Stearic Acid / Chitosan-Modified Multi-Walled Carbon Nanotubes Modified Waterborne Epoxy Resin and Its Preparation Method and Application

Abstract

The present invention discloses a stearic acid / chitosan-modified multi-walled carbon nanotube modified waterborne epoxy resin and its preparation method and application, which relates to the technical field of anticorrosive coatings. First, the present invention uses the surface deposition cross-linking method to adsorb and wrap chitosan on the surface of multi-walled carbon nanotubes to improve the dispersibility of multi-walled carbon nanotubes, and then grafts stearic acid through a water-soluble coupling agent to synthesize stearic acid / chitosan-modified multi-walled carbon nanotubes. Adding it to waterborne epoxy resin can effectively increase the cross-linking density of epoxy resin and reduce the surface energy of the epoxy resin coating, reduce the contact area between the hydrophobic surface and corrosive media, effectively prevent the adsorption of corrosive media, and delay the time for it to enter the interior of the coating.

Description

Technical Field

[0001] The invention relates to the technical field of anti-corrosion coatings, and in particular to a stearic acid / chitosan modified multi-walled carbon nanotube modified waterborne epoxy resin and a preparation method and application thereof. Background Art

[0002] People use a lot of metal materials in daily production, and water-based epoxy resin anti-corrosion coating is an effective anti-corrosion coating. However, the condensation and cross-linking of organic molecules in the curing process of water-based epoxy resin coating will affect the density of the coating, resulting in a large number of micropores, microcracks and other defects. These defects will become diffusion channels for corrosive ions, thus causing the coating to fail quickly.

[0003] Multi-walled carbon nanotubes (MWCNTs) have attracted attention for enhancing the mechanical and corrosion properties of polymer coatings due to their excellent chemical resistance, ultra-high aspect ratio, and mechanical stability. However, MWCNTs exhibit chemical inertness and aggregate in solutions and coating matrices within a short period of time through π-π interactions and van der Waals forces, which affects the reinforcing effect of MWCNTs in composites. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a preparation method of stearic acid / chitosan modified multi-walled carbon nanotube modified water-based epoxy resin. The epoxy resin is modified by stearic acid / chitosan modified multi-walled carbon nanotubes, which can effectively increase the cross-linking density of the epoxy resin and reduce the surface energy of the epoxy resin coating, so that the contact area between the hydrophobic surface of the coating and the corrosive medium is reduced, which effectively prevents the adsorption of the corrosive medium and delays the time for it to enter the interior of the coating.

[0005] The technical problem to be solved by the present invention is achieved by adopting the following technical solutions:

[0006] One of the purposes of the present invention is to provide a method for preparing a waterborne epoxy resin modified with stearic acid / chitosan modified multi-walled carbon nanotubes, comprising the following steps:

[0007] S1, chitosan modified multi-walled carbon nanotubes and stearic acid undergo condensation reaction under the action of a coupling agent to obtain stearic acid / chitosan modified multi-walled carbon nanotubes;

[0008] S2, stearic acid / chitosan modified multi-walled carbon nanotubes undergo cross-linking reaction with water-based epoxy resin and water-based epoxy curing agent to obtain stearic acid / chitosan modified multi-walled carbon nanotubes modified water-based epoxy resin.

[0009] The second object of the present invention is to provide a stearic acid / chitosan modified multi-walled carbon nanotube modified waterborne epoxy resin prepared by the above-mentioned preparation method.

[0010] The third object of the present invention is to provide the application of the stearic acid / chitosan modified multi-walled carbon nanotubes modified waterborne epoxy resin in an anticorrosive coating.

[0011] The beneficial effects of the present invention are as follows:

[0012] (1) Chitosan adopted in the present invention belongs to the only cationic polysaccharide among natural polysaccharides, is non-toxic and has good film-forming property, and has a strong chelating ability with metals, and can be used as an efficient green corrosion inhibitor; in addition, using chitosan to modify multi-walled carbon nanotubes can significantly improve the agglomeration phenomenon of multi-walled carbon nanotubes in the matrix.

[0013] (2) Stearic acid adopted in the present invention is a fatty acid containing a long carbon chain and low surface energy, and is widely used for preparing hydrophobic coatings. Introducing low-surface-energy materials on the metal surface to prepare hydrophobic coatings is also an effective method to enhance corrosion resistance to prevent corrosive ions from etching the metal.

[0014] (3) The synthesized stearic acid / chitosan modified multi-walled carbon nanotubes of the present invention can enhance the interfacial bonding strength between multi-walled carbon nanotubes and the epoxy resin matrix, the internal structure of the epoxy resin coating is denser, the formation of microporous defects is reduced, and the shielding performance of the coating against corrosive electrolytes is effectively improved. Description of the Drawings

[0015] Figure 1 The figure shows the effect diagrams of salt spray aging experiments on coatings cured from the modified waterborne epoxy resins prepared in Examples 1-3 and Comparative Example 1 and the waterborne epoxy resin prepared in Comparative Example 2, respectively. Detailed Embodiments

[0016] In order to make the technical means, creative features, achieved purposes and functions of the present invention easy to understand, the present invention will be further described below in conjunction with specific embodiments and illustrations.

[0017] The present invention provides a preparation method of a stearic acid / chitosan modified multi-walled carbon nanotubes modified waterborne epoxy resin, including the following steps:

[0018] S1. A condensation reaction occurs between chitosan modified multi-walled carbon nanotubes and stearic acid under the action of a coupling agent to obtain stearic acid / chitosan modified multi-walled carbon nanotubes;

[0019] S2. A crosslinking reaction occurs between stearic acid / chitosan modified multi-walled carbon nanotubes, waterborne epoxy resin and a waterborne epoxy curing agent to obtain a stearic acid / chitosan modified multi-walled carbon nanotubes modified waterborne epoxy resin.

[0020] Furthermore, the coupling agent includes but is not limited to 1-ethyl-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDC·HCl). In the present invention, a water-soluble coupling agent is preferred.

[0021] Furthermore, the mass ratio of the chitosan-modified multi-walled carbon nanotubes, stearic acid, and coupling agent is 1:1:(2 - 5).

[0022] Furthermore, the waterborne epoxy curing agent includes, but is not limited to, at least one of polyetheramine, ethylenediamine, and diethylenetriamine.

[0023] Furthermore, the mass ratio of the waterborne epoxy resin to the waterborne epoxy curing agent is 2:(0.5 - 1).

[0024] Furthermore, the dosage of the stearic acid / chitosan-modified multi-walled carbon nanotubes is 0.5 - 1.5% of the total mass of the epoxy resin and the waterborne epoxy curing agent.

[0025] Furthermore, the chitosan-modified multi-walled carbon nanotubes are prepared by depositing chitosan on the surface of multi-walled carbon nanotubes through a cross-linking agent.

[0026] Furthermore, the cross-linking agent includes, but is not limited to, at least one of glutaraldehyde and formaldehyde.

[0027] Furthermore, the dosage ratio of chitosan, multi-walled carbon nanotubes, and cross-linking agent is (2 - 5) g:1 g:(3 - 8) mL.

[0028] In the present invention, glutaraldehyde and / or formaldehyde is used as the cross-linking agent, and chitosan is adsorbed on the surface of multi-walled carbon nanotubes by electrostatic adsorption to improve the dispersibility of multi-walled carbon nanotubes; then stearic acid is grafted through a water-soluble coupling agent to synthesize stearic acid / chitosan-modified multi-walled carbon nanotubes, which are blended with waterborne epoxy resin. Chitosan can cross-link with the epoxy resin, enhancing the interfacial bonding strength between the multi-walled carbon nanotubes and the epoxy resin matrix. The cross-linked epoxy resin coating structure is denser, reducing the formation of micropore defects; the grafting of stearic acid enhances the hydrophobicity of the coating, effectively improving the shielding performance of the coating against corrosive electrolytes. In addition, the amino and hydroxyl groups on the side chain of the chitosan molecular structure have strong chemical activity and strong chelating ability with metals, and can be used as an efficient green corrosion inhibitor.

[0029] The present invention provides a stearic acid / chitosan-modified multi-walled carbon nanotube-modified waterborne epoxy resin prepared by the foregoing preparation method.

[0030] The present invention provides the application of the foregoing stearic acid / chitosan-modified multi-walled carbon nanotube-modified waterborne epoxy resin in anticorrosive coatings.

[0031] Example 1

[0032] 1) Weigh 0.8 g of chitosan and dissolve it in 200 mL of dilute acetic acid solution, stir for 12 h to obtain a chitosan solution; weigh 0.2 g of multi-walled carbon nanotubes and disperse them in 20 mL of deionized water. After ultrasonic treatment for 30 min, slowly add them to the chitosan solution. The obtained mixed solution is stirred and reacted at 98 °C for 6 h; cool to room temperature, adjust the pH of the solution to 10 with dilute ammonia water, then add 1 mL of glutaraldehyde, and stir and react at 60 °C for 3 h; after the reaction, wash and centrifuge with dilute acetic acid and deionized water, and freeze-dry to obtain chitosan-modified multi-walled carbon nanotubes.

[0033] 2) Weigh 0.2 g of chitosan-modified multi-walled carbon nanotubes and disperse them in 20 mL of deionized water, ultrasonic for 30 min to obtain a chitosan-modified multi-walled carbon nanotube solution; weigh 0.2 g of stearic acid and 0.67 g of EDC·HCl and dissolve them in a mixed solution of 28 mL of acetone and 12 mL of absolute ethanol, add them to the chitosan-modified multi-walled carbon nanotube solution, and stir and react at 60 °C for 24 h; after the reaction, wash and centrifuge with deionized water and ethanol, and dry at 60 °C to obtain stearic acid / chitosan-modified multi-walled carbon nanotubes.

[0034] 3) Weigh 0.03 g of stearic acid / chitosan-modified multi-walled carbon nanotubes and disperse them in 1.5 mL of absolute ethanol, then mix them with 4 g of waterborne epoxy resin E-51. After ultrasonic treatment for 30 min, add 2 g of polyetheramine (molecular weight 190.283), and stir for 20 min to obtain stearic acid / chitosan-modified multi-walled carbon nanotube modified waterborne epoxy resin (SCCNTs / EP1).

[0035] Example 2

[0036] According to the method of Example 1, the difference is that: in step 3), the dosage of stearic acid / chitosan-modified multi-walled carbon nanotubes is 0.06 g, and the dosage of absolute ethanol is 3 mL, then stearic acid / chitosan-modified multi-walled carbon nanotube modified waterborne epoxy resin (SCCNTs / EP2) is obtained.

[0037] Example 3

[0038] According to the method of Example 1, the difference is that: in step 3), the dosage of stearic acid / chitosan-modified multi-walled carbon nanotubes is 0.09 g, and the dosage of absolute ethanol is 4.5 mL, then stearic acid / chitosan-modified multi-walled carbon nanotube modified waterborne epoxy resin (SCCNTs / EP3) is obtained.

[0039] Example 4

[0040] According to the method of Example 2, the difference is that: in step 2), the dosage of EDC·HCl is 1 g, then stearic acid / chitosan-modified multi-walled carbon nanotube modified waterborne epoxy resin is obtained.

[0041] Example 5

[0042] According to the method of Example 2, the difference is that: the dosage of polyetheramine in step 3) is 1 g, and the stearic acid / chitosan modified multi-walled carbon nanotube modified waterborne epoxy resin is obtained.

[0043] Example 6

[0044] According to the method of Example 2, the difference is that: the dosage of chitosan in step 1) is 1 g, and the dosage of glutaraldehyde is 1.6 mL, and the stearic acid / chitosan modified multi-walled carbon nanotube modified waterborne epoxy resin is obtained.

[0045] Comparative Example 1

[0046] According to the method of Example 2, the difference is that: step 2) is not carried out, and the chitosan modified multi-walled carbon nanotubes are directly used to replace the stearic acid / chitosan modified multi-walled carbon nanotubes, and the chitosan modified multi-walled carbon nanotube modified waterborne epoxy resin (CCNTs / EP) is obtained.

[0047] Comparative Example 2

[0048] Weigh 4 g of waterborne epoxy resin E-51, ultrasonically treat it for 30 min, then add 2 g of polyetheramine, and stir for 20 min to obtain waterborne epoxy resin (EP).

[0049] Pour the stearic acid / chitosan modified multi-walled carbon nanotube modified waterborne epoxy resin prepared in Examples 1-6, the chitosan modified multi-walled carbon nanotube modified waterborne epoxy resin prepared in Comparative Example 1, and the waterborne epoxy resin prepared in Comparative Example 2 into a mold to form a coating, cure it in an oven at 70 °C for 24 h, and perform performance tests on the coating. The test results are shown in Table 1.

[0050] Water absorption test:

[0051] Soak a coating film of a certain mass in ultrapure water for 24 h, weigh its mass before and after soaking, and calculate the water absorption rate of the coating film according to formula (1):

[0052]

[0053] Among them: Q represents the water absorption rate (%); M represents the mass (g) of the coating film sample after water absorption; m represents the mass (g) of the coating film sample before water absorption.

[0054] Contact angle test:

[0055] Use a DSA10-MK2 contact angle measuring instrument to perform water contact angle tests on the coating films with flat surfaces. Each coating film is tested three times, and the median value is taken.

[0056] Impact resistance test:

[0057] Using the KX-DB-501 impact testing machine, in accordance with the standard of GB / T 6739-1996.

[0058] Table 1

[0059] Test Items Example 1 Example 2 Example 3 Example 4 Water Absorption Rate (%) 4.89 4.12 4.73 4.26 Contact Angle (°) 98.3 104.3 102.8 103.9 Impact Resistance (kg·cm) 40 45 45 45 Test Items Example 5 Example 6 Comparative Example 1 Comparative Example 2 Water Absorption Rate (%) 4.35 3.98 5.84 11.23 Contact Angle (°) 103.0 105.4 77.5 62.8 Impact Resistance (kg·cm) 46 47 40 40

[0060] As can be seen from Table 1, compared with Comparative Example 1 and Comparative Example 2, the coatings formed by curing the stearic acid / chitosan modified multi-walled carbon nanotube modified waterborne epoxy resin prepared in Examples 1-6 have good hydrophobicity and mechanical properties.

[0061] The stearic acid / chitosan modified multi-walled carbon nanotube modified waterborne epoxy resin prepared in Examples 1-3, the chitosan modified multi-walled carbon nanotube modified waterborne epoxy resin prepared in Comparative Example 1, and the waterborne epoxy resin prepared in Comparative Example 2 were respectively coated on tinplate, the film thickness was controlled to be 100±2 μm, cured in an oven at 70 °C for 24 h, a "×" was drawn on the coating surface, and then placed in a salt spray test chamber for salt spray aging experiment. The temperature of the salt spray test chamber was 35±2 °C, and a 5wt% NaCl solution was used as the spray solution, and continuous spraying was carried out for 30 d.

[0062] The test results show that: after 10 days of salt spray experiment, a large amount of corrosion products appeared around the scratches of the EP coating, and the coating had whitening and blistering phenomena; after 30 days of salt spray experiment, the rust marks of the EP coating spread to the entire coating surface, and the coating showed signs of peeling; the rust marks of the CCNTs / EP coating were significantly reduced compared with the EP coating, and the blistering phenomenon of the coating was significantly improved. Compared with the EP and CCNTs coatings, the SCCNTs / EP1-3 coatings showed slight rust marks at and around the scratches after 30 days of salt spray experiment, and the corrosion inhibition effect was significantly enhanced. Among them, the SCCNTs / EP2 coating had the fewest rust spots on the surface, mainly concentrated around the scratches, the coating surface was smooth and did not blister, and had the best barrier performance.

[0063] The above shows and describes the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited by the above embodiments. The above embodiments and the descriptions in the specification only illustrate the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention will have various changes and improvements, and these changes and improvements all fall within the scope of the present invention claimed. The scope of protection claimed by the present invention is defined by the appended claims and their equivalents.

Claims

1. A preparation method of stearic acid / chitosan modified multi-walled carbon nanotube modified waterborne epoxy resin, characterized in that, It includes the following steps: S1. Condensation reaction occurs between chitosan-modified multi-walled carbon nanotubes and stearic acid under the action of a coupling agent to obtain stearic acid / chitosan-modified multi-walled carbon nanotubes; S2. Crosslinking reaction occurs between stearic acid / chitosan-modified multi-walled carbon nanotubes, waterborne epoxy resin and waterborne epoxy curing agent to obtain stearic acid / chitosan-modified multi-walled carbon nanotube modified waterborne epoxy resin.

2. The preparation method according to claim 1, characterized in that: The coupling agent is 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride.

3. The preparation method according to claim 1, characterized in that: The mass ratio of the chitosan-modified multi-walled carbon nanotubes, stearic acid and coupling agent is 1:1:(2-5).

4. The preparation method according to claim 1, characterized in that: The waterborne epoxy curing agent is at least one of polyetheramine, ethylenediamine and diethylenetriamine.

5. The preparation method according to claim 1, characterized in that: The mass ratio of the waterborne epoxy resin to the waterborne epoxy curing agent is 2:(0.5-1); the dosage of the stearic acid / chitosan-modified multi-walled carbon nanotubes is 0.5-1.5% of the total mass of the epoxy resin and the waterborne epoxy curing agent.

6. The preparation method according to claim 1, characterized in that: The chitosan-modified multi-walled carbon nanotubes are prepared by depositing chitosan on the surface of multi-walled carbon nanotubes through a crosslinking agent.

7. The preparation method according to claim 6, characterized in that: The crosslinking agent is at least one of glutaraldehyde and formaldehyde.

8. The preparation method according to claim 6, characterized in that: The dosage ratio of the chitosan, multi-walled carbon nanotubes and crosslinking agent is (2-5)g:1g:(3-8)mL.

9. Stearic acid / chitosan-modified multi-walled carbon nanotube modified waterborne epoxy resin prepared by the preparation method according to any one of claims 1-8.

10. Application of the stearic acid / chitosan-modified multi-walled carbon nanotube modified waterborne epoxy resin according to claim 9 in an anticorrosive coating.

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