Preparation of Metal–Organic Frameworks and Their Application as Flame Retardants for Polystyrene

In this work, iron-based and cobalt-based metal–organic frameworks (MOFs) were successfully synthesized by a facile solvothermal method. The obtained MOFs were added into polystyrene (PS) as flame retardants for the first time. The results of thermal gravimetric analysis and cone calorimetry indicated the addition of MOFs significantly enhanced the thermostability and flame retardancy of the PS composites. Compared with that of neat PS, greater than 14% and 28% decreases in the peak heat release rate were observed for PS/Fe-MOF and PS/Co-MOF, respectively, suggesting a flame retardant effect of MOFs. Based on thermogravimetric analysis–​infrared spectrometry results and the analysis of combustion residues, the possible mechanism of the enhanced thermostability and flame retardancy of the PS composites was proposed as the combination of thermal barrier effect and catalytic effect of MOFs, which would allow promising application in the development of fire safety polymer materials

Synthesis of Phosphorus–Sulfur-Containing Polyols for Intrinsic Flame Retardant Flexible Polyurethane Foams with Enhanced Mechanical Properties

The development and preparation of intrinsic flexible polyurethane foam (FPUF) with low-load flame retardancy and high mechanical properties are challenging. Herein, a reactive flame retardant, poly(ethylene methylphosphonothioate) (PEMPT), was synthesized by the polycondensation of methylphosphonothioic dichloride and ethylene glycol. Subsequently, PEMPT was chemically bound to the FPUF chain. When the PEMPT content was 2.5 wt % polyols, the FPUFs exhibited self-extinguishing properties in less than 3 s after removing the igniter and passed the TB 117-2000 vertical burning test. Furthermore, the flame retardant FPUF with only 10 wt % PEMPT loading (FPUF10) showed an oxygen index value of 23.5%. Also, its peak heat release and total heat release rates were reduced by 25.8 and 24.0%, respectively. Concurrently, the incorporation of PEMPT improved the compressive and reversible properties of the foams. These results indicate that PEMPT is a promising flame retardant to endow FPUF with excellent flame retardancy and mechanical properties

Facile Synthesis of a Highly Efficient, Halogen-Free, and Intumescent Flame Retardant for Epoxy Resins: Thermal Properties, Combustion Behaviors, and Flame-Retardant Mechanisms

A novel branched poly­(phosphonamidate-phosphonate) (BPPAPO) oligomer was synthesized from the polycondensation of phenylphosphonic dichloride and tri­hydroxy­methyl­phosphine oxide followed by end-capping with aniline in a one-pot synthesis. BPPAPO exhibited excellent flame-retardant efficiency in epoxy resins (EP). With only 5.0 wt % loading, the EP composite reached UL-94 V-0 rating with a limiting oxygen index (LOI) value of 35.5%. BPPAPO catalyzed the early degradation of EP and promoted the formation of more char residue. Glass transition temperatures were partially lowered. When 7.5 wt % BPPAPO was incorporated, the peak heat release rate and total heat release were decreased by 66.2% and 37.3%, respectively, with a delayed ignition and the formation of a highly intumescent char residue. Combination of gas-phase and condensed-phase flame-retardant mechanisms was verified

An Individualized Core–Shell Architecture Derived from Covalent Triazine Frameworks: Toward Enhancing the Flame Retardancy, Smoke Release Suppression, and Toughness of Bismaleimide Resin

Although the bismaleimide (BMI) resin is a star material in industries, its further applications have been plagued by the serious brittleness and fire hazard for a long time. Hence, a core–shell architecture (MPPM) derived from covalent triazine frameworks was designed to overcome the shortcomings. Excitedly, compared to those of neat BMI, the resultant BMI-2 with only 1 wt % MPPM was capable of achieving 23.4%, 48.6%, and 39.7% decrements on the peak of heat release rate, total heat release, and total smoke release, respectively, exhibiting unprecedented flame-retardant effects under a low addition of flame retardants. Besides, the impact strength of BMI-2 was enhanced by 62.7% with a close tensile strength and storage modulus to those of neat BMI, implying that the toughness of BMI was improved successfully without sacrificing its rigidity. This work provided a unique clue for designing efficient multifunctional modifiers and promoted the development of advanced BMI

Construction of Bimetallic ZIF-Derived Co–Ni LDHs on the Surfaces of GO or CNTs with a Recyclable Method: Toward Reduced Toxicity of Gaseous Thermal Decomposition Products of Unsaturated Polyester Resin

This work proposed an idea of recycling in preparing Co–Ni layered double hydroxide (LDH)-derived flame retardants. A novel and feasible method was developed to synthesize CO–Ni LDH-decorated graphene oxide (GO) and carbon nanotubes (CNTs), by sacrificing bimetal zeolitic imidazolate frameworks (ZIFs). Organic ligands that departed from ZIFs were recyclable and can be reused to synthesize ZIFs. ZIFs, as transitional objects, in situ synthesized on the surfaces of GO or CNTs directly suppressed the re-stacking of the carbides and facilitated the preparation of GO@LDHs and CNTs@LDHs. As-prepared hybrids catalytically reduced toxic CO yield during the thermal decomposition of unsaturated polyester resin (UPR). What is more, the release behaviors of aromatic compounds were also suppressed during the pyrolysis process of UPR composites. The addition of GO@LDHs and CNTs@LDHs obviously inhibited the heat release and smoke emission behaviors of the UPR matrix during combustion. Mechanical properties of the UPR matrix also improved by inclusion of the carbides derivatives. This work paved a feasible method to prepare well-dispersed carbides@Co–Ni LDH nanocomposites with a more environmentally friendly method

Innovative Design and Preparation of Hierarchical BP–OH@HAP Structure: Study on Flame Retardancy and Mechanical Characteristics of UPR Nanocomposites

The flammability and brittleness of unsaturated polyester resin (UPR) were two serious problems that limited its application in high-precision fields. Here, the rod-shaped hydroxyapatite (HAP) was anchored on the surface of hydroxylated black phosphorus nanosheets (BP–OH) through a hydrothermal reaction to obtain a highly stable black phosphorus-based nano flame retardant (BP–OH@HAP). Owing to the exposure of many hydroxyl groups, BP–OH@HAP was well dispersed in the UPR matrix, and UPR nanocomposites with 0.5 wt % BP–OH@HAP realized a 71% increase in impact strength. The presence of BP–OH@HAP also greatly inhibited the combustion of UPR nanocomposites. In detail, the UPR composites with 2 wt % BP–OH@HAP achieved a 47.0% decrease in peak heat release rate (PHRR) along with 23.1% reductions in total heat release (THR), revealing the excellent ability of BP–OH@HAP to inhibit polymer combustion. In addition, UPR/BP–OH@HAP 2.0 achieved a 46 s increase in the time to PHRR (tPHRR) and a 62% reduction in the fire growth index (FGI), indicating that the fire spread of UPR/BP–OH@HAP 2.0 was significantly suppressed. Therefore, this work obtained the UPR/BP–OH@HAP nanocomposite with high fire safety through the innovation of inorganic nanotechnology, which provided new research ideas for improving the toughness and flame-retardant properties of UPR-based nanocomposites

Boron-Based Polyphosphazene-Functionalized Mxene Nanosheets for Polypropylene Composites with Improved Mechanical Properties and Flame Retardancy Applications

Developing high-performance resins with exceptional thermal oxidation stability, flame retardancy, smoke release suppression, and mechanical properties is an important industrial challenge. However, current flame-retardant design strategies often compromise other composite material properties. Especially when using polyolefin, unsaturated polyester, and other noncharred materials, it is usually necessary to add large amounts of flame-retardant fillers. In this study, a nanosynergist (Ti3C2Tx@PPD) for functionalizing Ti3C2Tx nanosheets with boron-based polyphosphazene was designed and adopted for a piperazine pyrophosphate/polypropylene (PAPP/PP) system as an application example. By controlling the chemical environment of cyclotriphosphazene, the condensed phase characteristics of polyphosphazene were preserved, but also an atypical vapor phase flame-retardant mechanism was activated. The combination of P/N/B elements and Ti3C2Tx exhibited excellent catalytic char-forming performance compared to others in the literature. Only 2% of incorporated Ti3C2Tx@PPD reduced the total heat released from the composite by 66.3%, the total smoke released by 71.8%, and the fire growth index by 49.4%. The incorporation of Ti3C2Tx@PPD inhibited deterioration of the mechanical properties of the composite. In addition, the pyrolysis path of Ti3C2Tx was revealed under a special environment. This study lays the foundation for the functional design of Ti3C2Tx nanomaterials that can be used in various applications that require high-performance resins

Magnetic Fe₃O₄ Nanoparticle/ZIF‑8 Composites for Contaminant Removal from Water and Enhanced Flame Retardancy of Flexible Polyurethane Foams

In order to separate heavy-metal ions from contaminated wastewater and further realize the reutilization of waste adsorbent, magnetic composites with flowerlike structure were successfully synthesized. After the absorption of Cu2+ ions, hybrids can be used as effective coatings to enhance the fire safety of flexible polyurethane foam (FPUF) through a dip-coating method. As-fabricated metal–organic framework (MOF)-based composites exhibited a core–shell and flowerlike structure with high thermal stability. The maximum adsorption capacity for Cu2+ could reach 292.13 mg·g–1, calculated from the Langmuir isotherm model. In order to reutilize the adsorbed Cu2+ ions, the CuO-loaded MOF-derived Fe3O4@ZnO@CuO (MO) was obtained with a simple heat treatment. The effectivity of MO as a fire-safety coating for inhibiting the release of heat and toxic gases of FPUF was satisfactory. The application of this MOF-based composite will provide useful insights into the design of bifunctional materials for efficient wastewater remediation and fire-safety coatings