Preparation method of castor oil-based waterborne polyurethane dispersion

Abstract

The invention belongs to the technical field of organic polymer synthesis, and particularly relates to a preparation method of a castor oil-based waterborne polyurethane dispersion. In order to solve the problems of low solubility and slow reaction speed of dimethylolpropionic acid, high cost of dimethylolbutyric acid and influence on product hardness in the prior art, the invention provides the preparation method of the castor oil-based waterborne polyurethane dispersoid, N, N '-bis (2-hydroxyethyl) piperazine is used as a hydrophilic chain extender, a tertiary amino group is introduced, and then the castor oil-based waterborne polyurethane dispersoid is prepared by using the amino group and 1, 2-dihydroxy-N, N'-bis (2-hydroxyethyl) piperazine as a hydrophilic chain extender. According to the preparation method, sulfo groups are introduced through ring-opening reaction of 1, 3-propane sultone, and sodium ethylenediamine ethanesulfonate is used as a chain extender in final chain extension reaction, so that the problem of low solubility of dimethylolpropionic acid in a polymerization system is solved, and high cost and difficulty in separation and purification caused by use of dimethylolbutyric acid are avoided.

Description

Technical Field

[0001] The present invention belongs to the technical field of organic polymer synthesis, and in particular relates to a method for preparing a castor oil-based waterborne polyurethane dispersion. Background Art

[0002] Waterborne polyurethane is a polyurethane material that uses water as a dispersion medium. It has been widely used in many fields such as coatings, adhesives, textile coatings, and leather processing due to its environmental protection and low VOC emissions. Although traditional solvent-based polyurethane has excellent performance, the organic solvents used in its production process pose a threat to the environment and human health. In contrast, waterborne polyurethane not only reduces the release of harmful substances, but also has good mechanical properties, flexibility, wear resistance, and chemical resistance, which can meet the needs of different application scenarios.

[0003] At present, the commonly used waterborne polyurethane is a carboxylic acid-based waterborne polyurethane, which uses dimethylol propionic acid as a hydrophilic chain extender. The disadvantage is that the solubility of dimethylol propionic acid in the polymerization system is low, and it is basically insoluble in polyether, polyester, and polyisocyanate polymerization systems. It is very slightly soluble in ketone solvents and has a higher solubility in N-methylpyrrolidone. We all know that condensation reactions can only be carried out in a homogeneous phase, so dimethylol propionic acid is basically unreactive in a solvent-free reaction system, and the dimethylol propionic acid reaction speed is also relatively slow in the acetone process. Dimethylol propionic acid is slightly dissolved in acetone, and the dissolved dimethylol propionic acid reacts with isocyanate, and dimethylol propionic acid is redissolved and reacted again until dimethylol propionic acid completely dissolves and reacts. In fact, the reaction of dimethylol propionic acid with isocyanate is a dissolution-controlled reaction, and the dissolution rate controls the reaction speed.

[0004] In order to improve the performance of the product or solve the problems caused by dimethylol propionic acid, it is proposed to replace dimethylol propionic acid with dimethylol butyric acid. Although the two are similar in synthesis process, the separation and purification process of dimethylol butyric acid is much more complicated than that of dimethylol propionic acid. Dimethylol butyric acid can only be obtained as a pure product after a long time of crystallization in an organic solvent such as ethyl acetate, and the recrystallization recovery rate is low, which undoubtedly increases the synthesis cost of dimethylol butyric acid. In addition, the ethyl side chain in the dimethylol butyric acid molecule will produce an internal plasticizing effect inside the polymer structure, so that the waterborne polyurethane dispersion synthesized with dimethylol butyric acid as a raw material shows a lower hardness than the dimethylol propionic acid product. Summary of the invention

[0005] In order to solve the problems of low solubility, slow reaction speed, high cost and influence on product hardness of dimethylolpropionic acid in the prior art, the present application provides a method for preparing a castor oil-based waterborne polyurethane dispersion, using N,N'-bis(2-hydroxyethyl)piperazine as a hydrophilic chain extender, introducing a tertiary amine group, and then introducing a sulfonic acid group by a ring-opening reaction of the amine group with 1,3-propane sultone, and in the final chain extension reaction, sodium ethylenediamine ethanesulfonate is used as a chain extender, thereby solving the problem of low solubility of dimethylolpropionic acid in a polymerization system and avoiding the high cost and difficulty of separation and purification caused by the use of dimethylolbutyric acid.

[0006] The present application provides a method for preparing a castor oil-based aqueous polyurethane dispersion, comprising the following steps:

[0007] S1. Add isophorone diisocyanate to ricinoleic acid, pass nitrogen protection, heat to 80-90°C, react, detect NCO value to reach 2%-3.3%, cool to 50-55°C, add N,N'-bis(2-hydroxyethyl)piperazine, pass nitrogen protection, heat to 80-85°C, react for 6-8h, detect NCO value to reach 1%-1.8%, and obtain oligomer;

[0008] S2, adding n-hexane to the oligomer obtained in step S1, and then adding 1,3-propane sultone, raising the temperature to 50-55° C., and then adding triethylamine to continue the reaction for 1-1.5 hours to obtain a hydrophilic prepolymer;

[0009] S3, adding water dropwise to the hydrophilic prepolymer obtained in step S2, emulsifying in a high shear emulsifier while adding sodium ethylenediamine sulfonate dropwise, reacting at 50-55° C. for 1.5-3 hours, and then distilling the emulsion under reduced pressure at 60° C. for 20-40 minutes, and obtaining a castor oil-based waterborne polyurethane dispersion after the solvent evaporates.

[0010] Furthermore, the mass ratio of isophorone diisocyanate to ricinoleic acid in step S1 is 1:1-1.2.

[0011] Furthermore, in step S1, the amount of N,N'-bis(2-hydroxyethyl)piperazine added is 1.7%-3.6% of the total mass of isophorone diisocyanate and ricinoleic acid.

[0012] Furthermore, the amount of n-hexane used in step S2 is 40%-80% of the total mass of isophorone diisocyanate and ricinoleic acid.

[0013] Furthermore, the amount of 1,3-propane sultone used in step S2 is 1.3%-2.7% of the total mass of isophorone diisocyanate and ricinoleic acid.

[0014] Furthermore, in step S2, the mass ratio of triethylamine to 1,3-propane sultone is 1:1-3.

[0015] Furthermore, in step S3, the mass ratio of the total mass of water, isophorone diisocyanate and ricinoleic acid is 1:0.84-1.05.

[0016] Furthermore, the amount of sodium ethylenediaminesulfonate used in step S3 is 2%-3.4% of the total mass of isophorone diisocyanate and ricinoleic acid.

[0017] The present application provides a method for preparing a castor oil-based waterborne polyurethane dispersion, which overcomes the solubility problem, cost problem and slow reaction speed problem in the preparation of traditional carboxylic acid-based waterborne polyurethane dispersions through component selection and process design. The present application uses ricinoleic acid, a renewable resource, as a raw material, which not only conforms to the principles of green chemistry, but also reduces the dependence on petroleum-derived chemicals. Sulfonate is used as a hydrophilic group to solve the problem of low solubility of dimethylol propionic acid in the polymerization system, and avoids the high cost and difficulty of separation and purification caused by the use of dimethylol butyric acid.

[0018] First, in the preparation process of oligomers, ricinoleic acid reacts with isophorone diisocyanate under nitrogen protection to generate a prepolymer containing unreacted isocyanate groups. This step controls the temperature and time to ensure sufficient NCO groups for subsequent reactions. At the same time, N,N'-bis(2-hydroxyethyl)piperazine is added to introduce tertiary amine groups to prepare for the introduction of sulfonic acid groups in the next step. This process effectively improves the selectivity and efficiency of the reaction, and also gives the final product better performance.

[0019] Next, in order to prepare the hydrophilic prepolymer, n-hexane is added to the above oligomer to reduce viscosity and facilitate handling and operation, followed by the addition of 1,3-propane sultone, and then triethylamine is used to catalyze the ring-opening reaction to introduce the sulfonic acid group into the molecular chain. This method of introducing hydrophilic groups makes the product have good water solubility and stability without relying on traditional chain extenders that are difficult to dissolve or costly.

[0020] Finally, when preparing castor oil-based waterborne polyurethane dispersion, high shear emulsification technology is used to add water drops to the hydrophilic prepolymer to form a stable emulsion, and sodium ethylenediamine sulfonate is added to further extend the chain and enhance the hydrophilicity. This step ensures that the dispersion has good mechanical stability and storage stability. DETAILED DESCRIPTION

[0021] The technical scheme of the present invention and its effects are further described below by specific examples. The following examples are only used to illustrate the content of the present invention and are not used to limit the protection scope of the present invention. Simple changes made to the present invention by applying the concept of the present invention are all within the scope of the protection claimed by the present invention.

[0022] The equipment used in the preparation method of the present invention can be the well-known equipment in the art. The raw materials used in the present invention are commercially available unless otherwise specified.

[0023] Example 1

[0024] S1. In a 1000ml reaction apparatus equipped with a constant pressure dropping funnel, a reflux condenser, a thermometer and an electric stirrer, add 300g of ricinoleic acid and 250g of isophorone diisocyanate, pass nitrogen protection, slowly heat to 80°C, react for 3.5 hours, detect the NCO value, and when it reaches the predetermined value of 2%, cool to 50°C, add 10g of N,N'-bis(2-hydroxyethyl)piperazine, pass nitrogen protection, heat to 80°C, react for 6h, detect the NCO value, and when it reaches the predetermined NCO value of 1%, obtain an oligomer.

[0025] S2. Add 330 g of n-hexane to the oligomer obtained in S1 to reduce the viscosity, then add 8 g of 1,3-propane sultone, raise the temperature to 50°C, and then add 5 g of triethylamine to continue the reaction for 1 hour to obtain a hydrophilic prepolymer.

[0026] S3. Add 550 g of water dropwise to the hydrophilic prepolymer obtained in S2, emulsify in a high shearing machine at a speed of 1000 r / min and simultaneously add 12 g of sodium ethylenediaminesulfonate dropwise. React at 50° C. for 1.5 hours, then place the emulsion in a rotary evaporator and evaporate it under reduced pressure at 60° C. for 20 minutes. Evaporate the solvent to obtain a castor oil-based waterborne polyurethane dispersion.

[0027] Example 2

[0028] S1. In a 1000ml reaction apparatus equipped with a constant pressure dropping funnel, a reflux condenser, a thermometer and an electric stirrer, add 300g of ricinoleic acid, add 280g of isophorone diisocyanate, pass nitrogen protection, slowly heat up to 90°C, react for 3.5 hours, detect the NCO value, and after reaching the predetermined value of 3.3%, cool to 50°C, add 20g of N,N'-bis(2-hydroxyethyl)piperazine, pass nitrogen protection, heat up to 80°C, react for 8h, detect the NCO value, and after reaching the predetermined NCO value of 1.8%, obtain an oligomer.

[0029] S2. Add 220 g of n-hexane to the oligomer obtained in S1 to reduce the viscosity, then add 1,3-propane sultone in an amount of 15 g, raise the temperature to 55°C, and then add 8 g of triethylamine to continue the reaction for 1.5 hours to obtain a hydrophilic prepolymer.

[0030] S3. Add 650 g of water dropwise to the hydrophilic prepolymer obtained in S2, emulsify in a high shearing machine at a speed of 1500 r / min and simultaneously add 19 g of sodium ethylenediaminesulfonate dropwise. React at 50° C. for 3 hours, then place the emulsion in a rotary evaporator and evaporate it under reduced pressure at 60° C. for 40 minutes. Evaporate the solvent to obtain a castor oil-based waterborne polyurethane dispersion.

[0031] Example 3

[0032] S1. In a 1000ml reaction apparatus equipped with a constant pressure dropping funnel, a reflux condenser, a thermometer and an electric stirrer, add 300g of ricinoleic acid, add 260g of isophorone diisocyanate, pass nitrogen protection, slowly heat up to 85°C, react for 3.5 hours, detect the NCO value, and after reaching the predetermined value of 3%, cool to 50°C, add 15g of N,N'-bis(2-hydroxyethyl)piperazine, pass nitrogen protection, heat up to 80°C, react for 7h, detect the NCO value, and after reaching the predetermined NCO value of 1.5%, obtain an oligomer.

[0033] S2. Add 440 g of n-hexane to the oligomer obtained in S1 to reduce the viscosity, then add 1,3-propane sultone in an amount of 11 g, raise the temperature to 53° C., then add 6 g of triethylamine and continue the reaction for 1.5 hours to obtain a hydrophilic prepolymer.

[0034] S3. Add 600 g of water dropwise to the hydrophilic prepolymer obtained in S2, emulsify in a high shearing machine at a speed of 1200 r / min and simultaneously add 15 g of sodium ethylenediaminesulfonate dropwise. React at 50° C. for 2 hours, then place the emulsion in a rotary evaporator and evaporate it under reduced pressure at 60° C. for 30 minutes. Evaporate the solvent to obtain a castor oil-based waterborne polyurethane dispersion.

[0035] Example 4

[0036] S1. In a 1000ml reaction apparatus equipped with a constant pressure dropping funnel, a reflux condenser, a thermometer and an electric stirrer, add 300g of ricinoleic acid, add 280g of isophorone diisocyanate, pass nitrogen protection, slowly heat up to 85°C, react for 3.5 hours, detect the NCO value, and after reaching the predetermined value of 3%, cool to 50°C, add 15g of N,N'-bis(2-hydroxyethyl)piperazine, pass nitrogen protection, heat up to 80°C, react for 7h, detect the NCO value, and after reaching the predetermined NCO value of 1.5%, obtain an oligomer.

[0037] S2. Add 440 g of n-hexane to the oligomer obtained in S1 to reduce the viscosity, then add 1,3-propane sultone in an amount of 11 g, raise the temperature to 53° C., then add 6 g of triethylamine and continue the reaction for 1.5 hours to obtain a hydrophilic prepolymer.

[0038] S3. Add 552 g of water dropwise to the hydrophilic prepolymer obtained in S2, emulsify in a high shearing machine at a speed of 1200 r / min and simultaneously add 15 g of sodium ethylenediaminesulfonate dropwise. React at 50° C. for 2 hours, then place the emulsion in a rotary evaporator and evaporate it under reduced pressure at 60° C. for 30 minutes. Evaporate the solvent to obtain a castor oil-based waterborne polyurethane dispersion.

[0039] Comparative Example 1

[0040] S1. In a 1000ml reaction apparatus equipped with a constant pressure dropping funnel, a reflux condenser, a thermometer and an electric stirrer, add 300g of ricinoleic acid and 280g of isophorone diisocyanate, pass nitrogen protection, slowly heat to 90°C, react for 3.5 hours, detect the NCO value, and after reaching the predetermined value of 3.3%, cool to 50°C, add 13.5g of dihydroxymethylpropionic acid, pass nitrogen protection, heat to 80°C, react for 16 hours, and obtain an oligomer.

[0041] S2. Add 220 g of n-hexane to the oligomer obtained in S1 to reduce the viscosity, then add 5 g of 1,4-butanediol, raise the temperature to 55°C, and then add 10 g of triethylamine to continue the reaction for 1.5 hours to obtain a hydrophilic prepolymer.

[0042] S3. Add 650 g of water dropwise to the hydrophilic prepolymer obtained in S2, emulsify in a high shearing machine at a speed of 1500 r / min and simultaneously add 7 g of sodium ethylenediaminesulfonate dropwise. React at 50° C. for 3 hours, then place the emulsion in a rotary evaporator and evaporate it under reduced pressure at 60° C. for 40 minutes. Evaporate the solvent to obtain a castor oil-based waterborne polyurethane dispersion.

[0043] Comparative Example 2

[0044] S1. In a 1000ml reaction apparatus equipped with a constant pressure dropping funnel, a reflux condenser, a thermometer and an electric stirrer, add 300g of ricinoleic acid, add 280g of isophorone diisocyanate, pass nitrogen protection, slowly heat to 90°C, react for 3.5 hours, detect the NCO value, and after reaching the predetermined value of 3.3%, cool to 50°C, add 14.5g of dihydroxymethylbutyric acid, pass nitrogen protection, heat to 80°C, react for 8h, detect the NCO value, and after reaching the predetermined NCO value of 1.8%, obtain an oligomer.

[0045] S2. Add 220 g of n-hexane to the oligomer obtained in S1 to reduce the viscosity, then add 5 g of 1,4-butanediol, raise the temperature to 55°C, and then add 10 g of triethylamine to continue the reaction for 1.5 hours to obtain a hydrophilic prepolymer.

[0046] S3. Add 650 g of water dropwise to the hydrophilic prepolymer obtained in S2, emulsify in a high shearing machine at a speed of 1500 r / min and simultaneously add 7 g of sodium ethylenediaminesulfonate dropwise. React at 50° C. for 3 hours, then place the emulsion in a rotary evaporator and evaporate it under reduced pressure at 60° C. for 40 minutes. Evaporate the solvent to obtain a castor oil-based waterborne polyurethane dispersion.

[0047] Comparative Example 3

[0048] S1. In a 1000ml reaction apparatus equipped with a constant pressure dropping funnel, a reflux condenser, a thermometer and an electric stirrer, add 300g of ricinoleic acid, add 260g of isophorone diisocyanate, pass nitrogen protection, slowly heat up to 85°C, react for 3.5 hours, detect the NCO value, and after reaching the predetermined value of 3%, cool to 50°C, add 15g of N,N'-bis(2-hydroxyethyl)piperazine, pass nitrogen protection, heat up to 80°C, react for 7h, detect the NCO value, and after reaching the predetermined NCO value of 1.5%, obtain an oligomer.

[0049] S2. Add 220 g of n-hexane to the oligomer obtained in S1 to reduce the viscosity, then add 6 g of 1,3-propane sultone, raise the temperature to 53°C, and then add 6 g of triethylamine to continue the reaction for 1.5 hours to obtain a hydrophilic prepolymer.

[0050] S3. Add 600 g of water dropwise to the hydrophilic prepolymer obtained in S2, emulsify in a high shearing machine at a speed of 1200 r / min and simultaneously add 15 g of sodium ethylenediaminesulfonate dropwise. React at 50° C. for 2 hours, then place the emulsion in a rotary evaporator and evaporate it under reduced pressure at 60° C. for 30 minutes. Evaporate the solvent to obtain a castor oil-based waterborne polyurethane dispersion.

[0051] Comparative Example 4

[0052] S1. In a 1000ml reaction apparatus equipped with a constant pressure dropping funnel, a reflux condenser, a thermometer and an electric stirrer, add 300g of ricinoleic acid, add 260g of isophorone diisocyanate, pass nitrogen protection, slowly heat up to 85°C, react for 3.5 hours, detect the NCO value, and after reaching the predetermined value of 3%, cool to 50°C, add 15g of N,N'-bis(2-hydroxyethyl)piperazine, pass nitrogen protection, heat up to 80°C, react for 7h, detect the NCO value, and after reaching the predetermined NCO value of 1.5%, obtain an oligomer.

[0053] S2. Add 330 g of n-hexane to the oligomer obtained in S1 to reduce the viscosity, then add 1,3-propane sultone in an amount of 11 g, raise the temperature to 53°C, and then add 6 g of triethylamine to continue the reaction for 1.5 hours to obtain a hydrophilic prepolymer.

[0054] S3. Add 600 g of water dropwise to the hydrophilic prepolymer obtained in S2, emulsify in a high shearing machine at a speed of 1200 r / min and simultaneously add 10 g of sodium ethylenediaminesulfonate dropwise. React at 50° C. for 2 hours, then place the emulsion in a rotary evaporator and evaporate it under reduced pressure at 60° C. for 30 minutes. Evaporate the solvent to obtain a castor oil-based waterborne polyurethane dispersion.

[0055] Comparative Example 5

[0056] S1. In a 1000ml reaction apparatus equipped with a constant pressure dropping funnel, a reflux condenser, a thermometer and an electric stirrer, add 300g of ricinoleic acid, add 260g of isophorone diisocyanate, pass nitrogen protection, slowly heat up to 85°C, react for 3.5 hours, detect the NCO value, and after reaching the predetermined value of 3%, cool to 50°C, add 15g of N,N'-bis(2-hydroxyethyl)piperazine, pass nitrogen protection, heat up to 80°C, react for 7h, detect the NCO value, and after reaching the predetermined NCO value of 1.5%, obtain an oligomer.

[0057] S2. Add 440 g of n-hexane to the oligomer obtained in S1 to reduce the viscosity, then add 1,3-propane sultone in an amount of 11 g, raise the temperature to 53° C., then add 6 g of triethylamine and continue the reaction for 1.5 hours to obtain a hydrophilic prepolymer.

[0058] S3. Add 600 g of water dropwise to the hydrophilic prepolymer obtained in S2, emulsify in a high shearing machine at a speed of 1200 r / min and simultaneously add 20 g of sodium ethylenediaminesulfonate dropwise, react at 50° C. for 2 hours, then evaporate the emulsion in a rotary evaporator and distill under reduced pressure at 60° C. for 30 minutes, evaporate the solvent to obtain a castor oil-based waterborne polyurethane dispersion.

[0059] Comparative Example 6

[0060] S1. In a 1000ml reaction apparatus equipped with a constant pressure dropping funnel, a reflux condenser, a thermometer and an electric stirrer, add 300g of ricinoleic acid, add 260g of isophorone diisocyanate, pass nitrogen protection, slowly heat up to 85°C, react for 3.5 hours, detect the NCO value, and after reaching the predetermined value of 3%, cool to 50°C, add 15g of N,N'-bis(2-hydroxyethyl)piperazine, pass nitrogen protection, heat up to 80°C, react for 7h, detect the NCO value, and after reaching the predetermined NCO value of 1.5%, obtain an oligomer.

[0061] S2. Add 330 g of n-hexane to the oligomer obtained in S1 to reduce the viscosity, then add 1,3-propane sultone in an amount of 17 g, raise the temperature to 53°C, and then add 6 g of triethylamine to continue the reaction for 1.5 hours to obtain a hydrophilic prepolymer.

[0062] S3. Add 600 g of water dropwise to the hydrophilic prepolymer obtained in S2, emulsify in a high shearing machine at a speed of 1200 r / min and simultaneously add 15 g of sodium ethylenediaminesulfonate dropwise. React at 50° C. for 2 hours, then place the emulsion in a rotary evaporator and evaporate it under reduced pressure at 60° C. for 30 minutes. Evaporate the solvent to obtain a castor oil-based waterborne polyurethane dispersion.

[0063] Comparative Example 7

[0064] S1. In a 1000ml reaction apparatus equipped with a constant pressure dropping funnel, a reflux condenser, a thermometer and an electric stirrer, add 300g of ricinoleic acid and 260g of isophorone diisocyanate, pass nitrogen protection, slowly heat to 85°C, react for 3.5 hours, detect the NCO value, and when it reaches the predetermined value of 3%, cool to 50°C, add 15g of N,N-dimethyl-2-(dihydroxymethyl)butylamine, pass nitrogen protection, heat to 80°C, react for 7h, detect the NCO value, and when it reaches the predetermined NCO value of 1.5%, obtain an oligomer.

[0065] S2. Add 220 g of n-hexane to the oligomer obtained in S1 to reduce the viscosity, then add 1,3-propane sultone in an amount of 11 g, raise the temperature to 53° C., then add 6 g of triethylamine and continue the reaction for 1.5 hours to obtain a hydrophilic prepolymer.

[0066] S3. Add 600 g of water dropwise to the hydrophilic prepolymer obtained in S2, emulsify in a high shearing machine at a speed of 1200 r / min and simultaneously add 15 g of sodium ethylenediaminesulfonate dropwise. React at 50° C. for 2 hours, then place the emulsion in a rotary evaporator and evaporate it under reduced pressure at 60° C. for 30 minutes. Evaporate the solvent to obtain a castor oil-based waterborne polyurethane dispersion.

[0067] The dispersions obtained in the examples and comparative examples were tested for performance:

[0068] Storage stability of dispersions The storage stability of dispersions is simulated by centrifugal acceleration test. At 25°C, the waterborne polyurethane dispersion is centrifuged at 3000r / min in a high-speed centrifuge. If there is no precipitation or stratification, the dispersion can be considered to have a storage stability period of 6 months.

[0069] The properties of the obtained castor oil-based aqueous polyurethane dispersion were tested. The castor oil-based aqueous polyurethane dispersions obtained in Examples 1-3 and Comparative Examples 1-7 were coated, and adhesion tests were performed in accordance with national standard GB / T9286-1998, water resistance tests were performed in accordance with national standard GB / T1733-1993, and hardness tests were performed in accordance with national standard GB / T6739-2006. The test results are shown in the table below.

[0070]

Claims

1. A method for preparing a castor oil-based aqueous polyurethane dispersion, characterized in that: The following steps are involved: S1. Add isophorone diisocyanate to ricinoleic acid, pass nitrogen protection, heat up for reaction, detect NCO value reaches 2%-3.3% and then cool down, then add N,N'-bis(2-hydroxyethyl)piperazine, pass nitrogen protection, heat up for reaction for 6-8h, detect NCO value reaches 1%-1.8% and then obtain oligomer; S2, adding n-hexane to the oligomer obtained in step S1, and then adding 1,3-propane sultone, wherein the amount of 1,3-propane sultone is 1.3%-2.7% of the total mass of isophorone diisocyanate and ricinoleic acid, and then adding triethylamine after heating to continue the reaction for 1-1.5 hours to obtain a hydrophilic prepolymer; S3, adding water dropwise to the hydrophilic prepolymer obtained in step S2, and simultaneously adding sodium ethylenediamine ethanesulfonate dropwise during emulsification in a high shear emulsifier, and reacting for 1.5-3 hours, wherein the amount of sodium ethylenediamine ethanesulfonate used is 2%-3.4% of the total mass of isophorone diisocyanate and ricinoleic acid, and then heating the emulsion and performing reduced pressure distillation for 20-40 minutes, and obtaining a castor oil-based waterborne polyurethane dispersion after the solvent evaporates.

2. The method for preparing the castor oil-based aqueous polyurethane dispersion according to claim 1, characterized in that: The mass ratio of isophorone diisocyanate to ricinoleic acid in step S1 is 1:1-1.

2.

3. The method for preparing the castor oil-based aqueous polyurethane dispersion according to claim 2, characterized in that: The amount of N,N'-bis(2-hydroxyethyl)piperazine added in step S1 is 1.7%-3.6% of the total mass of isophorone diisocyanate and ricinoleic acid.

4. The method for preparing the castor oil-based aqueous polyurethane dispersion according to claim 1, characterized in that: The amount of n-hexane used in step S2 is 40%-80% of the total mass of isophorone diisocyanate and ricinoleic acid.

5. The method for preparing the castor oil-based aqueous polyurethane dispersion according to claim 1, characterized in that: The mass ratio of triethylamine to 1,3-propane sultone in step S2 is 1:1-3.

6. The method for preparing the castor oil-based aqueous polyurethane dispersion according to claim 1, characterized in that: The mass ratio of the water, isophorone diisocyanate and ricinoleic acid in step S3 is 1:0.84-1.05.

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