Plant oil-based aqueous polyurethane acrylate prepolymer, and preparation method and application thereof

Abstract

The application discloses a vegetable oil-based waterborne polyurethane acrylate prepolymer, which is mainly prepared by jointly reacting castor oil-based diethanolamide and epoxy soybean oil acrylate as main reaction raw materials, a hydrophilic chain extender, a catalyst, diisocyanate and a blocking agent, and finally adding a neutralizing agent for neutralization. Water is used as a diluent and a dispersant, the vegetable oil-based waterborne polyurethane acrylate prepolymer provided by the application is emulsified and dispersed in water, and a vegetable oil-based waterborne polyurethane acrylate dispersion can be prepared. The vegetable oil-based waterborne polyurethane acrylate dispersion is mixed with a photoinitiator, and a bio-based ultraviolet light-cured coating can be prepared. The light-cured film prepared from the bio-based ultraviolet light-cured coating provided by the application has high bio-based content, excellent adhesion, pencil hardness, flexibility and chemical corrosion resistance, and the thermal mechanical performance, thermal stability and tensile strength can be adjusted.

Description

Technical Field

[0001] This invention relates to the field of ultraviolet curable materials technology, specifically to a plant oil-based waterborne polyurethane acrylate prepolymer, its preparation method, and its application. Background Technology

[0002] Ultraviolet (UV) curing refers to the process of using ultraviolet light to induce the rapid polymerization and cross-linking of chemically reactive liquid materials, which then solidifies into solid materials in a very short time. Compared to traditional thermosetting coatings, UV-cured coatings have advantages such as energy saving, environmental friendliness, fast curing speed, and low solvent release, and are currently widely used in coatings, adhesives, and printing inks.

[0003] UV-curable coatings consist of photosensitive oligomers, reactive diluents, photoinitiators, and various additives (fillers, pigments, auxiliaries, etc.). Among these, oligomers are the main component of UV-curable coatings, and their properties determine the main properties of the cured material. Therefore, the design and synthesis of oligomers are a crucial step in the formulation design of UV-curable coatings. The photosensitive oligomers used in UV-curable coatings generally have a large molecular weight, and their main chains often contain epoxy groups or unsaturated double bonds.

[0004] Polyurethane is one of the commonly used oligomers in UV-curable coatings. Traditional solvent-based polyurethanes contain a large amount of volatile organic solvents or reactive diluents, and sometimes even some toxic isocyanate monomers, which can cause certain harm to human health and the ecological environment. In addition, more and more laws and regulations have put forward stricter requirements on VOC emissions. Therefore, there is an urgent need to find a green and environmentally friendly product to replace traditional solvent-based polyurethanes.

[0005] Waterborne polyurethane is a polyurethane system that uses water as a diluent and dispersant. Its synthesis generally employs an internal emulsification method, where hydrophilic chain extenders are grafted onto hydrophobic polyurethane chains, followed by the addition of a neutralizing agent to form a salt, and finally, high-speed stirring to emulsify and disperse it in water. Compared to solvent-based polyurethane, waterborne polyurethane also possesses properties such as weather resistance, abrasion resistance, high flexibility, high tensile strength, and high adhesion, but it has lower viscosity, produces less pollution, and is not only easier to apply but also safer and more reliable. Furthermore, it contains virtually no volatile organic compounds, making it considered a green and environmentally friendly chemical product. However, waterborne polyurethane also has some drawbacks, such as slow drying speed, poor substrate wettability, and poor water resistance. Currently, the soft segments used in the synthesis of waterborne polyurethane are mostly petroleum-based polyether diols or polyester diols, which are not only non-renewable but also difficult to degrade, causing pollution to the environment. Summary of the Invention

[0006] The first objective of this invention is to provide a plant oil-based waterborne polyurethane acrylate prepolymer and its preparation method, in order to solve at least one of the above-mentioned technical problems.

[0007] A second objective of this invention is to provide a vegetable oil-based waterborne polyurethane acrylate dispersion and its preparation method, in order to solve at least one of the above-mentioned technical problems.

[0008] A third objective of the present invention is to provide a bio-based ultraviolet curable coating to solve at least one of the above-mentioned technical problems.

[0009] According to one aspect of the present invention, a plant oil-based waterborne polyurethane acrylate prepolymer is provided, the preparation method of which includes the following steps:

[0010] Castor oil-based diethanolamide, hydrophilic chain extender, crosslinking agent diisocyanate and catalyst are mixed and reacted at 50-70℃ for 2-4 hours to obtain the first reaction mixture.

[0011] Epoxidized soybean oil acrylate is dissolved in an organic solvent and then added to the first reaction mixture. The mixture is reacted at a temperature of 50-70°C for 3-5 hours to obtain the second reaction mixture.

[0012] The capping agent, hydroxy acrylate monomer, is added to the second reaction mixture and the reaction continues for 2-4 hours. After the reaction is completed, the mixture is cooled to 25-35°C and neutralized with a neutralizing agent to obtain a vegetable oil-based waterborne polyurethane acrylate prepolymer.

[0013] Castor oil-based diethanolamide and epoxidized soybean oil acrylate can be synthesized from castor oil and epoxidized soybean oil, respectively, two biomass plant oils. Therefore, this invention uses castor oil-based diethanolamide and epoxidized soybean oil acrylate as the main reactants to prepare plant oil-based waterborne polyurethane acrylate prepolymers. On the one hand, this can reduce the use of petrochemical resources and increase the bio-based content in UV-curable coatings. On the other hand, castor oil-based diethanolamide can improve the reactivity of the raw materials and shorten the reaction time, while epoxidized soybean oil acrylate has the dual effect of chain extension and increasing the content of active double bonds in the system. By adjusting the content of the two plant oil-based polyols, a waterborne UV-curable polyurethane acrylate curing film with superior performance can be obtained.

[0014] In some embodiments, the molar ratio of hydroxyl groups in castor oil-based diethanolamide, epoxidized soybean oil acrylate, hydrophilic chain extender, and hydroxyl acrylate monomer can be (0.1–6):(0.1–6):7.5:1.5. Therefore, by adjusting the content ratio of castor oil-based diethanolamide and epoxidized soybean oil acrylate, a waterborne UV-curable polyurethane acrylate film with desired properties can be prepared. The higher the content of epoxidized soybean oil acrylate, the higher the thermomechanical properties, thermal stability, and tensile strength of the cured film. Within the formulation range provided by this invention, cured films prepared from any ratio of castor oil-based diethanolamide and epoxidized soybean oil acrylate exhibit excellent adhesion, pencil hardness, flexibility, and chemical resistance.

[0015] In some embodiments, the hydrophilic chain extender may be selected from at least one of N-methyldiethanolamine, N,N-dimethylethanolamine, N,N-bis(hydroxymethyl)tert-butylamine, and 3-dimethylamino-1,2-propanediol.

[0016] In some embodiments, the diisocyanate may be selected from at least one of isophorone diisocyanate, toluene diisocyanate, diphenylmethane diisocyanate, dicyclohexylmethane diisocyanate, hexamethylene diisocyanate, and lysine diisocyanate.

[0017] In some embodiments, the molar ratio of the isocyanate group in the diisocyanate to the total amount of hydroxyl groups in castor oil diethanolamide, epoxidized soybean oil acrylate, hydrophilic chain extender, and hydroxyl acrylate monomer can be 1:(1 to 1.05).

[0018] In some embodiments, the catalyst may be selected from at least one of dibutyltin dilaurate, dibutyltin diacetate, stannous octoate, dialkyltin dimaleate, dithioalkyltin, and zinc naphthenate.

[0019] In some embodiments, the amount of catalyst used may be 0.05% to 1% of the total mass of diisocyanate, castor oil-based diethanolamide, epoxidized soybean oil acrylate, hydrophilic chain extender, and hydroxy acrylate.

[0020] In some embodiments, the organic solvent may be selected from at least one of butanone and acetone.

[0021] In some embodiments, the amount of organic solvent used can be 30% to 50% of the mass of epoxidized soybean oil acrylate.

[0022] In some embodiments, the hydroxy acrylate monomer may be selected from at least one of hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate, hydroxypropyl methacrylate, 4-hydroxybutyl acrylate, and 2-hydroxybutyl methacrylate.

[0023] In some embodiments, the neutralizing agent may be selected from at least one of hydrochloric acid, acetic acid, and phosphoric acid.

[0024] In some embodiments, the amount of neutralizing agent can be 90% to 100% of the molar amount of the hydrophilic chain extender.

[0025] Using water as a diluent and dispersant, the plant oil-based waterborne polyurethane acrylate prepolymer provided by this invention is emulsified and dispersed in water to obtain a plant oil-based waterborne polyurethane acrylate dispersion. Mixing the plant oil-based waterborne polyurethane acrylate dispersion with a photoinitiator yields a bio-based UV-curable coating. After drying the bio-based UV-curable coating at room temperature, it is cured under UV light to form a film, resulting in a high-performance waterborne UV-curable polyurethane acrylate cured film. Compared with other waterborne polyurethane acrylate cured films, the waterborne UV-curable polyurethane acrylate cured film provided by this invention has a higher bio-based content, which is more in line with the trend of green development.

[0026] According to a second aspect of the present invention, a vegetable oil-based aqueous polyurethane acrylate dispersion is provided, the preparation method of which includes the following steps:

[0027] Water is added to the vegetable oil-based waterborne polyurethane acrylate prepolymer, and after emulsification, the organic solvent is removed to obtain the final product.

[0028] In some embodiments, the mass ratio of water to vegetable oil-based waterborne polyurethane acrylate prepolymer can be (3-8):(2-3).

[0029] According to a third aspect of the present invention, a bio-based ultraviolet curable coating is provided, which is mainly composed of a vegetable oil-based waterborne polyurethane acrylate dispersion and a photoinitiator.

[0030] In some embodiments, the amount of photoinitiator can be 3% to 5% of the mass of the vegetable oil-based waterborne polyurethane acrylate prepolymer.

[0031] In some embodiments, the photoinitiator may be selected from at least one of photoinitiator 1173, photoinitiator 184, photoinitiator 907, photoinitiator TPO, and photoinitiator 659. Attached Figure Description

[0032] Figure 1 This is a schematic diagram of the synthesis route of the plant oil-based waterborne polyurethane acrylate prepolymer of the present invention;

[0033] Figure 2 The total reflectance infrared spectra of AESO and the prepolymer before and after curing;

[0034] Figure 3 Particle size distribution curve of WPUA emulsion;

[0035] Figure 4 The storage modulus (E') and loss factor (Tanδ) of the WPUA cured film;

[0036] Figure 5 The stress-strain curve of the WPUA cured film;

[0037] Figure 6 TGA(a) and DTG(b) curves of the WPUA cured film;

[0038] Figure 7 This refers to the gel content of the WPUA cured film. Detailed Implementation

[0039] The present invention will be further described in detail below with reference to the embodiments. The embodiments are for illustrative purposes only and do not limit the invention in any way. Unless otherwise specified, the raw materials and reagents used in the embodiments are conventional products that can be obtained commercially; experimental methods that do not specify specific conditions in the embodiments are generally performed under conventional conditions in the art or according to the conditions recommended by the manufacturer.

[0040] In this invention, epoxidized soybean oil acrylate (AESO) is mainly prepared by epoxidized soybean oil and acrylic acid through an epoxidation ring-opening reaction. It can be obtained through commercial channels or synthesized by referring to methods disclosed in the prior art.

[0041] The synthetic route for AESO is shown below:

[0042]

[0043] For example, a specific synthesis method for AESO may include the following steps:

[0044] (1) 24.38g of epoxidized soybean oil (ESO, analytical grade, purchased from Shanghai Maclean Biochemical Co., Ltd.), 0.30g of triphenylphosphine (TPP) and 0.05g of hydroquinone were added as catalyst and polymerization inhibitor to a three-necked flask equipped with a mechanical stirrer and a constant pressure dropping funnel, respectively.

[0045] (2) Add 5.40g of acrylic acid (AA) dropwise over 0.5h at a constant rate;

[0046] (3) Stir the reaction system at 80°C for 1 hour, then heat it to 120°C and stir for about 3 hours to obtain the crude product;

[0047] (4) The crude product was cooled to room temperature and extracted with dichloromethane and washed with 1 wt% NaHCO3 and distilled water; then, the organic layer was collected and dried with anhydrous magnesium sulfate; after filtration, the filtrate was transferred to a rotary evaporator for distillation to finally obtain pure AESO.

[0048] In this invention, the small-molecule castor oil-based diethanolamide (RADEA) is mainly synthesized by ammonolysis of castor oil with diethanolamine under the action of an alkaline catalyst. The synthetic route is shown below:

[0049]

[0050] For example, a specific method for synthesizing RADEA may include the following steps:

[0051] (1) Place 7.89 g of diethanolamine and 0.31 g of basic catalyst sodium methoxide into a three-necked flask equipped with a mechanical stirrer and heat to 100 °C; then add 23.35 g of castor oil (CO, analytical grade, purchased from Tianjin Fuyu Fine Chemical Reagent Co., Ltd.) to the above reaction system within 0.5 h, and then keep stirring for 4 h;

[0052] (2) After the reaction is complete, the crude product is cooled to room temperature, extracted with ethyl acetate, washed three times with saturated NaCl solution, the organic layer is collected after separation and dried with anhydrous magnesium sulfate; finally, the product RADEA is obtained by rotary evaporation.

[0053] Preparation of vegetable oil-based waterborne polyurethane acrylate prepolymers (PUA) in Examples 1-4

[0054] In Examples 1-4, the molar ratios of the isocyanate group (NCO) in the diisocyanate (isophorone diisocyanate IPDI), the hydroxyl group in epoxidized soybean oil acrylate (AESO), the hydroxyl group in castor oil diethanolamide (RADEA), the hydroxyl group in the hydrophilic chain extender (N-methyldiethanolamine MDEA), and the hydroxyl group in the hydroxyl acrylate monomer (hydroxyethyl acrylate HEA) are shown in Table 1.

[0055] Table 1. Composition of plant oil-based waterborne polyurethane acrylate prepolymers

[0056]

[0057]

[0058] The preparation method includes the following steps:

[0059] (1) RADEA, MDEA, IPDI and dibutyltin dilaurate (0.5% of the total mass of IPDI, AESO, RADEA, MDEA and HEA) were added to a 250ml three-necked flask equipped with a dropping funnel and a mechanical stirrer. The system was kept at 60℃ for 3h to obtain the first reaction mixture.

[0060] (2) Dissolve AESO in butanone (50% of the mass of AESO) and add it dropwise to the first reaction mixture over 0.5 h. Continue the reaction for 4 h to obtain the second reaction mixture.

[0061] (3) Add HEA dropwise to the second reaction mixture and continue stirring for 3 hours to obtain the third reaction mixture;

[0062] (4) Cool the third reaction mixture to 30°C, add an equal amount of hydrochloric acid (N-methyldiethanolamine) to neutralize and stir for 0.5 h to obtain the vegetable oil-based waterborne polyurethane acrylate prepolymer.

[0063] Synthetic routes for plant oil-based waterborne polyurethane acrylate prepolymers are as follows: Figure 1 As shown.

[0064] Examples 5-8: Preparation of vegetable oil-based waterborne polyurethane acrylate dispersions (WPUA emulsions)

[0065] Add 1.5 times the mass of distilled water to the plant oil-based waterborne polyurethane acrylate prepolymer and stir the mixture at high speed (approximately 1500 rpm) for 1 hour to emulsify the plant oil-based waterborne polyurethane acrylate prepolymer. After the emulsification is completed, remove methyl ethyl ketone by rotary evaporation to obtain a plant oil-based waterborne polyurethane acrylate dispersion (named WPUA emulsion).

[0066] The plant oil-based waterborne polyurethane acrylate dispersions prepared from the plant oil-based waterborne polyurethane acrylate prepolymers obtained in Examples 1 to 4 are named WPUA1 to 4 respectively.

[0067] Examples 9-12 Bio-based UV-curable coatings

[0068] Add 5 wt% (as PUA) of PI-1173 to the WPUA emulsion and stir for about 30 minutes to obtain a bio-based UV-curable coating.

[0069] The bio-based UV-curable coating was poured into a glass dish and dried at room temperature for 12 hours. Then, the film was placed in an oven at 60°C and dried for 5 hours to completely remove moisture. Finally, it was cured under a UV curing lamp at a distance of 10 cm for 30 seconds to obtain a WPUA cured film.

[0070] The curing behavior of the UV-curable film before and after curing was studied using AFT-IR total internal reflection infrared spectroscopy. A Bruker Vertex 70 AFT-IR spectrometer was used in the range of 4000–500 cm⁻¹. -1 The structure of the cured coating (after UV curing) was characterized within the wavenumber range.

[0071] The infrared spectra of the prepolymer obtained by AESO and Example 3 before curing and the cured film of the prepolymer after curing are as follows: Figure 2 As shown.

[0072] like Figure 2 As shown, unlike AESO, the spectrum of the prepolymer before curing is located at 3466 cm⁻¹. -1 The hydroxyl absorption peak disappears at 3323 cm⁻¹, while at 3323 cm⁻¹... -1 A new absorption peak appeared at 2268 cm⁻¹, which is attributed to the stretching vibration absorption of NH in the urethane group. -1 No infrared characteristic peaks belonging to -NCO were found at 1636 cm⁻¹, indicating that the hydroxyl groups in AESO reacted relatively completely with the -NCO groups in IPDI, proving the successful synthesis of the waterborne polyurethane-acrylic acid prepolymer. By comparing the infrared spectra of the two different forms of prepolymer, it can be found that after UV curing, the prepolymer exhibits a peak at 1636 cm⁻¹. -1 and 810cm -1 The intensity of the carbon-carbon double bond peak and carbon-hydrogen absorption peak at the point of curing decreases significantly or even disappears gradually, which proves that the curing process is carried out under the combined action of photoinitiator and ultraviolet light irradiation.

[0073] Experimental Example 1: Particle Size Analysis of WPUA Emulsion

[0074] The particle size distribution and zeta potential of WPUA emulsions were investigated using a Malvern Zeta-sizer Nano ZSE (Malvern Instruments). Test samples were prepared by diluting all dispersions with distilled water at a dilution factor of 100-fold before testing. The particle size distribution of the WPUA emulsions is shown below. Figure 3 As shown in Table 2, the specific values ​​are as follows.

[0075] Depend on Figure 3 As shown in Table 2, with the increase of AESO content in the system, the average particle size of the emulsion gradually increases, and the particle size distribution gradually widens. This is because AESO has a larger molecular weight than RADEA. When the AESO content is low, the proportion of MDEA in the dispersion system increases relatively. After neutralization with hydrochloric acid, more ionic groups are generated, leading to increased electrostatic repulsion and reduced interparticle association, resulting in smaller particle size and more uniform dispersion. Simultaneously, AESO has three long fatty acid chains, making it more hydrophobic than RADEA, which makes it more difficult to disperse in the aqueous phase. Furthermore, with the continuous increase of AESO, the cross-linking degree of the system continuously increases due to the intertwining of its long fatty acid chains, restricting the migration of hydrophilic groups to the surface. After neutralization, the number of ionic groups generated is small, reducing the hydrophilicity of the system and causing a sharp increase in particle size.

[0076] Table 2 Physical parameters of different WPUA emulsions

[0077] sample Average particle size (nm) Dispersion Index (PDI) Zeta potential (mV) WPUA1 39.87±0.23 0.163±0.006 43.44±3.37 WPUA2 43.80±0.21 0.130±0.009 47.35±1.73 WPUA3 122.73±0.28 0.164±0.007 49.03±1.42 WPUA4 142.06±0.18 0.248±0.005 57.55±1.36

[0078] Experimental Example 2: Dynamic Thermomechanical Properties Analysis of Cured Film

[0079] Dynamic mechanical analysis of the specimens was performed using a Netzsch DMA 242C dynamic thermomechanical analyzer. The specimen dimensions were 20.0 mm × 6.0 mm × 0.5 mm (length × width × thickness). The tensile mode frequency used was 1 Hz, the test temperature range was -80 to 170 °C, and the heating rate was 3 °C / min. The temperature corresponding to the peak value of the Tanδ curve is the glass transition temperature of the specimen.

[0080] The glass transition temperature (Tg) of the cured film was obtained through dynamic mechanical analysis. g The relationship between energy storage modulus (E') and loss factor (Tanδ) is shown in the following results. Figure 4 As shown, at low temperatures, the cured film exhibits a glassy state and maintains a high storage modulus. However, as the temperature increases, the storage modulus of the cured film begins to decrease rapidly, indicating some relative motion between the chain segments. The temperature at which the cured film transitions from the glassy state to the highly elastic state is the glass transition temperature, corresponding to the peak temperature in the Tanδ curve. Notably, all Tanδ curves show only a single peak, indicating that the cured film is uniform. Furthermore, it can be observed that as the entanglement of the crosslinked network increases, the peak intensity decreases and the distribution becomes wider.

[0081] Crosslinking density is another important parameter for evaluating the quality of cured films, and it can be calculated using the following formula:

[0082] Crosslinking density of cured coating (ν) e ) is calculated by equation (eq 3.1).

[0083] E'=3RT'×ν e (eq 3.1)

[0084] Where T' is the cured film in the rubber state (T g The absolute temperature at +30℃, E' is the storage modulus at T', and R is the gas constant.

[0085] E' was derived and calculated through DMA analysis. 25 T g and ν eThe values ​​are listed in Table 3. Table 3 shows that with the increase of AESO content, the storage modulus, glass transition temperature, and crosslinking density of the cured film also increase accordingly. This is because the introduction of AESO increases the relative content of carbon-carbon double bonds. After ultraviolet irradiation, the chains in the polymer are no longer attracted by intermolecular forces but are connected by chemical bonds. This effectively increases the crosslinking density of the cured film and enhances the polymer network structure, leading to an increase in the glass transition temperature of the cured film from 38.3℃ to 63.8℃ and an increase in the crosslinking density from 153.89 mol / m³. 3 Increased to 1772.92 mol / m 3 .

[0086] Table 3 Dynamic mechanical properties and crosslinking density of WPUA cured films

[0087] sample <![CDATA[E' 25 (MPa)]]> <![CDATA[T g (℃)]]> <![CDATA[E'at T g +30℃(MPa)]]> <![CDATA[ν e (mol / m 3 )]]> WPUA1 91.32 38.3 1.31 153.89 WPUA2 343.90 55.5 2.00 223.67 WPUA3 846.33 63.5 9.65 1055.66 WPUA4 1195.96 63.8 16.22 1772.92

[0088] Mechanical property analysis of the cured film in Experiment Example 3

[0089] The tensile properties of the cured film were tested using a UTM 4204 universal testing machine manufactured by Shenzhen Sansi. The crosshead speed was set to 20 mm / min, and the sample size was 40.0 mm × 10.0 mm × 0.5 mm (length × width × thickness). To ensure the accuracy of the experimental results, all samples were tested at least 5 times, and the average value was taken.

[0090] The tensile properties test results of the cured film are as follows: Figure 5 As shown in Table 4, the results indicate that with the increasing proportion of AESO, the tensile strength and Young's modulus of the cured film continuously increase, while the elongation at break decreases. The average tensile strength of the WPUA film increased from 6.56 MPa to 22.42 MPa, the Young's modulus increased from 4.84 MPa to 141.75 MPa, while the elongation at break decreased from 137.36% to 15.88%. This is because, with the same molar amount of hydroxyl groups, the content of active double bonds in AESO is higher than that in RADEA. With the increasing content of AESO, the content of carbon-carbon active double bonds in the cured film continuously increases, forming more crosslinking sites after UV irradiation. This makes the polymer crosslinking network more compact, and the relative sliding between molecular chain segments more difficult, thus leading to a continuous increase in the crosslinking density of the cured film and improving the tensile strength and Young's modulus of the cured film. This is consistent with the measured T... gThe trend is consistent with that of crosslinking density. Meanwhile, RADEA, as the soft segment providing hydroxyl functional groups in the system, has a relatively long and flexible fatty acid chain, which imparts excellent flexibility to the film, acting as a plasticizer and improving the film's elongation at break to a certain extent. By controlling the relative content of AESO and RADEA, WPUA cured films with the desired tensile properties can be formulated.

[0091] Table 4 Mechanical properties of WPUA cured film

[0092] sample Tensile strength (MPa) Elongation at break (%) Young's modulus (MPa) WPUA1 6.56±0.44 137.36±11.09 4.81±0.56 WPUA2 11.65±1.59 58.15±3.12 20.10±3.04 WPUA3 15.49±0.17 16.82±2.38 94.17±14.53 WPUA4 22.42±0.69 15.88±0.94 141.75±10.52

[0093] Thermal performance analysis of the cured film in Experiment Example 4

[0094] Thermogravimetric analysis (TGA) of the experimental samples was performed using a Netzsch STA 449C thermal analyzer under a nitrogen atmosphere. The nitrogen flow rate was set to 20 ml / min, the test temperature range was 30-900℃, and the heating rate was 10℃ / min.

[0095] Figure 6 The figure shows the TGA and DTG curves of the cured film, with WPUA thermogravimetric curves for different AESO and RADEA contents. The UV-cured film's thermal degradation temperature at 10% weight loss (T0) is also shown. 10％ ), 50% thermal degradation temperature (T) 50％ ) and the temperature of maximum degradation rate (T max Listed in Table 5.

[0096] The results showed that under a nitrogen atmosphere, the WPUA cured film mainly underwent rapid degradation within the temperature range of 200℃ to 450℃. The first stage below 200℃ was primarily due to the thermal degradation of moisture and small molecules such as catalysts in the cured film. The second stage of thermal degradation, occurring within the temperature range of 200℃ to 300℃, was mainly caused by the breaking and degradation of the hard segments of the urethane bonds formed by the reaction of isocyanate and hydroxyl groups. The third stage of thermal degradation, occurring between 300℃ and 450℃, was mainly caused by the breaking and decomposition of cross-linking bonds and the soft segments of the polyurethane chains. With increasing AESO content, the cured film experienced a 10% weight loss (T... 10％ ) and 50% weight loss (T 50％ The decomposition temperatures of AESO increased from 200.2℃ and 311.9℃ to 241.3℃ and 350.6℃, respectively. This indicates that the addition of AESO increased the functionality of the system and promoted the increase of crosslinking density in the cured film. Therefore, a higher temperature is required to break the interaction forces between polymer segments, which macroscopically manifests as improved thermal stability of the cured film. Overall, the addition of AESO improved the heat resistance of the cured film, enabling its use under high-temperature conditions.

[0097] Table 5 Thermal decomposition data of WPUA cured film

[0098] sample <![CDATA[T 10％ (℃)]]> <![CDATA[T 50％ (℃)]]> <![CDATA[T max (1 st / 2 nd )(℃)]]> WPUA1 200.2 311.9 277.6 / 341.9 WPUA2 211.2 337.1 280.1 / 360.8 WPUA3 232.1 347.5 273.8 / 357.6 WPUA4 241.3 350.6 261.0 / 352.7

[0099] Analysis of gelation rate of cured film in Experiment 5

[0100] The gel content in the cured film was determined using the acetone extraction method. First, a cured film of mass w0 was accurately weighed and immersed in a 20 ml sealed glass bottle containing acetone at room temperature for 48 hours. Then, the cured film was removed and dried in a vacuum oven at 60°C until constant weight, and its weight w1 was recorded. Finally, the gelation rate of each photocurable film was calculated using formula (eq 2.2).

[0101] Gel ratio = (w1 / w0) × 100% (eq 2.2)

[0102] The results are as follows Figure 7 As shown, the gel content of the cured film exhibits a regular variation, with the gel content increasing from 76.78% to 93.26% with increasing AESO content. This is because introducing more AESO increases the content of active carbon-carbon double bonds in the polymer, which promotes the formation of crosslinking sites after UV curing and increases the crosslinking density of the polymer system. The results indicate that the addition of AESO significantly improves the gelation rate of the cured film, resulting in a higher degree of curing.

[0103] Experimental Example 6: General Performance Analysis of Cured Film

[0104] Pencil Hardness Test: The pencil hardness of the cured coating is determined according to GB / T 6739-1996. The specific experimental method is as follows: The pencil hardness of the cured coating surface is measured using a hardness tester with a three-point contact method (two points are the rollers, and one point is the pencil lead). The angle between the pencil and the coating surface is adjusted to 45° with the hardness tester as the carrier. The hardness tester slides on the coating surface with a pressure of 1±0.05 kg and the damage condition of the coating surface after sliding is observed. Each sample is tested in parallel 5 times. When the coating breaks no more than 2 times, the pencil of the next higher hardness grade can be replaced for the next level of testing. When the coating breaks more than 2 times, the pencil grade can be read and the next grade can be recorded. The hardness grade range is divided into 6B~HB~6H from hardest to softest, with 6H being the hardest and 6B being the softest.

[0105] Flexibility Test: The flexibility of the cured coating is measured using the conical mandrel of a QTX-1731 coating elasticity testing machine, according to the test method of GB 1731-93. The minimum diameter of the conical mandrel that allows the cured film to be bent 180° around itself without cracking is the flexibility grade of the cured film. The conical mandrel models include... wait.

[0106] Adhesion test: The adhesion of the UV-cured coating was tested according to the standard requirements of ASTM D3359, "Standard Test Method for Determining Adhesion Grades by Tape Test".

[0107] Chemical corrosion resistance test: At room temperature, weigh appropriate amounts of cured film samples and place them in sealed glass bottles containing tetrahydrofuran and chloroform, respectively. After soaking for 48 hours, remove the samples and observe the morphological changes of the cured films. Perform three parallel experiments on each group of samples to ensure the accuracy of the test.

[0108] The results are shown in Table 6.

[0109] The pencil hardness test results show that the pencil hardness of the WPUA cured film increases with increasing AESO content, which is due to the increased crosslinking density. Almost all cured films exhibit good flexibility, reaching 2mm, 4mm, or 5mm. Due to the increased crosslinking density, WPUA4 exhibits lower elongation, reaching only 10mm. The adhesion rating of all cured films is 0, mainly due to the hydrogen bonding between the urethane in the cured film and the substrate. After immersion in tetrahydrofuran or chloroform for 2 days, the cured film remains insoluble in the solvent and shows no significant surface changes, indicating good chemical resistance.

[0110] Table 6 General Properties of WPUA Cured Film

[0111]

[0112] The above descriptions are merely some embodiments of the present invention. Those skilled in the art can make various modifications and improvements without departing from the inventive concept of the present invention, and these all fall within the scope of protection of the present invention.

Claims

1. A method for preparing vegetable oil-based waterborne polyurethane acrylate prepolymers, characterized in that, Includes the following steps: Take castor oil-based diethanolamide, hydrophilic chain extender, diisocyanate and catalyst, mix them, and react them at a temperature of 50~70℃ for 2~4 h to obtain the first reaction mixture; Epoxidized soybean oil acrylate is dissolved in an organic solvent and then added to the first reaction mixture. The mixture is reacted at a temperature of 50-70℃ for 3-5 hours to obtain the second reaction mixture. The hydroxy acrylate monomer was added to the second reaction mixture and the reaction continued for 2-4 hours. After the reaction was completed, the mixture was cooled to 25-35°C and neutralized with a neutralizing agent to obtain a vegetable oil-based waterborne polyurethane acrylate prepolymer. The structural formula of the castor oil-based diethanolamide is shown below: The hydrophilic chain extender is selected from at least one of N-methyldiethanolamine, N,N-bis(hydroxymethyl)tert-butylamine, and 3-dimethylamino-1,2-propanediol.

2. The preparation method according to claim 1, characterized in that, The molar ratio of hydroxyl groups in the castor oil-based diethanolamide, epoxidized soybean oil acrylate, hydrophilic chain extender, and hydroxyl acrylate monomer is (0.1~6):(0.1~6):7.5:1.

5.

3. The preparation method according to claim 2, characterized in that, The diisocyanate is selected from at least one of isophorone diisocyanate, toluene diisocyanate, diphenylmethane diisocyanate, dicyclohexylmethane diisocyanate, hexamethylene diisocyanate, and lysine diisocyanate; the molar ratio of the isocyanate group in the diisocyanate to the total amount of hydroxyl groups in the castor oil diethanolamide, epoxidized soybean oil acrylate, hydrophilic chain extender, and hydroxy acrylate monomer is 1:(1~1.05).

4. The preparation method according to any one of claims 1 to 3, characterized in that, The catalyst is selected from at least one of dibutyltin dilaurate, dibutyltin diacetate, stannous octoate, zinc naphthenate, dialkyltin dimaleate, and dithioalkyltin.

5. The preparation method according to claim 4, characterized in that, The neutralizing agent is selected from at least one of hydrochloric acid, phosphoric acid, and acetic acid.

6. The vegetable oil-based waterborne polyurethane acrylate prepolymer prepared by the preparation method according to any one of claims 1 to 5.

7. A method for preparing a vegetable oil-based waterborne polyurethane acrylate dispersion, characterized in that, The process includes the following steps: adding water to the vegetable oil-based waterborne polyurethane acrylate prepolymer of claim 6, emulsifying it, and then removing the organic solvent to obtain the product. The mass ratio of the water to the vegetable oil-based waterborne polyurethane acrylate prepolymer is (3~8):(2~3).

8. The vegetable oil-based waterborne polyurethane acrylate dispersion prepared by the method according to claim 7.

9. A bio-based ultraviolet-curable coating, characterized in that, It is mainly composed of the plant oil-based waterborne polyurethane acrylate dispersion as described in claim 8 and a photoinitiator; the amount of the photoinitiator is 3 to 5% of the mass of the plant oil-based waterborne polyurethane acrylate prepolymer; the photoinitiator is selected from at least one of photoinitiator 1173, photoinitiator 184, photoinitiator 907, photoinitiator TPO, and photoinitiator 659.

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