High Flame Retardancy Research Articles

A novel epoxy resin system containing bismaleimide and DOPO‐based flame retardant with excellent flame retardancy and toughness

Abstract9,10‐dihydro‐9‐oxo‐10‐phosphaphenanthrene‐10‐oxide (DOPO) and special tetra functional epoxy resin (EP) AG‐601 were combined to synthesize a reactive flame retardant (FREP) and then incorporated into EP, obtaining the flame retardant material EP/FREP. To achieve EPs with higher flame retardancy and mechanical properties, a new intrinsically flame retardant EP system named EP/FRDM was produced by modifying EP/FREP with high thermal resistance bismaleimide (BDM). In the presence of a distinct FRDM structure comprising phosphaphenanthrene/nitrogen, the EP possessed superior flame retardancy and impact toughness. The curing process of EP/FRDM was investigated using Real‐Time Fourier‐transform Infrared. In terms of fire performance, the limiting oxygen index of the EP/FRDM‐3 was raised from 31.4% to 38.2%, and the vertical burning rating was improved after BDM was added to the EP/FREP system. It was discovered that EP/FRDM exhibited a classic two‐phase flame retardant influence by analyzing the residual carbon morphology and pyrolysis behavior. Simultaneously, the glass transition temperature (Tg) of EP/FRDM remained essentially stable, and the char residue yield rose markedly, which indicated that the system had outstanding thermal stability, according to the results of the dynamic mechanical analysis and thermogravimetric analysis tests. Notably, the EP/FRDM experienced an internal chain expansion reaction when BDM was added, giving flame retardant materials excellent flexural and impact strengths and promising future application opportunities.

Construction of a boron nitride nanosheet hybrid for tough, strong, and flame-retardant phenolic resins

Simultaneously endowing phenolic resins (PRs) with high toughness, strength, and flame retardancy is a challenging task and is greatly important. Inspired by the organic–inorganic hybrid nature of oyster adhesives, this work constructed a nanohybrid network in phenolic resin by using hyperbranched polysiloxane-functionalized boron nitride nanosheets (HPSi@BNNSs), which were produced using bulk hexagonal boron nitride via a HPSi-assisted ball-milling strategy. The resulting PR (HPSi@BNNSs/PF) exhibited considerable toughness improvements over PF, with 82.8% and 521% increments in debonding work and flexural toughness, respectively, and 42.0% and 173% increases in bonding and flexural strength, respectively. This outstanding performance is attributed to the functionalization of HPSi to promote the uniform dispersion of BNNSs in the resin matrix and the formation of an organic–inorganic hybrid structure with multiple interfacial interactions, which effectively facilitates the transfer and dissipation of load energy during stressing. In addition, the flame retardancy of HPSi@BNNSs/PF was notably improved from that of PF, as evidenced by a UL-94 V-0 rating, high limited oxygen index of 52.9 vol%, and decreased peak heat release rate (530 vs. 361 kW/m2). This improvement was mainly due to the coupling of organic HPSi and inorganic BNNSs promoting the formation of a compact and continuous char layer and the release of PO and PO2 radicals during combustion. Overall, this work provides an attractive organic–inorganic hybrid strategy for improving the toughness, strength, and flame retardancy of PRs, thereby advancing the enhancement and versatile modification of adhesives and other polymer composites.

Degradable Waterborne Polyurethane with Flame Retardancy and High Mechanical Strength via Synergy of Hydrogen Bonds

Waterborne polyurethane (WPU) with degradability is critical to the environment. Especially, degradable WPU with high mechanical strength and flame retardancy features various important industrial applications, while the increased flame retardancy often leads to reduced mechanical strength. Herein, we report the simultaneous realization of degradability, flame retardancy, and high mechanical strength into one design. The tensile strength of degradable WPU is up to 39 MPa and can be tuned by the ratio of soft segments. The strong synergistic hydrogen bond interactions of different components confirmed by FTIR and XPS as well as molecular dynamics simulation are responsible for the excellent mechanical strength. Moreover, WPU achieves the highest “V0” level of flame retardancy. The simultaneous realization of the stress of 35 MPa and a limiting oxygen index of 27.55% is obtained by changing the flame retardant contents. Importantly, WPU possesses degradability with a mass loss rate of 37% after natural burial in soil for 3 months. The dense WPU coatings can be adhered to different substrates and also have good anticorrosion ability. This work provides a promising strategy for high-performance biodegradable materials and expands the industrial application of polyurethane.

Recent Advance in Low‐Dielectric‐Constant Organosilicon Polymers

Comprehensive SummaryLow dielectric (low‐k) organosilicon polymers have received extensive interests from industry and academia due to good electrical insulation, high temperature resistance, flame retardancy and hydrophobicity. These attractive properties enable them to be utilized as low‐k materials in fabrication of electronic devices in high‐frequency communication technology. This review summarizes recent progress in developing low‐k organosilicon polymers, including the synthetic methods and properties of different organosilicon polymers classified according to the chemical structures. It may provide some inspiration to design new low‐k organosilicon polymers for application in the future.

Phosphorus-free curcumin-derived epoxy resin with exceptional flame retardancy, glass transition temperature and mechanical properties

The fabrication of bio-based epoxy resins having better intrinsic flame retardancy and mechanical performances than petroleum-based epoxy thermosets is important for alleviation of energy and health concerns. In this study, bio-based monomer of diglycidyl ether of curcumin (DGEC) was successfully synthesized from a natural and renewable curcumin through a facile one-step process. The biocompatible epoxy resin obtained was then cured with 4,4′-diaminodiphenyl sulfone (DDS) and compared with petroleum-based diglycidyl ether of bisphenol A (DGEBA). The DGEC/DDS exhibited a higher glass-transition temperature (300 °C) than DGEBA/DDS (215 °C), indicating the outstanding heat resistance. The tensile strength of DGEC/DDS was 65.9 MPa, higher than that of DGEBA/DDS (56.1 MPa). Furthermore, DGEC/DDS showed excellent charring ability with char yield of 50.15% at 800 °C in N2, which was approximatively 3.5 times as much as that of the cured DGEBA/DDS (14.68%). Microscale combustion calorimeter (MCC) test demonstrated that the DGEC/DDS possessed lower heat release capacity (HRC, 130 J/gk), peak heat release rate (PHRR, 115.0 W/g) and total heat release (THR, 9.9 kJ/g), which were reduced by 80.2%, 74.8% and 59.4%, respectively, compared to those of DGEBA/DDS (658 J/gk, 457.3 W/g, 24.4 kJ/g). The DGEC/DDS passed the UL-94 test and attained the V-0 rating, revealing the good flame retardancy. This work provided an opportunity to prepare bio-based epoxy resins with better properties than DGEBA, which exhibited promising applications in high heat and flame retardancy fields.

Robust and thermostable C/SiOC composite aerogel for efficient microwave absorption, thermal insulation and flame retardancy

Carbon aerogel (CA) has been generally regarded as a potential electromagnetic wave (EMW) absorber, but unsatisfactory microwave absorption, mechanical and anti-oxidation properties are still the primary challenges for its application. Herein, a novel C/SiOC composite aerogel (CSA) was successfully synthesized by a simple copolymerization of dual sols, ambient pressure drying and thermal treatment process for the first time. The morphology and performance of the as-prepared CSA could be tailored just by controlling the initial ratio of silane and phenolic resin (PR) to adjust the content of SiOC in CSA, whose density was in the range of 0.252 to 0.294 g·cm−3 with a low thermal conductivity from 0.061 to 0.067 W·m−1·K−1. Notably, the EMW absorption capacity of CSA was greatly enhanced with the increase of SiOC content, with the optimal reflection loss (RL) value of −67.85 dB and effective absorption bandwidth (EAB) of 6.88 GHz, which was dramatically improved than CA (–22.89 dB, 5.34 GHz) and mainly ascribed to the optimized impedance matching characteristics and strong attenuation capacity. Meanwhile, compared with CA (2.63 MPa) with a density of 0.248 g·cm−3, the mechanical properties of CSA (3.30–5.12 MPa) were also remarkably improved, and the maximum compression strength was nearly doubled. Furthermore, CSA obtained superior oxidation resistance than CA and exhibited excellent flame-retardant properties. All the results indicated that CSA could be considered as a highly promising candidate for applications in extreme environments due to its lightweight, high strength and outstanding microwave absorption capacity along with good oxidation resistance, superior thermal insulation performance and high flame retardancy.

Application of the PAPP/MCA/APP intumescent flame retardant system in polypropylene

AbstractAmmonium polyphosphate (APP), piperazine pyrophosphate (PAPP), and melamine cyanurate (MCA) were used as raw materials to develop an intumescent flame retardant system (IFRS) for polypropylene (PP). The synergistic flame retardancy among APP, PAPP, and MCA was explored. The effect of the proportion of APP, PAPP, and MCA on the IFRS flame‐retardant performance was studied. For the range of samples tested, the IFRS with the proportion of PAPP, MCA, and APP at 4:1:7.5 showed the best flame retardancy. When the addition of PAPP/MCA/APP IFRS in PP was 20%, the prepared flame‐retardant PP composite (PP‐PMA‐3) passed UL‐94 V‐0 rating. Moreover, the PP‐PMA‐3 total heat release (THR) decreased by 46.4% compared with PP‐0. Meanwhile, PAPP/MCA/APP IFRS showed good smoke suppression performance because the total smoke production (TSP) of PP‐PMA‐3 decreased by 65.0% compared with PP‐0. In addition, the high flame retardancy and the flame‐retardant mechanism of the prepared IFRS was explained.

Formulation of environmentally robust flame-retardant and superhydrophobic coatings for wood materials

Developing flame-retardant wood with integrated anti-wetting property, self-cleaning and good weatherability, has received intensive attention, which is vital to the rapid advancements in construction and building materials. Here, a superhydrophobic and flame-retardant coating is constructed based on a trinity monocomponent intumescent flame retardant, polydimethylsiloxane resin and modified SiO2 nanoparticles. Such a coating can endow wood materials with high flame retardancy and self-cleaning performances. In comparison to pristine woods, the surface-treated wood shows a self-extinguish behavior in the vertical burning test with an obviously increased limiting oxygen index of 31.0% and UL 94 rating of V0. The peak heat release rate is reduced by 24.4% and the total heat release after surface treatment is decreased to 24.5 MJ/m2. The water-repellency of sample is greatly improved with water contact angle over 154° and slide angle below 5°, exhibiting appreciable resistance to dust contamination. Due to the significant anti-wetting property, the coating can effectively protect the inner flame-retardant layer from water penetration, thereby the treated wood can preserve high flame-retardant performances even after being immersed in water for 24 h. More importantly, the modified wood material can endure different harsh environmental conditions, including high temperatures, UV light irradiation, hydrothermal environment and mechanical impact, without losing the superhydrophobicity or flame retardancy, presenting high weatherability and mechanical robustness. The findings provide an effective approach to prepare high-weatherability fire-safety wood materials that have application potential in outdoor environments.

Li-Ion Transfer Mechanism of Gel Polymer Electrolyte with Sole Fluoroethylene Carbonate Solvent.

Although gel polymer electrolytes (GPEs) represent a promising candidate to address the individual limitations of liquid and solid electrolytes, their extensive development is still hindered due to the veiled Li-ion conduction mechanism. Herein, the related mechanism in GPEs is extensively studied by developing an in situ polymerized GPE comprising fluoroethylene carbonate (FEC) solvent and carbonate ester segments (F-GPE). Practically, although with high dielectric constant, FEC fails to effectively transport Li ions when acting as the sole solvent. By sharp contrast, F-GPE demonstrates superior electrochemical performances, and the related Li-ion transfer mechanism is investigated using molecular dynamics simulations and 7 Li/6 Li solid-state nNMR spectroscopy. The polymer segments are extended with the swelling of FEC, then an electron-delocalization interface layer is generated between abundant electron-rich groups of FEC and the polymer ingredients, which works as an electron-rich "Milky Way" and facilitates the rapid transfer of Li ions by lowering the diffusion barrier dramatically, resulting in a high conductivity of 2.47× 10-4 Scm-1 and a small polarization of about 20mV for Li//Li symmetric cell after 8000h. Remarkably, FEC provides high flame-retardancy and makes F-GPE remains stable under ignition and puncture tests.

Solvent-Free Preparation of Thermally Stable Poly(urethane-imide) Elastomers

Polyurethanes (PUs) are widely used in many applications due to their versatile chemical and physical properties. To meet the increasing demands on PU with respect to intrinsic mechanical and thermal properties, they can be modified with thermally stable aromatic imide structures to form poly(urethane imide) (PUI). However, the preparation of PUI materials has been limited by the need for strong polar solvents, which hinder their industrial scale development. In this work, we prepared imide-containing isocyanate-terminated prepolymers via the reaction of polymeric aromatic or aliphatic isocyanates and pyromellitic dianhydride in completely solvent-free conditions. The subsequent PUI elastomers made from these prepolymers exhibited enhanced char formation and stiffness in comparison to the reference elastomers without imide structures, among which the aromatic PUI elastomer shows improved flame retardancy according to the initial cone calorimetry measurement. This work demonstrates the potential use of imide prepolymers in other PU applications where high thermal stability and flame retardancy are required. The solvent-free synthesis also paves a way for the large-scale production of PUI materials.

Amorphous biomineral-reinforced hydrogels with dramatically enhanced toughness for strain sensing

Ionic conductive hydrogels are promising candidates for flexible wearable strain sensors and artificial skin. However, achieving high mechanical and sensing performance concurrently remains challenging. Herein, a novel biomineral-reinforced hydrogel composed of polyacrylamide (PAM) and highly stable amorphous calcium carbonate (ACC) is reported. Benefiting from the dual ionic doping strategy (Mg2+ and PO43−), ACC nanoparticles in hybrid hydrogels show a super stable amorphous nature. The resulting mineral hydrogel displays a high stretchability (>1150% strain), a dramatically enhanced fracture toughness (9.57±1.28 vs. 0.91±0.12 kJ m−2), and a desirable linear strain sensitivity. Moreover, the novel mineral hydrogel exhibits high biocompatibility and flame retardance, making it an appealing candidate for wearable device applications.

Flexible, Flame-Resistant, and Anisotropic Thermally Conductive Aerogel Films with Ionic Liquid Crystal-Armored Boron Nitride.

With the rapid development of miniaturization and high-power portable electronics, the accumulation of undesired heat can degrade the performance of electronic devices and even cause fires. Therefore, multifunctional thermal interface materials that combine high thermal conductivity and flame retardancy remain a challenge. Herein, an ILC (ionic liquids crystal)-armored boron nitride nanosheet (BNNS) with flame retardant functional groups was first developed. The high in-plane orientation structure aerogel film made of such an ILC-armored BNNS and aramid nanofiber and polyvinyl alcohol matrix through directional freeze-drying and mechanical pressing exhibits strong anisotropy thermal conductivity (λ// of 17.7 W m-1 K-1 and λ⊥ of 0.98 W m-1 K-1). In addition, the highly oriented IBAP aerogel films have excellent flame retardancy (peak heat release rate = 44.5 kW/m2 and heat release rate = 0.8 MJ/m2) due to the physical barrier effect and catalytic carbonization effect of ILC-armored BNNS. Meanwhile, IBAP aerogel films exhibit good flexibility and mechanical properties, even in harsh environments such as acids and bases. Further, IBAP aerogel films can also be used as a substrate for paraffin phase change composites. The ILC-armored BNNS provides a practical way to produce flame-resistant polymer composites with high thermal conductivity for TIMs in modern electronic devices.

Microporous-micronucleus composite structure endowing heterogenous polyamide 6 with low-temperature toughness, low dielectric constant, fire retardancy and antibacterial activity

Utilizing the difference in compatibility and phase transition among PA6, monoglyceride (MG), octaphenylsilsesquioxane (OPS) and zinc diethylphosphinate (ZDP), a PA6 composite with microporous-micronucleus structure is simulated and designed. Due to the passivation micro-cracks effect of microporous-micronucleus structure, the MG/OPS/ZDP/PA6 composite exhibits excellent low-temperature impact strength (5.58 kJ m−2, 203.3% higher than neat PA6 at −170 °C). The nano-gap and nano-cage OPS endows the MG/OPS/ZDP/PA6 with low dielectric constant (2.95 at 100 Hz). The thermal insulation effect of micropores and the synergistic effect of OPS and ZDP in the micronucleus lead to the high flame retardancy of MG/OPS/ZDP/PA6. Meanwhile, the MG on the inner surface of the micropore and the ZDP in the micronucleus endow a dual antibacterial activity. This work provides a guideline for the construction of microporous-micronucleus structure to realize the functional design of composite.

Intumescent closed-cell porous molecular engineering towards high flame retardancy and ultra-low smoke release epoxy resin

Wide applications of high-flammable epoxy resin (EP) bring potential fire risks with huge heat and smoke hazards. Although effective strategies for flame retardancy and heat suppression have been developed, there are still few measures for reducing smoke release synchronously. Herein, 2-aminobenzimidazole modified ammonium polyphosphate intumescent flame-retardant co-curing agent (ABMZ-APP), possessing excellent char-forming performance, is designed and endows EP/ABMZ-APP thermosets with excellent flame retardancy, heat suppressing, and smoke suppressing performance. It is worth mentioning that the total smoke production (TSP), and maximum smoke density (DSmax) of EP with 20 wt% ABMZ-APP decrease by 73.2%, and 67.6%, respectively. Deep investigation illustrates EP/ABMZ-APP suppresses the smoke by obstructing soot-precursor transfer through the special porous char structure, rather than altering the chemical changes in nucleation and growth processes of mature soot. Meanwhile, the closed-cell porous char layers, acting as physical barriers, obstruct the heat/fuels transfer simultaneously which is beneficial for suppressing sustained burning.

Thermal performance and condensation analysis of insulated concrete panels using a thermal-meta structure

Sandwich panels are widely employed in warehouses and factories due to their cost-effectiveness and workability. However, recent major fires in Korea, caused by the combustion of sandwich panels, have necessitated the development of limited combustible panels wgyith comparable thermal performance. In this study, we introduce an innovative panel that satisfies both fire resistance and insulation performance requirements. The panel comprises a fire-resistant concrete-based material and a honeycomb insulation material for enhanced insulation. The experimental results demonstrate that the developed honeycomb-meta precast concrete panel exhibits excellent insulation and fire resistance, outperforming traditional panels with an 18% higher flame retardancy. The panel effectively mitigates common issues typically encountered in prefabricated panels, such as decreased insulation performance and condensation at connection points. These findings highlight the potential of the developed panel in various construction applications, particularly in buildings requiring superior fire resistance and insulation performance.

Impact of a Novel Phosphoramide Flame Retardant on the Fire Behavior and Transparency of Thermoplastic Polyurethane Elastomers.

In many application fields of thermoplastic polyurethane (TPU), excellent flame retardancy and transparency are required. However, higher flame retardancy is often at the expense of transparency. It is difficult to achieve high flame retardancy while maintaining the transparency of TPU. In this work, a kind of TPU composite with good flame retardancy and light transmittance was obtained by adding a new synthetic flame retardant named DCPCD, which was synthesized by the reaction of diethylenetriamine and diphenyl phosphorochloridate. Experimental results showed that 6.0 wt % DCPCD endowed TPU with a limiting oxygen index value of 27.3%, passing the UL 94 V-0 rating in the vertical burning test. The cone calorimeter test results showed that the peak heat release rate (PHRR) of the TPU composite was dramatically reduced from 1292 kW/m2 (pure TPU) to 514 kW/m2 by adding only 1 wt % DCPCD. With the increase of DCPCD contents, the PHRR and total heat release gradually decreased, and the char residue gradually increased. More importantly, the addition of DCPCD has little effect on the transparency and haze of TPU composites. In addition, scanning electron microscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy were carried out to investigate the morphology and composition of the char residue for TPU/DCPCD composites and explore the flame retardant mechanism of DCPCD in TPU.

A bio‐based multifunctional composite material: Boron nitride and wood fiber to construct thermally conductive cross network

AbstractThe high demand for thermally conductive materials in the housing and packaging industry of electronic device highlights the necessity for the development of novel thermal conductivity materials. In this study, waste poplar wood was delignified and combined with boron nitride (hBN) to establish a blend system with a cross thermally conductive network. Using the vacuum‐assisted resin transfer molding process, a biobased composite material was prepared with high thermal conductivity (1.41 W m−1 K−1), mechanical strength (flexural strength of 100.7 MPa and tensile strength of 40.0 MPa), flame retardancy, and water resistance. Compared with raw wood, the incorporation of hBN increased the thermal conductivity of the prepared material by 1324.2%. The high thermal conductivity performance surpassed that of most polymers and elastomers commonly used in electronic component heat dissipation materials, indicating the enormous potential of the prepared composite material in the field of heat dissipation materials.

PRACTICAL APPLICATION OF A HIGH VOLTAGE POWER SUPPLY CABLE FASTENING

High flame retardant drag chain power sheathed cables are used for equipment power supply, and in the outdoor environment, the power transmission power cable needs to be fixed to the wall, usually along the industrial route. The cable bridge moves, extends more frequently, the power supply cable needs to be fixed with a cable sling device, because there is no such special sling device on the market, so the use of the existing card fixing method leads to the cable often squeezed and damaged insulation layer cable failure power outage. This article addresses this problem and proposes for feasible countermeasures.

Synthesis phosphorus–sulfur reactive flame retardant for polyamide 66 with high flame retardant efficiency and low smoke

A sulfur- and phosphorus-containing flame retardant monomer phosphonic diamide, P-phenyl-N, N′-bis(p-sulfanilylphenyl) (PDDDS) was designed, synthesized, and incorporated into polyamide 66 (PA66) through polycondensation to suppress smoke generation upon combustion and achieve satisfactory mechanical properties, a good UL-94 rating (V-0), and a high limiting oxygen index (31.6%). The increased flame retardancy of the PA66-PDDDS copolymer was ascribed to its decomposition into (i) gas-phase P–O and SO2 species scavenging free radicals such as H• and OH• and (ii) condensed-phase products catalyzing the dehydration of PA66 to form char layer. Thus, our work presents a strategy for improving the fire safety of PA66 to significantly expand its practical application value.

Highly water retention, flexible and self-extinguished temperature sensors based on double network hydrogel for early fire warning

Early fire warning represents an active and effective way to avoid potential fire hazards. The hydrogel-based temperature sensor shows high temperature sensitivity, flexibility, and flame retardancy, etc., which makes it an ideal candidate for early fire warning. Herein, we prepared double network (DN) SA-PAM-Fe hydrogels with sodium alginate (SA), acrylamide (AM) and FeCl3, and studied the influence of different water content and Fe3+ concentration on their sensing properties. The ion-conductive DN hydrogels are highly sensitive to temperatures, and the temperature sensitivity of SA-PAM-Fe hydrogels can reach a maximum of 1.28%/°C in the temperature range of 25–90 °C. This means that the SA-PAM-Fe hydrogel temperature sensor can be applied to monitor temperature changes with high resolution. The hydrogel sensor showed enhanced water retention performance with glycerol in SA-PAM-Fe hydrogel via solution replacement, because evaporation and crystallization of free water molecules in the hydrogel system could be suppressed by forming strong hydrogen bonds between glycerol and water molecules. Its maximum fluctuation of temperature sensitivity does not exceed 5.4% and 10% after 72 h preservation at room temperature and 24 h at 90 °C, respectively. The hydrogel sensor also exhibits excellent flame retardancy and flexibility due to the high water content. It is self-extinguished immediately as well as can be twisted, bent and lifted 500 g weight after being subjected to the flame. This work sheds light on the fabrication of self-extinguished and flexible temperature sensors for early fire warning.