Flame-retardant thermoplastic polyurethane elastomer material and preparation method thereof

Abstract

The invention discloses a flame-retardant thermoplastic polyurethane elastomer material and a preparation method thereof, and belongs to the technical field of modified nano materials. The preparation method comprises the following steps: dissolving melamine, phytic acid and boron nitride in deionized water, carrying out oil bath, adding a coupling agent, stirring, carrying out vacuum filtration, washing with water, and drying to obtain a layered nano flame retardant; the preparation method comprises the following steps: dispersing a flame retardant in deionized water containing a nonionic dispersant, and carrying out ultrasonic treatment; the preparation method comprises the following steps: reacting polyether polyol with diisocyanate to obtain a primary prepolymer; adding other auxiliary agents, stirring, and carrying out gradient heating polymerization; and injecting into a mold, curing for 6-12 hours at 105-125 DEG C, and drying for 12-24 hours at 80-90 DEG C. A phosphorus-nitrogen-silicon ternary synergistic flame-retardant system is introduced, the boron nitride nanosheet surface grafting and dynamic pre-polymerization-gradient heating process is optimized, the dispersity is improved, and smoke suppression and thermal stability are achieved. Compared with the prior art, the flame retardant efficiency is high, the mechanical property is excellent, and environmental friendliness is achieved.

Description

Technical Field

[0001] The present invention belongs to the technical field of modified nanomaterials, and in particular relates to a flame retardant thermoplastic polyurethane elastomer material and a preparation method thereof. Background Art

[0002] Thermoplastic polyurethane elastomer (TPU) is a polymer material composed of alternating soft segments and hard segments, with excellent elasticity, wear resistance, oil resistance, low temperature resistance and processing performance. It is widely used in automobiles, electronic appliances, construction, medical equipment, footwear and textiles. For example, in the automotive industry, TPU is often used for seals and interior materials; in the electronics field, it is used for cable sheaths and flexible circuits; in the medical field, it is used for catheters and implant materials. With the increasing global demand for high-performance materials, the market size of TPU continues to expand. However, as an organic polymer compound, TPU contains a large number of carbon-hydrogen bonds in its molecular chain and is extremely flammable in the air. The limiting oxygen index (LOI) is usually only 17%-19%. It releases a lot of heat and toxic smoke when burning, and the peak heat release rate (PHRR) can be as high as 1000kW / m 2 This not only limits its application in places with high fire protection requirements, but may also cause serious safety hazards, such as casualties and property losses caused by fire accidents.

[0003] To address the flammability of TPU, researchers have developed a variety of flame-retardant modification technologies, primarily categorized as additive and reactive. Additive flame-retardant modification involves physically doping flame retardants into the TPU matrix through melt blending or solution mixing. This method is simple to operate and low-cost, making it the mainstream path for industrial production. Common additive flame retardants include halogen, phosphorus, nitrogen, and inorganic fillers. Halogen-based flame retardants, such as brominated or chlorinated compounds (e.g., decabromodiphenyl ether or chlorinated paraffin), offer high flame retardancy and require minimal use (typically 10%-20%). They can increase the LOI of TPU to over 25% and achieve a UL-94 V-0 rating. However, halogen-based flame retardants release corrosive gases (e.g., hydrohalic acids) and carcinogens (e.g., dioxins) during combustion, posing serious risks to the environment and human health. The EU's RoHS Directive and REACH Regulation have gradually restricted their use, causing the global halogen flame retardant market share to drop from 80% in 2000 to less than 50% at present.

[0004] Phosphorus-based flame retardants have gradually become a research hotspot as halogen-free alternatives. Phosphorus-based flame retardants mainly play a role through the condensed phase mechanism, promoting the formation of carbon in the matrix and forming a carbon layer that blocks the transmission of oxygen and heat. Common phosphorus-based additives include ammonium polyphosphate (APP), melamine polyphosphate (MPP), and aluminum hydroxide (ATH). For example, adding APP and expanded graphite (EG) to TPU can increase the LOI to more than 30% and reduce the PHRR by 50% when the total addition amount is 20%-30%. However, the addition of phosphorus-based flame retardants often leads to a decrease in the mechanical properties of TPU, such as a decrease in elongation at break from more than 500% to 300%-400% and a decrease in tensile strength of 20%-30%. This is because the flame retardant particles have poor compatibility with the matrix, which can cause stress concentration and phase separation. In addition, high addition amounts can increase material density and processing difficulty, affecting the transparency and flexibility of TPU. Nitrogen-based flame retardants, such as melamine (MA), play a gas-phase flame-retardant role by releasing ammonia gas to dilute oxygen concentration, but their efficiency is low when used alone and often need to be used in combination with other flame retardants. Inorganic fillers such as magnesium hydroxide (MH) or montmorillonite (MMT) can be used as synergists to improve the stability of the carbon layer, but high loadings (>40%) can severely deteriorate the mechanical properties and processing flowability of TPU.

[0005] Reaction-type flame retardant modification is a method that introduces flame-retardant elements into the TPU molecular chain through chemical bonds to achieve intrinsic flame retardation. This method has strong flame-retardant durability and is not prone to migration, making it suitable for long-term use. Reaction-type flame retardants mainly include phosphorus-, nitrogen-, or silicon-containing polyols, isocyanates, or chain extenders. For example, using phosphorus-containing polyols (such as polyphosphate polyols) instead of traditional polyether polyols can increase the LOI of TPU to 28%-32% while maintaining good mechanical properties. Studies have shown that chain extenders with phosphorus-nitrogen synergistic structures, such as bis(diphenyl phosphate) (BDP), can significantly reduce PHRR and form an expanded carbon layer to inhibit smoke release when the addition amount is 5%-10%. However, the disadvantages of reaction-type modification are complex synthesis, high cost, and potential impact on polymerization, leading to uneven molecular weight distribution and fluctuations in mechanical properties. In addition, phosphorus-containing reaction-type flame retardants are prone to hydrolysis at high temperatures, affecting the weather resistance of the material.

[0006] In recent years, multi-element synergistic flame retardant systems have become a key approach to improving the flame retardancy of TPU. Phosphorus-nitrogen synergy is a typical example. Phosphorus promotes char formation, while nitrogen releases inert gases, forming an intumescent flame retardant (IFR) mechanism. For example, adding APP and MA to TPU can achieve a flame retardancy index (LOI) exceeding 35% and improve smoke suppression by 40%. However, single-phosphorus-nitrogen systems still suffer from high addition requirements (20%-30%), poor dispersibility, and loss of mechanical properties. To further optimize this, researchers have introduced silicon to form a phosphorus-nitrogen-silicon ternary synergistic system. Silicon forms a siloxane network, enhancing the density and thermal stability of the char layer. Related research has shown that combining hexagonal boron nitride (h-BN) modified with a silicon-containing coupling agent with a phosphorus-nitrogen flame retardant can achieve a TPU LOI exceeding 32%, reduce the flame retardancy reduction (PHRR) by 60%, and maintain an elongation at break exceeding 500%. The addition of silicon also improves the dispersion of the flame retardant and reduces phase separation. However, existing phosphorus-nitrogen-silicon systems still face challenges: low flame retardant surface activity leads to poor interfacial compatibility with the TPU matrix; difficult to control the polymerization process, prone to gelation or uneven products; and while smoke suppression performance has improved, the total smoke release (TSP) remains above environmental standards. Furthermore, the agglomeration of nano-scale flame retardants can further degrade mechanical properties, such as a 15%-25% decrease in tensile strength.

[0007] Another problem with existing technologies is environmental friendliness. Traditional halogen-based flame retardants have been restricted. Although halogen-free phosphorus-based flame retardants are more environmentally friendly, the bioaccumulation of phosphorus compounds and the risk of eutrophication of water bodies cannot be ignored. Bio-based flame retardants, such as phytic acid (PA), as a phosphorus-nitrogen source, have been explored for TPU modification, but their thermal stability is poor, and the initial decomposition temperature is only around 200°C, which cannot meet the requirements of high-temperature processing. Surface modification technologies, such as coupling agent grafting or ultrasonic dispersion, can improve dispersibility, but increase process complexity and cost. A gradient polymerization process has been proposed to improve the uniform distribution of flame retardants, but industrial applications still need to be optimized.

[0008] In addition, existing TPU flame-retardant materials face a trade-off in overall performance. High flame retardancy often comes at the expense of flexibility and transparency. For example, although TPU with added inorganic fillers has an LOI > 30%, its transparency decreases and its haze increases by more than 50%, limiting its application in the optical field. Thermal stability is also a pain point. The thermal decomposition temperature (Td) of flame-retardant TPU is usually reduced by 10-20°C, affecting its long-term service life. Insufficient smoke suppression is another problem. The smoke density (Ds) generated during combustion is > 200, which can easily lead to secondary disasters. International standards such as UL-94V-0 and LOI ≥ 32% are becoming increasingly stringent, and existing technologies make it difficult to simultaneously achieve high flame retardancy, high mechanical properties, and low smoke release.

[0009] In summary, although the existing technology has made progress in the flame retardant modification of TPU, there are still problems such as low flame retardant efficiency, large loss of mechanical properties, heavy environmental burden and uneven overall performance. There is an urgent need to develop new flame retardant systems, such as optimizing phosphorus-nitrogen-silicon ternary synergistic flame retardants, combining surface grafting and dynamic polymerization processes to achieve efficient dispersion, long-lasting flame retardancy and multifunctional integration. The present invention is precisely aimed at these defects and proposes a flame retardant TPU material and a preparation method thereof that introduces a phosphorus-nitrogen-silicon ternary synergistic system. By optimizing the surface modification of nano flame retardants and gradient temperature polymerization, the flame retardancy, smoke suppression and mechanical properties of the material are improved to meet the application requirements of high safety and environmental protection requirements. Summary of the Invention

[0010] In the existing technology, traditional flame-retardant thermoplastic polyurethane elastomer materials are mostly modified with halogen, phosphorus or nitrogen flame retardants. Although this can improve the flame retardant properties of the materials to a certain extent, it still has many defects: First, the flame retardant efficiency is low, and a high addition amount (usually 20%-40%) is required to achieve UL-94V-0 level and LOI ≥ 30%, which leads to increased material density, decreased processing fluidity, and significantly reduced mechanical properties. For example, the elongation at break is reduced from more than 500% to 300%-400%, and the tensile strength is reduced by 20%-30%; second, the compatibility is poor, and the flame retardants are prone to agglomeration or phase separation, affecting the uniformity and transparency of the material; third, the smoke suppression effect is poor, the smoke density is too high during combustion, and toxic gases are released, causing secondary pollution; fourth, the environmental friendliness is insufficient, halogen flame retardants release corrosive gases, and phosphorus flame retardants may cause eutrophication of water bodies; fifth, the thermal stability is weak, and the thermal decomposition temperature is reduced by 10-20°C, which limits high-temperature applications. In addition, traditional preparation methods such as simple melt blending or reactive modification make it difficult to achieve uniform dispersion of flame retardants and multi-element synergy, resulting in unbalanced overall performance and unable to simultaneously meet the requirements of high flame retardancy, high toughness and low smoke release.

[0011] To solve the above problems, the present invention adopts the following technical solutions.

[0012] A method for preparing a flame-retardant thermoplastic polyurethane elastomer material, comprising the following steps: (1) preparation of a nano flame retardant: preparing 3-10 parts of melamine (CAS No. 108-78-1), 2-7 parts of phytic acid (CAS No. 83-86-3), and 2-5 parts of boron nitride (CAS No. 10043-11-5), and 100-200 parts of deionized water, then oil bath, forming a uniform solution, then 0.5-3 parts of coupling agent is dropped and mechanically stirred, then vacuum filtration at 60-80℃, then washed with water at 60-90℃, and finally vacuum dried to obtain a layered nano flame retardant; (2) surface grafting treatment: dispersing the layered nano flame retardant in 80-100 parts of deionized water containing 2-10 parts of non-ionic dispersant, and ultrasonic treatment to obtain grafted nano flame retardant; (3) preparation of thermoplastic polyurethane prepolymer: mixing 100-140 parts of polyether polyol and 10-30 parts of diisocyanate (CAS No. 4098-71-9) to obtain a preliminary prepolymer; then, stirring and reacting the grafted nano flame retardant, 5-10 parts of ethyl triphenyl phosphonic acid (CAS No. 35835-94-0), 5-8 parts of chain extender, 2-3 parts of catalyst, and 5-10 parts of antioxidant to obtain a modified prepolymer; then, gradient temperature control under an inert gas (nitrogen) atmosphere to obtain a thermoplastic polyurethane prepolymer; (4) molding and curing: injecting the thermoplastic polyurethane prepolymer into a mold (such as the Roboshot Alpha-SiA series mold produced by Japan's Fanuc company), curing and drying to obtain a flame-retardant thermoplastic polyurethane elastomer material.

[0013] Preferably, the parameters of the oil bath in step (1) are as follows: 70-90℃, 80-120 rpm, and 10-30 min; the coupling agent in step (1) is 3-aminopropyl triethoxysilane (CAS No. 919-30-2), γ-methacryloyloxypropyltrimethoxysilane (CAS No. 2530-85-0), vinyltriethoxysilane (CAS No. 78-08-0), 3-mercaptopropyltriethoxysilane (CAS No. 14814-09-6), titanium isopropoxide tetraisooctyl titanate (CAS No. 1070-10-6), 2-mercaptoethanol (CAS No. 60-24-2), or acetylacetone titanate (CAS No. 17927-72-9); the mechanical stirring speed in step (1) is 200-300 rpm, and the time is 1-2 h.

[0014] Preferably, the filter membrane for vacuum filtration in step (1) is a 0.45μm polytetrafluoroethylene filter membrane; the temperature for vacuum drying in step (1) is 70-85℃, and the time for vacuum drying is 18-36 h.

[0015] Preferably, the nonionic dispersant in step (2) is polyethylene glycol (CAS No.: 25322-68-3), Tween 20 (CAS No.: 9005-64-5), Triton X-100 (CAS No.: 9002-93-1), polyoxyethylene decylphenol ether (CAS No.: 9016-45-9) or Span-80 (CAS No.: 1338-43-8); the parameters of the ultrasonic treatment in step (2) are as follows: ultrasonic power 500-800 W, ultrasonic frequency 40-60 kHz and ultrasonic time 10-20 min.

[0016] Preferably, the polyether polyol in step (3) is polyoxypropylene ether polyol (CAS No.: 25322-69-4), polyoxyethylene ether polyol (CAS No.: 25322-68-3) or polytetramethylene ether glycol (CAS No.: 25190-06-1); the parameters of the mixing reaction in step (3) are as follows: 60-85°C, 40-60rpm and 60-90min.

[0017] Preferably, the chain extender in step (3) is 1,4-butanediol (CAS No.: 110-63-4), 1,6-hexanediol (CAS No.: 629-11-8), dihydroxymethylpropionic acid (CAS No.: 4767-03-7) or 4,4'-diaminodiphenylmethane (CAS No.: 101-77-9); the catalyst in step (3) is stannous octoate (CAS No.: 301-10-0), dibutyltin dilaurate (CAS No.: 7 7-58-7), triphenylbismuth (CAS No.: 603-33-8), triethylenediamine (CAS No.: 280-57-9) or N, N-dimethylethanolamine (CAS No.: 108-01-0); the antioxidant in step (3) is 2,6-di-tert-butyl-p-cresol (CAS No.: 128-37-0), dilaurylthiodipropionate (CAS No.: 693-36-7) or triphenylphosphine (CAS No.: 603-35-0).

[0018] Preferably, the parameters of the stirring reaction in step (3) are as follows: 200-260 rpm, 60-75°C, and 15-30 min; the parameters of the gradient temperature control in step (3) are as follows: 70-80°C for 60-80 min, 110-120°C for 20-30 min, and 130-150°C for 30-60 min.

[0019] Preferably, the curing temperature in step (4) is 105-125° C., and the curing time is 6-12 hours.

[0020] Preferably, the drying temperature in step (4) is 80-90° C., and the drying time is 12-24 h.

[0021] A flame retardant thermoplastic polyurethane elastomer material is obtained by the above-mentioned preparation method.

[0022] Compared to existing technologies, this invention offers the following advantages: By constructing a phosphorus-nitrogen-silicon (PN-Si) ternary synergistic flame-retardant system, combined with optimized nanomaterial surface grafting technology and a dynamic prepolymerization-gradient temperature polymerization process, it successfully overcomes the existing challenges of achieving a balance between flame retardancy, mechanical properties, and environmental friendliness. These benefits are manifested in the following aspects, achieved through profound internal mechanisms: highly effective synergistic flame retardancy and excellent smoke suppression, with significantly improved safety. The core of this invention lies in the construction of a multi-mode, multi-stage synergistic flame-retardant network, with a dual condensed phase "charring and expansion" action. Phytic acid (the phosphorus source) dehydrates upon heating to form polyphosphoric acid, a potent dehydration catalyst and charring agent. This polyphosphoric acid rapidly catalyzes the dehydration and crosslinking of the polyurethane matrix, forming a preliminary char layer. Simultaneously, melamine (the nitrogen source) decomposes at high temperatures, releasing large amounts of non-flammable inert gases (such as NH3 and N2). On the one hand, these gases dilute the concentration of oxygen and combustible gases in the gas phase, acting as a gas-phase flame retardant. On the other hand, the gases impact and push the forming char layer, causing it to expand and foam, forming a porous, fluffy, and dense expanded char layer. This expanded char layer offers exponentially greater insulation and oxygen isolation compared to traditional dense char layers. Carbon layer "skeleton" reinforcement and "barrier" effect: Traditional phosphorus-nitrogen carbon layers often lack strength at high temperatures (>500°C) and are prone to cracking and failure. The layered nano-boron nitride (BN) introduced in this invention plays a key role in strengthening the "skeleton." First, boron nitride nanosheets, grafted and modified with a silane coupling agent, are uniformly dispersed in the matrix. During combustion, these highly thermally stable nanosheets are fixed within the expanded char layer, much like rebar in reinforced concrete, significantly enhancing the mechanical strength and oxidation resistance of the char layer. Secondly, the silica or silicon oxycarbide (Si-OC) formed after the decomposition of the silane coupling agent further fills the pores of the carbon layer, forming a ceramic physical barrier that effectively prevents heat transfer and the escape of combustible decomposition products. This synergistic mechanism of "PN foaming and B-Si reinforcement" ensures the integrity and stability of the carbon layer throughout the combustion process, achieving a limiting oxygen index (LOI) exceeding 32% and a top-tier flame retardant rating of UL-94 V-0. Highly effective physical smoke suppression: The reinforced, dense, expanded carbon layer acts as a "filter," effectively capturing and adsorbing smoke particles produced by combustion, preventing them from entering the air. This significantly reduces smoke density, minimizing the risk of suffocation and escape difficulties caused by dense smoke during a fire. Compared to traditional flame retardants that focus solely on flame retardancy while ignoring smoke suppression, this invention offers greater safety. Excellent mechanical property retention resolves the conflict between flame retardancy and strength: high addition levels (>20%) of traditional flame retardants, particularly inorganic fillers, can severely degrade the material's mechanical properties.The present invention maintains the original high elasticity and high toughness of TPU while achieving high flame retardancy through the following synergistic technologies: Nano effect and low addition amount: The nano-scale layered boron nitride is used, and its huge specific surface area enables it to play a significant reinforcing and flame retardant synergistic role at a lower addition amount, avoiding the performance sacrifice caused by the high filling amount of traditional micron-scale fillers. Strong interface compatibility design: This is the key to maintaining mechanical properties. The present invention optimizes the interface through a two-step method: (1) Molecular bridge effect of silane coupling agent: The hydrolyzed silanol group at one end of the silane coupling agent (such as 3-aminopropyltriethoxysilane) can chemically bond with the hydroxyl group on the surface of boron nitride; the organic functional group (such as amino group) at the other end can react with the isocyanate group in the TPU matrix or form a hydrogen bond, thereby establishing a strong chemical connection between the inorganic filler and the organic polymer, eliminating interface defects. This allows stress to be effectively transferred from the flexible TPU matrix to the rigid nanosheet, achieving nano-enhancement rather than stress concentration. (2) Non-ionic dispersant and ultrasonic treatment: Through the physical coating of non-ionic dispersant and the cavitation effect of ultrasonic wave, the agglomerates of nano flame retardant are completely broken up, ensuring that it is evenly dispersed at the monolithic level in the prepolymer, laying the foundation for subsequent strong interface bonding. The contribution of dynamic prepolymerization-gradient temperature rise process: The traditional one-step method or melt blending easily causes the nano filler to re-agglomerate during the polymerization process. The present invention adopts a process of first preparing the prepolymer, then adding the modified nano flame retardant, and finally performing a gradient temperature rise polymerization process. This method introduces the filler at a lower initial viscosity, which is conducive to its uniform dispersion; the subsequent gradient temperature rise achieves a smooth and controllable polymerization reaction, allowing the polyurethane molecular chain to grow in situ around the evenly dispersed nano sheets, forming a perfect core-shell structure, and fundamentally avoiding phase separation and loss of mechanical properties. Therefore, the elongation at break of the final product can still be maintained at more than 500%, and the tensile strength is also much higher than that of traditional flame retardant TPU. Improved Thermal Stability and Processing Performance: Improved thermal stability: Hexagonal boron nitride possesses extremely high thermal stability and thermal conductivity, effectively conducting and dissipating localized heat and delaying thermal degradation of the polymer matrix. The synergistic effect of PN-Si forms a stable carbon layer, raising the material's initial thermal decomposition temperature (Td) to over 300°C, 10-20°C higher than traditional flame-retardant TPU, broadening its application range in high-temperature environments. Optimized Processing: The gradient temperature polymerization process avoids exothermic reaction peaks and sudden increases in system viscosity, ensuring the prepolymer maintains excellent fluidity before injection into the mold. This facilitates the molding of complex parts and reduces defects such as bubbles and sink marks. Significant Environmental Friendliness and Green Sustainability: Completely Halogen-Free: The flame-retardant system is completely halogen-free, eliminating the risk of generating highly toxic carcinogens such as dioxins and corrosive hydrogen halide gases during combustion, complying with the most stringent environmental regulations, including EU RoHS and REACH. Incorporating a bio-based renewable resource: Phytic acid is innovatively used as a phosphorus source.Phytic acid, a naturally occurring organophosphate compound found in plant seeds, is a renewable bioresource. Using phytic acid to replace traditional petroleum-based phosphorus flame retardants not only reduces dependence on fossil resources but also increases the product's bio-based content and sustainability, aligning with the global trend toward carbon neutrality and green chemistry.

[0023] In summary, the present invention is not a simple superposition of components, but through a deep understanding and systematic innovation of flame retardant mechanism, interfacial chemistry and polymerization kinetics, it achieves a high degree of unity of the four major properties of high-efficiency flame retardancy, strong mechanics, stable smoke suppression, and green environmental protection. Its comprehensive performance far exceeds the existing technical level. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a transmission image of the layered nano flame retardant prepared in Example 1.

[0025] Figure 2 1 is a scanning electron microscope image of the flame retardant thermoplastic polyurethane elastomer material prepared in Example 1.

[0026] Figure 3 This is a physical picture of the flame retardant thermoplastic polyurethane elastomer material prepared in Example 1. DETAILED DESCRIPTION

[0027] The present invention is described in detail below through specific examples. However, the use and purpose of these exemplary embodiments are merely illustrative of the present invention and are not intended to limit the actual scope of protection of the present invention in any form, nor are they intended to limit the scope of protection of the present invention to these examples. For parameter ranges not mentioned, intermediate values ​​are selected. In addition, for mass percentages or weight percentages not explicitly stated or mentioned, they generally refer to the final concentration after addition.

[0028] Example 1

[0029] The preparation method of flame-retardant thermoplastic polyurethane elastomer material comprises the following steps: (1) preparation of nano flame retardant: preparing 3 g of melamine (CAS No.: 108-78-1), 2 g of phytic acid (CAS No.: 83-86-3), 2 g of boron nitride (CAS No.: 10043-11-5) and 100 g of deionized water, followed by oil bath (parameters: 70°C, 80 rpm and 10 min) to form a uniform solution, then dropping 0.5 g of coupling agent 3-aminopropyltriethoxysilane (CAS No.: 919-30-2) and mechanically stirring (speed 200 rpm, time 1 h), followed by vacuum filtration at 60°C (filter membrane is 0.45 μm polytetrafluoroethylene filter membrane), then washing with water at 60°C, and finally vacuum drying (temperature 70°C, time 18 h) to obtain a layered nano flame retardant. (2) Surface grafting treatment: The layered nano flame retardant was dispersed in 80 g of deionized water containing 2 g of non-ionic dispersant polyethylene glycol (CAS No.: 25322-68-3), and ultrasonic treatment was performed (parameters: ultrasonic power 500 W, ultrasonic frequency 40 kHz and ultrasonic time 10 min) to obtain the grafted nano flame retardant, such as Figure 1 (3) Preparation of thermoplastic polyurethane prepolymer: 100g of polyether polyol polyoxypropylene ether polyol (CAS No.: 25322-69-4) and 10g of diisocyanate were mixed and reacted (parameters: 60℃, 40rpm and 60min) to obtain a preliminary prepolymer; then, the grafted nano flame retardant, 5g of ethyl triphenylphosphine acetate, 5g of chain extender 1,4-butanediol (CAS No.: 110-63-4), 2g of catalyst octanoic acid were added. Tin (CAS No.: 301-10-0) and 5g of antioxidant 2,6-di-tert-butyl-p-cresol (CAS No.: 128-37-0), stirred for reaction (parameters: 200rpm, 60℃ and 15min), to obtain a modified prepolymer; then, gradient temperature control (parameters: 70℃ for 60min, 110℃ for 20min, 130℃ for 30min) was carried out under an inert gas (nitrogen) atmosphere to obtain a thermoplastic polyurethane prepolymer. (4) Molding and curing: The thermoplastic polyurethane prepolymer was injected into a mold, cured (temperature 105℃, time 6h) and dried (temperature 80℃, time 12h) to obtain a flame-retardant thermoplastic polyurethane elastomer material, such as Figure 2 and Figure 3 shown.

[0030] Example 2-18

[0031] The process flow of Examples 2-18 refers to that of Example 1, with some parameters adjusted. The specific formulas and process parameters are shown in the table.

[0032] Comparative Examples 1-16 were designed to verify the necessity of key components and technical requirements. By omitting key components, replacing them with other commonly used similar components, or exceeding the parameter range, the specific formulas and process parameters are shown in the table. Comparative Example 1 differs from Example 1 in that melamine is not added and an equal amount of deionized water (3g) is used instead. The remaining steps are the same as in Example 1. Comparative Example 2 differs from Example 1 in that phytic acid is not added and an equal amount of deionized water (2g) is used instead. The remaining steps are the same as in Example 1. Comparative Example 3 differs from Example 1 in that boron nitride is not added and an equal amount of deionized water (2g) is used instead. The remaining steps are the same as in Example 1. Comparative Example 4 differs from Example 5 in that a coupling agent is not added and an equal amount of deionized water (1.5g) is used instead. The remaining steps are the same as in Example 5. Comparative Example 5 differs from Example 5 in that the coupling agent is replaced with ethyl titanate (CAS No.: 3087-36-3) in an amount of 1.5g. The remaining steps are the same as in Example 5. Comparative Example 6 differs from Example 5 in that the nonionic dispersant is not added and an equal amount of deionized water (5 g) is used instead. The remaining steps are the same as in Example 5. Comparative Example 7 differs from Example 8 in that the nonionic dispersant is replaced with an anionic dispersant, sodium lauryl sulfate (CAS No.: 151-21-3), in an amount of 5 g. The remaining steps are the same as in Example 8. Comparative Example 8 differs from Example 8 in that ethyltriphenylphosphine acetate is not added and an equal amount of deionized water (7.5 g) is used instead. The remaining steps are the same as in Example 8. Comparative Example 9 differs from Example 10 in that the chain extender is not added and an equal amount of deionized water (6.5 g) is used instead. The remaining steps are the same as in Example 10. Comparative Example 10 differs from Example 10 in that the chain extender is replaced with ethylene glycol (CAS No.: 107-21-1), in an amount of 6.5 g. The remaining steps are the same as in Example 10. Comparative Example 11 differs from Example 12 in that the catalyst is not added and an equal amount of deionized water (2.5 g) is used instead. The remaining steps are the same as in Example 12. Comparative Example 12 differs from Example 12 in that the catalyst is replaced with an organozinc catalyst (e.g., diethylzinc) in an amount of 2.5 g, and the remaining steps are the same as in Example 12. Comparative Example 13 differs from Example 14 in that the antioxidant is not added, but an equal amount of deionized water (7.5 g) is used instead, and the remaining steps are the same as in Example 14. Comparative Example 14 differs from Example 14 in that the antioxidant is replaced with vitamin E (CAS No.: 59-02-9) in an amount of 7.5 g, and the remaining steps are the same as in Example 14. Comparative Example 15 differs from Example 16 in that the oil bath temperature is adjusted to 100°C (outside the range of 70-90°C), and the remaining steps are the same as in Example 16. Comparative Example 16 differs from Example 16 in that the vacuum drying time is adjusted to 40 hours (outside the required range of 18-36 hours), and the remaining steps are the same as in Example 16.

[0033] Table 1: Examples 1-6 formulations and process parameters

[0034]

[0035] Table 1 shows the formulations and process parameters for Examples 1-6, used to prepare specific materials. The formulations include melamine (3-10g), phytic acid (2-7g), boron nitride (2-5g), and deionized water (100-200g) as the primary raw materials. Process parameters include oil bath temperature (70-90°C), rotation speed (80-120 rpm), and duration (10-30 minutes), as well as mechanical stirring speed (200-300 rpm) and duration (1-2 hours). Various coupling agents, such as 3-aminopropyltriethoxysilane, are used in amounts of 0.5-3g. Nonionic dispersants (such as polyethylene glycol) are used in amounts of 2-10g. Vacuum filtration and water washing temperatures are 60-80°C and 60-90°C, respectively, and vacuum drying is performed at 70-85°C for 18-36 hours. The significant differences in parameters between the examples demonstrate the diversity and flexibility of process optimization, adapting to varying performance requirements.

[0036] Table 2: Examples 1-6 Formulations and Process Parameters 2

[0037]

[0038]

[0039] Table 2 describes the preparation of polyurethane materials. The main ingredients in the formula are deionized water (80-100g), polyether polyol (100-140g, such as polyoxypropylene ether polyol), diisocyanate (10-30g), ethyltriphenylphosphine acetate (5-10g), chain extender (5-8g, such as 1,4-butanediol), catalyst (2-3g, such as stannous octoate), and antioxidant (5-10g, such as 2,6-di-tert-butyl-p-cresol). Process parameters include ultrasonic treatment (power 500-800W, frequency 40-60kHz, time 10-20min), mixing reaction (temperature 60-85°C, rotation speed 40-60rpm, time 60-90min), stirring reaction (temperature 60-75°C, rotation speed 200-260rpm, time 15-30min), gradient temperature control (70-150°C, 20-60min), curing (105-125°C, 6-12h), and drying (80-90°C, 12-24h). The formulations and process parameters vary significantly between examples, optimizing material properties and making them suitable for different application scenarios.

[0040] Table 3: Examples 7-12 Formulations and Process Parameters 1

[0041]

[0042]

[0043] Table 3 relates to material preparation process. Formulation includes melamine (3-10 g), phytic acid (2-7 g), boron nitride (2-5 g), deionized water (step 1: 100-200 g, step 2: 80-100 g), polyether polyol (100-140 g, such as polyoxypropylene ether polyol, etc.), diisocyanate (10-30 g), coupling agent (0.5-3 g, such as titanium acetylacetate, etc.), and non-ionic dispersant (2-10 g, such as Tween 20, etc.). Process parameters cover oil bath (temperature 70-90℃, rotation speed 80-120 rpm, time 10-30 min), mechanical stirring (rotation speed 200-300 rpm, time 1-2 h), vacuum filtration (60-80℃), water washing (60-90℃), vacuum drying (70-85℃, 18-36 h), ultrasonic treatment (power 500-800 W, frequency 40-60 kHz, time 10-20 min). The formulation and process parameters of each example are significantly different, which optimizes the material performance and adapts to various application requirements.

[0044] Table 4: Formulation and process parameters two of examples 7-12

[0045]

[0046] Table 4 relates to polyurethane material preparation, detailing the formulation and process parameters two of examples 7-12 in the polyurethane material preparation process, covering key steps such as mixing reaction, catalyst selection, antioxidant application, stirring reaction, gradient temperature control, curing treatment and drying, providing diverse process conditions for optimizing material performance. Table 4 demonstrates the diversity and optimization space of examples 7-12 in material preparation by changing the formulation and process parameters. This flexibility provides a reference for preparing high-performance polyurethane materials to meet the needs of different application scenarios. Formulation includes ethyl triphenylphosphine acetate (5-10 g), chain extender (5-8 g, such as dimethylol propionic acid, etc.), catalyst (2-3 g, such as dibutyl tin dilaurate, etc.), and antioxidant (5-10 g, such as 2,6-di-tert-butyl-p-cresol, etc.). Process parameters cover mixing reaction (temperature 60-85℃, rotation speed 40-60 rpm, time 60-90 min), stirring reaction (temperature 60-75℃, rotation speed 200-260 rpm, time 15-30 min), gradient temperature control (70-150℃, 20-60 min), curing treatment (105-125℃, 6-12 h), and drying (80-90℃, 12-24 h). The formulation and process parameters of each example are significantly different, which optimizes the material performance and is suitable for various application scenarios, reflecting the flexibility and pertinence of the process.

[0047] Table 5: Formulation and process parameters one of examples 13-18

[0048]

[0049]

[0050] Table 5 demonstrates the versatility and flexibility of Examples 13-18 in polyurethane-based composite material preparation by varying the formulation and process parameters. This parameter optimization provides a reference for different application scenarios (such as high strength, heat resistance, or economy) to ensure targeted improvement of material performance.

[0051] Table 6: Formulation and Process Parameters Two for Examples 13-18

[0052]

[0053] Table 6 details the formulation and process parameters two for Examples 13-18 in the preparation of polyurethane-based composites, covering key steps such as chain extenders, catalysts, antioxidants, and stirring reactions, gradient temperature control, curing treatment, and drying, aiming to optimize material performance.

[0054] Table 7: Formulation and Process Parameters One for Comparative Examples 1-8

[0055]

[0056] Table 7 demonstrates the role of different components in material preparation through the formulation and process parameter design of Comparative Examples 1-8. Comparative Examples 1-3 respectively lack melamine, phytic acid, or boron nitride, investigating the impact of the absence of a single component; Comparative Example 4 lacks a coupling agent, Comparative Examples 5-6 use different titanium ester coupling agents, and Comparative Examples 7-8 use high dosage formulations and higher temperature processes. This comparative design helps reveal the contribution of each component and process condition to material performance, providing data support for optimizing formulations, and is suitable for exploring preparation schemes for economy or specific performance requirements.

[0057] Table 8: Formulation and Process Parameters Two for Comparative Examples 1-8

[0058]

[0059]

[0060] Table 8 demonstrates the role of different components and process conditions in the preparation of polyurethane-based composites through the formulation and process parameter design of Comparative Examples 1-8. Comparative Examples 1-3 maintain low-strength processes, using the same dispersant and polyether polyol; Comparative Examples 4-6 increase process strength and change the type of polyether polyol; Comparative Examples 7-8 further adjust the dispersant and catalyst to investigate their necessity.

[0061] Table 9: Formulation and Process Parameters Three for Comparative Examples 1-8

[0062]

[0063] Table 9 demonstrates the effects of antioxidant type and dosage on the properties of polyurethane-based composites by comparing the formulations and process parameter designs of Examples 1-8. This comparative design provides data support for optimizing antioxidant performance and process efficiency, such as in the preparation of industrial materials with high durability requirements.

[0064] Table 10: Comparative Examples 9-16 Formulations and Process Parameters 1

[0065]

[0066] Table 10 demonstrates the effects of different raw materials and process conditions in material preparation through the formulation and process parameter design of Comparative Examples 9-16.

[0067] Table 11: Comparative Examples 9-16 Formulations and Process Parameters 2

[0068]

[0069]

[0070]

[0071] Table 11 demonstrates the role of different components and process conditions in the preparation of polyurethane-based composites, using the formulations and process parameter designs of Comparative Examples 9-16. Comparative Examples 9-10 employ high-dosage formulations and aggressive process conditions, suitable for high-performance materials. Comparative Examples 11-12 reduce catalysts or replace chain extenders to test the impact of specific components. Comparative Examples 13-14 and 15-16 favor lower dosages and milder conditions, suiting economic requirements. In particular, the omission of a chain extender in Comparative Example 9 and a catalyst in Comparative Example 11 highlight the role of individual components.

[0072] Table 12: Comparative Examples 9-16 Formulations and Process Parameters 3

[0073]

[0074] Table 12 demonstrates the impact of antioxidant type and dosage on the performance of polyurethane-based composites, using the formulation and process parameter designs of Comparative Examples 9-16. Comparative Examples 9-10 utilize high dosages of 2,6-di-tert-butyl-p-cresol and aggressive process conditions, suiting high stability requirements. Comparative Examples 11-12 use dilaurylthiodipropionate, with a slightly less aggressive process, balancing performance and cost. Comparative Example 13 omits an antioxidant, examining its necessity. Comparative Examples 14-16 utilize vitamin E or triphenylphosphine, combined with a mild process, suiting economic or specific performance requirements. This comparative design provides data support for optimizing antioxidant performance and process efficiency, suitable for diverse application scenarios, such as the preparation of materials for high durability or low cost.

[0075] To comprehensively evaluate the performance of flame-retardant thermoplastic polyurethane elastomers, the following test methods were designed to cover flame retardancy, mechanical properties, heat resistance, and smoke suppression. These test methods reference national standards (e.g., "Test Methods for Combustion Performance of Plastics: Oxygen Index Method" GB / T2406.2-2009) to ensure scientific and reasonable results.

[0076] Limiting Oxygen Index (LOI, %) test method: Tested in accordance with the "Plastics Combustion Performance Test Method: Oxygen Index Method" (GB / T2406.2-2009). The prepared material was processed into a specimen measuring 80 mm × 10 mm × 4 mm and ignited in an oxygen-nitrogen mixture. The oxygen concentration was adjusted until the specimen burned continuously for 50 mm or 3 minutes. Test conditions: Room temperature 23±2°C, relative humidity 50±5%. Significance: Evaluates the flame retardancy of the material, with a target value of ≥32%. UL-94 Vertical Burning Rating (1.6 mm Specimen) Test Method: Based on the "Standard for Flammability of Plastic Materials" (UL94), a vertical burning test was conducted using 1.6 mm thick specimens. The bottom of the specimen was ignited, and the burning time, dripping behavior, and afterflame duration were recorded. Test conditions: Room temperature 23±2°C, relative humidity 50±5%. Significance: Assess the flame retardancy of the material, with a target of V-0 (no dripping, afterflame time ≤10 seconds). Test method for elongation at break (%): In accordance with "Plastics: Determination of Tensile Properties" (GB / T1040.1-2018), a dumbbell-shaped specimen is used to perform a tensile test on a universal material testing machine with a tensile speed of 50 mm / min. Test conditions: Room temperature 23±2°C. Significance: Reflects the toughness and elasticity of the material, with a target value >500%. Test method for tensile strength (MPa): Same as the elongation at break test, use a universal material testing machine to record the maximum tensile force and calculate the strength. Test conditions: Room temperature 23±2°C. Significance: Evaluate the mechanical strength of the material, with a target value >20 MPa. Test method for smoke density (Ds, dimensionless): In accordance with "Test method for smoke generation performance of plastics" (GB / T8323.2-2018), use a smoke density tester in flameless mode to test and record the maximum smoke density Ds. Test conditions: Heat flux 25kW / m 2 Significance: Evaluates smoke suppression performance, target value <150. Thermal Decomposition Temperature (°C) Test Method: Heat the sample (heating rate 10°C / min, from room temperature to 800°C) under a nitrogen atmosphere using a thermogravimetric analyzer (TGA), recording the temperature at which 5% mass loss occurs. Test Conditions: Sample mass 5-10 mg. Significance: Reflects the thermal stability of the material, target value >300°C.

[0077] Table 13: Flame retardant performance test results of Examples and Comparative Examples

[0078]

[0079]

[0080] Results Analysis: In Examples 1-18, the flame retardant properties achieved a Limiting Oxygen Index (LOI) of 32.4-34.5% and a UL-94 rating of V-0, meeting the target (LOI ≥ 32%, V-0). This was achieved thanks to the phosphorus-nitrogen-silicon ternary synergistic flame retardant system and the dynamic prepolymerization-gradient heating process. Mechanical properties: Elongation at break ranged from 512.7-548.8%, and tensile strength from 21.3-23.6 MPa, maintaining excellent toughness (>500%). Smoke suppression and thermal stability: Smoke density from 133.7-142.6°C and thermal decomposition temperature from 312.4-327.5°C demonstrated both smoke suppression and thermal stability. In Comparative Examples 1-16, the absence of key components, including Comparative Example 1 (no melamine), Comparative Example 2 (no phytic acid), and Comparative Example 3 (no boron nitride), resulted in reduced flame retardancy, with LOIs of only 25.9-28.9% and UL-94 ratings dropping to V-1 or V-2. Replacement or Out-of-Range: Comparative Examples 5 (coupling agent replacement), 7 (dispersant replacement), and 15 (oil bath temperature out of range) exhibited weakened mechanical properties due to poor dispersion or uneven reaction, with elongation at break ranging from 365.7-428.6% and smoke density ranging from 168.3-192.1. By optimizing the phosphorus-nitrogen-silicon system and surface grafting technology, Examples 1-18 comprehensively outperformed the comparative examples, meeting the UL94 V-0 rating, LOI ≥ 32%, and elongation at break > 500%. The performance deficiencies of the comparative examples further validated the essentiality of key components and process parameters. These test results are highly consistent with the patented improvements, demonstrating the technological advancement and practicality. Overall, excellent flame retardancy was achieved by introducing a phosphorus-nitrogen-silicon ternary synergistic flame retardant system and optimizing the surface grafting technology of hexagonal boron nitride nanosheets to achieve an LOI of 32.4-34.5% and a UL-94 V-0 rating. High mechanical properties: The dynamic prepolymerization-gradient temperature rise polymerization process improves the dispersion of the flame retardant, with an elongation at break of 512.7-548.8%, while maintaining the elasticity of the polyurethane. Smoke suppression and thermal stability: Integrated expansion flame retardancy and smoke suppression functions, smoke density of 133.7-142.6, thermal decomposition temperature of 312.4-327.5°C. Compared with the existing technology: By comparing Examples 1-18 and Comparative Examples 1-16 (such as the lack of coupling agent in Comparative Example 4, the lack of non-ionic dispersant in Comparative Example 6, and the lack of chain extender in Comparative Example 9), the technical solution of the present invention significantly improves the flame retardancy, mechanical properties and smoke suppression effects, overcoming the defects of traditional materials.

[0081] The above content is a further detailed description of the present invention in conjunction with specific implementation methods. It cannot be determined that the specific implementation of the present invention is limited to these descriptions. For ordinary technicians in the technical field to which the present invention belongs, they can make several simple deductions or substitutions without departing from the concept of the present invention, which should be regarded as falling within the scope of protection determined by the claims submitted for the present invention.

Claims

1. A method for preparing a flame retardant thermoplastic polyurethane elastomer material, characterized in that: The method comprises the following steps, in parts by mass: (1) preparation of nano flame retardant: preparing 3-10 parts of melamine, 2-7 parts of phytic acid, 2-5 parts of boron nitride and 100-200 parts of deionized water, followed by oil bath to form a uniform solution, and then dropping 0.5-3 parts of coupling agent and mechanically stirring, followed by vacuum filtration at 60-80°C, followed by water washing at 60-90°C, and finally vacuum drying to obtain layered nano flame retardant; (2) surface grafting treatment: dispersing the layered nano flame retardant in 80-100 parts of deionized water containing 2-10 parts of non-ionic dispersant, and ultrasonically treating to obtain grafted nano flame retardant. Flame retardant; (3) Preparation of thermoplastic polyurethane prepolymer: 100-140 parts of polyether polyol and 10-30 parts of diisocyanate are mixed and reacted to obtain a preliminary prepolymer; then, the grafted nano flame retardant, 5-10 parts of ethyl triphenylphosphine acetate, 5-8 parts of chain extender, 2-3 parts of catalyst and 5-10 parts of antioxidant are stirred and reacted to obtain a modified prepolymer; then, gradient temperature control is performed under an inert gas atmosphere to obtain a thermoplastic polyurethane prepolymer; (4) Molding and curing: The thermoplastic polyurethane prepolymer is injected into a mold, cured and dried to obtain a flame retardant thermoplastic polyurethane elastomer material.

2. The method for preparing a flame retardant thermoplastic polyurethane elastomer material according to claim 1, wherein: The parameters of the oil bath in step (1) are as follows: 70-90° C., 80-120 rpm, and 10-30 min; the coupling agent in step (1) is 3-aminopropyltriethoxysilane, γ-methacryloxypropyltrimethoxysilane, vinyltriethoxysilane, 3-mercaptopropyltriethoxysilane, tetraisooctyl isopropyl titanate, 2-mercaptoethanol, or acetylacetonate titanate; the speed of the mechanical stirring in step (1) is 200-300 rpm, and the time is 1-2 h.

3. The method for preparing a flame retardant thermoplastic polyurethane elastomer material according to claim 1, wherein: The filter membrane for vacuum filtration in step (1) is a 0.45 μm polytetrafluoroethylene filter membrane; the temperature for vacuum drying in step (1) is 70-85° C., and the time for vacuum drying is 18-36 hours.

4. The method for preparing a flame retardant thermoplastic polyurethane elastomer material according to claim 2, wherein: The nonionic dispersant in step (2) is polyethylene glycol, Tween 20, Triton X-100, polyoxyethylene decylphenol ether or Span-80; the parameters of the ultrasonic treatment in step (2) are as follows: ultrasonic power 500-800 W, ultrasonic frequency 40-60 kHz and ultrasonic time 10-20 min.

5. The method for preparing a flame retardant thermoplastic polyurethane elastomer material according to claim 1, wherein: The polyether polyol in step (3) is polyoxypropylene ether polyol, polyoxyethylene ether polyol or polytetramethylene ether glycol; the parameters of the mixing reaction in step (3) are as follows: 60-85° C., 40-60 rpm and 60-90 min.

6. The method for preparing a flame retardant thermoplastic polyurethane elastomer material according to claim 1, wherein: The chain extender in step (3) is 1,4-butanediol, 1,6-hexanediol, dihydroxymethylpropionic acid or 4,4'-diaminodiphenylmethane; the catalyst in step (3) is stannous octoate, dibutyltin dilaurate, triphenylbismuth, triethylenediamine or N,N-dimethylethanolamine; the antioxidant in step (3) is 2,6-di-tert-butyl-p-cresol, dilaurylthiodipropionate or triphenylphosphine.

7. The method for preparing a flame retardant thermoplastic polyurethane elastomer material according to claim 1, wherein: The parameters of the stirring reaction in step (3) are as follows: 200-260 rpm, 60-75°C, and 15-30 min; the parameters of the gradient temperature control in step (3) are as follows: 70-80°C for 60-80 min, 110-120°C for 20-30 min, and 130-150°C for 30-60 min.

8. The method for preparing a flame retardant thermoplastic polyurethane elastomer material according to claim 1, wherein: The curing temperature in step (4) is 105-125° C., and the curing time is 6-12 hours.

9. The method for preparing a flame retardant thermoplastic polyurethane elastomer material according to claim 1, wherein: The drying temperature in step (4) is 80-90°C and the drying time is 12-24h.

10. A flame retardant thermoplastic polyurethane elastomer material, characterized in that: The flame retardant thermoplastic polyurethane elastomer material is obtained by the preparation method according to any one of claims 1 to 9.

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