Self-emulsifying palm oil-based aqueous polyurethane, and preparation method and application thereof

Abstract

This invention belongs to the field of bio-based polymer materials technology, specifically relating to a self-emulsifying palm oil-based waterborne polyurethane, its preparation method, and its application. The waterborne polyurethane is prepared by using palm oil as a raw material to prepare a carboxyl-grafted palm oil-based diol, which is then subjected to a condensation reaction with diisocyanate and 1,6-naphthol to synthesize a linear polyurethane oligomer. This oligomer is then emulsified and dispersed in deionized water under the action of triethylamine to obtain a self-emulsifying palm oil-based waterborne polyurethane emulsion. This emulsion can be coated onto steel surfaces to prepare environmentally friendly metal coatings, featuring environmentally friendly raw material sources and a preparation process that requires no additional emulsifiers. The resulting waterborne polyurethane emulsion exhibits excellent properties of high solids content and low viscosity, and the material possesses excellent mechanical and anti-corrosion properties, including good adhesion, flexibility, impact resistance, and excellent water and salt spray resistance.

Description

Technical Field

[0001] This invention relates to the field of bio-based polymer materials, and more particularly to a self-emulsifying palm oil-based waterborne polyurethane, its preparation method, and its application in the field of metal anti-corrosion coatings. Background Technology

[0002] Polyurethane materials are widely used in various industrial fields such as coatings, adhesives, elastomers, footwear materials, sealing materials, and sound insulation materials due to their highly designable molecular structure, excellent chemical stability, adjustable mechanical strength, and outstanding wear resistance. However, traditional solvent-based polyurethanes release large amounts of volatile organic compounds (VOCs) during production and use, causing not only environmental pollution but also harming human health. Waterborne polyurethane, as an environmentally friendly alternative, effectively solves the VOC emission problem by using water as a dispersion medium. It has safe properties such as being non-flammable, non-toxic, and odorless, while also possessing excellent wetting and penetration properties, meeting the coating needs of various substrates.

[0003] Traditional polyurethanes primarily rely on petroleum-based raw materials, facing challenges such as resource depletion and carbon emissions. In recent years, developing sustainable polyurethane materials using renewable resources has become a research hotspot, with vegetable oils attracting significant attention due to their wide availability, low cost, and biodegradability. However, existing technologies for preparing vegetable oil-based waterborne polyurethanes generally suffer from low solids content (typically below 40%), leading to high transportation costs and long drying times, making it difficult to meet the demands of industrial production. Furthermore, the contradiction between high solids content and low viscosity remains unresolved, severely restricting the practical application of vegetable oil-based waterborne polyurethanes. Therefore, developing a method for preparing vegetable oil-based waterborne polyurethanes that combines high solids content, low viscosity, and excellent performance has significant theoretical and practical value. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of existing technologies by proposing a self-emulsifying palm oil-based waterborne polyurethane, its preparation method, and its applications. It features environmentally friendly raw material sources and a preparation process that requires no additional emulsifiers. The resulting waterborne polyurethane emulsion possesses excellent properties of high solids content and low viscosity, along with good adhesion, flexibility, impact resistance, and excellent water and salt spray resistance.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A self-emulsifying palm oil-based waterborne polyurethane, the raw materials used comprising, by weight, 50 parts of palm oil-based polyurethane linear oligomer and 50-100 parts of deionized water;

[0007] The raw materials of the palm oil-based polyurethane linear oligomer comprise, by mass parts: 40-58 parts of carboxyl-grafted palm oil-based diol, 0-13 parts of 1,6-naphthol, 32-36 parts of hexamethylene diisocyanate, and 10-12 parts of triethylamine.

[0008] Furthermore, the carboxyl-grafted palm oil-based diol is obtained by grafting mercaptopropionic acid onto palm oil-based diethanolamide via a mercapto-olefin click reaction.

[0009] A method for preparing a self-emulsifying palm oil-based waterborne polyurethane includes the following steps:

[0010] S1: Synthesize carboxyl-grafted palm oil-based diol;

[0011] S2: Carboxyl-grafted palm oil-based diol and hexamethylene diisocyanate were mixed with butanone in parts by mass, and N2 was introduced. The mixture was magnetically stirred in an oil bath at 75±5 ℃ for 2-8 h. 1,6-naphthol was added in parts by mass, and the reaction was continued with stirring. After the reaction was completed, the mixture was transferred to an ice bath, triethylamine was added, and stirring was continued to obtain linear oligomers of palm oil-based polyurethane.

[0012] S3: Add deionized water, mechanically stir at room temperature, and then remove methyl ethyl ketone by rotary evaporation to obtain a self-emulsifying palm oil-based waterborne polyurethane emulsion;

[0013] Furthermore, step S4 involves uniformly pouring the self-emulsifying palm oil-based waterborne polyurethane emulsion into a mold, allowing it to stand at room temperature for 2±0.5 h, and then transferring it to an oven at 60±10℃ to dry and remove moisture, thus obtaining the self-emulsifying palm oil-based waterborne polyurethane. This method facilitates storage and transportation, and also makes it convenient for conducting mechanical property tests.

[0014] Furthermore, the carboxyl-grafted palm oil-based diol in step S1 is synthesized using palm oil, diethanolamine, and 3-mercaptopropionic acid as raw materials, sodium methoxide as a catalyst, and benzoin dimethyl ether as a photoinitiator; specifically including:

[0015] A 1000 mL three-necked flask equipped with a mechanical stirrer was placed in an oil bath under N2 protection. Diethanolamine and sodium methoxide were added, and the mixture was stirred at 80 °C and 200 r / min for 20–30 min. After adding palm oil, the temperature was raised to 120 °C, and the mixture was stirred for 4–5 h. After cooling, the mixture was purified 3–5 times with ethyl acetate and saturated NaCl solution, and then rotary evaporated for 3–5 h to obtain palm oil-based diethanolamide. Subsequently, 3-mercaptopropionic acid, palm oil-based diethanolamide, and 3 wt% benzoin dimethyl ether were added to a beaker, and the mixture was magnetically stirred at room temperature for 10–15 min. The beaker was then placed under a 360 W ultraviolet light source, and the reaction was allowed to proceed for 5–6 h. After the reaction was completed, the mixture was thoroughly mixed with ethyl acetate, purified 3–5 times with saturated NaCl solution, and then rotary evaporated to obtain the carboxyl-grafted palm oil-based diol.

[0016] This invention synthesizes a carboxyl-grafted palm oil-based diol monomer (POEA-MA) via a two-step method. Due to the uneven distribution of unsaturated double bonds in the carbon chains of palm oil, the carboxyl content of POEA-MA monomers varies, resulting in differences in molecular weight and steric hindrance. During the polycondensation process, POEA-MA monomers with different carboxyl contents exhibit differentiated polycondensation rates. Therefore, chains with high carboxyl content form smaller particle sizes, while chains with low carboxyl content form larger particle sizes, ultimately yielding a self-emulsifying palm oil-based waterborne polyurethane with a bimodal distribution.

[0017] Furthermore, the mass ratio of carboxyl-grafted palm oil-based diol to 1,6-naphthol is 1–18:0–1. Preferably, the mass ratio of carboxyl-grafted palm oil-based diol to 1,6-naphthol is 8:1.

[0018] Furthermore, steps S2 and S3, by mass parts, include: 195-325 parts of carboxyl-grafted palm oil diol, 177-180 parts of hexamethylene diisocyanate, 1000 parts of butanone, 0-64 parts of 1,6-naphthol, 34-57 parts of triethylamine, and 1000-1500 parts of deionized water.

[0019] Application of a self-emulsifying palm oil-based waterborne polyurethane in the preparation of anti-corrosion coatings for steel. This waterborne polyurethane, when used to prepare anti-corrosion coatings for steel, exhibits good mechanical strength, high solids content, and excellent corrosion resistance, solving the problems of non-renewable raw materials and low emulsion solids content inherent in traditional waterborne polyurethanes.

[0020] Furthermore, in use, a palm oil-based waterborne polyurethane emulsion is evenly applied to the surface of the steel, and after drying, a self-emulsifying palm oil-based waterborne polyurethane anti-corrosion coating for steel is obtained.

[0021] Further, the specific steps are as follows: After wiping and drying the steel with ethanol, a self-emulsifying palm oil-based waterborne polyurethane emulsion is uniformly coated onto the steel surface using a 100μm wet film preparation device; the coated steel is placed in a 60 ℃ oven and dried for 12 h, and after cooling to room temperature, the self-emulsifying palm oil-based waterborne polyurethane anti-corrosion coating for steel is obtained.

[0022] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) The self-emulsifying palm oil-based waterborne polyurethane polymer prepared by the present invention has the characteristics of high bio-based content, high emulsion solid content, low viscosity and environmental friendliness; using inexpensive, abundant and green and harmless palm oil as raw material, it provides a new idea for preparing high solid content waterborne polyurethane using palm oil as raw material.

[0023] (2) This invention utilizes the uneven distribution of carboxylic acids in the side chains of palm oil-based diols grafted with carboxyl groups. By varying the content of carboxyl groups in different molecular chains, the emulsion particle size exhibits a bimodal distribution. This bimodal distribution, through the accumulation of particles of different sizes, endows the emulsion with high solids content and low viscosity.

[0024] (3) By optimizing process parameters, the present invention uses an emulsion with a mass ratio of carboxyl-grafted palm oil-based diol to 1,6-naphthol of 8:1 to achieve lower viscosity and higher solid content, and successfully prepares a waterborne polyurethane emulsion with high solid content and low viscosity. This emulsion has excellent tensile properties, adhesion, flexibility and impact resistance. Attached Figure Description

[0025] Figure 1 This is a stability test diagram of the self-emulsifying palm oil-based waterborne polyurethane emulsion in an embodiment of the present invention. (a)-(e) represent the sample before centrifugation, and (a')-(e') represent the sample after centrifugation.

[0026] Figure 2 This is a viscosity bar graph of the self-emulsifying palm oil-based waterborne polyurethane emulsion in an embodiment of the present invention;

[0027] Figure 3 This is a particle size and distribution diagram of self-emulsifying palm oil-based waterborne polyurethane in an embodiment of the present invention;

[0028] Figure 4 This is a particle size and distribution diagram of palm oil-based waterborne polyurethane with added emulsifier in the comparative example of this invention.

[0029] Figure 5 These are transmission electron microscopy (TEM) particle morphology images of the self-emulsifying palm oil-based waterborne polyurethane (WPU2) component in an embodiment of the present invention.

[0030] Figure 6 This is a graph showing the relationship between the viscosity and solid content of the WPU2 emulsion in an embodiment of the present invention;

[0031] Figure 7 These are stability test diagrams of WPU2 emulsions with different solid contents in the embodiments of the present invention. (a)-(f) represent the samples before centrifugation, and (a')-(f') represent the samples after centrifugation.

[0032] Figure 8 This is the differential calorimetric scanning curve of self-emulsifying palm oil-based waterborne polyurethane in an embodiment of the present invention;

[0033] Figure 9 This is a tensile stress and tensile strain diagram of self-emulsifying palm oil-based waterborne polyurethane in an embodiment of the present invention.

[0034] Among them, WPU0 represents a self-emulsifying palm oil-based waterborne polyurethane with a mass ratio of carboxyl-grafted palm oil-based diol to 1,6-naphthol of 1:0; WPU1 represents a self-emulsifying palm oil-based waterborne polyurethane with a mass ratio of carboxyl-grafted palm oil-based diol to 1,6-naphthol of 18:1; WPU2 represents a self-emulsifying palm oil-based waterborne polyurethane with a mass ratio of carboxyl-grafted palm oil-based diol to 1,6-naphthol of 8:1; WPU3 represents a self-emulsifying palm oil-based waterborne polyurethane with a mass ratio of carboxyl-grafted palm oil-based diol to 1,6-naphthol of 5:1; WPU4 represents a self-emulsifying palm oil-based waterborne polyurethane with a mass ratio of carboxyl-grafted palm oil-based diol to 1,6-naphthol of 3:1; POEA-WPU represents a self-emulsifying palm oil-based waterborne polyurethane with a mass ratio of palm oil-based diol to 1,6-naphthol of 7:1. 1. Aqueous polyurethane emulsion prepared using traditional emulsification methods. Detailed Implementation

[0035] To further understand the purpose, structure, features, and functions of this invention, detailed descriptions are provided below with reference to specific embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without inventive effort are within the scope of protection of this invention. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0036] Raw materials: Palm oil (melting point: 18 °C; acid value: 0.16 mg KOH / g) was purchased from Shanghai Dingfen Chemical Technology Co., Ltd., China; 3-mercaptopropionic acid, 1,6-naphthol, hexamethylene diisocyanate, triethylamine, benzoin dimethyl ether and diethanolamine were purchased from Shanghai Jingchun (Aladdin) Industrial Co., Ltd.; sodium chloride, ethyl acetate and sodium methoxide were purchased from Shanghai Guoyao Group Chemical Reagent Co., Ltd.; butanone was purchased from Tianjin Daqiuzhuang Hongda Co., Ltd.

[0037] The synthesis process of carboxyl-grafted palm oil diol is as follows:

[0038] A 1000 mL three-necked flask equipped with a mechanical stirrer was placed in an oil bath under N2 protection. 124.9 g of diethanolamine and 1.62 g of sodium methoxide were added, and the mixture was stirred at 80 °C and 200 r / min for 20 min. After adding 200 g of palm oil, the temperature was raised to 120 °C and stirred for 4 h. After cooling, the mixture was purified 3-5 times with 200 mL of ethyl acetate and 1 L of saturated NaCl solution, and then rotary evaporated for 3 h to obtain palm oil-based diethanolamide. Subsequently, 18 g of 3-mercaptopropionic acid, 26.5 g of palm oil-based diethanolamide, and 0.54 g of 3wt% benzoin dimethyl ether were added to a beaker and magnetically stirred at room temperature for 10 min. The beaker was then placed under a 360 W ultraviolet light source and reacted for 5 h. After the reaction was completed, the mixture was thoroughly mixed with 100 mL of ethyl acetate, purified 3-5 times with 1 L of saturated NaCl solution, and then rotary evaporated to obtain the carboxyl-grafted palm oil-based diol. Example 1

[0039] Preparation of self-emulsifying palm oil-based waterborne polyurethane and anti-corrosion coatings for steel:

[0040] Carboxyl-grafted palm oil-based diol (3.25 g), hexamethylene diisocyanate (1.77 g), and butanone (10 g) were added to a 250 mL three-necked flask, and N2 was introduced. The mixture was magnetically stirred (200 r / min) for 8 h in an oil bath at 75 ℃. The flask was then transferred to an ice bath, and triethylamine (0.57 g) was added. The mixture was stirred for another 30 min to obtain a linear oligomer of palm oil-based polyurethane. Deionized water (15 mL) was added, and the mixture was mechanically stirred (1500 r / min) at room temperature for 2 h. The butanone was removed by rotary evaporation to obtain a self-emulsifying palm oil-based aqueous polyurethane emulsion.

[0041] After wiping and drying Q215 steel with ethanol, an appropriate amount of self-emulsifying palm oil-based waterborne polyurethane emulsion was uniformly coated onto the steel surface using a 100 μm wet film preparation device. The coated steel was then placed in a 60 ℃ oven for 12 h and cooled to room temperature to obtain a self-emulsifying palm oil-based waterborne polyurethane anti-corrosion coating for steel.

[0042] In Example 1, the mass ratio of carboxyl-grafted palm oil diol to 1,6-naphthol was 1:0. Example 2

[0043] Preparation of self-emulsifying palm oil-based waterborne polyurethane and anti-corrosion coatings for steel:

[0044] Carboxyl-grafted palm oil-based diol (2.92 g), hexamethylene diisocyanate (1.77 g), and butanone (10 g) were added to a 250 mL three-necked flask, and N2 was introduced. The mixture was magnetically stirred (200 r / min) for 2 h in an oil bath at 75 ℃. Then, 1,6-naphthol (0.16 g) was added, and stirring was continued for 6 h. The flask was then transferred to an ice bath, and triethylamine (0.52 g) was added. Stirring was continued for 30 min to obtain a linear oligomer of palm oil-based polyurethane. Deionized water (15 mL) was added, and the mixture was mechanically stirred (1500 r / min) at room temperature for 2 h. Butanone was removed by rotary evaporation to obtain a self-emulsifying palm oil-based aqueous polyurethane emulsion.

[0045] After wiping and drying Q215 steel with ethanol, an appropriate amount of self-emulsifying palm oil-based waterborne polyurethane emulsion was uniformly coated onto the steel surface using a 100 μm wet film preparation device. The coated steel was then placed in a 60 ℃ oven for 12 h and cooled to room temperature to obtain a self-emulsifying palm oil-based waterborne polyurethane anti-corrosion coating for steel.

[0046] In Example 2, the mass ratio of carboxyl-grafted palm oil diol to 1,6-naphthol was 18:1. Example 3

[0047] Preparation of self-emulsifying palm oil-based waterborne polyurethane and anti-corrosion coatings for steel:

[0048] Carboxyl-grafted palm oil-based diol (2.60 g), hexamethylene diisocyanate (1.77 g), and butanone (10 g) were added to a 250 mL three-necked flask, and N2 was introduced. The mixture was magnetically stirred (200 r / min) for 2 h in an oil bath at 75 ℃. Then, 1,6-naphthol (0.32 g) was added, and stirring was continued for 6 h. The flask was then transferred to an ice bath, and triethylamine (0.46 g) was added. Stirring was continued for 30 min to obtain a linear oligomer of palm oil-based polyurethane. Deionized water (10 mL) was added, and the mixture was mechanically stirred (1500 r / min) at room temperature for 2 h. Butanone was removed by rotary evaporation to obtain a self-emulsifying palm oil-based aqueous polyurethane emulsion.

[0049] After wiping and drying Q215 steel with ethanol, an appropriate amount of self-emulsifying palm oil-based waterborne polyurethane emulsion was uniformly coated onto the steel surface using a 100 μm wet film preparation device. The coated steel was then placed in a 60 ℃ oven for 12 h and cooled to room temperature to obtain a self-emulsifying palm oil-based waterborne polyurethane anti-corrosion coating for steel.

[0050] In Example 3, the mass ratio of carboxyl-grafted palm oil diol to 1,6-naphthol was 8:1. Example 4

[0051] Preparation of self-emulsifying palm oil-based waterborne polyurethane and anti-corrosion coatings for steel:

[0052] Carboxyl-grafted palm oil-based diol (2.27 g), hexamethylene diisocyanate (1.77 g), and butanone (10 g) were added to a 250 mL three-necked flask, and N2 was introduced. The mixture was magnetically stirred (200 r / min) for 2 h in an oil bath at 75 ℃. Then, 1,6-naphthol (0.48 g) was added, and stirring was continued for 6 h. The flask was then transferred to an ice bath, and triethylamine (0.40 g) was added. Stirring was continued for 30 min to obtain a linear oligomer of palm oil-based polyurethane. Deionized water (10 mL) was added, and the mixture was mechanically stirred (1500 r / min) at room temperature for 2 h. Butanone was removed by rotary evaporation to obtain a self-emulsifying palm oil-based aqueous polyurethane emulsion.

[0053] After wiping and drying Q215 steel with ethanol, an appropriate amount of self-emulsifying palm oil-based waterborne polyurethane emulsion was uniformly coated onto the steel surface using a 100 μm wet film preparation device. The coated steel was then placed in a 60 ℃ oven for 12 h and cooled to room temperature to obtain a self-emulsifying palm oil-based waterborne polyurethane anti-corrosion coating for steel.

[0054] In Example 4, the mass ratio of carboxyl-grafted palm oil diol to 1,6-naphthol was 5:1. Example 5

[0055] Preparation of self-emulsifying palm oil-based waterborne polyurethane and anti-corrosion coatings for steel:

[0056] Carboxyl-grafted palm oil-based diol (1.95 g), hexamethylene diisocyanate (1.77 g), and butanone (10 g) were added to a 250 mL three-necked flask, and N2 was introduced. The mixture was magnetically stirred (200 r / min) for 2 h in an oil bath at 75 ℃. 1,6-Naphthol (0.64 g) was added, and stirring continued for 6 h. The flask was then transferred to an ice bath, and triethylamine (0.34 g) was added. Stirring continued for 30 min to obtain a linear oligomer of palm oil-based polyurethane. Deionized water (10 mL) was added, and the mixture was mechanically stirred (1500 r / min) at room temperature for 2 h. Butanone was removed by rotary evaporation to obtain a self-emulsifying palm oil-based waterborne polyurethane emulsion. After wiping and drying Q215 steel with ethanol, an appropriate amount of the self-emulsifying palm oil-based waterborne polyurethane emulsion was uniformly coated onto the steel surface using a 100 μm wet film preparation device. The coated steel was then placed in a 60 ℃ oven for 12 hours. h, after cooling to room temperature, yields a self-emulsifying palm oil-based waterborne polyurethane anti-corrosion coating for steel.

[0057] In Example 5, the mass ratio of carboxyl-grafted palm oil diol to 1,6-naphthol was 3:1.

[0058] Comparative Example 1

[0059] Preparation of palm oil-based waterborne polyurethane and anti-corrosion coatings for steel with added emulsifiers:

[0060] Palm oil-based diol (2.12 g), hexamethylene diisocyanate (1.77 g), and butanone (10 g) were added to a 250 mL three-necked flask, and N2 was introduced. The mixture was magnetically stirred (200 r / min) for 2 h in an oil bath at 75 ℃. 1,6-naphthol (0.32 g) was added, and stirring was continued for 2 h. Dimethylolbutyric acid (0.68 g) was added as an emulsifier. The flask was then transferred to an ice bath, and triethylamine (0.46 g) was added. Stirring was continued for 30 min to obtain a linear oligomer of palm oil-based polyurethane. Deionized water (10 mL) was added, and the mixture was mechanically stirred (1500 r / min) at room temperature for 2 h. Butanone was removed by rotary evaporation to obtain a palm oil-based aqueous polyurethane emulsion.

[0061] In Comparative Example 1, the mass ratio of palm oil-based diol to 1,6-naphthol was 7:1.

[0062] Performance testing:

[0063] 1. Stability and viscosity test of waterborne polyurethane emulsion:

[0064] The stability of the emulsion was determined according to the centrifugal stability method specified in GB / T 11543-2008: 10 mL of emulsion was injected into a centrifuge tube, centrifuged at 4000 r / min for 10 min, and then visually evaluated. The viscosity of the WPUs emulsion was measured using a Lichen rotary digital viscometer (LC-NDJ-5T). Measurements were performed at 25 ℃ using rotors No. 0 and No. 1, both at a rotation speed of 6 rpm.

[0065] Specifically, such as Figure 1 As shown, Figure 1 In the original text, (a)-(e) represent samples of the aqueous polyurethane emulsions prepared in Examples 1-5 before centrifugation, and (a')-(e') represent samples of the aqueous polyurethane emulsions prepared in Examples 1-5 after centrifugation. Figure 1 It is known that self-emulsifying palm oil-based aqueous polyurethane emulsions (solid content approximately 46±5%) prepared with different mass ratios of carboxyl-grafted palm oil-based diols and 1,6-naphthol showed good stability, except for WPU4 which had a slight milky white precipitate. This indicates that the stability of the emulsion is positively correlated with the carboxylic acid content.

[0066] Depend on Figure 2 As shown, the viscosity of the aqueous polyurethane emulsions prepared in Examples 1-5 generally showed an increasing trend, from 305.3 mPa·s to 305.5 mPa·s. -1 385.8 mPa·s -1 277.3 mPa·s -1468.3 mPa·s -1 615.4 mPa·s -1 Example 3 showed the lowest viscosity at 277.3 mPa·s. -1 .

[0067] 2. Particle size distribution test of waterborne polyurethane emulsion:

[0068] The particle size and distribution of the dispersion were analyzed by dynamic light scattering (DLS), using a monochromatic coherent helium-neon laser (633 nm) as the light source and a detector that detects the scattered light at a 90-degree angle. The sample was diluted to a concentration of 0.1 wt% in deionized water and then subjected to ultrasonic treatment to homogenize the dispersion.

[0069] Specifically, such as Figure 3 As shown, by Figure 3 It is known that the emulsion particle size and distribution of WPU0, WPU1, WPU2, WPU3 and WPU4 are all bimodal. As the carboxylic acid content increases, the emulsion particle size decreases, indicating that the emulsion particle size is positively correlated with the carboxylic acid content.

[0070] like Figure 4 As shown, the emulsion particle size and unimodal distribution of POEA-WPU prepared by the traditional emulsification method demonstrate that the scheme of preparing bimodal particle size distribution emulsions by grafting carboxyl groups onto palm oil diols is effective. The particle size, particle diameter ratio, and volume percentage of large particles in the emulsions of WPU0, WPU1, WPU2, WPU3, and WPU4 are summarized in Table 1.

[0071]

[0072] 3. Transmission electron microscopy test of self-emulsifying palm oil-based waterborne polyurethane emulsion:

[0073] Radio electron microscopy (TEM) images of the transemulsion were obtained using a JEM-2100Plus (JEOL, Japan) microscope with an accelerating voltage of 80 kV. The samples were stained with 0.2 wt% phosphotungstic acid hydrate before observation.

[0074] Specifically, such as Figure 5 As shown, by Figure 5 The TEM morphology of WPU2 emulsion particles shows that the emulsion particles have both large and small morphologies, which is consistent with the DLS test results.

[0075] The solid content of WPU2 was adjusted by adding 27 g, 22 g, 17 g, 12 g, 7 g, and 2 g of deionized water, respectively. The viscosity of the WPU2 emulsions with different solid contents was then measured using a Lichen rotary digital viscometer (LC-NDJ-5T). Measurements were performed at 25°C using rotors No. 0 and No. 1, at a rotation speed of 6 rpm.

[0076] Depend on Figure 6 It is known that the viscosity of WPU2 emulsion increases with increasing solid content. The viscosities of emulsions with solid contents of 18%, 24%, 36%, 45%, 51%, and 60% are 40.8 mPa·s. -1 69.6 mPa·s -1 88.0 mPa·s -1 162.4 mPa·s -1 277.3 mPa·s -1 409.2 mPa·s -1 This indicates that WPU2 emulsion can meet the requirements of high solids content and low viscosity.

[0077] The stability of the emulsion was determined according to the centrifugal stability method specified in GB / T 11543-2008: 10 mL of emulsion was injected into a centrifuge tube, centrifuged at 4000 r / min for 10 min, and then visually evaluated.

[0078] Depend on Figure 7 It can be seen that no precipitation was observed in the WPU2 emulsion when the solid content reached 51%, while a milky white precipitate appeared when the solid content reached 60%, indicating that the WPU2 emulsion can still maintain good stability when the solid content reaches 51%.

[0079] 4. Differential scanning calorimetry analysis of waterborne polyurethane:

[0080] Differential scanning calorimetry was performed on a DSC 25 instrument (TA Instruments, Inc., USA); approximately 10 mg of powder sample was placed in a standard covered aluminum crucible; the experimental temperature was -50 to 250 °C, the heating rate was 10 °C / min, and the experiment was conducted in a N2 atmosphere (20 mL / min).

[0081] Specifically, such as Figure 8 As shown, by Figure 8 It is known that the glass transition temperatures of self-emulsifying palm oil-based waterborne polyurethanes WPU0, WPU1, WPU2, WPU3 and WPU4 are 16.94 ℃, 27.04 ℃, 38.59 ℃, 40.19 ℃ and 45.20 ℃, respectively, which increase significantly with the increase of 1,6-naphthodiol content.

[0082] 5. Mechanical property testing of waterborne polyurethane:

[0083] The self-emulsifying palm oil-based waterborne polyurethane emulsion was uniformly poured into the mold and allowed to stand at room temperature for 2±0.5 h. Then, it was transferred to an oven at 60±10℃ to dry and remove moisture. The sample was then made into a dumbbell-shaped specimen (specifications: 75 mm long, 10 mm wide at both ends, 5 mm wide in the middle, and 3 mm thick) to test its tensile properties. The tensile property test was performed according to ASTM D638-10 standard. The tensile properties were tested on a microcomputer-controlled electronic universal testing machine.

[0084] Specifically, such as Figure 9 As shown, by Figure 9 It is known that the tensile strengths of self-emulsifying palm oil-based waterborne polyurethanes WPU0, WPU1, WPU2, WPU3, and WPU4 are 1.3 MPa, 1.5 MPa, 3.1 MPa, 6.5 MPa, and 13.7 MPa, respectively; and the elongation at break of the self-emulsifying palm oil-based waterborne polyurethanes WPU0, WPU1, WPU2, WPU3, and WPU4 are 115%, 195%, 164%, 211%, and 119%, respectively.

[0085] 6. Performance testing of water-based polyurethane anti-corrosion coatings for steel:

[0086] The adhesion of anti-corrosion coatings for steel shall be tested according to GB / T9286-2021; flexibility shall be tested according to GB / T1731-2020; impact resistance shall be tested according to GB / T1732-2020; water resistance shall be tested according to GB / T1733-1993; salt spray resistance shall be tested according to GB / T1771-2007; and solvent wiping resistance shall be tested according to GB / T 23989-2009. Pencil hardness shall be tested at room temperature using a pencil hardness tester (model QHQ-A, China) according to the national standard GB / T6739-2006.

[0087] The specific properties are shown in Table 2 below. Table 2 shows the various properties of the self-emulsifying palm oil-based waterborne polyurethane anti-corrosion coating for steel.

[0088]

[0089] As shown in Table 2, the self-emulsifying palm oil-based waterborne polyurethane steel coating has excellent adhesion, flexibility, impact resistance, water resistance, and salt spray resistance.

[0090] This invention uses palm oil as a raw material to prepare carboxyl-grafted palm oil-based diols, which are then subjected to a condensation reaction with diisocyanate and 1,6-naphthol to synthesize linear polyurethane oligomers. These oligomers are then emulsified and dispersed in deionized water under the action of triethylamine to obtain a self-emulsifying palm oil-based waterborne polyurethane emulsion. This emulsion can be coated onto steel surfaces to prepare environmentally friendly metal coatings. It features environmentally friendly raw material sources and a preparation process that requires no additional emulsifiers. The resulting waterborne polyurethane emulsion exhibits excellent properties of high solids content and low viscosity, and the material possesses excellent mechanical and anti-corrosion properties, including good adhesion, flexibility, impact resistance, and excellent water and salt spray resistance.

[0091] The present invention has been described by the above-described embodiments; however, these embodiments are merely examples for implementing the present invention. It must be noted that the disclosed embodiments do not limit the scope of the present invention. Conversely, any modifications and refinements made without departing from the spirit and scope of the present invention are within the scope of patent protection of the present invention.

Claims

1. A method for preparing a self-emulsifying palm oil-based aqueous polyurethane emulsion, characterized in that: Includes the following steps: S1: Synthesize carboxyl-grafted palm oil-based diol; The carboxyl-grafted palm oil-based diol was obtained by grafting 3-mercaptopropionic acid onto palm oil-based diethanolamide via a mercapto-olefin click reaction. The synthesis process of palm oil-based diethanolamide is as follows: a 1000 mL three-necked flask equipped with a mechanical stirrer is placed in an oil bath under N2 protection, diethanolamine and sodium methoxide are added, and the mixture is stirred at 80 ℃ and 200 r / min for 20-30 min; after adding palm oil, the temperature is raised to 120 ℃ and stirred for 4-5 h; after cooling, the mixture is purified 3-5 times with ethyl acetate and saturated NaCl solution, and then rotary evaporated for 3-5 h to obtain palm oil-based diethanolamide; S2: Carboxyl-grafted palm oil-based diol and hexamethylene diisocyanate were mixed with butanone in parts by mass, and N2 was introduced. The mixture was magnetically stirred in an oil bath at 75±5 ℃ for 2-8 h. 1,6-naphthol was added in parts by mass, and the reaction was continued with stirring. After the reaction was completed, the mixture was transferred to an ice bath, triethylamine was added, and stirring was continued to obtain linear oligomers of palm oil-based polyurethane. S3: Add deionized water, mechanically stir at room temperature, and then remove methyl ethyl ketone by rotary evaporation to obtain a self-emulsifying palm oil-based waterborne polyurethane emulsion; Steps S2 and S3, by mass parts, include: 195-325 parts of carboxyl-grafted palm oil diol, 177-180 parts of hexamethylene diisocyanate, 1000 parts of butanone, 0-64 parts of 1,6-naphthol, 34-57 parts of triethylamine, and 1000-1500 parts of deionized water.

2. The method for preparing the self-emulsifying palm oil-based aqueous polyurethane emulsion as described in claim 1, characterized in that: The mass ratio of carboxyl-grafted palm oil diol to 1,6-naphthol is 1–18:0–1.

3. A self-emulsifying palm oil-based waterborne polyurethane emulsion prepared by a method according to any one of claims 1-2.

4. The application of the self-emulsifying palm oil-based waterborne polyurethane emulsion as described in claim 3 in the preparation of anti-corrosion coatings for steel.

5. The application of the self-emulsifying palm oil-based waterborne polyurethane emulsion as described in claim 4 in the preparation of anti-corrosion coatings for steel, characterized in that: When using, apply the palm oil-based waterborne polyurethane emulsion evenly to the steel surface, and after drying, obtain a self-emulsifying palm oil-based waterborne polyurethane anti-corrosion coating for steel.

6. The application of the self-emulsifying palm oil-based waterborne polyurethane emulsion as described in claim 4 in the preparation of anti-corrosion coatings for steel, characterized in that: The specific steps are as follows: After wiping and drying the steel with ethanol, use a 100 μm wet film preparation device to evenly coat the self-emulsifying palm oil-based waterborne polyurethane emulsion onto the steel surface; place the coated steel in a 60℃ oven to dry for 12 h, and after cooling to room temperature, the self-emulsifying palm oil-based waterborne polyurethane anti-corrosion coating for steel is obtained.

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