A bio-based aqueous polyurethane surface treatment and method of making the same

Abstract

The application belongs to the field of waterborne polyurethane and specifically relates to a bio-based waterborne polyurethane surface treatment agent and a preparation method thereof. The waterborne polyurethane surface treatment agent is prepared from a waterborne polyurethane, a wetting agent, a leveling agent and a thickening agent, and the waterborne polyurethane is prepared from isocyanate, dihydric alcohol, a multi-hydroxyl bio-based crosslinking agent, a catalyst, a hydrophilic chain extender, a neutralizing agent, an amine chain extender and water. The waterborne polyurethane is modified by introducing the multi-hydroxyl bio-based crosslinking agent, so that the resistance of the leather treated by the waterborne polyurethane surface treatment agent to jungle aging, the resistance to wet and hot yellowing, the resistance to high-temperature yellowing, the resistance to light yellowing and the wet rub fastness are effectively improved, the comprehensive performance of the synthetic leather is improved, and the application field of the synthetic leather is widened.

Description

Technical Field

[0001] This invention belongs to the field of waterborne polyurethane, specifically relating to a bio-based waterborne polyurethane surface treatment agent and its preparation method. Background Technology

[0002] Currently, most surface treatment agents for artificial leather are solvent-based systems, containing a large amount of volatile solvents. The surface treatment of artificial leather is carried out in an open environment during production, resulting in the release of large amounts of organic solvents after production, causing serious environmental pollution. These organic solvents also remain in the finished product, not only causing an unpleasant solvent odor but also posing a health hazard to users. Therefore, there is a need to develop environmentally friendly water-based surface treatment agents for artificial leather to solve the solvent pollution problem in the surface treatment process and promote the sustainable development of the artificial leather industry.

[0003] Compared to solvent-based surface treatment agents, water-based surface treatment agents lag significantly behind in waterproofing, physical properties, and resistance to yellowing, failing to meet the entry requirements of high-end sectors such as aircraft, high-speed rail, automobiles, and home decoration. Water-based surface treatment agents for synthetic leather are an effective way to eliminate organic solvent pollution in the industry at its source. However, due to the long-term monopoly of foreign companies on the supporting water-based functional additives, domestic research and development of high-performance, functional water-based synthetic leather faces numerous difficulties, severely limiting the application areas of domestically produced synthetic leather.

[0004] Chinese patent application CN 116397446 A discloses a coating method and equipment for bio-based polyurethane synthetic leather for footwear, comprising the following steps: S1, impregnation: impregnating a bio-based substrate with a bio-based aqueous PU slurry with a solid content of 5% to 20%, followed by drying at 90 to 130°C to obtain a semi-finished product with a full hand feel; S2, surface layer: coating the aqueous PU slurry onto release paper with a coating blade depth of 0.03 to 0.15 mm, drying, and then transferring the release paper texture to the surface, with the surface layer having a film thickness of 0.01 to 0.1 mm after drying. The bio-based polyurethane synthetic leather coated by this invention has high abrasion resistance, flexural strength, and a good hand feel, but it suffers from poor heat resistance and water resistance, greatly limiting its application areas. Summary of the Invention

[0005] Based on the above technical background, the present invention provides a waterborne polyurethane surface treatment agent and its preparation method. The waterborne polyurethane surface treatment agent is prepared from waterborne polyurethane, wetting agent, leveling agent and thickener as raw materials. The waterborne polyurethane is prepared from isocyanate, diol, polyhydroxy bio-based crosslinking agent, catalyst, hydrophilic chain extender, neutralizing agent, amine chain extender and water as raw materials. Through the modification of polyhydroxy bio-based crosslinking agent, the synthetic leather treated with waterborne polyurethane surface treatment agent has higher resistance to forest aging, damp heat, high temperature yellowing, light yellowing and wet rubbing fastness, thereby improving the comprehensive performance of synthetic leather and expanding its application fields.

[0006] A first aspect of this invention is to provide a waterborne polyurethane surface treatment agent, said waterborne polyurethane surface treatment agent being prepared from the following raw materials in parts by weight:

[0007]

[0008] The waterborne polyurethane is prepared from the following raw materials in parts by weight:

[0009]

[0010]

[0011] Preferably, the waterborne polyurethane surface treatment agent is prepared from the following raw materials in parts by weight:

[0012]

[0013] The waterborne polyurethane is prepared from the following raw materials in parts by weight:

[0014]

[0015] Preferably, the isocyanate is selected from one or more of isophorone diisocyanate, dicyclohexylmethane diisocyanate, and toluene diisocyanate;

[0016] The diol is selected from one or more of polycaprolactone diol, polyhexyl adipate diol, polybutylene adipate diol, polycarbonate diol, and polytetrahydrofuran ether diol.

[0017] The multihydroxy biocrosslinking agent is a multihydroxy castor oil bio-based crosslinking agent;

[0018] The catalyst is selected from one or more organic bismuth catalysts;

[0019] The hydrophilic chain extender is selected from one or more of 2,2-dimethylolpropionic acid (DMPA), 2,2-dimethylolbutyric acid, and N-methyldiethanolamine;

[0020] The neutralizing agent is selected from one or more of ammonia, sodium hydroxide, and triethylamine;

[0021] The amine chain extender is selected from one or more of hydrazine hydrate, ethylenediamine, diethylenetriamine, and polyethertriamine;

[0022] The wetting agent is selected from one or more of the organosilicon wetting agents silok-8030, byk-331 and tego500;

[0023] The leveling agent is selected from one or more of the leveling agents tego432, byk-333 and 5211;

[0024] The thickener is selected from one or more of acrylic thickeners or polyurethane thickeners.

[0025] More preferably, the polyhydroxy castor oil bio-based crosslinking agent is prepared from castor oil, hydrogen peroxide, and acid;

[0026] The molar ratio of castor oil, hydrogen peroxide and acid is 1:(1-1.1):(1-1.1).

[0027] Preferably, the waterborne polyurethane is prepared by a method comprising the following steps:

[0028] Wetting agent, leveling agent and thickener are added to waterborne polyurethane and stirred evenly to obtain waterborne polyurethane surface treatment agent;

[0029] The waterborne polyurethane is prepared by a method comprising the following steps:

[0030] Isocyanate and diol were heated and reacted. After the reaction was completed, the temperature was lowered. A hydrophilic chain extender, a polyhydroxy bio-based crosslinking agent, a catalyst and acetone were added to the reaction system. After mixing evenly, the temperature was raised and the reaction was carried out.

[0031] After cooling, a neutralizing agent is added for neutralization, followed by water dispersion, and finally an amine chain extender is added for chain extension reaction. After removing acetone, waterborne polyurethane is obtained.

[0032] A second aspect of the present invention is to provide a method for preparing the waterborne polyurethane surface treatment agent described in the first aspect of the present invention, the method comprising the following steps:

[0033] Wetting agent, leveling agent and thickener are added to waterborne polyurethane and stirred evenly to obtain waterborne polyurethane surface treatment agent;

[0034] The waterborne polyurethane is prepared by a method comprising the following steps:

[0035] Isocyanate and diol were heated and reacted. After the reaction was completed, the temperature was lowered. A hydrophilic chain extender, a polyhydroxy bio-based crosslinking agent, a catalyst and acetone were added to the reaction system. After mixing evenly, the temperature was raised and the reaction was carried out.

[0036] After cooling, a neutralizing agent is added for neutralization, followed by water dispersion, and finally an amine chain extender is added for chain extension reaction. After removing acetone, waterborne polyurethane is obtained.

[0037] Preferably, the polyhydroxy bio-based crosslinking agent is prepared by the following steps:

[0038] S1. Castor oil and hydrogen peroxide are epoxidized at 70-80℃ for 12-18 hours to obtain epoxidized castor oil;

[0039] S2. Place epoxidized castor oil and acid in water and react at 80-100℃ for 6-10 hours.

[0040] Preferably, stirring is carried out at room temperature for 2 to 5 hours.

[0041] The isocyanate and diol are heated to 85-95℃ and reacted for 1-3 hours.

[0042] After the reaction, the temperature is lowered to 55-65℃, and a hydrophilic chain extender, a polyhydroxy bio-based crosslinking agent, a catalyst, and acetone are added. After mixing evenly, the temperature is raised to 55-70℃ and the reaction is carried out for 3-7 hours.

[0043] Add the neutralizing agent after cooling to 45–53°C;

[0044] The chain extension reaction was carried out at room temperature for 30 to 60 minutes.

[0045] The beneficial effects of this invention are as follows:

[0046] (1) The water-based polyurethane surface treatment agent of the present invention can effectively improve the waterproof performance of synthetic leather after being treated with water-based polyurethane surface treatment agent, and can significantly improve the physical properties of synthetic leather, thereby improving the overall performance of synthetic leather and increasing the application value of synthetic leather products.

[0047] (2) The preparation method of the waterborne polyurethane surface treatment agent of the present invention is simple, and no high temperature and high pressure are required during the preparation process, and no toxic or harmful substances are generated. Detailed Implementation

[0048] The present invention will now be described in detail, and its features and advantages will become clearer and more apparent from these descriptions.

[0049] A first aspect of this invention is to provide a waterborne polyurethane surface treatment agent, said waterborne polyurethane surface treatment agent being prepared from the following raw materials in parts by weight:

[0050]

[0051] The waterborne polyurethane is prepared from the following raw materials in parts by weight:

[0052]

[0053] Preferably, the waterborne polyurethane surface treatment agent is prepared from the following raw materials in parts by weight:

[0054]

[0055] The waterborne polyurethane is prepared from the following raw materials in parts by weight:

[0056]

[0057]

[0058] The isocyanate is selected from one or more of isophorone diisocyanate, dicyclohexylmethane diisocyanate and toluene diisocyanate, preferably isophorone diisocyanate.

[0059] The diol is selected from one or more of polycaprolactone diol, polyhexamethylene adipate diol, polybutylene adipate diol, polycarbonate diol, and polytetrahydrofuran ether diol, preferably polycarbonate diol (Mn = 2000).

[0060] The polyhydroxy biocrosslinker is a polyhydroxy castor oil bio-based crosslinker, which is prepared from castor oil, hydrogen peroxide, and acid.

[0061] The acid is preferably hydrochloric acid.

[0062] Preferably, the molar ratio of castor oil, hydrogen peroxide and acid is 1:(1-1.1):(1-1.1).

[0063] The catalyst is selected from one or more organic bismuth catalysts, preferably bismuth isooctanoate.

[0064] The hydrophilic chain extender is selected from one or more of 2,2-dimethylolpropionic acid (DMPA), 2,2-dimethylolbutyric acid and N-methyldiethanolamine, preferably 2,2-dimethylolpropionic acid.

[0065] The neutralizing agent is selected from one or more of ammonia, sodium hydroxide and triethylamine, preferably triethylamine.

[0066] The amine chain extender is selected from one or more of hydrazine hydrate, ethylenediamine, diethylenetriamine, and polyethertriamine, preferably hydrazine hydrate.

[0067] The wetting agent is selected from one or more of silok-8030, byk-331 and tego500 silicone wetting agents, preferably tego500 silicone wetting agent.

[0068] The leveling agent is selected from one or more of tego432, byk-333 and 5211 leveling agents, preferably 5211 leveling agent.

[0069] The thickener is selected from one or more of acrylic thickeners or polyurethane thickeners, preferably NY-12W polyurethane thickener.

[0070] The wetting agent used in this invention reduces the surface tension of the waterborne polyurethane surface treatment agent, increasing its wetting performance and adhesion. The leveling agent enhances the leveling effect of the waterborne polyurethane surface treatment agent, resulting in better smoothness. The thickener increases the liquid viscosity of the waterborne polyurethane surface treatment agent, facilitating roller coating and improving production efficiency.

[0071] The waterborne polyurethane surface treatment agent prepared by this invention contains a bio-based multi-hydroxy crosslinking agent, which increases the crosslinking structure of the resin, giving the waterborne polyurethane surface treatment agent better physical properties and improving its water resistance, wear resistance and other properties.

[0072] A second aspect of the present invention is to provide a method for preparing the waterborne polyurethane surface treatment agent described in the first aspect of the present invention, the method comprising the following steps:

[0073] Wetting agent, leveling agent and thickener are added to waterborne polyurethane and stirred evenly to obtain waterborne polyurethane surface treatment agent;

[0074] The waterborne polyurethane is prepared by a method comprising the following steps:

[0075] Isocyanate and diol were heated and reacted. After the reaction was completed, the temperature was lowered. A hydrophilic chain extender, a polyhydroxy bio-based crosslinking agent, a catalyst and acetone were added to the reaction system. After mixing evenly, the temperature was raised and the reaction was carried out.

[0076] After cooling, a neutralizing agent is added for neutralization, followed by water dispersion, and finally an amine chain extender is added for chain extension reaction. After removing acetone, waterborne polyurethane is obtained.

[0077] The steps described above are described in detail below.

[0078] Stirring is carried out at room temperature for 2 to 5 hours, preferably 3 hours.

[0079] The isocyanate and diol are heated to 85-95°C and reacted for 1-3 hours, preferably to 90-92°C and reacted for 2 hours.

[0080] After the reaction, the temperature is lowered to 55-65℃, and a hydrophilic chain extender, a polyhydroxy bio-based crosslinking agent, a catalyst, and acetone are added. After mixing evenly, the temperature is raised to 55-70℃ and the reaction is carried out for 3-7 hours.

[0081] Preferably, after the reaction, the temperature is lowered to 60°C, and after mixing evenly, the temperature is raised to 60-65°C and reacted for 5 hours.

[0082] Add the neutralizing agent after cooling to 45-53°C, preferably after cooling to 50°C.

[0083] The chain extension reaction is carried out at room temperature for 30 to 60 minutes, preferably at room temperature for 40 to 50 minutes.

[0084] According to a preferred embodiment of the present invention, the polyhydroxy bio-based crosslinking agent is prepared by the following steps:

[0085] S1. Castor oil and hydrogen peroxide are epoxidized at 70-80℃ for 12-18 hours to obtain epoxidized castor oil;

[0086] S2. Place epoxidized castor oil and acid in water and react at 80-100℃ for 6-10 hours.

[0087] Preferably, the epoxidation reaction is carried out at 75°C for 15 hours.

[0088] Epoxy castor oil and acid were placed in water and reacted at 90°C for 8 hours.

[0089] The preparation processes for steps S1 and S2 are shown in equations (1) and (2), respectively:

[0090]

[0091] Example

[0092] The present invention is further illustrated by specific examples below. These embodiments are only for illustrating the present invention and are not intended to limit the scope of the present invention.

[0093] All raw materials used in the embodiments of this invention were purchased.

[0094] Example 1

[0095] Epoxidized castor oil was obtained by epoxidizing 0.05 mol castor oil and 0.05 mol hydrogen peroxide at 75 °C for 15 h. Epoxidized castor oil was obtained by placing 0.05 mol epoxidized castor oil and 0.05 mol hydrochloric acid in deionized water and reacting at 90 °C for 8 h.

[0096] After removing moisture from 60g of polycarbonate diol (Mn=2000) under vacuum, 18g of isophorone diisocyanate was added, and the mixture was heated to 90℃ and reacted for 2h. The mixture was then cooled to 60℃ and 3.5g of DMPA, 0.3g of polyhydroxy bio-based crosslinking agent, 0.05g of bismuth isooctanoate catalyst, and 30g of acetone were added. After stirring evenly, the mixture was heated to 65℃ and reacted for 5h. After the reaction was completed, the mixture was cooled to 50℃ and 2.6g of triethylamine was added for neutralization. After neutralization, 1500g of dispersing water was added for dispersion. After good dispersion, 1g of hydrazine hydrate was added and chain extension reaction was carried out at room temperature for 45min. Acetone was removed under vacuum to obtain an aqueous polyurethane emulsion.

[0097] Take 100g of the prepared waterborne polyurethane, then add 0.5g of Tego500, 0.3g of 5211 and 2.5g of NY-12W polyurethane thickener, and stir at room temperature for 3h to obtain waterborne polyurethane surface treatment agent.

[0098] Example 2

[0099] Epoxidized castor oil was obtained by epoxidizing 0.05 mol castor oil and 0.05 mol hydrogen peroxide at 75 °C for 15 h. Epoxidized castor oil was obtained by placing 0.05 mol epoxidized castor oil and 0.05 mol hydrochloric acid in deionized water and reacting at 90 °C for 8 h.

[0100] After removing moisture from 60g of polycarbonate diol (Mn=2000) under vacuum, 18g of isophorone diisocyanate was added, and the mixture was heated to 92℃ and reacted for 2h. The mixture was then cooled to 60℃ and 3.5g of DMPA, 0.6g of polyhydroxy bio-based crosslinking agent, 0.05g of bismuth isooctanoate catalyst, and 30g of acetone were added. After stirring evenly, the mixture was heated to 60℃ and reacted for 5h. After the reaction was completed, the mixture was cooled to 50℃ and 2.6g of triethylamine was added for neutralization. After neutralization, 1500g of dispersing water was added for dispersion. After good dispersion, 1g of hydrazine hydrate was added and chain extension reaction was carried out at room temperature for 40min. Acetone was removed under vacuum to obtain an aqueous polyurethane emulsion.

[0101] Take 100g of the prepared waterborne polyurethane, then add 0.5g of Tego500, 0.3g of 5211 and 2.5g of NY-12W polyurethane thickener, and stir at room temperature for 3h to obtain waterborne polyurethane surface treatment agent.

[0102] Example 3

[0103] Epoxidized castor oil was obtained by epoxidizing 0.05 mol castor oil and 0.05 mol hydrogen peroxide at 70 °C for 18 h. Epoxidized castor oil was obtained by placing 0.05 mol epoxidized castor oil and 0.05 mol hydrochloric acid in deionized water and reacting at 80 °C for 10 h.

[0104] After removing moisture from 60g of polycarbonate diol (Mn=2000) under vacuum, 18g of isophorone diisocyanate was added, and the mixture was heated to 95℃ and reacted for 1h. The mixture was then cooled to 60℃ and 3.5g of DMPA, 0.3g of polyhydroxy bio-based crosslinking agent, 0.05g of bismuth isooctanoate catalyst, and 30g of acetone were added. After stirring evenly, the mixture was heated to 70℃ and reacted for 3h. After the reaction was completed, the mixture was cooled to 45℃ and 2.6g of triethylamine was added for neutralization. After neutralization, 1500g of dispersing water was added for dispersion. After good dispersion, 1g of hydrazine hydrate was added and chain extension reaction was carried out at room temperature for 50min. Acetone was removed under vacuum to obtain an aqueous polyurethane emulsion.

[0105] Take 100g of the prepared waterborne polyurethane, then add 0.5g of Tego500, 0.3g of 5211 and 2.5g of NY-12W polyurethane thickener, and stir at room temperature for 2 hours to obtain waterborne polyurethane surface treatment agent.

[0106] Comparative Example

[0107] Comparative Example 1

[0108] The waterborne polyurethane surface treatment agent was prepared in a manner similar to that in Example 1, except that: no multi-hydroxyl bio-based crosslinking agent was prepared, and no multi-hydroxyl bio-based crosslinking agent was added.

[0109] Experimental Example

[0110] Experimental Example 1: Fastness, resistance to yellowing, and resistance to jungle aging tests

[0111] The testing process is as follows: The surface of synthetic leather was treated with the water-based polyurethane surface treatment agents prepared in Examples 1-2 and Comparative Example 1, respectively. The dosage of the water-based polyurethane surface treatment agent was 25g per square meter of synthetic leather. The treated synthetic leather was then tested for resistance to yellowing, resistance to aging, and wet rubbing fastness according to the test conditions in Table 1. The test results are shown in Table 1.

[0112] Table 1

[0113]

[0114] As shown in Table 1, the synthetic leather treated with the waterborne polyurethane surface treatment agents prepared in Examples 1 and 2 of this invention exhibits superior resistance to forest aging, far exceeding the resistance of synthetic leather treated with the waterborne polyurethane surface treatment agent prepared in Comparative Example 1. Furthermore, the synthetic leather treated with the waterborne polyurethane surface treatment agents prepared in Examples 1 and 2 of this invention also shows superior resistance to damp heat yellowing, high temperature yellowing, light yellowing, and wet rubbing fastness. This indicates that the addition of a polyhydroxy bio-based crosslinking agent can effectively improve the resistance to forest aging, damp heat yellowing, high temperature yellowing, light yellowing, and wet rubbing fastness of synthetic leather treated with the waterborne polyurethane surface treatment agent.

[0115] The present invention has been described in detail above with reference to specific embodiments and exemplary examples; however, these descriptions should not be construed as limiting the present invention. Those skilled in the art will understand that various equivalent substitutions, modifications, or improvements can be made to the technical solutions and embodiments of the present invention without departing from the spirit and scope of the invention, and all such modifications and improvements fall within the scope of the present invention. The scope of protection of the present invention is defined by the appended claims.

Claims

1. A water-based polyurethane surface treatment agent, characterized in that, The waterborne polyurethane surface treatment agent is prepared from the following raw materials in parts by weight: 100 parts of waterborne polyurethane; Wetting agent 0.3–0.7 parts; Leveling agent 0.1-0.5 parts; Thickener 2-3 parts; The waterborne polyurethane is prepared from the following raw materials in parts by weight: 15-20 parts isocyanate; 50-70 parts of diol; 0.1 to 1 part of polyhydroxy bio-based crosslinking agent; Catalyst 0.03–0.07 parts; 2-5 parts of hydrophilic chain extender; 2-3 parts neutralizing agent; 0.5–2 parts of amine chain extender; 1200-1700 parts water; The isocyanate is selected from one or more of isophorone diisocyanate, dicyclohexylmethane diisocyanate and toluene diisocyanate; The diol is selected from one or more of polycaprolactone diol, polyhexyl adipate diol, polybutylene adipate diol, polycarbonate diol, and polytetrahydrofuran ether diol. The multihydroxyl bio-based crosslinking agent is a multihydroxyl castor oil bio-based crosslinking agent; The catalyst is selected from one or more organic bismuth catalysts; The hydrophilic chain extender is selected from one or more of 2,2-dimethylolpropionic acid (DMPA) and 2,2-dimethylolbutyric acid; The neutralizing agent is selected from one or more of ammonia, sodium hydroxide, and triethylamine; The amine chain extender is selected from one or more of hydrazine hydrate, ethylenediamine, diethylenetriamine, and polyethertriamine; The wetting agent is selected from one or more of silok-8030 and byk-331 organosilicon wetting agents; The leveling agent is selected from one or more of the leveling agents tego432, byk-333 and 5211; The thickener is selected from one or more of acrylic thickeners or polyurethane thickeners; The polyhydroxy castor oil bio-based crosslinking agent is prepared from castor oil, hydrogen peroxide, and acid; The molar ratio of castor oil, hydrogen peroxide, and acid is 1:(1-1.1):(1-1.1). The aqueous polyurethane is prepared by a method comprising the following steps: Wetting agent, leveling agent and thickener are added to waterborne polyurethane and stirred evenly to obtain waterborne polyurethane surface treatment agent; The waterborne polyurethane is prepared by a method comprising the following steps: Isocyanate and diol were heated and reacted. After the reaction was completed, the temperature was lowered. A hydrophilic chain extender, a polyhydroxy bio-based crosslinking agent, a catalyst and acetone were added to the reaction system. After mixing evenly, the temperature was raised and the reaction was carried out. After cooling, a neutralizing agent is added for neutralization, followed by water dispersion, and finally an amine chain extender is added for chain extension reaction. After removing acetone, waterborne polyurethane is obtained.

2. The waterborne polyurethane surface treatment agent according to claim 1, characterized in that, The waterborne polyurethane surface treatment agent is prepared from the following raw materials in parts by weight: 100 parts of waterborne polyurethane; 0.5 parts wetting agent; 0.3 parts leveling agent; Thickener 2.5 parts; The waterborne polyurethane is prepared from the following raw materials in parts by weight: 18 parts isocyanate; 60 parts of diol; 0.3–0.6 parts of polyhydroxy bio-based crosslinking agent; 0.05 parts catalyst; 3.5 parts of hydrophilic chain extender; Neutralizing agent 2.6 parts; One part of amine chain extender; 1500 portions of water.

3. A method for preparing the waterborne polyurethane surface treatment agent according to claim 1 or 2, characterized in that, The method includes the following steps: Wetting agent, leveling agent and thickener are added to waterborne polyurethane and stirred evenly to obtain waterborne polyurethane surface treatment agent; The waterborne polyurethane is prepared by a method comprising the following steps: Isocyanate and diol were heated and reacted. After the reaction was completed, the temperature was lowered. A hydrophilic chain extender, a polyhydroxy bio-based crosslinking agent, a catalyst and acetone were added to the reaction system. After mixing evenly, the temperature was raised and the reaction was carried out. After cooling, a neutralizing agent is added for neutralization, followed by water dispersion, and finally an amine chain extender is added for chain extension reaction. After removing acetone, waterborne polyurethane is obtained.

4. The method according to claim 3, characterized in that, The polyhydroxy bio-based crosslinking agent is prepared by the following steps: S1. Castor oil and hydrogen peroxide are epoxidized at 70-80℃ for 12-18 hours to obtain epoxidized castor oil; S2. Place epoxidized castor oil and acid in water and react at 80-100℃ for 6-10 hours.

5. The method according to claim 3, characterized in that, Stirring was carried out at room temperature for 2–5 hours.

6. The method according to claim 3, characterized in that, The isocyanate and diol are heated to 85-95℃ and reacted for 1-3 hours. After the reaction, the temperature is lowered to 55-65℃, and a hydrophilic chain extender, a polyhydroxy bio-based crosslinking agent, a catalyst, and acetone are added. After mixing evenly, the temperature is raised to 55-70℃ and the reaction is carried out for 3-7 hours.

7. The method according to claim 3, characterized in that, Add the neutralizing agent after cooling to 45–53°C; The chain extension reaction was carried out at room temperature for 30 to 60 minutes.

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