A flame-retardant polyurethane resin and its preparation method and application

Abstract

The present invention belongs to the field of fine chemical technology, and more particularly relates to a flame-retardant polyurethane resin, its preparation method, and its application. The flame-retardant polyurethane resin comprises the following components, by weight: 50-65 parts of a bio-based polyol, 25-35 parts of an isocyanate, 5-10 parts of a bio-based synergist, 3-6 parts of a chain extender, 0.05-0.15 parts of a catalyst, and 0.03-0.5 parts of a flame retardant. The polyurethane resin of the present invention combines excellent flame retardancy with mechanical strength. As a bio-based polyurethane material, it can be decomposed by microorganisms in soil and has a good degradation rate, expanding its application in the preparation of automotive leather surface treatment agents.

Description

Technical Field

[0001] The present invention belongs to the technical field of fine chemicals, and in particular relates to a flame-retardant polyurethane resin and a preparation method and application thereof. Background Art

[0002] Polyurethane (PU) is a polymer material prepared by the stepwise polymerization of polyols and isocyanates. It is primarily derived from fossil-based materials and is non-renewable. The alternating distribution of soft and hard segments within its molecular chain endows the material with exceptional designability. Through molecular design and compositional manipulation, these materials can exhibit diverse physical and chemical properties, leading to widespread application in foams, textile fibers, rubber products, leather, surface coatings, adhesives, road construction materials, and biomedical materials. In recent years, the development of multifunctional polyurethane resins has become a research hotspot.

[0003] With the increasing awareness of environmental protection, the sustainability and low-carbon environmental protection of polyurethane resins have become industry hotspots. Bio-based materials reduce carbon emissions during production and can be degraded into non-toxic small molecules through burning or composting after disposal, re-entering the natural cycle and avoiding environmental pollution. From a long-term development perspective, the bio-based industry will gradually replace the traditional high-energy-consuming and high-emission petrochemical industry. Invention patent CN104725633A discloses a method for preparing a bio-based non-isocyanate polyurethane elastomer. A five-membered ring carbonate is prepared by a catalytic addition reaction of epoxy soybean oil and carbon dioxide. The five-membered ring carbonate is mixed with 1,10-decanediamine and then degassed and cured to obtain a polyurethane elastomer. The tensile strength is only 1.8 MPa, and no modification of flame retardancy and degradability is involved, which greatly limits its scope of application. In addition, in traditional flame-retardant polyurethane materials, the interfacial bonding between the flame retardant and the polyurethane matrix is ​​insufficient, which easily causes stress concentration and further weakens the mechanical properties of the material. At present, how to achieve a balance between flame retardancy and mechanical properties is still the key in the field of polyurethane resin modification.

[0004] In order to cope with the problems of oil resource depletion and environmental pollution, the research and development of bio-based polyurethanes has become an important trend. Among them, carnosic acid is a natural plant component and a complex phenolic compound. It contains multiple functional groups such as phenolic hydroxyl groups and carboxyl groups. It has good heat resistance and is suitable for the preparation of bio-based polyurethane materials with flame retardant properties.

[0005] Therefore, in response to the above technical problems, improvements are made in the molecular design and composition regulation of polyurethane resins to achieve a multi-objective balance among the flame retardancy, mechanical properties and degradability of polyurethane resins, which has broad development prospects and industrial application value. Summary of the Invention

[0006] To overcome the shortcomings of the prior art, one of the objectives of the present invention is to provide a flame-retardant polyurethane resin. This polyurethane resin combines excellent flame retardancy with mechanical strength. As a bio-based polyurethane material, it can be decomposed by microorganisms in soil and has a good degradation rate.

[0007] One of the purposes of the present invention is achieved by the following technical solution:

[0008] A flame-retardant polyurethane resin comprises the following components, calculated by weight: 50-65 parts of bio-based polyol, 25-35 parts of isocyanate, 5-10 parts of bio-based synergist, 3-6 parts of chain extender, 0.05-0.15 parts of catalyst, and 0.03-0.5 parts of flame retardant; the general structural formula of the bio-based synergist is

[0009] ;

[0010] Where n is any integer from 1 to 3.

[0011] Furthermore, the preparation process of the bio-based synergist includes the following steps:

[0012] (1) adding trimethylsilylated diazomethane solution dropwise to the carnosic acid solution to carry out reaction; after the reaction, extracting, drying, concentrating and purifying the reaction solution to obtain carnosic acid methyl ester;

[0013] (2) adding a methyl carnosate solution to a lithium aluminum tetrahydride solution to carry out a reaction; after the reaction, extracting, drying, concentrating and purifying the reaction solution to obtain carnosyl alcohol;

[0014] (3) adding carnosyl alcohol and Dess-Martin oxidant into a solvent for reaction; after the reaction, filtering, washing, concentrating and purifying the reaction solution to obtain carnosyl aldehyde;

[0015] (4) Adding the diamino aromatic compound and carnauba aldehyde into a solvent for reaction; after the reaction, filtering, washing, and drying the reaction liquid to obtain a bio-based synergist.

[0016]

[0017] In the above chemical reaction formula, C6H4NH2(CH2) n C6H4NH2 refers to a diamino aromatic compound, where n is an integer from 1 to 3.

[0018] Furthermore, in step (1), the concentration of the carnosic acid solution is 0.125-0.2 mol / L, and the solvent of the carnosic acid solution is a toluene / methanol mixed solution prepared by mixing in a volume ratio of (3-5):1; the concentration of the trimethylsilylated diazomethane solution is 0.36-0.5 mol / L, and the solvent of the trimethylsilylated diazomethane solution is n-hexane; the molar ratio of the carnosic acid to the trimethylsilylated diazomethane is 1:(1.8-2.5); and the reaction time is 5-8 h.

[0019] Furthermore, in step (2), the solvent of the lithium aluminum tetrahydride solution is tetrahydrofuran, and the concentration of the lithium aluminum tetrahydride solution is 0.6~0.8 mol / L; the solvent of the methyl carnosate solution is tetrahydrofuran, and the concentration of the methyl carnosate solution is 0.2~0.4 mol / L; the molar ratio of the methyl carnosate to the lithium aluminum tetrahydride is 1:(3~4); the reaction temperature is 55~65°C, and the reaction time is 2~5h.

[0020] Furthermore, in step (3), the molar ratio of the carnosyl alcohol to the Dess-Martin oxidant is 1:(2-2.5), the concentration of the carnosyl alcohol in the solvent is 0.2-0.4 mol / L; the solvent is hexadecane, and the reaction time is 16-20 h.

[0021] Furthermore, in step (4), the molar ratio of the carnauba aldehyde to the diamino aromatic compound is 1:(2-2.5); the amount ratio of the carnauba aldehyde to the solvent is 1 mmol:2-5 mL; the solvent is cyclohexanol; the reaction temperature is 95-135°C, and the reaction time is 12-16 h.

[0022] Furthermore, the diamino aromatic compound is one of 4,4'-diaminodiphenylmethane, 4,4'-diaminobibenzyl, and 1,3-bis(4-aminophenyl)propane.

[0023] Furthermore, the bio-based polyol is soybean oil polyol or castor oil; the isocyanate is 4,4'-diphenylmethane diisocyanate; the chain extender is xylitol or glycerol; the catalyst is an organic bismuth catalyst; and the flame retardant is melamine.

[0024] The bio-based synergist is prepared from carnosic acid as raw material, which is then esterified, reduced and oxidized to obtain carnosic aldehyde, which is then reacted with diamino aromatic compounds through Schiff base reaction.

[0025] A second object of the present invention is to provide a method for preparing a flame-retardant polyurethane resin.

[0026] The method for preparing the flame-retardant polyurethane resin comprises the following steps:

[0027] a. Mix the bio-based polyol, bio-based synergist, catalyst, and flame retardant and heat them to 130-150°C to obtain a mixed solution A;

[0028] b. Add isocyanate and chain extender to mixed solution A separately, react at 75-100℃ for 3-4h, pour into a mold and let stand for 1.5-2.5h. After demoulding, mature at 90-110℃ for 10-14h to obtain the product.

[0029] A third object of the present invention is to provide a flame-retardant polyurethane resin for use in preparing a leather surface treatment agent.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] The present invention combines bio-based polyols, isocyanates, bio-based synergists, chain extenders, catalysts, and flame retardants in a scientifically formulated ratio and then reacts to produce a flame-retardant polyurethane resin. The carbon-nitrogen double bonds and aromatic rings in the Schiff base structure introduced by the bio-based synergist form a large conjugated structure, which self-crosslinks at high temperatures. This promotes charring of the polyurethane under high-temperature conditions, forming a dense barrier layer and improving flame retardancy. Furthermore, the bio-based synergist synergizes with the flame retardant (melamine) to further enhance the flame retardancy of the polyurethane. Furthermore, the dynamic covalent bonds of the Schiff base in the bio-based synergist can be decomposed by microorganisms, thereby disrupting the polyurethane backbone and accelerating its degradation.

[0032] The aromatic rings of the sage and diamino aromatic compounds introduced into the bio-based synergist in this invention attract each other through a π-π stacking interaction. This interaction strengthens the attraction between the molecular chains, enabling them to better coordinate motion when subjected to stress, thereby improving the mechanical properties of the material. The presence of the benzene rings makes the molecular chains more rigid in space, making them less able to move freely and more resistant to deformation, thereby increasing the tensile strength and elongation at break of the bio-based polyurethane. DETAILED DESCRIPTION

[0033] Below, in conjunction with specific embodiments, the present invention is further described. It should be noted that, under the premise of no conflict, the various embodiments described below or the various technical features can be arbitrarily combined to form new embodiments. Specific conditions not specified in the embodiments are carried out according to conventional conditions or conditions recommended by the manufacturer. Reagents or instruments used, unless otherwise specified, are conventional products obtained through commercial channels.

[0034] Example 1

[0035] A flame-retardant polyurethane resin, comprising the following components, by weight: 55 parts of castor oil, 30 parts of 4,4'-diphenylmethane diisocyanate, 8 parts of a bio-based synergist, 5 parts of xylitol, 0.1 parts of an organic bismuth catalyst DY-20, and 0.4 parts of melamine;

[0036] The preparation process of the bio-based synergist includes the following steps:

[0037] (1) First, a toluene / methanol mixed solution was prepared by mixing toluene and methanol in a volume ratio of 5:1, and then carnosic acid was added to prepare a carnosic acid solution with a concentration of 0.125 mol / L. Trimethylsilyl diazomethane was added to n-hexane to prepare a trimethylsilyl diazomethane solution with a concentration of 0.4 mol / L. At 0°C, under a nitrogen atmosphere, the trimethylsilyl diazomethane solution was added dropwise to the carnosic acid solution, wherein the molar ratio of carnosic acid to trimethylsilyl diazomethane was 1:2.0; after the addition was completed, the temperature was gradually raised to room temperature and the reaction was carried out for 6 hours; acetic acid was added to quench the reaction, the solvent was concentrated to remove, and the concentrated residue was dispersed with water, the aqueous phase was extracted with ethyl acetate, the ethyl acetate phase was washed with saturated brine, dried over anhydrous sodium sulfate, concentrated, and purified by silica gel chromatography (petroleum ether: ethyl acetate = 10:1) to obtain carnosic acid methyl ester; 1 H NMR (C 21 H 30 O4, 400MHz, DMSO-d6): δ 9.52 (s, 2H), 6.45 (s, 1H), 3.67 (s,3H), 3.09 (m, 1H), 2.90-2.80 (m, 2H), 2.26-2.20 (m, 2H), 1.85 (t, 1H), 1.67-1.30 (m, 6H), 1.16 (d, 6H), 0.94 (s, 6H).MS (ESI) m / z=346.21 [M].

[0038] (2) At 0°C, under a nitrogen atmosphere, lithium aluminum tetrahydride was added to tetrahydrofuran and stirred evenly to obtain a lithium aluminum tetrahydride solution with a concentration of 0.7 mol / L, and then a tetrahydrofuran solution with a concentration of 0.2 mol / L methyl sanoate was slowly added, wherein the molar ratio of methyl sanoate to lithium aluminum tetrahydride was 1:3.5. After the addition was completed, the temperature was gradually raised to room temperature, stirred at room temperature for 10 minutes, and then the reaction solution was heated to 60°C for 3 hours; the reaction was cooled to room temperature, and the reaction was quenched with water until the heat release was no longer severe, and the quenched reaction solution was neutralized with hydrochloric acid (1 M), and then extracted with ethyl acetate, the organic phase was dried, concentrated, and purified by silica gel chromatography (petroleum ether: ethyl acetate = 10:1) to obtain sanosanol; 1H NMR (C 20 H 30 O3,400 MHz, DMSO-d6): δ 9.52 (s, 2H), 6.45 (s, 1H), 4.62 (s, 1H), 3.89-3.64 (m,2H), 3.09 (m, 1H), 2.90-2.80 (m, 2H), 2.04-1.30 (m, 8H), 1.16-1.13 (m, 7H), 0.94 (s, 6H).MS (ESI) m / z=318.22 [M].

[0039] (3) Add carnosyl alcohol and Dess-Martin oxidant to dioxane at a molar ratio of 1:2.2, respectively, with the concentration of carnosyl alcohol in dioxane being 0.2 mol / L; react at room temperature for 18 h; filter the reaction solution, rinse the filter cake with ethyl acetate during the filtration process, and purify the concentrated filtrate by silica gel chromatography (petroleum ether: ethyl acetate = 10:1) to obtain carnosyl aldehyde; the yield is 45%. 1 H NMR (C 20 H 28 O3, 400 MHz, DMSO-d6): δ 9.72 (s, 1H), 9.52 (s,2H), 6.45 (s, 1H), 3.09 (m, 1H), 2.90-2.80 (m, 2H), 2.15-1.30 (m, 9H), 1.16(d, 6H), 0.94 (s, 6H).MS (ESI) m / z=316.20 [M].

[0040] The reaction formula of the above preparation process is as follows:

[0041]

[0042] (4) A diamino aromatic compound (1,3-bis(4-aminophenyl)propane, CAS: 2767-73-9) and carnauba aldehyde were added to cyclohexanol at a molar ratio of 1:2.2 and stirred evenly at room temperature. The amount ratio of carnauba aldehyde to cyclohexanol was 1 mmol:2 mL. The temperature was gradually raised to 105°C and the reaction was carried out for 14 h. The mixture was filtered while hot and the filter cake was washed with n-hexane. The filter cake was dried to obtain a bio-based synergist. The yield was 65%.

[0043] The chemical structural formula of the bio-based synergist obtained in this example is:

[0044]

[0045] 1 H NMR (C55 H 70 N2O4, 400 MHz, DMSO-d6): δ 9.52 (s, 4H), 8.50 (s, 2H), 7.26-7.21 (m, 8H), 6.45 (s, 2H), 3.99 (s, 2H), 3.09-2.80 (m, 6H), 2.65 (t,2H), 2.12-1.30 (m, 18H), 1.19-1.16 (m, 14H), 0.94 (s, 12H).MS (ESI) m / z=822.53 [M].

[0046] This embodiment also provides a method for preparing a flame-retardant polyurethane resin, comprising the following steps:

[0047] a. The castor oil, bio-based synergist, organic bismuth catalyst DY-20, and melamine were mixed and heated to 150 ° C to obtain a mixture A;

[0048] b. Add 4,4'-diphenylmethane diisocyanate and xylitol to the mixture A respectively, react at 90℃ for 3.5h, pour into a mold and let it stand for 1.5h. After demolding, mature at 100℃ for 12h to obtain the product.

[0049] Example 2

[0050] A flame-retardant polyurethane resin, comprising the following components, by weight: 50 parts of castor oil, 25 parts of 4,4'-diphenylmethane diisocyanate, 5 parts of a bio-based synergist, 3 parts of xylitol, 0.05 parts of an organic bismuth catalyst DY-20, and 0.03 parts of melamine;

[0051] The preparation process of the bio-based synergist includes the following steps:

[0052] (1) First, a toluene / methanol mixed solution was prepared by mixing toluene and methanol in a volume ratio of 5:1, and then carnosic acid was added to prepare a carnosic acid solution with a concentration of 0.125 mmol / L. Trimethylsilyl diazomethane was added to n-hexane to prepare a trimethylsilyl diazomethane solution with a concentration of 0.36 mmol / L. At 0°C, under a nitrogen atmosphere, trimethylsilyl diazomethane solution was added dropwise to the carnosic acid solution, wherein the molar ratio of carnosic acid to trimethylsilyl diazomethane was 1:1.8; after the addition was completed, the temperature was gradually raised to room temperature and the reaction was carried out for 5 hours; acetic acid was added to quench the reaction, the solvent was concentrated to remove, and the concentrated residue was dispersed with water, the aqueous phase was extracted with ethyl acetate, the ethyl acetate phase was washed with saturated brine, dried over anhydrous sodium sulfate, concentrated, and purified by silica gel chromatography (petroleum ether: ethyl acetate = 10:1) to obtain carnosic acid methyl ester; 1The results of H NMR were the same as those in Example 1;

[0053] (2) At 0°C, under a nitrogen atmosphere, lithium aluminum tetrahydride was added to tetrahydrofuran and stirred evenly to obtain a lithium aluminum tetrahydride solution with a concentration of 0.6 mmol / L, and then a tetrahydrofuran solution with a concentration of 0.2 mol / L methyl sanoate was slowly added, wherein the molar ratio of methyl sanoate to lithium aluminum tetrahydride was 1:3. After the addition was completed, the temperature was gradually raised to room temperature, stirred at room temperature for 10 minutes, and then the reaction solution was heated to 65°C for 2 hours; the reaction was cooled to room temperature, and the reaction was quenched with water until the heat release was no longer severe, and the quenched reaction solution was neutralized with hydrochloric acid (1 M), and then extracted with ethyl acetate, the organic phase was dried, concentrated, and purified by silica gel chromatography (petroleum ether: ethyl acetate = 10:1) to obtain sanosanol; 1 The results of H NMR were the same as those in Example 1;

[0054] (3) Add carnosyl alcohol and Dess-Martin oxidant to dioxane at a molar ratio of 1:2, respectively, wherein the concentration of carnosyl alcohol in dioxane is 0.2 mol / L; react at room temperature for 16 hours; filter the reaction solution, rinse the filter cake with ethyl acetate during the filtration process, and purify the concentrated filtrate by silica gel chromatography (petroleum ether: ethyl acetate = 10:1) to obtain carnosyl aldehyde; the yield is 42%. 1 The results of H NMR were the same as those in Example 1;

[0055] (4) A diamino aromatic compound (4,4'-diaminobibenzyl, CAS: 621-95-4) and carnosine aldehyde were added to cyclohexanol at a molar ratio of 1:2.5, and stirred evenly at room temperature. The amount ratio of carnosine aldehyde to cyclohexanol was 1 mmol:2 mL. The temperature was gradually raised to 135°C and reacted for 12 h. The mixture was filtered while hot, and the filter cake was washed with n-hexane. The filter cake was dried to obtain a bio-based synergist. The yield was 57%.

[0056] The chemical structural formula of the bio-based synergist obtained in this example is:

[0057]

[0058] 1 H NMR (C 54 H 68N2O4, 400 MHz, DMSO-d6): δ 9.52 (s, 4H), 8.50 (s, 2H), 7.26-7.21 (m, 8H), 6.45 (s, 2H), 3.99 (s, 2H), 3.09-2.80 (m, 8H), 2.12-1.30(m, 16H), 1.19-1.16 (m, 14H), 0.94 (s, 12H).MS (ESI) m / z=808.52[M].

[0059] This embodiment also provides a method for preparing a flame-retardant polyurethane resin, comprising the following steps:

[0060] a. The castor oil, bio-based synergist, organic bismuth catalyst DY-20, and melamine were mixed and heated to 150 ° C to obtain a mixture A;

[0061] b. Add 4,4'-diphenylmethane diisocyanate and xylitol to the mixture A respectively, react at 75℃ for 4h, pour into a mold and let stand for 1.5h. After demolding, mature at 90℃ for 14h to obtain the product.

[0062] Example 3

[0063] A flame-retardant polyurethane resin, comprising the following components, by weight: 65 parts of castor oil, 35 parts of 4,4'-diphenylmethane diisocyanate, 10 parts of a bio-based synergist, 6 parts of glycerol, 0.15 parts of an organic bismuth catalyst DY-20, and 0.5 parts of melamine;

[0064] The preparation process of the bio-based synergist includes the following steps:

[0065] (1) First, a toluene / methanol mixed solution was prepared by mixing toluene and methanol in a volume ratio of 5:1, and then carnosic acid was added to prepare a carnosic acid solution with a concentration of 0.125 mmol / L. Trimethylsilyl diazomethane was added to n-hexane to prepare a trimethylsilyl diazomethane solution with a concentration of 0.5 mmol / L. At 0°C, under a nitrogen atmosphere, trimethylsilyl diazomethane solution was added dropwise to the carnosic acid solution, wherein the molar ratio of carnosic acid to trimethylsilyl diazomethane was 1:2.5; after the addition was completed, the temperature was gradually raised to room temperature and the reaction was carried out for 8 hours; acetic acid was added to quench the reaction, the solvent was concentrated to remove, and the concentrated residue was dispersed with water, the aqueous phase was extracted with ethyl acetate, the ethyl acetate phase was washed with saturated brine, dried over anhydrous sodium sulfate, concentrated, and purified by silica gel chromatography (petroleum ether: ethyl acetate = 10:1) to obtain carnosic acid methyl ester; 1 The results of H NMR were the same as those in Example 1.

[0066] (2) At 0°C, under a nitrogen atmosphere, lithium aluminum tetrahydride was added to tetrahydrofuran and stirred evenly to obtain a lithium aluminum tetrahydride solution with a concentration of 0.8 mmol / L, and then a tetrahydrofuran solution with a concentration of 0.2 mol / L methyl sanoate was slowly added, wherein the molar ratio of methyl sanoate to lithium aluminum tetrahydride was 1:4. After the addition was completed, the temperature was gradually raised to room temperature, stirred at room temperature for 10 minutes, and then the reaction solution was heated to 65°C for 5 hours; the reaction was cooled to room temperature, and the reaction was quenched with water until the heat release was no longer severe, and the quenched reaction solution was neutralized with hydrochloric acid (1 M), and then extracted with ethyl acetate, the organic phase was dried, concentrated, and purified by silica gel chromatography (petroleum ether: ethyl acetate = 10:1) to obtain sanosanol; 1 The results of H NMR were the same as those in Example 1.

[0067] (3) Add carnosyl alcohol and Dess-Martin oxidant to dioxane at a molar ratio of 1:2.5, respectively, with the concentration of carnosyl alcohol in dioxane being 0.2 mol / L; react at room temperature for 20 h; filter the reaction solution, rinse the filter cake with ethyl acetate during the filtration process, and purify the concentrated filtrate by silica gel chromatography (petroleum ether: ethyl acetate = 10:1) to obtain carnosyl aldehyde; the yield is 44%. 1 The results of H NMR were the same as those in Example 1.

[0068] (4) A diamino aromatic compound (4,4'-diaminodiphenylmethane, CAS: 101-77-9) and carnosine aldehyde were added to cyclohexanol at a molar ratio of 1:2.5, and stirred evenly at room temperature. The amount ratio of carnosine aldehyde to cyclohexanol was 1 mmol:2 mL. The temperature was gradually raised to 95°C and the reaction was carried out for 16 hours. The mixture was filtered while hot, and the filter cake was washed with n-hexane. The filter cake was dried to obtain a bio-based synergist. The yield was 61%.

[0069] The chemical structural formula of the obtained bio-based synergist is:

[0070]

[0071] 1 H NMR (C 53 H 66 N2O4, 400 MHz, DMSO-d6): δ 9.52 (s, 4H), 8.50 (s, 2H), 7.26-7.21 (m, 8H), 6.45 (s, 2H), 3.99 (s, 2H), 3.09-2.80 (m, 6H), 2.12-1.30 (m, 16H), 1.19-1.16 (m, 14H), 0.94 (s, 12H). MS (ESI) m / z=794.50 [M].

[0072] This embodiment also provides a method for preparing a flame-retardant polyurethane resin, comprising the following steps:

[0073] a. The castor oil, bio-based synergist, organic bismuth catalyst DY-20, and melamine were mixed and heated to 150 ° C to obtain a mixture A;

[0074] b. Add 4,4'-diphenylmethane diisocyanate and glycerol to the mixture A respectively, react at 100℃ for 3h, pour into the mold and let it stand for 1.5h. After demolding, mature at 110℃ for 10h to obtain the product.

[0075] Comparative Example 1

[0076] The difference between Comparative Example 1 and Example 1 is that the bio-based synergist is replaced by an equal amount of methyl carnosate.

[0077] Test Example 1

[0078] The tensile strength and elongation at break of the polyurethane resins obtained in Examples 1-3 and Comparative Example 1 were tested according to the standard GB / T528-2009. The test results are recorded in Table 1.

[0079] Table 1

[0080]

[0081] The test results in Table 1 show that the polyurethane resins obtained in Examples 1-3 of the present application exhibit excellent mechanical and flame retardant properties, far exceeding those of Comparative Example 1 (in which the bio-based synergist was replaced with methyl carnosate). This result is due to the aromatic ring structure introduced by the bio-based synergist, where the benzene rings within the aromatic rings attract each other through a π-π stacking effect. This interaction enhances the attraction between the molecular chains, allowing them to better coordinate motion when subjected to force, thereby improving the material's mechanical properties. Furthermore, the presence of the benzene rings makes the molecular chains more rigid in space, making them less able to move freely and more resistant to deformation, thereby increasing the tensile strength of the bio-based polyurethane. This improves the tensile strength and elongation at break of the polyurethane.

[0082] Among them, Example 1 has the highest elongation at break, followed by Example 2 and Example 3. This is because the structures of the bio-based synergists introduced in Examples 1 to 3 are different. As the fatty chain length of the diamino aromatic compound introduced during the preparation of the bio-based synergist increases, its elongation at break is significantly improved.

[0083] Test Example 2

[0084] The oxygen index of the polyurethane material was tested according to the test standard of GB / T2406.2-2009, and the test results are recorded in Table 2.

[0085] Table 2

[0086]

[0087] The test results in Table 2 show that the oxygen index of Examples 1-3 is higher than that of Comparative Example 1. This is because the carbon-nitrogen double bond and aromatic ring in the bio-based synergist form a large conjugated structure, which self-crosslinks at high temperatures. This promotes the carbonization of the polyurethane under high-temperature conditions, forming a dense barrier layer and improving flame retardancy. Furthermore, the bio-based synergist can synergize with melamine to further enhance the flame retardancy of the polyurethane.

[0088] Test Example 3

[0089] Biodegradability: The polyurethane material obtained in the experiment was cut into sheets with a thickness of approximately 0.2 mm. Composting tests were conducted according to the method specified in GB / T 19277.2-2013. After 60 days of testing, the biodegradation rate of the samples was measured gravimetrically. The degradation rate was calculated according to the following formula: Degradation rate (%) = (M0 - M1) / M0 × 100%, where M0 represents the initial weight of the sample and M1 represents the constant weight of the material measured on the 60th day. The experimental results are shown in Table 3.

[0090] Table 3

[0091]

[0092] The test results in Table 3 show that Examples 1-3 exhibit superior flame retardancy to Comparative Example 1, with a 60-day degradation rate of 89.3%. This demonstrates that the addition of the bio-based synergist in the present invention can enhance the flame retardancy of polyurethane materials. This result is attributed to the fact that the Schiff base dynamic covalent bonds introduced into the bio-based synergist can be decomposed by microorganisms, thereby disrupting the polyurethane backbone structure and accelerating its degradation.

[0093] The above embodiments are only preferred embodiments of the present invention and cannot be used to limit the scope of protection of the present invention. Any non-substantial changes and replacements made by technicians in this field on the basis of the present invention fall within the scope of protection required by the present invention.

Claims

1. A flame retardant polyurethane resin, characterized in that: The composition includes the following components by weight: 50-65 parts of bio-based polyol, 25-35 parts of isocyanate, 5-10 parts of bio-based synergist, 3-6 parts of chain extender, 0.05-0.15 parts of catalyst, and 0.03-0.5 parts of flame retardant; the general structural formula of the bio-based synergist is: ； Where n is any integer from 1 to 3.

2. The flame-retardant polyurethane resin according to claim 1, wherein The preparation process of the bio-based synergist comprises the following steps: (1) adding trimethylsilylated diazomethane solution dropwise to the carnosic acid solution to carry out reaction; after the reaction, extracting, drying, concentrating and purifying the reaction solution to obtain carnosic acid methyl ester; (2) adding a methyl carnosate solution to a lithium aluminum tetrahydride solution to carry out a reaction; after the reaction, extracting, drying, concentrating and purifying the reaction solution to obtain carnosyl alcohol; (3) adding carnosyl alcohol and Dess-Martin oxidant into a solvent for reaction; after the reaction, filtering, washing, concentrating and purifying the reaction solution to obtain carnosyl aldehyde; (4) Adding the diamino aromatic compound and carnauba aldehyde into a solvent for reaction; after the reaction, filtering, washing, and drying the reaction liquid to obtain a bio-based synergist.

3. The flame-retardant polyurethane resin according to claim 2, characterized in that In step (1), the concentration of the carnosic acid solution is 0.125~0.2 mol / L, and the solvent of the carnosic acid solution is a toluene / methanol mixed solution prepared by mixing in a volume ratio of (3~5):1; the concentration of the trimethylsilylated diazomethane solution is 0.36~0.5 mol / L, and the solvent of the trimethylsilylated diazomethane solution is n-hexane; the molar ratio of the carnosic acid to the trimethylsilylated diazomethane is 1:(1.8~2.5); and the reaction time is 5-8 h.

4. The flame-retardant polyurethane resin according to claim 2, characterized in that In step (2), the solvent of the lithium aluminum tetrahydride solution is tetrahydrofuran, and the concentration of the lithium aluminum tetrahydride solution is 0.6~0.8 mol / L; the solvent of the methyl carnosate solution is tetrahydrofuran, and the concentration of the methyl carnosate solution is 0.2~0.4 mol / L; the molar ratio of the methyl carnosate to the lithium aluminum tetrahydride is 1:(3~4); the reaction temperature is 55~65°C, and the reaction time is 2~5h.

5. The flame-retardant polyurethane resin according to claim 2, characterized in that In step (3), the molar ratio of the carnosyl alcohol to the Dess-Martin oxidant is 1:(2-2.5), the concentration of the carnosyl alcohol in the solvent is 0.2-0.4 mol / L; the solvent is hexadecane, and the reaction time is 16-20 h.

6. The flame-retardant polyurethane resin according to claim 2, characterized in that In step (4), the molar ratio of the carnauba aldehyde to the diamino aromatic compound is 1:(2-2.5); the amount ratio of the carnauba aldehyde to the solvent is 1 mmol:2-5 mL; the solvent is cyclohexanol; the reaction temperature is 95-135°C, and the reaction time is 12-16 h.

7. The flame-retardant polyurethane resin according to claim 2, characterized in that The diamino aromatic compound is one of 4,4'-diaminodiphenylmethane, 4,4'-diaminobibenzyl and 1,3-bis(4-aminophenyl)propane.

8. The flame-retardant polyurethane resin according to claim 1, wherein The bio-based polyol is soybean oil polyol or castor oil; the isocyanate is 4,4'-diphenylmethane diisocyanate; the chain extender is xylitol or glycerol; the catalyst is an organic bismuth catalyst; and the flame retardant is melamine.

9. The method for preparing a flame-retardant polyurethane resin according to any one of claims 1 to 8, characterized in that: The following steps are involved: a. Mix the bio-based polyol, bio-based synergist, catalyst, and flame retardant and heat them to 130-150°C to obtain a mixed solution A; b. Add isocyanate and chain extender to mixed solution A respectively, react at 75-100℃ for 3-4h, pour into a mold and let stand for 1.5-2.5h. After demoulding, mature at 90-110℃ for 10-14h to obtain the product.

10. Use of the flame-retardant polyurethane resin according to any one of claims 1 to 8 in the preparation of a leather surface treatment agent.

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