A bio-based multiple cross-linking underwater adhesive as well as a preparation method and application thereof

Abstract

The application belongs to the technical field of polymer adhesives, and discloses a bio-based underwater adhesive with multiple cross-linking structures, and a preparation method and application thereof. The underwater adhesive is prepared from the following raw materials in parts by mass: 40-60 parts of epoxy vegetable oil, 6-12 parts of polyphenol compounds, 15-25 parts of isocyanate, 2-5 parts of silane coupling agent, 0.3-1 parts of metal salt, and 0.1-0.5 parts of catalyst. In the epoxy vegetable oil, epoxy groups form a hydroxyl-containing prepolymer with phenolic hydroxyl groups in the polyphenol compounds, and then a polyurethane cross-linking structure is constructed through isocyanate reaction, and a silicon-oxygen structure is formed through the silane coupling agent, and a multiple cross-linking network structure is constructed through the coordination between metal ions and phenolic hydroxyl groups. The underwater adhesive has good mechanical properties, underwater adhesion and water resistance, and has a simple preparation process, a wide source of raw materials, and is suitable for the bonding of various substrates in a water environment, and has a good application prospect.

Description

Technical Field

[0001] This invention belongs to the field of underwater adhesive materials technology, and relates to a bio-based multi-crosslinked underwater adhesive, its preparation method and application. Specifically, it relates to an underwater adhesive based on an epoxy vegetable oil-polyurethane-polyphenol coordination multi-crosslinked network, its preparation method and application, which is particularly suitable for underwater structure repair, wet environment bonding and structural connection in complex aquatic environments. Background Technology

[0002] Underwater adhesives are functional materials capable of achieving interfacial adhesion and structural bonding in aquatic or high-humidity environments. They are widely used in marine engineering, underwater structure repair, wet environment bonding, and biomedical materials. Because a stable hydration layer typically exists on the surface of substrates in aquatic environments, this layer hinders direct contact between the adhesive and the substrate, thereby reducing interfacial forces. Therefore, developing underwater adhesives capable of stable adhesion in aquatic environments is of great significance.

[0003] In recent years, underwater adhesives based on bio-based materials have gradually become a research hotspot. Among them, epoxidized vegetable oils, due to their wide availability, high bio-based content, and multiple reactive groups in their structure, can form three-dimensional network structures through ring-opening reactions or further cross-linking, showing promising application prospects in the field of green adhesives. Meanwhile, polyphenolic compounds, due to the presence of multiple phenolic hydroxyl functional groups in their molecular structure, can enhance interfacial bonding through hydrogen bonding, coordination, and π–π interactions, demonstrating good application potential in underwater adhesion systems. Furthermore, polyurethane materials, due to their excellent mechanical properties and structural stability, are also widely used in adhesive systems. However, existing patents still have certain limitations in the structural design and functional regulation of underwater adhesive systems.

[0004] Patent CN113493665B discloses a palm oil-based underwater adhesive. This patent constructs an underwater adhesion structure through the copolymerization reaction of plant oil-derived monomers and acrylic monomers, giving the material a certain underwater adhesion capability. However, this system mainly uses free radical copolymerization to form a network structure, resulting in a relatively simple cross-linking method and difficulty in forming a multi-linked structure with good energy dissipation capabilities, leading to insufficient stability of the material in long-term aquatic environments. Patent CN118715298A discloses an underwater adhesive containing a polyphenol structure. This system enhances the interfacial adhesion capability of the material by introducing tannic acid to form a coordination structure with metal ions. However, this system mainly relies on coordination to form a network structure, lacking a stable chemical cross-linking skeleton, resulting in certain deficiencies in the overall mechanical properties and long-term environmental stability of the material. Patent CN113817432B discloses a polyurethane-based underwater adhesive. This patent improves the mechanical properties of the material by constructing a polyurethane cross-linked network, giving the material a certain structural strength. However, the system has limited interfacial adhesion functional units and lacks structural units that can significantly enhance interfacial forces, making it prone to interfacial adhesion failure in aquatic environments.

[0005] In summary, while existing underwater adhesive systems can achieve a certain degree of adhesion in aquatic environments, they still suffer from problems such as simple cross-linking structures, insufficient interfacial forces, and poor long-term stability, making it difficult to meet the application requirements of complex aquatic environments. Therefore, there is an urgent need to develop a multi-crosslinked underwater adhesive system based on bio-based epoxy vegetable oil and polyphenol structures to improve the adhesion performance and environmental stability of the material. Summary of the Invention

[0006] In view of the shortcomings and deficiencies of the prior art, the primary objective of this invention is to provide a bio-based multi-crosslinked underwater adhesive.

[0007] Another object of the present invention is to provide a method for preparing a bio-based multi-crosslinked underwater adhesive.

[0008] Another object of the present invention is to provide applications of the above-mentioned bio-based multi-crosslinked underwater adhesive. The present invention solves the problems of existing underwater adhesives, such as single crosslinking structure, insufficient interfacial adhesion ability, and poor environmental stability; the prepared underwater adhesive has good underwater adhesion performance, high mechanical strength, and excellent environmental stability.

[0009] To achieve the above objectives, the present invention adopts the following technical solution:

[0010] A bio-based multi-crosslinked underwater adhesive is prepared from the following raw materials in parts by weight: 40-60 parts of epoxidized vegetable oil, 6-12 parts of polyphenolic compounds, 15-25 parts of isocyanate, 2-5 parts of silane coupling agent, 0.3-1 parts of metal salt, and 0.1-0.5 parts of catalyst.

[0011] Preferably, the epoxidized vegetable oil is selected from one or more of epoxidized linseed oil (ELO), epoxidized soybean oil (ESO), and epoxidized castor oil; its molecular structure contains multiple epoxy groups, which can undergo ring-opening reactions with phenolic hydroxyl groups in polyphenolic compounds to form hydroxyl-containing prepolymers.

[0012] The polyphenolic compounds are natural polyphenolic compounds selected from one or more of gallic acid (GA), catechin, and pyrogallol.

[0013] The epoxy group in the epoxy vegetable oil has an epoxy / OH equivalent ratio of 1 to 3 to the phenolic hydroxyl group in the polyphenol compound.

[0014] Preferably, the isocyanate is selected from one or more of hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI), and diphenylmethane diisocyanate (MDI);

[0015] The NCO / OH equivalent ratio between the isocyanate group and the hydroxyl group is 1.0 to 1.4; the hydroxyl group includes hydroxyl groups formed after ring opening of epoxidized vegetable oil and unreacted hydroxyl groups in polyphenolic compounds.

[0016] The silane coupling agent is selected from γ-glycidoxypropyltrimethoxysilane (KH560) or γ-aminopropyltriethoxysilane (KH550).

[0017] Preferably, the metal salt is ferric chloride (FeCl3), but may also be selected from one or more of aluminum chloride (AlCl3) or zinc chloride (ZnCl3).

[0018] Preferably, the catalyst is selected from one or more of boric acid, 2-methylimidazole, 2-ethyl-4-methylimidazole, and boron trifluoride diethyl ether complex, with boric acid being the most preferred.

[0019] Preferably, the bio-based multi-crosslinked underwater adhesive comprises an epoxy ring-opening structure, a polyurethane crosslinking structure, a silicon-oxygen structure, and a metal coordination structure.

[0020] A method for preparing a bio-based multi-crosslinked underwater adhesive includes the following steps:

[0021] (1) Under stirring conditions, polyphenolic compounds and catalysts were added to epoxidized vegetable oil, and a prepolymer system containing hydroxyl structure was obtained through ring-opening reaction;

[0022] (2) Cool the prepolymer system containing hydroxyl structure to 60-70 °C, add isocyanate under inert atmosphere protection and continue the reaction to allow the isocyanate groups to react with the hydroxyl groups in the system to obtain polyurethane;

[0023] (3) Cool the system to 40-50 °C, add silane coupling agent and continue the reaction to form a silicon-oxygen structure in the system;

[0024] (4) Finally, a metal salt solution is added to the system and the reaction continues, so that the phenolic hydroxyl groups in the polyphenolic compound form a coordination structure with the metal ions. After the reaction is completed, the mixture is cooled to obtain the bio-based multi-crosslinked underwater adhesive.

[0025] Preferably, the ring-opening reaction in step (1) is carried out at a temperature of 80~100℃ and for a reaction time of 1~3h;

[0026] The reaction time described in step (2) is 1 to 2 hours.

[0027] Preferably, the reaction time in step (3) is 20-40 min;

[0028] The temperature for the continued reaction in step (4) is 40-50 °C and the time is 20-40 min.

[0029] The above-mentioned bio-based multi-crosslinked underwater adhesives are used in bonding, sealing or repairing in aquatic environments.

[0030] Preferably, the adhesive material includes metal, wood, glass, ceramic or polymer substrate.

[0031] The polymer substrate is epoxy resin or PET; the metal is steel plate or tinplate.

[0032] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0033] (1) This invention provides a novel and tunable multi-crosslinked underwater adhesive based on epoxy vegetable oil. By rationally designing the equivalence relationship between epoxy groups and phenolic hydroxyl groups and combining it with the isocyanate crosslinking reaction, a branched network system containing epoxy ring-opening structure and polyurethane structure is constructed, so that the resulting adhesive has high crosslinking density and good mechanical properties. At the same time, the material structure and properties can be controlled by adjusting the proportion of each component, which is suitable for the needs of different application environments.

[0034] (2) By introducing gallic acid containing polyphenol structure and utilizing the stable coordination structure formed between metal ions and phenolic hydroxyl groups, the present invention constructs a reversible coordination network structure inside the material, which improves the interfacial adhesion ability and energy dissipation ability of the material, so that the adhesive can still maintain high adhesion strength and stability in the water environment, and significantly improves the underwater adhesion performance.

[0035] (3) By introducing a silane coupling agent, the present invention forms a silicon-oxygen structure inside the material and constructs an organic-inorganic hybrid network structure, which improves the water resistance and environmental stability of the adhesive, while enhancing the interfacial bonding ability between the material and the surface of various substrates, so that it still has good adhesion stability in complex water environments.

[0036] (4) The underwater adhesive obtained by the present invention has a high bio-based content, a wide range of raw material sources, a simple preparation process, mild reaction conditions, and the resulting material has a stable structure and excellent performance. It is suitable for underwater bonding of various substrates such as metal, glass, ceramics and polymer materials, and has good application prospects and promotion value. Attached Figure Description

[0037] Figure 1 The diagram shows the underwater shear strength and debonding work test results of the underwater adhesive obtained in Example 1 of the present invention on different substrates, including tinplate, steel plate, epoxy board, wood board and PET board.

[0038] Figure 2 The graph shows the test results of shear strength and debonding work of the underwater adhesive obtained in Example 1 of the present invention under long-term immersion in water environment. The test time is 0 to 30 days, which is used to characterize the water resistance stability of the adhesive. Detailed Implementation

[0039] The present invention will be further described in detail below with reference to specific embodiments, but the implementation of the present invention is not limited thereto. For process parameters not specifically noted, conventional techniques can be referred to.

[0040] The raw materials used in the examples are all available from conventional commercial sources.

[0041] Example 1

[0042] 50 g of epoxy linseed oil was added to a 250 mL three-necked flask and heated to 90 °C under mechanical stirring to form a homogeneous and transparent liquid. Then, 9 g of gallic acid and 0.2 g of boric acid were added, and the mixture was stirred continuously at 90 °C for 2 h to allow the phenolic hydroxyl groups in the gallic acid to undergo a ring-opening reaction with the epoxy groups in the epoxy linseed oil, forming a prepolymer system containing hydroxyl structures. The system was then cooled to 65 °C, and 18 g of hexamethylene diisocyanate (HDI) was slowly added under nitrogen protection. The reaction continued for 1.5 h to allow the isocyanate groups to react with the hydroxyl groups in the system, forming a stable polyurethane crosslinked structure. Finally, the system was cooled to 45 °C, and 3 g of γ-glycidoxypropyltrimethoxysilane (KH560) was added. The reaction was continued with stirring for 30 min to form a silicon-oxygen structure in the system. Finally, 0.5 g of ferric chloride (FeCl3) was dissolved in a small amount of ethanol to form a homogeneous solution, and then slowly added to the reaction system. The mixture was stirred at 45°C for 30 min to allow the phenolic hydroxyl groups in gallic acid to react with the Fe3+. + A coordination structure is formed; after the reaction is completed, the mixture is cooled to room temperature to obtain the underwater adhesive.

[0043] In the preparation process, the epoxy / OH equivalent ratio between epoxy linseed oil and gallic acid is approximately 1.8, and the NCO / OH equivalent ratio between isocyanate and hydroxyl groups is approximately 1.2.

[0044] Example 2

[0045] 50 g of epoxy linseed oil was added to a 250 mL three-necked flask and heated to 90 °C under mechanical stirring. Then, 6 g of gallic acid and 0.2 g of boric acid were added, and the mixture was stirred continuously at 90 °C for 2 h to allow partial ring-opening of the epoxy groups. The system was then cooled to 65 °C, and 18 g of hexamethylene diisocyanate (HDI) was slowly added under nitrogen protection. The reaction continued for 1.5 h to allow the isocyanate groups to react with the hydroxyl groups in the system, forming a stable polyurethane crosslinking structure. The temperature was then lowered to 45 °C, 3 g of KH560 was added, and the reaction continued for 30 min. Finally, 0.5 g of FeCl3 solution was added, and the reaction continued for 30 min. The mixture was then cooled to room temperature to obtain the underwater adhesive.

[0046] In the preparation process, the epoxy / OH equivalent ratio between epoxy linseed oil and gallic acid is approximately 2.7.

[0047] Example 3

[0048] 50 g of epoxidized linseed oil was added to a 250 mL three-necked flask and heated to 90 °C with mechanical stirring. Then, 12 g of gallic acid and 0.2 g of boric acid were added, and the mixture was stirred continuously at 90 °C for 2 h to allow for a more complete ring-opening reaction of the epoxy groups. The system was then cooled to 65 °C, and 18 g of hexamethylene diisocyanate (HDI) was slowly added under nitrogen protection, with the reaction continuing for 1.5 h. The temperature was then lowered to 45 °C, 3 g of KH560 was added, and the reaction continued for 30 min. Finally, 0.5 g of FeCl3 solution was added, and the reaction continued for 30 min. The mixture was then cooled to room temperature to obtain the underwater adhesive.

[0049] In the preparation process, the epoxy / OH equivalent ratio between epoxy linseed oil and gallic acid is approximately 1.3.

[0050] Example 4

[0051] 50 g of epoxy linseed oil was added to a 250 mL three-necked flask and heated to 90 °C under mechanical stirring to form a homogeneous, transparent liquid. Then, 9 g of gallic acid and 0.2 g of boric acid were added, and the mixture was stirred continuously at 90 °C for 2 h to allow the phenolic hydroxyl groups in the gallic acid to undergo a ring-opening reaction with the epoxy groups in the epoxy linseed oil, forming a prepolymer system containing hydroxyl groups. The system was then cooled to 65 °C, and 16 g of hexamethylene diisocyanate (HDI) was slowly added under nitrogen protection. The reaction continued for 1.5 h to allow the isocyanate groups to react with the hydroxyl groups in the system, forming a polyurethane structure. Finally, the system was cooled to 45 °C, and 3 g of γ-glycidoxypropyltrimethoxysilane (KH560) was added, with the mixture stirred for 30 min. Finally, 0.5 g of ferric chloride (FeCl3) was dissolved in a small amount of ethanol and added to the system. The reaction was continued at 45°C for 30 min. After the reaction was completed, the mixture was cooled to room temperature to obtain the underwater adhesive.

[0052] In the preparation process, the NCO / OH equivalent ratio between isocyanate and hydroxyl groups is approximately 1.0.

[0053] Example 5

[0054] 50 g of epoxidized linseed oil was added to a 250 mL three-necked flask and heated to 90 °C with mechanical stirring. Then, 9 g of gallic acid and 0.2 g of boric acid were added, and the mixture was stirred continuously at 90 °C for 2 h. The mixture was then cooled to 65 °C, and 20 g of hexamethylene diisocyanate (HDI) was slowly added under nitrogen protection, with the reaction continuing for 1.5 h. The mixture was then cooled to 45 °C, 3 g of KH560 was added, and the reaction continued for 30 min. Finally, 0.5 g of FeCl3 solution was added, and the reaction continued at 45 °C for 30 min. The mixture was then cooled to room temperature to obtain the underwater adhesive.

[0055] In the preparation process, the NCO / OH equivalent ratio between isocyanate and hydroxyl groups is approximately 1.4.

[0056] Example 6

[0057] 50 g of epoxidized linseed oil was added to a 250 mL three-necked flask and heated to 90 °C with mechanical stirring. Then, 9 g of gallic acid and 0.2 g of boric acid were added, and the mixture was stirred continuously at 90 °C for 2 h. The temperature was then lowered to 65 °C, and 18 g of HDI was added, with the reaction continuing for 1.5 h. Afterward, the temperature was lowered to 45 °C, and 2 g of γ-glycidoxypropyltrimethoxysilane (KH560) was added, with the mixture stirred for 30 min. Finally, 0.5 g of FeCl3 solution was added, and the reaction continued for 30 min. The mixture was then cooled to room temperature to obtain the underwater adhesive.

[0058] Example 7

[0059] 50 g of epoxidized linseed oil was added to a 250 mL three-necked flask and heated to 90 °C with mechanical stirring. Then, 9 g of gallic acid and 0.2 g of boric acid were added, and the mixture was stirred continuously at 90 °C for 2 h. The temperature was then lowered to 65 °C, and 18 g of HDI was added, with the reaction continuing for 1.5 h. Afterward, the temperature was lowered to 45 °C, and 4 g of γ-glycidoxypropyltrimethoxysilane (KH560) was added, with the reaction continuing for 30 min. Finally, 0.5 g of FeCl3 solution was added, and the reaction continued for 30 min. The mixture was then cooled to room temperature to obtain the underwater adhesive.

[0060] Example 8

[0061] 50 g of epoxidized linseed oil was added to a 250 mL three-necked flask and heated to 90 °C with mechanical stirring. Then, 9 g of gallic acid and 0.2 g of boric acid were added, and the mixture was stirred continuously at 90 °C for 2 h. The temperature was then lowered to 65 °C, and 18 g of HDI was added, continuing the reaction for 1.5 h. Afterward, the temperature was lowered to 45 °C, and 3 g of KH560 was added, continuing the reaction for 30 min. Finally, 0.7 g of ferric chloride (FeCl3) was dissolved in a small amount of ethanol and added to the system, and the reaction was continued at 45 °C for 30 min. The mixture was then cooled to room temperature to obtain the underwater adhesive.

[0062] Example 9

[0063] 50 g of epoxidized linseed oil was added to a 250 mL three-necked flask and heated to 90 °C with mechanical stirring. Then, 9 g of gallic acid and 0.2 g of boric acid were added, and the mixture was stirred continuously at 90 °C for 2 h. The temperature was then lowered to 65 °C, and 18 g of HDI was added, continuing the reaction for 1.5 h. Afterward, the temperature was lowered to 45 °C, and 3 g of KH560 was added, continuing the reaction for 30 min. Finally, 0.3 g of ferric chloride (FeCl3) was dissolved in a small amount of ethanol and added to the system, and the reaction was continued at 45 °C for 30 min. The mixture was then cooled to room temperature to obtain the underwater adhesive.

[0064] Example 10

[0065] 50 g of epoxidized soybean oil was added to a 250 mL three-necked flask and heated to 90 °C under mechanical stirring to form a homogeneous and transparent liquid. Then, 9 g of gallic acid and 0.2 g of boric acid were added to the system, and the mixture was stirred continuously at 90 °C for 2 h to allow the phenolic hydroxyl groups in the gallic acid to undergo a ring-opening reaction with the epoxy groups in the epoxidized soybean oil, forming a prepolymer system containing hydroxyl structures. The system was then cooled to 65 °C, and 18 g of hexamethylene diisocyanate (HDI) was slowly added under nitrogen protection, with the reaction continuing for 1.5 h to allow the isocyanate groups to react with the hydroxyl groups in the system. The system was then cooled to 45 °C, and 3 g of KH560 was added, with the reaction continuing for 30 min. Finally, 0.5 g of FeCl3 solution was slowly added to the system, and the reaction continued for 30 min. The mixture was then cooled to room temperature to obtain the underwater adhesive.

[0066] Example 11

[0067] 50 g of epoxy linseed oil was added to a 250 mL three-necked flask and heated to 90 °C under mechanical stirring to form a homogeneous and transparent liquid. Then, 9.8 g of catechol and 0.2 g of boric acid were added to the system, and the mixture was stirred continuously at 90 °C for 2 h to allow the phenolic hydroxyl groups in the catechol to undergo a ring-opening reaction with the epoxy groups in the epoxy linseed oil, forming a prepolymer system containing hydroxyl structures. The system was then cooled to 65 °C, and 18 g of hexamethylene diisocyanate (HDI) was slowly added under nitrogen protection, with the reaction continuing for 1.5 h. The system was then cooled to 45 °C, 3 g of KH560 was added, and the reaction continued for 30 min. Finally, 0.5 g of FeCl3 solution was added, and the reaction continued for 30 min. The mixture was then cooled to room temperature to obtain the underwater adhesive.

[0068] In the preparation process, the epoxy / OH equivalent ratio between epoxy linseed oil and catechol is approximately 1.6, and the NCO / OH equivalent ratio between isocyanate and hydroxyl groups is approximately 1.2.

[0069] Example 12

[0070] 50 g of epoxidized linseed oil was added to a 250 mL three-necked flask and heated to 90 °C under mechanical stirring until a homogeneous, transparent liquid was formed. Then, 9 g of gallic acid and 0.2 g of boric acid were added, and the mixture was stirred continuously at 90 °C for 2 h to allow the phenolic hydroxyl groups in the gallic acid to undergo a ring-opening reaction with the epoxy groups in the epoxidized linseed oil, forming a prepolymer system containing hydroxyl groups. The system was then cooled to 65 °C, and 18 g of hexamethylene diisocyanate (HDI) was slowly added under nitrogen protection. The reaction was continued for 1.5 h to allow the isocyanate groups to react with the hydroxyl groups in the system. Finally, the system was cooled to 45 °C, 3 g of KH560 was added, and the reaction was continued for 30 min. Finally, 0.5 g of aluminum chloride (AlCl3) was dissolved in a small amount of ethanol to form a homogeneous solution, and then slowly added to the reaction system. The reaction was continued to be stirred at 45°C for 30 min to allow the phenolic hydroxyl groups in gallic acid to form a coordination structure with the metal ions. After the reaction was completed, the mixture was cooled to room temperature to obtain the underwater adhesive.

[0071] Example 13

[0072] 50 g of epoxy linseed oil was added to a 250 mL three-necked flask and heated to 90 °C under mechanical stirring to form a homogeneous and transparent liquid. Then, 9 g of gallic acid and 0.2 g of boric acid were added to the system, and the mixture was stirred continuously at 90 °C for 2 h to allow the phenolic hydroxyl groups in the gallic acid to undergo a ring-opening reaction with the epoxy groups in the epoxy linseed oil, forming a prepolymer system containing hydroxyl structures. The system was then cooled to 65 °C, and 20 g of isophorone diisocyanate (IPDI) was slowly added under nitrogen protection. The reaction was continued for 1.5 h to allow the isocyanate groups to react with the hydroxyl groups in the system. The system was then cooled to 45 °C, 3 g of KH560 was added, and the reaction was continued for 30 min. Finally, 0.5 g of FeCl3 solution was added, and the reaction was continued for 30 min. The mixture was then cooled to room temperature to obtain the underwater adhesive.

[0073] In the preparation process, the NCO / OH equivalent ratio between isocyanate and hydroxyl groups is approximately 1.1.

[0074] Comparative Example 1

[0075] 50 g of epoxy linseed oil was added to a 250 mL three-necked flask and heated to 90 °C under mechanical stirring to form a homogeneous and transparent liquid. Then, 9 g of gallic acid and 0.2 g of boric acid were added, and the mixture was stirred continuously at 90 °C for 2 h to allow the phenolic hydroxyl groups in the gallic acid to undergo a ring-opening reaction with the epoxy groups in the epoxy linseed oil, forming a prepolymer system containing hydroxyl structures. The system was then cooled to 65 °C, and 18 g of hexamethylene diisocyanate (HDI) was slowly added under nitrogen protection. The reaction continued for 1.5 h to allow the isocyanate groups to react with the hydroxyl groups in the system, forming a stable polyurethane crosslinking structure. The system was then cooled to 45 °C, and 3 g of γ-glycidoxypropyltrimethoxysilane (KH560) was added. The reaction was continued with stirring for 30 min to form a silicon-oxygen structure. Ferric chloride (FeCl3) was not added during the reaction. After the reaction was completed, the mixture was cooled to room temperature to obtain the comparative underwater adhesive.

[0076] In the preparation process, the epoxy / OH equivalent ratio between epoxy linseed oil and gallic acid is approximately 1.8.

[0077] Comparative Example 2

[0078] 50 g of epoxidized linseed oil was added to a 250 mL three-necked flask and heated to 90 °C under mechanical stirring until a homogeneous, transparent liquid was formed. Then, 9 g of gallic acid and 0.2 g of boric acid were added, and the mixture was stirred continuously at 90 °C for 2 h to allow the phenolic hydroxyl groups in the gallic acid to undergo a ring-opening reaction with the epoxy groups in the epoxidized linseed oil, forming a prepolymer system containing hydroxyl groups. The system was then cooled to 65 °C, and 18 g of hexamethylene diisocyanate (HDI) was slowly added under nitrogen protection. The reaction continued for 1.5 h to allow the isocyanate groups to react with the hydroxyl groups in the system, forming a stable polyurethane crosslinked structure. The system was then cooled to 45 °C without adding γ-glycidoxypropyltrimethoxysilane (KH560). Finally, 0.5 g of ferric chloride (FeCl3) was dissolved in a small amount of ethanol to form a homogeneous solution and slowly added to the reaction system. The mixture was stirred continuously at 45 °C for 30 min to allow the phenolic hydroxyl groups in the gallic acid to react with the epoxy groups in the epoxidized linseed oil, forming a prepolymer system containing hydroxyl groups. 3+ A coordination structure is formed; after the reaction is complete, the mixture is cooled to room temperature to obtain the comparative underwater adhesive.

[0079] In the preparation process, the epoxy / OH equivalent ratio between epoxy linseed oil and gallic acid is approximately 1.8.

[0080] Comparative Example 3

[0081] 50 g of epoxidized linseed oil was added to a 250 mL three-necked flask and heated to 90 °C under mechanical stirring to form a homogeneous, transparent liquid. Then, 9 g of gallic acid and 0.2 g of boric acid were added, and the mixture was stirred continuously at 90 °C for 2 h to allow the phenolic hydroxyl groups in the gallic acid to undergo a ring-opening reaction with the epoxy groups in the epoxidized linseed oil, forming a prepolymer system containing hydroxyl groups. The system was then cooled to 65 °C without the addition of hexamethylene diisocyanate (HDI), and stirring continued for 1.5 h. Afterward, the temperature was lowered to 45 °C, and 3 g of γ-glycidoxypropyltrimethoxysilane (KH560) was added, and the reaction continued for 30 min. Finally, 0.5 g of FeCl3 solution was added, and the reaction continued for 30 min. The mixture was then cooled to room temperature to obtain a comparative underwater adhesive.

[0082] The mechanical properties of the epoxy linseed oil-based underwater adhesives prepared in each embodiment and comparative example were tested, and the results are shown in Table 1.

[0083] Table 1 Product Parameters

[0084]

[0085] Test method:

[0086] 1. Underwater Shear Strength Test: A 100 mm × 20 mm × 2 mm substrate (steel plate) was used as the bonding specimen. The surface was cleaned with ethanol and deionized water and then dried at room temperature. The adhesive was evenly applied to the overlapping area (20 mm × 10 mm) of the two substrates in an underwater environment and pressed firmly with a 2 kg weight for 2 min to ensure full contact. After underwater curing, an electronic universal testing machine was used to perform an overlap shear test at a tensile rate of 20 mm / min. The maximum load at specimen failure was recorded, and the shear strength (MPa) and debonding work (N / m) were calculated. Each test was repeated 5 times, and the average value was taken.

[0087] 2. Underwater Adhesion Performance Test on Multiple Substrates: Wood, steel plate, epoxy resin board, tinplate, and PET board were selected as bonding substrates. The dimensions of each substrate were 100 mm × 20 mm × 2 mm, and the overlap area was 20 mm × 10 mm. Adhesion and testing were conducted according to the underwater shear strength test method described above, and the shear strength on different substrates was recorded to evaluate the multi-substrate applicability of the adhesive.

[0088] 3. Long-term water resistance stability test: The bonded sample was immersed in room temperature pure water for long-term soaking treatment. The sample was taken out after soaking in water for 1 day, 7 days, 14 days and 30 days, and tested according to the underwater shear strength test method. The shear strength changes at different times were recorded to evaluate the water resistance stability of the adhesive.

[0089] 4. Shear strength calculation method:

[0090] Shear strength = Maximum load / Overlap area

[0091] The maximum load is the maximum force (N) recorded when the specimen fails, and the overlap area is the area of ​​the bonded region (mm²). 2 ).

[0092] 5. Debonding Energy Test and Calculation Method: Tensile shear tests were performed on the bonded specimens using an electronic universal testing machine, and the load-displacement curves during specimen failure were recorded. The specimen preparation method was the same as for the underwater shear strength test, with an overlap area of ​​20 mm × 10 mm. During the test, the specimens were loaded at a constant tensile rate (20 mm / min) until failure. The debonding energy was calculated based on the load-displacement curve. The calculation method is as follows: Integrate the load-displacement curve to obtain the total energy W (N·mm) consumed during specimen failure, then divide this energy by the overlap area A (mm²) to obtain the debonding energy per unit area G (J / m²). The calculation formula is as follows:

[0093] G = W / A

[0094] Where: G is the debonding work (J / m²); W is the integral area under the load-displacement curve (N·mm); A is the overlap area of ​​the specimen (mm²).

[0095] As shown in Table 1, the underwater adhesives obtained in Examples 1-3 of this invention all exhibited high underwater shear strength, with Example 1 showing the highest shear strength at 5.8 MPa, indicating that the system could form a relatively stable cross-linked network structure under these conditions. In contrast, the shear strength of Comparative Example 1 without the addition of metal salt was significantly lower, at only 3.2 MPa, indicating that the coordination effect between metal ions and the polyphenol structure could significantly improve the interfacial adhesion performance of the adhesive. The shear strength of Comparative Example 2 without the addition of silane coupling agent also decreased, indicating that the introduction of the silicon-oxygen structure helps to enhance the structural stability and interfacial bonding ability of the material. The shear strength of Comparative Example 3 without the addition of isocyanate was significantly lower, at only 2.6 MPa, indicating that isocyanate can form a polyurethane cross-linked network with the hydroxyl groups in the system, increasing the cross-linking density and cohesive strength of the system, thereby enhancing the underwater adhesion performance of the adhesive.

[0096] Depend on Figure 1 As can be seen, the underwater adhesive obtained in Example 1 of the present invention exhibits good adhesion performance on the surfaces of various substrates. It can effectively bond to substrates such as wood, steel plate, epoxy resin board, tinplate and PET board, indicating that the adhesive has good interface adaptability and multi-substrate applicability, and can meet the bonding requirements of different materials in the water environment.

[0097] Depend on Figure 2 It can be seen that the underwater adhesive obtained in Example 1 of the present invention still maintains a high shear strength after being immersed in a water environment. The shear strength is above 5.5 MPa after 3 days underwater. As the immersion time increases, the shear strength decreases slightly, but it still remains above 5.0 MPa after 30 days of immersion. This indicates that the adhesive has good water resistance stability in a water environment and can meet the requirements for medium and long-term underwater use.

[0098] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A bio-based multi-crosslinked underwater adhesive, characterized in that, It is prepared from the following raw materials in parts by weight: 40-60 parts of epoxidized vegetable oil, 6-12 parts of polyphenolic compounds, 15-25 parts of isocyanate, 2-5 parts of silane coupling agent, 0.3-1 parts of metal salt, and 0.1-0.5 parts of catalyst.

2. The underwater adhesive according to claim 1, characterized in that, The epoxidized vegetable oil is selected from one or more of epoxidized linseed oil, epoxidized soybean oil, and epoxidized castor oil; The polyphenolic compound is a natural polyphenolic compound selected from one or more of gallic acid, catechol, and pyrogallic acid; the epoxy / OH equivalent ratio of the epoxy group in the epoxidized vegetable oil to the phenolic hydroxyl group in the polyphenolic compound is 1 to 3.

3. The bio-based multi-crosslinked underwater adhesive according to claim 1, characterized in that, The isocyanate is selected from one or more of hexamethylene diisocyanate, isophorone diisocyanate, and diphenylmethane diisocyanate; the NCO / OH equivalent ratio between the isocyanate group and the hydroxyl group is 1.0 to 1.4; the hydroxyl group includes hydroxyl groups formed after ring opening of epoxidized vegetable oil and unreacted hydroxyl groups in polyphenolic compounds; the silane coupling agent is selected from γ-glycidoxypropyltrimethoxysilane or γ-aminopropyltriethoxysilane.

4. The bio-based multi-crosslinked underwater adhesive according to claim 1, characterized in that, The metal salt is selected from one or more of ferric chloride, aluminum chloride, or zinc chloride.

5. The bio-based multi-crosslinked underwater adhesive according to claim 1, characterized in that, The catalyst is selected from one or more of boric acid, 2-methylimidazole, 2-ethyl-4-methylimidazole, and boron trifluoride diethyl ether complex.

6. The bio-based multi-crosslinked underwater adhesive according to claim 1, characterized in that, The bio-based multi-crosslinked underwater adhesive comprises an epoxy ring-opening structure, a polyurethane crosslinking structure, a silicon-oxygen structure, and a metal coordination structure.

7. A method for preparing the bio-based multi-crosslinked underwater adhesive according to any one of claims 1 to 6, characterized in that, Includes the following steps: (1) Under stirring conditions, polyphenolic compounds and catalysts were added to epoxidized vegetable oil, and a prepolymer system containing hydroxyl structure was obtained through ring-opening reaction; (2) Cool the prepolymer system containing hydroxyl structure to 60-70 °C, add isocyanate under inert atmosphere protection and continue the reaction to allow the isocyanate groups to react with the hydroxyl groups in the system to obtain polyurethane; (3) Cool the system to 40-50°C, add silane coupling agent and continue the reaction to form a silicon-oxygen structure in the system; (4) Finally, a metal salt solution is added to the system and the reaction continues, so that the phenolic hydroxyl groups in the polyphenolic compound form a coordination structure with the metal ions. After the reaction is completed, the mixture is cooled to obtain the bio-based multi-crosslinked underwater adhesive.

8. The method for preparing the bio-based multi-crosslinked underwater adhesive according to claim 7, characterized in that, The ring-opening reaction in step (1) is carried out at a temperature of 80~100℃ for 1~3h. The reaction time described in step (2) is 1 to 2 hours.

9. The method for preparing the bio-based multi-crosslinked underwater adhesive according to claim 7, characterized in that, The reaction time described in step (3) is 20-40 minutes. The temperature for the continued reaction in step (4) is 40-50℃ and the time is 20-40 min.

10. The use of the bio-based multi-crosslinked underwater adhesive according to any one of claims 1 to 6 in bonding, sealing or repairing in an aquatic environment.

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