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A tris(DOPO-grafted piperazine)-triazine phosphoramide (DOPO-TPT) was synthesized, and its structure was well characterized by Fourier transform infrared spectroscopy and nuclear magnetic resonance spectroscopy. DOPO-TPT was used as a flame retardant additive to modify the epoxy resin to obtain a series of flame retardant epoxy thermosets. The effects of DOPO-TPT on the thermomechanical properties, thermal stability and flame retardancy of the resulting epoxy thermosets were investigated. The results showed that when the addition of DOPO-TPT was 5 mass% (phosphorus content was 0.47 mass%), the limiting oxygen index of the epoxy thermoset reached 30.0%, and it passed the UL-94 V-0 classification. Compared with unmodified epoxy resin, the maximum heat release rate and total heat release of EP/DOPO-TPT-5.0 decreased by 28% and 20%, respectively. Additionally, the presence of DOPO-TPT did not deteriorate the thermomechanical properties of the resulting epoxy thermosets. TG-FTIR test confirmed that the incorporation of DOPO-TPT could significantly inhibit the release of gaseous products. The char layer analysis results showed that DOPO-TPT had good catalytic charring performance, which was conducive to decreasing the escape of combustible gas during combustion, thus improving the flame retardancy. [ABSTRACT FROM AUTHOR]

Modern society relies heavily on producing commercial and industrial plastics to improve the quality and quantity of our lives. However, increased fire risks threaten commercial operations and the potential impact of high‐performance electronic and transportation technologies that utilize polymeric materials. Despite significant monitoring and reduction of commonly used halogenated flame retardants, their worldwide usage still poses environmental hazards. Many non‐halogenated flame‐retardant compounds are viable additives for synthetic polymers; however, their incorporation often results in reduced composite homogeneity and mechanical strength. This review focuses on reactive flame retardants and the effect of polymer structure on inherent flame retardance in recent studies. The synthesis and characterization of polymeric systems (e.g. polyurethanes, polyamides, polyimides, polyesters and epoxy resins) are discussed in terms of structure–flame‐retardant performance using a complement of analytical tools, including thermogravimetric analysis, cone calorimetry, limiting oxygen index and UL 94 testing. These commercially important polymeric systems represent a broad compositional space for future adaptation and the discovery of increasingly modular polymeric materials with, while also contributing to the fundamental understanding of unique combinations of gas‐ and condensed‐phase mechanisms of flame retardance. © 2024 Society of Chemical Industry. [ABSTRACT FROM AUTHOR]

It is difficult to effectively manage the emission of harmful smoke from flame‐retardant modified epoxy resins (EP). In order to solve this difficulty, a highly efficient flame‐resistant PAD containing phosphorus, nitrogen, and sulfur was synthesized using a simply one‐pot method employing 9,10‐dihydro‐9‐oxa‐10‐phosphaphenanthrene‐10‐oxide (DOPO), 2‐amino‐5‐mercapto‐1,3,4‐thiadiazole (AMT), and terephthalaldehyde for not only enhancing its flame retardant properties but also effectively suppressing the emission of fumes. Results have confirmed that the incorporation of 5 wt% flame retardant into the EP successfully passed the UL‐94 V‐0 rating, besides 24.2% reduction in the peak of smoke produce rate (PSPR), with outstanding fire‐resistant properties and effectively reduce smoke emissions. In addition, incorporating 7.5% of PAD into EP increased its flexural strength and modulus, from 78.4 and 2917.5 to 86.6 and 3162.9 MPa, respectively. Due to the abundance of reactive groups including sulfhydryl and secondary amine in PAD, as well as the nitrogen atoms presented in the thiadiazole and benzene rings of the phosphaphenanthrene structure, which could create hydrogen bonds with the matrix and participated in π‐π interactions, therefore, the mechanical properties of flame retardant epoxy resin (FREP) were greatly enhanced. [ABSTRACT FROM AUTHOR]

This paper presents a study of the flammability and thermal decomposition products of glass fiber-reinforced epoxy resin (GFRER) with the addition of cardanol-based phosphorus-containing benzoxazine monomer (CBz) and graphene and their combinations in different proportions (up to 20 wt.%). The addition of CBz alone or in combination with graphene resulted in an increase in the limiting oxygen index (LOI) and self-extinguishing in the UL-94 HB test. The flame-retardant samples had better tensile mechanical properties than the sample without additives. The differential mass-spectrometric thermal analysis (DMSTA) of the thermal decomposition products of GFRER without additives and with the addition of CBz and graphene was carried out. CBz addition promoted the thermal decomposition of high-molecular-weight products of epoxy resin decomposition in the condensed phase and at the same time decreased the time of release of low-molecular-weight thermal decomposition products into the gas phase. Graphene addition resulted in an increase in the relative intensities of high-molecular-mass peaks compared to GFRER without additives. [ABSTRACT FROM AUTHOR]

High‐efficient flame retardants (ZrP‐DDM) were synthesized successfully via ion‐exchange method, using diaminodiphenylmethane (DDM) modified layered zirconium phosphate (α‐ZrP). Trace addition of ZrP‐DDM in epoxy resins (EP) can enhance the flame‐retardant, smoke‐inhibition, mechanical, and thermal stability properties of EP composites. As shown in the results, ZrP‐DDM exhibits a better synergistic effect than α‐ZrP, and the EP composites containing 0.5 wt% ZrP‐DDM (EP/0.5ZrP‐DDM) show excellent flame‐retardant and smoke‐inhibition properties. Especially, EP/0.5ZrP‐DDM possesses a limiting oxygen index (LOI) of 33.7% with UL94 V‐1 rating, while the EP composites containing 0.5 wt% ZrP (EP/0.5ZrP) has a LOI of 30.1% and fails to achieve the UL94 rating. Furthermore, the peak heat release rate (PHRR), total heat release rate (THR), and smoke density rating of EP/0.5ZrP‐DDM decrease by 10.2%, 3.7%, and 8.2% compared with EP/0.5ZrP. Based on condensed‐phase product analysis, EP/ZrP‐DDM sample provides a gas source for intumescent char layer, and produces a stable phosphorus‐rich crosslinking structures during combustion, thus decreasing the fire hazard of the composite material. Meanwhile, the introduction of ZrP‐DDM has a less impact on tensile strength of EP composites compared with α‐ZrP, suggesting the addition of ZrP‐DDM effectively enhances the compatibility with the EP matrix, thereby maintaining excellent mechanical properties of the EP matrix. [ABSTRACT FROM AUTHOR]

Ammonium polyphosphate (APP), 9, 10-dihydro-9-oxa-10-phosphame-10-oxide (DOPO), and melamine polyphosphate (MPP) were intercalated into magnesia-aluminum hydrotalcite (MAH) to obtain intercalation complexes (APP-MAH-6H, DOPO-MAH-6H, MPP-MAH-6H) . EP/DOPO-MAH-6H, EP/APPMAH-6H, and EP/MPP-MAH-6H were prepared by mixing the intercalation complexes and hot curing with epoxy resin (EP) . The structures and properties of EP/DOPO-MAH-6H, EP/APP-MAH-6H, and EP/MPPMAH-6H were characterized by cone calorimetry, vertical combustion, limiting oxygen index（LOI), scanning electron microscopy (SEM) and Raman spectrum, and their flame retardant properties were investigated. The experimental results show that： Compared with pure EP, the peak heat release rate（pHRR) of EP/DOPOMAH-6H, EP/APP-MAH-6H and EP/MPP-MAH-6H decreased from 1079. 2 kW/m² to 481. 3, 445. 7 and 385. 8 kW/m², respectively, and the LOI increased from 25. 1% to 32. 2%, 32. 9% and 33. 8%, respectively. In addition, in the UL-94 test of vertical combustion, EP/DOPO-MAH-6H, EP/APP-MAH-6H and EP/MPPMAH-6H all achieved V-0 levels. According to SEM, the morphologies of char residue for EP/DOP-MAH-6H and EP/APP-MAH-6H are large and continuous, while the morphologies of char residue for EP/MPP-MAH-6H are dense and continuous. The test results of Raman spectrum show that the three EP composites form a continuous, high-quality carbon layer, which can effectively isolate the transfer of oxygen and heat to the internal matrix during the combustion process. Therefore, the addition of the three phosphorus intercalation complexes can greatly improve the flame retardancy of epoxy resin. [ABSTRACT FROM AUTHOR]

[Display omitted] • Effective utilization of the "synchronous etching" effect caused by the preparation of polyphosphazene coating to induce structural remodeling of ZIF-67. • A series of ZIF-derived cyclomatrix polyphosphazene flame retardants were prepared. • Polyphosphazene serves to enhance the compatibility between flame retardant and the matrix, creating increased mechanical strength. Cyclomatrix polyphosphazenes have attracted widespread attention in the field of polymer flame retardancy. Nevertheless, the optimal manifestation of their distinctive structural attributes and flame-retardant properties necessitates a judicious selection of condensation monomers and synergistic templates during the fabrication of polyphosphazene flame retardants. In our previous studies, it was discovered that when ZIF-67 is functionalized with polyphosphazene, the by-product HCl from phosphazene polycondensation causes etching on ZIF-67. Based on this "synchronous etching" effect, a series of hybrid materials comprising cyclomatrix polyphosphazene and ZIF-67, denoted as ZIF-67@PDS (PDS, poly-(cyclotriphosphazene-co-4,4'-diaminodiphenyl sulfone)), ZIF-67@PBS (PBS, poly-(cyclotriphosphazene-co-Bisphenol A)), and ZIF-67@PZS (PZS, poly-(cyclotriphosphazene-co-4,4'-sulfonyldiphenol)), was synthesized utilizing DDS (4,4'-diaminodiphenyl sulfone), BPA (Bisphenol A), and BPS (4,4'-sulfonyldiphenol) monomers as precursors, respectively. Upon the incorporation of 2.0 wt.% of ZIF-67@PDS, ZIF-67@PBS, and ZIF-67@PZS, the flame retardant and mechanical characteristics of EP composites exhibited marked enhancement. The unique structural characteristics of hybrid and the synergistic effects of Co-P-N contribute to the improvement of comprehensive properties. Compared with pure EP, EP/ZIF-67@PZS has the best enhancement effect, and its pHRR, THR, and TSP decreased by 34.0%, 30.0%, and 40.5%, respectively. In terms of mechanical strength, ZIF-67@PZS also increases the flexural strength of EP by 37.42%. Relying on the "synchronous etching" effect, this study explores and verifies the effective combination of ZIF-67 and different types of polyphosphazenes, and obtains a series of ZIF-67-derived cyclomatrix polyphosphazene hybrids with different morphologies and properties in one step. It provides a new idea and strategy for the simultaneous modification of polyphosphazene materials and the preparation of multifunctional flame retardants in the future. [ABSTRACT FROM AUTHOR]

Epoxy sheet molding compound (ESMC) composites have excellent mechanical properties, dimensional stability and electrical insulation, and are widely used in the automotive industry. In our previous work silane coupling agent modified, hollow glass microspheres (SiHGM) and montmorillonite (MMT) were incorporated to enhance the mechanical properties of the ESMC composites. It was found that the ESMC composites containing MMT (EP/SiHGM/MMT-1) exhibited excellent mechanical strength. However, the flammability of the epoxy resin (EP) limits the use of ESMC composites for applications that require good flame retardancy. In this paper we describe our research in which MMT was used to increase the flame retardancy of ESMC composites. The results showed that the addition of MMT made the ESMC composites have excellent flame retardancy. The limiting oxygen index (LOI) of the ESMC composites containing 1 phr MMT (EP/SiHGM/MMT-1) was 26.8%, which was 8.94% higher than that of the ESMC composites without MMT (EP/SiHGM/MMT-0). In addition, the peak heat release rate (PHRR), average heat release rate (AHRR) and total heat release (THR) of the EP/SiHGM/MMT-1 were 322.8 kW/m2, 95.3 kW/m2 and 38.6 MJ/m2, respectively, which were 22.6%, 8.2% and 8.0% lower than those of EP/SiHGM/MMT-0. The carbon monoxide production (COP) and carbon dioxide production (CO2P) of EP/SiHGM/MMT-1 were 0.0092 g/s and 0.2071 g/s, respectively, which were 34.3% and 22.8% lower than those of EP/SiHGM/MMT-0. The fire growth index (FGI) of EP/SiHGM/MMT-1 was 2.4, which was a decrease by 29.4% compared to EP/SiHGM/MMT-0. In addition, the flame retardant mechanisms were revealed. We suggest that MMT promoted dehydration and charring of the epoxy resin and helped construct an intact physical barrier, which had good blocking effects. The prepared composite has great application prospects for those occasions that require high flame retardancy. Thus, this work provides an innovative strategy for preparing low density epoxy composites with excellent flame retardancy and high mechanical properties. [ABSTRACT FROM AUTHOR]

A biomass-based charring agent was synthesized and applied to the modification of ammonium polyphosphate (APP) flame retardant to enhance the fire safety performance of epoxy resin (EP). After the reaction of melamine (MA) and vanillin in different ratios to form a carbonized coating (MV), APP was coated to obtain the bio-based charcoal-forming agent modified APP flame retardant (MV@APP), which was added to EP. It was found that the flame retardant obtained from the 1:2 mass ratio of MA to vanillin in the same flame retardant additive ratio (5%) was the most effective in EP (MV@APP/EP-2), with the peak heat release rate, total heat release and total smoke production reduced by 57.2%, 66.4% and 62.7%, respectively. Thermal stability analysis shows that the addition of MV@APP improves the thermal stability as well as the amount of residual carbon. In addition, the compatibility between the flame retardant and EP was improved by the modification of APP by the organic charcoal-forming agent, and the flexural properties of EP were enhanced by the addition of the flame retardant. [ABSTRACT FROM AUTHOR]

Integrating flame‐retardant additives into epoxy resins is an essential strategy for improving their fire resistance. However, introducing flame‐retardant groups often compromises the processability and mechanical integrity of such resins. In this research, we synthesized a novel, biobased flame retardant, referred to as DPN, using naringenin and chlorodiphenylphosphine as precursors via a straightforward single‐step process. The addition of DPN markedly decreased the viscosity of hydantoin epoxy resin, from 7468 to 1285 mPa s. Furthermore, when cured with 4,4‐diaminodiphenylmethane, the composite containing five equivalents of DPN (DPN‐5) exhibited a marked improvement in mechanical strength, reaching 190 MPa, significantly outperforming the pure thermoset (DPN‐0: 104 MPa), while preserving high transparency. Combustion tests further confirmed that DPN significantly boosts the flame resistance of the thermoset, with DPN‐5 achieving a limiting oxygen index of 37% and securing a UL‐94 V‐0 rating. Cone calorimetry analysis showed that DPN‐5 effectively reduced heat and smoke production during combustion, achieving a 13.4% reduction in peak heat release rate and a 28.2% decrease in total heat release compared to DPN‐0. This study underscores the potential of multifunctional biobased flame retardants derived from renewable resources in advancing the development of high‐performance materials. © 2024 Society of Industrial Chemistry. [ABSTRACT FROM AUTHOR]

In view of the serious problem of recycling and insolubility of thermosetting resin matrix composites in automobile manufacturing, a curing agent containing dynamic imine bond was synthesized by using biovanillin and 4, 4-diaminophenylsulfone. It was further used to cure epoxy resins into a vitreous matrix for fiberglass composite that could be reprocessed and recycled. The composite shows excellent mechanical properties, with a tensile strength and modulus of 670 MPa and 29 GPa, flexural strength and modulus of 752 MPa and 27 GPa, and shear strength of 55 MPa, which are comparable to the commercial battery pack composite material such as BAC 449. This new vitrimer-based composite has better mechanical properties, and its flame retardant can reach UL-94 V-0 level. In addition, owing to the nature of dynamic imine bonds, this vitrimer-based composite can be chemically degraded so that the fiber and resin in the composite can be recycled and reused, helping with carbon reduction and environmental protection. It has potential application in the manufacturing of composite covers of battery packs for electric vehicles. [ABSTRACT FROM AUTHOR]

This research aims to develop fiber-reinforced composites (FRC) with enhanced fire resistance, which can be particularly useful for the transport industry (e.g., aviation, automotive, and train production). The fire retardation was achieved through epoxy matrix modification with hexachlorocyclotriphosphazene (HCTP). First, the fire-resistant and mechanical properties of the epoxy matrix filled with different HCTP contents (4.8, 7.2, and 9.5 wt.%) were studied to select the most effective HCTP content for the impregnation of FRC. Then, glass, basalt, and carbon fiber fabrics were impregnated with epoxy filled with 7.2 wt.% of HCTP, and the fire resistance, flexural, and interlaminar fracture properties were studied to select the most effective HCTP-modified type of fiber reinforcement based on the test results. It was concluded that basalt fiber impregnated with epoxy filled with HCTP could be selected as the most effective reinforcement type, allowing excellent mechanical and flame-retardant properties. [ABSTRACT FROM AUTHOR]

Carbon fiber (CF)‐reinforced epoxy resin (EP) composites are lightweight materials with excellent comprehensive performance. However, the flammability of EP and the poor interfacial bonding between CF and EP are two key disadvantages that limit their further applications. Here, a kind of water‐soluble lignin‐based CF sizing agent (ELBEDK) is prepared through hydrophilic modification of enzymatic lignin, which can significantly enhance the interfacial interaction between CF and EP. Additionally, a highly efficient intumescent flame retardant (LMA) is prepared. The EP, enzymatic lignin, LMA and CF sized ELBEDK are compounded to obtain the fire‐safety CF reinforced composites (SCF/FEP/L). The flame retardancy of SCF/FEP/L with 7% LMA (SCF/FEP7) reached V‐0 rating. Moreover, SCF/FEP/L with 7% LMA and 15% lignin (SCF/FEP7/L15) present an limiting oxygen index (LOI)of 30.2% and V‐0 of UL‐94. Specifically, the total smoke production and the heat release rate are 47.8% and 46.81% lower than that of SCF/EP, respectively, indicating the improved smoke suppression and flame retardancy. The IFSS and flexural strength of SCF/FEP7/L15 are improved to be 59.4 MPa and 511.1 MPa, respectively. This study presents a simple approach to fabricate low‐cost high performance lignin‐based flame retardant CF/EP biocomposites with wide application potential. [ABSTRACT FROM AUTHOR]

In order to obtain an efficient flame retardant and smoke suppressor without sacrificing mechanical properties of epoxy resin (EP). A cyano group‐containing 9,10‐dihydro‐9‐oxa‐10‐phosphaphenanthrene‐10‐oxide (DOPO) derivative (CP‐DOPO) was proposed and synthesized through one‐step Atherton–Todd reaction between DOPO and 4‐cyanophenol. The comprehensive performance analysis of CP‐DOPO‐based EP composite was conducted by measuring the flame retardancy, smoke suppression, and mechanical properties. The flame‐retardant test findings shows that the EP/4CP‐DOPO sample achieves UL‐94 V‐0 rating with 4 wt% low addition of CP‐DOPO. Moreover, EP/6CP‐DOPO sample presents a LOI of 36.5%, a 28.1% reduction in the peak heat release rate, and a 42.1% substantial decrease in total smoke production, demonstrating its desirable flame retardancy and smoke suppression properties. Significantly, different from the traditionally additive flame retardants, the mechanical properties of EP matrix will not be affected by the incorporation of CP‐DOPO but a 17.7% increasement of flexural properties compared to EP. This research not only provides an ingenious strategy for designing and preparing high‐effective flame retardant but also enhances the comprehensive performance of EP resins in practical applications. [ABSTRACT FROM AUTHOR]

Bio-based materials as flame retardants meet the requirements of green strategy and sustainable development. Here nitrogen and phosphorus-modified bio-based cellulose nanocrystal composite (NPCNCs) were designed and added to epoxy resin (EP) to determine fire safety and mechanical properties. NPCNCs were successfully synthesized using ice bath polymerization and exhibited a fibrous appearance with rough surface. When corresponding into EP, NPCNCs endowed EP composite with excellent flame retardancy. For EP/6NPCNCs, the LOI value was 27.6% which was higher than that of pure EP (23.5%). Compared with pure EP, the total heat release, peak heat release rate, total smoke production and peak smoke production rate values of EP/6NPCNCs decreased by 27.27%, 43.34%, 70.21% and 66.67%. This was attributed to catalysis-dehydration and carbonization, carbon support of cellulose nanocrystals and gas phase dilution. In addition, the flame retardant EP composite mechanical properties were basically maintained compared with the pure EP. This article will provide a new way for the design bio-based P and N-modified flame retardants. [ABSTRACT FROM AUTHOR]

Among the various fire‐retardants (FRs) known, phosphorus is vital to the development of effective FRs due to its flexibility. Additionally, the additives and combinations of phosphorus with various multicomponent moieties (e. g. P−Si, P−P, P−B, etc.) can serve the purpose in different phases to improve flame retardance properties. With an increased cognizance of recyclable, eco‐friendly, and bio‐based materials, phosphine oxide‐based materials/coatings can fulfill the criteria for flawless and future FRs. In this regard, the present review highlights the most promising organophosphorus‐based compositions as non‐intrusive FRs. The classification, synthetic methods, related mechanisms, and high‐end FR applications of various recently developed organophosphorus‐based molecules and materials are demonstrated. Among various organophosphorus compounds, the phosphorus‐based polyurethane materials display remarkable FR properties and non‐toxic behavior. Notably, the flame retardance of the epoxy resins is enhanced significantly with the presence of more P=O bonds and amino groups. The limitations and advantages of organophosphorus‐based materials are compared with the traditional FRs. Also, the challenges persisting in improving current flame‐retardant materials need to be addressed. However, the success of these materials and treatment methods strongly depends on the ability to impart desired functionality, durability, and scalability without compromising environmental problems. [ABSTRACT FROM AUTHOR]

The systematic transfer of solvent‐free, additive flame retardant (FR) formulations from epoxy resins to glass fiber‐reinforced epoxy composites (GFRECs) through prepregs is difficult. Additionally, obtaining data on their post‐fire mechanics is often challenging. Utilizing melamine polyphosphate (MPP), ammonium polyphosphate (APP), and silane‐coated ammonium polyphosphate (SiAPP) FRs with low‐melting inorganic silicates (InSi) in an 8:2 proportion and 10% loading by weight in a diglycidyl ether of bisphenol A (DGEBA) resin, a systematic investigation of the processing properties, room‐temperature mechanics, and temperature‐based mechanics of the systems was performed. The resin was cured with a dicyandiamide hardener (DICY) and a urone accelerator. The results revealed no substantial impact of these FRs at the current loading on the resin's glass transition temperature or processability. However, the fire residues from cone calorimetry tests of the composites containing FRs were found to be only 15‐20% of the thickness of the resins, implying a suppression of intumescence upon transfer. At room temperature, the decrease in the flexural modulus for the composites containing FRs was negligible. Exposure of the composites in a furnace at 400°C as a preliminary study before ignition tests was shown to cause significant flexural moduli reductions after 2.5 min of exposure and complete delamination after 3 min making further testing unviable. This study emphasizes the need for future research on recovering modes of action upon transfer of FR formulations from resins to composites. Based on the challenges outlined in this investigation, sample adaptation methods for post‐fire analysis will be developed in a future study. Highlights: Processibility of resins for prepreg production unaffected by polyphosphate/inorganic silicate flame retardants (FRs).FR formulations had a negligible effect on the mechanics of the composites.15%–25% increase in the fracture toughness of the DGEBA‐based resin matrix with FRs.Suppression of intumescent behavior in the composites verified quantitatively.Significant reduction in flexural moduli of the composites post‐400°C exposure in a furnace. [ABSTRACT FROM AUTHOR]

Ammonium polyphosphate (APP) is often used to construct intumescent flame retardant systems together, but it is faced with the problem of adding too much flame retardant. This paper envisions the construction of a modified APP flame retardant (TR@ZIFAPP) with a sandwich structure by the method of covering, which, in order to endow APP flame retardant with better flame retardant effect. By constructing a metal catalytic layer and a triazine carbon formation layer, the modified APP flame retardant has both catalytic carbon formation and phosphorus–nitrogen synergistic flame retardant functions. TR@ZIFAPP is expected to be used in flame‐retardant polymer composites with low addition requirements, adding it to epoxy resin (EP) reveals that the TR@ZIFAPP flame retardant could achieve the optimal flame retardant effect when the addition amount was only 3 wt%. The UL‐94 rating reached V‐0 grade, and the two off‐fire auto‐ignition time levels were only 0.7 s. The analysis of its flame retardant mechanism showed that the flame retardant in EP was mainly through the rapid formation of carbon to isolate oxygen and dilute the flammable gas to reach a strong flame retardant effect. [ABSTRACT FROM AUTHOR]

Currently, epoxy resin (EP) is widely used in various fields, but its flammability greatly limits the wider application of EP. In recent years, additive flame retardants have been widely used to enhance the flame retardancy of EPs, but poor resistance to weather and aging is a prevalent issue encountered with additive flame retardants. To improve the weather fastness, researchers have successfully created and synthesized EP molecules that possess a combined effect of P, N, and B. The results demonstrate a significant enhancement in the mechanical properties of materials containing 20% BVN/10% VPD/EP compared with those of pure EP. 20% BVN/20% VPD/EP exhibited a vertical combustion rating of V‐1 with a limiting oxygen index measuring at 29.8%. The flame retardant epoxy thermosets exhibited a notable decrease in both the maximum heat release rate and total heat release. The findings indicate that the inherent flame‐retardant properties of the P‐N‐B coacting EP are not only characterized by exceptional curing and flame retardancy but also by superior resistance to weathering and aging compared with the additive flame retardant. [ABSTRACT FROM AUTHOR]

In this work, the flame retardant ISA-APP, obtained by modification of ammonium polyphosphate (APP) with isopropanolamine (ISA), was employed in epoxy resins (EP) in an attempt to enhance the fire resistance of EP. The findings indicate that, with an incorporation of 20 wt% ISA-APP in the EP, the limiting oxygen index (LOI) of EP/ISA-APP attains 33.5%, accompanied by a UL94 test V-0 rating. This performance surpasses the flame retardancy observed in EP/APP composites at equivalent content. The outcomes derived from the cone calorimeter test (CCT) demonstrate that EP/ISA-APP significantly suppresses the release of heat, generation of smoke, and emission of noxious gas during EP/ISA-APP combustion. The peak-heat release rate (pHRR) and total heat release (THR) of EP/ISA-APP are decreased by 74.4% and 63.6%, respectively, compared to pure EP. Further analysis of the char residues of EP/ISA-APP shows that the P-O-C structure generated during combustion effectively contributes to a high-quality char layer formation. This investigation presents a viable approach for enhancing flame retardant and economic benefits of APP and advancing the development of highly effective flame retardants. [ABSTRACT FROM AUTHOR]

An N, P co‐doped carbon quantum dot (NP‐CQD) was prepared using citric acid as the carbon source and hexachlorotripolyphosphonitrile as the nitrogen and phosphorus source. The structure and morphology of NP‐CQD were characterized. Subsequently, NP‐CQD was blended with ammonium polyphosphate (APP) to come into being a synergistic phosphorus‐nitrogen flame retardant system (SPFRS). The SPFRS was applied in epoxy resin (EP) to enhance the flame retardancy of EP. Thermal stability, flame retardancy, combustion behavior, and char residue morphology of the EP samples were determined by multiple testing methods such as thermogravimetric analysis, vertical burning (UL‐94) and limiting oxygen index (LOI) tests, microscale combustion calorimetry test, and scanning electron microscopy. When the weight ratio of NP‐CQD to APP was kept at 1:9 and 8% SPFRS was added to EP, the obtained flame‐retardant EP (EP/CQD‐APP2:18) passed the UL‐94 V‐0 level and the LOI value of EP/CQD‐APP2:18 reached 33.2%. The MCC test showed that the heat release capacity (HRC) of EP/CQD‐APP2:18 was reduced by 48.7% compared with pure EP. Morphology observation on the char residue of EP/CQD‐APP2:18 after the UL‐94 test indicated that the addition of SPFRS promoted the formation of the dense char residue layer to improve the flame retardancy of EP. Highlight: An N, P co‐doped carbon quantum dot (NP‐CQD) was prepared and applied as a flame retardant.NP‐CQD and ammonium polyphosphate (APP) showed synergistic flame retardancy in epoxy resin.The proper weight ratio of NP‐CQD to APP was 1:9. [ABSTRACT FROM AUTHOR]

To address the shortcomings of poor thermal stability, easy migration, and over‐plasticization of the liquid organic phosphorus flame retardant, cresyl diphenyl phosphate (CDP), we employed halloysite nanotube (HNT) as a carrier to load CDP, thus forming a novel composite (HNT‐CDP). The results demonstrated that the CDP loaded into HNT channels was 41 wt%. HNT‐CDP composites exhibited higher thermal stability, water resistance, and flame retardancy than mixtures of HNT and CDP in epoxy resin (EP). With a loading of 15 wt%, the limiting oxygen index of EP/HNT‐CDP increased to 48.3 and achieved a V‐0 rating in UL94 tests. Additionally, HNT‐CDP exhibited better inhibitory effects on the peak heat release rate and total heat release of EP, as well as a longer time to ignition, compared with the mixture. Moreover, as opposed to EP/HNT + CDP, EP/HNT‐CDP exhibited a significant 114.5% increase in tensile strength. These excellent thermal, water resistance, and mechanical properties can be primarily attributed to the loading of CDP by HNT channels. HNT effectively utilizes the channel confinement effect to isolate CDP from directly interacting with EP. The outstanding flame retardancy is mainly due to the synergistic effect between HNT and CDP after the formation of the composite. [ABSTRACT FROM AUTHOR]

In order to improve the fire safety of epoxy resins (EPs), the SBA‐15 based hybrid flame retardant (SNAZD) was synthesized via an organic–inorganic hybridization strategy of mesoporous silica SBA‐15. Relying on electrostatic interaction, the zinc amino‐tris‐(methylenephosphonate) (Zn‐ATMP) was successfully introduced into the pore channels of SBA‐15. Then, 9,10‐dihydro‐9‐oxa‐10‐phosphaphenanthrene‐10‐oxide (DOPO) was successfully loaded into the pores of SBA‐15 under vacuum. The results show that the EP composites with the 5%SNAZD sample (sample EP‐5%SNAZD) showed a LOI value of 30.9% and achieved the vertical burning V‐0 rating. In comparison to EP, the peak heat release rate, peak smoke production rate, and production rate of CO of EP‐3%SNAZD were reduced by 32.2%, 31.9%, and 20.0%, respectively. This is due to the presence of Si, P, N, and Zn elements in the SNAZD, which promoted the generation of a high yield of dense char residue and inhibited the release of toxic gasses. And the impact strength and flexural strength of EP‐1%SNAZD were increased by 19.5% and 15.6%, respectively, and the E' of EP‐5%SNAZD increased by 49.1% when compared with the neat EP. This work provides a general strategy for the design of mesoporous hybrid flame retardant and creates additional opportunities for applications of EP. [ABSTRACT FROM AUTHOR]

Magnesium hydroxide, as a green inorganic flame-retardancy additive, has been widely used in polymer flame retardancy. However, magnesium hydroxide is difficult to disperse with epoxy resin (EP), and its flame-retardancy performance is poor, so it is difficult to use in flame-retardant epoxy resin. In this study, an efficient magnesium hydroxide-based flame retardant (MH@PPAC) was prepared by surface modification of 2-(diphenyl phosphine) benzoic acid (PPAC) using a simple method. The effect of MH@PPAC on the flame-retardancy properties for epoxy resins was investigated, and the flame-retardancy mechanism was studied. The results show that 5 wt% MH@PPAC can increase the limiting oxygen index for EP from 24.1% to 38.9%, achieving a V-0 rating. At the same time, compared to EP, the peak heat release rate, peak smoke production rate, total smoke production rate, and peak CO generation rate for EP/5 wt% MH@PPAC composite material decreased by 53%, 45%, 51.85%, and 53.13% respectively. The cooperative effect for PPAC and MH promotes the formation of a continuous and dense char layer during the combustion process for the EP-blend material, significantly reducing the exchange for heat and combustible gases, and effectively hindering the combustion process. Additionally, the surface modification of PPAC enhances the dispersion of MH in the EP matrix, endowing EP with superior mechanical properties that meet practical application requirements, thereby expanding the application scope for flame-retardant EP-blend materials. [ABSTRACT FROM AUTHOR]

Polybenzoxazines (PBz) are a new type of resin belonging to the category of phenolic resins. As polybenzoxazines are addition-curable polymers, this obviates many of the shortcomings associated with conventional phenolic resins while endowing them with excellent thermal, physical, and thermo-physical properties and surpass the features of many conventional and state-of-the-art polymers. They even possess excellent design flexibility. In this study, a benzoxazine monomer was successfully synthesized from eugenol (Eu), ethylenediamine, and paraformaldehyde utilizing a solventless approach. The synthesized benzoxazine resin was characterized for its structural elucidation via FTIR, 1H, and 13C NMR spectroscopy and was used for crosslinking a petroleum-based epoxy and a gallic acid-based epoxy. The effects of the presence of benzoxazine on the thermal and flame retardant properties of the films were evaluated using TGA and DSC analysis and the LOI and UL 94 tests, respectively. It was found that the benzoxazine in the epoxy systems led to an increase in thermal stability and flame retardancy. The gallic acid-based epoxy system showed better thermal and flame retardant properties compared to the petroleum-based epoxy system, thus showing potential to replace the petroleum-based epoxy for high-performance applications. [ABSTRACT FROM AUTHOR]

A fully biobased waterborne flame‐retarded epoxy system was prepared using sorbitol polyglycidyl ether epoxy resin (SPE) and phytic acid (PA) as a reactive flame retardant (FR). The flame‐retardant efficiency was evaluated by comparing the reference SPE‐PA system with solventborne and waterborne SPE systems. Additional enhancement of intumescence and reduction of flammability was achieved by incorporating ammonium polyphosphate (APP) and melamine (MEL) into the SPE–PA system. PA, serving as a curing agent, contributed approximately 1% phosphorous content, resulting in an increased limiting oxygen index (LOI). UL‐94 flammability tests demonstrated improved FR properties with PA, and the addition of 2% phosphorous from APP to SPE‐PA achieved a self‐extinguishing V0 UL‐94 rating. Thermogravimetric analysis (TGA) revealed enhanced thermal stability and higher char yield with PA compared with other curing agents. Mass loss calorimetry (MLC) confirmed the superior charring effect of PA compared with other curing agents. The thermal insulation properties of the residual char were assessed by measuring the temperature on the back surface (Tb) of coated steel plates exposed to a 25 kW/m2 heat flux for 1 h. The PA sample containing 3%P of APP exhibited a Tb decrease of 130°C compared with the solventborne reference sample. Scanning electron microscopy analysis of the char morphology supported these findings, indicating the effectiveness of the intumescent FR system. Infrared spectra of the char residues and pyrolysis gaseous products were obtained to gain insights into the flame‐retardant mechanism of the different systems. [ABSTRACT FROM AUTHOR]

For effectively strengthening the comprehensive properties of intumescent flame‐retardant epoxy resins (EPs), a microencapsulating γ‐Fe2O3 by polypyrrole (PPy) named PPy‐Fe2O3 was synthesized and used as a synergist to simultaneously enhance the flame retardancy, smoke toxicity suppression and mechanical strength of EP composites containing diaminodiphenylmethane modified ammonium polyphosphate (DDP). The results demonstrate that the mixture of PPy‐Fe2O3 and DDP exhibits a surprising synergistic effect on strengthening the comprehensive properties of EP composites. Specifically, EP composite containing 0.2 wt% PPy‐Fe2O3 and 9.8 wt% DDP achieves the UL94 V‐0 rating with a limiting oxygen index (LOI) value of 35.5%, while 10 wt% DDP only imparts a UL94 V‐1 rating and a LOI value of 34.0% to EP. Furthermore, 0.2 wt% PPy‐Fe2O3 shows a 11.0% reduction in peak smoke production rate and a 12.3% reduction in peak heat release rate of the EP/DDP system. The enhanced fire security of EP/DDP/PPy‐Fe2O3 is attributed to the formation of more phosphorus‐rich structures retained in the char, thus reducing the release of harmful gases including NH3, CO, and CO2, and generating more incombustible gases including H2O to weaken burning intensity. Meanwhile, the satisfactory compatibility of PPy‐Fe2O3 with epoxy matrix imparts a superior mechanical strength to EP composites. [ABSTRACT FROM AUTHOR]

This research study focused on the effect of adding boric acid to epoxy resin in order to obtain a composite material with improved properties and performance. To this end, a fine powder of boric acid (H3BO3) was introduced into epoxy resin in different amounts, i.e., 0.5 g, 1.0 g, and 1.5 g. As the matrix of the epoxy composites, styrene-modified epoxy resin based on bisphenol A (BPA) (Epidian 53) was used. It was cross-linked with two types of curing agents, i.e., an amine (ET) and a polyamide (PAC). The mechanical properties of the obtained epoxy composites (in terms of compressive strength, compressive modulus, and compressive strain) were determined at room temperature in order to assess the effect of the addition of boron acid and of the type of curing agent employed to cure the epoxy on these characteristics. Calorimetric measurements were made to highlight any changes in the glass transition temperature (Tg) as a result of the addition of boric acid to epoxy resin. Finally, flammability tests were performed on both Epidian 53/PAC and Epidian 53/ET epoxy composites to analyze their fire behavior and consequently establish the effectiveness of the selected additive as a flame retardant. [ABSTRACT FROM AUTHOR]

The flammability of epoxy resins and knowing how to achieve curing are particularly important factors during use. A novel approach for enhancing the fire resistance and reducing the smoke emission of epoxy resin during the curing process is suggested, which involves the utilization of a three-source integrated polymerization intumescent flame-retardant. In this study, the synthesis of poly 4,4-diaminodiphenylsulfone spirocyclic pentaerythritol bisphosphonate (PCS) is achieved through using solution polymerization, utilizing 4,4′-diaminodiphenylsulfone (DDS) and spirocyclic pentaerythritol bisphosphorate disphosphoryl chloride (SPDPC) as initial components. Following that, the EP underwent the inclusion of PCS to examine its resistance to heat, its ability to prevent flames, its effectiveness in reducing smoke and its curing effect. Compared to the unmodified epoxy resin, the addition of PCS can not only cure the epoxy resin, but also decompose before the epoxy resin and has a good carbonization effect. With the addition of 7 wt.% PCS, the LOI value can achieve 31.2% and successfully pass the UL-94 test with a V-0 rating. Moreover, the cone calorimeter experiment demonstrated a noteworthy decline of 59.7% in the maximum heat release rate (pHRR), 63.7% in overall heat release (THR), and 42.3% in total smoke generation (TSP). Based on the examination of TG-FTIR and SEM findings, there is ample evidence to suggest that PCS, functioning as a phosphorus-nitrogen intumescent flame-retardant that combines three origins, has the potential to exhibit a favorable flame-retardant impact in both its gas and condensed phases. [ABSTRACT FROM AUTHOR]

Over the past few decades, the development of highly efficient phosphorus-based flame retardants has become one of the research focuses in the field of halogen-free flame-retardant polymer technology. In this work, three kinds of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO)-based derivatives were synthesized through integrating multiple phosphorous oxidation states into one molecular structure. The influence of DOPO-based derivatives on the thermal decomposition and flame-retardant properties of EP composites were investigated. DOPO-based derivatives promoted the slightly earlier decomposition of the epoxy matrix, resulting in better thermal stability at high temperatures and higher char yield. The unmodified EP showed a LOI value of 27.0% and no UL-94 rating, while all the EP composites containing 2 wt.% DOPO-based derivatives passed the UL-94 V-0 rating and achieved a LOI value of higher than 30.0%. Among the three DOPO-based derivatives, TDCA-DOPO-2 behaved the best flame-retardant efficiency owing to the highest synergistic effect. Specifically, the peak of heat release rate, total heat release and average effective heat combustion (av-EHC) of EP/TDCA-DOPO-2 was 62.0%, 54.2% and 39.9% lower than those of the unmodified EP, respectively. The high flame-retardant efficiency of DOPO-based derivatives was ascribed to the synergism between the barrier effect in the condensed phase (proved by the high yield and stability of char residues) and the flame inhibition effect in the gaseous phase (proved by the decreased av-EHC values). [ABSTRACT FROM AUTHOR]

Imparting good flame retardancy and mechanical properties to epoxy resin (EP), while pursuing the sustainable and safe application of EP, we synthesized a novel reactive phosphorus/nitrogen flame retardant for biomass through nucleophilic addition reaction, which contains flexible ether bonds and rigid aromatic ring structure (DVD). Owing to the cooperative effect of aryl ether diamine, phosphorus phenanthrene, and biomass vanillin, the DVD exhibited excellent flame retardancy. EP/DVD‐1 (0.4 wt% phosphorus content) achieved UL‐94 V‐0 rating, with an improvement in limiting oxygen index value from 26.5% (pure EP) to 32.5%. In the CCT, the modified DVD EP showed a 44.5% reduction in peak peak of heat release rate (PHRR) and a 38.0% reduction in total heat release compared to pure EPs. And flame retardant epoxy resin (FREP) still had good transparency after the addition of DVD, which indicated the nice compatibility between DVD andEP. What was noteworthiness was that at high levels of addition, the mechanical properties of modified EP for DVD was still improved compared to pure EP. These results demonstrate that DVD is an excellent and multifunctional bio‐based flame retardant with broad application prospects in the field of EP material modification. [ABSTRACT FROM AUTHOR]

Highly flame‐resistant epoxy composites have important application value in many industrial fields. Unfortunately, epoxy resins (EPs) are inherently flammable materials and exhibit great fire hazard. In this study, the commercially available 9,10‐dihydro‐9‐oxa‐10‐phosphaphenanthrene‐10‐oxide (DOPO) was chemically immobilized on the surface of natural halloysite nanotubes (HNTs) via the linkage of vinyltrimethoxysilane to obtain a novel flame‐retardant VD@HNTs containing P/Si/Al elements. It was found that the flame‐retardant VD@HNTs can effectively improve the thermal stability and flame resistance of epoxy composites. Typically, when 10% of VD@HNTs is added in EP, the limiting oxygen index of as‐prepared VD@HNTs/EP composites reaches 30.3%, and it also successfully reaches V‐0 classification in the UL‐94 test. Besides, the ignition time of VD@HNTs/EP composites was enhanced from 42 s for pure EP to 60 s, and the maximum heat release rate was reduced from 1221 to 758 kW∙m−2. These great findings promise an innovative and efficient strategy for improving the fire safety of EP products and may also offer valuable insight toward fabricating various novel organic–inorganic flame retardants as well as highly flame‐resistant polymer composites. Highlights: A novel flame‐retardant VD@HNTs containing P/Si/Al elements was prepared by the chemical decoration of HNTs with organophosphorous.The VD@HNT can effectively improve the thermal stability and flame resistance of epoxy composites.Synergistic flame‐retardant mechanism of phosphorus‐based flame retardants and natural HNTs was classified. [ABSTRACT FROM AUTHOR]

The zirconium‐based metal–organic framework material (UiO‐66‐NH2) was synthesized by solvothermal method, and its excellent adsorption performance was used to combine it with the phosphorus‐based flame retardant triethyl phosphate (TEP) and to improve the flame retardant and smoke suppression properties of epoxy resin (EP). The morphology, chemical composition, and structure of the synthesized flame retardant were analyzed by scanning electron microscope, energy dispersion spectrum, Fourier transform infrared spectroscopy, and x‐ray diffractometer. The cone calorimeter measurement of EP composite materials shows that EP composite materials have good flame retardant and smoke suppression properties. Compared with EP, after the UiO‐66‐NH2 flame retardant which adsorbs TEP is added, the peak heat release rate, total heat release, peak smoke release rate, total smoke production, carbon monoxide release rate, and carbon dioxide release rate of EP composites have been reduced. From the results of thermal analysis and scanning electron microscope, it can be seen that the synthesized flame retardant can act both in the condensed phase and in the gas phase. Thereby, the combustion of the matrix and the diffusion of the toxic gas, smoke and heat generated during the combustion are inhibited, and the flame retardant and smoke suppression effects are achieved. Highlights: Make full use of the excellent adsorption performance of MOF.TEP was fully adsorbed in UiO‐66‐NH2 pores.UiO‐66‐NH2 in synergy with TEP improves EP flame retardancy. [ABSTRACT FROM AUTHOR]

It is imperative to develop efficient flame retardants to solve the issues of high heat and smoke release for epoxy resin (EP) polymeric materials plagued over time. Hence, a phosphorus–nitrogen modified Ti3C2Tx MXene nanohybrids (MXene@MPA) were synthesized by in situ assembly melamine phytate macromolecules (MPA) to boost the fire hazards of EP composites. The introduction of MPA improved the dispersion of MXene in epoxy matrix, contributing to the improved thermal stability and flame-retardant properties for EP composites. With the addition of 2 mass% MXene@MPA, EP composites achieved the decreased maximum mass loss rate (MLRmax) by 41.8%, indicating the enhanced thermal properties. Also, the peak heat release rate (PHRR) and peak smoke production rate (PSPR) of EP-MXene@MPA composites were down by 27.9% and 43.6% compared to pure EP, respectively, accompanied by significantly increased char production. The synergistic effects between MPA and MXene contributed to the elevated fire safety of EP-MXene@MPA composites: the catalytic charring of transition metals and phosphorus-containing acid and the barrier effect of MXene nanosheets, as well as the quenching effects of phosphorus–oxygen free radicals and dilution of nitrogen-containing inert gases due to the decomposition of MPA. The multiple hybridization route provided a reference for the development of efficient MXene-based flame retardants. [ABSTRACT FROM AUTHOR]

With a rapid expansion in applications of epoxy resins (EP) and derived composites, there is a high demand for improving their flame retardant and dielectric properties. In this work, a facile and convenient strategy for loading a dimethyl methylphosphonate (DMMP) flame retardant into the channels of ZIF-8 (zeolitic imidazolate framework) was developed, followed by the assembly of a hybrid ZIF-8@DMMP material with epoxy resin (EP). The obtained MOF-containing hybrid EP composites, abbreviated as 820/EP (with 20 wt% ZIF-8) and 8 FR20/EP (with 20wt% ZIF-8@DMMP), were fully characterized and shown to feature superior flame retardant behavior, contributing to an enhanced safety of such material in terms of total smoke suppression, lower levels of total heat release and carbon monoxide generation. The results demonstrated that the formation of an intumescent dense char layer restrained further combustion, thus enabling this composite material to feature a better flame retardant performance. Besides, the composite exhibited a dielectric permittivity and dielectric loss of as low as 3.0 at a high frequency, which significantly outperforms the neat epoxy resin. This work thus showcases a simple and efficient route to enhance dielectric and flame retardant properties of polymeric epoxy resins, while merging the inherent porosity of ZIF-8 and traditional flame retardant behavior of DMMP. [ABSTRACT FROM AUTHOR]

Epoxy resin was often applied in fiber-reinforced composite materials, adhesives, and encapsulation materials. However, epoxy was easily flammable and limited its usage in certain applications. The study recycled and reused agricultural waste sugarcane bagasse to prepare a halogen-free bio-based intumescent flame retardant and then mixed with epoxy resin to prepare a composite containing polymer with improved thermal properties and flame retardancy of the materials. The work followed the concept of circular economy and sustainability. Bagasse-ammonium dihydrogen phosphate (ADP) flame retardant was added to an epoxy resin to prepare epoxy/bagasse-ADP composites, an effective flame-retarding composite material through hydrothermal method. Adding bagasse-ADP increased the thermal stability and flame retardancy of the composite materials compared with that of pure epoxy. For the material with 30 wt % added bagasse-ADP, the char yield was 32.3 wt%, which was 18.2 wt% higher than that of pure epoxy (14.1 wt%) through thermogravimetric analysis. In addition, the limiting oxygen index increased from 21% to 30%, and the UL-94 classification improved from "Fail" to "V-0." This performance was attributed to the nitrogen, phosphorus, and silicon content of the flame retardant. [ABSTRACT FROM AUTHOR]

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

To improve the compatibility and flame retardance of kaolinite (Kaol) in polymeric materials, ammonium dihydrogen phosphate (ADP) was intercalated into kaolinite to obtain a novel intercalated kaolinite (K‐ADP) for enhancing thermal stability, flame retardance, smoke suppression, and mechanical performance of epoxy resins (EPs). The results show that the presence of K‐ADP exerts a more positive effect on reducing the heat release and smoke generation of EPs than the same addition of Kaol. Condensed phase analysis shows that EP/K‐ADP composite generates more aromatic cross‐links in the condensed phase to reinforce the compactness and intumescence of char compared to EP/Kaol composite. Especially, 5 wt% K‐ADP confers a 43.7% reduction in peak heat release rate value and a 36.3% reduction in peak smoke production rate value to EP. Toxic gases analysis shows that K‐ADP conduces to inhibiting the release of combustible gases including isocyanates and aromatic volatiles, and generating incombustible gases including ammonia and carbon dioxide to reduce the intensity of EP combustion. The mechanical test shows that K‐ADP imparts less adverse impact on mechanical behavior to EP composites than Kaol due to the good dispersion and compatibility between K‐ADP with EP matrix. [ABSTRACT FROM AUTHOR]

Epoxy resin compositions are used in modern railways, replacing other materials. However, epoxy composites in public transport are subject to many requirements, including that they should be flame retardant and resistant to weather conditions. The aim of the research was to analyse the resistance to solar ageing of epoxy resin composites containing flame retardants and the addition of the natural stabilising substance—quercetin. The homogeneity of the samples (optical microscopy and FTIR spectroscopy) and their thermal stability (TGA thermogravimetry) were analysed. The T5 temperature, which is the initial temperature of thermal decomposition of the samples, was 7 °C higher for the epoxy resin containing quercetin, so the material with polyphenol was characterised by better thermal resistance. Changes in material properties (hardness, surface energy, carbonyl index, colour) after 800 h solar ageing were investigated. The tensile tests on materials were executed for three different directions before and after ageing effect. The samples showed good resistance to degradation factors, i.e., they retained the functional properties (hardness and mechanical properties). However, analysis of carbonyl indices and surface energies showed that changes appeared in the composites after solar ageing, suggesting the beginning of material degradation. An approximately 3-fold increase in the polar component in epoxy resin compositions (from approximately 3 mN/m to approximately 11 mN/m) is associated with an increase in their hydrophilicity and the progress of ageing of the materials' surface. The obtained results are an introduction to further research on the long-term degradation processes of epoxy resins with plant stabilisers. [ABSTRACT FROM AUTHOR]

To meet the environmental protection and flame retardancy requirements for epoxy resins (EPs) in certain fields, in this study, a novel triazine-ring-containing DOPO-derived compound (VDPD), derived from vanillin, 2,4-Diamino-6-phenyl-1,3,5-triazine, and 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO), was synthesized using a one-pot method. Flame-retardant epoxy resin (FREP) was prepared by adding various ratios of VDPD to EP and curing with 4,4-diaminodiphenylmethane (DDM). The curing behavior, thermal stability, mechanical properties, and flame-retardant properties of the FREP were examined in various tests. According to the results, when the amount of VDPD added to the EP increased, the glass transition temperature of the FREP decreased linearly, and the flame-retardant properties gradually improved. With a 0.4 wt.% P content, the vertical burning rating of EP/DDM/VDPD-0.4 (according to the theoretical content of VDPD) reached the V-0 level, and the LOI value reached 33.1%. In addition, the results of a CCT showed that the peak heat release rate (PHRR) of EP/DDM/VDPD-0.4 decreased by 32% in comparison with that of the EP. Furthermore, compared with those of the EP, the tensile strength of EP/DDM/VDPD-0.4 decreased from 80.2 MPa to 74.3 MPa, only decreasing by 6 MPa, and the tensile modulus increased. Overall, VDPD can maintain the mechanical properties of EP and effectively improve its flame-retardant properties. [ABSTRACT FROM AUTHOR]

A reactive flame retardant containing biphenyl structure (DEU-2DOPO) was prepared from the bio-based raw material eugenol. The incorporation of DEU-2DOPO into the epoxy resin serves to enhance the ring-opening reaction of the epoxy. Furthermore, the inclusion of DEU-2DOPO has been found to have a positive impact on the glass transition temperature and residual carbon rate of the epoxy resin. This additive also significantly improves the mechanical properties of the epoxy resin, leading to a 49.3% increase in tensile strength, an 81.9% increase in breaking elongation, and a 15.8% increase in flexural strength. Notably, when DEU-2DOPO is introduced at a concentration of 5 wt%, it not only achieves a V-0 rating in the UL-94 test but also exhibits an impressive ultimate oxygen index of 34.5%. Additionally, the cone calorimetric testing revealed that the presence of DEU-2DOPO results in lower combustion metrics compared to pure epoxy, as evidenced by a reduction of 15.1% in total heat release (THR) and 10.8% in total smoke release (TSR). An analysis of the flame retardant mechanism elucidates that DEU-2DOPO promotes the formation of a stable and dense residual carbon, thereby impeding gas and heat exchange. Furthermore, the decomposition of DEU-2DOPO generates PO · and PO2 · radicals, which effectively neutralize reactive radicals. [ABSTRACT FROM AUTHOR]

Biobased epoxy resins are gaining attention as a renewable alternative to petroleum‐based resins. However, their inherent flammability requires flame‐retardant treatment. In this study, hexaphenoxycyclotriphosphazene (HPCP) and various synergists were utilized to improve the flame retardancy of lignin‐based epoxy resin (EP‐L). Results showed that (3‐aminopropyl)triethoxysilane (APTES) had the most effective synergistic effect for HPCP to form a P/N/Si‐containing system, resulting in a compact crosslinked char layer. Upon the incorporation of HPCP and APTES (6∶1, 12 wt% of EP mass) into EP, a V‐0 classification was achieved in the UL‐94 vertical burning assessment, with a limiting oxygen index of 33.6% and a 47.77% decrease in the peak of heat release rate. This system minimally influenced the tensile strength of the composite (a 16.51% reduction), and maximumly increased its initial degradation temperature by 83 °C, compared with EP‐L. © 2023 Society of Industrial Chemistry. [ABSTRACT FROM AUTHOR]

A novel organic salt containing DOPO and pyrimidine (AD) was successfully synthesized through a simple acid--base neutralization reaction. The salt was used as a reactive flame retardant for epoxy resin. Non-isothermal DSC tests disclosed that the epoxy resin displayed a lower temperature of onset curing and exothermic peak in the presence of AD. By using only 3 wt% AD, the epoxy resin achieved a UL-94 V-0 rating and a limited oxygen index value of 27.4%, revealing the high flame-retardant efficiency of AD. AD inhibited the release of heat and smoke. The analysis of the flameretardant mode of action indicated that AD was able to impede combustion not only by the dilution and quenching effects in the gas phase but also by the charring effect in the condensed phase. During UL-94 testing, 3 wt% AD gave the epoxy resin good flame retardancy due to the charring and blowing-out effects formed by adding AD. The blowing-out effect was that the release of strong airflows suppressed or even blew out the flame based on the dilution and quenching effects of phosphorous-containing radicals and numerous non-combustible gases produced by the degradation of AD and epoxy resin matrix. Additionally, the incorporation of AD slightly increased the glass transition temperature and the tensile and flexural strengths of the epoxy resin. This study provided a meaningful attempt to improve the flame retardance of epoxy resin by introducing a reactive pyrimidine-organophosphonic acid salt. [ABSTRACT FROM AUTHOR]

A phosphorous‐containing benzoxazine, (3‐(4‐hydroxyphenyl)‐3,4‐dihydro‐2H‐benzo[e][1,3]oxazin‐4‐yl)diphenylphosphine oxide (DPOBH), was synthesized and used as flame retardant and co‐curing agent in the presence of 4,4′‐diaminodiphenylsulfone (DDS) for diglycidyl ether of bisphenol‐A (DGEBA) epoxy resin. The flame retardancy, thermal stability, Tg, dielectric properties, and water absorption properties of epoxy resins (EP) were investigated and compared. The incorporation of DPOBH results in ca. 40%–45% increase of limiting oxygen index (LOI) values. UL‐94 V‐0 rating could be achieved for EP/DPOBH1.2 sample with the LOI value of 35.1%. Compared with EP, ca. 47% decrease of peak heat release rate (PHRR) could be obtained for EP/DPOBH1.2. According to the results of cone calorimetry tests (CCT), DPOBH could play roles in both gas and condensed phases. Moreover, the incorporation of DPOBH could reduce the water absorption rate, dielectric constant, and dielectric loss. All results suggest that DPOBH is a type of flame retardant suitable for EP used in electronic fields. [ABSTRACT FROM AUTHOR]

In this study, thiol-functionalized ladder-like polysesquioxanes end-capped with methyl and phenyl groups were synthesized via a simple sol-gel method and characterized through gel permeation chromatography (GPC), Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance (NMR), and thermogravimetric analysis (TGA). Additionally, epoxy blends of different formulations were prepared. Their structural, flame-retardant, thermal, and mechanical properties, as well as volatile organic compound (VOC) emissions, were determined using differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), TGA, scanning electron microscopy (SEM), limiting oxygen index (LOI), cone calorimetry, and a VOC analyzer. Compared to epoxy blends with flame retardants containing elemental phosphorus alone, those with flame retardants containing elemental phosphorus combined with silicon and sulfur exhibited superior thermal, flame-retardant, and mechanical properties with low VOC emissions. SEM of the residual char revealed a dense and continuous morphology without holes or cracks. In particular, LOI values for the combustion of methyl and phenyl end-capped polysilsesquioxane mixtures were 32.3 and 33.7, respectively, compared to 28.4% of the LOI value for the blends containing only phosphorus compounds. The silicon–sulfur–phosphorus-containing blends displayed reduced flammability concerning the blends using a flame retardant containing only phosphorus. This reflects the cooperative effects of various flame-retardant moieties. [ABSTRACT FROM AUTHOR]

Currently, the mechanical performance reduction caused by excessive phosphorus content in the halogen-free flame-retardant EP has been an obstacle to its extensive application. This study presents the effective synthesis of a novel flame-retardant BDD with great efficiency, achieving an optimum phosphorus level of merely 0.25 wt %. The structure of BDD was verified by FTIR, 1H NMR, 31P NMR and XPS spectra. To investigate the flame-retardant properties of BDD, several EPs with various phosphorus levels were synthesized. The addition of phosphorus to the EP significantly increases its LOI value from 25.8% to 33.4% at a phosphorus level of 0.25 wt%. Additionally, the resin achieves a V-0 grade in the UL 94 test. The P-HRR and THR of the modified resin measured by the cone calorimeter are also significantly reduced. At the same time, the addition of a modest quantity of BDD has a minimal impact on the mechanical properties of epoxy resin. This study shows that the removal of hydroxyl groups significantly enhances the fire resistance of phosphate-based flame retardants, thereby providing a novel approach to synthesizing efficient flame retardants. [ABSTRACT FROM AUTHOR]

The morphology of the material has a great influence on its flame retardancy. In order to study the effects of magnesium hydroxide with different morphologies on the flame retardancy of epoxy resin, magnesium chloride and magnesium sulfate were used as raw materials to prepare magnesium hydroxide with rod, flake and flower, and were added to epoxy resin to prepare epoxy resin composite to explore the flame retardancy and the flame retardant mechanism. The results show that the diameter of rod magnesium hydroxide ranges from 250 nm to 500 nm and the length is about 5 μm. The flaky magnesium hydroxide has a hexagonal sheet structure with a size of 100 nm. The size of flower ball magnesium hydroxide is 1~2 μm. When the addition of magnesium hydroxide is 3%, the flame retardancy of epoxy resin is improved as: flake>flower>rod. Compared with pure epoxy resin, the addition of flaky magnesium hydroxide reduceds the TSP by 35.1%, the PHRR by 36.6%, and the PCOP by 39.4%. The research provides the direction for the application of magnesium hydroxide in polymers. [ABSTRACT FROM AUTHOR]

The surface treatment of chopped glass fiber (GF) can significantly improve the strength, impact resistance, and durability of epoxy resin (EP), and the homogeneity of GF modified EP material is better than that of continuous fiber reinforced EP, which has an important application in the engineering field. The effects of surface treatment and addition of chopped GF on the rheological behavior and mechanical properties of EP/modified chopped GF composites were studied by alcohol washing, coupling agent treatment, and acid etching modification methods. In addition, a reactive flame retardant containing phosphorus, nitrogen and bromine was synthesized, and the flame retardant application was studied in the EP/modified chopped GF system. The results show that the surface micromorphology of the chopped GF treated with acid etching is relatively rough, which can greatly increase the initial shear viscosity of the system, and the mechanical properties of the cured composites are significantly better than those of the GF treated with alcohol treatment and coupling agent. The chopped GF content of acid etching treatment is 2.0%, and the tensile strength of the composite is the highest, which is 59.75 MPa. When the flame retardant content is 10%, the peak heat release rate and total heat release of the composite are significantly lower than those of pure EP, and the mechanical properties are improved at the same time. [ABSTRACT FROM AUTHOR]

A novel epoxy-based self-intumescent fire protective coating has been developed by formulating a combination of ammonium polyphosphate (APP) and copper (I) oxide (Cu2O) in epoxy resin (EP). The effects of various combinations on fire protective performance for steel plate were evaluated using a lab-scale simulated big panel test. Formulations with different mass ratios of APP to Cu2O ranging from 10:0 to 2:8 exhibit good fire protective performance for steel plate. While the final equilibrium backside temperature of un-protected steel plate reached 529 °C, it did not exceed 282 °C for the protected plates with 2 mm thick coatings, which is much lower than the failure temperature of steel (ca. 500 °C). The lowest final equilibrium backside temperature of coated steel plate was 234.5 °C for the optimal formulation (EP/24APP/16Cu2O) with an APP/Cu2O mass ratio of 6/4 in EP. Interestingly, the limiting oxygen index (LOI) value (46.8%) for the optimized formulation (EP/24APP/16Cu2O) is not the highest, being lower than those of (EP/40APP/0Cu2O) and (EP/32APP/8Cu2O) formulations. The fire behavior of the optimized formulation (EP/24APP/16Cu2O) and control EP was compared using the cone calorimetry. The main fire hazard parameters such as peak heat release rate, total smoke production and peak CO production for EP/24APP/16Cu2O are reduced by 80.0%, 59.5% and 75.0%, respectively, relative to those for EP. This indicates that the EP/24APP/16Cu2O formulation provides significantly better fire safety than does control EP alone. A possible mode of action for the combination of APP/Cu2O in terms of the expansion ratio and heat insulation degree of the formed intumescent char layer may be proposed. Thus, this work contributed a reference for developing intumescent fire protective coating with high fire safety. [ABSTRACT FROM AUTHOR]