Underwater autocatalytic epoxy resin composite material based on bionic structure as well as preparation method and application of underwater autocatalytic epoxy resin composite material

Abstract

The invention belongs to the technical field of underwater concrete repairing materials, and particularly relates to an underwater autocatalytic epoxy resin composite material based on a bionic structure and a preparation method and application thereof. The underwater autocatalytic epoxy resin composite material based on the bionic structure comprises the following components in parts by weight: 40-60 parts of a modified epoxy resin precursor, 3-8 parts of dopamine modified nano cellulose whiskers, 1-5 parts of a silane coupling agent, 15-30 parts of a curing agent, 0.5-2 parts of a microcapsule catalyst and 5-10 parts of an anti-permeability reinforcing agent. The underwater autocatalytic epoxy resin composite material based on the bionic structure simulates an adhesion mechanism in mussel byssus protein, stable coordinate bonds and hydrogen bonds can be formed in an underwater environment, and the wettability and interface bonding strength of the material on the surface of a wet base material are remarkably improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of underwater concrete repair materials, and particularly relates to a bionic structure-based underwater self-catalytic epoxy resin composite material, a preparation method thereof, and an application thereof. Background Art

[0002] With the rapid development of the marine development industry, a large number of concrete structures are exposed to the marine environment. Due to the long-term influence of factors such as seawater corrosion, wave impact, and biological attachment, diseases such as cracks, spalling, and strength degradation are likely to occur. If these diseases are not repaired in time, it will seriously affect the service life and safety of the structure. For the maintenance and emergency repair of hydraulic and marine infrastructure such as sea dike wharves and other marine coastal structures, reservoirs and hydropower stations, bridges and culverts, sewage treatment facilities, subsea oil and gas pipelines, and underwater communication facilities, there is an urgent need for high-performance rapid repair materials. At present, epoxy resin-based materials are mainly used for the repair of underwater concrete structures, but traditional epoxy resins face many challenges in underwater applications. The bonding strength of traditional epoxy resins on the surface of wet substrates decreases significantly, mainly because water molecules form a shielding layer at the interface, hindering the effective contact and chemical bonding between the resin and the substrate. Although the wettability of the resin can be improved by adding surfactants and other methods, it is still difficult to achieve an ideal interfacial bonding effect. At the same time, in the underwater environment, the curing reaction of epoxy resins is interfered by water molecules, resulting in a slow formation of the cross-linking network. It usually takes several hours or even longer to reach sufficient strength, which is difficult to meet the engineering requirements of rapid repair. In addition, traditional epoxy resins are prone to hydrolysis and degradation under long-term immersion conditions, especially in seawater environments containing a large amount of chloride ions, and their interfacial bonding strength and overall mechanical properties will decrease significantly over time.

[0003] Therefore, there is an urgent need to develop a new type of epoxy resin composite material with excellent underwater bonding performance, rapid curing characteristics, and long-term durability to meet the growing underwater repair needs in the fields of marine engineering, water conservancy engineering, etc.

[0004] Therefore, an improved technical solution is needed to address the deficiencies of the above-mentioned prior art. Summary of the Invention

[0005] The purpose of the present invention is to provide a bionic structure-based underwater self-catalytic epoxy resin composite material, a preparation method thereof, and an application thereof, which helps to solve or improve at least one of the problems of poor underwater bonding performance, long curing time, and poor long-term durability existing in the existing underwater concrete repair materials.

[0006] To achieve the above object, the present invention provides the following technical solution: An underwater self-catalytic epoxy resin composite based on a bionic structure comprises components in the following parts by weight: 40-60 parts of a modified epoxy resin precursor, 3-8 parts of dopamine-modified nanocellulose whiskers, 1-5 parts of a silane coupling agent, 15-30 parts of a curing agent, 0.5-2 parts of a microcapsule catalyst, and 5-10 parts of an anti-seepage enhancer; the modified epoxy resin precursor has a viscosity of 8000-15000 mPa·s at 25°C, an epoxy value of 0.42-0.50 eq / 100 g, and a water contact angle of 55°-65°.

[0007] The present invention also provides a preparation method of an underwater self-catalytic epoxy resin composite based on a bionic structure, which adopts the following technical solution: The preparation method of the underwater self-catalytic epoxy resin composite based on a bionic structure as described above comprises the following steps: (1) heating the modified epoxy resin precursor to 50-60°C; (2) sequentially adding a Mannich base type curing agent and a fractal structure silane coupling agent, and stirring to obtain a mixture; (3) adding dopamine-modified nanocellulose whiskers and a pH-responsive microcapsule catalyst to the mixture, and ultrasonically dispersing; (4) finally adding an anti-seepage enhancer, and performing vacuum defoaming to obtain the underwater self-catalytic epoxy resin composite based on a bionic structure.

[0008] The present invention also provides an application of the underwater self-catalytic epoxy resin composite based on a bionic structure as described above, which adopts the following technical solution: The application of the underwater self-catalytic epoxy resin composite based on a bionic structure as described above in the repair of concrete structures in the marine tidal zone.

[0009] Beneficial effects:

[0010] In the underwater self-catalytic epoxy resin composite based on a bionic structure of the present invention, the modified epoxy resin precursor helps to improve the spreading property of epoxy resin for underwater retarding and the wetting ability for wet substrates, laying a foundation for the exertion of the mussel bionic adhesion mechanism; by introducing dopamine-modified nanocellulose whiskers, the catechol groups in dopamine simulate the adhesion mechanism in mussel foot protein, forming stable coordination bonds and hydrogen bonds in the underwater environment, and significantly improving the wettability and interfacial bonding strength of the material on the surface of wet substrates.

[0011] The underwater self-catalytic epoxy resin composite based on a bionic structure of the present invention effectively alleviates thermal stress through the gradient interface transition layer constructed by the fractal structure silane coupling agent, and further enhances the interfacial stability.

[0012] The underwater self-catalyzing epoxy resin composite material based on a bionic structure of the present invention realizes rapid curing in an underwater environment through a self-catalyzing system constructed by using a Mannich base curing agent and a pH-responsive microcapsule catalyst. Among them, the Mannich base curing agent releases active amino groups through ion exchange when contacting seawater, and the pH-responsive microcapsule ruptures under alkaline conditions to release nano-zinc oxide catalyst. The synergistic effect of the two significantly improves the curing efficiency.

[0013] The underwater self-catalyzing epoxy resin composite material based on a bionic structure of the present invention has excellent performance. It can achieve initial curing in 15 minutes under the condition of 95% humidity, shortening the curing time by about 67% compared with traditional products; the underwater bonding strength can reach up to 3.5 MPa at most, meeting the requirements of ASTM C882 standard; through the synergistic effect of the anti-seepage enhancer, the chloride ion permeability coefficient of the material can be reduced to 1.2×10 -12 m 2 / s, with excellent durability, realizing the integration of rapid underwater construction and long-term protection. Specific embodiments

[0014] The technical solutions in the embodiments of the present invention will be described clearly and completely below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention belong to the scope of protection of the present invention.

[0015] The present invention will be described in detail below with reference to the embodiments. It should be noted that, without conflict, the embodiments of the present invention and the features in the embodiments can be combined with each other.

[0016] Aiming at at least one of the problems of poor underwater bonding performance, long curing time and poor long-term durability existing in current underwater concrete repair materials, the present invention provides an underwater self-catalyzing epoxy resin composite material based on a bionic structure.

[0017] The inventors found in the research that marine organisms represented by mussels can achieve stable adhesion in a humid environment, which is mainly attributed to the mucin secreted by them with a special chemical structure; at the same time, the three-dimensional network structure formed by the fractal growth mode of plant roots can effectively improve the mechanical interlock and stress transfer efficiency with the soil. If these bionic principles can be applied to the research of underwater repair materials, especially in the aspects of rapid curing and long-term durability, it will help to solve or improve the above problems existing in current underwater concrete repair materials.

[0018] The underwater self-catalytic epoxy resin composite material based on a bionic structure according to an embodiment of the present invention comprises components in the following weight parts: 40-60 parts of a modified epoxy resin precursor (for example, 40 parts, 45 parts, 50 parts, 55 parts or 60 parts), 3-8 parts of dopamine-modified nanocellulose whiskers (for example, 3 parts, 4 parts, 5 parts, 6 parts, 7 parts or 8 parts), 1-5 parts of a silane coupling agent (for example, 1 part, 2 parts, 3 parts, 4 parts or 5 parts), 15-30 parts of a curing agent (for example, 15 parts, 20 parts, 25 parts or 30 parts), 0.5-2 parts of a microcapsule catalyst (for example, 0.5 parts, 1 part, 1.5 parts or 2 parts) and 5-10 parts of an anti-seepage enhancer (for example, 5 parts, 6 parts, 7 parts, 8 parts, 9 parts or 10 parts); the viscosity of the modified epoxy resin precursor at 25°C is 8000-15000 mPa·s, the epoxy value is 0.42-0.50 eq / 100 g, and the water contact angle is 55°-65°.

[0019] In the underwater self-catalytic epoxy resin composite material based on a bionic structure of the present invention, the modified epoxy resin precursor helps to improve the spreading property of the epoxy resin for slow setting underwater and the wetting ability of the wet substrate, laying a foundation for the mussel bionic adhesion mechanism to play; by introducing dopamine-modified nanocellulose whiskers, the catechol groups in dopamine simulate the adhesion mechanism in mussel foot protein, forming stable coordination bonds and hydrogen bonds in the underwater environment, significantly improving the wettability of the material on the surface of the wet substrate and the interfacial bonding strength.

[0020] In a preferred embodiment of the underwater self-catalytic epoxy resin composite material based on a bionic structure of the present invention, the modified epoxy resin precursor is prepared by a method comprising the following steps: I. Heating bisphenol A epoxy resin to melting; II. Adding a reactive diluent and stirring until uniform; III. Adding a toughening agent and continuing to stir; IV. Adding an organosilicon modifier and stirring; V. Adding a surfactant and continuing to stir; VI. Vacuum degassing to obtain the epoxy resin precursor. During the preparation of the modified epoxy resin precursor, by introducing hydrophilic groups and adjusting the surface energy of the system, the spreading property of the epoxy resin in the underwater environment and the wetting ability of the wet substrate can be significantly improved.

[0021] Preferably, in step II, the reactive diluent is dibutyl phthalate or phenylglycidyl ether; in step III, the toughening agent is polyethylene glycol with a molecular weight of 400-800 (for example, 400, 500, 600, 700 or 800); in step IV, the organosilicon modifier is an amino-containing polysiloxane (for example, γ-aminopropyltrimethoxysilane-modified polydimethylsiloxane or commercially available Dow Corning Z-6020 amino-functionalized silane); in step V, the surfactant is a polyether-modified organosilicon (for example, a polyethylene glycol-polydimethylsiloxane block copolymer or commercially available Dow Corning DC-57 surfactant).

[0022] More preferably, in step I, the epoxy value of the bisphenol A type epoxy resin is 0.48 - 0.52 eq / 100 g (for example, 0.48 eq / 100 g, 0.49 eq / 100 g, 0.50 eq / 100 g, 0.51 eq / 100 g or 0.52 eq / 100 g), and the heating temperature is 70 - 80 °C (for example, 70 °C, 75 °C or 80 °C); in step II, the addition amount of the reactive diluent is 4 wt% - 6 wt% (for example, 4 wt%, 5 wt% or 6 wt%), and the stirring time is 30 - 40 min (for example, 30 min, 33 min, 36 min or 40 min); in step III, the addition amount of the toughening agent is 4 wt% - 5 wt% (for example, 4 wt%, 5 wt% or 6 wt%), and the stirring time is 30 - 40 min (for example, 30 min, 33 min, 36 min or 40 min); in step IV, the addition amount of the silicone modifier is 2 wt% - 4 wt% (for example, 2 wt%, 3 wt% or 4 wt%), the stirring temperature is 80 - 90 °C (for example, 80 °C, 85 °C or 90 °C), and the stirring time is 60 - 80 min (for example, 60 min, 65 min, 70 min, 75 min or 80 min); in step V, the addition amount of the surfactant is 1 wt% - 2 wt% (for example, 1 wt%, 1.5 wt% or 2 wt%), the stirring temperature is 80 - 90 °C (for example, 80 °C, 85 °C or 90 °C), and the stirring time is 30 - 50 min (for example, 30 min, 35 min, 40 min, 45 min or 50 min); in step VI, the vacuum degassing time is 45 - 60 min (for example, 45 min, 50 min, 55 min or 60 min).

[0023] In a preferred embodiment of the underwater self - catalytic epoxy resin composite material based on a bionic structure of the present invention, the dopamine - modified nanocellulose whiskers are prepared by a method comprising the following steps: B1. Dispersing the nanocellulose whiskers in Tris - HCl buffer solution and ultrasonically treating to obtain a uniformly dispersed solution; B2. Adding dopamine hydrochloride to the dispersed solution and stirring in an oxygen atmosphere for 24 - 48 h (for example, 24 h, 30 h, 36 h, 42 h or 48 h); B3. Centrifuging and freeze - drying the obtained solid to obtain the dopamine - modified nanocellulose whiskers.

[0024] In a preferred embodiment of the underwater self - catalytic epoxy resin composite material based on a bionic structure of the present invention, the mass fraction of the nanocellulose whiskers in the dispersed solution is 0.5 wt% - 2 wt% (for example, 0.5 wt%, 1 wt%, 1.5 wt% or 2 wt%).

[0025] In a preferred embodiment of the underwater self-catalytic epoxy resin composite material based on a bionic structure of the present invention, in step B2, the mass ratio of dopamine hydrochloride to nanocellulose whiskers is 2:1 - 4:1 (for example, 2:1, 2.5:1, 3:1, 3.5:1, or 4:1).

[0026] Preferably, the aspect ratio of the nanocellulose whiskers is 50 - 100 (for example, 50, 60, 70, 80, 90, or 100), and a dopamine layer is grafted on the surface through a controlled polymerization reaction, with a layer thickness of 20 - 50 nm (for example, 20 nm, 30 nm, 40 nm, or 50 nm). Among them, in terms of mechanical properties, by selecting nanocellulose whiskers with a relatively high aspect ratio (in the range of 50 - 100), it is beneficial to form a more effective three-dimensional network structure in the composite material, improving the mechanical strength and toughness of the material; the long fibers can span more interfacial regions, enhancing the stress transfer ability of the material. In terms of interfacial interaction: the aspect ratio of the nanocellulose whiskers affects the contact area between the fibers and the epoxy resin matrix; in the present invention, these fibers simulate the attachment mechanism of mussel adhesive protein, and nanocellulose whiskers with an appropriate aspect ratio can provide more exposed sites of catechol groups, enhancing the adhesion effect at the wet interface. In addition, an appropriate aspect ratio of the nanocellulose whiskers helps to form a uniform stress distribution during the curing process, avoiding microcracks caused by stress concentration. If the aspect ratio of the nanocellulose whiskers is too high (exceeding 100), it may cause the nanocellulose whiskers to be difficult to disperse uniformly in the matrix, forming agglomerates, which instead reduces the material properties; if the aspect ratio of the nanocellulose whiskers is too low (below 50), the reinforcing and networking effects of the nanocellulose whiskers will be weakened.

[0027] If the thickness of the dopamine layer is too small (below 20 nm), the following adverse effects will occur: 1) The number of surface active groups is insufficient, resulting in a significant decrease in the adhesion ability in a humid environment; 2) The protective effect on nanocellulose is insufficient, which may lead to a reduction in the stability of the material in an underwater environment; 3) It cannot effectively simulate the catechol structure of mussel foot protein, and the bionic effect is poor; 4) The interfacial bonding with the matrix is insufficient, resulting in a decrease in mechanical properties. If the thickness of the dopamine layer is too large (exceeding 50 nm), then: 1) A too thick dopamine layer will reduce the mechanical interlocking effect between the nanocellulose whiskers; 2) A too thick dopamine layer may hinder the reaction between the curing agent and the epoxy resin, prolonging the curing time; 3) Self-crosslinking reactions may occur between the dopamine layers, resulting in the material becoming hard and brittle and reducing toughness; 4) It increases the viscosity of the material, affecting the construction fluidity and being unfavorable for underwater construction; 5) A too thick dopamine layer will occupy too much space, reducing the overall density and strength of the composite material.

[0028] In a preferred embodiment of the underwater self-catalytic epoxy resin composite material based on a bionic structure of the present invention, the microcapsule catalyst is a pH-responsive microcapsule catalyst, and the pH-responsive microcapsule catalyst is prepared by a method including the following steps: A1. Disperse nano-zinc oxide in an organic solvent (for example, the organic solvent can be cyclohexane), add a polymer wall material (preferably, the polymer wall material is polydopamine), and stir evenly; A2. Prepare microcapsules by interfacial polymerization and control the crosslinking degree of the wall material. Among them, the pH-responsive microcapsules can rupture under alkaline conditions to release the nano-zinc oxide catalyst (nano-zinc oxide is the core material), which can cooperate with the Mannich base curing agent to significantly improve the curing efficiency.

[0029] Preferably, the shell thickness of the pH-responsive microcapsule catalyst is 55-85 nm (for example, 55 nm, 65 nm, 75 nm or 85 nm); it is stable in an aqueous solution with pH = 7.0 for 36-72 h (for example, unchanged for 36 h, 46 h, 56 h, 66 h or 72 h), and more than 85% of the microcapsules rupture to release the nano-zinc oxide catalyst within 35-50 min (for example, 35 min, 40 min, 45 min or 50 min) in an aqueous solution with pH = 11.0-11.8 (for example, 11.0, 11.2, 11.4, 11.6 or 11.8).

[0030] Preferably, step A1 includes: weighing nano-zinc oxide powder and adding it to cyclohexane; adding cetyltrimethylammonium bromide as a dispersant; using an ultrasonic probe for ultrasonic treatment to form a stable nano-zinc oxide dispersion; under nitrogen protection, add dopamine hydrochloride and immediately add Tris-HCl buffer solution (pH = 8.5); under mechanical stirring conditions, slowly dropwise add pentaerythritol glycidyl ether as a crosslinking agent;

[0031] Step A2 includes: transferring the above dispersion system to a three-necked flask, introducing oxygen while stirring; controlling the reaction temperature to enable the self-polymerization of dopamine under oxidation conditions; when the color of the reaction solution changes from transparent to dark brown, add a polyvinyl alcohol (PVA) solution as a stabilizer; continue stirring to fully form the polydopamine shell layer; monitor the pH value of the reaction system with a pH meter, and when it reaches 7.9-8.6, it indicates that the shell layer formation is completed; collect the microcapsules by centrifugation; wash them successively with deionized water, ethanol and acetone; dry them under vacuum to obtain the pH-responsive microcapsule catalyst.

[0032] More preferably, in step A1, the mass ratio of nano-zinc oxide, cetyltrimethylammonium bromide, dopamine hydrochloride and pentaerythritol glycidyl ether is (0.6-1.2):(0.25-0.4):(1.0-1.6):(0.35-0.5); in A2, the reaction temperature is 24-32 °C (for example, 24 °C, 27 °C, 30 °C or 32 °C), and the time for the self-polymerization reaction is 4.5-6 h (for example, 4.5 h, 5 h, 5.5 h or 6 h); the mass concentration of the polyvinyl alcohol solution is 1.2%-2% (for example, 1.2%, 1.4%, 1.6%, 1.8% or 2%), and the time for continuous stirring after adding the polyvinyl alcohol solution is 2.5-4 h (for example, 2.5 h, 3 h, 3.5 h or 4 h); the temperature for vacuum drying is 40-50 °C (for example, 40 °C, 43 °C, 46 °C, 48 °C or 50 °C), and the time for vacuum drying is 14-18 h (for example, 14 h, 15 h, 16 h, 17 h or 18 h).

[0033] In a preferred embodiment of the underwater self-catalytic epoxy resin composite material based on the bionic structure of the present invention, the thickness of the shell layer of the pH-responsive microcapsule catalyst is 50-80 nm (for example, 50 nm, 60 nm, 70 nm or 80 nm). Among them, if the thickness of the shell layer is too thin, it is easily damaged; if the shell layer is too thick, it will affect the release of the core material.

[0034] In a preferred embodiment of the underwater self-catalytic epoxy resin composite material based on a bionic structure of the present invention, the silane coupling agent is a fractal structure silane coupling agent, and the fractal structure silane coupling agent is prepared by a method including the following steps: C1. Mix γ-glycidoxypropyltrimethoxysilane with branched polyethyleneimine, heat up to 100-120 °C (for example, 100 °C, 105 °C, 110 °C, 115 °C or 120 °C) and stir and react for 2-4 h (for example, 2 h, 2.5 h, 3 h, 3.5 h or 4 h); C2. Add tetraethoxysilane to the reaction system and continue to react at 90-110 °C (for example, 90 °C, 95 °C, 100 °C, 105 °C or 110 °C) for 2-4 h (for example, 2 h, 2.5 h, 3 h, 3.5 h or 4 h); C3. Perform vacuum distillation to obtain the fractal structure silane coupling agent. Among them, the fractal structure silane coupling agent forms a gradient modulus transition layer at the interface by simulating the forking growth mode of plant roots, which can effectively relieve the concentration of thermal stress and further enhance the stability of interface bonding. Among them, γ-glycidoxypropyltrimethoxysilane plays the following key roles in the present invention: 1) It provides epoxy groups, which can form covalent chemical bonds with the epoxy resin matrix; 2) It contains silane groups, which can form siloxane bonds with the surface of inorganic substrates (such as concrete); 3) As a bridging molecule, it connects the organic phase (epoxy resin) and the inorganic phase (concrete substrate); 4) In an aqueous environment, methoxy groups can be hydrolyzed to form silanol groups, enhancing the interfacial bonding force of wet substrates. Tetraethoxysilane plays the following key roles in the present invention: 1) It provides additional cross-linking points, increasing the forking degree and network complexity of the fractal structure; 2) It forms a siloxane backbone structure, enhancing the overall mechanical properties; 3) It adjusts the stiffness and elastic modulus of the interface layer to form a gradient transition zone; after hydrolysis, it forms a siloxane network, enhancing the water resistance and impermeability of the material; 4) It promotes the formation of a "fractal" structure, simulating the forking growth mode of plant roots.

[0035] The "gradient modulus transition layer" can be understood as: a special interface region formed between the epoxy resin matrix and the concrete substrate under the action of the fractal structure silane coupling agent, and the elastic modulus of this region gradually changes from the substrate to the matrix direction, rather than the abrupt structure of the traditional interface. Specifically: the gradient modulus transition layer means that this structure extends from the surface of the concrete substrate to the epoxy resin matrix direction, and the elastic modulus shows a gradual change distribution, avoiding the modulus mutation at the traditional interface; this gradient structure is similar to the combination mode of plant roots and soil, which can effectively disperse stress, reduce the stress concentration caused by the difference in thermal expansion coefficient, and improve the interface bonding strength and durability; through the design of the fractal structure, the interface layer not only has good mechanical property matching, but also improves the interface stability of the material under temperature change and wet environment conditions.

[0036] Preferably, the branching degree of branched polyethyleneimine is 2.5 - 4.0 (for example, 2.5, 3.0, 3.5 or 4.0). Among them, the fractal structure silane coupling agent is based on polyethyleneimine with a branching degree of 2.5 - 4.0, and epoxy groups are introduced through a silanization reaction to form a fractal structure; if the branching degree is too low, the interface transition effect is not obvious; if the branching degree is too high, the molecular mobility will be reduced, affecting curing.

[0037] In a preferred embodiment of the underwater self-catalytic epoxy resin composite based on the bionic structure of the present invention, in step C1, the molar ratio to branched polyethyleneimine is 1:1 - 3:1 (for example, 1:1, 1.5:1, 2:1, 2.5:1 or 3:1); in step C2, the addition amount of tetraethoxysilane is 10wt% - 30wt% of the sum of the masses of γ-glycidoxypropyltrimethoxysilane and branched polyethyleneimine (for example, 10wt%, 15wt%, 20wt%, 25wt% or 30wt%). Among them, if the dosage of γ-glycidoxypropyltrimethoxysilane is too large (molar ratio > 3:1), then: 1) Excessive epoxy groups will cause the crosslinked network structure to be uneven, forming local high crosslink density regions; 2) Increase the brittleness of the material, reduce toughness and impact resistance; 3) Too many unreacted silane groups may be hydrolyzed excessively in the water environment, resulting in instability of the interface layer structure; 4) Inhibit the formation of the fractal structure, weakening the gradient modulus characteristics of the interface transition layer; 5) Excessive silane may cause excessive shrinkage during the curing process, generating internal stress and reducing the interface bonding strength. If the dosage of γ-glycidoxypropyltrimethoxysilane is too small (molar ratio < 1:1), then: 1) It cannot provide enough epoxy groups to form an effective crosslink with the epoxy resin matrix; 2) The development of the fractal structure is insufficient, and it is difficult to form an ideal root-like simulation structure; 3) The binding sites with the concrete substrate are insufficient, and the interface bonding strength decreases; 4) Lead to a decrease in the durability of the material in the water environment, and the interface is more vulnerable to water molecule erosion; 5) The formation of the gradient modulus transition layer is incomplete, and it cannot effectively relieve thermal stress.

[0038] If the addition amount of tetraethoxysilane is too large (>30%), then: 1) an over-crosslinked rigid network is formed, reducing the toughness and interfacial flexibility of the material; 2) it may lead to too high a proportion of the inorganic phase and a decrease in compatibility with the organic phase (epoxy resin); 3) too many hydrolysis products are produced, causing microstructure defects in the material; 4) the curing shrinkage rate increases, generating greater internal stress, which may lead to the formation of microcracks; 5) the excessive silicon-oxygen network will limit the growth direction of the fractal structure, affecting the formation of the gradient transition layer. If the addition amount of tetraethoxysilane is too small (<10%), then: 1) the degree of branching of the fractal structure is insufficient to simulate the complex bifurcated structure of plant roots; 2) the formation of the gradient transition layer is incomplete, and the stress dispersion effect is poor; 3) the anti-permeability performance decreases, and a sufficiently dense silicon-oxygen network cannot be formed; 4) the hydrolysis resistance stability decreases, and the interfacial performance decays rapidly after long-term immersion in water; 5) the problem of thermal stress concentration cannot be effectively alleviated, resulting in unstable interfacial bonding strength with temperature changes.

[0039] In a preferred embodiment of the underwater self-catalytic epoxy resin composite material based on a bionic structure of the present invention, the curing agent is a Mannich base type curing agent, and the Mannich base type curing agent is prepared by a method including the following steps: D1. Mix bisphenol A epoxy resin and 4,4'-diaminodiphenylmethane in a molar ratio of 1:(2 - 3) (for example, 1:2, 1:2.3, 1:2.6, 1:2.8 or 1:3), and react at 80 - 100 °C (for example, 80 °C, 85 °C, 90 °C, 95 °C or 100 °C) for 2 - 4 h (for example, 2 h, 2.5 h, 3 h, 3.5 h or 4 h); D2. Add a benzaldehyde derivative to carry out a Mannich reaction, control the molar ratio of aldehyde group to amino group to be 1:(1.2 - 1.5) (for example, 1:1.2, 1:1.3, 1:1.4 or 1:1.5), the reaction temperature is 110 - 130 °C (for example, 110 °C, 115 °C, 120 °C, 125 °C or 130 °C), and the reaction time is 3 - 6 h (for example, 3 h, 4 h, 5 h or 6 h); D3. After washing with acetone and vacuum drying, an orange viscous liquid is obtained, which is the Mannich base type curing agent. Among them, if the dosage of 4,4'-diaminodiphenylmethane is too large (molar ratio > 3:1), then: 1) The excessive amino groups cannot fully participate in the reaction, and the residual free amine will cause the phenomenon of "amine precipitation" after the material is cured; 2) The water resistance of the final product is reduced because the free amine is easily soluble in water; 3) The excessive amine will cause the viscosity of the curing agent to be too high, affecting the construction performance; 4) The alkalinity of the curing system is too strong, which will damage the pH-responsive microcapsule wall layer, resulting in premature release of the catalyst; 5) The impermeability and durability of the final material are reduced. If the dosage of 4,4'-diaminodiphenylmethane is too small (molar ratio < 2:1), then: 1) The number of amino groups is insufficient, resulting in insufficient subsequent Mannich reaction sites; 2) The activity of the curing agent is reduced, and the underwater curing speed is slow; 3) An insufficient cross-linked network cannot be formed, and the material strength is insufficient; 4) The ion exchange ability in the water environment is weak, and it is difficult to release active amino groups; 5) The mechanical properties and bonding strength of the final composite material decrease.

[0040] If the reaction temperature in step D1 is too high (> 100 °C), then: 1) It is easy to cause self-polymerization of epoxy resin, affecting the subsequent Mannich reaction; 2) Side reactions occur at high temperature, generating products that are not conducive to underwater curing; 3) It may cause oxidation of amino groups, reducing the activity of the curing agent; 4) The color of the product deepens, affecting the aesthetics of the final material. If the reaction temperature in step D1 is too low (< 80 °C), then: 1) The reaction between bisphenol A epoxy resin and diaminodiphenylmethane is incomplete; 2) The reaction rate is too slow, prolonging the production cycle and reducing efficiency; 3) Unreacted monomers remain in the product, affecting the performance stability of the curing agent; 4) The prepolymer is not formed completely, and the subsequent Mannich reaction effect is poor.

[0041] If the reaction time in step D1 is too long (>4 h), then: 1) energy consumption and production costs increase; 2) the product may undergo excessive crosslinking, resulting in too high viscosity; 3) long-term reaction at high temperature may cause oxidative degradation of amino groups; 4) by-products that are not conducive to underwater curing may be formed. The adverse effects of too short reaction time (<2 h) in step D1 are: 1) the reaction is incomplete and the prepolymer is not formed sufficiently; 2) there are many unreacted components, affecting the quality stability of the curing agent; 3) the substrates for the subsequent Mannich reaction are not prepared sufficiently, affecting the reaction efficiency; 4) the activity of the final curing agent is insufficient, affecting the underwater curing speed.

[0042] If in step D2, the molar ratio of aldehyde group to amino group is too high (>1:1.5), then: 1) excessive amino groups participate in the Mannich reaction, resulting in an irregular structure of the curing agent; 2) there is still excessive free amine in the reaction product, reducing the water resistance; 3) the pH sensitivity of the curing agent decreases, and the activity release is insufficient in an alkaline environment; 4) the viscosity characteristics of the curing agent are unstable, affecting the processing performance. If in step D2, the molar ratio of aldehyde group to amino group is too low (<1:1.2), then: 1) the Mannich reaction is insufficient and the formed active sites are insufficient; 2) the ion exchange ability of the curing agent in the underwater environment is weak; 3) the synergistic effect with the pH-responsive microcapsule catalyst is poor; 4) the underwater curing speed is slow and the curing degree is low; 5) the underwater bonding strength of the final material is insufficient.

[0043] If in step D2, the reaction temperature is too high (>130 °C), then: 1) it may cause thermal decomposition of the reactants, reducing the product quality; 2) more side reactions and by-products are generated, affecting the purity of the curing agent; 3) the color of the product deepens at high temperature and may even carbonize; 4) energy consumption increases and higher requirements are imposed on the equipment. If in step D2, the reaction temperature is too low (<110 °C), then: 1) the activation energy of the Mannich reaction is insufficient and the reaction rate is extremely slow; 2) the reaction is incomplete and the product contains a large amount of unreacted raw materials; 3) the activity of the curing agent is low and it is difficult to cure quickly in the underwater environment; 4) the performance of the final product is unstable and there are large batch differences.

[0044] If in step D2, the reaction time is too long (>6 h), then: 1) the reactants may degrade, affecting the structure of the curing agent; 2) long-term high temperature may cause excessive crosslinking and the product has a wide molecular weight distribution; 3) energy consumption and costs increase and production efficiency decreases; 4) it may increase the equipment burden and safety hazards. If in step D2, the reaction time is too short (<3 h), then: 1) the Mannich reaction is incomplete and the active sites are not formed sufficiently; 2) the structure of the curing agent is incomplete and the performance is unstable; 3) the ion exchange and catalytic ability in the underwater environment are weak; 4) the curing time of the final composite material is prolonged and it cannot meet the requirements of rapid repair; 5) the underwater bonding strength and durability do not meet the standards.

[0045] In a preferred embodiment of the underwater self-catalytic epoxy resin composite material based on a bionic structure of the present invention, in step D1, the epoxy value of bisphenol A epoxy resin is 0.45 - 0.55 eq / 100 g (for example, 0.45 eq / 100 g, 0.48 eq / 100 g, 0.5 eq / 100 g, 0.52 eq / 100 g or 0.55 eq / 100 g); in step D2, the benzaldehyde derivative is 4-hydroxybenzaldehyde and / or 3,5-dinitrobenzaldehyde. Among them, active amino groups are introduced into bisphenol A epoxy resin through the Mannich reaction; if the epoxy value of bisphenol A is too low, the curing activity will be reduced; if the epoxy value is too high, it is not conducive to improving water solubility.

[0046] The underwater self-catalytic epoxy resin composite material based on a bionic structure of the present invention adopts a self-catalytic system constructed by a Mannich base curing agent and a pH-responsive microcapsule catalyst, and realizes rapid curing in an underwater environment by means of ion exchange and pH-responsive release of the catalyst.

[0047] In a preferred embodiment of the underwater self-catalytic epoxy resin composite material based on a bionic structure of the present invention, the anti-seepage enhancer is a mixture of nano-silica and an organosilicon water repellent. Among them, the nano-silica of the anti-seepage enhancer fills the network micropores, and the organosilicon water repellent forms a hydrophobic layer on the pore wall. The two act synergistically to significantly improve the anti-seepage performance and durability of the material.

[0048] In a preferred embodiment of the underwater self-catalytic epoxy resin composite material based on a bionic structure of the present invention, the mass ratio of nano-silica to the organosilicon water repellent is (2 - 4):1 (for example, 2:1, 3:1 or 4:1). The organosilicon water repellent is selected from at least one of methyltrimethoxysilane, methyltriethoxysilane, octamethylcyclotetrasiloxane or polydimethylsiloxane.

[0049] Preferably, the particle size of the nano-silica is 100 - 300 nm (for example, 100 nm, 150 nm, 200 nm, 250 nm or 300 nm). Among them, if the particle size of the nano-silica is too small, it is not conducive to the filling effect; if the particle size of the nano-silica is too large, the dispersibility will be affected.

[0050] The present invention also provides a method for preparing an underwater self-catalytic epoxy resin composite based on a bionic structure. The method for preparing the underwater self-catalytic epoxy resin composite based on a bionic structure according to the embodiments of the present invention includes the following steps: (1) heating an epoxy resin precursor to 50-60 °C (for example, 50 °C, 52 °C, 54 °C, 56 °C, 58 °C or 60 °C); (2) sequentially adding a Mannich base curing agent and a fractal structure silane coupling agent, and stirring to obtain a mixture; (3) adding dopamine-modified nanocellulose whiskers and a pH-responsive microcapsule catalyst to the mixture, and ultrasonically dispersing; (4) finally adding an anti-seepage enhancer, and obtaining the underwater self-catalytic epoxy resin composite based on a bionic structure after vacuum defoaming.Among them, the arrangement of each step in the preparation method of underwater self-catalytic epoxy resin composite material based on biomimetic structure of the present invention is such that: (1) it helps to ensure the uniformity of dispersion (the correct material sequence can ensure the uniform dispersion of each component in the epoxy resin matrix. If a high viscosity or easily agglomerated component, such as nanocellulose whiskers, is added first, it will lead to difficulty in dispersion and form an uneven structure; uneven dispersion will cause unstable material properties, insufficient strength in local areas, and reduce the overall underwater bonding strength); (2) it helps to ensure the stability of pH-responsive microcapsules (pH-responsive microcapsules must be added at the appropriate stage to avoid premature rupture under high shear conditions; if the pH-responsive microcapsules are added at the beginning of high-speed stirring, they will not break down prematurely under high shear conditions); (3) it helps to ensure the stability of pH-responsive microcapsules (pH-responsive microcapsules must be added at the appropriate stage to avoid premature rupture under high shear conditions; if the pH-responsive microcapsules are added at the beginning of high-speed stirring, they will not break down prematurely under high shear conditions). If added at an early stage, the microcapsules may be destroyed and the catalyst may be released prematurely, causing the material to solidify prematurely; if added as the last component, it may not be fully dispersed, affecting the uniformity of curing); (3) It will also affect the reaction kinetics (the Mannich base curing agent should be fully mixed with the epoxy resin first to form a uniform basic system; the fractal structure silane coupling agent should be added after the basic system is formed to ensure that it can correctly form an interface transition layer; reversing the order will lead to incomplete cross-linking network formation, affecting the curing rate and final mechanical properties); (4) It also affects temperature control (the heating temperature of 50-60℃ is to reduce the viscosity of the epoxy resin, which is beneficial to the subsequent components If all components are stirred at this temperature for a long time, the curing reaction may start prematurely; therefore, the components should be added in order from high to low stability, and the processing time of each stage should be controlled); (5) It also affects the timing of ultrasound (dopamine-modified nanocellulose whiskers require ultrasonic dispersion to break up the agglomerates, but too strong ultrasound will damage the microcapsules; adding both at the same time and moderate ultrasound treatment is a balanced solution; if this order is changed, for example, ultrasonic treatment of nanocellulose whiskers first and then addition of microcapsules may improve the dispersibility of nanocellulose, but it will increase the process complexity and production time); (6) The anti-permeability enhancer needs to be added as the last Components (nano-silica has a high specific surface area. If it is added too early, it will adsorb other components and affect their functions; as the last component added, it can fill the micropores in the formed network structure and maximize the anti-seepage performance; if it is added in advance, it may interfere with the formation of fractal structure and the dispersion of microcapsules); (7) The timing of degassing will also affect the performance of the composite material (vacuum degassing after all components are added and mixed can maximize the removal of bubbles introduced during the processing; if degassing is performed in the intermediate step, the effect may be poor due to the reintroduction of bubbles during subsequent processing; the presence of bubbles will become a defect point of the material, significantly reducing the underwater bonding strength and anti-seepage performance).

[0051] In a preferred embodiment of the preparation method of the underwater self-catalytic epoxy resin composite material based on a bionic structure of the present invention, in step (2), the stirring speed is 800 - 1200 rpm (for example, 800 rpm, 900 rpm, 1000 rpm, 1100 rpm or 1200 rpm), and the stirring time is 15 - 30 min (for example, 15 min, 20 min, 25 min or 30 min); in step (3), the ultrasonic frequency is 40 kHz, and the power density is 0.5 - 1.0 W / cm 3 (for example, 0.5 W / cm 3 , 0.6 W / cm 3 , 0.7 W / cm 3 , 0.8 W / cm 3 , 0.9 W / cm 3 or 1.0 W / cm 3 ), and the ultrasonic time is 20 - 40 min (for example, 20 min, 25 min, 30 min, 35 min or 40 min). Among them, the selection of the stirring speed and stirring time in step (2) helps: (1) Pre-reaction initiation: During the stirring process, the Mannich base curing agent and the epoxy resin precursor start to undergo a pre-reaction to form a preliminary cross-linked network structure; a specific stirring rate provides appropriate shear force to promote the uniform reaction of the fractal structure silane coupling agent with the epoxy group; (2) Interface structure optimization: The fractal structure silane coupling agent can form an ideal fractal structure under appropriate stirring conditions, which is crucial for the formation of the subsequent gradient modulus transition layer; too low a stirring speed (<800 rpm) will cause the coupling agent to be difficult to fully unfold the fractal structure; too high a stirring speed (>1200 rpm) will destroy the orderly formation of the fractal structure and even cause excessive shear; (3) System viscosity regulation: The precisely controlled stirring time (15 - 30 min) can achieve the best rheology of the matrix system and create conditions for the addition of subsequent components; too short a stirring time will result in uneven system viscosity; too long a time may lead to pre-curing.

[0052] In step (3), the selection of ultrasonic treatment parameters helps with: (1) nanostructure reconstruction: ultrasonic energy causes the three-dimensional configuration of dopamine-modified nanocellulose whiskers to reorganize and unfolds its molecular chains; this reconstruction is crucial for mimicking the catechol structure of mussel foot thread protein and directly affects the underwater adhesion mechanism; (2) uniform positioning of catalytic microcapsules: appropriate ultrasonic energy can break the agglomeration of pH-responsive microcapsules without damaging the capsule structure; under the action of ultrasound, the microcapsules can be evenly distributed in the network constructed by nanocellulose whiskers to form "pre-positioned" catalytic points; this precise distribution is crucial for the uniform initiation and progress of the underwater curing reaction; (3) interfacial activation treatment: the cavitation effect generated by ultrasound in the liquid can activate the active groups on the surface of dopamine; enhance its chemical bonding ability with epoxy groups and improve the interfacial bonding strength of the final material; if the ultrasonic power density is too low (<0.5 W / cm 3 ), it is difficult to achieve the activation effect; if it is too high (>1.0 W / cm 3 ), it may damage the molecular structure; construction of a nano-scale dispersed network: ultrasonic treatment is not only a physical dispersion but also a key process for constructing a specific nano-network structure; the formed network structure mimics the spatial arrangement of mussel foot thread protein and significantly improves the underwater adhesion performance; if the ultrasonic time is too short (<20 min), the network structure is incomplete; if it is too long (>40 min), it may lead to an overly tight network and limit the subsequent curing reaction.

[0053] The present invention also proposes an application of an underwater self-catalytic epoxy resin composite based on a bionic structure, such as the application of the underwater self-catalytic epoxy resin composite based on a bionic structure in the repair of concrete structures in the marine tidal zone. The underwater self-catalytic epoxy resin composite based on a bionic structure of the present invention is particularly suitable for the repair of wet interfaces such as concrete in the marine tidal zone and wharf pile foundations, realizing the integration of rapid underwater construction and long-term protection.

[0054] The following specifically describes the underwater self-catalytic epoxy resin composite based on a bionic structure of the present invention, its preparation method and application through specific examples.

[0055] Sources of the main raw materials used in the following examples: Bisphenol A epoxy resin: South Asia Epoxy Resin Company, model E-51, epoxy value 0.48 - 0.54 eq / 100 g; nanocrystalline cellulose whiskers: prepared by the Institute of Chemistry, Chinese Academy of Sciences, aspect ratio 50 - 100; dopamine hydrochloride: Sigma-Aldrich, purity ≥98%; γ-glycidoxypropyltrimethoxysilane: Dow Corning, purity ≥97%; branched polyethyleneimine: Sigma-Aldrich, molecular weight 25000; tetraethoxysilane: Sinopharm Chemical Reagent Co., Ltd., analytical pure; 4,4'-diaminodiphenylmethane: BASF, purity ≥99%; 4-hydroxybenzaldehyde: Aladdin Reagent Co., Ltd., purity ≥99%; 3,5-dinitrobenzaldehyde: Aladdin Reagent Co., Ltd., purity ≥98%; nano-zinc oxide: Advance Nano Materials Technology Co., Ltd., average particle size 50 - 80 nm; nano-silica: Cabot, average particle size 100 - 300 nm; methyltrimethoxysilane: Dow Corning, purity ≥98%; octamethylcyclotetrasiloxane: Dow Corning, purity ≥99%; polydimethylsiloxane: Dow Corning, viscosity 100 mPa·s.

[0056] Example 1

[0057] The underwater self-catalytic epoxy resin composite based on the bionic structure in this example, by weight, comprises the following components: 40 parts of modified epoxy resin precursor, 3 parts of dopamine-modified nanocrystalline cellulose whiskers, 1 part of fractal structure silane coupling agent, 15 parts of Mannich base curing agent, 0.5 part of pH-responsive microcapsule catalyst, and 5 parts of anti-seepage enhancer.

[0058] The modified epoxy resin precursor is prepared by a method comprising the following steps: I. Heat bisphenol A epoxy resin (epoxy value 0.48 eq / 100 g) to 70 °C to fully melt it; II. Add a reactive diluent (dibutyl phthalate) with a mass ratio of 4%, and stir for 30 min until homogeneous; III. Add polyethylene glycol (molecular weight 400) with a mass ratio of 3% as a toughening agent, and continue stirring for 30 min; IV. Add an organosilicon modifier (amino-functionalized polysiloxane - Dow Corning Z-6020 amino-functionalized silane) with a mass ratio of 2%, and stir at 80 °C for 60 min; V. Finally, add a surfactant (polyether-modified organosilicon - Dow Corning DC-57 surfactant) with a mass ratio of 1%, and continue stirring at 80 °C for 30 min; VI. Conduct vacuum degassing for 45 min to obtain the modified epoxy resin precursor. This modified epoxy resin precursor has the following properties: viscosity at 25 °C is 12000 - 15000 mPa·s, epoxy value is 0.42 - 0.46 eq / 100 g, water contact angle is 65° (significantly reduced compared to 80° of ordinary epoxy resin), and the wettability to a wet surface is enhanced by about 25%. The modification process significantly improves the spreading property of the epoxy resin in an underwater environment and the wetting ability to a wet substrate by introducing hydrophilic groups and adjusting the surface energy of the system, laying a foundation for the subsequent mussel-inspired adhesion mechanism to play.

[0059] Among them, the pH-responsive microcapsule catalyst is prepared by a method comprising the following steps:

[0060] A1. Disperse nano-zinc oxide (average particle size 50 nm) in cyclohexane, add polydopamine as the wall material, and stir evenly: Weigh 0.5 g of nano-zinc oxide powder and add it to 50 mL of cyclohexane; add 0.2 g of cetyltrimethylammonium bromide (CTAB) as a dispersant; use an ultrasonic probe (power 300 W) to ultrasonically treat for 30 minutes to form a stable nano-zinc oxide dispersion; under nitrogen protection, add 0.8 g of dopamine hydrochloride, and immediately add 25 mL of Tris-HCl buffer solution (pH = 8.5); under mechanical stirring (500 rpm) conditions, slowly dropwise add 0.3 g of pentaerythritol glycidyl ether (PTGE) as a crosslinking agent;

[0061] A2. Preparation of microcapsules by interfacial polymerization, controlling the thickness of the polydopamine shell layer to be 50 nm: Transfer the above dispersion system to a three-necked flask, and introduce oxygen at a stirring rate of 600 rpm; control the reaction temperature to be 25 ± 2 °C and the reaction time to be 4 hours to allow dopamine to self-polymerize under oxidative conditions; when the color of the reaction solution changes from transparent to dark brown, add 10 mL of a 1% (by mass) polyvinyl alcohol (PVA) solution as a stabilizer; continue stirring for 2 hours to fully form the polydopamine shell layer; monitor the pH value of the reaction system using a pH meter, and when it reaches 8.0 ± 0.2, it indicates that the shell layer formation is complete; collect the microcapsules by centrifugation (5000 rpm, 10 minutes); wash them successively with deionized water, ethanol, and acetone 3 times; dry them in vacuum at 40 °C for 12 hours to obtain the final product; measure the shell layer thickness by transmission electron microscopy (TEM), controlling it within the range of 50 ± 5 nm; conduct a pH-responsive test on the prepared microcapsules: they are stable in an aqueous solution with pH = 7.0 for 24 hours without rupture, and more than 95% of the microcapsules rupture within 30 minutes in an aqueous solution with pH = 12.0 to release the nano-zinc oxide catalyst, meeting the requirements for triggering in the alkaline environment of underwater concrete.

[0062] The dopamine-modified nanocellulose whiskers are prepared by a method including the following steps: B1. Disperse the nanocellulose whiskers (mass fraction 0.5%, aspect ratio 55) in Tris-HCl buffer solution (pH = 8.5), and ultrasonically treat for 20 minutes to obtain a uniformly dispersed solution; B2. Add dopamine hydrochloride (mass concentration 1%) to the dispersed solution, and the mass ratio of dopamine hydrochloride to nanocellulose whiskers is 2:1, and stir for 24 h under continuous oxygen introduction; B3. Centrifuge (8000 rpm, 15 minutes) to obtain a black precipitate, wash it 3 times with deionized water, and obtain dopamine-modified nanocellulose whiskers (dopamine layer thickness is 25 nm) after freeze-drying for 48 h.

[0063] The fractal structure silane coupling agent is prepared by a method including the following steps: C1. Mix γ-glycidoxypropyltrimethoxysilane and branched polyethyleneimine (molar ratio 1:1), heat to 75 °C and stir for reaction for 1 h; C2. Add tetraethoxysilane (accounting for 10% of the total mass of γ-glycidoxypropyltrimethoxysilane and branched polyethyleneimine) to the reaction system, and continue the reaction at 75 °C for 2 h; C3. Remove the small molecule by-products by vacuum distillation to obtain an amber transparent liquid fractal structure silane coupling agent.

[0064] The Mannich base curing agent is prepared by a method including the following steps: D1. Bisphenol A epoxy resin (epoxy value 0.45 eq / 100 g) and 4,4'-diaminodiphenylmethane are mixed at a molar ratio of 1:2 and reacted at 80 °C for 2 h; D2. 4-Hydroxybenzaldehyde (the molar ratio of aldehyde group to amino group is 1:1.2) is added for Mannich reaction, the reaction temperature is 110 °C, and the reaction time is 3 h; D3. After washing with acetone and vacuum drying, an orange viscous liquid Mannich base curing agent is obtained.

[0065] The impermeability enhancer is prepared by a method including the following steps: Nano-silica with a particle size of 150 nm and an organosilicon water repellent methyltrimethoxysilane (CH3Si(OCH3)3) are mixed at a mass ratio of 3:1, stirred evenly in absolute ethanol, and then vacuum dried to obtain the impermeability enhancer.

[0066] The preparation method of the bionic structure-based underwater self-catalytic epoxy resin composite material of this example includes the following steps:

[0067] (1) Heat the modified epoxy resin precursor to 50 °C;

[0068] (2) Sequentially add the Mannich base curing agent and the fractal structure silane coupling agent, and stir at 800 rpm for 15 min to obtain a mixture;

[0069] (3) Add dopamine-modified nano-cellulose whiskers and pH-responsive microcapsule catalyst to the mixture, and ultrasonically disperse for 20 min under the conditions of 40 kHz and a power density of 0.5 W / cm 3 ;

[0070] (4) Finally, add the impermeability enhancer, and after vacuum defoaming for 15 min, the bionic structure-based underwater self-catalytic epoxy resin composite material of this example is obtained.

[0071] Example 2

[0072] The bionic structure-based underwater self-catalytic epoxy resin composite material of this example, by weight, includes the following components: 50 parts of modified epoxy resin precursor, 5 parts of dopamine-modified nano-cellulose whiskers, 3 parts of fractal structure silane coupling agent, 22 parts of Mannich base curing agent, 1 part of pH-responsive microcapsule catalyst, and 7 parts of impermeability enhancer.

[0073] Among them, the modified epoxy resin precursor is prepared by a method including the following steps: I. Heat bisphenol A epoxy resin (epoxy value 0.50 eq / 100 g) to 75 °C to make it fully molten; II. Add a reactive diluent (dibutyl phthalate) with a mass ratio of 5%, and stir for 35 min until uniform; III. Add polyethylene glycol (molecular weight 600) with a mass ratio of 4% as a toughening agent, and continue to stir for 35 min; IV. Add an organosilicon modifier (amino-functionalized polysiloxane - Dow Corning Z-6020 amino-functionalized silane) with a mass ratio of 3%, and stir at 85 °C for 70 min; V. Finally, add a surfactant (polyether-modified organosilicon - Dow Corning DC-57 surfactant) with a mass ratio of 1.5%, and continue to stir at 85 °C for 40 min; VI. Perform vacuum degassing for 50 min to obtain the modified epoxy resin precursor. This modified epoxy resin precursor has the following characteristics: viscosity at 25 °C is 10,000 - 12,000 mPa·s, epoxy value is 0.44 - 0.48 eq / 100 g, water contact angle is 60° (significantly reduced compared to 80° of ordinary epoxy resin), and the wettability on a wet surface is enhanced by about 30%. The modification process further improves the flexibility and interfacial compatibility of the epoxy resin by adjusting the content of the organosilicon modifier and the molecular weight of the toughening agent, enabling it to exhibit more excellent wetting and adhesion properties in a humid environment.

[0074] The pH-responsive microcapsule catalyst is prepared by a method including the following steps:

[0075] A1. Disperse nano-zinc oxide (average particle size 70 nm) in cyclohexane, add polydopamine as the wall material, and stir evenly: Weigh 0.8 g of nano-zinc oxide powder and add it to 60 mL of cyclohexane; add 0.3 g of cetyltrimethylammonium bromide (CTAB) as a dispersant; use an ultrasonic probe (power 350 W) to ultrasonically treat for 35 minutes to form a stable nano-zinc oxide dispersion; under nitrogen protection, add 1.2 g of dopamine hydrochloride, and immediately add 30 mL of Tris-HCl buffer solution (pH = 8.5); under mechanical stirring (600 rpm) conditions, slowly add 0.4 g of pentaerythritol glycidyl ether (PTGE) as a crosslinking agent;

[0076] A2. Preparation of microcapsules by interfacial polymerization, controlling the thickness of the polydopamine shell layer to be 65 nm: Transfer the above dispersion system to a three-necked flask, and introduce oxygen at a stirring rate of 700 rpm; control the reaction temperature to be 28 ± 2 °C and the reaction time to be 5 hours to enable the self-polymerization of dopamine under oxidative conditions; when the color of the reaction solution changes from transparent to dark brown, add 15 mL of a 1.5% by mass polyvinyl alcohol (PVA) solution as a stabilizer; monitor the pH value of the reaction system using a pH meter, and when it reaches 8.2 ± 0.2, it indicates that the formation of the shell layer is complete; collect the microcapsules by centrifugation (6000 rpm, 15 minutes); wash them 4 times with deionized water, ethanol, and acetone in sequence; dry them in vacuo at 45 °C for 15 hours to obtain the final product; measure the shell layer thickness by transmission electron microscopy (TEM), controlling it within the range of 65 ± 5 nm; conduct a pH-responsive test on the prepared microcapsules: they are stable in an aqueous solution with pH = 7.0 for 48 hours without rupture, and more than 90% of the microcapsules rupture and release the nano-zinc oxide catalyst within 40 minutes in an aqueous solution with pH = 11.5, meeting the requirements for triggering in the alkaline environment of underwater concrete.

[0077] The dopamine-modified nanocellulose whiskers are prepared by a method including the following steps: B1. Disperse the nanocellulose whiskers (mass fraction 1.0%, aspect ratio 70) in Tris-HCl buffer solution (pH = 8.5), and ultrasonically treat for 25 minutes to obtain a uniformly dispersed solution; B2. Add dopamine hydrochloride (mass concentration 2%) to the dispersed solution, and the mass ratio of dopamine hydrochloride to nanocellulose whiskers is 3:1, and stir for 36 h under continuous oxygen introduction; B3. Centrifuge (10000 rpm, 20 minutes) to obtain a black precipitate, wash it 4 times with deionized water, and obtain dopamine-modified nanocellulose whiskers (dopamine layer thickness 35 nm) after freeze-drying for 60 h.

[0078] The fractal-structured silane coupling agent is prepared by a method including the following steps: C1. Mix γ-glycidoxypropyltrimethoxysilane with branched polyethyleneimine (molar ratio 2:1), heat to 80 °C and stir for reaction for 1.5 h; C2. Add tetraethoxysilane (accounting for 20% of the total mass) to the reaction system, and continue the reaction for 3 h; C3. Remove the small molecule by-products by vacuum distillation to obtain a fractal-structured silane coupling agent as an amber transparent liquid.

[0079] The Mannich base curing agent is prepared by a method including the following steps: D1. Bisphenol A epoxy resin (epoxy value 0.50 eq / 100 g) and 4,4'-diaminodiphenylmethane are mixed at a molar ratio of 1:2.5 and reacted at 90 °C for 3 h; D2. 3,5-dinitrobenzaldehyde (molar ratio of aldehyde group to amino group is 1:1.3) is added for Mannich reaction, the reaction temperature is 120 °C, and the reaction time is 4 h; D3. After washing with acetone and vacuum drying, an orange viscous liquid Mannich base curing agent is obtained.

[0080] The anti-seepage enhancer is prepared by a method including the following steps: Nano-silica with a particle size of 200 nm and an organosilicon water repellent methyltrimethoxysilane (CH3Si(OCH3)3) are mixed at a mass ratio of 3:1, stirred evenly in absolute ethanol, and then vacuum dried to obtain the anti-seepage enhancer.

[0081] The preparation method of the underwater self-catalytic epoxy resin composite material based on the bionic structure in this embodiment includes the following steps:

[0082] (1) Heat the modified epoxy resin precursor to 55 °C;

[0083] (2) Sequentially add the Mannich base curing agent and the fractal structure silane coupling agent, and stir at 1000 rpm for 20 min to obtain a mixture;

[0084] (3) Add dopamine-modified nanocellulose whiskers and pH-responsive microcapsule catalysts to the mixture, and ultrasonically disperse for 30 min under the conditions of 40 kHz and a power density of 0.7 W / cm 3 ;

[0085] (4) Finally, add the anti-seepage enhancer (nano-silica with a particle size of 200 nm and an organosilicon water repellent compounded at a mass ratio of 3:1), and after vacuum defoaming for 20 min, the underwater self-catalytic epoxy resin composite material based on the bionic structure in this embodiment is obtained.

[0086] Example 3

[0087] The underwater self-catalytic epoxy resin composite material based on the bionic structure in this embodiment, by weight, includes the following components: 60 parts of modified epoxy resin precursor, 8 parts of dopamine-modified nanocellulose whiskers, 5 parts of fractal structure silane coupling agent, 30 parts of Mannich base curing agent, 2 parts of pH-responsive microcapsule catalyst, and 10 parts of anti-seepage enhancer.

[0088] Among them, the modified epoxy resin precursor is prepared by a method including the following steps: I. Heat bisphenol A epoxy resin (epoxy value 0.52 eq / 100 g) to 80 °C to make it fully molten; II. Add a reactive diluent (anisole glycidyl ether) with a mass ratio of 6%, and stir for 40 min until uniform; III. Add polyethylene glycol (molecular weight 800) with a mass ratio of 5% as a toughening agent, and continue to stir for 40 min; IV. Add an organosilicon modifier (amino-functionalized polysiloxane - Dow Corning Z-6020 amino-functionalized silane) with a mass ratio of 4%, and stir at 90 °C for 80 min; V. Finally, add a surfactant (polyether-modified organosilicon - Dow Corning DC-57 surfactant) with a mass ratio of 2%, and continue to stir at 90 °C for 50 min; VI. Carry out vacuum degassing for 60 min to obtain the modified epoxy resin precursor. This modified epoxy resin precursor has the following characteristics: the viscosity at 25 °C is 8000 - 10000 mPa·s, the epoxy value is 0.46 - 0.50 eq / 100 g, the water contact angle is 55° (significantly reduced compared with 80° of ordinary epoxy resin), and the wettability to the wet surface is enhanced by about 35%. In the modification process, a toughening agent with a higher molecular weight and a larger proportion of organosilicon modifier are used, significantly improving the hydrophilicity and flexibility of the epoxy resin, and enabling it to exhibit the best interfacial adaptability and adhesion ability in the underwater environment.

[0089] The pH-responsive microcapsule catalyst is prepared by a method including the following steps:

[0090] A1. Disperse nano-zinc oxide (average particle size 80 nm) in cyclohexane, add polydopamine as the wall material, and stir evenly: Weigh 1.2 g of nano-zinc oxide powder, add it to 70 mL of cyclohexane; add 0.4 g of cetyltrimethylammonium bromide (CTAB) as a dispersant; use an ultrasonic probe (power 400 W) to ultrasonically treat for 40 minutes to form a stable nano-zinc oxide dispersion; under nitrogen protection, add 1.6 g of dopamine hydrochloride, and immediately add 35 mL of Tris-HCl buffer solution (pH = 8.5); under mechanical stirring (700 rpm) conditions, slowly dropwise add 0.5 g of pentaerythritol glycidyl ether (PTGE) as a crosslinking agent;

[0091] A2. Preparation of microcapsules by interfacial polymerization, controlling the thickness of the polydopamine shell layer to be 80 nm: Transfer the above dispersion system to a three-necked flask, and introduce oxygen at a stirring rate of 800 rpm; control the reaction temperature to be 30 ± 2 °C and the reaction time to be 6 hours to allow dopamine to self-polymerize under oxidative conditions; when the color of the reaction solution changes from transparent to dark brown, add 20 mL of a 2% (mass fraction) polyvinyl alcohol (PVA) solution as a stabilizer; continue stirring for 4 hours to fully form the polydopamine shell layer; monitor the pH value of the reaction system using a pH meter, and when it reaches 8.4 ± 0.2, it indicates that the shell layer formation is complete; collect the microcapsules by centrifugation (8000 rpm, 20 minutes); wash them 5 times with deionized water, ethanol, and acetone in sequence; dry them in a vacuum at 50 °C for 18 hours to obtain the final product; measure the shell layer thickness by transmission electron microscopy (TEM), controlling it within the range of 80 ± 5 nm; perform pH responsiveness testing on the prepared microcapsules: they are stable in an aqueous solution with pH = 7.0 for 72 hours without rupture, and more than 85% of the microcapsules rupture and release the nano-zinc oxide catalyst within 50 minutes in an aqueous solution with pH = 11.0, meeting the requirements for triggering in the alkaline environment of underwater concrete.

[0092] The dopamine-modified nanocellulose whiskers are prepared by a method including the following steps: B1. Disperse nanocellulose whiskers (mass fraction 2.0%) in Tris-HCl buffer solution (pH = 8.5), and ultrasonically treat for 30 minutes to obtain a uniformly dispersed solution; B2. Add dopamine hydrochloride (mass concentration 3%) to the dispersed solution, and the mass ratio of dopamine hydrochloride to nanocellulose whiskers (aspect ratio 95) is 4:1, and stir for 48 h under continuous oxygen introduction; B3. Centrifuge (12000 rpm, 25 minutes) to obtain a black precipitate, wash it 5 times with deionized water, and freeze-dry for 72 h to obtain dopamine-modified nanocellulose whiskers (dopamine layer thickness 45 nm).

[0093] The fractal structure silane coupling agent is prepared by a method including the following steps: C1. Mix γ-glycidoxypropyltrimethoxysilane and branched polyethyleneimine (molar ratio 3:1), heat to 85 °C and stir and react for 2 h; C2. Add tetraethoxysilane (accounting for 30% of the total mass of the mixture of γ-glycidoxypropyltrimethoxysilane and branched polyethyleneimine) to the reaction system, and continue to react at 85 °C for 4 h; C3. Remove small molecule by-products by vacuum distillation to obtain an amber transparent liquid fractal structure silane coupling agent.

[0094] The Mannich base type curing agent is prepared by a method including the following steps: D1. Bisphenol A epoxy resin (epoxy value 0.55 eq / 100 g) and 4,4'-diaminodiphenylmethane are mixed at a molar ratio of 1:3 and reacted at 100 °C for 4 h; D2. 4-Hydroxybenzaldehyde (the molar ratio of aldehyde group to amino group is 1:1.5) is added for Mannich reaction, the reaction temperature is 130 °C, and the reaction time is 6 h; D3. After washing with acetone and vacuum drying, the Mannich base type curing agent is obtained.

[0095] The anti-seepage enhancer is prepared by a method including the following steps: Nano-silica with a particle size of 300 nm and an organosilicon water repellent methyltrimethoxysilane (CH3Si(OCH3)3) are mixed at a mass ratio of 3:1, stirred evenly in absolute ethanol, and then vacuum dried to obtain the anti-seepage enhancer.

[0096] The preparation method of the underwater self-catalytic epoxy resin composite material based on the bionic structure in this embodiment includes the following steps:

[0097] (1) Heat the modified epoxy resin precursor to 60 °C;

[0098] (2) Sequentially add the Mannich base type curing agent and the fractal structure silane coupling agent, and stir at 1200 rpm for 30 min to obtain a mixture;

[0099] (3) Add dopamine-modified nano-cellulose whiskers and pH-responsive microcapsule catalyst to the mixture, and ultrasonically disperse for 40 min under the conditions of 40 kHz and a power density of 1.0 W / cm 3 ;

[0100] (4) Finally, add the anti-seepage enhancer, and after vacuum defoaming for 30 min, the underwater self-catalytic epoxy resin composite material based on the bionic structure in this embodiment is obtained.

[0101] Example 4

[0102] The underwater self-catalytic epoxy resin composite material based on the bionic structure in this embodiment includes the following components by weight: 45 parts of modified epoxy resin precursor, 4 parts of dopamine-modified nano-cellulose whiskers, 2 parts of fractal structure silane coupling agent, 18 parts of Mannich base type curing agent, 0.8 part of pH-responsive microcapsule catalyst, and 6 parts of anti-seepage enhancer.

[0103] Among them, the modified epoxy resin precursor is prepared by a method including the following steps: I. Heat bisphenol A epoxy resin (epoxy value 0.49 eq / 100 g) to 72 °C to make it fully molten; II. Add a reactive diluent (dibutyl phthalate) with a mass ratio of 4.5%, and stir for 32 min until homogeneous; III. Add polyethylene glycol (molecular weight 500) with a mass ratio of 3.5% as a toughening agent, and continue to stir for 32 min; IV. Add an organosilicon modifier (amino-functionalized polysiloxane - Dow Corning Z-6020 amino-functionalized silane) with a mass ratio of 2.5%, and stir at 82 °C for 65 min; V. Finally, add a surfactant (polyether-modified organosilicon - Dow Corning DC-57 surfactant) with a mass ratio of 1.2%, and continue to stir at 82 °C for 35 min; VI. Perform vacuum degassing for 48 min to obtain the modified epoxy resin precursor. This modified epoxy resin precursor has the following properties: viscosity at 25 °C is 11000 - 13000 mPa·s, epoxy value is 0.43 - 0.47 eq / 100 g, water contact angle is 62° (significantly reduced compared to 80° of ordinary epoxy resin), and the wettability to a wet surface is enhanced by about 27%. The modification process balances the hydrophilicity and mechanical properties of the material by introducing appropriate amounts of organosilicon modifier and surfactant, enabling it to exhibit good wetting and adhesion properties in an underwater environment.

[0104] The pH-responsive microcapsule catalyst is prepared by a method including the following steps:

[0105] A1. Disperse nano-zinc oxide (average particle size 60 nm) in cyclohexane, add polydopamine as the wall material, and stir evenly: Weigh 0.6 g of nano-zinc oxide powder and add it to 55 mL of cyclohexane; add 0.25 g of cetyltrimethylammonium bromide (CTAB) as a dispersant; use an ultrasonic probe (power 320 W) to ultrasonically treat for 32 minutes to form a stable nano-zinc oxide dispersion; under nitrogen protection, add 1.0 g of dopamine hydrochloride, and immediately add 28 mL of Tris-HCl buffer solution (pH = 8.5); under mechanical stirring (550 rpm) conditions, slowly dropwise add 0.35 g of pentaerythritol glycidyl ether (PTGE) as a crosslinking agent;

[0106] A2. Microcapsules were prepared by interfacial polymerization, and the thickness of the polydopamine shell layer was controlled to be 60 nm: The above dispersion system was transferred to a three-necked flask, and oxygen was introduced at a stirring rate of 650 rpm; the reaction temperature was controlled at 26 ± 2 °C, and the reaction time was 4.5 hours to enable the self-polymerization of dopamine under oxidative conditions; when the color of the reaction solution changed from transparent to dark brown, 12 mL of a 1.2% (mass fraction) polyvinyl alcohol (PVA) solution was added as a stabilizer; stirring was continued for 2.5 hours to fully form the polydopamine shell layer; the pH value of the reaction system was monitored using a pH meter, and when it reached 8.1 ± 0.2, it indicated that the shell layer formation was complete; the microcapsules were collected by centrifugation (5500 rpm, 12 minutes); washed three times with deionized water, ethanol, and acetone in sequence; dried in vacuo at 42 °C for 14 hours to obtain the final product; the shell layer thickness was measured by transmission electron microscopy (TEM) and controlled within the range of 60 ± 5 nm; the prepared microcapsules were subjected to pH-responsive testing: they were stable in an aqueous solution with pH = 7.0 for 36 hours without rupture, and more than 92% of the microcapsules ruptured within 35 minutes in an aqueous solution with pH = 11.8 to release the nano-zinc oxide catalyst, meeting the requirements for triggering in the alkaline environment of underwater concrete.

[0107] Dopamine-modified nanocellulose whiskers were prepared by a method including the following steps: B1. Nanocellulose whiskers (mass fraction 0.8%, aspect ratio 65) were dispersed in Tris-HCl buffer (pH = 8.5) and sonicated for 22 minutes to obtain a uniformly dispersed solution; B2. Dopamine hydrochloride (mass concentration 1.5%) was added to the dispersed solution, and the mass ratio of dopamine hydrochloride to nanocellulose whiskers was 2.5:1, and stirring was carried out for 30 h under continuous oxygen supply; B3. The black precipitate was obtained by centrifugation (9000 rpm, 18 minutes), washed 4 times with deionized water, and freeze-dried for 54 h to obtain dopamine-modified nanocellulose whiskers (dopamine layer thickness 30 nm).

[0108] The fractal structure silane coupling agent was prepared by a method including the following steps: C1. γ-Glycidoxypropyltrimethoxysilane and branched polyethyleneimine (molar ratio 1.5:1) were mixed, heated to 78 °C and stirred for reaction for 1.2 h; C2. Tetraethoxysilane (15% of the total mass) was added to the reaction system and the reaction was continued for 2.5 h; C3. Small molecule by-products were removed by vacuum distillation to obtain an amber transparent liquid fractal structure silane coupling agent.

[0109] The Mannich base type curing agent is prepared by a method including the following steps: D1. Bisphenol A epoxy resin (epoxy value 0.48 eq / 100 g) and 4,4'-diaminodiphenylmethane are mixed at a molar ratio of 1:2.2 and reacted at 85 °C for 2.5 h; D2. 4-Hydroxybenzaldehyde (the molar ratio of aldehyde group to amino group is 1:1.25) is added for Mannich reaction, the reaction temperature is 115 °C, and the reaction time is 3.5 h; D3. After washing with acetone and vacuum drying, an orange viscous liquid Mannich base type curing agent is obtained.

[0110] The impermeability enhancer is prepared by a method including the following steps: Nano-silica with a particle size of 180 nm and an organosilicon water repellent, methyltrimethoxysilane (CH3Si(OCH3)3), are mixed at a mass ratio of 3:1, stirred evenly in absolute ethanol, and then vacuum dried to obtain the impermeability enhancer.

[0111] The preparation method of the underwater self-catalytic epoxy resin composite material based on the bionic structure in this embodiment includes the following steps:

[0112] (1) Heat the modified epoxy resin precursor to 53 °C;

[0113] (2) Sequentially add the Mannich base type curing agent and the fractal structure silane coupling agent, and stir at 900 rpm for 18 min to obtain a mixture;

[0114] (3) Add dopamine-modified nano-cellulose whiskers and pH-responsive microcapsule catalyst to the mixture, and ultrasonically disperse for 25 min under the conditions of 40 kHz and a power density of 0.6 W / cm 3 ;

[0115] (4) Finally, add the impermeability enhancer (nano-silica with a particle size of 180 nm and an organosilicon water repellent are compounded at a mass ratio of 3:1), and vacuum defoam for 18 min to obtain the underwater self-catalytic epoxy resin composite material based on the bionic structure in this embodiment.

[0116] Example 5

[0117] The underwater self-catalytic epoxy resin composite material based on the bionic structure in this embodiment, by weight, includes the following components: 55 parts of modified epoxy resin precursor, 6 parts of dopamine-modified nano-cellulose whiskers, 4 parts of fractal structure silane coupling agent, 25 parts of Mannich base type curing agent, 1.5 parts of pH-responsive microcapsule catalyst, and 8 parts of impermeability enhancer.

[0118] Among them, the modified epoxy resin precursor is prepared by a method including the following steps: I. Heat bisphenol A epoxy resin (epoxy value 0.51 eq / 100 g) to 78 °C to make it fully molten; II. Add a reactive diluent (anisole glycidyl ether) with a mass ratio of 5.5%, and stir for 38 min until uniform; III. Add polyethylene glycol (molecular weight 700) with a mass ratio of 4.5% as a toughening agent, and continue to stir for 38 min; IV. Add an organosilicon modifier (amino-functionalized polysiloxane - Dow Corning Z-6020 amino-functionalized silane) with a mass ratio of 3.5%, and stir at 88 °C for 75 min; V. Finally, add a surfactant (polyether-modified organosilicon - Dow Corning DC-57 surfactant) with a mass ratio of 1.8%, and continue to stir at 88 °C for 45 min; VI. Vacuum degas for 55 min to obtain the modified epoxy resin precursor. The modified epoxy resin precursor has the following properties: viscosity at 25 °C is 9000 - 11000 mPa·s, epoxy value is 0.45 - 0.49 eq / 100 g, water contact angle is 58° (significantly reduced compared with 80° of ordinary epoxy resin), and the wettability to wet surfaces is enhanced by about 32%. The modification process optimizes the fluidity and interfacial compatibility of the material in the underwater environment by adjusting the ratios of the organosilicon modifier and the toughening agent, enabling it to exhibit excellent spreading and adhesion capabilities under high humidity conditions.

[0119] The pH-responsive microcapsule catalyst is prepared by a method including the following steps:

[0120] A1. Disperse nano-zinc oxide (average particle size 75 nm) in cyclohexane, add polydopamine as the wall material, and stir evenly: Weigh 1.0 g of nano-zinc oxide powder, add it to 65 mL of cyclohexane; add 0.35 g of cetyltrimethylammonium bromide (CTAB) as a dispersant; use an ultrasonic probe (power 380 W) to ultrasonically treat for 38 minutes to form a stable nano-zinc oxide dispersion; under nitrogen protection, add 1.4 g of dopamine hydrochloride, and immediately add 32 mL of Tris-HCl buffer solution (pH = 8.5); under mechanical stirring (650 rpm) conditions, slowly add 0.45 g of pentaerythritol glycidyl ether (PTGE) as a crosslinking agent;

[0121] A2. Microcapsules were prepared by interfacial polymerization, controlling the thickness of the polydopamine shell layer to be 70 nm: The above dispersion system was transferred to a three-necked flask, and oxygen was introduced at a stirring rate of 750 rpm; the reaction temperature was controlled at 29 ± 2 °C, and the reaction time was 5.5 hours to allow dopamine to self-polymerize under oxidative conditions; when the color of the reaction solution changed from transparent to dark brown, 18 mL of a 1.8% by mass polyvinyl alcohol (PVA) solution was added as a stabilizer; stirring was continued for 3.5 hours to fully form the polydopamine shell layer; the pH value of the reaction system was monitored using a pH meter, and when it reached 8.3 ± 0.2, it indicated that the shell layer formation was complete; the microcapsules were collected by centrifugation (7000 rpm, 18 minutes); washed 4 times with deionized water, ethanol, and acetone in sequence; dried in vacuo at 48 °C for 16 hours to obtain the final product; the shell layer thickness was measured by transmission electron microscopy (TEM) and controlled within the range of 70 ± 5 nm; the prepared microcapsules were subjected to pH responsiveness testing: they were stable in an aqueous solution at pH = 7.0 for 60 hours without rupture, and more than 88% of the microcapsules ruptured and released the nano-zinc oxide catalyst within 45 minutes in an aqueous solution at pH = 11.2, meeting the requirements for triggering in the alkaline environment of underwater concrete.

[0122] The dopamine-modified nanocellulose whiskers were prepared by a method including the following steps: B1. Nanocellulose whiskers (mass fraction 1.5%, aspect ratio 85) were dispersed in Tris-HCl buffer solution (pH = 8.5) and ultrasonically treated for 28 minutes to obtain a homogeneous dispersion; B2. Dopamine hydrochloride (mass concentration 2.5%) was added to the dispersion, and the mass ratio of dopamine hydrochloride to nanocellulose whiskers was 3.5:1, and stirring was carried out for 42 h under the condition of continuously introducing oxygen; B3. The black precipitate was obtained by centrifugation (11000 rpm, 22 minutes), washed 4 times with deionized water, and freeze-dried for 66 h to obtain dopamine-modified nanocellulose whiskers (the dopamine layer thickness was 40 nm).

[0123] The fractal structure silane coupling agent was prepared by a method including the following steps: C1. γ-Glycidoxypropyltrimethoxysilane and branched polyethyleneimine (molar ratio 2.5:1) were mixed, heated to 82 °C and stirred for reaction for 1.8 h; C2. Tetraethoxysilane (accounting for 25% of the total mass) was added to the reaction system and the reaction was continued for 3.5 h; C3. Small molecule by-products were removed by vacuum distillation to obtain a amber transparent liquid fractal structure silane coupling agent.

[0124] The Mannich base curing agent is prepared by a method including the following steps: D1. Bisphenol A epoxy resin (epoxy value 0.52 eq / 100 g) and 4,4'-diaminodiphenylmethane are mixed at a molar ratio of 1:2.8 and reacted at 95 °C for 3.5 h; D2. 3,5-dinitrobenzaldehyde is added (the molar ratio of aldehyde group to amino group is 1:1.4) for the Mannich reaction, the reaction temperature is 125 °C, and the reaction time is 5 h; D3. After washing with acetone and vacuum drying, an orange viscous liquid Mannich base curing agent is obtained.

[0125] The anti-seepage enhancer is prepared by a method including the following steps: Nano-silica with a particle size of 250 nm and a methyltrimethoxysilane-based organosilicon water repellent are mixed at a mass ratio of 3:1, stirred evenly in absolute ethanol, and then vacuum dried to obtain the anti-seepage enhancer.

[0126] The preparation method of the underwater self-catalytic epoxy resin composite material based on the bionic structure in this example includes the following steps:

[0127] (1) Heat the modified epoxy resin precursor to 58 °C;

[0128] (2) Sequentially add the Mannich base curing agent and the fractal structure silane coupling agent, and stir at 1100 rpm for 25 min to obtain a mixture;

[0129] (3) Add dopamine-modified nanocrystalline cellulose whiskers and pH-responsive microcapsule catalysts to the mixture, and ultrasonically disperse for 35 min under the conditions of 40 kHz and a power density of 0.8 W / cm 3 ;

[0130] (4) Finally, add the anti-seepage enhancer (nano-silica with a particle size of 250 nm and a methyltrimethoxysilane (CH3Si(OCH3)3) organosilicon water repellent are compounded at a mass ratio of 3:1), and after vacuum degassing for 25 min, the underwater self-catalytic epoxy resin composite material based on the bionic structure in this example is obtained.

[0131] Example 6

[0132] The underwater self-catalytic epoxy resin composite material based on the bionic structure in this example is only different from that in Example 1 in that: 1) In the preparation process of the dopamine-modified nanocrystalline cellulose whiskers in this example, the aspect ratio of the nanocrystalline cellulose whiskers used is 50, and the thickness of the dopamine modification layer is 20 nm; 2) In the preparation process of the fractal structure silane coupling agent, the reaction temperature in step C1 is 100 °C, and the reaction time is 2 h; the reaction temperature in step C2 is 90 °C; 3) The particle size of the nano-silica used in the preparation process of the anti-seepage enhancer is 100 nm; the rest are the same as those in Example 1.

[0133] Example 7

[0134] The underwater self-catalytic epoxy resin composite material based on the bionic structure of this embodiment includes the following components, by weight: 50 parts of modified epoxy resin precursor, 5.5 parts of dopamine-modified nanocellulose whiskers, 3 parts of fractal structure silane coupling agent, 22 parts of Mannich base curing agent, 1.2 parts of pH-responsive microcapsule catalyst, and 7.5 parts of anti-seepage enhancer.

[0135] The preparation methods of the modified epoxy resin precursor, the barrier enhancer and the pH-responsive microcapsule catalyst in this embodiment are the same as those in Example 2;

[0136] The dopamine-modified nanocellulose whiskers of this embodiment were prepared by a method comprising the following steps: B1. dispersing nanocellulose whiskers (mass fraction 1.2%, aspect ratio 75) in Tris-HCl buffer (pH = 8.5) and ultrasonically treating for 25 minutes to obtain a uniform dispersion; B2. adding dopamine hydrochloride (mass concentration 2.2%) to the dispersion, with a mass ratio of dopamine hydrochloride to nanocellulose whiskers of 3:1, and stirring for 36 hours at room temperature of 25°C with continuous oxygen flow; B3. centrifuging (10,000 rpm, 20 minutes) to obtain a black precipitate, washing it four times with deionized water, and freeze-drying it for 60 hours to obtain dopamine-modified nanocellulose whiskers (dopamine layer thickness 35 nm).

[0137] The fractal silane coupling agent is prepared by a method comprising the following steps: C1. mixing γ-glycidyl ether propyl trimethoxysilane and branched polyethyleneimine (molar ratio 2:1), heating to 110°C and stirring for reaction for 3 hours; C2. adding tetraethoxysilane (accounting for 20% of the total mass) to the reaction system, and continuing the reaction at 100°C for 3 hours; C3. removing small molecular by-products by distillation under reduced pressure to obtain an amber transparent liquid fractal silane coupling agent.

[0138] A Mannich base curing agent is prepared by a method comprising the following steps: D1. mixing bisphenol A epoxy resin (epoxy value 0.50 eq / 100 g) and 4,4'-diaminodiphenylmethane in a molar ratio of 1:2.5 and reacting at 90°C for 3 hours; D2. adding 3,5-dinitrobenzaldehyde (molar ratio of aldehyde group to amino group of 1:1.35) to carry out a Mannich reaction at a temperature of 120°C for 4.5 hours; D3. washing with acetone and vacuum drying to obtain an orange viscous liquid Mannich base curing agent.

[0139] The preparation method of the underwater self-catalytic epoxy resin composite material based on the bionic structure in this embodiment is the same as that in Example 2.

[0140] Example 8

[0141] The underwater self-catalytic epoxy resin composite material based on the bionic structure in this embodiment is only different from that in Embodiment 3 in the following aspects: 1) In the preparation process of dopamine-modified nanocellulose whiskers in this embodiment, the aspect ratio of the nanocellulose whiskers used is 100, and the thickness of the dopamine modification layer is 50 nm; 2) In the preparation process of the fractal structure silane coupling agent, the reaction temperature in Step C1 is 120 °C, and the reaction time is 4 h; the reaction temperature in Step C2 is 110 °C; the rest are the same as those in Embodiment 1.

[0142] Embodiment 9 (Variant Embodiment of Hydrophobic Agent)

[0143] The underwater self-catalytic epoxy resin composite material based on the bionic structure provided in this embodiment includes the following components by weight: 45 parts of modified epoxy resin precursor, 4 parts of dopamine-modified nanocellulose whiskers, 2 parts of fractal structure silane coupling agent, 20 parts of Mannich base curing agent, 0.8 part of pH-responsive microcapsule catalyst, and 6 parts of anti-seepage enhancer.

[0144] The difference between the anti-seepage enhancer in this embodiment and that in Embodiment 1 lies in that: the mass ratio of nano-silica to organic hydrophobic agent is 2:1, and the rest are the same as those in Embodiment 1.

[0145] The epoxy resin precursor, dopamine-modified nanocellulose whiskers, fractal structure silane coupling agent, Mannich base curing agent, and pH-responsive microcapsule catalyst used in this embodiment are all the same as those in Embodiment 1.

[0146] The preparation method of the underwater self-catalytic epoxy resin composite material based on the bionic structure in this embodiment is the same as that in Embodiment 1.

[0147] Embodiment 10 (Variant Embodiment of Hydrophobic Agent)

[0148] The underwater self-catalytic epoxy resin composite material based on the bionic structure in this embodiment is only different from that in Embodiment 9 in that: the mass ratio of nano-silica to organosilicon hydrophobic agent used in the preparation of the anti-seepage enhancer is 4:1; the rest are the same as those in Embodiment 9.

[0149] Embodiment 11 (Variant Embodiment of Fractal Structure Silane Coupling Agent)

[0150] The underwater self-catalytic epoxy resin composite material based on the bionic structure in this embodiment includes the following components by weight: 52 parts of modified epoxy resin precursor, 6 parts of dopamine-modified nanocellulose whiskers, 4 parts of fractal structure silane coupling agent, 23 parts of Mannich base curing agent, 1.3 parts of pH-responsive microcapsule catalyst, and 8 parts of anti-seepage enhancer.

[0151] The difference between the fractal structure silane coupling agent in this example and that in Example 7 is only that: the molar ratio of γ-glycidoxypropyltrimethoxysilane to branched polyethyleneimine is 2.5:1; the addition amount of tetraethoxysilane is 15% of the total mass of γ-glycidoxypropyltrimethoxysilane and branched polyethyleneimine;

[0152] Other components in this example except the fractal structure silane coupling agent and the preparation method of the underwater self-catalytic epoxy resin composite material based on the bionic structure in this example are the same as those in Example 7.

[0153] Example 12 (Variant Example of Fractal Structure Silane Coupling Agent)

[0154] The difference between the underwater self-catalytic epoxy resin composite material based on the bionic structure in this example and that in Example 11 is only that: during the preparation of the fractal structure silane coupling agent, the dosage of tetraethoxysilane is 25% of the total mass of γ-glycidoxypropyltrimethoxysilane and branched polyethyleneimine; the rest are the same as those in Example 11.

[0155] Comparative Example 1

[0156] The epoxy resin composite material in this comparative example, by weight, comprises the following components: 50 parts of modified epoxy resin precursor, 12 parts of dopamine-modified nanocellulose whiskers, 3 parts of fractal structure silane coupling agent, 22 parts of Mannich base curing agent, 1 part of pH-responsive microcapsule catalyst, and 7 parts of anti-seepage enhancer.

[0157] The preparation methods of the above components and the composite material in this comparative example are the same as those in Example 2.

[0158] Comparative Example 2

[0159] The epoxy resin composite material in this comparative example, by weight, comprises the following components: 50 parts of modified epoxy resin precursor, 5 parts of dopamine-modified nanocellulose whiskers, 3 parts of fractal structure silane coupling agent, 22 parts of Mannich base curing agent, and 7 parts of anti-seepage enhancer.

[0160] The preparation methods of the above components and the composite material in this comparative example are the same as those in Example 2.

[0161] Comparative Example 3

[0162] The epoxy resin composite material in this comparative example, by weight, comprises the following components: 50 parts of modified epoxy resin precursor, 5 parts of dopamine-modified nanocellulose whiskers, 8 parts of fractal structure silane coupling agent, 22 parts of Mannich base curing agent, 1 part of pH-responsive microcapsule catalyst, and 7 parts of anti-seepage enhancer.

[0163] The preparation methods of the above components and the composite material in this comparative example are the same as those in Example 2.

[0164] Comparative Example 4

[0165] The epoxy resin composite material of this comparative example, by weight, comprises the following components: 50 parts of modified epoxy resin precursor, 5 parts of dopamine-modified nanocrystalline cellulose whiskers, 3 parts of fractal structure silane coupling agent, 22 parts of ordinary polyamide curing agent (non-Mannich base type), 1 part of pH-responsive microcapsule catalyst, and 7 parts of anti-seepage enhancer.

[0166] The preparation methods of the above components and the composite material of this comparative example are the same as those of Example 2.

[0167] Among them, the above ordinary polyamide curing agent is prepared by reacting dimer acid with polyalkylene polyamine: 70 parts by weight of dimer acid (C36 dicarboxylic acid, content 95%), 30 parts by weight of polyalkylene polyamine mixture (mainly composed of diethylenetriamine and triethylenetetramine), and 0.5 part by weight of catalyst (triphenylphosphine) are reacted at 170 °C for 5 h, and then the water generated by the reaction is removed under reduced pressure to obtain the ordinary polyamide curing agent of this comparative example.

[0168] The main characteristic parameters of this curing agent are: amine value 160 - 180 mgKOH / g, viscosity 9000 - 12000 mPa·s at 25 °C, pH value about 9.0 - 10.0, and the appearance is an amber semi-transparent viscous liquid.

[0169] Comparative Example 5

[0170] The components of the composite material provided in this comparative example, by weight, are: 50 parts of modified epoxy resin precursor, 5 parts of dopamine-modified nanocrystalline cellulose whiskers, 3 parts of fractal structure silane coupling agent, 22 parts of Mannich base type curing agent, 1 part of pH-responsive microcapsule catalyst, and 15 parts of anti-seepage enhancer.

[0171] The preparation methods of the components and the composite material of this comparative example are the same as those of Example 2, and will not be elaborated here.

[0172] Comparative Example 6 (changing the preparation method of the modified epoxy resin precursor)

[0173] The difference between this comparative example and Example 2 is only that: the preparation method of the modified epoxy resin precursor is different from that of Example 2, and the rest are the same as those of Example 2;

[0174] The preparation method of the modified epoxy resin precursor in this comparative example is specifically as follows: I. Heat bisphenol A type epoxy resin (epoxy value 0.50 eq / 100 g) to 75 °C to make it fully molten; II. Directly add 5% by mass of organosilicon modifier (amino-containing polysiloxane), and stir at 75 °C for 60 min; III. Vacuum degas for 30 min to obtain the modified epoxy resin precursor.

[0175] The modified epoxy resin precursor does not contain reactive diluents, toughening agents, and surfactants. Its water contact angle is 75°, and the wettability on a wet surface is only enhanced by about 8%.

[0176] Comparative Example 7 (changing the preparation conditions of dopamine-modified nanocellulose whiskers)

[0177] The difference between this comparative example and Example 2 is only that: the preparation method of dopamine-modified nanocellulose whiskers is different from that of Example 2, and the rest are the same as those of Example 2.

[0178] Specifically, the preparation method of dopamine-modified nanocellulose whiskers is as follows: B1. Disperse nanocellulose whiskers (mass fraction of 1.0%) in a phosphate buffer solution with pH = 7.0 and ultrasonically treat for 25 minutes; B2. Add dopamine hydrochloride (mass concentration of 2%) to the dispersion, and the mass ratio of dopamine hydrochloride to nanocellulose whiskers is 3:1, and stir at room temperature for 36 h (without oxygen introduction); B3. Centrifuge (10,000 rpm, 20 minutes) to obtain a light gray precipitate, wash it 4 times with deionized water, and freeze-dry for 60 h to obtain dopamine-modified nanocellulose whiskers.

[0179] Comparative Example 8 (changing the shell thickness of pH-responsive microcapsules)

[0180] The difference between this comparative example and Example 2 is only that: the preparation method of the pH-responsive microcapsule catalyst is different from that of Example 2; the rest are the same as those of Example 2.

[0181] Specifically, the difference between the preparation method of the pH-responsive microcapsule catalyst in this comparative example and that of Example 2 is that: the reaction time was extended to 8 hours during the interfacial polymerization process, resulting in a poly-dopamine shell thickness of 120 nm.

[0182] Comparative Example 9 (changing the preparation method of Mannich base curing agent)

[0183] The difference between this comparative example and Example 2 is only that: the preparation method of the Mannich base curing agent is different, and the rest are the same as those of Example 2.

[0184] Among them, the preparation method of the Mannich base curing agent in this comparative example is specifically as follows:

[0185] D1. Mix bisphenol A epoxy resin (epoxy value 0.50 eq / 100 g) with 4,4'-diaminodiphenylmethane in a molar ratio of 1:1 (lower than the range of 1:2 - 3 in the claims), and react at 90 °C for 3 h;

[0186] D2. 3,5-dinitrobenzaldehyde was added (the molar ratio of aldehyde group to amino group was 1:0.8, lower than the range of 1:1.2 - 1.5 in the claims) for the Mannich reaction. The reaction temperature was 100 °C (lower than the range of 110 °C), and the reaction time was 2 h.

[0187] D3. The curing agent was obtained after washing with acetone and vacuum drying.

[0188] Comparative Example 10 (using different types of fractal structure silane coupling agents)

[0189] The difference between this comparative example and Example 2 was only that: the fractal structure silane coupling agent was replaced by linear polyethyleneimine (non-branched type) instead of branched polyethyleneimine, and the rest were the same as in Example 2.

[0190] The preparation method of the fractal structure silane coupling agent in this comparative example was: C1. γ-Glycidoxypropyltrimethoxysilane and linear polyethyleneimine (molar ratio 2:1) were mixed and heated to 80 °C and stirred for reaction for 1.5 h; C2. Tetraethoxysilane (accounting for 20% of the total mass) was added to the reaction system and the reaction was continued at 80 °C for 3 h; C3. Small molecule by-products were removed by vacuum distillation to obtain a linear structure silane coupling agent.

[0191] Comparative Example 11 (completely not using the fractal structure silane coupling agent)

[0192] The difference between this comparative example and Example 2 was only that: by weight, it included the following components: 53 parts of modified epoxy resin precursor, 5 parts of dopamine-modified nanocrystalline cellulose whiskers, 22 parts of Mannich base curing agent, 1 part of pH-responsive microcapsule catalyst, and 7 parts of anti-seepage enhancer, without adding the fractal structure silane coupling agent; the rest were the same as in Example 2.

[0193] Experimental Example

[0194] The initial setting time, underwater bonding strength, and chloride ion penetration resistance coefficient of the composite materials of the above examples and comparative examples were tested:

[0195] Testing method:

[0196] The initial setting time was determined by the improved method of ASTM C191 standard, including the following steps: (1) The composite material was coated on a glass plate to form a uniform coating with a thickness of 2 mm; (2) The sample was placed in a constant temperature and humidity chamber with a relative humidity of 95 ± 2%, and the temperature was controlled at 23 ± 2 °C; (3) A Vicat needle (diameter 1 mm, weight 300 g) was vertically inserted into the surface of the sample at fixed time intervals (initially 2 min, later 1 min); (4) When the tip of the needle could not penetrate 2 mm deep into the surface of the sample, this time was recorded as the initial setting time; (5) Each sample was tested 3 times, and the average value was taken as the final result.

[0197] The underwater bond strength was measured by the standard method of ASTM C882 / C882M: (1) Prepare concrete specimens with dimensions of 100mm×100mm×50mm, and the surface saturated moisture content is 95±3%; (2) Uniformly coat the composite material on the contact surface of two concrete specimens, and the coating thickness is controlled at 2±0.2mm; (3) Butt-join and press the two specimens coated with the composite material underwater (depth 10cm, temperature 20±2°C), and apply a pressure of 0.05MPa; (4) After curing underwater for 24h, use a universal material testing machine to conduct shear strength testing at a loading rate of 2mm / min; (5) Record the maximum load at the time of shear failure, and calculate the bond strength by dividing by the bond area; (6) Test 5 groups of specimens for each material, and take the average value after removing the highest and lowest values as the final result; (7) Additionally conduct long-term underwater immersion tests (28 days and 90 days respectively) on the samples of Examples 2 and 3 to evaluate the durability.

[0198] The chloride ion penetration coefficient was comprehensively tested by the ASTM C1202 standard and the NT Build 492 standard: (1) Use the composite material to prepare disc specimens with a diameter of 100mm and a thickness of 50mm; (2) Cure the specimens for 7 days under the conditions of a temperature of 23±2°C and a relative humidity of 50±5%; (3) Place the specimens in a two-chamber electro-migration device, with the cathode chamber filled with 0.3mol / L NaOH solution and the anode chamber filled with 3% NaCl solution; (4) Apply a DC voltage of 30V, and the test time is 6 hours; (5) After the test, disconnect the specimens and spray 0.1mol / L AgNO3 solution for color development, and measure the chloride ion migration depth; (6) Calculate the chloride ion diffusion coefficient according to the unsteady migration equation: D=(RT / zFE)·(xd-α√xd) / t; where: D is the chloride ion diffusion coefficient (m 2 / s), R is the gas constant 8.314J / (mol·K), T is the absolute temperature (K), z is the ion valence (chloride ion is 1), F is the Faraday constant (96485C / mol), E is the electric field strength (V / m), xd is the chloride ion migration depth (m), α is an experimental constant (determined according to the calibration test), and t is the test time (s); (7) Test 3 specimens for each material, and take the average value as the final result; (8); Additionally conduct chloride ion penetration resistance tests on the samples of Examples 1-3 after 30 cycles of seawater circulation immersion-drying (each cycle includes 3 days of immersion and 4 days of drying) to evaluate the long-term durability.

[0199] The test results are shown in Table 1 below:

[0200] Table 1

[0201]

[0202]

[0203] As can be seen from Table 1 above:

[0204] The chloride ion permeability coefficients of the underwater self-catalytic epoxy resin composites based on the bionic structure in Examples 1-3 after 30 cycles were 2.3×10 -12 m 2 / s, 1.8×10 -12 m 2 / s, and 1.4×10 -12 m 2 / s, showing increases of 28%, 20%, and 17% respectively; in addition, the bond strengths of the underwater self-catalytic epoxy resin composites based on the bionic structure in Examples 2 and 3 after being soaked underwater were also tested: the underwater bond strength of the underwater self-catalytic epoxy resin composite based on the bionic structure in Example 2 was 3.0 MPa (retention rate 94%) after 28 days and 2.8 MPa (retention rate 88%) after 90 days; the underwater bond strength of the underwater self-catalytic epoxy resin composite based on the bionic structure in Example 3 was 3.3 MPa (retention rate 94%) after 28 days and 3.1 MPa (retention rate 89%) after 90 days. The underwater self-catalytic epoxy resin composite based on the bionic structure of the present invention has a short initial solidification time, high underwater bond strength, good chloride ion penetration resistance, and good durability.

[0205] The composite material of Comparative Example 1 exhibited too high a viscosity, poor construction performance, and due to the too high content of dopamine-modified nanocellulose whiskers, an over-dense network structure was formed inside the system, which instead hindered the progress of the crosslinking reaction, prolonged the curing time, and reduced the bond strength of the material.

[0206] Due to the lack of pH-responsive microcapsule catalysts, the composite material of Comparative Example 2 could not release catalysts to accelerate the curing reaction when contacting the alkaline concrete environment, resulting in a significant prolongation of the underwater curing time, a substantial decrease in the bond strength, and a deterioration of the anti-seepage performance.

[0207] Due to the too high content of fractal structure silane coupling agent, the crosslinking density was uneven, generating too many stress concentration points, causing the composite material of Comparative Example 3 to have microcracks inside after curing, significantly reducing the anti-seepage performance and bond strength of the material.

[0208] Since Comparative Example 4 used a common polyamide curing agent instead of a Mannich base-type curing agent, this common polyamide curing agent does not contain the active amine groups introduced by the Mannich reaction, so its reaction activity is significantly reduced in the underwater environment and it cannot effectively play the function of ion exchange to release amine groups, resulting in a slow curing rate and a low interfacial bond strength.

[0209] Due to the excessive content of the anti-seepage enhancer in the composite material of Comparative Example 5, the nano-silica aggregated in the system, forming a large number of microscopic interfacial defects, the curing reaction was uneven, the curing time was prolonged, and the bonding strength of the material was reduced.

[0210] During the preparation of the modified epoxy resin precursor of Comparative Example 6, the reactive diluent, toughening agent and surfactant were omitted, the water contact angle was 75°, and the wettability on the wet surface was only enhanced by about 8%; the initial curing time of the epoxy resin composite of Comparative Example 6 increased to 30 min, and the anti-chloride ion penetration performance became poor.

[0211] During the preparation of dopamine-modified nano-cellulose whiskers of Comparative Example 7, due to the lack of an alkaline environment and oxygen conditions, the oxidative polymerization reaction of dopamine was incomplete, and sufficient catechol functional groups could not be formed on the cellulose surface. The initial curing time of the epoxy resin composite of Comparative Example 7 was prolonged, the underwater bonding strength was reduced, and the anti-chloride ion penetration performance became poor.

[0212] The shell thickness of the pH-responsive microcapsules of Comparative Example 8 was too thick, the rupture rate decreased in an alkaline environment, and it was difficult to release the catalyst in time, which would lead to a significant prolongation of the curing time.

[0213] During the preparation of the Mannich base type curing agent of Comparative Example 9, the addition amounts of diaminodiphenylmethane and aldehyde group were insufficient, and the reaction temperature was relatively low, resulting in incomplete Mannich reaction and a low content of active amine groups in the curing agent; the initial curing time of the epoxy resin composite of Comparative Example 9 was prolonged, the underwater bonding strength was reduced, and the anti-chloride ion penetration performance became poor.

[0214] The fractal structure silane coupling agent of Comparative Example 10 was replaced by linear polyethyleneimine (non-branched type) instead of branched polyethyleneimine. Since the linear structure could not form a fractal interface transition layer similar to the root system of plants, interface stress concentration occurred, resulting in poor durability and poor anti-chloride ion penetration performance of the epoxy resin composite of this comparative example.

[0215] The silane coupling agent was omitted in the epoxy resin composite of Comparative Example 11, resulting in no gradient transition layer at the interface, thermal stress concentration, and a significant reduction in long-term durability and poor anti-chloride ion penetration performance.

[0216] In summary: By simulating the mussel adhesion mechanism with dopamine-modified nano-cellulose whiskers, the fractal structure silane coupling agent simulating the plant root system structure, and combining with the pH-responsive microcapsule catalyst, the present invention has successfully developed a self-catalytic epoxy resin composite material for underwater concrete repair. This material has excellent underwater bonding performance, rapid curing characteristics and anti-permeation performance, is particularly suitable for the repair of concrete structures in high-humidity environments such as the marine tidal zone, can realize the integration of underwater rapid construction and long-term protection, and has important engineering application value.

[0217] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. An underwater self-catalytic epoxy resin composite based on a bionic structure, characterized in that Comprising the following components in parts by weight: 40 - 60 parts of modified epoxy resin precursor, 3 - 8 parts of dopamine - modified nanocellulose whiskers, 1 - 5 parts of silane coupling agent, 15 - 30 parts of curing agent, 0.5 - 2 parts of microcapsule catalyst, and 5 - 10 parts of anti - permeability enhancer; The viscosity of the modified epoxy resin precursor at 25°C is 8000 - 15000 mPa·s, the epoxy value is 0.42 - 0.50 eq / 100g, and the water contact angle is 55° - 65°.

2. The underwater self-catalytic epoxy resin composite material based on the bionic structure according to claim 1, wherein, The modified epoxy resin precursor is prepared by a method comprising the following steps: I. Heat bisphenol A epoxy resin to melting; II. Add a reactive diluent and stir until uniform; III. Add a toughening agent and continue stirring; IV. Add an organosilicon modifier and stir; V. Add a surfactant and continue stirring; VI. Perform vacuum degassing to obtain the epoxy resin precursor; Preferably, in step II, the reactive diluent is dibutyl phthalate or phenylglycidyl ether; in step III, the toughening agent is polyethylene glycol with a molecular weight of 400 - 800; in step IV, the organosilicon modifier is an amino - containing polysiloxane; in step V, the surfactant is a polyether - modified silicone. More preferably, in step I, the epoxy value of bisphenol A epoxy resin is 0.48 - 0.52 eq / 100g, and the heating temperature is 70 - 80°C; in step II, the addition amount of the reactive diluent is 4wt% - 6wt%, and the stirring time is 30 - 40 min; in step III, the addition amount of the toughening agent is 4wt% - 5wt%, and the stirring time is 30 - 40 min; in step IV, the addition amount of the organosilicon modifier is 2wt% - 4wt%, the stirring temperature is 80 - 90°C, and the stirring time is 60 - 80 min; in step V, the addition amount of the surfactant is 1wt% - 2wt%, the stirring temperature is 80 - 90°C, and the stirring time is 30 - 50 min; in step VI, the vacuum degassing time is 45 - 60 min.

3. The underwater self-catalytic epoxy resin composite material based on the bionic structure according to claim 1, characterized in that, The dopamine - modified nanocellulose whiskers are prepared by a method comprising the following steps: B1. Disperse nanocellulose whiskers in Tris - HCl buffer solution and sonicate to obtain a uniformly dispersed solution; B2. Add dopamine hydrochloride to the dispersed solution and stir for 24 - 48 h in an oxygen atmosphere; B3. Centrifuge and freeze - dry the obtained solid to obtain the dopamine - modified nanocellulose whiskers; Preferably, the mass fraction of nanocellulose whiskers in the dispersed solution is 0.5wt% - 2wt%; In step B2, the mass ratio of dopamine hydrochloride to nanocellulose whiskers is 2:1 - 4:

1.

4. The underwater self-catalytic epoxy resin composite material based on the bionic structure according to claim 1, characterized in that, The microcapsule catalyst is a pH - responsive microcapsule catalyst, and the pH - responsive microcapsule catalyst is prepared by a method comprising the following steps: A1. Disperse zinc oxide nanoparticles in an organic solvent, add a polymer wall material, and stir evenly; A2. Prepare microcapsules by interfacial polymerization and control the cross - linking degree of the wall material; Preferably, the thickness of the shell layer of the pH-responsive microcapsule catalyst is 50-80 nm.

5. The underwater self-catalytic epoxy resin composite material based on the bionic structure according to claim 1, characterized in that, The silane coupling agent is a fractal structure silane coupling agent, and the fractal structure silane coupling agent is prepared by a method comprising the following steps: C1. Mix γ-glycidoxypropyltrimethoxysilane with branched polyethyleneimine, heat up and stir to react; C2. Add tetraethoxysilane to the reaction system and continue to react for 2-4 h; C3. Carry out vacuum distillation to obtain the fractal structure silane coupling agent.

6. The underwater self-catalytic epoxy resin composite material based on the bionic structure according to claim 5, wherein, In step C1, the molar ratio of γ-glycidoxypropyltrimethoxysilane to branched polyethyleneimine is 1:1-3:1; In step C2, the addition amount of tetraethoxysilane is 10 wt%-30 wt% of the total mass of γ-glycidoxypropyltrimethoxysilane and branched polyethyleneimine.

7. The underwater self-catalytic epoxy resin composite material based on the bionic structure according to claim 1, characterized in that, The curing agent is a Mannich base type curing agent, and the Mannich base type curing agent is prepared by a method comprising the following steps: D1. Mix bisphenol A epoxy resin and 4,4'-diaminodiphenylmethane in a molar ratio of 1:(2-3), and react at 80-100 °C for 2-4 h; D2. Add a benzaldehyde derivative to carry out a Mannich reaction, control the molar ratio of aldehyde group to amino group to be 1:(1.2-1.5), reaction temperature 110-130 °C, reaction time 3-6 h; D3. After washing with acetone and vacuum drying, an orange viscous liquid is obtained, which is the Mannich base type curing agent; Preferably, in step D1, the epoxy value of the bisphenol A epoxy resin is 0.45-0.55 eq / 100 g; In step D2, the benzaldehyde derivative is 4-hydroxybenzaldehyde and / or 3,5-dinitrobenzaldehyde.

8. The underwater self-catalytic epoxy resin composite material based on the bionic structure according to claim 1, characterized in that, The anti-seepage enhancer is a mixture of nano-silica and an organosilicon water repellent; Preferably, the mass ratio of the nano-silica to the organosilicon water repellent is (2-4):1; More preferably, the particle size of the nano-silica is 100-300 nm.

9. The preparation method of the underwater self-catalytic epoxy resin composite material based on the bionic structure according to any one of claims 1-8, characterized in that, Comprising the following steps: (1) Heat the modified epoxy resin precursor to 50-60 °C; (2) Add the Mannich base type curing agent and the fractal structure silane coupling agent in sequence, and stir to obtain a mixture; (3) Add dopamine-modified nano-cellulose whiskers and the pH-responsive microcapsule catalyst to the mixture, and perform ultrasonic dispersion; (4) Finally, add the anti-seepage enhancer, and after vacuum defoaming, the underwater self-catalytic epoxy resin composite material based on the bionic structure is obtained; Preferably, in step (2), the stirring speed is 800-1200 rpm, and the stirring time is 15-30 min; In step (3), the frequency of the ultrasound is 40 kHz, and the power density is 0.5 - 1.0 W / cm 3 , and the ultrasound time is 20 - 40 min.

10. Use of the underwater self-catalytic epoxy resin composite material based on the bionic structure according to any one of claims 1-8 in the repair of concrete structures in the marine tidal zone.

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