A method for preparing a zero voc flame-retardant waterborne polyurethane

Abstract

This invention discloses a method for preparing zero-VOC flame-retardant waterborne polyurethane, belonging to the field of waterborne polyurethane synthesis technology. This invention uses a functionalized ionic liquid to replace acetone in emulsifying a polyurethane prepolymer to obtain emulsion A. Then, a photoinitiator is added, and the functionalized ionic liquid undergoes a photo-initiated polymerization reaction to obtain emulsion B. After curing, the waterborne polyurethane is obtained. This invention utilizes the non-volatile properties of the functionalized ionic liquid to replace traditional acetone as an emulsifying agent, thereby obtaining a zero-VOC waterborne polyurethane emulsion without introducing any organic solvents. Simultaneously, the functionalized ionic liquid is non-flammable and, after being introduced into the polyurethane system, can exist stably through photopolymerization and other methods, effectively solving the flammability safety hazards of waterborne polyurethane products and possessing the dual advantages of environmental protection and flame retardancy.

Description

Technical Field

[0001] This invention relates to the field of waterborne polyurethane synthesis technology, and more specifically, to a method for preparing zero-VOC waterborne polyurethane. Background Technology

[0002] Waterborne polyurethanes are widely used in coatings, adhesives, and leather finishing due to their excellent flexibility, abrasion resistance, adhesion, and environmentally friendly properties (low VOC, solvent-free). However, the preparation of traditional waterborne polyurethanes typically requires the addition of volatile organic solvents such as acetone to reduce prepolymer viscosity and aid emulsification, and the use of organic amine neutralizers such as triethylamine during the neutralization stage. These additives still release VOCs during subsequent removal or use, failing to meet increasingly stringent environmental requirements. Furthermore, conventional waterborne polyurethane materials are inherently flammable, limiting their application in scenarios with high flame retardancy requirements, such as electronics, automotive interiors, and building materials. Therefore, developing zero-VOC waterborne polyurethanes with flame-retardant properties has become a pressing technical challenge in this field. Summary of the Invention

[0003] To address the aforementioned problems in existing technologies, the present invention aims to provide a method for preparing waterborne polyurethane emulsions assisted by functionalized ionic liquids. This invention utilizes the non-volatile properties of functionalized ionic liquids to replace traditional acetone as an emulsifying agent, thereby obtaining a zero-VOC waterborne polyurethane emulsion without introducing any organic solvents. Simultaneously, this functionalized ionic liquid is non-flammable and, after being introduced into the polyurethane system, can remain stable through photopolymerization and other methods, effectively solving the flammability hazards of waterborne polyurethane products and possessing the dual advantages of environmental protection and flame retardancy.

[0004] To solve the above problems, the technical solution adopted by the present invention is as follows: The method for preparing waterborne polyurethane involves using a functionalized ionic liquid to replace acetone in the emulsification of polyurethane prepolymer to obtain emulsion A, then adding a photoinitiator to initiate the polymerization reaction of the functionalized ionic liquid by light irradiation to obtain emulsion B, and finally curing it to obtain the waterborne polyurethane. The structural formula of the functionalized ionic liquid is:

[0005] Where R′ is methyl or ethyl, and Rˉ is... , , , , Any one of them.

[0006] Furthermore, the specific steps are as follows: S1, add diol, diisocyanate and dimethylolpropionic acid (DMPA) to the reaction vessel, then add catalyst to react and obtain prepolymer C; S2, add a chain extender to prepolymer C to react, then add the functionalized ionic liquid to adjust the viscosity to obtain prepolymer D; S3, a neutralizing agent is added to the cooled prepolymer D to react, and then deionized water is added for shear emulsification to obtain emulsion A; S4, add a photoinitiator to emulsion A, and react with stirring under ultraviolet light to obtain emulsion B; S5, after emulsion B is cured, the waterborne polyurethane is obtained.

[0007] Furthermore, the diol is selected from one or more of polypropylene glycol, polyethylene glycol, polytetrahydrofuran ether glycol, polyethylene glycol adipate diol, 1,4-butanediol adipate diol, polycaprolactone diol, polycarbonate diol, 1,6-hexanediol adipate diol, neopentyl adipate diol, and propylene glycol adipate diol, and the number average molecular weight of the diol is 1000-3000 g / mol.

[0008] Furthermore, the diisocyanate is selected from one or more of isophorone diisocyanate, hexamethylene diisocyanate, and dicyclohexylmethane diisocyanate; the catalyst is selected from one or more of dibutyltin dilaurate, dibutyltin diacetate, bismuth laurate, bismuth octanoate, bismuth carboxylate, bismuth neodecanoate, bismuth naphthenate, and bismuth nitrate; and the chain extender is one or more of ethylene glycol, diethylene glycol, methyl propylene glycol, 1,4-butanediol, 1,6-hexanediol, trimethylolpropane, pentaerythritol, and neopentyl glycol.

[0009] Furthermore, the neutralizing agent is selected from one or more of sodium hydroxide, potassium hydroxide, lithium hydroxide, calcium hydroxide, and beryllium hydroxide.

[0010] Furthermore, the photoinitiator is Irgacure 2959 (2-hydroxy-2-methyl-1-[4-(2-hydroxyethoxy)phenyl]-1-propanone), VA-086 (2,2'-azobis[2-methyl-N-(2-hydroxyethyl)propionamide]), or LAP (lithium phenyl-2,4,6-trimethylbenzoylphosphonate).

[0011] Furthermore, the reaction conditions for S1 are as follows: the reaction is carried out under a nitrogen atmosphere, the molar ratio of hydroxyl groups to isocyanate is 1:(2~6), the amount of dimethylolpropionic acid is 20%-45% of the amount of diol, the amount of catalyst is 0.01~0.1 wt% of the prepolymer mass, the reaction temperature is 60-100℃, and the reaction time is 4~8 hours, thereby obtaining a polyurethane prepolymer with isocyanate end-capping.

[0012] Furthermore, the reaction conditions for S2 are as follows: the reaction is carried out under a nitrogen atmosphere, the mass of the chain extender accounts for 6-15% of the total mass of the prepolymer C, the mass of the functionalized ionic liquid accounts for 80-150% of the total mass of the prepolymer C, the reaction temperature is 60-100℃, and the reaction time is 1-5 hours.

[0013] Furthermore, the reaction conditions for S3 are as follows: the prepolymer D is cooled to 40-50℃, the amount of neutralizing agent accounts for 70-95% of the amount of dimethylolpropionic acid; the mass of deionized water accounts for 100-500% of the mass of prepolymer D; the emulsification stirring rate is 1000-5000 rpm, and the emulsification stirring time is 15-30 min.

[0014] Furthermore, the reaction conditions for S4 are as follows: the amount of photoinitiator is 0.5-1% of the amount of functionalized ionic liquid, the stirring rate is 100-500 rpm, the ultraviolet light wavelength is 320-380 nm, and the light intensity is 50-200 mW / cm². 2 The illumination time is 30-60 minutes.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention utilizes a non-volatile functionalized ionic liquid to assist in the emulsification of polyurethane prepolymers, without introducing any organic solvents (such as acetone) and using an inorganic alkali as a neutralizing agent, successfully producing a zero-VOC waterborne polyurethane emulsion. This solves the VOC problem inherent in traditional waterborne polyurethane preparation processes, which involve the use of acetone for emulsification and triethylamine for neutralization. Simultaneously, the introduction of a non-flammable functionalized ionic liquid into the polyurethane system, through photo-induced polymerization, significantly imparts flame-retardant properties to the waterborne polyurethane product, thus overcoming the lack of flame retardancy in traditional waterborne polyurethane products. Detailed Implementation

[0016] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0017] The key to the preparation method of waterborne polyurethane of the present invention is to use a functionalized ionic liquid to replace acetone emulsifying polyurethane prepolymer to obtain emulsion A, and then add a photoinitiator to initiate the polymerization reaction of the functionalized ionic liquid by light irradiation to obtain emulsion B, which is then cured to obtain waterborne polyurethane. The structural formula of the above-mentioned functionalized ionic liquid is:

[0018] Where R′ is methyl or ethyl, and Rˉ is... , , , , Any one of them.

[0019] Functionalized ionic liquids may include 1-vinyl-3-methylimidazolium tetrafluoroboric acid, 1-vinyl-3-methylimidazolium acetic acid, 1-vinyl-3-methylimidazolium trifluoromethanesulfonic acid, 1-vinyl-3-methylimidazolium diethyl phosphate, 1-vinyl-3-methylimidazolium dimethyl phosphate, 1-vinyl-3-ethylimidazolium diethyl phosphate, and 1-vinyl-3-ethylimidazolium dimethyl phosphate.

[0020] The functionalized ionic liquid of this invention is used as a diluent and auxiliary emulsifier. Structurally, it contains no hydroxyl or amino groups and does not participate in the polymerization of polyurethane monomers. The role of the vinyl group is to dilute and emulsify the polyurethane, then initiate polymerization through ultraviolet light to form a polyionic liquid. This polyionic liquid is a solid polymer with high mechanical strength, ensuring the mechanical strength of the resulting waterborne polyurethane.

[0021] Example 1 The preparation method of waterborne polyurethane in this embodiment includes the following steps: (1) At room temperature, 21.2 g of polyoxypropylene polyol (number average molecular weight 1000 g / mol), 20.2 g of isophorone diisocyanate and 1.3 g of dimethylolpropionic acid were added to the reaction vessel, and then 0.03 g of dibutyltin dilaurate was added. Nitrogen gas was introduced and the reaction was carried out at 70°C for 6 h to obtain polyurethane prepolymer with isocyanate end capping.

[0022] (2) Add 2.6 g of 1,4-butanediol to the system obtained in step 1, react at 70°C for 2 h, and then add 34.0 g of 1-vinyl-3-methylimidazolium tetrafluoroboric acid to adjust the viscosity to obtain polyurethane prepolymer.

[0023] (3) Cool the polyurethane prepolymer obtained in step 2 to 40 °C, add 0.33 g of sodium hydroxide to the cooled prepolymer for neutralization, and then add 100 g of deionized water. Perform high-speed shear emulsification for 15 min in an emulsifier at 2000 rpm to obtain an aqueous polyurethane emulsion.

[0024] (4) Add 0.17 g Irgacure 2959 to the aqueous polyurethane emulsion obtained in step 3, and expose it to 365 nm ultraviolet light (70 mW / cm²). 2 Under light, the mixture is stirred (150 rpm) and reacted under light for 30 minutes to obtain a flame-retardant, zero-VOC waterborne polyurethane emulsion.

[0025] Example 2 The preparation method of waterborne polyurethane in this embodiment includes the following steps: (1) At room temperature, 19.7 g of polytetrahydrofuran ether diol (number average molecular weight 2000 g / mol), 12.5 g of isophorone diisocyanate and 0.6 g of dimethylolpropionic acid were added to the reaction vessel, and then 0.04 g of dibutyltin dilaurate was added. Nitrogen gas was introduced and the reaction was carried out at 80 °C for 5 h to obtain polyurethane prepolymer with isocyanate end capping.

[0026] (2) Add 3.1 g of ethylene glycol to the system obtained in step 1, react at 70°C for 2 h, and then add 40.0 g of 1-vinyl-3-methylimidazolium phosphate diethyl ester salt to adjust the viscosity to obtain polyurethane prepolymer.

[0027] (3) After cooling the polyurethane prepolymer obtained in step 2 to 40 °C, add 0.2 g of potassium hydroxide to the cooled prepolymer for neutralization, and then add 80 g of deionized water. Perform high-speed shear emulsification for 20 min in an emulsifier at 2000 rpm to obtain an aqueous polyurethane emulsion.

[0028] (4) Add 0.21 g Irgacure 2959 to the aqueous polyurethane emulsion obtained in step 3, and expose it to 365 nm ultraviolet light (70 mW / cm). 2 Under light, the mixture is stirred (150 rpm) and reacted under light for 30 minutes to obtain a flame-retardant, zero-VOC waterborne polyurethane emulsion.

[0029] Example 3 The preparation method of waterborne polyurethane in this embodiment includes the following steps: (1) At room temperature, 19.7 g of polytetrahydrofuran ether diol (number average molecular weight 2000 g / mol), 14.6 g of dicyclohexylmethane diisocyanate and 0.6 g of dimethylolpropionic acid were added to the reaction vessel, followed by 0.04 g of dibutyltin dilaurate. Nitrogen gas was introduced and the reaction was carried out at 80 °C for 5 h to obtain polyurethane prepolymer with isocyanate end capping.

[0030] (2) Add 3.1 g of 1,6-hexanediol to the system obtained in step 1, react at 70°C for 2 h, and then add 20.0 g of 1-vinyl-3-methylimidazolium tetrafluoroboric acid and 20.0 g of 1-vinyl-3-methylimidazolium diethyl phosphate salt to adjust the viscosity to obtain polyurethane prepolymer.

[0031] (3) After cooling the polyurethane prepolymer obtained in step 2 to 40 °C, add 0.2 g of potassium hydroxide to the cooled prepolymer for neutralization, and then add 80 g of deionized water. Perform high-speed shear emulsification for 20 min in an emulsifier at 2000 rpm to obtain an aqueous polyurethane emulsion.

[0032] (4) Add 0.21 g Irgacure 2959 to the aqueous polyurethane emulsion obtained in step 3, and expose it to 365 nm ultraviolet light (70 mW / cm). 2 Under light, the mixture is stirred (150 rpm) and reacted under light for 30 minutes to obtain a flame-retardant, zero-VOC waterborne polyurethane emulsion.

[0033] Comparative Example 1 A method for preparing waterborne polyurethane includes the following steps: (1) At room temperature, 21.2 g of polyoxypropylene polyol (number average molecular weight 1000 g / mol), 20.2 g of isophorone diisocyanate and 1.3 g of dimethylolpropionic acid were added to the reaction vessel, and then 0.03 g of dibutyltin dilaurate was added. Nitrogen gas was introduced and the reaction was carried out at 70°C for 6 h to obtain polyurethane prepolymer with isocyanate end capping.

[0034] (2) Add 2.6 g of 1,4-butanediol to the system obtained in step 1, react at 70°C for 2 h, cool down to 50°C, and add 50 mL of acetone to adjust the viscosity to obtain polyurethane prepolymer.

[0035] (3) After cooling the polyurethane prepolymer obtained in step 2 to 40 °C, add 0.91 g of triethylamine to the cooled prepolymer for neutralization, and then add 100 g of deionized water. Perform high-speed shear emulsification for 15 min in an emulsifier at 2000 rpm to obtain an aqueous polyurethane emulsion.

[0036] Comparative Example 2 A method for preparing waterborne polyurethane includes the following steps: (1) At room temperature, 19.7 g of polytetrahydrofuran ether diol (number average molecular weight 2000 g / mol), 12.5 g of isophorone diisocyanate and 0.6 g of dimethylolpropionic acid were added to the reaction vessel, and then 0.04 g of dibutyltin dilaurate was added. Nitrogen gas was introduced and the reaction was carried out at 80 °C for 5 h to obtain polyurethane prepolymer with isocyanate end capping.

[0037] (2) Add 3.1 g of ethylene glycol to the system obtained in step 1, react at 70°C for 2 h, cool down to 50°C, and then add 50 mL of acetone to adjust the viscosity to obtain polyurethane prepolymer.

[0038] (3) After cooling the polyurethane prepolymer obtained in step 2 to 40 °C, add 0.45 g of triethylamine to the cooled prepolymer for neutralization, and then add 80 g of deionized water. Perform high-speed shear emulsification for 20 min in an emulsifier at 2000 rpm to obtain an aqueous polyurethane emulsion.

[0039] Comparative Example 3 A method for preparing waterborne polyurethane includes the following steps: (1) At room temperature, 19.7 g of polytetrahydrofuran ether diol (number average molecular weight 2000 g / mol), 14.6 g of dicyclohexylmethane diisocyanate and 0.6 g of dimethylolpropionic acid were added to the reaction vessel, followed by 0.04 g of dibutyltin dilaurate. Nitrogen gas was introduced and the reaction was carried out at 80 °C for 5 h to obtain polyurethane prepolymer with isocyanate end capping.

[0040] (2) Add 3.1 g of 1,6-hexanediol to the system obtained in step 1, react at 70°C for 2 h, cool down to 50°C, and then add 50 mL of acetone to adjust the viscosity to obtain polyurethane prepolymer.

[0041] (3) After cooling the polyurethane prepolymer obtained in step 2 to 40 °C, add 0.45 g of triethylamine to the cooled prepolymer for neutralization, and then add 80 g of deionized water. Perform high-speed shear emulsification for 20 min in an emulsifier at 2000 rpm to obtain an aqueous polyurethane emulsion.

[0042] Comparative Example 4 A method for preparing waterborne polyurethane includes the following steps: (1) At room temperature, 19.7 g of polytetrahydrofuran ether diol (number average molecular weight 2000 g / mol), 14.6 g of dicyclohexylmethane diisocyanate and 0.6 g of dimethylolpropionic acid were added to the reaction vessel, followed by 0.04 g of dibutyltin dilaurate. Nitrogen gas was introduced and the reaction was carried out at 80 °C for 5 h to obtain polyurethane prepolymer with isocyanate end capping.

[0043] (2) Add 3.1 g of 1,6-hexanediol to the system obtained in step 1, react at 70°C for 2 h, and then add 20.0 g of 1-vinyl-3-methylimidazolium tetrafluoroboric acid and 20.0 g of 1-vinyl-3-methylimidazolium diethyl phosphate salt to adjust the viscosity to obtain polyurethane prepolymer.

[0044] (3) After cooling the polyurethane prepolymer obtained in step 2 to 40 °C, add 0.2 g of potassium hydroxide to the cooled prepolymer for neutralization, and then add 80 g of deionized water. Perform high-speed shear emulsification for 20 min in an emulsifier at 2000 rpm to obtain an aqueous polyurethane emulsion.

[0045] The aqueous polyurethane emulsions prepared in Examples 1-3 and Comparative Examples 1-4 were uniformly spread on polytetrafluoroethylene (PTFE) plates and cast into films. These films were then dried at room temperature and finally placed in a vacuum oven at 70°C for 6 hours to obtain polyurethane coatings. The limiting oxygen index and UL 94 flame retardancy rating were determined according to GB / T 2406, and the tensile strength and elongation at break of the coatings were determined according to GB / T 528-2009. The results are shown in Table 1.

[0046] Table 1

[0047] According to the data in Table 1, the limiting oxygen index (LOI) of Examples 1-3 is not lower than 29. Examples 1 and 2 achieve a UL-94 flame retardancy rating of V1, and Example 3 achieves V0, indicating that these materials have good flame retardant properties. In contrast, the LIO of Comparative Examples 1-3 is lower than 19, and their UL-94 flame retardancy rating cannot be measured, indicating that they lack flame retardancy. The tensile strength of Examples 1-3 is greater than 22 MPa, and their elongation at break is greater than 600%. The tensile strength and elongation at break of Comparative Examples 1-3 are not lower than 21 MPa and 600%, respectively, indicating that the mechanical properties of the waterborne polyurethane prepared by the functionalized ionic liquid method in the Examples are comparable to those of the waterborne polyurethane prepared by the acetone method in the Comparative Examples. The flame retardancy of Comparative Example 4 is comparable to that of Example 3, but its mechanical properties are significantly lower. Because the functionalized ionic liquid in Comparative Example 4 was not polymerized into a polyionic liquid under ultraviolet light, the liquid functionalized ionic liquid acts as a plasticizer in the waterborne polyurethane film, reducing the mechanical properties of the polyurethane film.

Claims

1. A method for preparing waterborne polyurethane, characterized in that, Emulsion A was prepared by replacing acetone with a functionalized ionic liquid to emulsify the polyurethane prepolymer. Then, a photoinitiator was added, and the functionalized ionic liquid polymerization reaction was initiated by light irradiation to obtain emulsion B. After curing, the waterborne polyurethane was obtained. The structural formula of the functionalized ionic liquid is: Where R′ is methyl or ethyl, and Rˉ is... , , , , Any one of them.

2. A method for preparing waterborne polyurethane according to claim 1, characterized in that, The specific steps are as follows: S1, add diol, diisocyanate and dimethylolpropionic acid into a reaction vessel, then add a catalyst to react and obtain prepolymer C; S2, add a chain extender to prepolymer C to react, then add the functionalized ionic liquid to adjust the viscosity to obtain prepolymer D; S3, a neutralizing agent is added to the cooled prepolymer D to react, and then deionized water is added for shear emulsification to obtain emulsion A; S4, add a photoinitiator to emulsion A, and react with stirring under ultraviolet light to obtain emulsion B; S5, after emulsion B is cured, the waterborne polyurethane is obtained.

3. A method for preparing waterborne polyurethane according to claim 2, characterized in that, The diol is selected from one or more of polypropylene glycol, polyethylene glycol, polytetrahydrofuran ether glycol, polyethylene glycol adipate diol, 1,4-butanediol adipate diol, polycaprolactone diol, polycarbonate diol, 1,6-hexanediol adipate diol, neopentyl adipate diol, and propylene glycol adipate diol, and the number average molecular weight of the diol is 1000-3000 g / mol.

4. A method for preparing waterborne polyurethane according to claim 2, characterized in that, The diisocyanate is selected from one or more of isophorone diisocyanate, hexamethylene diisocyanate, and dicyclohexylmethane diisocyanate; the catalyst is selected from one or more of dibutyltin dilaurate, dibutyltin diacetate, bismuth laurate, bismuth octanoate, bismuth carboxylate, bismuth neodecanoate, bismuth naphthenate, and bismuth nitrate; the chain extender is one or more of ethylene glycol, diethylene glycol, methyl propylene glycol, 1,4-butanediol, 1,6-hexanediol, trimethylolpropane, pentaerythritol, and neopentyl glycol.

5. A method for preparing waterborne polyurethane according to claim 2, characterized in that, The neutralizing agent is selected from one or more of sodium hydroxide, potassium hydroxide, lithium hydroxide, calcium hydroxide, and beryllium hydroxide.

6. A method for preparing waterborne polyurethane according to claim 2, characterized in that, The photoinitiator is Irgacure 2959, VA-086, or LAP.

7. A method for preparing waterborne polyurethane according to claim 2, characterized in that, The reaction conditions for S1 are as follows: the reaction is carried out under a nitrogen atmosphere, the molar ratio of hydroxyl groups to isocyanates is 1:(2~6), the amount of dimethylolpropionic acid is 20%-45% of the amount of diol, the amount of catalyst is 0.01~0.1 wt% of the prepolymer mass, the reaction temperature is 60-100℃, and the reaction time is 4~8 hours.

8. A method for preparing waterborne polyurethane according to claim 2, characterized in that, The reaction conditions for S2 are as follows: the reaction is carried out under a nitrogen atmosphere, the mass of the chain extender accounts for 6-15% of the total mass of the prepolymer C, the mass of the functionalized ionic liquid accounts for 80-150% of the total mass of the prepolymer C, the reaction temperature is 60-100℃, and the reaction time is 1-5 hours.

9. A method for preparing waterborne polyurethane according to claim 2, characterized in that, The reaction conditions for S3 are as follows: the prepolymer D is cooled to 40-50℃, the amount of neutralizing agent accounts for 70-95% of the amount of dimethylolpropionic acid, the mass of deionized water accounts for 100-500% of the mass of prepolymer D, the emulsification stirring rate is 1000-5000 rpm, and the emulsification stirring time is 15-30 min.

10. A method for preparing waterborne polyurethane according to claim 2, characterized in that, The reaction conditions for S4 are as follows: the amount of photoinitiator is 0.5-1% of the amount of functionalized ionic liquid; the stirring rate is 100-500 rpm; the ultraviolet light wavelength is 320-380 nm; and the light intensity is 50-200 mW / cm². 2 The illumination time is 30-60 minutes.

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