Low-temperature-resistant flame-retardant TPU foaming material and preparation method thereof

Abstract

The present application relates to the technical field of TPU foaming material, and discloses a low-temperature-resistant flame-retardant TPU foaming material and a preparation method thereof, which comprises the following raw materials: TPU prepolymer, polytetrahydrofuran ether glycol, diphenyl methane diisocyanate, isophorone diisocyanate, dibutyl tin dilaurate, a composite flame-retardant system, a low-temperature modifier, a crosslinking agent, a lubricant, an antioxidant, an ultraviolet absorber, and a solvent (anhydrous ethanol). The composite flame-retardant system containing phosphorus and a benzoxazine ring is designed, and a wet gel is prepared by a sol-gel method to interpenetrate and crosslink with the TPU prepolymer, so that a dual-pore structure coexisting microporous and nanometer aerogel pores is constructed. Significant technical progress is achieved in terms of flame retardation, smoke suppression, low-temperature resistance, lightweight heat insulation and the like, and the present application is suitable for the fields of aerospace, cold chain transportation, building thermal insulation and the like which have strict requirements for fire safety and adaptability to extremely cold environments.

Description

Technical Field

[0001] This invention relates to the field of TPU foaming material technology, specifically to a low-temperature resistant flame-retardant TPU foaming material and its preparation method. Background Technology

[0002] Thermoplastic polyurethane (TPU) foam is a non-metallic additive material widely used in footwear, automotive interiors, sporting goods, and electronic packaging due to its high resilience, excellent abrasion resistance, and lightweight properties. However, as applications expand to harsh environments such as aerospace, cold chain logistics, and polar equipment, traditional TPU foam materials have revealed two major technical bottlenecks. Firstly, its low-temperature resistance is insufficient. Ordinary polyester-based TPU experiences restricted molecular chain movement at low temperatures, leading to hardening and brittleness, making the foam prone to brittle fracture or collapse upon impact. Secondly, there is the issue of flammability. TPU's limiting oxygen index is typically only 18% to 20%, classifying it as a flammable material. Furthermore, combustion is accompanied by severe dripping and the release of large amounts of toxic fumes, severely limiting its application in safety-critical fields such as electronic packaging, building insulation, and vehicle interiors. Therefore, developing a TPU foam material that maintains good flexibility, high toughness at low temperatures, and efficient flame-retardant and smoke-suppressing properties has significant market value and practical importance. Summary of the Invention

[0003] (a) Technical problems to be solved To address the shortcomings of existing technologies, this invention provides a low-temperature resistant flame-retardant TPU foam material and its preparation method.

[0004] (II) Technical Solution To achieve the above objectives, the present invention provides the following technical solution: In a first aspect, a low-temperature resistant flame-retardant TPU foam material comprises the following raw materials in parts by weight: TPU prepolymer: 60-65 parts polytetrahydrofuran ether diol, 20-30 parts diphenylmethane diisocyanate, 10-15 parts isophorone diisocyanate, 0.1-0.2 parts dibutyltin dilaurate; 15-18 parts of composite flame retardant system, 3-5 parts of low temperature modifier, 0.3-0.5 parts of crosslinking agent, 0.5-1 part of lubricant, 0.3-0.5 parts of antioxidant, and 0.2-0.3 parts of ultraviolet absorber; Solvent: Anhydrous ethanol, balance.

[0005] Furthermore, the preparation method of the composite flame-retardant system includes the following steps: A1. Purge the three-necked flask with nitrogen 1-3 times, maintaining a slight positive pressure throughout. Add 80-100 parts of (2-cyanoethyl) phosphonate diethyl ester and 500-800 parts of anhydrous ethanol. Stir at 300-500 r / min for 10-15 min. Then add 40-50 parts of 2-mercaptoethylamine. Stir at room temperature for 3-5 min. Slowly add triethylamine dropwise, maintaining the pH at 8-9. Turn on the oil bath and heat to 60-70℃. Keep the temperature and stir for 4-5 h. After the reaction is complete, stop heating and allow to cool naturally to room temperature. Remove the solvent using a rotary evaporator and recrystallize with ethyl acetate to obtain intermediate 1. A2. Add 30-45 parts of vanillin to 500-600 parts of anhydrous ethanol, stir to dissolve, heat the oil bath to 50-55℃, slowly add 80-100 parts of intermediate 1, react for 1-2 h, remove the solvent with a rotary evaporator after the reaction is complete, and dry in a vacuum drying oven at 60-80℃ for 6-8 h to obtain intermediate 2. A3. Add 60-80 parts of intermediate 2 to 600-800 parts of anhydrous N,N-dimethylformamide, purge with nitrogen 1-3 times while maintaining a slight positive pressure, stir at 300-500 r / min until completely dissolved, add 30-40 parts of epoxy-functionalized benzoxazine, stir at room temperature for 5-10 min, then add 2-4 parts of 2-ethyl-4-methylimidazole, turn on oil bath heating, slowly raise the temperature to 90-110℃, keep warm and stir for 5-7 h, after the reaction is complete, cool naturally to room temperature, remove the solvent by rotary evaporation under reduced pressure, and dry in a vacuum drying oven at 60-70℃ for 6-8 h to obtain the composite flame retardant system.

[0006] Furthermore, the preparation method of the epoxy-functionalized benzoxazine includes the following steps: Under nitrogen protection, 80-100 parts of phenol and 50-60 parts of paraformaldehyde were dispersed in 800-1000 parts of 1,4-dioxane. The mixture was stirred and heated to 50-55°C. 60-80 parts of propylene oxide were slowly added dropwise. Triethylamine was added to maintain the pH of the system at 8-9. After the addition was complete, the temperature was raised to 80-85°C and reacted for 3-4 hours. The temperature was then raised to 95-100°C and reacted for 1-2 hours. After the reaction was completed, the mixture was cooled to room temperature and the solvent was removed under reduced pressure to obtain epoxy-functionalized benzoxazine.

[0007] Furthermore, the preparation method of the low-temperature modifier includes the following steps: B1. In a dry three-necked flask, add 50-60 parts of hydroxyl-terminated polydimethylsiloxane and 18-25 parts of methyltriethoxysilane in sequence. Purge with nitrogen for protection, stir at 300-500 r / min for 10-20 min, add 150-200 parts of N,N-dimethylformamide, heat to 40-50℃, and continue stirring for 10-15 min to obtain a premixed solution. B2. Slowly add 2-3 parts of 10-20% (w / w) aqueous solution of glacial acetic acid to the premixed solution at a dropping rate of 1-2 mL / min, stirring at 400-500 r / min and at a temperature of 40-45℃. After the addition is complete, add 3-6 parts of dimethyl disulfide, raise the temperature to 50-60℃, stir and react for 3-4 h, turn off the heating, and let it stand at room temperature for 8-12 h to obtain the low-temperature modifier.

[0008] Furthermore, the crosslinking agent is composed of IPDI trimer and polycarbodiimide in a mass ratio of 2:0.5~1.

[0009] Furthermore, the lubricant is composed of calcium stearate and polyethylene glycol in a mass ratio of 1:0.4~0.8.

[0010] Furthermore, the antioxidant is a compound of antioxidant 1010 and antioxidant 168 in a mass ratio of 1:1.

[0011] Furthermore, the ultraviolet absorber is composed of UV-531 and UV-327 in a mass ratio of 1:1 to 1.2.

[0012] A second aspect of the present invention provides a method for preparing a low-temperature resistant flame-retardant TPU foam material, comprising the following steps: S1. Place the low-temperature modifier into a high-speed shear disperser, add 3 to 5 times the volume of the low-temperature modifier in anhydrous ethanol, set the rotation speed to 10,000 to 15,000 r / min, shear for 10 to 30 min, and obtain a wet gel dispersion for later use. S2. In a dry reaction vessel, nitrogen gas is introduced for protection. Polytetrahydrofuran ether diol, diphenylmethane diisocyanate, and isophorone diisocyanate are added. The temperature is raised to 70-80°C. Dibutyltin dilaurate is added. The reaction is carried out for 2-3 hours to obtain TPU prepolymer. S3. Slowly add the wet gel dispersion to the TPU solution, and simultaneously add the composite flame retardant system. Stir at a speed of 600-800 r / min, keep warm at 50-60℃ for 1-2 h, add crosslinking agent, lubricant, antioxidant, and ultraviolet absorber, continue stirring for 10-30 min, mature at 55-60℃ for 0.5-1 h, transfer to a sealed displacement tank, add 3-5 times the volume of the above system of anhydrous ethanol, and soak at 40-50℃ for 10-12 h. S4. Transfer the above system to a supercritical foaming reactor, seal it, introduce supercritical CO2, set the pressure to 18~20 MPa, the temperature to 60~65℃, maintain the pressure for 40~60 min, then depressurize at a rate of 5~10 MPa / h, depressurize to atmospheric pressure, and maintain the temperature for 30~60 min to obtain the foamed preform. S5. Take out the foamed preform and put it into a vacuum drying oven. Dry it at 50~60℃ and -0.07~-0.09 MPa for 8~12 hours. Then cool it down to 20~25℃ and keep it at that temperature for 1~2 hours to obtain low-temperature resistant flame-retardant TPU foam material.

[0013] (iii) Beneficial technical effects This invention provides a low-temperature resistant flame-retardant TPU foam material and its preparation method. A composite flame-retardant system containing phosphorus and benzoxazine rings was designed. This system introduces a thioether structure through the click reaction of diethyl (2-cyanoethyl)phosphonate with mercaptoethylamine, followed by condensation with vanillin to form a Schiff base, and finally ring-opening addition with epoxy-functionalized benzoxazine to form a flame-retardant network, achieving high-efficiency and low-smoke flame retardancy. Using hydroxyl-terminated polydimethylsiloxane as raw material, a wet gel was prepared as a low-temperature modifier via the sol-gel method. After micronizing and dispersing the wet gel, it was interpenetratingly crosslinked with TPU prepolymer. Through simultaneous solvent replacement and supercritical carbon dioxide foaming treatment, a bilevel porous structure with micron-sized pores and nano-aerogel pores was constructed, greatly improving the low-temperature resistance of the material. In addition, the supercritical foaming process used in this invention has low temperature, low energy consumption, and uniform pore size. All additives, such as crosslinking agents, lubricants, antioxidants, and ultraviolet absorbers, are optimized and compounded to ensure the overall processing stability and long-term durability of the material. In summary, this invention has achieved significant technological advancements in flame retardancy, smoke suppression, low-temperature resistance, and lightweight thermal insulation, making it suitable for fields with stringent requirements for fire safety and adaptability to extremely cold environments, such as aerospace, cold chain transportation, and building insulation. Detailed Implementation

[0014] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0015] Unless otherwise specified, all components of the TPU foam material formulation of this invention are commercially available. All parts used in this invention are parts by weight; Polytetrahydrofuran ether diol: molecular weight 950~1050, purchased from Mitsubishi Chemical, Japan; Vanillin was purchased from Jiaxing Zhonghua Chemical Co., Ltd. Paraformaldehyde was purchased from Nantong Jiangtian Chemical Co., Ltd. Hydroxyl-terminated polydimethylsiloxane: hydroxyl value 35~45 mg KOH / g, purchased from Wacker Chemie; Example

[0016] A low-temperature resistant flame-retardant TPU foam material, comprising the following raw materials in parts by weight: TPU prepolymer: 60 parts polytetrahydrofuran ether diol, 20 parts diphenylmethane diisocyanate, 10 parts isophorone diisocyanate, 0.1 parts dibutyltin dilaurate; 15 parts composite flame retardant system, 3 parts low temperature modifier, 0.3 parts crosslinking agent, 0.5 parts lubricant, 0.3 parts antioxidant, 0.2 parts ultraviolet absorber; Solvent: Anhydrous ethanol, balance.

[0017] The crosslinking agent is composed of IPDI trimer and polycarbodiimide in a mass ratio of 2:0.5.

[0018] The lubricant is a compound of calcium stearate and polyethylene glycol in a mass ratio of 1:0.4.

[0019] The antioxidant is a compound of antioxidant 1010 and antioxidant 168 in a mass ratio of 1:1.

[0020] The ultraviolet absorber is a compound of UV-531 and UV-327 in a mass ratio of 1:1.

[0021] The preparation method of the composite flame retardant system includes the following steps: A1. Purge the three-necked flask with nitrogen once, maintaining a slight positive pressure throughout. Add 80 parts of (2-cyanoethyl) phosphonate diethyl ester and 500 parts of anhydrous ethanol, stir at 300 r / min for 10 min, then add 40 parts of 2-mercaptoethylamine, stir at room temperature for 3 min, slowly add triethylamine, maintain pH to 8, turn on oil bath heating, raise the temperature to 60℃, keep the temperature and stir for 4 h, stop heating after the reaction is completed, cool naturally to room temperature, remove the solvent using a rotary evaporator, recrystallize with ethyl acetate to obtain intermediate 1; A2. Add 30 parts of vanillin to 500 parts of anhydrous ethanol, stir to dissolve, heat the oil bath to 50°C, slowly add 80 parts of intermediate 1, react for 1 h, remove the solvent with a rotary evaporator after the reaction is complete, and dry in a vacuum drying oven at 60°C for 6 h to obtain intermediate 2. A3. Add 60 parts of intermediate 2 to 600 parts of anhydrous N,N-dimethylformamide, purge with nitrogen once and maintain a slight positive pressure, stir at 300 r / min until completely dissolved, add 30 parts of epoxy-functionalized benzoxazine, stir at room temperature for 5 min, then add 2 parts of 2-ethyl-4-methylimidazole, turn on oil bath heating, slowly raise the temperature to 90℃, keep warm and stir for 5 h, after the reaction is completed, cool naturally to room temperature, remove solvent by rotary evaporation under reduced pressure, and dry in a vacuum drying oven at 60℃ for 6 h to obtain the composite flame retardant system.

[0022] The preparation method of the epoxy-functionalized benzoxazine includes the following steps: Under nitrogen protection, 80 parts of phenol and 50 parts of paraformaldehyde were dispersed in 800 parts of 1,4-dioxane. The mixture was stirred and heated to 50°C. 60 parts of propylene oxide were slowly added dropwise. Triethylamine was added to maintain the pH of the system to 8. After the addition was complete, the temperature was raised to 80°C and reacted for 3 h. The temperature was then raised to 95°C and reacted for 1 h. After the reaction was completed, the mixture was cooled to room temperature and the solvent was removed under reduced pressure to obtain epoxy-functionalized benzoxazine.

[0023] The preparation method of the low-temperature modifier includes the following steps: B1. In a dry three-necked flask, add 50 parts of hydroxyl-terminated polydimethylsiloxane and 18 parts of methyltriethoxysilane in sequence, purge with nitrogen for protection, stir at 300 r / min for 10 min, add 150 parts of N,N-dimethylformamide, heat to 40℃, and continue stirring for 10 min to obtain a premixed solution. B2. Slowly add 2 parts of 10% glacial acetic acid aqueous solution to the premixed solution at a dropping rate of 1 mL / min, stirring speed of 400 r / min, and temperature of 40℃. After the addition is complete, add 3 parts of dimethyl disulfide, heat to 50℃, stir and react for 3 hours, turn off the heating, and let it stand at room temperature for 8 hours to obtain the low-temperature modifier.

[0024] A method for preparing a low-temperature resistant flame-retardant TPU foam material includes the following steps: S1. Place the low-temperature modifier into a high-speed shear disperser, add anhydrous ethanol at a volume of 3 times that of the low-temperature modifier, set the rotation speed to 10000 r / min, shear for 10 min, and obtain a wet gel dispersion for later use. S2. In a dry reaction vessel, nitrogen gas is introduced for protection. Polytetrahydrofuran ether diol, diphenylmethane diisocyanate, and isophorone diisocyanate are added. The temperature is raised to 70°C, and dibutyltin dilaurate is added. The reaction is carried out for 2 hours to obtain TPU prepolymer. S3. Slowly add the wet gel dispersion to the TPU solution, and simultaneously add the composite flame retardant system. Stir at 600 r / min, keep warm at 50℃ for 1 h, add crosslinking agent, lubricant, antioxidant, and UV absorber, continue stirring for 10 min, mature at 55℃ for 0.5 h, transfer to a sealed displacement tank, add anhydrous ethanol three times the volume of the above system in sequence, and soak at 40℃ for 10 h. S4. Transfer the above system to a supercritical foaming reactor, seal it, introduce supercritical CO2, set the pressure to 18 MPa, the temperature to 60℃, maintain the pressure for 40 min, then depressurize at a rate of 5 MPa / h, depressurize to atmospheric pressure and maintain the temperature for 30 min to obtain the foamed preform. S5. Take out the foamed preform and put it into a vacuum drying oven. Dry it at 50℃ and -0.07 MPa for 8 hours, then cool it down to 20℃ and keep it warm for 1 hour to obtain low-temperature resistant flame-retardant TPU foam material.

[0025] Example 2 A low-temperature resistant flame-retardant TPU foam material, comprising the following raw materials in parts by weight: TPU prepolymer: 62 parts polytetrahydrofuran ether diol, 25 parts diphenylmethane diisocyanate, 12 parts isophorone diisocyanate, 0.15 parts dibutyltin dilaurate; 16 parts composite flame retardant system, 4 parts low temperature modifier, 0.4 parts crosslinking agent, 0.8 parts lubricant, 0.4 parts antioxidant, 0.2 parts ultraviolet absorber; Solvent: Anhydrous ethanol, balance.

[0026] The crosslinking agent is composed of IPDI trimer and polycarbodiimide in a mass ratio of 2:0.8.

[0027] The lubricant is a compound of calcium stearate and polyethylene glycol in a mass ratio of 1:0.6.

[0028] The antioxidant is a compound of antioxidant 1010 and antioxidant 168 in a mass ratio of 1:1.

[0029] The ultraviolet absorber is a compound of UV-531 and UV-327 in a mass ratio of 1:1.2.

[0030] The preparation method of the composite flame retardant system includes the following steps: A1. Purge the three-necked flask twice with nitrogen, maintaining a slight positive pressure throughout. Add 90 parts of (2-cyanoethyl) phosphonate diethyl ester and 600 parts of anhydrous ethanol, and stir at 400 r / min for 15 min. Then add 45 parts of 2-mercaptoethylamine, stir at room temperature for 4 min, and slowly add triethylamine dropwise. Maintain the pH to 8.2, turn on the oil bath heating, raise the temperature to 65℃, and stir for 5 h. After the reaction is complete, stop heating, allow to cool naturally to room temperature, remove the solvent using a rotary evaporator, and recrystallize with ethyl acetate to obtain intermediate 1. A2. Add 40 parts of vanillin to 550 parts of anhydrous ethanol, stir to dissolve, heat the oil bath to 52°C, slowly add 90 parts of intermediate 1, react for 1.5 h, remove the solvent with a rotary evaporator after the reaction is completed, and dry in a vacuum drying oven at 70°C for 7 h to obtain intermediate 2. A3. Add 70 parts of intermediate 2 to 700 parts of anhydrous N,N-dimethylformamide, purge with nitrogen twice while maintaining a slight positive pressure, stir at 400 r / min until completely dissolved, add 35 parts of epoxy-functionalized benzoxazine, stir at room temperature for 10 min, then add 3 parts of 2-ethyl-4-methylimidazole, turn on oil bath heating, slowly raise the temperature to 100℃, keep warm and stir for 6 h, after the reaction is completed, cool naturally to room temperature, remove solvent by rotary evaporation under reduced pressure, and dry in a vacuum drying oven at 65℃ for 7 h to obtain the composite flame retardant system.

[0031] The preparation method of the epoxy-functionalized benzoxazine includes the following steps: Under nitrogen protection, 90 parts of phenol and 55 parts of paraformaldehyde were dispersed in 900 parts of 1,4-dioxane. The mixture was stirred and heated to 52°C. 70 parts of propylene oxide were slowly added dropwise. Triethylamine was added to maintain the pH of the system at 8.5. After the addition was complete, the temperature was raised to 82°C and reacted for 4 h. Then the temperature was raised to 98°C and reacted for 1 h. After the reaction was completed, the mixture was cooled to room temperature and the solvent was removed under reduced pressure to obtain epoxy-functionalized benzoxazine.

[0032] The preparation method of the low-temperature modifier includes the following steps: B1. In a dry three-necked flask, add 55 parts of hydroxyl-terminated polydimethylsiloxane and 20 parts of methyltriethoxysilane in sequence, purge with nitrogen for protection, stir at 400 r / min for 15 min, add 180 parts of N,N-dimethylformamide, heat to 45℃ and continue stirring for 10 min to obtain a premixed solution. B2. Slowly add 2 parts of 15% glacial acetic acid aqueous solution to the premixed solution at a dropping rate of 1.5 mL / min, stirring speed of 450 r / min, and temperature of 42℃. After the addition is complete, add 4 parts of dimethyl disulfide, heat to 55℃, stir and react for 3 h, turn off the heating, and let it stand at room temperature for 10 h to obtain the low temperature modifier.

[0033] A method for preparing a low-temperature resistant flame-retardant TPU foam material includes the following steps: S1. Place the low-temperature modifier into a high-speed shear disperser, add anhydrous ethanol at 4 times the volume of the low-temperature modifier, set the rotation speed to 12000 r / min, shear for 20 min, and obtain a wet gel dispersion for later use. S2. In a dry reaction vessel, nitrogen gas is introduced for protection. Polytetrahydrofuran ether diol, diphenylmethane diisocyanate, and isophorone diisocyanate are added. The temperature is raised to 75°C, and dibutyltin dilaurate is added. The reaction is carried out for 3 hours to obtain TPU prepolymer. S3. Slowly add the wet gel dispersion to the TPU solution, and simultaneously add the composite flame retardant system. Stir at 700 r / min, keep warm at 55℃ for 2 h, add crosslinking agent, lubricant, antioxidant, and ultraviolet absorber, continue stirring for 20 min, mature at 60℃ for 1 h, transfer to a sealed displacement tank, add anhydrous ethanol four times the volume of the above system in sequence, and soak at 45℃ for 10 h. S4. Transfer the above system to a supercritical foaming reactor, seal it, introduce supercritical CO2, set the pressure to 20 MPa and the temperature to 65℃, maintain the pressure for 50 min, then depressurize at a rate of 10 MPa / h, depressurize to atmospheric pressure and maintain the temperature for 60 min to obtain the foamed preform. S5. Take out the foamed preform and put it into a vacuum drying oven. Dry it at 55℃ and -0.08 MPa for 10 h, then cool it down to 22℃ and keep it at that temperature for 1.5 h to obtain low-temperature resistant flame-retardant TPU foam material.

[0034] Example 3 A low-temperature resistant flame-retardant TPU foam material, comprising the following raw materials in parts by weight: TPU prepolymer: 65 parts polytetrahydrofuran ether diol, 30 parts diphenylmethane diisocyanate, 15 parts isophorone diisocyanate, 0.2 parts dibutyltin dilaurate; 18 parts composite flame retardant system, 5 parts low temperature modifier, 0.5 parts crosslinking agent, 1 part lubricant, 0.5 parts antioxidant, 0.3 parts ultraviolet absorber; Solvent: Anhydrous ethanol, balance.

[0035] The crosslinking agent is composed of IPDI trimer and polycarbodiimide in a mass ratio of 2:1.

[0036] The lubricant is a compound of calcium stearate and polyethylene glycol in a mass ratio of 1:0.8.

[0037] The antioxidant is a compound of antioxidant 1010 and antioxidant 168 in a mass ratio of 1:1.

[0038] The ultraviolet absorber is a compound of UV-531 and UV-327 in a mass ratio of 1:1.2.

[0039] The preparation method of the composite flame retardant system includes the following steps: A1. Purge the three-necked flask with nitrogen three times, maintaining a slight positive pressure throughout. Add 100 parts of (2-cyanoethyl) phosphonate diethyl ester and 800 parts of anhydrous ethanol, stir at 500 r / min for 15 min, then add 50 parts of 2-mercaptoethylamine, stir at room temperature for 5 min, slowly add triethylamine, maintain pH to 9, turn on oil bath heating, raise the temperature to 70℃, keep the temperature and stir for 5 h, stop heating after the reaction is completed, cool naturally to room temperature, remove the solvent using a rotary evaporator, recrystallize with ethyl acetate to obtain intermediate 1; A2. Add 45 parts of vanillin to 600 parts of anhydrous ethanol, stir to dissolve, heat the oil bath to 55°C, slowly add 100 parts of intermediate 1, react for 2 h, remove the solvent with a rotary evaporator after the reaction is completed, and dry in a vacuum drying oven at 80°C for 8 h to obtain intermediate 2. A3. Add 80 parts of intermediate 2 to 800 parts of anhydrous N,N-dimethylformamide, purge with nitrogen three times while maintaining a slight positive pressure, stir at 500 r / min until completely dissolved, add 40 parts of epoxy-functionalized benzoxazine, stir at room temperature for 10 min, then add 4 parts of 2-ethyl-4-methylimidazole, turn on oil bath heating, slowly raise the temperature to 110℃, keep warm and stir for 7 h, after the reaction is completed, cool naturally to room temperature, remove solvent by rotary evaporation under reduced pressure, and dry in a vacuum drying oven at 70℃ for 8 h to obtain the composite flame retardant system.

[0040] The preparation method of the epoxy-functionalized benzoxazine includes the following steps: Under nitrogen protection, 100 parts of phenol and 60 parts of paraformaldehyde were dispersed in 1000 parts of 1,4-dioxane. The mixture was stirred and heated to 55°C. 80 parts of propylene oxide were slowly added dropwise. Triethylamine was added to maintain the pH of the system at 9. After the addition was complete, the temperature was raised to 85°C and reacted for 4 h. The temperature was then raised to 100°C and reacted for 2 h. After the reaction was completed, the mixture was cooled to room temperature and the solvent was removed under reduced pressure to obtain epoxy-functionalized benzoxazine.

[0041] The preparation method of the low-temperature modifier includes the following steps: B1. In a dry three-necked flask, add 60 parts of hydroxyl-terminated polydimethylsiloxane and 25 parts of methyltriethoxysilane in sequence, purge with nitrogen for protection, stir at 500 r / min for 20 min, add 200 parts of N,N-dimethylformamide, heat to 50℃, and continue stirring for 15 min to obtain a premixed solution. B2. Slowly add 3 parts of 20% glacial acetic acid aqueous solution to the premixed solution at a dropping rate of 2 mL / min, stirring speed of 500 r / min, and temperature of 45℃. After the addition is complete, add 6 parts of dimethyl disulfide, heat to 60℃, stir for 4 hours, turn off the heating, and let it stand at room temperature for 12 hours to obtain the low-temperature modifier.

[0042] A method for preparing a low-temperature resistant flame-retardant TPU foam material includes the following steps: S1. Place the low-temperature modifier into a high-speed shear disperser, add anhydrous ethanol at 5 times the volume of the low-temperature modifier, set the rotation speed to 15000 r / min, shear for 30 min, and obtain a wet gel dispersion for later use. S2. In a dry reaction vessel, nitrogen gas is introduced for protection. Polytetrahydrofuran ether diol, diphenylmethane diisocyanate, and isophorone diisocyanate are added. The temperature is raised to 80°C, and dibutyltin dilaurate is added. The reaction is carried out for 3 hours to obtain TPU prepolymer. S3. Slowly add the wet gel dispersion to the TPU solution, and simultaneously add the composite flame retardant system. Stir at 800 r / min, keep warm at 60℃ for 2 h, add crosslinking agent, lubricant, antioxidant, and ultraviolet absorber, continue stirring for 30 min, mature at 60℃ for 1 h, transfer to a sealed displacement tank, add anhydrous ethanol 5 times the volume of the above system in sequence, and soak at 50℃ for 12 h. S4. Transfer the above system to a supercritical foaming reactor, seal it, introduce supercritical CO2, set the pressure to 20 MPa, the temperature to 65℃, maintain the pressure for 60 min, then depressurize at a rate of 10 MPa / h, depressurize to atmospheric pressure and maintain the temperature for 60 min to obtain the foamed preform. S5. Take out the foamed preform and put it into a vacuum drying oven. Dry it at 60℃ and -0.09 MPa for 12 h, then cool it down to 25℃ and keep it at that temperature for 2 h to obtain low-temperature resistant flame-retardant TPU foam material.

[0043] Comparative Example 1: The composite flame retardant system was replaced with an equal mass of ammonium polyphosphate, and the remaining parameters and processes were the same as in Example 1.

[0044] Comparative Example 2: No low-temperature modifier was added, and the remaining parameters and processes were the same as in Example 1.

[0045] Comparative Example 3: Step S4 was changed to foaming with a foaming agent, and supercritical CO2 was not used, as detailed below: In step S3, after solvent replacement is completed, the system is transferred to a mold, 2.5 parts of azodicarbonamide are added, and the mixture is stirred evenly. The mold is then placed in a flat vulcanizing machine, heated to 190°C, and pressured at 5 MPa. The temperature and pressure are maintained for 20 minutes, and the mixture is allowed to cool naturally to room temperature before demolding to obtain the foamed preform.

[0046] The remaining parameters and processes are the same as in Example 1.

[0047] Performance testing: 1. Density Basis: GB / T 6343-2009 Method: Cut the foamed material into 50 mm × 50 mm × 20 mm samples, measure the dimensions and mass, calculate the apparent density, and take the average value of 5 samples.

[0048] 2. Limiting Oxygen Index (LOI) Basis: GB / T 2406-2009 Method: Cut the specimens to size 120 mm × 10 mm × 4 mm, and test the minimum oxygen concentration required to sustain combustion in an oxygen-nitrogen mixed gas flow. Take the average value of 5 specimens in each group.

[0049] 3. Vertical flammability rating (UL 94) Basis: UL 94-2018 Method: Cut the sample to size 125 mm × 13 mm × 3 mm, place it vertically, ignite it with a Bunsen lamp for 10 s, record the afterflame time and dripping phenomenon, and determine the V-0, V-1 or V-2 level.

[0050] 4. Total Tobacco Production (TSP) Standard: ISO 5660-1 (Cone Calorimeter) Method: Cut 100 mm × 100 mm × 6 mm samples and irradiate with a power of 35 kW / m². 2 Record TSP(m) 2 ).

[0051] 5. Low-temperature resilience (-30℃) Basis: GB / T 1681-2009 (Shore rebound) and cryogenic chamber Method: Cut cylindrical specimens with a diameter of 30 mm and a thickness of 12 mm, freeze them in a -30℃ low-temperature chamber for 24 h, and immediately test the rebound rate using a rebound hammer (ball drop height 500 mm) after removal. Take the average value of 5 specimens in each group. Record whether the specimens show cracks or fractures.

[0052] 6. Thermal conductivity (λ) Basis: GB / T 10295-2008 (Heat Flow Method) Method: Cut 200 mm × 200 mm × 20 mm samples, use a thermal conductivity meter with heat flow method, test temperature 25℃, and take the average value of 3 samples in each group.

[0053] Table 1

[0054] Table 2

[0055] As shown in Table 1, the limiting oxygen index (LOI) of Examples 1-3 were 31.5%, 32.2%, and 33.0%, respectively, all significantly higher than that of Comparative Example 1 (26.5%). Furthermore, all examples achieved a UL 94 V-0 vertical burning rating with no dripping, indicating that the composite flame-retardant system has excellent synergistic flame-retardant effects. Comparative Example 1 used ammonium polyphosphate instead of the composite flame-retardant system, resulting in an LOI of 26.5%, a UL 94 V-1 rating, and slight dripping, indicating that the flame-retardant efficiency of ammonium polyphosphate was lower than that of the flame-retardant system of this invention. The total smoke production of Examples 1-3 was 12.5 m³. 2 11.2 m 2 10.0 m 2 This is significantly lower than that of Comparative Example 1 (18.5 m). 2 The density of Comparative Example 3 is 0.35 g / cm³. 3 It has poor lightweight design.

[0056] As shown in Table 2, Examples 1-3 showed no cracks after freezing at -30℃ for 24 hours, with rebound rates of 82%, 85%, and 88%, respectively, significantly better than Comparative Example 2 (rebound rate 65%, severe cracks). This indicates that the low-temperature modifier of the present invention significantly improves the low-temperature toughness of the TPU foam material. Comparative Examples 1 and 3 both showed a rebound rate of 80% and no cracks. Comparative Example 2, lacking a low-temperature modifier, experienced micro-freezing of the TPU hard segments at low temperatures, leading to brittle fracture of the material.

[0057] The thermal conductivity of Examples 1-3 is 0.032, 0.030, and 0.030 W / (m·K), respectively, which is significantly better than that of Comparative Example 3 (0.042). This indicates that the wet gel dispersion aerogel process and supercritical CO2 foaming used in this invention form a bilevel porous structure, which effectively blocks convective heat transfer and thermal radiation.

[0058] Example 3 exhibits the best overall performance in terms of flame retardancy, smoke suppression, low temperature resistance, and lightweight, and is the best implementation scheme of the present invention.

[0059] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A low-temperature resistant flame-retardant TPU foam material, characterized in that, Includes the following quantities of raw materials: TPU prepolymer: 60-65 parts polytetrahydrofuran ether diol, 20-30 parts diphenylmethane diisocyanate, 10-15 parts isophorone diisocyanate, 0.1-0.2 parts dibutyltin dilaurate; 15-18 parts of composite flame retardant system, 3-5 parts of low temperature modifier, 0.3-0.5 parts of crosslinking agent, 0.5-1 part of lubricant, 0.3-0.5 parts of antioxidant, and 0.2-0.3 parts of ultraviolet absorber; Solvent: Anhydrous ethanol, balance.

2. The low-temperature resistant flame-retardant TPU foam material according to claim 1, characterized in that, The preparation method of the composite flame retardant system includes the following steps: A1. Purge the three-necked flask with nitrogen 1-3 times, maintaining a slight positive pressure throughout. Add 80-100 parts of (2-cyanoethyl) phosphonate diethyl ester and 500-800 parts of anhydrous ethanol. Stir at 300-500 r / min for 10-15 min. Then add 40-50 parts of 2-mercaptoethylamine. Stir at room temperature for 3-5 min. Slowly add triethylamine dropwise, maintaining the pH at 8-9. Turn on the oil bath and heat to 60-70℃. Keep the temperature and stir for 4-5 h. After the reaction is complete, stop heating and allow to cool naturally to room temperature. Remove the solvent using a rotary evaporator and recrystallize with ethyl acetate to obtain intermediate 1. A2. Add 30-45 parts of vanillin to 500-600 parts of anhydrous ethanol, stir to dissolve, heat the oil bath to 50-55℃, slowly add 80-100 parts of intermediate 1, react for 1-2 h, remove the solvent with a rotary evaporator after the reaction is complete, and dry in a vacuum drying oven at 60-80℃ for 6-8 h to obtain intermediate 2. A3. Add 60-80 parts of intermediate 2 to 600-800 parts of anhydrous N,N-dimethylformamide, purge with nitrogen 1-3 times while maintaining a slight positive pressure, stir at 300-500 r / min until completely dissolved, add 30-40 parts of epoxy-functionalized benzoxazine, stir at room temperature for 5-10 min, then add 2-4 parts of 2-ethyl-4-methylimidazole, turn on oil bath heating, slowly raise the temperature to 90-110℃, keep warm and stir for 5-7 h, after the reaction is complete, cool naturally to room temperature, remove the solvent by rotary evaporation under reduced pressure, and dry in a vacuum drying oven at 60-70℃ for 6-8 h to obtain the composite flame retardant system.

3. The low-temperature resistant flame-retardant TPU foam material according to claim 2, characterized in that, The preparation method of the epoxy-functionalized benzoxazine includes the following steps: Under nitrogen protection, 80-100 parts of phenol and 50-60 parts of paraformaldehyde were dispersed in 800-1000 parts of 1,4-dioxane. The mixture was stirred and heated to 50-55°C. 60-80 parts of propylene oxide were slowly added dropwise. Triethylamine was added to maintain the pH of the system at 8-9. After the addition was complete, the temperature was raised to 80-85°C and reacted for 3-4 hours. The temperature was then raised to 95-100°C and reacted for 1-2 hours. After the reaction was completed, the mixture was cooled to room temperature and the solvent was removed under reduced pressure to obtain epoxy-functionalized benzoxazine.

4. The low-temperature resistant flame-retardant TPU foam material according to claim 1, characterized in that, The preparation method of the low-temperature modifier includes the following steps: B1. In a dry three-necked flask, add 50-60 parts of hydroxyl-terminated polydimethylsiloxane and 18-25 parts of methyltriethoxysilane in sequence. Purge with nitrogen for protection, stir at 300-500 r / min for 10-20 min, add 150-200 parts of N,N-dimethylformamide, heat to 40-50℃, and continue stirring for 10-15 min to obtain a premixed solution. B2. Slowly add 2-3 parts of 10-20% (w / w) aqueous solution of glacial acetic acid to the premixed solution at a dropping rate of 1-2 mL / min, stirring at 400-500 r / min and at a temperature of 40-45℃. After the addition is complete, add 3-6 parts of dimethyl disulfide, raise the temperature to 50-60℃, stir and react for 3-4 h, turn off the heating, and let it stand at room temperature for 8-12 h to obtain the low-temperature modifier.

5. The low-temperature resistant flame-retardant TPU foam material according to claim 1, characterized in that, The crosslinking agent is composed of IPDI trimer and polycarbodiimide in a mass ratio of 2:0.5~1.

6. The low-temperature resistant flame-retardant TPU foam material according to claim 1, characterized in that, The lubricant is composed of calcium stearate and polyethylene glycol in a mass ratio of 1:0.4~0.

8.

7. The low-temperature resistant flame-retardant TPU foam material according to claim 1, characterized in that, The antioxidant is a compound of antioxidant 1010 and antioxidant 168 in a mass ratio of 1:

1.

8. The low-temperature resistant flame-retardant TPU foam material according to claim 1, characterized in that, The ultraviolet absorber is a compound of UV-531 and UV-327 in a mass ratio of 1:1 to 1.

2.

9. A method for preparing a low-temperature resistant flame-retardant TPU foam material according to any one of claims 1 to 8, characterized in that, Includes the following steps: S1. Place the low-temperature modifier into a high-speed shear disperser, add 3 to 5 times the volume of the low-temperature modifier in anhydrous ethanol, set the rotation speed to 10,000 to 15,000 r / min, shear for 10 to 30 min, and obtain a wet gel dispersion for later use. S2. In a dry reaction vessel, nitrogen gas is introduced for protection. Polytetrahydrofuran ether diol, diphenylmethane diisocyanate, and isophorone diisocyanate are added. The temperature is raised to 70-80°C. Dibutyltin dilaurate is added. The reaction is carried out for 2-3 hours to obtain TPU prepolymer. S3. Slowly add the wet gel dispersion to the TPU solution, and simultaneously add the composite flame retardant system. Stir at a speed of 600-800 r / min, keep warm at 50-60℃ for 1-2 h, add crosslinking agent, lubricant, antioxidant, and ultraviolet absorber, continue stirring for 10-30 min, mature at 55-60℃ for 0.5-1 h, transfer to a sealed displacement tank, add 3-5 times the volume of the above system of anhydrous ethanol, and soak at 40-50℃ for 10-12 h. S4. Transfer the above system to a supercritical foaming reactor, seal it, introduce supercritical CO2, set the pressure to 18~20 MPa, the temperature to 60~65℃, maintain the pressure for 40~60 min, then depressurize at a rate of 5~10 MPa / h, depressurize to atmospheric pressure, and maintain the temperature for 30~60 min to obtain the foamed preform. S5. Take out the foamed preform and put it into a vacuum drying oven. Dry it at 50~60℃ and -0.07~-0.09 MPa for 8~12 hours. Then cool it down to 20~25℃ and keep it at that temperature for 1~2 hours to obtain low-temperature resistant flame-retardant TPU foam material.

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