Bio-based polyurethane waterproof coating and preparation method thereof

Abstract

The invention relates to the technical field of coatings, in particular to a bio-based polyurethane waterproof coating and a preparation method thereof. The coating is prepared from organic fluorine-silicon cross-linked castor oil, dibutyltin dilaurate, an HDI tripolymer, polytetrahydrofuran ether glycol, 1, 4-butanediol, a filler, a plasticizer and an ultraviolet light absorber, and the organic fluorine-silicon cross-linked castor oil is obtained by silanization modification of methyl ricinoleate and hydrolysis cross-linking of fluorine-containing silane. The preparation method is simple, and the material has excellent performance, is suitable for the fields of building waterproofing, weather-resistant coatings and the like, and has wide application potential and market value.

Description

Technical Field

[0001] The present invention relates to the technical field of coatings, and in particular to a bio-based polyurethane waterproof coating and a preparation method thereof. Background Art

[0002] In recent years, with the increasingly stringent environmental regulations and the deepening of the concept of sustainable development, bio-based polyurethane coatings have attracted widespread attention due to their renewable and low VOC emission characteristics. Castor oil is a typical bio-based polyol raw material. The hydroxyl groups in its molecular structure can directly react with isocyanate to form a polyurethane network, which has formed a certain application foundation in the field of coatings.

[0003] As an important natural bio-based material, castor oil has attracted extensive attention from researchers due to its excellent chemical reactivity and rich chemical modification sites. Castor oil molecules contain a variety of functional sites, such as hydroxyl groups and double bonds, which can be functionalized by a variety of chemical modification methods to design and prepare bio-based polymer materials with excellent performance. However, when castor oil is directly used in the preparation of polyurethane-based resins, the non-polar segments in its molecular structure are relatively long, which easily leads to insufficient hydrophobicity of the coating. In addition, the hydroxyl functionality of natural castor oil is low (about 2.7 on average), and the hydroxyl activity is significantly affected by steric hindrance, resulting in insufficient cross-linking network density formed by the reaction with isocyanate. This structural defect is directly manifested in the low mechanical strength of the coating, and interfacial peeling often occurs. More prominently, the proportion of rigid ring structures in its molecular chain is too high, which makes the glass transition temperature (Tg) of the material generally higher than -10°C, and brittle fracture is prone to occur in low temperature environments (such as -25°C).

[0004] In recent years, the application of silicone and fluorine-containing compounds in the field of high-performance coatings has gradually increased. Silicone materials can significantly improve the mechanical properties and durability of coatings due to their high chemical stability, low surface energy and high crosslinking density. At the same time, the extremely low surface energy and special hydrophobicity of fluorine-containing materials in the chemical structure can further improve the waterproof performance of the coating. However, traditional fluorine-containing silicon-modified coatings are usually based on petroleum-based raw materials, and their complex synthesis process and high production costs limit their large-scale promotion. Therefore, the realization of fluorine-silicon organic crosslinking modification based on castor oil bio-based raw materials can not only greatly improve the material performance, but also conform to the direction of green chemistry and sustainable development. Summary of the invention

[0005] In view of this, the purpose of the present invention is to provide a bio-based polyurethane waterproof coating and a preparation method thereof, so as to solve the problems of poor waterproofness and high low-temperature brittleness of castor oil-based polyurethane coatings.

[0006] Based on the above purpose, the present invention provides a bio-based polyurethane waterproof coating, which is prepared from the following raw materials, by weight: 80-100 parts of organic fluorine silicon cross-linked castor oil, 0.03-0.05 parts of dibutyltin dilaurate, 46-58 parts of HDI trimer, 7-9 parts of polytetramethylene ether glycol, 3-4 parts of 1,4-butanediol, 4-6 parts of filler, 1-3 parts of plasticizer and 0.1-1 parts of ultraviolet absorber.

[0007] Furthermore, the preparation method of the organic fluorine-silicon cross-linked castor oil is as follows: methyl ricinoleate, 3-mercaptopropyltriethoxysilane and 2-hydroxy-2-methyl-1-phenylacetone are added to tetrahydrofuran, stirred at room temperature for 5-7 hours, irradiated with ultraviolet light during stirring, and the solvent was removed by rotary evaporation. Deionized water, anhydrous ethanol and tridecafluorooctyltriethoxysilane were added, and the pH was adjusted to 8.0-8.5 with ammonia water. The mixture was stirred for 2.5-3.5 hours, and the solvent was removed by rotary evaporation to obtain organic fluorine-silicon cross-linked castor oil.

[0008] Preferably, the weight ratio of methyl ricinoleate, 3-mercaptopropyltriethoxysilane, 2-hydroxy-2-methyl-1-phenylpropanone, tetrahydrofuran, deionized water, anhydrous ethanol and tridecafluorooctyltriethoxysilane is 40-60:30.5-45.8:0.7-1:80-120:180-220:40-60:3.4-4.5.

[0009] Preferably, the ricinoleic acid methyl ester is obtained by hydrolyzing castor oil with methanol.

[0010] Preferably, the preparation steps of methyl ricinoleate are as follows: adding anhydrous methanol and potassium hydroxide to castor oil, heating to 43-48° C., stirring for 5-7 hours, then neutralizing the reaction product with sulfuric acid, taking the upper oil phase, washing it with deionized water until it is neutral, and then removing water by rotary evaporation to obtain methyl ricinoleate.

[0011] Preferably, the weight ratio of anhydrous methanol, potassium hydroxide and castor oil is 8-12:0.4-0.6:40-60.

[0012] Preferably, the wavelength of the ultraviolet light irradiation is 365 nm and the intensity is 6 mW / cm.

[0013] Preferably, the NCO content of the HDI trimer is 20-23 g / 100 g.

[0014] Preferably, the weight average molecular weight of the polytetramethylene ether diol is 800-1500.

[0015] Preferably, the filler is nano-silicon dioxide with an average particle size of 10-50 nm.

[0016] Preferably, the plasticizer is epoxidized soybean oil.

[0017] Preferably, the ultraviolet absorber is UV-531.

[0018] Furthermore, the present invention also provides a method for preparing a bio-based polyurethane waterproof coating, comprising the following steps: under nitrogen protection, heating the organic fluorine silicon cross-linked castor oil to 78-85°C, adding dibutyltin dilaurate and HDI trimer, stirring and reacting for 2-3h, cooling to 60-68°C, adding polytetrahydrofuran ether glycol, continuing to stir and react for 30-50min, then adding 1,4-butanediol, continuing to stir and react for 25-35min, then adding filler, plasticizer and ultraviolet absorber, dispersing at 1800-2200rpm for 20-30min, and finally maintaining at a vacuum degree of -0.093-7MPa for 30-50min to obtain the bio-based polyurethane waterproof coating.

[0019] Beneficial effects of the present invention:

[0020] The present invention prepares a coating material having an organic fluorine-silicon cross-linked structure by silylation modification of methyl ricinoleate, thereby significantly improving the comprehensive performance of the coating. The organic fluorine-silicon cross-linked system combines the low surface energy characteristics of the fluorocarbon chain with the high cross-linking stability of the silicon-oxygen network, so that the coating has excellent mechanical strength, water resistance and low-temperature flexibility. The introduction of the fluorocarbon segment forms a hydrophobic layer on the coating surface, effectively reducing the free energy of the coating surface and the permeability of water molecules, thereby improving the waterproof performance of the material. At the same time, the interpenetration of the silicon-oxygen network structure and the coating matrix gives the material higher strength and durability.

[0021] The present invention introduces methyl ricinoleate, and the material shows excellent controllability in molecular reactivity and network formation. The linear structure reduces the steric hindrance between molecules, promotes the efficient grafting of silanized components and forms a more uniform cross-linked structure. The synergistic effect of the flexible ester chain segment and the cross-linked network improves the low-temperature bending performance of the coating by dispersing stress, effectively avoiding crack propagation. In addition, mercaptosilane provides efficient chemical activity, further improves the regularity and functionalization of the molecular chain, and achieves a perfect balance between the surface performance and internal toughness of the material. The coating prepared by the present invention has excellent comprehensive performance and has wide application potential and market value. DETAILED DESCRIPTION

[0022] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with specific embodiments.

[0023] In the specific implementation manner of the present invention, castor oil was purchased from Shanghai Aladdin Biochemical Technology Co., Ltd. with a product number of C110663.

[0024] Embodiment 1:

[0025] (1) adding 8 g of anhydrous methanol and 0.4 g of potassium hydroxide to 40 g of castor oil, heating to 43° C., stirring for 5 h, and then neutralizing the reaction product with sulfuric acid, washing the upper oil phase with deionized water until neutral, and then removing water by rotary evaporation to obtain methyl ricinoleate;

[0026] (2) 40 g of methyl ricinoleate, 30.5 g of 3-mercaptopropyltriethoxysilane and 0.7 g of 2-hydroxy-2-methyl-1-phenylacetone were added to 80 g of tetrahydrofuran, and the mixture was stirred at room temperature for 5 h. During the stirring process, ultraviolet light was irradiated at a wavelength of 365 nm and an intensity of 6 mW / cm. The solvent was removed by rotary evaporation. Then, 180 g of deionized water, 40 g of anhydrous ethanol and 3.4 g of tridecafluorooctyltriethoxysilane were added. The pH was adjusted to 8.0 with aqueous ammonia, and the mixture was stirred for 2.5 h. The solvent was removed by rotary evaporation to obtain an organic fluorine-silicon cross-linked castor oil;

[0027] (3) Under nitrogen protection, 80g of organic fluorine silicon cross-linked castor oil was heated to 78°C, 0.03g of dibutyltin dilaurate and 46g of HDI trimer (NCO content 21.5g / 100g) were added, and the mixture was stirred for reaction for 2h. The mixture was cooled to 60°C, 7g of polytetrahydrofuran ether glycol (weight average molecular weight of 1000) was added, and the mixture was stirred for reaction for 30min. Then 3g of 1,4-butanediol was added, and the mixture was stirred for reaction for 25min. Then 4g of nano-silica (average particle size of 20nm), 1g of epoxy soybean oil and 0.1g of ultraviolet absorber UV-531 were added, and the mixture was dispersed at 1800rpm for 20min. Finally, the mixture was maintained at a vacuum degree of -0.093MPa for 30min to obtain a bio-based polyurethane waterproof coating.

[0028] Embodiment 2:

[0029] (1) adding 10 g of anhydrous methanol and 0.5 g of potassium hydroxide to 50 g of castor oil, heating to 45° C., stirring for 6 h, and then neutralizing the reaction product with sulfuric acid, washing the upper oil phase with deionized water until neutral, and then removing water by rotary evaporation to obtain methyl ricinoleate;

[0030] (2) 50 g of methyl ricinoleate, 38.2 g of 3-mercaptopropyltriethoxysilane and 0.8 g of 2-hydroxy-2-methyl-1-phenylacetone were added to 100 g of tetrahydrofuran, and stirred at room temperature for 6 h. During the stirring process, ultraviolet light was irradiated at a wavelength of 365 nm and an intensity of 6 mW / cm. The solvent was removed by rotary evaporation. Then 200 g of deionized water, 50 g of anhydrous ethanol and 3.8 g of tridecafluorooctyltriethoxysilane were added, and the pH was adjusted to 8.2 with aqueous ammonia. The mixture was stirred for 3 h, and the solvent was removed by rotary evaporation to obtain an organic fluorine-silicon cross-linked castor oil;

[0031] (3) Under nitrogen protection, 90g of organic fluorine silicon cross-linked castor oil was heated to 80°C, 0.04g of dibutyltin dilaurate and 52g of HDI trimer (NCO content 21.5g / 100g) were added, and the mixture was stirred for reaction for 2.5h. The mixture was cooled to 65°C, 8g of polytetramethylene glycol (weight average molecular weight 1000) was added, and the mixture was stirred for reaction for 40min. Then 3.5g of 1,4-butanediol was added, and the mixture was stirred for reaction for 30min. Then 5g of nano-silica (average particle size 20nm), 2g of epoxy soybean oil and 0.5g of ultraviolet absorber UV-531 were added, and the mixture was dispersed at 2000rpm for 25min. Finally, the mixture was maintained at a vacuum degree of -0.095MPa for 40min to obtain a bio-based polyurethane waterproof coating.

[0032] Embodiment 3:

[0033] (1) adding 12 g of anhydrous methanol and 0.6 g of potassium hydroxide to 60 g of castor oil, heating to 48° C., stirring for 7 h, and then neutralizing the reaction product with sulfuric acid, washing the upper oil phase with deionized water until neutral, and then removing water by rotary evaporation to obtain methyl ricinoleate;

[0034] (2) 60 g of methyl ricinoleate, 45.8 g of 3-mercaptopropyltriethoxysilane and 1 g of 2-hydroxy-2-methyl-1-phenylacetone were added to 120 g of tetrahydrofuran, and the mixture was stirred at room temperature for 7 h. During the stirring process, ultraviolet light was irradiated at a wavelength of 365 nm and an intensity of 6 mW / cm. The solvent was removed by rotary evaporation. Then 220 g of deionized water, 60 g of anhydrous ethanol and 4.5 g of tridecafluorooctyltriethoxysilane were added. The pH was adjusted to 8.5 with aqueous ammonia, and the mixture was stirred for 3.5 h. The solvent was removed by rotary evaporation to obtain an organic fluorine-silicon cross-linked castor oil;

[0035] (3) Under nitrogen protection, 100 g of organic fluorine-silicon cross-linked castor oil was heated to 85°C, 0.05 g of dibutyltin dilaurate and 58 g of HDI trimer (NCO content 21.5 g / 100 g) were added, and the mixture was stirred for reaction for 3 h. The mixture was cooled to 68°C, 9 g of polytetramethylene glycol (weight average molecular weight 1000) was added, and the mixture was stirred for reaction for 50 min. 4 g of 1,4-butanediol was added, and the mixture was stirred for reaction for 35 min. 6 g of nano-silicon dioxide (average particle size 20 nm), 3 g of epoxy soybean oil and 1 g of ultraviolet absorber UV-531 were added, and the mixture was dispersed at 2200 rpm for 20-30 min. Finally, the mixture was maintained at a vacuum degree of -0.097 MPa for 50 min to obtain a bio-based polyurethane waterproof coating.

[0036] Comparative Example 1:

[0037] The difference between Comparative Example 1 and Example 2 is that ricinoleic acid methyl ester in step (2) is replaced by castor oil;

[0038] Comparative Example 2:

[0039] The difference between Comparative Example 2 and Example 2 is that the organic fluorine-silicon cross-linked castor oil in step (3) is replaced by castor oil;

[0040] Comparative Example 3:

[0041] The difference between Comparative Example 3 and Example 2 is that the 3-mercaptopropyltriethoxysilane in step (2) is replaced by methyltriethoxysilane;

[0042] Comparative Example 4:

[0043] The difference between Comparative Example 4 and Example 2 is that: tridecafluorooctyltriethoxysilane is not added in step (2);

[0044] Performance Testing:

[0045] Coating preparation: The coatings prepared in the examples and comparative examples were applied to the concrete substrate by a scraper coating method, and the wet film thickness was controlled to be 1.2±0.1 mm. The coatings were first pre-cured in an oven at 40° C. for 2 h, and then transferred to a constant temperature room at 25° C. for curing for 5 days to obtain a coating.

[0046] Adhesion test: According to GB / T 5210-2006, the coating sample was fixed on the fixture of the tensile testing machine, and a 20 mm diameter aluminum ingot was used to bond the joint. The coating was vertically stretched at a rate of 1 mm / min until the coating fell off. The maximum tensile force was recorded and converted to megapascals (MPa). The average value of three samples was taken. The results are shown in Table 1.

[0047] Water resistance test: According to GB / T 1733-1993, the coating sample was immersed in (23±2)℃ deionized water with the liquid level 10mm above the sample. After immersion for 168h, it was taken out and wiped dry. The coating retention rate was evaluated by the cross-hatch method (1mm×1mm square). The results are shown in Table 1.

[0048] Moisture permeability test: According to GB / T 17146-2015, the demoulding coating is placed in a test chamber, and the test chamber temperature is controlled at (38±0.6)℃ and relative humidity is (90±2)%. The 24h moisture permeability is weighed and converted to g / (m 2 h), and the results are shown in Table 1.

[0049] Low temperature bendability: According to GB / T 17146-2015, the demoulded coating sample is placed in a -25℃ low temperature box for 2 hours, and then immediately bent 180° on a bending machine to observe whether cracks occur on the coating surface.

[0050] Table 1 Performance test results

[0051]

[0052] Data Analysis:

[0053] From the data of Examples 1-3 in Table 1, it can be seen that the coating prepared by the present invention exhibits excellent comprehensive performance in terms of adhesion, water resistance, moisture permeability and low-temperature bending performance. This is mainly due to the organic fluorine-silicon cross-linking system formed by silanization modification of methyl ricinoleate, and the low surface energy characteristics of the fluorocarbon segment help to reduce the surface free energy of the coating. During the polyurethane chain extension process, the flexible segment of polytetrahydrofuran ether diol forms a microphase separation with the rigid structure of the HDI trimer, which may enhance the mechanical strength through the hard segment crystallization area, while the soft segment maintains the elastic deformation ability.

[0054] From the data of Example 2 and Comparative Example 1 in Table 1, it can be seen that Example 2 exhibits more outstanding performance than Comparative Example 1, which may be due to the fact that the introduction of methyl ricinoleate enhances the reactivity of the coating and the controllability of the molecular structure. Compared with castor oil, methyl ricinoleate has a linear structure and has less steric hindrance, which is conducive to the grafting of 3-mercaptopropyltriethoxysilane and is more conducive to cross-linking after silane hydrolysis, thereby forming a uniform cross-linked network, improving the mechanical properties of the coating while reducing the penetration of water molecules, and the moderate flexibility of the ester group and the structural stability of the silicon oxygen network work synergistically, so that the material can disperse stress through the micro-region slip of the molecular chain segment when deformed at low temperature, avoiding crack expansion caused by stress concentration.

[0055] From the data of Example 2 and Comparative Example 2 in Table 1, it can be seen that, relative to castor oil, organic fluorine-silicon cross-linked castor oil can significantly improve the water resistance and low-temperature bendability of the coating, which is mainly due to the formation of a hydrophobic layer on the surface of the coating by the fluoroalkyl chain, which effectively reduces the adsorption energy of water molecules. The interpenetrating structure of the siloxane cross-linked network and the polyurethane matrix may produce a synergistic enhancement effect, in which the rigid silicon-oxygen network bears the mechanical stress, while the elastic polyurethane matrix absorbs the deformation energy. This composite structure may improve the flexibility of the material at low temperatures by limiting the thermal motion of the molecular segments.

[0056] From the data of Example 2 and Comparative Example 3 in Table 1, it can be seen that after replacing 3-mercaptopropyltriethoxysilane with methyltriethoxysilane, the adhesion, water resistance and low-temperature bendability of the coating all decreased. This is mainly because the high reactivity of the mercapto group may promote the click chemistry reaction between the silane reagent and methyl ricinoleate to form a more regular grafting structure. This directional grafting may optimize the arrangement orientation of the molecular chain and make the fluorocarbon segments more orderly enriched on the coating surface.

[0057] It can be seen from the data of Example 2 and Comparative Example 4 in Table 1 that tridecafluorooctyl triethoxysilane not only significantly affects the water resistance of the coating, but also affects the low-temperature bendability. This may be because the steric hindrance effect of the fluorinated group regulates the spatial distribution of the cross-linking reaction and adjusts the cross-linking density, so that the coating has both surface hydrophobicity and internal toughness.

[0058] Those skilled in the art should understand that the discussion of any of the above embodiments is merely illustrative and is not intended to imply that the scope of the present invention is limited to these examples. Under the concept of the present invention, the technical features in the above embodiments or different embodiments may be combined, the steps may be implemented in any order, and there are many other variations of the different aspects of the present invention as described above, which are not provided in detail for the sake of simplicity.

Claims

1. A bio-based polyurethane waterproof coating, characterized in that: The invention is prepared from the following raw materials by weight: 80-100 parts of organic fluorine silicon cross-linked castor oil, 0.03-0.05 parts of dibutyltin dilaurate, 46-58 parts of HDI trimer, 7-9 parts of polytetramethylene ether glycol, 3-4 parts of 1,4-butanediol, 4-6 parts of filler, 1-3 parts of plasticizer and 0.1-1 parts of ultraviolet absorber; The preparation method of the organic fluorine-silicon cross-linked castor oil is as follows: methyl ricinoleate, 3-mercaptopropyltriethoxysilane and 2-hydroxy-2-methyl-1-phenylacetone are added to tetrahydrofuran, stirred at room temperature for 5-7 hours, irradiated with ultraviolet light during the stirring process, and the solvent is removed by rotary evaporation, and then deionized water, anhydrous ethanol and tridecafluorooctyltriethoxysilane are added, and the pH is adjusted to 8.0-8.5 with ammonia water, stirred for 2.5-3.5 hours, and the solvent is removed by rotary evaporation to obtain the organic fluorine-silicon cross-linked castor oil; The weight ratio of ricinoleic acid methyl ester, 3-mercaptopropyltriethoxysilane, 2-hydroxy-2-methyl-1-phenylacetone, tetrahydrofuran, deionized water, anhydrous ethanol and tridecafluorooctyltriethoxysilane is 40-60:30.5-45.8:0.7-1:80-120:180-220:40-60:3.4-4.

5.

2. The bio-based polyurethane waterproof coating according to claim 1, characterized in that: The preparation steps of methyl ricinoleate are as follows: adding anhydrous methanol and potassium hydroxide to castor oil, heating to 43-48° C., stirring for 5-7 hours, neutralizing the reaction product with sulfuric acid, washing the upper oil phase with deionized water until neutral, and then rotary evaporating to remove water to obtain methyl ricinoleate.

3. The bio-based polyurethane waterproof coating according to claim 2, characterized in that: The weight ratio of the anhydrous methanol, potassium hydroxide and castor oil is 8-12:0.4-0.6:40-60.

4. The bio-based polyurethane waterproof coating according to claim 1, characterized in that: The wavelength of the ultraviolet light irradiation is 365 nm, and the intensity is 6 mW / cm.

5. The bio-based polyurethane waterproof coating according to claim 1, characterized in that: The NCO content of the HDI trimer is 20-23 g / 100 g.

6. The bio-based polyurethane waterproof coating according to claim 1, characterized in that: The weight average molecular weight of the polytetramethylene ether glycol is 800-1500.

7. The bio-based polyurethane waterproof coating according to claim 1, characterized in that: The filler is nano silicon dioxide with an average particle size of 10-50nm.

8. The bio-based polyurethane waterproof coating according to claim 1, characterized in that: The plasticizer is epoxidized soybean oil, and the ultraviolet absorber is UV-531.

9. A method for preparing the bio-based polyurethane waterproof coating according to any one of claims 1 to 8, characterized in that: The following steps are involved: Under nitrogen protection, the organic fluorosilicone cross-linked castor oil is heated to 78-85°C, dibutyltin dilaurate and HDI trimer are added, stirred and reacted for 2-3 hours, cooled to 60-68°C, polytetramethylene ether glycol is added, and the stirring reaction is continued for 30-50 minutes, and then 1,4-butanediol is added, and the stirring reaction is continued for 25-35 minutes, and then fillers, plasticizers and ultraviolet absorbers are added. Dispersed at 1800-2200rpm for 20-30 minutes, and finally maintained at a vacuum degree of -0.093-7MPa for 30-50 minutes to obtain a bio-based polyurethane waterproof coating.

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