High-strength recoverable cross-linking type epoxy adhesive as well as preparation method and application thereof

Abstract

The invention relates to the technical field of adhesives, in particular to a high-strength recoverable cross-linking type epoxy adhesive and a preparation method and application thereof.The cross-linking type epoxy adhesive is prepared from, by weight, 40-60 parts of epoxy resin, 0-40 parts of epoxy reactive diluent, 40-100 parts of amine curing agent, 10-100 parts of activated alkyne compound, 20-40 parts of solvent and 0-130 parts of lignin. Wherein the activated alkyne compound comprises one or more of a bifunctional / trifunctional ester group activated alkyne compound and a bifunctional carbonyl group activated alkyne compound. The adhesive prepared by the invention not only has excellent bonding strength and toughness, but also can be recycled through thermal excitation dynamic bond exchange, and can effectively eliminate internal stress generated by volume shrinkage or mismatching of thermal expansion coefficients in the curing process; and the dimensional stability and durability of a bonding interface under long-term use or environment change are obviously improved.

Description

Technical Field

[0001] This invention relates to the field of adhesive technology, and in particular to a high-strength recyclable crosslinked epoxy adhesive, its preparation method, and its application. Background Technology

[0002] Epoxy adhesives are widely used in various fields such as electronics, aerospace, automotive machinery, and sporting goods due to their excellent adhesion, mechanical strength, and chemical resistance. They are commonly used for bonding materials such as metals, ceramics, glass, and fiber-reinforced plastics (FRP). In the automotive industry, epoxy adhesives can replace traditional welding and riveting processes, effectively improving production efficiency and reducing manufacturing costs, making them one of the most widely used structural adhesives.

[0003] However, existing epoxy adhesives still have significant technical defects: First, they generally have high hardness but insufficient toughness after curing, making them prone to brittleness under impact or vibration, affecting bonding reliability. Second, traditional epoxy adhesives form a stable three-dimensional cross-linked network after curing, which is difficult to degrade or recycle, and the waste generated after use can easily cause environmental pollution, which does not meet the current environmental protection development requirements. Third, some adhesives have insufficient bonding strength to specific substrates (such as wood panels), and additional catalysts, toughening agents, and other components need to be added in industrial production, increasing production costs and process complexity. Fourth, internal stress is easily generated during the curing process due to volume shrinkage or mismatch in coefficients of thermal expansion, which may lead to cracking of the adhesive layer under long-term use or temperature changes, especially in precision equipment. Therefore, there is an urgent need to provide a high-strength, recyclable, and stress-releasing cross-linked epoxy adhesive. Summary of the Invention

[0004] The purpose of this invention is to provide a high-strength, recyclable cross-linked epoxy adhesive, its preparation method, and its applications. The resulting adhesive not only possesses excellent bonding strength and toughness but also achieves recyclability through reversible exchange of dynamic bonds. Furthermore, it effectively releases internal stress generated during the bonding process, significantly improving the long-term stability and durability of the adhesive layer. This makes it particularly suitable for high-end applications sensitive to dimensional stability and internal stress, such as precision instruments and optical devices. In addition, this cross-linked epoxy adhesive exhibits good compatibility with various substrates, solving problems such as high hardness, insufficient toughness, and non-recyclability of existing epoxy adhesives after curing.

[0005] To achieve the above objectives, the present invention provides a high-strength recyclable crosslinked epoxy adhesive, comprising, by weight, 40-60 parts epoxy resin, 0-40 parts epoxy reactive diluent, 40-100 parts amine curing agent, 10-100 parts activated acetylene compound, 20-40 parts solvent, and 0-130 parts lignin, wherein the activated acetylene compound includes one or more of difunctional ester activated acetylene compounds, trifunctional ester activated acetylene compounds, and difunctional carbonyl activated acetylene compounds, and the above crosslinked epoxy adhesive contains a crosslinked network of enamine-ketone dynamic bonds.

[0006] Preferably, the epoxy resin is a liquid epoxy resin, including one or more of bisphenol A type epoxy resin, bisphenol F type epoxy resin, polyphenol type glycidyl ether epoxy resin, aliphatic glycidyl ether epoxy resin, and phenolic epoxy resin.

[0007] Preferably, the epoxy reactive diluent includes one or more of the following: 1,4-butanediol glycidyl ether, polyethylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, propylene glycol diglycidyl ether, 1,6-hexanediol diglycidyl ether, propylene glycol glycidyl ether, propyl glycidyl ether, n-butyl glycidyl ether, phenyl glycidyl ether, ethylene glycol diglycidyl ether, resorcinol diglycidyl ether, and alkylene glycidyl ether.

[0008] Preferably, the amine curing agent includes one or more of the following: ethylenediamine, 1,6-hexanediamine, 1,12-dodecanediamine, m-phenylenediamine, 4,4-diaminocyclohexylmethane, p-phenylenediamine, m-phenylenediamine, N,N-dimethylethylenediamine, N,N-diethylethylenediamine, 1,3-bis-4-piperidinylpropane, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, and polyetheramine.

[0009] Preferably, the structures of the difunctional ester-activated alkyne compound, the trifunctional ester-activated alkyne compound, and the difunctional carbonyl-activated alkyne compound are as follows: .

[0010] Preferably, the solvent includes one or more of acetone, dichloromethane, tetrahydrofuran, ethyl acetate, and ethanol.

[0011] Preferably, the lignin is sodium lignin sulfonate.

[0012] The preparation method of the above-mentioned high-strength recyclable crosslinked epoxy adhesive includes the following steps: S1. Prepolymerization: Dissolve epoxy resin, epoxy reactive diluent and amine curing agent in a partial solvent and react at 20-40℃ for 8-16 hours to obtain prepolymer; S2. Preparation of prepolymer solution: Dissolve the activated alkyne compound in the remaining solvent, add it to the prepolymer obtained in step S1, and stir thoroughly to obtain the adhesive prepolymer solution. S3. Curing and molding: Pour the adhesive prepolymer liquid from step S2 into a polytetrafluoroethylene mold, evaporate the solvent, and keep it at 70-90℃ for 10-14 hours to obtain a cross-linked epoxy adhesive.

[0013] Preferably, in step S2, if lignin needs to be added, lignin is added after the mixture is stirred evenly in step S2, and then stirred again until uniform to obtain the adhesive prepolymer solution.

[0014] The above-mentioned high-strength recyclable cross-linked epoxy adhesive is used for bonding iron plates, aluminum plates, steel plates, wood boards, ABS boards, PC boards, glass, and precision equipment, including precision instruments, optical devices, and microelectronic components that are sensitive to dimensional stability and internal stress.

[0015] Mechanism of the invention: This invention utilizes the prepolymerization reaction of epoxy resin and amine curing agent, followed by the formation of a dynamic crosslinking network with activated alkyne compounds. This allows the adhesive to possess both high hardness and excellent toughness without the need for external catalysts or toughening agents. The dynamic covalent bonds within the crosslinking network can undergo reversible breakage and recombination under hot-pressing conditions. This not only enables multiple recycling of the adhesive but also effectively releases internal stress caused by substrate deformation or thermal expansion through the exchange and recombination of dynamic bonds, preventing bond failure due to stress concentration. This significantly improves the dimensional stability and durability of the bonding interface.

[0016] Therefore, the present invention, employing the above-mentioned high-strength recyclable crosslinked epoxy adhesive, its preparation method, and its application, has the following beneficial effects: (1) The adhesive of the present invention has high strength and toughness, solving the problem of brittleness of traditional epoxy adhesives. The stable cross-linking structure improves the cohesive energy of the adhesive, thereby achieving high bonding strength. In addition, it can be recycled multiple times through hot pressing, reducing resource waste and environmental pollution.

[0017] (2) The adhesive of the present invention can also effectively eliminate the internal stress caused by volume shrinkage or mismatch of thermal expansion coefficients during the curing process. It is particularly suitable for bonding precision equipment that is sensitive to dimensional stability and internal stress, such as optical lenses, sensor packaging, microelectronic components, etc.

[0018] (3) The adhesive of the present invention can be used to bond various substrates such as iron plate, aluminum plate, steel plate, wood board, ABS board, PC board, and glass, to meet the needs of different fields.

[0019] (4) The preparation process of the present invention is simple and cost-controllable. It does not require complex equipment and additional additives. The process steps are simple, and the introduction of lignin can reduce the cost of raw materials. At the same time, the solvent can be recovered through volatilization, which meets the requirements of industrial production.

[0020] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the iron plate bonded in Application Example 1 of the present invention; Figure 2 This is a schematic diagram of the iron plate bonded in Application Example 1 of the present invention after it has been pulled apart; Figure 3 This is a schematic diagram showing the tensile test results of iron plates bonded using the adhesive prepolymer liquid prepared in Examples 4 and 8-10 of this invention. Figure 3 a) in the figure is a schematic diagram of the results of tensile load and standard deformation. Figure 3 b) in the diagram is a schematic diagram of shear strength; Figure 4 This is a schematic diagram of the adhesive recycling process of the present invention. Figure 4 a) in the diagram is a schematic diagram of a single recycling of adhesive. Figure 4 b) in the diagram is a schematic diagram of secondary recycled adhesive; Figure 5 This is a schematic diagram of the micro-deformation curve of the adhesive obtained in Example 4 of the present invention after heat treatment as a function of time. Figure 6 This is a schematic diagram of the tensile curves of the initial hot-pressed bonded iron plate and the hot-pressed bonded iron plate with recycled adhesive in Application Example 1 of the present invention; Figure 7 This is a schematic diagram of the adhesive prepolymer liquid obtained in step S2 of embodiment 4-7 of the present invention after the bonded wooden board is pulled apart; Figure 8 This is a schematic diagram of the tensile curve of the adhesive prepolymer liquid obtained in step S2 of embodiments 4-7 of the present invention bonded to the wood board; Figure 9 This is a schematic diagram illustrating the mechanism by which the adhesive of this invention eliminates internal stress during the curing process. Figure 9 (a) in the figure shows the change in the crosslinking network structure of traditional adhesives after heating; Figure 9 (b) in the figure shows the change in the crosslinking network structure of the adhesive of the present invention after heating. Detailed Implementation

[0022] The present invention will be further described below with reference to the accompanying drawings and embodiments. Unless otherwise defined, the technical or scientific terms used in this invention should have the ordinary meaning understood by one of ordinary skill in the art to which this invention pertains. The features mentioned above or in the specific embodiments of the present invention can be combined arbitrarily, and these specific embodiments are for illustrative purposes only and are not intended to limit the scope of the invention.

[0023] This invention provides a high-strength, recyclable, cross-linked epoxy adhesive. The cross-linked epoxy adhesive comprises, by weight, 40-60 parts epoxy resin, 0-40 parts epoxy reactive diluent, 40-100 parts amine curing agent, 10-100 parts activated acetylene compound, 20-40 parts solvent, and 0-130 parts lignin. The activated acetylene compound includes one or more of difunctional ester-activated acetylene compounds, trifunctional ester-activated acetylene compounds, and difunctional carbonyl-activated acetylene compounds. The cross-linked epoxy adhesive contains a cross-linked network of enamine-ketone dynamic bonds, which can achieve dynamic bond exchange under thermal excitation, thereby eliminating internal stress generated during the curing process.

[0024] Preferably, the epoxy resin is a liquid epoxy resin, including one or more of bisphenol A type epoxy resin, bisphenol F type epoxy resin, polyphenolic glycidyl ether epoxy resin, aliphatic glycidyl ether epoxy resin, and phenolic epoxy resin. As the matrix of the adhesive, the epoxy resin's epoxy groups can undergo ring-opening polymerization with the amine curing agent to form a cross-linked structure, providing the adhesive with basic mechanical strength.

[0025] Preferably, the epoxy reactive diluent includes one or more of the following: 1,4-butanediol glycidyl ether, polyethylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, propylene glycol diglycidyl ether, 1,6-hexanediol diglycidyl ether, propylene glycol glycidyl ether, propyl glycidyl ether, n-butyl glycidyl ether, phenyl glycidyl ether, ethylene glycol diglycidyl ether, resorcinol diglycidyl ether, and alkylene glycidyl ether. The epoxy reactive diluent can reduce the viscosity of epoxy resin, improve its workability, and its own epoxy groups can participate in the polymerization reaction without affecting the strength of the adhesive.

[0026] More preferably, the epoxy reactive diluent includes one or more of 1,4-butanediol glycidyl ether, 1,6-hexanediol diglycidyl ether, ethylene glycol diglycidyl ether, and propylene glycol diglycidyl ether.

[0027] Preferably, the amine curing agent includes one or more of the following: ethylenediamine, 1,6-hexanediamine, 1,12-dodecanediamine, m-phenylenediamine, 4,4-diaminocyclohexylmethane, p-phenylenediamine, m-phenylenediamine, N,N-dimethylethylenediamine, N,N-diethylethylenediamine, 1,3-bis-4-piperidinylpropane, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, and polyetheramine. The amino groups in the amine curing agent undergo a ring-opening reaction with the epoxy groups of the epoxy resin to form a cross-linked network, which is a key component determining the strength of the adhesive.

[0028] More preferably, the polyetheramines include one or more of the following types: D230, T403, D400, D2000, FL1000, T5000, and ED900.

[0029] More preferably, the amine curing agent includes one or more of m-phenylenediamine, N,N-dimethylethylenediamine, diethylenetriamine, triethylenetetramine, and tetraethylenepentamine.

[0030] Preferably, the structures of the difunctional ester-activated alkyne compound, the trifunctional ester-activated alkyne compound, and the difunctional carbonyl-activated alkyne compound are as follows: .

[0031] More preferably, the activated alkyne compound includes one or more of the following structures: .

[0032] Activated alkyne compounds can undergo addition reactions with excess amino groups in the prepolymerization reaction to further construct a dynamic cross-linked structure. This not only improves the toughness of the adhesive but also enables the recycling and reuse of the adhesive through the reversible breaking and recombination of dynamic covalent bonds.

[0033] Preferably, the solvent includes one or more of acetone, dichloromethane, tetrahydrofuran, ethyl acetate, and ethanol. The solvent is used to dissolve the components, ensuring a uniform reaction, and is subsequently removed by evaporation, leaving no residue in the final product.

[0034] More preferably, the solvent includes one or both of dichloromethane and ethyl acetate.

[0035] Preferably, the lignin is sodium lignin sulfonate. As a natural polymer material, lignin contains hydroxyl and carboxyl groups in its molecular structure, which can form hydrogen bonds or chemical bonds with the substrate surface, significantly improving the bonding strength of adhesives to substrates such as wood panels, while reducing production costs.

[0036] Preferably, the molar ratio of the total epoxy groups in the epoxy resin and epoxy reactive diluent to the amino groups in the amine curing agent is 1:1.01-1.5; the molar ratio of the amine curing agent to the activated alkyne compound is 1:0.2-0.99. These ratio ranges ensure sufficient reaction of the epoxy groups, while the excess amino groups react with the alkyne compounds to form a dynamic cross-linked structure, balancing strength and recyclability to ensure optimal adhesive performance.

[0037] The preparation method of the above-mentioned high-strength recyclable crosslinked epoxy adhesive includes the following steps: S1. Prepolymerization: Dissolve epoxy resin, epoxy reactive diluent and amine curing agent in a partial solvent and react at 20-40℃ for 8-16 hours to obtain prepolymer; S2. Preparation of prepolymer solution: Dissolve the activated alkyne compound in the remaining solvent, add it to the prepolymer obtained in step S1, and stir thoroughly to obtain the adhesive prepolymer solution. S3. Curing and Molding: Pour the adhesive prepolymer solution from step S2 into a polytetrafluoroethylene mold, evaporate the solvent, and keep it at 70-90℃ for 10-14 hours to obtain a cross-linked epoxy adhesive. The adhesive prepared by this method is recyclable and can eliminate internal stress through dynamic bond exchange under thermal excitation.

[0038] Preferably, the solvent used in S1 accounts for 80% of the total solvent mass, and the remaining solvent in S2 accounts for 20% of the total solvent mass.

[0039] Preferably, in step S2, if lignin needs to be added, lignin is added after the mixture is stirred evenly in step S2, and then stirred again until uniform to obtain the adhesive prepolymer solution.

[0040] In an even more preferred embodiment, in S3, the length, width, and height of the polytetrafluoroethylene mold are 10cm × 10cm × 2cm.

[0041] The above-mentioned high-strength recyclable cross-linked epoxy adhesive is used for bonding iron plates, aluminum plates, steel plates, wood plates, ABS boards, PC boards, and glass.

[0042] More preferably, in application, the adhesive prepolymer obtained in S2 can be directly dropped onto one of the substrates to be bonded, then covered with another substrate, placed at room temperature for 6 hours to evaporate the solvent, and then dried at 80°C for 12 hours.

[0043] Preferably, during use, the adhesive prepolymer liquid prepared in S2 can be applied to the surface of the substrate, and the adhesive can be dried at 80°C for 12 hours. Then, it can be kept at 90-150°C for 15-120 minutes. The exchange and recombination of dynamic bonds can effectively release the residual stress during the bonding process and improve the long-term reliability of the component under temperature changes or mechanical vibration.

[0044] In a more preferred application, a small portion of the cross-linked epoxy adhesive of S3 can be placed between the two substrates and hot-pressed at 90-120℃ and 2-10MPa for 1 hour to bond the two substrates together.

[0045] The mechanism of adhesive recycling is as follows: Under hot pressing, the enamine-ketone dynamic bonds in the adhesive undergo an exchange reaction with similar amino groups, thereby achieving network recombination and recycling.

[0046] .

[0047] The adhesive of this invention can also effectively eliminate internal stress caused by volume shrinkage or mismatch in coefficients of thermal expansion during the curing process. Its mechanism lies in: traditional adhesives (such as...) Figure 9 The cross-linked network shown in (a) is static, and the internal stress cannot be released, which may lead to irregular deformation after heating. In contrast, the adhesive of this invention (such as...) Figure 9 As shown in (b) in the figure, under heating conditions, the enamine-ketone dynamic bonds can undergo reversible exchange, driving the entire cross-linked network to rearrange, thereby releasing and eliminating internal stress.

[0048] Example 1 This invention provides a high-strength recyclable cross-linked epoxy adhesive, comprising, by weight, 40 parts of bisphenol F type epoxy resin, 10 parts of polyethylene glycol diglycidyl ether, 40 parts of ethylenediamine, 10 parts of tripropynyl methylpropane (trimethylpropynyl ester compound), and 20 parts of acetone.

[0049] The structural formula of tripropynyl methylpropane (trimethylpropynyl ester compound) is: .

[0050] The above-mentioned cross-linked epoxy adhesive is prepared by the following steps: S1. Prepolymerization: Bisphenol F type epoxy resin, polyethylene glycol diglycidyl ether and ethylenediamine are dissolved in 16 parts of acetone and reacted at 20°C for 8 hours to obtain the prepolymer.

[0051] S2. Preparation of prepolymer solution: Dissolve tripropynyl methylpropane in 4 parts of acetone, add it to the prepolymer obtained in step S1, and stir thoroughly to obtain the adhesive prepolymer solution.

[0052] S3. Curing and molding: Pour the adhesive prepolymer liquid from step S2 into a polytetrafluoroethylene mold, evaporate the solvent, and keep it at 70°C for 10 hours to obtain a cross-linked epoxy adhesive.

[0053] Example 2 This invention provides a high-strength recyclable cross-linked epoxy adhesive, comprising, by weight, 50 parts of polyphenolic glycidyl ether epoxy resin, 20 parts of polypropylene glycol diglycidyl ether, 70 parts of 1,6-hexanediamine, 14 parts of methyl 1,3-phenylpropynate and 30 parts of tetrahydrofuran.

[0054] The structural formula of methyl 1,3-phenylpropynate is: .

[0055] The above-mentioned cross-linked epoxy adhesive is prepared by the following steps: S1. Prepolymerization: Polyphenolic glycidyl ether epoxy resin, polypropylene glycol diglycidyl ether and 1,6-hexanediamine are dissolved in 24 parts of dichloromethane and reacted at 30°C for 12 hours to obtain the prepolymer.

[0056] S2. Preparation of prepolymer solution: Dissolve methyl 1,3-phenylpropynate in 6 parts of dichloromethane, add it to the prepolymer obtained in step S1, and stir thoroughly to obtain the adhesive prepolymer solution.

[0057] S3. Curing and molding: Pour the adhesive prepolymer liquid from step S2 into a polytetrafluoroethylene mold, evaporate the solvent, and keep it at 80°C for 12 hours to obtain a cross-linked epoxy adhesive.

[0058] Example 3 This invention provides a high-strength recyclable cross-linked epoxy adhesive, comprising, by weight, 60 parts aliphatic glycidyl ether epoxy resin, 40 parts propylene glycol diglycidyl ether, 100 parts 1,12-dodecanediamine, 30 parts biphenyl dicarbonyl ytylene, and 40 parts ethanol.

[0059] The structural formula of biphenyl dicarbonyl yne is .

[0060] The above-mentioned cross-linked epoxy adhesive is prepared by the following steps: S1. Prepolymerization: Aliphatic glycidyl ether epoxy resin, propylene glycol diglycidyl ether and 1,12-dodecanediamine are dissolved in 32 parts of tetrahydrofuran and reacted at 40°C for 16 h to obtain the prepolymer.

[0061] S2. Preparation of prepolymer solution: Dissolve biphenyl dicarbonyl ytylene in 8 parts of tetrahydrofuran, add it to the prepolymer obtained in step S1, and stir thoroughly to obtain the adhesive prepolymer solution.

[0062] S3. Curing and molding: Pour the adhesive prepolymer liquid from step S2 into a polytetrafluoroethylene mold, evaporate the solvent, and keep it at 90°C for 14 hours to obtain a cross-linked epoxy adhesive.

[0063] Example 4 This invention provides a high-strength recyclable crosslinked epoxy adhesive, comprising, by weight, 40 parts of bisphenol A type epoxy resin, 40 parts of 1,4-butanediol glycidyl ether, 90 parts of m-phenylenediamine, 20 parts of hexyl 1,6-dipropynate, 40 parts of dichloromethane, and 19 parts of sodium lignosulfonate.

[0064] The structural formula of 1,6-dipropynyl hexyl ester is as follows: .

[0065] The above-mentioned cross-linked epoxy adhesive is prepared by the following steps: S1. Prepolymerization: Bisphenol A type epoxy resin, 1,4-butanediol glycidyl ether and m-phenylenediamine are dissolved in 32 parts of ethanol and reacted at 30°C for 12 hours to obtain the prepolymer.

[0066] S2. Preparation of prepolymer solution: Dissolve 1,6-dipropynyl hexyl ester in 8 parts of ethanol, add it to the prepolymer obtained in step S1, and stir thoroughly to obtain the adhesive prepolymer solution.

[0067] S3. Curing and molding: Pour the adhesive prepolymer liquid from step S2 into a polytetrafluoroethylene mold with dimensions of 10cm×10cm×2cm. After the solvent evaporates, keep it at 80℃ for 12 hours to obtain a cross-linked epoxy adhesive.

[0068] Example 5 The difference from Example 4 is that in step S2, after stirring evenly, 19 parts of sodium lignosulfonate are added to prepare the adhesive prepolymer solution. The rest is the same as in Example 4.

[0069] Example 6 The difference from Example 5 is that the amount of sodium lignosulfonate used in step S2 is 48 parts, while the rest is the same as in Example 5.

[0070] Example 7 The difference from Example 5 is that the amount of sodium lignosulfonate used in step S2 is 95 parts, while the rest is the same as in Example 5.

[0071] Example 8 The difference from Example 4 is that the amount of 1,6-dipropynyl hexyl ester used is 40 parts, while the rest is the same as in Example 4.

[0072] Example 9 The difference from Example 4 is that the amount of 1,6-dipropynyl hexyl ester used is 60 parts, while the rest is the same as in Example 4.

[0073] Example 10 The difference from Example 4 is that the activated alkyne compound is p-phenylenedicarbonyl alkyne, with the following specific structure: .

[0074] Application Example 1 A high-strength, recyclable, cross-linked epoxy adhesive is used to bond iron plates. 0.033g of the adhesive prepolymer liquid prepared in step S2 of Example 4 is dropped onto one of the iron plates to be bonded, and then another iron plate is placed on top. The mixture is left at room temperature for 6 hours to allow the solvent to evaporate, and then dried at 80°C for 12 hours.

[0075] Application Example 2 A high-strength, recyclable cross-linked epoxy adhesive is used to bond wooden boards. 0.003g of the cross-linked epoxy adhesive prepared in step S3 of Example 4 is placed between two wooden boards, and the boards are hot-pressed at 100°C and 6MPa for 1 hour to bond them together.

[0076] Performance testing Figure 1 This is a schematic diagram of the iron plate bonded in Example 1 of the present invention, as shown. Figure 1 As shown, the two iron plates are glued together.

[0077] Figure 2 This is a schematic diagram of the iron plate bonded in Example 1 of the present invention after it has been pulled apart, as shown. Figure 2 As shown, after the iron plate was pulled apart, a large amount of adhesive remained at the bonding interface, with no obvious peeling of the substrate.

[0078] The adhesive prepolymer solutions prepared in Examples 4 and 8-10 were used to bond iron plates using the method in Application Example 1. Tensile tests were then performed on the bonded iron plates, and the experimental results are as follows: Figure 3 As shown, Example 4 exhibits a tensile load of 2038 N and a shear strength of 9.48 MPa; Example 8 exhibits a tensile load of 1875 N and a shear strength of 8.70 MPa; Example 9 exhibits a tensile load of 1790 N and a shear strength of 8.08 MPa; and Example 10 exhibits a tensile load of 1273 N and a shear strength of 7.67 MPa. Comparing Examples 4, 8, and 9 demonstrates that both tensile load and shear strength decrease with increasing amounts of hexyl 1,6-dipropynate. Since the adhesive strength of an adhesive is determined by the combined effects of interfacial adhesion and cohesive energy, increasing the crosslinking density of the crosslinking agent increases the cohesive energy, but may also lead to increased brittleness, interfacial stress concentration, and interfacial failure. Comparing Examples 4 and 10 shows that changing the flexible long-chain alkyl propynate to a rigid benzene ring structure (p-phenylene dicarbonyl ytylene) may also increase the brittleness of the material, leading to a decrease in adhesive strength.

[0079] The initially hot-pressed bonded iron plate from Application Example 2 was subjected to a tensile test. After being pulled apart, the adhesive residue on the surface of the iron plate was collected and recorded as one instance of adhesive recovery. Figure 4(a) The recycled adhesive is reused for hot-pressing bonding of iron plates under the same initial hot-pressing conditions. After tensile testing, the residual adhesive is collected and recorded as the secondary recycled adhesive. Figure 4 (b) The recycled adhesive was reused in a hot-pressed bonding test on the iron sheet, and the results are as follows. Figure 6 As shown, the adhesive shear-tensile curves of the adhesive recycled twice in Application Example 1 are similar to those of the tensile load in Application Example 1, indicating that the adhesive properties remain constant after two hot-press recycling processes.

[0080] Stress relief experiment: Connect the strain gauge wire to the bridge arm interface of the strain gauge, turn on the strain gauge, adjust the "zero point knob" of the strain gauge to make the strain display 0, pick up the strain gauge with tweezers, and gently place the sensitive grid axis on the adhesive (avoid touching the sensitive grid and the substrate with your hands). The micro-strain relief is achieved by using the dynamic bond exchange of the adhesive (in a 120℃ oven). During this process, do not touch the strain gauge and the lead wire. Fix the lead wire with tape to avoid pulling the lead wire and damaging the strain gauge. Record the strain value simultaneously.

[0081] Figure 5 This shows the release curve of the internal minute deformation (internal stress) of the adhesive in Application Example 1 under heating at 120°C over time. The deformation was monitored in real-time using strain gauges. Figure 5 As shown, the initial deformation was approximately 890 microstrain, which rapidly decreased to near zero within 15 minutes of heating and remained stable thereafter. This curve visually confirms that the enamine-ketone dynamic bonds in the adhesive undergo reversible exchange under thermal excitation, driving the rearrangement of the crosslinked network and thus rapidly and uniformly eliminating internal stress caused by coating or curing. This property is of great significance for precision bonding applications requiring high dimensional stability, such as optical assembly and sensor packaging.

[0082] In Examples 4-7, the adhesive prepolymer liquid obtained in step S2 was used to bond wood boards, and a tensile test was performed. The wood boards after being pulled apart were as follows: Figure 7 As shown, after the wooden board was pulled apart, the adhesive not only remained at the interface of the wooden board, but also accompanied by the breakage of some wooden board fibers. In Example 4, the substrate failed completely, while in Examples 5-7, interface failure and substrate failure occurred to varying degrees. It can be clearly observed that Example 7 showed more adhesive components (including brown sodium lignin sulfonate) compared to Examples 5 and 6, indicating an increase in the degree of interface failure.

[0083] Tensile test results as follows Figure 8As shown, the tensile load of Example 4 reached 2738 N, the tensile load of Example 5 reached 2507 N, the tensile load of Example 6 reached 3003 N, and the tensile load of Example 7 reached 1959 N. This demonstrates that the addition of sodium lignin sulfonate initially increases the adhesion of wood, then decreases. Furthermore, appropriate addition of sodium lignin sulfonate can not only reduce the cost of adhesives but also improve the bonding strength to wood.

[0084] Therefore, the present invention employs the above-mentioned high-strength recyclable cross-linked epoxy adhesive, its preparation method, and its application. The prepared adhesive has excellent bonding strength and recyclability, and the addition of lignin can significantly improve the bonding performance to wood boards, meeting the application needs of different fields.

[0085] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A high-strength recyclable cross-linked epoxy adhesive, characterized by: The cross-linking type epoxy adhesive comprises, by weight fraction, 40-60 parts of epoxy resin, 0-40 parts of epoxy active diluent, 40-100 parts of amine curing agent, 10-100 parts of activated alkyne compound, 20-40 parts of solvent and 0-130 parts of lignin, wherein the activated alkyne compound comprises one or more of di-ester group activated alkyne compound, tri-ester group activated alkyne compound and di-carbonyl group activated alkyne compound, and the cross-linking type epoxy adhesive comprises a cross-linking network of enamine-ketone dynamic bond.

2. The high-strength recyclable cross-linked epoxy adhesive according to claim 1, characterized in that: The epoxy resin is a liquid epoxy resin, comprising one or more of bisphenol A type epoxy resin, bisphenol F type epoxy resin, polyphenol type glycidyl ether epoxy resin, aliphatic glycidyl ether epoxy resin and phenolic epoxy resin.

3. The high-strength recyclable cross-linked epoxy adhesive according to claim 1, characterized in that: The epoxy active diluent comprises one or more of 1,4-butanediol glycidyl ether, polyethylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, propylene glycol diglycidyl ether, 1,6-hexanediol diglycidyl ether, propenyl glycidyl ether, propyl glycidyl ether, n-butyl glycidyl ether, phenyl glycidyl ether, ethylene glycol diglycidyl ether, resorcinol diglycidyl ether and alkylene glycidyl ether.

4. The high-strength recyclable crosslinking type epoxy adhesive according to claim 1, characterized by: The amine curing agent comprises one or more of ethylenediamine, 1,6-hexanediamine, 1,12-dodecanediamine, m-xylylenediamine, 4,4-diaminocyclohexylmethane, p-phenylenediamine, m-phenylenediamine, N,N-dimethylethylenediamine, N,N-diethylethylenediamine, 1,3-bis-4-piperidinopropane, diethylenetriamine, triethylenetetramine, tetraethylenepentamine and polyether amine.

5. The high-strength recyclable crosslinking type epoxy adhesive according to claim 1, characterized by: The structures of the di-ester group activated alkyne compound, tri-ester group activated alkyne compound and di-carbonyl group activated alkyne compound are as follows: 。 6. The high-strength recyclable crosslinking type epoxy adhesive according to claim 1, characterized by: The solvent comprises one or more of acetone, dichloromethane, tetrahydrofuran, ethyl acetate and ethanol.

7. The high-strength recyclable crosslinking type epoxy adhesive according to claim 1, characterized by: The lignin is sodium lignosulfonate.

8. A process for the preparation of high strength recyclable crosslinkable epoxy adhesives as claimed in any one of claims 1 to 7, characterized by: The method comprises the following steps: S1, pre-polymerization: dissolving the epoxy resin, epoxy active diluent and amine curing agent with part of the solvent, and reacting at 20-40℃ for 8-16h to obtain a pre-polymer; S2, preparation of pre-polymer solution: dissolving the activated alkyne compound with the remaining solvent, and adding the pre-polymer obtained in step S1 to obtain an adhesive pre-polymer solution after sufficient stirring; S3, curing and forming: pouring the adhesive pre-polymer solution of step S2 into a polytetrafluoroethylene mold, evaporating the solvent, and then incubating at 70-90℃ for 10-14h to obtain the cross-linking type epoxy adhesive.

9. The method for preparing the high-strength recyclable crosslinked epoxy adhesive according to claim 8, characterized in that: In step S2, if the lignin is to be added, the lignin is added after the uniform stirring in step S2, and the adhesive pre-polymer solution is obtained after the lignin is stirred again until uniform.

10. Use of a high-strength recyclable cross-linked epoxy adhesive according to any one of claims 1 to 7, characterized in that: The adhesive is applied to bonding of iron plate, aluminum plate, steel plate, wood plate, ABS plate, PC plate, glass and precision equipment, and the precision equipment includes optical lens, sensor package and microelectronic assembly.

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