Two-component adhesive based on dynamic polycarboxylic acid epoxy curing agent and preparation method thereof

Abstract

The invention belongs to the technical field of adhesives, and particularly relates to a two-component adhesive based on a dynamic polycarboxylic acid epoxy curing agent and a preparation method of the two-component adhesive. The invention provides a dynamic polycarboxylic acid underwater epoxy curing agent with a hydrophobic long chain and a dynamic disulfide bond, and an underwater curing two-component adhesive composed of a component X and a component D is prepared based on the curing agent, specifically, the dynamic polycarboxylic acid underwater epoxy curing agent is used as the component X, liquid epoxy resin, an active epoxy diluent, a flexibilizer, a coupling agent and a filler are taken as a component D; the underwater curing adhesive disclosed by the invention can be completely constructed and cured underwater, has excellent bonding strength, can effectively reduce the phenomenon of material bonding failure in an underwater environment, has excellent reliability, and can be soaked in seawater for a long time; in addition, the adhesive is solvent-free, and due to the existence of the dynamic disulfide bond, the adhesive is endowed with excellent recoverability, so that the pollution to the marine environment is reduced.

Description

Technical Field

[0001] The present invention belongs to the technical field of adhesives, and particularly relates to a two-component adhesive based on a dynamic polycarboxylic acid epoxy curing agent and a preparation method thereof. Background Art

[0002] With the development of the marine economy (such as seawater pastures, offshore oil fields, and maritime transportation), the construction of marine infrastructure has become a top priority in the development of the marine economy. Therefore, as an important material that can bond different materials, adhesives have great advantages in replacing or assisting traditional connection means such as riveting or welding. Among them, epoxy adhesives, as an important functional chemical, have broad application prospects in underwater engineering due to their light weight, wide bonding range, and easy construction.

[0003] However, compared with dry conditions, achieving strong adhesion in underwater or humid environments faces major challenges. This is because water molecules can form a hydration layer on the substrate surface, hindering molecular contact between the adhesive and the adherend, thereby reducing the interfacial adhesion. In addition, water molecules can penetrate between polymer chains, resulting in plasticization and reducing the cohesive strength of the adhesive. In particular, adhesive joints exposed to long-term humid and hot conditions will experience accelerated diffusion of water molecules and increased molecular chain mobility, resulting in reduced adhesive reliability.

[0004] Current epoxy underwater curing agents are mainly Mannich bases obtained by the Mannich reaction of formaldehyde, amines, and phenols. Although Mannich base underwater curing agents have excellent properties, their curing time underwater is long and the bonding strength is not strong enough, which affects their actual use effect in underwater engineering and marine engineering. In addition, this type of underwater epoxy curing agent has residual small-molecule organic pollutants (such as formaldehyde and phenols), which seriously affect the water environment. More importantly, these adhesives are difficult to recycle after being discarded, causing solid waste pollution in the water and harming aquatic organisms. At the same time, existing commonly used carboxylic acid curing agents also have significant shortcomings. On the one hand, their curing temperatures are generally high, which not only greatly increases energy consumption and production costs but also limits the application scenarios. On the other hand, this curing agent cannot be cured in an underwater environment, making it difficult to play a role in underwater operation scenarios such as water conservancy projects and ship repairs. Therefore, it is necessary to develop new curing agents and adhesives suitable for underwater construction and curing. Summary of the Invention

[0005] To overcome the problems of existing epoxy underwater curing agents (such as Mannich bases, etc.) having low underwater curing adhesion, the existence of toxic residues such as formaldehyde and phenols, solvent pollution, and being unable to be recycled, as well as the problems of existing carboxylic acid curing agents having high curing temperatures and being unable to cure underwater, the present invention provides a dynamic polycarboxylic acid underwater epoxy curing agent with a hydrophobic long chain and dynamic disulfide bonds, and based on this curing agent, an underwater curing two-component adhesive is prepared, thereby solving the above problems.

[0006] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0007] The first aspect of the present invention provides a dynamic polycarboxylic acid underwater epoxy curing agent, and the dynamic polycarboxylic acid underwater epoxy curing agent has a structure as shown in Formula 1:

[0008]

[0009] In Formula 1, R 1 is an alkyl group of C 6 -C 12 , HS-R 11 -, or (CH 3 CH 2 O) 3 Si(CH 2 ) 3 -, R 2 is an alkyl group of C 1 -C 10 or a polyethylene glycol group with a molecular weight of 200 to 2000, x and y are both integers greater than 1; the R 11 is C 3 -C 6 or C 8 alkyl group, -(CH 2 CH 2 O) 2 CH 2 CH 2 -, or -CH 2 CH 2 SCH 2 CH(CH 2 SH)SCH 2 CH 2 -.

[0010] The molecular structure of the prepared dynamic polycarboxylic acid underwater epoxy curing agent contains a dynamic disulfide bond long chain and branched carboxylic acid functional groups grafted on the long chain. The dynamic disulfide bond long chain has excellent water-blocking performance, which can exclude the interstitial water between the adhesive main body and the adherend, thereby enhancing the interfacial interaction and providing a reaction environment for the curing reaction at the same time. At the same time, the carboxyl functional group can also react with the epoxy group to form a three-dimensional curing network. The above characteristics lay the foundation for the preparation of a new type of adhesive suitable for underwater construction and curing.

[0011] Preferably, the dynamic polycarboxylic acid underwater epoxy curing agent is selected from at least one of the structural formulas shown in Formula 3, Formula 4, and Formula 5:

[0012]

[0013] In Formula 3, Formula 4, and Formula 5, 0 < x, y < 1, and x + y = 1.

[0014] In the second aspect of the present invention, a preparation method of the dynamic polycarboxylic acid underwater epoxy curing agent described in the first aspect is provided, specifically: heating the thiol R 1 -SH and the thioctic acid ester shown in Formula 2 until the viscosity becomes lower, then adding thioctic acid, and then carrying out a ring-opening polymerization reaction under stirring until a viscous yellow transparent liquid product is obtained, that is, the dynamic polycarboxylic acid underwater epoxy curing agent is obtained;

[0015]

[0016] R 1 、R 2 have the same values as those in Formula 1.

[0017] Preferably, the temperature for heating until the viscosity becomes lower is 40 - 100 °C; thioctic acid is added in batches, and the feeding time is 10 - 60 min; the temperature of the ring-opening polymerization reaction is 40 - 100 °C, and the time is 1 - 12 h.

[0018] Preferably, the molar ratio of the thioctic acid ester to thioctic acid is 0.1 - 0.5:1, and the molar ratio of the thiol R 1 -SH to thioctic acid is 0.1 - 0.3:1.

[0019] In the third aspect of the present invention, an underwater-curing two-component adhesive is provided. The adhesive is composed of a D component and an X component mixed. The D component is composed of liquid epoxy resin, active epoxy diluent, toughening agent, coupling agent, and filler mixed; the X component is the dynamic polycarboxylic acid underwater epoxy curing agent described in the first aspect.

[0020] In the adhesive, the segment containing dynamic disulfide bonds has good water-blocking performance underwater and can exclude water molecules at the interface through hydrophobic interactions. Moreover, dynamic covalent bonds can undergo dynamic dissociation-rearrangement under external stimuli, making it an important choice for preparing recyclable materials. Carboxylic acid can undergo a curing reaction with epoxy functional groups at room temperature, having excellent mechanical strength, and the carboxylic acid and the interface can form a tight connection through multiple interactions. A carboxylic acid functional group that reacts with epoxy groups is incorporated into the segment containing dynamic disulfide bonds to prepare a novel underwater epoxy curing agent. On this basis, a cured epoxy resin adhesive for underwater environments is prepared using this curing agent. This adhesive can be completely constructed and cured underwater, has excellent bonding strength, can effectively reduce the phenomenon of material bonding failure in underwater environments, and has excellent reliability and can be immersed in seawater for a long time. In addition, this adhesive is solvent-free, and the presence of dynamic disulfide bonds endows it with excellent recyclable performance, reducing pollution to the marine environment.

[0021] Preferably, the mass ratio of the D component to the X component is 1:0.6 - 0.8; in the D component, the content of liquid epoxy resin is 50 - 80 parts by weight, the content of active epoxy diluent is 5 - 25 parts by weight, the content of toughening agent is 5 - 15 parts by weight, the content of coupling agent is 0.5 - 2 parts by weight, and the content of filler is 10 - 25 parts by weight.

[0022] Preferably, the liquid epoxy resin is at least one of bisphenol A epoxy resin, bisphenol F epoxy resin, phenolic epoxy resin, and tetraglycidylamine epoxy resin; the active epoxy diluent is at least one of butyl glycidyl ether, 1,4-butanediol diglycidyl ether, ethylene glycol diglycidyl ether, phenyl glycidyl ether, polypropylene glycol diglycidyl ether, C12 - C14 fatty glycidyl ether, and benzyl glycidyl ether; the toughening agent is at least one of polysulfide rubber, polybutyronitrile ester, and polyimide; the coupling agent is at least one of KH550, KH560, KH570, and KH590; the filler is at least one of fumed silica, carbon black, nano-montmorillonite, and nano-calcium carbonate.

[0023] The fourth aspect of the present invention provides a preparation method of the underwater-curing two-component adhesive described in the third aspect, and this method includes the following steps:

[0024] S1: Mix liquid epoxy resin, active epoxy diluent, toughening agent, coupling agent, and filler, and stir to defoam to prepare the D component;

[0025] S2: Add the dynamic polycarboxylic acid underwater epoxy curing agent to the D component and mix evenly.

[0026] The underwater-curing adhesive prepared by the above method can be completely constructed and cured underwater, and has excellent bonding strength, which can effectively reduce the phenomenon of material bonding failure in the underwater environment. Moreover, the adhesive has excellent reliability and can be immersed in seawater for a long time. In addition, the adhesive is solvent-free, and the presence of dynamic disulfide bonds endows it with excellent recyclability, thereby reducing pollution to the marine environment.

[0027] Preferably, the rotation speed of the stirring and defoaming is 800 - 1000 rpm, and the time is 5 - 10 min.

[0028] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0029] The present invention discloses a dynamic polycarboxylic acid underwater epoxy curing agent with hydrophobic long chains and dynamic disulfide bonds, and based on this curing agent, an underwater-curing two-component adhesive is prepared. The underwater-curing two-component adhesive is composed of component D and component X. Component D includes liquid epoxy resin, active epoxy diluent, toughening agent, coupling agent and filler, and component X is a dynamic polycarboxylic acid underwater epoxy curing agent. The underwater-curing adhesive prepared by the present invention can be completely constructed and cured underwater, and has excellent bonding strength, which can effectively reduce the phenomenon of material bonding failure in the underwater environment. At the same time, the adhesive has excellent reliability and can be immersed in seawater for a long time. The adhesive is also solvent-free and has excellent recyclability, reducing pollution to the marine environment. Specifically, the present invention has the following advantages:

[0030] (1) Due to the chain segments containing dynamic disulfide bonds, the dynamic polycarboxylic acid underwater epoxy curing agent provided by the present invention has good water-blocking performance underwater and can exclude water molecules at the interface by hydrophobic interaction. Moreover, due to the performance of dynamic disassembly-rearrangement of dynamic covalent bonds under external stimuli, the curing agent also has recyclability. Furthermore, carboxylic acid can react with epoxy functional groups at room temperature, has excellent mechanical strength, and carboxylic acid can form a tight connection with the interface through multiple interactions.

[0031] (2) The underwater two-component adhesive prepared based on the dynamic polycarboxylic acid underwater epoxy curing agent of the present invention can be completely constructed and cured underwater, and has excellent bonding strength, which can effectively reduce the phenomenon of material bonding failure in the underwater environment. Moreover, the adhesive has excellent reliability and can be immersed in seawater for a long time. In addition, the adhesive is solvent-free, and the presence of dynamic disulfide bonds endows it with excellent recyclability, reducing pollution to the marine environment.

[0032] (3) The preparation method of the underwater epoxy adhesive can achieve the preparation from small batches to large batches, and make the filler disperse evenly in the liquid without agglomeration. At the same time, it can also achieve effective defoaming to avoid the influence of bubbles on the adhesive. In addition, this preparation method can also produce a liquid polysulfide curing agent, which is convenient for two-component mixing.

[0033] (4) The underwater epoxy adhesive has excellent recyclability. The underwater epoxy adhesive provided by the present invention can be decomposed in a medium-strong alkaline aqueous solution, and then through acidification, washing and drying, a hot-melt adhesive with excellent cyclic performance can be obtained. The whole process does not involve organic solvents and has environmental friendliness and recyclability. Description of the Drawings

[0034] Figure 1 It is the test result of the lap shear strength of the underwater-curing two-component adhesive after multiple cycles. Detailed Embodiments

[0035] The following further describes the detailed embodiments of the present invention. It should be noted here that the description of these embodiments is used to help understand the present invention, but does not constitute a limitation to the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0036] The experimental methods in the following examples are all conventional methods unless otherwise specified, and the test materials used in the following examples are all available through conventional commercial channels unless otherwise specified.

[0037] Example 1: Preparation of a Dynamic Polycarboxylic Acid Underwater Epoxy Curing Agent

[0038] Add 10 mmol of hexanedithiol and 10 mmol of methyl thioacetate into a three-necked flask equipped with mechanical stirring and a thermometer, and slowly heat it to 60 °C in an oil bath. After reacting for 10 min at this temperature until its viscosity becomes lower, add 0.1 mol of thioctic acid in batches (add 0.01 mol each time, that is, 2.06 g, add 10 times), and the feeding time is 20 min. Then start mechanical stirring and stir at a speed of 800 rpm for 3 h to carry out ring-opening polymerization reaction, and a viscous yellow transparent liquid product, a dynamic polycarboxylic acid underwater epoxy curing agent, can be obtained, denoted as X-1. Its structure is shown in Formula 3 (x = 0.91, y = 0.09), and its viscosity is 12470 mPa·s.

[0039]

[0040] Example 2: Preparation of a Dynamic Polycarboxylic Acid Underwater Epoxy Curing Agent

[0041] Add 20 mmol of mercaptan HSCH 2 CH 2 SCH 2 CH(CH 2 SH)SCH 2 CH 2 SH and 20 mmol of ethyl thiooctoate into a three-necked flask equipped with a mechanical stirrer and a thermometer, and slowly heat it to 70 °C in an oil bath. After its viscosity decreases, add 0.1 mol of thioctic acid in batches, and the feeding time is 30 min. Then start the mechanical stirring and stir at a speed of 1000 rpm for 6 h to carry out the ring-opening polymerization reaction, and a viscous yellow transparent liquid product, the dynamic polycarboxylic acid underwater epoxy curing agent, can be obtained, denoted as X-2. Its structure is shown in Formula 4 (X = 0.83, y = 0.17), and the viscosity is 8560 mPa·s.

[0042]

[0043] Example 3: Preparation of dynamic polycarboxylic acid underwater epoxy curing agent

[0044] Add 15 mmol of mercaptan (CH 3 CH 2 O) 3 Si(CH 2 ) 3 SH and 15 mmol of n-octyl thiooctoate into a three-necked flask equipped with a mechanical stirrer and a thermometer, and slowly heat it to 90 °C in an oil bath. After its viscosity decreases, add 0.1 mol of thioctic acid in batches, and the feeding time is 25 min. Then start the mechanical stirring and stir at a speed of 1000 rpm for 5 h to carry out the ring-opening polymerization reaction, and a viscous yellow transparent liquid product, the dynamic polycarboxylic acid underwater epoxy curing agent, can be obtained, denoted as X-3. Its structure is shown in Formula 5 (X = 0.87, y = 0.13), and the viscosity is 7840 mPa·s.

[0045]

[0046] Examples 4-6: Preparation of underwater-curing two-component adhesives

[0047] First, accurately weigh each raw material according to the parts by weight in Table 1 to prepare Component D: Mix liquid epoxy resin, active epoxy diluent, toughening agent, coupling agent and filler in a closed container, stir and defoam using a planetary stirring defoaming machine, and then pour it into a 50 mL DX rubber tube for later use. Then add Component X to make a two-component epoxy adhesive: Pour the dynamic polycarboxylic acid underwater epoxy curing agent prepared in Examples 1-3 into the above 50 mL DX rubber tube and mix well.

[0048] Table 1 Adhesive formulation table in Examples 4-6

[0049]

[0050] Note: The numbers in Table 1 are parts by mass (Examples 4 - 6 are illustrated in grams).

[0051] Comparative Example 1:

[0052] A two-component epoxy adhesive was prepared according to the method of Example 4, except that the dynamic polycarboxylic acid underwater epoxy curing agent X-1 in Example 4 was replaced with the same weight part of dihydrolipoic acid, and the other conditions were the same as those in Example 4.

[0053] Comparative Example 2:

[0054] A two-component epoxy adhesive was prepared according to the method of Example 4, except that the dynamic polycarboxylic acid underwater epoxy curing agent X-1 in Example 4 was replaced with the same weight part of 1,8-octanedioic acid, and the other conditions were the same as those in Example 4.

[0055] Experimental Example:

[0056] (1) The two-component epoxy adhesives of Examples 4 - 6 and Comparative Examples 1 - 2 were subjected to a lap shear test using 304 stainless steel; the mixed adhesive was coated underwater on a 304 stainless steel plate in water, and another stainless steel plate was overlapped with it. The size of the bonding surface was 12.5 mm * 25 mm, and then it was placed in a water tank and left at room temperature for 24 hours. Then, an underwater lap shear strength test and a lap shear strength test after 30 days of seawater immersion were carried out according to ASTM E28 standard, and the test data are shown in Table 2.

[0057] As shown in Table 2, it can be seen from Examples 1 - 3 that the prepared underwater-curing epoxy adhesive has good underwater bonding performance, and the lap shear strength can reach up to 16.42 MPa after 24 hours of curing. Moreover, the underwater-curing epoxy adhesives prepared in Examples 4 - 6 can still maintain more than 90% of the initial lap shear strength after being immersed in seawater for one month. At the same time, it can be seen from Example 4 and Comparative Example 1 that the underwater lap shear strength of Comparative Example 1 is very low. It shows that the hydrophobic long-chain curing agent containing dynamic disulfide bonds can endow epoxy resin with excellent bonding performance underwater, while the curing agent made of small molecule monomers cannot perform effective bonding underwater. In addition, it can be seen from Example 4 and Comparative Example 2 that Comparative Example 2 can hardly complete effective bonding underwater, while the dynamic polycarboxylic acid epoxy underwater curing agent of Example 4 can form a dense cross-linked network with epoxy resin due to its multiple carboxylic acid functional groups, thus possessing excellent mechanical properties.

[0058] Table 2 Bonding Performance Test Table

[0059]

[0060] (2) The adhesive cured for 24 hours in Example 4 was crushed, and 5 mg was taken and added to a 50 mL round-bottom flask. Then 30 mL of 1 mol / L NaOH aqueous solution was added. After reacting for 24 h at room temperature, the resulting yellow viscous liquid was dropped into 0.1 mol / L hydrochloric acid to obtain a pale yellow flocculent precipitate. Finally, the precipitate was collected and dried in an oven, and a film was obtained after hot pressing.

[0061] The film obtained by recycling the underwater adhesive was cut into a size of 12.5 * 25 mm, placed between two aluminum plates, and then heated to 100 °C for 5 min. After cooling to room temperature, its lap shear strength was tested. After the test sample was damaged by lap shear test, then the damaged sample was continuously heated at 100 °C for 5 min and cooled to room temperature to complete one cycle, and a total of 10 cycles were carried out.

[0062] As Figure 1 shown, different from the fully cured epoxy adhesive, the recycled adhesive can be used as a tough hot melt adhesive, and has the characteristics of strong and tough thermoplasticity. After 10 cycles, it can still maintain the initial bonding strength, proving its excellent reusability.

[0063] In summary, the underwater-curing adhesive prepared by the present invention can be completely constructed and cured underwater, has excellent bonding strength, can effectively reduce the phenomenon of material bonding failure in the underwater environment, and the adhesive has excellent reliability and can be immersed in seawater for a long time; in addition, the adhesive is solvent-free, and the presence of dynamic disulfide bonds endows it with excellent recyclability, thus reducing the pollution to the marine environment.

[0064] The above has described the embodiments of the present invention in detail, but the present invention is not limited to the described embodiments. For those skilled in the art, without departing from the principle and spirit of the present invention, various changes, modifications, substitutions and variations to these embodiments still fall within the protection scope of the present invention.

Claims

1. A dynamic polycarboxylic acid underwater epoxy curing agent, characterized in that: The dynamic polycarboxylic acid underwater epoxy curing agent has a structure as shown in Formula 1: In formula 1, R1 is C6-C 12 Alkyl, HS-R 11 -, or (CH3CH2O)3Si(CH2)3-, R2 is C1-C 10 An alkyl group or a polyethylene glycol group with a molecular weight of 200 to 2000, x and y are both integers greater than 1; said R 11 It is C3-C6 or C8 alkyl, -(CH2CH2O)2CH2CH2- or -CH2CH2SCH2CH(CH2SH)SCH2CH2-.

2. A dynamic polycarboxylic acid underwater epoxy curing agent according to claim 1, characterized in that: The dynamic polycarboxylic acid underwater epoxy curing agent is selected from at least one of the structural formulas shown in Formula 3, Formula 4, and Formula 5: In formula 3, formula 4, and formula 5, 0 <x,y<1,x+y=1。 3. The method for preparing the dynamic polycarboxylic acid underwater epoxy curing agent according to claim 1 or 2, characterized in that: The thiol R1-SH and the thioctic ester shown in Formula 2 are heated until the viscosity becomes low, and then thioctic acid is added, and then a ring-opening polymerization reaction is carried out under stirring until a viscous yellow transparent liquid product is obtained, that is, a dynamic polycarboxylic acid underwater epoxy curing agent is obtained; The values ​​of R1 and R2 are the same as those in claim 1.

4. The method for preparing the dynamic polycarboxylic acid underwater epoxy curing agent according to claim 3, characterized in that: The temperature at which the viscosity becomes low is 40-100° C.; the lipoic acid is added in batches for 10-60 minutes; the temperature of the ring-opening polymerization reaction is 40-100° C. for 1-12 hours.

5. The method for preparing the dynamic polycarboxylic acid underwater epoxy curing agent according to claim 3, characterized in that: The molar ratio of the lipoic acid ester to lipoic acid is 0.1-0.5:1, and the molar ratio of the thiol R1-SH to lipoic acid is 0.1-0.3:

1.

6. An underwater curing two-component adhesive, characterized in that: The adhesive is formed by mixing a component D and a component X, wherein the component D is formed by mixing a liquid epoxy resin, an active epoxy diluent, a toughening agent, a coupling agent, and a filler; and the component X is the dynamic polycarboxylic acid underwater epoxy curing agent according to claim 1 or 2.

7. The underwater curing two-component adhesive according to claim 6, characterized in that: The mass ratio of the D component to the X component is 1:0.6-0.8; in the D component, the content of the liquid epoxy resin is 50-80 parts by weight, the content of the active epoxy diluent is 5-25 parts by weight, the content of the toughening agent is 5-15 parts by weight, the content of the coupling agent is 0.5-2 parts by weight, and the content of the filler is 10-25 parts by weight.

8. The underwater curing two-component adhesive according to claim 6, characterized in that: The liquid epoxy resin is at least one of bisphenol A epoxy resin, bisphenol F epoxy resin, phenolic epoxy resin, and tetraglycidylamine epoxy resin; the active epoxy diluent is at least one of butyl glycidyl ether, 1,4-butanediol diglycidyl ether, ethylene glycol diglycidyl ether, phenyl glycidyl ether, polypropylene glycol diglycidyl ether, C12-C14 fatty glycidyl ether, and benzyl glycidyl ether; the toughening agent is at least one of polysulfide rubber, polybutyronitrile, and polyimide; the coupling agent is at least one of KH550, KH560, KH570, and KH590; and the filler is at least one of fumed silica, carbon black, nano-montmorillonite, and nano-calcium carbonate.

9. The method for preparing the underwater curing two-component adhesive according to any one of claims 6 to 8, characterized in that: The following steps are involved: S1: Mix liquid epoxy resin, active epoxy diluent, toughening agent, coupling agent and filler, and stir to degas to prepare component D; S2: Add the dynamic polycarboxylic acid underwater epoxy curing agent into component D and mix well.

10. The method for preparing an underwater curing two-component adhesive according to claim 9, characterized in that: The stirring and degassing is performed at a speed of 800 to 1000 rpm and for a time of 5 to 10 minutes.

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