CN114806367A

CN114806367A - Preparation method of chitosan modified graphene oxide composite coating

Info

Publication number: CN114806367A
Application number: CN202210327456.3A
Authority: CN
Inventors: 陈蓉蓉; 孙月; 刘琦; 刘培礼; 王君; 张宏森
Original assignee: Harbin Engineering University
Current assignee: Harbin Engineering University
Priority date: 2022-03-30
Filing date: 2022-03-30
Publication date: 2022-07-29
Anticipated expiration: 2042-03-30
Also published as: CN114806367B

Abstract

The invention discloses a preparation method of a chitosan modified graphene oxide composite coating, which comprises the following operation steps: s1, preparing GO-CS: a. adding chitosan into 1-3% acetic acid solution to form uniform solution, namely product A; b. adding graphene oxide into deionized water, uniformly mixing, and adding the mixture into the product A to obtain a product B; c. adjusting the pH value of the product B to 4-6, uniformly stirring and centrifuging to obtain GC; s2, preparing GO-CS-PASP: a. adding polyaspartic acid into deionized water, and mixing to obtain product C; b. adding GC into the product C for dissolving, adjusting the pH value to 4-6, and adding glutaraldehyde to obtain a product D; c. washing the product D to obtain GCP; s3: and mixing the GCP with the epoxy modified polyurethane resin to obtain the GCP/EP-PU composite coating. The invention has the characteristics of simple preparation, high corrosion resistance and strong self-repairing capability of the prepared composite coating.

Description

Preparation method of chitosan modified graphene oxide composite coating

Technical Field

The invention relates to a graphene oxide composite coating, in particular to a preparation method of a chitosan modified graphene oxide composite coating.

Background

Corrosion is a natural phenomenon, and in general, most of the used metallic materials and alloys are thermodynamically corroded except for the noble metals of silver, gold and platinum. They are susceptible to chemical or electrochemical reactions with environmental elements and to corrosion to form corrosion products such as rust and scale. Thus, corrosion can be defined as an electrochemical process or chemical degradation of the metal/alloy properties due to interfacial interactions with its environment. The process involves the exchange of metal ions into the electrolyte at the anode, and the cathode reaction requires the presence of an "electron acceptor," such as oxygen or hydrogen ions. Furthermore, corrosion may be initiated by natural or man-made activities, which are normal and unavoidable processes, and worsen when the metal substrate interacts with certain elements present in the environment.

The process of forming a protective film having properties different from those of a metal substrate on a metal surface by a chemical or physical method is called surface treatment of a metal. The method is often used for improving various properties of metal, such as heat resistance, friction resistance, corrosion resistance and the like, Graphene Oxide (GO) has potential application value in the field of corrosion protection due to the unique two-dimensional layered structure and excellent properties, but the enhancement efficiency of the Graphene Oxide (GO) is generally lower than expected after a complex preparation process, the graphene oxide tends to agglomerate in the preparation of a composite functional coating, and the agglomerated graphene oxide sheets cannot provide enough protection effect and even influence the continuity of the coating and aggravate corrosion; the load capacity is limited by the weak interaction and compatibility between the graphene oxide and the coating substrate; GO has poor dispersibility and compatibility in epoxy resin (EP), and when a coating is damaged, GO can only play a passive protection role on a base material, does not show a self-healing behavior, and greatly limits the application of GO in the field of corrosion prevention.

Disclosure of Invention

The invention aims to provide a preparation method of a chitosan modified graphene oxide composite coating. The invention has the characteristics of simple preparation, high corrosion resistance and strong self-repairing capability of the prepared composite coating.

The technical scheme of the invention is as follows: the preparation method of the chitosan modified graphene oxide composite coating comprises the following operation steps:

s1, preparing GO-CS:

a. adding chitosan into 1-3% acetic acid solution to form uniform solution, namely product A;

b. adding graphene oxide into deionized water, uniformly mixing, and adding the mixture into the product A to obtain a product B;

c. adjusting the pH value of the product B to 4-6, uniformly stirring and centrifugally separating to obtain a precipitate, namely chitosan-modified graphene oxide, which is marked as GC;

s2, preparing GO-CS-PASP:

a. adding polyaspartic acid into deionized water, and mixing to obtain product C;

b. adding GC into the product C for dissolving, adjusting the pH value to 4-6, and adding glutaraldehyde to obtain a product D;

c. washing the product D for many times to obtain PASP-CS-GO which is marked as GCP;

s3, preparing a GCP/EP-PU composite coating:

and mixing the GCP with the epoxy modified polyurethane resin to obtain the GCP/EP-PU composite coating.

In the preparation method of the chitosan-modified graphene oxide composite coating, in the step S1, the mass ratio of chitosan to GO to graphene oxide is 15: 1-25: 1.

In the preparation method of the chitosan-modified graphene oxide composite coating, the S1 specifically includes: preparing GO-CS: a. adding 0.1-0.3 g of chitosan into 30-60mL of 1-3% acetic acid solution, and stirring to form a uniform solution, namely product A; b. adding 0.005-0.02 g of GO into 15-25 mL of deionized water, carrying out ultrasonic treatment for 8-13 min, uniformly mixing, adding into the product A, and uniformly mixing to obtain a product B; c. and adjusting the pH value of the product B to 4-6 by using a NaOH solution, stirring at 55-65 ℃ for 1.5-2.5 h, and centrifuging to obtain the chitosan modified graphene oxide, which is recorded as GC.

In the preparation method of the chitosan-modified graphene oxide composite coating, the S1 specifically includes: preparing GO-CS: a. adding 0.2g chitosan into 50mL 2% acetic acid solution, and stirring to form uniform solution A; b. adding 0.01g of GO into 20mL of deionized water, carrying out ultrasonic treatment for 10min, uniformly mixing, adding into the product A, and uniformly mixing to obtain a product B; c. and adjusting the pH value of the product B to 5 by using 1mol/L NaOH solution, stirring at 60 ℃ for 2h, and centrifuging to obtain chitosan modified graphene oxide, which is recorded as GC.

In the preparation method of the chitosan-modified graphene oxide composite coating, the S1 specifically includes: in the S2, the mass ratio of polyaspartic acid to GC is 1: 1-3: 1.

In the preparation method of the chitosan-modified graphene oxide composite coating, the S2 specifically includes: preparing GO-CS-PASP: a. adding 0.1-0.3 g of polyaspartic acid into 30-50 mL of deionized water, and uniformly mixing to obtain a product C; b. adding 0.005-0.2 g of GC into the product C for dissolving, adjusting the pH to 4-6 by using a NaOH solution, adding 0.5-1 mL of glutaraldehyde, and uniformly mixing at room temperature to obtain a product D; c. washing the product D for many times to obtain PASP-CS-GO which is marked as GCP.

In the preparation method of the chitosan-modified graphene oxide composite coating, the S2 specifically includes: preparing GO-CS-PASP: a. adding 0.2g of polyaspartic acid into 40mL of deionized water, and uniformly mixing to obtain a product C; b. adding 0.1g GC into the product C for dissolving, adjusting the pH to 5 by using 1mol/L NaOH solution, adding 0.8mL of glutaraldehyde, stirring for 24h at room temperature, and uniformly mixing to obtain a product D; c. and washing the product D with deionized water for many times to obtain PASP-CS-GO which is marked as GCP.

In the preparation method of the chitosan-modified graphene oxide composite coating, the step S3 specifically includes: and uniformly mixing GCC, the epoxy modified polyurethane resin and the amine curing agent, wherein the weight of the GCC accounts for 0.10-0.20% of the total weight of the epoxy modified polyurethane resin and the amine curing agent, and thus obtaining the GCP/EP-PU composite coating.

In the preparation method of the chitosan-modified graphene oxide composite coating, the step S3 specifically includes: GCP is uniformly mixed with 2.27g of epoxy modified polyurethane resin and 1g of amine curing agent, wherein the weight of GCC accounts for 0.15% of the total weight of the epoxy modified polyurethane resin and the amine curing agent, and the GCP/EP-PU composite coating is prepared by fully mixing.

Compared with the prior art, the invention has the beneficial effects that:

according to the invention, Chitosan (CS) and glutaraldehyde are used as crosslinking components between Graphene Oxide (GO) and environment-friendly corrosion inhibitor Polyaspartic Acid (PASP), grafting of polyaspartic acid and chitosan on graphene oxide is realized through a two-step method, PASP-CS-GO is embedded into EP-PU resin to form a high-density composite coating, the dispersion performance of GO nanosheets in a matrix resin coating is effectively improved, the self-repairing capability of the coating is provided, and efficient and long-term utilization of metal materials protected by the GCP/EP-PU coating is realized.

Experiments show that the GCP in the solution phase has better corrosion inhibition performance on Q235 low-carbon steel, and the GCP/EP-PU coating has excellent barrier protection performance, corrosion resistance, adhesive force and self-repairing performance.

Drawings

FIG. 1 is a schematic structural diagram of the synthetic scheme of GCP in the present invention;

FIG. 2 is a FT-IR characterization of GCP;

figure 3 is an XRD characterization pattern of GCP;

FIG. 4 is a TGA profile of GCP;

FIG. 5 is an SEM topography representation of GCP;

FIG. 6 is a TEM topography of GCP;

FIG. 7 is a graph of water absorption for different coatings;

FIG. 8 is an adhesion diagram of different coatings;

FIG. 9 is a graph of polarization curves of mild steel after immersion in various solutions;

FIG. 10 is a Niquist plot and a Bode plot of the different coatings intact after immersion in a 3.5 wt% NaCl solution for different periods of time;

FIG. 11 depicts | Z! Y of the complete different coating _10mHz -graph of soaking time;

FIG. 12 is a Niquist plot and Bode plot of different coatings with scratches after immersion in a 3.5 wt% NaCl solution for different times;

FIG. 13 is | Z |. of different coatings with scratch _10mHz -graph of soaking time;

FIG. 14 is a fitted equivalent circuit diagram of EIS results;

FIG. 15 is R of different coatings _c And R _ct Graph relating to soaking time;

FIG. 16 is C for different coatings _c And C _dl Graph relating to soaking time;

FIG. 17 is a self-healing mechanism diagram of a GCP/EP-PU composite coating.

Detailed Description

The present invention is further illustrated by the following examples, which are not to be construed as limiting the invention.

As shown in fig. 1, the preparation method of the chitosan-modified graphene oxide composite coating comprises the following operation steps:

s1, preparing GO-CS:

a. adding Chitosan (CS) into 1-3% acetic acid solution to form uniform solution, namely product A;

b. adding Graphene Oxide (GO) into deionized water, uniformly mixing, and adding into the product A to obtain a product B;

c. adjusting the pH value of the product B to 4-6, uniformly stirring and centrifugally separating to obtain a precipitate, namely chitosan-modified graphene oxide, which is marked as GC; wherein the mass ratio of chitosan to GO to graphene oxide is 15: 1-25: 1.

S2, preparing GO-CS-PASP:

a. adding Polyaspartic Acid (PASP) into deionized water, and mixing to obtain product C;

c. washing the product D for many times to obtain PASP-CS-GO which is marked as GCP; wherein the mass ratio of the polyaspartic acid to the GC is 1: 1-3: 1.

S3, preparing a GCP/EP-PU composite coating:

GCP is mixed with epoxy modified polyurethane resin (EP-PU) and amine curing agent to prepare the GCP/EP-PU composite coating. Wherein the GCP accounts for 0.10-0.20% of the total mass of the epoxy modified polyurethane resin and the amine curing agent.

Example 1:

s1, preparing GO-CS:

a. adding 0.2g chitosan into 50mL 2% acetic acid solution, and stirring to form uniform solution A;

b. adding 0.01g of GO into 20mL of deionized water, carrying out ultrasonic treatment for 10min, uniformly mixing, adding into the product A, and uniformly mixing to obtain a product B;

c. and adjusting the pH value of the product B to 5 by using 1mol/L NaOH solution, stirring for 2 hours at 60 ℃, and separating to obtain a precipitate which is chitosan modified graphene oxide and is recorded as GC.

S2, preparing GO-CS-PASP:

a. adding 0.2g of polyaspartic acid into 40mL of deionized water, and uniformly mixing to obtain a product C;

b. adding 0.1g GC into the product C for dissolving, adjusting the pH to 5 by using 1mol/L NaOH solution, adding 0.8mL of glutaraldehyde, stirring for 24h at room temperature, and uniformly mixing to obtain a product D;

c. and washing the product D with deionized water for many times to obtain PASP-CS-GO which is marked as GCP.

S3, preparing a GCP/EP-PU composite coating:

GCP is uniformly mixed with 2.27g of epoxy modified polyurethane resin and 1g of amine curing agent, wherein the mass of GCP accounts for 0.15% of the total mass of the epoxy modified polyurethane resin and the amine curing agent, N-dimethylformamide is added as a viscosity regulator according to the requirement, and the GCP/EP-PU composite coating is prepared by fully stirring and mixing.

Comparative example:

GC is uniformly mixed with 2.27g of epoxy modified polyurethane resin and 1g of amine curing agent, wherein the mass of GC accounts for 0.15% of the total mass of the epoxy modified polyurethane resin and the amine curing agent, N-dimethylformamide is added as a viscosity regulator according to requirements, and the mixture is fully stirred and mixed to prepare a GC/EP-PU composite coating as a comparison.

And respectively dip-coating the GCP/EP-PU composite coating and the GC/EP-PU composite coating on the pretreated Q235 carbon steel, and curing. The curing operation is as follows: after drying at room temperature for 3d, it was then cured at 90 ℃ for 12 h.

The pretreatment of the Q235 carbon steel comprises the following steps: the Q235 carbon steel was polished with 600, 800, 1200 mesh sandpaper, respectively, and then degreased with an organic reagent.

The dry film thickness of the GCP/EP-PU composite coating and the GC/EP-PU composite coating is 35-45 mu m.

1. Performance testing of GCP:

as shown in FIG. 2, the FT-IR spectrum of CS, PASP, GO, GC and GCP is shown in FIG. 2, which is the FT-IR characterization chart of GCP. At 3410cm in FT-IR spectrum of GO ^-1 The peak of (A) indicates the stretching vibration of O-H, which is related to water adsorbed on the surface of the material, at 1625cm ^-1 The peak of (A) indicates the stretching vibration of C ═ O at 1063cm ^-1 And 862cm ^-1 The peak of (b) indicates the vibration of the epoxy group. In the FT-IR spectrum of CS at 1090, 1600 and 1650cm ^-1 The peaks at (A) respectively indicate stretching vibration of C-O-C bond of epoxy group, amino group (-NH) ₂ ) The bending of the N-H bond of (a) and the C ═ O stretching vibration of-NHCO-. In the FT-IR spectrum of GC, 1664cm ^-1 The nearby peak indicates the vibration of the amide bond, 1430cm ^-1 And 1380cm ^-1 The peak is caused by coupling of C-N axial tension and N-H angular deformation, 1100cm ^-1 The peaks at the range are due to stretching vibrations of the polysaccharide backbone, indicating that GO and CS are linked by amide bonds. FT-IR spectrum of GCP at 1600cm after crosslinking of polyaspartic acid ^-1 The peak at (A) is ascribed to the N-H bend of 1400cm ^-1 The peak at (B) is related to the C-N stretching vibration of the amide group. Indicating that PASP was successfully deposited on the GC nanoplatelets.

As shown in fig. 3, the XRD signature of GCP is shown. The XRD patterns of GO, GC and GCP are given in fig. 3. As can be seen from fig. 3, GO exhibits a strong characteristic peak at 11.8 ° 2 θ, corresponding to the (001) crystal plane of GO, and a characteristic peak at 43.1 ° 2 θ, corresponding to the (100) crystal plane, and the (001) crystal plane interlayer distance (d) calculated according to the bragg equation _sp ) At 0.74nm, demonstrating the successful preparation of GO, which is related to the presence of oxygen-containing functional groups on the GO nanosheets. After chitosan modification, the peak of GC at 11.8 ° disappeared and a new peak appeared at 24.5 ° 2 θ, confirming that chitosan successfully modified GO. XRD pattern at GCPIn the spectra, a broad diffraction peak at 22.4 ° corresponds to the amorphous structure of PASP, indicating successful preparation of GCP.

As shown in FIG. 4, a TGA profile of GCP is shown. The TGA curves for GO, GC and GCP are given in FIG. 4. GO is between 25 and 130 ℃, and the weight is reduced by about 11 percent due to the evaporation of the adsorbed water. At the temperature of 130-318 ℃, GO is subjected to second weight loss due to decomposition of oxygen-containing functional groups, and the weight loss rate of GO at the temperature of 600 ℃ is 78.54%. After the chitosan modification, the thermal stability of GC is improved, and the weight loss rate at 600 ℃ is 62.68%. The thermal properties of GCP showed a similar trend as GC, but the weight loss at 600 ℃ was 48.56%, indicating that growth of PASP polymer on GC nanoplatelets enhances their thermal stability.

As shown in fig. 5, is an SEM topography characterization of GCP. FIG. 5 gives SEM images of GO, GC and GCP. Fig. 5(a) is an SEM image of GO, and it can be seen that GO is a semitransparent sheet structure, and the surface has wrinkles, and has a good application prospect as a support material for subsequent modification. Fig. 5(b) is an SEM image of GC, and it can be seen that CS modified GO to improve the degree of agglomeration of GO. Fig. 5(c) is an SEM image of GCP, and it can be seen that after PASP and GC are compounded, the GCP roughness increases and the thickness significantly increases, PASP grows on the surface of the GC nanosheet, which is beneficial to reducing pi-pi interaction between graphene oxide layers, and moreover, the inter-interlaced structure of PASP is beneficial to forming a compact protective layer, thereby being more beneficial to preventing the penetration of aggressive ions.

As shown in fig. 6, a TEM topography characterization of GCP. Fig. 6 gives TEM images of GO, GC and GCP. Fig. 6(a) is a TEM image of GO, and the semi-transparent lamellar structure of GO can be clearly seen, which is consistent with the conclusion of SEM. Fig. 6(b) is a TEM image of GC, and it can be seen that chitosan and graphene oxide are successfully compounded, and the size of chitosan reaches about 1 μm. FIG. 6 (c-d) is a TEM image of GCP, in which a lamellar structure of about 4 μm can be clearly seen, demonstrating successful crosslinking of PASP. FIGS. 6 (e-f) are elemental distribution plots for GCP, consisting essentially of both C and N elements, with the elements being uniformly distributed, where the presence of N demonstrates successful crosslinking of PASP.

2. Water absorption test of the GCP/EP-PU composite coating:

respectively and uniformly coating the pure EP-PU coating, the GC/EP-PU composite coating and the GCP/EP-PU composite coating on a glass slide, soaking in deionized water for 20 days, and calculating the water absorption of the coatings according to the mass ratio change before and after soaking.

As can be observed from fig. 7, the water absorption process can be divided into two stages. In the first stage, the corrosive medium rapidly penetrates the coating and fills the pores. In the second stage, the coating reaches saturation. As the pure EP-PU coating has the defects of micropores, cracks and the like in the curing process, the absorption of the coating to water is promoted, and after 20 days of soaking, the water absorption rate of the pure EP-PU coating can reach 0.071%. The water absorption of the GC/EP-PU composite coating reaches 0.075 percent, because rich oxygen-containing groups on the surface of GC are more easily associated with water molecules, so that the anti-permeability capability of the coating is weakened, and the water absorption is increased. The water absorption of the GCP/EP-PU coating is 0.049%, which is obviously lower than that of other two coatings, because PASP covers the GC surface, a large amount of oxygen-containing groups are eliminated, and GCP is uniformly distributed in the coating, so that the density of the coating is improved, and the water absorption is reduced.

3. Adhesion test of GCP/EP-PU composite coating:

the pure EP-PU coating, the GC/EP-PU composite coating and the GCP/EP-PU composite coating are subjected to an adhesion test, the pure EP-PU coating is used as a blank control group, and the test results are shown in FIG. 8. The adhesion of the pure EP-PU coating in a dry state is 3.31MPa, the adhesion of the pure EP-PU coating in a wet state (soaked in 3.5 wt% NaCl for 7d) is 0.98MPa, and the adhesion of the GC/EP-PU composite coating in the dry state and the wet state is 3.68MPa and 1.42MPa respectively. Compared with a pure EP-PU coating and a GC/EP-PU composite coating, the adhesive force of the GCP/EP-PU coating is obviously improved, and the adhesive force in a dry state and the adhesive force in a wet state are respectively 4.62MPa and 2.78 MPa. The GCP nano material fills gaps in the EP-PU matrix, so that the compactness of the coating is improved, and the corrosion resistance of the material is improved. These results show that the use of GCP as a filler effectively prevents the coating from peeling off from the steel substrate, demonstrating excellent barrier properties of the composite coating.

4. Corrosion resistance testing of GCP in solution phase:

putting Q235 low-carbon steel in a container containing GO, GC and,The concentration of the dispersion in 3.5 wt% NaCl dispersion of GCP was maintained at 5g L ^-1 The GCP corrosion inhibition capability in the solution phase is studied by keeping the oscillation for 24h at room temperature in a constant temperature vibrator.

E of low carbon steel in GO dispersion, as shown in FIG. 9 and Table 1 _corr 、I _corr And R _p Respectively at-0.66776V and 546.22 muA cm ^-2 And 235.04 Ω cm ^-2 The corrosion rate was 7.5190 mm/year. E of low carbon steel in GC and GCP containing dispersions compared to low carbon steel soaked in 3.5 wt% NaCl GO containing dispersions _corr Are respectively positively shifted to-0.56652V and-0.50611V, I _corr Respectively reduced to 240.97 mu A cm ^-2 And 149.69. mu.A cm ^-2 ，R _p The values increased to 476.98. omega. cm, respectively ^-2 And 812.04 Ω cm ^-2 The corrosion rates were reduced to 3.6702mm/year and 1.7394mm/year, respectively. It can be seen that the addition of polyaspartic acid provides some improvement in corrosion inhibition performance. However, the E of the low carbon steel in the GCP dispersion is comparable to GC _corr Positive shift of 0.06V, I _corr And the corrosion rate is reduced by 37.88 percent _p An improvement of 41.26% was demonstrated, which demonstrates excellent corrosion inhibition by GCP.

TABLE 1 polarization curve parameter table for low carbon steel soaked in 3.5 wt% NaCl dispersion containing GO, GC and GCP

5. Testing the barrier property of the GCP/EP-PU composite coating:

a blank EP-PU coating is used as a comparison sample, a GC/EP-PU composite coating and a GCP/EP-PU composite coating are used as experimental samples, and after the samples are soaked in 3.5 wt% NaCl solution for 35 days, electrochemical impedance test is carried out.

As shown in fig. 10, fig. 10(a1) shows a Niquist plot for a blank EP-PU coating, which consists of two typical capacitor circuits. At high frequencies, a semicircle is shown, and at low frequencies, a straight line is shown. The semi-circular area reflects the charge transfer resistance and double layer capacitance at the coating electrolyte interface, and the linear area is related to the Warburg impedance. With followingThe diameter of the semicircular area is sharply reduced due to the prolonged soaking time, which means that the coating is seriously damaged and cannot be preserved for a long time. FIG. 10(a2, a3) is a Bode plot of a blank EP-PU coating, with lower frequency of the impedance modulus (| Z _10mHz ) From 3.64X 10 ⁹ Ωcm ² Sharply decreases to 9.40 × 10 ⁷ Ωcm ² . It is noteworthy that 2 time constants appeared after 10d of soaking, indicating that the corrosive medium entered the coating through intrinsic defects (such as cracks, vacancy defects, etc.), thus deteriorating the barrier capability of the coating. For the GC/EP-PU coating (fig. 10(b1)), after 20d of soaking, the straight line region appears in the Niquist plot and the semi-circle diameter shrinks sharply, indicating that the barrier properties of the coating decrease, gradually losing the corrosion protection ability. FIG. 10(c1) shows a Niquist plot for the GCP/EP-PU coating, showing a semi-circle throughout the immersion process, showing good barrier capability, with only one peak in the Bode plot for the GCP/EP-PU coating (10) ⁵ ～10 ³ Hz)，|Z| _10mHz The temperature is maintained at 10 ℃ after soaking for 35d ¹⁰ Ωcm ² 2 orders of magnitude higher than the blank EP-PU. It shows that GCP is added into EP-PU resin as filler, and the compactness and the permeability resistance of the resin are improved, so that the resin has excellent corrosion resistance.

As shown in FIG. 11, pure EP-PU coatings were immersed in | Z! Y cells of 1d, 10d, and 35d _10mHz Are respectively 3.63 multiplied by 10 ⁹ Ωcm ² 、1.91×10 ⁸ Ωcm ² And 9.40X 10 ⁷ Ωcm ² This indicates that the corrosive media passes through the coating to the carbon steel substrate by intrinsic defects, causing the coating to gradually lose corrosion resistance. GC/EP-PU composite coating immersed in | Z! Y cells of 1d, 10d and 35d _10mHz Are respectively 3.15 multiplied by 10 ¹⁰ Ωcm ² 、6.49×10 ⁹ Ωcm ² And 1.02X 10 ⁹ Ωcm ² And the thickness of the coating is 1 order of magnitude higher than that of a pure EP-PU coating, so that the addition of GC fills partial defects of the coating and reduces the permeation path of corrosive media. GCP/EP-PU composite coating soaked in | Z | (Z |) cells of 1d, 10d and 35d _10mHz Are respectively 5.81X 10 ¹⁰ Ωcm ² 、3.77×10 ¹⁰ Ωcm ² And 2.42X 10 ¹⁰ Ωcm ² Is about 1 order of magnitude higher than GB,exhibiting higher | Z ∞ _10mHz The value is obtained. The GCP has a large specific surface area, so that CS and PASP grown on GO nano sheets can be connected with GO sheets, and when the CS and PASP are added into an EP-PU coating, defects in the coating can be blocked, and a blocking effect is achieved. Meanwhile, it provides a tortuous path for the penetration of corrosive media, greatly prolonging the time for the corrosive media to reach the interface between the coating and the metal.

6. Self-repairing performance test of the GCP/EP-PU composite coating:

the self-repairing performance of the coating is explored through an EIS test, and the coating is scratched by a blade with the length of 1cm and the depth reaching the scratch of a carbon steel substrate. Fig. 12 shows the Niquist plot and the Bode plot for the different coatings after scribing. For Bode diagram, the intermediate frequency (100-10) ³ Hz) is the coating defect response, low frequency (10) ^-2 100Hz) are the metal corrosion response and the corrosion product response. In addition, the peak in the mid-frequency range may shift slightly to high frequencies due to the build-up of corrosion products. Fig. 12(a2, a3) is a blank EP-PU coating Bode plot, with low frequency impedance values rising inversely after 4h soaking, indicating that the build-up of corrosion products temporarily blocks the penetration of electrolyte solution, as in the Niquist plot (fig. 12(a1)), but after 4h soaking, the semi-circle is gradually shrinking, gradually losing corrosion resistance. FIG. 12(b2, b3) is a Bode plot of a GC/EP-PU coating showing the same trend of change as a pure EP-PU coating, but with a higher low frequency impedance value of the GC/EP-PU coating. FIG. 12(c2, c3) is a Bode plot of GCP/EP-PU coatings, with only one peak in the first 4h of the intermediate frequency region, after which the peak broadens and gradually evolves into two peaks with higher peak intensity in the intermediate frequency region and a more gradual drop, demonstrating that the corrosion reaction at the defect is suppressed and the degree of corrosion is reduced. Wherein the peak in the high frequency range is associated with passivation film formation.

| Z | -of different coatings with scratches _10mHz The soaking time curve is shown in fig. 13. Pure EP-PU coating is soaked in early stage (0-4 h) | Z | _10mHz This is elevated, which proves the penetration of the coating by the corrosive medium, leading to the accumulation of corrosion products at the scratches, which temporarily hinder the penetration of the corrosive medium. For GC/EP-PU coatings, the entire | Z _10mHz Bipure EP-PU coatingThe layer was large, but its rate of decline was relatively fast due to the presence of hydrophilic groups on the GC, thereby increasing the channels for water permeation. For GCP/EP-PU coatings, | Z _10mHz After 4h of soaking, the increase is observed, indicating the release of polyaspartic acid corrosion inhibitors and the formation of passive films. Soaking for 24h to count Z _10mHz The change tends to be smooth, indicating that the passivation film formed in GCP has better corrosion protection. In addition, the | Z tintgradually decreases after soaking for 72h _10mHz Illustrating the process of the electrolyte continuously attacking the substrate and the gradual collapse of the passivation film.

The EIS results were fitted by zsimpwn and the corresponding equivalent circuit is shown in fig. 14. Intermediate frequency (10) observed in Bode phase angle diagram of pure EP-PU coatings ³ 100Hz) region as the coating response (Q) _c And R _c ). The peaks of the medium frequency in the early immersion (2h and 4h) are designated as interfacial processes between the electrolyte and the steel. Based on this, the electric double layer capacitance (Q) can be determined _dl ) And a charge transfer resistance (R) _ct ). After 24h of soaking, another peak at low frequency can be observed in the figure, indicating the presence of electrochemical reactions and corrosion products at the coating/metal interface. The capacitance (Q) of the oxide film was estimated from this region _o ) And resistance (R) _o ). In the Bode plot of GC/EP-PU, the peak of the medium frequency shifts to higher frequencies as the immersion time increases. Furthermore, R _ct The value is higher than that of a blank sample, and the value has a rising trend during soaking for 2-4 hours. This is due to the formation of corrosion products at the scratch, blocking the intrusion of corrosive media, R after 4h _ct The value begins to decrease. R of GCP/EP-PU _ct The value of R is significantly higher than that of GC/EP-PU _ct Value R after 24h of soaking _ct The curve slowly drops to a plateau due to defect propagation and deactivation of the passivation layer under alternating current. Thus, it was confirmed that polyaspartic acid was released from GCP/EP-PU and the corrosion reaction was inhibited when local corrosion occurred.

R of different coatings _c And R _ct The relationship with the soaking time is shown in FIG. 15. By R _c Can evaluate the physical barrier property of the composite coating. R _c The higher the more difficult it is for corrosive media to penetrate into the coating. Apparently, R of EP-PU and GC/EP-PU _c Lower value and R as the soaking time is prolonged _c The value gradually decreases. As shown in FIG. 15(a), the R of the GCP/EP-PU composite coating layer is present during the whole soaking process _c The values are all higher than other coatings, indicating that they have good corrosion protection. Furthermore, R of EP-PU and GC/EP-PU coatings _ct The value decreases significantly with increasing immersion time, but the R of the GCP/EP-PU coating decreases significantly _ct Higher values and more stable, due to the uniform distribution of polyaspartic acid on graphene oxide nanoplatelets, the uniform dispersion of GCP in the coating prolongs the permeation path of corrosive media.

C of different coatings _c And C _dl The relation with the soaking time is shown in FIG. 16, and an EP-PU coating, a GC/EP-PU composite coating and a GCP/EP-PU composite coating are sequentially arranged from left to right. Low carbon steel exposed to solution due to the extent of passive film formation and defects in the film contributes to double layer capacitance (C) _dl ). Thus, it can be explained that the samples of blank EP-PU and GC/EP-PU have higher C _dl The value is obtained. In contrast, GCP/EP-PU composite coatings exhibit lower C _dl This is attributable to polyaspartic acid enhancing dispersibility of graphene oxide in the resin matrix, forming a protective film in the scratched area and suppressing corrosion.

The anticorrosion mechanism of the GCP/EP-PU coating is as follows: on the one hand, the barrier properties of GCP/EP-PU coatings are a major factor in corrosion protection. First, a corrosive medium (e.g., H) is caused to flow through the graphene oxide-based sheet structure ₂ O、O ₂ And Cl ^- ) The permeation pathway is complicated and the corrosion process is slowed down. Secondly, the grafting of the chitosan reduces Van der Waals force between graphene oxide layers, and the crosslinked polyaspartic acid further increases interlayer spacing, so that the stacking and agglomeration phenomena between graphene oxide layers are effectively improved. Again, polyaspartic acid can react with epoxy groups in the EP-PU coating, thereby increasing the crosslink density with the EP-PU coating, resulting in a uniform distribution of GCP nanomaterials in the coating matrix.

As shown in FIG. 17, the protection mechanism proposed by GCP/EP-PU coating in 3.5 wt% NaCl solution is shown. After the formation of scratches in the GCP/EP-PU coating, the mild steel substrate begins to corrode upon contact with the corrosive medium. The reduction process of the electrochemical corrosion results in an increase in the pH at the defect. Hydrolysis of the cation partially offsets the increase in pH. The change in pH results in the dissociation of the functional groups of chitosan and PASP. Therefore, PASP is stimulated to be released from the nano material, the PASP delays the speed of anode reaction when corrosion occurs on a metal interface, PASP-Fe compound is formed, a precipitation layer is formed on the surface of low-carbon steel, the corrosion is reduced to the maximum extent, the self-repairing function is exerted, and the PASP is adsorbed on the low-carbon steel to form a protective film. The water permeating to the surface can cause the expansion of chitosan and PASP, the defects formed in the coating can be covered due to the fluidity of the polyelectrolyte multilayer film, and the uniform dispersion of the GCP nano material in the coating is beneficial to compensating the defects (such as micropores, cracks and the like) of EP-PU. Therefore, the GCP/EP-PU composite coating has excellent barrier property.

Claims

1. The preparation method of the chitosan modified graphene oxide composite coating is characterized by comprising the following steps: the method comprises the following operation steps:

s1, preparing GO-CS:

s2, preparing GO-CS-PASP:

s3, preparing a GCP/EP-PU composite coating:

2. The method for preparing the chitosan-modified graphene oxide composite coating according to claim 1, wherein the method comprises the following steps: in the S1, the mass ratio of chitosan to GO to graphene oxide is 15: 1-25: 1.

3. The method for preparing the chitosan-modified graphene oxide composite coating according to claim 1, wherein the method comprises the following steps: the S1 specifically includes: preparing GO-CS: a. adding 0.2g chitosan into 50mL 2% acetic acid solution, and stirring to form uniform solution A; b. adding 0.01g of graphene oxide into 20mL of deionized water, carrying out ultrasonic treatment for 10min, uniformly mixing, adding into the product A, and uniformly mixing to obtain a product B; c. and adjusting the pH value of the product B to 5 by using 1mol/L NaOH solution, stirring at 60 ℃ for 2h, and centrifuging to obtain chitosan modified graphene oxide, which is recorded as GC.

4. The method for preparing the chitosan-modified graphene oxide composite coating according to claim 1, wherein the method comprises the following steps: in the S2, the mass ratio of polyaspartic acid to GC is 1: 1-3: 1.

5. The method for preparing the chitosan-modified graphene oxide composite coating according to claim 1, wherein the method comprises the following steps: the S2 specifically includes: preparing GO-CS-PASP: a. adding 0.2g of polyaspartic acid into 40mL of deionized water, and uniformly mixing to obtain a product C; b. adding 0.1g of GC into the product C for dissolving, adjusting the pH value to 5 by using a NaOH solution, adding 0.8mL of glutaraldehyde, stirring for 24h at room temperature, and uniformly mixing to obtain a product D; c. and washing the product D with deionized water for many times to obtain PASP-CS-GO which is marked as GCP.

6. The method for preparing the chitosan-modified graphene oxide composite coating according to claim 1, wherein the method comprises the following steps: the step S3 specifically includes: and uniformly mixing GCP, the epoxy modified polyurethane resin and the amine curing agent, wherein the weight of GCP accounts for 0.10-0.20% of the total weight of the epoxy modified polyurethane resin and the amine curing agent, and obtaining the GCP/EP-PU composite coating.

7. The method for preparing the chitosan-modified graphene oxide composite coating according to claim 6, wherein the method comprises the following steps: the step S3 specifically includes: GCP is uniformly mixed with 2.27g of epoxy modified polyurethane resin and 1g of amine curing agent, wherein the weight of GCC accounts for 0.15% of the total weight of the epoxy modified polyurethane resin and the amine curing agent, and the GCP/EP-PU composite coating is prepared by fully mixing.