Flame-retardant activity of ternary integrated modified boron nitride nanosheets to epoxy resin

Intrinsically reactive hyperbranched interface governs graphene oxide dispersion and crosslinking in epoxy for enhanced flame retardancy

Enhancing the flame retardancy of epoxy (EP) resins typically entailed a trade-off with other physical properties. Herein, hyperbranched poly(amidoamine) (HPAA) and phytic acid (PA) were used to functionalize graphene oxide (GO) via electrostatic self-assembly in water to prepare a phosphorus-nitrogen functionalized graphene oxide nanosheet (PN-GOs), which could be utilized as high efficient flame-retardant additive of epoxy resin without sacrificing other properties. The PN-GOs demonstrated improved dispersion and compatibility within the EP matrix, which resulted in significant concurrent enhancements in both the mechanical performance and flame-retardant properties of the PN-GOs/EP nanocomposites over virgin EP. Notably, the incorporation of just 1.0 wt% PN-GOs yielded a 20.4, 6.4 and 42.7 % increases in flexural strength, flexural modulus and impact strength for the PN-GOs/EP nanocomposites, respectively. Furthermore, simultaneous reductions were achieved in the peak heat release rate (pHRR) by 60.0 %, total smoke production (TSP) by 43.0 %, peak CO production rate (pCOP) by 57.9 %, and peak CO2 production rate (pCO2P) by 63.9 %. This study presented a facile method for the design of GO-based nano flame retardants, expanding their application potential in polymer-matrix composites.

Chitosan-based biopolyelectrolyte complexes intercalated montmorillonite: A strategy for green flame retardant and mechanical reinforcement of polypropylene composites

Due to dwindling petroleum resources and the need for environmental protection, the development of bio-based flame retardants has received much attention. In order to explore the feasibility of fully biomass polyelectrolyte complexes (PEC) for polyolefin flame retardant applications, chitosan (CS), sodium alginate (SA), and sodium phytate (SP) were used to prepare CS-based fully biomass PEC intercalated montmorillonite (MMT) hybrid biomaterials (SA-CS@MMT and SP-CS@MMT). The effects of two hybrid biomaterials on the fire safety and mechanical properties of intumescent flame-retardant polypropylene (PP) composites were compared. The SP-CS@MMT showed the best flame retardancy and toughening effect at the same addition amount. After adding 5 wt% SP-CS@MMT, the limiting oxygen index (LOI) value of PP5 reached 30.9 %, and the peak heat release rate (pHRR) decreased from 1348 kW/m2 to 163 kW/m2. In addition, the hydrogen bonding between polyelectrolyte complexes significantly improved the mechanical properties of PP composites. Compared with PP2, the tensile strength of PP5 increased by 59 %. This study provided an efficient and eco-friendly strategy for the large-scale production of renewable biomaterials with good thermal stability and expanded the application of macromolecular biomaterials in the field of fire safety.

Simultaneously Flame Retarding and Toughening of Epoxy Resin Composites Based on Two-Dimensional Polyhedral Oligomeric Silsesquioxane/Polyoxometalate Supramolecular Nanocrystals with Ultralow Loading

For industrial practical applications, it is difficult to simultaneously endow epoxy resin (EP) composites with superior flame retardancy, smoke suppression, toughness, and low-dielectric constants. Herein, unique polyhedral oligomeric silsesquioxane/polyoxometalate (POM(Mo)-POSS(ibu-Li)) nanosheets were synthesized via a simple one-pot method using laboratory-made lithium-containing hepta-isobutyl-POSS (ibu-Li-POSS) and the low-cost industrial chromogenic agent H3PMo12O40 as raw materials. The incorporation of 2 wt % POM(Mo)-POSS(ibu-Li) nanoflakes into EP significantly enhanced the compatibility between nanoadditives and the EP matrix. Compared with EP, the flexural and impact strengths increased by 36.2 and 78.2%, respectively. Therefore, POM(Mo)-POSS(ibu-Li) has significant advantages in enhancing the toughness of EP compared with existing flame retardants. The dielectric constant and loss were apparently reduced to meet the increasing requirements of EP-type electronic packaging materials and components. Notably, the synthesized POM(Mo)-POSS(ibu-Li) contained various flame-retardant and smoke-suppression elements such as P, Mo, and Si. The ultralow loading (2 wt %) of POM(Mo)-POSS(ibu-Li) significantly reduced the peak heat release rate, peak of smoke production rate, and CO production rate by 43.9, 40.6, and 65.8%, respectively. Meanwhile, the value of LOI increased directly from 24.0% for EP to 30.2% and passed the V-0 rating in the UL-94 test. However, incorporating 5 wt % POSS derivatives into EP alone to ensure that the prepared composites pass the V-0 rating of the UL-94 test has always been an extraordinarily difficult problem. Therefore, the dilemmas of poor dielectric properties, inherent flammability, and brittleness of EP were completely overcome through the successful application of POM(Mo)-POSS(ibu-Li) supramolecular nanosheets.

Advances in Inorganic Foam Materials Fabricated Via Blowing Strategy: A Comprehensive Review

Two-dimensional (2D) materials with excellent properties and widespread applications have been explosively investigated. However, their conventional synthetic methods exhibit concerns of limited scalability, complex purification process, and incompetence of prohibiting their restacking. The blowing strategy, characterized by gas-template, low-cost, and high-efficiency, presents a valuable avenue for the synthesis of 2D-based foam materials and thereby addresses these constraints. Whereas, its comprehensive introduction has been rarely outlined so far. This review commences with a synopsis of the blowing strategy, elucidating its development history, the statics and kinetics of the blowing process, and the choice of precursor and foaming agents. Thereafter, we dwell at length on across-the-board foams enabled by the blowing route, like BxCyNz foams, carbon foams, and diverse composite foams consisting of carbon and metal compounds. Following that, a wide-ranging evaluation of the functionality of the foam products in fields such as energy storage, electrocatalysis, adsorption, etc. is discussed, revealing their distinctive strength originated from the foam structure. Finally, after concluding the current progress, we provide some personal discussions on the existing challenges and future research priorities in this rapidly developing method.

Controllable Self-Assembly of Carbon Nanotubes on Ammonium Polyphosphate as a Game-Changer for Flame Retardancy and Thermal Conductivity in Epoxy Resin

The optimization of flame retardancy and thermal conductivity in epoxy resin (EP), utilized in critical applications such as mechanical components and electronics packaging, is a significant challenge. This study introduces a novel, ultrasound-assisted self-assembly technique to create a dual-functional filler consisting of carbon nanotubes and ammonium polyphosphate (CNTs@APP). This method, leveraging dynamic ligand interactions and strategic solvent selection, allows for precise control over the assembly and distribution of CNTs on APP surfaces, distinguishing it from conventional blending approaches. The integration of 7.5 wt.% CNTs@APP10 into EP nanocomposites results in substantial improvements in flame retardancy, as evidenced by a limiting oxygen index (LOI) value of 31.8% and achievement of the UL-94 V-0 rating. Additionally, critical fire hazard indicators, including total heat release (THR), total smoke release (TSR), and the peak intensity of CO yield (PCOY), are significantly reduced by 45.9% to 77.5%. This method also leads to a remarkable 3.6-fold increase in char yield, demonstrating its game-changing potential over traditional blending techniques. Moreover, despite minimal CNTs addition, thermal conductivity is notably enhanced, showing a 53% increase. This study introduces a novel approach in the development of multifunctional EP nanocomposites, offering potential for wide range of applications.

Protective and Flame-Retardant Bifunctional Epoxy-Based Nanocomposite Coating by Intercomponent Synergy between Modified CaAl-LDH and rGO

Extensive utilization in various settings poses extra requirements of coatings beyond just anticorrosion properties. Herein, 8-hydroxyquinoline (8-HQ) intercalated CaAl-based layered double hydroxide (CaAl-8HQ-LDH) was loaded on reduced GO (rGO) through a one-pot hydrothermal reaction, which was employed as the nanofiller endowing the epoxy (EP/CaAl-8HQ LDH@rGO) with excellent flame-retardancy while ensuring efficient protection for mild steel. Results of electrochemical impedance spectroscopy (EIS) demonstrated the durability of the EP/CaAl-8HQ LDH@rGO-coated specimen, with the impedance at the lowest frequency (|Z|0.01Hz) maintained as 1.84 × 1010 Ω cm2 after 120 days of immersion in a 3.5 wt % NaCl solution. Even for the scratched EP/CaAl-8HQ LDH@rGO system, only a slight decline in |Z|0.01Hz was observed during 180 h of exposure to the NaCl solution, indicating a self-healing feature supported by salt spray tests. UL-94 burning tests revealed the V-0 rating for EP/CaAl-8HQ LDH@rGO with improved thermostability. Strong physical barrier from two-dimensional rGO and the release of 8-HQ from LDH interlayers accounted for the anticorrosive and self-healing properties. However, O2-concentration dilution and charring-layer promotion governed the flame-retardant behavior of the nanocomposite coating. The intercomponent synergy of nanofillers achieved in this work may provide a useful reference for designing multifunctional coatings.

Construction of hierarchical SiO2 microcapsule towards flame retardation, low toxicity and mechanical enhancement of epoxy resins

A novel approach for improving the flame retardancy, smoke suppression and mechanical properties of epoxy resins (EPs) has been proposed by incorporating functionalized hollow mesoporous silica microcapsules (SHP) loaded with phosphorous silane flame retardants (SCA) and coated with polydopamine (PDA) and transition metals. The proposed approach involves a multi-level structure that combines several mechanisms to enhance the flame-retardant properties of EP. The physical barrier provided by silica serves to impede heat and mass transfer during combustion, while the catalytic carbonization effect of phosphorus and transition metals promotes the formation of a protective char layer, which acts as a barrier to further flame propagation. Incorporating a low loading amount of 3 wt% SHP into the epoxy matrix resulted in EP/SHP-3 composites with significantly improved flame retardancy, as evidenced by a limiting oxygen index of 31.5% and a V-1 rating, in contrast to the values obtained for unmodified EP, which were 23.8% and no rating, respectively. In addition, cone calorimeter test (CCT) results indicated that the total heat release, peak heat release rate and total smoke production of EP/SHP-3 decreased by 18.2%, 25.2% and 18.4%, respectively. Moreover, the improved interfacial compatibility facilitated by polydopamine assists in the dispersion and compatibility of the SHP with the epoxy matrix, leading to better mechanical properties. Herein, the addition of 1 wt% SHP to EP significantly improved its mechanical performance, with a 16.7% increase in tensile strength and a 19.2% increase in impact strength. The design of the multi-level structural approach has the potential to provide new ideas for the simultaneous improvement of fire safety as well as mechanical properties of polymers.

Design of P-decorated POSS towards flame-retardant, mechanically-strong, tough and transparent epoxy resins

Epoxy resins (EPs) are known for their durability, strength, and adhesive properties, which make them a versatile and popular material for use in a variety of applications, including chemical anticorrosion, small electronic devices, etc. However, EP is highly flammable due to its chemical nature. In this study, phosphorus-containing organic-inorganic hybrid flame retardant (APOP) was synthesized by introducing 9, 10-dihydro-9-oxa-10‑phosphaphenathrene (DOPO) into cage-like octaminopropyl silsesquioxane (OA-POSS) via Schiff base reaction. The improved flame retardancy of EP was achieved by combining the physical barrier of inorganic Si-O-Si with the flame-retardant capability of phosphaphenanthrene. EP composites containing 3 wt% APOP passed the V-1 rating with a value of LOI of 30.1% and showed an apparent reduction in smoke release. Additionally, the combination of the inorganic structure and the flexible aliphatic segment in the hybrid flame retardant provides EP with molecular reinforcement, while the abundance of amino groups facilitates a good interface compatibility and outstanding transparency. Accordingly, EP containing 3 wt% APOP increased in tensile strength, impact strength, and flexural strength by 66.0 %, 78.6 %, and 32.3 %, respectively. The EP/APOP composites had a bending angle lower than 90°, and their successful transition to a tough material highlights the potential of this innovative combination of the inorganic structure and the flexible aliphatic segment. In addition, the relevant flame-retardant mechanism revealed that the APOP promoted the formation of a hybrid char layer containing P/N/Si for EP and produced phosphorus-containing fragments during combustion, showing flame-retardant effects in both condensed and vapor phases. This research offers innovative solutions for reconciling flame retardancy & mechanical performances and strength & toughness for polymers.

Dual char-forming strategy driven MXene-based fire-proofing epoxy resin coupled with good toughness

It is challenging that the functionalized MXene-based nanofillers are designed to modify the inherent flammability and poor toughness of epoxy polymeric materials and further to facilitate the application of EP composites. Herein, silicon-reinforced Ti₃C₂T_x MXene-based nanoarchitectures (MXene@SiO₂) are synthesized by simple self-growth method, and its enhancement effects on epoxy resin (EP) are investigated. The as-prepared nanoarchitectures realize homogeneous dispersion in EP matrix, indicating well performance-enhancing potential. The incorporation of MXene@SiO₂ achieves improved thermal stability for EP composites with higher T_-5% and lower R_max values. Moreover, EP/2 wt% MXene@SiO₂ composites obtain a 30.2% and 34.0% reduction in peak heat release rate (PHRR) and peak smoke production rate (PSPR) compared to those of pure EP, respectively, also achieving a 52.5% fall in smoke factor (SF) values and increased yield and stability of chars. The dual char-forming effects of MXene@SiO₂ nanoarchitectures, including the catalytic charring of MXene and the migration of SiO₂ to induce charring, are accounted for the results, as well as lamellar barrier effects. Additionally, EP/MXene@SiO₂ composites achieve an enhanced storage modulus of 51.5%, along with improved tensile strength and elongation at break, compared to those of pure EP.

Growth of copper organophosphate nanosheets on graphene oxide to improve fire safety and mechanical strength of epoxy resins

With the high integration of electronic products in our daily life, high-performance epoxy resins (EP) with excellent flame retardancy, smoke suppression, and mechanical strength are highly desired for applications. In this study, copper organophosphate nanosheets were evenly grown on the surface of graphene oxide (GO) via a self-assembly process based on coordination bonding and electrostatic interactions. The resultant nanohybrid endowed EP with satisfactory flame retardant effect and improved mechanical properties. Incorporating functionalized nanosheets of merely 1 wt% loading, the impact strength of the EP nanocomposites improved by 147% when compared to 1% EP-GO. Additionally, the nanosheets inhibited the smoke and heat release of EP, and the limiting oxygen value of EP-EGOPC reached ∼29%. The mechanism analysis verified that the existence of organophosphate and copper-containing components associated with the physical barrier of GO promoted the hybrid aromatization of the char layer, thereby improving the fire safety of epoxy matrix. This research offers a new interfacial method for designing functional nanosheets with good interface compatibility and high flame-retardant efficiency in polymers.

Interfacial engineering to construct P-loaded hollow nanohybrids for flame-retardant and high-performance epoxy resins

Nano flame retardants, as one of the key flame retardants in recent years, have been limited by poor efficiency and weak compatibility. In this study, we propose an interfacial hollow engineering strategy to tackle this problem by assembling P-phytic acid into the hollow cavity of mesoporous SiO₂ grafted with a polydopamine transition metal. In this design, the grafted polydopamine-metal coatings on the hybrids can greatly improve their interface compatibility with the polymer matrix, while the loaded phytic acid in the cavity contributes to enhance flame retardancy. Consequently, the resultant hierarchical P-loaded nanohybrids show both high flame retardancy and mechanical reinforcement for the polymer. Taking epoxy resin (EP, a typical thermosetting resin used in large quantities) as a representative, at only 1 wt% loading of the nanohybrids, the impact strength of the nanocomposites improved by 35.7% compared to pure EP. Remarkably, the hybrids can simultaneously endow EP with high flame retardancy (low heat release rate) and satisfactory smoke inhibition. Additionally, the flame-retardant mechanism analysis confirmed that the nanohybrid had a better catalytic carbonization effect on promoting the highly graphitized carbon layer, thereby suppressing the fire hazard of epoxy resins. This research offers a new interfacial hollow engineering method for the construct and design of high-performance EP with nanohybrids.

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.

LED-light-activated photocatalytic performance of metal-free carbon-modified hexagonal boron nitride towards degradation of methylene blue and phenol

The present study outlines the transformation of non-photoresponsive hexagonal boron nitride (HBN) into a visible-light-responsive material. The carbon modification was achieved through a solid-state reaction procedure inside a tube furnace under nitrogen atmosphere. In comparison to HBN (bandgap of 5.2 eV), the carbon-modified boron nitride could efficiently absorb LED light irradiation with a light harvesting efficiency of ≈90% and a direct bandgap of 2 eV. The introduction of carbon into the HBN lattice led to a significant change in the electronic environment through the formation of C-B and C-N bonds which resulted in improved visible light activity, lower charge transfer resistance, and improved charge carrier density (2.97 × 1019 cm-3). This subsequently enhanced the photocurrent density (three times) and decreased the photovoltage decay time (two times) in comparison to those of HBN. The electronic band structure (obtained through Mott-Schottky plots) and charge trapping analysis confirmed the dominance of e-, O2 -•, and •OH as dominant reactive oxygen species. The carbon modification could effectively remove 93.83% of methylene blue (MB, 20 ppm solution) and 48.56% of phenol (10 ppm solution) from the aqueous phase in comparison to HBN which shows zero activity in the visible region.

Nanohybrid of Co3O4 Nanoparticles and Polyphosphazene-Decorated Ultra-Thin Boron Nitride Nanosheets for Simultaneous Enhancement in Fire Safety and Smoke Suppression of Thermoplastic Polyurethane

Thermoplastic polyurethane (TPU) is widely used in daily life due to its characteristics of light weight, high impact strength, and compression resistance. However, TPU products are extremely flammable and will generate toxic fumes under fire attack, threatening human life and safety. In this article, a nanohybrid flame retardant was designed for the fire safety of TPU. Herein, Co₃O₄ was anchored on the surface of exfoliated ultra-thin boron nitride nanosheets (BNNO@Co₃O₄) via coprecipitation and subsequent calcination. Then, a polyphosphazene (PPZ) layer was coated onto BNNO@Co₃O₄ by high temperature polymerization to generate a nanohybrid flame retardant named BNNO@Co₃O₄@PPZ. The cone calorimeter results exhibited that the heat release and smoke production during TPU combustion were remarkably restrained after the incorporation of the nanohybrid flame retardant. Compared with pure TPU, the peak heat release rate (PHRR) decreased by 44.1%, the peak smoke production rate (PSPR) decreased by 51.2%, and the peak CO production rate (PCOPR) decreased by 72.5%. Based on the analysis of carbon residues after combustion, the significant improvement in fire resistance of TPU by BNNO@Co3O4@PPZ was attributed to the combination of quenching effect, catalytic carbonization effect, and barrier effect. In addition, the intrinsic mechanical properties of TPU were well maintained due to the existence of the PPZ organic layer.

A novel approach simultaneously imparting well-hydrophobicity and photothermal conversion effect to polymer materials: solar-promoted absorption of organic solvents and oils

In this work, a series of polymer materials including pomelo peel, cotton fabric, polyurethane foam, and so on, are treated by heated CH₃SiCl₃, presenting desirable photo-thermal conversion function and hydrophobicity. As a representative material, the surface element and skeleton morphology of pomelo peel foam treated by CH₃SiCl₃ are analyzed detailedly. It is found that well-hydrophobicity (water contact angle of ~147°) and photo-thermal conversion performance (~91.2 °C under one sun) are attributed to the surface carbonization reaction and formation of CH₃-SiO₂ nanoparticles. Meanwhile, the treatment of CH₃SiCl₃ significantly increases the BET surface area to 3.0635 m²/g from 0.0973 m²/g. Therefore, pomelo peel-derived carbon foam presents a desirable adsorption capacity of organic solvents and oils (up to 43.2 times its original weight) and excellent removal efficiency (>99.0%). In addition, the rapid photo-thermal response (achieve ~73 °C at 40 s) and high equilibrium temperature (~91.2 °C) are als° demonstrated in pomelo peel-derived carbon foam. As a result, the absorption rate of highly-viscous oils is effectively promoted by the higher fluidity and capillary action caused by the solar-promoted mechanism. This study offers a scalable, easily operated, and environmentally friendly approach to prepare hydrophobic and photo-thermal materials, thus demonstrating a huge potential in oil/water separation application.

Electrochemical Preparation of Hydroxylated Boron Nitride Nanosheets for Solid-State Flexible Supercapacitors Using Deep Eutectic Solvent and Water Mixture as Electrolytes

One-step and efficient preparation of few-layer hydroxylated boron nitride nanosheets (OH-BNNSs) in electrochemical methods is still challenging. Here, we developed an electrolyte composed of a mixture of deep eutectic solvent (DES, choline chloride-urea) and water for electrochemical methods to enhance the exfoliation and oxidation processes, enabling the one-step preparation of OH-BNNSs. It was found that the obtained OH-BNNSs were an average lateral size of 625 nm and thickness of six layers. Furthermore, the OH-BNNSs and DES were added to the poly(vinyl alcohol) (PVA) substrate to prepare composite gel polymer electrolyte (PVA/DES/OH-BNNSs GPE) for solid-state flexible supercapacitor. The OH-BNNSs can effectively shorten the ionic transport distance and enhance ion conductivity. In addition, their excellent mechanical properties can significantly prevent the electrolyte structure from collapsing during reuse. In the meantime, DES was introduced to improve ionic conductivity and broaden the operating voltage window of supercapacitor. As a result, the symmetric solid-state flexible supercapacitor consisting of activated carbon electrodes and PVA/DES/OH-BNNSs GPE appeared a wide voltage window of 2.3 V, high specific capacitance of 151.22 F g^-1 at 0.1 A g^-1 and remained 98% capacitance after 1500 charge-discharge cycles. This study not only opened a new pathway to efficient exfoliation of insulating layered materials but also found a novel gel polymer electrolyte for solid-state flexible supercapacitors.