An adhesive with strong underwater adhesion and rapid onset of action, its preparation method and application.

Abstract

This invention belongs to the field of adhesive technology, and relates to an adhesive with strong underwater adhesion and rapid onset of action, its preparation method, and its applications. The adhesive is prepared by melt reaction of raw materials including thioctic acid, polyethyleneimine, and catechol under solvent-free conditions. Thioctic acid undergoes ring-opening polymerization to form a polymer network containing dynamic disulfide bonds, providing the adhesive with cohesive strength and recyclability; polyethyleneimine participates in network construction through its amino groups and enhances the cohesive effect of the system; catechol enhances the interfacial interaction between the adhesive and the substrate surface. The synergistic effect of these three components enables rapid and effective adhesion underwater, exhibiting high adhesion strength, long-term stability, environmental adaptability, and recyclability. The underwater adhesion strength reaches 8.35 MPa, maintaining high adhesion strength even in special environments. The preparation method of this invention is simple, requires no external solvent, and is suitable for underwater repair, wet surface bonding, and adhesion and fixation of various substrates.

Description

Technical Field

[0001] This invention relates to the field of adhesive technology, specifically to a solvent-free melt-reactive strong underwater adhesion adhesive, its preparation method and application, and more particularly to an adhesive composed of thioctic acid, polyethyleneimine and catechol, suitable for underwater or humid environments. Background Technology

[0002] Adhesives are widely used in building repair, equipment manufacturing, electronic packaging, marine engineering, and routine maintenance. Conventional adhesives typically require application to dry interfaces. When the bonding interface is wet or completely submerged underwater, the hydration layer on the substrate surface hinders effective contact between the adhesive and the substrate, leading to a significant decrease in interfacial bond strength. Therefore, developing high-strength adhesives that can be used directly underwater or in humid environments is of significant application value.

[0003] Existing underwater adhesives mainly include solid tape adhesives and liquid adhesives. Solid tapes are relatively easy to apply, but they are often difficult to fully adhere to complex and rough surfaces, and their bond strength is limited. Liquid adhesives can fill irregular interfaces to some extent, but their formation of strong bonds underwater usually depends on a long curing time. Some systems also require light, heat, metal ion cross-linking, or other external stimuli, increasing the difficulty of underwater operation.

[0004] In recent years, lipoic acid has attracted attention in recyclable, self-healing, and wet interface adhesion materials due to its ring-opening polymerizable 1,2-dithiopentane structure, which can form a polymer network containing dynamic disulfide bonds. Various modification approaches have been disclosed for lipoic acid-based adhesives. For example, CN118436843A discloses an anti-swelling lipoic acid-based gel adhesive, its preparation method, and its application. This technology adds lipoic acid powder and catechol powder to a polyethyleneimine solution, obtaining aggregates or patches through liquid-liquid phase separation, primarily for medical adhesion on wet tissue surfaces. Another example is CN113621342A, which discloses a solvent-free adhesive, its preparation method, and its application. Its raw materials include lipoic acid and / or its derivatives, polyphenolic compounds, and inorganic iron salts. The adhesive is formed through high-temperature self-polymerization and cross-linking via non-covalent and metal coordination bonds, and can be used for adhesion in wet or acidic environments.

[0005] However, the above-mentioned technical solutions still cannot solve the main technical problems of this invention. The former mainly relies on liquid-liquid phase separation in an aqueous system to form gel aggregates, and its application is mainly focused on wet tissue adhesion. Therefore, its adhesive strength is not strong and it is difficult to apply to fields requiring strong adhesion, such as underwater construction adhesion. The latter introduces inorganic iron salts to construct an adhesive network through metal coordination. It is also applied to the medical adhesion field. Therefore, its adhesive strength is only 20 kPa, which is also unsuitable for applications requiring strong adhesion. The prior art has not disclosed a technical solution for forming a strong underwater adhesive by a one-step melt reaction of thioctic acid, low molecular weight polyethyleneimine, and catechol without the addition of external solvents. Nor has it revealed the synergistic enhancement effect of small molecule catechol and low molecular weight polyethyleneimine on underwater interfacial adhesion and network cohesive strength in the thioctic acid melt reaction system. Therefore, this invention is proposed to provide an adhesive system with a simple composition, mild preparation conditions, no need for external solvents, and the ability to achieve rapid and effective adhesion and high-strength and durable adhesion in underwater or humid environments. Summary of the Invention

[0006] The purpose of this invention is to overcome the problems of insufficient interfacial bonding, long onset time, complex operation, and difficulty in balancing long-term stability and recyclability of existing underwater adhesives in humid or underwater environments, and to provide an adhesive with strong underwater adhesion and rapid onset capability, as well as its preparation method and application.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: An adhesive with strong underwater adhesion and rapid onset of action is provided, wherein the adhesive is prepared by melt reaction of raw materials including thioctic acid, polyethyleneimine and catechol under conditions without external solvent; wherein, based on a mass fraction of 1 part of thioctic acid, a mass fraction of 0.25-1.0 part of polyethyleneimine and a mass fraction of 0.25-1.0 part of catechol.

[0008] In this invention, lipoic acid, as the main component, undergoes ring-opening polymerization under heating conditions to form a polymer network containing dynamic disulfide bonds, providing the adhesive with cohesive strength, deformability, and recyclability. Polyethyleneimine, rich in amino groups, can participate in network construction through hydrogen bonding, electrostatic interactions, and / or acid-base interactions, enhancing the network stability within the adhesive. Catechol, as a small-molecule phenolic interfacial component, can form multiple interfacial interactions with metal oxide layers, inorganic substrates, and polar surfaces through its phenolic hydroxyl groups, thereby improving underwater interfacial adhesion. Compared to existing lipoic acid-based gel adhesives, this invention does not involve adding lipoic acid and catechols to a polyethyleneimine solution and forming aggregates or patches through liquid-liquid phase separation. Instead, it uses lipoic acid, low-molecular-weight polyethyleneimine, and catechol as the three components to directly form an adhesive through a one-step melt reaction without added solvents. This technical solution does not rely on liquid phase separation processes, nor does it require the introduction of inorganic metal salts for coordination crosslinking. The preparation process is simpler, and the resulting adhesive can be directly used for bonding various substrates in underwater or humid environments, exhibiting strong underwater adhesion performance and rapid onset of action.

[0009] Preferably, the relative molecular mass of the polyethyleneimine is 400-1000, more preferably 600-1000.

[0010] Preferably, the mass percentage of lipoic acid in the raw material is not higher than 65%, and / or the mass percentage of catechol in the raw material is not higher than 43%, and / or the mass percentage of polyethyleneimine in the raw material is not lower than 15%.

[0011] Preferably, based on 1 part by mass of lipoic acid, the mass of polyethyleneimine is 0.3-0.7 parts by mass, and the mass of catechol is 0.3-0.7 parts by mass.

[0012] More preferably, the mass ratio of thioctic acid, polyethyleneimine, and catechol is 3:1:1.

[0013] Preferably, the melting reaction temperature is 150-180℃, more preferably 160-170℃, and even more preferably 160℃.

[0014] Preferably, the stirring speed for the melting reaction is 400-600 r / min, more preferably 500-550 r / min.

[0015] Preferably, the melting reaction time is 10-30 min, more preferably 20 min.

[0016] Preferably, the adhesive exhibits an underwater adhesion strength of not less than 2 MPa on aluminum sheets, and this adhesion strength is maintained for at least 3 weeks, demonstrating excellent and sustained underwater adhesion strength. It can be recycled and reused at least 5 times underwater and in air, exhibiting a high recycling rate. The underwater adhesive demonstrates strong and stable adhesion in underwater and acidic / alkaline / salt environments. More preferably, under optimal mass ratio and optimal melting temperature conditions, the adhesive achieves an underwater adhesion strength of over 8 MPa on aluminum sheets, and maintains an adhesion strength of not less than 5.5 MPa even after being placed in water or seawater for more than 3 weeks, exhibiting significantly superior performance.

[0017] The present invention also provides a method for preparing any of the above-mentioned adhesives with strong underwater adhesion and rapid onset of action, the method comprising: mixing thioctic acid, polyethyleneimine and catechol, heating and stirring at a heating temperature for a preset time, and obtaining an underwater adhesive with strong underwater adhesion and rapid onset of action after the reaction is completed.

[0018] The present invention also provides an application of any of the above-mentioned adhesives with strong underwater adhesion and rapid onset of action in the field of adhesives.

[0019] Preferably, the application is in underwater repair, wet surface bonding, underwater equipment fixing, underwater pipeline repair, underwater concrete repair, or underwater sensor encapsulation.

[0020] Preferably, the application involves coating the adhesive onto a substrate underwater to achieve an adhesive bond between the substrates. More preferably, the adhesive is suitable for substrates such as aluminum, copper, stainless steel, wood, ceramics, iron, and glass, which are suitable for bonding. After underwater bonding, a bonding strength of over 3 MPa can be achieved after at least 0.5 hours of storage, more preferably after 9-10 hours, and even more preferably after 9 hours, an excellent bonding strength of up to 8.35 MPa can be achieved, demonstrating highly efficient and rapid curing capabilities.

[0021] Compared with the prior art, the present invention has the following advantages and beneficial effects: (1) The present invention uses thioctic acid, polyethyleneimine and catechol to construct an underwater adhesive system. No external solvent is required. It can be prepared by a one-step melting reaction. The preparation process is simple and suitable for large-scale preparation.

[0022] (2) In this invention, the dynamic disulfide bond network formed by lipoic acid provides cohesive strength and recyclability, polyethyleneimine enhances network stability, and catechol enhances interfacial interaction. The three work together to achieve strong underwater adhesion.

[0023] (3) The adhesive of the present invention can quickly form effective adhesion underwater and further enhance the adhesion strength as the action time increases; in the preferred embodiment, the underwater adhesion strength of the aluminum sheet can reach 8.35 MPa.

[0024] (4) The adhesive of the present invention is applicable to a variety of substrates, including aluminum, iron, copper, stainless steel, glass, ceramics, wood and polymer materials, and has good substrate adaptability.

[0025] (5) The adhesive of the present invention can maintain high adhesion strength in water, seawater, acidic, alkaline and salt solution environments, and has good environmental adaptability and long-term adhesion stability.

[0026] (6) The adhesive of the present invention can be recycled and reused by heating. After multiple recycling, it still maintains a high underwater adhesion strength, which helps to reduce the cost of use and improve the utilization rate of materials. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the adhesive sample prepared in Example 3; Figure 2 To test the adhesion strength of the aluminum sheet in underwater and in air in Example 1; Figure 3 To test the adhesion strength of aluminum sheets for different times underwater and in air in Example 1; Figure 4 To test the adhesion strength of the aluminum sheet at different water temperatures in Example 2; Figure 5 The test results in Example 3 show the bond strength of the glass substrates bonded underwater and for the same curing time to different substrates; × in the figure indicates that the inherent brittleness of the glass substrate caused the breakage during the test. Figure 6 To test the adhesion strength of aluminum sheets in different pH solutions in Example 4; Figure 7 To test the adhesion strength of aluminum sheets in sodium chloride solutions of different concentrations in Example 5; Figure 8 The graph shows the long-term adhesion results of the aluminum sheet in seawater at different times in Test Example 6; Figure 9 The graph shows the long-term adhesion results of the aluminum sheet at different times in water or air in Test Example 7. Figure 10 This is a schematic diagram of the recycling method in Test Example 8; Figure 11 To test the bond strength of the aluminum sheet in water five times in Example 8. Detailed Implementation

[0028] To better clarify and understand the objectives, process solutions, and advantages of this invention, the technical solutions and implementation methods of this invention will be further described clearly, completely, and in detail below through specific embodiments and in conjunction with the accompanying drawings. It should be understood that the embodiments described in this invention are implemented under the premise of the technical solutions of this invention, providing detailed implementation methods and specific operating procedures, but are only some embodiments of this invention, not all embodiments. The specific implementation methods described are limited to illustrating and explaining this invention and do not limit this invention. Based on the embodiments of this invention, all other implementation methods obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0029] Unless otherwise specified, the experimental methods and conditions used in the embodiments of this invention are conventional methods and conditions. The materials, reagents, instruments, and equipment used in the embodiments, unless otherwise specified, are all conventional substances or equipment known to those skilled in the art and can be obtained commercially or prepared by conventional methods. The reaction conditions described in the invention's content can all achieve the stated reactions and obtain the desired products. Due to space limitations, some embodiments are listed below to further illustrate the advantages of the technical solution of this invention.

[0030] In this invention, lipoic acid was purchased from Shanghai Titan Technology Co., Ltd., polyethyleneimine (molecular weight 600), polyethyleneimine (molecular weight 1800), polyethyleneimine (molecular weight 10000) and polyethylene polyamine were purchased from Shanghai Maclean Biochemical Technology Co., Ltd., catechol was purchased from Shanghai Aladdin Biochemical Technology Co., Ltd., caffeic acid was purchased from Shanghai Titan Technology Co., Ltd., and tannic acid was purchased from Shanghai E-En Chemical Technology Co., Ltd.

[0031] In this invention, the underwater adhesive includes an adhesive that can perform adhesive properties in a humid or liquid environment.

[0032] Example 1, TPC-111 Weigh 1g of lipoic acid, 1g of polyethyleneimine with a molecular weight of 600, and 1g of catechol and mix them in a small experimental bottle. Place the bottle on a magnetic stirring table with an oil bath and heat it to 160℃. Set the stirring speed to 550 rpm. When the lipoic acid, polyethyleneimine, and catechol are completely melted, stir for 20 minutes to obtain a brown liquid, which is TPC-111 adhesive.

[0033] 1 mL of the prepared adhesive was drawn onto an aluminum sheet using a syringe, and aluminum-aluminum bonding was performed in water. The sheet was then clamped and cured for 9 hours before tensile property testing was conducted. Test results: Aluminum-aluminum bond tensile strength: 3.56 MPa.

[0034] Example 2, TPC-211 Weigh 1g of lipoic acid, 0.5g of polyethyleneimine with a molecular weight of 600, and 0.5g of catechol and mix them in a small experimental vial. Place the vial on a magnetic stirring table equipped with an oil bath and heat it to 160℃. Set the stirring speed to 550 rpm. When the lipoic acid, polyethyleneimine, and catechol are completely melted, stir for 20 minutes to obtain a brown liquid, which is TPC-211 adhesive.

[0035] The prepared adhesive was drawn into an aluminum sheet using a syringe (1 mL). Aluminum-aluminum bonding was then performed in water and clamped in place. After curing, tensile properties were tested. Test results: Aluminum-aluminum bond tensile strength: 4.81 MPa.

[0036] Example 3, TPC-311 Weigh 1.2g of lipoic acid, 0.4g of polyethyleneimine (molecular weight 600), and 0.4g of catechol and mix them in a small experimental vial. Place the vial on a magnetic stirrer equipped with an oil bath and heat it to 160℃. Set the stirring speed to 550 rpm. When the lipoic acid, polyethyleneimine, and catechol are completely melted, stir for 20 minutes to obtain a brown liquid, which is the adhesive TPC-311. Figure 1 As shown.

[0037] 1 mL of the prepared adhesive was drawn onto an aluminum sheet using a syringe, and aluminum-aluminum bonding was performed in water. The sheet was then clamped in place. After curing, tensile properties were tested. Test results: Aluminum-aluminum bond tensile strength: 8.35 MPa.

[0038] Example 4, TPC-411 Weigh 1.2g of lipoic acid, 0.3g of polyethyleneimine with a molecular weight of 600, and 0.3g of catechol and mix them in a small experimental vial. Place the vial on a magnetic stirring table equipped with an oil bath and heat it to 160℃. Set the stirring speed to 550 rpm. When the lipoic acid, polyethyleneimine, and catechol are completely melted, stir for 20 minutes to obtain a brown liquid, which is the adhesive TPC-411.

[0039] 1 mL of the prepared adhesive was drawn onto an aluminum sheet using a syringe, and aluminum-aluminum bonding was performed in water. The sheet was then clamped in place. After curing, tensile properties were tested. Test results: Aluminum-aluminum bond tensile strength: 0.32 MPa.

[0040] Example 5, TPC-312 Weigh 1.2g of lipoic acid, 0.4g of polyethyleneimine with a molecular weight of 600, and 0.8g of catechol and mix them in a small experimental vial. Place the vial on a magnetic stirring table equipped with an oil bath and heat it to 160℃. Set the stirring speed to 550 rpm. When the lipoic acid, polyethyleneimine, and catechol are completely melted, stir for 20 minutes to obtain a brown liquid, which is the adhesive TPC-312.

[0041] 1 mL of the prepared adhesive was drawn onto an aluminum sheet using a syringe, and aluminum-aluminum bonding was performed in water. The sheet was then clamped in place. After curing, tensile properties were tested. Test results: Aluminum-aluminum bond tensile strength: 2.52 MPa.

[0042] Example 6, TPC-313 Weigh 1.2g of lipoic acid, 0.4g of polyethyleneimine with a molecular weight of 600, and 1.2g of catechol and mix them in a small experimental vial. Place the vial on a magnetic stirring table equipped with an oil bath and heat it to 160℃. Set the stirring speed to 550 rpm. When the lipoic acid, polyethyleneimine, and catechol are completely melted, stir for 20 minutes to obtain a brown liquid, which is the adhesive TPC-313.

[0043] 1 mL of the prepared adhesive was drawn onto an aluminum sheet using a syringe, and aluminum-aluminum bonding was performed in water. The sheet was then clamped in place. After curing, tensile properties were tested. Test results: Aluminum-aluminum bond tensile strength: 1 MPa.

[0044] Example 7, TPC-321 Weigh 1.2g of lipoic acid, 0.8g of polyethyleneimine with a molecular weight of 600, and 0.4g of catechol and mix them in a small experimental vial. Place the vial on a magnetic stirring table equipped with an oil bath and heat it to 160℃. Set the stirring speed to 550 rpm. When the lipoic acid, polyethyleneimine, and catechol are completely melted, stir for 20 minutes to obtain a brown liquid, which is the adhesive TPC-321.

[0045] 1 mL of the prepared adhesive was drawn onto an aluminum sheet using a syringe, and aluminum-aluminum bonding was performed in water. The sheet was then clamped in place. After curing, tensile properties were tested. Test results: Aluminum-aluminum bond tensile strength: 2.20 MPa.

[0046] Example 8, TPC-322 Weigh 1.2g of lipoic acid, 0.8g of polyethyleneimine with a molecular weight of 600, and 0.8g of catechol and mix them in a small experimental vial. Place the vial on a magnetic stirring table equipped with an oil bath and heat it to 160℃. Set the stirring speed to 550 rpm. When the lipoic acid, polyethyleneimine, and catechol are completely melted, stir for 20 minutes to obtain a brown liquid, which is the adhesive TPC-322.

[0047] 1 mL of the prepared adhesive was drawn onto an aluminum sheet using a syringe, and aluminum-aluminum bonding was performed in water. The sheet was then clamped in place. After curing, tensile properties were tested. Test results: Aluminum-aluminum bond tensile strength: 2.49 MPa.

[0048] Example 9, TPC-311-1 Weigh 1.2g of lipoic acid, 0.4g of polyethyleneimine with a molecular weight of 600, and 0.4g of catechol and mix them in a small experimental vial. Place the vial on a magnetic stirring table equipped with an oil bath and heat it to 150℃. Set the stirring speed to 550 rpm. When the lipoic acid, polyethyleneimine, and catechol are completely melted, stir for 20 minutes to obtain a brown liquid, which is the adhesive TPC-311-1.

[0049] 1 mL of the prepared adhesive was drawn onto an aluminum sheet using a syringe, and aluminum-aluminum bonding was performed in water. The sheet was then clamped in place, and tensile properties were tested after curing. Test results: Aluminum-aluminum bond tensile strength: 4.66 MPa.

[0050] Example 10, TPC-311-2 Weigh 1.2g of lipoic acid, 0.4g of polyethyleneimine with a molecular weight of 600, and 0.4g of catechol and mix them in a small experimental vial. Place the vial on a magnetic stirring table equipped with an oil bath and heat it to 180℃. Set the stirring speed to 550 rpm. When the lipoic acid, polyethyleneimine, and catechol are completely melted, stir for 20 minutes to obtain a brown liquid, which is the adhesive TPC-311-2.

[0051] 1 mL of the prepared adhesive was drawn onto an aluminum sheet using a syringe, and aluminum-aluminum bonding was performed in water. The sheet was then clamped in place. After curing, tensile properties were tested. Test results: Aluminum-aluminum bond tensile strength: 3.09 MPa.

[0052] Example 11, TPC-311-3 Weigh 1.2g of thioctic acid, 0.4g of polyethyleneimine with a molecular weight of 600, and 0.4g of catechol and mix them in a small experimental vial. Place the vial on a magnetic stirring table with an oil bath and heat it to 130℃. Set the stirring speed to 550 rpm. Due to the low temperature, the three raw materials cannot form a low eutectic copolymer and cannot be completely melted, making it difficult to produce TPC-311-3 adhesive.

[0053] Comparative Example 1, TPC-310 Weigh 1.2g of lipoic acid and 0.4g of polyethyleneimine with a molecular weight of 600 and mix them in a small experimental vial. Place the vial on a magnetic stirring table with an oil bath and heat it to 160℃. Set the stirring speed to 550 rpm. When the lipoic acid and polyethyleneimine are completely melted, stir for 20 minutes to obtain a light yellow liquid, which is the adhesive TPC-310.

[0054] 1 mL of the prepared adhesive was drawn onto an aluminum sheet using a syringe, and aluminum-aluminum bonding was performed in water. The sheet was then clamped in place. After curing, tensile properties were tested. Test results: Aluminum-aluminum bond tensile strength: 3.94 MPa.

[0055] Comparative Example 2, TPC-320 Weigh 1.2g of lipoic acid and 0.8g of polyethyleneimine with a molecular weight of 600 and mix them in a small experimental vial. Place the vial on a magnetic stirring table equipped with an oil bath and heat it to 160℃. Set the stirring speed to 550 rpm. When the lipoic acid and polyethyleneimine are completely melted, stir for 20 minutes to obtain a light yellow liquid, which is the adhesive TPC-320.

[0056] 1 mL of the prepared adhesive was drawn onto an aluminum sheet using a syringe, and aluminum-aluminum bonding was performed in water. The sheet was then clamped in place. After curing, tensile properties were tested. Test results: Aluminum-aluminum bond tensile strength: 2.74 MPa.

[0057] Comparative Example 3, TPC-301 Weigh 1.2g of thioctic acid and 0.4g of catechol and mix them in a small experimental vial. Place the vial on a magnetic stirring table with an oil bath and heat it to 160℃. Set the stirring speed to 550 rpm. When the thioctic acid and catechol are completely melted, stir for 20 minutes to obtain a light brown liquid, which is the adhesive TPC-301.

[0058] 1 mL of the prepared adhesive was drawn onto an aluminum sheet using a syringe, and aluminum-aluminum bonding was performed in water. The sheet was then clamped in place. After curing, tensile properties were tested. Test results: Aluminum-aluminum bond tensile strength: 0.45 MPa.

[0059] Comparative Example 4, TPC-302 Weigh 1.2g of thioctic acid and 0.8g of catechol and mix them in a small experimental vial. Place the vial on a magnetic stirrer equipped with an oil bath and heat it to 160℃. Set the stirring speed to 550 rpm. When the thioctic acid and catechol are completely melted, stir for 20 minutes to obtain a dark brown liquid, which is the adhesive TPC-302.

[0060] 1 mL of the prepared adhesive was drawn onto an aluminum sheet using a syringe, and aluminum-aluminum bonding was performed in water. The sheet was then clamped in place. After curing, tensile properties were tested. Test results: Aluminum-aluminum bond tensile strength: 0.53 MPa.

[0061] As can be seen from the comparison between Comparative Examples 1-4 and Example 3, the adhesive performance of Example 3 is far inferior in the absence of any one of the raw materials.

[0062] Comparative Example 5, TPPC-311 Weigh 1.2g of lipoic acid, 0.4g of polyethylene polyamine, and 0.4g of catechol and mix them in a small experimental vial. Place the vial on a magnetic stirring table equipped with an oil bath and heat it to 160℃. Set the stirring speed to 550 rpm. When the lipoic acid, polyethylene polyamine, and catechol are completely melted, stir for 20 minutes to obtain a brown liquid, which is the adhesive TPPC-311.

[0063] 1 mL of the prepared adhesive was drawn onto an aluminum sheet using a syringe, and aluminum-aluminum bonding was performed in water. The sheet was then clamped in place, and after curing, tensile properties were tested. Although the polyethylene polyamine has a high total amino group count, the amino groups are concentrated on short chains, resulting in excessively dense local crosslinking and an uneven overall network. This easily leads to stress concentration, which in turn reduces the overall bond strength. Test results: Aluminum-aluminum bond tensile strength: 5.56 MPa. It can be seen that the adhesion strength is reduced compared to Example 3.

[0064] Comparative Example 6, TPCA-311 Weigh 1.2g of lipoic acid, 0.4g of polyethyleneimine with a molecular weight of 600, and 0.4g of caffeic acid and mix them in a small experimental vial. Place the vial on a magnetic stirring table equipped with an oil bath and heat it to 160℃. Set the stirring speed to 550 rpm. When the lipoic acid, polyethyleneimine, and caffeic acid are completely melted, stir for 20 minutes to obtain a brown liquid, which is the adhesive TPCA-311.

[0065] The prepared adhesive was adhered to an aluminum sheet, and aluminum-aluminum bonding was performed in water, clamped in place, and after curing, tensile properties were tested. Test results: Aluminum-aluminum bond tensile strength: 6.38 MPa. Although caffeic acid has more catechol groups and is generally considered to improve adhesion strength more than catechol (similar to tannic acid), the results of this application show a decrease in adhesion strength compared to Example 3.

[0066] Comparative Example 7, TPT-311 Weigh 1.2g of lipoic acid, 0.4g of polyethyleneimine with a molecular weight of 600, and 0.4g of tannic acid and mix them in a small experimental vial. Place the vial on a magnetic stirring table equipped with an oil bath and heat it to 160℃. Set the stirring speed to 550 rpm. When the lipoic acid, polyethyleneimine, and tannic acid melt, stir for 20 minutes to obtain the adhesive TPT-311.

[0067] The prepared adhesive was adhered to an aluminum sheet, and aluminum-aluminum bonding was performed in water, clamped in place, and after curing, tensile properties were tested. Test results: Aluminum-aluminum bond tensile strength: 2.09 MPa. Although tannic acid has more catechol groups than catechol, tannic acid is a large-molecule polyphenol with a large molecular weight and significant steric hindrance. It exhibits poor melt flow at 160°C, weak compatibility with the system, and large molecular entanglement, easily leading to a loose cross-linking network, numerous defects, and a significant decrease in cohesion. This results in fewer effective adhesion interface sites, thus significantly reducing the bond strength compared to Example 3.

[0068] Comparative Example 8, TP1C-311 Weigh 1.2g of lipoic acid, 0.4g of polyethyleneimine with a molecular weight of 1800, and 0.4g of catechol and mix them in a small experimental vial. Place the vial on a magnetic stirring table equipped with an oil bath and heat it to 160℃. Set the stirring speed to 550 rpm. When the lipoic acid, polyethyleneimine, and catechol are completely melted, stir for 20 minutes to obtain a brown liquid, which is the adhesive TP1C-311.

[0069] The prepared adhesive was adhered to an aluminum sheet, and aluminum-aluminum bonding was performed in water, clamped in place, and after curing, tensile properties were tested. Test results: Aluminum-aluminum bond tensile strength: 1.97 MPa. When the molecular weight was increased to 1800, the PEI molecular chains became longer, and molecular entanglement significantly intensified. The viscosity of the 160℃ molten system increased, and its fluidity deteriorated, hindering component mixing and diffusion. Simultaneously, some amino active sites were encapsulated by long chains, inhibiting the crosslinking reaction with lipoic acid and catechol, resulting in a significant decrease in crosslinking density, a loose network structure with many defects, and a significant reduction in cohesion and adhesion, thus leading to a decrease in strength.

[0070] Comparative Example 9, TP2C-311 Weigh 1.2g of lipoic acid, 0.4g of polyethyleneimine with a molecular weight of 10000, and 0.4g of catechol and mix them in a small experimental vial. Place the vial on a magnetic stirring table equipped with an oil bath and heat it to 160℃. Set the stirring speed to 550 rpm. When the lipoic acid, polyethyleneimine, and catechol are completely melted, stir for 20 minutes to obtain a brown liquid, which is the adhesive TP2C-311.

[0071] The prepared adhesive was adhered to an aluminum sheet, and aluminum-aluminum bonding was performed in water, clamped in place, and after curing, tensile properties were tested. Test results: Aluminum-aluminum bond tensile strength: 2.15 MPa. High molecular weight polyethyleneimine has longer molecular chains and more severe molecular entanglement compared to low molecular weight polyethyleneimine. At the same temperature, its melt viscosity increases sharply, and its fluidity is extremely poor. It cannot be uniformly compatible and dispersed with lipoic acid and catechol. The long-chain entanglement also encapsulates and blocks amino active sites, significantly weakening the cross-linking reaction with phenolic hydroxyl groups and lipoic acid. The system has low cross-linking density, a loose and uneven network, many internal defects, a significant decrease in cohesion, and a reduction in effective adhesion sites at the interface.

[0072] Comparative Example 10, TCC-311 This example uses a zinc sulfate-based binder from the existing technology for comparison. Details are as follows: Weigh 1.2g of lipoic acid, 0.4g of caffeic acid, and 0.4g of citric acid and mix them in a small experimental vial. Place the vial on a magnetic stirrer equipped with an oil bath and heat it to 160℃. Set the stirring speed to 550 rpm. When the lipoic acid, caffeic acid, and citric acid are completely melted, stir for 20 minutes to obtain a dark brown liquid, which is the adhesive TCC-311.

[0073] The prepared adhesive was adhered to an aluminum sheet, and aluminum-aluminum bonding was performed in water. The sheet was then clamped in place, and after curing, tensile properties were tested.

[0074] Test results: Aluminum-aluminum bond tensile strength: 2.46 MPa. This experiment used another thioctic acid-based underwater adhesive, prepared under the same conditions. After curing this adhesive for 30 min, 9 h, and 24 h, it was found that the adhesion strength of this thioctic acid-based adhesive after 30 min curing was 0.89 MPa, far lower than the 3.35 MPa adhesion strength of the present invention. This proves that at the same onset time, this thioctic acid-based underwater adhesive is significantly inferior to the adhesive of the present invention. Furthermore, it was found that the onset time of this example of the thioctic acid-based underwater adhesive was 24 h, with an adhesion strength of 3.06 MPa. The strength at 24 h was lower than the strength of the present invention at 30 min, and it decreased after 24 h. It is evident that the method of the present invention, compared with existing zinc sulfate-based adhesives (in this example), has significantly higher strength and a rapid onset, which is not immediately obvious. The slow onset of action and low strength after onset are mainly due to the lack of a continuous polymer backbone and cationic adhesion sites in the citric acid system. At the same time, the use of caffeic acid with lower adhesion activity and the addition of a large number of hydrophilic small molecules to disrupt the network result in a slow onset of action and low strength after onset. In contrast, the PEI system uses high-strength, water-resistant three-dimensional cross-linked network constructed with high-molecular amino groups and combined with the optimal adhesion unit, catechol, to achieve both high bulk cohesion and strong underwater interfacial adhesion. Therefore, it is superior in terms of melt underwater adhesion strength and long-term effectiveness.

[0075] The adhesives obtained in each embodiment and comparative example were subjected to underwater adhesion strength tests for 9 hours. The substrate was an aluminum sheet. The specific tensile property test method was to place the aluminum sheet into a high and low temperature double column tester for tensile testing, obtain the tensile force, measure the adhesion area, and calculate the adhesion strength. The conditions and adhesion strength test results for each example are summarized in Table 1 below: Table 1 Summary of conditions and underwater adhesion strength for each example

[0076] As can be seen from the table, the adhesives within the specified feeding range of this invention all exhibit good adhesive performance, such as in Examples 1-3, 5, and 7-10. The effect is even better when the proportion of lipoic acid is 50%-60% and the proportions of polyethyleneimine and catechol are 20%-25%, especially when the mass ratio of lipoic acid to polyethyleneimine and catechol is 3:1:1, the effect is particularly good, and the bonding strength is significantly improved to 8.35 MPa. However, when the proportion of lipoic acid is too high, such as in Example 4 where the proportion exceeds 65%, it will lead to a significant decrease in bonding strength. At the same time, if the proportion of catechol is too high and the proportion of polyethyleneimine is too low, such as in Example 6 where the proportion of catechol is higher than 40% and the proportion of polyethyleneimine is lower than 15%, it will also lead to a significant decrease in adhesive performance. Meanwhile, to further verify the good compatibility of catechol and polyethyleneimine with a molecular weight of 600 with this system, catechol was replaced with caffeic acid or tannic acid, as in Comparative Examples 6-7. Polyethyleneimine with a molecular weight of 600 was replaced with polyethyleneimine or polyethylenepolyamine with molecular weights of 1800 or 10000, as in Comparative Examples 5 and 8-9. Only a single variable was replaced. When catechol was replaced, polyethyleneimine with a molecular weight of 600 was used. When polyethyleneimine with a molecular weight of 600 was replaced, the catechol remained unchanged. The adhesive adhesion effect of this adhesive was far inferior to that of Example 3. This shows that the proportion and type of each substance have a significant but unpredictable impact on the adhesive adhesion. Furthermore, Comparative Example 10 verified that the underwater adhesive prepared by this invention has a shorter onset time and higher strength after onset.

[0077] Test Example 1 The adhesive prepared in Example 3 was placed on an aluminum sheet and bonded in water and air at room temperature for different times: 1 minute, 5 minutes, 15 minutes, 30 minutes, 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 20 hours, and 30 hours. It was found that an underwater adhesion strength of 0.72 MPa was achieved after 1 minute of curing, and 3.35 MPa was achieved after 30 minutes of curing. The underwater adhesion strength reached 5.73 MPa after 5 hours of curing, and the strongest underwater adhesion strength of 8.35 MPa was observed after 9 hours of curing. The TPC-311 adhesive showed a higher adhesion strength at 5 hours than most of the comparative examples at their optimal adhesion time. This demonstrates that this adhesive has rapid adhesion and curing capabilities, achieving adhesion strength exceeding that of most comparative examples in a relatively short curing time. Figure 2 and 3 As shown.

[0078] Test Example 2 The adhesive prepared in Example 3 was placed on an aluminum sheet in water at different temperatures: 5°C, 25°C, 50°C, and 70°C, and the results were tested after 9 hours (based on...). Figure 2 The optimal adhesion strength was determined at the optimal adhesion time. The adhesion strengths were 3.57 MPa, 8 MPa, 5.21 MPa, and 5.02 MPa, with the best adhesion effect observed at 25°C. The adhesion strength is as follows: Figure 4 As shown.

[0079] Test Example 3 The adhesive prepared in Example 3 was applied underwater to aluminum (Al), iron (Fe), copper (Cu), steel, glass, ceramic, wood, polymethyl methacrylate (PMMA), and polytetrafluoroethylene (PTFE). Tensile properties were tested after 9 hours of bonding. The adhesion strengths were 8.07 MPa, 7.54 MPa, 6.99 MPa, 7.25 MPa, 5.5 MPa, 4.5 MPa, 1.08 MPa, 0.21 MPa, and 0.19 MPa, respectively. The inherent brittleness of the glass substrate caused breakage during the test. The adhesive exhibited strong interfacial bonding during underwater adhesion, making it almost impossible to peel off from the glass substrate. This demonstrates that the adhesive of this invention has good adaptability to different substrates. The adhesion strength is as follows... Figure 5 As shown.

[0080] Test Example 4 The adhesive prepared in Example 3 was subjected to adhesion tests on aluminum sheets at pH values ​​of 1, 4, 10, and 13 for 9 hours. The adhesion strengths were 3.7 MPa, 3.92 MPa, 4.06 MPa, and 4.01 MPa, respectively, indicating that the adhesive of the present invention exhibits strong and stable adhesion to the substrate at different salt concentrations. The bond strength is as follows: Figure 6 As shown.

[0081] Test Example 5 The adhesive prepared in Example 3 was used to adhere aluminum sheets to sodium chloride solutions of 0 M, 0.5 M, 1 M, and 2 M concentrations for 9 hours. The adhesion strengths were 7.98 MPa, 5.53 MPa, 5.44 MPa, and 4.99 MPa, respectively, indicating that the adhesive of the present invention exhibits strong and relatively stable adhesion to the substrate at different salt concentrations. The bond strength is as follows: Figure 7 As shown.

[0082] Test Example 6 The adhesive prepared in Example 3 was bonded to an aluminum sheet in artificial seawater for different periods: 1 week, 2 weeks, and 3 weeks. The adhesion strengths were 7.92 MPa, 6.01 MPa, 5.84 MPa, and 5.64 MPa, respectively, demonstrating that the adhesive of the present invention exhibits strong and stable long-term adhesion even in a seawater environment. The bonding strength is as follows... Figure 8 As shown.

[0083] Test Example 7 The adhesive prepared in Example 3 was bonded to aluminum sheets underwater or in air for different periods: 1 week, 2 weeks, and 3 weeks. It can be seen that even in the 3rd week, it still exhibited an underwater bonding strength of not less than 5.9 MPa, and the bonding strength in air was still 4 MPa, demonstrating excellent long-term stability. The bonding strength is as follows... Figure 9As shown.

[0084] Test Example 8 The adhesive prepared in Example 3 was applied to an aluminum sheet underwater, and then the following steps were performed: Figure 10 The process involves melting the recycled material from an aluminum substrate in a 160°C oil bath, repeating this process five times. All recycled materials exhibit a bond strength of at least 7 MPa, demonstrating excellent recycling efficiency. (Bond strength is as follows...) Figure 11 As shown.

[0085] Unless otherwise specified, the raw materials and equipment used in this invention are all commonly used in the field; the methods used in this invention, unless otherwise specified, are all conventional methods in the field. To ensure the comparability of the experimental data across groups, each test was conducted separately.

[0086] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any simple modifications, alterations, and equivalent transformations made to the above embodiments based on the technical essence of the present invention shall still fall within the protection scope of the present invention.

Claims

1. An adhesive having strong underwater adhesion and rapid onset capability, characterized by, The adhesive is prepared by melting reaction of raw materials including thioctic acid, polyethyleneimine and catechol under conditions without external solvent; wherein, based on a mass fraction of 1 part of thioctic acid, a mass fraction of 0.25-1.0 part of polyethyleneimine and a mass fraction of 0.25-1.0 part of catechol.

2. The adhesive according to claim 1, characterized in that, The relative molecular mass of the polyethyleneimine is 400-1000.

3. The adhesive according to claim 1, characterized in that, The mass percentage of lipoic acid in the raw material is not higher than 65%, and / or the mass percentage of catechol in the raw material is not higher than 43%, and / or the mass percentage of polyethyleneimine in the raw material is not lower than 15%.

4. The adhesive according to claim 1, characterized in that, Based on a mass fraction of 1 part lipoic acid, the mass fraction of polyethyleneimine is 0.3-0.7, and the mass fraction of catechol is 0.3-0.

7. And / or, the relative molecular mass of polyethyleneimine is 600-1000.

5. The adhesive according to claim 1, characterized in that, The mass ratio of lipoic acid, polyethyleneimine, and catechol is 3:1:1; and / or, the relative molecular mass of polyethyleneimine is 600.

6. The adhesive according to claim 1, characterized in that, The thioctic acid is ring-opening polymerized to form a polymer network containing dynamic disulfide bonds, polyethyleneimine participates in the network construction through amino groups, and catechol is used to enhance the interfacial interaction between the adhesive and the substrate surface; and / or, the adhesive has an underwater adhesion strength of not less than 2 MPa on aluminum sheets.

7. A method for preparing the adhesive according to any one of claims 1-6, characterized in that, The process includes the following steps: mixing thioctic acid, polyethyleneimine, and catechol, and carrying out a melt reaction at 150-180°C, after which the adhesive is obtained.

8. The preparation method according to claim 7, characterized in that, The melting reaction temperature is 160-170℃, the stirring speed is 400-600 r / min, and the reaction time is 10-30 min.

9. The preparation method according to claim 7, characterized in that, The melting reaction temperature was 160℃, the stirring speed was 550 r / min, and the reaction time was 20 min.

10. The application of the adhesive as described in any one of claims 1-6 in the fields of underwater repair, wet surface bonding, underwater equipment fixing, underwater pipeline repair, underwater concrete repair, or underwater sensor encapsulation.

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