A biomimetic underwater self-catalytic epoxy resin composite material, its preparation method and application

Abstract

This invention belongs to the technical field of underwater concrete repair materials, specifically relating to an underwater self-catalytic epoxy resin composite material based on a biomimetic structure, its preparation method, and its application. The biomimetic underwater self-catalytic epoxy resin composite material of this invention comprises 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 reinforcing agent. This biomimetic underwater self-catalytic epoxy resin composite material mimics the adhesion mechanism in mussel byssal proteins, forming stable coordination bonds and hydrogen bonds in an underwater environment, significantly improving the material's wettability and interfacial bonding strength on damp substrate surfaces.

Description

Technical Field

[0001] This invention belongs to the technical field of underwater concrete repair materials, specifically relating to an underwater self-catalytic epoxy resin composite material based on a biomimetic structure, its preparation method, and its application. Background Technology

[0002] With the rapid development of marine development, a large number of concrete structures are exposed to the marine environment. Due to long-term exposure to seawater corrosion, wave impact, and biofouling, they are prone to cracking, spalling, and strength degradation. If these defects are not repaired in time, they will seriously affect the service life and safety of the structure. There is an urgent need for high-performance, rapid repair materials for the maintenance and emergency repair of marine and coastal structures such as seawalls and wharves, reservoirs and hydropower stations, bridges and culverts, sewage treatment facilities, subsea oil and gas pipelines, and underwater communication facilities. Currently, epoxy resins are mainly used for underwater concrete structure repair, but traditional epoxy resins face many challenges in underwater applications. The bonding strength of traditional epoxy resins on damp substrates decreases significantly, mainly because water molecules form a shielding layer at the interface, hindering effective contact and chemical bonding between the resin and the substrate. Although the wettability of the resin can be improved by adding surfactants, it is still difficult to achieve ideal interfacial bonding results. Meanwhile, in underwater environments, the curing reaction of epoxy resin is interfered with by water molecules, resulting in slow cross-linking network formation. It typically takes several hours or even longer to reach sufficient strength, making it difficult to meet the engineering requirements for rapid repair. In addition, traditional epoxy resins are prone to hydrolysis and degradation under long-term immersion conditions, especially in seawater environments containing large amounts of chloride ions, where their interfacial bonding strength and overall mechanical properties decrease significantly over time.

[0003] Therefore, there is an urgent need to develop a new type of epoxy resin composite material that combines excellent underwater adhesion, rapid curing properties, and long-term durability to meet the growing underwater repair needs in fields such as marine engineering and water conservancy projects.

[0004] Therefore, there is a need to provide an improved technical solution that addresses the shortcomings of the existing technology. Summary of the Invention

[0005] The purpose of this invention is to provide an underwater self-catalytic epoxy resin composite material based on a biomimetic structure, its preparation method, and its application, so as to help solve or improve at least one of the problems of poor underwater bonding performance, long curing time, and poor long-term durability of existing underwater concrete repair materials.

[0006] To achieve the above objectives, the present invention provides the following technical solution: an underwater self-catalytic epoxy resin composite material based on a biomimetic structure comprises 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 reinforcing agent; wherein 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 / 100g, and a water contact angle of 55°-65°.

[0007] The present invention also provides a method for preparing an underwater self-catalytic epoxy resin composite material based on a biomimetic structure, which adopts the following technical solution: the method for preparing an underwater self-catalytic epoxy resin composite material based on a biomimetic structure as described above includes the following steps: (1) heating the modified epoxy resin precursor to 50-60℃; (2) sequentially adding Mannich base-type curing agent and fractal structure silane coupling agent, and stirring to obtain a mixture; (3) adding dopamine-modified nanocellulose whiskers and pH-responsive microcapsule catalyst to the mixture, and ultrasonically dispersing; (4) finally adding an anti-permeability reinforcing agent, and obtaining the underwater self-catalytic epoxy resin composite material based on a biomimetic structure after vacuum degassing.

[0008] This invention also provides the application of the underwater self-catalytic epoxy resin composite material based on the biomimetic structure as described above, which adopts the following technical solution: the application of the underwater self-catalytic epoxy resin composite material based on the biomimetic structure as described above in the repair of concrete structures in marine tidal zones.

[0009] Beneficial effects:

[0010] In the biomimetic underwater self-catalytic epoxy resin composite material of this invention, the modified epoxy resin precursor helps to improve the spreadability of the epoxy resin under underwater slow setting and its wettability on wet substrates, laying the foundation for the mussel biomimetic adhesion mechanism. By introducing dopamine-modified nanocellulose whiskers, the catechol groups in dopamine simulate the adhesion mechanism in mussel byssal proteins, forming stable coordination bonds and hydrogen bonds in the underwater environment, which significantly improves the wettability and interfacial bonding strength of the material on the surface of wet substrates.

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

[0012] The biomimetic underwater autocatalytic epoxy resin composite material of this invention achieves rapid underwater curing through an autocatalytic system constructed using a Mannich basic curing agent and a pH-responsive microcapsule catalyst. Specifically, the Mannich basic curing agent releases active amine groups through ion exchange upon contact with seawater, while the pH-responsive microcapsules rupture under alkaline conditions to release nano-zinc oxide catalyst. The synergistic effect of these two components significantly improves curing efficiency.

[0013] The biomimetic underwater self-catalytic epoxy resin composite material of this invention exhibits excellent performance, achieving initial curing in 15 minutes under 95% humidity conditions, shortening the curing time by approximately 67% compared to traditional products; the underwater bond strength can reach up to 3.5 MPa, meeting the requirements of ASTM C882 standard; through the synergistic effect of anti-permeability reinforcing agents, the material's chloride ion permeability coefficient can be reduced to 1.2 × 10⁻⁶. -12 m 2 / s, with excellent durability, realizes the integration of rapid underwater construction and long-term protection. Detailed Implementation

[0014] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention are within the scope of protection of the present invention.

[0015] The present invention will now be described in detail with reference to embodiments. It should be noted that, unless otherwise specified, the embodiments and features described in the embodiments of the present invention can be combined with each other.

[0016] This invention addresses at least one of the problems of poor underwater adhesion, long curing time, and poor long-term durability in current underwater concrete repair materials, and provides an underwater self-catalytic epoxy resin composite material based on a biomimetic structure.

[0017] The inventors discovered that marine organisms, such as mussels, can achieve stable adhesion in humid environments, primarily due to the secretion of mucins with unique chemical structures. Simultaneously, the three-dimensional network structure formed by plant roots through fractal growth effectively enhances mechanical interlocking and stress transfer efficiency with the soil. Applying these biomimetic principles to the research of underwater repair materials, particularly in areas of rapid curing and long-term durability, could help solve or improve the aforementioned problems existing in current underwater concrete repair materials.

[0018] The underwater self-catalytic epoxy resin composite material based on a biomimetic structure according to embodiments of the present invention comprises the following components in parts by weight: 40-60 parts of modified epoxy resin precursor (e.g., 40, 45, 50, 55, or 60 parts), 3-8 parts of dopamine-modified nanocellulose whiskers (e.g., 3, 4, 5, 6, 7, or 8 parts), 1-5 parts of silane coupling agent (e.g., 1, 2, 3, 4, or 5 parts), and 15-3 parts of curing agent. 0 parts (e.g., 15, 20, 25 or 30 parts), 0.5-2 parts (e.g., 0.5, 1, 1.5 or 2 parts) of microencapsulated catalyst and 5-10 parts (e.g., 5, 6, 7, 8, 9 or 10 parts) of antipermeability 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 / 100g, and a water contact angle of 55°-65°.

[0019] In the biomimetic underwater self-catalytic epoxy resin composite material of this invention, the modified epoxy resin precursor helps to improve the spreadability of the epoxy resin under underwater slow setting and its wettability on wet substrates, laying the foundation for the mussel biomimetic adhesion mechanism. By introducing dopamine-modified nanocellulose whiskers, the catechol groups in dopamine simulate the adhesion mechanism in mussel byssal proteins, forming stable coordination bonds and hydrogen bonds in the underwater environment, which significantly improves the wettability and interfacial bonding strength of the material on the surface of wet substrates.

[0020] In a preferred embodiment of the biomimetic underwater self-catalytic epoxy resin composite material of the present invention, the modified epoxy resin precursor is prepared by a method comprising the following steps: I. heating bisphenol A type epoxy resin to melt; II. adding a reactive diluent and stirring until homogeneous; 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 spreadability of the epoxy resin in an underwater environment and its wetting ability on wet substrates can be significantly improved.

[0021] Preferably, in step II, the reactive diluent is dibutyl phthalate or anisole glycidyl ether; in step III, the toughening agent is polyethylene glycol with a molecular weight of 400-800 (e.g., 400, 500, 600, 700 or 800); in step IV, the organosilicon modifier is an amino-containing polysiloxane (e.g., γ-aminopropyltrimethoxysilane modified polydimethylsiloxane or commercially available Dow Corning Z-6020 amino-functionalized silane); and in step V, the surfactant is a polyether-modified organosilicon (e.g., 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 / 100g (e.g., 0.48 eq / 100g, 0.49 eq / 100g, 0.50 eq / 100g, 0.51 eq / 100g, or 0.52 eq / 100g), and the heating temperature is 70-80°C (e.g., 70°C, 75°C, or 80°C); in step II, the amount of the reactive diluent added is 4wt%-6wt% (e.g., 4wt%, 5wt%, or 6wt%), and the stirring time is 30-40 min (e.g., 30 min, 33 min, 36 min, or 40 min); in step III, the amount of the toughening agent added is 4wt%-5wt% (e.g., 4wt%, 5wt%, or 6wt%), and the stirring time is 30-40 min (e.g., 30 min, 33 min, 36 min, or 40 min). In step IV, the amount of silicone modifier added is 2wt%-4wt% (e.g., 2wt%, 3wt%, or 4wt%), the stirring temperature is 80-90℃ (e.g., 80℃, 85℃, or 90℃), and the stirring time is 60-80min (e.g., 60min, 65min, 70min, 75min, or 80min); in step V, the amount of surfactant added is 1wt%-2wt% (e.g., 1wt%, 1.5wt%, or 2wt%), the stirring temperature is 80-90℃ (e.g., 80℃, 85℃, or 90℃), and the stirring time is 30-50min (e.g., 30min, 35min, 40min, 45min, or 50min); in step VI, the vacuum degassing time is 45-60min (e.g., 45min, 50min, 55min, or 60min).

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

[0024] In a preferred embodiment of the biomimetic underwater self-catalytic epoxy resin composite material of the present invention, the mass fraction of nanocellulose whiskers in the dispersion is 0.5wt%-2wt% (e.g., 0.5wt%, 1wt%, 1.5wt%, or 2wt%).

[0025] In a preferred embodiment of the biomimetic underwater self-catalytic epoxy resin composite material of the present invention, in step B2, the mass ratio of dopamine hydrochloride to nanocellulose whiskers is 2:1-4:1 (e.g., 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 (e.g., 50, 60, 70, 80, 90, or 100), and a dopamine layer is grafted onto the surface via a controlled polymerization reaction, with a layer thickness of 20-50 nm (e.g., 20 nm, 30 nm, 40 nm, or 50 nm). From a mechanical property perspective, by selecting nanocellulose whiskers with a higher aspect ratio (in the range of 50-100), this invention facilitates the formation of a more effective three-dimensional network structure in the composite material, improving the material's mechanical strength and toughness; the long fibers can span more interfacial regions, enhancing the material's stress transfer capability. From an interfacial interaction perspective: the aspect ratio of the nanocellulose whiskers affects the contact area between the fibers and the epoxy resin matrix; in this invention, these fibers mimic the adhesion mechanism of mussel adhesive proteins, and nanofiber whiskers with a suitable aspect ratio can provide more catechol group exposure sites, enhancing adhesion at moist interfaces. Furthermore, an appropriate aspect ratio of the nanocellulose whiskers helps to form a uniform stress distribution during curing, avoiding microcracks caused by stress concentration. If the aspect ratio of nanocellulose whiskers is too high (above 100), it may cause the nanocellulose whiskers to be difficult to disperse uniformly in the matrix, forming agglomerates, which will reduce the material properties; if the aspect ratio of nanocellulose whiskers is too low (below 50), it will weaken the reinforcing and networking effect of nanocellulose whiskers.

[0027] If the thickness of the dopamine layer is too small (below 20 nm), the following adverse effects will occur: 1) Insufficient number of surface-active groups, resulting in a significant decrease in adhesion in humid environments; 2) Insufficient protection for nanocellulose, which may lead to reduced stability of the material in underwater environments; 3) Inability to effectively mimic the catechol structure of mussel byssal protein, resulting in poor biomimetic effect; 4) Insufficient interfacial bonding with the matrix, leading to a decrease in mechanical properties. If the thickness of the dopamine layer is too large (above 50 nm), then: 1) An excessively thick dopamine layer will reduce the mechanical interlocking effect between nanocellulose whiskers; 2) An excessively thick dopamine layer may hinder the reaction between the curing agent and epoxy resin, prolonging the curing time; 3) Self-crosslinking reaction may occur between dopamine layers, leading to brittleness and reduced toughness of the material; 4) Increased material viscosity, affecting construction fluidity and hindering underwater construction; 5) An excessively 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 biomimetic underwater self-catalytic epoxy resin composite material of the present invention, the microcapsule catalyst is a pH-responsive microcapsule catalyst, which is prepared by a method comprising the following steps: A1. Dispersing nano-zinc oxide in an organic solvent (e.g., cyclohexane), adding a polymer wall material (preferably polydopamine), and stirring until homogeneous; A2. Preparing microcapsules using interfacial polymerization, controlling the degree of crosslinking of the wall material. The pH-responsive microcapsules can rupture and release the nano-zinc oxide catalyst (nano-zinc oxide as the core material) under alkaline conditions, and can synergistically work with the Mannich basic curing agent to significantly improve curing efficiency.

[0029] Preferably, the shell thickness of the pH-responsive microcapsule catalyst is 55-85 nm (e.g., 55 nm, 65 nm, 75 nm, or 85 nm); it is stable in an aqueous solution at pH 7.0 for 36-72 h (e.g., 36 h, 46 h, 56 h, 66 h, or 72 h) without rupture, and more than 85% of the microcapsules rupture and release the nano zinc oxide catalyst within 35-50 min (e.g., 35 min, 40 min, 45 min, or 50 min) in an aqueous solution at pH 11.0-11.8 (e.g., 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 hexadecyltrimethylammonium bromide as a dispersant; sonicating it using an ultrasonic probe to form a stable nano zinc oxide dispersion; adding dopamine hydrochloride under nitrogen protection and immediately adding Tris-HCl buffer (pH=8.5); and slowly adding pentaerythritol glycidyl ether as a crosslinking agent under mechanical stirring.

[0031] Step A2 includes: transferring the above dispersion system to a three-necked flask and introducing oxygen while stirring; controlling the reaction temperature to allow dopamine to self-polymerize under oxidative conditions; adding polyvinyl alcohol (PVA) solution as a stabilizer when the color of the reaction solution changes from transparent to dark brown; continuing stirring to allow the polydopamine shell to fully form; monitoring the pH value of the reaction system with a pH meter, and when it reaches 7.9-8.6, it indicates that the shell formation is complete; collecting the microcapsules by centrifugation; washing them sequentially with deionized water, ethanol, and acetone; and vacuum drying to obtain the pH-responsive microcapsule catalyst.

[0032] More preferably, in step A1, the mass ratio of nano-zinc oxide, hexadecyltrimethylammonium 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 (e.g., 24°C, 27°C, 30°C, or 32°C), and the self-polymerization reaction time is 4.5-6 h (e.g., 4.5 h, 5 h, 5.5 h, or 6 h); polyethylene The mass concentration of the alcohol solution is 1.2%-2% (e.g., 1.2%, 1.4%, 1.6%, 1.8%, or 2%), and the stirring time after adding the polyvinyl alcohol solution is 2.5-4 hours (e.g., 2.5 hours, 3 hours, 3.5 hours, or 4 hours); the vacuum drying temperature is 40-50°C (e.g., 40°C, 43°C, 46°C, 48°C, or 50°C), and the vacuum drying time is 14-18 hours (e.g., 14 hours, 15 hours, 16 hours, 17 hours, or 18 hours).

[0033] In a preferred embodiment of the biomimetic underwater self-catalytic epoxy resin composite material of the present invention, the thickness of the shell layer of the pH-responsive microcapsule catalyst is 50-80 nm (e.g., 50 nm, 60 nm, 70 nm, or 80 nm). If 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 biomimetic underwater self-catalytic epoxy resin composite material of the present invention, the silane coupling agent is a fractal structure silane coupling agent, which is prepared by a method comprising the following steps: C1. Mixing γ-glycidyl ether propyltrimethoxysilane with branched polyethyleneimine, heating to 100-120°C (e.g., 100°C, 105°C, 110°C, 115°C or 120°C) and stirring for 2-4 h (e.g., 2 h, 2.5 h, 3 h, 3.5 h or 4 h); C2. Adding tetraethoxysilane to the reaction system and continuing the reaction at 90-110°C (e.g., 90°C, 95°C, 100°C, 105°C or 110°C) for 2-4 h (e.g., 2 h, 2.5 h, 3 h, 3.5 h or 4 h); C3. Vacuum distillation to obtain the fractal structure silane coupling agent. The fractal structure silane coupling agent, by mimicking the branching growth of plant roots, forms a gradient modulus transition layer at the interface, effectively alleviating thermal stress concentration and further enhancing the stability of the interfacial bonding. γ-glycidyl ether propyltrimethoxysilane plays the following key roles in this invention: 1) it provides epoxy groups, enabling it to form covalent chemical bonds with the epoxy resin matrix; 2) it contains silane groups, allowing it to form siloxane bonds with the surface of inorganic substrates (such as concrete); 3) it acts as a bridging molecule, connecting the organic phase (epoxy resin) and the inorganic phase (concrete substrate); 4) in an aqueous environment, the methoxy group can hydrolyze to form silanol groups, enhancing the interfacial bonding force of wet substrates. Tetraethoxysilane plays the following key roles in this invention: 1) It provides additional crosslinking points, increasing the branching degree and network complexity of the fractal structure; 2) It forms a silicon-oxygen skeleton structure, enhancing the overall mechanical properties; 3) It adjusts the stiffness and elastic modulus of the interface layer, forming a gradient transition zone; after hydrolysis, it forms a silicon-oxygen network, enhancing the water resistance and impermeability of the material; 4) It promotes the formation of "fractal" structures, simulating the branching growth pattern 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 a fractal silane coupling agent. The elastic modulus of this region gradually transitions from the substrate towards the matrix, rather than the abrupt change at traditional interfaces. Specifically, the gradient modulus transition layer refers to a structure that extends from the concrete substrate surface towards the epoxy resin matrix, with a gradually changing elastic modulus distribution, avoiding abrupt modulus changes at traditional interfaces. This gradient structure is similar to the bonding between plant roots and soil, effectively dispersing stress, reducing stress concentration caused by differences in thermal expansion coefficients, and improving interfacial 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 interfacial stability of the material under temperature changes and humid conditions.

[0036] Preferably, the branching degree of the branched polyethyleneimine is 2.5-4.0 (e.g., 2.5, 3.0, 3.5, or 4.0). The fractal 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 interfacial transition effect will be insignificant; if the branching degree is too high, it will reduce molecular mobility and affect curing.

[0037] In a preferred embodiment of the biomimetic underwater self-catalytic epoxy resin composite material of the present invention, in step C1, the molar ratio of the epoxy resin to the branched polyethyleneimine is 1:1-3:1 (e.g., 1:1, 1.5:1, 2:1, 2.5:1 or 3:1); in step C2, the amount of tetraethoxysilane added is 10wt%-30wt% (e.g., 10wt%, 15wt%, 20wt%, 25wt% or 30wt%) of the sum of the masses of γ-glycidyl etherpropyltrimethoxysilane and branched polyethyleneimine. If the amount of γ-glycidyl ether propyltrimethoxysilane is too large (molar ratio > 3:1), then: 1) Excessive epoxy groups will lead to uneven cross-linking network structure and the formation of local high cross-linking density regions; 2) It will increase the brittleness of the material and reduce its toughness and impact resistance; 3) Too many unreacted silane groups may be over-hydrolyzed in the aqueous environment, resulting in unstable interfacial layer structure; 4) It will inhibit the formation of fractal structure and weaken the gradient modulus characteristics of the interfacial transition layer; 5) Excessive silane may cause excessive shrinkage during the curing process, generating internal stress and reducing interfacial bonding strength. If the amount of γ-glycidyl ether propyltrimethoxysilane is too small (molar ratio <1:1), then: 1) it cannot provide enough epoxy groups to form effective crosslinks with the epoxy resin matrix; 2) the fractal structure is not developed sufficiently, making it difficult to form an ideal root system simulation structure; 3) there are insufficient bonding sites with the concrete substrate, resulting in a decrease in interfacial bonding strength; 4) it leads to a decrease in the durability of the material in the water environment, and the interface is more susceptible to water molecule erosion; 5) the gradient modulus transition layer is not fully formed, and it cannot effectively alleviate thermal stress.

[0038] If the amount of tetraethoxysilane added is too high (>30%), then: 1) an over-crosslinked rigid network will be formed, reducing the material's toughness and interfacial flexibility; 2) the proportion of inorganic phase may be too high, reducing compatibility with the organic phase (epoxy resin); 3) excessive hydrolysis products will be produced, causing microstructural defects in the material; 4) the curing shrinkage rate will increase, generating greater internal stress, which may lead to the formation of microcracks; 5) excessive silicon-oxygen networks will restrict the growth direction of fractal structures and affect the formation of gradient transition layers. If the amount of tetraethoxysilane added is too low (<10%), then: 1) the branching degree of the fractal structure is insufficient, failing to simulate the complex branching structure of plant roots; 2) the gradient transition layer will not form completely, resulting in poor stress dispersion; 3) the impermeability will decrease, failing to form a sufficiently dense silicon-oxygen network; 4) the hydrolytic stability will decrease, and the interfacial performance will degrade rapidly after long-term immersion in water; 5) the problem of thermal stress concentration cannot be effectively alleviated, leading to unstable interfacial bonding strength with temperature changes.

[0039] In a preferred embodiment of the biomimetic underwater self-catalytic epoxy resin composite material of the present invention, the curing agent is a Mannich base type curing agent, which is prepared by a method comprising the following steps: D1. Bisphenol A epoxy resin and 4,4'-diaminodiphenylmethane are mixed at a molar ratio of 1:(2-3) (e.g., 1:2, 1:2.3, 1:2.6, 1:2.8 or 1:3), and reacted at 80-100°C (e.g., 80°C, 85°C, 90°C, 95°C or 100°C) for 2-4 hours (e.g., 2 hours, 2 hours, 2 hours). D2. Add benzaldehyde derivative to carry out the Mannich reaction, controlling the molar ratio of aldehyde group to amino group to be 1:(1.2-1.5) (e.g., 1:1.2, 1:1.3, 1:1.4 or 1:1.5), reaction temperature 110-130℃ (e.g., 110℃, 115℃, 120℃, 125℃ or 130℃), reaction time 3-6h (e.g., 3h, 4h, 5h or 6h); D3. After washing with acetone and vacuum drying, an orange viscous liquid is obtained, which is the Mannich base type curing agent. If the amount of 4,4'-diaminodiphenylmethane is too large (molar ratio > 3:1), then: 1) Excessive amine groups cannot fully participate in the reaction, and residual free amine will cause "amine precipitation" after the material is cured; 2) The water resistance of the final product will be reduced because free amine is easily soluble in water; 3) Excessive amine will cause the curing agent viscosity to be too high, affecting the construction performance; 4) The curing system will be too alkaline, which will destroy the pH-responsive microcapsule wall layer, causing the catalyst to be released prematurely; 5) The impermeability and durability of the final material will be reduced. If the amount of 4,4'-diaminodiphenylmethane is too small (molar ratio < 2:1), then: 1) The number of amines is insufficient, resulting in insufficient Mannich reaction sites; 2) The activity of the curing agent will be reduced, and the underwater curing speed will be slow; 3) Sufficient cross-linking network cannot be formed, resulting in insufficient material strength; 4) The ion exchange capacity in the water environment is weak, making it difficult to release active amine groups; 5) The mechanical properties and bonding strength of the final composite material will decrease.

[0040] If the reaction temperature in step D1 is too high (>100℃), then: 1) it easily causes epoxy resin self-polymerization, affecting the subsequent Mannich reaction; 2) side reactions occur at high temperatures, generating products that are not conducive to underwater curing; 3) it may lead to amine oxidation, reducing the activity of the curing agent; 4) the product color deepens, affecting the aesthetics of the final material. If the reaction temperature in step D1 is too low (<80℃), 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 fully formed, resulting in poor performance of the subsequent Mannich reaction.

[0041] If the reaction time in step D1 is too long (>4h), then: 1) energy consumption and production costs will increase; 2) the product may be over-crosslinked, resulting in excessively high viscosity; 3) high-temperature and long-term reaction may lead to amine oxidative degradation; 4) byproducts that are detrimental to underwater curing may be formed. If the reaction time in step D1 is too short (<2h), the adverse effects are: 1) incomplete reaction and insufficient prepolymer formation; 2) more unreacted components, affecting the quality stability of the curing agent; 3) insufficient preparation of substrate for subsequent Mannich reaction, affecting reaction efficiency; 4) insufficient activity of the final curing agent, affecting the underwater curing speed.

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

[0043] If the reaction temperature in step D2 is too high (>130℃), then: 1) it may cause thermal decomposition of the reactants, reducing product quality; 2) it will generate more side reactions and byproducts, affecting the purity of the curing agent; 3) the product color will darken at high temperatures, and it may even carbonize; 4) energy consumption will increase, and the requirements for equipment will be higher. If the reaction temperature in step D2 is too low (<110℃), 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 curing agent has low activity and is difficult to cure quickly in an underwater environment; 4) the final product performance is unstable, and there are large batch-to-batch differences.

[0044] If the reaction time in step D2 is too long (>6h), then: 1) the reactants may degrade, affecting the structure of the curing agent; 2) prolonged high temperature may lead to excessive cross-linking, resulting in a wide molecular weight distribution of the product; 3) energy consumption and cost will increase, and production efficiency will decrease; 4) it may increase the burden on equipment and pose safety hazards. If the reaction time in step D2 is too short (<3h), then: 1) the Mannich reaction will be incomplete, and the active sites will not be sufficiently formed; 2) the curing agent structure will be incomplete, and its performance will be unstable; 3) the ion exchange and catalytic capacity in the underwater environment will be weak; 4) the curing time of the final composite material will be prolonged, failing to meet the requirements for rapid repair; 5) the underwater bonding strength and durability will not meet the standards.

[0045] In a preferred embodiment of the biomimetic underwater self-catalytic epoxy resin composite material of the present invention, in step D1, the epoxy value of the bisphenol A epoxy resin is 0.45-0.55 eq / 100g (e.g., 0.45 eq / 100g, 0.48 eq / 100g, 0.5 eq / 100g, 0.52 eq / 100g, or 0.55 eq / 100g); in step D2, the benzaldehyde derivative is 4-hydroxybenzaldehyde and / or 3,5-dinitrobenzaldehyde. The bisphenol A epoxy resin introduces active amine groups 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 will be detrimental to improving water solubility.

[0046] The biomimetic underwater self-catalytic epoxy resin composite material of the present invention uses a self-catalytic system constructed with Mannich base-type curing agent and pH-responsive microcapsule catalyst to achieve rapid curing in the underwater environment through ion exchange and pH-responsive catalyst release.

[0047] In a preferred embodiment of the biomimetic underwater self-catalytic epoxy resin composite material of the present invention, the impermeability reinforcing agent is a mixture of nano-silica and organosilicon hydrophobic agent. The nano-silica of the impermeability reinforcing agent fills the network micropores, while the organosilicon hydrophobic agent forms a hydrophobic layer on the pore walls. The two work synergistically to significantly improve the impermeability and durability of the material.

[0048] In a preferred embodiment of the biomimetic underwater self-catalytic epoxy resin composite material of the present invention, the mass ratio of nano-silica to organosilicon hydrophobic agent is (2-4):1 (e.g., 2:1, 3:1, or 4:1). The organosilicon hydrophobic agent 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 (e.g., 100 nm, 150 nm, 200 nm, 250 nm, or 300 nm). If the particle size of the nano-silica is too small, it will negatively impact the filling effect; if the particle size is too large, it will affect the dispersibility.

[0050] This invention also proposes a method for preparing an underwater self-catalytic epoxy resin composite material based on a biomimetic structure. The method for preparing the underwater self-catalytic epoxy resin composite material based on a biomimetic structure according to the embodiments of this invention includes the following steps: (1) heating the epoxy resin precursor to 50-60℃ (e.g., 50℃, 52℃, 54℃, 56℃, 58℃ or 60℃); (2) sequentially adding Mannich base-type curing agent and fractal structure silane coupling agent, and stirring to obtain a mixture; (3) adding dopamine-modified nanocellulose whiskers and pH-responsive microcapsule catalyst to the mixture, and ultrasonically dispersing; (4) finally adding an anti-permeability reinforcing agent, and obtaining the underwater self-catalytic epoxy resin composite material based on a biomimetic structure after vacuum degassing.The steps in the preparation method of the underwater self-catalytic epoxy resin composite material based on the biomimetic structure of the present invention are designed to: (1) help ensure uniform dispersion (the correct order of materials can ensure uniform dispersion of each component in the epoxy resin matrix. If high viscosity or easily agglomerated components, such as nanocellulose whiskers, are added first, it will lead to difficulty in dispersion and the formation of an uneven structure; uneven dispersion will cause unstable material properties, insufficient strength in local areas, and reduced overall underwater bonding strength); (2) help ensure the stability of pH-responsive microcapsules (pH-responsive microcapsules must be added at an appropriate stage to avoid premature rupture under high shear stress conditions; if added at the beginning of high-speed stirring, the pH-responsive microcapsules will be added later; if added later ... Adding it at the last stage may damage the microcapsules, cause premature release of the catalyst, and lead to premature curing of the material; if added as the last component, it may not be fully dispersed, affecting the curing uniformity); (3) It will also affect the reaction kinetics (Mannich base type curing agent should be fully mixed with epoxy resin first to form a uniform base system; fractal structure silane coupling agent should be added after the base system is formed to ensure that it can correctly form the interface transition layer; reversing the order will lead to incomplete crosslinking network formation, affecting the curing rate and final mechanical properties); (4) It also affects the temperature control (the heating temperature of 50-60℃ is to reduce the viscosity of epoxy resin, which is beneficial to the subsequent components). The mixing of components; if all components are stirred for a long time at this temperature, the curing reaction may start prematurely; therefore, components should be added in order of stability from high to low, and the processing time of each stage should be controlled); (5) It also affects the timing of ultrasound (dopamine-modified nanocellulose whiskers need to be dispersed by ultrasound to break the agglomerates, but excessive ultrasound will damage the microcapsules; adding both at the same time and treating with appropriate ultrasound is a balanced solution; if this order is changed, for example, treating the nanocellulose whiskers with ultrasound first and then adding the microcapsules, although it may improve the dispersibility of nanocellulose, it will increase the complexity of the process and the production time); (6) The antipermeability reinforcing agent needs to be added last. The components (nano silica has a high specific surface area. If it is added too early, it will adsorb other components and affect its function. As the last component added, it can fill the micropores in the already formed network structure and maximize the impermeability. 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. (After all components are added and mixed, vacuum degassing can remove the bubbles introduced during the processing to the maximum extent. If degassing is carried out in the middle step, the effect may be poor due to the introduction of bubbles again in the subsequent processing. The presence of bubbles will become a defect point of the material, significantly reducing the underwater bonding strength and impermeability).

[0051] In a preferred embodiment of the preparation method of the underwater self-catalytic epoxy resin composite material based on the biomimetic structure of the present invention, in step (2), the stirring speed is 800-1200 rpm (e.g., 800 rpm, 900 rpm, 1000 rpm, 1100 rpm or 1200 rpm), and the stirring time is 15-30 min (e.g., 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 / cm². 3 (For example, 0.5W / cm) 3 0.6W / cm 3 0.7W / cm 3 0.8W / cm 3 0.9W / cm 3 Or 1.0W / cm 3 The ultrasound time is 20-40 min (e.g., 20 min, 25 min, 30 min, 35 min or 40 min). In step (2), the selection of stirring speed and stirring time helps to: (1) initiate the pre-reaction: during the stirring process, the Mannich base curing agent and the epoxy resin precursor begin to react pre-react and form a preliminary cross-linked network structure; a specific stirring rate provides appropriate shear force to promote the uniform reaction between the fractal structure silane coupling agent and the epoxy group; (2) optimize the interface structure: under appropriate stirring conditions, the fractal structure silane coupling agent can form an ideal fractal structure, which is crucial for the formation of the subsequent gradient modulus transition layer; too low a stirring speed (<800 rpm) will make it difficult for the coupling agent to fully unfold the fractal structure; too high a stirring speed (>1200 rpm) will destroy the orderly formation of the fractal structure and even produce excessive shear; (3) control the viscosity of the system: a precisely controlled stirring time (15-30 min) can achieve the best rheological properties of the matrix system and create conditions for the addition of subsequent components; too short a stirring time will result in uneven viscosity of the system; too long a stirring time may lead to pre-curing.

[0052] The selection of ultrasonic treatment parameters in step (3) helps to: (1) Nanostructure reconstruction: Ultrasonic energy causes the three-dimensional configuration of dopamine-modified nanocellulose whiskers to reorganize and unfold their molecular chains; this reconstruction is crucial for simulating the catechol structure of mussel foot silk protein and directly affects the underwater adhesion mechanism; (2) Uniform positioning of catalytic microcapsules: Appropriate ultrasonic energy can break the aggregation of pH-responsive microcapsules without destroying the capsule structure; under ultrasonic action, microcapsules can be uniformly 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 solidification reaction; (3) Interface 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 interface bonding strength of the final material; if the ultrasonic power density is too low (<0.5W / cm), the reaction will be more effective. 3 It is difficult to achieve the activation effect; too high (>1.0W / cm) 3 This may damage the molecular structure; Nanoscale dispersion network construction: Ultrasonic treatment is not only a physical dispersion, but also a key process for constructing specific nanoscale network structures; The formed network structure simulates the spatial arrangement of mussel byssal proteins, significantly improving underwater adhesion performance; If the ultrasonic time is too short (<20min), the network structure will be incomplete; If it is too long (>40min), the network may be too dense, limiting the subsequent curing reaction.

[0053] This invention also proposes an application of an underwater self-catalytic epoxy resin composite material based on a biomimetic structure, as described above, in the repair of concrete structures in marine tidal zones. The underwater self-catalytic epoxy resin composite material based on a biomimetic structure of this invention is particularly suitable for the repair of wet interface concrete in marine tidal zones and wharf pile foundations, achieving integrated rapid underwater construction and long-term protection.

[0054] The following detailed description of the biomimetic underwater self-catalytic epoxy resin composite material, its preparation method, and its application are illustrated through specific embodiments.

[0055] The sources of the main raw materials used in the following examples are as follows: Bisphenol A epoxy resin: Nan Ya Epoxy Resin Co., Ltd., model E-51, epoxy value 0.48-0.54 eq / 100g; Nanocellulose whiskers: Prepared by the Institute of Chemistry, Chinese Academy of Sciences, aspect ratio 50-100; Dopamine hydrochloride: Sigma-Aldrich, purity ≥98%; γ-glycidyl ether propyltrimethoxysilane: Dow Corning, purity ≥97%; Branched polyethyleneimine: Sigma-Aldrich, molecular weight 25000; Tetraethoxysilane: Sinopharm Chemical Reagent Co., Ltd., analytical grade. Pure; 4,4'-Diaminodiphenylmethane: BASF, purity ≥99%; 4-Hydroxybenzaldehyde: Aladdin Reagents, purity ≥99%; 3,5-Dinitrobenzaldehyde: Aladdin Reagents, purity ≥98%; Nano zinc oxide: Advans Nanomaterials Technology Co., Ltd., average particle size 50-80 nm; Nano silica: Cabot Corporation, 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 material based on biomimetic structure in this embodiment includes the following components by weight: 40 parts modified epoxy resin precursor, 3 parts dopamine-modified nanocellulose whiskers, 1 part fractal structure silane coupling agent, 15 parts Mannich base type curing agent, 0.5 parts pH-responsive microcapsule catalyst, and 5 parts anti-permeability reinforcing agent.

[0058] The modified epoxy resin precursor was prepared by the following steps: I. Bisphenol A type epoxy resin (epoxy value 0.48 eq / 100g) was heated to 70°C to fully melt it; II. 4% by mass of reactive diluent (dibutyl phthalate) was added and stirred for 30 min until homogeneous; III. 3% by mass of polyethylene glycol (molecular weight 400) was added as a toughening agent and stirred for another 30 min; IV. 2% by mass of organosilicon modifier (amino-containing polysiloxane - Dow Corning Z-6020 amino-functionalized silane) was added and stirred at 80°C for 60 min; V. Finally, 1% by mass of surfactant (polyether-modified organosilicon - Dow Corning DC-57 surfactant) was added and stirred at 80°C for another 30 min; VI. Vacuum degassing was performed for 45 min to obtain the modified epoxy resin precursor. The modified epoxy resin precursor exhibits the following characteristics: a viscosity of 12000-15000 mPa·s at 25°C, an epoxy value of 0.42-0.46 eq / 100g, a water contact angle of 65° (significantly lower than the 80° of ordinary epoxy resin), and an approximately 25% increase in wetness to damp surfaces. The modification process, through the introduction of hydrophilic groups and adjustment of the system's surface energy, significantly improves the epoxy resin's spreadability in underwater environments and its wettability to damp substrates, laying the foundation for the subsequent application of a mussel-inspired biomimetic adhesion mechanism.

[0059] The pH-responsive microcapsule catalyst was prepared using a method comprising the following steps:

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

[0061] A2. Microcapsules were prepared by interfacial polymerization, with the polydopamine shell thickness controlled at 50 nm: The above dispersion system was transferred to a three-necked flask, and oxygen was introduced while stirring at 600 rpm; the reaction temperature was controlled at 25 ± 2 °C, and the reaction time was 4 hours, allowing dopamine to self-polymerize under oxidative conditions; when the color of the reaction solution changed from transparent to dark brown, 10 mL of 1% polyvinyl alcohol (PVA) solution was added as a stabilizer; stirring was continued for 2 hours to allow the polydopamine shell to fully form; the pH value of the reaction system was monitored using a pH meter, and when it reached 8.0 ± 0.2, the pH was determined. The shell layer was formed; microcapsules were collected by centrifugation (5000 rpm, 10 minutes); washed three times sequentially with deionized water, ethanol, and acetone; and vacuum dried at 40℃ for 12 hours to obtain the final product; the shell layer thickness was measured by transmission electron microscopy (TEM) and controlled within the range of 50±5 nm; the prepared microcapsules were subjected to pH responsiveness testing: they remained stable for 24 hours without rupture in an aqueous solution with pH=7.0, and more than 95% of the microcapsules ruptured within 30 minutes in an aqueous solution with pH=12.0, releasing nano-zinc oxide catalyst, which meets the triggering requirements of the alkaline environment of underwater concrete.

[0062] Dopamine-modified cellulose nanofibers were prepared by the following steps: B1. Cellulose nanofibers (mass fraction 0.5%, aspect ratio 55) were dispersed in Tris-HCl buffer (pH = 8.5) and sonicated for 20 minutes to obtain a uniform dispersion; B2. Dopamine hydrochloride (mass concentration 1%) was added to the dispersion, with a mass ratio of dopamine hydrochloride to cellulose nanofibers of 2:1, and the mixture was stirred for 24 hours under continuous oxygen purging; B3. The mixture was centrifuged (8000 rpm, 15 minutes) to obtain a black precipitate, washed three times with deionized water, and freeze-dried for 48 hours to obtain dopamine-modified cellulose nanofibers (dopamine layer thickness 25 nm).

[0063] The fractal structure silane coupling agent was prepared by the following steps: C1. γ-glycidyl ether propyltrimethoxysilane and branched polyethyleneimine (molar ratio 1:1) were mixed, heated to 75°C and stirred for 1 h; C2. Tetraethoxysilane (10% of the total mass of γ-glycidyl ether propyltrimethoxysilane and branched polyethyleneimine) was added to the reaction system, and the reaction was continued at 75°C for 2 h; C3. Small molecule byproducts were removed by vacuum distillation to obtain an amber-colored transparent liquid fractal structure silane coupling agent.

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

[0065] The antipermeability reinforcing agent is prepared by the following steps: 150 nm nano-silica and methyltrimethoxysilane (CH3Si(OCH3)3) organosilicon hydrophobic agent are mixed at a mass ratio of 3:1, stirred evenly in anhydrous ethanol, and then vacuum dried to obtain the antipermeability reinforcing agent.

[0066] The preparation method of the underwater self-catalytic epoxy resin composite material based on the biomimetic structure in this embodiment includes the following steps:

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

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

[0069] (3) Add dopamine-modified nanocellulose whiskers and pH-responsive microcapsule catalyst to the mixture, and run at 40 kHz and a power density of 0.5 W / cm². 3 Disperse under ultrasonic conditions for 20 minutes;

[0070] (4) Finally, add the anti-permeability reinforcing agent and vacuum degas for 15 minutes to obtain the underwater self-catalytic epoxy resin composite material based on the biomimetic structure of this embodiment.

[0071] Example 2

[0072] The underwater self-catalytic epoxy resin composite material based on biomimetic structure in this embodiment includes the following components by weight: 50 parts modified epoxy resin precursor, 5 parts dopamine-modified nanocellulose whiskers, 3 parts fractal structure silane coupling agent, 22 parts Mannich base type curing agent, 1 part pH-responsive microcapsule catalyst, and 7 parts anti-permeability reinforcing agent.

[0073] The modified epoxy resin precursor was prepared by the following steps: I. Bisphenol A type epoxy resin (epoxy value 0.50 eq / 100g) was heated to 75°C to fully melt it; II. 5% by mass of reactive diluent (dibutyl phthalate) was added and stirred for 35 min until homogeneous; III. 4% by mass of polyethylene glycol (molecular weight 600) was added as a toughening agent and stirred for another 35 min; IV. 3% by mass of organosilicon modifier (amino-containing polysiloxane - Dow Corning Z-6020 amino-functionalized silane) was added and stirred at 85°C for 70 min; V. Finally, 1.5% by mass of surfactant (polyether-modified organosilicon - Dow Corning DC-57 surfactant) was added and stirred at 85°C for another 40 min; VI. Vacuum degassing was performed for 50 min to obtain the modified epoxy resin precursor. The modified epoxy resin precursor has the following characteristics: a viscosity of 10000-12000 mPa·s at 25℃, an epoxy value of 0.44-0.48 eq / 100g, a water contact angle of 60° (significantly lower than the 80° of ordinary epoxy resin), and an increase in wettability to damp surfaces of approximately 30%. The modification process, by adjusting the content of the organosilicon modifier and the molecular weight of the toughening agent, further improves the flexibility and interfacial compatibility of the epoxy resin, enabling it to exhibit superior wetting and adhesion properties in humid environments.

[0074] pH-responsive microcapsule catalysts were prepared using a method comprising the following steps:

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

[0076] A2. Microcapsules were prepared by interfacial polymerization, with the polydopamine shell thickness controlled at 65 nm: The above dispersion system was transferred to a three-necked flask, and oxygen was introduced while stirring at 700 rpm; the reaction temperature was controlled at 28 ± 2 °C, and the reaction time was 5 hours, allowing dopamine to self-polymerize under oxidative conditions; when the color of the reaction solution changed from transparent to dark brown, 15 mL of 1.5% polyvinyl alcohol (PVA) solution was added as a stabilizer; the pH value of the reaction system was monitored using a pH meter, and when it reached 8.2 ± 0.2, it indicated that the shell formation was complete; Microcapsules were collected by centrifugation (6000 rpm, 15 minutes); washed four times sequentially with deionized water, ethanol, and acetone; and vacuum dried at 45°C for 15 hours to obtain the final product. The shell thickness was measured by transmission electron microscopy (TEM) and controlled within the range of 65 ± 5 nm. The prepared microcapsules were subjected to pH responsiveness testing: they remained stable for 48 hours without rupture in an aqueous solution with pH = 7.0, and more than 90% of the microcapsules ruptured within 40 minutes in an aqueous solution with pH = 11.5, releasing the nano-zinc oxide catalyst, which meets the triggering requirements of the alkaline environment of underwater concrete.

[0077] Dopamine-modified cellulose nanofibers were prepared by the following steps: B1. Cellulose nanofibers (mass fraction 1.0%, aspect ratio 70) were dispersed in Tris-HCl buffer (pH = 8.5) and sonicated for 25 minutes to obtain a uniform dispersion; B2. Dopamine hydrochloride (mass concentration 2%) was added to the dispersion, with a mass ratio of dopamine hydrochloride to cellulose nanofibers of 3:1, and the mixture was stirred for 36 hours under continuous oxygen purging; B3. The mixture was centrifuged (10,000 rpm, 20 minutes) to obtain a black precipitate, washed four times with deionized water, and freeze-dried for 60 hours to obtain dopamine-modified cellulose nanofibers (dopamine layer thickness 35 nm).

[0078] The fractal structure silane coupling agent was prepared by the following steps: C1. γ-glycidyl ether propyltrimethoxysilane was mixed with branched polyethyleneimine (molar ratio 2:1), heated to 80°C and stirred for 1.5 h; C2. Tetraethoxysilane (20% of the total mass) was added to the reaction system and the reaction was continued for 3 h; C3. Small molecule byproducts were removed by vacuum distillation to obtain an amber transparent liquid fractal structure silane coupling agent.

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

[0080] The antipermeability reinforcing agent is prepared by the following steps: 200 nm nano-silica and methyltrimethoxysilane (CH3Si(OCH3)3) organosilicon hydrophobic agent are mixed at a mass ratio of 3:1, stirred evenly in anhydrous ethanol, and then vacuum dried to obtain the antipermeability reinforcing agent.

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

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

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

[0084] (3) Add dopamine-modified cellulose nanofibers and pH-responsive microcapsule catalyst to the mixture, and run at 40 kHz and a power density of 0.7 W / cm². 3 Disperse under ultrasonic conditions for 30 minutes;

[0085] (4) Finally, add the impermeability reinforcing agent (nano silica with a particle size of 200nm and organosilicon hydrophobic agent are compounded in a mass ratio of 3:1), and after vacuum degassing for 20 minutes, the underwater self-catalytic epoxy resin composite material based on the biomimetic structure of this embodiment is obtained.

[0086] Example 3

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

[0088] The modified epoxy resin precursor was prepared by the following steps: I. Bisphenol A type epoxy resin (epoxy value 0.52 eq / 100g) was heated to 80°C to fully melt it; II. 6% by mass of reactive diluent (anisole glycidyl ether) was added and stirred for 40 min until homogeneous; III. 5% by mass of polyethylene glycol (molecular weight 800) was added as a toughening agent and stirred for another 40 min; IV. 4% by mass of organosilicon modifier (amino-containing polysiloxane - Dow Corning Z-6020 amino-functionalized silane) was added and stirred at 90°C for 80 min; V. Finally, 2% by mass of surfactant (polyether-modified organosilicon - Dow Corning DC-57 surfactant) was added and stirred at 90°C for another 50 min; VI. Vacuum degassing was performed for 60 min to obtain the modified epoxy resin precursor. The modified epoxy resin precursor has the following characteristics: a viscosity of 8000-10000 mPa·s at 25°C, an epoxy value of 0.46-0.50 eq / 100g, a water contact angle of 55° (significantly lower than the 80° of ordinary epoxy resin), and an increase in wetness to damp surfaces of approximately 35%. The modification process utilizes a higher molecular weight toughening agent and a larger proportion of organosilicon modifiers, significantly improving the hydrophilicity and flexibility of the epoxy resin, enabling it to exhibit optimal interfacial adaptability and adhesion in underwater environments.

[0089] pH-responsive microcapsule catalysts were prepared using a method comprising the following steps:

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

[0091] A2. Microcapsules were prepared by interfacial polymerization, with the polydopamine shell thickness controlled at 80 nm: The above dispersion system was transferred to a three-necked flask, and oxygen was introduced while stirring at 800 rpm; the reaction temperature was controlled at 30 ± 2 °C, and the reaction time was 6 hours, allowing dopamine to self-polymerize under oxidative conditions; when the color of the reaction solution changed from transparent to dark brown, 20 mL of 2% (w / w) polyvinyl alcohol (PVA) solution was added as a stabilizer; stirring was continued for 4 hours to allow the polydopamine shell to fully form; the pH value of the reaction system was monitored using a pH meter, and when it reached 8.4 ± 0.2, the pH was determined. The shell layer was formed; microcapsules were collected by centrifugation (8000 rpm, 20 minutes); washed five times sequentially with deionized water, ethanol, and acetone; and vacuum dried at 50°C for 18 hours to obtain the final product; the shell layer thickness was measured by transmission electron microscopy (TEM) and controlled within the range of 80±5 nm; the prepared microcapsules were subjected to pH responsiveness testing: they remained stable for 72 hours without rupture in an aqueous solution with pH=7.0, and more than 85% of the microcapsules ruptured within 50 minutes in an aqueous solution with pH=11.0, releasing nano-zinc oxide catalyst, which meets the triggering requirements of the alkaline environment of underwater concrete.

[0092] Dopamine-modified cellulose nanofibers were prepared by the following steps: B1. Cellulose nanofibers (2.0% by mass) were dispersed in Tris-HCl buffer (pH=8.5) and sonicated for 30 minutes to obtain a uniform dispersion; B2. Dopamine hydrochloride (3% by mass) was added to the dispersion, with a mass ratio of dopamine hydrochloride to cellulose nanofibers (aspect ratio of 95) of 4:1, and the mixture was stirred for 48 hours under continuous oxygen purging; B3. The mixture was centrifuged (12000 rpm, 25 minutes) to obtain a black precipitate, washed 5 times with deionized water, and freeze-dried for 72 hours to obtain dopamine-modified cellulose nanofibers (dopamine layer thickness of 45 nm).

[0093] The fractal structure silane coupling agent was prepared by the following steps: C1. γ-glycidyl ether propyltrimethoxysilane and branched polyethyleneimine (molar ratio 3:1) were mixed, heated to 85°C and stirred for 2 h; C2. Tetraethoxysilane (30% of the total mass of the mixture of γ-glycidyl ether propyltrimethoxysilane and branched polyethyleneimine) was added to the reaction system, and the reaction was continued at 85°C for 4 h; C3. Small molecule byproducts were removed by vacuum distillation to obtain an amber-colored transparent liquid fractal structure silane coupling agent.

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

[0095] The antipermeability reinforcing agent is prepared by the following steps: 300 nm nano-silica and methyltrimethoxysilane (CH3Si(OCH3)3) organosilicon hydrophobic agent are mixed at a mass ratio of 3:1, stirred evenly in anhydrous ethanol, and then vacuum dried to obtain the antipermeability reinforcing agent.

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

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

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

[0099] (3) Add dopamine-modified nanocellulose whiskers and pH-responsive microcapsule catalyst to the mixture, and run at 40 kHz and a power density of 1.0 W / cm². 3 Under the condition of ultrasonic dispersion for 40 min;

[0100] (4) Finally, add the anti-permeability reinforcing agent and vacuum degas for 30 minutes to obtain the underwater self-catalytic epoxy resin composite material based on the biomimetic structure of this embodiment.

[0101] Example 4

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

[0103] The modified epoxy resin precursor was prepared by the following steps: I. Bisphenol A type epoxy resin (epoxy value 0.49 eq / 100g) was heated to 72°C to fully melt it; II. 4.5% by mass of reactive diluent (dibutyl phthalate) was added and stirred for 32 min until homogeneous; III. 3.5% by mass of polyethylene glycol (molecular weight 500) was added as a toughening agent and stirred for another 32 min; IV. 2.5% by mass of organosilicon modifier (amino-containing polysiloxane - Dow Corning Z-6020 amino-functionalized silane) was added and stirred at 82°C for 65 min; V. Finally, 1.2% by mass of surfactant (polyether-modified organosilicon - Dow Corning DC-57 surfactant) was added and stirred at 82°C for another 35 min; VI. Vacuum degassing was performed for 48 min to obtain the modified epoxy resin precursor. The modified epoxy resin precursor has the following characteristics: a viscosity of 11000-13000 mPa·s at 25℃, an epoxy value of 0.43-0.47 eq / 100g, a water contact angle of 62° (significantly lower than the 80° of ordinary epoxy resin), and an increase in wettability to damp surfaces of approximately 27%. The modification process, through the introduction of appropriate amounts of organosilicon modifiers and surfactants, balances the hydrophilicity and mechanical properties of the material, enabling it to exhibit excellent wetting and adhesion properties in underwater environments.

[0104] pH-responsive microcapsule catalysts were prepared using a method comprising the following steps:

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

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

[0107] Dopamine-modified cellulose nanofibers were prepared by the following steps: B1. Cellulose nanofibers (mass fraction 0.8%, aspect ratio 65) were dispersed in Tris-HCl buffer (pH = 8.5) and sonicated for 22 minutes to obtain a uniform dispersion; B2. Dopamine hydrochloride (mass concentration 1.5%) was added to the dispersion, with a mass ratio of dopamine hydrochloride to cellulose nanofibers of 2.5:1, and the mixture was stirred for 30 hours under continuous oxygen purging; B3. The mixture was centrifuged (9000 rpm, 18 minutes) to obtain a black precipitate, washed four times with deionized water, and freeze-dried for 54 hours to obtain dopamine-modified cellulose nanofibers (dopamine layer thickness 30 nm).

[0108] The fractal structure silane coupling agent was prepared by the following steps: C1. γ-glycidyl ether propyltrimethoxysilane was mixed with branched polyethyleneimine (molar ratio 1.5:1), heated to 78°C and stirred 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 byproducts were removed by vacuum distillation to obtain an amber transparent liquid fractal structure silane coupling agent.

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

[0110] The antipermeability reinforcing agent is prepared by the following steps: 180 nm nano-silica and methyltrimethoxysilane (CH3Si(OCH3)3) organosilicon hydrophobic agent are mixed at a mass ratio of 3:1, stirred evenly in anhydrous ethanol, and then vacuum dried to obtain the antipermeability reinforcing agent.

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

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

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

[0114] (3) Add dopamine-modified nanocellulose whiskers and pH-responsive microcapsule catalyst to the mixture, and run at 40 kHz and a power density of 0.6 W / cm². 3 Disperse under ultrasonic conditions for 25 minutes;

[0115] (4) Finally, add the impermeability reinforcing agent (nano silica with a particle size of 180nm and organosilicon hydrophobic agent are compounded in a mass ratio of 3:1), and after vacuum degassing for 18 minutes, the underwater self-catalytic epoxy resin composite material based on the biomimetic structure of this embodiment is obtained.

[0116] Example 5

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

[0118] The modified epoxy resin precursor was prepared by the following steps: I. Bisphenol A type epoxy resin (epoxy value 0.51 eq / 100g) was heated to 78°C to fully melt it; II. 5.5% by mass of reactive diluent (anisole glycidyl ether) was added and stirred for 38 min until homogeneous; III. 4.5% by mass of polyethylene glycol (molecular weight 700) was added as a toughening agent and stirred for another 38 min; IV. 3.5% by mass of organosilicon modifier (amino-containing polysiloxane - Dow Corning Z-6020 amino-functionalized silane) was added and stirred at 88°C for 75 min; V. Finally, 1.8% by mass of surfactant (polyether-modified organosilicon - Dow Corning DC-57 surfactant) was added and stirred at 88°C for another 45 min; VI. Vacuum degassing was performed for 55 min to obtain the modified epoxy resin precursor. The modified epoxy resin precursor has the following characteristics: a viscosity of 9000-11000 mPa·s at 25℃, an epoxy value of 0.45-0.49 eq / 100g, a water contact angle of 58° (significantly lower than the 80° of ordinary epoxy resin), and an increase in wetness to damp surfaces of approximately 32%. The modification process, by adjusting the ratio of organosilicon modifier and toughening agent, optimized the material's flowability and interfacial compatibility in underwater environments, enabling it to exhibit excellent spreadability and adhesion under high humidity conditions.

[0119] pH-responsive microcapsule catalysts were prepared using a method comprising the following steps:

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

[0121] A2. Microcapsules were prepared by interfacial polymerization, with the polydopamine shell thickness controlled at 70 nm: The above dispersion system was transferred to a three-necked flask, and oxygen was introduced while stirring at 750 rpm; the reaction temperature was controlled at 29±2℃, and the reaction time was 5.5 hours, allowing 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% (w / w) polyvinyl alcohol (PVA) solution was added as a stabilizer; stirring was continued for 3.5 hours to allow the polydopamine shell to fully form; the pH value of the reaction system was monitored using a pH meter, and when it reached 8.3±0.2... The shell formation was complete when the time was reached; the microcapsules were collected by centrifugation (7000 rpm, 18 minutes); they were washed four times sequentially with deionized water, ethanol, and acetone; and the final product was obtained by vacuum drying at 48°C for 16 hours; the shell 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 remained stable for 60 hours without rupture in an aqueous solution with pH=7.0, and more than 88% of the microcapsules ruptured and released the nano-zinc oxide catalyst within 45 minutes in an aqueous solution with pH=11.2, which meets the triggering requirements of the alkaline environment of underwater concrete.

[0122] Dopamine-modified cellulose nanofibers were prepared by the following steps: B1. Cellulose nanofibers (mass fraction 1.5%, aspect ratio 85) were dispersed in Tris-HCl buffer (pH = 8.5) and sonicated for 28 minutes to obtain a uniform dispersion; B2. Dopamine hydrochloride (mass concentration 2.5%) was added to the dispersion, with a mass ratio of dopamine hydrochloride to cellulose nanofibers of 3.5:1, and the mixture was stirred for 42 hours under continuous oxygen purging; B3. The mixture was centrifuged (11000 rpm, 22 minutes) to obtain a black precipitate, washed four times with deionized water, and freeze-dried for 66 hours to obtain dopamine-modified cellulose nanofibers (dopamine layer thickness 40 nm).

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

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

[0125] The antipermeability reinforcing agent is prepared by the following steps: 250 nm nano-silica and methyltrimethoxysilane-based organosilicon hydrophobic agent are mixed at a mass ratio of 3:1, stirred evenly in anhydrous ethanol, and then vacuum dried to obtain the antipermeability reinforcing agent.

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

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

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

[0129] (3) Add dopamine-modified nanocellulose whiskers and pH-responsive microcapsule catalyst to the mixture, and run at 40 kHz and a power density of 0.8 W / cm². 3 Disperse under ultrasonic conditions for 35 minutes;

[0130] (4) Finally, add the impermeability reinforcing agent (250nm nano-silica and methyltrimethoxysilane (CH3Si(OCH3)3) organosilicon hydrophobic agent in a mass ratio of 3:1), and after vacuum degassing for 25 minutes, the underwater self-catalytic epoxy resin composite material based on the biomimetic structure of this embodiment is obtained.

[0131] Example 6

[0132] The underwater self-catalytic epoxy resin composite material based on the biomimetic structure in this embodiment differs from that in Example 1 only in the following aspects: 1) The aspect ratio of the nanocellulose whiskers used in the preparation of the dopamine-modified nanocellulose whiskers in this embodiment is 50, and the thickness of the dopamine-modified layer is 20 nm; 2) In the preparation 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 of the anti-permeability reinforcing agent is 100 nm; all other aspects are consistent with those in Example 1.

[0133] Example 7

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

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

[0136] The dopamine-modified cellulose nanofiber whiskers of this embodiment were prepared by the following steps: B1. Cellulose nanofiber whiskers (mass fraction 1.2%, aspect ratio 75) were dispersed in Tris-HCl buffer (pH = 8.5) and sonicated for 25 minutes to obtain a uniform dispersion; B2. Dopamine hydrochloride (mass concentration 2.2%) was added to the dispersion, with a mass ratio of dopamine hydrochloride to cellulose nanofiber whiskers of 3:1, and stirred for 36 hours under continuous oxygen purging at room temperature (25°C); B3. The mixture was centrifuged (10000 rpm, 20 minutes) to obtain a black precipitate, washed four times with deionized water, and freeze-dried for 60 hours to obtain dopamine-modified cellulose nanofiber whiskers (dopamine layer thickness 35 nm).

[0137] The fractal structure silane coupling agent was prepared by the following steps: C1. γ-glycidyl ether propyltrimethoxysilane was mixed with branched polyethyleneimine (molar ratio 2:1), heated to 110°C and stirred for 3 h; C2. Tetraethoxysilane (20% of the total mass) was added to the reaction system and the reaction was continued at 100°C for 3 h; C3. Small molecule byproducts were removed by vacuum distillation to obtain an amber transparent liquid fractal structure silane coupling agent.

[0138] The Mannich basic curing agent was prepared by the following steps: D1. Bisphenol A epoxy resin (epoxy value 0.50 eq / 100g) was mixed with 4,4'-diaminodiphenylmethane at a molar ratio of 1:2.5 and reacted at 90℃ for 3h; D2. 3,5-dinitrobenzaldehyde (aldehyde to amino molar ratio of 1:1.35) was added to carry out the Mannich reaction at 120℃ for 4.5h; D3. After washing with acetone and vacuum drying, an orange viscous liquid Mannich basic curing agent was obtained.

[0139] The preparation method of the underwater self-catalytic epoxy resin composite material based on the biomimetic 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 biomimetic structure in this embodiment differs from that in Example 3 only in the following aspects: 1) The aspect ratio of the nanocellulose whiskers used in the preparation of the dopamine-modified nanocellulose whiskers in this embodiment is 100, and the thickness of the dopamine modification layer is 50 nm; 2) In the preparation 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 consistent with Example 1.

[0142] Example 9 (Water-repellent agent variant example)

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

[0144] The difference between the impermeability reinforcing agent in this embodiment and that in Example 1 is that the mass ratio of nano-silica to organic hydrophobic agent is 2:1, while the rest are the same as in Example 1.

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

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

[0147] Example 10 (Variant Example of a Water-Repellent Agent)

[0148] The only difference between the biomimetic underwater self-catalytic epoxy resin composite material of this embodiment and that of Example 9 is that the mass ratio of nano-silica to organosilicon hydrophobic agent used in the preparation of the impermeability reinforcing agent is 4:1; all other aspects are the same as those of Example 9.

[0149] Example 11 (Example of a variant of a fractal silane coupling agent)

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

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

[0152] In this embodiment, the other components except for the fractal structure silane coupling agent and the preparation method of the underwater self-catalytic epoxy resin composite material based on the biomimetic structure are the same as in Example 7.

[0153] Example 12 (Example of a variant of a fractal silane coupling agent)

[0154] The difference between the biomimetic underwater self-catalytic epoxy resin composite material of this embodiment and that of Example 11 is that: in the preparation process of the fractal structure silane coupling agent, the amount of tetraethoxysilane used is 25% of the total mass of γ-glycidyl ether propyltrimethoxysilane and branched polyethyleneimine; the rest are consistent with Example 11.

[0155] Comparative Example 1

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

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

[0158] Comparative Example 2

[0159] The epoxy resin composite material of this comparative example, by weight, includes 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-type curing agent, and 7 parts of anti-permeability reinforcing agent.

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

[0161] Comparative Example 3

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

[0163] The preparation methods of the above components and the composite material of 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, includes the following components: 50 parts modified epoxy resin precursor, 5 parts dopamine-modified nanocellulose whiskers, 3 parts fractal structure silane coupling agent, 22 parts ordinary polyamide curing agent (non-Mannich base type), 1 part pH-responsive microcapsule catalyst, and 7 parts impermeability reinforcing agent.

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

[0167] The aforementioned common polyamide curing agent is prepared by reacting dimer acid with polyethylene polyamine: 70 parts by weight of dimer acid (C36 dicarboxylic acid, content 95%), 30 parts by weight of polyethylene polyamine mixture (main components are diethylenetriamine and triethylenetetramine) and 0.5 parts by weight of catalyst (triphenylphosphine) are reacted at 170°C for 5 hours, and then the water generated in the reaction is removed under reduced pressure to obtain the common polyamide curing agent of this comparative example.

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

[0169] Comparative Example 5

[0170] The composite material components provided in this comparative example are, by weight, 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-type curing agent, 1 part of pH-responsive microcapsule catalyst, and 15 parts of impermeability reinforcing agent.

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

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

[0173] The only difference between this comparative example and Example 2 is that the preparation method of the modified epoxy resin precursor is different from that in Example 2, while all other aspects are the same as in Example 2.

[0174] The preparation method of the modified epoxy resin precursor in this comparative example is as follows: I. Heating bisphenol A type epoxy resin (epoxy value 0.50 eq / 100g) to 75℃ to fully melt it; II. Directly adding 5% by mass of organosilicon modifier (amino-containing polysiloxane) and stirring at 75℃ for 60 min; III. Vacuum degassing for 30 min to obtain the modified epoxy resin precursor.

[0175] This modified epoxy resin precursor contains no reactive diluents, toughening agents, or surfactants, has a water contact angle of 75°, and only enhances wettability on damp surfaces by approximately 8%.

[0176] Comparative Example 7 (Changing the preparation conditions of dopamine-modified cellulose nanofibers)

[0177] The only difference between this comparative example and Example 2 is that the preparation method of dopamine-modified nanocellulose whiskers is different from that in Example 2; all other aspects are consistent with Example 2.

[0178] The specific preparation method of dopamine-modified nanocellulose whiskers is as follows: B1. Disperse nanocellulose whiskers (mass fraction of 1.0%) in phosphate buffer solution with pH=7.0 and sonicate for 25 minutes; B2. Add dopamine hydrochloride (mass concentration of 2%) to the dispersion, with a mass ratio of dopamine hydrochloride to nanocellulose whiskers of 3:1, and stir at room temperature for 36 hours (without oxygen introduction); B3. Centrifuge (10000 rpm, 20 minutes) to obtain a light gray precipitate, wash with deionized water 4 times, and freeze-dry for 60 hours to obtain dopamine-modified nanocellulose whiskers.

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

[0180] The only difference between this comparative example and Example 2 is that the preparation method of the pH-responsive microcapsule catalyst is different from that in Example 2; all other aspects are consistent with Example 2.

[0181] Specifically, the preparation method of the pH-responsive microcapsule catalyst in this comparative example differs from that in Example 2 in that the reaction time was extended to 8 hours during the interfacial polymerization process, resulting in a polydopamine shell thickness of 120 nm.

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

[0183] The only difference between this comparative example and Example 2 is that the preparation method of the Mannich alkaline curing agent is different; all other aspects are the same as in Example 2.

[0184] The preparation method of the Mannich base-type curing agent in this comparative example is as follows:

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

[0186] D2. Add 3,5-dinitrobenzaldehyde (the molar ratio of aldehyde to amino groups is 1:0.8, which is lower than the range of 1:1.2-1.5 in the claims) to carry out the Mannich reaction at a reaction temperature of 100°C (lower than 110°C) for 2 hours.

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

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

[0189] The only difference between this comparative example and Example 2 is that the fractal silane coupling agent is replaced with linear polyethyleneimine (non-branched) instead of branched polyethyleneimine; all other aspects are consistent with Example 2.

[0190] The preparation method of the fractal structure silane coupling agent in this comparative example is as follows: C1. Mix γ-glycidyl ether propyltrimethoxysilane with linear polyethyleneimine (molar ratio 2:1), heat to 80℃ and stir for 1.5h; C2. Add tetraethoxysilane (accounting for 20% of the total mass) to the reaction system and continue to react at 80℃ for 3h; C3. Remove small molecule byproducts by vacuum distillation to obtain the linear structure silane coupling agent.

[0191] Comparative Example 11 (without using any fractal silane coupling agent)

[0192] The only difference between this comparative example and Example 2 is that, by weight, it includes the following components: 53 parts modified epoxy resin precursor, 5 parts dopamine-modified nanocellulose whiskers, 22 parts Mannich base-type curing agent, 1 part pH-responsive microcapsule catalyst, and 7 parts antipermeability enhancer, without the addition of fractal structure silane coupling agent; all other components are consistent with Example 2.

[0193] Experimental Example

[0194] The initial curing time, underwater bond strength, and chloride ion permeation resistance of the composite materials of the above embodiments and comparative examples were tested:

[0195] Test method:

[0196] The initial curing time was determined using a modified method of ASTM C191 standard, including the following steps: (1) Coating the composite material onto a glass plate to form a uniform coating with a thickness of 2 mm; (2) Placing the sample in a constant temperature and humidity chamber with a relative humidity of 95 ± 2% and controlling the temperature at 23 ± 2℃; (3) Using a Vicat needle (1 mm in diameter and 300 g in weight), vertically inserting it into the sample surface at fixed time intervals (2 min for the initial stage and 1 min for the later stage); (4) Recording the time when the needle tip cannot penetrate 2 mm into the sample surface as the initial curing time; (5) Testing each sample 3 times and taking the average value as the final result.

[0197] The underwater bond strength was determined using the ASTM C882 / C882M standard method: (1) Prepare concrete test blocks with dimensions of 100mm×100mm×50mm and a surface saturated water content of 95±3%; (2) Apply the composite material uniformly to the contact surface of the two concrete test blocks, with the coating thickness controlled at 2±0.2mm; (3) Press the two test blocks coated with the composite material together underwater (depth 10cm, temperature 20±2℃) and apply a pressure of 0.05MPa; (4) After underwater curing for 24h, perform shear strength testing using a universal testing machine at a loading rate of 2mm / min; (5) Record the maximum load at shear failure and divide it by the bond area to calculate the bond strength; (6) Test 5 sets of samples for each material, remove the highest and lowest values ​​and take the average value as the final result; (7) Perform long-term underwater immersion tests (28 days and 90 days, respectively) on the samples of Examples 2 and 3 to evaluate durability.

[0198] The chloride ion permeability coefficient was tested using a combination of ASTM C1202 and NT Build 492 standards: (1) A disc sample with a diameter of 100 mm and a thickness of 50 mm was prepared using composite materials; (2) The sample was cured for 7 days at a temperature of 23±2℃ and a relative humidity of 50±5%; (3) The sample was placed in a two-chamber electromigration device, with the cathode chamber filled with 0.3 mol / L NaOH solution and the anode chamber filled with 3% NaCl solution; (4) A DC voltage of 30 V was applied, and the test time was 6 hours; (5) After the test, the sample was disconnected and sprayed with 0.1 mol / L AgNO3 solution for color development, and the chloride ion migration depth was measured; (6) The chloride ion diffusion coefficient was calculated according to the unsteady-state 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 the experimental constant (determined according to the calibration test), and t is the test time (s); (7) Three samples of each material were tested, and the average value was taken as the final result; (8) The samples of Examples 1-3 were additionally subjected to seawater cyclic immersion-drying (each cycle includes 3 days of immersion and 4 days of drying) for 30 cycles to test the chloride ion penetration resistance performance in order to evaluate the long-term durability.

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

[0200] Table 1

[0201]

[0202]

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

[0204] The chloride ion permeability resistance coefficients of the biomimetic underwater self-catalytic epoxy resin composite materials in Examples 1-3 after 30 cycles were 2.3 × 10⁻⁶. -12 m 2 / s, 1.8×10 -12 m 2 / s, 1.4×10 -12 m 2 / s, increasing by 28%, 20%, and 17% respectively; in addition, the bonding strength of the biomimetic underwater self-catalytic epoxy resin composites of Examples 2 and 3 after underwater immersion was tested: the underwater bonding strength of the biomimetic underwater self-catalytic epoxy resin composite of Example 2 was 3.0 MPa after 28 days (retention rate 94%) and 2.8 MPa after 90 days (retention rate 88%); the underwater bonding strength of the biomimetic underwater self-catalytic epoxy resin composite of Example 3 was 3.3 MPa after 28 days (retention rate 94%) and 3.1 MPa after 90 days (retention rate 89%). The biomimetic underwater self-catalytic epoxy resin composite of the present invention has a short initial curing time, high underwater bonding strength, good resistance to chloride ion penetration, and good durability.

[0205] The composite material in Comparative Example 1 exhibited excessively high viscosity and poor workability. Furthermore, due to the excessively high content of dopamine-modified nanocellulose whiskers, an overly dense network structure was formed within the system, which hindered the cross-linking reaction, prolonged the curing time, and reduced the bonding strength of the material.

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

[0207] The excessively high content of fractal structure silane coupling agent resulted in uneven crosslinking density and excessive stress concentration points. This caused microcracks to exist inside the composite material of Comparative Example 3 after curing, which significantly reduced the material's impermeability and bonding strength.

[0208] Because Comparative Example 4 used a common polyamide curing agent instead of the Mannich basic curing agent, the common polyamide curing agent does not contain the active amine groups introduced by the Mannich reaction. Therefore, its reactivity is significantly reduced in the underwater environment, and it cannot effectively exert the function of releasing amine groups through ion exchange, resulting in a slow curing rate and low interfacial bonding strength.

[0209] Because the impermeability reinforcing agent content in the composite material of Comparative Example 5 was too high, nano-silica agglomerated in the system, forming a large number of micro-interface defects, resulting in uneven curing reaction, prolonged curing time, and reduced bonding strength of the material.

[0210] In the preparation of the modified epoxy resin precursor of Comparative Example 6, reactive diluents, toughening agents and surfactants were omitted, the water contact angle was 75°, and the wettability to wet surfaces was only enhanced by about 8%; the initial curing time of the epoxy resin composite material of Comparative Example 6 increased to 30 min, and the resistance to chloride ion penetration deteriorated.

[0211] In the preparation of dopamine-modified nanocellulose whiskers in Comparative Example 7, the oxidative polymerization reaction of dopamine was incomplete due to the lack of an alkaline environment and oxygen conditions, resulting in insufficient formation of catechol functional groups on the cellulose surface. Consequently, the initial curing time of the epoxy resin composite material in Comparative Example 7 was prolonged, its underwater bonding strength decreased, and its resistance to chloride ion penetration deteriorated.

[0212] The pH-responsive microcapsules in Comparative Example 8 had an excessively thick shell, which reduced their rupture rate in an alkaline environment, making it difficult to release the catalyst in a timely manner and resulting in a significantly prolonged curing time.

[0213] In the preparation of the Mannich alkaline curing agent of Comparative Example 9, the amount of diaminodiphenylmethane and aldehyde group added was insufficient, and the reaction temperature was low, resulting in incomplete Mannich reaction and low content of active amine groups in the curing agent. The epoxy resin composite material of Comparative Example 9 had prolonged initial curing time, reduced underwater bonding strength, and poor resistance to chloride ion penetration.

[0214] In Comparative Example 10, the fractal structure silane coupling agent used linear polyethyleneimine (non-branched) instead of branched polyethyleneimine. Since the linear structure could not form a fractal interface transition layer similar to plant roots, the interface stress was concentrated, which reduced the durability and resistance to chloride ion penetration of the epoxy resin composite material in this comparative example.

[0215] The omission of silane coupling agent in the epoxy resin composite material of Comparative Example 11 resulted in the absence of a gradient transition layer at the interface, thermal stress concentration, significantly reduced long-term durability, and poorer resistance to chloride ion penetration.

[0216] In summary, this invention successfully developed a self-catalytic epoxy resin composite material for underwater concrete repair by using dopamine-modified nanocellulose whiskers to simulate mussel adhesion, fractal silane coupling agents to mimic plant root structures, and combining them with a pH-responsive microcapsule catalyst. This material exhibits excellent underwater adhesion, rapid curing characteristics, and impermeability, making it particularly suitable for concrete structure repair in high-humidity environments such as marine tidal zones. It enables integrated rapid underwater construction and long-term protection, demonstrating significant engineering application value.

[0217] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. An underwater self-catalytic epoxy resin composite material based on a biomimetic structure, characterized in that, The components include the following 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 reinforcing agent; 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 / 100g, and a water contact angle of 55°-65°. The modified epoxy resin precursor was prepared by a method comprising the following steps: I. Heat the bisphenol A type epoxy resin until it melts; II. Add the reactive diluent and stir until homogeneous; III. Add toughening agent and continue stirring; IV. Add the organosilicon modifier and stir; V. Add surfactant and continue stirring; VI. Vacuum degassing yields the epoxy resin precursor; In step II, the reactive diluent is dibutyl phthalate or anisole glycidyl 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 organosilicon.

2. The underwater self-catalytic epoxy resin composite material based on a biomimetic structure as described in claim 1, characterized in that, In step I, the epoxy value of the bisphenol A type epoxy resin is 0.48-0.52 eq / 100g, and the heating temperature is 70-80℃; in step II, the amount of the reactive diluent added is 4wt%-6wt%, and the stirring time is 30-40min; in step III, the amount of the toughening agent added is 4wt%-5wt%, and the stirring time is 30-40min; in step IV, the amount of the organosilicon modifier added is 2wt%-4wt%, the stirring temperature is 80-90℃, and the stirring time is 60-80min; in step V, the amount of the surfactant added is 1wt%-2wt%, the stirring temperature is 80-90℃, and the stirring time is 30-50min; in step VI, the vacuum degassing time is 45-60min.

3. The underwater self-catalytic epoxy resin composite material based on a biomimetic structure as described in claim 1, characterized in that, The dopamine-modified cellulose nanofibers were prepared by a method comprising the following steps: B1. Disperse cellulose nanofibers in Tris-HCl buffer solution and sonicate to obtain a uniform dispersion; B2. Add dopamine hydrochloride to the dispersion and stir for 24-48 h under an oxygen atmosphere; B3. Centrifuge and freeze-dry the resulting solid to obtain the dopamine-modified cellulose nanofiber whiskers.

4. The underwater self-catalytic epoxy resin composite material based on a biomimetic structure as described in claim 3, characterized in that, The mass fraction of nanocellulose whiskers in the dispersion is 0.5wt%-2wt%. In step B2, the mass ratio of the dopamine hydrochloride to the nanocellulose whiskers is 2:1-4:

1.

5. The underwater self-catalytic epoxy resin composite material based on a biomimetic structure as described in claim 1, characterized in that, The microcapsule catalyst is a pH-responsive microcapsule catalyst, which is prepared by a method including the following steps: A1. Disperse nano zinc oxide in an organic solvent, add polymer wall material, and stir until homogeneous; A2. Microcapsules were prepared using interfacial polymerization, and the degree of crosslinking of the wall material was controlled. The thickness of the shell of the pH-responsive microcapsule catalyst is 50-80 nm.

6. The underwater self-catalytic epoxy resin composite material based on a biomimetic structure as described in claim 1, characterized in that, The silane coupling agent is a fractal structure silane coupling agent, which is prepared by a method including the following steps: C1. Mix γ-glycidyl ether propyltrimethoxysilane with branched polyethyleneimine, heat and stir to react; C2. Add tetraethoxysilane to the reaction system and continue the reaction for 2-4 hours; C3. Vacuum distillation yields a fractal silane coupling agent.

7. The underwater self-catalytic epoxy resin composite material based on a biomimetic structure as described in claim 6, characterized in that, In step C1, the molar ratio of γ-glycidyl ether propyltrimethoxysilane to branched polyethyleneimine is 1:1 to 3:

1. In step C2, the amount of tetraethoxysilane added is 10wt%-30wt% of the total mass of γ-glycidyl ether propyltrimethoxysilane and branched polyethyleneimine.

8. The underwater self-catalytic epoxy resin composite material based on a biomimetic structure as described in claim 1, characterized in that, The curing agent is a Mannich basic curing agent, which is prepared by a method including the following steps: D1. Mix bisphenol A epoxy resin with 4,4'-diaminodiphenylmethane at a molar ratio of 1:(2-3) and react at 80-100℃ for 2-4 hours; D2. Add benzaldehyde derivative to carry out Mannich reaction, control the molar ratio of aldehyde group to amino group to be 1:(1.2-1.5), reaction temperature 110-130℃, reaction time 3-6h; D3. After washing with acetone and vacuum drying, an orange viscous liquid is obtained, which is the Mannich base-type curing agent.

9. The underwater self-catalytic epoxy resin composite material based on a biomimetic structure as described in claim 8, characterized in that, In step D1, the epoxy value of the bisphenol A epoxy resin is 0.45-0.55 eq / 100g; In step D2, the benzaldehyde derivative is 4-hydroxybenzaldehyde and / or 3,5-dinitrobenzaldehyde.

10. The underwater self-catalytic epoxy resin composite material based on a biomimetic structure as described in claim 1, characterized in that, The impermeability enhancement agent is a mixture of nano-silica and organosilicon hydrophobic agent; The mass ratio of the nano-silica to the organosilicon hydrophobic agent is (2-4):1; The particle size of the nano-silica is 100-300 nm.

11. The method for preparing underwater self-catalytic epoxy resin composite material based on biomimetic structure as described in any one of claims 1-10, characterized in that, Includes the following steps: (1) Heat the modified epoxy resin precursor to 50-60℃; (2) Add Mannich base-type curing agent and fractal structure silane coupling agent in sequence, and stir to obtain a mixture; (3) Add dopamine-modified nanocellulose whiskers and pH-responsive microcapsule catalyst to the mixture and disperse by ultrasonication; (4) Finally, add the anti-permeability reinforcing agent and vacuum degassing to obtain the underwater self-catalytic epoxy resin composite material based on the biomimetic structure.

12. The method for preparing underwater self-catalytic epoxy resin composite material based on biomimetic structure as described in claim 11, characterized in that, In step (2), the stirring speed is 800-1200 rpm and the stirring time is 15-30 min; In step (3), the frequency of ultrasound is 40kHz, the power density is 0.5-1.0W / cm³, and the ultrasound time is 20-40 min.

13. The application of the biomimetic underwater self-catalytic epoxy resin composite material as described in any one of claims 1-10 in the repair of concrete structures in marine tidal zones.

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