowest curing temperatures of 272 and 189 °C, respectively, which is based on their substituents and their position that can act as an internal catalyst. The resulting polybenzoxazines possess higher char yield (49% ≤ 63%) and higher values of LOI (37 ≤ 43) including excellent flame retardant (UL94‐V0) behaviors suggesting that the polybenzoxazine can be used as coatings for high‐performance industrial applications.

Effect of silane coupling agent on mechanical properties, flame retardancy, and ceramifiable behavior of ceramifiable flame‐retardant silicone rubber composite

AbstractIn order to improve the dispersibility of inorganic fillers and enhance its ceramifiable flame‐retardant efficiency, the ceramifiable flame‐retardant silicone rubber composites were prepared using glass powder, zinc borate, ammonium polyphosphate, mica powder, platinum catalyst as ceramifiable flame‐retardant agent, and various silane coupling agents as interfacial modifier. The micromorphology, mechanical properties, flame retardancy, thermal stability, and combustion behavior of ceramifiable flame‐retardant silicone rubber composites, as well as the flexural strength of the corresponding ceramics generated after pyrolysis of the composites were examined. The results reveal that the inclusion of silane coupling agents improves the dispersibility of ceramifiable flame‐retardant agents substantially. The mechanical properties, flame retardancy, thermal stability, and combustion behavior of ceramifiable flame‐retardant silicone rubber composites are all improved. When compared to a composite without a silane coupling agent, the tensile strength of the composite can be improved by up to 1.9 times. Only 0.5phr silane coupling agent is required to raise the vertical combustion rating from V‐1 to V‐0, and the composite with 3 phr KH570 has a LOI value of 38.6. Meanwhile, the heat release rate of the composite is reduced to a certain extent, and the time to ignition and residue are dramatically enhanced after the addition of silane coupling agent in the cone calorimetry test. Moreover, flexural strength of the corresponding ceramics generated after pyrolysis of the composites rapidly increases with increasing silane coupling agent content, which can reach to 24.7 MPa with addition of 3 phr KH570.

Effect of ammonium polyphosphate on flame retardancy of bio-based rigid polyurethane foams

Rigid polyurethane foam (RPUF) has attracted a lot of attention as a multifunctional material. However, the use of fossil fuels in various fields is limited due to their flammability and excessive consumption in the preparation process. In order to solve this problem, a sustainable bio-based RPUF was prepared by ammonium polyphosphate (APP) and lignin-based polyol flame-retardant modification. The impact of APP on the smoke characteristics, flame retardancy, and thermal behavior of lignin-based polyol RPUFs was examined. The modified RPUF (RPUF-20) with 20 wt.% APP had the greatest starting temperature and residual rate. The maximum activation energy (E) and best thermal stability were found in the pyrolysis kinetics calculation utilizing the thermogravimetric trajectory compared with other specimens. Cone showed that when RPUF-20 was compared with RPUF-0, the peak heat release rate was lowered by 79.43%, 72.79%, and 67.91%, and the total heat release was reduced by 50.59%, 56.29%, and 37.14%, respectively. In addition, RPUF-20 had the lowest smoke density, according to the statistics. The current results showed that RPUF-20 had low smoke toxicity and outstanding flame retardancy, which gave rise to a novel notion for RPUFs following flame-retardant modification using biomass.

Synthesis of novel reactive flame retardant to improve fire resistance and mechanical properties in epoxy resin

A novel reactive flame-retardant (FR), phosphorus-modified tetraethylenepentamine (TEPA-m-MVP), was prepared via aza-Michael addition process, using dimethyl vinylphosphonate (MVP). TEPA-m-MVP was successfully covalently introduced into the structure of the epoxy system, into the epoxy resin matrix synthesised from tetraethylenepentamine (TEPA) and diglycidyl ether bisphenol A (DGEBA) reaction, leading to the development of a flame-retardant epoxy resin (FR-EP). The curing behaviour, mechanical properties, thermal stability and flame-retardant behaviour of FR-EP samples were investigated and compared to the behaviour of the neat epoxy resin (EP). FR-EPs showed an increase in glass transition temperature (Tg), from 120 to 147 °C upon integrating TEPA-m-MVP into the epoxy resin structure, while the value of the E modulus remained unaffected. Furthermore, FR-EP-2%P sample with the optimal P content, approximately 2 wt%, displayed excellent flame-retardant properties. In comparison to EP, total heat release (THR) and peak heat release rate (pHRR) for FR-EP-2%P decreased from 22.6 to 15.3 kJ.g−1 and from 1557 to 572 kW.m−2, respectively. In addition, an interesting impact of the crosslinking density of FR-EP samples on the fire behaviour was observed. This work presents a new strategy for the simultaneous modification of the flame retardancy and mechanical properties of epoxy systems.

Investigation of flame-retardant characteristics of natural flax coated with hydrothermally synthesized calcium borate and organic PDA

Flame-retardant behavior of flax fabric coated by calcium borate powders with clove-like and elongated morphologies was investigated by thermal analysis and cone calorimeter. PDA was used to form strong and uniform adhesion of calcium borate onto fabric. Thermal analysis showed a 20% of decrease in mass loss, while detected exothermic/endothermic peaks as a result of the degradation of fabric and PDA. Significant reductions in HRR, p-HRR, EHC and CO2 amount were observed for fabric coated by PDA and elongated calcium borate powder. PDA was carbonized at low temperatures and formed a char layer that prevented flame propagation. At the same time, calcium borate powder dilutes the flammable gases in the environment with the release of water within its body. Among the calcium borate powders, rod-like morphology showed the best flame-retardant performance.

High-Value and Environmentally Friendly Recycling Method for Coal-Based Solid Waste Based on Polyurethane Composite Materials.

This study aims to provide a high-value and environmentally friendly method for the application of coal-based solid waste. Modified fly ash/polyurethane (MFA/PU) and modified coal gangue powder/polyurethane (MCG/PU) composites were prepared by adding different contents of MFA and MCG (10%, 20%, 30%, 40%). At the filler content of 30%, the compressive strengths of MFA/PU and MCG/PU are 84.1 MPa and 46.3 MPa, respectively, likely due to an improvement in interface compatibility, as indicated by scanning electron microscopy (SEM). The MFA/PU and MCG/PU composites present their highest limiting oxygen index (LOI) values of 29% and 23.5%, respectively, when their filler content is 30%. MFA has advantages in improving the LOIs of composites. Cone calorimetry (CCT) and SEM demonstrate that the two composites exhibit similar condensed-phase flame-retardant behaviors during combustion, which releases CO2 in advance and accelerates the formation of a dense barrier layer. Compared with the MFA/PU composites, the MCG/PU composites could produce a more stable and dense barrier structure. Water quality tests show that heavy metals do not leak from FA and CG embedded in PU. This work provided a new strategy for the safe and high-value recycling of coal-based solid waste.

Synthesis and Flame Retardant Behavior of Phosphorous- and Nitrogen-Containing Copolymer and Its Application in Polypropylene.

In this study, a 4-(hydroxymethyl)-2,6,7-trioxa-1-phosphabicyclo[2.2.2]octane 1-oxide (PEPA)-functionalized acrylate monomer, PEPAA, is designed and utilized for the synthesis of macromolecular flame retardants poly(PEPAA-co-AM) with varying PEPAA/AM ratio through copolymerization with acrylamide (AM). The poly(PEPAA-co-AM) is then incorporated into polypropylene (PP) to prepare PP/poly(PEPAA-co-AM) composites. The flame retardant effect of poly(PEPAA-co-AM) on PP is investigated using cone calorimetric test (CCT), and compared with that of PEPAA homopolymer (P-PEPAA), AM homopolymer (PAM), and blends of P-PEPAA/PAM. The results demonstrate that, in comparison with P-PEPAA, PAM, and blends of P-PEPAA/PAM, the incorporation of poly(PEPAA-co-AM) significantly enhances the flame retardancy of PP. Notably, the best flame retardancy is achieved when the ratio of PEPAA/AM copolymerization in poly(PEPAA-co-AM) is 2/8. The morphology and composition of residual chars from combustion are analyzed using SEM-EDS while the residual graphitization degree is examined through Raman spectroscopy. Additionally, TG-FTIR-MS is utilized to investigate the pyrolysis products in gas phase during thermal decomposition of poly(PEPAA-co-AM). Based on these experimental results, a flame retardant mechanism for poly(PEPAA-co-AM) is proposed. The PP/poly(PEPAA-co-AM) composites not only retain the excellent processing properties of pure PP but also exhibit enhanced mechanical properties.

Effects of polymer matrix and temperature on pyrolysis of tetrabromobisphenol A: Product profiles and transformation pathways

Plastics are crucial constituents in electronic waste (e-waste) and part of the issue in e-waste recycling and environmental protection. However, previous studies have mostly focused on plastic recovery or thermal behavior of flame retardants, but not both simultaneously. The present study simulated the process of e-waste thermal treatment to explore tetrabromobisphenol A (TBBPA) pyrolysis at various temperatures using polystyrene (PS), polyvinyl chloride (PVC), and e-waste plastics as polymer matrices. Pyrolysis of TBBPA produced bromophenol, bromoacetophenone, bromobenzaldehyde, and bromobisphenol A. Co-pyrolysis with the polymer matrices increased emission factors by 1 − 2 orders of magnitude. The pyrolytic products of TBBPA, TBBPA+PS, and TBBPA+PVC were mainly low-brominated bisphenol A, while that of TBBPA in e-waste plastics was consistently bromophenol. Increasing temperature drove up the proportions of gaseous and particulate products, but lowered the relative abundances of inner wall adsorbed and residual products in pyrolysis of pure TBBPA. In co-pyrolysis of TBBPA with polymer matrix, the proportions of products in different phases were no longer governed solely by temperature, but also by polymer matrix. Co-pyrolysis of TBBPA with PS generated various bromophenols, while that with PVC produced chlorophenols and chlorobrominated bisphenol A. Transformation pathways, deduced by ab initio calculations, include hydrogenation-debromination, isopropylphenyl bond cleavage, oxidation, and chlorination.

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.

Facile Fabrication of Highly Efficient Chitosan-Based Multifunctional Coating for Cotton Fabrics with Excellent Flame-Retardant and Antibacterial Properties.

Interest in the development of eco-friendly, sustainable, and convenient bio-based coatings to enhance flame retardancy and antibacterial properties in cotton fabrics is growing. In this work, chitosan was protonated at its amino groups using a method with a high atom economy using an equimolar amount of amino trimethylene phosphonic acid (ATMP), resulting in the fabrication of a single-component chitosan-based multifunctional coating (ATMP-CS), thereby avoiding any additional neutralization or purification steps. Cotton fabrics coated with various loads of ATMP-CS were prepared through a padding-drying-curing process. The morphology, thermal stability, mechanical properties, antibacterial properties, flame-retardant behavior, and flame-retardant mechanism of these fabrics were investigated. The coating exhibited excellent film-forming properties, and it imparted a uniform protective layer onto the surfaces of the cotton fabrics. When the load capacity reached 11.5%, the coated fabrics achieved a limiting oxygen index of 29.7% and successfully passed the VFT test. Moreover, the ATMP-CS coating demonstrated antibacterial rates against Escherichia coli and Staphylococcus aureus reaching 95.1% and 99.9%, respectively. This work presents a straightforward and gentle approach to fabricating colorless, environmentally friendly, and highly efficient fabric coatings that have potential applications in promoting the use of bio-based materials.

Synergistic flame‐retardant effects between silane coupling agents modified expanded graphite and Pt catalyst in silicone rubber composites

AbstractIn this work, different kinds of silane coupling agents modified expanded graphite (MEG) fillers were successfully prepared and then incorporated into silicon rubber matrix to fabricate flame‐retardant composite materials (SR/MEG). The inserted MEG fillers with siloxane chains exhibited good compatibility with the silicon rubber matrix, which cannot only reduce the negative impact of adding fillers on mechanical properties but also endow the silicon rubber composites with ideal flame retardancy. Subsequently, platinum (Pt) catalyst was incorporated into the SR/MEG composites to prepare SR/MEG/Pt composites, and the synergistic effects of MEG and Pt catalyst on the thermal stability, flame retardancy, and combustion behavior of silicon rubber composites were systematically investigated. The target SR/MEG/Pt composite with appropriate addition of MEG and Pt catalyst can obtain relatively high char residue of 41.9% and limiting oxygen index value of 29.6%, as well as achieve V‐0 rating in the vertical combustion test, owing to the formation of expanded and dense silicon–carbon protective layer under the catalysis of Pt catalyst. Moreover, the cone calorimeter test results showed that the peak of heat release rate and total heat release of SR/MEG composites were further reduced after the addition of an appropriate amount of Pt catalyst, manifesting the good synergistic effect of MEG and Pt catalyst on the flame retardancy performance of silicon rubber. The method proposed herein may provide a promising way for fabricating high‐performance flame‐retardant silicone rubber materials.

Protective and Flame-Retardant Bifunctional Epoxy-Based Nanocomposite Coating by Intercomponent Synergy between Modified CaAl-LDH and rGO.

Extensive utilization in various settings poses extra requirements of coatings beyond just anticorrosion properties. Herein, 8-hydroxyquinoline (8-HQ) intercalated CaAl-based layered double hydroxide (CaAl-8HQ-LDH) was loaded on reduced GO (rGO) through a one-pot hydrothermal reaction, which was employed as the nanofiller endowing the epoxy (EP/CaAl-8HQ LDH@rGO) with excellent flame-retardancy while ensuring efficient protection for mild steel. Results of electrochemical impedance spectroscopy (EIS) demonstrated the durability of the EP/CaAl-8HQ LDH@rGO-coated specimen, with the impedance at the lowest frequency (|Z|0.01Hz) maintained as 1.84 × 1010 Ω cm2 after 120 days of immersion in a 3.5 wt % NaCl solution. Even for the scratched EP/CaAl-8HQ LDH@rGO system, only a slight decline in |Z|0.01Hz was observed during 180 h of exposure to the NaCl solution, indicating a self-healing feature supported by salt spray tests. UL-94 burning tests revealed the V-0 rating for EP/CaAl-8HQ LDH@rGO with improved thermostability. Strong physical barrier from two-dimensional rGO and the release of 8-HQ from LDH interlayers accounted for the anticorrosive and self-healing properties. However, O2-concentration dilution and charring-layer promotion governed the flame-retardant behavior of the nanocomposite coating. The intercomponent synergy of nanofillers achieved in this work may provide a useful reference for designing multifunctional coatings.

Flame retardant behavior of bio-based epoxy resin bearing pyridazinone and dynamic ester bond via self-blow-out and vesicular carbon formation

Aromatic nitrogen heterocyclic structure is a key building block of high-performance polymer materials and nitrogen-doped porous carbons, yet systematic studies on its flame-retardant effects and carbonization mechanisms in thermoset materials is still lacking. Here, a pyridazinone embedded bio-based epoxy resin (CSPZ-EP) cured by 4,4ʹ-methylenedianiline (DDM) was prepared. Benefiting from the rigid biphenyl-like pyridazinone structure and the high cross-linking density originated from the self-catalyzed transesterification, the cured CSPZ-EP/DDM can easily pass the UL-94 test with a V-0 rating suggesting excellent intrinsic flame retardancy. The cone calorimeter results further demonstrated that the peak heat release rate, the total heat release and flame growth rate of CSPZ-EP/DDM were significantly reduced by 84.4 %, 28.4 % and 90.5 %, respectively, compared with those of bisphenol A epoxy resin. The higher graphitization degree of the char residues and a large amount of non-flammable pyrolysis gas ejection synergistically prevented the further spread of fire. Strong yet tough nitrogen-rich char layer formed after thermal ablation together with the renewable features and the facile preparation route of CSPZ-EP/DDM make it a potential precursor for heteroatom porous carbons.

Influence of two-phase structure of PET/PPSU alloys and selective distribution of flame retardants on the flame retardancy of polymer alloys

Polymer alloys can obtain the excellent performance of a variety of polymers. The polymer blending system has been studied by many scholars, especially the multi-component system containing additives, which is receiving more and more attention from researchers. The flame retardancy behavior of polyethylene terephthalate (PET)/Polyphenylene sulfone (PPSU) blends containing A 9,10-dihydro-9-oxa-10 phosphophenanthrene-10-oxide based derivative tris-(3-dopo-propyl) -triazine trione (TAD) is explored. Flame retardancy of PET/PPSU composite was characterized by Limiting oxygen index (LOI), vertical combustion test (UL 94), and cone calorimeter test. PPSU is a less flammable material with an LOI value of 40.0 % when used alone. With a 5 % flame retardant TAD addition, the LOI value of the PPSU/TAD-5 composite can be increased to 42.6 %. Interestingly, the LOI of PET with 5 wt% of TAD was 30.2 %, whereas the LOI of PET/PPSU(70/30) composites with the same 5 wt% of TAD was reduced to 26.3 %. We investigated by SEM-EDS that the flame retardant TAD always preferred to be distributed in the PPSU phase in PET/PPSU composites with different ratios. When PPSU was wrapped by the PET phase, which is the sea structure, the flame tended to follow the sea structure combustion channel of the polymer alloys during combustion, and the island structure of PPSU had little effect on the overall flame retardancy of the polymer alloys. Similarly, when PPSU becomes a continuous matrix, even without flame retardant, it significantly reduces the combustibility of the blends. However, with the addition of flame retardants, most of the flame retardants are distributed in the PPSU matrix, which significantly increases the LOI value of the PET/PPSU(40/60)/TAD-5 composite. Therefore, we conclude that there is an uneven distribution of flame retardants in the two phases, so for polymer alloys, the distribution of flame retardant in the two phases, as well as the construction of the continuous phase and the dispersion phase, determine the overall flame retardant properties of the composites.

Load Bearing, Time Dependent, Thermal and Flame Retardant Behavior of Peanut Husk Derived Si3N4 Basalt Fibre-Reinforced Polyester Composite

Load Bearing, Time Dependent, Thermal and Flame Retardant Behavior of Peanut Husk Derived Si3N4 Basalt Fibre-Reinforced Polyester Composite

Synthesis of PMM and Synergistic Flame Retardant Effect with Ammonium polyphosphate

A novel flame retardant poly {[(2-Methyl-acrylic acid 2-(dimethoxyphosphoryloxy)-ethyl ester]-co-[2-Methyl-acrylic acid 2-(trimethoxysiloxy)-ethyl ester]} (PMM) containing dimethoxyphosphoryloxy and trimethoxysiloxy groups in side chains was synthesized. The structure of PMM was characterized by Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance (1H NMR), and the thermal performance of PMM was characterized by thermal gravimetric analysis (TGA) and differential scanning calorimetry (DSC). The effect of PMM on polypropylene’s flame retardancy and thermal behaviors was investigated by limited oxygen index (LOI), vertical burning test (UL-94), and TG tests. The experimental results indicate that the addition of PMM helps to improve the flame retardancy and thermal stability of PP. When the addition of PMM and APP in PC was 15% and 20%, the LOI value of PC reached 28.4%, and the UL-94 test rating reached V-0 level. The charred structure observed by scanning electron microscopy (SEM) indicated that the char surface for PP/APP/PMM system holds an intumescent char structure compared to neat PP, and the synergy exists in the composites. The PMM slightly decreased the tensile property in terms of strength but increased the elongation at break for PP composites.

Flame-Retardant Behavior and Nanocrystal Synthesis through Formation of Multilayers of Poly(acrylic acid) and Zinc Phosphate on Cotton Fabric.

Cotton fabric with improved flame retardancy was prepared by introducing a zinc phosphate compound into cotton fabric using a layer-by-layer (LBL) deposition method with poly(acrylic acid) as a polymer electrolyte layer. In a vertical burning (VB) test, it was found that the flame retardancy improved as the number of depositions increased. As a result of thermogravimetric and inductively coupled plasma-atomic emission spectroscopy analyses, the residual amount increased to 20 wt % for the 20 deposited sample, and the weight ratio of Zn and P elements reached more than 40 wt %. As a result of SEM analysis, the cotton fibers not treated with LBL were destroyed after the VB test, but the shape of the fabric was maintained in the LBL-treated cotton fabrics. It was observed by TEM that numerous single crystals of about 10 nm formed on the surface of the sample subjected to the VB test. Through FT-IR and XPS analyses, it was confirmed that the zinc phosphate compound layer was formed by LBL deposition by the reaction between the phosphate anion and zinc cation. XRD analysis confirmed that the orthorhombic hopeite crystals produced by LBL deposition were transformed into zinc phosphate Zn3(PO4)2 crystals by flame during the VB test. These results show that flame retardancy was improved by a mechanism in which a noncombustible zinc phosphate barrier was formed during firing. These results are significant in suggesting a new method for preparing zinc phosphate single crystals of about 10 nm in size and providing anticorrosion coating for cotton fabric by an environmentally friendly LBL method.

Study on flame retardancy of EPDM reinforced by ammonium polyphosphate.

Currently, the most widely used material for solid rocket motor (SRM) insulation is ethylene propylene diene monomer (EPDM) filled with flame-retardant and ablation-resistant fillers. Researchers have been working hard to find a flame-retardant filler that can simultaneously meet the complex requirements of mechanical strength, density, flame retardancy and ablative performance of the insulation layer. This requires research on the flame retardant properties of flame retardants in oxygen-poor environments. In this paper, ammonium polyphosphate (APP) is used as a flame retardant filler, which is filled into an EPDM premix (p-EPDM) containing fumed silica and aluminum hydroxide to prepare composite materials. By creating an anoxic environment, the flame retardant behavior of APP under anoxic conditions on EPDM was studied. The results show that composites prepared with APP show better flame retardant properties in tests such as limiting oxygen index and UL-94, with less impact on mechanical strength and density. The surface morphology and elemental composition of the composite combustion residues were studied using Raman spectroscopy, scanning electron microscopy (SEM) and energy dispersion spectroscopy (EDS). In an oxygen-depleted environment, APP will thermally decompose to form ammonia, water vapor and phosphorus-containing acidic substances. These gases dilute the flammable gas and reduce the thermal conductivity. The acidic substances containing phosphorus are concentrated on the surface of the pyrolysis layer to promote the formation of the carbon layer. This provides guidance for us to design insulation layer materials with properties that are more in line with actual use requirements.

Synthesis of bio‐based reactive N/P flame retardant and its curing and flame retarding behavior in epoxy resins

AbstractIn this study, a pioneering bio‐based nitrogen–phosphorus flame retardant and curing accelerator named oxime‐phosphazene hexakis [(4‐(hydroxyimino) 2‐methoxy) phenoxy] cyclotriphosphazene (HAPV) was successfully synthesized using hexachlorocyclotriphosphazene and vanillin. When 5 wt % HAPV was added into epoxy, the limiting oxygen index increased from 22% to 27% and passed UL‐94 V‐0 (UL is defined as Underwriters Laboratories) rating. Meanwhile, with the addition 5 wt% HAPV, the apparent activation energy (Ea) of HAPV/EP decreased from 20.22 to 67.15 kJ/mol, and the pHRR value was suppressed from 581.21 to 330.18 kW/m2. It was due to that the HAPV quenched the combustion chain reaction through the gas phase and condensed phase, forming a dense char layer for blocking the heat transfer. Overall, the study provides an environmentally friendly epoxy flame retardant curing accelerator that shows great potential in epoxy flame retardant applications.