Flame Retardant Mechanism Research Articles

Synergistic Flame Retardant Properties of Polyoxymethylene with Surface Modified Intumescent Flame Retardant and Calcium Carbonate.

Ammonium polyphosphate (APP) was successfully modified by a titanate coupling agent which was compounded with benzoxazine (BOZ) and melamine (ME) to become a new type of intumescent flame retardant (Ti-IFR). Ti-IFR and CaCO3 as synergists were utilized to modify polyoxymethylene (POM), and the flame-retardant properties and mechanism of the composites were analyzed by vertical combustion (UL-94), limiting oxygen index (LOI), TG-IR, and cone calorimeter (Cone), etc. The results show that Ti-IFR can enhance the gas phase flame retardant effect, while CaCO3 further strengthens the barrier effect in the condensed phase. When they were used together, they can exert their performance, respectively, at the same time showing excellent synergistic effect. The FR-POM composite with 29% Ti-IFR and 1% CaCO3 can pass the UL-94 V0 level. The LOI reaches 58.2%, the average heat release (Av HRR) is reduced by 81.1% and the total heat release (THR) is decreased by 35.3%.

Synergies between phosphomolybdate and aluminum diethylphosphinate acting as temperature-response microparticles for promoting fire safety of epoxy resin

In this work, ammonium phosphomolybdate (AMP) and aluminum diethylphosphinate (ADP) acting as temperature-response microparticles, were incorporated into epoxy resin (EP) together to promote fire safety and dynamic mechanical performance of EP composites at the same time. Both ADP and AMP acted as chemical inertness fillers to enhance the EP matrix at the normal service temperature and processing temperature. When the temperature rose after heating or even burning, both ADP and AMP presented chemical functions. On one hand, AMP exhibited excellent catalytic charring activity and smoke suppression efficiency. On the other hand, the combination between AMP and ADP in the EP/AMP/ADP composites showed excellent synergistic effects in improving the flame retardancy of EP. Compared to the case of EP, the peak heat release rate (PHRR) of EP/AMP/ADP composites (1.2 wt% AMP and 3.6 wt% ADP) was decreased by 54%, the total heat release (THR) was reduced by 25%, and the total smoke production (TSP) was reduced by 25%. Meanwhile, the UL-94 V-0 rating was obtained, and the limiting oxygen index (LOI) of the composite was increased from 26.2 to 31.2%. The mechanism of flame retardancy was analyzed and discussed. In addition, compared with EP, EP/AMP/ADP composites showed a higher dynamic mechanical property without affecting the glass transition temperature.

Flame-Retardant and Recyclable Soybean Oil-Based Thermosets Enabled by the Dynamic Phosphate Ester and Tannic Acid

The demands of safety and sustainability have driven the development of intrinsic flame-retardant biobased polymers from renewable materials. Herein, a mechanically robust, good flame-retardant, and recyclable thermoset was developed from renewable epoxidized soybean oil (ESO) by using 2-hydroxyethyl methacrylate phosphate (HEMAP) as the reactive flame retardant and tannic acid (TA) as the charring agent. The flame resistance of the obtained ESO-based thermoset achieved the highest UL-94 of V-0 rating and a limited oxygen index value of 26.7% due to the synergistic flame-retardant effect of phosphate and TA. The flame-retardant mechanisms of the gaseous phase and condensed phase were fully investigated by thermogravimetric infrared, scanning electron microscopy-energy-dispersive spectrometry, X-ray photoelectron spectroscopy, and Raman spectra. It is confirmed that the incorporation of phosphate and TA could effectively promote the formation of dense carbon layers and delay the pyrolysis of long aliphatic chains. The ternary crosslinking of ESO, HEMAP, and TA via free-radical polymerization and epoxy-ring opening reaction resulted in a rigid network with a high crosslink density, bestowing the thermoset with superior tensile strength (20.0 MPa), flexural strength (36.3 MPa), and bonding strength (16.7 MPa on steel). Moreover, the ESO-based thermoset exhibited a fast stress relaxation behavior due to the transesterification of dynamic β-hydroxyl phosphate esters, which enables the network with thermal-healing ability and recyclability. This study explores a feasible method to prepare an intrinsic flame-retardant polymer from commercially available and renewable vegetable oils and natural polyphenols.

Synergistic Effect of 4A Molecular Sieve on Intumescent Ternary H-Bonded Complex in Flame-Retarding of Polypropylene

In this study, a ternary hydrogen (H)-bonded complex intumescent flame retardant (TH-IFR) of melamine (ME) · phosphoric acid (PA)…pentaerythritol (PER) was synthesized through hydrothermal reaction. The combination of the synthesized TH-IFR with 4A molecular sieve as the synergist was used for the first time to improve the flame retardancy of polypropylene (PP). The involved structure, morphology, flame retardancy, flame-retarding mechanism and mechanical properties of the prepared PP composites were systematically investigated. The results show that incorporation of 1 wt% synergist 4A shows the optimum synergistic effect, and the flame retardancy and mechanical properties of the flame-retarded (FR) PP composites are significantly improved. Incorporation of 4A could change the pyrolysis process of the entire system and promote the char-forming chemical interaction, thereby further enhancing the flame retardancy of FR PP composite. The synergistically flame-retarding mechanism of 4A is explained by the significantly improved quality and quantity of the solid-phase char layer, which is formed through generation of SiO2 and Al2O3 substances, and also participation of PP macromolecular chains in the final char layer formation during burning. Furthermore, the improved dispersion and compatibility of TH-IFR in the composite is largely beneficial to the improvement of flame retardancy and mechanical properties.

Preparation and properties of flame retardant biobased polyamide elastomer with shape memory

AbstractNylon is the general name of high molecular polymers with amide bonds repeat structure in the main chain. Because of its good wear resistance, excellent chemical resistance and outstanding impact resistance, it is widely used in various fields of national life, such as automobile parts, oil pipelines, electronic parts, gears, connectors, coating materials and medical applications. Using isocyanate terminated polyamide prepolymer as hard segment, polypropylene glycol as soft segment and triethanolamine as crosslinking agent, polyamide elastomer was flame retardant modified by adding reactive P flame retardant and P/N synergistic flame retardant mechanism. The sample was named IAHDP‐x, in which IAHD is the synthetic hexamethylene diamine polyaitaconic acid, and x is the mass of the added flame retardant DDP. Its tensile properties, fatigue resistance, self‐recovery and tear resistance were investigated. The results revealed that the synthesized phosphorus flame retardant (9,10‐dihydro‐9‐oxa‐10‐[N,N‐bis‐(2‐hydroxyethylamino methylene)]‐10‐phenanthroline‐10‐oxide (DDP)) could not only enhance the flame retardancy, but also strengthen the mechanical properties of polyamide. Among them, the LOI and UL‐94 of IAHDP‐1.2 were 27.6% and V‐0, respectively, indicating that it could be used as flame retardant material; Cyclic tensile test demonstrated that it had good fatigue resistance and self‐recovery; Besides, the tear resistance of IAHDP‐1.2 could reach 35.24 kJ/m2. Interestingly, IAHDP‐1.2 also displayed shape memory characteristics, and the sample could be restored to its original state at 60°C. The synthetic IAHDP‐x also had excellent flame retardancy, high mechanical properties, fatigue resistance, tear resistance, shape memory, so the material can be used in satellite wings, solar panels, electronic and electrical equipment, and smart materials.

Recent advances in metal-family flame retardants: a review.

The use of polymer materials is inextricably linked to our manufacturing life. However, most of them are easily combusted in the air and the combustion process generates a large amount of toxic fumes and dangerous smoke. This can result in injuries and property damage, as well as limiting their use. It is essential to enhance the flame-retardant properties and smoke suppression performance by using multiple flame retardants. Metal-based flame retardants have a unique chemical composition. They are environmentally friendly flame retardants, which can impart good smoke suppression, flame retardancy to polymers and further reduce the production of toxic gases. The differences in the compounds formed between the transition metals and the main group metals make them act differently as flame retardants for polymers. As a result, this study presents the research progress and flame-retardant mechanism of flame-retardant polymers for flame retardants from different groups of metals in the periodic table of elements in a systematic manner. In view of the differences between the main group metals and transition metals, the mechanism of their application in flame retardant polymer materials is carefully detailed, as are their distinct advantages and disadvantages. And ultimately, prospects for the development of transition metals and main group metals are outlined. It is hoped that this paper will provide valuable references and insights for scholars in the field.

Reactive P/S/N-containing synergistic flame retardant towards eco-friendly durable flame-retardant cotton fabric: Flame-retardant property, durability and mechanism

Developing eco-friendly durable flame-retardant cotton fabric not only expands its application area, but also caters to the healthy and environmentally friendly concept of consumers. Herein, a reactive P/S/N-containing synergistic flame retardant (PSN) was synthesized to prepare eco-friendly durable flame-retardant cotton fabric through chemical modifying method. Flame-retardant finishing deteriorated the softness, whiteness, tensile strength and air permeability of cotton fabric. PSN conferred outstanding flame retardancy, fire safety and durability to cotton fabric. For treated fabric with the add-on of 14.2%, it achieved an LOI value of 36.5% and extinguished spontaneously even after 50 laundering cycles. Its peak heat release rate, total heat release and fire growth rate index values decreased sharply than those of the control fabric. PSN exhibited high-efficiency flame-retardant behavior, and the synergy between P, S and N elements facilitated the formation of intumescent barrier on the fiber surface during combustion. The hydrolysis of covalent bond and formation of phosphate/sulphonate during laundering both accounted for the decrease in flame retardancy of treated fabric.

Effect of sepiolite on properties of silicone rubber/melamine/starch/sepiolite flame retardant composites

AbstractIn this work, a novel silicone rubber composite with low smoke, good mechanical property, and excellent flame retardant was prepared by introducing melamine (MEL), starch (St), and sepiolite (SEP) into SR. The effect of the amount of SEP on the mechanical properties of SR composites was investigated. The results showed that the mechanical properties were optimal when the amount of SEP was 30 phr. The tensile sections of the composites were characterized by SEM. The flame retardant properties of the composites were evaluated by oxygen index, vertical combustion, and cone calorimetry test (CCT). The thermal stability of the composites was tested by TGA. The flame retardant mechanism of the composites was also discussed. It was found that the strength and stability of the carbon layer of the composite were remarkably enhanced, and the flame retardant properties of the materials were improved with the addition of SEP. The SEM images of CCT carbon residues revealed that the carbon layer of the composite with SEP was more stable and had fewer cracks than that without SEP. This work provides new insights for the preparation of high‐performance SR composite.

Construction of polyphosphazene-functionalized Ti3C2TX with high efficient flame retardancy for epoxy and its synergetic mechanisms

As a promising flame retardant, Titanium carbide (Ti3C2TX) MXene has shown synergetic flame retardancy with various modifying agents, especially phosphorus/nitrogen-containing flame retardants. However, the synergetic flame-retardancy mechanism of Ti3C2TX and modifying agent are unclear due to the complexity of reactions during the combustion process. Herein, polyphosphazene-functionalized Ti3C2TX nanosheets (MXene-PZN) were prepared and then added to epoxy resin (EP) to prepare the EP/MXene-PZN composites. Subsequently, the mechanical properties and the flame-retardant performance and mechanism were systematically investigated. The results showed an improved interfacial interaction and excellent compatibility of MXene-PZN nanosheets in the EP matrix, resulting in the storage modulus and tensile strength of EP/MXene-PZN-2.0 being increased by 46.5% and 68.4% respectively, as 2 wt% MXene-PZN was added into the EP matrix. Moreover, the flame-retardant tests showed that the peak heat release rate and total heat release of EP/MXene-PZN-2.0 were reduced by 44.8% and 54.8%, respectively, compared with pure EP, while 49.4% and 41.9% decrease in the peak CO production rate and the peak CO2 production rate were also achieved. Finally, focusing on the main existing forms of MXene-PZN in the EP matrix during different combustion stages, the flame-retardant mechanism of MXene-PZN functioned both in the condensed phase and gaseous phase was established. Thus, this work demonstrates a facile yet promising strategy to design efficient synergetic flame retardants.

An eco-friendly, bio-inspired and synergistic flame retardant system with outstanding water tolerance and ultra-low addition for silicone rubber

To address the bottleneck problem for flame-retarding silicone rubber (SR) in poor water resistance and low efficiency, a halogen-free and synergistic system was fabricated by the introduction of hydrophobic melamine polyphosphate (MPP) modified by layered double hydroxide (P-MPP@LDH) and expandable graphite (EG) in this paper. Dramatically, the limited oxygen index (LOI) of composites (SR/P-MPP@LDH2.5/EG2.5) can reach as high as 36.4 % with UL-94V-0 rating when the total flame retardant loadings is only 5 phr, revealing the superior efficiency of novel system. Compared with neat SR, the fire risk of SR composites is observably decreased by conducting cone calorimeter tests. Significantly, bio-inspired hydrophobic modification is feasible for the excellent balance in simultaneously improving the flame retardancy, water resistance, and mechanical properties of SR in one system. Based on the analysis for residue and thermal degradation process, the effective flame retardant mechanism for SR composites can be attributed to the joint effect of LDH-catalyzed char-formation and physicochemical synergistic intumescence barrier. Therefore, this paper has provided a new and effective strategy to achieve the goal of flame retardancy with high performance in SR, which offers a new choice for designing and applying rubber composite materials in buildings.

A highly efficient melamine/red phosphorus flame retardant for polyurethane‐based foams

AbstractA highly dispersed melamine/red phosphorus (MA/RP) composite flame retardant was prepared by means of simple mechanical grinding. After co‐thermal pretreatment with polyether polyol (PPG‐2000) at 135°C, organic–inorganic hybrid foams (MA/RP/HF) containing MA/RP flame retardant were prepared by the one‐step method using main raw materials such as polyisocyanate and sodium silicate. When 0.5 wt% MA/RP with the mass ratio of 1:5 is added, MA can realize the uniform dispersion of RP in the substrate and enhance its flame retardancy, and the obtained MA/RP/HF presents uniform and closed pores and excellent basic properties. The TG results reveal that MA/RP/HF shows good thermal stability and the corresponding char residual rate reaches 37.9% at 800°C. The flame retardant test results prove that MA/RP/HF is capable of passing the V‐0 grade, with the LOI value being 26.8%. According to the cone calorimeter analysis, its peak heat release rate and total heat release decrease by 30.1% and 51.7% compared with those of rigid polyurethane‐based foam and by 40.1% and 30.0% compared with those of pure HF, respectively. Finally, the synergistic flame retardancy mechanism of MA and RP on polyurethane‐based foam was discussed.

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.

Solvent‐free synthesis of phosphate‐containing imidazole fluid for flame retardant one‐component epoxy resin with long pot life, low curing temperature and fast curing rate

AbstractThe design of flame retardant one‐component epoxy resin (EP) with long pot life, low curing temperature and fast curing rate has been challenging in the industry. Herein, we synthesized a phosphate‐containing imidazole fluid (TA) as the thermal latent curing agent of EP. Based on simple structural design, TA endows EP with excellent curing properties, storage properties, and flame retardant properties. According to DSC results, EP/TA systems exhibit low curing temperature and fast curing rate during operation. The rotary rheometer test confirms that the viscosity curve of EP/TA system maintains long‐term stability at 40°C. The X‐ray photoelectron spectroscopy (XPS) data reveals that TA releases imidazole intermediates and phosphorous compounds during curing. The former provides conditions for fast curing of EP, while the latter gives EP intrinsic flame retardant properties. With the addition of 20 wt.% TA, EP/TA‐4 achieves UL‐94 V‐0 rating and 28.5% of LOI value. The study of flame retardant mechanism shows that the flame retardancy of TA mainly comes from the protective effect of phosphorus‐rich char layer, the dilution effect of non‐combustible gas and quenching effect of phosphorous compound. Besides, due to no solvent involved, the synthesis strategy of TA is environmentally friendly, showing a great potential of industrial application.

Combustion characteristics and fire hazard of polystyrene exterior wall thermal insulation materials

AbstractTo study the combustion characteristics and fire hazard of polystyrene building exterior wall thermal insulation materials, the combustion, fire, and pyrolysis characteristics of thermosetting polystyrene (TPS) insulation, graphite polystyrene (GEPS), and expanded polystyrene (EPS) are compared and analyzed using a cone calorimeter and a thermo‐gravimetric analyzer. From the structure and flame retardant components of thermal insulation board, their flame retardant mechanisms are described. Results show that in a nitrogen atmosphere, the pyrolysis range is 30–600°C. Only one weight loss stage in EPS and GEPS and two weight loss stages in TPS are observed. Comparison of the combustion characteristics of the three demonstrates that TPS has short ignition time, low fire performance index. This result indicates that TPS has the characteristics of good flammability and easy to explode. The smoke generation rate, total smoke production, time heat release index and total heat release of TPS are lower than those of EPS and GEPS. This result indicates that the fire thermal hazard and fire smoke risk of TPS are relatively small. Comparison of various indexes presents that the flammability and fire risk of TPS are evidently better than those of EPS and GEPS.

Zinc hydroxystannate dripped on magnesium hydroxide flower for enhancing smoke suppression and toxicity reduction properties of epoxy resin

AbstractIn order to reduce the emission of smoke and toxic gases during the combustion of epoxy resin (EP), inspired by the structure of “flowers after rain,” a novel low‐cost flame retardant (FMH@ZHS) was prepared by using flower‐like magnesium hydroxide (FMH) as the flower and zinc hydroxystannate (ZHS) as the raindrop. The tensile strength of EP/3FMH@ZHS increased by 13.7% compared with EP/3FMH. Moreover, the 3 wt% FMH@ZHS hybrid material increased the limited oxygen index value of the EP composite to 27.6% while suppressing the dripping phenomenon during combustion, achieving self‐extinguishing characteristic. Meanwhile, compared with pure EP, peak heat release rate, peak smoke production rate, total smoke production, and peak carbon monoxide production rate of EP/3FMH@ZHS decreased by 34.6%, 55.6%, 41.8%, and 50.0%, respectively. The flame retardant mechanism showed that during the combustion process, the catalytic char formation of magnesium oxide, zinc oxide, and stannic oxide generated from FMH@ZSH can promote the formation of a denser and continuous char layer, inhibiting the transport of flammable gases, toxic gases and heat and improving the fire safety of EP composites. In conclusion, this biomimetic material provided a good approach for the industrial application of EP.

Facile Fabrication of Superhydrophobic and Flame-Retardant Coatings on Cotton Fabrics.

The hydrophilicity and inherent flammability of cotton textiles severely limit their usage. To solve these drawbacks, a superhydrophobic and flame-retardant (SFR) coating made of chitosan (CH), ammonium polyphosphate (APP), and TiO2-SiO2-HMDS composite was applied to cotton fabric using simple layer-by-layer assembly and dip-coating procedures. First, the fabric was alternately immersed in CH and APP water dispersions, and then immersed in TiO2-SiO2-HMDS composite to form a CH/APP@TiO2-SiO2-HMDS coating on the cotton fabric surface. SEM, EDS, and FTIR were used to analyze the surface morphology, element composition, and functional groups of the cotton fabric, respectively. Vertical burning tests, microscale combustion calorimeter tests, and thermogravimetric analyses were used to evaluate the flammability, combustion behavior, thermal degradation characteristics, and flame-retardant mechanism of this system. When compared to the pristine cotton sample, the deposition of CH and APP enhanced the flame retardancy, residual char, heat release rate, and total heat release of the cotton textiles. The superhydrophobic test results showed that the maximal contact angle of SFR cotton fabric was 153.7°, and possessed excellent superhydrophobicity. Meanwhile, the superhydrophobicity is not lost after 10 laundering cycles or 50 friction cycles. In addition, the UPF value of CH/APP@TiO2-SiO2-HMDS cotton was 825.81, demonstrating excellent UV-shielding properties. Such a durable SFR fabric with a facile fabrication process exhibits potential applications for both oil/water separation and flame retardancy.

Composites Filled with Metal Organic Frameworks and Their Derivatives: Recent Developments in Flame Retardants

Polymer matrix is vulnerable to fire hazards and needs to add flame retardants to enhance its performance and make its application scenarios more extensive. At this stage, it is more necessary to add multiple flame-retardant elements and build a multi-component synergistic system. Metal organic frameworks (MOFs) have been studied for nearly three decades since their introduction. MOFs are known for their structural advantages but have only been applied to flame-retardant polymers for a relatively short period of time. In this paper, we review the development of MOFs utilized as flame retardants and analyze the flame-retardant mechanisms in the gas phase and condensed phase from the original MOF materials, modified MOF composites, and MOF-derived composites as flame retardants, respectively. The effects of carbon-based materials, phosphorus-based materials, nitrogen-based materials, and biomass on the flame-retardant properties of polymers are discussed in the context of MOFs. The construction of MOF multi-structured flame retardants is also introduced, and a variety of MOF-based flame retardants with different morphologies are shown to broaden the ideas for subsequent research.

Boosting fire safety and mechanical performance of thermoplastic polyurethane by the face-to-face two-dimensional phosphorene/MXene architecture

• A black phosphorus-MXene@polydopamine nanohybrid was synthesized. • The TPU/BP-MXene@PDA nanocomposite simultaneously showed reinforcing and toughening effects towards TPU. • The TPU/BP-MXene@PDA nanocomposite could be achieved excellent thermal stability, mechanical properties and flame retardancy. • A synergistic flame-retardant mechanism between black phosphorus and MXene in the TPU were discussed and clarified. Black phosphorus (BP), as one of the most promising fillers for flame retarding polymer, has been seriously limited in practical application, due to the agglomeration and poor structural stability challenges. Here, the BP was modified by MXene and polydopamine (PDA) via ultrasonication and dopamine modification strategy to improve the structural stability and dispersibility in the matrix. Then, the obtained (BP-MXene@PDA) nanohybrid was employed to promote the mechanical performance, thermal stability, and flame retardancy of thermoplastic polyurethane elastomer (TPU). The resultant TPU composite containing 2 wt.% of BP1-MXene2@PDA showed a 19.2% improvement in the tensile strength and a 13.8% increase in the elongation at break compared to those of the pure TPU. The thermogravimetric analysis suggested that BP-MXene@PDA clearly enhances the thermal stability of TPU composites. Furthermore, the introduction of the BP-MXene@PDA nanohybrids could considerably improve the flame retardancy of TPU composite, i.e., 64.2% and 27.3% decrease in peak heat release rate and total heat release, respectively. The flame-retardant mechanisms of TPU/BP-MXene@PDA in the gas phase and condensed phase were investigated systematically. This work provides a novel strategy to simultaneously enhance the fire safety and mechanical properties of TPU, thus expanding its industrial applications.

A novel Ti(OH)4/graphene flame retardant towards reducing fire hazards of phenolic resin

Ti(OH) 4 /graphene was synthesized by hydrolysis of titanium tetrachloride into titanium hydroxide and precipitation on the surface of graphene nanosheets, and was incorporated into phenolic resin to prepare phenolic composites using hexamethylenetetramine as a curing agent. After that, the effects of Ti(OH) 4 /graphene on the thermal stability, flame retardancy, and smoke suppression properties of phenolic matrix were studied. When the content of Ti(OH) 4 /graphene was 5 wt.%, phenolic composites passed the UL-94 V-0 rating with a limiting oxygen index (LOI) of 28.6%, and the residual char at 800 °C was 56.83 wt.%. Cone calorimeter tests demonstrated that the peak heat release rate (pHRR), total heat release (THR) and total smoke production (TSP) of phenolic composite contained 10 wt.% Ti(OH) 4 /graphene were 86.3 kW/m 2 , 30.74 MJ/m 2 and 1.8 m 2 , respectively, which were reduced by 41.85%, 24.82%, and 30.78% compared with pure phenolic resin. And the smoke density test also showed that the smoke density of phenolic composite contained 10 wt.% Ti(OH) 4 /graphene had a 51.89% reduction. These data indicated that Ti(OH) 4 /graphene can effectively improve the flame retardant and smoke suppression performance. Moreover, the char residue after combustion is investigated using SEM, FTIR, XRD and Raman technologies, and the results demonstrated that Ti(OH) 4 /graphene could greatly promote the formation of a continuous and dense char residue layer in phenolic composites. Py-GC/MS results further revealed that the degradation products contents of phenolic resins were decreased by incorporating Ti(OH) 4 /graphene. Therefore, the flame retardancy of phenolic composite is significantly improved through the mechanism of endothermic effect, coverage effect, and dilution effect of combustible gas. This feasible method can provide new insights for reducing fire hazards of phenolic resin. • Ti(OH) 4 /graphene was prepared and incorporated into phenolic resin as an additive flame retardant. • Phenolic composites containing only 5 wt.% Ti(OH) 4 /graphene passed UL-94 V-0 rating. • Ti(OH) 4 /graphene significantly improved flame retardancy performances of phenolic composites. • The flame retardant mechanism of Ti(OH) 4 /graphene in phenolic composites was investigated.

Highly efficiency flame-retardant and anti-dripping performance with dual effect of phosphaphenanthrene-benzimidazole for poly (lactic acid) film

To improve the flammability and severe melt-dripping behavior of poly (lactic acid) (PLA), we designed and successfully synthesized a flame retardant structure (D-AB) based on phosphaphenanthrene and benzimidazole groups with hydrogen bonds and π-π stacking effect. Then, D-AB was blended with PLA in solution to prepare PLA/D-ABs films. The results showed that the incorporation of D-AB significantly enhances the viscoelasticity and complex viscosity of PLA due to the synergistic effect of hydrogen bonds and π-π stacking of D-AB. Meanwhile, with the good char formation ability of benzimidazole group, PLA/D-ABs exhibit excellent flame retardancy. With only a 5 wt % addition of D-AB, the PLA film with 0.15 mm thickness easily achieve UL-94 VTM-0 rating and high LOI value of 30.5%, while its melt-dripping behavior is improved. In addition, the flame retardant mechanism of D-AB in PLA is studied in detail. It is found that the release of PO· radicals and non-combustible gas in the gas phase, as well as the formation of a dense and intact carbon layers in the condensed phase contribute to the good flame retardant performance of D-AB. This work provides a method for designing highly efficient flame retardants for PLA.