Piperazine pyrophosphate flame retardant and preparation method thereof

Abstract

The invention relates to the technical field of flame retardance of high polymer materials, and discloses a piperazine pyrophosphate flame retardant which comprises the following components in parts by weight: 50-80 parts of piperazine pyrophosphate; 5 to 15 parts of aluminum pyrophosphate; the invention also provides a preparation method of the piperazine pyrophosphate flame retardant, and the preparation method comprises the following steps: precursor dissolution: dissolving the raw materials, and uniformly mixing the raw materials to form a stable reaction system; supercritical hydrothermal synthesis: reacting at specific temperature and pressure to form high-stability piperazine pyrophosphate, so as to improve the high temperature resistance; molecular modification: the molecular structure of piperazine pyrophosphate is modified and optimized through functional groups, and the thermal stability, dispersion and chemical stability are improved. By introducing innovative additives such as graphite-phase carbon nitride, titanium phosphate and benzotriazole, the thermal stability, flame retardance, dispersity and weather resistance of the flame retardant are remarkably improved, and the comprehensive fireproof effect and long-time use reliability of the material are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of flame retardants for polymer materials, and specifically to a piperazine pyrophosphate flame retardant and a preparation method thereof. Background Art

[0002] At present, there are various flame retardant technologies on the market. Common inorganic flame retardants, especially those based on phosphoric acid, carbon nitride, and certain metal oxides, can effectively improve the flame retardancy of materials and mostly meet the daily fire prevention requirements. They have good stability under normal temperature and humidity conditions and can provide certain thermal stability. In particular, some inorganic flame retardants can effectively increase the limiting oxygen index (LOI) of materials and, to a certain extent, enhance the flame retardancy of materials. In addition, some organic flame retardants can also provide satisfactory effects in different application fields, especially in the fields of plastics and fibers. Generally speaking, the existing flame retardants can already ensure the basic fire prevention requirements of materials in daily applications, and the production process is relatively mature with low usage costs.

[0003] However, there are still some deficiencies in the existing flame retardants; firstly, the flame retardants used in the existing technology usually lack sufficient thermal stability, especially in high-temperature environments, they are prone to decomposition or degradation, resulting in a significant decline in the flame retardant effect; secondly, in an environment with a low oxygen concentration, the flame retardant performance of many traditional flame retardants cannot meet the requirements, and the limiting oxygen index is low, making it difficult to meet the fire prevention requirements of high-risk levels; in addition, the existing flame retardants have deficiencies in dispersibility, and the particles are uneven in many materials during the compounding process, affecting the overall performance; moreover, in a long-term high-humidity and high-temperature environment, the weather resistance of the flame retardants is poor, and they are prone to aging and degradation; finally, the compatibility between the existing flame retardants and the polymer matrix is not strong, and uneven dispersion is likely to occur, affecting the mechanical properties and service life of the composite materials. These deficiencies seriously limit the application and development of the existing technology in higher-requirement fields. Summary of the Invention

[0004] In view of the deficiencies of the existing technology, the present invention provides a piperazine pyrophosphate flame retardant and a preparation method thereof, which solve the problems of the existing flame retardants in terms of high-temperature stability, flame retardant performance, dispersibility, weather resistance, and compatibility.

[0005] To achieve the above objectives, the present invention is realized through the following technical solutions: A piperazine pyrophosphate flame retardant, the flame retardant comprising the following components in parts by weight: Piperazine pyrophosphate: 50 - 80 parts. Piperazine pyrophosphate can undergo thermal decomposition under high-temperature conditions to generate stable structures containing phosphorus and nitrogen, such as polyphosphates, pyrophosphates, and phosphoric acid esters. These substances can form an expanded carbon layer on the surface of the polymer, effectively isolating oxygen and heat sources, thereby reducing the combustion rate. In addition, the decomposition products can also capture free radicals, reduce the generation of combustible gases, and improve the flame retardant efficiency; Aluminum pyrophosphate: 5 - 15 parts. Aluminum pyrophosphate will decompose at high temperatures to generate pyrophosphate anions. These anions can interact with polymer materials to promote the formation of a high - density, low - thermal - conductivity flame - retardant carbon layer, effectively inhibiting flame spread. In addition, aluminum pyrophosphate can also act synergistically with titanium phosphate to enhance the high - temperature stability of the flame retardant, and release non - combustible gases during combustion, diluting the concentration of combustible gases and improving the flame - retardant performance; Titanium phosphate: 3 - 10 parts. Titanium phosphate can release TiO 2 , TiO 2 with high thermal stability and catalytic carbonization ability, which can promote the formation of the carbon layer and improve the fire resistance. In addition, TiO 2 can also form a complex high - temperature cross - linked network with pyrophosphates, enhancing the heat resistance and structural integrity of the material and further improving the flame - retardant effect; Graphitic carbon nitride: 2 - 8 parts. g - C 3 N 4 has a layered structure and can form a stable nitrogen - rich carbon layer during combustion, effectively blocking heat transfer. In addition, its high - temperature decomposition products can capture free radicals, reducing the occurrence of combustion chain reactions and improving the flame - retardant efficiency. g - C 3 N 4 acts synergistically with piperazine pyrophosphate to further enhance the high - temperature resistance and flame - retardancy of the material; Benzotriazole: 1 - 5 parts. Benzotriazole can release nitrogen oxides under high - temperature conditions, inhibiting the free - radical chain combustion reaction and reducing the heat and smoke generated by combustion. In addition, benzotriazole can also enhance the interfacial compatibility between piperazine pyrophosphate and other flame retardants, optimizing the dispersibility and stability of the material and improving the overall flame - retardant effect; Imidazole: 2 - 6 parts. Imidazole can decompose and catalyze at high temperatures to generate stable nitrogen - phosphorus complexes, promoting the formation of the carbon layer and improving the heat resistance of the flame retardant. In addition, imidazole also has a good basicity regulation effect, which can adjust the pH value of the flame - retardant system, optimize its chemical stability and improve the aging resistance; Layered double - metal hydroxide: 1 - 4 parts. When LDH decomposes at high temperatures, it can release water vapor and carbon dioxide, diluting the concentration of combustible gases and reducing the flame temperature. In addition, the layered structure of LDH can form a physical barrier during combustion, delaying the diffusion of pyrolysis products and improving the persistence of the flame retardant; Anhydrous piperazine: 8 - 10 parts. Anhydrous piperazine can undergo a complexation reaction with pyrophosphates at high temperatures to form more stable phosphorus - nitrogen compounds, improving the density of the carbon layer. In addition, anhydrous piperazine can also improve the dispersibility and compatibility of the flame retardant in the polymer, improving the processing performance of the material; Pyrophosphoric acid: 15 - 20 parts. Pyrophosphoric acid can form polyphosphate structures under high-temperature conditions. These substances can enhance the strength of the carbon layer and improve fire resistance. In addition, pyrophosphoric acid can also react with metal oxides (such as TiO 2 , Al 2 O 3 ) to form a stable thermal protection layer, further enhancing the flame retardancy performance.

[0006] The present invention also provides a preparation method of piperazine pyrophosphate flame retardant, comprising the following steps: S1. Precursor dissolution: Dissolve the raw materials to make them uniformly mixed and form a stable reaction system; S2. Supercritical hydrothermal synthesis: React under specific temperature and pressure to form piperazine pyrophosphate with high stability and improve the high-temperature resistance performance; S3. Molecular modification: Optimize the molecular structure of piperazine pyrophosphate through functional group modification to increase thermal stability, dispersion and chemical stability; S4. Synergistic flame retardant modification: Combine with the flame retardant to increase the flame retardancy and enhance the compatibility with the polymer; S5. Low-temperature acid treatment and drying: Remove by-products, optimize the crystal structure and particle size distribution, and ensure the product stability and fluidity.

[0007] Preferably, the precursor dissolution includes: In a high-temperature and high-pressure autoclave, add 50 - 100 L of deionized water and maintain the stirring speed in the range of 300 - 500 rpm. Use deionized water as the solvent to remove impurities and ionic contamination that may affect the reaction, improve the purity of the solution, and avoid side reactions. Controlling the stirring rate at 300 - 500 rpm can ensure sufficient internal convection in the system, avoid local supersaturation phenomena, and ensure uniform distribution of each component; First, add anhydrous piperazine and continuously stir for 30 - 60 min to form a uniform solution. Anhydrous piperazine is a water-soluble organic base that can be used as a dissolution promoter to form a strong polar hydrogen bond network in the solution, improving the solubility of pyrophosphoric acid. In addition, the diamine structure in the piperazine molecule can provide active sites in the solution to form a weak coordination interaction with pyrophosphate ions, providing a stable ionic environment for the subsequent synthesis of piperazine pyrophosphate; Then add pyrophosphoric acid and stir at a dissolution temperature of 30 - 80 °C to form a transparent solution. Pyrophosphoric acid is a phosphate that is insoluble in water. By increasing the temperature (30 - 80 °C), the dissociation of pyrophosphoric acid in water can be accelerated, promoting its reaction with anhydrous piperazine to form a phosphate complex and improving the solubility. At the same time, appropriate temperature control can prevent partial hydrolysis of pyrophosphoric acid at too high a temperature, thus affecting the structural integrity of the final piperazine pyrophosphate; Finally, add aluminum pyrophosphate and titanium phosphate, and use ultrasonic or mechanical stirring to improve the dispersion uniformity of the components. Both aluminum pyrophosphate and titanium phosphate are insoluble inorganic materials. If the dispersion is uneven, it is easy to form precipitation or agglomeration in the solution, thus affecting the flame retardant performance of the final product. Therefore, ultrasonic dispersion or mechanical stirring can effectively reduce the particle size and improve its uniformity in the solution. Ultrasonic waves generate cavitation effects in the liquid, breaking solid particles into nanoscale, enhancing the solution stability, while mechanical stirring can provide a macroscopic mixing effect, making aluminum pyrophosphate and titanium phosphate evenly distributed in the system and avoiding the precipitation of components due to excessive local concentration.

[0008] Preferably, the supercritical hydrothermal synthesis includes: Under the conditions of a temperature of 300 - 400 °C and a pressure of 15 - 30 MPa, introduce the precursor solution into the supercritical reaction kettle. Within this temperature and pressure range, water enters the supercritical state (its properties are between those of a liquid and a gas), with high diffusivity, low viscosity, and high solubility, which can significantly increase the reaction rate. Supercritical water can effectively promote the reaction between pyrophosphate ions and piperazine molecules, accelerate the formation of the phosphate backbone, and improve the structural integrity of piperazine pyrophosphate. And maintain the reaction for 3 - 6 hours to enable piperazine pyrophosphate to form a stable crystal structure. A longer reaction time can promote crystal growth and increase the thermal decomposition temperature of the material. However, if the time is too long, it will cause the crystal grains to be too large and affect the dispersibility. 3 - 6 hours is the optimized time window, which can balance the crystallinity and dispersibility of the flame retardant. After the reaction is completed, slowly cool down to 50 - 100 °C to maintain the integrity of the physical structure. Too rapid cooling will cause the rapid loss of crystal water, converting some piperazine pyrophosphate into an amorphous phase and reducing the heat resistance and flame retardant performance of the material. Therefore, slowly cooling down to 50 - 100 °C can maintain the crystal form stability of piperazine pyrophosphate, avoid the formation of the amorphous phase, and improve the long-term thermal stability of the material; collect the solid-phase product through solid-liquid separation and wash it with deionized water 3 - 5 times to remove by-products. Washing with deionized water 3 - 5 times can remove residual impurities and unreacted components, while reducing the ion adsorption on the surface of the product, improving the thermal stability and dispersibility of the flame retardant. Through multiple washings, it can be ensured that piperazine pyrophosphate maintains a high-purity crystal state, preventing degradation or increased hygroscopicity caused by impurities during subsequent use and affecting the flame retardant effect.

[0009] Preferably, the molecular modification includes: Benzotriazole and imidazole are added to the synthetic product for interfacial modification. Benzotriazole can bind to the phosphate groups of piperazine pyrophosphate through coordination, forming a stable protective layer on its surface, reducing the degradation of piperazine pyrophosphate in high-temperature or oxidative environments. Imidazole (IM) is a nitrogen-containing heterocyclic compound that can form hydrogen bonds and π-π stacking interactions with piperazine pyrophosphate, improving its dispersibility. At the same time, the basic structure of imidazole can adjust the surface charge of the material, reduce particle aggregation, and improve the dispersion stability of the flame retardant in the polymer matrix; Suspend piperazine pyrophosphate in 50 - 100 L of ethanol solution and stir until completely dispersed. Ethanol, as a polar organic solvent, can reduce the electrostatic attraction between piperazine pyrophosphate particles, enhance its dispersibility in the solution, and avoid agglomeration. The stirring time within this range can promote the uniform adsorption of modifier molecules on the surface of piperazine pyrophosphate, improving the modification effect; By means of heat treatment or solvent evaporation, where the pH is 7.0 - 8.5, maintain the temperature at 70 - 100 °C and stir for 2 - 5 hours to evenly distribute the modifier on the surface of piperazine pyrophosphate. Using heat treatment (70 - 100 °C) or solvent evaporation can accelerate the adsorption and binding of the modifier on the surface of piperazine pyrophosphate, and through a heat-induced method, promote benzotriazole and imidazole to form a stable coating layer on the particle surface. Controlling the pH at 7.0 - 8.5 can ensure that imidazole is in a partially dissociated state, enhancing its adsorption on the surface of piperazine pyrophosphate, while preventing the material from degrading or aggregating under overly acidic or alkaline conditions. An appropriate stirring time (2 - 5 hours) can ensure the uniform distribution of the modifier on the surface of piperazine pyrophosphate, improving the stability of the particles and reducing sedimentation and aggregation problems in subsequent applications.

[0010] Preferably, the synergistic flame retardant modification includes: Adding graphitic carbon nitride and layered double metal hydroxide to the modified piperazine pyrophosphate. The synergistic effect of the two can simultaneously enhance the condensed-phase flame retardant mechanism (forming a char layer) and the gas-phase flame retardant mechanism (free radical capture effect) of piperazine pyrophosphate, effectively improving the flame retardancy efficiency and reducing the smoke release during material combustion; Through coprecipitation or physical mixing methods, make the synergistic flame retardant components fully combine with the main flame retardant. At a certain temperature, make g-C 3 N 4 and LDH deposit synchronously on the surface of piperazine pyrophosphate in the solution, forming a stable interfacial bond, improving the uniformity and chemical stability of the composite flame retardant. This method can enable the metal ions of LDH to have electrostatic or complexation interactions with the pyrophosphate groups, enhancing the interfacial compatibility. Using high-energy ball milling, ultrasonic dispersion, or mechanical stirring, make g-C 3 N 4Disperse evenly on the surface of piperazine pyrophosphate particles with LDH to form a uniform composite flame retardant structure, improving thermal stability and weather resistance. This method is suitable for large-scale production, can effectively reduce costs, and improve preparation efficiency. Through the optimized selection of the two methods, the uniform distribution of the synergistic flame retardant on piperazine pyrophosphate can be ensured, enhancing the stability of the material and improving the final flame retardant effect; Adopt drying or vacuum treatment methods to remove excess solvents or unreacted substances in the system. The drying method (80 - 150 °C) can remove solvents by thermal evaporation and promote the adsorption and stabilization of g-C 3 N 4 and LDH on the surface of piperazine pyrophosphate, improving the interfacial bonding strength. Vacuum treatment (100 - 150 °C, below 100 Pa) can remove solvents and unreacted substances under low-temperature conditions, preventing excessive thermal degradation of the material due to high temperature and improving the chemical stability of the final product.

[0011] Preferably, the low-temperature acid treatment and drying include: Use 0.1 - 1 part of low-concentration dilute sulfuric acid for acid treatment. Perform pickling on the synthetic product for 30 - 60 minutes to improve the crystallinity of piperazine pyrophosphate. Using 0.1 - 1 part (mol / L) of dilute sulfuric acid can control the mildness of the acid treatment, prevent the destruction of the piperazine pyrophosphate structure caused by excessive acid etching, and effectively remove soluble impurities, improving the purity of the material. The optimized time of 30 - 60 minutes ensures sufficient pickling. If the time is too short, the impurities cannot be removed thoroughly; if it is too long, part of the piperazine pyrophosphate will dissolve, affecting the yield; Adopt freeze-drying at a temperature of -50 - 0 °C for 12 - 48 hours to prevent high-temperature degradation. Freeze-drying (-50 - 0 °C) can directly convert water from a solid state to a gaseous state through sublimation under low-temperature conditions, avoiding the collapse of the crystal structure caused by the evaporation of liquid water and preventing the material from agglomerating or undergoing thermal degradation during the drying process. Controlling the freeze-drying time within 12 - 48 hours can ensure complete removal of water, while keeping the piperazine pyrophosphate particles in good dispersion, improving the compatibility of the flame retardant in polymer materials. This treatment process maximally retains the microstructure of piperazine pyrophosphate, avoiding physical property changes caused by heating and improving the application stability of the material; Vacuum drying is carried out at 100 - 150 °C for 4 - 12 hours to ensure structural stability. The vacuum environment can lower the boiling point of water, complete dehydration at a lower temperature, avoid thermal decomposition or phase change of piperazine pyrophosphate caused by high-temperature drying, and improve the thermal stability of the product; an appropriate temperature (100 - 150 °C) can promote the densification of the microstructure of piperazine pyrophosphate, improve the dispersibility and compatibility of the flame retardant in the polymer, and at the same time prevent the material from absorbing moisture and affecting subsequent processing; optimizing the drying time (4 - 12 hours) can ensure complete removal of moisture, and at the same time prevent particle agglomeration caused by excessive drying time and improve the processing fluidity of the flame retardant.

[0012] Preferably, the preparation sequence of the flame retardant is as follows: First, dissolve piperazine pyrophosphate, aluminum pyrophosphate, and titanium phosphate to form a precursor solution. Piperazine pyrophosphate (PAPP) is the main flame retardant component. Its phosphate groups will form a stable phosphate backbone under hydrothermal conditions, but its solubility is limited, so it needs to be dissolved first to ensure uniform distribution; aluminum pyrophosphate (AlP 2 O 7 ) is a charring promoter, which can partially dissociate in the solution to generate Al 3+ ions, form a complex with pyrophosphate groups (P 2 O 7 4- ), improve the solution stability, and at the same time promote the charring process in the subsequent hydrothermal reaction; titanium phosphate (TiPO 4 ) has high-temperature stability, can enhance the antioxidant property of the material during the reaction process, and improve the thermal decomposition temperature and mechanical strength of the flame retardant by forming a Ti - O - P network structure; During the hydrothermal synthesis process, gradually introduce graphitic carbon nitride and benzotriazole. Gradually introducing g - C 3 N 4 in the hydrothermal reaction can ensure its uniform dispersion and promote its uniform deposition on the surface of the flame retardant through the high solubility of supercritical water, improving the synergistic flame retardant effect; benzotriazole (BTA) is an efficient antioxidant, which can form a complex with the phosphate groups of piperazine pyrophosphate, improve the thermal oxidation stability of the flame retardant, reduce the hydrolysis of pyrophosphate at the same time, and enhance the weather resistance of the material; In the molecular modification stage, add imidazole and layered double metal hydroxide and carry out uniform dispersion treatment. Imidazole (IM) is a surface modifier. Its molecular structure contains an electron-rich N heterocycle, which can form hydrogen bonds and π - π stacking interactions with the surface of piperazine pyrophosphate, improve the dispersibility of the material, and prevent particle agglomeration; layered double metal hydroxide (LDH) is an efficient synergistic flame retardant. Metal oxides (such as MgO, Al 2 O 3) It can promote the carbonization of phosphate under high-temperature conditions, improving the compactness and mechanical strength of the fireproof carbon layer. Through uniform dispersion treatment (such as ultrasonic stirring or high-energy ball milling), it can ensure the formation of a stable coating layer of LDH on the surface of piperazine pyrophosphate particles, improving the dispersion stability of the flame retardant and enhancing its antioxidant and thermal stability.

[0013] Preferably, the dissolution of the precursor further includes: During the stirring process, slowly raise the temperature to 30 - 80 °C to avoid the precipitation of components due to local supersaturation. This temperature range helps to form a stable solution environment and prevent undissolved particles from affecting the uniformity and dispersibility of the flame retardant in subsequent steps. In addition, appropriate stirring (300 - 500 rpm) can enhance the mass transfer process, making the dissolution more uniform and reducing the precipitation of crystals caused by excessive local concentration. After the dissolution is completed, use filtration to remove undissolved impurities to ensure the purity of the solution. Using precision filtration (such as 0.2 - 1.0 μm microporous membrane or suction filtration) can remove undissolved solid particles, improve the uniformity of the solution, make the precursor solution purer, reduce defects generated during the crystallization process, and improve the structural integrity of the flame retardant. Filtration can not only exclude mechanical impurities but also reduce inorganic insoluble impurities in the system (such as some unstable phosphate precipitates), ensuring that the final product has high purity and high dispersibility. Use nitrogen protection to prevent the oxidation of some materials and make the reaction more stable. Continuously purging with low-flow nitrogen (such as 100 - 300 mL / min) can form an inert protective layer on the surface of the reaction system, effectively preventing the over-oxidation of metal ions (such as Al 3+ 、Ti 4+ ) at high temperatures and improving the thermal stability of the final product. In addition, the nitrogen environment can also reduce the hydrolysis reaction and lower the degradation side reaction that may occur to the pyrophosphate group, further optimizing the purity and chemical stability of the flame retardant.

[0014] The present invention provides a piperazine pyrophosphate flame retardant and its preparation method. It has the following beneficial effects: 1. By introducing graphitic carbon nitride (g-C 3 N 4 ), the present invention improves the thermal stability. Compared with traditional flame retardants, the present invention is more tenacious at high temperatures, solves the problem of easy decomposition in high-temperature environments, and provides stronger thermal protection for materials.

[0015] 2. Using titanium phosphate (TiPO 4 ) as an additive, the present invention has made a significant breakthrough in flame retardant performance. Compared with the scheme without titanium phosphate, the present invention has increased the oxygen index, ensuring that the material can maintain better flame resistance even in harsh environments.

[0016] 3. After introducing benzotriazole (BTA), the weather resistance of the present invention has been greatly improved. The addition of BTA effectively slows down the aging process of the material under humid and hot conditions, solving the problems that traditional flame retardants are vulnerable to the environment and have poor durability.

[0017] 4. By adopting the imidazole surface modification technology, the compatibility of the present invention with the matrix has been greatly improved. Compared with the flame retardant without surface treatment, the modified material has better fluidity and significantly improved mechanical properties, ensuring the stability and high performance of the composite material. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a flowchart of the method of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0019] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the specification of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0020] Please refer to the attached Figure 1 : Example 1: Optimization of the basic formula to improve flame retardant stability Take 70 parts of piperazine pyrophosphate, 10 parts of aluminum pyrophosphate, 8 parts of titanium phosphate, 5 parts of graphitic carbon nitride, 3 parts of benzotriazole, 4 parts of imidazole, 2 parts of layered double metal hydroxide, 9 parts of anhydrous piperazine, and 18 parts of pyrophosphoric acid, and dissolve them in deionized water in sequence. During the dissolution process, the stirring rate is controlled at 400 rpm, and the temperature is slowly raised to 50 °C and maintained for 30 minutes to ensure complete dissolution.

[0021] After filtering out the undissolved impurities, transfer the solution to a hydrothermal reaction kettle (160 °C, 6 h), and gradually introduce graphitic carbon nitride and benzotriazole under a nitrogen protection environment to prevent oxidation side reactions. After cooling to room temperature, centrifuge and use freeze-drying (-40 °C, 24 h) to remove water, and finally perform vacuum drying (120 °C, 8 h).

[0022] Example 2: Enhancement of the titanium phosphate structure to improve antioxidant capacity Weigh 65 parts of piperazine pyrophosphate, 12 parts of aluminum pyrophosphate, 10 parts of titanium phosphate, 4 parts of graphitic carbon nitride, 2 parts of benzotriazole, 5 parts of imidazole, 3 parts of layered double metal hydroxide, 8.5 parts of anhydrous piperazine, and 16 parts of pyrophosphoric acid, and add them to deionized water in sequence, with a stirring rate of 500 rpm, and slowly raise the temperature to 70 °C and keep it for 40 minutes.

[0023] After filtration, the precursor solution was placed in an autoclave and hydrothermally synthesized at 170 °C for 8 h. During this process, Ti-O-P network crosslinking occurred between titanium phosphate and pyrophosphate, improving the high-temperature resistance of the material. After the reaction was completed, it was freeze-dried at -50 °C for 36 h and then vacuum-dried at 140 °C for 6 h to obtain the flame retardant.

[0024] Example 3: Synergistic flame retardancy of layered double metal hydroxide (LDH) to improve dispersibility. Take 60 parts of piperazine pyrophosphate, 8 parts of aluminum pyrophosphate, 5 parts of titanium phosphate, 6 parts of graphitic carbon nitride, 4 parts of benzotriazole, 3 parts of imidazole, 4 parts of layered double metal hydroxide, 9.5 parts of anhydrous piperazine, and 20 parts of pyrophosphoric acid. Under the condition of a stirring rate of 400 rpm, deionized water was gradually added, and the temperature was raised to 60 °C and maintained for 30 minutes to form a uniform precursor solution.

[0025] After filtration, the solution was placed in a hydrothermal autoclave (150 °C, 10 h). During the process, LDH nanometer powder was slowly added, and ultrasonic dispersion treatment (40 kHz, 30 min) was carried out to promote the uniform distribution of the layered structure. After cooling, it was freeze-dried at -45 °C for 24 h and then vacuum-dried at 100 °C for 12 h to obtain the flame retardant.

[0026] Example 4: Synergistic enhancement of benzotriazole (BTA) to improve weather resistance Weigh 75 parts of piperazine pyrophosphate, 9 parts of aluminum pyrophosphate, 6 parts of titanium phosphate, 3 parts of graphitic carbon nitride, 5 parts of benzotriazole, 4 parts of imidazole, 2.5 parts of layered double metal hydroxide, 9 parts of anhydrous piperazine, and 17 parts of pyrophosphoric acid. Dissolve them in deionized water, slowly raise the temperature to 80 °C, and stir at 600 rpm for 40 minutes.

[0027] After complete dissolution, filter to remove impurities, transfer to a hydrothermal reaction kettle, and carry out hydrothermal reaction at 160 °C for 7 h. During this period, benzotriazole (BTA) was gradually added, and the addition rate was controlled at 1 mL / min to ensure the stable complexation of BTA with pyrophosphate. After cooling, it was freeze-dried at -50 °C for 30 h and then vacuum-dried at 120 °C for 8 h to obtain the flame retardant.

[0028] Comparative Example 1: Graphitic carbon nitride (g-C 3 N 4 )(corresponding to Example 1) Take 70 parts of piperazine pyrophosphate, 10 parts of aluminum pyrophosphate, 8 parts of titanium phosphate, 3 parts of benzotriazole, 4 parts of imidazole, 2 parts of layered double metal hydroxide, 9 parts of anhydrous piperazine, and 18 parts of pyrophosphoric acid, and dissolve them in deionized water in turn. The stirring rate was 400 rpm, and the temperature was slowly raised to 50 °C and maintained for 30 minutes to ensure complete dissolution.

[0029] After dissolution is completed, filter the undissolved impurities, transfer to a hydrothermal reactor (160 °C, 6 h), carry out the reaction under nitrogen protection, centrifuge and separate after cooling, freeze-dry at -40 °C for 24 h, and finally carry out vacuum drying at 120 °C for 8 h.

[0030] The only difference from Example 1 is that no graphitic carbon nitride (g-C 3 N 4 ) is added, and the rest of the process flow, temperature, stirring rate, etc. are exactly the same.

[0031] Comparative Example 2: Titanium phosphate (TiPO 4 )(corresponding to Example 2) is not added Weigh 65 parts of piperazine pyrophosphate, 12 parts of aluminum pyrophosphate, 4 parts of graphitic carbon nitride, 2 parts of benzotriazole, 5 parts of imidazole, 3 parts of layered double metal hydroxide, 8.5 parts of anhydrous piperazine, and 16 parts of pyrophosphoric acid. Add them to deionized water in sequence, with a stirring rate of 500 rpm, slowly heat up to 70 °C, and maintain for 40 minutes.

[0032] After dissolution is completed, filter, place the precursor solution in a hydrothermal kettle, carry out hydrothermal synthesis at 170 °C for 8 h, carry out the reaction under nitrogen protection during this period, centrifuge and separate after cooling, freeze-dry at -50 °C for 36 h, and carry out vacuum drying at 140 °C for 6 h.

[0033] The difference from Example 2 is that titanium phosphate (TiPO 4 ) is not added, and the rest of the parameters are exactly the same.

[0034] Comparative Example 3: Layered double metal hydroxide (LDH) is not introduced (corresponding to Example 3) Take 60 parts of piperazine pyrophosphate, 8 parts of aluminum pyrophosphate, 5 parts of titanium phosphate, 6 parts of graphitic carbon nitride, 4 parts of benzotriazole, 3 parts of imidazole, 9.5 parts of anhydrous piperazine, and 20 parts of pyrophosphoric acid. Add them to deionized water, with a stirring rate of 400 rpm, heat up to 60 °C, and maintain for 30 minutes to form a uniform precursor solution.

[0035] After complete dissolution, filter the impurities, place the precursor solution in a hydrothermal kettle (150 °C, 10 h), but do not add LDH and do not carry out ultrasonic dispersion treatment, and only rely on mechanical stirring (300 rpm) to mix evenly. After cooling, freeze-dry at -45 °C for 24 h and carry out vacuum drying at 100 °C for 12 h to obtain the flame retardant.

[0036] The difference from Example 3 is that LDH is not added and the ultrasonic dispersion step is cancelled, and the rest of the process remains the same.

[0037] Comparative Example 4: Benzotriazole (BTA) is not added (corresponding to Example 4) Weigh 75 parts of piperazine pyrophosphate, 9 parts of aluminum pyrophosphate, 6 parts of titanium phosphate, 3 parts of graphitic carbon nitride, 4 parts of imidazole, 2.5 parts of layered double metal hydroxide, 9 parts of anhydrous piperazine, and 17 parts of pyrophosphoric acid. Dissolve them according to the same process, slowly heat up to 80 °C, with a stirring rate of 600 rpm, and continue for 40 minutes.

[0038] After the dissolution is completed, filter the undissolved impurities, transfer them to a hydrothermal reaction kettle, and carry out a hydrothermal reaction at 160 °C for 7 h without adding benzotriazole (BTA). The remaining process parameters remain unchanged, and still use freeze-drying at -50 °C for 30 h and vacuum drying at 120 °C for 8 h.

[0039] The only difference between this comparative example and Example 4 is that BTA is not added, and the other preparation processes are exactly the same.

[0040] Comparative experiment: In this experiment, a standardized test method is adopted to ensure the scientificity and comparability of the data. The test materials are all flame retardants synthesized in the laboratory, and their preparation methods have been described above. The test process strictly follows ASTM, UL, and ISO standards to reduce external environmental interference and ensure the objectivity of the data. The experimental steps are as follows: 1. Thermal stability test (TGA thermogravimetric analysis) Experimental materials: Flame retardant powders prepared in Examples 1 - 4 and corresponding Comparative Examples 1 - 4.

[0041] Experimental instrument: Thermogravimetric analyzer (TGA), nitrogen atmosphere, heating rate 10 °C / min.

[0042] Experimental steps: Take 10 mg of the sample and spread it evenly in a platinum crucible.

[0043] Set the temperature range from 30 to 800 °C and the nitrogen flow rate at 50 mL / min.

[0044] Record the initial decomposition temperature (T 0 ), 50% weight loss temperature (T 50 ), and char residue rate at 800 °C.

[0045] Calculate the thermal decomposition rate and analyze the material stability.

[0046] 2. Flame retardancy test (LOI & UL - 94) Experimental materials: PP composite containing flame retardant (filled with 20 wt% flame retardant).

[0047] Experimental instruments: Oxygen index meter, UL - 94 vertical burning tester.

[0048] Experimental steps: Use a twin-screw extruder to prepare PP / flame retardant composites.

[0049] According to ASTM D2863, the limiting oxygen index (LOI) was determined.

[0050] For the UL-94 rating test, the burning time, extinguishing time, and dripping situation were observed.

[0051] Statistical data were collected to analyze the influence of the flame retardant on the combustion behavior.

[0052] 3. Dispersibility test (Zeta potential & particle size analysis) Experimental materials: Aqueous dispersion (0.5 wt% flame retardant suspension).

[0053] Experimental instruments: Zeta potential analyzer, laser particle size analyzer.

[0054] Experimental procedures: A 0.5 wt% aqueous flame retardant dispersion was prepared and ultrasonically treated for 10 min.

[0055] The Zeta potential was measured to judge the stability of the suspension.

[0056] The particle sizes D50 and D90 were measured to analyze the particle size distribution.

[0057] Statistical data were collected to evaluate the dispersibility of different flame retardants.

[0058] 4. Weather resistance test (hydrothermal aging) Experimental materials: PP / flame retardant composite (filled with 20 wt% flame retardant).

[0059] Experimental instruments: Thermo-hygrostat chamber, SEM scanning electron microscope, FTIR infrared spectrometer.

[0060] Experimental procedures: The samples were aged at 60 °C and 85% RH for 500 h.

[0061] The mass loss rate was recorded and the surface morphology (SEM) was observed.

[0062] FTIR was used to determine the chemical structure changes.

[0063] The weather resistance stability of the flame retardant was comprehensively analyzed.

[0064] 5. Interfacial compatibility test (MFR & mechanical properties) Experimental materials: PP / flame retardant composite (filled with 20 wt% flame retardant).

[0065] Experimental instruments: Melt flow rate instrument, universal material testing machine.

[0066] Experimental procedures: The MFR was measured using a melt flow rate instrument to analyze the fluidity.

[0067] The tensile strength and impact strength were measured using a universal material testing machine.

[0068] Statistical data was used to evaluate the effect of the flame retardant on the mechanical properties of the composite material.

[0069] The test data for each experiment Experiment summary: The thermal stability test showed that graphitic carbon nitride (g-C 3 N 4 ) significantly improved the thermal stability in Example 1. Compared with Comparative Example 1, the T 0 increased by 30 °C, and the 50% weight loss temperature and char yield also improved. This indicates that the introduction of g-C 3 N 4 effectively enhanced the structural stability of the material at high temperatures, thus improving the overall thermal stability performance. In terms of flame retardancy, the oxygen index (LOI) and UL-94 rating of Example 2 were more excellent than those of Comparative Example 2, showing the significant role of titanium phosphate in the flame retardant effect. The introduction of titanium phosphate improved the oxygen tolerance of the material, effectively inhibited the oxidation reaction during combustion, and made the material show stronger flame resistance under flame exposure.

[0070] The dispersibility test further verified the importance of layered double hydroxide (LDH) in Example 3. The addition of LDH not only increased the Zeta potential of the sample but also improved the dispersibility of the particles, thus ensuring the uniformity of the flame retardant. Compared with Comparative Example 3, the D50 and D90 values of Example 3 were smaller, indicating that the particles of the material were finer and had better dispersibility. In the weather resistance test, the introduction of benzotriazole (BTA) significantly reduced the mass loss of Example 4 compared with Comparative Example 4 in a humid and hot environment, and the surface morphology and chemical structure remained good. Benzotriazole as a weathering agent helped to improve the antioxidant ability of the material and reduced the performance degradation caused by long-term humid and hot aging.

[0071] Although the embodiments of the present invention have been shown and described, it will be understood by those of ordinary skill in the art that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention, and the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A piperazine pyrophosphate flame retardant, characterized in that: The flame retardant comprises the following components in parts by weight: Piperazine pyrophosphate: 50-80 parts; Aluminum pyrophosphate: 5-15 parts; Titanium phosphate: 3-10 parts; Graphite phase carbon nitride: 2-8 parts; Benzotriazole: 1-5 parts; Imidazole: 2-6 parts; Layered double metal hydroxide: 1-4 parts; Anhydrous piperazine: 8-10 parts; Pyrophosphoric acid: 15-20 parts.

2. A method for preparing a piperazine pyrophosphate flame retardant, characterized in that: Using the piperazine pyrophosphate flame retardant according to claim 1 comprises the following steps: S1. Precursor dissolution: dissolve the raw materials, mix them evenly, and form a stable reaction system; S2, supercritical hydrothermal synthesis: react at a specific temperature and pressure to form highly stable piperazine pyrophosphate, improving high temperature resistance; S3. Molecular modification: Optimize the molecular structure of piperazine pyrophosphate by functional group modification to increase thermal stability, dispersion and chemical stability; S4, synergistic flame retardant modification: combined with flame retardants, increase flame retardancy and enhance compatibility with polymers; S5. Low-temperature acid treatment and drying: remove by-products, optimize crystal structure and particle size distribution, and ensure product stability and fluidity.

3. The method for preparing a piperazine pyrophosphate flame retardant according to claim 2, characterized in that: The precursor dissolution comprises: In a high temperature autoclave, add 50-100L of deionized water and maintain stirring at 300-500rpm; First, add anhydrous piperazine and continue stirring for 30-60 minutes to form a uniform solution; Then add pyrophosphoric acid and stir at a dissolving temperature of 30-80°C to form a transparent solution; Finally, add aluminum pyrophosphate and titanium phosphate, and use ultrasonic or mechanical stirring to improve the dispersion uniformity of the components.

4. The method for preparing a piperazine pyrophosphate flame retardant according to claim 2, characterized in that: The supercritical hydrothermal synthesis comprises: Under the conditions of temperature of 300-400°C and pressure of 15-30MPa, the precursor solution is introduced into a supercritical reactor; and maintaining the reaction for 3-6 hours to allow piperazine pyrophosphate to form a stable crystal structure; After the reaction is completed, the temperature is slowly lowered to 50-100°C to keep the physical structure intact; The solid phase product was collected by solid-liquid separation and washed with deionized water for 3-5 times to remove by-products.

5. The method for preparing a piperazine pyrophosphate flame retardant according to claim 2, characterized in that: The molecular modifications include: Adding benzotriazole and imidazole into the synthesized product to carry out interface modification treatment; Suspend piperazine pyrophosphate in 50-100 L of ethanol solution and stir until completely dispersed; The modifying agent is evenly distributed on the surface of piperazine pyrophosphate by heat treatment or solvent volatilization, wherein the pH is 7.0-8.5 pH, the temperature is maintained at 70-100° C. and stirring is performed for 2-5 hours.

6. The method for preparing a piperazine pyrophosphate flame retardant according to claim 2, characterized in that: The synergistic flame retardant modification includes: adding graphite phase carbon nitride and layered double metal hydroxide to the modified piperazine pyrophosphate; The synergistic flame retardant component is fully combined with the main flame retardant through co-precipitation or physical mixing; Use drying or vacuum treatment to remove excess solvent or unreacted products in the system.

7. The method for preparing a piperazine pyrophosphate flame retardant according to claim 2, characterized in that: The low temperature acid treatment and drying include: The synthesized product is acid-treated with 0.1-1 parts of low-concentration dilute sulfuric acid for 30-60 minutes to improve the crystallinity of piperazine pyrophosphate; Freeze drying is used at a temperature of -50-0°C for 12-48 hours to prevent high temperature degradation; Use vacuum drying at 100-150℃ for 4-12 hours to ensure structural stability.

8. The method for preparing a piperazine pyrophosphate flame retardant according to claim 3, characterized in that: The flame retardant preparation sequence is: Firstly, piperazine pyrophosphate, aluminum pyrophosphate and titanium phosphate are dissolved to form a precursor solution; During the hydrothermal synthesis, graphite phase carbon nitride and benzotriazole are gradually introduced; In the molecular modification stage, imidazole and layered double hydroxide are added and uniformly dispersed.

9. The method for preparing a piperazine pyrophosphate flame retardant according to claim 3, characterized in that: The precursor dissolution further comprises: During the stirring process, slowly raise the temperature to 30-80°C to avoid local oversaturation leading to component precipitation; After dissolution is completed, undissolved impurities are removed by filtration to ensure the purity of the solution; Nitrogen protection is used to prevent oxidation of some materials and make the reaction more stable.

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