Epoxy-based adhesive with self-healing and shape memory and preparation method thereof

Abstract

The present application relates to epoxy structural adhesive technical field, especially IPCC09J163 field, more particularly, a kind of epoxy adhesive with self-healing, shape memory and excellent bonding performance and its preparation method.Preparation raw materials include: polyurethane prepolymer, bisphenol A type epoxy resin, double sulfur bond aromatic amine curing agent and epoxy accelerant.By using double sulfur bond aromatic amine curing agent as curing agent, polyurethane can be combined with epoxy resin, and a dense crosslinking network structure is constructed, and the shear strength is as high as 11.9MPa;The molar ratio of the polyurethane prepolymer and bisphenol A type epoxy resin is 1: (1.5-4), so that the adhesive can achieve high efficiency balance between mechanical strength, toughness and reshaping.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of epoxy-based structural adhesives, in particular to the field of IPCC09J163, and more particularly to an epoxy-based adhesive with self-healing, shape memory and excellent bonding performance and a preparation method thereof. BACKGROUND

[0002] Thermosetting polymers play an indispensable role in modern society due to their outstanding physical and chemical stability, and are widely used in various fields. Epoxy resins, as an important branch of thermosetting materials, are known for their unique permanent cross-linked structure. This structure endows epoxy resins with excellent chemical stability, electrical insulation performance, mechanical strength and bonding strength, making them the preferred material in multiple industries such as construction, electronic packaging and military. However, it is this permanent cross-linked structure that poses challenges to the processing and recycling of epoxy resins. Traditional thermosetting polymers are difficult to reshape or reuse through conventional methods, which not only leads to a great waste of resources, but also causes an environmental burden that cannot be ignored. In addition, due to their highly cross-linked and rigid molecular chain structure, epoxy resins often exhibit low flexibility in practical applications, which limits their application potential in a wider range of fields. In order to overcome these limitations, researchers have been exploring innovative methods to improve the processability, reshaping and reuse, and toughness of epoxy resins, so as to expand their application range and reduce the environmental impact. The emergence of covalent adaptive networks (CAN) provides a promising way for the sustainable development of thermosetting polymers. Although there have been many works that achieve the reshaping processability, even degradability of epoxy resins through dynamic covalent bonds. However, adaptive dynamic networks are often accompanied by mechanical brittleness and poor toughness.

[0003] CN114195984B discloses a kind of dynamic enamine bond-containing bisphenol A type epoxy curing agent and degradable epoxy resin and its preparation, reshaping, degradation method, its preparation method includes: acetoacetic acid epoxy monomer is stirred under heating at 30-130 DEG C with amine curing agent;The preparation method of degradable epoxy resin includes: epoxy curing agent is mixed with bisphenol A type epoxy monomer and is heated and cured at 60-150 DEG C and obtains;Reshaping method includes: degradable epoxy resin is hot-pressed at 160-220 DEG C and obtains;Degradation method includes: degradable epoxy resin is placed in acidolysis liquid under stirring at 25-180 DEG C for 0.5-48 h, then sequentially after neutralization, solid-liquid separation, washing, drying, complete degradation.Compared with prior art, the epoxy resin material containing dynamic amide bond in the application has the advantages of degradable recycling and recyclable use, which is conducive to promoting the industrial application of dynamic epoxy resin. But it does not solve the problem that adaptive dynamic networks are often accompanied by mechanical brittleness and poor toughness. Summary of the Invention

[0004] The first aspect of the present invention provides an epoxy-based adhesive with self-healing, shape memory and excellent bonding properties. The raw materials for preparation include: polyurethane prepolymer, bisphenol A epoxy resin, disulfide bond-containing aromatic amine curing agent and epoxy accelerator.

[0005] The raw materials for preparing the polyurethane prepolymer include: polyether polyol, diisocyanate and a catalyst.

[0006] The isocyanate includes at least one of toluene diisocyanate, 4-methoxy-1,3-phenylene diisocyanate, 4-isopropyl-1,3-phenylene diisocyanate, 1,4-tetramethylene diisocyanate, 1,6-hexamethylene diisocyanate, 1,10-decamethylene diisocyanate, 1,4-cyclohexylene diisocyanate, xylene diisocyanate, 4,4-methylenebis(cyclohexyl isocyanate), 1,5-tetrahydronaphthalene diisocyanate, and isophorone diisocyanate.

[0007] The catalyst includes one or more of dibutyltin dilaurate, stannous octoate, dibutyltin didodecylsulfide, dibutyltin diacetate, dialkyltin dimaleate, and alkyltin dithiolate.

[0008] The molar ratio of the polyether polyol to the diisocyanate is 1:(2-3).

[0009] The polyether polyol includes a first polyether polyol and a second polyether polyol, wherein the hydroxyl value of the first polyether polyol is 120-250 mgKOH / g, and the hydroxyl value of the second polyether polyol is 30-100 mgKOH / g.

[0010] Preferably, the hydroxyl value of the first polyether polyol is 180-220 mgKOH / g, and the hydroxyl value of the second polyether polyol is 40-60 mgKOH / g.

[0011] The molar ratio of the first polyether polyol to the second polyether polyol is (1-3):1.

[0012] The molar ratio of the polyurethane prepolymer to the bisphenol A epoxy resin is 1:(1.5-4).

[0013] Preferably, the molar ratio of the polyurethane prepolymer to the bisphenol A epoxy resin is 1:(1.5-3).

[0014] More preferably, the molar ratio of the polyurethane prepolymer to the bisphenol A epoxy resin is 1:(2-3).

[0015] Preferably, the molar ratio of the bisphenol A epoxy resin to the disulfide bond-containing aromatic amine curing agent is 1:(1-2).

[0016] The disulfide bond-containing aromatic amine curing agent includes at least one of 4,4'-disulfodiphenylamine, bis(3-fluoro-4-aminophenyl)disulfide, 2-[(2-amino-5-isopropylphenyl)disulfide]-4-isopropylaniline, bis(2-aminophenyl)disulfide, [2-(2-amino-5-methoxy-phenyl)disulfide-4-methoxy-phenyl]amine, 2-[(2-amino-5-methylphenyl)disulfide]-4-methylaniline, 2-[(2-amino-5-ethylphenyl)disulfide]-4-ethylaniline, 5,5'-disulfanediylbis(2-chloroaniline), bis(2-amino-4-methylphenyl)disulfide, 2,2'-dithiodi(1-naphthylamine), and 6,6-disulfodiylbis(2-methylaniline).

[0017] Preferably, the disulfide bond-containing aromatic amine curing agent includes bis(2-aminophenyl)disulfide.

[0018] The epoxy accelerator includes at least one of DMP-30 (2,4,6-tris(dimethylaminomethyl)phenol), imidazole, triethanolamine, and resorcinol.

[0019] Preferably, the epoxy accelerator includes DMP-30.

[0020] The second aspect of the present invention provides a method for preparing an epoxy-based adhesive with self-healing, shape memory and excellent bonding properties, comprising the following steps: mixing a polyurethane prepolymer, a bisphenol A epoxy resin, a disulfide bond-containing aromatic amine curing agent and an epoxy accelerator, and stirring them evenly in a vacuum defoaming mixer, and curing to obtain the adhesive.

[0021] The curing is carried out in sequence of low-temperature curing and high-temperature curing; the conditions for the low-temperature curing are: curing at 60-90°C for 10-15 hours; the conditions for the high-temperature curing are: curing at 110-130°C for 4-7 hours.

[0022] Preferably, the curing is performed sequentially by low-temperature curing and high-temperature curing; the conditions for the low-temperature curing are: curing at 70-90°C for 10-12 hours; the conditions for the high-temperature curing are: curing at 110-120°C for 5-7 hours.

[0023] Traditional epoxy resins, due to their high cross-linking density and rigidity, have a relatively high modulus but relatively low mechanical strength. This phenomenon is attributed to the lack of toughness, which results in the inability to effectively dissipate energy when subjected to external forces, thereby causing the failure of the entire structure within a relatively short displacement. The applicant has found that by using aromatic amine curing agents as curing agents, polyurethane can be combined with epoxy resin, with the bisphenol A structure and diamine structure having rigid characteristics linearly connected, and a chemically cross-linked network is constructed by a flexible polyurethane resin. It may be that polyurethane, due to its highly branched structure, can form microphase separation in epoxy resin. This structure can serve as a barrier to crack propagation, improve the toughness of the material, and thus toughen the epoxy resin. The active functional groups (such as hydroxyl or amino) in polyurethane can react chemically with the epoxy groups in epoxy resin to form covalent bonds, which helps to enhance interfacial bonding and improve overall mechanical properties. At the same time, polyurethane has flexible molecular chains, and these segments can provide additional flexibility in the epoxy resin matrix, helping to absorb impact energy, thereby improving the impact resistance of the material. At the same time, the introduction of polyurethane can increase the free volume of epoxy resin and lower the glass transition temperature (Tg) of the resin, so that the material can maintain good flexibility at lower temperatures, and can more effectively absorb and disperse stress to avoid stress concentration.

[0024] Further research revealed that a molar ratio of 1:1.5-4 between the polyurethane prepolymer and bisphenol A epoxy resin provides an adhesive with an optimal balance between mechanical strength, toughness, and reshaping reprocessability. As the polyurethane content increases, the room temperature modulus of the material decreases (becoming softer). This is due to the polyurethane's flexible segments enhancing the material's flexibility and reducing its overall rigidity, making it less susceptible to breakage upon impact. Furthermore, increasing polyurethane content is accompanied by a decrease in the glass transition temperature (Tg). Compared to the rigidity of the high benzene rings in the epoxy resin, the contribution of the polyether soft segments to Tg is relatively low. However, this lower glass transition temperature also imparts shape memory at room temperature. When polyurethane toughens epoxy resin, a unique phase-separated structure is formed, with the polyurethane as the dispersed phase and the epoxy resin as the continuous phase. This structure allows the polyurethane phase to act as a stress concentration area upon impact, thereby improving overall mechanical properties. As the polyurethane content increases, the degree of phase separation increases, and the phases become more continuous. The appropriate degree of phase separation helps achieve a balance between the toughness and strength of the material, thanks to the dissociation and association of multi-level hydrogen bonds and dynamic covalent disulfide bonds.

[0025] Beneficial effects

[0026] 1. By using a disulfide bond-containing aromatic amine curing agent as a curing agent, polyurethane and epoxy resin can be combined to construct a dense cross-linked network structure with a shear strength of up to 11.9MPa.

[0027] 2. The molar ratio of the polyurethane prepolymer to the bisphenol A epoxy resin is 1:(1.5-4), which enables the adhesive to achieve an efficient balance between mechanical strength, toughness and reshaping and reprocessing.

[0028] 3. The adhesive prepared in this application obtains continuous shape memory cycles through stress control mode.

[0029] 4. The adhesive prepared in this application can still maintain its strength at 9.6 MPa after 6 cycles of bonding.

[0030] 5. The adhesive prepared in this application can bond a variety of substrates, including steel-titanium, steel-iron, steel-zinc, steel-aluminum, and steel-magnesium.

[0031] 6. The adhesive prepared in this application has excellent bonding properties at 0-55°C. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 This is the NMR spectrum of Example 1.

[0033] Figure 2 The infrared spectra of Examples 1-5 are shown.

[0034] Figure 3 This is the DSC curve of Example 1-5.

[0035] Figure 4 These are stress-strain curves for Examples 1-5.

[0036] Figure 5 Microscope images of the adhesive used in Example 3 after the incision was repaired at 120°C for different times.

[0037] Figure 6 This is the engineering diagram of the adhesive shape memory recovery in Example 3. DETAILED DESCRIPTION

[0038] Examples 1-5

[0039] An epoxy-based adhesive with self-healing, shape memory and excellent bonding properties is prepared from the following raw materials: polyurethane prepolymer, bisphenol A epoxy resin (epoxy resin NPEL128 (E51), purchased from Nanya Electronic Materials Co., Ltd.), a disulfide bond-containing aromatic amine curing agent and an epoxy accelerator. The raw material components are shown in Table 1.

[0040] The disulfide bond-containing aromatic amine curing agent is bis(2-aminophenyl) disulfide, and the epoxy accelerator is DMP-30, both of which are brands: Adamas.

[0041] The added amount of DMP-30 is 0.2 wt %.

[0042] The raw materials for preparing the polyurethane prepolymer are: polyether polyol, diisocyanate and catalyst.

[0043] The isocyanate is isophorone diisocyanate; the catalyst is dibutyltin dilaurate; the hydroxyl value of the first polyether polyol is 180-207 mgKOH / g, model: PPG600, brand: Adamas; the hydroxyl value of the second polyether polyol is 56 mgKOH / g, model: C3050A, brand: INOVOL.

[0044] The polyurethane prepolymer was prepared by placing PPG600 (6 g, 10 mmol) and C3050A (15 g, 5 mmol) in a four-necked flask and vacuum dehydrating the mixture at 110°C for 2 hours. The temperature was then lowered to 80°C, and isophorone diisocyanate (7.78 g, 35 mmol) was added and stirred for 1 hour. Subsequently, a catalyst, dibutyltin dilaurate (0.01 wt%), was added and prepolymerized for 3 hours.

[0045] A method for preparing an epoxy-based adhesive with self-healing, shape memory and excellent bonding properties comprises the following steps: mixing a polyurethane prepolymer, a bisphenol A epoxy resin, a disulfide bond-containing aromatic amine curing agent and an epoxy accelerator; stirring the mixture in a vacuum defoaming mixer at a speed of 2000 rpm for 120 seconds; curing the mixture at 80°C for 12 hours; and curing the mixture at 120°C for 6 hours to obtain the epoxy-based adhesive.

[0046] The adhesives prepared in Examples 1-5 were named PDA-20, PDA-25, PDA-30, PDA-35 and PDA-40, respectively.

[0047] Table 1

[0048] Example polyurethane prepolymer Bisphenol A epoxy resin Bis(2-aminophenyl) disulfide Example 1 (PDA-20) 17.5mmol 70.0mmol 87.5mmol Example 2 (PDA-25) 17.5mmol 52.5mmol 70.0mmol Example 3 (PDA-30) 17.5mmol 40.9mmol 58.4mmol Example 4 (PDA-35) 17.5mmol 32.5mmol 50.0mmol Example 5 (PDA-40) 17.5mmol 26.3mmol 43.8mmol

[0049] Performance testing methods and data

[0050] 1. Gel permeation chromatography (GPC) was used to measure the molecular weight and molecular weight distribution of Examples 1-5. GPC was performed using an Agilent LC1200 in the United States with DMF as the mobile phase at 25°C, a flow rate of 1 mL / min, and a sample concentration of 1 mg / mL. The test data are listed in Table 2.

[0051] 2. Nuclear magnetic resonance characterization, Example 1: Nuclear magnetic resonance proton spectrum (1HNMR) was obtained using a Bruker Avance 400 MHz NMR instrument from Germany with tetramethylsilane (TMS) as the internal standard. About 10 mg of sample was dissolved in 0.50 mL of deuterated dimethyl sulfoxide (DMSO-d6) and scanned at 25°C. The test data are listed in Figure 1 middle.

[0052] 3. Infrared characterization, Examples 1-5: Infrared spectroscopy (FTIR) tests were performed using a Bruker ALPHAII Fourier transform infrared spectrometer from Germany. The dissociation process of the samples was monitored using a variable temperature Fourier transform infrared spectrometer with a range of 30°C to 150°C, a detection interval of 10°C, and a heating rate of 5°C / min. The test data are listed in Figure 2 middle.

[0053] 4. Thermal analysis, Examples 1-5: DSC tests were performed using DSCQ2000 (TA, USA) under nitrogen at a heating rate of 10°C / min. The test data are listed in Figure 3 middle.

[0054] 5. Uniaxial tensile and tensile shear strength test, where the lap shear test and tensile test were carried out at a speed of 100 mm / min, referring to ASTM D5045 / E399. The test data are listed in Table 3, and the stress-strain curve is shown in Table 3. Figure 4 shown.

[0055] 6. Example 3, shear strength test at different temperatures, the test data are listed in Table 4.

[0056] 7. Example 3, shear strength test at different cycle times. The test data are listed in Table 5, where the cycle scheme is as follows: Initially, it is raised to 70°C at 5°C / min, held for 5 minutes, and balanced at 0.1 MPa for 5 minutes. It is then lowered to 0°C at 4°C / min to release the force, and then heated to 70°C at 5°C / min and held for a certain time to ensure complete shape recovery.

[0057] 8. Example 3, shear strength test under different bonding substrates, the test data are listed in Table 6.

[0058] 9. Repair performance test: The adhesive of Example 3 was cut from the middle of the specimen at room temperature, and then the sections were spliced ​​together. The repaired specimen was repaired in a 120°C oven for different times. The microscope images of the cuts repaired at 120°C for different times are as follows: Figure 5 shown.

[0059] 10. Shape memory test: Figure 6As shown, the adhesive of Example 3 was raised to 70°C at 5°C / min, held for 5 minutes, and balanced at 0.1 MPa for 5 minutes, then dropped to 0°C at 4°C / min to release the force, and then heated to 70°C at 5°C / min and held for a certain time to fully recover the shape.

[0060] Table 2

[0061] Example Mn (g / mol) Mw(g / mol) PDI (polydispersity index) Example 1 (PDA-20) 20288 52457 2.5856 Example 2 (PDA-25) 21926 54545 3.0550 Example 3 (PDA-30) 23415 69778 2.9801 Example 4 (PDA-35) 30171 198889 6.5921 Example 5 (PDA-40) 29678 158849 5.3524

[0062] Table 3

[0063]

[0064] Table 4

[0065] Temperature (℃) Shear strength (MPa) 0 7.143 25 11.909 35 10.413 45 7.201 55 5.617

[0066] Table 5

[0067]

[0068]

[0069] Table 6

[0070] Bonding substrate Shear strength (MPa) Steel-Titanium 10.977 Steel-Iron 9.941 Steel-Zinc 9.665 Steel-Aluminum 7.673 Steel-Magnesium 6.091

Claims

1. An epoxy-based adhesive with self-healing and shape memory properties, characterized in that: The preparation raw materials include: polyurethane prepolymer, bisphenol A epoxy resin, disulfide bond-containing aromatic amine curing agent and epoxy accelerator; the molar ratio of the polyurethane prepolymer to the bisphenol A epoxy resin is 1: (1.5-4); the disulfide bond-containing aromatic amine curing agent includes 4,4'-dithiodiphenylamine, bis(3-fluoro-4-aminophenyl) disulfide, 2-[(2-amino-5-isopropylphenyl) disulfide]-4-isopropylaniline, bis(2-aminophenyl) disulfide, [2-(2 at least one of -amino-5-methoxy-phenyl)disulfide-4-methoxy-phenyl]amine, 2-[(2-amino-5-methylphenyl)disulfide]-4-methylaniline, 2-[(2-amino-5-ethylphenyl)disulfide]-4-ethylaniline, 5,5'-disulfanediylbis(2-chloroaniline), bis(2-amino-4-methylphenyl)disulfide, 2,2'-disulfidedi(1-naphthylamine), and 6,6-disulfidediylbis(2-methylaniline).

2. The self-healing, shape-memory epoxy adhesive according to claim 1, wherein: The raw materials for preparing the polyurethane prepolymer include: polyether polyol, diisocyanate and a catalyst.

3. The self-healing, shape-memory epoxy adhesive according to claim 2, wherein: The molar ratio of the polyether polyol to the diisocyanate is 1:(2-3).

4. The self-healing, shape-memory epoxy adhesive according to claim 2 or 3, characterized in that: The polyether polyol includes a first polyether polyol and a second polyether polyol, wherein the hydroxyl value of the first polyether polyol is 120-250 mgKOH / g, and the hydroxyl value of the second polyether polyol is 30-100 mgKOH / g.

5. The self-healing, shape-memory epoxy adhesive according to claim 4, characterized in that: The molar ratio of the first polyether polyol to the second polyether polyol is (1-3):

1.

6. The self-healing, shape-memory epoxy adhesive according to claim 1, wherein: The epoxy accelerator includes at least one of DMP-30, imidazole, triethanolamine, and resorcinol.

7. A method for preparing the self-healing, shape-memory epoxy adhesive according to any one of claims 1 to 6, characterized in that: The method comprises the following steps: mixing polyurethane prepolymer, bisphenol A epoxy resin, disulfide bond-containing aromatic amine curing agent and epoxy accelerator, stirring evenly in a vacuum defoaming mixer, and curing to obtain the product.

8. The method for preparing the self-healing, shape-memory epoxy adhesive according to claim 7, wherein: The curing is carried out in sequence of low-temperature curing and high-temperature curing; the conditions for the low-temperature curing are: curing at 60-90°C for 10-15 hours; the conditions for the high-temperature curing are: curing at 110-130°C for 4-7 hours.

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