Flame-retardant polyurethane foam material and preparation method thereof
By combining water-soluble polyurethane with flame retardants to form a three-dimensional cross-linked network and an intumescent flame-retardant system, the problems of flammability and poor stability of polyurethane foam are solved, and high-strength and highly efficient flame-retardant polyurethane foam materials are achieved.
Patent Information
- Application Number
- CN202511900401.7
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-12-16
- Publication Date
- 2026-02-27
AI Technical Summary
Existing polyurethane foam materials are flammable, and the synthesis process is environmentally sensitive, posing significant construction difficulties and pollution risks. Therefore, it is necessary to improve their flame retardancy and stability.
By combining water-soluble polyurethane, surfactants, gelling agents, curing agents, and flame retardants, and through freeze foaming, curing, and flame retardant coating, a three-dimensional cross-linked network and an intumescent flame retardant system are formed, thereby improving mechanical strength and flame retardant performance.
The prepared flame-retardant polyurethane foam material has a compressive strength of 8 MPa, a maximum thermal decomposition temperature of 410 ℃, and a char rate of 38% at 800 ℃, which significantly enhances its mechanical properties and flame-retardant effect.
Smart Images
Figure CN121574534A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of polyurethane technology, specifically to a flame-retardant polyurethane foam material and its preparation method. Background Technology
[0002] The information disclosed in this background section is intended only to enhance understanding of the overall background of the invention and is not necessarily to be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.
[0003] Polyurethane foam (PUF) is a polymer material containing repeating urethane segments in its molecular chain. It is formed through addition polymerization of molecules with two or more isocyanate functional groups and polyols containing two or more reactive hydroxyl groups in a suitable catalyst and appropriate proportions. Polyurethane can be divided into two main categories: rigid and flexible. Due to its excellent flexibility, mechanical strength, abrasion resistance, and weather resistance, it occupies a very important position in the new materials industry. Flexible polyurethane mainly has a thermoplastic linear structure, possessing excellent properties such as light weight, good elasticity, and low price, and is widely used in furniture, sound insulation, shock absorption, and filtration materials. Rigid polyurethane foam has intramolecular cross-linking, high strength, and is insoluble, mainly used in structural materials for construction, home appliances, automobiles, aerospace, and thermal insulation.
[0004] Currently, there are two main methods for synthesizing polyurethane foam: a one-step method, which directly prepares polyols, polyisocyanates, catalysts, and blowing agents in one step; and a prepolymer method, which first reacts polyisocyanates with polyols to obtain a prepolymer with isocyanate-terminated groups, and then mixes the prepolymer with blowing agents and other additives to prepare polyurethane foam. However, the aforementioned methods for synthesizing polyurethane foam have the following problems: due to the involvement of isocyanate groups in the reaction, it is extremely sensitive to environmental humidity and other factors during storage, affecting foam stability; at the same time, if chemical blowing agents such as water are used, the reaction rate of isocyanate groups with water is relatively fast, resulting in difficult construction; if physical blowing agents are used, such as fluorinated blowing agents, it will cause environmental pollution, and hydrocarbon blowing agents have high storage requirements and are prone to hazards.
[0005] Furthermore, polyurethane foam, as a foam material, contains flammable hydrogen bonds and possesses characteristics such as low density and large specific surface area. Polyurethane itself is a flammable organic polymer material; untreated polyurethane is extremely flammable when exposed to fire, with a limiting oxygen index (LOI) typically around 18%. When burning, its cellular structure has a large contact area with oxygen, producing a large amount of toxic fumes. Therefore, improving the flame retardancy of polyurethane foam is essential. Summary of the Invention
[0006] To overcome the above problems, the present invention provides a flame-retardant polyurethane foam material and its preparation method.
[0007] To achieve the above technical objectives, the present invention adopts the following technical solution: In a first aspect, the present invention provides a flame-retardant polyurethane foam material, the raw materials of which include: Water-soluble polyurethane, foaming agent, gelling agent, curing agent, flame retardant and water; The raw materials of the water-soluble polyurethane include: poly(1,4-butanediol adipate) (PBA), isophorone diisocyanate (IPDI), catalyst, hydrophilic chain extender dimethylolpropionic acid, small molecule chain extender 1,4-butanediol, crosslinking agent and salt forming agent. The foaming agent includes a surfactant; The gelling agent includes potassium salt or sodium salt; The curing agent is a zinc salt ethanol solution; The flame retardant includes tris(hydroxymethyl)aminomethane (tris) modified ammonium polyphosphate and tannic acid.
[0008] In one or more embodiments, the number-average molecular weight Mn of poly(1,4-butanediol adipate) (PBA) in the raw materials of the water-soluble polyurethane is 2000. The catalyst is dibutyl dilaurate; The crosslinking agent is one or more of trimethylolpropane, glycerol, pentaerythritol and butanetetraol, preferably trimethylolpropane; The salt-forming agent is one or more of trimethylamine, triethylamine, tributylamine and triethanolamine, preferably triethylamine.
[0009] In one or more embodiments, the mass ratio of poly(1,4-butanediol adipate) (PBA), isophorone diisocyanate (IPDI), catalyst, hydrophilic chain extender dimethylolpropionic acid, small molecule chain extender 1,4-butanediol, crosslinking agent and salting agent is (28~32):(15~18):(0.008~0.012):(2~3):(1.5~1.9):(0.5~0.6):(1.7~2.0).
[0010] In one or more embodiments, the method for preparing water-soluble polyurethane includes the following steps: Under nitrogen or an inert atmosphere, poly(1,4-butanediol adipate) (PBA), isophorone diisocyanate (IPDI), and a catalyst are mixed for the first reaction. Then, dimethylolpropionic acid, a hydrophilic chain extender, is added for the second reaction. Finally, 1,4-butanediol, a small molecule chain extender, and a crosslinking agent are added for the third reaction. Finally, a salt-forming agent is added, and a fourth reaction is carried out to obtain water-soluble polyurethane.
[0011] Preferably, the temperature of the first, second, and third reactions is the same, which is 75~90 ℃; the time of the first reaction is 80~100 min; the time of the second reaction is 100~130 min; the time of the third reaction is 80~100 min; the temperature of the fourth reaction is 40~50 ℃; and the time of the fourth reaction is 50~70 min.
[0012] In one or more embodiments, the surfactant comprises sodium dodecyl sulfate (SDS).
[0013] In one or more embodiments, the sodium salt includes one of NaCl, sodium silicate, or NaHCO3; the potassium salt includes one of KCl or KHCO3.
[0014] In one or more embodiments, the zinc salt includes one of zinc chloride, zinc bromide, or zinc sulfate, preferably zinc chloride.
[0015] In one or more embodiments, a method for preparing tris(hydroxymethyl)aminomethane (tris)-modified ammonium polyphosphate includes: Tris(hydroxymethyl)aminomethane (tris) and ammonium polyphosphate were dispersed in water and reacted to obtain tris(hydroxymethyl)aminomethane (tris) modified ammonium polyphosphate.
[0016] Preferably, the mass ratio of tris(hydroxymethyl)aminomethane (tris) to ammonium polyphosphate is 1:(1.5~2.0).
[0017] Preferably, the degree of polymerization of ammonium polyphosphate is n > 1500.
[0018] Preferably, the reaction temperature is 70~90 ℃, more preferably 80 ℃.
[0019] In one or more embodiments, the maximum thermal decomposition temperature can reach 410 °C, and the char residue at 800 °C can reach 38%.
[0020] A second aspect of the present invention provides a method for preparing the flame-retardant polyurethane foam material described in the first aspect, comprising the following steps: (1) Disperse water-soluble polyurethane, foaming agent, tris-hydroxymethylaminomethane (tris) modified ammonium polyphosphate and gelling agent in water, and obtain gel foam after homogenization; (2) Freeze the gel foam, then add a curing agent to the frozen gel foam, and after reaction and drying, obtain a polyurethane foam intermediate; (3) Immerse the polyurethane foam intermediate in tannic acid solution, remove it and dry it to obtain flame-retardant polyurethane foam.
[0021] In one or more embodiments, in step (1), the mass ratio of water-soluble polyurethane, foaming agent, tris-hydroxymethylaminomethane (tris) modified ammonium polyphosphate, gelling agent and water is (430~480):(12~13):(28~32):(100~110):(130~160).
[0022] In one or more embodiments, in step (1), the rotation speed during homogenization is 7500~8500 r / min, and the homogenization time is 100~150 s.
[0023] In one or more embodiments, in step (2), the freezing time is 3 hours or more.
[0024] In one or more embodiments, in step (2), the concentration of the curing agent zinc salt ethanol solution is 0.08~0.12 mol / L, preferably 0.1 mol / L.
[0025] In one or more embodiments, in step (2), the volume of the curing agent zinc salt ethanol solution is slightly larger than the volume of the frozen gel foam.
[0026] In one or more embodiments, in step (2), the reaction time is 20-30 h, preferably 24 h.
[0027] In one or more embodiments, in step (3), the concentration of the tannic acid solution is 1.5 to 3 wt%, preferably 2 wt%.
[0028] In one or more embodiments, in step (3), the soaking time is 40-60 h, preferably 48 h.
[0029] The beneficial effects of this invention are as follows: This invention provides a flame-retardant polyurethane foam material. Water-soluble polyurethane is foamed using a surfactant and a gelling agent to obtain a gel foam. After freezing, it is cured using a zinc salt ethanol solution as a curing agent, resulting in a polyurethane foam material with significantly improved mechanical strength. Furthermore, the addition of tris(hydroxymethyl)aminomethane (tris)-modified ammonium polyphosphate flame retardant, along with tannic acid coated on the outer surface of the polyurethane foam material, synergistically enhances the flame-retardant effect. Specifically, the flame-retardant polyurethane foam material provided by this invention has a compressive strength of up to 8 MPa, higher than the compressive strength (2-5 MPa) of polyurethane foam materials of the same density prepared by conventional methods. The maximum thermal decomposition temperature of the flame-retardant polyurethane foam material can reach 410 °C, and the char residue at 800 °C can reach 38%.
[0030] Waterborne polyurethane contains a large number of carboxyl groups (-COOH), which are converted into carboxylates (-COO) after treatment with the neutralizing agent triethylamine (TEA).- This not only enables polyurethane to be stably dispersed in water (forming an aqueous emulsion), but also, when a zinc salt ethanol solution of a curing agent is added, Zn... 2+ It will interact with the -COO on the polyurethane chain - Coordination occurs (Zn) 2+ With multiple COOs - (Forming coordination bonds) and forming a three-dimensional cross-linked network can significantly enhance the intermolecular interaction, thereby resulting in better mechanical properties of polyurethane foam.
[0031] The added tris(hydroxymethyl)aminomethane (tris) modified ammonium polyphosphate flame retardant contains a large number of hydroxyl groups (OH), which will form an intumescent flame retardant system when it synergistically flame retards with tannic acid (TA), thereby improving the char-forming ability of the flame retardant system and thus enhancing the flame retardant performance of flame retardant polyurethane foam materials. Attached Figure Description
[0032] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.
[0033] Figure 1 The preparation process of ammonium polyphosphate modified with tris(hydroxymethyl)aminomethane (tris); Figure 2 The images are scanning electron microscope (SEM) images of the flame-retardant polyurethane foam material prepared in Example 3 and the polyurethane foam materials prepared in Comparative Examples 1-3, where a, b, c, and d correspond to Example 3, Comparative Example 1, Comparative Example 2, and Comparative Example 3, respectively. Detailed Implementation
[0034] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.
[0035] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of exemplary embodiments according to the invention. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.
[0036] To enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below with reference to specific embodiments.
[0037] Example 1 Preparation of water-soluble polyurethane: Under a nitrogen atmosphere, 30.0 g of poly(1,4-butanediol adipate) (PBA), 16.71 g of isophorone diisocyanate (IPDI), and 0.01 g of dibutyltin dilaurate (DBDTL) were dispersed in 35 mL of acetone and reacted at 80 °C for 90 min. Then, 2.39 g of dimethylolpropionic acid (DMPA) was added, and the reaction was continued at 80 °C for 120 min. Next, 1.7 g of 1,4-butanediol (BDO) and 0.53 g of trimethylolpropane (TMP) were added, and the reaction was continued at 80 °C for 90 min. The system temperature was then lowered to 45 °C, and 1.81 g of triethylamine was added. The reaction was carried out at 45 °C for 60 min to obtain waterborne polyurethane.
[0038] The aqueous polyurethane was transferred to a beaker, deionized water was added, and emulsification was carried out at room temperature using a high-speed shear emulsifier (8000 r / min) for 10 min. The emulsified product was then evaporated at 50 °C using a rotary evaporator until no solvent dripped to obtain the aqueous polyurethane emulsion with an R value (isocyanate index) of 1.3.
[0039] Example 2 Figure 1 The preparation process of tris(hydroxymethyl)aminomethane (tris) modified ammonium polyphosphate is described in reference [reference needed]. Figure 1 Tris-hydroxymethylaminomethane (tris)-modified ammonium polyphosphate was synthesized.
[0040] Under a nitrogen atmosphere, 8.4 g of tris(hydroxymethyl)aminomethane (tris) and 15 g of ammonium polyphosphate were dispersed in 150 mL of deionized water. The mixture was heated to 80 °C in an oil bath and stirred (200 r / min) for 4 h. The solution was cooled to room temperature and filtered to obtain a clear and transparent solution, which is tris(hydroxymethyl)aminomethane (tris) modified ammonium polyphosphate.
[0041] Example 3 (1) Disperse 1.5 g of waterborne polyurethane emulsion with a solid content of 30%, 0.225 g of sodium dodecyl sulfate (SDS) with a solid content of 5.7 wt%, 0.03 g of tris(hydroxymethyl)aminomethane (tris) modified ammonium polyphosphate and 1.1 g of sodium bicarbonate solution with a solid content of 9.6 wt% in 0.145 g of water. After mixing thoroughly, homogenize (8000 r / min, 120 s). Stop stirring when the foam liquid becomes slightly viscous. If the beaker containing the foam liquid stands still and does not flow when inverted, then gel foam is successfully obtained.
[0042] (2) The gel foam was frozen in a refrigerator for 5 h. After taking it out, 0.1 mol / L zinc chloride-ethanol solution with a volume 5 mL higher than the volume of the gel foam was added to the frozen gel foam. After reacting for 24 h, it was dried at room temperature. After drying, a polyurethane foam intermediate was obtained.
[0043] (3) Immerse the polyurethane foam intermediate in a 2 wt% tannic acid solution to coat its surface with tannic acid. After immersion for 48 h, remove it and air dry it at room temperature to obtain flame-retardant polyurethane foam.
[0044] Comparative Example 1 (1) Disperse 1.5 g of waterborne polyurethane emulsion with a solid content of 30%, 0.225 g of 5.7 wt% sodium dodecyl sulfate (SDS) and 1.1 g of 9.6 wt% sodium bicarbonate solution in 0.145 g of triterpenoid water. After mixing thoroughly, homogenize (8000 r / min, 120 s). Stop stirring when the foam liquid becomes slightly viscous. If the beaker containing the foam liquid stands still and does not flow when inverted, then gel foam is successfully obtained.
[0045] (2) The gel foam was frozen in a refrigerator for 5 h. After taking it out, 0.1 mol / L zinc chloride-ethanol solution with a volume 5 mL higher than the volume of the gel foam was added to the frozen gel foam. After reacting for 24 h, it was dried at room temperature. After drying, polyurethane foam material was obtained.
[0046] Comparative Example 2 (1) Disperse 1.5 g of waterborne polyurethane emulsion with a solid content of 30%, 0.225 g of sodium dodecyl sulfate (SDS) with a solid content of 5.7 wt%, 0.03 g of tris(hydroxymethyl)aminomethane (tris) modified ammonium polyphosphate and 1.1 g of sodium bicarbonate solution with a solid content of 9.6 wt% in 0.145 g of water. After mixing thoroughly, homogenize (8000 r / min, 120 s). Stop stirring when the foam liquid becomes slightly viscous. If the beaker containing the foam liquid stands still and does not flow when inverted, then gel foam is successfully obtained.
[0047] (2) The gel foam was frozen in a refrigerator for 5 h. After taking it out, 0.1 mol / L zinc chloride-ethanol solution with a volume 5 mL higher than the volume of the gel foam was added to the frozen gel foam. After reacting for 24 h, it was dried at room temperature. After drying, polyurethane foam material was obtained.
[0048] Comparative Example 3 (1) Disperse 1.5 g of waterborne polyurethane emulsion with a solid content of 30%, 0.225 g of 5.7 wt% sodium dodecyl sulfate (SDS) and 1.1 g of 9.6 wt% sodium bicarbonate solution in 0.145 g of triterpenoid water. After mixing thoroughly, homogenize (8000 r / min, 120 s). Stop stirring when the foam liquid becomes slightly viscous. If the beaker containing the foam liquid stands still and does not flow when inverted, then gel foam is successfully obtained.
[0049] (2) The gel foam was frozen in a refrigerator for 5 h. After taking it out, 0.1 mol / L zinc chloride-ethanol solution with a volume 5 mL higher than the volume of the gel foam was added to the frozen gel foam. After reacting for 24 h, it was dried at room temperature. After drying, a polyurethane foam intermediate was obtained.
[0050] (3) Immerse the polyurethane foam intermediate in a 2 wt% tannic acid solution to coat its surface with tannic acid. After immersion for 48 h, remove it and air dry it at room temperature to obtain the polyurethane foam material.
[0051] Figure 2 These are scanning electron microscope (SEM) images of the flame-retardant polyurethane foam material prepared in Example 3 and the polyurethane foam materials prepared in Comparative Examples 1-3. Figure 1 As can be seen from the example, the flame-retardant polyurethane foam material prepared in Example 3 has a uniform and continuous microstructure, which is an important reason for its good compressive strength and flame-retardant properties.
[0052] The flame-retardant polyurethane foam material prepared in Example 3 and the polyurethane foam materials prepared in Comparative Examples 1-3 were tested for mechanical properties and density according to the national standard GB / T 8813-2020. The results are shown in Table 1 below.
[0053] The mechanical property testing method is as follows: compression tests are performed on different samples with a diameter of 20 mm and a height of 10 mm using the compression mode of a universal testing machine with a sensor of 2000 N.
[0054] The density test method is as follows: pour an appropriate amount of water into a graduated cylinder and read the volume as V1. Immerse the product in the graduated cylinder and read the volume as V2. The density calculation expression is: ρ=m / (V2-V1).
[0055] Table 1. Results of Mechanical Properties and Density Tests
[0056] As shown in Table 1, the compressive strength of the flame-retardant polyurethane foam material prepared in Example 3 can reach 8 MPa, which is higher than the compressive strength (2~5 MPa) of polyurethane foam material of the same density prepared by conventional methods; and the subsequent flame-retardant modification of the flame-retardant polyurethane foam material did not significantly affect the compressive strength of the foam material.
[0057] The thermal stability of the flame-retardant polyurethane foam material prepared in Example 3 and the polyurethane foam materials prepared in Comparative Examples 1-3 was studied using thermogravimetric analysis. The tests were conducted under a nitrogen atmosphere with a heating rate of 10 °C / min from 30 °C to 800 °C. The results are shown in Table 2.
[0058] Table 2 Thermal stability results
[0059] The results in Table 2 show that the maximum thermal decomposition temperature and char rate at 800°C of the flame-retardant polyurethane foam material prepared in Example 3 were significantly improved compared with those of the unmodified polyurethane foam material in Comparative Example 1. This indicates that the synergistic effect of the ammonium polyphosphate flame-retardant filler and the tannic acid flame-retardant coating successfully enhanced the thermal stability of the polyurethane foam, which is beneficial to improving the flame-retardant performance of the material.
[0060] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.
Claims
1. A flame-retardant polyurethane foam material, characterized in that, Its raw materials include: Water-soluble polyurethane, foaming agent, gelling agent, curing agent, flame retardant and water; The raw materials of the water-soluble polyurethane include: poly(1,4-butanediol adipate) (PBA), isophorone diisocyanate (IPDI), catalyst, hydrophilic chain extender dimethylolpropionic acid, small molecule chain extender 1,4-butanediol, crosslinking agent and salt forming agent. The foaming agent includes a surfactant; The gelling agent includes potassium salt or sodium salt; The curing agent is a zinc salt ethanol solution; The flame retardant includes tris(hydroxymethyl)aminomethane (tris) modified ammonium polyphosphate and tannic acid.
2. The flame-retardant polyurethane foam material as described in claim 1, characterized in that, In the raw materials of the water-soluble polyurethane, the number-average molecular weight Mn of poly(1,4-butanediol adipate) (PBA) is 2000. The catalyst is dibutyl dilaurate; The crosslinking agent is one or more of trimethylolpropane, glycerol, pentaerythritol and butanetetraol, preferably trimethylolpropane; The salt-forming agent is one or more of trimethylamine, triethylamine, tributylamine and triethanolamine, preferably triethylamine; Alternatively, the mass ratio of poly(1,4-butanediol adipate) (PBA), isophorone diisocyanate (IPDI), catalyst, hydrophilic chain extender dimethylolpropionic acid, small molecule chain extender 1,4-butanediol, crosslinking agent and salting agent is (28~32):(15~18):(0.008~0.012):(2~3):(1.5~1.9):(0.5~0.6):(1.7~2.0).
3. The flame-retardant polyurethane foam material as described in claim 1, characterized in that, The preparation method of water-soluble polyurethane includes the following steps: Under nitrogen or an inert atmosphere, poly(1,4-butanediol adipate) (PBA), isophorone diisocyanate (IPDI) and a catalyst are mixed for the first reaction. Then, the hydrophilic chain extender dimethylolpropionic acid is added for the second reaction. Finally, the small molecule chain extender 1,4-butanediol and a crosslinking agent are added for the third reaction. Finally, a salt-forming agent is added, and the fourth reaction yields water-soluble polyurethane. Preferably, the temperatures for the first, second, and third reactions are all the same, at 75-90 °C; the time for the first reaction is 80-100 min; the time for the second reaction is 100-130 min; the time for the third reaction is 80-100 min; and the temperature for the fourth reaction is 40-50 °C, with a time of 50-70 min.
4. The flame-retardant polyurethane foam material as described in claim 1, characterized in that, The surfactant includes sodium dodecyl sulfate (SDS). Alternatively, the sodium salt may include one of NaCl, sodium silicate, or NaHCO3; the potassium salt may include one of KCl or KHCO3. Alternatively, the zinc salt may include one of zinc chloride, zinc bromide, or zinc sulfate, preferably zinc chloride.
5. The flame-retardant polyurethane foam material as described in claim 1, characterized in that, The preparation method of tris(hydroxymethyl)aminomethane (tris) modified ammonium polyphosphate includes: Tris(hydroxymethyl)aminomethane (tris) and ammonium polyphosphate were dispersed in water, and after reaction, tris(hydroxymethyl)aminomethane (tris) modified ammonium polyphosphate was obtained. Preferably, the mass ratio of tris(hydroxymethyl)aminomethane (tris) to ammonium polyphosphate is 1:(1.5~2.0). Preferably, the degree of polymerization of ammonium polyphosphate, n, is greater than 1500; Preferably, the reaction temperature is 70~90 ℃, more preferably 80 ℃.
6. A method for preparing the flame-retardant polyurethane foam material according to any one of claims 1 to 5, characterized in that, Includes the following steps: (1) Disperse water-soluble polyurethane, foaming agent, tris-hydroxymethylaminomethane (tris) modified ammonium polyphosphate and gelling agent in water, and obtain gel foam after homogenization; (2) Freeze the gel foam, then add a curing agent to the frozen gel foam, and after reaction and drying, obtain a polyurethane foam intermediate; (3) Immerse the polyurethane foam intermediate in tannic acid solution, remove it and dry it to obtain flame-retardant polyurethane foam.
7. The preparation method according to claim 6, characterized in that, In step (1), the mass ratio of water-soluble polyurethane, foaming agent, tris-hydroxymethylaminomethane (tris) modified ammonium polyphosphate, gelling agent and water is (430~480):(12~13):(28~32):(100~110):(130~160). Alternatively, in step (1), the rotation speed during homogenization is 7500~8500 r / min, and the homogenization time is 100~150 s.
8. The preparation method according to claim 6, characterized in that, In step (2), the freezing time is more than 3 hours; Alternatively, in step (2), the concentration of the curing agent zinc salt ethanol solution is 0.08~0.12 mol / L, preferably 0.1 mol / L.
9. The preparation method according to claim 6, characterized in that, In step (2), the volume of the curing agent zinc salt ethanol solution is slightly larger than the volume of the frozen gel foam; Alternatively, in step (2), the reaction time is 20-30 h, preferably 24 h.
10. The preparation method according to claim 6, characterized in that, In step (3), the concentration of the tannic acid solution is 1.5~3wt%, preferably 2wt%; Alternatively, in step (3), the soaking time is 40-60 h, preferably 48 h.