High Limiting Oxygen Index Research Articles

One Pot Facile Synthesis of Self-extinguishable Metal Based Flame Retardant for Cotton Fabric

ABSTRACT An efficient metal-based flame-retardant was prepared for cotton fabric (CF) by a convenient pad-dry-cure method, which involves the consecutive deposition of intumescent containing different combination of ammonium polyphosphate, melamine, pentaerythritol with Copper and Zinc metal ions. We studied different properties like thermal, mechanical, flammability, and laundering durability of treated CF samples. The intumescent-coated CF shows remarkable high-efficiency flame-retardant properties: (1) a self-extinguishing property (5 s) without lateral spreading of flame during the vertical flame test with a lower smoke release character; (2) the limiting oxygen index (LOI) values of coated CF are improved with increasing add-on level. The Zn-based samples exhibited a high limiting oxygen index value of 36%. Consequently, the resultant fabrics were observed to show great flame retardancy with high thermal stability as 35% of char yield at 600°C. The durability of modified cotton was tested after five laundering cycles, which showed that the coating maintains 84% of its initial mass. It is reported that in addition to durable flame retardancy, the mechanical properties of cotton were also enhanced. The present work provides eco-friendly one pot facile synthesis of intumescent-based flame retardant for CF which may be used in numerous applications. Abbreviations: ammonium polyphosphate; PER: pentaerythritol; MEL: melamine; LOI: limiting oxygen index; TGA: thermogravimetric analysis; DTG: derivative thermogravimetry; GSM: gram per square meter; FR: flame retardant; CP: plain cotton fabric; CT: twill cotton fabric; CF: cotton fabric; Int: intumescent; FTIR: Fourier Transformation Infrared; BEL: burn entire length; DNI: did not ignite; SE: self-extinguish; HGMs: hollow glass microspheres; CH/PA/Ba/PA: Chitosan/ Phytic Acid/Barium/Phytic Acid; DPPMA: diphenylphosphinic acid with melamine; PBS/30PA-GU: poly(butylene succinate/30 phytic acid-guanosine; PET: polyethyleneimine; Tri-HTAC: 2,4,6-tri[(2-hydroxy-3-trimethyl-ammonium)propyl]-1,3,5-triazine chloride; TA/B@PDA: tannic acid/Borax@polydopamine; P10H5: 5wt% HCCP(Hexachlorocyclotriphosphazene). ammonium polyphosphate; PER: pentaerythritol; MEL: melamine; LOI: limiting oxygen index; TGA: thermogravimetric analysis; DTG: derivative thermogravimetry; GSM: gram per square meter; FR: flame retardant; CP: plain cotton fabric; CT: twill cotton fabric; CF: cotton fabric; Int: intumescent; FTIR: Fourier Transformation Infrared; BEL: burn entire length; DNI: did not ignite; SE: self-extinguish; HGMs: hollow glass microspheres; CH/PA/Ba/PA: Chitosan/ Phytic Acid/Barium/Phytic Acid; DPPMA: diphenylphosphinic acid with melamine; PBS/30PA-GU: poly(butylene succinate/30 phytic acid-guanosine; PET: polyethyleneimine; Tri-HTAC: 2,4,6-tri[(2-hydroxy-3-trimethyl-ammonium)propyl]-1,3,5-triazine chloride; TA/B@PDA: tannic acid/Borax@polydopamine; P10H5: 5wt% HCCP(Hexachlorocyclotriphosphazene).

From herbicide to flame retardant: The lamellar-like phosphorus-bridged amitrole toward high fire safety epoxy resin with light smoke and low toxicity

In an attempt to alleviate the harmful impact of the flammability of epoxy resin on the environment, amitrole, a herbicide, has been converted to a novel flame retardant (PBA) with lamellar morphology through organophosphorus modification. This material has been utilized to fabricate fire safe epoxy thermosets (EP). EP containing 7.5 wt% PBA undergoes quick self-extinguishment upon ignition. This blend displays a high limiting oxygen index (LOI) value of 34%. More importantly, hazardous products (heat, smoke, toxic gases including CO/CO2) released during combustion of EP, are strongly suppressed in the presence of PBA. The mechanical properties of EP-PBA blends are comparable to those of virgin EP. The tensile strength of EP containing PBA is 90% of that of unmodified EP. The flexural strength of PBA blends is somewhat greater than that for EP containing no additive. A tactful strategy for the transformation of amitrole, a potential environmental contaminant to a benign flame retardant for polymers has been developed.

A phosphorous/nitrogen/silicon containing diphenylphosphoramide silicon oil toward effective flame retardancy for polycarbonate with comparable mechanical properties

AbstractA P/N/Si containing diphenylphosphoramide silicone oil (PASO) was synthesized using amino phenyl silicone oil and diphenylphosphinyl chloride as raw materials. The as‐synthesized PASO displayed better flame retardancy toward polycarbonate (PC) meanwhile maintaining the mechanical performances of PC. At loading level of 1 wt% PASO, UL 94V‐0 rating and a high limited oxygen index value of 31% were achieved for the flame retardant composite in the presence of 5 wt% talc as anti‐dripping agent. Additionally, it gave a tensile strength of 65.5 MPa, elongation at break of 96.4%, and impact strength of 52.6 kJ/m2, which were comparable to the pure PC. The analysis of the char residue after cone calorimeter test and the pyrolysis gaseous products demonstrated that PASO exhibited flame retardant mechanism of both gas and condensed phases.

Fabrication of Lightweight Polyphenylene Oxide/High‐Impact Polystyrene Composite Bead Foam Parts via In‐Mold Foaming and Molding Technology

Bead foam is one kind of important polymeric foam product, which has the advantages of complex product shape, a wide range of parts density, and a wide variety of available materials. Steam‐chest molding is usually used to prepare bead foams. However, it is challenging to prepare polymers with high melting point (T m) or glass transition temperature (T g). Herein, in‐mold foaming and molding technology (IMFM) is proposed to prepare bead foams from polyphenylene oxide/high‐impact polystyrene composite (PHC). PHC bead foam parts (PHCPs) with densities from 0.11 to 0.25 g cm−3 are successfully prepared by controlling the process parameters. Due to good interbead bonding, the bead foams have superior mechanical properties. The tensile and compression strength for PHCPs with a density of 0.25 g cm−3 are 2.84 and 2.93 MPa, respectively. The PHCPs also show high dimensional stability at 120 °C and good flame‐retardant properties, characterized by a high limiting oxygen index (LOI) value and HBF rating. In addition, the fabrication mechanism behind IMFM is proposed. This technology provides a new way to produce polymer bead foams, especially for engineering materials.

Trinity effect of potassium sulfonate-benzimidozale towards self-intumescent flame-retarded polyester with low fire hazards

Additive-type Intumescent flame retardants (IFRs) are widely used in many polymeric materials to reduce fire hazards. However, the migration behavior of IFRs in the long-term use process leads to poor flame retardance durability and undesirable health issue. To address these problems, a novel reactive monomer (MS-K) containing potassium sulfonate and benzimidozale groups was synthesized and chemically linked into the backbones of model polymer (Polyethylene terephthalate, PET). When the PET-copolymer burnt, the sulfonate group worked as acid and gas sources, and the benzimidozale group acted as carbon source. The trinity effect (acid, gas and carbon sources) of benzimidozale-potassium sulfonate structure gave rise to the self-intumescent carbonization behavior of PET matrix. As a result, the formed intumescent char-layer exerted a significant condensed-phase flame retardant effect that can hinder the oxygen exchange, isolate from the heat source and suppress the volatilization of combustible small molecules. Thus, the corresponding PET-copolymer exhibited extremely low fire hazards with UL-94 V-0 rating, a high limiting oxygen index of 32.5 vol%, greatly decreased peak heat release rate (decreased by 58%) and total smoke production (decreased by 39%). The strategy of reactive trinity-macromolecule not only exhibits excellent intumescent flame-retardant effect, but also completely eliminates the migration issue, which represents a promising way to replace the traditional additive-type IFRs.

Synergistic Flame Retardant Effect of Barium Phytate and Intumescent Flame Retardant for Epoxy Resin.

Recently, widespread concern has been aroused on environmentally friendly materials. In this article, barium phytate (Pa-Ba) was prepared by the reaction of phytic acid with barium carbonate in deionized water, which was used to blend with intumescent flame retardant (IFR) as a flame retardant and was added to epoxy resin (EP). Afterward, the chemical structure and thermal stability of Pa-Ba were characterized by Fourier transform infrared (FTIR) spectroscopy and thermogravimetric analysis (TGA), respectively. On this basis, the flammability and flame retardancy of EP composites were researched. It is shown that EP/14IFR/2Ba composite has the highest limiting oxygen index (LOI) value of 30.7%. Moreover, the peak heat release rate (PHRR) of EP/14IFR/2Ba decreases by 69.13% compared with pure EP. SEM and Raman spectra reveal the carbonization quality of EP/14IFR/2Ba is better than that of other composites. The results prove that Pa-Ba can cooperate with IFR to improve the flame retardancy of EP, reducing the addition amount of IFR in EP, thus expanding the application range of EP. In conclusion, adding Pa-Ba to IFR is a more environmentally friendly and efficient method compared with others.

Synthesis of a Compound Phosphorus-Nitrogen Intumescent Flame Retardant for Applications to Raw Lacquer.

Raw lacquer (RL) is a natural polymer compound with highly promising applications; however, its inflammable attribute restricts the industrial applications. In this study, melamine is used to formulate tri (1-melamine-2-propanol) phosphate (FR-1), after which it is synthesized with ammonium phosphate (FR-2) and diatomite to form a compound phosphorus-nitrogen intumescent flame retardant (IFR). Next, IFR is used as the filling agent that then cross-links with RL, and as such RL/IFR membranes are formed after the curing. The limiting oxygen index (LOI) measurement, the vertical combustion test (UL-94), the microshape calorimetric analysis (CCT), and the thermal gravimetric analysis (TGA) are conducted to examine the combustion resistance and thermal stability of the membranes. Fourier transform infrared spectroscopy (FT-IR) and electron scanning microscope (SEM) are performed to separately characterize the structure and compatibility; the mechanical properties of the membranes are also evaluated. The vertical combustion test results confirm that with 30 wt% of IFR, RL/IFR membranes acquire 12.3% higher LOI and a vertically combustion of V-0 level. The TGA indicates that RL/IFR membranes demonstrate a greater adhesion level, a higher rigidity, and better luster than pure RL membranes.

Luteolin-based epoxy resin with exceptional heat resistance, mechanical and flame retardant properties

Recently, tremendous attentions have been paid to the fabrication of bio-based intrinsic fire-retarded epoxy resins with outstanding thermal and mechanical properties from renewable resources. Herein, the bio-based epoxy monomer of diglycidyl ether luteolin (DGEL) was synthesized via one-step method from sustainable luteolin. The biocompatible epoxy resin was manufactured via the curing reaction between DGEL and 4, 4′-diaminodiphenyl sulfone (DDS). DGEL/DDS showed higher glass transition temperature (Tg) (314.4 °C) than diglycidyl ether bisphenol A (DGEBA)/DDS (217.4 °C), demonstrating the distinguished heat resistance. Tensile testing results exhibited that DGEL/DDS possessed superior tensile strength (69.2 MPa) compared to DGEBA/DDS (57.2 MPa). Thermogravimetric analysis (TGA) illustrated that the char yield of DGEL/DDS was 44.0 wt%, much higher than that of DGEBA/DDS (11.6 wt%). In addition, DGEL/DDS passed the V-0 rating in UL-94 tests with a high limiting oxygen index (LOI) (32.5%) as well as extremely low peak heat release rate (107.5 W/g) indicating the excellent flame retardant properties. Smoke density testing results showed that the peak density of smoke for DGEL/DDS was 304.7, much lower than that for DGEBA/DDS (660.7), indicating the remarkable reduction of toxicity hazards. This work provides a facile approach for the preparation of bio-based epoxy resins with outstanding overall properties that show promising applications in high heat resistance and flame retardant fields.

High-Efficiency Flame Retardants of a P-N-Rich Polyphosphazene Elastomer Nanocoating on Cotton Fabric.

Modification by intumescent flame retardants is an effective way to impart antiflame properties to fabric materials. Polyphosphazene elastomers contain all three elements required by intumescent flame retardants: an acid source, a gas source, and a carbon source, making them all-in-one integrated intumescent flame retardants. In this work, halogen-free poly(dimethoxy)phosphazene (PDMP) loaded with 29.0 wt % phosphorus and 13.1 wt % nitrogen is shown to be an ideal flame retardant for fabric materials. For the first time, transparent and elastic PDMP was applied as an intumescent flame retardant for cotton fabric. The PDMP-coated cotton shows remarkable high-efficiency flame-retardant properties: (1) a self-extinguishing property during the vertical flame test is obtained when the add-on level reaches 5.3 wt %, with a lower smoke release character; (2) the limiting oxygen index (LOI) values of coated cotton are improved with increasing add-on level, and the thickness of the coating is measured to be at the nanolevel, 2540 nm when 10.9 wt % PDMP is coated. The coated cotton shows enhanced carbonization ability at lower temperatures, which is the key to imparting flame-retardant properties to cotton, and the PDMP-coated cotton shows remarkably lower peak heat release rate and total heat release compared to the control cotton during combustion. The durability of modified cotton was tested after 50 laundering cycles, which showed that the coating maintains 80% of its initial mass, and the after-laundering sample preserves the characteristics of self-extinguishing and a high LOI. Thus, the PDMP nanocoating-modified flame-retardant cotton fabric is sufficiently durable for practical application.

Small change, big impact: Simply tailoring the substitution position towards significant improvement of flame retardancy

The use of conventional flame-retardant elements such as Cl, Br, P for carbon-based polymers usually leads to the deterioration of smoke and toxic gas release, and possesses serious environmental and ecological issues. Herein, we proposed a facile strategy to largely improve the flame-retardant efficiency of an eco-friendly flame-retardant method. By simply tailoring the substitution position of the functional polymerization monomer, the corresponding copolymer exhibited extremely high flame retardancy, including a 59% lower peak heat release rate (pHRR), a 48% lower smoke density, a high limiting oxygen index (LOI) of 30%, and passed the UL-94 V-0 rating without dripping. More importantly, the para-substitution copolymer showed a much higher flame-retardant efficiency than the meta-substitution copolymer, for which the monomer content needed for UL-94 V-0 rating, high LOI value, and low smoke and toxic gas release largely decreased by 25%. The detailed mechanism and the different performance between the two copolymers were comprehensively investigated. The results first confirmed the “end-group-capturing” mechanism, then revealed that the different flame-retardant efficiency was owing to the different thermal rearrangement capability of the two functional monomers. The molecular-level mechanism revealed here provided a novel thinking for designing flame-retardant polymers.

Highly efficient, transparent, and environment-friendly flame-retardant coating for cotton fabric

Environmentally friendly flame-retardant coatings for fabrics urgently need to have both high efficiency and transparency, but their development faces severe challenges. In this study, we reported a highly flame-retardant coating without halogen and formaldehyde via a facile one-pot sol–gel approach derived from ammonium polyphosphate (APP), sodium alginate (SA), and tetraethoxysilane (TEOS). In this system, SA serving as a negatively charged stabilizer can effectively inhibit APP agglomeration and further co-gelatinize with TEOS, thus leading to high transparency (transmittance in the visible region >90%) and colorlessness of the coating. Meanwhile, SA as a charring agent, APP as both acid and blowing sources, and TEOS as a silicon source together constructed a P/N/Si-containing hybrid intumescent system, so that the coating showed highly flame-retardant efficiency for cotton fabric at an ultralow loading of 10 wt%, much superior to other coatings previously reported. The resultant cotton fabric showed a high limiting oxygen index of 31%, self-extinguishing ability in the vertical burning test. Additionally, the total heat release value and total smoke production significantly decreased by 63.5% and 70.0%, respectively in the cone calorimeter test, while the mechanical property remained almost unchanged. The mechanism analysis confirmed that the dense P/N/Si-containing graphitized char layer formed in the condensed phase could effectively prevent the release of heat and the diffusion of combustible gases. This work provides new insights into the design and fabrication of the flame-retardant coating combined with the advantages of high efficiency, environment friendliness, transparency, and colorlessness.

High-flame retarding properties of polyacrylonitrile copolymer nanocomposites with synergistic effect of elemental sulfur-doped reduced graphene oxide and bio-derived catechol units

Polyacrylonitrile (PAN)-based flame retardants have been investigated as environmentally friendly high-flame retarding materials. High-flame retarding properties can be achieved in PAN copolymers via efficient thermal oxidative stabilization (TOS). In this study, PAN copolymers of dihydroxy styrene monomers with simple catechol units were synthesized as high-flame retardants using an efficient TOS process. To further improve the flame-retarding properties, PAN copolymer composites were prepared with graphene oxide (GO) and sulfur-doped reduced GO (SrGO). Differential scanning calorimetry (DSC) analysis revealed that the activation energy of the composites for cyclization reaction during TOS decreased with SrGO content. Micro combustion calorimeter revealed enhanced flame-retarding properties of P(AN-co-DHS3)-SrGO composites, resulting in a low heat release capacity (21 J/gK) and high limiting oxygen index (44.7%) (superior to Nomex®). The high-flame retarding properties could be attributed to the high char layer produced by efficient TOS of the copolymer with the catechol unit and radical scavenging effect of sulfur-functionalized SrGO. Therefore, the incorporation of SrGO into PAN copolymers with catechol units is a good alternative for developing environmentally friendly high-flame retardants.

Preparation and mechanism of phosphoramidate-based sol-gel coating for flame-retardant viscose fabric

To prepare efficiently flame-retardant sol-gel coating for viscose fabric, a novel phosphoramidate siloxane (TSPDP) was synthesized and fire-safety viscose fabrics were prepared via sol-gel method with different contents of TSPDP. When the weight gain (WG) was more than 13%, higher limiting oxygen index (LOI) value was obtained and the coated viscose fabric passed the vertical flammability test with self-extinguishing behavior. A sharp reduction of more than 42% in peak of heat release rate (pHRR) was discovered for coated viscose fabric in contrast with pure sample. The good flame retardancy of TSPDP-coated viscose fabric was due to the co-presence of P, N and Si elements, which can form a char layer barrier in condensed phase during the combustion and inhibit the release of flammable volatiles in high temperature. Moreover, this coating had few effects on the tensile strength of viscose fabric.

Tannin-furanic foams modified by soybean protein isolate (SPI) and industrial lignin substituting formaldehyde addition

Soybean protein isolate (SPI) was tested in this study as a crosslinker and formaldehyde substitute for preparing high biomass content sustainable rigid tannin-furanic-SPI (TFS) and lignin-tannin-furanic-SPI (LTFS) versatile foams. Additionally, flame retardancy was improved by lignin used as a natural fire-retardant. Fourier-transform infrared spectroscopy (FT-IR), coupled with matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-ToF-MS), revealed a covalent cross-linking reaction between tannin and SPI. TFS and LTFS foams showed by scanning electron microscopy (SEM) a closed cell structure without any pores. The incorporation of SPI resulted in enhanced mechanical properties and reduced pulverization ratios, improved thermal stability and increased thermal conductivity (approximately 0.042–0.044 W/m K compared with control foam. Furthermore, the TFS foams exhibited outstanding flame retardancy and suppressed smoke generation while undergoing combustion. These results were supported by a higher limiting oxygen index (LOI) value, a lower heat-release rate, and a higher char residue, obtained by LOI and cone calorimetry. The addition of lignin further enhanced the thermal properties and flame retardancy of TFS foams although it decreased their mechanical performance. The TFS and LTFS foams were environmentally friendly, as shown by the low formaldehyde emission measurements. This novel sustainable TFS foam appears to have a good potential for industrial application.

Bioinspired Adenosine Triphosphate as an "All-In-One" Green Flame Retardant via Extremely Intumescent Char Formation.

The development of eco-friendly flame retardants is crucial due to the hazardous properties of most conventional flame retardants. Herein, adenosine triphosphate (ATP) is reported to be a highly efficient "all-in-one" green flame retardant as it consists of three essential groups, which lead to the formation of char with extreme intumescence, namely, three phosphate groups, providing an acid source; one ribose sugar, working as a char source; and one adenine, acting as a blowing agent. Polyurethane foam was used as a model flammable material to demonstrate the exceptional flame retardancy of ATP. The direct flammability tests have clearly shown that the ATP-coated polyurethane (PU) foam almost did not burn upon exposure to the torch flame. Importantly, ATP exhibits an extreme volume increase, whereas general phosphorus-based flame retardants show a negligible increase in volume. The PU foam coated with 30 wt % of ATP (PU-ATP 30 wt %) exhibits a significant reduction in the peak heat release rate (94.3%) with a significant increase in the ignition time, compared to bare PU. In addition, PU-ATP 30 wt % exhibits a high limiting oxygen index (LOI) value of 31% and HF-1 rating in the UL94 horizontal burning foamed material test. Additionally, we demonstrated that ATP's flame retardancy is sufficient for other types of matrices such as cotton, as confirmed from the results of the standardized ASTM D6413 test; cotton-ATP 30 wt % exhibits an LOI value of 32% and passes the vertical flame test. These results strongly suggest that ATP has great potential to be used as an "all-in-one" green flame retardant.

Mechanically robust and flame-retardant polylactide composites based on molecularly-engineered polyphosphoramides

Intrinsic flammability significantly impedes practical applications of polylactide (PLA), despite many merits. Phosphoramides have shown exceptional flame retardancy efficiency in PLA, but to date it remains a grand challenge to create strong, tough and flame-retardant PLA based on phosphoramides due to lack of fundamental understanding of structure-property correlation. Herein, we design a series of polyphosphoramides (PPDA-x) with tunable structures and compositions. With 1.0 wt% of PPDA-8, tensile strength and toughness of PLA are increased by 11% and 44%, respectively, because of balanced hydrogen-bonding and interfacial tension. Meanwhile, the final PLA achieves a desirable UL-94V-0 rating and a high limited oxygen index (LOI) of ~26.8% because phosphorus contents and interfacial tension govern flame retardancy. This work offers a general methodology for creating robust and flame-retardant polymers by molecularly tailoring flame retardants and shedding light on their structure-property relationship.

A novel efficient nonflammable coating containing g-C3N4 and intumescent flame retardant fabricated via layer-by-layer assembly on cotton fiber

Flame retardant is essential for cotton fabric because of the restrictions in applications caused by poor flammability. Herein, a novel flame-retardant coating assembled on the surface of cotton fabric consists of polyethyleneimine/g-C3N4 and polyethyleneimine/phytic acid as the underlying insulating coating and the upper intumescent coating, respectively. Different amounts of the composite coatings were deposited onto the fabric by the layer-by-layer self-assembled technique. The char residue of TGA over 20 wt% has indicated the significantly enhanced performance of the thermal stability of all the coated samples and the achievement of the samples with composite coatings in a self-extinguished level proving through vertical combustion test. The samples prepared with binary hybrid coatings exhibited a high limiting oxygen index value of 30.5%. From the MCC test, the peak heat release rate and total heat release of (P/G + P/PA)4+4 showed a significant decrease of 76.9% and 77.1%, respectively. All these results demonstrated that the composite coatings endowed the cotton fabric with outstanding thermal stability and flame retardancy.

Facile Strategy to Fabricate the Flame Retardant Polyamide 66 Fabric Modified with an Inorganic-Organic Hybrid Structure.

Recently, traditional flame retardant finishing with a single metal compound has been rarely applied owing to its low effectiveness and durability. This study reports metal ion finishing in combination with surface photografting modification (M/P technology) as a novel approach to incorporate an inorganic-organic hybrid structure containing an Fe3+ ion onto the surface of the polyamide (PA) 66 fabric. Specifically, the PA fabric was first surface-modified in the presence of acrylic acid (AA) and N,N'-methylene bisacrylamide (MBAAn) during photografting pretreatment under UV irradiation (step I), then further reacted with the Fe3+ ion in the metal ion finishing (step II). After treatment with M/P technology, the fabric exhibits the required excellent flame retardancy and dripping resistance. Here, flame retardant tests show that the treated PA fabric has the highest limiting oxygen index (LOI) value of 33.4 and no melt dripping during combustion. An interesting inorganic/organic composite thermal barrier consisting of an inorganic iron oxide nanoparticle (NP) outer layer and an organic micro-intumescent inner layer can be observed on the surface of the burnt fabric. This structure could be responsible for the significant enhancement in the fire performance of the treated fabric. Importantly, the treated fabric is also highly stable during the laundering procedure, which could retain a high Fe/C ratio and an acceptable LOI value of 27.8 after washing 45 times. This confirms the achievement of durable flame retardancy after treatment with M/P technology, and its possible interaction mechanism has been discussed here.

Superior flame retardancy of glass fiber-reinforced polyamide 6T composites by synergism between DOPO-based derivative and carbon nanotube

How to create high-performance flame-retardant semi-aromatic polyamide with minimum flame retardant loading remain a major challenge. Herein, glass fiber-reinforced polyamide 6T (GFPA6T) composites with superior flame retardancy were obtained by synergism between DOPO-based derivative (PN-DOPO) and carbon nanotube (CNT). The introduction of 9 mass% PN-DOPO and 1 mass% CNT into GFPA6T, which is significantly lower than the loading reported (15 mass%), leads to superior flame retardancy with V-0 rating during UL-94 test and a higher limiting oxygen index (LOI) value of 28.5%. Thermogravimetry, cone calorimeter and char residue analysis suggest that the addition of CNT can enhance the thermal stability and promote the formation of stable char layers, effectively protecting the matrix from fire. By quantitative analysis, the flame retardancy mechanism of the resulting GFPA6T composites includes three aspects: 14.3% flame inhibition, 8.5% charring effect and 34.7% protective-barrier effect. Besides, the introduction of CNTs can compensate the loss of mechanical properties due to the incorporation of flame-retardant PN-DOPO.

Thermal and flame-retardant properties of intrinsic flame-retardant epoxy resin containing biphenyl structures and phosphorus

An intrinsic flame-retardant epoxy resin was synthesized by introducing biphenyl structures and phosphorous into epoxy resin. The biphenyl structures could increase the glass transition temperature by more than 10 °C, as well thermal stability as indicated by the elevation in char yield. They could also enhance mechanical properties as reflected by the increments of 86.4% and 176.5% in tensile strength and breaking elongation, respectively, and offset the negative effects of phosphorus-containing structures. The introduction of elemental phosphorus could improve the flame-retardant properties of epoxy resin. The resulting epoxy resin presented a high limiting oxygen index of 32.4% and a V-0 rating in the UL-94 test. Moreover, it exhibited better flame-retardant parameters than pure epoxy resin in the cone calorimeter test. It could be decomposed to generate PO∙ and PO2∙ radicals to quench active free radicals, reduce toxic and smoke gas generation, and form a dense and stable char layer. It could simultaneously achieve gas and condensed phase flame retardancy. The presence of the biphenyl structure and phosphorus element in the epoxy resin system improved the thermal, mechanical, and flame-retardant properties of epoxy resin simultaneously. This work offered a facile method for preparing intrinsic phosphorus-containing flame-retardant epoxy resin without sacrificing thermal and mechanical properties.