A high-temperature stable pyrophosphoric acid piperazine / MOF composite material and a preparation method thereof

Abstract

The application relates to the field of flame-retardant materials, and provides a high-temperature stable pyrophosphoric acid piperazine / MOF composite material and a preparation method thereof, aiming to improve the flame-retardant performance and high-temperature stability of the material. The composite material is composed of a columnar porous Zr-MOF host material and Cr-MOF coated pyrophosphoric acid piperazine guest particles with a core-shell structure. The Zr-MOF is prepared through an ice template method and has columnar pores with a size of 1.5-3.5 microns; the Cr-MOF coated particle size is 300-500 nm, and the mass ratio is 3:1-8:1. The preparation method comprises synthesis of Cr-MOF coated particles, Zr-MOF activation treatment and loading combination of the two, and involves process steps such as ultrasonic dispersion, solvent immersion, centrifugal separation and vacuum drying. The material has excellent structural stability and thermal stability and is suitable for flame-retardant application in a high-temperature environment.

Description

Technical Field

[0001] This invention relates to the field of flame retardant materials, specifically to a high-temperature stable piperazine pyrophosphate / MOF composite material and its preparation method. Background Technology

[0002] In modern industrial systems where high-temperature working environments are increasingly common, especially in aerospace, rail transportation, power cable sheathing materials, and thermal protection systems for high-end electronic devices, more stringent requirements are placed on the flame-retardant and thermal stability properties of materials. Taking power engineering as an example, cable sheaths in power distribution systems are exposed to high temperatures, electric arcs, and even fire sources for extended periods. If materials cannot maintain structural stability and possess effective flame-retardant capabilities at high temperatures, equipment failure or safety accidents are highly likely. In the aerospace field, the thermal insulation layers and cabin interiors of aircraft must also maintain their integrity and functionality under high-temperature impact or short-term flame exposure. Therefore, the core performance requirements for materials in these applications are concentrated in two aspects: first, excellent flame-retardant properties, meaning the material should effectively delay flame spread and prevent heat conduction in heated or combustion environments; second, excellent high-temperature stability, meaning it should maintain structural integrity and not undergo thermal degradation under continuous high temperatures or transient high temperatures. These properties not only affect the stable operation of the equipment itself but also directly impact personnel safety and environmental protection. Therefore, developing materials that combine high flame retardancy and high thermal stability not only helps to significantly improve the service capability of materials in extreme environments, but also expands their application boundaries in high-end manufacturing and safety engineering, which has important practical significance and application prospects.

[0003] Despite recent advancements in the synthesis and functional design of flame-retardant and high-temperature structural materials, a common challenge remains: simultaneously achieving both flame retardancy and high-temperature stability. For instance, Chinese patent CN115448893A discloses a method for preparing a piperazine pyrophosphate flame retardant. While it demonstrates some initial flame suppression, it is prone to structural decomposition at high temperatures, resulting in insufficient overall thermal stability and failing to meet the dual requirements of heat resistance and flame retardancy in various scenarios. The root cause of this problem lies in the fact that most existing flame-retardant materials rely on introducing flame retardants, such as halogenated, phosphorus-, or nitrogen-containing organic small molecules or polymer modifiers. Although these components can release flame-suppressing factors in the early stages of a flame, their own thermal stability is often low, easily volatilizing, decomposing, or migrating at high temperatures, thus weakening overall thermal stability. Furthermore, some inorganic fillers with high thermal stability often suffer from poor dispersibility or insufficient interfacial compatibility, hindering effective synergistic flame-retardant function. In addition, traditional material design often focuses on optimizing single functions, lacking systematic structural control strategies, making it difficult to achieve a synergistic improvement in flame-retardant efficiency and high-temperature stability. Therefore, it is urgent to explore new functional units and composite systems with multi-scale structural control capabilities in order to achieve performance breakthroughs in materials under extreme thermal environments and promote the development of high-performance thermal protection materials. Summary of the Invention

[0004] (1) Technical problems to be solved

[0005] The purpose of this invention is to provide a high-temperature stable piperazine pyrophosphate / MOF composite material and its preparation method, thereby solving the problems of insufficient flame retardant properties and high-temperature stability of current materials.

[0006] (2) Technical solution

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] A high-temperature stable piperazine pyrophosphate / MOF composite material, the composite material comprising a columnar porous Zr-MOF host material and Cr-MOF-coated piperazine pyrophosphate guest particles with a core-shell structure loaded on the pore surface of the Zr-MOF host material;

[0009] The porous Zr-MOF host material was prepared by the ice template method and the columnar pore width was 1.5~3.5μm;

[0010] The average size of the Cr-MOF-coated piperazine pyrophosphate guest particles is 300~500 nm, and the mass ratio of Cr-MOF to piperazine pyrophosphate is 3:1~8:1.

[0011] Further, the preparation method of the piperazine pyrophosphate / MOF composite material is as follows: 5-15 parts by weight of Cr-MOF-coated piperazine pyrophosphate particles are dispersed in 30-60 parts of ethanol, and 0.1-0.5 parts of polyvinylpyrrolidone surfactant are added. The mixture is then ultrasonically treated at 100-300 W for 5-15 min to form a uniform dispersion. The activated Zr-MOF host material is added to the dispersion and impregnated at 20-60°C and 200-500 rpm for 12-24 h. Optionally, ultrasonic treatment at 100-300 W for 10-30 min is performed. After sedimentation for 1-3 h, the mixture is centrifuged at 3000-5000 rpm for 5-15 min to retain the solid product. The supernatant is removed, and the product is washed 2-3 times with 3-5 times its weight of ethanol to remove unloaded particles. Finally, the washed product is placed under a vacuum of 0.05-0.1 ppm. The piperazine pyrophosphate / MOF composite material was obtained by drying at MPa and temperature of 60-80°C for 8-12 h.

[0012] Furthermore, the preparation method of the activated Zr-MOF host material is as follows: by weight, 20-40 parts of porous Zr-MOF host material are immersed in 3-5 times their weight of ethanol, ultrasonically cleaned for 10-30 min, and centrifuged to remove residual solvent. Then, the material is activated for 12-24 h under a vacuum of 0.05-0.1 MPa and a temperature of 100-120°C to obtain the activated Zr-MOF host material.

[0013] Further, the preparation method of the porous Zr-MOF host material is as follows: 1.5-2.5 parts of trimesic acid and 8.5-10.5 parts of zirconium oxychloride octahydrate are dissolved in a mixed solvent of 50-150 parts of N,N-dimethylformamide and formic acid in a volume ratio of 1:1. After forming a homogeneous solution, the solution is transferred to a closed reaction vessel and heated to 80-100°C with a stirring rate of 300-600 rpm for 12-36 h. After the reaction is completed, the solution is naturally cooled to 25-30°C. The resulting suspension is centrifuged at 3000-5000 rpm for 5-15 min. The supernatant is discarded, and the solid precipitate is collected. The precipitate is washed alternately with N,N-dimethylformamide and ethanol 3-5 times to remove unreacted monomers and solvent residues. The amount of solvent used for each wash is 3-5 times the weight of the solid precipitate. After washing, the solid is dispersed in deionized water to form 5-10... The dispersion of wt% was freeze-dried to obtain a porous Zr-MOF host material with a columnar pore structure.

[0014] Furthermore, the specific process of freeze drying is as follows: the dispersion is pre-frozen at -50~-30°C for 4~8 h, and then transferred to a freeze dryer for freeze drying at a vacuum of 0.01~0.05 mbar and a condenser temperature of -80~-60°C for 24~48 h.

[0015] This invention employs a composite structure design using porous Zr-MOF host material and Cr-MOF-coated piperazine pyrophosphate guest particles, primarily to enhance the flame retardant properties and thermal stability of the material under high-temperature conditions. By introducing core-shell structured Cr-MOF-coated piperazine pyrophosphate particles into Zr-MOF with a columnar pore structure, the excellent thermal stability and highly ordered pore structure of Zr-MOF are utilized to effectively load and fix the functional particles, preventing their migration or decomposition under high-temperature conditions. Furthermore, the Cr-MOF coating layer imparts stronger interfacial stability and thermal protection to the piperazine pyrophosphate, thereby improving the thermal response consistency and flame retardant efficiency of the entire system. The Cr-MOF shell structure forms a protective barrier at the microscale, effectively delaying the thermal decomposition process of piperazine pyrophosphate while coordinating its slow-release behavior under high-temperature conditions, thus enhancing the persistence of flame retardant activity. The Zr-MOF host material, with its highly porous structure, provides a high specific surface area and a good dispersion platform, enabling Cr-MOF coated particles to be uniformly distributed and stably embedded in the overall framework. This enhances the structural integrity and synergistic thermal shielding effect of the composite material under high-temperature environments. During the preparation process, multiple steps, including ethanol dispersion, polyvinylpyrrolidone-assisted dispersion, ultrasonic homogenization, low-temperature freeze-drying, and activation under vacuum conditions, ensured stable bonding and interfacial compatibility between functional components, forming a structurally stable and uniformly distributed composite material system. This composite structure construction approach, through the synergistic effect between materials, achieves a thermal protection capability far exceeding that of single materials in macroscopic performance. Especially when facing variable thermal fields and high-temperature combustion environments, it exhibits significantly superior comprehensive performance compared to conventional flame-retardant materials, demonstrating the systematic and forward-looking nature of the material design in this invention.

[0016] Furthermore, the preparation method of the Cr-MOF-coated piperazine pyrophosphate guest particles includes the following steps: dispersing piperazine pyrophosphate in deionized water and ultrasonically treating it to form a suspension; sequentially adding chromium nitrate nonahydrate, terephthalic acid, and hydrochloric acid to the suspension to form a precursor mixture; and then subjecting the mixture to a hydrothermal reaction to allow the Cr to form a Cr-MOF-coated piperazine pyrophosphate guest particle. 3+ The Cr-MOF is generated by coordination with terephthalic acid and simultaneously coated on the surface of piperazine pyrophosphate particles to form a core-shell structure. After the reaction is completed, the Cr-MOF-coated piperazine pyrophosphate is obtained by centrifugation, washing and drying.

[0017] Furthermore, the hydrothermal reaction temperature is 180~200°C, and the reaction time is 12~24h;

[0018] Furthermore, the weight ratio of each component in the precursor mixture is as follows: piperazine pyrophosphate 0.3~0.8 parts, deionized water 20~30 parts, chromium nitrate nonahydrate 1.0~1.5 parts, terephthalic acid 0.5~1 parts, and 10wt.% hydrochloric acid 0.01~0.1 parts.

[0019] Furthermore, the centrifugal separation process involves centrifuging at 5000-8000 rpm for 5-10 minutes, and the washing process involves repeated washing with deionized water 3-5 times until the pH of the washing solution reaches 6.5-7.5.

[0020] Furthermore, the drying process is a vacuum drying process, with the drying temperature controlled at 60~80°C and the drying time at 8~12 hours.

[0021] This invention employs a Cr-MOF-coated piperazine pyrophosphate guest particle design primarily to enhance the flame retardant properties and thermal stability of materials under high-temperature environments. The technical solution involves dispersing piperazine pyrophosphate in deionized water to form an initial suspension system, then introducing chromium nitrate nonahydrate, terephthalic acid, and hydrochloric acid to form a precursor mixture. Hydrothermal reaction conditions are then used to... 3+ A Cr-MOF structure was formed by coordination with terephthalic acid and simultaneously coated onto the surface of piperazine pyrophosphate particles, constructing a stable core-shell structure at the microscale. This core-shell structure significantly improved the dispersion stability and interfacial thermal stability of piperazine pyrophosphate. The Cr-MOF shell not only acted as a physical barrier to inhibit the rapid volatilization or structural disintegration of piperazine pyrophosphate under high-temperature conditions, but also slowed the thermal response process of the overall structure through its thermal resistance characteristics, effectively extending the functional continuity of the flame-retardant component under thermal action. Furthermore, the structural stability and interfacial bonding ability of Cr-MOF enhanced the uniformity of particle distribution and loading efficiency in subsequent composites, providing a good structural foundation for further composites with Zr-MOF host materials. During the coating process, by controlling the reaction temperature, reaction time, and raw material ratio, it was ensured that Cr-MOF could grow stably on the surface of piperazine pyrophosphate without particle agglomeration. Subsequent centrifugation and multiple deionized water washing effectively removed residual reactants and byproducts, improving the purity and dispersibility of the composite particles. The vacuum drying process further ensured the integrity of the material structure and its adaptability to heat treatment. The Cr-MOF-coated piperazine pyrophosphate constructed in this way not only integrates the thermal protection properties of the two materials, but also achieves a synergistic improvement in flame retardant performance and high-temperature stability through structural synergy. It overcomes the problems of easy decomposition and poor stability of single flame retardants under thermal conditions, demonstrating the effectiveness and advancement of this invention in the design of multifunctional composite materials.

[0022] (3) Beneficial technical effects

[0023] 1. This invention significantly improves flame retardancy and thermal stability at high temperatures through the synergistic construction of Zr-MOF and Cr-MOF-coated piperazine pyrophosphate, achieving structural stability and uniform distribution, solving the problem of easy decomposition of traditional flame retardants, and is suitable for the field of high-temperature protective materials, with broad application prospects.

[0024] 2. This invention achieves a synergistic improvement in flame retardancy and thermal stability by coating piperazine pyrophosphate with Cr-MOF to form a core-shell structure. It exhibits strong structural stability and good dispersibility, which is significantly superior to traditional single flame retardant systems. It is suitable for high-temperature safety protection and has broad application prospects. Attached Figure Description

[0025] Figure 1 This is a morphology diagram of the porous Zr-MOF host material prepared in Example 1 of the present invention.

[0026] Figure 2 This is a morphology diagram of the piperazine pyrophosphate / MOF composite material prepared in Example 1 of the present invention. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings.

[0028] Example 1

[0029] A high-temperature stable piperazine pyrophosphate / MOF composite material, the composite material comprising a columnar porous Zr-MOF host material and Cr-MOF-coated piperazine pyrophosphate guest particles with a core-shell structure loaded on the pore surface of the Zr-MOF host material;

[0030] The porous Zr-MOF host material was prepared by the ice template method and the columnar pore width was 1.5 μm; the average size of the Cr-MOF-coated piperazine pyrophosphate guest particles was 300 nm, and the mass ratio of Cr-MOF to piperazine pyrophosphate was 3:1.

[0031] The preparation method of the piperazine pyrophosphate / MOF composite material in this embodiment is as follows: 5 parts by weight of Cr-MOF-coated piperazine pyrophosphate particles are dispersed in 30 parts of ethanol and 0.1 parts of polyvinylpyrrolidone surfactant are added. The mixture is ultrasonically treated at 100 W for 5 min to form a uniform dispersion. The activated Zr-MOF host material is added to the dispersion and impregnated at 20°C and 200 rpm for 12 h. Optionally, it is ultrasonically treated at 100 W for 10 min. After settling for 1 h, the solid product is centrifuged at 3000 rpm for 5 min to remove the supernatant. The supernatant is removed and the product is washed twice with 3 times its weight of ethanol to remove unloaded particles. Finally, the washed product is dried under a vacuum of 0.05 MPa and a temperature of 60°C for 8 h to obtain the piperazine pyrophosphate / MOF composite material.

[0032] The preparation method of the activated Zr-MOF host material in this embodiment is as follows: 20 parts by weight of porous Zr-MOF host material are immersed in 3 times the weight of ethanol, ultrasonically cleaned for 10 min, and centrifuged to remove residual solvent. Then, the material is activated for 12 h under a vacuum of 0.05 MPa and a temperature of 100°C to obtain the activated Zr-MOF host material.

[0033] The preparation method of the porous Zr-MOF host material in this embodiment is as follows: 1.5 parts of trimesic acid and 8.5 parts of zirconium oxychloride octahydrate are dissolved in 50 parts of a mixed solvent of N,N-dimethylformamide and formic acid in a volume ratio of 1:1 to form a homogeneous solution. The solution is then transferred to a closed reaction vessel, heated to 80°C and maintained at a stirring rate of 300 rpm for 12 h. After the reaction is completed, the solution is naturally cooled to 25°C. The resulting suspension is centrifuged at 3000 rpm for 5 min. The supernatant is discarded and the solid precipitate is collected. The solid precipitate is washed three times alternately with N,N-dimethylformamide and ethanol to remove unreacted monomers and solvent residues. The amount of solvent used for each wash is three times the weight of the solid precipitate. After washing, the solid is dispersed in deionized water to form a 5 wt% dispersion, which is then freeze-dried to obtain a porous Zr-MOF host material with a columnar pore structure.

[0034] The specific process of freeze-drying in this embodiment is as follows: the dispersion is pre-frozen at -50°C for 4 h, and then transferred to a freeze dryer for freeze-drying at a vacuum of 0.01 mbar and a condenser temperature of -80°C for 24 h.

[0035] The preparation method of Cr-MOF-coated piperazine pyrophosphate guest particles in this embodiment includes the following steps: dispersing piperazine pyrophosphate in deionized water and ultrasonically treating it to form a suspension; sequentially adding chromium nitrate nonahydrate, terephthalic acid, and hydrochloric acid to the suspension to form a precursor mixture; and then subjecting the mixture to a hydrothermal reaction to allow Cr to form a Cr-MOF-coated piperazine pyrophosphate guest particle. 3+ The Cr-MOF is generated by coordination with terephthalic acid and simultaneously coated on the surface of piperazine pyrophosphate particles to form a core-shell structure. After the reaction is completed, the Cr-MOF-coated piperazine pyrophosphate is obtained by centrifugation, washing and drying.

[0036] In this embodiment, the hydrothermal reaction temperature is 180°C and the reaction time is 12 hours.

[0037] The weight ratio of each component in the precursor mixture in this embodiment is as follows: 0.3 parts piperazine pyrophosphate, 20 parts deionized water, 1.0 part chromium nitrate nonahydrate, 0.5 parts terephthalic acid, and 0.01 parts 10 wt.% hydrochloric acid.

[0038] In this embodiment, centrifugation was performed at 5000 rpm for 5 minutes, and the washing process involved repeated washing with deionized water 3 times until the pH of the washing solution reached 6.5.

[0039] In this embodiment, the drying process is a vacuum drying process, with the drying temperature controlled at 60°C and the drying time at 8 hours.

[0040] Depend on Figure 1 As can be seen, the Zr-MOF host material prepared in Example 1 of this invention exhibits a regular columnar morphology with obvious pore structure on the surface, proving that it has an ideal porous columnar morphology, which is beneficial for the subsequent loading and fixation of guest molecules. Figure 2 The morphological characteristics of the composite of piperazine pyrophosphate and MOF are further shown. In the figure, it can be observed that particles of appropriate size are uniformly distributed on the pore surface of columnar Zr-MOF. These particles exhibit a typical core-shell structure. Combined with energy dispersive spectroscopy or elemental distribution information, it can be determined that the structure is Cr-MOF-coated piperazine pyrophosphate guest particles. This proves that the composite material not only maintains the columnar porous structure of Zr-MOF, but also achieves a stable loading form of piperazine pyrophosphate on the pore surface by Cr-MOF. This structural feature provides a structural basis for the slow release of flame retardants and provides morphological support for the subsequent synergistic flame retardant performance of the material. It verifies the rationality of the structural design and the effectiveness of the functional realization of the present invention.

[0041] Example 2

[0042] A high-temperature stable piperazine pyrophosphate / MOF composite material, the composite material comprising a columnar porous Zr-MOF host material and Cr-MOF-coated piperazine pyrophosphate guest particles with a core-shell structure loaded on the pore surface of the Zr-MOF host material;

[0043] The porous Zr-MOF host material was prepared by the ice template method and the columnar pore width was 2.1 μm; the average size of the Cr-MOF-coated piperazine pyrophosphate guest particles was 360 nm, and the mass ratio of Cr-MOF to piperazine pyrophosphate was 4.5:1.

[0044] The preparation method of the piperazine pyrophosphate / MOF composite material in this embodiment is as follows: 8 parts by weight of Cr-MOF-coated piperazine pyrophosphate particles were dispersed in 39 parts of ethanol and 0.2 parts of polyvinylpyrrolidone surfactant were added. The mixture was ultrasonically treated at 160 W for 8 min to form a uniform dispersion. The activated Zr-MOF host material was added to the dispersion and impregnated at 32°C and 290 rpm for 16 h. Optionally, the mixture was ultrasonically treated at 160 W for 16 min. After settling for 2 h, the solid product was centrifuged at 3600 rpm for 8 min to remove the supernatant. The supernatant was removed and the product was washed twice with 4 times its weight of ethanol to remove unloaded particles. Finally, the washed product was dried under a vacuum of 0.07 MPa and a temperature of 66°C for 9 h to obtain the piperazine pyrophosphate / MOF composite material.

[0045] The preparation method of the activated Zr-MOF host material in this embodiment is as follows: 26 parts by weight of porous Zr-MOF host material are immersed in 4 times the weight of ethanol, ultrasonically cleaned for 16 min, and centrifuged to remove residual solvent. Then, the material is activated for 16 h under a vacuum of 0.07 MPa and a temperature of 106°C to obtain the activated Zr-MOF host material.

[0046] The preparation method of the porous Zr-MOF host material in this embodiment is as follows: 1.8 parts of trimesic acid and 9.1 parts of zirconium oxychloride octahydrate are dissolved in a mixed solvent of 80 parts of N,N-dimethylformamide and formic acid in a volume ratio of 1:1. After forming a homogeneous solution, the solution is transferred to a closed reaction vessel, heated to 86°C and maintained at a stirring rate of 390 rpm for 19 h. After the reaction is completed, the solution is naturally cooled to 27°C. The resulting suspension is centrifuged at 3600 rpm for 8 min. The supernatant is discarded and the solid precipitate is collected. The solid precipitate is washed four times alternately with N,N-dimethylformamide and ethanol to remove unreacted monomers and solvent residues. The amount of solvent used for each wash is four times the weight of the solid precipitate. After washing, the solid is dispersed in deionized water to form a 7 wt% dispersion, which is then freeze-dried to obtain a porous Zr-MOF host material with a columnar pore structure.

[0047] The specific process of freeze-drying in this embodiment is as follows: the dispersion is pre-frozen at -44°C for 5 h, and then transferred to a freeze dryer for freeze-drying at a vacuum of 0.02 mbar and a condenser temperature of -74°C for 31 h.

[0048] The preparation method of Cr-MOF-coated piperazine pyrophosphate guest particles in this embodiment includes the following steps: dispersing piperazine pyrophosphate in deionized water and ultrasonically treating it to form a suspension; sequentially adding chromium nitrate nonahydrate, terephthalic acid, and hydrochloric acid to the suspension to form a precursor mixture; and then subjecting the mixture to a hydrothermal reaction to allow Cr to form a Cr-MOF-coated piperazine pyrophosphate guest particle. 3+ The Cr-MOF is generated by coordination with terephthalic acid and simultaneously coated on the surface of piperazine pyrophosphate particles to form a core-shell structure. After the reaction is completed, the Cr-MOF-coated piperazine pyrophosphate is obtained by centrifugation, washing and drying.

[0049] In this embodiment, the hydrothermal reaction temperature is 186°C and the reaction time is 16 hours.

[0050] The weight ratio of each component in the precursor mixture in this embodiment is as follows: 0.5 parts piperazine pyrophosphate, 23 parts deionized water, 1.2 parts chromium nitrate nonahydrate, 0.7 parts terephthalic acid, and 0.04 parts 10 wt.% hydrochloric acid.

[0051] In this embodiment, centrifugation was performed at 5900 rpm for 7 minutes, and the washing process involved repeated washing with deionized water 4 times until the pH of the washing solution reached 6.8.

[0052] In this embodiment, the drying process is a vacuum drying process, with the drying temperature controlled at 66°C and the drying time at 9 hours.

[0053] Example 3

[0054] A high-temperature stable piperazine pyrophosphate / MOF composite material, the composite material comprising a columnar porous Zr-MOF host material and Cr-MOF-coated piperazine pyrophosphate guest particles with a core-shell structure loaded on the pore surface of the Zr-MOF host material;

[0055] The porous Zr-MOF host material was prepared by the ice template method and the columnar pore width was 3.5 μm; the average size of the Cr-MOF-coated piperazine pyrophosphate guest particles was 500 nm, and the mass ratio of Cr-MOF to piperazine pyrophosphate was 8:1.

[0056] The preparation method of the piperazine pyrophosphate / MOF composite material in this embodiment is as follows: 15 parts by weight of Cr-MOF-coated piperazine pyrophosphate particles are dispersed in 60 parts of ethanol and 0.5 parts of polyvinylpyrrolidone surfactant are added. The mixture is ultrasonically treated at 300 W for 15 min to form a uniform dispersion. The activated Zr-MOF host material is added to the dispersion and impregnated at 60°C and 500 rpm for 24 h. Optionally, it is ultrasonically treated at 300 W for 30 min. After settling for 3 h, the solid product is centrifuged at 5000 rpm for 15 min to remove the supernatant. The supernatant is removed and the product is washed three times with 5 times its weight of ethanol to remove unloaded particles. Finally, the washed product is dried under a vacuum of 0.1 MPa and a temperature of 80°C for 12 h to obtain the piperazine pyrophosphate / MOF composite material.

[0057] The preparation method of the activated Zr-MOF host material in this embodiment is as follows: 40 parts by weight of porous Zr-MOF host material are immersed in 5 times the weight of ethanol, ultrasonically cleaned for 30 min, and centrifuged to remove residual solvent. Then, the material is activated for 24 h under a vacuum of 0.1 MPa and a temperature of 120°C to obtain the activated Zr-MOF host material.

[0058] The preparation method of the porous Zr-MOF host material in this embodiment is as follows: 2.5 parts of trimesic acid and 10.5 parts of zirconium oxychloride octahydrate are dissolved in a mixed solvent of 150 parts of N,N-dimethylformamide and formic acid in a volume ratio of 1:1 to form a homogeneous solution. The solution is then transferred to a closed reaction vessel, heated to 100°C and maintained at a stirring rate of 600 rpm for 36 h. After the reaction is completed, the solution is naturally cooled to 30°C. The resulting suspension is centrifuged at 5000 rpm for 15 min. The supernatant is discarded and the solid precipitate is collected. The solid precipitate is washed five times alternately with N,N-dimethylformamide and ethanol to remove unreacted monomers and solvent residues. The amount of solvent used for each wash is five times the weight of the solid precipitate. After washing, the solid is dispersed in deionized water to form a 10 wt% dispersion and then freeze-dried to obtain a porous Zr-MOF host material with a columnar pore structure.

[0059] The specific process of freeze-drying in this embodiment is as follows: the dispersion is pre-frozen at -30°C for 8 hours, and then transferred to a freeze dryer for freeze-drying at a vacuum of 0.05 mbar and a condenser temperature of -60°C for 48 hours.

[0060] The preparation method of Cr-MOF-coated piperazine pyrophosphate guest particles in this embodiment includes the following steps: dispersing piperazine pyrophosphate in deionized water and ultrasonically treating it to form a suspension; sequentially adding chromium nitrate nonahydrate, terephthalic acid, and hydrochloric acid to the suspension to form a precursor mixture; and then subjecting the mixture to a hydrothermal reaction to allow Cr to form a Cr-MOF-coated piperazine pyrophosphate guest particle. 3+ The Cr-MOF is generated by coordination with terephthalic acid and simultaneously coated on the surface of piperazine pyrophosphate particles to form a core-shell structure. After the reaction is completed, the Cr-MOF-coated piperazine pyrophosphate is obtained by centrifugation, washing and drying.

[0061] In this embodiment, the hydrothermal reaction temperature is 200°C and the reaction time is 24 hours.

[0062] The weight ratio of each component in the precursor mixture in this embodiment is as follows: 0.8 parts piperazine pyrophosphate, 30 parts deionized water, 1.5 parts chromium nitrate nonahydrate, 1 part terephthalic acid, and 0.1 parts 10 wt.% hydrochloric acid.

[0063] In this embodiment, centrifugation was performed at 8000 rpm for 10 minutes, and the washing process involved repeated washing with deionized water 5 times until the pH of the washing solution reached 7.5.

[0064] In this embodiment, the drying process is a vacuum drying process, with the drying temperature controlled at 80°C and the drying time at 12 hours.

[0065] Example 4

[0066] A high-temperature stable piperazine pyrophosphate / MOF composite material, the composite material comprising a columnar porous Zr-MOF host material and Cr-MOF-coated piperazine pyrophosphate guest particles with a core-shell structure loaded on the pore surface of the Zr-MOF host material;

[0067] The porous Zr-MOF host material was prepared by the ice template method and the columnar pore width was 2.7 μm; the average size of the Cr-MOF-coated piperazine pyrophosphate guest particles was 420 nm, and the mass ratio of Cr-MOF to piperazine pyrophosphate was 6:1.

[0068] The preparation method of the piperazine pyrophosphate / MOF composite material in this embodiment is as follows: 11 parts by weight of Cr-MOF-coated piperazine pyrophosphate particles were dispersed in 48 parts of ethanol and 0.3 parts of polyvinylpyrrolidone surfactant were added. The mixture was ultrasonically treated at 220 W for 11 min to form a uniform dispersion. The activated Zr-MOF host material was added to the dispersion and impregnated at 44°C and 380 rpm for 19 h. Optionally, the mixture was ultrasonically treated at 220 W for 22 min. After settling for 2 h, the solid product was centrifuged at 4200 rpm for 11 min to remove the supernatant. The supernatant was removed and the product was washed three times with 4 times its weight of ethanol to remove unloaded particles. Finally, the washed product was dried at 0.08 MPa and 72°C for 10 h to obtain the piperazine pyrophosphate / MOF composite material.

[0069] The preparation method of the activated Zr-MOF host material in this embodiment is as follows: 32 parts by weight of porous Zr-MOF host material were immersed in 4 times the weight of ethanol, ultrasonically cleaned for 22 min, and centrifuged to remove residual solvent. Then, the material was activated for 19 h under a vacuum of 0.08 MPa and a temperature of 112°C to obtain the activated Zr-MOF host material.

[0070] The preparation method of the porous Zr-MOF host material in this embodiment is as follows: 2.1 parts of trimesic acid and 9.7 parts of zirconium oxychloride octahydrate are dissolved in a mixed solvent of 110 parts of N,N-dimethylformamide and formic acid in a volume ratio of 1:1 to form a homogeneous solution. The solution is then transferred to a closed reaction vessel, heated to 92°C and maintained at a stirring rate of 480 rpm for 26 h. After the reaction is completed, the solution is naturally cooled to 28°C. The resulting suspension is centrifuged at 4200 rpm for 11 min. The supernatant is discarded and the solid precipitate is collected. The solid precipitate is washed four times alternately with N,N-dimethylformamide and ethanol to remove unreacted monomers and solvent residues. The amount of solvent used for each wash is four times the weight of the solid precipitate. After washing, the solid is dispersed in deionized water to form an 8 wt% dispersion, which is then freeze-dried to obtain a porous Zr-MOF host material with a columnar pore structure.

[0071] The specific process of freeze-drying in this embodiment is as follows: the dispersion is pre-frozen at -38°C for 6 h, and then transferred to a freeze dryer for freeze-drying at a vacuum of 0.03 mbar and a condenser temperature of -68°C for 38 h.

[0072] The preparation method of Cr-MOF-coated piperazine pyrophosphate guest particles in this embodiment includes the following steps: dispersing piperazine pyrophosphate in deionized water and ultrasonically treating it to form a suspension; sequentially adding chromium nitrate nonahydrate, terephthalic acid, and hydrochloric acid to the suspension to form a precursor mixture; and then subjecting the mixture to a hydrothermal reaction to allow Cr to form a Cr-MOF-coated piperazine pyrophosphate guest particle. 3+ The Cr-MOF is generated by coordination with terephthalic acid and simultaneously coated on the surface of piperazine pyrophosphate particles to form a core-shell structure. After the reaction is completed, the Cr-MOF-coated piperazine pyrophosphate is obtained by centrifugation, washing and drying.

[0073] In this embodiment, the hydrothermal reaction temperature is 192°C and the reaction time is 19 hours.

[0074] The weight ratio of each component in the precursor mixture in this embodiment is as follows: 0.6 parts piperazine pyrophosphate, 26 parts deionized water, 1.3 parts chromium nitrate nonahydrate, 0.8 parts terephthalic acid, and 0.06 parts 10 wt.% hydrochloric acid.

[0075] In this embodiment, centrifugation was performed at 6800 rpm for 8 minutes, and the washing process involved repeated washing with deionized water 4 times until the pH of the washing solution reached 7.1.

[0076] In this embodiment, the drying process is a vacuum drying process, with the drying temperature controlled at 72°C and the drying time at 10 hours.

[0077] Comparative Example 1

[0078] The process was basically the same as in Example 1, except that hydrochloric acid (10 wt.% hydrochloric acid) was not added to the reaction mixture when preparing Cr-MOF-coated piperazine pyrophosphate guest particles. Instead, only piperazine pyrophosphate, deionized water, chromium nitrate nonahydrate, and terephthalic acid were used for the hydrothermal reaction.

[0079] Comparative Example 2

[0080] The process is basically the same as in Example 1, except that the porous Zr-MOF host material was not pre-frozen at -50°C during the freeze-drying process. Instead, the dispersion was directly transferred to the freeze dryer for drying.

[0081] Comparative Example 3

[0082] The process is basically the same as in Example 1, except that the hydrothermal reaction temperature of Cr-MOF-coated piperazine pyrophosphate is 150°C, which is lower than the 180°C hydrothermal reaction temperature in Example 1.

[0083] Comparative Example 4

[0084] The method is basically the same as in Example 1, except that when the activated Zr-MOF host material is added to the dispersion of Cr-MOF-coated piperazine pyrophosphate for impregnation, no polyvinylpyrrolidone surfactant is added.

[0085] Comparative Example 5

[0086] The process is basically the same as in Example 1, except that the solvent used to prepare the porous Zr-MOF host material is pure N,N-dimethylformamide, rather than a mixed solvent of N,N-dimethylformamide and formic acid in a volume ratio of 1:1.

[0087] Comparative Example 6

[0088] The process is basically the same as in Example 1, except that after preparing the Cr-MOF-coated piperazine pyrophosphate guest particles, the washing with deionized water was not performed until the pH of the washing solution reached 6.5. Instead, the particles were simply washed once with deionized water.

[0089] Comparative Example 7

[0090] It is basically the same as Example 1, except that piperazine pyrophosphate was not coated with Cr-MOF.

[0091] Comparative Example 8

[0092] The preparation of the porous Zr-MOF host material was basically the same as in Example 1, except that it was directly vacuum dried at 60°C for 24 hours instead of freeze-drying.

[0093] Comparative Example 9

[0094] The process is basically the same as in Example 1, except that the activation temperature of the Zr-MOF host material is 80°C, which is lower than the 100°C activation temperature in Example 1.

[0095] Comparative Example 10

[0096] The process is basically the same as in Example 1, except that when the Cr-MOF-coated piperazine pyrophosphate guest particles are dispersed in ethanol, they are not ultrasonically treated, but are mechanically stirred at 300 rpm for 30 minutes to form a dispersion.

[0097] Comparative Example 11

[0098] The process is basically the same as in Example 1, except that after preparing the piperazine pyrophosphate / MOF composite material, the drying process is carried out by natural air drying, rather than drying under a vacuum of 0.05 MPa and a temperature of 60°C.

[0099] Comparative Example 12

[0100] The process is basically the same as in Example 1, except that terephthalic acid is used instead of trimesic acid in the reaction with zirconium oxychloride octahydrate when preparing the porous Zr-MOF host material.

[0101] Comparative Example 13

[0102] The process is basically the same as in Example 1, except that when preparing Cr-MOF-coated piperazine pyrophosphate guest particles, chromium nitrate nonahydrate is replaced with aluminum nitrate nonahydrate, while other conditions remain unchanged.

[0103] Comparative Example 14

[0104] The process is basically the same as in Example 1, except that the immersion time of the activated Zr-MOF host material in the Cr-MOF-coated piperazine pyrophosphate dispersion is 6 hours, which is shorter than the 12-hour immersion time in Example 1.

[0105] Comparative Example 15

[0106] The process was basically the same as in Example 1, except that after preparing the porous Zr-MOF host material, only N,N-dimethylformamide was used for washing the solid precipitate, and ethanol was not used for alternating washing.

[0107] Performance testing:

[0108] Thermal stability analysis (TGA-DSC): Thermogravimetric-Differential Scanning Calorimetry (TGA-DSC, STA 449 F3 Jupiter, NETZSCH) was used to record the material mass loss and heat flow changes by heating to 800°C at a rate of 10°C / min under a nitrogen atmosphere.

[0109] Flame retardant performance testing (LOI and vertical burning): The vertical burning rating (UL-94, ASTM D3801) was tested, the burning time and whether the dripping material ignited the cotton were recorded, and the morphology of the char layer after burning was observed (SEM-assisted analysis) to verify the effect of the composite material on improving the flame retardant efficiency.

[0110] Micro Combustion Calorimetry (MCC) Experiment: The peak heat release rate (pHRR) and total heat release (THR) of the material under programmed temperature rise were tested using a micro combustion calorimeter (MCC) to qualitatively determine the improvement in flame retardant performance.

[0111] The properties of the composite materials from Examples 1-4 and Comparative Examples 1-15 are summarized in Table 1.

[0112] Table 1. Performance summary of the composite materials of Examples 1-4 and Comparative Examples 1-15

[0113]

[0114] As shown in Table 1, the factors affecting the comparative performance mainly include the following aspects: The integrity and stability of the MOF structure play a decisive role in the thermal stability and flame retardant performance of the material. Incomplete MOF structure or insufficient crystallinity will lead to a reduction in the flame retardant loading or a weakening of the slow-release effect, thus failing to form an effective gas-phase and condensed-phase flame retardant barrier during combustion; The synthesis solvent system has a significant impact on the pore structure and morphology control of MOF. For example, using a single solvent may lead to excessive crystal density or pore blockage, limiting the uniform dispersion and thermally triggered release of the flame retardant, thereby reducing the flame retardant efficiency. Even if the thermal stability of the material is improved, the LOI or UL-94 rating cannot be improved simultaneously; The type of ligand and its coordination ability determine the spatial structure and thermal response behavior of MOF. Weakly coordinated or poorly rigid ligands may form a MOF skeleton with low thermal stability and a loose structure, causing the flame retardant to desorb prematurely in the early stage of heating, weakening the flame retardant effect at high temperature; The reaction temperature and time directly affect the crystallization quality and particle size distribution of MOF. Too low a temperature may lead to insufficient crystallization and the formation of incomplete... Regular or non-porous structures, or conversely, microcrystalline agglomeration and reduced specific surface area, can weaken the dispersion and synergistic effect of flame retardants, resulting in poor thermal stability and flame retardant performance. Auxiliary processes such as ultrasonic treatment and washing purification play a crucial role in promoting uniform dispersion of precursors and removing impurities. Lack of these steps may introduce unreacted components or impurities, forming defective structures, affecting the integrity of MOFs and their compatibility with flame retardants, thereby reducing char residue and LOI, while increasing pHRR and THR values. The interaction mode between flame retardants and MOFs (such as hydrogen bonding, electrostatic interaction, or coordination) determines their slow-release behavior and thermal response sensitivity. If the interaction is too weak, the flame retardant is prone to volatilization in the early stage of combustion and cannot form an effective flame-retardant shield. If it is too strong, the release will be untimely and it will not play a role in the ignition stage, both of which will lead to a decrease in flame retardant performance. Therefore, the thermal stability and flame retardant performance of comparative materials are determined by the synergistic effect of multiple factors such as MOF structure regulation, synthesis parameters, flame retardant loading and release behavior. Even small changes in structure and process can lead to significant differences in performance.

[0115] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that any equivalent structural transformations made under the concept of the present invention and using the contents of the specification and drawings of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1.A high-temperature stable pyrophosphoriperazine / MOF composite material, comprising a columnar porous Zr-MOF host material, and Cr-MOF coated pyrophosphoriperazine guest particles with a core-shell structure loaded on the pore surface of the porous Zr-MOF host material; The porous Zr-MOF host material is prepared by an ice template method and has a columnar pore width of 1.5-3.5 μm; The average size of the Cr-MOF coated pyrophosphoriperazine guest particles is 300-500 nm, and the mass ratio of Cr-MOF to pyrophosphoriperazine is 3:1-8:1; The preparation method of the pyrophosphoriperazine / MOF composite material is as follows: 5-15 parts of Cr-MOF coated pyrophosphoriperazine particles are dispersed in 30-60 parts of ethanol and 0.1-0.5 parts of polyvinylpyrrolidone surfactant is added, and a uniform dispersion liquid is formed by ultrasonic power of 100-300 W for 5-15 min, then the activated Zr-MOF host material is added to the dispersion liquid, and the impregnation is carried out at a temperature of 20-60 °C and a stirring speed of 200-500 rpm for 12-24 h, and optionally assisted with ultrasonic power of 100-300 W for 10-30 min, then standing and settling for 1-3 h and centrifuging at 3000-5000 rpm for 5-15 min to retain the solid product, and after removing the supernatant, the un-loaded particles are removed by washing with 3-5 times the weight of ethanol for 2-3 times, and finally the washed product is dried at a vacuum degree of 0.05-0.1 MPa and a temperature of 60-80 °C for 8-12 h to obtain the pyrophosphoriperazine / MOF composite material; The preparation method of the activated Zr-MOF host material is as follows: 20-40 parts of the porous Zr-MOF host material is immersed in 3-5 times the weight of ethanol and ultrasonically cleaned for 10-30 min, and after removing the residual solvent by centrifugation, the activated Zr-MOF host material is obtained by activation treatment at a vacuum degree of 0.05-0.1 MPa and a temperature of 100-120 °C for 12-24 h. The preparation method of the porous Zr-MOF host material is as follows: 1.5-2.5 parts of trimesic acid and 8.5-10.5 parts of zirconium oxychloride octahydrate are dissolved in 50-150 parts of a mixed solvent of N,N-dimethylformamide and formic acid in a volume ratio of 1:1 to form a homogeneous solution, which is then transferred to a sealed reaction container, heated to 80-100°C, and maintained at a stirring speed of 300-600 rpm for 12-36 h, and then naturally cooled to 25-30°C. The obtained suspension is centrifuged at 3000-5000 rpm for 5-15 min, and the solid precipitate is collected after the supernatant is discarded. The solid is washed with N,N-dimethylformamide and ethanol alternately for 3-5 times to remove unreacted monomers and residual solvents, and the amount of washing solvent is 3-5 times the weight of the solid precipitate each time. After washing, the solid is dispersed in deionized water to form a 5-10 wt% dispersion solution for freeze-drying, and finally a porous Zr-MOF host material with a columnar pore structure is obtained; The specific process of freeze-drying is as follows: the dispersion solution is pre-frozen at -50 to -30°C for 4-8 h, and then transferred to a freeze-drying machine for freeze-drying under the conditions of a vacuum degree of 0.01-0.05 mbar and a condenser temperature of -80 to -60°C for 24-48 h; The preparation method of the Cr-MOF coated pyrithix guest particles comprises the following steps: Piperazine pyrophosphate is dispersed in deionized water and ultrasonically treated to form a suspension. Nine water chromium nitrate, terephthalic acid and hydrochloric acid are sequentially added to the suspension to form a precursor mixed solution. Cr³⁺ and terephthalic acid are coordinated to form Cr-MOF through hydrothermal reaction, and the Cr-MOF is simultaneously coated on the surface of the piperazine pyrophosphate particles to form a core-shell structure. After the reaction is completed, the Cr-MOF coated piperazine pyrophosphate is obtained through centrifugal separation, washing and drying treatment; The hydrothermal reaction temperature is 180-200°C, and the reaction time is 12-24 h; The weight ratio of each component in the precursor mixed solution is as follows: piperazine pyrophosphate 0.3-0.8 parts, deionized water 20-30 parts, nine water chromium nitrate 1.0-1.5 parts, terephthalic acid 0.5-1 part, and 10 wt.% hydrochloric acid 0.01-0.1 part; The centrifugal separation is treated at a centrifugal speed of 5000-8000 rpm for 5-10 min, and the washing process is repeated 3-5 times with deionized water until the pH of the washing liquid reaches 6.5-7.5; The drying treatment is a vacuum drying process, and the drying temperature is controlled at 60-80°C, and the drying time is 8-12 h.

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