Method for preparing waterborne polyurethane microporous membrane by flocculation method

Abstract

The invention discloses a method for preparing a waterborne polyurethane microporous membrane by a flocculation method. Adding a mixture of diisocyanate, a hydrophilic chain extender and a catalyst into the dihydric alcohol subjected to vacuum dehydration, and carrying out prepolymerization reaction to obtain a polyurethane prepolymer; sequentially adding acetone and a neutralizer into the polyurethane prepolymer, carrying out a neutralization reaction, then adding deionized water, and carrying out high-speed dispersion and emulsification to obtain a waterborne polyurethane emulsion; adding a post-chain extender into the waterborne polyurethane emulsion, and carrying out a post-chain extension reaction to obtain a high-molecular-weight waterborne polyurethane emulsion; adding a thickening agent into the high-molecular-weight waterborne polyurethane emulsion, and stirring for thickening, so as to obtain the thickened high-molecular-weight waterborne polyurethane emulsion; and coating the surface of a release film with the thickened high-molecular-weight waterborne polyurethane emulsion, immersing the release film into a flocculant aqueous solution, solidifying to form a film, stripping the film from the surface of the release film, washing, and drying to obtain the waterborne polyurethane microporous film. The technical route is simple and convenient, the reaction condition is mild, and the method is easy to popularize.

Description

Technical Field

[0001] The invention relates to the field of membrane technology, and in particular to a method for preparing a waterborne polyurethane microporous membrane by a flocculation method. Background Art

[0002] Polymer microporous membrane materials are widely used in water treatment, gas separation and other fields. With the development of science and technology and the improvement of people's living standards, the demand for polymer microporous membranes in industries such as automotive interiors and textile products is also increasing. The methods used to prepare microporous membranes include thermally induced phase separation, solution phase separation, track etching, electrospinning, and flocculation. The thermally induced phase separation method requires the recovery of high-boiling point solvents, which may have an impact on the environment; the solution phase separation method requires the selection of a suitable solvent and has certain limitations; the track etching method is relatively expensive; and the electrospinning method has higher requirements for equipment. Compared with the above methods, the flocculation method has the advantages of strong versatility, simple operation, low cost, and environmental friendliness.

[0003] In the early days, there were many types of polymer materials used to prepare microporous membranes, such as polytetrafluoroethylene, polysulfone, polyethersulfone, solvent-based polyurethane, etc. These raw materials all have the problem of polluting the environment. Waterborne polyurethane has gradually entered the public eye in recent years due to its advantages such as being non-toxic, non-flammable, and not polluting the air or producing wastewater. With the increasingly stringent environmental regulations and the continuous enhancement of people's environmental awareness, the application of waterborne polyurethane will be more extensive and in-depth.

[0004] Prior to this, the flocculation method for preparing polymer microporous membranes has made certain research progress. Patent CN112791604A discloses a bamboo powder / modified polyvinylidene fluoride composite membrane and its preparation method and application, which is prepared by using bamboo powder, polyvinylidene fluoride and other additives into a blended liquid, and using flocculation to obtain a composite membrane, so that the composite membrane can be applied to the treatment of heavy metal wastewater. Patent CN108465386A discloses an anion channel membrane, which uses polyamide 6 with sulfonic acid groups as a raw material and is made by flocculation, and can be used for organic pollutant wastewater treatment. However, there are relatively few studies on the preparation of waterborne polyurethane microporous membranes by flocculation. Therefore, using this method and designing different film-forming conditions is of great significance for the research of waterborne polyurethane microporous membranes. Summary of the invention

[0005] The purpose of the present invention is to provide a method for preparing a waterborne polyurethane microporous membrane by a flocculation method.

[0006] To achieve the above object, the present invention adopts the following technical solution: The first aspect of the present invention provides a method for preparing a waterborne polyurethane microporous membrane by a flocculation method, comprising the following steps: S1: adding a diol to a three-necked flask, and removing water in a vacuum manner to obtain a diol after vacuum removal of water; adding a mixture of a diisocyanate, a hydrophilic chain extender, and a catalyst to the obtained diol after vacuum removal of water, and performing a prepolymerization reaction to obtain a polyurethane prepolymer; S2: adding acetone and a neutralizing agent to the polyurethane prepolymer obtained in S1 in sequence to carry out a neutralization reaction, and then adding deionized water to disperse and emulsify at a high speed to obtain an aqueous polyurethane emulsion; adding a post-chain extender to the aqueous polyurethane emulsion to carry out a post-chain extension reaction to obtain a high molecular weight aqueous polyurethane emulsion; adding a thickener to the aqueous polyurethane emulsion to carry out a thickening reaction to obtain a thickened high molecular weight aqueous polyurethane emulsion; S3: coating the thickened high molecular weight aqueous polyurethane emulsion obtained in S2 on the surface of the release film, immersing it in an aqueous flocculant solution to coagulate it into a film, then peeling the film from the surface of the release film, washing it, and drying it to obtain an aqueous polyurethane microporous membrane; Wherein, in step S1, the diol is one or more of polyethylene glycol, polypropylene glycol, polybutylene glycol, polyethylene adipate, polycarbonate diol, and adipic acid-tetramethylene glycol polyester; the hydrophilic chain extender is one or more of dimethylol propionic acid, dimethylol butyric acid, and ethylenediaminohexanesulfonic acid sodium salt aqueous solution; the diisocyanate is one or more of toluene diisocyanate, diphenylmethane diisocyanate, isophorone diisocyanate, and hexamethylene diisocyanate; the catalyst is dibutyltin dilaurate; Wherein, in step S1, the weight ratio of the diol to the diisocyanate is 1.5:1 to 6:1; the weight of the hydrophilic chain extender accounts for 0.3% to 8% of the sum of the weights of the diol and the diisocyanate; the weight of the catalyst accounts for 0.2% of the sum of the weights of the diol and the diisocyanate; the conditions of the prepolymerization reaction are: reacting at a temperature of 85 to 95° C. until the NCO content of the system is 1.2wt% to 1.6wt%; Wherein, in step S2, the neutralizing agent is triethylamine; the post-chain extender is one or more of ethylenediamine and isophordiamine; the thickener is an associative thickener; Wherein, in step S2, the weight of the acetone accounts for 15% to 35% of the sum of the weights of the diol and the diisocyanate; the weight of the neutralizer accounts for 65% to 78% of the weight of the hydrophilic chain extender; the weight of the deionized water accounts for 150% to 200% of the weight of the prepolymer; the weight of the post-chain extender accounts for 0.1% to 5% of the sum of the weights of the diol and the diisocyanate; the weight of the thickener accounts for 0.5% to 2% of the weight of the waterborne polyurethane emulsion; the conditions of the neutralization reaction are: reacting at a temperature of 30 to 50° C. for 0.5 h; the conditions of the post-chain extension reaction are: reacting at a temperature of 40 to 50° C. for 1 to 1.5 h; Wherein, in step S3, the flocculant is one or more of oxalic acid, tartaric acid, and citric acid; the concentration of the flocculant aqueous solution is 3wt% to 20wt%; Wherein, in step S3, the coating thickness of the thickened high molecular weight aqueous polyurethane emulsion is 0.05 to 0.5 mm; and the immersion time is 5 s to 1 min.

[0007] In the above method, waterborne polyurethane is more environmentally friendly than other polymer materials, both in terms of raw material selection and synthesis process. The application of waterborne polyurethane in the field of microporous membrane materials is conducive to promoting sustainable development and in line with the national green development policy requirements. The key to preparing waterborne polyurethane microporous membranes by flocculation method is phase separation. When the waterborne polyurethane casting liquid contacts with a coagulation bath with oxalic acid, tartaric acid, citric acid, etc. as solvents and deionized water as non-solvents, liquid-liquid phase separation occurs through the interaction between the solvent and the non-solvent. The waterborne polyurethane casting liquid is separated into a lean phase and a rich phase. The lean phase forms fine pores, and the rich phase solidifies into a membrane skeleton. By changing the composition of the casting liquid and the coagulation bath conditions, the pore size, pore structure, and porosity can be adjusted to prepare a membrane material with good waterproof and moisture permeability.

[0008] The second aspect of the present invention provides a waterborne polyurethane microporous membrane, which is prepared by the above method.

[0009] The third aspect of the present invention provides application of the above-mentioned aqueous polyurethane microporous membrane in the field of microporous membrane materials.

[0010] The significant advantages of the present invention are: The present invention aims to solve the problem of environmental pollution existing in traditional polymer microporous membrane materials, and uses waterborne polyurethane as raw material to prepare microporous membrane, so as to achieve the purpose of protecting the environment. At the same time, waterborne polyurethane has good mechanical properties, low toxicity, non-flammable and other advantages. According to the process of preparing waterborne polyurethane by acetone method, the synthesis conditions are changed, such as the ratio of soft and hard segments, the content of hydrophilic chain extender, etc., to obtain waterborne polyurethane with different properties. Flocculation method is a method commonly used in preparing microporous membranes, which is easy to operate and does not pollute the environment. It is applied to the preparation of waterborne polyurethane microporous membranes, which can not only reduce resource consumption and production costs, but also help to open up the research direction of waterborne polyurethane microporous membranes and broaden the application field of waterborne polyurethane microporous membranes. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 This is the infrared spectrum of the waterborne polyurethane prepared in Example 1.

[0012] Figure 2 This is a diagram of the mechanical properties of the waterborne polyurethane microporous membrane prepared in Example 1.

[0013] Figure 3 This is a scanning electron microscope surface image of the waterborne polyurethane microporous membrane prepared in Example 1.

[0014] Figure 4 This is a scanning electron microscope cross-sectional image of the waterborne polyurethane microporous membrane prepared in Example 1. DETAILED DESCRIPTION

[0015] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments so that those skilled in the art can better understand the present invention and implement it. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. It should be understood that the specific embodiments are only used to explain the present invention, but the embodiments are not intended to limit the present invention.

[0016] The determination of NCO content in the examples of the present invention refers to the reference: Xiong Jun, Sun Fang, Du Hongguang. Determination of isocyanate groups in polyurethane by acetone-di-n-butylamine titration [J]. Analysis Laboratory, 2007, 26(8): 73-76.

[0017] The associative thickener in the embodiment of the present invention was purchased from Huayue Fine Chemicals (Kunshan) Co., Ltd., specifically the coating thickener HY660.

[0018] Embodiment 1: This embodiment provides a method for preparing a waterborne polyurethane microporous membrane by flocculation, which is carried out according to the following steps: S1: 4 g of polypropylene glycol with an average molecular weight of 1000 and 27.13 g of polypropylene glycol with an average molecular weight of 2000 are added to a three-necked flask, and vacuum dehydration is performed for 1 hour under the conditions of an oil bath temperature of 120° C. and a mechanical stirring speed of 165 r / min to obtain the polypropylene glycol after vacuum dehydration; a mixture of 11.05 g of isophorone diisocyanate, 3.25 g of dimethylolpropionic acid and 0.02 g of dibutyltin dilaurate is added to the obtained polypropylene glycol after vacuum dehydration, and then reacted under the conditions of an oil bath temperature of 95° C. and a mechanical stirring speed of 165 r / min until the NCO content of the system is 1.6 wt % to obtain a polyurethane prepolymer; S2: Add 9.19g of acetone to the polyurethane prepolymer obtained in S1, then add 2.33g of triethylamine, react for 30min at an oil bath temperature of 50°C and a mechanical stirring speed of 165r / min, then add 97.5g of deionized water, and high-speed disperse and emulsify for 30min at an oil bath temperature of 50°C and a mechanical stirring speed of 1000r / min to obtain an aqueous polyurethane emulsion; add 1.17g of ethylenediamine to the obtained aqueous polyurethane emulsion, react for 1h at an oil bath temperature of 40°C and a mechanical stirring speed of 150r / min to obtain a high molecular weight aqueous polyurethane emulsion; add 1.54g of an associative thickener to the obtained high molecular weight aqueous polyurethane emulsion, stir for 30min at room temperature and a mechanical stirring speed of 250r / min to obtain a thickened high molecular weight aqueous polyurethane emulsion; S3: The thickened high molecular weight aqueous polyurethane emulsion obtained in S2 is coated on the surface of the release film at a coating thickness of 0.2 mm, and completely immersed in a 10 wt % citric acid aqueous solution for 10 seconds to solidify into a film, and then the film is peeled off from the surface of the release film, washed with deionized water for 5 minutes, and then dried at 120°C for 20 minutes to obtain a water-based polyurethane microporous membrane.

[0019] The aqueous polyurethane microporous membrane prepared in this example exhibits an asymmetric pore structure, with finger-like pores accounting for the majority, a relatively small surface pore size, and most pore sizes distributed in the range of 100 to 350 nm. Large cavity structures exist locally inside the membrane.

[0020] Embodiment 2: This embodiment provides a method for preparing a waterborne polyurethane microporous membrane by flocculation, which is carried out according to the following steps: S1: 17 g of polypropylene glycol with an average molecular weight of 1000 and 17 g of polypropylene glycol with an average molecular weight of 2000 are added to a three-necked flask, and vacuum dehydration is performed for 1 hour under the conditions of an oil bath temperature of 120° C. and a mechanical stirring speed of 165 r / min to obtain the polypropylene glycol after vacuum dehydration; a mixture of 14.89 g of isophorone diisocyanate, 3 g of dimethylolpropionic acid and 0.02 g of dibutyltin dilaurate is added to the obtained polypropylene glycol after vacuum dehydration, and then reacted under the conditions of an oil bath temperature of 95° C. and a mechanical stirring speed of 165 r / min until the NCO content of the system is 1.6 wt % to obtain a polyurethane prepolymer; S2: Add 12g of acetone to the polyurethane prepolymer obtained in S1, then add 2.08g of triethylamine, react for 30min at an oil bath temperature of 50°C and a mechanical stirring speed of 165r / min, then add 115g of deionized water, and high-speed disperse and emulsify for 30min at an oil bath temperature of 50°C and a mechanical stirring speed of 1000r / min to obtain an aqueous polyurethane emulsion; add 1.44g of ethylenediamine to the obtained aqueous polyurethane emulsion, react for 1h at an oil bath temperature of 40°C and a mechanical stirring speed of 150r / min to obtain a high molecular weight aqueous polyurethane. emulsion; add 1.8g of associative thickener to the obtained high molecular weight water-based polyurethane emulsion, stir for 30min at room temperature and a mechanical stirring speed of 250r / min to obtain a thickened high molecular weight water-based polyurethane emulsion; S3: apply the thickened high molecular weight water-based polyurethane emulsion obtained in S2 on the surface of the release film at a coating thickness of 0.2mm, completely immerse it in a 10wt% citric acid aqueous solution for 10s to solidify into a film, then peel off the film from the surface of the release film, wash with deionized water for 5min, and then dry at 120°C for 20min to obtain a water-based polyurethane microporous membrane.

[0021] The aqueous polyurethane microporous membrane prepared in this example exhibits an asymmetric pore structure, with finger-shaped pores accounting for the majority, a relatively small surface pore size, and most pore sizes distributed in the range of 100 to 450 nm. Large cavity structures exist locally inside the membrane.

[0022] Embodiment 3: This embodiment provides a method for preparing a waterborne polyurethane microporous membrane by flocculation, which is carried out according to the following steps: S1: 15 g of polypropylene glycol with an average molecular weight of 1000 and 28 g of polypropylene glycol with an average molecular weight of 2000 are added to a three-necked flask, and vacuum dehydration is performed for 1 hour under the conditions of an oil bath temperature of 120° C. and a mechanical stirring speed of 165 r / min to obtain the polypropylene glycol after vacuum dehydration; a mixture of 14.89 g of isophorone diisocyanate, 3.65 g of dimethylolpropionic acid and 0.02 g of dibutyltin dilaurate is added to the obtained polypropylene glycol after vacuum dehydration, and then reacted under the conditions of an oil bath temperature of 95° C. and a mechanical stirring speed of 165 r / min until the NCO content of the system is 1.6 wt % to obtain a polyurethane prepolymer; S2: Add 12g of acetone to the polyurethane prepolymer obtained in S1, then add 2.48g of triethylamine, react for 30min at an oil bath temperature of 50°C and a mechanical stirring speed of 165r / min, then add 135g of deionized water, and high-speed disperse and emulsify for 30min at an oil bath temperature of 50°C and a mechanical stirring speed of 1000r / min to obtain an aqueous polyurethane emulsion; add 1.29g of ethylenediamine to the obtained aqueous polyurethane emulsion, react for 1h at an oil bath temperature of 40°C and a mechanical stirring speed of 150r / min to obtain a high molecular weight aqueous polyurethane. emulsion; add 2.11g of associative thickener to the obtained high molecular weight water-based polyurethane emulsion, stir for 30min at room temperature and a mechanical stirring speed of 250r / min to obtain a thickened high molecular weight water-based polyurethane emulsion; S3: apply the thickened high molecular weight water-based polyurethane emulsion obtained in S2 on the surface of the release film at a coating thickness of 0.2mm, completely immerse it in a 10wt% citric acid aqueous solution for 10s to solidify into a film, then peel off the film from the surface of the release film, wash with deionized water for 5min, and then dry at 120°C for 20min to obtain a water-based polyurethane microporous membrane.

[0023] The aqueous polyurethane microporous membrane prepared in this example exhibits an asymmetric pore structure, with finger-like pores accounting for the majority, small surface pores, most of which are distributed in the range of 100 to 300 nm, and large cavity structures partially existing inside the membrane.

[0024] Embodiment 4: This embodiment provides a method for preparing a waterborne polyurethane microporous membrane by flocculation, which is carried out according to the following steps: S1: 15 g of polypropylene glycol with an average molecular weight of 1000 and 20 g of polypropylene glycol with an average molecular weight of 2000 are added to a three-necked flask, and vacuum dehydration is performed for 1 hour under the conditions of an oil bath temperature of 120° C. and a mechanical stirring speed of 165 r / min to obtain the polypropylene glycol after vacuum dehydration; a mixture of 15.98 g of isophorone diisocyanate, 2.75 g of dimethylolpropionic acid and 0.02 g of dibutyltin dilaurate is added to the obtained polypropylene glycol after vacuum dehydration, and then reacted under the conditions of an oil bath temperature of 95° C. and a mechanical stirring speed of 165 r / min until the NCO content of the system is 1.6 wt % to obtain a polyurethane prepolymer; S2: add 15g of acetone to the polyurethane prepolymer obtained in S1, then add 2.07g of triethylamine, react for 30min at an oil bath temperature of 50°C and a mechanical stirring speed of 165r / min, then add 130g of deionized water, and high-speed disperse and emulsify for 30min at an oil bath temperature of 50°C and a mechanical stirring speed of 1000r / min to obtain an aqueous polyurethane emulsion; add 1.05g of ethylenediamine to the obtained aqueous polyurethane emulsion, react for 1h at an oil bath temperature of 40°C and a mechanical stirring speed of 150r / min to obtain a high molecular weight aqueous polyurethane emulsion; add 2g of an associative thickener to the obtained high molecular weight aqueous polyurethane emulsion, stir for 30min at room temperature and a mechanical stirring speed of 250r / min to obtain a thickened high molecular weight aqueous polyurethane emulsion; S3: The thickened high molecular weight aqueous polyurethane emulsion obtained in S2 is coated on the surface of the release film at a coating thickness of 0.2 mm, and completely immersed in a 10 wt % citric acid aqueous solution for 10 seconds to solidify into a film, and then the film is peeled off from the surface of the release film, washed with deionized water for 5 minutes, and then dried at 120°C for 20 minutes to obtain a water-based polyurethane microporous membrane.

[0025] The aqueous polyurethane microporous membrane prepared in this example exhibits an asymmetric pore structure, with finger-shaped pores accounting for the majority, small surface pores, most of which are distributed in the range of 300 to 700 nm, and large cavity structures partially existing inside the membrane.

[0026] Embodiment 5: This embodiment provides a method for preparing a waterborne polyurethane microporous membrane by flocculation, which is carried out according to the following steps: S1: 15 g of polypropylene glycol with an average molecular weight of 1000 and 30 g of polypropylene glycol with an average molecular weight of 2000 are added to a three-necked flask, and vacuum dehydration is performed for 1 hour at an oil bath temperature of 120° C. and a mechanical stirring speed of 165 r / min to obtain the polypropylene glycol after vacuum dehydration; a mixture of 18.5 g of isophorone diisocyanate, 3.36 g of dimethylol propionic acid and 0.02 g of dibutyltin dilaurate is added to the obtained polypropylene glycol after vacuum dehydration, and then reacted at an oil bath temperature of 95° C. and a mechanical stirring speed of 165 r / min until the NCO content of the system is 1.6 wt % to obtain a polyurethane prepolymer; S2: Add 15g of acetone to the polyurethane prepolymer obtained in S1, then add 2.37g of triethylamine, react for 30min at an oil bath temperature of 50°C and a mechanical stirring speed of 165r / min, then add 145g of deionized water, and high-speed disperse and emulsify for 30min at an oil bath temperature of 50°C and a mechanical stirring speed of 1000r / min to obtain an aqueous polyurethane emulsion; add 1.35g of ethylenediamine to the obtained aqueous polyurethane emulsion, react for 1h at an oil bath temperature of 40°C and a mechanical stirring speed of 150r / min to obtain a high molecular weight aqueous polyurethane. emulsion; add 2.29g of associative thickener to the obtained high molecular weight waterborne polyurethane emulsion, stir for 30min at room temperature and a mechanical stirring speed of 250r / min to obtain a thickened high molecular weight waterborne polyurethane emulsion; S3: apply the thickened high molecular weight waterborne polyurethane emulsion obtained in S2 on the surface of the release film at a coating thickness of 0.2mm, completely immerse it in a 10wt% citric acid aqueous solution for 10s to solidify into a film, then peel off the film from the surface of the release film, wash with deionized water for 5min, and then dry it at 120℃ for 20min to obtain a waterborne polyurethane microporous membrane.

[0027] The aqueous polyurethane microporous membrane prepared in this example exhibits an asymmetric pore structure, with finger-like pores accounting for the majority, small surface pores, most of which are distributed in the range of 100 to 300 nm, and large cavity structures partially existing inside the membrane.

[0028] Embodiment 6: This embodiment provides a method for preparing a waterborne polyurethane microporous membrane by flocculation, which is carried out according to the following steps: S1: 4 g of polypropylene glycol with an average molecular weight of 1000 and 27.13 g of polypropylene glycol with an average molecular weight of 2000 are added to a three-necked flask, and vacuum dehydration is performed for 1 hour under the conditions of an oil bath temperature of 120° C. and a mechanical stirring speed of 165 r / min to obtain the polypropylene glycol after vacuum dehydration; a mixture of 11.05 g of isophorone diisocyanate, 3.25 g of dimethylolpropionic acid and 0.02 g of dibutyltin dilaurate is added to the obtained polypropylene glycol after vacuum dehydration, and then reacted under the conditions of an oil bath temperature of 95° C. and a mechanical stirring speed of 165 r / min until the NCO content of the system is 1.6 wt % to obtain a polyurethane prepolymer; S2: Add 9.19g acetone to the polyurethane prepolymer obtained in S1, then add 2.33g triethylamine, react for 30min at an oil bath temperature of 50°C and a mechanical stirring speed of 165r / min, then add 97.5g deionized water, high-speed disperse and emulsify for 30min at an oil bath temperature of 50°C and a mechanical stirring speed of 1000r / min to obtain an aqueous polyurethane emulsion; add 1.17g ethylenediamine to the obtained aqueous polyurethane emulsion, react for 1h at an oil bath temperature of 40°C and a mechanical stirring speed of 150r / min to obtain a high molecular weight aqueous polyurethane. ester emulsion; add 1.54g of associative thickener to the obtained high molecular weight aqueous polyurethane emulsion, stir for 30min at room temperature and a mechanical stirring speed of 250r / min to obtain a thickened high molecular weight aqueous polyurethane emulsion; S3: apply the thickened high molecular weight aqueous polyurethane emulsion obtained in S2 on the surface of the release film at a coating thickness of 0.2mm, completely immerse it in a 3wt% citric acid aqueous solution for 10s to solidify into a film, then peel off the film from the surface of the release film, wash with deionized water for 5min, and then dry it at 120℃ for 20min to obtain a water-based polyurethane microporous membrane.

[0029] The aqueous polyurethane microporous membrane prepared in this example exhibits an asymmetric pore structure, with finger-shaped pores accounting for the majority, small surface pores, most of which are distributed in the range of 400 to 800 nm, and large cavity structures partially existing inside the membrane.

[0030] Embodiment 7: This embodiment provides a method for preparing a waterborne polyurethane microporous membrane by flocculation, which is carried out according to the following steps: S1: 4 g of polypropylene glycol with an average molecular weight of 1000 and 27.13 g of polypropylene glycol with an average molecular weight of 2000 are added to a three-necked flask, and vacuum dehydration is performed for 1 hour under the conditions of an oil bath temperature of 120° C. and a mechanical stirring speed of 165 r / min to obtain the polypropylene glycol after vacuum dehydration; a mixture of 11.05 g of isophorone diisocyanate, 3.25 g of dimethylolpropionic acid and 0.02 g of dibutyltin dilaurate is added to the obtained polypropylene glycol after vacuum dehydration, and then reacted under the conditions of an oil bath temperature of 95° C. and a mechanical stirring speed of 165 r / min until the NCO content of the system is 1.6 wt % to obtain a polyurethane prepolymer; S2: Add 9.19g acetone to the polyurethane prepolymer obtained in S1, then add 2.33g triethylamine, react for 30min at an oil bath temperature of 50°C and a mechanical stirring speed of 165r / min, then add 97.5g deionized water, high-speed disperse and emulsify for 30min at an oil bath temperature of 50°C and a mechanical stirring speed of 1000r / min to obtain an aqueous polyurethane emulsion; add 1.17g ethylenediamine to the obtained aqueous polyurethane emulsion, react for 1h at an oil bath temperature of 40°C and a mechanical stirring speed of 150r / min to obtain a high molecular weight aqueous polyurethane. ester emulsion; add 1.54g of associative thickener to the obtained high molecular weight waterborne polyurethane emulsion, stir for 30min at room temperature and a mechanical stirring speed of 250r / min to obtain a thickened high molecular weight waterborne polyurethane emulsion; S3: apply the thickened high molecular weight waterborne polyurethane emulsion obtained in S2 on the surface of the release film at a coating thickness of 0.2mm, completely immerse it in a 10wt% citric acid aqueous solution for 60s to solidify into a film, then peel off the film from the surface of the release film, wash with deionized water for 5min, and then dry it at 120℃ for 20min to obtain a waterborne polyurethane microporous membrane.

[0031] The aqueous polyurethane microporous membrane prepared in this example exhibits an asymmetric pore structure, with finger-shaped pores accounting for the majority, a relatively small surface pore size, most of which are distributed in the range of 350 to 600 nm, and a large cavity structure partially existing inside the membrane.

[0032] Figure 1 This is the infrared spectrum of the high molecular weight waterborne polyurethane prepared in Example 1. Figure 2 This is a diagram of the mechanical properties of the waterborne polyurethane microporous membrane prepared in Example 1. Figure 3 This is a scanning electron microscope surface image of the waterborne polyurethane microporous membrane prepared in Example 1. Figure 4 This is a scanning electron microscope cross-sectional image of the waterborne polyurethane microporous membrane prepared in Example 1.

[0033] Table 1 shows the parameters and performance characterization results of the waterborne polyurethane microporous membranes prepared in Examples 1 to 7. It can be seen from the results shown in Table 1 that with the decrease of dimethylolpropionic acid content, the decrease of coagulation bath concentration, and the increase of coagulation time, the pore size of the waterborne polyurethane microporous membrane will increase. Conversely, the pore size of the waterborne polyurethane microporous membrane will decrease.

[0034] Table 1 Parameters and performance characterization results of waterborne polyurethane microporous membranes prepared in Examples 1-7 project Dimethylolpropionic acid content / g Coagulation bath concentration / % Solidification time / s Pore ​​size distribution / nm Example 1 3.25 10 10 100～350 Example 2 3 10 10 100～450 Example 3 3.65 10 10 100～300 Example 4 2.75 10 10 300～700 Example 5 3.36 10 10 100～300 Example 6 3.25 3 10 400～800 Example 7 3.25 10 60 350～600 It should be noted that, although the above-mentioned examples have been described in this article, the patent protection scope of the present invention is not limited thereby. Therefore, based on the innovative concept of the present invention, changes and modifications made to the embodiments described herein, or equivalent structures or equivalent process changes made using the contents of the present invention specification, directly or indirectly applying the above technical solutions to other related technical fields are all included in the patent protection scope of the present invention.

Claims

1. A method for preparing a waterborne polyurethane microporous membrane by flocculation, characterized in that: The following steps are involved: S1: adding a diol to a three-necked flask, and removing water in a vacuum manner to obtain a diol after vacuum removal of water; adding a mixture of a diisocyanate, a hydrophilic chain extender, and a catalyst to the obtained diol after vacuum removal of water, and performing a prepolymerization reaction to obtain a polyurethane prepolymer; S2: adding acetone and a neutralizing agent to the polyurethane prepolymer obtained in S1 in sequence to carry out a neutralization reaction, and then adding deionized water to disperse and emulsify at a high speed to obtain an aqueous polyurethane emulsion; adding a post-chain extender to the aqueous polyurethane emulsion to carry out a post-chain extension reaction to obtain a high molecular weight aqueous polyurethane emulsion; adding a thickener to the aqueous polyurethane emulsion to carry out a thickening reaction to obtain a thickened high molecular weight aqueous polyurethane emulsion; S3: coating the thickened high molecular weight aqueous polyurethane emulsion obtained in S2 on the surface of the release film, immersing it in an aqueous flocculant solution to solidify it into a film, and then peeling the film from the surface of the release film, washing it, and drying it to obtain an aqueous polyurethane microporous membrane.

2. The method according to claim 1, characterized in that: In step S1, the diol is one or more of polyethylene glycol, polypropylene glycol, polybutylene glycol, polyethylene adipate, polycarbonate diol, and adipic acid-tetramethylene glycol polyester; the hydrophilic chain extender is one or more of dimethylol propionic acid, dimethylol butyric acid, and ethylenediaminohexanesulfonic acid sodium salt aqueous solution; the diisocyanate is one or more of toluene diisocyanate, diphenylmethane diisocyanate, isophorone diisocyanate, and hexamethylene diisocyanate; and the catalyst is dibutyltin dilaurate.

3. The method according to claim 1, characterized in that: In step S1, the weight ratio of the diol to the diisocyanate is 1.5:1-6:1; the weight of the hydrophilic chain extender accounts for 0.3%-8% of the sum of the weights of the diol and the diisocyanate; the weight of the catalyst accounts for 0.2% of the sum of the weights of the diol and the diisocyanate; and the conditions of the prepolymerization reaction are: reacting at a temperature of 85-95°C until the NCO content of the system is 1.2wt%-1.6wt%.

4. The method according to claim 1, characterized in that: In step S2, the neutralizing agent is triethylamine; the post-chain extender is one or more of ethylenediamine and isophordiamine; and the thickener is an associative thickener.

5. The method according to claim 1, characterized in that: In step S2, the weight of the acetone accounts for 15% to 35% of the total weight of the diol and the diisocyanate; the weight of the neutralizer accounts for 65% to 78% of the weight of the hydrophilic chain extender; the weight of the deionized water accounts for 150% to 200% of the weight of the prepolymer; the weight of the post-chain extender accounts for 0.1% to 5% of the total weight of the diol and the diisocyanate; the weight of the thickener accounts for 0.5% to 2% of the weight of the aqueous polyurethane emulsion; the conditions of the neutralization reaction are: reacting at a temperature of 30 to 50° C. for 0.5 h; the conditions of the post-chain extension reaction are: reacting at a temperature of 40 to 50° C. for 1 to 1.5 h.

6. The method according to claim 1, characterized in that: In step S3, the flocculant is one or more of oxalic acid, tartaric acid, and citric acid; and the concentration of the flocculant aqueous solution is 3wt% to 20wt%.

7. The method according to claim 1, characterized in that: In step S3, the coating thickness of the thickened high molecular weight aqueous polyurethane emulsion is 0.05-0.5 mm; and the immersion time is 5 s-1 min.

8. A waterborne polyurethane microporous membrane, characterized in that: Prepared by the method according to any one of claims 1 to 7.

9. Use of the aqueous polyurethane microporous membrane as claimed in claim 8 in the field of microporous membrane materials.

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