Highest Limiting Oxygen Index Value Research Articles

Synthesis and characterization of non-ionic flame-retardant waterborne polyurethane.

Waterborne polyurethane (WPU) offers many advantages and is widely used in coatings, leathers, adhesives, biomaterials, and other consumer products. However, WPU is highly flammable. Many reactive flame retardants have been developed, but their char formation efficiency is still unsatisfactory, and the melt dripping during combustion has not been effectively suppressed. In this paper, a novel phosphorus-containing flame retardant with dihydroxy groups, (6-((4-hydroxyphenyl)((4-hydroxyphenyl)amino)methyl) dibenzo[c,e][1,2]oxaphosphinine 6-oxide) (PHAD), was successfully synthesized and incorporated into WPU molecular chain as a chain extender, thereby synthesizing a series of non-ionic flame-retardant waterborne polyurethane (NFRWPU) emulsions. The chemical structure of NFRWPU was successfully characterized by Fourier transform infrared spectroscopy and nuclear magnetic resonance. With the help of a thermogravimetric analyzer, scanning electron microscope and other instruments, some key performance parameters of NFRWPU in applications were investigated, including: physical, mechanical, and thermal stability and flammability. Some important experimental results include: both the particle size and viscosity of the emulsion increase gradually with increasing PHAD content, and when the PHAD content reaches 12%, the average particle size of emulsion increases to 106.6 nm with a viscosity of 89 mPa s; with the addition of PHAD, the tensile strength of NFRWPU initially increased and then decreased, while the elongation at break showed a continuous downward trend. The maximum tensile strength reached 22.63 MPa, and the minimum elongation at break dropped to 1060%; the addition of PHAD improved the thermal stability and flame retardancy of the film, with the highest limiting oxygen index value reaching 25.6% and the maximum carbon residue increasing to 6.5%. All these results indicate that NFRWPU is a promising flame retardant WPU considering the comprehensive performance.

Enhancing foamability and flame‐retardancy of polylactic acid bead foams through inter‐beads bulk polymerization and continuous phase dispersion of LDHs

AbstractPoly (lactic acid) (PLA) bead foam has a promising application because of its renewable and naturally degradable nature. However, its processing is greatly limited by inherent shortcomings such as the complex polycrystals‐inducing strategy. Herein, we developed a strategy of bulk polymerization reaction of polyvinyl acetate (PVAc) to sinter PLA beads to prepare EPLA foams accompanied by supercritical CO2 foaming technology. In order to enhance the sintering behavior and flame‐retardancy of EPLA foams, two‐dimensional nanolayered double hydroxides (LDHs) were introduced and dispersed in the continuous phase of the sintering layers. The formation of unique dispersion of LDHs and sintering structure of PVAc generated substantial increase in the crystallinity, melt elasticity, and sintering strength of EPLA foams, which facilitated the growth and stabilization of cells. Thus, the cell‐density and expansion ratio could be increased to 8.62 × 106 cell/cm3 to 9.31‐fold, respectively. Moreover, the mechanical properties of the EPLA foams were improved. The tensile strength and the compression strength increased to 2.96 and 62.5 MPa. Additionally, with adding 7 wt.% LDH, the EPLA foam reached UL‐94 V‐0 rating with high limiting oxygen index value of 29.1% and char residue of 20.4%. This study provides a novel strategy for the preparation of flame‐retardant EPLA foams with low density, three dimensional complex shapes, as well as excellent mechanical properties.

Eco-friendly multifunctional coating for polyester-cotton blended fabrics with superior flame retardancy and antibacterial properties

Since the fire hazards of polyester-cotton blended (PTCO) fabrics and the hidden dangers of bacterial infection concerns caused by the contained cotton fiber, the design of flame retardant and antibacterial PTCO fabrics has received considerable attention. In this work, flame-retardant PTCO fabrics with satisfactory antibacterial properties were fabricated via a convenient and eco-friendly impregnation treatment involving guanidine phosphate (GP) and polyethylenimine (PEI). The prepared PTCO fabrics demonstrated excellent flame retardancy with a high limiting oxygen index value of 30.5 % and self-extinguishing capability, the damaged length was only 34 mm in the vertical flammability test. Furthermore, the peak heat release rate and the total heat release of coated PTCO fabrics were reduced significantly by 49 % and 38 %, respectively, indicating a substantial enhancement in fire safety. According to the analysis of the char residues and volatiles, GP presented great catalytic carbonization property, and PEI assisted the formation of the dense and stable carbon layer. The stable carbon layer effectively restricted mass and oxygen transfer between the PTCO fabrics and the environment. In addition, the introduction of PEI also produced more nonflammable gases to enhance the flame retardancy of the PTCO fabrics. Importantly, the GP/PEI coating barely deteriorate the physical and mechanical properties of the PTCO fabrics. The antibacterial rate of the GP/PEI-coated PTCO fabrics against Escherichia coli and Staphylococcus aureus was 99.99 %, similar to that of GP-coated fabrics, indicating the efficacy antibacterial properties of GP, and the addition of PEI did not compromise the antibacterial properties of GP. This work offers an efficient and simple approach to producing multifunctional PTCO fabrics with excellent flame retardancy and antibacterial properties, which are hopeful to expand the promising application of PTCO fabrics.

Development of Halogen‐Free Flame Retardant Acrylonitrile Butadiene Styrene (ABS) Based Composite Materials

AbstractNatural flammability properties of acrylonitrile butadiene styrene (ABS) seriously limit the use of ABS polymers in industries. Improving the flammability performance of ABS by using halogenated additives has been a very common method in the past. However, with increasing environmental awareness, the use of halogen‐containing additives has been severely limited over time. Therefore, we aimed to use halogen‐free flame‐retardant additives in our study to improve the flame‐retardant properties of ABS. ABS‐based composites containing 20, 25, 30 % aluminum diethyl‐phosphinate (AlPi) and ammonium polyphosphate (APP) halogen‐free flame‐retardant additives by weight, were prepared using a twin‐screw extruder. V0 rating according to UL 94 standard for the thickness of 1.5 mm, limiting oxygen index (LOI) value higher than 28 %, and glow wire flammability index of 960 °C were aimed in this study. To improve the LOI values of flame‐retardant ABS composites, pentaerythritol (PER), zinc borate (ZB), and magnesium hydroxide were used. The highest LOI value was obtained to be 28.1 % by using 12.5 wt.% AlPi, 12.5 wt.% APP, 5 wt.% PER and 3 wt.% ZB. The effect of flame retardants on mechanical properties (flexural and tensile properties), impact properties (Izod and Charpy‐notched impact strength), thermal properties, melt flow index, and morphology (scanning electron microscopy) of ABS were also examined.

Rationally designed lentinan outer layer to improve the comprehensive performance of flame-retardant cotton fabrics

As the most widely used natural fabric, cotton fabric is highly flammable with serious fire hazard concerns. The use of biomass materials to impart flame resistance to fabrics is always a hot topic of interest. In this work, a novel durable flame retardant cotton fabric (Cotton-APA/LNT) was fabricated by successively covalent bonding ammonium phytate (APA) and lentinan (LNT). The Cotton-APA/LNT fabric sample had a highly limiting oxygen index (LOI) value of 51.5 % and was self-extinguished in the vertical burning test (VBT) at 18.0 % weight gain. The peak heat release rate and total heat release values were decreased by 91.5 % and 46.0 %, respectively compared with those of the control cotton. Besides, after 50 laundering cycles (LCs), the fabric was still self-extinguished in the VBT with an LOI value of 34.2 %. APA fully strengthened the role of acid source by the presence of LNT. The constructed LNT outer layer showed comprehensive improvements in thermostability, flame retardancy, smoke suppression, durability, and breaking force. Specifically, the Cotton-APA/LNT sample had a higher LOI value (↑4.3 %), lower total heat release (↓23.8 %), lower total smoke production (↓29.1 %), higher thermostability (↑27 °C under air), better char formation ability (↑2.0 % under air), higher durability (self-extinguished in the VBT after 50 LCs), and higher breaking force (↑32.5 % in the warp direction and ↑33.9 % in the weft direction) compared with those of Cotton-APA sample. This work has proposed an advanced approach for fabricating eco-friendly durable fire-safety cotton fabrics.

A phosphonate‐derived epoxy vitrimer with intrinsic flame retardancy and catalyst‐free reprocessability

AbstractPhosphonate, as an effective flame‐retardant group, has a dynamic phosphonate exchange behavior similar to the transesterification of carboxylate; and introducing it into the network of epoxy resin (EP) is beneficial for solving the fire risk and waste disposal problems of EP in the meantime. Herein, a reprocessable and flame‐retardant epoxy vitrimer (EV) with dual dynamic covalent reactions of phosphonate and carboxylate transesterifications is constructed by introducing a phosphonate‐containing diol named GHPP into an epoxy‐anhydride curing system. The presence of the phosphonate makes the EV intrinsically flame‐retardant; meanwhile, both of the dynamic phosphonate and carboxylate transesterifications are accelerated by the abundant primary hydroxyl groups, which show much higher activity than the as‐generated β‐hydroxyls during curing, leading to enhanced dynamic properties of the EV. As a result, on the one hand, the EV achieves the UL‐94 V‐0 rating with a high limiting oxygen index value of 37.3%; and it shows a 41% reduction for the peak heat release rate and a 39% reduction for the total heat release in the cone calorimetry test. On the other hand, such EV exhibits rapid stress relaxation and is reprocessed easily to maintain its mechanical properties, thermal properties and flame retardancy to the hilt.

A highly efficient, colorless phosphorus–nitrogen synergistic flame retardant for durable flame retardancy in wood pulp paper

Wood pulp paper (WPP) is an exemplary substrate material, yet its flammability impedes the widespread application in diverse functional fields. Herein, a highly effective, colorless and transparent phosphorus–nitrogen flame retardant, namely ammonium salt of tris(hydroxymethyl)aminomethane diphosphonic acid (AMPAP-NH4+) without halogen and formaldehyde, has been synthesized for WPP. Chemical grafting was employed to confer highly durable flame retardancy to the WPP, enabling it to maintain excellent fire resistance after functionalization. X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and Energy Dispersive Spectroscopy (EDS) analysis demonstrated that AMPAP-NH4+ was directly linked to cellulose fibers via POC bonds, effectively introducing P and N elements into the WPP without altering the surface morphology of the fibers. Results from thermogravimetric analysis, vertical burning test, limiting oxygen index test, cone calorimeter test and thermogravimetric-Fourier infrared spectrometer test demonstrated that the treated WPP exhibited outstanding flame retardancy. The peak heat release rate (pHRR) and total heat release (THR) values decreased by 80.8% and 70.9%, respectively, and the limiting oxygen index (LOI) increased to 41.4%. Furthermore, due to the stability of the POC bond, the treated samples remained unignited after 168 h, with a high LOI value of 35.3%. In summary, AMPAP-NH4+ serves as a phosphorus–nitrogen synergistic transparent flame retardant that can effectively and durably impart paper with flame retardancy without altering its surface morphology.

Construction of green versatile coating integrating fireproof, electric-conduction and self-cleaning performance for cotton fabrics

The development of conductive cotton fabrics possessing superb self-cleaning and fire-proof performances exhibits vast vistas in wearable electronic devices. However, the secretion substances from human body or contaminants from the environment may interpret the normal functions of the devices and induces short-circuiting and even fire. Herein, a new strategy for the fabrication of multifunctional cotton fabrics was introduced, involving with the sequent coating of bio-based flame-retardant, conductive two-dimensional material and hydrophobic long chain alkyl silane. The multiple coating endowed the cotton fabric with a higher limited oxygen index value of 36.7% and a dramatical reduction in peak of heat release rate (74.4%) and total heat release rate (62.4%), also with a rapid self-extinguishing ability during burning. The deposition of MXene tremendously promoted the conductivity of the fabric and the coated fabric could make a steady-state electrothermal response of 129.3 °C at 5 V. Moreover, the fabric showed an excellent self-cleaning ability for common dyes and contaminants which allowed it to retain the normal functions under various conditions. The multifunctional cotton fabric designed in this work showed a high prospective in the practical applications of wearable electronics, flexible sensors, early warning, and even special membranes for extreme environments.

Bio-based long-chain aliphatic polyamide with intrinsic flame retardancy and great overall properties

Bio-based long-chain aliphatic polyamides show remarkable potential in pursuing high-performance, sustainable bio-plastics. However, the aliphatic structure also leads to high flammability that severely restricts their applications. Herein, we demonstrate a novel flame-retardant system to fabricate high-performance, flame-retardant bio-based long-chain aliphatic polyamide. In this system, a novel reactive nitrogen-based flame-retardant monomer, PDB, was designed and synthesized. Subsequently, the corresponding bio-based long-chain polyamide copolymer was prepared through a facile polycondensation process. The nitrogen-based groups exhibited highly efficient free-radical-capturing effect, helping the copolymer achieve a high limiting oxygen index value of 32.6%, the UL-94 V-0 rating, a 33.3% lower peak heat release rate, and inhibited the release of toxic gasses at a PDB content of 6 wt%. Furthermore, the copolymer exhibited largely maintained crystallinity, thermal stability, and mechanical properties, owing to the high reactivity of PBD with polyamide monomers. At the same time, the incorporation of PBD increased the rigidity of the copolymer, resulting in a significant increase of 16.4 °C in the glass transition temperature and lower dielectric properties. This work provides a new perspective on the preparation of bio-based long-chain aliphatic polyamide with enhanced overall properties.

Flame retardancy, combustion, and ceramization behavior of ceramifiable flame‐retardant room temperature vulcanized silicone rubber foam

AbstractTwo types of ceramifiable flame‐retardant room temperature vulcanized (RTV) silicone rubber foam containing mica power (MP) were prepared by using glass powder (GP) as fluxing agents and aluminum hydroxide (ATH) as flame‐retardant agent, respectively. The flame retardant, combustion behavior, and thermal stability of ceramifiable flame‐retardant RTV silicone rubber foams were investigated. The results show that GP is not conducive to the flame retardancy and thermal stability improvement of the foams. On the contrary, MP and ATH can significantly improve the flame retardancy and thermal stability at high temperatures of the foams. The foams with addition of MP and ATH can reach to a high limiting oxygen index value of 35.8 with V‐0 rating in the vertical combustion test, and the total heat release and total smoke production of the foams are 21.0% and 61.7% lower than of the pure RTV silicone rubber foam, respectively. Furthermore, the structural and morphological changes of the foams under different pyrolysis conditions were studied, so as to reveal its ceramifiable mechanism under different fire scenarios. The results show that GP does not promote the formation of more char residue during pyrolysis, but it can greatly lower the ceramifiable temperature, resulting in a superior ceramic phase char residue. The foams including MP and ATH have a high char residue content; nevertheless, a comparatively higher temperature is necessary to create ceramic phase char residue.

Aerogels containing ionomers and microwave assisted growth of carbon nanostructures on carbon urchins for multifunctional electromagnetic interference shielding

Hierarchal 3D porous carbon materials show huge potential for EMI shielding because of their adjustable pore structure, tunable morphology and high electrical conductivity. However, poor graphitic nature and improper contact between materials lead to reduce the inherent conductivity, which supress the EMI shielding performance. In this work, we designed a hierarchical Carbon–Carbon nanostructure, which resembles a ‘sea-urchin’, exhibiting high shielding performance. A facile strategy of microwave assisted growth of carbon nanofiber (CNF) on the ‘self-assembled’ carbon urchin (CU) holds the rank of hierarchy, which enhance the electrical contact between the urchins. In order to obtain a 3D construct, a classical Ionomers pair-PEDOT:PSS was chosen as the matrix and CNF@CU was infused and subjected to freeze-drying to design ultra-light aerogel. The morphological assessment reveals that CNF@CU in the aerogel offers trapping centers by providing multiple interfaces. The aerogels exhibited two orders of jump in electrical conductivity and showed excellent thermal stability. The high limiting oxygen index value begins to suggest that these aerogels can extend their utility to flame retardant materials. The EMI shielding properties of the construct were studied in the X-band (8.2–12.4 GHz). The aerogel with 1.7 wt% of CNF@CU exhibited −50.8 dB of shielding efficiency (representing 99.999% blocking). The excellent EMI performance achieved here is mainly due to the conductive losses, dipole polarization, interface polarization, and wave trappers. These wave trappers are extremely beneficial for shielding EM radiations through multiple scattering. The utility of these materials were further evaluated using a Bluetooth module, wherein the aerogel potentially blocked all the transmitting Bluetooth signals confirming the quick shielding quality of the proposed aerogel. Taken together, this work provides a facile approach for designing and developing lightweight aerogel based EMI shielding materials.

A Machine‐Braided Flame‐Retardant Triboelectric Yarn/Textile for Fireproof Application

AbstractWith the rapid development of the textile‐based triboelectric nanogenerators (T‐TENGs), it is highly desired to create a simple and cheap fabrication strategy for the T‐TENGs with high flame‐retardant performances (FRT‐TENGs), which can present reliable electrical performance in the fire disaster. In this work, by covering the flame‐retardant polyethylene terephthalate filaments around the conductive fiber, a flame‐retardant triboelectric yarn is successfully developed through a simple and continuous high‐speed braiding process. The obtained composite yarns are further woven into an FRT‐TENG, which presents excellent comprehensive performances, including good energy harvesting ability, long‐term durability and washability, excellent flame retardancy, and high comfortability. The open‐circuit voltage (VOC) and short‐circuit current (ISC) can reach nearly 12 V and 0.36 µA, respectively. The FRT‐TENG shows a high limiting oxygen index value of 31.3% and self‐extinguishing behavior, and still presents high energy output performances after the burning, making it a perfect candidate for intelligent devices with high fireproof ability, such as the smart firefighter uniform and the intelligent carpet for escape direction indication.

Eco-Friendly and Facile Integrated Intumescent Polyelectrolyte Complex Coating with Universal Flame Retardancy and Smoke Suppression for Cotton and its Blending Fabrics

Cotton and its blended fabrics are widely used textile materials in daily life; however, their high flammability brings serious fire hazards. It remains a huge challenge to endow cotton and its blended fabrics through simple and universal technology. In this work, a novel water-based polyelectrolyte complex (PEC) coating was developed from chitosan and a water treatment agent (amino trimethylphosphonic acid). By controlling the degree of ion pair aggregation through pH adjustment, the intumescent and stable PEC coating can be constructed quickly via facile blading coating and curing processes. High transparency allows for the deposition of the coating with little effect on the original pattern of the coated fabric. Additionally, when the coated fabrics were exposed to flame, the PEC coating underwent a quick self-char-forming reaction in advance and formed a protective char layer covered on the fibers. Thus, the PEC coating with low adding-on (11.5–21.5 wt %) shows universally high flame retardancy for cotton, polyester/cotton blends, and polyester/poly(vinyl alcohol)/cotton blends. The coated fabrics show excellent extinguishing performances, high limiting oxygen index values of 27.5%–28.5%, and total release smoke inhibition of 42%. This work provides a promising universal technology for manufacturing fire-safety cotton and its blends in a simple and eco-friendly way.

Flame-Retardant and Smoke-Suppressant Flexible Polyurethane Foams Based on Phosphorus-Containing Polyester Diols and Expandable Graphite

A liquid-phosphorus-containing polyester diol, PPE, was prepared via condensation polymerization using commercial reactive flame retardant 9,10-dihydro-10-[2,3-di(hydroxycarbonyl)propyl]-10-phospha-phenanthrene-10-oxide, adipic acid, ethylene glycol, and 1,4-butanediol. PPE and/or expandable graphite (EG) were then incorporated into phosphorus-containing flame-retardant polyester-based flexible polyurethane foams (P-FPUFs). The structure and properties of the resultant P-FPUFs were characterized using scanning electron microscopy tensile measurements, limiting oxygen index (LOI), vertical burning tests, cone calorimeter tests, thermogravimetric analysis coupled with Fourier-transform infrared spectroscopy, X-ray photoelectron spectroscopy, and Raman spectroscopy. Unlike the FPUF prepared using regular polyester polyol (R-FPUF), PPE increased the flexibility and elongation at break of the resultant forms. More importantly, the peak heat release rate (PHRR) and total heat release (THR) of P-FPUF were reduced by 18.6% and 16.3%, respectively, via gas-phase-dominated flame-retardant mechanisms, compared with those of R-FPUF. The addition of EG further reduced the peak smoke production release (PSR) and total smoke production (TSP) of the resultant FPUFs while increasing the LOI and char formation. Interestingly, it was observed that EG noticeably improved the residual quantity of phosphorus in the char residue. When the EG loading was 15 phr, the resulting FPUF (P-FPUF/15EG) attained a high LOI value (29.2%) and exhibited good anti-dripping performance. Meanwhile, the PHRR, THR, and TSP of P-FPUF/15EG were significantly decreased by 82.7%, 40.3%, and 83.4%, respectively, compared with those of P-FPUF. This superior flame-retardant performance can be attributed to the combination of the bi-phase flame-retardant behavior of PPE and condensed-phase flame-retardant characteristics of EG.

Influence of boron bearing fillers on flame retardancy properties of huntite hydromagnesite filled ductile PLA biocomposites

In this work, the flame retardant influences of colemanite and boron oxide are investigated in huntite-hydromagnesite (HH) containing plasticized poly (lactic acid) (PLA) biocomposites. The composites are characterized using limiting oxygen index (LOI), horizontal (UL 94 HB) and vertical (UL-94 V) burning tests, mass loss calorimeter and thermo gravimetric analysis (TGA). The addition of colemanite causes enhanced fire retardant performance with higher UL-94 V rating and LOI value and lower pHRR value. V0 rating and the highest LOI value is observed with the addition 1 wt % colemanite. When the concentration of colemanite reaches to 3 and 5 wt %, the samples get V1 rating. When the concentration of colemanite reaches to 5 wt %, pHRR and avHRR values are lower than those of the reference sample. The addition of boron oxide caused only improvement in LOI value. The highest LOI value (33.2) is observed in 5 and 10 wt % boron oxide containing samples.

Development of ductile green flame retardant poly(lactic acid) composites using hydromagnesite&huntite and bio‐based plasticizer

AbstractTurning brittle poly(lactic acid) (PLA) to ductile form via plasticizer inclusion is an effective option in the case of processing with high amounts of additives. Additionally, the integration of natural flame retardants to PLA involving bio‐based plasticizer enables to use of environmentally friendly composites in conditions where fire resistance performance is required. In the current study, ductile green fire retardant PLA composites were manufactured using hydromagnesite&huntite (HH) as a natural fire retardant additive and acetyl tributyl citrate as a bio‐based plasticizer. The influences of plasticizer and HH contents on the fire retardant, thermal and mechanical performances of the composites were explored. According to test results, the limiting oxygen index (LOI) value of PLA reduced from 29.2 to 28.0 and the UL‐94 V rating changed from V2 to BC with the addition of 20 wt% plasticizer owing to the reduction in melt viscosity. The peak heat release rate (pHRR) and average heat release rate (avHRR) values increased steadily as the concentration of plasticizer increased due to the formation of a more porous residue structure stemming from the increased transportation rate of gases. In order to produce ductile flame retardant material, the plasticizer content was required to 20 wt% of HH. The highest LOI value (36.2) and UL‐94 rating of V0 were achieved with the inclusion of 70 wt% HH in the presence of 20 wt% plasticizer. Improvement in impact resistance and reduction in tensile strength were observed as the added amount of plasticizer increased.

Nickel alginate‐enhanced fire safety of aluminum diethylphosphinate on epoxy resin

AbstractTo attain superior fire safety epoxy resins (EP), aluminum diethylphosphonate (AlPi) and nickel alginate were incorporated to EP in different proportions. The synergistic flame retardant effects between AlPi and nickel alginate on fire safety and mechanical properties of EP were investigated in detail. EP/AlPi9.5‐Nickel Alginate0.5 acquired the UL‐94 V‐0 rating with the highest limiting oxygen index value (28.9%). Besides, the thermal decomposition behaviors of the samples were researched by thermogravimetric analysis, implying that EP/AlPi‐Nickel Alginate exhibited the better thermal stability and char‐forming ability. Compared with EP, the peak heat release rate and total heat release were declined by 58.3% and 12.8%. And the addition of nickel alginate reduced the release of smoke. In particular, the incorporation of AlPi and nickel alginate increased the impact strength, flexural strength and glass transition temperature of EP. In perspective, the synergistic effect of bio‐based nickel alginate and AlPi opens a practicable avenue in decreasing the fire risk and improving the mechanical properties of EP.

A Bridge-Linked Phosphorus-Containing Flame Retardant for Endowing Vinyl Ester Resin with Low Fire Hazard

The high flammability of vinyl ester resin (VE) significantly limits its widespread application in the fields of electronics and aerospace. A new phosphorus-based flame retardant 6,6'-(1-phenylethane-1,2 diyl) bis (dibenzo[c,e][1,2]oxaphosphinine 6-oxide) (PBDOO), was synthesized using 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) and acetophenone. The synthesized PBDOO was further incorporated with VE to form the VE/PBDOO composites, which displayed an improved flame retardancy with higher thermal stability. The structure of PBDOO was investigated using Fourier transformed infrared spectrometry (FTIR) and nuclear magnetic resonances (NMR). The thermal stability and flame retardancy of VE/PBDOO composites were investigated by thermogravimetric analysis (TGA), vertical burn test (UL-94), limiting oxygen index (LOI), and cone calorimetry. The impacts of PBDOO weight percentage (wt%) on the flame-retardant properties of the formed VE/PBDOO composites were also examined. When applying 15 wt% PBDOO, the formed VE composites can meet the UL-94 V-0 rating with a high LOI value of 31.5%. The peak heat release rate (PHRR) and the total heat release (THR) of VE loaded 15 wt% of PBDOO decreased by 76.71% and 40.63%, respectively, compared with that of untreated VE. In addition, the flame-retardant mechanism of PBDOO was proposed by analyzing pyrolysis behavior and residual carbon of VE/PBDOO composites. This work is expected to provide an efficient method to enhance the fire safety of VE.

Synergistic action of expandable graphite on fire safety of a self‐intumescent flame retardant epoxy resin

AbstractPreviously, it was reported that epoxy resin (EP) filled with ammonium polyphosphate (APP) and copper (I) oxide (Cu2O) at a mass ratio of 8/2 (APP8‐Cu2O2) as a self‐intumescent system demonstrated promising fire retardancy. To further improve the flame retardant efficiency, the possibility of expandable graphite (EG) as an effective synergist for the self‐intumescent EP system was revealed by limiting oxygen index (LOI) test. The results showed that the incorporation of EG increased the LOI value of EP/APP8‐Cu2O2 obviously. The highest LOI value was obtained at the EG/APP8‐Cu2O2 mass ratio of 3/7, indicating the optimal synergistic effect being achieved. Furthermore, UL‐94 test results showed that the excellent synergistic effect resulted in the addition of 13 wt% EG/APP8‐Cu2O2 of 3/7 not only endowed EP a relatively high LOI value of 34.3%, but also made it pass UL‐94 V‐0 rating. Moreover, the main fire hazard parameters obtained from cone calorimeter tests, such as peak heat release rate, total smoke production, and peak CO production were reduced 40.3%, 30.3%, and 46.2%, respectively by the combination effect of EG/APP8‐Cu2O2 with mass ratio of 3/7, suggesting the excellent improvement in the fire safety of EP significantly. Finally, a possible action mode, which would be beneficial for developing other flame retardant polymers with high fire safety, was proposed.

Understanding the Flame Retardant Mechanism of Intumescent Flame Retardant on Improving the Fire Safety of Rigid Polyurethane Foam.

Combinations of multiple inorganic fillers have emerged as viable synergistic agents for boosting the flame retardancy of intumescent flame retardant (IFR) polymer materials. However, few studies on the effect of multiple inorganic fillers on the flame retardant behavior of rigid polyurethane (RPU) foam have been carried out. In this paper, a flame retardant combination of aluminum hydroxide (ATH) and traditional flame retardants ammonium polyphosphate (APP), pentaerythritol (PER), melamine cyanurate (MC), calcium carbonate (CC), and expandable graphite (EG) was incorporated into RPU foam to investigate the synergistic effects of the combination of multiple IFR materials on the thermal stability and fire resistance of RPU foam. Scanning electron microscopy (SEM) and thermogravimetric analysis (TGA) revealed that 8 parts per hundred polyols by weight (php) filler concentrations were compatible with RPU foam and yielded an increased amount of char residue compared to the rest of the RPU samples. The flame retardancy of multiple fillers on intumescent flame retardant RPU foam was also investigated using cone calorimeter (CCTs) and limiting oxygen index (LOI) tests, which showed that RPU/IFR1 (APP/PER/MC/EG/CC/ATH) had the best flame retardant performance, with a low peak heat release rate (PHRR) of 82.12 kW/m2, total heat release rate (THR) of 15.15 MJ/m2, and high LOI value of 36%. Furthermore, char residue analysis revealed that the use of multiple fillers contributed to the generation of more intact and homogeneous char after combustion, which led to reduced decomposition of the RPU foam and hindered heat transfer between the gas and condensed phases.