Self-healing toughened epoxy resin material based on dynamic covalent network and preparation method thereof

Abstract

The present application relates to the technical field of epoxy resin, in particular to a self-repairing toughened epoxy resin material based on dynamic covalent network and a preparation method thereof. The material is composed of a reactive precursor containing aromatic disulfide bond and a rigid epoxy continuous phase component by specific process, wherein the precursor is prepared by stepwise reaction of 4,4'- and 2,2'-diaminodiphenyl disulfide and two glycidyl ethers in a specific ratio. The method cooperatively constructs the microphase separation structure by controlling the precursor structure (stepwise introduction of flexible chain segments) and the two-phase composite sequence (nano-silica is only added to the rigid phase). The obtained material has high glass transition temperature, high modulus and good dimensional stability, and also has excellent fracture toughness, bonding strength and efficient thermal triggered self-repairing ability.

Description

Technical Field

[0001] This invention relates to the field of epoxy resin technology, and in particular to a self-healing and toughening epoxy resin material based on a dynamic covalent bond network and its preparation method. Background Technology

[0002] Epoxy resins are widely used in electronic packaging, structural adhesives, and composite materials due to their excellent bonding strength, electrical insulation, and chemical stability. However, their inherent brittleness and crack sensitivity limit their long-term use in dynamic or high-reliability environments. Conventional methods to improve toughness include adding rubber elastomers or thermoplastics, but this often comes at the cost of significantly reducing the material's glass transition temperature and modulus, compromising its high-temperature dimensional stability and load-bearing capacity required as a structural material.

[0003] In recent years, introducing dynamic covalent bonds (such as disulfide bonds) into crosslinking networks to achieve self-healing functions has provided a new approach to improving the durability of epoxy resins. Existing technologies typically involve directly mixing and curing small-molecule curing agents containing dynamic bonds (such as diamines containing disulfide bonds) with epoxy resins. While this method can impart a certain degree of thermal repair capability to the material, the uniform distribution of dynamic bonds within the crosslinking network leads to an overall increase in chain segment mobility. As a result, while the material gains repair functionality, its glass transition temperature and rigidity often experience an unacceptable decrease, making it difficult to meet the requirements of applications demanding high-temperature mechanical properties and dimensional accuracy.

[0004] To address these contradictions, some studies have attempted to construct microscopic phase-separated structures within epoxy networks, such as by locally combining flexible segments with dynamic bonds. However, simply introducing flexible segments through blending with flexible diglycidyl ethers can easily lead to excessive diffusion of the flexible component during curing, failing to effectively form clearly defined dynamic microregions. While this ambiguous phase structure can improve fracture toughness, it also softens the material overall, increases the coefficient of linear expansion, and degrades thermomechanical properties.

[0005] On the other hand, the introduction of inorganic nanoparticles (such as nano-silica) is often used to compensate for modulus loss caused by toughening or the introduction of flexible components. However, if they are mixed too early with precursors of dynamic bonds and flexible segments, the nanoparticles may interfere with the controllable formation of dynamic micro-region structures or become encapsulated in the flexible phase, making it difficult for them to effectively enhance and constrain the rigid epoxy continuous phase, thereby weakening their effect on improving the overall thermal stability and dimensional accuracy of the material. Therefore, achieving high toughness and high-efficiency self-healing synergistically without sacrificing high-temperature performance remains a deep technical problem that urgently needs to be solved in this field. Summary of the Invention

[0006] In view of this, the purpose of this invention is to propose a self-healing and toughened epoxy resin material based on a dynamic covalent bond network and its preparation method, so as to solve the problem that the existing technology is unable to endow the material with efficient self-healing ability while taking into account high fracture toughness, high glass transition temperature and good thermomechanical stability.

[0007] To achieve the above objectives, this invention provides a self-healing and toughening epoxy resin material based on a dynamic covalent bond network, prepared from the following raw materials: by mass parts, 16-19 parts of 4,4′-diaminodiphenyl disulfide, 1-4 parts of 2,2′-diaminodiphenyl disulfide, 5-8 parts of 1,4-butanediol diglycidyl ether, 8-12 parts of polypropylene glycol diglycidyl ether, 47-55 parts of bisphenol A type epoxy resin, 4-6 parts of 4,4′-diaminodiphenyl sulfone, 6-10 parts of nano-silica dispersed bisphenol A type epoxy resin concentrate, and 0.20-0.40 parts of 1-methylimidazole; In this process, 4,4′-diaminodiphenyl disulfide, 2,2′-diaminodiphenyl disulfide, and 1,4-butanediol diglycidyl ether are reacted first, followed by the addition of polypropylene glycol diglycidyl ether to continue the reaction, yielding a reactive precursor containing aromatic disulfide bonds. The bisphenol A epoxy resin is mixed with 4,4′-diaminodiphenyl sulfone, and then the nano-silica-dispersed bisphenol A epoxy resin concentrate is added to obtain a rigid epoxy continuous phase component. The reactive precursor containing aromatic disulfide bonds is mixed with the rigid epoxy continuous phase component, and then cured after the addition of 1-methylimidazole to obtain the self-healing and toughening epoxy resin material based on a dynamic covalent network.

[0008] Preferably, the bisphenol A type epoxy resin has an epoxy equivalent of 184-194 g / eq and a viscosity of 11000-15000 mPa·s at 25°C.

[0009] Preferably, the silica mass fraction in the nano-silica dispersed bisphenol A type epoxy resin concentrate is 40%, the average particle size is 20nm, the maximum particle size is 50nm, and the epoxy equivalent is 295g / eq.

[0010] Preferably, the self-healing toughened epoxy resin material based on dynamic covalent bond network is obtained by graded curing, wherein the graded curing includes holding at 100-110℃ for 1 hour, holding at 125-135℃ for 2 hours, holding at 155-165℃ for 2 hours, and holding at 165-175℃ for 2 hours in sequence.

[0011] Preferably, the number-average molecular weight of the polypropylene glycol diglycidyl ether is 200-600.

[0012] Furthermore, the present invention also provides a method for preparing a self-healing and toughened epoxy resin material based on a dynamic covalent bond network, comprising the following steps: (1) Under nitrogen protection, 4,4′-diaminodiphenyl disulfide, 2,2′-diaminodiphenyl disulfide and 1,4-butanediol diglycidyl ether were mixed and reacted, and then polypropylene glycol diglycidyl ether was added dropwise to continue the reaction to obtain a reactive precursor containing aromatic disulfide bonds; (2) Under nitrogen protection, bisphenol A type epoxy resin was mixed with 4,4′-diaminodiphenyl sulfone, and then nano-silica was added to disperse the bisphenol A type epoxy resin concentrate to obtain a rigid epoxy continuous phase component. (3) Mix the aromatic disulfide bond reactive precursor obtained in step (1) with the rigid epoxy continuous phase component obtained in step (2), add 1-methylimidazole, degas and then cast; (4) The casting system obtained in step (3) is graded and cured to obtain a self-healing toughened epoxy resin material based on a dynamic covalent bond network.

[0013] Preferably, in step (1), nitrogen gas is first purged for 15-20 minutes, the mixture is stirred at 280-320 r / min, the temperature is first raised to 90-95℃ and held for 10-20 minutes, then the temperature is raised to 95-100℃ and held for 10-20 minutes, and then the temperature is raised to 110-115℃. The polypropylene glycol diglycidyl ether is added dropwise within 15-20 minutes, and the reaction continues at 110-115℃ for 80-100 minutes.

[0014] Preferably, in step (2), the mixture is stirred at 240-270 r / min under nitrogen protection, heated to 145-155℃ and held for 25-35 min, then cooled to 95-105℃, the nano-silica dispersed bisphenol A epoxy resin concentrate is added, and stirring is continued for 10-20 min.

[0015] Preferably, in step (3), the aromatic disulfide bond-containing reactive precursor obtained in step (1) is kept at 90-100°C and added to the rigid epoxy continuous phase component obtained in step (2). The mixture is stirred at 330-380 r / min for 8-12 min, and then the system is cooled to 75-85°C. The 1-methylimidazole is added and stirred for 2-5 min. The system is then vacuumed at 75-85°C and kept at 6-10 min for degassing. Finally, the mixture is poured into a mold preheated to 75-85°C. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in this invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only for this invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 The infrared spectrum is shown for the self-healing and toughened epoxy resin material based on a dynamic covalent network prepared in Example 1 of this invention. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments.

[0019] Example 1: The raw materials used are as follows: Bisphenol A type epoxy resin is CYD-128E from Sinochem Nanjing Co., Ltd., with an epoxy equivalent of 184-194 g / eq and a viscosity of 11000-15000 mPa·s at 25℃; the nano silica-dispersed bisphenol A type epoxy resin concentrate is NANOPOX HP100 from Evonik, with a silica mass fraction of 40%, an average particle size of 20 nm, a maximum particle size of 50 nm, and an epoxy equivalent of 295 g / eq; polypropylene glycol diglycidyl ether is Sigma-Aldrich 406732, with a number average molecular weight of approximately 380.

[0020] Step 1: Add 18g of 4,4′-diaminodiphenyl disulfide, 2g of 2,2′-diaminodiphenyl disulfide and 6g of 1,4-butanediol diglycidyl ether to a dry three-necked flask. After purging with nitrogen for 15 min, stir at 300 rpm. First, raise the temperature to 90℃ and hold for 15 min, then raise the temperature to 95℃ and hold for 15 min, and then raise the temperature to 110℃. Add 10g of polypropylene glycol diglycidyl ether dropwise over 15 min, and continue to react at 110℃ for 90 min to obtain the precursor. Step 2: Add 50g of bisphenol A epoxy resin and 5g of 4,4′-diaminodiphenyl sulfone to another dry container, stir at 250r / min under nitrogen protection, heat to 150℃ and hold for 30min, then cool to 100℃, add 8g of nano silica to disperse the bisphenol A epoxy resin concentrate, and continue stirring at 250r / min for 15min to obtain a rigid epoxy continuous phase component; Step 3: Keep all the precursors obtained in Step 1 at 95°C and add them to the rigid epoxy continuous phase component obtained in Step 2. Stir at 350 r / min for 10 min, then lower the system to 80°C, add 0.30 g of 1-methylimidazole, stir for 3 min, evacuate to a gauge pressure of -0.095 MPa at 80°C and maintain for 8 min to remove bubbles, then immediately pour into a mold preheated to 80°C. Step 4: The cast system is cured in stages at 100℃ for 1 hour, 130℃ for 2 hours, 160℃ for 2 hours and 170℃ for 2 hours. After curing, the system is cooled to below 60℃ in the furnace and demolded. Then it is placed at 23℃ for 24 hours to obtain a self-healing toughened epoxy resin material based on a dynamic covalent bond network.

[0021] Example 2: The source and type of raw materials used are the same as those described above.

[0022] Step 1: Add 17g of 4,4′-diaminodiphenyl disulfide, 3g of 2,2′-diaminodiphenyl disulfide and 5g of 1,4-butanediol diglycidyl ether to a dry three-necked flask. After purging with nitrogen for 15 min, stir at 290 r / min, first raise the temperature to 90℃ and hold for 15 min, then raise the temperature to 95℃ and hold for 15 min, then raise the temperature to 110℃, and add 11g of polypropylene glycol diglycidyl ether dropwise over 15 min. Continue to react at 110℃ for 85 min to obtain the precursor. Step 2: Add 48g of bisphenol A epoxy resin and 5g of 4,4′-diaminodiphenyl sulfone to another dry container, stir at 250r / min under nitrogen protection, heat to 145℃ and hold for 30min, then cool to 100℃, add 7g of nano silica to disperse the bisphenol A epoxy resin concentrate, and continue stirring at 250r / min for 15min to obtain a rigid epoxy continuous phase component; Step 3: Keep all the precursors obtained in Step 1 at 95°C and add them to the rigid epoxy continuous phase component obtained in Step 2. Stir at 350 r / min for 10 min, then lower the system to 80°C, add 0.25 g of 1-methylimidazole, stir for 3 min, evacuate to a gauge pressure of -0.095 MPa at 80°C and maintain for 8 min to remove bubbles, then immediately pour into a mold preheated to 80°C. Step 4: The cast system is cured in stages at 100℃ for 1 hour, 130℃ for 2 hours, 160℃ for 2 hours and 170℃ for 2 hours. After curing, the system is cooled to below 60℃ in the furnace and demolded. Then it is placed at 23℃ for 24 hours to obtain a self-healing toughened epoxy resin material based on a dynamic covalent bond network.

[0023] Example 3: The source and type of raw materials used are the same as those described above.

[0024] Step 1: Add 19g of 4,4′-diaminodiphenyl disulfide, 1g of 2,2′-diaminodiphenyl disulfide and 8g of 1,4-butanediol diglycidyl ether to a dry three-necked flask. After purging with nitrogen for 20 min, stir at 310 r / min, first raise the temperature to 95℃ and hold for 15 min, then raise the temperature to 100℃ and hold for 15 min, then raise the temperature to 115℃, and add 8g of polypropylene glycol diglycidyl ether dropwise over 20 min. Continue to react at 115℃ for 95 min to obtain the precursor. Step 2: Add 55g of bisphenol A type epoxy resin and 6g of 4,4′-diaminodiphenyl sulfone to another dry container, stir at 260r / min under nitrogen protection, heat to 155℃ and hold for 35min, then cool to 105℃, add 10g of nano silica to disperse the bisphenol A type epoxy resin concentrate, and continue stirring at 260r / min for 20min to obtain a rigid epoxy continuous phase component; Step 3: Keep all the precursors obtained in Step 1 at 100°C and add them to the rigid epoxy continuous phase component obtained in Step 2. Stir at 360 r / min for 10 min, then lower the system to 85°C, add 0.35 g of 1-methylimidazole, stir for 4 min, evacuate to a gauge pressure of -0.098 MPa at 85°C and maintain for 10 min to remove bubbles, then immediately pour into a mold preheated to 85°C. Step 4: The cast system is cured in stages at 105℃ for 1 hour, 135℃ for 2 hours, 165℃ for 2 hours and 175℃ for 2 hours. After curing, the system is cooled to below 60℃ in the furnace and demolded. Then it is placed at 23℃ for 24 hours to obtain a self-healing toughened epoxy resin material based on a dynamic covalent bond network.

[0025] Example 4: The source and type of raw materials used are the same as those described above.

[0026] Step 1: Add 16g of 4,4′-diaminodiphenyl disulfide, 4g of 2,2′-diaminodiphenyl disulfide and 6g of 1,4-butanediol diglycidyl ether to a dry three-necked flask. After purging with nitrogen for 15 min, stir at 280 r / min, first raise the temperature to 90℃ and hold for 10 min, then raise the temperature to 95℃ and hold for 10 min, then raise the temperature to 110℃, and add 12g of polypropylene glycol diglycidyl ether dropwise over 15 min. Continue to react at 110℃ for 80 min to obtain the precursor. Step 2: Add 47g of bisphenol A type epoxy resin and 4g of 4,4′-diaminodiphenyl sulfone to another dry container, stir at 240r / min under nitrogen protection, heat to 145℃ and hold for 25min, then cool to 95℃, add 8g of nano silica to disperse the bisphenol A type epoxy resin concentrate, and continue stirring at 240r / min for 12min to obtain a rigid epoxy continuous phase component; Step 3: Keep all the precursors obtained in Step 1 at 90°C and add them to the rigid epoxy continuous phase component obtained in Step 2. Stir at 330 r / min for 8 min, then lower the system to 75°C, add 0.20 g of 1-methylimidazole, stir for 2 min, evacuate to a gauge pressure of -0.090 MPa at 75°C and hold for 6 min to remove bubbles, then immediately pour into a mold preheated to 75°C. Step 4: The cast system is cured in stages at 100℃ for 1 hour, 125℃ for 2 hours, 155℃ for 2 hours and 165℃ for 2 hours. After curing, the system is cooled to below 60℃ in the furnace and demolded. Then it is placed at 23℃ for 24 hours to obtain a self-healing toughened epoxy resin material based on a dynamic covalent bond network.

[0027] Example 5: The source and type of raw materials used are the same as those described above.

[0028] Step 1: Add 18g of 4,4′-diaminodiphenyl disulfide, 2g of 2,2′-diaminodiphenyl disulfide and 7g of 1,4-butanediol diglycidyl ether to a dry three-necked flask. After purging with nitrogen for 20 min, stir at 320 r / min. First, raise the temperature to 95℃ and hold for 20 min, then raise the temperature to 100℃ and hold for 20 min, and then raise the temperature to 115℃. Add 9g of polypropylene glycol diglycidyl ether dropwise over 20 min, and continue to react at 115℃ for 100 min to obtain the precursor. Step 2: Add 54g of bisphenol A type epoxy resin and 5g of 4,4′-diaminodiphenyl sulfone to another dry container, stir at 270r / min under nitrogen protection, heat to 155℃ and hold for 35min, then cool to 105℃, add 6g of nano silica to disperse the bisphenol A type epoxy resin concentrate, and continue stirring at 270r / min for 10min to obtain a rigid epoxy continuous phase component; Step 3: Keep all the precursors obtained in Step 1 at 100°C and add them to the rigid epoxy continuous phase component obtained in Step 2. Stir at 380 r / min for 12 min, then lower the system to 85°C, add 0.40 g of 1-methylimidazole, stir for 5 min, evacuate to a gauge pressure of -0.098 MPa at 85°C and maintain for 10 min to remove bubbles, then immediately pour into a mold preheated to 85°C. Step 4: After casting, the system is cured in stages at 110℃ for 1 hour, 135℃ for 2 hours, 165℃ for 2 hours and 175℃ for 2 hours. After curing, the system is cooled to below 60℃ in the furnace and demolded. Then it is placed at 23℃ for 24 hours to obtain a self-healing toughened epoxy resin material based on a dynamic covalent bond network.

[0029] Comparative Example 1: The difference between Comparative Example 1 and Example 1 is that the precursor pre-addition in step 1 is not performed. Instead, the original amounts of 4,4′-diaminodiphenyl disulfide, 2,2′-diaminodiphenyl disulfide, 1,4-butanediol diglycidyl ether and polypropylene glycol diglycidyl ether in Example 1 are retained. In step 3, 1-methylimidazole is added after mixing with the rigid epoxy continuous phase component obtained in step 2 and then degassing and casting are performed. The remaining conditions are the same as in Example 1.

[0030] Comparative Example 2: The difference between Comparative Example 2 and Example 1 is that only 20g of 4,4′-diaminodiphenyldisulfide was added in step 1, and 2,2′-diaminodiphenyldisulfide was not added; the other conditions were the same as in Example 1.

[0031] Comparative Example 3: The difference between Comparative Example 3 and Example 1 is that only 20g of 2,2′-diaminodiphenyldisulfide was added in step 1, and 4,4′-diaminodiphenyldisulfide was not added; the other conditions were the same as in Example 1.

[0032] Comparative Example 4: The difference between Comparative Example 4 and Example 1 is that in step 1, 6g of 1,4-butanediol diglycidyl ether and 10g of polypropylene glycol diglycidyl ether are added together at the beginning of the reaction, instead of adding 1,4-butanediol diglycidyl ether first and then polypropylene glycol diglycidyl ether; the other conditions are the same as in Example 1.

[0033] Comparative Example 5: The difference between Comparative Example 5 and Example 1 is that in step 1, 10g of polypropylene glycol diglycidyl ether was added first and reacted at 110°C for 15 minutes, and then 6g of 1,4-butanediol diglycidyl ether was added; the other conditions were the same as in Example 1.

[0034] Comparative Example 6: The difference between Comparative Example 6 and Example 1 is as follows: In step 1, 8g of nano-silica dispersed bisphenol A type epoxy resin concentrate was added simultaneously with the addition of 4,4′-diaminodiphenyl disulfide, 2,2′-diaminodiphenyl disulfide and 1,4-butanediol diglycidyl ether, and this nano-silica dispersed bisphenol A type epoxy resin concentrate was retained throughout the subsequent precursor reaction process; in step 2, the nano-silica dispersed bisphenol A type epoxy resin concentrate was no longer added; the remaining conditions were the same as in Example 1.

[0035] Sample preparation before performance testing: The mixtures obtained in Examples 1-5 and Comparative Examples 1-6 were poured into stainless steel molds and polytetrafluoroethylene molds treated with release agent, respectively. After curing according to the curing regime of their respective examples or comparative examples, plates with thicknesses of 1.0±0.1 mm, 3.0±0.1 mm, and 4.0±0.2 mm were obtained. The plate with a thickness of 1.0±0.1 mm was used for electrical performance testing, the plate with a thickness of 3.0±0.1 mm was used for dynamic thermomechanical analysis and thermomechanical analysis, and the plate with a thickness of 4.0±0.2 mm was used for fracture toughness testing. After curing, all plates were conditioned for 24 hours at 23±2℃ and 50±5% relative humidity according to GB / T 2918-2018. The lap shear test specimens were made of Baosteel Q235 cold-rolled steel sheets, measuring 100mm × 25mm × 1.5mm, with an overlap length of 12.5 ± 0.5mm. The adhesive layer thickness was controlled by 0.20 ± 0.02mm stainless steel shims. The bonding surfaces of the steel sheets were first sanded along the length with 400-grit sandpaper, then wiped with anhydrous ethanol for degreasing and dried. In the self-healing test, after the initial test or preparation of defects, the fracture toughness specimens and lap shear test specimens were re-attached, subjected to a contact pressure of 0.02MPa at 150℃ for 2 hours, then cooled to 23℃ and left to stand for 2 hours before being retested. Five specimens were tested in parallel for each group of samples, and the arithmetic mean was taken as the final result.

[0036] Fourier transform infrared spectroscopy characterization: Fourier transform infrared spectrometer in attenuated total reflectance mode was used, and the results are as follows: Figure 1 As shown.

[0037] Crosslinking degree and glass transition temperature tests: Differential scanning calorimetry (DSC) was used to determine the crosslinking degree of crosslinked epoxy resin according to GB / T 41928-2022, and the glass transition temperature was determined according to GB / T 19466.2-2004. 5-10 mg of sample was placed in an aluminum crucible, and the temperature was increased from 25℃ to 250℃ at a rate of 10℃ / min under nitrogen flow of 50 mL / min. A first temperature scan was performed, and the residual enthalpy of reaction was recorded. The sample was then cooled to 25℃, and a second temperature scan was performed, with the glass transition temperature read using the baseline inflection point method. The crosslinking degree was calculated as the relative value of the residual enthalpy of reaction to the theoretical total enthalpy of reaction.

[0038] Dynamic thermomechanical analysis: Tests were conducted using a dynamic thermomechanical analyzer according to GB / T 33061.1-2016 and GB / T33061.11-2022. The sample size was 35mm × 10mm × 3mm. A double cantilever configuration was used, with a vibration frequency of 1Hz, an amplitude of 15μm, a heating range of 30-220℃, and a heating rate of 3℃ / min. The storage modulus at 25℃, the peak loss tangent temperature in the glass transition region, and the storage modulus of the rubber plateau were recorded.

[0039] Linear thermal expansion coefficient test: The test was conducted using a thermomechanical analyzer according to GB / T 36800.2-2018. The sample size was 10mm×10mm×4mm, and the sample was vacuum dried at 60℃ for 12h before the test. During the test, a constant indenter force of 0.02N was applied, and the temperature was increased from 30℃ to 180℃ at a heating rate of 5℃ / min. The linear thermal expansion coefficients in the 40-80℃ and 120-160℃ ranges were calculated respectively.

[0040] Fracture toughness and self-healing fracture recovery rate tests: The three-point bending fracture toughness test method was adopted according to GB / T41932-2022. The specimen size was 80mm×10mm×4mm, the span was 64mm, and the depth of the pre-made mechanical notch was controlled to be 0.45-0.55 times the specimen width. Then, a new blade was used to lightly press and introduce a natural sharp crack. The test speed was 10mm / min. The maximum load was recorded and KIC was calculated according to the linear elastic fracture mechanics method. In the self-healing fracture recovery rate test, the specimen fractured first, then the fracture interface was accurately aligned and heat-repaired at 150℃ and 0.02MPa for 2h. After cooling, KIC was retested. The self-healing fracture recovery rate was calculated by multiplying the ratio of the repaired KIC to the initial KIC by 100%.

[0041] Overlap shear strength and self-healing lap shear recovery rate tests: These were conducted using an electronic universal testing machine according to GB / T7124-2008. The substrate was the Q235 cold-rolled steel sheet described in the sample preparation section. The overlap length was 12.5±0.5 mm, the bonding width was 25.0±0.5 mm, and the adhesive layer thickness was 0.20±0.02 mm. After application of the adhesive, curing was performed according to the curing regime of the corresponding embodiment or comparative example, with a test speed of 1.3 mm / min. The initial lap shear strength was recorded. Another sample from the same batch was subjected to shear separation at the lap interface. The separated interface was then re-bonded and heat-repaired for 2 hours at 150℃ and 0.02 MPa. The test was repeated. The self-healing lap shear recovery rate was calculated by multiplying the ratio of the repaired lap shear strength to the initial lap shear strength by 100%.

[0042] Electrical strength testing: A power frequency withstand voltage breakdown test apparatus was used, and the test was conducted according to GB / T 1408.1-2016. The sample size was 100mm × 100mm × 1.0mm, and polished stainless steel cylindrical electrodes were used. The sample was immersed in insulating oil at 25℃ for testing, with a voltage ramp rate of 0.5kV / s. The breakdown voltage was recorded, and the electrical strength was calculated based on the sample thickness. Five parallel samples were tested for each group of samples, and the highest and lowest values ​​were removed before taking the average value.

[0043] Table 1 Performance Test Results

[0044] Data Analysis: As can be seen from the data in Table 1, the self-healing and toughened epoxy resin material based on a dynamic covalent network prepared in this invention exhibits a relatively balanced matching relationship among fracture toughness, self-healing recovery ability, glass transition temperature, storage modulus, coefficient of linear expansion, and electrical strength. This indicates that the system does not rely on single toughening or a single increase in crosslinking density to achieve performance improvement, but rather on the synergistic construction of an aromatic disulfide bond-containing reactive precursor and a rigid epoxy continuous phase to form a network structure within the material that combines rearrangement capability and load-bearing capacity. The stepwise introduction of 1,4-butanediol diglycidyl ether and polypropylene glycol diglycidyl ether in the precursor allows flexible segments to preferentially participate in the construction of local dynamic domains, which not only alleviates stress concentration at crack tips but also avoids excessive spread of flexible components throughout the network. The addition of nano-silica-dispersed bisphenol A type epoxy resin concentrate after the formation of the rigid continuous phase further enhances interfacial constraint and load transfer, thereby enabling the material to exhibit coordinated improvements in structural adhesion, electrical insulation, and thermal stability during service.

[0045] As can be seen from the data in Example 1 and Comparative Example 1 in Table 1, without precursor pre-addition, 4,4′-diaminodiphenyl disulfide, 2,2′-diaminodiphenyl disulfide, 1,4-butanediol diglycidyl ether, and polypropylene glycol diglycidyl ether simultaneously enter the curing system during the final mixing stage, resulting in a more random spatial distribution between dynamic bonds, flexible segments, and the rigid epoxy continuous phase. Although a disulfide bond-containing network can still be formed, the lack of pre-organization between the local dynamic domain and the load-bearing phase leads to insufficient stress dispersion during crack propagation and inadequate interface reconstruction during repair. Consequently, thermal properties, bond strength, fracture toughness, and recovery ability all decrease simultaneously.

[0046] As can be seen from the data in Example 1 and Comparative Example 2 in Table 1, when only 4,4′-diaminodiphenyl disulfide is used, the glass transition temperature, storage modulus, and electrical stability of the material remain at a high level, but the improvement in repair-related indicators and fracture toughness is limited. The main reason for this is that the para-position structure is more conducive to forming a more regular and compact network with stronger static load-bearing capacity, but it weakens the adjustability space of local chain segments, making the network rearrangement under thermal triggering more slow.

[0047] As can be seen from the data in Example 1 and Comparative Example 3 in Table 1, when only 2,2′-diaminodiphenyl disulfide is used, the improvement in repair indicators is more significant, but the decrease in glass transition temperature, storage modulus, lap shear strength, and electrical strength is more pronounced. This is because the steric hindrance effect of the adjacent structure makes it easier for the chain segments around the aromatic disulfide bond to undergo conformational adjustment, which is more conducive to interface re-adhesion during thermal repair; however, the same steric hindrance also weakens the network regularity and effective load-bearing path, making the material more prone to softening and dimensional instability under service conditions.

[0048] As can be seen from the data in Table 1 for Examples 1, 4, and 5, the order in which 1,4-butanediol diglycidyl ether and polypropylene glycol diglycidyl ether are added has a significant impact on the final performance. When both are added simultaneously, the competitive reaction between flexible segments and shorter segments during the precursor formation stage is enhanced, the local structural distribution tends to be more even, and the dynamic domain boundary is not clear enough. However, when polypropylene glycol diglycidyl ether is added first and then 1,4-butanediol diglycidyl ether, the flexible segments occupy the reaction sites earlier, which easily leads to excessive flexibility in the early stage of the precursor and insufficient subsequent rigidity compensation. Therefore, its thermal properties, modulus, and adhesive load-bearing capacity further decline.

[0049] As can be seen from the data in Table 1 for Example 1 and Comparative Example 6, placing the nano-silica-dispersed bisphenol A epoxy resin concentrate prematurely in the precursor stage causes the inorganic phase to intervene too early in the formation process of the aromatic disulfide bond-containing reactive precursor. This leads to changes in the viscosity environment and local diffusion conditions around the precursor, which is detrimental to the division of labor between the dynamic structural units and the subsequent rigid epoxy continuous phase. Although the system still contains nano-silica, its reinforcing, expansion-reducing, and interface-stabilizing effects are difficult to fully release in the continuous phase, and instead weaken the effective energy dissipation and electrical insulation stability during crack propagation.

[0050] from Figure 1 It can be seen that the self-healing and toughening epoxy resin material based on a dynamic covalent network obtained in Example 1 of this invention exhibits good performance at a depth of 3400 cm. -1 A broad and strong absorption band appears nearby, corresponding to the hydroxyl association vibration formed after the ring opening of the epoxide group; 1604 cm⁻¹ -1 and 1508cm -1 The vicinity is characterized by aromatic ring skeletal vibrational absorption, 1324 cm⁻¹. -1and 1154cm -1 The surrounding area can be attributed to the characteristic absorption of sulfone O=S=O, 1243-1035 cm⁻¹ -1 The region is a strong absorption band formed by the superposition of vibrations of ether bonds COC, CN, and part of Si-O-Si, 500-550 cm⁻¹. -1 The region exhibits characteristic absorption for disulfide bonds, indicating that flexible segments, aromatic amine-cured structures, disulfide bonds, and nano-silica have collectively participated in network construction; simultaneously, 915 cm⁻¹ -1 The presence of only very weak residual or even almost disappearing characteristic peaks of the nearby epoxy indicates that the system has been sufficiently cured.

[0051] Those skilled in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of the invention is limited to these examples; within the framework of the invention, the technical features of the above embodiments or different embodiments can also be combined, and there are many other variations of the different aspects of the invention as described above, which are not provided in detail for the sake of brevity.

Claims

1. A self-healing and toughening epoxy resin material based on a dynamic covalent bond network, characterized in that, It is prepared from the following raw materials: by weight, 16-19 parts of 4,4′-diaminodiphenyl disulfide, 1-4 parts of 2,2′-diaminodiphenyl disulfide, 5-8 parts of 1,4-butanediol diglycidyl ether, 8-12 parts of polypropylene glycol diglycidyl ether, 47-55 parts of bisphenol A type epoxy resin, 4-6 parts of 4,4′-diaminodiphenyl sulfone, 6-10 parts of nano-silica dispersed bisphenol A type epoxy resin concentrate, and 0.20-0.40 parts of 1-methylimidazole; In this process, 4,4′-diaminodiphenyl disulfide, 2,2′-diaminodiphenyl disulfide, and 1,4-butanediol diglycidyl ether are reacted first, followed by the addition of polypropylene glycol diglycidyl ether to continue the reaction, yielding a reactive precursor containing aromatic disulfide bonds. The bisphenol A epoxy resin is mixed with 4,4′-diaminodiphenyl sulfone, and then the nano-silica-dispersed bisphenol A epoxy resin concentrate is added to obtain a rigid epoxy continuous phase component. The reactive precursor containing aromatic disulfide bonds is mixed with the rigid epoxy continuous phase component, and then cured after the addition of 1-methylimidazole to obtain the self-healing and toughening epoxy resin material based on a dynamic covalent network.

2. The self-healing and toughening epoxy resin material based on a dynamic covalent bond network according to claim 1, characterized in that, The bisphenol A type epoxy resin has an epoxy equivalent of 184-194 g / eq and a viscosity of 11000-15000 mPa·s at 25°C.

3. The self-healing and toughened epoxy resin material based on a dynamic covalent bond network according to claim 1, characterized in that, The nano-silica dispersed bisphenol A type epoxy resin concentrate has a silica mass fraction of 40%, an average particle size of 20 nm, a maximum particle size of 50 nm, and an epoxy equivalent of 295 g / eq.

4. The self-healing and toughening epoxy resin material based on a dynamic covalent bond network according to claim 1, characterized in that, The self-healing and toughening epoxy resin material based on dynamic covalent bond network is obtained through graded curing, which includes sequentially holding at 100-110℃ for 1 hour, 125-135℃ for 2 hours, 155-165℃ for 2 hours, and 165-175℃ for 2 hours.

5. The self-healing and toughening epoxy resin material based on a dynamic covalent bond network according to claim 1, characterized in that, The number-average molecular weight of the polypropylene glycol diglycidyl ether is 200-600.

6. A method for preparing a self-healing and toughened epoxy resin material based on a dynamic covalent bond network according to any one of claims 1-5, characterized in that, Includes the following steps: (1) Under nitrogen protection, 4,4′-diaminodiphenyl disulfide, 2,2′-diaminodiphenyl disulfide and 1,4-butanediol diglycidyl ether were mixed and reacted, and then polypropylene glycol diglycidyl ether was added dropwise to continue the reaction to obtain a reactive precursor containing aromatic disulfide bonds; (2) Under nitrogen protection, bisphenol A type epoxy resin was mixed with 4,4′-diaminodiphenyl sulfone, and then nano-silica was added to disperse the bisphenol A type epoxy resin concentrate to obtain a rigid epoxy continuous phase component. (3) Mix the aromatic disulfide bond reactive precursor obtained in step (1) with the rigid epoxy continuous phase component obtained in step (2), add 1-methylimidazole, degas and then cast; (4) The casting system obtained in step (3) is graded and cured to obtain a self-healing toughened epoxy resin material based on a dynamic covalent bond network.

7. The method for preparing the self-healing and toughened epoxy resin material based on a dynamic covalent bond network according to claim 6, characterized in that, In step (1), nitrogen gas is first passed through for 15-20 minutes, and the mixture is stirred at 280-320 r / min. The temperature is first raised to 90-95℃ and held for 10-20 minutes, then raised to 95-100℃ and held for 10-20 minutes, and then raised to 110-115℃. The polypropylene glycol diglycidyl ether is added dropwise over 15-20 minutes, and the reaction continues at 110-115℃ for 80-100 minutes.

8. The method for preparing the self-healing and toughened epoxy resin material based on a dynamic covalent bond network according to claim 6, characterized in that, In step (2), the mixture is stirred at 240-270 r / min under nitrogen protection, heated to 145-155℃ and held for 25-35 min, then cooled to 95-105℃, and the nano-silica dispersed bisphenol A epoxy resin concentrate is added, and stirring is continued for 10-20 min.

9. The method for preparing the self-healing and toughened epoxy resin material based on a dynamic covalent bond network according to claim 6, characterized in that, In step (3), the aromatic disulfide bond-containing reactive precursor obtained in step (1) is kept at 90-100°C and added to the rigid epoxy continuous phase component obtained in step (2). The mixture is stirred at 330-380 r / min for 8-12 min, and then the system is cooled to 75-85°C. The 1-methylimidazole is added and stirred for 2-5 min. The system is then vacuumed at 75-85°C and kept at 6-10 min for degassing. Finally, the mixture is poured into a mold preheated to 75-85°C.

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