阅读说明：本技术 一种水性聚氨酯乳液及其制备方法和应用 (Waterborne polyurethane emulsion and preparation method and application thereof ) 是由 蒋平平 代注顶 张萍波 夏琪 郑付林 俞晓琴 于 2019-11-27 设计创作，主要内容包括：本发明提供了一种水性聚氨酯乳液及其制备方法和应用,所述水性聚氨酯乳液的制备原料包括：生物基乳化剂、二异氰酸酯、第一扩链剂、第二扩链剂、成盐剂、降粘剂和和去离子水。本发明所述制备原料首次使用了生物基乳化剂,其不仅含有能与异氰酸根反应的羟基,还有能发生成盐反应的羧基。因此,不仅能够避免传统水性聚氨酯乳液制备过程中需要使用催化剂以及有机溶剂,还可以减少亲水扩链剂的消耗。另外,生物基乳化剂作为聚氨酯分子链中的软段,由于其分子结构上含有羧基,会使水性聚氨酯乳液的粒径变小,提高粒子的分散性和稳定性。本发明所述制备方法简单易操作,且整个制备过程无溶剂和催化剂的使用,更加绿色环保。(The invention provides an aqueous polyurethane emulsion and a preparation method and application thereof, wherein the preparation raw materials of the aqueous polyurethane emulsion comprise: the adhesive comprises a bio-based emulsifier, diisocyanate, a first chain extender, a second chain extender, a salt forming agent, a viscosity reducer and deionized water. The raw materials for preparation of the invention use the bio-based emulsifier for the first time, which not only contains hydroxyl capable of reacting with isocyanic acid radical, but also contains carboxyl capable of undergoing salt-forming reaction. Therefore, the method can avoid the need of using a catalyst and an organic solvent in the traditional preparation process of the aqueous polyurethane emulsion, and can reduce the consumption of the hydrophilic chain extender. In addition, the bio-based emulsifier is used as a soft segment in a polyurethane molecular chain, and the molecular structure of the bio-based emulsifier contains carboxyl, so that the particle size of the aqueous polyurethane emulsion is reduced, and the dispersibility and the stability of the particles are improved. The preparation method is simple and easy to operate, and the whole preparation process is free of solvent and catalyst, so that the preparation method is more environment-friendly.)

1. The aqueous polyurethane emulsion is characterized in that the preparation raw materials of the aqueous polyurethane emulsion comprise: the adhesive comprises a bio-based emulsifier, diisocyanate, a first chain extender, a second chain extender, a salt forming agent, a viscosity reducer and deionized water.

2. The aqueous polyurethane emulsion according to claim 1, wherein the aqueous polyurethane emulsion has a solid content of 15 to 30%.

3. The aqueous polyurethane emulsion according to claim 1 or 2, wherein the hydroxyl value of the bio-based emulsifier is 60 to 100mgKOH/g, and the acid value is 50 to 70 mgKOH/g;

preferably, raw materials for preparing the bio-based emulsifier comprise polyhydroxy vegetable oil and maleic anhydride;

preferably, the polyhydroxy vegetable oil is selected from any one of castor oil, modified soybean oil, modified cottonseed oil or modified linseed oil or a combination of at least two of the castor oil, the modified soybean oil, the modified cottonseed oil and the modified linseed oil;

preferably, the modified soybean oil is prepared by epoxidizing soybean oil and then opening a ring;

preferably, the modified cottonseed oil is prepared by epoxidizing cottonseed oil and then opening a ring;

preferably, the modified linseed oil is prepared by epoxidizing linseed oil and then opening a ring;

preferably, the molar ratio of the polyhydroxy vegetable oil to the maleic anhydride is (0.5-1): 1;

preferably, the preparation method of the bio-based emulsifier comprises the following steps: mixing polyhydroxy vegetable oil and maleic anhydride, regulating the temperature to 90-130 ℃, reacting for 5-8h at the stirring speed of 500-900rpm, and then cooling to 18-25 ℃ to obtain the bio-based emulsifier.

4. The aqueous polyurethane emulsion according to any one of claims 1 to 3, wherein the diisocyanate is selected from any one of toluene diisocyanate, isophorone diisocyanate, diphenylmethane diisocyanate or dicyclohexylmethane diisocyanate or a combination of at least two thereof, preferably isophorone diisocyanate;

preferably, the first chain extender is selected from any one of 1, 4-butanediol, glycerol, ethylene glycol or hexanediol or a combination of at least two thereof;

preferably, the second chain extender is ethylene diamine;

preferably, the salt forming agent is triethylamine;

preferably, the viscosity reducer is acetone and/or methyl ethyl ketone.

5. The aqueous polyurethane emulsion of any one of claims 1-4, wherein the molar ratio of hydroxyl groups in the bio-based emulsifier to isocyanate groups in the diisocyanate is (0.2-0.5) to 1;

preferably, the molar ratio of hydroxyl groups in the first chain extender to isocyanate groups in the diisocyanate is (0.1-0.5): 1;

preferably, the molar ratio of the salt forming agent to the carboxyl groups in the bio-based emulsifier is (0.8-1): 1;

preferably, the molar ratio of the second chain extender to the first chain extender is (1-3): 1.

6. A method for preparing the aqueous polyurethane emulsion according to any one of claims 1 to 5, wherein the method comprises the following steps:

1) mixing a bio-based emulsifier, diisocyanate and at least part of a viscosity reducer, and reacting to obtain a prepolymer;

2) adding a first chain extender into the prepolymer obtained in the step 1) for reaction;

3) adding a salt forming agent into the system after the reaction in the step 2), reacting and cooling;

4) and (3) cooling the system cooled in the step 3), adding a second chain extender and deionized water, mixing, and reacting to obtain the waterborne polyurethane emulsion.

7. The method of claim 6, wherein the temperature of the reaction of step 1) is 78-82 ℃;

preferably, the reaction time of the step 1) is 1-1.5 h;

preferably, the stirring speed of the reaction in the step 1) is 500-700 rpm;

preferably, when part of the viscosity reducer is added in the step 1), the rest of the viscosity reducer is added in the step 2) or the step 3), or the rest of the viscosity reducer is divided into two parts and added in the step 2) and the step 3);

preferably, the temperature of the reaction in step 2) is 75-82 ℃;

preferably, the reaction time in step 2) is 2.5-3 h;

preferably, the stirring speed of the reaction in the step 2) is 500-700 rpm.

8. The method of claim 6 or 7, wherein step 3) further comprises: before adding the salt forming agent, cooling the system after the reaction in the step 2) to 48-50 ℃;

preferably, the reaction time of the step 3) is 0.5-1 h;

preferably, the stirring speed of the reaction in the step 3) is 500-700 rpm;

preferably, the temperature of the cooling in the step 3) is 18-25 ℃;

preferably, the temperature of said re-cooling of step 4) is 0-5 ℃;

preferably, the stirring speed of the reaction in the step 4) is 1800-1900 rpm;

preferably, the reaction time of step 4) is 30-35 min.

9. A polyurethane film obtained by curing the aqueous polyurethane emulsion according to any one of claims 1 to 5.

10. The polyurethane film of claim 9, wherein the temperature of the curing is 50-60 ℃;

preferably, the curing time is 48-72 h.

Technical Field

The invention relates to the technical field of waterborne polyurethane preparation, and particularly relates to a waterborne polyurethane emulsion and a preparation method and application thereof.

Background

Aqueous polyurethanes are new polyurethane systems in which water is used as the dispersion medium instead of an organic solvent, and are also referred to as water-dispersed polyurethanes, aqueous polyurethanes, or water-based polyurethanes. The waterborne polyurethane takes water as a solvent, and has the advantages of no pollution, safety, reliability, excellent mechanical property, good compatibility, easy modification and the like.

Waterborne Polyurethane (WPU), as a multifunctional polymer, has been currently used in a variety of fields, such as inks, leathers, foams, coatings, adhesives, and the like. However, WPU uses a large amount of organic solvents in the manufacturing process, which poses certain hazards to the environment and human health. Meanwhile, the raw material for preparing the traditional WPU is petroleum-based polyol, and the excessive use of the petroleum-based polyol increases the consumption of petroleum resources.

CN103044649B discloses fluorine-containing cationic waterborne polyurethane with better surface performance and a preparation method thereof. The chemical stability, mechanical property, oil and water repellency and other properties of the waterborne polyurethane are obviously improved, and simultaneously, the usage amount of fluorine is greatly reduced, and the cost is reduced. However, the preparation process of the waterborne polyurethane uses organic solvents, catalysts and the like, which is not beneficial to the requirement of environmental protection.

CN105801790A discloses waterborne polyurethane and a preparation method thereof, and also discloses a waterborne polyurethane automotive interior adhesive and a preparation method thereof, solving the technical problems of poor water resistance and poor mechanical properties of the existing waterborne polyurethane. However, the raw materials for preparing the waterborne polyurethane mainly adopt petroleum-based polyester polyol, and excessive use of the polyester polyol can increase the consumption of petroleum resources and can not meet the requirement of environmental protection.

Therefore, the market needs to develop a waterborne polyurethane emulsion and a preparation method thereof, so that the whole preparation process is more environment-friendly.

Disclosure of Invention

Aiming at the defects of the prior art, the invention aims to provide a waterborne polyurethane emulsion and a preparation method and application thereof, the raw material for preparing the waterborne polyurethane emulsion adopts a bio-based emulsifier, the bio-based emulsifier not only contains hydroxyl which can react with diisocyanate, and carboxyl can react with a salt forming agent to form salt, so that the use of 2, 2-dimethylolpropionic acid or 2, 2-dimethylolbutyric acid as a hydrophilic chain extender in the traditional preparation process is omitted, further omits an organic solvent and a catalyst used in the hydrophilic chain extension reaction, overcomes the defects of using the solvent and the catalyst in the preparation process of the waterborne polyurethane at the present stage, ensures that the preparation process of the whole waterborne polyurethane emulsion is more environment-friendly, in addition, the use of the bio-based emulsifier can reduce the use of the existing petroleum-based polyol, and can reduce the consumption of petroleum energy.

In order to achieve the purpose, the invention adopts the following technical scheme:

in a first aspect, the present invention provides an aqueous polyurethane emulsion, wherein the raw materials for preparing the aqueous polyurethane emulsion comprise: the adhesive comprises a bio-based emulsifier, diisocyanate, a first chain extender, a second chain extender, a salt forming agent, a viscosity reducer and deionized water.

The raw materials for preparing the waterborne polyurethane emulsion firstly use the green and environment-friendly bio-based emulsifier which is used as the derivative of the vegetable oil-based polyol, and the molecular structure of the bio-based emulsifier not only contains hydroxyl (-OH) capable of reacting with isocyanate (-NCO), but also contains carboxyl (-COOH) capable of undergoing a salt forming reaction. Therefore, by using the compound as a preparation raw material, the steps of dissolving 2, 2-dimethylolpropionic acid (DMPA) by using a catalyst and N-methylpyrrolidone (NMP) or N, N-Dimethylformamide (DMF) in the traditional WPU preparation process can be avoided, and the consumption of a hydrophilic chain extender (DMPA or DMBA) can be reduced. In addition, the bio-based emulsifier is used as a soft segment in the WPU molecular chain, and the molecular structure of the bio-based emulsifier contains carboxyl, so that the particle size of the prepared aqueous polyurethane emulsion is reduced, and the dispersibility and the stability of the particles are improved.

Preferably, the solid content of the aqueous polyurethane emulsion is 15-30%, and may be, for example, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 19%, 30%, or the like.

Preferably, the hydroxyl value of the bio-based emulsifier is 60-100mgKOH/g, such as 60mgKOH/g, 63mgKOH/g, 65mgKOH/g, 68mgKOH/g, 70mgKOH/g, 72mgKOH/g, 75mgKOH/g, 80mgKOH/g, 84mgKOH/g, 85mgKOH/g, 88mgKOH/g, 90mgKOH/g, 93mgKOH/g, 95mgKOH/g, 97mgKOH/g, 98mgKOH/g or 100mgKOH/g, etc., and the acid value is 50-70mgKOH/g, such as 50mgKOH/g, 51mgKOH/g, 52mgKOH/g, 53mgKOH/g, 54mgKOH/g, 55mgKOH/g, 56mgKOH/g, 57mgKOH/g, 58mgKOH/g, 59mgKOH/g, 60mgKOH/g, 61mgKOH/g, 62mgKOH/g, 63mgKOH/g, 64mgKOH/g, 65mgKOH/g, 66mgKOH/g, 67mgKOH/g, 68mgKOH/g, 69mgKOH/g, or 70mgKOH/g, etc.

The molar weight of hydroxyl and carboxyl in the bio-based emulsifier can be calculated according to the hydroxyl value and the acid value of the bio-based emulsifier, and the specific calculation formula is as follows:

-OH (mol/g) ═ hydroxyl number of bio-based emulsifiers (gKOH/g)/56.1;

-COOH (mol/g) ═ acid number of bio-based emulsifiers (gKOH/g)/56.1;

wherein 56.1 is the relative molecular mass of KOH.

In addition, the hydroxyl value and acid value of the bio-based emulsifier are determined as follows:

(1) the hydroxyl value was determined as follows:

the hydroxyl number of the polyol starting material is titrated in accordance with ASTM D4247-99 (acetic anhydride-pyridine method) and, for a certain simplification, the detailed procedure is as follows:

a) preparation of solution and indicator

i) Preparation of acetylation reagent

127mL of acetic anhydride is accurately weighed into a brown bottle, dissolved in 1000mL of pyridine, and sealed for temporary storage (namely, the acetic anhydride is prepared and used).

ii)0.5mol/L NaOH standard solution

The preparation of a 0.5mol/L NaOH standard solution was carried out according to ASTM standards.

iii) phenolphthalein indicator

1g of phenolphthalein was weighed out and dissolved in 100mL of ethanol.

b) Measurement Process

About 1g of sample (accurate to 0.0001g) is accurately weighed and placed in a 100mL clean and dry round bottom flask, 10mL of acetylation reagent is removed by a pipette, a condenser tube is connected, and the mixture is stirred for 2h at 98 +/-2 ℃. The flask was cooled to room temperature, 10mL of pyridine was added, stirring was continued for 10min under reflux, the reaction was terminated and cooled, the condenser was flushed with 10mL of absolute ethanol, the reaction solution and the flushing solution were transferred to a conical flask, 4 drops of phenolphthalein indicator were added thereto, titrated with 0.5mol/L NaOH standard solution, and a parallel blank control was performed.

c) Calculation of hydroxyl number

The hydroxyl number X (mg KOH/g) of the sample was calculated as follows:

X＝[(B-A)×N×56.1]/W

in the formula: b-volume of NaOH standard solution (mL) used for blank control;

a-volume of NaOH standard solution (mL) used for sample testing;

n-concentration of NaOH standard solution (mol/L);

w-exact mass of sample (g).

(2) The acid value was determined as follows:

the acid value is determined by referring to a hot ethanol method in GB 5009.229-2016, and the specific steps are as follows:

the preparation of the standard solution and the phenolphthalein indicator is the same as in the above-described hydroxyl value determination process, and will not be described herein again.

Taking a 250mL first conical flask, weighing the prepared sample by using a balance, taking another 250mL second conical flask, adding 90-100mL 95% ethanol, and then adding 0.5-1mL phenolphthalein indicator. The second conical flask was then placed in a water bath at 90-100 ℃ and heated to 80-85 ℃. The conical flask was removed and immediately titrated with a graduated burette containing a standard titration solution while the temperature of the ethanol was maintained above 70 ℃. When the ethanol appeared reddish and no significant discoloration occurred within 15s, the titration was immediately stopped and the acidity of the ethanol was neutralized. Pouring the neutralized ethanol solution into a first conical flask containing a sample immediately when the neutralized ethanol solution is hot, then putting the first conical flask into a water bath at 90-100 ℃ for heating until the ethanol reaches 80-85 ℃, taking out the conical flask, immediately titrating the hot ethanol solution of the sample by using a graduated burette containing a standard titration solution within 5min, stopping titration immediately when the sample solution turns reddish initially and does not fade obviously within 15s, and recording the milliliter number of the standard titration solution consumed by titration.

The calculation formula of the acid value Y (mg KOH/g) of the sample is as follows:

Y＝V×N×56.1/m

v-volume consumed Standard solution (mL)

N-concentration of Standard solution (mol/L)

m-weight of sample (g)

Preferably, the raw materials for preparing the bio-based emulsifier comprise polyhydroxy vegetable oil and maleic anhydride.

The raw materials for preparing the bio-based emulsifier disclosed by the invention preferably use polyhydroxy vegetable oil and maleic anhydride, namely the polyhydroxy vegetable oil is used for replacing petroleum-based polyol, so that the consumption of petroleum energy is obviously reduced, and the whole preparation process is more environment-friendly.

Preferably, the polyhydroxy vegetable oil is selected from any one of castor oil, modified soybean oil, modified cottonseed oil or modified linseed oil or a combination of at least two of the castor oil, the modified soybean oil, the modified cottonseed oil and the modified linseed oil.

Preferably, the modified soybean oil is prepared by epoxidizing soybean oil and then opening a ring.

Preferably, the modified cottonseed oil is prepared by epoxidizing cottonseed oil and then opening a ring.

Preferably, the modified linseed oil is prepared by epoxidizing linseed oil and then opening a ring.

Preferably, the molar ratio of the polyhydroxy vegetable oil to maleic anhydride is (0.5-1: 1), and may be, for example, 0.5:1, 0.6:1, 0.7:1, 0.8:1, 0.9:1, or 1:1, etc.

The invention preferably controls the molar ratio of the polyhydroxy vegetable oil to the maleic anhydride within the range, mainly aims to control the proportion of hydroxyl and carboxyl on the molecular chain of the prepared bio-based emulsifier, and when the proportion of the hydroxyl and the carboxyl is higher than the range, the hydroxyl content and the carboxyl content of the prepared bio-based emulsifier are increased and reduced, and when the aqueous polyurethane synthesis reaction is carried out, crosslinking is easy to occur, dispersion is difficult, hydrophilicity is reduced, and precipitates are formed; when the ratio of the two is lower than the range, the carboxyl content of the bio-based emulsifier is increased, and the water-based polyurethane film is too soft, so that the comprehensive performance of the polyurethane film is influenced.

Preferably, the preparation method of the bio-based emulsifier comprises the following steps: mixing polyhydroxy vegetable oil and maleic anhydride, regulating the temperature to 90-130 ℃, reacting for 5-8h at the stirring speed of 500-900rpm, and then cooling to 18-25 ℃ to obtain the bio-based emulsifier.

The temperature of 90-130 ℃ can be, for example, 90 ℃, 95 ℃, 100 ℃, 105 ℃, 110 ℃, 115 ℃, 120 ℃, 125 ℃ or 130 ℃.

The 500-900rpm may be, for example, 500rpm, 550rpm, 600rpm, 650rpm, 700rpm, 750rpm, 800rpm, 850rpm, 900rpm, or the like.

The above-mentioned 5 to 8 hours may be, for example, 5 hours, 5.5 hours, 6 hours, 6.5 hours, 7 hours, 7.5 hours or 8 hours.

The temperature of 18-25 ℃ may be, for example, 18 ℃, 19 ℃, 20 ℃, 21 ℃, 22 ℃, 23 ℃, 24 ℃ or 25 ℃.

Preferably, the diisocyanate is selected from any one of toluene diisocyanate, isophorone diisocyanate, diphenylmethane diisocyanate or dicyclohexylmethane diisocyanate or a combination of at least two of the toluene diisocyanate, the isophorone diisocyanate is preferred.

Preferably, the first chain extender is selected from any one of 1, 4-butanediol, glycerol, ethylene glycol or hexanediol or a combination of at least two thereof.

Preferably, the second chain extender is ethylene diamine.

The second chain extender is preferably ethylene diamine, and the ethylene diamine can react with isocyanate in diisocyanate to produce urea bonds, so that the tensile strength of the finally obtained polyurethane film is effectively improved.

Preferably, the salt forming agent is triethylamine.

Preferably, the viscosity reducer is acetone and/or methyl ethyl ketone.

Preferably, the molar ratio of hydroxyl groups in the bio-based emulsifier to isocyanate groups in the diisocyanate is (0.2-0.5: 1, and may be, for example, 0.2:1, 0.3:1, 0.4:1, or 0.5:1, etc.

The hydroxyl in the bio-based emulsifier and the isocyanic acid radical in the diisocyanate are preferably controlled within the above range, so that the addition amount of the isocyanic acid radical in the diisocyanate is excessive relative to the hydroxyl in the bio-based emulsifier, the proportion of soft segments and hard segments in a polyurethane molecular chain can be better controlled, and the strength and the flexibility of the prepared polyurethane film can be further regulated and controlled.

Preferably, the molar ratio of hydroxyl groups in the first chain extender to isocyanate groups in the diisocyanate is (0.1-0.5: 1, and may be, for example, 0.1:1, 0.2:1, 0.3:1, 0.4:1, 0.5:1, or the like.

The invention preferably controls the molar ratio of the hydroxyl in the first chain extender to the isocyanate in the diisocyanate within the above range, so as to regulate the proportion of soft segments and hard segments in the prepared polyurethane molecular chain.

Preferably, the molar ratio of the salt-forming agent to the carboxyl groups in the bio-based emulsifier is (0.8-1):1, and may be, for example, 0.8:1, 0.85:1, 0.9:1, 0.95:1, or 1:1, etc.

Preferably, the molar ratio of the second chain extender to the first chain extender is (1-3: 1, and may be, for example, 1:1, 1.5:1, 2:1, 2.5:1, or 3:1, etc.

In a second aspect, the present invention also provides a method for preparing the aqueous polyurethane emulsion according to the first aspect, wherein the method comprises the following steps:

1) mixing a bio-based emulsifier, diisocyanate and at least part of a viscosity reducer, and reacting to obtain a prepolymer;

2) adding a first chain extender into the prepolymer obtained in the step 1) for reaction;

3) adding a salt forming agent into the system after the reaction in the step 2), reacting and cooling;

4) and (3) cooling the system cooled in the step 3), adding a second chain extender and deionized water, mixing, and reacting to obtain the waterborne polyurethane emulsion.

The preparation method is simple and easy to operate, and the whole preparation process does not use solvents (N, N-dimethyl pyrrolidone, N-dimethyl formamide) and catalysts (stannous octoate), so that the preparation method meets the requirements of environmental protection.

Preferably, the reaction temperature in step 1) is 78-82 deg.C, such as 78 deg.C, 79 deg.C, 80 deg.C, 81 deg.C or 82 deg.C.

Preferably, the reaction time in step 1) is 1-1.5h, for example, 1h, 1.1h, 1.2h, 1.3h, 1.4h or 1.5h, etc.

Preferably, the stirring speed of the reaction in step 1) is 500-700rpm, such as 500rpm, 550rpm, 600rpm, 650rpm or 700 rpm.

Preferably, when part of the viscosity reducer is added in the step 1), the rest of the viscosity reducer is added in the step 2) or the step 3), or the rest of the viscosity reducer is divided into two parts and added in the step 2) and the step 3).

Preferably, the reaction temperature in step 2) is 75-82 deg.C, such as 75 deg.C, 76 deg.C, 77 deg.C, 78 deg.C, 79 deg.C, 80 deg.C, 81 deg.C or 82 deg.C.

Preferably, the reaction time in step 2) is 2.5-3h, for example, 2.5h, 2.6h, 2.7h, 2.8h, 2.9h or 3h, etc.

Preferably, the stirring speed of the reaction in step 2) is 500-700rpm, such as 500rpm, 550rpm, 600rpm, 650rpm or 700 rpm.

Preferably, step 3) further comprises: before adding the salt forming agent, the system after the reaction in step 2) is cooled to 48-50 ℃, for example, 48 ℃, 48.5 ℃, 49 ℃, 49.5 ℃ or 50 ℃ and the like.

Preferably, the reaction time of step 3) is 0.5 to 1h, and may be, for example, 0.5h, 0.6h, 0.7h, 0.8h, 0.9h or 1 h.

Preferably, the stirring speed of the reaction in step 3) is 500-700rpm, such as 500rpm, 550rpm, 600rpm, 650rpm or 700 rpm.

Preferably, the cooling temperature in step 3) is 18-25 deg.C, such as 18 deg.C, 19 deg.C, 20 deg.C, 21 deg.C, 22 deg.C, 23 deg.C, 24 deg.C or 25 deg.C.

Preferably, the temperature for said re-cooling in step 4) is 0-5 ℃, for example, 0 ℃, 1 ℃,2 ℃, 3 ℃,4 ℃ or 5 ℃ and the like.

Preferably, the stirring speed of the reaction in step 4) is 1800-1900rpm, such as 1800rpm, 1810rpm, 1820rpm, 1850rpm, 1870rpm, 1890rpm or 1900 rpm.

Preferably, the reaction time of step 4) is 30-35min, such as 30min, 31min, 32min, 33min, 34min or 35 min.

In a third aspect, the present invention also provides a polyurethane film obtained by curing the aqueous polyurethane emulsion according to the first aspect.

Preferably, the curing temperature is 50-60 ℃, for example, 50 ℃, 51 ℃, 52 ℃, 53 ℃, 54 ℃, 55 ℃, 56 ℃, 57 ℃, 58 ℃, 59 ℃ or 60 ℃.

Preferably, the curing time is 48-72h, such as 48h, 50h, 52h, 55h, 58h, 60h, 64h, 65h, 68h, 70h or 72 h.

Compared with the prior art, the invention has the following beneficial effects:

(1) the raw materials for preparing the waterborne polyurethane emulsion firstly use the green and environment-friendly bio-based emulsifier which is used as the derivative of the vegetable oil-based polyol, and the molecular structure of the bio-based emulsifier not only contains hydroxyl (-OH) capable of reacting with isocyanate (-NCO) but also contains carboxyl (-COOH) capable of reacting with a salt forming agent in a salt forming manner. Therefore, by using the compound as a preparation raw material, the steps of dissolving 2, 2-dimethylolpropionic acid (DMPA) by using a catalyst and N-methylpyrrolidone (NMP) or N, N-Dimethylformamide (DMF) in the traditional WPU preparation process can be avoided, and the consumption of a hydrophilic chain extender (DMPA or DMBA) can be reduced. In addition, the bio-based emulsifier is used as a soft segment in a WPU molecular chain, and the molecular structure of the bio-based emulsifier contains carboxyl, so that the particle size of the prepared waterborne polyurethane emulsion is reduced, and the dispersibility and stability of the particles are improved;

(2) the preparation method is simple and easy to operate, and the whole preparation process does not use solvents (N, N-dimethyl pyrrolidone, N-dimethyl formamide) and catalysts (stannous octoate), so that the preparation method meets the requirements of environmental protection.

Drawings

FIG. 1 is a Fourier transform infrared spectrum of the bio-based emulsifier prepared in example 1, wherein CO is castor oil and MCO is the bio-based emulsifier.

FIG. 2 is a nuclear magnetic hydrogen spectrum of the bio-based emulsifier prepared in example 1, wherein CO is castor oil and MCO is the bio-based emulsifier.

FIG. 3 is a Fourier infrared conversion spectrum of the waterborne polyurethane prepared in example 1.

Detailed Description

The present invention is described in further detail below. The following examples are merely illustrative of the present invention and do not represent or limit the scope of the claims, which are defined by the claims.