Waterproof bio-based polyurethane coating and preparation process thereof

Abstract

The invention relates to the field of polyurethane coating processing, in particular to a waterproof bio-based polyurethane coating and a preparation technology thereof.The waterproof bio-based polyurethane coating is prepared from, by weight, 25%-40% of castor oil polyester polyol, 15%-25% of isocyanate, 5%-10% of bio-based polybasic acid, 0.2%-0.6% of a catalyst, 0.5%-1% of a chain extender, 15%-20% of modified nanofiller, 3%-5% of a wetting agent and 1%-2% of a curing agent. By adopting the formula, the prepared waterproof bio-based polyurethane coating has good weather resistance, high and low temperature resistance, strength and waterproofness, and can be used in Tibet, Xinjiang, Inner Mongolia, Qinghai and other regions for a long time without aging, and the service life of the waterproof coating is prolonged.

Description

Technical Field

[0001] The present application relates to the field of polyurethane coating processing, and more specifically, to a waterproof bio-based polyurethane coating and a preparation process thereof. Background Art

[0002] Bio-based polyurethane coating is a green, non-toxic, odorless, and environmentally friendly coating that is commonly used in the construction industry, especially for roof waterproofing. By applying bio-based polyurethane coating on the roof to form a continuous and dense waterproof membrane, it effectively prevents moisture penetration and protects the roof structure from water damage.

[0003] In roof waterproofing treatment, bio-based polyurethane coatings can be evenly and tightly applied to the roof surface to form a continuous and dense waterproof membrane, which can not only effectively isolate the penetration of rainwater and prevent the roof structure from being damaged due to long-term immersion in water, but also resist some common chemical corrosion and physical wear, thereby extending the service life of the building.

[0004] However, in certain areas such as Tibet, Xinjiang, Inner Mongolia and Qinghai, due to the extreme natural environmental conditions, such as long sunshine hours in summer, high solar radiation intensity and large temperature differences between winter and summer, these environmental factors pose more stringent challenges to the use of bio-based polyurethane coatings. Long-term strong sunlight exposure in the northwest will accelerate the oxidation process of the coating, which can easily lead to the breakage of the molecular chain of the bio-based polyurethane coating, thus causing the coating to age, discolor or even powder. At the same time, large temperature changes will cause the coating material to experience cyclic stress of thermal expansion and contraction, and the coating is prone to fine cracks that gradually expand, which will eventually affect the overall waterproof effect and durability of the coating and shorten its service life. Summary of the invention

[0005] In order to solve the problem of short service life of bio-based polyurethane coatings in the northwest, the present application provides a waterproof bio-based polyurethane coating and a preparation process thereof.

[0006] In a first aspect, the present application provides a waterproof bio-based polyurethane coating, which adopts the following technical solution: a waterproof bio-based polyurethane coating is prepared from the following raw materials in weight percentage: Castor oil polyester polyol 25-40% Isocyanate 15-25% Bio-based polyacids 5-10% Catalyst 0.2-0.6% Chain extender 0.5-1% Modified nano filler 15-20% Wetting agent 3-5% Curing agent 1-2% The remainder is diluent.

[0007] By adopting the above technical scheme, the prepared waterproof bio-based polyurethane coating has good weather resistance, high and low temperature resistance, strength and waterproofness. It can be used for a long time in Tibet, Xinjiang, Inner Mongolia and Qinghai and other regions without aging, thereby extending the service life of the waterproof coating.

[0008] Among them, isocyanate reacts with castor oil polyester polyol and bio-based polyacid to form a three-dimensional network structure of polyurethane, which makes the coating oxidatively degraded under long-term strong sunlight, delays the aging process of the coating, and reduces discoloration and powdering. The reasonable ratio of isocyanate and chain extender ensures that the coating forms a high-strength and stable cross-linked structure after curing, which can effectively resist the thermal expansion and contraction stress caused by large temperature changes, reduce the formation of fine cracks in the coating, and maintain the integrity and waterproof performance of the coating. The cross-linking reaction of the bio-based polyacid coating enhances the rigidity and toughness of the polyurethane molecular chain, making the coating more resistant to aging, discoloration and powdering in extreme environments, and maintaining a long-term appearance and performance. The modified nanofiller can improve the UV resistance, anti-aging ability and mechanical strength of the waterproof bio-based polyurethane coating. The reason is that the small size effect and surface effect of the modified nanofiller can effectively block the penetration of ultraviolet rays and slow down the oxidation process of the coating; at the same time, its high specific surface area provides more cross-linking points, which enhances the density and durability of the coating. The right amount of wetting agent and diluent is added to the formula to improve the wettability and fluidity of the coating, making the construction process smoother and forming a uniform, defect-free coating. The curing agent further promotes the cross-linking and curing of the coating, making the coating have higher hardness and better chemical corrosion resistance after curing.

[0009] Preferably, the modified nanofiller is prepared by the following method: 1) drying the nanofiller, and then placing the nanofiller in ethanol for ultrasonic dispersion to obtain a turbid solution; 2) stirring the turbid liquid, 3-aminopropyltriethoxysilane and benzotriazole at 50-70° C. for 1-2 hours to obtain a mixed solution 1; 3) dissolving isocyanate and organosilicon diol in ethanol to obtain a mixed solution 2; 4) Mixed solution 1 and mixed solution 2 are stirred at 60-70° C. for reaction for 1-2 hours, filtered, and the filter residue is collected to obtain a modified nanofiller.

[0010] Preferably, the weight parts of the raw materials used to prepare the modified nanofiller are as follows: Nano filler 30-40 parts 3-aminopropyltriethoxysilane 5-8 parts 1-3 parts of benzotriazole Isocyanate 10-13 parts 8-10 parts of silicone diol 25-35 parts of ethanol.

[0011] By adopting the above technical scheme, the modified nanofiller prepared can be evenly dispersed in the waterproof bio-based polyurethane coating system, further improving the UV resistance, aging resistance and strength of the waterproof bio-based polyurethane coating, and extending the service life of the coating after curing.

[0012] In step 1), the nanofiller particles are uniformly dispersed in ethanol at the nano level by ultrasonic action, which provides good conditions for subsequent reactions. In step 2), 3-aminopropyltriethoxysilane can form a layer of organosilicon layer on the surface of the nanofiller, improving the compatibility and interfacial bonding force of the nanofiller and the polyurethane matrix. Benzotriazole, as an anti-aging agent, can give the nanofiller better anti-ultraviolet and anti-oxidation properties, thereby protecting the entire coating system. In step 3), isocyanate groups are successfully introduced on the surface of the nanofiller by reacting isocyanate with organosilicon diol in ethanol, and then further reacting with mixed solution 1, so that the modified nanofiller can react chemically with the polyester polyol in the polyurethane coating to form a strong chemical bond, enhance the stability and dispersibility of the nanofiller in the coating, thereby improving the anti-ultraviolet property, anti-aging property and strength of the waterproof bio-based polyurethane coating.

[0013] Preferably, the average particle size of the nanofiller is 20-300 nm.

[0014] By adopting the above technical solution, the particle size of the nanofiller is optimized, the specific surface area of ​​the nanofiller is increased, and the contact area between the nanofiller and the polyurethane matrix is ​​greatly increased, thereby enhancing the interface interaction and bonding force, which helps the nanofiller to be more stably dispersed in the coating and more effectively transfer stress, thereby improving the overall performance of the coating.

[0015] Preferably, the diluent is obtained by mixing ethanol and an ester solvent in a weight ratio of (7-8):10, and the ester solvent is one of ethyl acetate, butyl acetate or dimethyl carbonate.

[0016] By adopting the above technical solution, the type of diluent is optimized and the viscosity of the waterproof bio-based polyurethane coating is adjusted, so that it can be more easily applied and leveled during construction. At the same time, both ethanol and ester solvents have good volatility and solubility, which can ensure that the coating is quickly and evenly applied to the surface of the substrate during construction and quickly dries to form a film. Ethanol and ester solvents (ethyl acetate, butyl acetate or dimethyl carbonate) are both environmentally friendly solvents with low toxicity and volatile organic compound (VOC) emissions, which meet the requirements of the modern coatings industry for environmental performance and help reduce the harm to the environment and human body during the use of coatings.

[0017] Preferably, the castor oil polyester polyol has a hydroxyl value of 85-150 mgKOH / g and a functionality of 1-3.

[0018] By adopting the above technical solution, the hydroxyl value and functionality of castor oil are optimized, the reactivity of castor oil polyol is improved, and a dense cross-linked network is formed in the coating during the curing process, thereby improving the waterproof performance of the coating. At the same time, it helps to enhance the cohesion and adhesion of the coating, so that the coating can better adhere to the surface of the substrate to form a continuous waterproof layer. Preferably, the bio-based polyacid is one of furandicarboxylic acid, sugar alcohol, palmitic acid, oleic acid, malic acid, and citric acid.

[0019] By adopting the above technical solutions, the types of bio-based polyacids are optimized, the cross-linking reaction of the coating is further promoted, and the rigidity and toughness of the polyurethane molecular chain are enhanced, so that the coating can better resist aging, discoloration and chalking in extreme environments and maintain long-term appearance and performance.

[0020] Preferably, the chain extender is obtained by mixing diethyltoluenediamine and ethanolamine in a weight ratio of (3-4):1.

[0021] By adopting the above technical solution, diethyltoluenediamine and ethanolamine jointly promote the crosslinking reaction of polyurethane coating, improve the crosslinking density and strength of the coating, and also improve the flexibility and low temperature resistance of the coating. Among them, the isocyanate group of diethyltoluenediamine reacts to form a urea bond crosslinking structure, which improves the cohesion and strength of the polyurethane coating, making it have better wear resistance, tear resistance and chemical resistance; ethanolamine forms hydrogen bonds with other groups in the polyurethane molecular chain through hydroxyl groups, thereby enhancing the interaction between molecules, improving the low temperature resistance of the coating, and enabling the coating to maintain good physical properties at low temperatures.

[0022] Preferably, the wetting agent is obtained by mixing nonylphenol polyoxyethylene ether and polyoxyethylene fatty alcohol ether in a weight ratio of (5-6):3.

[0023] By adopting the above technical solution, the wettability and spreadability of the waterproof bio-based polyurethane coating are improved, making it easier to apply the waterproof bio-based polyurethane coating to the surface of the roof substrate. At the same time, the fluidity and leveling of the waterproof bio-based polyurethane coating can be improved, and defects such as bubbles and pinholes in the coating process can be reduced, and the gloss and smoothness of the coating can be improved.

[0024] In a second aspect, the present application provides a process for preparing a waterproof bio-based polyurethane coating, using the following technical solution: A preparation process of a waterproof bio-based polyurethane coating comprises the following preparation steps: S1. Under the protection of dry nitrogen, castor oil polyol is added into a reaction vessel, the temperature is raised to 110-120°C, water is removed under reduced pressure, and then the system temperature is lowered to 60-80°C; S2, adding bio-based polyacid, isocyanate and catalyst into the reaction container, mixing evenly, adjusting the viscosity of the mixture with solvent, and maintaining the temperature at 60-80° C. for 7-9 hours; S3. After the reaction in step S2 is completed, a chain extender is added to carry out a cross-linking reaction, and the mixture is stirred. Then, a modified nano-filler, a wetting agent, and a curing agent are added and stirred to obtain a bio-based polyurethane coating.

[0025] The bio-based polyurethane coating produced by the above-mentioned preparation process has excellent waterproofness, weather resistance, high and low temperature resistance and aging resistance. It can maintain stable performance under extreme natural environmental conditions, effectively prevent moisture penetration, and protect the roof structure from water damage.

[0026] In summary, this application has the following beneficial effects: 1. Enhanced weather resistance and anti-aging properties: Castor oil polyester polyol in the formula is one of the main ingredients. Its bio-based characteristics not only meet environmental protection requirements, but also effectively resist oxidative degradation under long-term strong sunlight due to its good UV resistance. The addition of bio-based polyacids further enhances the molecular stability of the coating, slows down the aging process caused by light, and ensures that the coating maintains excellent appearance and performance under extreme sunlight conditions.

[0027] 2. Good high and low temperature resistance: The formula forms a highly cross-linked polyurethane structure by precisely controlling the ratio of isocyanate to chain extender. This structure can better resist the stress of thermal expansion and contraction when experiencing large temperature changes, and reduce the generation and expansion of fine cracks. The addition of modified nanofillers further improves the microstructural strength of the coating, enhances its ability to resist temperature changes, and maintains the integrity and waterproof performance of the coating.

[0028] 3. Good waterproof performance: The coating can be evenly and tightly applied to the roof surface to form a continuous and dense waterproof film, effectively isolating the penetration of rainwater and other liquids. At the same time, its good chemical stability can resist common chemical corrosion, such as acid rain, salt spray, etc., and protect the roof structure from damage. In addition, the physical wear resistance of the coating is also improved, which can resist physical wear caused by natural factors such as wind and sand, and extend the service life. DETAILED DESCRIPTION Example

[0029] Example 1 A waterproof bio-based polyurethane coating is prepared by the following method: S1. Under the protection of dry nitrogen, add 250 g of castor oil polyol into a reaction vessel, heat to 110° C. and remove water under reduced pressure for 1 h, then reduce the system temperature to 60° C.; S2, add 250 g of bio-based polyacid (furandicarboxylic acid), 50 g of isocyanate (hexamethylene diisocyanate) and 2 g of catalyst (dibutyltin dilaurate) into the reaction container, mix well, use 203 g of diluent (ethanol) to adjust the viscosity of the mixed solution, and keep the reaction at 60° C. for 7 h; S3. After the reaction in step S2 is completed, 5 g of chain extender (diethyltoluenediamine) is added to carry out a cross-linking reaction, and the mixture is stirred. Then, 200 g of modified nano-filler (modified nano-silica), 30 g of wetting agent (nonylphenol polyoxyethylene ether), and 10 g of curing agent (trimethylolpropane tri(3-propyleneimide) propionate) are added and stirred to obtain a bio-based polyurethane coating.

[0030] Modified nano-silica was purchased from Shanghai Zhenlishi Network Technology Co., Ltd., model M5.

[0031] The difference between Example 2-3 and Example 1 is that the types, amounts and experimental parameters of some raw materials for preparing the bio-based polyurethane coating are different. The specific differences are shown in Table 1: Table 1: Types, amounts and experimental parameters of raw materials for preparing bio-based polyurethane coatings in Examples 1-3 Example 4 A waterproof bio-based polyurethane coating, this embodiment is different from embodiment 1 in that the modified nanofiller is prepared by the following method: 1) drying 300 g of nanofiller (nanosilicon dioxide, with an average particle size of 20-50 nm), and then placing the nanofiller in 200 g of ethanol for ultrasonic dispersion to obtain a turbid solution; 2) The turbid liquid, 50 g of 3-aminopropyltriethoxysilane and 10 g of benzotriazole were stirred at 50° C. for 1 h to obtain a mixed solution 1; 3) dissolving 100 g of isocyanate (hexamethylene diisocyanate) and 80 g of silicone diol (silicone polyether diol) in 50 g of ethanol to obtain a mixed solution 2; 4) Mixed solution 1 and mixed solution 2 were stirred and reacted at 60° C. for 1 h, filtered, and the filter residue was collected to obtain a modified nanofiller.

[0032] The silicone polyether diol is a hydroxyl-terminated silicone diol with a molecular weight of 1500.

[0033] The difference between Example 5-6 and Example 4 is that the types, amounts and experimental parameters of some raw materials for preparing the modified nanofillers are different. The specific differences are shown in Table 2: Table 2 Types, amounts and experimental parameters of raw materials used to prepare modified nanofillers in Examples 4-6 Example 7 A waterproof bio-based polyurethane coating. The difference between this embodiment and embodiment 1 is that the chain extender is obtained by mixing diethyltoluenediamine and ethanolamine in a weight ratio of 3:1.

[0034] Example 8 A waterproof bio-based polyurethane coating. The difference between this embodiment and embodiment 4 is that the chain extender is obtained by mixing diethyltoluenediamine and ethanolamine in a weight ratio of 4:1.

[0035] Example 9 A waterproof bio-based polyurethane coating. The difference between this embodiment and embodiment 1 is that the wetting agent is nonylphenol polyoxyethylene ether and polyoxyethylene fatty alcohol ether in a weight ratio of 5:3.

[0036] Example 10 A waterproof bio-based polyurethane coating. The difference between this embodiment and embodiment 4 is that the wetting agent is nonylphenol polyoxyethylene ether and polyoxyethylene fatty alcohol ether in a weight ratio of 6:3.

[0037] Embodiment 11 A waterproof bio-based polyurethane coating. The difference between this embodiment and embodiment 1 is that the diluent is obtained by mixing ethanol and an ester solvent (ethyl acetate) in a weight ratio of 7:10.

[0038] Example 12 A waterproof bio-based polyurethane coating. The difference between this embodiment and embodiment 4 is that the diluent is obtained by mixing ethanol and an ester solvent (ethyl acetate) in a weight ratio of 8:10.

[0039] Comparative Example Comparative Example 1 A waterproof bio-based polyurethane coating. The difference between this embodiment and embodiment 1 is that tung oil polyol is used instead of castor oil polyester polyol of equal mass.

[0040] Comparative Example 2 A water-resistant bio-based polyurethane coating, the difference between this embodiment and embodiment 1 is that a solvent is used instead of an equal mass of bio-based polyacid.

[0041] Comparative Example 3 A waterproof bio-based polyurethane coating. The difference between this embodiment and embodiment 1 is that the amount of castor oil polyester polyol used is 500g, and the amount of solvent used is 34g.

[0042] Comparative Example 4 A waterproof bio-based polyurethane coating. The difference between this embodiment and embodiment 1 is that the amount of castor oil polyester polyol used is 200g, and the amount of solvent used is 253g.

[0043] Comparative Example 5 A waterproof bio-based polyurethane coating. The difference between this embodiment and embodiment 1 is that the amount of modified nanofiller used is 250g and the amount of solvent used is 153g.

[0044] Detection method / test method Tensile strength: Tested in accordance with GB / T19250-2003 "Polyurethane Waterproof Coating".

[0045] High and low temperature resistance: Tested in accordance with the GB / T1735-2009 test standard, the low temperature is -40℃, 24h, the high temperature is 250℃, 24h, and cycled 20 times. Observe the coating for bubbles, peeling, cracking, and discoloration. If not, measure the tensile strength again and calculate the retention rate of tensile strength.

[0046] UV aging resistance test: The coatings prepared in Examples 1-12 and Comparative Examples 1-5 were applied on substrates and dried. They were then irradiated with ultraviolet light in a xenon arc lamp aging test chamber with a cumulative irradiation of 2000 MJ / ㎡ for 1000 h. The coatings were observed for bubbles, peeling, cracking, and discoloration. If not, the tensile strength was measured again, and the retention rate of the tensile strength was calculated.

[0047] Wear resistance: Tested in accordance with GB / T 1768 test standard.

[0048] Fluidity: Tested in accordance with GB / T 9264 test standard. Test data are shown in Table 3: Table 3 Experimental data of Examples 1-12 and Comparative Examples 1-5 It can be seen from Examples 1-12 and Comparative Examples 1-5 in combination with Table 3 that the waterproof bio-based polyurethane coating prepared by the formula in the present application has good strength, high and low temperature resistance, weather resistance, wear resistance and fluidity, and can adapt to complex environmental changes.

[0049] Comparing Example 1 with Comparative Examples 1-2, the tensile strength of Comparative Example 1 is lower than that of Example 1; and in the high and low temperature resistance and UV resistance tests, Comparative Examples 1-2 show cracking, bubbles and discoloration; in the wear resistance test, Comparative Example 1 has a large loss and poor fluidity, indicating that the use of castor oil polyol, bio-based polyacid and other raw materials together is beneficial to improving the strength, high and low temperature resistance, weather resistance, wear resistance and fluidity of the waterproof bio-based polyurethane coating.

[0050] Comparing Example 1 with Comparative Examples 3-5, the tensile strength of Comparative Examples 3-5 decreased; in the high and low temperature resistance test and the UV resistance test, cracking and bubbling occurred in Comparative Example 4, and the retention rate decreased in Comparative Example 5; in the wear resistance test, Comparative Examples 3-5 had a large loss and poor fluidity, indicating that by optimizing the amount of castor oil polyether polyol and modified nanofiller, it is beneficial to improve the strength, high and low temperature resistance, weather resistance, wear resistance and fluidity of the waterproof bio-based polyurethane coating.

[0051] Comparing Example 1 with Example 4-6, the tensile strength in Example 4-6 is improved, the retention rate of high and low temperature resistance and purple line resistance is improved, the loss after the wear resistance test is reduced, and the fluidity is improved, indicating that the modified nanofiller prepared in this application can improve the strength, high and low temperature resistance, weather resistance, wear resistance and fluidity of the waterproof bio-based polyurethane coating.

[0052] From the experimental results of Example 1 and Example 7, Example 4 and Example 8, it can be seen that optimizing the type and amount of the chain extender is beneficial to improving the strength, high and low temperature resistance, weather resistance and wear resistance of the waterproof bio-based polyurethane coating.

[0053] From the experimental results of Example 1 and Example 9, Example 4 and Example 10, it can be seen that optimizing the type and amount of the wetting agent is beneficial to improving the strength, weather resistance, wear resistance and fluidity of the waterproof bio-based polyurethane coating.

[0054] From Example 1 and Example 11, Example 4 and Example 12, it can be seen that optimizing the type and amount of the diluent is beneficial to improving the wear resistance and fluidity of the waterproof bio-based polyurethane coating.

[0055] This specific embodiment is merely an explanation of the present application and is not a limitation of the present application. After reading this specification, those skilled in the art may make modifications to the present embodiment without any creative contribution as needed, but such modifications are protected by the patent law as long as they are within the scope of the claims of the present application.

Claims

1. A waterproof bio-based polyurethane coating, characterized in that: Prepared from the following raw materials in weight percentage: Castor oil polyester polyol 25-40% Isocyanate 15-25% Bio-based polyacids 5-10% Catalyst 0.2-0.6% Chain extender 0.5-1% Modified nano filler 15-20% Wetting agent 3-5% Curing agent 1-2% The remainder is diluent.

2. A waterproof bio-based polyurethane coating according to claim 1, characterized in that: The modified nanofiller is prepared by the following method: 1) Dry the nanofiller, and then ultrasonically disperse the nanofiller in ethanol to obtain a turbid solution; 2) stirring the turbid liquid, 3-aminopropyltriethoxysilane and benzotriazole at 50-70° C. for 1-2 hours to obtain a mixed solution 1; 3) dissolving isocyanate and organosilicon diol in ethanol to obtain a mixed solution 2; 4) Mixed solution 1 and mixed solution 2 are stirred at 60-70° C. for 1-2 hours, filtered, and the filter residue is collected to obtain a modified nanofiller.

3. A waterproof bio-based polyurethane coating according to claim 2, characterized in that: The weight parts of the raw materials used to prepare the modified nanofiller are as follows: Nano filler 30-40 parts 5-8 parts of aminopropyltriethoxysilane 1-3 parts of benzotriazole Isocyanate 10-13 parts 8-10 parts of silicone diol 25-35 parts of ethanol.

4. A waterproof bio-based polyurethane coating according to claim 2, characterized in that: The average particle size of the nanofiller is 20-300 nm.

5. The waterproof bio-based polyurethane coating according to claim 1, characterized in that: The diluent is obtained by mixing ethanol and an ester solvent in a weight ratio of (7-8):10, and the ester solvent is one of dimethyl carbonate in ethyl acetate and butyl acetate.

6. A waterproof bio-based polyurethane coating according to claim 4, characterized in that: The castor oil polyester polyol has a hydroxyl value of 85-150 mgKOH / g and a functionality of 1-3.

7. The waterproof bio-based polyurethane coating according to claim 1, characterized in that: The bio-based polyacid is one of furandicarboxylic acid, sugar alcohol, palmitic acid, oleic acid, malic acid and citric acid.

8. The waterproof bio-based polyurethane coating according to claim 1, characterized in that: The chain extender is obtained by mixing diethyltoluenediamine and ethanolamine in a weight ratio of (3-4):

1.

9. The waterproof bio-based polyurethane coating according to claim 1, characterized in that: The wetting agent is composed of nonylphenol polyoxyethylene ether and polyoxyethylene fatty alcohol ether in a weight ratio of (5-6):

3.

10. A process for preparing a waterproof bio-based polyurethane coating according to any one of claims 1 to 9, characterized in that: The method comprises the following preparation steps: S1. Under the protection of dry nitrogen, castor oil polyol is added into a reaction vessel, the temperature is raised to 110-120°C, water is removed under reduced pressure, and then the system temperature is lowered to 60-80°C; S2, adding bio-based polyacid, isocyanate and catalyst into the reaction container, mixing evenly, adjusting the viscosity of the mixture with solvent, and maintaining the temperature at 60-80° C. for 7-9 hours; S3. After the reaction in step S2 is completed, a chain extender is added to carry out a cross-linking reaction, and the mixture is stirred. Then, a modified nano-filler, a wetting agent, a curing agent and a diluent are added and stirred to obtain a bio-based polyurethane coating.

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