CN120399397A

CN120399397A - An underwater self-catalytic epoxy resin composite material based on a bionic structure and its preparation method and application

Info

Publication number: CN120399397A
Application number: CN202510377766.XA
Authority: CN
Inventors: 逄博; 赵玲玲; 王大富; 陈逸东; 宋晓云; 刘力荣; 孙培峰
Original assignee: Qingdao University of Technology
Current assignee: Jiangsu Qiqing New Materials Technology Co ltd; Qingdao University of Technology
Priority date: 2025-03-28
Filing date: 2025-03-28
Publication date: 2025-08-01
Anticipated expiration: 2045-03-28
Also published as: CN120399397B

Abstract

本发明属于水下混凝土修复材料技术领域，具体涉及一种基于仿生结构的水下自催化环氧树脂复合材料及其制备方法和应用。本发明的基于仿生结构的水下自催化环氧树脂复合材料包括下述重量份数的组分：改性环氧树脂前驱体40‑60份、多巴胺修饰纳米纤维素晶须3‑8份、硅烷偶联剂1‑5份、固化剂15‑30份、微胶囊催化剂0.5‑2份和抗渗增强剂5‑10份。本发明的基于仿生结构的水下自催化环氧树脂复合材料模拟贻贝足丝蛋白中的粘附机制，可在水下环境中形成稳定的配位键和氢键，显著提高材料在潮湿基材表面的浸润性和界面结合强度。The present invention belongs to the technical field of underwater concrete repair materials, and specifically relates to an underwater self-catalytic epoxy resin composite material based on a bionic structure, and its preparation method and application. The underwater self-catalytic epoxy resin composite material based on a bionic structure of the present invention includes the following components in parts by weight: 40-60 parts of a modified epoxy resin precursor, 3-8 parts of dopamine-modified nanocellulose whiskers, 1-5 parts of a silane coupling agent, 15-30 parts of a curing agent, 0.5-2 parts of a microcapsule catalyst, and 5-10 parts of an anti-permeation enhancer. The underwater self-catalytic epoxy resin composite material based on a bionic structure of the present invention simulates the adhesion mechanism in mussel byssus protein, can form stable coordination bonds and hydrogen bonds in an underwater environment, and significantly improves the wettability and interfacial bonding strength of the material on a wet substrate surface.

Description

Underwater self-catalytic epoxy resin composite material based on bionic structure and preparation method and application thereof

Technical Field

The invention belongs to the technical field of underwater concrete repair materials, and particularly relates to an underwater self-catalyzed epoxy resin composite material based on a bionic structure, and a preparation method and application thereof.

Background

With the rapid development of ocean development industry, a large number of concrete structures are exposed to the ocean environment, and are easily damaged by the long-term influence of factors such as seawater corrosion, wave impact, organism adhesion and the like, such as cracks, flaking, strength degradation and the like. These diseases, if not repaired in time, will seriously affect the service life and safety of the structure. The high-performance rapid repair material is urgently required for maintenance and rush repair of marine coastal structures such as seawall wharfs, reservoirs, hydropower stations, bridges, culverts, sewage treatment facilities, submarine oil and gas pipelines, underwater communication facilities and other hydraulic engineering and marine infrastructure. At present, epoxy resin materials are mainly adopted for repairing the underwater concrete structure, but the conventional epoxy resin has a plurality of challenges in underwater application. The bond strength of conventional epoxy resins on the surface of a wet substrate is significantly reduced, mainly because water molecules form a barrier layer at the interface, impeding the effective contact and chemical bonding of the resin to the substrate. Although wettability of the resin can be improved by adding a surfactant or the like, it is still difficult to achieve an ideal interface bonding effect. Meanwhile, in an underwater environment, the curing reaction of the epoxy resin is interfered by water molecules, so that a crosslinked network is slow to form, and usually, a few hours or even more are required to reach enough strength, so that the engineering requirement of quick repair is difficult to meet. In addition, the traditional epoxy resin is easy to hydrolyze and degrade under the condition of long-term soaking, and especially in a seawater environment containing a large amount of chloride ions, the interface bonding strength and the overall mechanical property of the traditional epoxy resin can be obviously reduced with time.

Therefore, development of a novel epoxy resin composite material with excellent underwater adhesive property, rapid curing property and long-term durability is urgently needed to meet the increasing underwater repair demands in the fields of ocean engineering, hydraulic engineering and the like.

Accordingly, there is a need to provide an improved solution to the above-mentioned deficiencies of the prior art.

Disclosure of Invention

The invention aims to provide an underwater self-catalytic epoxy resin composite material based on a bionic structure, and a preparation method and application thereof, which are beneficial to solving or improving at least one of the problems of poor underwater bonding performance, long curing time and poor long-term durability of the existing underwater concrete repair material.

The underwater self-catalyzed epoxy resin composite material based on the bionic structure comprises, by weight, 40-60 parts of a modified epoxy resin precursor, 3-8 parts of dopamine modified nanocellulose whiskers, 1-5 parts of a silane coupling agent, 15-30 parts of a curing agent, 0.5-2 parts of a microcapsule catalyst and 5-10 parts of a permeation resistance enhancer, wherein the viscosity of the modified epoxy resin precursor is 8000-15000 mPa.s at 25 ℃, the epoxy value is 0.42-0.50eq/100g, and the water contact angle is 55-65 degrees.

The invention also provides a preparation method of the underwater self-catalyzed epoxy resin composite material based on the bionic structure, which adopts the following technical scheme that the preparation method of the underwater self-catalyzed epoxy resin composite material based on the bionic structure comprises the following steps of (1) heating a modified epoxy resin precursor to 50-60 ℃, sequentially adding a Mannich base curing agent and a fractal structure silane coupling agent, stirring to obtain a mixture, (3) adding dopamine modified nano cellulose whiskers and a pH responsive microcapsule catalyst into the mixture, performing ultrasonic dispersion, and (4) finally adding an anti-permeability reinforcing agent, and performing vacuum defoaming to obtain the underwater self-catalyzed epoxy resin composite material based on the bionic structure.

The invention also provides application of the underwater self-catalyzed epoxy resin composite material based on the bionic structure, which adopts the following technical scheme that the underwater self-catalyzed epoxy resin composite material based on the bionic structure is applied to repairing of a concrete structure in a sea tidal range area.

The beneficial effects are that:

In the underwater self-catalytic epoxy resin composite material based on the bionic structure, the modified epoxy resin precursor is beneficial to improving the spreadability of epoxy resin in underwater delayed coagulation and the wetting ability of the epoxy resin on a wet substrate, laying a foundation for the exertion of a bionic adhesion mechanism of mussels, and by introducing dopamine modified nanocellulose whiskers, catechol groups in dopamine simulate the adhesion mechanism in mussel podoglobin, stable coordination bonds and hydrogen bonds are formed in an underwater environment, so that the wetting ability and interface bonding strength of the material on the surface of the wet substrate are remarkably improved.

According to the underwater self-catalyzed epoxy resin composite material based on the bionic structure, the thermal stress is effectively relieved through the gradient interface transition layer constructed by the fractal structure silane coupling agent, and the interface stability is further enhanced.

The underwater self-catalyzed epoxy resin composite material based on the bionic structure realizes the quick solidification of the underwater environment by adopting the self-catalyzed system constructed by the Mannich base type curing agent and the pH response type microcapsule catalyst. Wherein, when the Mannich base curing agent contacts seawater, active amino is released through ion exchange, the pH response microcapsule breaks under alkaline condition to release the nano zinc oxide catalyst, and the synergistic effect of the active amino and the pH response microcapsule obviously improves the curing efficiency.

The underwater self-catalyzed epoxy resin composite material based on the bionic structure has excellent performance, can realize primary solidification for 15min under the condition of 95% humidity, shortens the solidification time by 67% compared with the traditional product, has the highest underwater bonding strength of 3.5MPa, meets the ASTM C882 standard requirement, can reduce the chloride ion permeation resistance coefficient of the material to 1.2 multiplied by 10 ^-12m²/s through the synergistic effect of the anti-permeability reinforcing agent, has excellent durability, and realizes the integration of underwater quick construction and long-term protection.

Detailed Description

The following description of the technical solutions in the embodiments of the present invention will be clear and complete, and it is obvious that the described embodiments are only some embodiments of the present invention, but not all embodiments. All other embodiments, which are derived by a person skilled in the art based on the embodiments of the invention, fall within the scope of protection of the invention.

The present invention will be described in detail with reference to examples. It should be noted that, without conflict, the embodiments of the present invention and features of the embodiments may be combined with each other.

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

The inventor finds that marine organisms represented by mussels can realize stable adhesion in a humid environment, which is mainly attributed to mucin secreted by the marine organisms and having a special chemical structure, and meanwhile, the three-dimensional network structure formed by the plant root system through a fractal growth mode can effectively improve the mechanical interlocking and stress transmission efficiency with soil. If the bionic principles can be applied to the research of underwater repair materials, particularly the research on quick solidification and long-term durability, the bionic principles are helpful to solve or improve the problems existing in the current underwater concrete repair materials.

The underwater self-catalyzed epoxy resin composite material based on the bionic structure comprises, by weight, 40-60 parts (for example, 40 parts, 45 parts, 50 parts, 55 parts or 60 parts) of a modified epoxy resin precursor, 3-8 parts (for example, 3 parts, 4 parts, 5 parts, 6 parts, 7 parts or 8 parts) of dopamine modified nanocellulose whiskers, 1-5 parts (for example, 1 part, 2 parts, 3 parts, 4 parts or 5 parts) of a silane coupling agent, 15-30 parts (for example, 15 parts, 20 parts, 25 parts or 30 parts) of a curing agent, 0.5-2 parts (for example, 0.5 parts, 1 part, 1.5 parts or 2 parts) of a microcapsule catalyst and 5-10 parts (for example, 5 parts, 6 parts, 7 parts, 8 parts, 9 parts or 10 parts) of an anti-permeation enhancer, wherein the viscosity of the modified epoxy resin precursor is 8000-15000 mPa.s at 25 ℃ and the epoxy value is 0.42-0.50eq/100g, and the water contact angle is 55 ℃.

In the preferred embodiment of the underwater self-catalytic epoxy resin composite material based on the bionic structure, the modified epoxy resin precursor is prepared by adopting a method comprising the following steps of heating bisphenol A type epoxy resin to be molten, adding a reactive diluent, stirring to be uniform, adding a toughening agent, continuing stirring, adding an organosilicon modifier, stirring, V adding a surfactant, continuing stirring, and VI carrying out vacuum defoaming to obtain the epoxy resin precursor. In the preparation process of the modified epoxy resin precursor, the spreadability of the epoxy resin in an underwater environment and the wetting capability of the epoxy resin on a wet substrate can be obviously improved by introducing hydrophilic groups and adjusting the surface energy of a system.

Preferably, in step II, the reactive diluent is dibutyl phthalate or anisole glycidyl ether, in step III, the toughening agent is polyethylene glycol having a molecular weight of 400-800 (e.g., 400, 500, 600, 700, or 800), in step IV, the silicone modifier is an amino-containing polysiloxane (e.g., gamma-aminopropyl trimethoxysilane modified polydimethylsiloxane or commercially available dakaning Z-6020 amino functionalized silane), and in step V, the surfactant is a polyether modified silicone (e.g., polyethylene glycol-polydimethylsiloxane block copolymer or commercially available dakaning DC-57 surfactant).

More preferably, in step I, the epoxy value of the bisphenol A type epoxy resin is 0.48-0.52eq/100g (e.g., 0.48eq/100g, 0.49eq/100g, 0.50eq/100g, 0.51eq/100g or 0.52eq/100 g), the heating temperature is 70-80 ℃ (e.g., 70 ℃, 75 ℃ or 80 ℃), in step II, the addition amount of the reactive diluent is 4-6 wt% (e.g., 4wt%, 5wt% or 6 wt%), the stirring time is 30-40min (e.g., 30min, 33min, 36min or 40 min), the addition amount of the toughening agent is 4-5 wt% (e.g., 4wt%, 5wt% or 6 wt%), the stirring time is 30-40min (e.g., 30min, 33min, 36min or 40 min), the addition amount of the organosilicon modifier is 2-4 wt% (e.g., 70 ℃, 75 ℃ or 80 ℃) in step IV, the addition amount is 4wt% (e.g., 2wt%, 5wt%, or 6 wt%), the stirring time is 80-60% (e.g., 60 ℃ or 80 wt%), the addition amount of the toughening agent is 80-60% (e.g., 60 ℃ or 80 wt%), the stirring time is 80% (e.g., 60 ℃ or 60 ℃ in the step III), the addition amount is 80 wt%, 60 ℃ or 80 ℃ in the step III, the stirring time is 80% (e.g., 60 ℃ or 60 ℃ in the following) in the following steps).

In the preferred embodiment of the underwater self-catalyzed epoxy resin composite material based on the bionic structure, the dopamine-modified nano cellulose whisker is prepared by adopting a method comprising the following steps of B1. Dispersing the nano cellulose whisker in Tris-HCl buffer solution, carrying out ultrasonic treatment to obtain uniform dispersion liquid, B2. Adding dopamine hydrochloride into the dispersion liquid, stirring for 24-48h (for example, 24h, 30h, 36h, 42h or 48 h) under an oxygen atmosphere, and B3. Carrying out centrifugal separation, and freeze-drying the obtained solid to obtain the dopamine-modified nano cellulose whisker.

In a preferred embodiment of the underwater self-catalyzed epoxy resin composite material based on biomimetic structure 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 2 wt%).

In a preferred embodiment of the underwater self-catalyzed epoxy resin composite material based on a bionic structure according to the 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).

Preferably, the nanocellulose whiskers have an aspect ratio of 50-100 (e.g., 50, 60, 70, 80, 90 or 100), a dopamine layer is grafted onto the surface by controlled polymerization, and the layer is 20-50nm thick (e.g., 20nm, 30nm, 40nm or 50 nm). The invention is favorable for forming more effective three-dimensional network structure in the composite material by selecting the nano cellulose whisker with higher length-diameter ratio (within the range of 50-100) from the aspect of mechanical property, improves the mechanical strength and toughness of the material, and can span more interface areas by long fibers to enhance the stress transmission capability of the material. In terms of interface interaction, the length-diameter ratio of the nanocellulose whisker influences the contact area between the fiber and the epoxy resin matrix, and in the invention, the fiber simulates the adhesion mechanism of mussel mucin, and the nanofiber whisker with the proper length-diameter ratio can provide more catechol group exposure sites, so that the adhesion effect at a wet interface is enhanced. In addition, the proper length-diameter ratio of the nanocellulose whisker is beneficial to forming uniform stress distribution in the curing process and avoiding microcracks caused by stress concentration. If the aspect ratio of the nanocellulose whisker is too high (more than 100), the nanocellulose whisker can be difficult to uniformly disperse in a matrix to form agglomeration, but the material performance is reduced, and if the aspect ratio of the nanocellulose whisker is too low (less than 50), the reinforcing and networking effects of the nanocellulose whisker can be weakened.

If the thickness of the dopamine layer is too small (less than 20 nm), adverse effects such as 1) insufficient number of surface active groups, which leads to a significant decrease in adhesion capability in a humid environment, 2) insufficient protective effect on nanocellulose, which may lead to a decrease in stability of the material in an underwater environment, 3) inability to effectively simulate catechol structure of mussel bylonin, poor bionic effect, and 4) insufficient interface bonding with a matrix, which leads to a decrease in mechanical property, are generated. If the thickness of the dopamine layer is too large (more than 50 nm), 1) the mechanical interlocking effect between the nanocellulose whiskers is reduced due to the fact that the dopamine layer is too thick, 2) the reaction of a curing agent and epoxy resin is possibly hindered by the too thick dopamine layer, the curing time is prolonged, 3) the self-crosslinking reaction between the dopamine layers is possibly caused, so that the material is hard and brittle, the toughness is reduced, 4) the viscosity of the material is increased, the construction fluidity is affected, underwater construction is not facilitated, and 5) the overall density and strength of the composite material are reduced due to the fact that the too thick dopamine layer occupies too much space.

In the preferred embodiment of the underwater self-catalyzed epoxy resin composite material based on the bionic structure, the microcapsule catalyst is a pH-responsive microcapsule catalyst, and the pH-responsive microcapsule catalyst is prepared by a method comprising the following steps of A1 dispersing nano zinc oxide in an organic solvent (for example, the organic solvent can be cyclohexane), adding a polymer wall material (preferably, the polymer wall material is polydopamine), stirring uniformly, and A2 preparing microcapsules by adopting an interfacial polymerization method, and controlling the crosslinking degree of the wall material. The pH response microcapsule can be broken under alkaline conditions to release a nano zinc oxide catalyst (nano zinc oxide is taken as a core material), and can be synergistic with a Mannich base curing agent to remarkably improve the curing efficiency.

Preferably, the pH responsive microcapsule catalyst has a shell thickness of 55-85nm (e.g., 55nm, 65nm, 75nm, or 85 nm), is stable for 36-72h (e.g., 36h, 46h, 56h, 66h, or 72 h) in an aqueous solution having pH=7.0, has no cracking, and releases the nano zinc oxide catalyst by cracking of 85% or more of the microcapsules within 35-50min (e.g., 35min, 40min, 45min, or 50 min) in an aqueous solution having pH=11.0-11.8 (e.g., 11.0, 11.2, 11.4, 11.6, or 11.8).

Preferably, the step A1 comprises weighing nanometer zinc oxide powder, adding into cyclohexane, adding hexadecyl trimethyl ammonium bromide as dispersant, performing ultrasonic treatment by using an ultrasonic probe to form stable nanometer zinc oxide dispersion, adding dopamine hydrochloride under the protection of nitrogen, immediately adding Tris-HCl buffer (pH=8.5), and slowly dropwise adding pentaerythritol glycidyl ether as a cross-linking agent under the condition of mechanical stirring;

The step A2 comprises transferring the dispersion system into a three-neck flask, introducing oxygen under stirring, controlling the reaction temperature to enable dopamine to self-polymerize under the oxidation condition, adding a polyvinyl alcohol (PVA) solution as a stabilizer when the color of the reaction liquid changes from transparent to dark brown, continuing stirring to enable a polydopamine shell layer to be fully formed, monitoring the pH value of the reaction system by adopting a pH meter, indicating that the shell layer is formed to be completed when the pH value reaches 7.9-8.6, collecting microcapsules by centrifugal separation, washing sequentially by deionized water, ethanol and acetone, and drying in vacuum to obtain the pH response type microcapsule catalyst.

More preferably, in step A1, the mass ratio of nano zinc oxide, cetyl trimethyl ammonium 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 ℃ (e.g. 24 ℃, 27 ℃, 30 ℃ or 32 ℃), the time for the self-polymerization is 4.5-6 hours (e.g. 4.5 hours, 5.5 hours or 6 hours), the mass concentration of the polyvinyl alcohol solution is 1.2% -2% (e.g. 1.2%, 1.4%, 1.6%, 1.8% or 2%), the time for continuing stirring 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 temperature for the vacuum drying is 40-50 ℃ (e.g. 40 ℃, 43 ℃, 46 ℃, 48 ℃ or 50 ℃ or 14 hours, 18 hours, 16 hours.

In a preferred embodiment of the underwater self-catalyzed epoxy resin composite material based on biomimetic structures of the present invention, the shell layer of the pH-responsive microcapsule catalyst has a thickness of 50-80nm (e.g., 50nm, 60nm, 70nm or 80 nm). If the thickness of the shell layer is too thin, the shell layer is easy to damage, and if the shell layer is too thin, the release of the core material is affected.

In the preferred embodiment of the underwater self-catalytic epoxy resin composite material based on the bionic structure, the silane coupling agent is a fractal structure silane coupling agent, the fractal structure silane coupling agent is prepared by mixing gamma-glycidyl ether propyl trimethoxy silane and branched polyethylenimine, heating to 100-120 ℃ (for example, 100 ℃, 105 ℃, 110 ℃, 115 or 120 ℃) and stirring for reacting for 2-4 hours (for example, 2h, 2.5h, 3h, 3.5h or 4 h), C2. adding tetraethoxysilane into a reaction system, and continuing to react for 2-4 hours (for example, 2h, 2.5h, 3h, 3.5h or 4 h) at 90-110 ℃ (for example, 90 ℃, 95 ℃,100 ℃, 105 ℃ or 110 ℃), and performing reduced pressure distillation at C3. to obtain the fractal structure silane coupling agent. The fractal structure silane coupling agent forms a gradient modulus transition layer on the interface by simulating the bifurcation growth mode of a plant root system, so that the thermal stress concentration can be effectively relieved, and the interface bonding stability is further enhanced. The gamma-glycidyl ether propyl trimethoxy silane plays a key role in the invention in that 1) epoxy groups are provided and can form covalent chemical bonds with an epoxy resin matrix, 2) silane groups are contained and can form silica bonds with the surface of an inorganic substrate (such as concrete), 3) the gamma-glycidyl ether propyl trimethoxy silane is used as bridging molecules to connect an organic phase (epoxy resin) and an inorganic phase (concrete substrate), and 4) methoxy groups can be hydrolyzed to form silanol groups in water environment to strengthen the interface bonding force of a wet substrate. The tetraethoxysilane plays a key role in the invention in 1) providing additional crosslinking points, increasing the bifurcation degree and network complexity of the fractal structure, 2) forming a silicon-oxygen skeleton structure, enhancing the overall mechanical property, 3) adjusting the rigidity and the elastic modulus of an interface layer to form a gradient transition zone, forming a silicon-oxygen network after hydrolysis, enhancing the water resistance and the permeation resistance of the material, and 4) promoting the formation of the fractal structure and simulating the bifurcation growth mode of a plant root system.

The gradient modulus transition layer is understood to be a special interface area formed between the epoxy resin matrix and the concrete substrate under the action of the fractal structure silane coupling agent, and the elastic modulus of the area gradually transits from the substrate to the matrix direction instead of the abrupt structure of the traditional interface. The gradient modulus transition layer is characterized in that the structure extends from the surface of the concrete base material to the direction of the epoxy resin base material, elastic modulus is in gradual change distribution, modulus mutation at a traditional interface is avoided, the gradient structure is similar to a combination mode of a plant root system and soil, stress can be effectively dispersed, stress concentration caused by difference of thermal expansion coefficients is reduced, interface combination strength and durability are improved, and through design of the fractal structure, the interface layer not only has good mechanical property matching, but also improves interface stability of the material under the conditions of temperature change and wet environment.

Preferably, the branching polyethylenimine has a branching degree of 2.5 to 4.0 (e.g., 2.5, 3.0, 3.5, or 4.0). The fractal structure silane coupling agent is based on polyethyleneimine with the bifurcation degree of 2.5-4.0, epoxy groups are introduced through a silanization reaction, so that a fractal structure is formed, the interface transition effect is not obvious if the bifurcation degree is too low, and the molecular mobility is reduced if the bifurcation degree is too high, so that the solidification is affected.

In the preferred embodiment of the underwater self-catalyzed epoxy resin composite material based on the bionic structure, the molar ratio of the composite material to the branched polyethylenimine in the step C1 is 1:1-3:1 (for example, 1:1, 1.5:1, 2:1, 2.5:1 or 3:1), and the addition amount of tetraethoxysilane in the step C2 is 10-30 wt% (for example, 10-15 wt%, 20wt%, 25wt% or 30 wt%) of the sum of the gamma-glycidyl ether propyl trimethoxysilane and the branched polyethylenimine. If the dosage of the gamma-glycidyl ether propyl trimethoxy silane is too large (molar ratio is more than 3:1), 1) excessive epoxy groups can lead to uneven cross-linked network structure to form a local high cross-linked density area, 2) brittleness of the material is increased, toughness and impact resistance are reduced, 3) excessive silane groups which do not participate in reaction can be excessively hydrolyzed in water environment to lead to unstable interface layer structure, 4) fractal structure formation can be restrained, gradient modulus characteristics of an interface transition layer are weakened, 5) excessive silane can cause excessive shrinkage in the curing process to generate internal stress, and interface bonding strength is reduced. If the dosage of the gamma-glycidyl ether propyl trimethoxy silane is too small (the molar ratio is less than 1:1), 1) enough epoxy groups cannot be provided to form effective crosslinking with an epoxy resin matrix, 2) the fractal structure is insufficient in development and difficult to form an ideal root system simulation structure, 3) the bonding site with a concrete substrate is insufficient, the bonding strength of an interface is reduced, 4) the durability of the material in a water environment is reduced, the interface is more easily corroded by water molecules, and 5) a gradient modulus transition layer is incomplete and cannot effectively relieve the thermal stress.

If the amount of tetraethoxysilane added is too large (> 30%), 1) an excessively crosslinked rigid network is formed, the toughness and interfacial flexibility of the material are reduced, 2) the inorganic phase proportion is possibly too high, the compatibility with an organic phase (epoxy resin) is reduced, 3) hydrolysate is excessively caused, the microstructure defect of the material is caused, 4) the curing shrinkage rate is increased, larger internal stress is generated, microcrack formation is possibly caused, and 5) the growth direction of a fractal structure is limited by excessive silicon-oxygen network, so that the formation of a gradient transition layer is influenced. If the addition amount of tetraethoxysilane is too small (10%), 1) the branching degree of the fractal structure is insufficient, the complex branching structure of a plant root system cannot be simulated, 2) the gradient transition layer is incomplete to form, the stress dispersion effect is poor, 3) the permeation resistance performance is reduced, a sufficiently compact silica network cannot be formed, 4) the hydrolysis resistance stability is reduced, the interface performance decay is fast after long-term soaking, and 5) the problem of thermal stress concentration cannot be effectively relieved, so that the interface bonding strength is unstable along with the change of temperature.

In a preferred embodiment of the underwater self-catalyzed epoxy resin composite material based on the bionic structure, the curing agent is a Mannich base type curing agent, the Mannich base type curing agent is prepared by adopting a method comprising the steps of mixing bisphenol A epoxy resin and 4,4' -diaminodiphenyl methane according to a molar ratio of 1 (2-3) (for example, 1:2, 1:2.3, 1:2.6, 1:2.8 or 1:3), reacting for 2-4 hours (for example, 2 hours, 2.5 hours, 3 hours, 3.5 hours or 4 hours) at 80-100 ℃ at 85 ℃, 90 ℃, 95 ℃ or 100 ℃, adding a benzaldehyde derivative into D2. for Mannich reaction, controlling the molar ratio of aldehyde group to amino group to 1.2-1.5 (for example, 1:1.2, 1:3, 1:1.4 or 1:1.5), and obtaining the adhesive liquid, namely, the adhesive, which is dried at 110-130 ℃, for example, 115 ℃,3 hours, 3.5 hours or 3 hours at 120 ℃ after the step of drying. Wherein, if the dosage of 4,4' -diaminodiphenyl methane is too large (molar ratio is more than 3:1), 1) excessive amine groups cannot completely participate in the reaction, residual free amine can cause the phenomenon of ' amine precipitation ' after the material is cured, 2) the water resistance of the final product is reduced, because the free amine is easily dissolved in water, 3) excessive amine can cause the viscosity of a curing agent to be too high, the workability is influenced, 4) the curing system is too alkaline, the pH response type microcapsule wall layer is damaged, the catalyst is prematurely released, and 5) the permeation resistance and the durability of the final material are reduced. If the dosage of 4,4' -diaminodiphenyl methane is too small (molar ratio is less than 2:1), 1) the amino group is insufficient, so that the subsequent Mannich reaction sites are insufficient, 2) the activity of a curing agent is reduced, the underwater curing speed is low, 3) a sufficient cross-linked network cannot be formed, the material strength is insufficient, 4) the ion exchange capacity in water environment is weak, active amino groups are difficult to release, and 5) the mechanical property and the bonding strength of the final composite material are reduced.

If the reaction temperature in the step D1 is too high (> 100 ℃), the epoxy resin is easy to cause self-polymerization to influence the subsequent Mannich reaction, 2) side reaction is generated at high temperature to generate a product which is unfavorable for underwater curing, 3) amine oxidation can be caused to reduce the activity of a curing agent, and 4) the color of the product is deepened to influence the attractiveness of the final material. If the reaction temperature in the step D1 is too low (< 80 ℃), 1) the bisphenol A epoxy resin and the diaminodiphenyl methane are not completely reacted, 2) the reaction rate is too slow, the production period is prolonged, the efficiency is reduced, 3) unreacted monomers remain in the product to influence the performance stability of the curing agent, 4) the prepolymer is not completely formed, and the subsequent Mannich reaction effect is poor.

If the reaction time in the step D1 is too long (> 4 h), the energy consumption and the production cost are increased 1), the product may be excessively crosslinked to cause too high viscosity, the high-temperature long-time reaction may cause oxidative degradation of amino groups, and the byproduct which is unfavorable for underwater curing may be formed 4). If the reaction time in the step D1 is too short (< 2 h), the adverse effects are that 1) the reaction is incomplete, the prepolymer is not formed sufficiently, 2) the unreacted components are more, the quality stability of the curing agent is influenced, 3) the preparation of a subsequent Mannich reaction substrate is insufficient, the reaction efficiency is influenced, and 4) the activity of the final curing agent is insufficient, and the underwater curing speed is influenced.

If the molar ratio of aldehyde groups to amino groups in the step D2 is too high (> 1:1.5), 1) excessive amino groups participate in the Mannich reaction to cause irregular structure of the curing agent, 2) excessive free amine still exists in the reaction product to reduce water resistance, 3) the pH sensitivity of the curing agent is reduced, the activity release in an alkaline environment is insufficient, and 4) the viscosity characteristic of the curing agent is unstable to influence the processability. If the molar ratio of aldehyde groups to amino groups in step D2 is too low (< 1:1.2), 1) the Mannich reaction is insufficient, active sites are not formed, 2) the ion exchange capacity of the curing agent in an underwater environment is weak, 3) the synergistic effect of the curing agent and the pH-responsive microcapsule catalyst is poor, 4) the underwater curing speed is low, the curing degree is low, and 5) the underwater adhesive strength of the final material is insufficient.

If the reaction temperature is too high (> 130 ℃) in the step D2, 1) the thermal decomposition of the reactant may be caused, the product quality is reduced, 2) more side reactions and byproducts are generated to influence the purity of the curing agent, 3) the color of the product is deepened and even carbonized at high temperature, 4) the energy consumption is increased, and the requirement on equipment is higher. If the reaction temperature in the step D2 is too low (110 ℃), 1) the Mannich reaction activation energy is insufficient, the reaction rate is extremely slow, 2) the reaction is incomplete, the product contains a large amount of unreacted raw materials, 3) the activity of the curing agent is low, the curing agent is difficult to quickly cure in an underwater environment, and 4) the final product has unstable performance and large batch difference.

If the reaction time in the step D2 is too long (more than 6 hours), 1) the reactant may be degraded to affect the structure of the curing agent, 2) the long-time high temperature may cause excessive crosslinking, the molecular weight distribution of the product is wide, 3) the energy consumption and the cost are increased, the production efficiency is reduced, and 4) the equipment burden and the potential safety hazard may be increased. If the reaction time in the step D2 is too short (3 h), 1) the Mannich reaction is incomplete, active sites are not formed sufficiently, 2) the curing agent is incomplete in structure and unstable in performance, 3) the ion exchange and catalytic capability in the underwater environment is weak, 4) the curing time of the final composite material is prolonged, the quick repair requirement cannot be met, and 5) the underwater bonding strength and durability are not up to the standard.

In a preferred embodiment of the underwater self-catalyzed epoxy resin composite material based on a biomimetic structure of the present invention, in step D1, the bisphenol A epoxy resin has an epoxy value of 0.45-0.55eq/100g (e.g., 0.45eq/100g, 0.48eq/100g, 0.5eq/100g, 0.52eq/100g or 0.55eq/100 g), and in step D2, the benzaldehyde derivative is 4-hydroxybenzaldehyde and/or 3, 5-dinitrobenzaldehyde. The bisphenol A epoxy resin introduces active amine groups through a Mannich reaction, if the epoxy value of the bisphenol A is too low, the curing activity is reduced, and if the epoxy value is too high, the water solubility is not improved.

The underwater self-catalyzed epoxy resin composite material based on the bionic structure adopts a self-catalyzed system constructed by a Mannich base curing agent and a pH response microcapsule catalyst, and realizes the quick curing of the underwater environment by means of releasing the catalyst through ion exchange and pH response.

In the preferred embodiment of the underwater self-catalyzed epoxy resin composite material based on the bionic structure, the anti-seepage reinforcing agent is a mixture of nano silicon dioxide and an organosilicon water repellent. Wherein, nano silicon dioxide of the anti-permeability enhancer fills network micropores, and the organosilicon water repellent forms a water repellent layer on the pore wall, and the two cooperate to obviously improve the anti-permeability performance and durability of the material.

In a preferred embodiment of the underwater self-catalyzed epoxy resin composite material based on the bionic structure, the mass ratio of the nano silicon dioxide to the organosilicon water repellent is (2-4): 1 (for example, 2:1, 3:1 or 4:1). The organosilicon water repellent is at least one selected from methyltrimethoxysilane, methyltriethoxysilane, octamethyl cyclotetrasiloxane or polydimethylsiloxane.

Preferably, the nanosilica has a particle size of 100-300nm (e.g., 100nm, 150nm, 200nm, 250nm, or 300 nm). If the particle size of the nano silica is too small, the filling effect is not good, and if the particle size of the nano silica is too large, the dispersibility is affected.

The invention also provides a preparation method of the underwater self-catalyzed epoxy resin composite material based on the bionic structure, which comprises the following steps of (1) heating an epoxy resin precursor to 50-60 ℃ (for example, 50 ℃, 52 ℃, 54 ℃, 56 ℃, 58 ℃ or 60 ℃), sequentially adding a Mannich base curing agent and a fractal structure silane coupling agent, stirring to obtain a mixture, (3) adding dopamine modified nanocellulose whisker and a pH responsive microcapsule catalyst into the mixture, performing ultrasonic dispersion, and (4) finally adding an anti-permeability reinforcing agent, and performing vacuum defoamation to obtain the underwater self-catalyzed epoxy resin composite material based on the bionic structure. The preparation method of the underwater self-catalyzed epoxy resin composite material based on the bionic structure comprises the steps of (1) helping to ensure dispersion uniformity (the correct material sequence can ensure uniform dispersion of all components in an epoxy resin matrix, if components with high viscosity or easy agglomeration such as nanocellulose whiskers are added first, dispersion difficulty is caused, uneven structure is formed, uneven dispersion can cause unstable material performance, partial area strength is insufficient, integral underwater bonding strength is reduced), and (2) helping to ensure stability of pH response microcapsules (the pH response microcapsules must be added at a proper stage, premature rupture is avoided under the condition of high shearing force, the microcapsules can be damaged when the pH response microcapsules are added at an initial stage of high-speed stirring, the catalyst is released prematurely, the materials can not be fully dispersed and curing uniformity is influenced when the components are added as a final component, (3) influencing reaction kinetics (Mannich base curing agent is fully mixed with the epoxy resin first to form a uniform basic system, the fractal structure silane coupling agent is required to be added after the formation, so that the temperature of the epoxy resin is fully mixed with the basic system is influenced, and the temperature is controlled to be low in order of the proper order, and the temperature is influenced when the temperature is controlled to be in order of 60 ℃ from the final time, the temperature is influenced, the final time is influenced, and the temperature is controlled to be in order of forming the complete, and the temperature is influenced when the temperature is 50 ℃ when the final phase is mixed with the epoxy resin is fully, the final time is controlled, and the temperature is influenced by the final temperature is 50, and controlling the processing time of each stage), has an influence on the timing of ultrasound (5) (dopamine modified nanocellulose whiskers need to be dispersed by ultrasound to break aggregates, but too strong ultrasound can damage microcapsules, simultaneous addition and moderate ultrasound treatment of both are an equilibrium scheme, if this order is changed, for example, nanocellulose whiskers are added first and then microcapsules are added, although the dispersibility of nanocellulose can be improved, the process complexity and the production time can be increased), the impermeability enhancer needs to be used as a component of last addition (nanosilica has a high specific surface area, if other components can be adsorbed too early to affect the function exertion of the nanosilica, micropores in a formed network structure can be filled as a component of last addition, the impermeability performance can be maximized, if the last addition can interfere with the formation of a structure and the dispersion of microcapsules, and (7) the timing of deaeration can also influence the performance of a composite material (all components are added and mixed and then vacuum deaeration can be carried out to maximally remove bubbles introduced in the processing process, if the intermediate step is carried out, the subsequent deaeration can be carried out, and the bonding effect of bubbles cannot be well-formed as a defect point of the bonding material under water is remarkably reduced.

In a preferred embodiment of the preparation method of the underwater self-catalyzed epoxy resin composite material based on the bionic structure, in the step (2), the stirring speed is 800-1200rpm (for example, 800rpm, 900rpm, 1000rpm, 1100rpm or 1200 rpm), the stirring time is 15-30min (for example, 15min, 20min, 25min or 30 min), the ultrasonic frequency is 40kHz, the power density is 0.5-1.0W/cm ³ (for example, 0.5W/cm ³、0.6W/cm³、0.7W/cm³、0.8W/cm³、0.9W/cm³ or 1.0W/cm ³), and the ultrasonic time is 20-40min (for example, 20min, 25min, 30min, 35min or 40 min). The method comprises the steps of (1) starting a pre-reaction, namely starting the pre-reaction in the stirring process, wherein a Mannich base curing agent and an epoxy resin precursor start to react to form a preliminary cross-linked network structure, providing proper shearing force for a specific stirring speed to promote uniform reaction of a fractal structure silane coupling agent and an epoxy group, and (2) optimizing an interface structure, namely enabling the fractal structure silane coupling agent to form an ideal fractal structure under proper stirring conditions, wherein the ideal fractal structure can be formed on the formation of a subsequent gradient modulus transition layer, the fact that the fractal structure is difficult to fully develop due to the fact that the stirring speed is too low (800 rpm), the fact that the fractal structure is difficult to fully develop due to the fact that the stirring speed is too high (1200 rpm), even overshearing is generated, and (3) adjusting and controlling the viscosity of a system, wherein the precisely controlled stirring time (15-30 min) can reach the best rheological property of a matrix system, create conditions for adding subsequent components, and the fact that the system is uneven and overlength can possibly lead to pre-curing.

The selection of ultrasonic treatment parameters in the step (3) is beneficial to (1) the reconstruction of a nano structure, wherein ultrasonic energy causes the three-dimensional configuration recombination of dopamine modified nanocellulose whiskers and expands molecular chains of the nanocellulose whiskers, the reconstruction is critical to the catechol structure of the simulated mussel foot silk protein and directly influences an underwater adhesion mechanism, (2) the uniform positioning of the catalytic microcapsule, wherein the proper ultrasonic energy can break the agglomeration of the pH responsive microcapsule and simultaneously does not destroy the capsule structure, the microcapsule can be uniformly distributed in a network constructed by the nanocellulose whiskers under the ultrasonic action to form a 'pre-positioned' catalytic point, the precise distribution is critical to the uniform starting and the conducting of an underwater curing reaction, 3) the interface activation treatment, wherein the cavitation effect generated by ultrasonic waves in liquid can activate active groups on the dopamine surfaces, the chemical bonding capability of the ultrasonic waves and the epoxy groups is enhanced, the interface bonding strength of a final material is improved, the ultrasonic power density is too low (< 0.5W/cm ³) is difficult to achieve an activation effect, the molecular structure can be destroyed when the ultrasonic power density is too high (> 1.0W/cm ³), the nano-size distribution network is not completely distributed in the network is completely stable, the ultrasonic wave is completely-stable, the specific ultrasonic wave is completely-distributed in the underwater curing structure is completely, and the network is completely-stable, the critical to form a network is completely-stable, and the network is completely-stable, and the network is completely stable, the network is completely can completely stable, and the network is completely stable, and the network can be completely stable when the structure is completely stable.

The invention also provides application of the underwater self-catalyzed epoxy resin composite material based on the bionic structure, and application of the underwater self-catalyzed epoxy resin composite material based on the bionic structure in repairing a concrete structure in a sea tidal range area. The underwater self-catalytic epoxy resin composite material based on the bionic structure is particularly suitable for repairing wet interface concrete such as ocean tidal range areas, wharf pile foundations and the like, and realizes the integration of underwater rapid construction and long-acting protection.

The underwater self-catalyzed epoxy resin composite material based on the bionic structure, the preparation method and the application thereof are described in detail by specific examples.

The main raw materials used in the following examples were bisphenol A epoxy resin, nanya epoxy resin, model E-51, epoxy value 0.48-0.54eq/100g, nanocellulose whisker, prepared by national academy of sciences chemical research, aspect ratio 50-100, dopamine hydrochloride, sigma-Aldrich, gamma-glycidyl ether propyl trimethoxysilane, takanin, purity 97%, branched polyethylenimine, sigma-Aldrich, molecular weight 25000, tetraethoxysilane, national medicine group chemical reagent, analytical purity, 4' -diaminodiphenylmethane, basoff, purity 99%, 4-hydroxybenzaldehyde, ab Ding Shiji, purity 99%, 3, 5-dinitrobenzaldehyde, ab Ding Shiji, purity 98%, nano zinc oxide, ardisi nanomaterial technology, average particle size 50-80nm, nano silica, kabolt, average particle size 100-300nm, methyltrimethoxysilane, takanin, methyl tetramine, octanesoid, and octanesoid, purity 99.mPas.

Example 1

The underwater self-catalyzed epoxy resin composite material based on the bionic structure comprises, by weight, 40 parts of modified epoxy resin precursors, 3 parts of dopamine modified nanocellulose whiskers, 1 part of fractal-structure silane coupling agent, 15 parts of Mannich base curing agent, 0.5 part of pH response microcapsule catalyst and 5 parts of anti-permeability reinforcing agent.

The modified epoxy resin precursor is prepared by a method comprising the steps of heating bisphenol A epoxy resin (with an epoxy value of 0.48eq/100 g) to 70 ℃ to enable the bisphenol A epoxy resin to be fully melted, adding reactive diluent (dibutyl phthalate) with a mass ratio of 4% and stirring for 30min to be uniform, adding polyethylene glycol (with a molecular weight of 400) with a mass ratio of 3% as a toughening agent and continuing stirring for 30min, adding organosilicon modifier (polysiloxane-dakaning Z-6020 amino-functionalized silane) with a mass ratio of 2% and stirring for 60min at 80 ℃, and finally adding surfactant (polyether modified organosilicon-dakaning DC-57 surfactant) with a mass ratio of 1%, continuing stirring for 30min at 80 ℃ and conducting vacuum defoaming for 45min to obtain the modified epoxy resin precursor. The modified epoxy resin precursor has the characteristics that the viscosity is 12000-15000 mPa.s at 25 ℃, the epoxy value is 0.42-0.46eq/100g, the water contact angle is 65 degrees (obviously reduced compared with the 80 degrees of the common epoxy resin), and the wettability to a wet surface is enhanced by about 25 percent. The hydrophilic group is introduced in the modification process and the surface energy of the system is adjusted, so that the spreadability of the epoxy resin in an underwater environment and the wetting capability of the epoxy resin on a wet substrate are remarkably improved, and a foundation is laid for the subsequent exertion of a mussel bionic adhesion mechanism.

Wherein, the pH response type microcapsule catalyst is prepared by adopting a method comprising the following steps:

A1. Dispersing nano zinc oxide (average particle size of 50 nm) in cyclohexane, adding polydopamine as a wall material, stirring uniformly, weighing 0.5g of nano zinc oxide powder, adding into 50mL of cyclohexane, adding 0.2g of Cetyl Trimethyl Ammonium Bromide (CTAB) as a dispersing agent, performing ultrasonic treatment for 30 minutes by using an ultrasonic probe (power 300W) to form stable nano zinc oxide dispersion, adding 0.8g of dopamine hydrochloride under the protection of nitrogen, immediately adding 25mL of Tris-HCl buffer (pH=8.5), and slowly dropwise adding 0.3g of pentaerythritol glycidyl ether (PTGE) as a crosslinking agent under the condition of mechanical stirring (500 rpm);

A2. Preparing microcapsules by an interfacial polymerization method, controlling the thickness of polydopamine shell layers to be 50nm, transferring the dispersion system into a three-neck flask, introducing oxygen at a stirring rate of 600rpm, controlling the reaction temperature to be 25+/-2 ℃, controlling the reaction time to be 4 hours, enabling dopamine to self-polymerize under an oxidation condition, adding 10mL of 1% polyvinyl alcohol (PVA) solution as a stabilizer when the color of a reaction solution changes from transparent to dark brown, continuing stirring for 2 hours to enable polydopamine shell layers to be fully formed, monitoring the pH value of the reaction system by a pH meter, when the pH value reaches 8.0+/-0.2, indicating that the shell layers are formed to be finished, collecting the microcapsules by centrifugal separation (5000 rpm,10 minutes), washing 3 times by deionized water, ethanol and acetone in sequence, drying in vacuum at 40 ℃ for 12 hours, obtaining a final product, measuring the thickness of the shell layers by a Transmission Electron Microscope (TEM), and testing the pH responsiveness of the prepared microcapsules, wherein the prepared microcapsules are stable in an aqueous solution with the pH=7.0 for 24 hours, the microcapsules are free of cracks, and the microcapsules are triggered to release alkaline nano-zinc oxide solution more than 30 minutes in the aqueous solution with the pH=12.0, and the alkaline environment is triggered by the microcapsule.

The dopamine-modified nanocellulose whisker is prepared by a method comprising the following steps of B1 dispersing nanocellulose whisker (mass fraction is 0.5%, length-diameter ratio is 55) in Tris-HCl buffer solution (pH=8.5), carrying out ultrasonic treatment for 20 minutes to obtain uniform dispersion liquid, B2 adding dopamine hydrochloride (mass concentration is 1%) into the dispersion liquid, stirring for 24 hours under the condition of continuously introducing oxygen for 24 hours, B3 carrying out centrifugal separation (8000 rpm,15 minutes) to obtain black precipitate, washing 3 times with deionized water, and freeze-drying for 48 hours to obtain the dopamine-modified nanocellulose whisker (thickness of dopamine layer is 25 nm).

The fractal structure silane coupling agent is prepared by adopting a method comprising the following steps of C1, mixing gamma-glycidyl ether propyl trimethoxy silane and branched polyethylenimine (the molar ratio is 1:1), heating to 75 ℃, stirring and reacting for 1h, C2, adding tetraethoxysilane (accounting for 10% of the total mass of gamma-glycidyl ether propyl trimethoxy silane and branched polyethylenimine) into a reaction system, continuously reacting for 2h at 75 ℃, C3, removing small molecular byproducts by reduced pressure distillation, and obtaining the amber transparent liquid fractal structure silane coupling agent.

The Mannich base type curing agent is prepared by the following steps of D1. Mixing bisphenol A epoxy resin (with an epoxy value of 0.45eq/100 g) and 4,4' -diaminodiphenyl methane according to a molar ratio of 1:2, reacting for 2h at 80 ℃, D2. Adding 4-hydroxybenzaldehyde (with a molar ratio of aldehyde group to amino group of 1:1.2) to perform Mannich reaction at 110 ℃ for 3h, and D3. Washing with acetone and drying in vacuum to obtain the orange viscous liquid Mannich base type curing agent.

The anti-permeability reinforcing agent is prepared by mixing nano silicon dioxide with the particle size of 150nm with methyl trimethoxy silane (CH ₃Si(OCH₃)₃) organosilicon water repellent according to the mass ratio of 3:1, stirring uniformly in absolute ethyl alcohol, and then vacuum drying to obtain the anti-permeability reinforcing agent.

The preparation method of the underwater self-catalyzed epoxy resin composite material based on the bionic structure comprises the following steps:

(1) Heating the modified epoxy resin precursor to 50 ℃;

(2) Sequentially adding a Mannich base type curing agent and a fractal structure silane coupling agent, and stirring at 800rpm for 15min to obtain a mixture;

(3) Adding dopamine modified nano cellulose whiskers and pH responsive microcapsule catalysts into the mixture, and performing ultrasonic dispersion for 20min under the conditions of 40kHz and 0.5W/cm ³ of power density;

(4) Finally adding the anti-permeability reinforcing agent, and performing vacuum defoaming for 15min to obtain the underwater self-catalyzed epoxy resin composite material based on the bionic structure.

Example 2

The underwater self-catalyzed epoxy resin composite material based on the bionic structure comprises, by weight, 50 parts of modified epoxy resin precursor, 5 parts of dopamine modified nanocellulose whisker, 3 parts of fractal-structure silane coupling agent, 22 parts of Mannich base type curing agent, 1 part of pH response type microcapsule catalyst and 7 parts of anti-permeability reinforcing agent.

The modified epoxy resin precursor is prepared by a method comprising the steps of heating bisphenol A epoxy resin (with an epoxy value of 0.50eq/100 g) to 75 ℃ to enable the bisphenol A epoxy resin to be fully melted, adding reactive diluent (dibutyl phthalate) with a mass ratio of 5% to stir for 35min to be uniform, adding polyethylene glycol (with a molecular weight of 600) with a mass ratio of 4% to stir for 35min, continuously stirring for 35min, adding organosilicon modifier (polysiloxane-dakaning Z-6020 amino-functionalized silane) with a mass ratio of 3%, stirring for 70min at 85 ℃, adding surfactant (polyether modified organosilicon-dakaning DC-57 surfactant) with a mass ratio of 1.5%, continuously stirring for 40min at 85 ℃, and conducting vacuum defoaming for 50min to obtain the modified epoxy resin precursor. The modified epoxy resin precursor has the characteristics that the viscosity is 10000-12000 mPa.s at 25 ℃, the epoxy value is 0.44-0.48eq/100g, the water contact angle is 60 degrees (obviously reduced compared with the 80 degrees of the common epoxy resin), and the wettability to a wet surface is enhanced by about 30 percent. The modification process further improves the flexibility and interface compatibility of the epoxy resin by adjusting the content of the organosilicon modifier and the molecular weight of the toughening agent, so that the epoxy resin shows more excellent wetting and adhesion performance in a humid environment.

The pH response type microcapsule catalyst is prepared by adopting a method comprising the following steps:

A1. Dispersing nano zinc oxide (average particle size of 70 nm) in cyclohexane, adding polydopamine as a wall material, stirring uniformly, weighing 0.8g of nano zinc oxide powder, adding into 60mL of cyclohexane, adding 0.3g of Cetyl Trimethyl Ammonium Bromide (CTAB) as a dispersing agent, performing ultrasonic treatment for 35 minutes by using an ultrasonic probe (power of 350W) to form stable nano zinc oxide dispersion, adding 1.2g of dopamine hydrochloride under the protection of nitrogen, immediately adding 30mL of Tris-HCl buffer (pH=8.5), and slowly dropwise adding 0.4g of pentaerythritol glycidyl ether (PTGE) as a crosslinking agent under the condition of mechanical stirring (600 rpm);

A2. Preparing microcapsules by an interfacial polymerization method, controlling the thickness of a polydopamine shell layer to be 65nm, transferring the dispersion system into a three-neck flask, introducing oxygen at a stirring speed of 700rpm, controlling the reaction temperature to be 28+/-2 ℃, controlling the reaction time to be 5 hours, enabling dopamine to self-polymerize under an oxidation condition, adding 15mL of polyvinyl alcohol (PVA) solution with a mass fraction of 1.5% as a stabilizer when the color of a reaction solution changes from transparent to dark brown, monitoring the pH value of the reaction system by adopting a pH meter, indicating that the formation is completed when the pH value reaches 8.2+/-0.2, collecting the microcapsules by centrifugal separation (600 rpm,15 minutes), washing the microcapsules with deionized water, ethanol and acetone for 4 times sequentially, drying the microcapsules in vacuum at 45 ℃ for 15 hours, obtaining a final product, measuring the thickness by a Transmission Electron Microscope (TEM), controlling the pH responsiveness test of the prepared microcapsules to be 65+/-5 nm, stabilizing the microcapsules in an aqueous solution with pH=7.0 for 48 hours, releasing more than 90% of zinc oxide microcapsules in an aqueous solution with the pH=11.5, and triggering the alkaline nano-zinc oxide microcapsules to meet the requirements of an underwater alkaline concrete environment.

The dopamine-modified nanocellulose whisker is prepared by a method comprising the following steps of B1 dispersing nanocellulose whisker (the mass fraction is 1.0% and the length-diameter ratio is 70) in Tris-HCl buffer solution (pH=8.5), carrying out ultrasonic treatment for 25 minutes to obtain uniform dispersion liquid, B2 adding dopamine hydrochloride (the mass concentration is 2%), wherein the mass ratio of the dopamine hydrochloride to the nanocellulose whisker is 3:1, stirring for 36h under the condition of continuously introducing oxygen, B3, carrying out centrifugal separation (10000 rpm,20 minutes) to obtain black precipitate, washing for 4 times by deionized water, and carrying out freeze drying for 60h to obtain the dopamine-modified nanocellulose whisker (the thickness of a dopamine layer is 35 nm).

The fractal structure silane coupling agent is prepared by adopting a method comprising the following steps of C1. Mixing gamma-glycidyl ether propyl trimethoxy silane and branched polyethylenimine (the molar ratio is 2:1), heating to 80 ℃, stirring and reacting for 1.5h, C2. Adding tetraethoxysilane (accounting for 20% of the total mass) into a reaction system, continuing to react for 3h, C3. Removing small molecular byproducts by reduced pressure distillation, and obtaining the amber transparent liquid fractal structure silane coupling agent.

The Mannich base type curing agent is prepared by adopting a method comprising the following steps of D1. Mixing bisphenol A epoxy resin (with an epoxy value of 0.50eq/100 g) and 4,4' -diaminodiphenyl methane according to a molar ratio of 1:2.5, reacting for 3h at 90 ℃, D2. Adding 3, 5-dinitrobenzaldehyde (with a molar ratio of aldehyde group to amino group of 1:1.3) for Mannich reaction, wherein the reaction temperature is 120 ℃, the reaction time is 4h, and D3. Washing by acetone and drying in vacuum to obtain the orange viscous liquid Mannich base type curing agent.

The anti-permeability reinforcing agent is prepared by mixing nano silicon dioxide with the particle size of 200nm with methyl trimethoxy silane (CH ₃Si(OCH₃)₃) organosilicon water repellent according to the mass ratio of 3:1, stirring uniformly in absolute ethyl alcohol, and then vacuum drying to obtain the anti-permeability reinforcing agent.

(1) Heating the modified epoxy resin precursor to 55 ℃;

(2) Sequentially adding a Mannich base type curing agent and a fractal structure silane coupling agent, and stirring at 1000rpm for 20min to obtain a mixture;

(3) Adding dopamine modified nano cellulose whiskers and pH responsive microcapsule catalysts into the mixture, and performing ultrasonic dispersion for 30min under the conditions of 40kHz and 0.7W/cm ³ of power density;

(4) Finally adding an anti-permeability enhancer (the nano silicon dioxide with the particle size of 200nm and the organosilicon water repellent are compounded according to the mass ratio of 3:1), and carrying out vacuum defoaming for 20min to obtain the underwater self-catalyzed epoxy resin composite material based on the bionic structure.

Example 3

The underwater self-catalyzed epoxy resin composite material based on the bionic structure comprises, by weight, 60 parts of modified epoxy resin precursors, 8 parts of dopamine modified nanocellulose whiskers, 5 parts of fractal-structure silane coupling agents, 30 parts of Mannich base curing agents, 2 parts of pH response microcapsule catalysts and 10 parts of anti-permeability reinforcing agents.

The modified epoxy resin precursor is prepared by a method comprising the steps of heating bisphenol A epoxy resin (with an epoxy value of 0.52eq/100 g) to 80 ℃ to enable the bisphenol A epoxy resin to be fully melted, adding a reactive diluent (anisole glycidyl ether) with a mass ratio of 6% to stir for 40min to be uniform, III adding polyethylene glycol (with a molecular weight of 800) with a mass ratio of 5% as a toughening agent, continuously stirring for 40min, IV adding an organosilicon modifier (polysiloxane-dacorning Z-6020 amino functionalized silane) with a mass ratio of 4%, stirring for 80min at 90 ℃, V adding a surfactant (polyether modified organosilicon-dacorning DC-57 surfactant) with a mass ratio of 2%, continuously stirring for 50min at 90 ℃, VI, and conducting vacuum defoaming for 60min to obtain the modified epoxy resin precursor. The modified epoxy resin precursor has the characteristics that the viscosity is 8000-10000 mPa.s at 25 ℃, the epoxy value is 0.46-0.50eq/100g, the water contact angle is 55 degrees (obviously reduced compared with the 80 degrees of the common epoxy resin), and the wettability to a wet surface is enhanced by about 35 percent. The modification process adopts a toughening agent with higher molecular weight and an organosilicon modifier with larger proportion, so that the hydrophilicity and flexibility of the epoxy resin are obviously improved, and the epoxy resin has optimal interface adaptability and adhesion capability in an underwater environment.

A1. Dispersing nano zinc oxide (average particle size of 80 nm) in cyclohexane, adding polydopamine as a wall material, stirring uniformly, weighing 1.2g of nano zinc oxide powder, adding into 70mL of cyclohexane, adding 0.4g of Cetyl Trimethyl Ammonium Bromide (CTAB) as a dispersing agent, performing ultrasonic treatment for 40 minutes by using an ultrasonic probe (power 400W) to form stable nano zinc oxide dispersion, adding 1.6g of dopamine hydrochloride under the protection of nitrogen, immediately adding 35mL of Tris-HCl buffer (pH=8.5), and slowly dropwise adding 0.5g of pentaerythritol glycidyl ether (PTGE) as a crosslinking agent under the condition of mechanical stirring (700 rpm);

A2. Preparing microcapsules by an interfacial polymerization method, controlling the thickness of polydopamine shell layers to be 80nm, transferring the dispersion system into a three-neck flask, introducing oxygen at a stirring speed of 800rpm, controlling the reaction temperature to be 30+/-2 ℃, controlling the reaction time to be 6 hours, enabling dopamine to self-polymerize under an oxidation condition, adding 20mL of 2% polyvinyl alcohol (PVA) solution as a stabilizer by mass fraction when the color of the reaction solution changes from transparent to dark brown, continuing stirring for 4 hours, enabling polydopamine shell layers to be fully formed, monitoring the pH value of the reaction system by a pH meter, when the pH value reaches 8.4+/-0.2, indicating that the shell layers are formed, collecting the microcapsules by centrifugal separation (800 rpm,20 minutes), washing for 5 times by deionized water, ethanol and acetone in sequence, drying in vacuum at 50 ℃ for 18 hours, obtaining a final product, measuring the thickness of the shell layers by a Transmission Electron Microscope (TEM), and testing the pH responsiveness of the prepared microcapsules, wherein the prepared microcapsules are stable in an aqueous solution with pH=7.0 for 72 hours, the microcapsules are free of cracks, and the microcapsules are triggered to be broken in an aqueous solution with pH=11.0 for more than 50 minutes, and the alkaline environment is triggered by the alkaline solution of zinc oxide.

The dopamine-modified nanocellulose whisker is prepared by a method comprising the steps of dispersing nanocellulose whisker (the mass fraction is 2.0%) in Tris-HCl buffer solution (pH=8.5), carrying out ultrasonic treatment for 30 minutes to obtain uniform dispersion liquid, adding dopamine hydrochloride (the mass concentration is 3%), stirring for 48h under the condition of continuously introducing oxygen in a mass ratio of 4:1 into the dispersion liquid, centrifuging (12000 rpm,25 minutes) to obtain black precipitate, washing 5 times with deionized water, and freeze-drying for 72 hours to obtain the dopamine-modified nanocellulose whisker (the thickness of a dopamine layer is 45 nm).

The fractal structure silane coupling agent is prepared by adopting a method comprising the following steps of C1, mixing gamma-glycidyl ether propyl trimethoxy silane and branched polyethylenimine (the molar ratio is 3:1), heating to 85 ℃, stirring and reacting for 2 hours, C2, adding tetraethoxysilane (accounting for 30% of the total mass of the mixture of gamma-glycidyl ether propyl trimethoxy silane and branched polyethylenimine) into a reaction system, continuing to react for 4 hours at 85 ℃, C3, and removing small molecular byproducts by reduced pressure distillation to obtain the amber transparent liquid fractal structure silane coupling agent.

The Mannich base type curing agent is prepared by the following steps of D1. Mixing bisphenol A epoxy resin (epoxy value 0.55eq/100 g) and 4,4' -diaminodiphenyl methane according to a molar ratio of 1:3, reacting for 4h at 100 ℃, D2. Adding 4-hydroxybenzaldehyde (molar ratio of aldehyde group to amino group is 1:1.5) to perform Mannich reaction, reacting at 130 ℃ for 6h, and D3. Washing with acetone and drying in vacuum to obtain the Mannich base type curing agent.

The anti-permeability reinforcing agent is prepared by mixing nano silicon dioxide with the particle size of 300nm with methyl trimethoxy silane (CH ₃Si(OCH₃)₃) organosilicon water repellent according to the mass ratio of 3:1, stirring uniformly in absolute ethyl alcohol, and then vacuum drying to obtain the anti-permeability reinforcing agent.

(1) Heating the modified epoxy resin precursor to 60 ℃;

(2) Sequentially adding a Mannich base curing agent and a fractal structure silane coupling agent, and stirring at 1200rpm for 30min to obtain a mixture;

(3) Adding dopamine modified nano cellulose whiskers and pH responsive microcapsule catalysts into the mixture, and performing ultrasonic dispersion for 40min under the conditions of 40kHz and power density of 1.0W/cm ³;

(4) Finally adding the anti-permeability reinforcing agent, and performing vacuum defoaming for 30min to obtain the underwater self-catalyzed epoxy resin composite material based on the bionic structure.

Example 4

The underwater self-catalyzed epoxy resin composite material based on the bionic structure comprises, by weight, 45 parts of modified epoxy resin precursor, 4 parts of dopamine modified nanocellulose whisker, 2 parts of fractal-structure silane coupling agent, 18 parts of Mannich base type curing agent, 0.8 part of pH response type microcapsule catalyst and 6 parts of anti-permeability reinforcing agent.

The modified epoxy resin precursor is prepared by a method comprising the steps of heating bisphenol A epoxy resin (with an epoxy value of 0.49eq/100 g) to 72 ℃ to enable the bisphenol A epoxy resin to be fully melted, adding a reactive diluent (dibutyl phthalate) with a mass ratio of 4.5%, stirring for 32min to be uniform, adding polyethylene glycol (with a molecular weight of 500) with a mass ratio of 3.5% as a toughening agent, continuously stirring for 32min, adding an organosilicon modifier (polysiloxane-dakangnin Z-6020 amino-functionalized silane containing amino) with a mass ratio of 2.5%, stirring for 65min at 82 ℃, adding a surfactant (polyether modified organosilicon-dakangnin DC-57 surfactant) with a mass ratio of 1.2%, continuously stirring for 35min at 82 ℃, and carrying out vacuum defoaming for 48min to obtain the modified epoxy resin precursor. The modified epoxy resin precursor has the characteristics of 11000-13000 mPa.s of viscosity at 25 ℃, epoxy value of 0.43-0.47eq/100g, water contact angle of 62 degrees (obviously reduced compared with the 80 degrees of common epoxy resin), and enhanced wettability to a wet surface by about 27%. The modification process balances the hydrophilicity and mechanical property of the material by introducing proper amount of organosilicon modifier and surfactant, so that the material shows good infiltration and adhesion performance in an underwater environment.

A1. Dispersing nano zinc oxide (average particle size of 60 nm) in cyclohexane, adding polydopamine as a wall material, stirring uniformly, weighing 0.6g of nano zinc oxide powder, adding the powder into 55mL of cyclohexane, adding 0.25g of Cetyl Trimethyl Ammonium Bromide (CTAB) as a dispersing agent, performing ultrasonic treatment for 32 minutes by using an ultrasonic probe (power of 320W) to form stable nano zinc oxide dispersion, adding 1.0g of dopamine hydrochloride under the protection of nitrogen, immediately adding 28mL of Tris-HCl buffer (pH=8.5), and slowly and dropwise adding 0.35g of pentaerythritol glycidyl ether (PTGE) as a crosslinking agent under the condition of mechanical stirring (550 rpm);

A2. Preparing microcapsules by an interfacial polymerization method, controlling the thickness of polydopamine shell layers to be 60nm, transferring the dispersion system into a three-neck flask, introducing oxygen at a stirring rate of 650rpm, controlling the reaction temperature to be 26+/-2 ℃, controlling the reaction time to be 4.5 hours, enabling dopamine to self-polymerize under an oxidation condition, adding 12mL of polyvinyl alcohol (PVA) solution with the mass fraction of 1.2% as a stabilizer when the color of the reaction solution changes from transparent to dark brown, continuing stirring for 2.5 hours, enabling polydopamine shell layers to be fully formed, monitoring the pH value of the reaction system by a pH meter, when the pH value reaches 8.1+/-0.2, indicating that the shell layers are formed, collecting the microcapsules by centrifugal separation (5500 rpm,12 minutes), washing for 3 times sequentially by deionized water, ethanol and acetone, drying in vacuum for 14 hours at 42 ℃, obtaining a final product, measuring the thickness of the shell layers by a Transmission Electron Microscope (TEM), controlling the prepared microcapsules to be in a range of 60+/-5 nm, performing pH responsiveness test, stabilizing the microcapsules in an aqueous solution with pH=7.0 for 36 hours, triggering the microcapsules to crack in an aqueous solution with the pH=11.8% and triggering the alkaline solution to crack in an aqueous solution of the alkaline solution.

The dopamine-modified nanocellulose whisker is prepared by a method comprising the steps of dispersing nanocellulose whisker (mass fraction is 0.8% and length-diameter ratio is 65) in Tris-HCl buffer solution (pH=8.5), carrying out ultrasonic treatment for 22 minutes to obtain uniform dispersion liquid, adding dopamine hydrochloride (mass concentration is 1.5%) into the dispersion liquid, stirring for 30 hours under the condition of continuously introducing oxygen for 2.5:1, carrying out centrifugal separation (9000 rpm,18 minutes) to obtain black precipitate, washing for 4 times by deionized water, and carrying out freeze drying for 54 hours to obtain the dopamine-modified nanocellulose whisker (thickness of a dopamine layer is 30 nm).

The fractal structure silane coupling agent is prepared by adopting a method comprising the following steps of C1. Mixing gamma-glycidyl ether propyl trimethoxy silane and branched polyethylenimine (the molar ratio is 1.5:1), heating to 78 ℃ and stirring for reaction for 1.2h, C2. Adding tetraethoxysilane (accounting for 15% of the total mass) into a reaction system, continuing to react for 2.5h, C3. Removing small molecular byproducts by reduced pressure distillation, and obtaining the amber transparent liquid fractal structure silane coupling agent.

The Mannich base type curing agent is prepared by adopting a method comprising the following steps of D1. Mixing bisphenol A epoxy resin (with an epoxy value of 0.48eq/100 g) and 4,4' -diaminodiphenyl methane according to a molar ratio of 1:2.2, reacting for 2.5 hours at 85 ℃, D2. Adding 4-hydroxybenzaldehyde (with a molar ratio of aldehyde group to amino group of 1:1.25) for Mannich reaction, wherein the reaction temperature is 115 ℃, the reaction time is 3.5 hours, and D3. Washing by acetone and drying in vacuum to obtain the orange viscous liquid Mannich base type curing agent.

The anti-permeability reinforcing agent is prepared by mixing nano silicon dioxide with the particle size of 180nm with methyl trimethoxy silane (CH ₃Si(OCH₃)₃) organosilicon water repellent according to the mass ratio of 3:1, stirring uniformly in absolute ethyl alcohol, and then vacuum drying to obtain the anti-permeability reinforcing agent.

(1) Heating the modified epoxy resin precursor to 53 ℃;

(2) Sequentially adding a Mannich base curing agent and a fractal structure silane coupling agent, and stirring at 900rpm for 18min to obtain a mixture;

(3) Adding dopamine modified nano cellulose whiskers and pH responsive microcapsule catalysts into the mixture, and performing ultrasonic dispersion for 25min under the conditions of 40kHz and 0.6W/cm ³ of power density;

(4) Finally adding an anti-permeability enhancer (the nano silicon dioxide with the particle size of 180nm and the organosilicon water repellent are compounded according to the mass ratio of 3:1), and carrying out vacuum defoaming for 18min to obtain the underwater self-catalyzed epoxy resin composite material based on the bionic structure.

Example 5

The underwater self-catalyzed epoxy resin composite material based on the bionic structure comprises, by weight, 55 parts of modified epoxy resin precursors, 6 parts of dopamine modified nanocellulose whiskers, 4 parts of fractal-structure silane coupling agents, 25 parts of Mannich base curing agents, 1.5 parts of pH response microcapsule catalysts and 8 parts of anti-permeability reinforcing agents.

The modified epoxy resin precursor is prepared by a method comprising the steps of heating bisphenol A epoxy resin (with an epoxy value of 0.51eq/100 g) to 78 ℃ to enable the bisphenol A epoxy resin to be fully melted, adding a reactive diluent (anisole glycidyl ether) with a mass ratio of 5.5%, stirring for 38min to be uniform, adding polyethylene glycol (with a molecular weight of 700) with a mass ratio of 4.5% as a toughening agent, continuously stirring for 38min, adding an organosilicon modifier (polysiloxane-dakangnin Z-6020 amino-functionalized silane containing amino groups) with a mass ratio of 3.5%, stirring for 75min at 88 ℃, adding a surfactant (polyether modified organosilicon-dakangnin DC-57 surfactant) with a mass ratio of 1.8%, continuously stirring for 45min at 88 ℃, and carrying out VI, and carrying out vacuum defoaming for 55min to obtain the modified epoxy resin precursor. The modified epoxy resin precursor has the characteristics that the viscosity is 9000-11000 mPa.s at 25 ℃, the epoxy value is 0.45-0.49eq/100g, the water contact angle is 58 degrees (obviously reduced compared with the 80 degrees of the common epoxy resin), and the wettability to a wet surface is enhanced by about 32 percent. The fluidity and interfacial compatibility of the material in an underwater environment are optimized by adjusting the proportion of the organosilicon modifier and the toughening agent in the modification process, so that the material shows excellent spreadability and adhesion under the high humidity condition.

A1. Dispersing nano zinc oxide (average particle size of 75 nm) in cyclohexane, adding polydopamine as a wall material, uniformly stirring, namely weighing 1.0g of nano zinc oxide powder, adding into 65mL of cyclohexane, adding 0.35g of Cetyl Trimethyl Ammonium Bromide (CTAB) as a dispersing agent, performing ultrasonic treatment for 38 minutes by using an ultrasonic probe (power of 380W) to form stable nano zinc oxide dispersion, adding 1.4g of dopamine hydrochloride under the protection of nitrogen, immediately adding 32mL of Tris-HCl buffer (pH=8.5), and slowly dropwise adding 0.45g of pentaerythritol glycidyl ether (PTGE) as a crosslinking agent under the condition of mechanical stirring (650 rpm);

A2. preparing microcapsules by an interfacial polymerization method, controlling the thickness of polydopamine shell layers to be 70nm, transferring the dispersion system into a three-neck flask, introducing oxygen at a stirring rate of 750rpm, controlling the reaction temperature to be 29+/-2 ℃, controlling the reaction time to be 5.5 hours, enabling dopamine to self-polymerize under an oxidation condition, adding 18mL of polyvinyl alcohol (PVA) solution with mass fraction of 1.8% as a stabilizer when the color of the reaction solution changes from transparent to dark brown, continuing stirring for 3.5 hours, enabling polydopamine shell layers to be fully formed, monitoring the pH value of the reaction system by a pH meter, when the pH value reaches 8.3+/-0.2, indicating that the shell layers are formed, collecting the microcapsules by centrifugal separation (7000 rpm,18 minutes), washing for 4 times sequentially by deionized water, ethanol and acetone, drying in vacuum at 48 ℃ for 16 hours, obtaining a final product, measuring the thickness of the shell layers by a Transmission Electron Microscope (TEM), controlling the prepared microcapsules to be in a range of 70+/-5 nm, performing pH responsiveness test, stabilizing the microcapsules in an aqueous solution with pH=7.0 for 60 hours, triggering the microcapsules to crack in an aqueous solution with pH=11.45% and triggering the alkaline solution to crack in the aqueous solution of zinc oxide to meet the requirements of the alkaline environment.

The dopamine-modified nanocellulose whisker is prepared by a method comprising the steps of dispersing nanocellulose whisker (with the mass fraction of 1.5% and the length-diameter ratio of 85%) in Tris-HCl buffer solution (with the pH value of 8.5), carrying out ultrasonic treatment for 28 minutes to obtain uniform dispersion liquid, adding dopamine hydrochloride (with the mass concentration of 2.5%) into the dispersion liquid, stirring for 42 hours under the condition of continuously introducing oxygen for 42 hours, and carrying out centrifugal separation (11000 rpm,22 minutes) to obtain black precipitate, washing for 4 times by deionized water, and carrying out freeze drying for 66 hours to obtain the dopamine-modified nanocellulose whisker (with the dopamine layer thickness of 40 nm).

The fractal structure silane coupling agent is prepared by adopting a method comprising the following steps of C1. Mixing gamma-glycidyl ether propyl trimethoxy silane and branched polyethylenimine (the molar ratio is 2.5:1), heating to 82 ℃ and stirring for reaction for 1.8h, C2. Adding tetraethoxysilane (accounting for 25% of the total mass) into a reaction system, continuing to react for 3.5h, C3. Removing small molecular byproducts by reduced pressure distillation, and obtaining the amber transparent liquid fractal structure silane coupling agent.

The Mannich base type curing agent is prepared by the following steps of D1. Mixing bisphenol A epoxy resin (with an epoxy value of 0.52eq/100 g) and 4,4' -diaminodiphenyl methane according to a molar ratio of 1:2.8, reacting for 3.5 hours at 95 ℃, D2. Adding 3, 5-dinitrobenzaldehyde (with a molar ratio of aldehyde group to amino group of 1:1.4) to perform Mannich reaction, wherein the reaction temperature is 125 ℃, the reaction time is 5 hours, and D3. Washing by acetone and drying in vacuum to obtain the orange viscous liquid Mannich base type curing agent.

The anti-permeability reinforcing agent is prepared by mixing nano silicon dioxide with the particle size of 250nm and methyl trimethoxy silane organosilicon water repellent according to the mass ratio of 3:1, stirring uniformly in absolute ethyl alcohol, and then vacuum drying to obtain the anti-permeability reinforcing agent.

(1) Heating the modified epoxy resin precursor to 58 ℃;

(2) Sequentially adding a Mannich base curing agent and a fractal structure silane coupling agent, and stirring at 1100rpm for 25min to obtain a mixture;

(3) Adding dopamine modified nano cellulose whiskers and pH responsive microcapsule catalysts into the mixture, and performing ultrasonic dispersion for 35min under the conditions of 40kHz and 0.8W/cm ³ of power density;

(4) Finally adding an anti-permeability enhancer (nano silicon dioxide with the particle size of 250nm and methyl trimethoxy silane (CH ₃Si(OCH₃)₃) organic silicon water repellent are compounded according to the mass ratio of 3:1), and carrying out vacuum defoaming for 25min to obtain the underwater self-catalyzed epoxy resin composite material based on the bionic structure.

Example 6

The difference between the underwater self-catalyzed epoxy resin composite material based on the bionic structure and the embodiment 1 is that 1) the length-diameter ratio of the nano cellulose whisker adopted in the preparation process of the dopamine modified nano cellulose whisker of the embodiment is 50, the thickness of the dopamine modified layer is 20nm, 2) the reaction temperature of the step C1 is 100 ℃ and the reaction time is 2h in the preparation process of the fractal structure silane coupling agent, the reaction temperature of the step C2 is 90 ℃, 3) the particle size of the nano silicon dioxide adopted in the preparation process of the anti-permeability enhancer is 100nm, and the rest is the same as the embodiment 1.

Example 7

The underwater self-catalyzed epoxy resin composite material based on the bionic structure comprises, by weight, 50 parts of modified epoxy resin precursor, 5.5 parts of dopamine modified nanocellulose whisker, 3 parts of fractal structure silane coupling agent, 22 parts of Mannich base type curing agent, 1.2 parts of pH response type microcapsule catalyst and 7.5 parts of anti-permeability reinforcing agent.

The preparation methods of the modified epoxy resin precursor, the permeation resistance enhancer and the pH-responsive microcapsule catalyst in this example are the same as in example 2;

The dopamine-modified nanocellulose whisker is prepared by a method comprising the steps of dispersing nanocellulose whisker (mass fraction is 1.2% and length-diameter ratio is 75) in Tris-HCl buffer solution (pH=8.5), performing ultrasonic treatment for 25 minutes to obtain uniform dispersion liquid, adding dopamine hydrochloride (mass concentration is 2.2%) into the dispersion liquid, stirring for 36 hours under the condition that oxygen is continuously introduced at room temperature of 25 ℃ for 3:1, performing centrifugal separation (10000 rpm,20 minutes) to obtain black precipitate, washing for 4 times with deionized water, and performing freeze drying for 60 hours to obtain the dopamine-modified nanocellulose whisker (thickness of dopamine layer is 35 nm).

The fractal structure silane coupling agent is prepared by adopting a method comprising the following steps of C1, mixing gamma-glycidyl ether propyl trimethoxy silane and branched polyethylenimine (the molar ratio is 2:1), heating to 110 ℃, stirring and reacting for 3 hours, C2, adding tetraethoxysilane (accounting for 20% of the total mass) into a reaction system, continuously reacting for 3 hours at 100 ℃, C3, and removing small molecular byproducts by reduced pressure distillation to obtain the amber transparent liquid fractal structure silane coupling agent.

The Mannich base type curing agent is prepared by adopting a method comprising the following steps of D1. Mixing bisphenol A epoxy resin (with an epoxy value of 0.50eq/100 g) and 4,4' -diaminodiphenyl methane according to a molar ratio of 1:2.5, reacting for 3h at 90 ℃, D2. Adding 3, 5-dinitrobenzaldehyde (with a molar ratio of aldehyde group to amino group of 1:1.35) for Mannich reaction, wherein the reaction temperature is 120 ℃, the reaction time is 4.5h, and D3. Washing by acetone and drying in vacuum to obtain the orange viscous liquid Mannich base type curing agent.

The preparation method of the underwater self-catalyzed epoxy resin composite material based on the bionic structure in the embodiment is the same as that in the embodiment 2.

Example 8

The difference between the underwater self-catalyzed epoxy resin composite material based on the bionic structure and the embodiment 3 is that 1) the length-diameter ratio of the nano cellulose whisker adopted in the preparation process of the dopamine modified nano cellulose whisker of the embodiment is 100, the thickness of the dopamine modified layer is 50nm, 2) the reaction temperature of the step C1 is 120 ℃ and the reaction time is 4 hours in the preparation process of the fractal-structure silane coupling agent, the reaction temperature of the step C2 is 110 ℃, and the rest is the same as the embodiment 1.

Example 9 (Water repellent variant example)

The underwater self-catalyzed epoxy resin composite material based on the bionic structure comprises, by weight, 45 parts of modified epoxy resin precursor, 4 parts of dopamine modified nanocellulose whisker, 2 parts of fractal structure silane coupling agent, 20 parts of Mannich base type curing agent, 0.8 part of pH response type microcapsule catalyst and 6 parts of anti-permeability reinforcing agent.

The permeation resistant enhancer of this example was different from example 1 in that the mass ratio of nanosilicon dioxide to organic water repellent was 2:1, the remainder remaining consistent with example 1.

The epoxy resin precursor, dopamine modified nanocellulose whisker, fractal-structure silane coupling agent, mannich base curing agent and pH-responsive microcapsule catalyst employed in this example were all consistent with example 1.

The preparation method of the underwater self-catalyzed epoxy resin composite material based on the bionic structure in the embodiment is the same as that in the embodiment 1.

Example 10 (Water repellent modified example)

The underwater self-catalyzed epoxy resin composite material based on the bionic structure in the embodiment is different from the embodiment 9 only in that the mass ratio of nano silicon dioxide to organosilicon water repellent adopted in the preparation process of the anti-permeability enhancer is 4:1, and the rest is the same as the embodiment 9.

Example 11 (fractal Structure silane coupling agent variant example)

The underwater self-catalyzed epoxy resin composite material based on the bionic structure comprises, by weight, 52 parts of modified epoxy resin precursors, 6 parts of dopamine modified nanocellulose whiskers, 4 parts of fractal-structure silane coupling agents, 23 parts of Mannich base curing agents, 1.3 parts of pH response microcapsule catalysts and 8 parts of anti-permeability reinforcing agents.

The fractal structure silane coupling agent in the embodiment is different from the fractal structure silane coupling agent in the embodiment 7 only in that the molar ratio of gamma-glycidyl ether propyl trimethoxy silane to branched polyethylenimine is 2.5:1, and the addition amount of tetraethoxysilane is 15% of the total mass of gamma-glycidyl ether propyl trimethoxy silane and branched polyethylenimine;

the preparation method of the underwater self-catalyzed epoxy resin composite material based on the bionic structure of the embodiment is the same as that of the embodiment 7 except other components except the fractal structure silane coupling agent.

Example 12 (fractal Structure silane coupling agent variant example)

The bionic structure-based underwater self-catalyzed epoxy resin composite material is different from example 11 in that in the preparation process of the fractal structure silane coupling agent, the dosage of tetraethoxysilane is 25% of the total mass of gamma-glycidyl ether propyl trimethoxysilane and branched polyethyleneimine, and the balance is kept consistent with example 11.

Comparative example 1

The epoxy resin composite material of the comparative example comprises, by weight, 50 parts of a modified epoxy resin precursor, 12 parts of dopamine modified nanocellulose whiskers, 3 parts of a fractal structure silane coupling agent, 22 parts of a Mannich base type curing agent, 1 part of a pH response microcapsule catalyst and 7 parts of an anti-permeability reinforcing agent.

The preparation method of the above components and the composite material of this comparative example was the same as in example 2.

Comparative example 2

The epoxy resin composite material of the comparative example comprises, by weight, 50 parts of a modified epoxy resin precursor, 5 parts of dopamine modified nanocellulose whiskers, 3 parts of a fractal-structure silane coupling agent, 22 parts of a Mannich base curing agent and 7 parts of an anti-permeability reinforcing agent.

Comparative example 3

The epoxy resin composite material of the comparative example comprises, by weight, 50 parts of a modified epoxy resin precursor, 5 parts of dopamine modified nanocellulose whiskers, 8 parts of a fractal structure silane coupling agent, 22 parts of a Mannich base type curing agent, 1 part of a pH responsive microcapsule catalyst and 7 parts of an anti-permeability reinforcing agent.

Comparative example 4

The epoxy resin composite material of the comparative example comprises, by weight, 50 parts of a modified epoxy resin precursor, 5 parts of dopamine modified nanocellulose whiskers, 3 parts of a fractal structure silane coupling agent, 22 parts of a common polyamide curing agent (non-Mannich base), 1 part of a pH responsive microcapsule catalyst and 7 parts of an anti-permeability reinforcing agent.

Wherein the above-mentioned conventional polyamide curing agent is prepared by reacting dimer acid with polyethylene polyamine, which is obtained by reacting 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 part by weight of catalyst (triphenylphosphine) at 170℃for 5 hours, and then removing water generated by the reaction under reduced pressure.

The main characteristic parameters of the curing agent are amine value 160-180mgKOH/g, viscosity at 25 ℃ is 9000-12000 mPa.s, pH value is about 9.0-10.0, and the appearance is amber semitransparent viscous liquid.

Comparative example 5

The composite material provided by the comparative example comprises, by weight, 50 parts of a modified epoxy resin precursor, 5 parts of dopamine modified nanocellulose whiskers, 3 parts of a fractal structure silane coupling agent, 22 parts of a Mannich base curing agent, 1 part of a pH response microcapsule catalyst and 15 parts of an anti-permeability reinforcing agent.

The preparation method of each component and the composite material of the comparative example is the same as that of example 2, and is not repeated.

Comparative example 6 (preparation of modified epoxy resin precursor)

The comparative example differs from example 2 only in that the preparation method of the modified epoxy resin precursor is different from example 2, and the rest remains the same as example 2;

The preparation method of the modified epoxy resin precursor of the comparative example comprises the steps of I, heating bisphenol A type epoxy resin (with an epoxy value of 0.50eq/100 g) to 75 ℃ to enable the bisphenol A type epoxy resin to be fully melted, II, directly adding an organosilicon modifier (polysiloxane containing amino groups) with a mass ratio of 5%, stirring at 75 ℃ for 60min, III, and carrying out vacuum defoaming for 30min to obtain the modified epoxy resin precursor.

The modified epoxy resin precursor is free from adding reactive diluent, toughening agent and surfactant, the water contact angle is 75 degrees, and the wettability to a wet surface is only enhanced by about 8 percent.

Comparative example 7 (modification of conditions for the preparation of dopamine-modified nanocellulose whiskers)

The comparative example differs from example 2 only in that the method of preparing the dopamine-modified nanocellulose whiskers is different from example 2, the remainder remaining in agreement with example 2.

The preparation method of the dopamine-modified nanocellulose whisker comprises the following steps of B1, dispersing nanocellulose whisker (the mass fraction is 1.0%) in phosphate buffer with pH=7.0, carrying out ultrasonic treatment for 25 minutes, B2, adding dopamine hydrochloride (the mass concentration is 2%) into the dispersion, stirring for 36 hours (no oxygen is introduced) at normal temperature, B3, carrying out centrifugal separation (10000 rpm,20 minutes) to obtain a light gray precipitate, washing for 4 times by deionized water, and freeze-drying for 60 hours to obtain the dopamine-modified nanocellulose whisker.

Comparative example 8 (Shell thickness of pH responsive microcapsule)

This comparative example differs from example 2 only in that the preparation method of the pH-responsive microcapsule catalyst is different from example 2, and the remainder remains the same as example 2.

Specifically, the preparation method of the pH-responsive microcapsule catalyst of the present comparative example is different from example 2 in that the reaction time is prolonged to 8 hours during the interfacial polymerization, resulting in a polydopamine shell thickness of 120nm.

Comparative example 9 (preparation method of modified Mannich base type curing agent)

This comparative example differs from example 2 only in the preparation of the Mannich base type hardener, and remains the same as in example 2.

The preparation method of the Mannich base type curing agent of the comparative example specifically comprises the following steps:

D1. Bisphenol A epoxy resin (epoxy value 0.50eq/100 g) was mixed with 4,4' -diaminodiphenyl methane in a 1:1 molar ratio (lower than the range of 1:2-3 in the claims) and reacted at 90℃for 3h;

D2. Adding 3, 5-dinitrobenzaldehyde (the molar ratio of aldehyde groups to amino groups is 1:0.8, which is lower than the range of 1:1.2-1.5 in the claims), and carrying out Mannich reaction at 100 ℃ (the range of lower than 110 ℃) for 2 hours;

D3. Washing with acetone, and vacuum drying to obtain the curing agent.

Comparative example 10 (Using different types of fractal Structure silane coupling agents)

The comparative example is different from example 2 only in that the fractal structure silane coupling agent adopts linear polyethylenimine (non-bifurcated) instead of branched polyethylenimine, and the rest remains the same as example 2.

The fractal structure silane coupling agent of the comparative example is prepared by C1. Mixing gamma-glycidyl ether propyl trimethoxy silane and linear polyethylenimine (molar ratio 2:1), heating to 80 ℃ and stirring for reaction for 1.5h, C2. Adding tetraethoxysilane (accounting for 20% of the total mass) into a reaction system, continuing to react for 3h at 80 ℃, and C3. Removing small molecular byproducts by reduced pressure distillation to obtain the linear structure silane coupling agent.

Comparative example 11 (totally without fractal silane coupling agent)

The comparative example only differs from example 2 in that the modified epoxy resin precursor comprises 53 parts by weight of modified epoxy resin precursor, 5 parts by weight of dopamine modified nanocellulose whisker, 22 parts by weight of Mannich base type curing agent, 1 part by weight of pH responsive microcapsule catalyst and 7 parts by weight of anti-permeation enhancer, no fractal structure silane coupling agent is added, and the balance is kept consistent with example 2.

Experimental example

The composite materials of the above examples and comparative examples were tested for initial set time, underwater bond strength, and chloride ion permeation resistance:

The testing method comprises the following steps:

The initial setting time is measured by ASTM C191 standard improvement method, which comprises (1) coating composite material on a glass plate to form a uniform coating with thickness of 2mm, (2) placing the sample in a constant temperature and humidity box with relative humidity of 95+ -2%, controlling the temperature at 23+ -2 ℃, (3) vertically inserting a Vicat needle (diameter 1mm, weight 300 g) into the surface of the sample at fixed time intervals (initial 2min, later 1 min), recording the initial setting time when the needle tip cannot penetrate the surface of the sample for 2mm depth, (5) testing 3 times for each sample, and taking the average value as the final result.

The underwater bond strength was measured by the ASTM C882/C882M standard method (1) preparing concrete test pieces having dimensions of 100mm X50 mm and a surface saturation moisture content of 95.+ -. 3%, (2) uniformly coating the composite material on the contact surface of the two concrete test pieces with a coating thickness of 2.+ -. 0.2mm, (3) butt-pressing the two test pieces coated with the composite material under water (depth: 10cm, temperature: 20.+ -. 2 ℃ C.) and applying a pressure of 0.05MPa, (4) after the underwater maintenance for 24 hours, performing a shear strength test at a loading rate of 2mm/min using a universal material tester, (5) recording the maximum load at the time of shear failure divided by the bonding area, 6) testing 5 groups of test pieces for each material, taking the average value after removing the maximum value and the minimum value as the final result, (7) additionally performing a long-term underwater immersion test (28 days and 90 days, respectively) on the samples of examples 2 and 3 to evaluate the durability.

The method comprises the steps of (1) preparing a disc sample with a diameter of 100mm and a thickness of 50mm by using a composite material, (2) curing the sample for 7 days under the conditions of a temperature of 23+/-2 ℃ and a relative humidity of 50+/-5%, (3) placing the sample in a two-chamber electromigration device, filling a cathode chamber with 0.3mol/L NaOH solution and an anode chamber with 3% NaCl solution, (4) applying 30V direct voltage for 6 hours, (5) disconnecting the sample and spraying 0.1mol/L AgNO ₃ solution for color development after the test is finished, measuring the migration depth of chloride ions, (6) calculating the chloride ion diffusion coefficient D= (RT/zFE) · (xd-alpha ++xd)/T according to an unsteady migration equation, wherein 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 ionic valence (chloride ion) is 1), F is the C32/m 34, and the average value of the ionic value is 3 m/m (C) is the average value of the ionic value, and (m) is the average value of the ionic value is 3m (m) is the average value of the electrical constant (m) is the average value of 3 m) and (m) is the average value of the electrical value (m) is 8, and (m) is the absolute value) is 8, and the standard is determined, and the test is carried out 4 days of drying) after 30 cycles to evaluate long-term durability.

The test results are shown in table 1 below:

TABLE 1

As can be seen from table 1 above:

The biomimetic-structure-based underwater self-catalyzed epoxy resin composite of examples 1-3 has a chloride ion permeation resistance coefficient of 2.3X10 ^-12m²/s、1.8×10^-12m²/s、1.4×10^-12m²/s after 30 cycles, which increases by 28%, 20% and 17%, respectively, and the bonding strength of the biomimetic-structure-based underwater self-catalyzed epoxy resin composite of examples 2 and 3 after underwater soaking was tested, namely, the bonding strength of the biomimetic-structure-based underwater self-catalyzed epoxy resin composite of example 2 after 28 days was 3.0MPa (retention rate 94%), the bonding strength of the biomimetic-structure-based underwater self-catalyzed epoxy resin composite after 90 days was 2.8MPa (retention rate 88%), the bonding strength of the biomimetic-structure-based underwater self-catalyzed epoxy resin composite of example 3.3MPa (retention rate 94%) after 28 days, and the bonding strength of the biomimetic-structure-based underwater self-catalyzed epoxy resin composite after 90 days was 3.1MPa (retention rate 89%). The underwater self-catalyzed epoxy resin composite material based on the bionic structure has the advantages of short initial fixing time, high underwater bonding strength, good chloride ion permeation resistance and good durability.

The composite material of comparative example 1 shows too high viscosity and poor workability, and because the content of dopamine modified nanocellulose whisker is too high, an excessively dense network structure is formed inside the system, instead, the progress of the crosslinking reaction is hindered, the curing time is prolonged, and the bonding strength of the material is reduced.

Due to the lack of the pH-responsive microcapsule catalyst, the composite material of comparative example 2 failed to release the catalyst to accelerate the curing reaction when contacting the alkaline concrete environment, resulting in a significant extension of the underwater curing time, a significant decrease in the adhesive strength, and a deterioration in the permeation resistance.

Because the fractal structure silane coupling agent content is too high, the crosslinking density is uneven, and excessive stress concentration points are generated, so that microcracks exist in the composite material of the comparative example 3 after curing, and the impermeability and the bonding strength of the material are greatly reduced.

Because the conventional polyamide curing agent is used for replacing the Mannich base curing agent in the comparative example 4, the conventional polyamide curing agent does not contain active amine groups introduced by the Mannich reaction, so that the reaction activity is obviously reduced in an underwater environment, the function of releasing the amine groups by ion exchange cannot be effectively exerted, the curing rate is slow, and the interface bonding strength is low.

As the content of the anti-permeability reinforcing agent in the composite material of the comparative example 5 is too high, nano silicon dioxide is aggregated in the system to form a large number of microscopic interface defects, the curing reaction is uneven, the curing time is prolonged, and the bonding strength of the material is reduced.

The reactive diluent, the toughening agent and the surfactant are omitted in the preparation process of the modified epoxy resin precursor of the comparative example 6, the water contact angle is 75 degrees, the wettability to the wet surface is only enhanced by about 8 percent, the initial curing time of the epoxy resin composite material of the comparative example 6 is prolonged to 30 minutes, and the anti-chloride ion permeability is poor.

In the preparation process of the dopamine-modified nanocellulose whisker in comparative example 7, due to the lack of alkaline environment and oxygen conditions, the oxidation polymerization reaction of dopamine is incomplete, and enough catechol functional groups cannot be formed on the surface of cellulose. The epoxy resin composite material of comparative example 7 has prolonged initial curing time, reduced underwater adhesive strength, and poor resistance to penetration of chloride ions.

The pH-responsive microcapsule of comparative example 8 has an excessively thick shell layer, and the cracking rate in an alkaline environment is reduced, so that it is difficult to release the catalyst in time, resulting in a significant extension of the curing time.

In the preparation process of the Mannich base type curing agent of the comparative example 9, the addition amount of diamino diphenyl methane and aldehyde groups is insufficient, the reaction temperature is low, the Mannich reaction is incomplete, the content of active amine groups in the curing agent is low, and the initial curing time of the epoxy resin composite material of the comparative example 9 is prolonged, the underwater bonding strength is reduced, and the anti-chloride ion permeation performance is poor.

The fractal structure silane coupling agent of the comparative example 10 adopts linear polyethylenimine (non-bifurcation type) to replace branched polyethylenimine, and the linear structure can not form a fractal interface transition layer similar to a plant root system, so that interface stress is concentrated, the durability of the epoxy resin composite material of the comparative example is poor, and the anti-chloride ion permeation performance is poor.

The epoxy resin composite material of comparative example 11 omits the silane coupling agent, resulting in no gradient transition layer at the interface, concentrated thermal stress, significantly reduced long-term durability, and poor resistance to permeation of chloride ions.

In conclusion, the self-catalyzed epoxy resin composite material for underwater concrete repair is successfully developed by simulating a mussel adhesion mechanism through the dopamine modified nanocellulose whisker, simulating a plant root system structure through the fractal structure silane coupling agent and combining a pH response type microcapsule catalyst. The material has excellent underwater bonding performance, quick curing property and permeation resistance, is particularly suitable for repairing a concrete structure in a high-humidity environment such as a marine tidal range area, can realize the integration of quick underwater construction and long-acting protection, and has important engineering application value.

The above description is only of the preferred embodiments of the present invention and is not intended to limit the present invention, but various modifications and variations can be made to the present invention by those skilled in the art. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. An underwater autocatalytic epoxy resin composite material based on a biomimetic structure, characterized by comprising the following components in parts by weight:

40-60 parts of modified epoxy resin precursor, 3-8 parts of dopamine-modified nanocellulose whiskers, 1-5 parts of silane coupling agent, 15-30 parts of curing agent, 0.5-2 parts of microcapsule catalyst and 5-10 parts of anti-permeation enhancer;

The modified epoxy resin precursor has a viscosity of 8000-15000 mPa·s at 25° C., an epoxy value of 0.42-0.50 eq/100 g, and a water contact angle of 55°-65°.

2. The underwater autocatalytic epoxy resin composite material based on a biomimetic structure according to claim 1, wherein the modified epoxy resin precursor is prepared by a method comprising the following steps:

1. heating bisphenol A epoxy resin until it is melted;

II. Add reactive diluent and stir until uniform;

III. Add toughening agent and continue stirring;

IV. Add silicone modifier and stir;

V. Add surfactant and continue stirring;

VI. vacuum degassing to obtain the epoxy resin precursor;

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; in step IV, the organosilicon modifier is amino-containing polysiloxane; in step V, the surfactant is polyether-modified organosilicon;

More preferably, in step I, the epoxy value of the bisphenol A epoxy resin is 0.48-0.52 eq/100 g, and the heating temperature is 70-80° C.; in step II, the amount of the reactive diluent added is 4wt%-6wt%, and the stirring time is 30-40 min; in step III, the amount of the toughening agent added is 4wt%-5wt%, and the stirring time is 30-40 min; in step IV, the amount of the organosilicon modifier added is 2wt%-4wt%, the stirring temperature is 80-90° C., and the stirring time is 60-80 min; in step V, the amount of the surfactant added is 1wt%-2wt%, the stirring temperature is 80-90° C., and the stirring time is 30-50 min; and in step VI, the vacuum degassing time is 45-60 min.

3. The underwater autocatalytic epoxy resin composite material based on a biomimetic structure according to claim 1, wherein the dopamine-modified nanocellulose whiskers are prepared by a method comprising the following steps:

B1. Disperse the nanocellulose whiskers in Tris-HCl buffer and sonicate to obtain a uniform dispersion;

B2. dopamine hydrochloride was added to the dispersion and stirred under an oxygen atmosphere for 24-48h;

B3. Centrifugation and freeze-drying the resulting solid to obtain the dopamine-modified nanocellulose whiskers;

Preferably, the mass fraction of the 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.

4. The underwater autocatalytic epoxy resin composite material based on a biomimetic structure according to claim 1, wherein the microcapsule catalyst is a pH-responsive microcapsule catalyst, and the pH-responsive microcapsule catalyst is prepared by a method comprising the following steps:

A1. Disperse nano zinc oxide in an organic solvent, add polymer wall material, and stir evenly;

A2. Prepare microcapsules using interfacial polymerization to control the degree of crosslinking of the wall material;

Preferably, the shell layer of the pH-responsive microcapsule catalyst has a thickness of 50-80 nm.

5. The underwater autocatalytic epoxy resin composite material based on a biomimetic structure according to claim 1, wherein the silane coupling agent is a fractal silane coupling agent, and the fractal silane coupling agent is prepared by a method comprising the following steps:

C1. Mix γ-glycidyl ether propyl trimethoxysilane and branched polyethyleneimine, heat and stir to react;

C2. Tetraethoxysilane was added to the reaction system and the reaction was continued for 2-4 hours;

C3. Distill under reduced pressure to obtain a fractal silane coupling agent.

6. The underwater autocatalytic epoxy resin composite material based on a biomimetic structure according to claim 5, characterized in that in step C1, the molar ratio of γ-glycidyl ether propyl trimethoxysilane to branched polyethyleneimine is 1:1-3:1;

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

7. The underwater autocatalytic epoxy resin composite material based on a biomimetic structure according to claim 1, wherein the curing agent is a Mannich base curing agent, and the Mannich base curing agent is prepared by a method comprising the following steps:

D1. Mix bisphenol A epoxy resin and 4,4'-diaminodiphenylmethane in a molar ratio of 1:(2-3) and react at 80-100°C for 2-4h;

D2. Add a benzaldehyde derivative for Mannich reaction, control the aldehyde to amino molar ratio of 1: (1.2-1.5), the reaction temperature is 110-130 ° C, the reaction time is 3-6h;

D3 washed with acetone and dried in vacuo to obtain an orange viscous liquid, which is the Mannich base curing agent;

Preferably, in step D1, the epoxy value of the bisphenol A epoxy resin is 0.45-0.55eq/100g;

In step D2, the benzaldehyde derivative is 4-hydroxybenzaldehyde and/or 3,5-dinitrobenzaldehyde.

8. The underwater autocatalytic epoxy resin composite material based on a biomimetic structure according to claim 1, wherein the anti-permeation enhancer is a mixture of nano-silicon dioxide and an organosilicon hydrophobic agent;

Preferably, the mass ratio of the nano-silica to the organosilicon hydrophobic agent is (2-4):1;

More preferably, the particle size of the nano-silica is 100-300 nm.

9. The method for preparing an underwater autocatalytic epoxy resin composite material based on a biomimetic structure according to any one of claims 1 to 8, characterized in that it comprises the following steps:

(1) heating the modified epoxy resin precursor to 50-60° C.;

(2) adding a Mannich base curing agent and a fractal structure silane coupling agent in sequence, and stirring to obtain a mixture;

(3) adding dopamine-modified nanocellulose whiskers and pH-responsive microcapsule catalyst to the mixture and performing ultrasonic dispersion;

(4) finally adding an anti-seepage enhancer, and vacuum degassing to obtain the underwater autocatalytic epoxy resin composite material based on the bionic structure;

Preferably, in step (2), the stirring speed is 800-1200 rpm and the stirring time is 15-30 min;

In step (3), the ultrasound frequency is 40 kHz, the power density is 0.5-1.0 W/cm ³ , and the ultrasound time is 20-40 min.

10. Use of the underwater autocatalytic epoxy resin composite material based on a biomimetic structure according to any one of claims 1 to 8 in the repair of concrete structures in ocean tidal range areas.