Silane functionalized graphene oxide / waterborne polyurethane hydrophobic coating and preparation

Abstract

The invention discloses a silane functionalized graphene oxide / waterborne polyurethane hydrophobic coating and preparation, and belongs to the technical field of paints.The silane functionalized graphene oxide / waterborne polyurethane hydrophobic coating is prepared by the steps that natural graphite powder serves as a raw material, and graphene oxide is prepared through a Hummer method; n-(beta-aminoethyl)-gamma-aminopropyl trimethoxy silane is grafted to the surface of the graphene oxide through a chemical reduction method, and GO-AATS composite filler is obtained; then, castor oil is used as a soft segment, isophorone diisocyanate is used as a hard segment, and a series of GO-AATS-WPU emulsions are prepared. According to the silane functionalized graphene oxide / waterborne polyurethane hydrophobic coating and preparation, chemical bonds are formed between graphene oxide and waterborne polyurethane, and the interfacial compatibility of graphene oxide and waterborne polyurethane is improved, so that the mechanical property, water resistance, corrosion resistance and thermal stability of the waterborne polyurethane coating are improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of coating technology, and particularly to a silane functionalized graphene oxide / waterborne polyurethane hydrophobic coating and preparation. BACKGROUND

[0002] Waterborne polyurethane coating uses water as solvent, and has the advantages of low toxicity and flame retardancy, and the low organic content of waterborne polyurethane coating meets the increasingly stringent environmental requirements, and is highly valued by researchers, and becomes one of the fastest growing coating varieties in the world today. However, waterborne polyurethane coating also faces a series of problems, such as poor water resistance, poor corrosion resistance, and poor thermal stability.

[0003] Graphene oxide has good dispersibility, high specific surface area, excellent physical properties and thermal stability, and the honeycomb-like SP 2 The carbon atom structure has good barrier effect on various corrosive substances, and the introduction of graphene oxide into waterborne polyurethane can effectively improve the mechanical properties, heat resistance, flame retardancy and other properties of waterborne polyurethane coating. In addition, the surface of graphene oxide has a large number of oxygen-containing functional groups, which can be further reduced and modified. In the reduction process, functional groups with specific functions are introduced, and the modified composite material is obtained. However, there is a strong van der Waals force between the graphene oxide layers, which is easy to agglomerate and difficult to uniformly disperse in the waterborne polyurethane coating matrix, affecting the performance of the composite material. In addition, the interface compatibility between graphene oxide and waterborne polyurethane coating is poor, which also affects the performance of the composite material. SUMMARY

[0004] The purpose of the present application is to provide a silane functionalized graphene oxide / waterborne polyurethane hydrophobic coating and preparation, which uses natural graphite powder as raw material, graphene oxide (GO) is prepared by Hummer method, and N-(β-aminoethyl)-γ-aminopropyl trimethoxysilane (AATS) is grafted onto the surface of graphene oxide by chemical reduction method to obtain GO-AATS composite filler. The composite filler is introduced into waterborne polyurethane (WPU) to form a chemical bond between graphene oxide and waterborne polyurethane, thereby improving the interface compatibility of the two, and improving the mechanical properties, water resistance, corrosion resistance and thermal stability of the waterborne polyurethane coating.

[0005] To achieve the above purpose, the present application provides a preparation method of a silane functionalized graphene oxide / waterborne polyurethane hydrophobic coating, comprising the following steps:

[0006] S1, mixing concentrated sulfuric acid, phosphoric acid and acidic potassium permanganate to obtain a mixed solution, and slowly adding graphite powder into the mixed solution for reflux reaction;

[0007] S2, after the reaction in S1 is completed, hydrogen peroxide is slowly added alternately under the condition of ice water bath, the solution becomes bright yellow after ultrasonic dispersion, filtration, washing, drying, and GO powder is obtained;

[0008] S3, GO powder is dispersed in a solvent by ultrasonic dispersion, N-(β-aminoethyl)-γ-aminopropyl trimethoxysilane is added in the obtained mixed solution, and reaction is carried out under stirring; after the reaction is completed, acetic acid is added to adjust pH;

[0009] S4, the mixture obtained in S3 is heated, stirred under the condition of nitrogen, cooled to room temperature, dialyzed to neutral, dried, and GO-AATS is obtained;

[0010] S5, isophorone diisocyanate, castor oil and 2,2-bishydroxymethyl butyric acid are mixed, and the obtained mixed system is gradually heated and stirred uniformly under the protection of nitrogen; dibutyl tin dilaurate is added dropwise into the mixed system to carry out reaction;

[0011] S6, after the reaction in S5 is completed, trimethylolpropane is added to continue reaction; after the reaction is completed, GO-AATS is added to continue reaction; after the reaction is completed, triethylamine is added to continue reaction;

[0012] S7, after the reaction in S6 is completed, deionized water is added, and emulsification reaction is carried out under high-speed rotation; after the emulsification reaction is completed, standing defoaming, rotary evaporation, and the product GO-AATS-WPU emulsion is obtained.

[0013] Preferably, in S1, the amount of concentrated sulfuric acid is 350-370 ml, the amount of phosphoric acid is 30-50 ml, the amount of acidic potassium permanganate is 16-20 g, and the amount of graphite powder is 1-5 g; the reflux reaction is carried out in an oil bath, the reaction time of the oil bath reaction is 20-25 h, and the temperature of the oil bath is 40-60℃.

[0014] Preferably, in S2, the ultrasonic dispersion time is 0.5-1.5 h, the washing agent used for washing is 5% dilute hydrochloric acid solution and deionized water, the washing frequency is 3-5 times, and the drying time is 10-15 h.

[0015] Preferably, in S3, the solvent is ethanol and water, the volume ratio of ethanol to water is (2-4):1, the amount of N-(β-aminoethyl)-γ-aminopropyl trimethoxysilane is 5-7 g, the reaction time is 8-12 min, and the pH is adjusted to 4-5 by adding acetic acid.

[0016] Preferably, in S4, the mixture obtained in S3 is heated to 50-90℃, the stirring time is 2-4 h, the solvent used for dialysis is deionized water, the dialysis time is 2-4 days, and the drying time is 10-15 h.

[0017] Preferably, in S5, the mass of isophorone diisocyanate is 1-15g, the mass of castor oil is 1-20g, the mass of 2,2-bishydroxymethyl butyric acid is 1-10g, the stirring speed is 140-160r / min, the temperature is gradually increased to 70-90℃, the dropwise addition amount of dibutyltin dilaurate is 2-4 drops, and the reaction time is 1-3h.

[0018] Preferably, in S6, the mass of trimethylolpropane is 1-10g, the reaction time after adding trimethylolpropane is 0.5-1.5h; after the reaction is completed, the temperature is reduced to 40-60℃, the mass of GO-AATS added is 0-1000mg, the reaction time after adding GO-AATS is 0.5-1.5h; after the reaction is completed, the temperature is reduced to 20-40℃ again, the mass of triethylamine added is 0.1-2g, the reaction time after adding triethylamine is 10-50min, and the reaction temperature is room temperature.

[0019] Preferably, in S7, the speed of rotation is 1300-1800r / min, the reaction time of emulsification reaction is 20-40min, and the reaction temperature of emulsification reaction is room temperature.

[0020] The application further provides a silane functionalized graphene oxide / water-based polyurethane hydrophobic coating prepared by the above method.

[0021] Therefore, the silane functionalized graphene oxide / water-based polyurethane hydrophobic coating and the preparation method have the following beneficial effects:

[0022] 1. The application uses natural graphite powder as raw material, graphene oxide is prepared by the Hummer method, N-(β-aminoethyl)-γ-aminopropyl trimethoxysilane is grafted to the surface of graphene oxide by a chemical reduction method to obtain GO-AATS composite filler, and then GO-AATS-WPU emulsion is prepared by taking castor oil as a soft segment and isophorone diisocyanate as a hard segment.

[0023] 2. The application modifies the water-based polyurethane coating by using silane functionalized graphene oxide, thereby forming a chemical bond between graphene oxide and water-based polyurethane, improving the interfacial compatibility of the two, and further improving the mechanical properties, water resistance, corrosion resistance and thermal stability of the water-based polyurethane coating.

[0024] The technical solutions of the application are further described in detail below by means of the drawings and examples. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 is the XPS diagram of the intermediate product GO-AATS in the application;

[0026] Figure 2 is an infrared spectrum of the intermediate product GO-AATS and the product GO-AATS-WPU in the present application;

[0027] Figure 3 is a particle size distribution diagram of the product GO-AATS-WPU emulsion in the present application;

[0028] Figure 4 is the water absorption and water contact angle of the product GO-AATS-WPU coating in the present application;

[0029] Figure 5 is the water contact angle of the product GO-AATS-WPU coating in the present application;

[0030] Figure 6 is the stress-strain diagram of the product GO-AATS-WPU coating in the present application;

[0031] Figure 7 is the abrasion resistance diagram of the product GO-AATS-WPU coating in the present application;

[0032] Figure 8 is the thermogravimetric curve diagram of the product GO-AATS-WPU coating in the present application;

[0033] Figure 9 is the DTG curve diagram of the product GO-AATS-WPU coating in the present application;

[0034] Figure 10 is the steel plate corrosion diagram of the product GO-AATS-WPU coating in the present application;

[0035] Figure 11 is the SEM morphology diagram of the product GO-AATS-WPU coating in the present application. DETAILED DESCRIPTION

[0036] The technical solutions of the present application are further described below by means of the accompanying drawings and examples.

[0037] Unless otherwise defined, the technical terms or scientific terms used in the present application shall have the usual meanings understood by those with ordinary skills in the art to which the present application belongs.

[0038] The raw materials used in the present invention are: natural graphite powder: 99.95%, Shanghai Yien Chemical Technology Co., Ltd.; isophorone diisocyanate (IPDI): 99%, Shanghai MacLean Biochemical Technology Co., Ltd.; castor oil (CO): AR, Shanghai Yien Chemical Technology Co., Ltd.; 2,2-bis(hydroxymethyl)butyric acid (DMBA): 98%, Shanghai Yien Chemical Technology Co., Ltd.; hydrogen peroxide (H2O2): 3wt%, Shanghai Yien Chemical Technology Co., Ltd.; trimethylolpropane (TMP): 98%, Shanghai Yien Chemical Technology Co., Ltd.; dibutyltin dilaurate (DBTDL): purity 95%, Shanghai Yien Chemical Technology Co., Ltd.; triethylamine (TEA): 99.7%, Shanghai Yien Chemical Technology Co., Ltd.; acetone (AC): AR, Luoyang Chemical Reagent Factory, Shanghai Yien Chemical Technology Co., Ltd.; deionized water: homemade.

[0039] Example 1

[0040] The present invention provides a preparation method of a silane-functionalized graphene oxide / waterborne polyurethane hydrophobic coating, comprising the following steps:

[0041] S1. Place 360 ​​ml of concentrated sulfuric acid, 40 ml of phosphoric acid, and 18 g of acidic potassium permanganate in a 500 ml three-necked flask, slowly add 3 g of graphite powder, and reflux in a 50°C oil bath for 24 h.

[0042] After the reaction in S2 and S1 was completed, 20 ml of hydrogen peroxide was slowly added alternately in an ice-water bath. After the solution turned bright yellow, ultrasonic dispersion was performed for 1 h. The dispersion was filtered to obtain a filter cake. The filter cake was washed three times with 5% dilute hydrochloric acid solution and deionized water, and dried for 12 h to obtain graphene oxide powder, which was recorded as GO powder.

[0043] S3. GO powder was ultrasonically dispersed in a mixed solution of ethanol and water, with a volume ratio of ethanol to water of 2:1; 6 g of N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane was added to the mixed solution, and the mixture was reacted under stirring for 10 minutes. After the reaction was completed, acetic acid was added to adjust the pH to 4.5;

[0044] S4. The mixture obtained in S3 was heated to 70° C., stirred under nitrogen for 3 h, cooled to room temperature, and dialyzed in deionized water for 3 days until the pH value reached 7; the mixture was dried in a vacuum drying oven for 12 h to obtain a product, which was recorded as GO-AATS;

[0045] S5. 9 g of isophorone diisocyanate, 15 g of castor oil, and 1.4 g of 2,2-bis(hydroxymethyl)butyric acid were mixed and stirred uniformly under nitrogen at a stirring speed of 150 r / min. The resulting mixed system was gradually heated to 80° C., and 3 drops of dibutyltin dilaurate were added dropwise to the mixed system for reaction. The reaction time was 2 h.

[0046] After the reaction in S6 and S5 is completed, 3 g of trimethylolpropane is added to continue the reaction for 1 hour. After the reaction is completed, the temperature is lowered to 30° C., and 1 g of triethylamine is added to continue the reaction at room temperature for 30 minutes.

[0047] After the reaction in S7 and S6 is completed, deionized water is added and an emulsification reaction is carried out under high-speed rotation at a rotation speed of 1500 r / min, a reaction time of 30 min, and a reaction temperature of room temperature. After the emulsification reaction is completed, the mixture is allowed to stand for defoaming and then rotary evaporated to remove excess solvent to obtain a product GO-AATS-WPU emulsion, which is recorded as 0% GO-AATS.

[0048] Example 2

[0049] The operation of this example is the same as that of Example 1, except that: after the reaction of adding trimethylolpropane in S6 is completed, the temperature is first lowered to 50°C, and 2 mg of GO-AATS is added to continue the reaction for 1 hour; after the reaction is completed, the temperature is lowered to 30°C, and triethylamine is added to continue the reaction at room temperature for 30 minutes; and the product GO-AATS-WPU emulsion is obtained in S7, which is recorded as 0.13% GO-AATS.

[0050] Example 3

[0051] The operation of this embodiment is the same as that of embodiment 2, except that the mass of GO-AATS added in S6 is 50 mg, and the product GO-AATS-WPU emulsion obtained in S7 is recorded as 0.26% GO-AATS.

[0052] Example 4

[0053] The operation of this embodiment is the same as that of embodiment 2, except that the mass of GO-AATS added in S6 is 400 mg, and the product GO-AATS-WPU emulsion is obtained in S7, which is recorded as 0.39% GO-AATS.

[0054] Example 5

[0055] The operation of this embodiment is the same as that of embodiment 2, except that the mass of GO-AATS added in S6 is 530 mg, and the product GO-AATS-WPU emulsion obtained in S7 is recorded as 0.52% GO-AATS.

[0056] The elemental composition of the intermediate product GO-AATS obtained in Examples 1-5 was analyzed by X-ray photoelectron spectroscopy. Figure 1 As shown. Figure 1It can be seen that the peak position of O is at 530eV, the peak positions of N and C are at 370eV and 283eV respectively, and the peak corresponding to Si 2P appears at 102eV, which indicates that AATS is successfully grafted into GO. The content of various elements in the GO-AATS composite material is shown in Table 1.

[0057] Table 1 Element contents of GO-AATS

[0058]

[0059] The GO-AATS-WPU emulsion prepared in Examples 1-5 was dropped onto a polytetrafluoroethylene plate and air-dried at room temperature for 12 h to form a coating. The coating was then placed in an oven at 50° C. and dried for 24 h to obtain five types of GO-AATS-WPU coatings.

[0060] The chemical structures of the intermediate products GO-AATS and the product GO-AATS-WPU coatings prepared in Examples 1-5 were analyzed by infrared spectroscopy with a scanning wavelength range of 400 to 4000 cm -1 The infrared spectra of GO powder, AATS, GO-AATS and GO-AATS-WPU are shown in Figure 2. Figure 2 shown.

[0061] from Figure 2 It can be seen that in the spectrum of AATS, 780 cm -1 Corresponding to Si-C stretching vibration, 1189 cm -1 Corresponding to the symmetric stretching vibration of Si-O-Si, 1080 cm -1 The strong peak at 1187 cm corresponds to the stretching vibration of -OCH3. -1 The characteristic peak at 1460 cm corresponds to the stretching vibration of Si-O-Si. -1 The peak corresponds to the bending vibration of NH.

[0062] In the infrared spectrum of GO, 3428 cm -1 The broad peak at 1732 cm corresponds to -OH on the GO surface. -1 The characteristic peak at 1620 cm corresponds to the stretching vibration of the epoxy C=O on the GO surface. -1 The absorption peak at 1065 cm corresponds to the stretching vibration of carboxyl -COOH. -1 The absorption peak corresponds to the stretching vibration of COC.

[0063] In the infrared spectrum of GO-AATS, a new ions at 710 cm -1 、1120cm -1 and 1350cm -1The characteristic peaks of 1732 cm-1 correspond to the Si-C stretching vibration and the symmetric stretching vibration of Si-O-Si in AATS and the formation of new chemical bonds (CN). -1 The weakening of the stretching vibration of C=O at the GO site is due to the reaction between AATS and the epoxy groups on the GO surface. These changes indicate the successful synthesis of the GO-AATS composite material.

[0064] In the infrared spectrum of GO-AATS-WPU, the wavelength 2250 cm -1 The stretching vibration peak of -NCO at 2922cm -1 and 2842cm -1 The absorption peaks at 1120 cm-1 correspond to -CH2 and -CH3, respectively. -1 Symmetrical stretching vibrations of Si-O-Si appeared at the 300 nm lattice, and these changes indicated the successful synthesis of GO-AATS-WPU.

[0065] The particle size analysis of the GO-AATS-WPU emulsions prepared in Examples 1-5 was performed. 5 ml of each of the GO-AATS-WPU emulsions prepared in Examples 1-5 was taken, weighed, and diluted to 1% of the total mass using water as a dispersant. The particle size of the emulsion was measured using a nanoparticle size analyzer and a Zeta potential analyzer. The results are as follows: Figure 3 As shown, from Figure 3 It can be seen that the particle sizes of GO-AATS-WPU emulsions with different GO-AATS contents are 98.24nm, 109.6nm, 155.2nm, 170.8nm, and 187.3nm, respectively. Compared with the GO-AATS-WPU emulsion without adding GO-AATS composite filler, the particle size of GO-AATS-WPU emulsion increases and the particle size distribution is narrower. This is because with the increase of GO-AATS content, the GO-AATS composite filler and WPU emulsion agglomerate, and the -COO - NH 4+ The reduction of steric hindrance between WPU and GO-AATS causes cross-linking of WPU molecular chains and increases the overall particle size of the emulsion.

[0066] The water resistance of the five GO-AATS-WPU coatings was analyzed. The water contact angles of the coatings were measured using an optical contact angle meter and the sessile drop method. The water absorption rate was measured using the immersion method. The GO-AATS-WPU coatings were cut into 5 mm × 5 mm squares and weighed for their initial mass, recorded as m1. The coatings were then immersed in water for 72 hours, removed, and the surface water stains blotted with filter paper. The weight was then immediately weighed, recorded as m2. Three samples were collected for each group. The water absorption rate (W%) was calculated using Equation (1):

[0067]

[0068] The results of water absorption and contact angle test of GO-AATS-WPU coating are shown in Figure 4 and Figure 5 As can be seen from Figure 4 and Figure 5 , with the increase of GO-AATS content, the water absorption of the coating gradually decreases from 7.62% to 1.12%, and the water contact angle of the coating gradually increases from 83.4° to 102°, the hydrophobic performance is greatly improved, which shows that GO-AATS composite filler can effectively improve the water resistance of WPU coating.

[0069] The mechanical properties of the five prepared GO-AATS-WPU coatings were analyzed, and the electronic universal testing machine was used to stretch the WPU coating to break at room temperature at a speed of 100 mm / min, the length of the dumbbell-shaped sample was 25 mm, and the width was 5 mm. The maximum load at the time of fracture of the test piece was recorded, and the distance between the marks was accurate to 0.1 mm. Each sample was tested three times, and the average value was taken for statistical analysis. The results are shown in Figure 6 and Table 2. Figure 6 As can be seen from , the mechanical properties of WPU coating are obviously improved after adding GO-AATS filler, the tensile strength of all WPU coatings is improved, among which the tensile strength of WPU coating added with 0.52% GO-AATS composite filler reaches 15.84Mpa, because the composite filler acts as a skeleton structure in the WPU molecular network, and the rigid honeycomb carbon ring structure of GO significantly improves the tensile strength of WPU coating. The elongation at break of WPU coating added with 0.13% GO-AATS composite filler is also improved, because GO material has certain toughening performance; when the amount of composite filler exceeds 0.13%, the elongation at break of WPU coating is lower than that of WPU coating without adding filler, which may be because with the increase of GO content, the rigid structure in the WPU molecular structure increases, the strength increases, and the ductility of the molecular chain decreases.

[0070] Table 2 Mechanical properties of GO-AATS-WPU coating

[0071] Sample Hardness / H Tensile strength / MPa Elongation at break / % 0% GO-AATS 2 9.49 189.84 0.13% GO-AATS 3 12.4 219.7 0.26% GO-AATS 3 13.45 145.6 0.39% GO-AATS 3 13.7 60.3 0.52% GO-AATS 3 15.84 57.43

[0072] The wear resistance of the five prepared GO-AATS-WPU coatings was analyzed by using a friction tester, the coating was cut into a film with a size of 40mm×40mm, its mass was m3, and the film was polished for 500 times using 800 mesh special sandpaper, the load mass was set to 1000g, then the polished mass m4 was weighed. The wear resistance of the sample was calculated according to formula (2):

[0073] M=(m3-m4) (2)

[0074] The calculation results are as followsFigure 7 As shown. The effect of nanofillers on the wear resistance of waterborne polyurethane (WPU) is mainly achieved through mechanisms such as enhancing material hardness, improving interface bonding, and hindering crack propagation. Figure 7 It can be seen that after 500 sandpaper polishings, the friction mass loss of the WPU coating without the addition of GO-AATS filler is 17.7 mg, and the wear resistance is relatively weak; after adding GO-AATS filler, the mass loss of the coating gradually decreases to 4.7 mg. This is because the GO flakes hinder the expansion of cracks generated during the friction process, improve the toughness of the coating, and the interlayer sliding of GO can effectively reduce the friction coefficient. In addition, the covalent bonds formed by GO and the WPU matrix can enhance the interfacial bonding strength and enhance the wear resistance of the coating. However, the amount of filler added needs to be within a reasonable range. When the amount added exceeds the critical value, it will lead to an increase in coating interface defects and a decrease in wear resistance.

[0075] The thermal stability of the five GO-AATS-WPU coatings was analyzed. The TGA curves of the samples were recorded using a thermal analyzer. A sample weighing about 20 mg was heated from 10°C to 600°C at a heating rate of 10°C / min in a nitrogen atmosphere. The results are shown in Figure 2. Figure 8 and Figure 9 The thermal decomposition of the sample is divided into three stages. The thermal decomposition of the sample below 200℃ is mainly attributed to the volatilization of residual water and acetone and other solvents in the coating; the heat loss between 200℃ and 320℃ is mainly due to the decomposition of the hard segment in the WPU coating, namely the urethane bond; above 320℃ is due to the thermal decomposition of the CO bond (358kJ / mol) and CC bond (346kJ / mol) in the WPU soft chain and other small molecules. Figure 8It can be seen that the initial thermal decomposition of the WPU coating without the addition of GO-AATS occurs at 259°C, while the initial thermal decomposition temperature of the WPU coating with the addition of GO-AATS composite filler is around 270°C. Among them, the initial thermal decomposition temperature of the 0.26% GO-AATS-WPU coating is the highest, reaching 272°C. The upper temperature limit when the coating's quality retention rate is above 80% is increased from 299°C (0% GO-AATS) to 312°C (0.52% GO-AATS), an increase of 13°C. The quality retention rate in the range of 250-400°C is also improved by more than 5%. This is partly because the modified GO-AATS filler has a high-temperature resistant Si-O bond. The Si-O bond has a high energy bond and requires a high energy to break it, so it can withstand high temperatures and maintain the stability of its chemical structure, thereby improving the thermal stability of the coating and reducing the mass loss. On the other hand, the GO-AATS filler fills the gaps in the WPU coating, hindering the oxygen penetration and escape of volatile degradation products even in a high temperature environment, thereby improving the thermal stability of the GO-AATS-WPU coating.

[0076] The corrosion resistance of the five GO-AATS-WPU coatings was analyzed. The bare Q235 steel plates and the Q235 steel plates coated with the five GO-AATS-WPU coatings were immersed in salt solution for 168 hours. Figure 10 As shown, from Figure 10 It can be seen that after 168 hours of immersion in salt solution, the bare Q235 steel plate has been completely corroded, and the surface is covered with yellow-brown corrosion products, while the corrosion degree of the five Q235 steel plates coated with coatings is significantly reduced. In particular, the Q235 steel plates coated with 0.39% GO-AATS-WPU and 0.52% GO-AATS-WPU coatings have almost no yellow spots on the surface, which well protects the substrate. The effects of GO-AATS filler on the corrosion resistance of WPU coatings are mainly reflected in three aspects: (1) Physical shielding: The two-dimensional lamellar structure of GO can fill the defects of WPU coatings, reduce porosity, and hinder the diffusion of corrosive media to the metal substrate; (2) Electrochemical protection: The high conductivity of GO can accelerate the transfer of electrons, transfer the corrosion reaction of the metal anode to the coating surface, and inhibit the oxidation and dissolution of Fe. For example, when the GO coating is damaged, it can still delay the corrosion process through electron transfer; (3) Interface bonding optimization: After siloxane functionalization modification, the GO surface reacts with the WPU matrix to form a Si-O-Si network, which enhances the interface bonding force and reduces the failure of the coating caused by the penetration of the corrosive medium.

[0077] The surface morphology of the five GO-AATS-WPU coatings was analyzed by transmission electron microscopy. Figure 11The effect of GO on the surface morphology of WPU mainly reflects in its physical filling effect and chemical bonding. The nanosheet layers of GO after ultrasonic treatment are uniformly embedded in the WPU matrix, filling the micro-pores and defects on the surface of the coating, forming a more compact surface structure. A small amount of wrinkles and protrusions on the surface of the coating is because GO-AATS still retains a larger specific surface area, making the coating thicker, and the accumulation between layers. However, with the increase of the content of GO-AATS, the crosslinking degree of the WPU coating increases, and the surface gradually tends to be flat and tight with reduced voids. The ordered arrangement of GO nanosheet layers prolongs the penetration path of corrosive media such as water and oxygen, improving water resistance, which corresponds to the previous conclusion. In addition, the carboxyl groups (-COOH) on the surface of GO form hydrogen bonds or covalent bonds with the urethane groups (-NHCOO-) in WPU, reducing the interface gap.

[0078] Therefore, the present application adopts the above-mentioned silane functionalized graphene oxide / waterborne polyurethane hydrophobic coating and preparation, using natural graphite powder as raw material, graphene oxide is prepared by Hummer method, and N-(β-aminoethyl)-γ-aminopropyl trimethoxysilane is grafted onto the surface of graphene oxide by chemical reduction method to obtain GO-AATS composite filler. The composite filler is introduced into waterborne polyurethane, forming a chemical bond between graphene oxide and waterborne polyurethane, improving the interfacial compatibility of the two, thereby improving the mechanical properties, water resistance, corrosion resistance and thermal stability of the waterborne polyurethane coating.

[0079] Finally, it should be noted that: the above examples are only used to illustrate the technical solutions of the present application but not to limit it, although the present application has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present application can still be modified or replaced by equivalents, and these modifications or equivalent replacements cannot make the modified technical solutions deviate from the spirit and scope of the technical solutions of the present application.

Claims

1. Preparation of a silane-functionalized graphene oxide / waterborne polyurethane hydrophobic coating, characterized in that: The following steps are involved: S1. Mix concentrated sulfuric acid, phosphoric acid and acidic potassium permanganate, and slowly add graphite powder to the resulting mixed solution for reflux reaction; After the reaction in S2 and S1 was completed, hydrogen peroxide was added alternately and slowly in an ice-water bath. After the solution turned bright yellow, it was ultrasonically dispersed, filtered, washed, and dried to obtain GO powder. S3, dispersing GO powder in a solvent by ultrasonication, adding N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane to the obtained mixed solution, reacting under stirring conditions, and adding acetic acid to adjust the pH after the reaction is completed; S4, heating the mixture obtained in S3, stirring under nitrogen, cooling to room temperature, dialyzing to neutrality, and drying to obtain GO-AATS; S5, mixing isophorone diisocyanate, castor oil and 2,2-bis(hydroxymethyl)butyric acid, stirring uniformly under nitrogen protection, gradually heating the obtained mixed system, and adding dibutyltin dilaurate dropwise to the mixed system for reaction; After the reaction in S6 and S5 is completed, trimethylolpropane is added to continue the reaction; after the reaction is completed, the temperature is lowered and GO-AATS is added to continue the reaction; after the reaction is completed, the temperature is lowered again and triethylamine is added to continue the reaction; After the reaction in S7 and S6 is completed, deionized water is added and an emulsification reaction is carried out under high-speed rotation. After the emulsification reaction is completed, the mixture is allowed to stand for defoaming and rotary evaporated to obtain a product GO-AATS-WPU emulsion.

2. The preparation of a silane-functionalized graphene oxide / aqueous polyurethane hydrophobic coating according to claim 1, characterized in that: In S1, the amount of concentrated sulfuric acid is 350-370 ml, the amount of phosphoric acid is 30-50 ml, the amount of acidic potassium permanganate is 16-20 g, and the amount of graphite powder is 1-5 g. The reflux reaction is carried out in an oil bath. The reaction time of the oil bath reaction is 20-25 h, and the temperature of the oil bath is 40-60°C.

3. The preparation of a silane-functionalized graphene oxide / aqueous polyurethane hydrophobic coating according to claim 1, characterized in that: In S2, the ultrasonic dispersion time is 0.5-1.5 hours, the detergent used for washing is 5% dilute hydrochloric acid solution and deionized water, the washing times are 3-5 times, and the drying time is 10-15 hours.

4. The preparation of a silane-functionalized graphene oxide / waterborne polyurethane hydrophobic coating according to claim 1, characterized in that: In S3, the solvent is ethanol and water, the volume ratio of ethanol and water is (2-4):1, the amount of N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane is 5-7 g, the reaction time is 8-12 min, and acetic acid is added to adjust the pH to 4-5.

5. The preparation of a silane-functionalized graphene oxide / waterborne polyurethane hydrophobic coating according to claim 1, characterized in that: In S4, the mixture obtained in S3 is heated to 50-90° C. and stirred for 2-4 hours. The solvent used for dialysis is deionized water. The dialysis time is 2-4 days and the drying time is 10-15 hours.

6. The preparation of a silane-functionalized graphene oxide / waterborne polyurethane hydrophobic coating according to claim 1, characterized in that: In S5, the mass of isophorone diisocyanate is 1-15 g, the mass of castor oil is 1-20 g, the mass of 2,2-bishydroxymethylbutyric acid is 1-10 g, the stirring speed is 140-160 r / min, the temperature is gradually increased to 70-90°C, the amount of dibutyltin dilaurate added is 2-4 drops, and the reaction time is 1-3 h.

7. The preparation of a silane-functionalized graphene oxide / waterborne polyurethane hydrophobic coating according to claim 1, characterized in that: In S6, the mass of trimethylolpropane is 1-10 g, and the reaction time after adding trimethylolpropane is 0.5-1.5 hours; after the reaction is completed, the temperature is reduced to 40-60°C, the mass of GO-AATS added is 0-1000 mg, and the reaction time after adding GO-AATS is 0.5-1.5 hours; after the reaction is completed, the temperature is reduced to 20-40°C again, the mass of triethylamine added is 0.1-2 g, and the reaction time after adding triethylamine is 10-50 minutes, and the reaction temperature is room temperature.

8. The preparation of a silane-functionalized graphene oxide / waterborne polyurethane hydrophobic coating according to claim 1, characterized in that: In S7, the rotation speed is 1300-1800 r / min, the reaction time of the emulsification reaction is 20-40 min, and the reaction temperature of the emulsification reaction is room temperature.

9. A silane-functionalized graphene oxide / waterborne polyurethane hydrophobic coating, characterized in that: The silane-functionalized graphene oxide / waterborne polyurethane hydrophobic coating is prepared using the method described in any one of claims 1 to 8.

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