Enhancing low-temperature CO removal in complex flue gases: A study on La and Cu doped Co3O4 catalysts under real-world combustion environment.

Designing CO oxidation catalysts for complex flue gases conditions is particularly challenging in fire scenarios. Traditional flue gas simulations use a few representative gases but often fail to adequately evaluate catalyst performance in real-world combustion conditions. In this study, we developed doping strategies using La and Cu to enhance the water resistance of Co3O4 catalysts. Catalyst 0.1La-Co3O4-CuO/CeO2 exhibits exceptional low-temperature catalytic activity, achieving 100% conversion at 130 °C. This enhancement is largely due to the introduction of La, which increases the active Co3+/Co2+ ratio and suppresses hydroxyl group formation on the Co3O4 surface. Cu doping also changes the Co3O4 lattice structure, forming Cu+ as active sites and enhancing the activity at low temperatures. For the first time, steady-state tube furnace and fixed bed were employed to evaluate the catalytic performance of CO in actual combustion atmosphere. Catalyst 0.1La-Co3O4-CuO/CeO2 maintains excellent catalytic efficiency (T100 = 120 °C) under well-ventilated conditions. However, its activity significantly decreases in poorly ventilated environments, due to the competitive adsorption of small molecules at active sites, such as acetone, commonly found in smoke. This study provides valuable insights for designing water-resistant, low-temperature, non-noble metal catalysts and offers a methodology for evaluating CO catalytic activity in real-world environments.

Fully bio-based and intrinsically flame retardant unsaturated polyester cross-linked with isosorbide-based diluents.

Unsaturated polyester resins (UPR) are composed of prepolymers and styrene diluents, while the former are produced by co-polycondensation between diol, unsaturated diacid and saturated diacid. In this work, bio-based UPR prepolymers were synthesized from bio-based oxalic acid, itaconic acid, and ethylene glycol, which were then diluted with bio-based isosorbide methacrylate (MI). Meanwhile, the phenylphosphonate were introduced into the molecular chains of prepolymers to achieve intrinsic flame retardancy of bio-based UPR. The potential of the reactive MI diluents as substitutes of volatile styrene, was also assessed through the volatility test, curing kinetics and gel contents analysis. For UPR materials with styrene diluents, the UPR materials can achieve UL-94 V0 level and the 28% of limiting oxygen index (LOI) with 2.63 wt% of phosphorus contents. By contrast, the UPR materials with MI diluents can reach UL-94 V0 level with only 2.14 wt% of phosphorus contents. As the phosphorus contents were further increased to 2.63 wt%, UPR materials can achieve highest 29%, while the peak of heat release rate (PHRR) and total heat release (THR) were decreased by 68.01% and 48.62%, respectively. The Flame Retardancy Index (FRI) was also used to comprehensively evaluate the flame retardant performance of UPR composites. Compared with neat UPR, the composites with MI diluents and phosphorus containing structures increased from 1.00 to 6.46. The mechanism for improved flame retardancy was analyzed from gaseous and condensed phase. Additionally, the tensile strengths of bio-based UPR materials with styrene and MI diluents were studied. This work provides an effective method to prepared high-performance and fully bio-based UPR materials with improved flame retardant properties and safety application of reactive diluents.

A rational design of functionalized black phosphorus cooperates with piperazine pyrophosphate to significantly suppress the fire hazards of polypropylene.

The flammability of polypropylene (PP) not only has negative effects on human health but also causes environmental pollution. Herein, from the molecular polarity point of view, rationally designed hyperbranched charring foaming agents (HCFA) modified black phosphorus nanosheets by in situ polymerization to solve the fire hazards of PP. Based on the UL-94 test V-0 rating, the conventional flame retardant of piperazine pyrophosphate (PAPP) is substituted partly by the BP@PPC. Surprisingly, compared with 27 wt% of PAPP/PP, composites consisting of only 2 wt% of BP@PPC and 20 wt% PAPP/PP also passes the V-0 rating. The results of the cone calorimeter test confirmed that adding BP@PPC decreases the total heat release (THR) and peak heat release (PHRR) by a large amount, which are decreased by 23.4%, 85.8% respectively compared with PP. Moreover, it is uncommon for the fire growth index of BP@PPC composites to be 66.7% lower than that of PAPP/PP composites. In addition, the incorporation of BP@PPC has almost no impact on the mechanical characteristics of PP composites. This study offers a reference for combining established flame retardants with novel compounds to modify the burning behaviors of PP.

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.

MOF-derived 3D petal-like CoNi-LDH array cooperates with MXene to effectively inhibit fire and toxic smoke hazards of FPUF.

The toxic smoke produced by the combustion of flexible polyurethane foam (FPUF) may not only caused casualties, but also polluted the environment. Here, double metal hydroxide derived from ZIF-67 (MOF-LDH) modified Ti3C2TX (Ti3C2TX@MOF-LDH) was innovatively designed to solve the serious smoke and fire hazards of FPUF. The FPUF nanocomposite containing 6 wt% Ti3C2Tx@MOF-LDH achieved a 16.1% reduction in total smoke production (TSP) along with 22.2% reduction in peak smoke production rate (PSPR), which greatly reduced the hazard of smoke. At the same time, toxic gases, such as carbon monoxide (CO), carbon dioxide (CO2), and aromatic compounds, showed the same reduction pattern. In addition, the heat release of FPUF nanomaterials was also suppressed. In particular, the FPUF/Ti3C2Tx@MOF-LDH 3.0 achieved 110.4% and 76.1% increase in compressive strength and tensile strength, respectively, confirming the effective mechanical enhancement. Therefore, this work provided a new reference for the preparation of high-performance FPUF nanocomposites with low smoke, low fire hazard and excellent mechanical properties.

Construction of bismaleimide resin with enhanced flame retardancy and mechanical properties based on a novel DOPO-derived bismaleimide monomer.

It's known that the application of bismaleimide resins (BMI) is limited due to its brittleness and poor flame retardancy. A novel type of BMI monomer (MADQ) based on the typical phosphorus series flame retardant DOPO is designed to improve the fire safety of BMI. Besides, aliphatic long chain structure is introduced in MADQ, which is supposed to be conducive to reducing the rigidity of the BMI cross-linked network and thus to improve the toughness of BMI. It's seen that with the incorporation of 5.24 wt% MADQ, the peak of heat release rate (PHRR) and total heat release (THR) of resultant BMI/MADQ-5 is reduced by 37.7% and 33.9%, respectively. Meanwhile, with modification of 1.07 wt% MADQ, BMI/MADQ-1 possesses UL-94V-0 rating. The relevant mechanism analysis reveals that the phosphaphenanthrene group in MADQ can exert flame retardancy effect both in condensed and gas phase. Besides, the impact strength of the BMI/MADQ is maximally increased by nearly 90.1%. Furthermore, the BMI/MADQ still maintains high tensile strength and thermal stability, which indicates the modification of MADQ did not deteriorate other properties of BMI. An innovative research idea and research basis for the preparation of intrinsic flame-retardant and toughened BMI is provided in this work.

Functionalizing Ti3C2Tx for enhancing fire resistance and reducing toxic gases of flexible polyurethane foam composites with reinforced mechanical properties.

Flexible polyurethane foam (FPUF) is the most used polyurethane, but the highly flammable characteristic limits its widespread usage. In this work, ZIF-8@Ti3C2Txwas synthesized to reduce the heat and toxic gases of FPUF. Flame-retardant FPUF was characterized by cone calorimeter (Cone), thermogravimetric analysis/fourier-transform infrared spectroscopy (TG-FTIR), tensileand compression tests. Compared with pure FPUF, these results showed that the peak of heat release rate (PHRR), total heat release (THR), CO and HCN of FPUF6 decreased by 46%, 69%, 27% and 43.5%, respectively. Moreover, the tensile and compression strength of FPUF6 demonstrated a 52% and 130% increment, respectively. The superior dual metal catalytical charring-forming effect and physical barrier effect of ZIF-8@Ti3C2Tx were achieved. In summary, a simple and reliable strategy for preparing flame-retardant FPUF with reinforced mechanical and fire safety properties was provided.

Exploration on structural rules of highly efficient flame retardant unsaturated polyester resins.

Owing to the lack of research on structure-activity relationship and interaction mechanism between unsaturated polyester resins (UPR) and flame retardants, it has been a big challenge to prepare high-efficiency flame retardants for UPR in industry. In this research, to explore structural rules of high-efficiency flame retardants, several polymeric flame retardants were synthesized with varied main-chain, side-chain, phosphorus valence states and contents of flame retardant elements. The thermal stabilities of flame retardants and UPR composites were firstly assessed. It has been found the interaction existed between flame retardants and UPR, through transesterification reaction and ß scission pathway in polyester and polystyrene chains. With only 15 wt% of PCH3-S, UPR composites can reach V0 rating in UL-94. The PHRR and THR values can be maximumly decreased by 71.66 % and 77.67 %, with 20 wt% of PB-S. It has been found flame retardants with sulfone group and + 3 valence state of phosphorus in molecular backbone can release SO2 and phosphorus containing compounds in gaseous phase, which diluted fuel fragments and catalyzed H⋅ and HO⋅ radical removal. The mechanism for improved flame retardancy of UPR composites with various polymeric flame retardants were discussed in detail. Some general rules for highly efficient flame retardant UPR can be summarized: First, gaseous phase flame retardant mechanism plays the major role in improvement of flame retardant performance of UPR composites; Second, the combination of + 3 valence state of phosphorus structures, higher phosphorus contents and sulfone groups effectively improves the flame retardant efficiency of flame retardants.

Design of copper salt@graphene nanohybrids to accomplish excellent resilience and superior fire safety for flexible polyurethane foam.

Flexible polyurethane foam (FPUF) is the most commonly used polyurethane, but its highly flammable characteristics makes it ignite easily and release a lot of heat and toxic gases. Here, the effect of different forms of copper salt modified graphene (rGO@CuO, rGO@Cu2O and rGO@CSOH) on improving the fire protection efficiency and mechanical property of FPUF is explored. Hybrid FPUF is characterized by thermogravimetric analysis (TGA), cone calorimeter, thermogravimetric analysis/Fourier transform infrared spectroscopy (TG-IR), tension, compression, and falling ball rebound testing. Compared with pure FPUF, the FPUF/rGO@CSOH show a significant decreasement in reducing the heat release of FPUF, the PHRR and THR are reduced by 36.9% and 29.4%, respectively. While the FPUF/rGO@Cu2O demonstrate excellent smoke and toxic gases suppression in FPUF, the PSPR and TSR are reduced by 24.6% and 51.9%, and the COP and COY are also reduced by 51.9% and 55.3%, respectively. After adding the copper salt hybrid, the buffering performance of FPUF did not change. Fortunately, the tensile and compressive strength increase obviously. The flame retardant and smoke suppression mechanism of hybrid FPUF has also been studied. This article gives a effective strategy for the preparation of FPUF with outstanding mechanical property, flame retardant and smoke suppression properties.

The improvement of fire safety performance of flexible polyurethane foam by Highly-efficient P-N-S elemental hybrid synergistic flame retardant.

Herein, three different phosphorus-containing compounds (methyl phosphoryl dichloride, phenyl phosphoryl dichloride and phenyl dichlorophosphate) were reacted with 2-aminobenzothiazole respectively, and a series of synergistic flame retardants with phosphorus, nitrogen and sulfur elements were synthesized, named MPBT, PPBT and POBT respectively. Then, they were added to prepare flame-retardant flexible polyurethane foam (FPUF). Through the analysis of thermal stability, pyrolysis, heat release and smoke release behavior, the influence of different phosphorus-containing structures on the flame-retardant performance of FPUF was studied, and their flame-retardant mechanism was explored in detail. Among them, MPBT had the highest flame retardant efficiency with the same addition amount (10 wt%). The limiting oxygen index (LOI) value of PU/10.0% MPBT reached 22.5 %, and it successfully passed the vertical burning test. Subsequently, the addition amount of MPBT was increased and the best comprehensive performance of flame-retardant FPUF was explored. The results showed that the LOI value of PU/15.0% MPBT was increased to 23.5%. As for PU/15.0% MPBT, the peak heat release rate (PHRR) was 453 KW/m2, which was reduced by 46.64 %; and the flame retardancy index (FRI) value was also increased to 6.88. At the same time, the mechanical properties of flame-retardant FPUF were studied. The tensile strength of PU/15.0% MPBT reached 170 KPa, and the permanent deformation of FPUF/10% MPBT was only 4 %, showing its excellent resilience. The above results show that this phosphorus-containing element hybrid synergistic flame retardant (MPBT) has a very good application prospect in the field of flame-retardant polymer materials.

High-performance flexible polyurethane foam based on hierarchical BN@MOF-LDH@APTES structure: Enhanced adsorption, mechanical and fire safety properties.

Improving resilience, enhancing fire safety and adsorption properties were the key points for the preparation of high-performance flexible polyurethane foam (FPUF). Here, MOF-derived petal-like Co/Mg-double metal hydroxide (Co/Mg-LDH) and 3-aminopropyltriethoxysilane (APTES) were selected to modify the hydroxylated boron nitride (BNNS-OH) to obtain a hydrophobic BN@MOF-LDH@APTES. Compared with the previous work, BN@MOF-LDH@APTES demonstrated extremely high filler efficiency in reducing the heat release per unit mass (THR/TM) (18.2 % reduction) and smoke production per unit mass (TSP/TM) (19.1% reduction) of FUPF during combustion. In addition, the obtained FPUF nanocomposite exhibited high absorption capacity while achieving remarkable thermal stability and fire safety. Moreover, the FPUF nanocomposite containing 1 wt% BN@MOF-LDH@APTES achieved a 71% increase in compressive strength, indicating excellent resilience. Therefore, this work provided a new material for the preparation of high-resilience FPUF with both flame retardancy and adsorption capacity.

Polydopamine-Bridged Synthesis of Ternary h-BN@PDA@TiO2 as Nanoenhancers for Thermal Conductivity and Flame Retardant of Polyvinyl Alcohol.

In this study, h-BN@PDA@TiO2 hybrid nanoparticles were prepared and used as functional fillers to prepare PVA nanocomposites, and the effects of hybrid particles on PVA thermal conductivity and flame retardant properties were studied. The results showed that hybrid particles could significantly improve the thermal conductivity and flame retardant performance of PVA composites, and effectively inhibit the release of toxic gases such as combustible pyrolysis products and CO, which enhanced the fire safety of PVA composites. When the addition amount of hybrid particles is 5 wt%, the thermal conductivity of PVA composites is 239.1% higher than that of the pure PVA and the corresponding temperature of PVA composites with a mass loss of 5 wt% was 16.2°C higher than that of the pure PVA. This is due to the barrier effect of h-BN and the protective effect of dense carbon layer catalyzed by TiO2.

Construction of graphite oxide modified black phosphorus through covalent linkage: An efficient strategy for smoke toxicity and fire hazard suppression of epoxy resin.

The black phosphorus (BP) can be compounded with other two-dimensional materials with flame retardant effect to achieve better synergistic effect. Herein, the multifunctional BP-RGO nanohybrids was fabricated by solvothermal strategy to improve the dispersion state of BP in epoxy resin (EP) and enhance its fire safety performance, where the reduced graphene oxide (RGO) was attached on the surface of BP via PC and POC bonds. With the incorporation of 2.0 wt% BP-RGO into EP matrix, 54.4 % reduction in total heat release (THR) was achieved along with 55.2 % decrease in peak heat release rate (PHRR) compared with neat EP. As a similar trend, the toxic CO and aromatic compounds were significantly inhibited, and the maximum decrease (28.5 %) in total smoke production (TSP) was achieved, indicating the enhanced fire safety performance of EP nanocomposites. These positive results is attributed to the synergistic effect of physical nano-barrier, free radicals trapping and char formation between BP and RGO components. Meanwhile, the EP/BP-RGO2.0 nanocomposites exhibited satisfying air stability even after being immersed in water for a month. This work enriches the strategies for enhancing the air stability of BP, and confirms its potential for smoke toxicity and fire hazard suppression in polymer nanocomposites.

Natural antioxidant functionalization for fabricating ambient-stable black phosphorus nanosheets toward enhancing flame retardancy and toxic gases suppression of polyurethane.

Herein, as a natural antioxidant, tannin (TA) is firstly used to functionalize black phosphorous (BP) nanosheets to improve the ambient stability and toxic suppression, thus decreasing the fire hazards of polymer materials. Compared to pure BP nanosheets, higher temperature for thermal oxidation decomposition is achieved for TA-BP nanosheets, directly confirming the ambient stability of TA-BP nanosheets. Meanwhile, from high resolution TEM and XPS results, TA-BP nanosheets after being exposed at air for 10 days present well-organized crystal structure and low POx bonds content. Cone calorimeter results illustrate that the incorporation of 2.0 wt% TA-BP nanosheets significantly decreases the peak value of heat release rate (-56.5 %), total heat release (-43.0 %), CO2 concentration (-57.3 %) of TPU composite. Meanwhile, with addition of low to 1.5 wt%, the release of highly-toxic CO gas is significantly suppressed, confirmed by lower peak value (0.52 mg/m3) and decreased total release amount (-55.1 %). The obviously enlarged tensile strength (36.7 MPa) and desirable elongation at break (622 %) are also observed. This strategy not only firstly adopts bio-based antioxidant to impart excellent environmental stability for BP nanosheets, but also promotes the promising potentials of BP nanosheets in the fire safety application of polymer composites.

Hierarchical Structure: An effective Strategy to Enhance the Mechanical Performance and Fire Safety of Unsaturated Polyester Resin.

It is still a big challenge to prepare polymer/layered double hydroxide (LDH) composites with high performance, due to the strong agglomeration tendency of LDHs in the polymeric matrix. In this study, to avoid the agglomerated situation, the orientated LDH nanosheets were vertically grown on a ramie fabric surface, which was then embedded in unsaturated polyester resin (UPR) through the combination method of hand lay-up and vacuum bag. Due to the increased contact area and the restricted interfacial slip in the in-plane direction, the hierarchically LDH-functionalized ramie fabrics (denoted as Textile@LDH) significantly enhanced the mechanical performance of UPR composites. Then, the phosphorus- and silicon-containing coating (PSi) was used for the further improvement of the interfacial adhesion. The tensile strength of UPR/Textile@LDH@PSi composites increased by 121.67%, compared to that of neat UPR. The reinforcement mechanism was studied through analyzing the surface nano/microstructure and wetting properties of the raw and modified textiles, as well as the interfacial interaction between the ramie fabrics and UPR. Meanwhile, the thermal stability, thermal conductivity, and flame-retardant performance of ramie-reinforced UPR composites were improved. Particularly, as-prepared hierarchical Textile@LDH@PSi inhibited the heat release during the combustion process of fabric-reinforced UPR composites, and the peak heat release rate and total heat release values decreased by 36.56 and 47.57%, respectively, compared with the neat UPR/Textile composites. The suppression mechanism was further explored by analyzing the microstructure and chemical compositions of char residues. This research paved a feasible solution to improve the poor dispersion of LDHs in polymers and prepared the high-performance UPR composites with multifunctional applications.

Air-Stable Polyphosphazene-Functionalized Few-Layer Black Phosphorene for Flame Retardancy of Epoxy Resins.

Similar to graphene, few-layer black phosphorus (BP) features thermal stability, mechanical properties, and characteristic dimension effects, which has potential as a new member of nanofillers for fabricating polymer nanocomposites. Herein, a cross-linked polyphosphazene-functionalized BP (BP-PZN) is developed with abundant -NH2 groups via a one-pot polycondensation of 4,4'-diaminodiphenyl ether and hexachlorocyclotriphosphazene on the surface of BP nanosheets. Whereafter, the resulting BP-PZN is incorporated into epoxy resin (EP) to study the flame-retardant property and smoke suppression performance. Cone results show that the introduction of 2 wt% BP-PZN distinctly improves the flame-retardant property of EP, for instance, 59.4% decrease in peak heat release rate and 63.6% reduction in total heat release. The diffusion of pyrolysis products from EP during combustion is obviously suppressed after incorporating the BP-PZN nanosheets. Meanwhile, the EP/BP-PZN nanocomposites exhibit air stability after exposure to ambient conditions for four months. The air stability of the BP nanosheets in EP matrix is assigned to surface wrapping by PZN and embedded in the polymer matrix as dual protection. As a new member of the 2D nanomaterials, BP nanosheets have potential to be a new choice for fabricating high-performance nanocomposites.

Bi2Se3 decorated recyclable liquid-exfoliated MoS2 nanosheets: Towards suppress smoke emission and improve mechanical properties of epoxy resin.

Bimetallic compounds have been proved superior suppression effect on smoke emission during combustion of polymers. In this work, MoS2/Bi2Se3 (MB) hybrids were prepared by a facile wet chemical method and showed superior performance on smoke suppression of EP matrix during combustion. N-vinyl pyrrolidone (NVP) was employed to exfoliate molybdenum disulfide (MoS2) nanosheets in a recyclable method, which showed high efficiency and was recyclable. Exfoliated MoS2 exhibited large surface area and used as carriers to synthesize MB hybrids. Considering the catalytic effect of bismuth and molybdenum, the hybrids had a great influence on the smoke emission behaviors of EP composites. The smoke production was obviously suppressed during the flaming combustion (more than 22% and 23% decrease obtained from cone calorimeter and steady state tube furnace, respectively) or smolder processes (more than 23% decrease obtained from smoke chamber) at only 1 wt% content of MB hybrids. What's more, due to superior dispersion state, the addition of MB hybrids also enhanced the mechanical properties of EP matrix, including wear resistance and tensile property. This work provided a safe and green exfoliation method of MoS2 to prepare polymers/MoS2 composites and also constructed a novel binary hybrids for enhancing combination performances of polymers.

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.

Construction of Hierarchical Natural Fabric Surface Structure Based on Two-Dimensional Boron Nitride Nanosheets and Its Application for Preparing Biobased Toughened Unsaturated Polyester Resin Composites.

It has been a big challenge to prepare the unsaturated polyester resin (UPR) composites with good fire safety, interfacial quality, and impact strength in an environmentally friendly way. In this study, to improve interfacial performance of fabric-reinforced UPR composites, nontoxic two-dimensional hexagonal boron nitride (h-BN) nanosheets were assembled on the surface of ramie fabrics, where sodium alginate acts as a green dispersant to disperse h-BN sheets during the process. Then, the biobased phosphorus-containing toughening agent (PCTA) was synthesized to simultaneously improve the impact strength and fire safety of the composite. With application of h-BN nanosheets-assembled fabric (AF) and 20 wt % of PCTA, the AF/UPR@PCTA20 composite presented the maximum 41.2% decrease in the value of peak heat release rate and a maximum 17.8% decrease in the value of total heat release, which also reached V-0 rating in the vertical burning test. Meanwhile, the AF/UPR@PCTA20 composite showed an obvious increase in limiting oxygen index, from 24.0 to 29.5% compared with RF/UPR. The flame retardant mechanism was investigated from gas phase and condensed phase. Furthermore, compared to neat RF/UPR composite, the AF/UPR@PCTA20 composite showed a significant 68.8% improvement in impact strength, implying an extreme toughening effect of PCTA on UPR composites. The research provides a viable green method for the development of environmentally friendly UPR composites in the future.

Rapid Synthesis of Oxygen-Rich Covalent C2N (CNO) Nanosheets by Sacrifice of HKUST-1: Advanced Metal-Free Nanofillers for Polymers.

A covalent oxygen-rich C2N (CNO) network derived from metal-organic framework (HKUST-1) was innovatively synthesized by a rapid and green microwave irradiation method. This method can produce CNO multilayers efficiently, which paves a way for practical application of the nanosheets. Structural characterization and synthesis processes of CNO nanosheets were investigated to further understand the key role of HKUST-1. The as-prepared CNO has a layered feature, which theoretically favors to improve flame retardancy and mechanical performance of polymers. Desirable results were obtained as expected: the fire safety, antitensile, and impact resistance of polylactic acid (PLA) were prominently enhanced after adding CNO nanosheets, which can be attributed to the excellent dispersion and compatibility. PLA/CNO nanocomposite was self-distinguished at 2 wt % content of CNO, whereas the tensile strength was increased more than 36% compared with that of pure PLA, as well as the impact strength. This work broadens the application fields of CNO and endows it a possibility of actual application.