Composite flame retardant, preparation method thereof and flame-retardant functional master batch

Abstract

This invention belongs to the field of flame retardant materials technology, specifically relating to a composite flame retardant and its preparation method, as well as flame retardant functional masterbatch. Through multi-level composite and structural design, this invention efficiently synergizes char formation, physical barriers, and catalytic flame retardant mechanisms. The resulting composite flame retardant significantly improves flame retardant and smoke suppression performance while effectively addressing the shortcomings of traditional flame retardants, such as high hygroscopicity, poor compatibility with the matrix, and insufficient char layer strength. It is suitable for high-performance halogen-free flame retardant modification of various polymers, including polyolefins and engineering plastics.

Description

Technical Field

[0001] This invention belongs to the field of flame retardant materials technology, specifically relating to a composite flame retardant and its preparation method, and flame retardant functional masterbatch. Background Technology

[0002] Polymer materials are widely used in various sectors of the national economy due to their excellent properties, but their inherent flammability poses a significant fire safety hazard. Developing efficient and environmentally friendly flame-retardant technologies is crucial to ensuring their safe application. Intumescent flame retardants (IFRs), with their advantages of being halogen-free, producing low smoke, and resisting dripping, have become a research hotspot in the field of flame retardancy. A typical IFR system consists of an acid source (such as ammonium polyphosphate), a carbon source (such as pentaerythritol), and a gas source (such as melamine). When heated, it forms a porous and dense expanded char layer on the polymer surface, thereby providing heat insulation, oxygen barrier, and smoke suppression for flame retardant effects.

[0003] Pentaerythritol phosphate melamine salt (MPP), as a "three-in-one" single-molecule intumescent flame retardant integrating acid, carbon, and gas sources, has attracted much attention due to its fixed component ratio, good synergistic effect, and high flame retardant efficiency. However, traditional MPP still has some shortcomings in practical applications that urgently need to be addressed: First, it is highly hygroscopic and easily absorbs moisture in high humidity environments, which not only affects processing performance and product appearance but also seriously degrades the electrical insulation properties and long-term durability of the flame-retardant polymer; second, MPP has poor compatibility with some non-polar polymer matrices (such as polyolefins), and high addition levels can easily lead to a significant decrease in the mechanical properties of the material (especially toughness and impact strength); third, the expanded carbon layer formed by MPP catalysis often lacks sufficient strength, density, and adhesion under high temperature or strong heat flow impact, making it prone to cracking or detachment from the matrix, leading to "secondary ignition" and limiting its application in high-end or harsh environments.

[0004] To overcome these drawbacks, researchers typically employ physical compounding or chemical modification methods. Common strategies include: compounding with inorganic hydroxides (such as magnesium hydroxide and aluminum hydroxide) to utilize their smoke-suppressing, filling, and endothermic effects, but this often requires extremely high addition amounts; compounding with layered silicates (such as montmorillonite) to utilize their layered barrier effect to enhance the carbon layer, but simple physical mixing makes it difficult to achieve uniform dispersion at the nanoscale, resulting in weak interfacial interactions and limited synergistic efficiency; and introducing metal compounds (such as zinc oxide and ammonium molybdate) as synergists, but such additives may affect the matrix color or produce other side effects.

[0005] Therefore, it is crucial to develop a composite flame retardant that can impart excellent flame retardant properties, smoke suppression properties, and better mechanical property retention to polymer substrates at a low addition amount, while improving the hygroscopicity of MPP. Summary of the Invention

[0006] The purpose of this invention is to provide a composite flame retardant, its preparation method, and a flame-retardant masterbatch. The composite flame retardant provided by this invention combines the efficient expansion and char formation capability of MPP with the enhancement and catalytic function of core-shell nanounits on the char layer. It is expected to impart excellent flame-retardant properties, smoke suppression properties, and better mechanical property retention to polymer substrates at relatively low addition levels, while simultaneously improving the hygroscopicity of MPP.

[0007] To achieve the above objectives, the present invention provides the following technical solution: The present invention provides a composite flame retardant comprising a pentaerythritol phosphate melamine salt matrix and an additive dispersed in the matrix, wherein the additive has a core-shell structure, wherein the core is montmorillonite nanosheets and the shell is nickel phosphate.

[0008] Preferably, the montmorillonite nanosheets have a single-layer or few-layer structure with a thickness of 1~15nm and a lateral dimension of 2~10μm.

[0009] Preferably, the thickness of the shell layer is 2~50nm.

[0010] Preferably, the additive has a mass percentage content of 3-50% in the composite flame retardant.

[0011] This invention also provides a method for preparing the composite flame retardant described in the above technical solution, comprising the following steps: Step 1: Add soluble nickel source solution and phosphate source solution to the montmorillonite nanosheet suspension for in-situ coating to obtain the additive; Step 2: During the synthesis reaction of pentaerythritol phosphate melamine salt, the additive is added to disperse it evenly and combine it with the generated pentaerythritol phosphate melamine salt matrix to obtain the composite flame retardant.

[0012] Preferably, in step 1, the soluble nickel source includes at least one of nickel nitrate, nickel chloride, nickel sulfate, and nickel acetate; the phosphoric acid source includes at least one of phosphoric acid, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, sodium phosphate, and polyphosphoric acid. The pH value of the system during the in-situ coating is 3.0~8.0; the temperature of the in-situ coating is 20~60℃, and the time is 0.5~6h; the in-situ coating is carried out under stirring conditions.

[0013] Preferably, step 2 specifically involves: synthesizing the composite flame retardant by mixing pentaerythritol, phosphate source, melamine, and additives in water using a one-step method and carrying out a liquid-phase reaction; the temperature of the liquid-phase reaction is 90~130℃, and the time is 2~8h.

[0014] Preferably, step 2 specifically involves a two-step synthesis method, in which pentaerythritol is reacted with a phosphate source to generate a pentaerythritol phosphate intermediate; then, the pentaerythritol phosphate intermediate, melamine, and additives are mixed in water and subjected to a liquid-phase reaction to obtain the composite flame retardant; the temperature of the liquid-phase reaction is 70~110℃, and the time is 1~6h.

[0015] The present invention also provides a flame-retardant functional masterbatch, comprising a polymer and a flame retardant; The flame retardant is the composite flame retardant described in the above technical solution or the composite flame retardant prepared by the preparation method described in the above technical solution.

[0016] Preferably, the flame retardant content of the flame retardant masterbatch is 20-80% by mass; The polymer includes at least one of polypropylene, polybutylene terephthalate, and polycarbonate.

[0017] Compared with the prior art, the present invention has the following significant advantages and beneficial effects: Excellent synergistic flame retardant and smoke suppression properties: This invention achieves multiple synergistic effects at the nanoscale by combining the expansion and char formation of MPP with the physical barrier of montmorillonite nanosheets and the catalytic char formation of nickel phosphate. During combustion, MPP rapidly forms an expanded char layer framework, while the core-shell nanounits dispersed within it (i.e., additives, montmorillonite@nickel phosphate) act as reinforcement, penetrating the char layer to improve its density and strength. On the other hand, nickel phosphate catalyzes further dehydration and cross-linking of the incompletely reacted matrix, enhancing the quality of the char layer and reducing the generation of combustible smoke, thus achieving highly efficient "physical-chemical" dual flame retardancy and smoke suppression.

[0018] Significantly improved hygroscopicity and compatibility: A nickel phosphate shell covers the surface of hydrophilic montmorillonite nanosheets, while the core-shell nanounits are embedded within the matrix during MPP synthesis, and are to some extent encapsulated or isolated by organic MPP molecules. This structural design effectively reduces the overall surface polarity of the composite flame retardant, thus significantly improving its hygroscopicity. Simultaneously, the uniform dispersion of the core-shell nanounits in the MPP matrix and the potential interfacial interactions between them indirectly improve the overall compatibility of MPP with the polymer matrix, which is beneficial for maintaining mechanical properties.

[0019] Enhanced char layer stability and long-lasting protection: The introduced montmorillonite nanosheets act as a rigid "skeleton," significantly enhancing the mechanical strength and heat erosion resistance of the expanded char layer, preventing it from cracking or detaching under high heat flux. The catalytic effect of nickel phosphate makes the char layer denser and more cross-linked. This "enhanced" expanded char layer provides more durable and reliable protection to the matrix, broadening the application range of flame-retardant materials.

[0020] Excellent processing applicability and versatility: The preparation method provided by this invention offers controllable processes, enabling uniform and stable dispersion of the nano-reinforcing phase in the MPP matrix. Pre-forming the composite flame retardant into a high-concentration functional masterbatch greatly facilitates its use in various polymer processing equipment (such as twin-screw extruders and injection molding machines), solving the common problem of difficult dispersion of nanofillers. This composite flame retardant is suitable for various polymer systems, imparting excellent flame retardant properties to materials while potentially having a positive impact on their mechanical and thermal properties.

[0021] In summary, through meticulous structural design, this invention has successfully prepared a novel nanocomposite flame retardant and functional masterbatch that integrates high efficiency, low smoke, low moisture absorption, and easy processing. It effectively solves the inherent defects of traditional MPP and shows great application potential in high-requirement flame retardant fields such as electronics, electrical appliances, wires and cables, transportation, and building materials. Detailed Implementation

[0022] The present invention provides a composite flame retardant comprising a pentaerythritol phosphate melamine salt matrix and an additive dispersed in the matrix, wherein the additive has a core-shell structure, wherein the core is montmorillonite nanosheets and the shell is nickel phosphate.

[0023] In this invention, the montmorillonite nanosheets are single-layer or few-layer structures, wherein the number of layers in the few-layer structure is preferably no more than 8 layers, specifically 2 to 4 layers; the thickness is preferably 1 to 15 nm, specifically 8 to 12 nm; and the lateral dimension is preferably 2 to 10 μm, specifically 3 to 5 μm.

[0024] In this invention, the nickel phosphate is uniformly and continuously coated on the surface of montmorillonite nanosheets, and the thickness of the shell is 2~50nm, specifically 3~6nm or 7~10nm.

[0025] In this invention, the mass percentage of the additive in the composite flame retardant is preferably 3-50%, specifically 3%, 5%, 10%, 15%, 20%, 25%, or 30%.

[0026] This invention also provides a method for preparing the composite flame retardant described in the above technical solution, comprising the following steps: Step 1: Add soluble nickel source solution and phosphate source solution to the montmorillonite nanosheet suspension for in-situ coating to obtain the additive; Step 2: During the synthesis reaction of pentaerythritol phosphate melamine salt, the additive is added to disperse it evenly and combine it with the generated pentaerythritol phosphate melamine salt matrix to obtain the composite flame retardant.

[0027] Step 1 of the present invention involves adding a soluble nickel source solution and a phosphate source solution to a montmorillonite nanosheet suspension for in-situ coating to obtain an additive.

[0028] In this invention, the montmorillonite nanosheet suspension is preferably obtained by preparation; the preparation method preferably includes: Montmorillonite powder and water are mixed and stirred to swell. Then, a surfactant is added to carry out the reaction. After the reaction is completed, impurities are removed, and the resulting modified montmorillonite precipitate is redispersed in deionized water. The precipitate is then sonicated in an ice-water bath. The sonicated suspension is separated, and the upper dispersion is collected as the montmorillonite nanosheet suspension.

[0029] In this invention, the preferred mass ratio of montmorillonite powder to water is 10:1000; the preferred stirring and swelling time is 4 hours; the preferred surfactant includes at least one of dodecyltrimethylammonium bromide, disdecyldimethylammonium chloride, and hexadecyltrimethylammonium bromide; the preferred mass ratio of montmorillonite powder to surfactant is 10:25; the preferred reaction is carried out under stirring conditions, the preferred reaction temperature is 85°C, and the preferred reaction time is 10 hours. In this invention, the preferred method for impurity removal is to centrifuge the mixture and wash it three times with water to remove excess surfactant and exchanged ions; the preferred centrifugation speed is 10000 rpm, and the preferred centrifugation time is 15 minutes. In this invention, the preferred ultrasonic power is 750 W, with a 5-second working time followed by a 5-second interval, and the preferred total ultrasonic time is 1.5 hours. In this invention, the preferred separation speed is 4000 rpm, and the preferred separation time is 15 minutes. In this invention, the preferred solid content of the montmorillonite nanosheet suspension is 1.5 wt%.

[0030] In this invention, the soluble nickel source preferably includes at least one of nickel nitrate, nickel chloride, nickel sulfate, and nickel acetate; the mass concentration of the soluble nickel source solution is preferably 5-20 wt%, and the solvent is preferably deionized water; the phosphoric acid source preferably includes at least one of phosphoric acid, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, sodium phosphate, and polyphosphoric acid; the mass concentration of the phosphoric acid source solution is preferably 5-25%, specifically 5%, 6%, 10%, 15%, or 20%; and the solvent is preferably deionized water.

[0031] In this invention, the preferred order of adding the soluble nickel source solution and the phosphate source solution is as follows: the soluble nickel source solution is added dropwise to the montmorillonite nanosheet suspension, the pH of the system is adjusted to 3.0-8.0 using ammonia, and then the phosphate source solution is added dropwise. In this invention, the dropwise addition rate of both the soluble nickel source solution and the phosphate source solution is preferably 0.5-5 mL / min; the dropwise addition is preferably carried out under stirring conditions, and the dropwise addition temperature is preferably the same as the subsequent in-situ coating temperature. In this invention, the pH value of the system during in-situ coating is preferably 3.0 to 8.0, specifically 3.0, 4.0, 5.0, 6.0, 7.0, or 8.0; the temperature of the in-situ coating is preferably 20 to 60°C, specifically 20°C, 30°C, 40°C, 50°C, or 60°C; the time is preferably 0.5 to 6 hours, specifically 0.5 hours, 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, or 6 hours; and the in-situ coating is preferably carried out under stirring conditions.

[0032] In this invention, the in-situ coating process preferably includes: cooling the resulting gray-green suspension to room temperature and collecting the solid product by centrifugation; washing the solid product three times alternately with deionized water and anhydrous ethanol; and finally freeze-drying and grinding the product. The centrifugation speed is preferably 12,000 rpm and the time is preferably 20 min. The freeze-drying temperature is preferably -50°C and the time is preferably 48 h.

[0033] After obtaining the additive, step 2 of the present invention is to add the additive during the synthesis reaction of pentaerythritol phosphate melamine salt, so that it is uniformly dispersed and compounded in the generated pentaerythritol phosphate melamine salt matrix, thereby obtaining the composite flame retardant.

[0034] In this invention, step 2 is preferably performed as follows: a one-step synthesis is adopted, in which pentaerythritol, a phosphoric acid source, melamine, and additives are mixed in water and subjected to a liquid-phase reaction to obtain the composite flame retardant; the phosphoric acid source preferably includes at least one of phosphoric acid, ammonium dihydrogen phosphate, and diammonium hydrogen phosphate; the mass ratio of pentaerythritol, phosphoric acid source, and melamine is preferably 1:0.8~1.8:0.6~1.5, specifically 18:15:12; the mass ratio of the total mass of pentaerythritol, phosphoric acid source, and melamine to the mass of additives is preferably 100:3~50. In this invention, the temperature of the liquid-phase reaction is preferably 90~130℃, specifically 90℃, 100℃, 110℃, 120℃, or 130℃, and the time is preferably 2~8h, specifically 2h, 3h, 4h, 5h, 6h, 7h, or 8h; the liquid-phase reaction is preferably carried out under stirring and reflux conditions. In this invention, the liquid-phase reaction is preferably further subjected to post-processing, which preferably includes: cooling the reaction system to room temperature, collecting the white solid precipitate by filtration, washing it three times with hot water at 80°C, and then washing it once with anhydrous ethanol; placing the solid product in a vacuum drying oven and drying it at 100°C for 12 hours to obtain a white powder, which is the composite flame retardant.

[0035] In this invention, step 2 is preferably a two-step synthesis method, in which pentaerythritol is reacted with a phosphate source to generate a pentaerythritol phosphate intermediate; then the pentaerythritol phosphate intermediate, melamine and additives are mixed in water and subjected to a liquid-phase reaction to obtain the composite flame retardant.

[0036] In this invention, the phosphoric acid source preferably includes at least one of phosphoric acid and polyphosphoric acid; the mass ratio of pentaerythritol to phosphoric acid source is preferably 1:0.8~1.5; the reaction temperature is preferably 80~160℃, the reaction time is preferably 1~3h, and the reaction is preferably carried out under stirring conditions.

[0037] In this invention, the preferred mass ratio of pentaerythritol, melamine, and additives is 1:0.6~1.5:0.03~0.5; the preferred temperature of the liquid-phase reaction is 70~110℃, more preferably 90℃; and the preferred time is 1~6h, more preferably 4h. In this invention, the post-treatment process of the liquid-phase reaction preferably refers to the post-treatment process in the above technical solution, and will not be repeated here.

[0038] The present invention also provides a flame-retardant functional masterbatch, comprising a polymer and a flame retardant; wherein the flame retardant is the composite flame retardant described in the above technical solution or the composite flame retardant prepared by the preparation method described in the above technical solution; In this invention, the flame retardant content of the flame retardant in the flame retardant masterbatch is preferably 20-80% by mass, specifically 20%, 30%, 40%, 47.7%, 50%, 60%, 70%, or 80%; the polymer preferably includes at least one of polypropylene, polybutylene terephthalate, and polycarbonate.

[0039] In this invention, the flame-retardant masterbatch preferably includes additives, which preferably include at least one of lubricant and antioxidant; the lubricant preferably includes at least one of polyethylene wax, oxidized polyethylene wax, ethylene bis-stearamide, calcium stearate, zinc stearate, and montan wax; the mass percentage of lubricant in the flame-retardant masterbatch is preferably 0.5-5%; the antioxidant preferably includes hindered phenolic antioxidants or phosphite antioxidants (such as antioxidant 168), the hindered phenolic antioxidants preferably include antioxidant 1010 or antioxidant 1076, and the phosphite antioxidant is preferably antioxidant 168; the mass percentage of antioxidant in the flame-retardant masterbatch is preferably 0.1-2%; the mass percentage of additive in the flame-retardant masterbatch is preferably 1-10%.

[0040] In this invention, the preparation method of the flame-retardant functional masterbatch preferably includes: mixing the polymer and the flame retardant and then extruding and granulating; the extrusion is preferably carried out using a co-rotating twin-screw extruder, the screw diameter of the co-rotating twin-screw extruder is preferably 35 mm, and the length-to-diameter ratio is preferably 40:1; the co-rotating twin-screw extruder preferably includes five temperature zones.

[0041] In this invention, when the polymer is polypropylene (PP) (with a relatively low melting temperature): the temperature of the first temperature zone is preferably 160~180℃ (feeding section), the temperature of the second temperature zone is preferably 190~210℃ (melting section), the temperature of the third temperature zone is preferably 200~220℃ (plasticizing section), the temperature of the fourth temperature zone is preferably 200~220℃ (homogenization section), and the temperature of the fifth temperature zone is preferably 190~210℃ (die head section).

[0042] In this invention, when the polymer is polyethylene terephthalate (PET) (which has a high melting temperature and requires temperature gradient control): the first temperature zone is preferably 160~170℃, the second temperature zone is preferably 175~185℃, the third temperature zone is preferably 250~260℃, the fourth temperature zone is preferably 255~265℃, and the fifth temperature zone is preferably 245~255℃.

[0043] In this invention, when the polymer is polycarbonate (PC) (high melting temperature and high melt viscosity): the first temperature zone is preferably 70~90℃, the second temperature zone is preferably 230~270℃, the third temperature zone is preferably 260~310℃, the fourth temperature zone is preferably 290~320℃, and the fifth temperature zone is preferably 290~320℃.

[0044] In this invention, the screw speed of the co-rotating twin-screw extruder is preferably 200-300 rpm, more preferably 250 rpm. In this invention, the granulation method is preferably water-cooled pelletizing; after water-cooled pelletizing, drying is also preferred. For polypropylene masterbatch, the drying temperature is preferably 80°C, and the drying time is preferably 2-4 hours; for polyethylene terephthalate masterbatch, the drying temperature is preferably 120°C, and the drying time is preferably 4-6 hours; for polycarbonate masterbatch, the drying temperature is preferably 140°C, and the drying time is preferably 4-6 hours.

[0045] In this invention, when the flame-retardant masterbatch also includes additives, the additives are preferably added during the mixing process.

[0046] Unless otherwise specified, the materials and equipment used in this invention are all commercially available products in the field.

[0047] The technical solutions of this invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0048] Example 1 Preparation of montmorillonite nanosheet (MMT) dispersion: 10.0 g of montmorillonite powder was weighed and dispersed in 1000 mL of deionized water. The mixture was mechanically stirred for 4 hours to allow it to swell fully. 25.0 g of cetyltrimethylammonium bromide (CTAB) was added, and the mixture was stirred vigorously in an 85°C water bath for 10 hours. After the reaction, the mixture was centrifuged (10000 rpm, 15 min) and washed three times with water to remove excess CTAB and exchanged ions. The resulting modified montmorillonite precipitate was redispersed in 800 mL of deionized water and sonicated for 1.5 h using an ultrasonic cell disruptor (750 W power, work / interval = 5 s / 5 s) in an ice-water bath. Subsequently, the sonicated suspension was centrifuged at 4000 rpm for 15 minutes, and the upper stable milky white dispersion was collected. This was the exfoliated MMT nanosheet dispersion, with a solid content of approximately 1.5 wt%. In-situ chemical deposition coating of nickel phosphate: Take all of the above MMT nanosheet dispersions and transfer them to a 2000 mL three-necked flask. Heat to 70 °C and maintain mechanical stirring. Dissolve 17.8 g of nickel nitrate hexahydrate (Ni(NO3)2·6H2O) in 100 mL of deionized water, and dissolve 9.9 g of diammonium hydrogen phosphate ((NH4)2HPO4) in 100 mL of deionized water to obtain solutions A and B, respectively. Under stirring, slowly add solution A to the MMT dispersion over approximately 30 minutes. Then, adjust the pH of the system to 6.0 with ammonia. Maintaining the temperature and pH, slowly add solution B to the system. The addition time was about 30 minutes; after the addition was completed, the reaction was continued at 70℃ and pH=6.0 for 4 hours; after the reaction was completed, the resulting gray-green suspension was cooled to room temperature and the solid was collected by centrifugation (12000 rpm, 20 min); the solid product was washed three times alternately with deionized water and anhydrous ethanol; finally, the product was freeze-dried at -50℃ for 48 hours, and after grinding, a light gray-green MMT@NiP nanomaterial powder (i.e., additive) was obtained, which was designated as MMT@NiP-1 (MMT has 2-4 layers, a thickness of 8~12 nm, a lateral dimension of 3~5 μm; and a shell thickness of 3~6 nm).

[0049] Example 2 The additive was prepared according to the method of Example 1, wherein the amount of nickel nitrate hexahydrate was adjusted to 11.9 g and the amount of diammonium hydrogen phosphate was adjusted to 6.6 g; The resulting product is denoted as MMT@NiP-2 (MMT has 2-4 layers, a thickness of 8-12 nm, and a lateral dimension of 3-5 μm; the shell thickness is 7-10 nm).

[0050] Calculations show that the mass fraction of nickel phosphate in MMT@NiP-1 is approximately 40%, while the mass fraction of nickel phosphate in MMT@NiP-2 is approximately 25%.

[0051] Example 3 One-step preparation of MPP / MMT@NiP-1 composite flame retardant: Raw materials: 18.0 g pentaerythritol (PER), 15.0 g phosphoric acid (85%, H3PO4), 12.0 g melamine (MEL), 5.0 g MMT@NiP-1 powder prepared in Example 1, and 300 mL deionized water; Synthesis: Add all raw materials to a 500mL three-necked flask at once and stir to form a suspension; heat to 120℃ and start the reflux reaction, and continue stirring at this temperature for 5 hours; Post-processing: After the reaction was completed, the mixture was cooled to room temperature, the white solid precipitate was collected by filtration, and washed three times with hot water at 80°C, and then washed once with anhydrous ethanol; the solid product was placed in a vacuum drying oven and dried at 100°C for 12 hours to obtain a white powdery composite flame retardant, denoted as C-IFR-1.

[0052] The calculated mass fraction of MMT@NiP-1 in C-IFR-1 is 10%.

[0053] Example 4 Two-step preparation of MPP / MMT@NiP-2 composite flame retardant Synthesis of pentaerythritol phosphate (PEPA) intermediate: 20.0 g of pentaerythritol (PER) and 16.7 g of phosphoric acid (85%, H3PO4) were added to a 250 mL flask, heated to 160 °C in an oil bath, and stirred for 3 hours to obtain a viscous PEPA intermediate; Synthesis of composite flame retardant: The above-mentioned PEPA intermediate, 13.3g of melamine (MEL), 10.0g of MMT@NiP-2 powder prepared in Example 2 and 200mL of deionized water were added to a 500mL three-necked flask, heated to 90°C with stirring, and reacted at this temperature for 4 hours. Post-processing: Same as in Example 3, after cooling, filtering, washing, and drying, a composite flame retardant, denoted as C-IFR-2, was obtained. The mass fraction of MMT@NiP-2 in C-IFR-2 was 20%.

[0054] Comparative Example 1 Preparation of pure MPP The one-step method of Example 3 was followed, but without the addition of MMT@NiP-1. Specifically, only 18.0 g of PER, 15.0 g of H3PO4, 12.0 g of MEL, and 300 mL of water were used, and the reaction was carried out at 120°C for 5 hours. The post-treatment was the same, yielding pure MPP powder, denoted as P-IFR.

[0055] Comparative Example 2 Physical mixture of MPP and MMT The pure P-IFR powder prepared according to Comparative Example 1 was mixed with uncoated MMT nanosheets (obtained by freeze-drying the MMT nanosheet dispersion obtained in Example 1) in a high-speed mixer at a mass ratio of 90:10 for 5 minutes to obtain a physically mixed flame retardant, denoted as PM-IFR.

[0056] Comparative Example 3 Physical mixture of MPP and nickel phosphate The pure P-IFR powder prepared according to Comparative Example 1 was mixed with commercial nickel hydrogen phosphate (NiHPO4·H2O, analytical grade) powder at a mass ratio of 90:10 in a high-speed mixer for 5 minutes to obtain a physically mixed flame retardant, denoted as PN-IFR.

[0057] Performance testing The flame retardant (47.7 wt%) obtained above was mixed with polypropylene (PP, grade T30S, 50 wt%) granules, and 1.5 wt% antioxidant 1010 and 0.8 wt% calcium stearate were added as lubricants. The mixture was melt-blended and extruded into granules using a co-rotating twin-screw extruder (screw diameter 35 mm, length-to-diameter ratio 40:1; section temperatures: 180℃ / 190℃ / 200℃ / 205℃ / 200℃, main engine speed 250 rpm) to obtain flame retardant masterbatch. The above masterbatch was diluted with pure PP resin in a certain proportion so that the total amount of flame retardant added in the final composite material was 25wt%. Standard test specimens (such as UL-94 vertical burning specimens, tensile specimens, and impact specimens) were prepared by injection molding machine at an injection temperature of 200℃ and a mold temperature of 40℃.

[0058] Test items: Flame retardant performance: Vertical flammability is tested according to UL-94 standard.

[0059] Thermal stability: The initial decomposition temperature (T5%, the temperature at which 5% weight loss is achieved) and the amount of char residue at 700℃ were tested using a thermogravimetric analyzer (TGA, heating rate 10℃ / min) under a nitrogen atmosphere.

[0060] Mechanical properties: The tensile strength and notched impact strength of the specimens were tested according to GB / T 1040.1-2025 and GB / T 1043.1-2008, respectively.

[0061] Hygroscopicity: The flame retardant powder was placed in a constant temperature and humidity chamber (temperature 30℃, relative humidity 90%) for 48 hours, and its water absorption rate (percentage increase in mass) was measured.

[0062] Charcoal morphology: The microstructure of the char residue after vertical combustion test was observed by scanning electron microscopy (SEM).

[0063] The table below summarizes the main performance test results of each example and comparative example when PP is used as the matrix and the flame retardant content is 25wt%. Table 1 Test Results

[0064] Effect Analysis: Flame retardancy and smoke suppression: All samples containing MPP exhibited significant flame retardant effects. Comparative Example 2 (PM-IFR) only achieved a V-1 rating, indicating that the simple physical addition of MMT has limited effect on improving the flame retardancy rating of MPP. In contrast, the embodiments of this invention (C-IFR-1 and C-IFR-2) both achieved a V-0 rating, and in actual combustion tests, significantly less smoke was observed compared to the comparative example. Test results showed that the char layer formed by the C-IFR sample was continuous, dense, with fine pores and covered with sheet-like material (MMT), exhibiting a typical "brick-and-mortar" reinforced structure, while the char layer of the comparative sample was looser and more brittle.

[0065] Improved hygroscopicity: Pure MPP (P-IFR) has a water absorption rate as high as 4.8%. The composite flame retardants (C-IFR-1 and C-IFR-2) of this invention have a significantly reduced water absorption rate to 2.1-2.5%, with a hygroscopicity improvement of over 50%. This confirms that the introduction of core-shell structured nanounits and the in-situ composite process effectively shield some hydrophilic groups, improving the hydrophobicity of the product.

[0066] Thermal stability and charring ability: the initial decomposition temperature (T) of composite flame retardants 5% The slight increase indicates improved thermal stability. More importantly, the residual carbon content at 700℃ (C-IFR-1: 29.5%, C-IFR-2: 32.0%) was significantly higher than that of pure MPP (21.5%) and other physical mixtures, demonstrating a strong synergistic catalytic carbonization effect between core-shell nanounits and MPP.

[0067] Mechanical property retention: Compared with pure MPP, the PP composite material with the addition of the composite flame retardant of this invention showed a significant improvement in the retention rate of tensile strength and impact strength. C-IFR-1 (10% nanounits) exhibited the highest mechanical property retention rate (85% for tensile strength and 75% for impact strength compared to pure PP), indicating that an appropriate amount of core-shell nanounits, as a reinforcing phase, not only did not deteriorate the properties but also compensated for the mechanical losses caused by the addition of flame retardants to a certain extent. This is attributed to the good dispersion of nanounits in the matrix and the potentially improved interfacial interactions between them and the MPP and PP matrices.

[0068] in conclusion: This invention successfully prepared a high-performance composite flame retardant by first preparing montmorillonite@nickel phosphate core-shell nanomaterials and then introducing them in situ during the chemical synthesis of MPP. While maintaining V-0 high-efficiency flame retardancy, this product significantly reduces the hygroscopicity of MPP, greatly improves char residue and char layer quality, and effectively enhances the mechanical properties of the composite material. The preparation method is feasible, the resulting functional masterbatch is easy to process and apply, and its overall performance is significantly superior to traditional MPP and its simple physical compound products, demonstrating significant industrial application value.

[0069] Although the above embodiments have provided a detailed description of the present invention, they are only some embodiments of the present invention, and not all embodiments. Other embodiments can be obtained based on these embodiments without creative effort, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A composite flame retardant, characterized in that, It includes a pentaerythritol phosphate melamine salt matrix and an additive dispersed in the matrix, wherein the additive has a core-shell structure, wherein the core is montmorillonite nanosheets and the shell is nickel phosphate.

2. The composite flame retardant according to claim 1, characterized in that, The montmorillonite nanosheets have a single-layer or few-layer structure with a thickness of 1~15nm and a lateral dimension of 2~10μm.

3. The composite flame retardant according to claim 1, characterized in that, The thickness of the shell layer is 2~50nm.

4. The composite flame retardant according to claim 1, characterized in that, The additive has a mass percentage of 3-50% in the composite flame retardant.

5. The method for preparing the composite flame retardant according to any one of claims 1 to 4, characterized in that, Includes the following steps: Step 1: Add soluble nickel source solution and phosphate source solution to the montmorillonite nanosheet suspension for in-situ coating to obtain the additive; Step 2: During the synthesis reaction of pentaerythritol phosphate melamine salt, the additive is added to disperse it evenly and combine it with the generated pentaerythritol phosphate melamine salt matrix to obtain the composite flame retardant.

6. The preparation method according to claim 5, characterized in that, In step 1, the soluble nickel source includes at least one of nickel nitrate, nickel chloride, nickel sulfate, and nickel acetate; the phosphoric acid source includes at least one of phosphoric acid, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, sodium phosphate, and polyphosphoric acid. The pH value of the system during the in-situ coating is 3.0~8.0; the temperature of the in-situ coating is 20~60℃, and the time is 0.5~6h; the in-situ coating is carried out under stirring conditions.

7. The preparation method according to claim 5, characterized in that, Step 2 specifically involves a one-step synthesis method, in which pentaerythritol, a phosphoric acid source, melamine, and additives are mixed in water and subjected to a liquid-phase reaction to obtain the composite flame retardant; the temperature of the liquid-phase reaction is 90~130℃, and the time is 2~8h.

8. The preparation method according to claim 5, characterized in that, Step 2 specifically involves a two-step synthesis method, in which pentaerythritol is reacted with a phosphate source to generate a pentaerythritol phosphate intermediate; then, the pentaerythritol phosphate intermediate, melamine, and additives are mixed in water and subjected to a liquid-phase reaction to obtain the composite flame retardant; the temperature of the liquid-phase reaction is 70~110℃, and the time is 1~6h.

9. A flame-retardant functional masterbatch, characterized in that, Including polymers and flame retardants; The flame retardant is the composite flame retardant according to any one of claims 1 to 4 or the composite flame retardant prepared by the preparation method according to any one of claims 5 to 8.

10. The flame-retardant masterbatch according to claim 9, characterized in that, The flame retardant masterbatch contains 20-80% flame retardant by mass. The polymer includes at least one of polypropylene, polybutylene terephthalate, and polycarbonate.

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