The effects of graphene on the flammability and fire behavior of intumescent flame retardant polypropylene composites at different flame scenarios

Synergistic Effects of Black Phosphorus/Boron Nitride Nanosheets on Enhancing the Flame-Retardant Properties of Waterborne Polyurethane and Its Flame-Retardant Mechanism

We applied black phosphorene (BP) and hexagonal boron nitride (BN) nanosheets as flame retardants to waterborne polyurethane to fabricate a novel black phosphorus/boron nitride/waterborne polyurethane composite material. The results demonstrated that the limiting oxygen index of the flame-retarded waterborne polyurethane composite increased from 21.7% for pure waterborne polyurethane to 33.8%. The peak heat release rate and total heat release of the waterborne polyurethane composite were significantly reduced by 50.94% and 23.92%, respectively, at a flame-retardant content of only 0.4 wt%. The superior refractory performances of waterborne polyurethane composite are attributed to the synergistic effect of BP and BN in the gas phase and condensed phase. This study shows that black phosphorus-based nanocomposites have great potential to improve the fire resistance of polymers.

Experimental and theoretical study on thermal kinetics and reactive mechanism of nitrocellulose pyrolysis by traditional multi kinetics and modeling reconstruction

Nitrocellulose (NC) has been applied in many fields of daily life and military industry, but its instability brings large danger during storage and usage, which greatly limits its application. In this study, decomposition behavior and reaction model of NC were explored. To obtain its kinetic triplets during decomposition, NC samples were heated in nitrogen atmosphere with different heating rates of 5, 10, 15, 20 °C min^-1, respectively. A 3-th order reaction model was obtained by model fitting methods. Meanwhile, the relationship between activation energy and conversion was obtained by multi isoconversional methods, including KAS, FR, FWO, and Advanced Vyazovkin methods. Then the reaction model was reconstructed by introducing adjustment functions with result of an expression of f(α) = 19.38193α^1.41177(1-α)^4.60503.

Superhydrophobic and oleophobic ultra-fine dry chemical agent with higher chemical activity and longer fire-protection

The re-ignition of pool fires is a common hazard phenomenon in fire extinguishing. Dry chemicals with oleophobicity may solve this problem because powders can float on the oil surface and prevent evaporation of fuel pool. In this research, MAPP (modified ammonium polyphosphate) with superhydrophobicity, oleophobicity, and higher chemical activity is prepared which can quickly quench pool fires and provide longer protection. The activation indexes of MAPP for water, diesel, aviation kerosene and gasoline are 98.5%, 87.4%, 98.7% and 98.4%, respectively. Lower activation energy of MAPP means that it will show higher chemical activity in fire. The fire-extinguishing performance of MAPP is much higher than that of Commercial UDCA (ultra-fine dry chemical agent) during fire experiments. After extinguished by MAPP, the fuel pool is hard to be re-ignited. The significance of this study is to propose a new strategy for preventing the re-ignition of pool fires.

Nanoreinforcements of Two-Dimensional Nanomaterials for Flame Retardant Polymeric Composites: An Overview

Polymer materials are ubiquitous in daily life. While polymers are often convenient and helpful, their properties often obscure the fire hazards they may pose. Therefore, it is of great significance in terms of safety to study the flame retardant properties of polymers while still maintaining their optimal performance. Current literature shows that although traditional flame retardants can satisfy the requirements of polymer flame retardancy, due to increases in product requirements in industry, including requirements for durability, mechanical properties, and environmental friendliness, it is imperative to develop a new generation of flame retardants. In recent years, the preparation of modified two-dimensional nanomaterials as flame retardants has attracted wide attention in the field. Due to their unique layered structures, two-dimensional nanomaterials can generally improve the mechanical properties of polymers via uniform dispersion, and they can form effective physical barriers in a matrix to improve the thermal stability of polymers. For polymer applications in specialized fields, different two-dimensional nanomaterials have potential conductivity, high thermal conductivity, catalytic activity, and antiultraviolet abilities, which can meet the flame retardant requirements of polymers and allow their use in specific applications. In this review, the current research status of two-dimensional nanomaterials as flame retardants is discussed, as well as a mechanism of how they can be applied for reducing the flammability of polymers.

Synergistic Effects of Two-Dimensional MXene and Ammonium Polyphosphate on Enhancing the Fire Safety of Polyvinyl Alcohol Composite Aerogels

Fire and smoke suppressions of polyvinyl alcohol (PVA) aerogels are urgently required due to the serious fire hazard they present. MXene, a 2D transition-metal carbide with many excellent properties, is considered a promising synergist for providing excellent flame retardant performance. PVA/ammonium polyphosphate (APP)/transition metal carbide (MXene) composite aerogels were prepared via the freeze-drying method to enhance the flame retardancy. Thermogravimetric analysis, limiting oxygen index, vertical burning, and cone calorimeter tests were executed to investigate the thermal stability and flame retardancy of PVA/APP/MXene (PAM) composite aerogels. The results demonstrated that MXene boosted the flame retardancy of PVA-APP, and that PAM-2 (with 2.0 wt% MXene loading) passed the V-0 rating, and reached a maximum LOI value of 42%; Moreover, MXene endowed the PVA-APP system with excellent fire and smoke suppression performance, as the the peak heat release rate and peak smoke production rate were significantly reduced by 55% and 74% at 1.0 wt% MXene loading. The flame retardant mechanism was systematically studied, MXene facilitated the generation of compact intumescent residues via ita catalyst effects, thus further restraining the release of heat and smoke. This work provides a simple route to improve the flame retardancy of PVA aerogels via the synergistic effect of MXene and APP.

Suppression of wood dust explosion by ultrafine magnesium hydroxide

The suppression effects of ultrafine Mg (OH)₂ powders with different particle sizes and mass fractions on explosion flame of wood dust are experimentally studied in a half-closed vertical experimental duct. Flame structures and characteristic parameters, including flame light emission images, propagation velocity, temperature, during the flame propagation of wood dust explosion are recorded by high-speed photography and fine thermocouple. Thermal decomposition behaviors of wood dust and Mg(OH)₂ powders are studied using synchronous thermal analyzer. Chemical structures of residual dust samples after the explosion are characterized by Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. The experimental results show that explosion flame of wood dust is obviously suppressed by physical and chemical effects of Mg(OH)₂ powders, and the suppression effect of nano-Mg(OH)₂ is better than that of micron-Mg(OH)₂ under same mass fractions. By analyzing multiple characteristics of nano-powders, the advantages of nano-Mg(OH)₂ over micron-powders are further investigated.

Inclusion of graphene on LDPE properties

The spread of graphene in low-density polyethylene (LDPE) improves LDPE/graphene nanocompounds' thermal/mechanical/electrical characteristics. The images of scanning electron microscopy (SEM) verify full graphene exfoliation at 1000 °C. Inclusion graphene develops crystallinity; increases the local order of lattice and thermal stability of LDPE/graphene nanocompounds. The consistent distributions and further inclusion of graphene caused the great heat breakdown strength, increasing heat breakdown activation energy and a superior melting point (Tm) for LDPE nanocompounds. Percolation occurs with the graphene incorporation of 0.5 wt%. The complex viscosity test showed Newtonian behavior for LDPE at a very low frequency. But, graphene inclusion to LDPE changed the viscosity performance from liquid-like to solid-like which caused a decrease in the melt flow rate (MFR) values for all LDPE/graphene nanocompounds.

A novel organic-inorganic hybrid K-HBPE@APP performing excellent flame retardancy and smoke suppression for polypropylene

To overcome the flammability and severe dripping of polypropylene (PP), a novel organic-inorganic hybrid K-HBPE@APP (microencapsulated APP by a hyperbranched polyester (HBPE) via silane coupling agent (KH-550)) was obtained and used as a high-efficient flame retardant and smoke suppressant. Herein, HBPE acted as the charring agent for APP. 20 wt% of K-HBPE@APP imparted PP excellent flame retardancy, V-0 rating (UL-94 test) and 82.6% decrease in the peak of heat release rate (PHRR). However, PP with 25 wt% of mechanically mixed APP and HBPE achieved V-1 rating (UL-94 test) and 77.3% decrease in PHRR. That is because the direct contact and sufficient interaction between APP and HBPE gives full play to their synergy. Besides, K-HBPE@APP accelerated the formation of cross-linked POC/SiOSi/SiOC/SiOP/POΦ structures, leading to a strong and compact char layer with a result of dramatic reduction in heat release rate and smoke production. Furthermore, K-HBPE@APP was highly water-resistant and has good compatibility with PP matrix. In particular, the flame-retarded PP had similar tensile strength to pure PP and enhanced impact strength.

Thermal degradation kinetics investigation on Nano-ZnO/IFR synergetic flame retarded polypropylene/ethylene-propylene-diene monomer composites processed via different fields

In the field of polymer processing, disperse phase exhibited better dispersion and distribution performance in elongational field rather than shearing field. This property commonly brought a better functional feature for polymer composites. It could also be applied to Nano-ZnO/IFR synergetic flame retarded polypropylene/ ethylene-propylene-diene monomer composites. An experiment was designed to study the mechanism of improving flame retardant properties. In the experiment, the same formulas of composites were extruded by vane extruder (represents elongational field) and three-screw extruder (represents shearing field). Then Kissinger method and Flynn-Wall-Ozawa method were used to mutually proved that Nano-ZnO with better dispersion condition catalysed a more intense esterification of IFR in the whole thermal degradation process.

Thermal Degradation and Combustion Behaviors of Polyethylene/Alumina Trihydrate/Graphene Nanoplatelets

Graphene nanoplatelets (GNPs) were prepared from expanded graphite (EG) with fully exfoliated structure via ball milling coupled with ultrasonication. The structure of multi-layered GNPs was characterized with transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), atomic force microscopy (AFM) and Raman spectroscopy. By compounding alumina trihydrate (ATH) with GNPs, the well dispersed mixture of ATH/GNP was obtained, and it showed high flame retardant effectiveness in polyethylene (PE). The peak heat release rate (peak-HRR) decreased by 20% was proven by a cone calorimeter with the addition of GNPs as low as 0.2 wt % in PE/ATH. The results of thermogravimetric analysis (TG) illustrated the improved thermal stability and lower weight loss rate of PE/ATH/GNP than PE/ATH. A protective char with GNPs was evidenced by SEM and X-ray photoelectron spectroscopy (XPS). The well exfoliated structure and good dispersion of GNPs accounted for the formation of effective barrier, which made a profound contribution to the enhanced flame retardancy.

Effect of Graphene on Flame Retardancy of Graphite Doped Intumescent Flame Retardant (IFR) Coatings: Synergy or Antagonism

A comparative study between graphene and modified graphene oxide (mGO) on the flame retardancy of graphite doped intumescent flame retardant (IFR) coatings is preliminarily investigated by cone calorimeter (CC), XRD, and SEM, with the final aim of clarifying the interactions between different graphenes and graphite doped coatings (polyester resin-ammonium polyphosphate-urea-pentaerythritol). The CC results determine that graphene exerts an obviously antagonistic effect on flame resistance, evidenced by the increased peak heat release rate (p-HRR) of 56.9 kW·m−2 for SD8+graphene (sample coating contains graphite with a particle size of 8 μm and 0.5 wt.% graphene as dopant), which increased by 80.6% compared with SD8 (coating contains graphite with a particle size of 8 μm); substitution with graphene or mGO imparts an acceleration of fire growth, because graphene inertness improves the viscosity of melting system, evidenced by the cracked appearance and porous structure of SD8+graphene. However, the higher reactivity of mGO favors the combustion; the barrier effect inhibits the transfer of mass and heat simultaneously, leading to a slight influence on flame retarding efficiency.

Construction of multifunctional boron nitride nanosheet towards reducing toxic volatiles (CO and HCN) generation and fire hazard of thermoplastic polyurethane

Considerable toxic volatiles (CO and HCN) generation and high fire hazard has definitely compromised the application of thermoplastic polyurethane (TPU). Here, a novel functionalization strategy for bulky h-BN is adopted to obtain the multifunctional CPBN, aiming at the flame retardancy reinforcement of TPU. The multifunctional CPBN is successfully prepared via the wrapping of phytic acid doped polypyrrole shell, following with the adsorption of copper ions. The obviously decreased peak heat release rate, peak smoke production rate and total smoke production values, obtained from cone test, confirms the reduced fire hazard of TPU composite with CPBN. The dramatic suppressions on CO and HCN releases can also be observed from TG-IR test. Tensile test demonstrates that adding CPBN favors the reinforcement in mechanical property of TPU. Thus, the concurrent improvements in flame retardancy and mechanical performance are achieved by incorporating CPBN. This work opens up new avenues for the functionalization of h-BN, and thus facilitates its promising applications in polymer-matrix composite.

Study on the effect of PolyFR and its FR system on the flame retardancy and foaming behavior of polystyrene

Environmentally-friendly flame retardant, PolyFR, has an excellent effect on the flame retardancy and foaming behavior of polystyrene.

Construction of multifunctional MoSe2 hybrid towards the simultaneous improvements in fire safety and mechanical property of polymer

Organic modification of MoSe₂ sheets is firstly achieved by Atherton-Todd reaction, aiming at the acquisition of multifunctional MoSe₂ hybrid. Simultaneous enhancements in fire safety and mechanical property of thermalplastic polyurethane (TPU) are obtained with the presence of this hybrid. Strong interfacial interactions between the functionalized MoSe₂ sheets and TPU can be obtained, making more efficient load transfer from the weak polymer chains to the robust sheets. Besides, more coherent barrier network may be formed in polymer matrix, restraining the diffusion of decomposed fragments and reducing the supply for combustion fuel. Consequently, the decreases in heat release are observed for polymer composites. Notably, the releases of toxic gases, such as HCN and CO, are also suppressed by this barrier network, resulting in the reductions in fire toxicity. This work may open a new door for the functionalization of MoSe₂ sheets and evoke significant developments in its promising applications.

Mussel-inspired functionalization of electrochemically exfoliated graphene: Based on self-polymerization of dopamine and its suppression effect on the fire hazards and smoke toxicity of thermoplastic polyurethane

The suppression effect of graphene in the fire hazards and smoke toxicity of polymer composites has been seriously limited by both mass production and weak interfacial interaction. Though the electrochemical preparation provides an available approach for mass production, exfoliated graphene could not strongly bond with polar polymer chains. Herein, mussel-inspired functionalization of electrochemically exfoliated graphene was successfully processed and added into polar thermoplastic polyurethane matrix (TPU). As confirmed by SEM patterns of fracture surface, functionalized graphene possessing abundant hydroxyl could constitute a forceful chains interaction with TPU. By the incorporation of 2.0 wt % f-GNS, peak heat release rate (pHRR), total heat release (THR), specific extinction area (SEA), as well as smoke produce rate (SPR) of TPU composites were approximately decreased by 59.4%, 27.1%, 31.9%, and 26.7%, respectively. A probable mechanism of fire retardant was hypothesized: well-dispersed f-GNS constituted tortuous path and hindered the exchange process of degradation product with barrier function. Large quantities of degradation product gathered round f-GNS and reacted with flame retardant to produce the cross-linked and high-degree graphited residual char. The simple functionalization for electrochemically exfoliated graphene impels the application of graphene in the fields of flame retardant composites.

Studies on the flammability of polypropylene/ammonium polyphosphate and montmorillonite by using the cone calorimeter test

Fire performance of polypropylene (PP) containing different percentages of ammonium polyphosphate (APP) with montmorillonite (Mt) or treated montmorillonite (MtT) was carried out by using the cone calorimeter test (CCT). Different samples from ammonium polyphosphate and montmorillonite were mixed with 90% polypropylene. The characterization of the prepared samples indicates that there is incorporation between the components of the samples. Heat release rate (HRR), peak heat release rate (PHRR), average heat release rate (Av-HRR), and time to ignition (TTI) of the samples were obtained from the cone calorimeter test. Also, the fire performance index (FPI) and the fire growth rate (FIGRA) were calculated. The interpretation of the curves and the parameters results from the cone calorimeter test which indicates that the addition of montmorillonite to APP increases its action as a flame retardant for PP. Moreover, the samples contain acid treatment montmorillonite showed an increase in the efficiency of ammonium polyphosphate when used. This result may be due to an increase in the SiO2 content by acid treatment.

Preparation of novel phosphorus-nitrogen-silicone grafted graphene oxide and its synergistic effect on intumescent flame-retardant polypropylene composites

The combination of PMGO and IFR significantly improves the flame retardancy and surface hydrophobicity of PP materials.