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Polyurea (PU) elastomers have become increasingly popular in recent years due to their exceptional blast mitigation, ballistic protection, and wear resistance properties. However, their applications as protective materials are often limited as a result of their high flammability. In this study, aromatic dianhydrides (ArDAs) were employed to capture the thermal decomposing products of PU during combustion and facilitate the generation of highly heat-resistant aromatic polyimides (i.e., end group capturing effect), thus enhancing the material's char-forming ability and improving its flame retardancy. The ArDAs were found to significantly reduce the peak heat release rate (PHRR), total heat release (THR), total smoke release (TSR), and total CO release (TCO) of PU, and meanwhile increased the amount of char residue. At 20 wt% content of 3,3′,4,4′-benzophenonetetracarboxylic dianhydride (BTDA), PHRR, THR, TSR and TCO of PU were reduced by 70.6%, 32.5%, 44.7% and 58.8%, respectively, the char residue was increased by 405%, and the mechanical properties of PU were well maintained (88.5% tensile strength and 91.0% elongation at break of pure PU). These findings demonstrate that ArDAs could serve as a new kind of halogen/phosphorus-free flame retardant for PU elastomers. [Display omitted] • Novel halogen/phosphorus-free flame retardants were designed for PU elastomers. • The flame retardant mechanism is end group capturing by aromatic dianhydrides (ArDAs). • PHRR, THR, TSR and TCO were simultaneously reduced, and char residue was improved. • Both excellent flame retardant property and high mechanical property were achieved. [ABSTRACT FROM AUTHOR]

A flame retardation property of polymer composites is being considered important to minimize the amount of heat release and the smoke production during the combustion. Therefore, this work aims to improve the flame retardation property of epoxy composites using ammonium polyphosphate (APP), one of the intumescent flame retardants (IFRs). However, APP could be migrated to the surface of composite due to the weak compatibility with epoxy resin. To prevent the migration, the surface modification method has taken place using various amines, acting as charring agent. In this study, we select the 4,4′-diaminodiphenylmethane (DDM) as both curing agent and charring agent for the surface modification on the APP, and their epoxy composites were prepared. Interestingly, we observe both the fast curing effect by analyzing the curing behavior of epoxy composite by Friedman method, and significant improvements of the thermal degradation, and flame retardancy of epoxy with adding the amine-modified APP (mAPP). Moreover, the epoxy/mAPP composites showed higher flame retardation properties and formed the compact char structures due to the attached DDM, which acted as an efficient charring agent to promote to form the carbonaceous char structures. Finally, we also found the correlation between the improvements of flame retardation properties, and char structures of epoxy composites by calculating the crosslink density (M c) using the theory of rubber elasticity. • Amine-modified ammonium polyphosphate was prepared via cationic ion exchange reaction with 4,4′-diaminodiphenylmethane. • The attached DDM can contribute to accelerate the curing and improve the flame retardation properties of epoxy composites.. • The relationship of flame retardation properties and char structure was found using theory of rubber elasticity. [ABSTRACT FROM AUTHOR]

Enhancing simultaneously the flame retardancy and mechanical properties of polymer materials is a good expectation but always a tough challenge. In this work, two multifunctional compounds: phosphaphenanthrene/vinylsiloxane (DDVS) and phosphaphenanthrene/phenylsiloxane (DDPS) were synthesized, and both effectively improved the flame-retardant properties, toughness and UV shielding performance of epoxy resins (EPs) with high transparency. It was further found that the flame retardancy and toughness of EPs were greatly affected by simply changing the substituents from phenyl to vinyl groups on Si atom. Compared with DDPS, DDVS with vinyl group on Si showed more efficiency in improving flame retardancy (higher LOI value), self-extinguishing properties (higher UL 94 grade) and higher quality retention (more carbon residue) in EP. For example, DDVS was added in two-thirds of the amount of DDPS to make EPs achieve UL94 V-0 rating. This attributed to the high-temperature self-crosslinking of unsaturated carbon-carbon double bonds in DDVS, which can increase the charring ability of EPs and form more high-temperature stable char residues. Meantime, this also inhibited the release of volatile phosphorus-containing pieces from DDVS decomposition and retained more P in condense phase, thus improving the compactness and graphitization degree of char layers. The introduction of unsaturated bonds strengthened the condense-phase flame-retardant function of DDVS in EP, while retaining the original gas-phase flame-retardant actions of DOPO groups. The mechanism of gas-phase and condensed-phase mechanisms cooperated with each other, obtaining better flame retardant effect. Meanwhile, DDVS possessed greater efficiency than DDPS in increasing the fracture toughness of matrix due to the difference of steric hindrance between the substituents on silicon. Furthermore, the introduction of DDVS and DDPS did not significantly affect the transparency of EPs and the high visual transparency of materials was still maintained. In brief, the coordination design of phosphaphenanthrene and vinylsiloxane groups provided a theoretical basis to simultaneously improve the flame retardancy and toughening of EPs without losing glass transition temperature, while maintaining the high visual transparency of EPs with good UV shielding performance. [ABSTRACT FROM AUTHOR]

The aim of this work was to study the influence of a high efficient halogen-free phenylphosphonic amide flame retardant (FP1) to epoxy resin (brand name RTM6) on the rheological, mechanical and water absorption properties of the carbon fiber/RTM6 epoxy composite (CFR). With a 8 wt% loading FP1 in RMT6, the processing of CFR/FP1 was able to use the equal condition with that of CFR since the viscosity of RTM6 was maintained at a similar level in the minimum viscosity temperature region. The addition of FP1 showed negligible impacts on the interlayer share strength (ILSS) and in-plane share strength (IPSS) of CFR. The interfacial strength between RTM6 matrix and carbon fiber was decreased due to the impact of FP1 on cross-linking density and polarity of RTM6. The flame retardant efficiency of FP1 showed difference in presence of carbon fiber or not in RTM6. RTM6/FP1 (8 wt%) had a LOI value of 38%, achieved a V-0 rating at thickness of 3.2 mm in UL 94 test and showed 60% reduction in peak of heat release rate. RTM6/carbon fiber/FP1 (8 wt%) had a LOI of 43%, while it showed reduced performance in UL 94 and cone calorimeter tests. [ABSTRACT FROM AUTHOR]

To simultaneously improve the storage stability of epoxy/imidazole systems and flame retardancy without sacrificing the thermal, mechanical and dielectric properties of thermosets, a novel multifunctional polyetherimide containing benzimidazole and phosphorus (mPI) was synthesized and used as a hardener for diglycidyl ether of bisphenol A (DGEBA). In addition to retaining the effective curing behavior of imidazole, mPI, a macromolecular hardener and flame retardant, could endow the mixture of DGEBA and mPI (EP/mPI) with the long latent period and thermosets with the high performance. The results showed that mPI was unreactive at ambient temperature and underwent the rapid curing reaction at 170 °C that is a little higher than its glass transition temperature (T g) of 164.7 °C, and EP/mPI showed the long thermal latent period of 70 days or more. Meanwhile, the cured EP/mPI attained the UL-94 V-0 rating with the LOI value of 31.2%. Besides, EP/mPI thermoset showed a 42.9 °C, 47.6 °C, 18.2 °C, 135.4% and 60.6% increase in the T g , heat deflection temperature, temperature at 5% mass loss, storage modulus and Young's modulus, respectively, as well as a 3.6% decrease in the dielectric constant at 100 MHz, in comparison with those of the traditional cured DGEBA/benzimidazole (EP/BIM). This work provides a facile strategy to prepare one-pot epoxy/imidazole formulations and flame-retarded epoxy thermosets with high performance by using the well-designed multifunctional polyetherimides as a hardener and flame retardant, which has good application prospects in electronics. [Display omitted] [ABSTRACT FROM AUTHOR]

To simplify the manufacture and address the intrinsic flammability of epoxy resin (EP) products, the single-component, fire-safe EP systems are increasingly in demand. However, current design strategy is difficult to achieve the simultaneous improvement in storage stability, flame retardancy and smoke suppression. Herein, a phosphorus/imidazole-containing, aluminum-based complex (ADIM) was synthesized, and applied as a latent curing agent for EP. The shelf life of EP/ADIM system reached 30 days, and its gel time at 150 °C was only 42 min, indicative of great thermal latency and fast curing rate. EP/ADIM thermoset showed superior flame retardancy, as confirmed by a limiting oxygen index (LOI) of 35.0% and a UL-94 V-0 classification. In addition, the total smoke production and maximum smoke density of EP/ADIM thermoset were 38.7% and 22.3% lower than those of EP thermoset cured by imidazole (EP/IM), demonstrating obviously-enhanced smoke suppression. ADIM inhibited the heat release and smoke generation of the EP matrix via radical capturing and catalytic charring. Moreover, EP/ADIM thermoset exhibited comparable thermal resistance and mechanical properties to EP/IM thermoset. Hence, this work offers an integrated design strategy for creating high-performance, fire-safe, single-component EP with well-preserved mechanical and thermal properties. [Display omitted] [ABSTRACT FROM AUTHOR]

In this study, a phosphorus-containing bio-based monomer (MBDPP) was first synthesized from renewable magnolol, and subsequently photo-cured with tri-thiol (TPTMP) or tetra-thiol (PETMP) monomers via thiol–ene polymerization. The synthesized MBDPP/TPTMP and MBDPP/PETMP membranes exhibited high char residues at 700 °C in the TGA tests, which were 19.8 wt% and 24.2 wt% for nitrogen while 16.5 wt% and 20.2 wt% for air, respectively, indicating superior charring capacity of both membranes. DMA results indicated that both the higher stiffness and the T g of the cured MBDPP/PETMP membrane was ascribed to its higher cross-linking density than that of the cured MBDPP/TPTMP owing to the tetra-functional groups of PETMP. In the open flame test, both MBDPP/TPTMP and MBDPP/PETMP membranes self-extinguished immediately when removing the flame source, manifesting excellent intrinsic anti-flammability. The cone calorimeter results further demonstrated that MBDPP/TPTMP and MBDPP/PETMP membranes showed lower PHRR (419 and 388 kW/m2, respectively) and THR (41.38 and 38.98 MJ/m2, respectively) values than most of the thiol-ene photo-polymerized counterparts previously reported. The excellent anti-flammability of MBDPP/TPTMP and MBDPP/PETMP membranes originated from the formation of expandable char residues that played an efficient role in hampering the transfer of flammable pyrolysis products to flame zone as well as insulating the heat irradiation during combustion. Additionally, both MBDPP/TPTMP and MBDPP/PETMP membranes showed excellent transparency (transmittance >85% in the visible region) and flexibility (breaking elongation around 40%). Taking the intrinsic anti-flammability, exceptional transparency and high flexibility into account, the MBDPP/TPTMP and MBDPP/PETMP systems are suitable as intumescent flame retardant coating materials. [Display omitted] [ABSTRACT FROM AUTHOR]

The aggregation and plasticizing of most 9,10-dihydro-9-oxa-10-phosphaphenanthrene −10-oxide (DOPO) derived additives often result in deteriorating the glass transition temperature and mechanical properties of epoxy resins (EP). To address this issue, an imide-DOPO derivative (BMP) with bulky aromatic structure was successfully synthesized. Benefitting from the space hindering and intermolecular interaction (π-π stacking) of BMP, it does not lead to the loss of glass transition temperature, and only a minor damage of tensile and impact strengths is caused. Additionally, with only 0.78 wt% loading of phosphorus (10 wt% BMP), the EP/BMP 10% achieves UL-94 V-0 and high LOI value of 35%. Simultaneously, both the heat release rate and total smoke production are markedly reduced. More excitingly, BMP exhibits aggregation-induced emission enhancement of fluorescence in the N, N -dimethylformamide/water mixed solution as well as epoxy resin. This work provides a new insight in simultaneously imparting flame retardancy and fluorescence to epoxy resins without losing glass transition temperature. [Display omitted] • Imide-DOPO derivative exhibits aggregation-induced emission enhancement. • Imide-DOPO derivative endows epoxy resin with excellent flame retardancy. • No loss of T g while the improvement of flame retardancy. • Fluorescence is imparted to the flame retardant epoxy resin. [ABSTRACT FROM AUTHOR]

Epoxy resins (EPs) are a kind of widely used engineering materials, because of their excellent mechanical, chemical and physical properties, but a severe problem they faced is their poor flame retardancy. Single molecule flame retardants have met the bottleneck after the massive researches of the past decade, so, with the development of the polymer technology, hyperbranched flame retardants have been researched and applied, owing to their better and more efficient flame retardancy. Herein, a facile thermal treating procedure was applied to the cured EP thermosets which contained a crosslinkable additive flame retardant to in-situ form a hyperbranched flame retardant. The single molecule flame retardants with N/P elements and crosslinkable nitrile groups were synthesized through an easy method, and physically mixed with EP matrix. After the curing reaction of EP matrix, the thermosets were further treated with a thermal treating procedure, while transferring the single molecule flame retardant into hyperbranched flame retardant, the semi-interpenetrating network was formed at the same time. The flame-retardant properties have been measured by limiting oxygen index (LOI) tests, UL-94 vertical burning tests and cone calorimeter tests, the results showed the flame retardants were extremely efficient and greatly elevated the flame retardancy of EPs, since the 0.5 wt% content could make modified EP samples pass the UL-94 V-0 rate, and with 20 wt% content the LOI value reached 49.5 % and the peak heat release rate reduced for 71.6 % compared with pure EPs. [ABSTRACT FROM AUTHOR]

Abstract: The effect of mesoporous silica MCM-41 and SBA-15 as a synergistic agent on the flame retardancy of intumescent flame retardant polypropylene composites (PP-IFR) were studied, and the IFR system mainly consisted of the ammonium polyphosphate (APP) as an acid source and blowing agent, pentaerythriol (PER) as a carbonization agent. The mesoporous MCM-41 and SBA-15 were incorporated into flame retardant formulation at four different concentrations (1, 3, 5, 8wt.%) to investigate the synergism between the flame retardant materials. A synergistic effect in flame retardancy was best when a suitable amount of SBA-15 was used in combination with APP and PER. [Copyright &y& Elsevier]

Abstract: The mechanical properties, flame retardancy, thermal degradation and foaming properties of wood–fiber/PP composites have been investigated. Ammonium polyphosphate (APP) and silica were used as flame retardants. The limiting oxygen index (LOI), thermal gravimetric analysis (TGA) and cone colorimeter (CONE) were employed for the study of fire retardance. At the same time, wood–fiber/PP composite foams were produced with the batch foaming technique using CO2 as blowing agent. The effects of APP and silica content, pressure and temperature on the final cell structure were investigated. According to LOI, TGA and cone calorimeter results obtained from the experiments, APP and silica are effective flame retardants for wood–fiber/PP composites, and silica was shown to have a flame retardant synergistic effect with APP in wood–fiber/PP composite. The mechanical properties of the composites decreased with addition of flame retardants, except for the tensile strength of small amount of silica filled wood–fiber/PP composite. The results also revealed that the cellular morphologies of the foamed wood–fiber/PP composites are a strong function of the content of APP and silica as well as foaming conditions. [Copyright &y& Elsevier]

Abstract: The effects of halogen-free flame retardants (FR) such as intumescent ammonium polyphosphate (APP) and melamine cyanurate (MC) on the flammability and mechanical properties of epoxy/glass fiber composite systems were studied. Overall, intumescent APP shows better flammability results compared with MC. The composite with 5vol.% APP performed sufficiently well in the UL-94 test and LOI, whereas 20vol.% MC is required to achieve similar results. The addition of 1vol.% MC into 4vol.% APP had shown some improvement on the composite flame resistance. The composite attains the maximum flexural strength at 15vol.% while the dynamic mechanical analysis shows that the addition of flame retardants increased the storage modulus but did not change the glass transition temperature Tg . [Copyright &y& Elsevier]

Scientific researches have been focused on finding halogen-free solutions as effective as halogenated ones owing to environmental and health problems in recent years. This fact is the main driving force for upcoming academic works in the flame retardancy field. Boron compounds, are high potential flame retardant additive in polymer based materials owing to their low toxicity, molecular diversity, and various ways of flame retardant action. They have been used solely or as an adjuvant in combination with mineral fillers, intumescent systems, phosphorus, halogen, nitrogen, silicone and carbon containing additives. This review provides a comprehensive description of the flame retardant effect of boron compounds with general flame retardant mechanisms in natural polymers, biocomposite applications, thermoplastics, elastomers, and thermosets as well as the synergistic effect studies with other flame retardant additives. This review covers the related studies until the end of 2020. Remarkable future research opportunities and some challenges are also suggested. [Display omitted] [ABSTRACT FROM AUTHOR]

An urgent need is to reduce the flammability of polymers and manage their toxic thermal decomposition products. Although conventional halogenated, metallic and phosphorus-based flame retardants (FRs) proved effective, they are known to cause major damage to human health and the environment. Containing carbon nanomaterials as a new class of flame retarding additives, polymer nanocomposites have displayed high flame retardancy, mechanical performance and electrical and thermal conductivity – a feat unmatched by conventional FRs. In this article we review very recent advances in carbon nanomaterials as FRs for polymers and composites as well as new understanding of the underpinning flame retarding mechanisms. Carbon nanomaterials, i.e. graphene, carbon nanotubes and carbon black, are discussed as the alternatives to conventional fillers due to their effectiveness in improving the polymers' flammability, mechanical properties and conductivity. The synergy between carbon-based nanofillers and conventional FRs is comprehensively reviewed, concluding that adding small fractions of carbon nanomaterials with conventional FRs into polymers can not only synergistically improve the flame retardancy but result in multifunctionalities such as thermal and electrical conductivity, without compromising the polymers' mechanical performance. Chemically or physically combining carbon nanomaterials with other compounds or nanoadditives containing phosphorus and nitorgen elements can create significant synergies for multifunctional polymers and composites to attain superior flame-retardant properties. [ABSTRACT FROM AUTHOR]

In this manuscript, the Layer-by-Layer technique is used to modify the surface of flax fabrics using a quad-layer architecture (QL) prior to their assembly in polylactic acid biocomposites. The aim is to produce nanostructured interphases capable of conferring flame retardancy while maintaining mechanical properties. Only 2.5 QL significantly improve the flame retardancy and fire safety of the prepared composites as demonstrated by LOI values of 25.3%, considerably reduced flame spread rates and the substantial reduction in peak of heat release rate (−33%) and maximum average rate of heat emission (−30%) during cone calorimetry. Mechanical testing showed improved modulus and limited reductions in flexural strength. These results make the approach developed in this manuscript very attractive in the design of advanced biocomposites with optimized fire retardancy and mechanical properties. Image 1 • Layer-by-Layer nanostructured interphases are employed for biocomposites • Flame retardant confinement at the interphase avoids matrix degradation • Improved mechanical and flame retardant properties can be simultaneously achieved [ABSTRACT FROM AUTHOR]

A bio-flame retardant filler was synthesized via the self-polymerization of dopamine hydrochloride in alkaline condition, yielding nano-sized polydopamine (nano-PDA) particles ranging between 50 and 100 nm in diameters. Adding a small amount (2 wt%) of the nano-PDA particles into an epoxy can remarkably reduce the value of peak heat release rate by 53.6%, exceeding the performance aluminum trihydroxide (ATH) particles at 10 wt%. The significant improvement in flame retardancy at a relatively low loading of PDA has been found to originate from several key mechanisms including radical scavenging, higher char yield, and production of CO 2. Furthermore, the addition of nano-PDA in the epoxy resin increased the tensile strength by ~6%. In contrast, the addition of common flame retardant, such as ATH, to achieve the same increase in flame retardancy of epoxy would reduce the tensile strength by 22%. This improvement in mechanical properties is attributed to the better bonding between PDA particles with epoxy than ATH with epoxy. [ABSTRACT FROM AUTHOR]

This work reports our recent effort on the preparation of α-Phenyl-N-(2-propyl-2-hydroxymethyl-1, 3-dihydroxy)-imine-Nickel (Ⅱ) (Ni-MOF) containing polyhydroxy groups and its application in improving the fire performance of PLA composites in combination with ammonium polyphosphate (APP). The flame retardant evaluation revealed that the presence of 1.7% Ni-MOF and 3.3% APP in PLA increased the LOI value to 31.0%, upgraded the UL-94 level to V-0, decreased the peak heat release rate (pHRR), total heat release (THR) and total smoking production (TSP) by 27%, 19% and 50%, respectively, and substantially delayed the time to ignition (TTI) from 67 to 97 s. It was proposed that the flame retardants take effect in both vapor and condensed phases, and Ni-MOF nanosheets can synergistically improve the flame resistance of PLA with APP. The incorporation of Ni-MOF effectively inhibited the deterioration of mechanical properties for PLA composites caused by the presence of APP. • The Ni-MOF nanosheets containing polyhydroxy groups was prepared. • APP and Ni-MOF nanosheets significantly improved the fire safety of PLA composite. • The possible synergistic flame-retardant mechanism of Ni-MOF and APP was proposed. • Ni-MOF effectively improved the mechanical properties of PLA composites. [ABSTRACT FROM AUTHOR]

Flexible polyurethane foams (FPUFs) have been extensively used in furniture, carpet, automobiles, etc., due to their superior thermal insulation, low bulk density and superior chemical resistant properties. Unfortunately, they are extremely ignitable and flammable, and release a large amount of combustion heat accompanied by plenty of smoke and toxic gases upon ignited, thus posing a potential threat to lives and property. The minimization of their fire hazards is usually realized by the addition of flame retardants, and the creation of flame retardant coating. As compared with the former approach, the surface coating strategy has gained much more interests because it improves the flame retardancy of FPUFs without compromising mechanical properties. To date, several surface-coating approaches, including in situ deposition, sol-gel process, plasma technique and layer-by-layer (LBL) assembly have been developed for improving the fire safety performance of FPUFs. This review focuses on the recent advances in flame retarded FPUFs by employing the surface coating approaches. This work also summarizes the design of intumescent and non-intumesecent fire retardant coatings applied to the fire protection of FPUFs by depositing (nano)coatings on their surfaces. Special attention will be paid to the FPUFs treated with flame retardant nanocoating via the LBL assembly. Moreover, this work further compares the advantages and disadvantages of these surface coating methods, and finally presents some future research opportunities on flame retardant FPUFs materials. Image 1 • Recent progress in Flame retardant flexible polyurethane foams (FPUFs) has been reviewed in this work. • Creating flame retardant coatings is a highly effective strategy to develop flame retardant FPUFs without adverse impacts. • Surface-coating approaches include in situ deposition, sol-gel process, plasma technique and layer-by-layer assembly. [ABSTRACT FROM AUTHOR]

The SiO 2 @metal organic framework (Universitetet i Oslo-66, UiO-66) core–shell microspheres were constructed through covalent linkage between amine groups in UiO-66-NH 2 and epoxy groups on the surface of silica. The morphology and size of the SiO 2 @UiO-66 core–shell microspheres could be simply controlled by tuning the ratio between UiO-66-NH 2 and epoxy terminated silica (E-SiO 2). As observed by TEM, the SiO 2 @UiO-66 hybrids showed better dispersion state within epoxy matrix compared to either E-SiO 2 or UiO-66-NH 2. The incorporation of SiO 2 @UiO-66 hybrids slightly promoted the thermal degradation of the resultant epoxy composites but improved residual yield. The dynamic mechanical analysis results indicated that the SiO 2 @UiO-66 hybrids slightly increased the glass transition temperature and the modulus. The SiO 2 @UiO-66 hybrids exhibited higher efficiency in reducing the heat release rate and the smoke production rate compared to either E-SiO 2 or UiO-66-NH 2. The influence of the component ratio in SiO 2 @UiO-66 on flame retardancy of the epoxy composites was also studied by cone calorimeter. Specifically, the SiO 2 @UiO-66 hybrid with medium ratio (SiO 2 @UiO-66-2) exhibited maximum reduction in peak heat release rate (−31%), total heat release (−23%) and total smoke production (−16%). The char residues were investigated by the Fourier transform infrared spectra, scanning electron microscopy and X-ray photoelectron spectroscopy, which demonstrated that the enhanced flame retardancy of EP/SiO 2 @UiO-66-2 was attributable to the continual morphology and high thermal resistance originated from the presence of the silicon and zirconium complex. These favorable characteristics including high flame retardant efficiency and good smoke suppression make SiO 2 @UiO-66 hybrids promising for flame retardant polymers application. • The SiO 2 @UiO-66 hybrids showed core–shell microsphere structure. • The addition of 3 wt% SiO 2 @UiO-66-2 caused 31% reduction in peak heat release rate. • The addition of 3 wt% SiO 2 @UiO-66-2 led to 16% reduction in total smoke production. [ABSTRACT FROM AUTHOR]