Colorless, transparent and uvioresistant waterborne polyurethane film based on bio-based material and preparation method of colorless, transparent and uvioresistant waterborne polyurethane film

Abstract

The invention discloses a colorless, transparent and anti-ultraviolet waterborne polyurethane film based on a bio-based material and a preparation method of the colorless, transparent and anti-ultraviolet waterborne polyurethane film, and belongs to the technical field of polyurethane resin.The preparation method comprises the steps of preparing a compound 1, preparing a compound 2, preparing waterborne polyurethane emulsion and forming the film. In the preparation of the compound 1, a bio-based material methyl syringate is used, the compound 1 is used as a raw material and is subjected to a click chemical reaction with mercaptan to generate a compound 2, and then the compound 2 is used as a raw material to prepare the waterborne polyurethane emulsion. The preparation method disclosed by the invention can ensure that the waterborne polyurethane film has resistance to 275nm ultraviolet rays under the condition of being colorless and transparent, and a feasible method is provided for preparing a polyurethane material with ultraviolet shielding capability; the prepared waterborne polyurethane film can be used as an ultraviolet light shielding material to be applied to various fields with requirements on visible light and attractiveness, such as protection, wearable products and the like.

Description

Technical Field

[0001] This invention belongs to the field of polyurethane resin technology, and relates to a colorless, transparent, UV-resistant waterborne polyurethane membrane based on bio-based materials and its preparation method. Background Technology

[0002] With the depletion of the Earth's ozone layer, more and more ultraviolet (UV) radiation reaches the Earth's surface, especially in high-altitude areas. Excessive UV exposure can cause significant harm to human production and daily life. UV radiation also causes adverse effects such as food spoilage, paper yellowing, and plastic aging. Therefore, UV-resistant materials are used in medical protection, daily chemical products, building materials, and food packaging. Polyurethane (PU) elastomer is a linear polymer material with oligomeric polyols as soft segments and polyisocyanates and small-molecule polyols as hard segments. Compared with traditional UV protection materials, PU has been widely used in various industrial and daily life sectors due to its diverse formulations and excellent performance. However, prolonged UV exposure can cause PU to yellow, crack, blister, and peel, shortening its lifespan. Therefore, researching ways to improve the UV resistance of PU is of great significance.

[0003] There are three common methods to improve the UV resistance of polyurethane (PU): adding non-reactive UV-resistant additives, adding UV-resistant nanofillers, and using bio-based antioxidant molecules as reactants. Non-reactive UV-resistant additives can capture active free radicals generated during the UV aging process of polymers, thereby improving the UV resistance of PU. However, non-reactive UV-resistant additives in PU composites exist in free form and may migrate during long-term use, severely affecting the stability and mechanical properties of the composite. UV-resistant nanofillers include TiO2 and ZnO. These nanofillers can absorb UV energy by transitioning internal electrons from the valence band to the conduction band, converting it into other forms of energy with lower energy levels, thus absorbing and shielding UV rays. However, the addition of functional fillers may damage the mechanical properties of the composite and significantly reduce the transmittance in the visible light range, thus limiting its application range. Lignin, curcumin, quercetin and other bio-based antioxidant molecules contain ultraviolet-absorbing functional groups such as phenols, ketones, and conjugated double bonds, as well as other chromophores. Adding plant-derived antioxidant molecules to PU can improve its UV resistance and mechanical strength. However, these bio-based antioxidant molecules are usually colored, which will inevitably lead to the coloring of PU composite materials, thus limiting their application.

[0004] Existing technologies also disclose the use of 2,2'-dihydroxy-4-methoxybenzophenone (DHMB) as a chain extender to prepare a series of intrinsically UV-resistant polyurethanes. However, the addition of DHMB reduces the mechanical properties of the PU, and the prepared PU film is yellowish-brown, limiting the application of the PU. Therefore, the preparation of high-strength, colorless, transparent, non-migrating UV-resistant PU is very important for practical applications. Summary of the Invention

[0005] To address the aforementioned issues, this invention provides a colorless, transparent, and UV-resistant aqueous polyurethane film based on bio-based materials and its preparation method. This method ensures that the aqueous polyurethane film is colorless and transparent while resisting 275nm ultraviolet radiation, providing a feasible method for preparing polyurethane materials with UV shielding capabilities. The prepared aqueous polyurethane film can be used as a UV shielding material in various fields requiring both visible light and aesthetics, such as protective applications and wearable products.

[0006] To solve the above technical problems, the technical solution adopted by the present invention is as follows: A method for preparing a colorless, transparent, UV-resistant aqueous polyurethane membrane based on bio-based materials includes: preparing compound 1, preparing compound 2, preparing an aqueous polyurethane emulsion, and forming a film; To prepare compound 1, methyl eugenol and an organic solvent were mixed and stirred, a neutralizing agent was added, and the mixture was reacted in an ice bath. Methacryl chloride was then added, and the mixture was reacted at room temperature to obtain a mixture. The mixture was washed, dehydrated, and the solvent was removed to obtain compound 1. In the preparation of compound 1, the ratio of methyl eugenol to organic solvent is 9-11 g: 35-45 mL; The ratio of methyl eugenol to neutralizing agent is 9-11g:8-12g; The ratio of methyl eugenol to methacryl chloride is 9-11 g: 9-15 mL; The organic solvent is dichloromethane; The neutralizing agent is triethylamine; The ice bath reaction time is 15-30 minutes; Methacrylamide chloride is added dropwise over a period of 2-2.5 hours, and the reaction system is kept in an ice bath during the addition. The reaction time at room temperature is 23-25 ​​hours. The washing process involves repeated washing with a mixture of dichloromethane and water until the pH of the upper liquid is neutral, at which point the lower liquid is removed. In the washing process, the volume ratio of dichloromethane to water used in each wash is 1:1; The ratio of dichloromethane to methyl eugenol used in each wash is 250 mL: 9-11 g; The dehydrating agent used in the dehydration process is anhydrous magnesium sulfate. The solvent is removed by rotary evaporation. The structural formula of compound 1 is:

[0007] To prepare compound 2, under a nitrogen atmosphere, compound 1 is mixed with an organic solvent, and then bubbled once at room temperature. A thiol and a free radical initiator are added, and the mixture is bubbled a second time at room temperature. Then, the mixture is stirred and reacted under a nitrogen atmosphere at 60-90°C to obtain a mixed solution. The mixed solution is concentrated, the concentrated solution is precipitated, and the precipitate is dried to obtain compound 2. In the preparation of compound 2, the ratio of compound 1 to organic solvent is 9-11g:50-70mL; The ratio of compound 1 to thiol is 9-11 g: 140-170 mg; The ratio of compound 1 to free radical initiator is 9-11g:310-400mg; The organic solvent is tetrahydrofuran; The free radical initiator is azobisisobutyronitrile; The thiol is one of 3-mercapto-1,2-propanediol, mercaptoethanol, and mercaptosuccinic acid; The duration of each bubbling cycle is 30-40 minutes. The secondary bubbling time is 2-3 minutes; The reaction time when stirred at 55-65℃ is 20-24h. The concentration is achieved by rotary evaporation. The precipitate is obtained by adding the concentrated liquid to a cold solvent to precipitate, and then taking the bottom viscous polymer for filtration. In the precipitate, the cold solvent is anhydrous diethyl ether or n-hexane; The temperature of the cold solvent is -25°C to 0°C; The structural formula of compound 2 is:

[0008] The preparation of the waterborne polyurethane emulsion involves mixing a dry polyol, isocyanate, and compound 2, preheating the mixture at 68-72°C, then raising the reaction temperature to 78-86°C, adding a catalyst, and conducting a first reaction at 78-86°C. A chain extender is then added, and a second reaction is conducted at 78-86°C. Solvent 1 is used to adjust the viscosity during the second reaction. A neutralizing agent is then added, and a third reaction is conducted at 78-86°C. Solvent 2 is used to adjust the viscosity during the third reaction to obtain a polyurethane prepolymer. The polyurethane prepolymer is dispersed in deionized water, sheared, and aged to obtain the waterborne polyurethane emulsion. In the preparation of the aqueous polyurethane emulsion, the ratio of dried polyol to isocyanate is 45.5-49.5g:15-18g. The dosage ratio of compound 2 is 45.5-49.5g:0.5-4.5g; The ratio of dried polyol to catalyst is 45.5-49.5 g: 0.04-0.06 g; The ratio of dried polyol to chain extender is 45.5-49.5g:4.2-4.6g; The ratio of dried polyol to neutralizing agent is 45.5-49.5 g: 3.3-3.4; The polyol is one or more of the following: polypropylene glycol, polytetrahydrofuran ether glycol, polyethylene adipate glycol, poly(ε-caprolactone) glycol, acrylate polyol, and polycarbonate polyol. Preferably, the polyol is polytetrahydrofuran ether diol with a number average molecular weight of 2000 g / mol; The isocyanate is an aliphatic isocyanate or an aromatic isocyanate; Preferably, the isocyanate is isophorone diisocyanate; The catalyst is one or more of the following: organic bismuth catalyst, dibutyltin dilaurate, and stannous octoate. Preferably, the catalyst is bismuth lauryl precipitate, an organobismuth catalyst. The chain extender is one or more of 2,2-dimethylolpropionic acid, 2,2-dihydroxybutyric acid, and 1,4-butanediol; Solvent 1 is N-methylpyrrolidone; The neutralizing agent is one or more of triethylamine, tripropylamine, triethanolamine, and ammonia. Solvent 2 is one of acetone, butanone, and N-methylpyrrolidone; The method for preparing the dried polyol is to dehydrate the polyol under vacuum at 100°C for 23-25 ​​hours. The preheating time at 68-72℃ is 15-30 minutes. The heating rate when the reaction temperature is raised to 78-86℃ is 9-11℃ / min; The reaction time is 2-3 hours when carried out at 78-86℃. The time for the secondary reaction at 78-86℃ is 3-4 hours. The reaction time for three cycles at 78-86℃ is 15-20 minutes. When using solvent 1 to adjust the viscosity, first react for 30-50 minutes, then add the first portion of solvent 1 and react for 60-80 minutes, then add the second portion of solvent 2 and react for 90-110 minutes. The ratio of the dried polyol to the first solvent 1 and the second solvent 2 is 45.5-49.5g:5-5.5mL:4-4.5mL; When using solvent 2 to adjust the viscosity, add solvent 2 at the beginning of the third reaction. The ratio of dried polyol to solvent 2 is 45.5-49.5 g: 4-5 mL; The ratio of dried polyol to deionized water is 45.5-49.5g:140-150g; The shearing rate is 1000-2000 rpm, and the time is 30-60 min; The ripening process involves allowing the food to stand at room temperature for 3-5 days. The film formation involves preparing an aqueous polyurethane film from an aqueous polyurethane emulsion.

[0009] An aqueous polyurethane membrane prepared by the aforementioned preparation method.

[0010] The beneficial effects of this invention are as follows: (1) The waterborne polyurethane membrane of the present invention is prepared based on the bio-based material methyl eugenol. It can achieve colorless, transparent and UV resistant properties, and can also effectively reduce the use of petrochemical resources. It can utilize renewable resources and is a promising preparation method. (2) The waterborne polyurethane film of the present invention has high transparency, with a transmittance of 71-97.76% in the visible light range; (3) The waterborne polyurethane film of the present invention has good UV resistance, with a transmittance of 0.3-26.1% for 275nm ultraviolet light; (4) The waterborne polyurethane membrane made by the waterborne polyurethane of the present invention has high tensile strength and good toughness. The film breaking strength of the waterborne polyurethane membrane is 4.9-26.0 MPa and the elongation at break is 1319-2060%. Attached Figure Description

[0011] Figure 1This is the synthesis route diagram corresponding to Example 1; Figure 2 The 1H NMR spectrum of compound 1 prepared in Example 1; Figure 3 This is the synthesis route diagram corresponding to Example 2; Figure 4 The 1H NMR spectrum of compound 2 prepared in Example 2; Figure 5 This is the synthesis route diagram corresponding to Example 3; Figure 6 The transmittance curves of the aqueous polyurethane films made from the aqueous polyurethane emulsions of Examples 3-6 under different wavelengths of light are shown. Figure 7 The tensile strain-tensile stress curves are shown for waterborne polyurethane films made from the waterborne polyurethane emulsions of Examples 3-6. Detailed Implementation

[0012] The present invention will now be described in detail with reference to the above technical route and accompanying drawings. This description is only intended to illustrate the invention and is not intended to limit the scope of protection of the invention. Any non-essential improvements and adjustments made to the invention by those skilled in the art based on the above description are still within the scope of protection of the present invention.

[0013] The test method for the tensile strength and elongation at break of the aqueous polyurethane emulsion prepared in the embodiment after film formation is as follows: The aqueous polyurethane film formed after curing of the aqueous polyurethane emulsion is cut into dumbbell-shaped samples with a gauge length of 15 mm and a width of 2 mm using a dumbbell-shaped die cutter. The thickness of the sample at three points is measured with a thickness gauge, and the average value is taken. The sample is clamped on a tensile testing machine, and the sample thickness and original length (L0) are input. Then, a tensile test is performed. The tensile test is carried out at a constant speed of 100 mm / min at room temperature. The tensile strength and elongation at break of the film are tested by the tensile test. The elongation at break is the ratio of the length elongated from the start of the stretching to the original length of the sample. The elongation at break is represented by E1, E1=[(L1-L0) / L0]×100%. The tensile strength value can be directly read from the tensile testing machine.

[0014] Example 1 Preparation of compound 1 according to Figure 1The synthetic route involved adding 10.96 g of methyl eugenol and 40 mL of dichloromethane to a 250 mL round-bottom flask and stirring. Then, 10.45 g of triethylamine (TEA) was added, and the mixture was placed in an ice bath for 15 min. Next, 10 mL of methacryloyl chloride was added dropwise using a constant-pressure dropping funnel over a period of 2 h. After the addition was complete, the reaction continued at room temperature for 24 h to obtain a mixture. This mixture was then poured directly into a large beaker containing water and dichloromethane for repeated washing. Each wash used 250 mL of dichloromethane and 250 mL of water. The washing continued until the pH of the upper layer was neutral. The lower layer was then collected, and excess water was removed using anhydrous magnesium sulfate. Dichloromethane was then removed by rotary evaporation to obtain a white solid powder, which was compound 1. A total of 12.04 g of compound 1 was obtained.

[0015] The structural formula of compound 1 is as follows:

[0016] Nuclear magnetic resonance (NMR) analysis was performed on compound 1, and the resulting proton NMR spectrum is shown below. Figure 2 .

[0017] Example 2 Preparation of compound 2 according to Figure 3 The synthetic route was as follows: Under nitrogen atmosphere, 10g of Compound 1 prepared in Example 1 and 60mL of tetrahydrofuran solution were added to a 250mL round-bottom flask and stirred. The mixture was bubbled at room temperature for 30min, then 154mg of 3-mercapto-1,2-propanediol and 351mg of azobisisobutyronitrile were added, and the mixture was bubbled at room temperature for another 2min. The reaction was then transferred to an oil bath and stirred at 60℃ for 24h under nitrogen atmosphere to obtain a mixture. The mixture was concentrated using a rotary evaporator and precipitated in cold anhydrous diethyl ether (-20℃). The supernatant was discarded, and the viscous polymer at the bottom was filtered to remove excess solvent. The polymer was then dried in a vacuum dryer for 12h to obtain a white solid powder, which was the thiol-modified polymer, namely Compound 2. The structural formula of Compound 2 is as follows:

[0018] Nuclear magnetic resonance (NMR) analysis was performed on compound 2, and the resulting proton NMR spectrum is shown below. Figure 4 .

[0019] Example 3: Preparation of waterborne polyurethane membrane according to Figure 5The synthetic route involved dehydrating polytetrahydrofuran ether diol (Mn = 2000 g / mol) under vacuum at 100 °C for 24 h to obtain dried polytetrahydrofuran ether diol (PT-2000). 47.50 g of dried PT-2000, 16.63 g of isophorone diisocyanate (IPDI), and 2.5 g of compound 2 prepared in Example 2 were added to a 250 mL three-necked round-bottom flask equipped with a mechanical stirrer and stirred. The mixture was heated to 70 °C and preheated at 70 °C for 30 min. The reaction temperature was then increased to 86 °C at a rate of 10 °C / min. 0.05 g of bismuth laurate was added, and the reaction was continued for 2.5 h to obtain a prepolymer with isocyanate end groups of a certain viscosity. Then, 4.4 g of 2,2-dimethylolpropionic acid (DMPA) was added to the reaction system, and the reaction was continued for 30 min. 5 mL of N-methylpyrrolidone (NMP) was added, and the reaction was continued for 1 h. Finally, 4 mL of [the remaining mixture] was added... N-methylpyrrolidone (NMP) was reacted for 1.5 h. The reaction system was then cooled to 55 °C, and 3.34 g of triethylamine (TEA) was added for neutralization. 4 mL of acetone was added to reduce viscosity, and the reaction was continued for 20 min to obtain a polyurethane prepolymer. The polyurethane prepolymer was directly dispersed in 142 g of deionized water and dispersed for 30 min at a shear rate of 1500 rpm. The mixture was then allowed to mature at room temperature for 3 days to obtain an aqueous polyurethane emulsion. The aqueous polyurethane emulsion was then used to prepare a 300 μm thick membrane to obtain an aqueous polyurethane membrane.

[0020] This embodiment also provides an aqueous polyurethane membrane prepared by the aforementioned preparation method.

[0021] The waterborne polyurethane film obtained in this embodiment has a tensile strength of 18.43 MPa and an elongation at break of 1618%.

[0022] The aqueous polyurethane film obtained in this embodiment has a transmittance of 77% for visible light and a transmittance of 0.3% for 275nm ultraviolet light.

[0023] Example 4: Preparation of waterborne polyurethane membrane The same method as in Example 3 was used, except that compound 2 was not added and was replaced with an equal mass of dried PT-2000 (Mn=2000g / mol) to investigate the effect of bio-based materials on the UV resistance of waterborne polyurethane.

[0024] The waterborne polyurethane film obtained in this embodiment has a film tensile strength of 45 MPa and an elongation at break of 1287%. Compared with Example 3, the elongation at break is lower and the tensile strength is higher. It is inferred that this is because the reduction of flexible chain segments leads to an increase in rigidity, which in turn increases its tensile strength.

[0025] The aqueous polyurethane film obtained in this embodiment has a transmittance of 99.7% for visible light and 88.2% for 275nm ultraviolet light. It is inferred that compound 2, synthesized from bio-based methyl eugenol as the starting material, endows the polyurethane with UV resistance.

[0026] Example 5: Preparation of waterborne polyurethane membrane The same method as in Example 3 was used, except that the mass of compound 2 in Example 3 was reduced to 0.5 g, the mass of dried PT-2000 was increased to 49.5 g, and other raw materials remained unchanged. The purpose was to investigate the effect of changing the proportion of polyol added on the waterborne polyurethane resin.

[0027] The waterborne polyurethane film obtained in this embodiment has a film tensile strength of 26.0 MPa and an elongation at break of 1319%. Compared with Example 3, the elongation at break is lower and the tensile strength is higher. It is inferred that this may be because the reduction of flexible chain segments leads to an increase in rigidity, which in turn increases its tensile strength.

[0028] The aqueous polyurethane film obtained in this embodiment has a transmittance of 97.76% for visible light and 26.1% for 275nm ultraviolet light. Compared with Example 3, the blocking effect on 275nm ultraviolet light is smaller, which is inferred to be due to the lower content of compound 2.

[0029] Example 6: Preparation of waterborne polyurethane membrane The same method as in Example 3 was used, except that the mass of compound 2 in Example 3 was increased to 4.5 g, the mass of polytetrahydrofuran ether diol was reduced to 45.5 g, and other raw materials remained unchanged. The purpose was to investigate the effect of changing the proportion of polyol added on waterborne polyurethane resin.

[0030] The waterborne polyurethane film obtained in this embodiment has a film tensile strength of 4.9 MPa and an elongation at break of 2060%. Compared with Example 3, the elongation at break increases while the tensile strength decreases. It is inferred that this may be because the increase in the proportion of compound 2 leads to an increase in the flexible chain segment, which in turn increases the elongation at break.

[0031] The aqueous polyurethane film obtained in this embodiment has a transmittance of 71% for visible light and 0% for 275nm ultraviolet light.

[0032] The transmittance of the aqueous polyurethane films of Examples 2-6 under different wavelengths of light was tested, and curves were plotted with wavelength as the abscissa and transmittance as the ordinate. The obtained curves are shown in the figure. Figure 6 ; The tensile stress of the waterborne polyurethane membranes of Examples 2-6 under different tensile strains was tested, and curves were plotted with tensile strain as the abscissa and tensile stress as the ordinate. The obtained curves are shown in the figure. Figure 7 .

Claims

1. A method for preparing a colorless, transparent, UV-resistant waterborne polyurethane membrane based on bio-based materials, characterized in that, include: Prepare compound 1, prepare compound 2, prepare aqueous polyurethane emulsion, and form a film; To prepare compound 2, under a nitrogen atmosphere, compound 1 is mixed with an organic solvent, and then bubbled once at room temperature. A thiol and a free radical initiator are added, and the mixture is bubbled a second time at room temperature. Then, the mixture is stirred and reacted under a nitrogen atmosphere at 60-90°C to obtain a mixed solution. The mixed solution is concentrated, the concentrated solution is precipitated, and the precipitate is dried to obtain compound 2. The structural formula of compound 1 is: ； The structural formula of compound 2 is: ； The preparation of the waterborne polyurethane emulsion involves mixing a dry polyol, isocyanate, and compound 2, preheating the mixture at 68-72°C, then raising the reaction temperature to 78-86°C, adding a catalyst, and conducting a first reaction at 78-86°C. A chain extender is then added, and a second reaction is conducted at 78-86°C. Solvent 1 is used to adjust the viscosity during the second reaction. A neutralizing agent is then added, and a third reaction is conducted at 78-86°C. Solvent 2 is used to adjust the viscosity during the third reaction to obtain a polyurethane prepolymer. The polyurethane prepolymer is dispersed in deionized water, sheared, and aged to obtain the waterborne polyurethane emulsion.

2. The method for preparing a colorless, transparent, UV-resistant aqueous polyurethane membrane based on bio-based materials according to claim 1, characterized in that, To prepare compound 1, methyl eugenol and an organic solvent were mixed and stirred, a neutralizing agent was added, and the mixture was reacted in an ice bath. Methacryl chloride was then added, and the mixture was reacted at room temperature to obtain a mixture. The mixture was then washed, dehydrated, and the solvent was removed to obtain compound 1.

3. The method for preparing a colorless, transparent, UV-resistant aqueous polyurethane membrane based on bio-based materials according to claim 2, characterized in that, In the preparation of compound 1, the ratio of methyl eugenol to organic solvent is 9-11 g: 35-45 mL; The ratio of methyl eugenol to neutralizing agent is 9-11g:8-12g; The ratio of methyl eugenol to methacryl chloride is 9-11 g: 9-15 mL; The organic solvent is dichloromethane; The neutralizing agent is triethylamine.

4. The method for preparing a colorless, transparent, UV-resistant aqueous polyurethane membrane based on bio-based materials according to claim 2, characterized in that, In the preparation of compound 1, the ice bath reaction time is 15-30 min; Methacrylamide chloride is added dropwise over a period of 2-2.5 hours, and the reaction system is kept in an ice bath during the addition. The reaction time at room temperature is 23-25 ​​hours. The washing process involves repeated washing with a mixture of dichloromethane and water until the pH of the upper liquid is neutral, at which point the lower liquid is removed. In the washing process, the volume ratio of dichloromethane to water used in each wash is 1:1; The ratio of dichloromethane to methyl eugenol used in each wash is 250 mL: 9-11 g; The dehydrating agent used in the dehydration process is anhydrous magnesium sulfate. The solvent is removed by rotary evaporation.

5. The method for preparing a colorless, transparent, UV-resistant aqueous polyurethane membrane based on bio-based materials according to claim 1, characterized in that, In the preparation of compound 2, the ratio of compound 1 to organic solvent is 9-11g:50-70mL; The ratio of compound 1 to thiol is 9-11 g: 140-170 mg; The ratio of compound 1 to free radical initiator is 9-11g:310-400mg; The organic solvent is tetrahydrofuran; The free radical initiator is azobisisobutyronitrile; The thiol is one of 3-mercapto-1,2-propanediol, mercaptoethanol, and mercaptosuccinic acid.

6. The method for preparing a colorless, transparent, UV-resistant aqueous polyurethane membrane based on bio-based materials according to claim 5, characterized in that, In the preparation of compound 2, the time for one bubbling step is 30-40 minutes; The secondary bubbling time is 2-3 minutes; The reaction time when stirred at 55-65℃ is 20-24h. The concentration is achieved by rotary evaporation. The precipitate is obtained by adding the concentrated liquid to a cold solvent to precipitate, and then taking the bottom viscous polymer for filtration. In the precipitate, the cold solvent is anhydrous diethyl ether or n-hexane; The temperature of the cold solvent is -25°C to 0°C.

7. The method for preparing a colorless, transparent, UV-resistant aqueous polyurethane membrane based on bio-based materials according to claim 1, characterized in that, In the preparation of the aqueous polyurethane emulsion, the ratio of dried polyol to isocyanate is 45.5-49.5g:15-18g. The dosage ratio of compound 2 is 45.5-49.5g:0.5-4.5g; The ratio of dried polyol to catalyst is 45.5-49.5 g: 0.04-0.06 g; The ratio of dried polyol to chain extender is 45.5-49.5g:4.2-4.6g; The ratio of dried polyol to neutralizing agent is 45.5-49.5 g: 3.3-3.4; In the preparation of the aqueous polyurethane emulsion, the polyol is one or more selected from polypropylene glycol, polytetrahydrofuran ether glycol, polyethylene adipate, poly(ε-caprolactone) glycol, acrylate polyol, and polycarbonate polyol. The isocyanate is an aliphatic isocyanate or an aromatic isocyanate; The catalyst is one or more of the following: organic bismuth catalyst, dibutyltin dilaurate, and stannous octoate. The chain extender is one or more of 2,2-dimethylolpropionic acid, 2,2-dihydroxybutyric acid, and 1,4-butanediol; Solvent 1 is N-methylpyrrolidone; The neutralizing agent is one or more of triethylamine, tripropylamine, triethanolamine, and ammonia. Solvent 2 is one of acetone, butanone, or N-methylpyrrolidone.

8. The method for preparing a colorless, transparent, UV-resistant aqueous polyurethane membrane based on bio-based materials according to claim 7, characterized in that, In the preparation of the aqueous polyurethane emulsion, the method for preparing the dried polyol is to vacuum dehydrate the polyol at 100°C for 23-25 ​​hours. The preheating time at 68-72℃ is 15-30 minutes. The heating rate when the reaction temperature is raised to 78-86℃ is 9-11℃ / min; The reaction time is 2-3 hours when carried out at 78-86℃. The time for the secondary reaction at 78-86℃ is 3-4 hours. The reaction time for three cycles at 78-86℃ is 15-20 minutes. When using solvent 1 to adjust the viscosity, first react for 30-50 minutes, then add the first portion of solvent 1 and react for 60-80 minutes, then add the second portion of solvent 2 and react for 90-110 minutes. The ratio of the dried polyol to the first solvent 1 and the second solvent 2 is 45.5-49.5g:5-5.5mL:4-4.5mL; When using solvent 2 to adjust the viscosity, add solvent 2 at the beginning of the third reaction. The ratio of dried polyol to solvent 2 is 45.5-49.5 g: 4-5 mL; The ratio of dried polyol to deionized water is 45.5-49.5g:140-150g; The shearing rate is 1000-2000 rpm, and the time is 30-60 min; The maturation process involves allowing the food to stand at room temperature for 3-5 days.

9. The method for preparing a colorless, transparent, UV-resistant aqueous polyurethane membrane based on bio-based materials according to claim 1, characterized in that, The film formation involves preparing an aqueous polyurethane film from an aqueous polyurethane emulsion.

10. An aqueous polyurethane membrane prepared by the preparation method according to any one of claims 1-9.

Images