Self-healing coating with semi-interpenetrating network structure and preparation method and application thereof

Abstract

The application discloses a self-repairing coating with a semi-interpenetrating network structure and a preparation method and application thereof, and relates to the technical field of metal corrosion and protection. The preparation method of the self-repairing coating with the semi-interpenetrating network structure comprises the following steps: (1) reacting linear polyurethane, epoxy resin and a curing agent 1 at 50-60 DEG C for 3-4 h to obtain a mixed solution; or reacting linear polyurethane, linear polyimine, epoxy resin and a curing agent 2 at 50-60 DEG C for 3-4 h to obtain the mixed solution; (2) then coating the mixed solution on the surface of a coating substrate; and finally curing at 80-100 DEG C for 10-12 h to obtain the self-repairing coating with the semi-interpenetrating network structure. The self-repairing coating has super room-temperature self-repairing performance and excellent corrosion protection effect, and has important application prospects in the field of corrosion control of marine engineering equipment.

Description

Technical Field

[0001] This invention relates to the technical field of metal corrosion and protection, and in particular to a self-healing coating with a semi-interpenetrating network structure, its preparation method, and its application. Background Technology

[0002] The harsh service conditions in the marine environment have led to material corrosion, which has become a significant factor restricting the safety and service life of marine engineering structures. Coatings provide physical, chemical, and electrochemical protection to the metal substrate, extending the service life of the substrate material and reducing maintenance costs, thus becoming the mainstream corrosion protection method. However, due to the arduous tasks and harsh service environments of marine engineering equipment, the surface coatings inevitably fail, leading to a "point-to-area" corrosive effect. Furthermore, the "offshore" nature of marine engineering equipment greatly increases the difficulty of coating repair, resulting in extremely high maintenance costs. Therefore, the issue of coating failure places higher demands on the functionality of anti-corrosion coatings in terms of safety, reliability, and economy.

[0003] Inspired by the "self-repair" capabilities of living organisms, the concept of self-diagnostic / self-repairing intelligent coating materials was first proposed in 1986 to address coating failure. However, research on self-healing materials remained stagnant for over a decade. It wasn't until the development of microcapsules (core material + shell) embedded in the substrate, where the core material seeps out and cross-links to cure cracks upon substrate breakage, that the development of self-healing polymer materials was finally propelled. However, this repair method also has significant drawbacks: the limited storage capacity within the microcapsules means that when the material breaks, the microcapsule self-healing system can only achieve single-stage repair at specific sites. Therefore, utilizing the inherent dynamic and reversible chemical bonds within the material, and through rational design, to achieve intrinsic self-healing of the coating material has become a new direction in the development of self-healing coatings, attracting widespread attention in the past few decades. However, self-healing coatings based on covalent and non-covalent bonds have high repair energy, high self-healing temperature, and long repair response time, making it difficult to achieve self-healing of coating systems at room temperature. How to control the self-healing trigger conditions of coatings, achieve autonomous defect healing at room temperature, and combine with ingenious design to endow the coating with excellent corrosion protection performance remains a severe challenge. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a self-healing coating with a semi-interpenetrating network structure, its preparation method, and its applications. This invention utilizes the dynamic viscoelastic properties of polyurethane materials, and uses a fully cured epoxy resin network or an imine-epoxy dynamic cross-linked network as the framework structure, combined with polyurethane materials, to form a polyurethane-epoxy resin semi-interpenetrating network structure through reaction-induced microphase separation. This constructs a coating system that achieves a harmonious balance between "fluidity" and "stability," enabling self-repair of defects. Furthermore, in application, it can extend the service life of coatings and steel in harsh marine corrosive environments, indirectly forming an effective carbon emission control valve from the source. This has a strong promoting effect on achieving carbon peaking and carbon neutrality goals and can bring significant long-term economic benefits.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] In a first aspect, the present invention provides a method for preparing a self-healing coating with a semi-interpenetrating network structure, comprising the following steps:

[0007] (1) The linear polyurethane, epoxy resin and curing agent 1 are reacted at 50-60℃ for 3-4h to obtain a mixed solution, wherein the mass ratio of the linear polyurethane, epoxy resin and curing agent 1 is (1-3):(1-2):1;

[0008] Alternatively, linear polyurethane, linear polyimide, epoxy resin and curing agent 2 are reacted at 50-60℃ for 3-4 hours to obtain a mixed solution, wherein the mass ratio of linear polyurethane, linear polyimide, epoxy resin and curing agent 2 is (1-2):(1-2):1:1;

[0009] (2) The mixed solution is then applied to the surface of the coating substrate and cured at 80-100℃ for 10-12h to obtain a self-healing coating with a semi-interpenetrating network structure.

[0010] This invention utilizes the dynamic viscoelastic properties of polyurethane materials and uses a fully cured epoxy resin network or an imine-epoxy dynamic cross-linked network as the skeleton structure. In conjunction with the polyurethane material, a polyurethane-epoxy resin semi-interpenetrating network structure is formed through reaction-induced microphase separation. This constructs a coating system that coordinates and unifies "fluidity" and "stability" to achieve self-repair of defects, ensuring the mechanical properties and corrosion protection performance of the coating at the defect site after self-repair.

[0011] The semi-interpenetrating network structure coating constructed in this invention can achieve a harmonious balance between the "flowability" of polyurethane materials with dynamic viscoelastic properties at room temperature and the "dynamic stability" of the imine-epoxy dynamic crosslinked backbone network, exhibiting superior room temperature self-healing performance and outstanding corrosion protection effect, and has important application prospects in the field of corrosion control of marine engineering equipment.

[0012] Preferably, the molecular weight of the linear polyurethane in step (1) is 32,000-35,000.

[0013] Preferably, the linear polyimide in step (1) has a molecular weight of 1300-1650.

[0014] Preferably, the method for preparing linear polyurethane in step (1) includes the following steps:

[0015] A linear polyurethane is obtained by reacting a polyester / ether polyol with isophorone diisocyanate and 1,4-butanediol at 40-50°C for 1-2 hours under an inert atmosphere. The mass ratio of the polyester / ether polyol, isophorone diisocyanate and 1,4-butanediol is (2.9:6.77:0) to (0:6.77:2.612).

[0016] The linear polyurethane prepared by the above method has excellent dynamic viscoelastic properties and can better crosslink with the epoxy resin curing system through reaction-induced microphase separation to form a film, thereby improving the mechanical properties and corrosion protection performance of the self-healing coating.

[0017] Preferably, the polyester / ether polyol includes at least one of polytetrahydrofuran, polyethylene glycol, and polycaprolactone.

[0018] Preferably, the molecular weight range of the polyester / ether polyol is 980-1020.

[0019] More preferably, the mass ratio of the polyester / ether polyol, isophorone diisocyanate and 1,4-butanediol is 2.9:6.77:2.612.

[0020] Preferably, the method for preparing linear polyimide in step (1) includes the following steps:

[0021] Tetrahydrofuran, terephthalaldehyde, and triethylenetetramine were reacted at 50-60°C for 3-4 hours under an inert atmosphere to obtain linear polyimide. The mass ratio of tetrahydrofuran, terephthalaldehyde, and triethylenetetramine was (88.64:13.4:4.39) to (88:13.4:0.73).

[0022] The linear polyimide prepared by the above method in this invention facilitates the in-situ cross-linking of linear polyurethane molecular chains and imine-epoxy dynamic cross-linking system through reaction-induced microphase separation to form a film, thereby enabling the self-healing coating to have excellent mechanical properties and corrosion protection performance.

[0023] Preferably, the epoxy resin in step (1) is a bisphenol A type epoxy resin.

[0024] Preferably, in step (1), curing agent 1 is methylhexahydrophthalic anhydride and curing agent 2 is polyetheramine D-230.

[0025] Preferably, in step (2), the mixed solution is coated onto the surface of the coating substrate and then cured at 80°C and 100°C for 10-12 hours respectively.

[0026] The present invention employs a step-by-step curing method, which helps to ensure complete cross-linking of the epoxy resin.

[0027] Preferably, in step (2), the coating substrate is Q235 carbon steel, and the coating thickness is 200-700 micrometers, preferably 500 micrometers.

[0028] Secondly, the present invention also provides a self-healing coating with a semi-interpenetrating network structure prepared by the above method.

[0029] Thirdly, the present invention also provides the application of a self-healing coating with a semi-interpenetrating network structure in corrosion protection.

[0030] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0031] (1) The present invention synthesizes a polyurethane material in a viscous flow state at room temperature and confines it within a three-dimensional framework of an epoxy resin network or an imine-epoxy dynamic crosslinking network, thereby achieving a coordinated unity of the "flowability" and "stability" of the coating material. When defects occur in the coating system, the linear polyurethane molecules in the coating system move towards the coating defects to fill the coating gaps, thereby achieving the self-repair function of the coating.

[0032] (2) The self-healing coating system constructed in this invention can autonomously repair the mechanical properties and corrosion protection properties of the coating at the defect site. Furthermore, this invention can overcome the technical barrier of external energy input to the autonomous repair of the coating, and establish a self-healing coating theoretical system of "autonomous jointing of fractures, autonomous repair of defects, and integrated patching", which has positive scientific value and application prospects.

[0033] (3) The room-temperature self-healing polymer coating material with a semi-interpenetrating network structure described in this invention is obtained by in-situ crosslinking of linear polyurethane molecular chains and a bisphenol A type epoxy resin curing system with methylhexahydrophthalic anhydride as a curing agent through reaction-induced microphase separation; or by in-situ crosslinking of linear polyurethane molecular chains and an imine-epoxy dynamic crosslinking system with polyetheramine D-230 as a curing agent through reaction-induced microphase separation. This results in a self-healing material that is transparent, easy to process, and has high mechanical strength. Furthermore, the coating exhibits unique coating sealing properties, self-healing performance at ambient temperature, and excellent corrosion protection performance in artificial seawater, and is expected to be widely applied in the field of corrosion protection. Attached Figure Description

[0034] Figure 1 This is a schematic diagram of the semi-interpenetrating network structure of the coating material described in this invention.

[0035] Figure 2 The images show the 1H NMR spectrum (a) and 1C NMR spectrum (b) of the linear polyurethane described in Example 1 of this invention, and the 1H NMR spectrum (c) and 1C NMR spectrum (d) of the linear polyimide described in Example 3.

[0036] Figure 3 These are thermogravimetric images of the polyurethane / epoxy resin coating (a) described in Example 1 and the polyurethane / imide-epoxy resin coating (b) described in Example 3 of the present invention, wherein LPU / EP is the polyurethane / epoxy resin coating material; and PU / EPM is the polyurethane / imide-epoxy resin coating material.

[0037] Figure 4 These are polarized light microscope images of scratch repair on the polyurethane / epoxy resin coating (ac) described in Example 1 and the polyurethane / imine-epoxy resin coating (df) described in Example 3 of the present invention.

[0038] Figure 5 In the figure, (a, b), (c, d), and (e, f) are the electrochemical impedance spectra of the undamaged polyurethane / epoxy resin coating described in Example 1, the coating damaged and repaired at room temperature for 48 hours, and the unrepaired coating after damage, respectively, after being immersed in simulated seawater for 75 days (a, c, and e are Nernquist plots, and b, d, and f are Bode plots). Detailed Implementation

[0039] To better illustrate the purpose, technical solution, and advantages of the present invention, the present invention will be further described below in conjunction with specific embodiments, but the scope of protection and implementation of the present invention are not limited thereto.

[0040] Unless otherwise specified, the materials and reagents used in the following examples are commercially available.

[0041] Example 1

[0042] A method for preparing a self-healing coating with a semi-interpenetrating network structure includes the following steps:

[0043] (1) Preparation of linear polyurethane: Polytetrahydrofuran was added to a 100mL three-necked flask, and then dried under vacuum at 110℃ for 1.5h. After cooling to 70℃, it was reacted with isophorone diisocyanate under nitrogen atmosphere for 2h. Then 1,4-butanediol was added and reacted at 40℃ for 1.5h to obtain a dynamically viscoelastic linear polyurethane. The mass ratio of polytetrahydrofuran, isophorone diisocyanate and 1,4-butanediol was 2.9:6.77:2.612.

[0044] (2) A solution containing linear polyurethane (molecular weight 32000) and bisphenol A type epoxy resin (Guangzhou Pearl River Chemical Group Co., Ltd., E51) was stirred for 0.5 h. Then, 1-methylhexahydrophthalic anhydride curing agent was added to the solution to obtain a uniform mixed solution. The obtained mixed solution was stirred again at 50 °C for 3 h to reach a viscous state. The viscous mixed solution was then brushed onto the surface of Q235 carbon steel plate with a coating thickness of 500 micrometers. Finally, it was cured at 80 °C and 100 °C for 12 h respectively to obtain a self-healing coating with a semi-interpenetrating network structure. The mass ratio of linear polyurethane, epoxy resin and methylhexahydrophthalic anhydride was 3:1:1.

[0045] Example 2

[0046] A method for preparing a self-healing coating with a semi-interpenetrating network structure differs from Example 1 in that the mass ratio of linear polyurethane, epoxy resin and methylhexahydrophthalic anhydride in step (2) is 1:2:1, while all other steps are the same as in Example 1.

[0047] Comparative Example 1

[0048] A method for preparing a self-healing coating with a semi-interpenetrating network structure differs from Example 1 in that the mass ratio of linear polyurethane, epoxy resin and methylhexahydrophthalic anhydride in step (1) is 5:1:1, while the rest is the same as in Example 1.

[0049] Comparative Example 2

[0050] A method for preparing a self-healing coating with a semi-interpenetrating network structure differs from Example 1 in that the mass ratio of linear polyurethane, epoxy resin and methylhexahydrophthalic anhydride in step (1) is 1:5:1, while all other steps are the same as in Example 1.

[0051] Example 3

[0052] A method for preparing a self-healing coating with a semi-interpenetrating network structure includes the following steps:

[0053] (1) Preparation of linear polyurethane: Polytetrahydrofuran was added to a 100mL three-necked flask, and then dried under vacuum at 110℃ for 1.5h. After cooling to 70℃, it was reacted with isophorone diisocyanate under nitrogen atmosphere for 2h. Then 1,4-butanediol was added and reacted at 40℃ for 1.5h to obtain a dynamically viscoelastic linear polyurethane. The mass ratio of polytetrahydrofuran, isophorone diisocyanate and 1,4-butanediol was 2.9:6.77:2.612.

[0054] (2) Preparation of linear polyimide: Tetrahydrofuran and terephthalaldehyde were first added to a four-necked flask equipped with a mechanical stirrer and a condenser, and nitrogen gas was introduced for protection; then triethylenetetramine was injected into the flask with a syringe to start the reaction; after the above reactants were reacted at 60°C for 3 hours, a linear polyimide solution was obtained; the mass ratio of tetrahydrofuran, terephthalaldehyde and triethylenetetramine was 88.64:13.4:4.39;

[0055] (3) The linear polyurethane (molecular weight 32000) and linear polyimide solution (molecular weight 1300) were stirred for 0.5 h. Then, bisphenol A type epoxy resin (Guangzhou Pearl River Chemical Group Co., Ltd., E51) and curing agent 2-polyetheramine D-230 were added to the solution to obtain a uniform mixed solution. The mixed solution was then stirred again at 60℃ for 3 h to reach a viscous state. The viscous mixed solution was then brushed onto the surface of Q235 carbon steel plate. Finally, it was cured at 80℃ and 100℃ for 12 h respectively to obtain a self-healing coating with a semi-interpenetrating network structure. The mass ratio of linear polyurethane, linear polyimide, epoxy resin and polyetheramine D-230 was 2:1:1:1.

[0056] Example 4

[0057] A method for preparing a self-healing coating with a semi-interpenetrating network structure differs from Example 3 in that the mass ratio of linear polyurethane, linear polyimide, epoxy resin and polyetheramine D-230 in step (3) is 1:2:1:1, while the rest is the same as in Example 3.

[0058] Example 5

[0059] A method for preparing a self-healing coating with a semi-interpenetrating network structure differs from Example 3 in that the molecular weight of the linear polyurethane in step (3) is 35,000 and the molecular weight of the linear polyimide is 1,650, while the rest are the same as in Example 3.

[0060] Comparative Example 3

[0061] A method for preparing a self-healing coating with a semi-interpenetrating network structure differs from Example 3 in that the mass ratio of linear polyurethane, linear polyimide, epoxy resin and polyetheramine D-230 in step (3) is 4:1:1:1, while the rest is the same as in Example 3.

[0062] Comparative Example 4

[0063] A method for preparing a self-healing coating with a semi-interpenetrating network structure differs from Example 3 in that the mass ratio of linear polyurethane, linear polyimide, epoxy resin and polyetheramine D-230 in step (3) is 1:4:1:1, while all other steps are the same as in Example 3.

[0064] Performance testing

[0065] 1. Determination of rheological properties:

[0066] The rheological properties of the coating material at room temperature were analyzed by using a rheometer to perform frequency scanning from 0.01 Hz to 100 Hz and collect stress relaxation curves at a strain amplitude of 0.1%.

[0067] This invention uses materials rheology to characterize the flowability of coating materials. The loss modulus of the coating materials described in this invention is almost always higher than the storage modulus under low-frequency disturbances, which means that the materials tend to flow. As the epoxy resin content increases, the transition point from the viscoelastic state to the elastic state shifts to low frequencies, indicating that the relatively loose linear structure is more conducive to the plastic deformation of the material and is beneficial to the room temperature repair of the coating materials.

[0068] 2. Determination of thermal stability:

[0069] The thermal stability of the coating material was evaluated using a thermogravimetric analyzer (TGA, STA449F3) in a nitrogen atmosphere. The scan range was 30℃–600℃, and the heating rate was 10℃ / min. -1 .

[0070] Figure 3 The thermogravimetric images are of the polyurethane / epoxy resin coating (a) described in Example 1 and the polyurethane / imine-epoxy resin coating (b) described in Example 3, illustrating that the introduction of epoxy resin or imine-epoxy resin improves the thermal stability of the coating.

[0071] 3. Measurement of electrochemical performance:

[0072] The electrochemical impedance of the coating in 3.5 wt% NaCl solution was measured using a Gammy electrochemical workstation (Gammay reference 3000). The test conditions were as follows: 10 5 -10 -2 A voltage of 10mV was applied within Hz; the test adopted a classic three-electrode system, in which a coated Q235 carbon steel sheet was used as the working electrode, Ag / AgCl was used as the reference electrode, and a platinum sheet was used as the counter electrode. Figure 5 This is the electrochemical impedance spectroscopy of the polyurethane / epoxy resin coating described in Example 1.

[0073] 4. Determination of self-healing performance:

[0074] Defects approximately 150 micrometers wide and 500 micrometers deep were made into the coating with a scalpel, and the self-healing process of the coating was recorded and studied using a polarizing microscope at room temperature.

[0075] Figure 4These are images showing the repair effects of the polyurethane / epoxy resin coating (ac) described in Example 1 and the polyurethane / imide-epoxy resin coating (df) described in Example 3 at different times of room temperature. The self-healing time of the polyurethane / epoxy resin coating is 48 hours, and the self-healing time of the polyurethane / imide-epoxy resin coating is 135 minutes. However, the self-healing times of the coatings in Comparative Examples 1-2 are much greater than 48 hours, and the self-healing times of the coatings in Comparative Examples 3-4 are much greater than 135 minutes. Figure 4 This directly reflects the excellent room temperature self-healing properties of the self-healing coating prepared by this invention.

[0076] 5. Determination of corrosion resistance:

[0077] Generally speaking, Nyquist plots ( Figure 5 a, c, e) The radius of the capacitive arc and the impedance value at low frequencies in the Bode plot ( Figure 5 b, d, and f) can be used as semi-quantitative indicators of the coating's corrosion resistance. A larger capacitive arc and a higher low-frequency impedance value indicate better corrosion resistance. Generally, a low-frequency impedance value below 10 is considered acceptable. 6 This indicates that the coating has lost its corrosion protection function. Figure 5 This indicates that the coating was not repaired after being damaged. Figure 5 e, f) In simulated seawater, the Nyquist curve radius and Bode plot low-frequency impedance values ​​are the lowest, indicating that the coating has lost its protective function. Undamaged ( Figure 5 a, b), Coating repaired at room temperature for 48 hours after damage ( Figure 5 (c) and (d) Although the capacitive arc radius and low-frequency impedance values ​​decreased with immersion time, neither failed within 70 days. Furthermore, the small difference in the data indicates that the coating's corrosion protection function was almost completely restored after 48 hours of room temperature repair following damage.

[0078] Application examples

[0079] After creating defects with a width of 150 micrometers and a depth of 700 micrometers using polyurethane / epoxy resin self-healing coatings (Example 1) and polyurethane / imine-epoxy resin self-healing coatings (Example 3) applied to the surface of Q234 carbon steel, the damaged coatings were placed at room temperature for 48 hours for repair, and then immersed in simulated seawater for 75 days, or in dilute sulfuric acid (pH=2) or sodium hydroxide solution (pH=10) for 7 days. No rust occurred on the protected Q234 carbon steel. Both the polyurethane / epoxy resin coating and the polyurethane / imine-epoxy resin coating achieved excellent self-healing performance and good corrosion protection effect, thereby achieving a corrosion inhibition effect on the protected metal and improving the service life of the protected metal structural components. This invention has high practical value.

[0080] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for preparing a self-healing coating with a semi-interpenetrating network structure, characterized in that, Includes the following steps: (1) Linear polyurethane, linear polyimide, epoxy resin and curing agent 2 are reacted at 50-60℃ for 3-4h to obtain a mixed solution. The mass ratio of the linear polyurethane, linear polyimide, epoxy resin and curing agent 2 is (1-2):(1-2):1:1; the curing agent 2 is polyetheramine D-230. (2) Then the mixed solution is applied to the surface of the coating substrate and cured at 80-100℃ for 10-12h to obtain a self-healing coating with a semi-interpenetrating network structure. In step (1), the molecular weight of the linear polyurethane is 32,000-35,000; the molecular weight of the linear polyimide is 1,300-1,650.

2. The method for preparing a self-healing coating with a semi-interpenetrating network structure as described in claim 1, characterized in that, The method for preparing linear polyurethane in step (1) includes the following steps: A linear polyurethane is obtained by reacting a polyester / ether polyol with isophorone diisocyanate and 1,4-butanediol at 40-50°C for 1-2 hours under an inert atmosphere. The mass ratio of the polyester / ether polyol, isophorone diisocyanate, and 1,4-butanediol is (2.9:6.77:0) to (0:6.77:2.612). The polyester / ether polyol includes at least one of polytetrahydrofuran, polyethylene glycol, and polycaprolactone.

3. The method for preparing a self-healing coating with a semi-interpenetrating network structure as described in claim 1, characterized in that, The preparation method of the linear polyimide in step (1) includes the following steps: Tetrahydrofuran, terephthalaldehyde, and triethylenetetramine were reacted at 50-60°C for 3-4 hours under an inert atmosphere to obtain linear polyimide. The mass ratio of tetrahydrofuran, terephthalaldehyde, and triethylenetetramine was (88.64:13.4:4.39) to (88:13.4:0.73).

4. The method for preparing a self-healing coating with a semi-interpenetrating network structure as described in claim 1, characterized in that, The epoxy resin used in step (1) is a bisphenol A type epoxy resin.

5. The method for preparing a self-healing coating with a semi-interpenetrating network structure as described in claim 1, characterized in that, In step (2), the coating substrate is Q235 carbon steel and the coating thickness is 200-700 micrometers.

6. A self-healing coating having a semi-interpenetrating network structure, prepared by the method for preparing a self-healing coating having a semi-interpenetrating network structure according to any one of claims 1-5.

7. The application of the self-healing coating with a semi-interpenetrating network structure as described in claim 6 in corrosion protection.

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