Degradable and recoverable epoxy Vitrimer as well as preparation method and application thereof

Abstract

The invention discloses a degradable and recoverable epoxy Vitrimer as well as a preparation method and application thereof, and belongs to the technical field of functional materials and preparation thereof. The problems that existing epoxy resin is not melted and unrecyclable, and the mechanical property and breakdown field strength are seriously reduced after recycling are solved. According to the invention, 2-AFD is used as a curing agent of DGEBA, and a dynamic disulfide bond is introduced in the curing process of DGEBA, so that the epoxy resin is endowed with degradable and recoverable properties. DGEBA is used as a raw material, and vanillin-based epoxy resin (VOEP) with a reversible dynamic covalent bond (-C = N-) is further used for replacing a part of DGEBA, so that the epoxy resin realizes high-performance retention rate hot-pressing recovery, and meanwhile, the epoxy resin can be degraded in a mercaptan solution and can also be degraded in an n-hexylamine solution.

Description

Technical Field

[0001] This invention relates to a biodegradable and recyclable epoxy vitrimer, its preparation method, and its application, belonging to the field of functional materials and their preparation technology. Background Technology

[0002] Epoxy resin (EP) is an important thermosetting polymer. Its molecules contain two or more epoxy groups and, based on their chemical structure, are classified into glycidyl ethers, glycidyl esters, glycidyl amines, etc. It exists in viscous liquid or solid form and, due to its excellent mechanical properties, thermal properties, processability, and chemical resistance, is widely used in coatings, adhesives, composite materials, electronic packaging, aerospace, and industrial tools.

[0003] However, traditional epoxy resins form a permanent three-dimensional cross-linked network structure during the curing process. This structure cannot be melted or dissolved in organic solvents, making recycling very difficult. As a result, they are usually disposed of by incineration or landfill, causing serious waste of resources and environmental pollution, which limits their application in fields such as electronic packaging.

[0004] Currently, modifying epoxy resins is one of the main research directions for achieving their degradation and recycling. The preparation of degradable and recyclable epoxy resins generally involves introducing reversible dynamic bonds into the epoxy network. There are typically three methods for introducing reversible dynamic bonds into epoxy resins: the first method is through the synthesis of a curing agent containing reversible dynamic bonds; the second method is through the synthesis of an epoxy resin containing reversible dynamic bonds; and the third method is through the simultaneous synthesis of an epoxy resin containing reversible dynamic bonds and a curing agent. These reversible dynamic bonds include dynamic ester bonds, dynamic imine bonds, and dynamic disulfide bonds. After introducing dynamic bonds into the epoxy resin, the properties of these dynamic bonds allow for the application of corresponding external stimuli (light, heat, pH, etc.) to induce exchange reactions between dynamic crosslinking points, altering the topology of its crosslinking network, thereby completing the degradation and recycling of the thermosetting resin.

[0005] This invention synthesizes a vanillin-based epoxy resin containing dynamic imine bonds using vanillin, 4,4'-diaminodiphenyl ether, and epichlorohydrin as raw materials. Subsequently, the obtained epoxy resin was blended with a commercial epoxy resin (DGEBA) at different mass fractions and cured using a curing agent containing disulfide bonds, ultimately constructing a dual-dynamic covalent crosslinked network possessing both imine and disulfide bonds. The synergistic effect of the two dynamic bonds effectively improves the recyclability of the epoxy resin, providing a new strategy and useful reference for the development of green technologies in the electrical engineering field. Summary of the Invention

[0006] To address the problems of existing epoxy resins being non-meltable, non-recyclable, and exhibiting a significant decrease in mechanical properties and breakdown field strength after recycling, this invention provides a biodegradable and recyclable epoxy vitrimer, its preparation method, and its applications.

[0007] The technical solution of the present invention: One objective of this invention is to provide a method for preparing a biodegradable and recyclable epoxy vitrimer, the method comprising the following steps: (1) Add curing agent 2-AFD to epoxy resin DGEBA, heat to 90~110℃, and continue stirring until a uniform and transparent premixed liquid is formed; (2) Heat the premixed liquid obtained in (1) to 120~130℃, add vanillin-based epoxy resin in batches, and after all the resin has been added, place it in an oven and heat it to obtain a mixed liquid; (3) Pour the mixed liquid obtained in (2) into a mold, place it in a forced-air oven, and cure it to obtain a biodegradable and recyclable epoxy Vitrimer.

[0008] Further specified, the stoichiometric ratio of the amino group (-NH2) in curing agent 2-AFD to the epoxy group in epoxy resin is 1:2.

[0009] Further specify that (2) the amount of vanillin-based epoxy resin VOEP added accounts for 20% to 80% of the total mass of vanillin-based epoxy resin VOEP and epoxy resin DGEBA.

[0010] Furthermore, (2) the amount of vanillin-based epoxy resin VOEP added is 20%, 40%, 60%, or 80% of the total mass of vanillin-based epoxy resin VOEP and epoxy resin DGEBA.

[0011] Further specifying, (2) the preparation method of vanillin-based epoxy resin VOEP includes: Step 1: Add vanillin / ethanol solution dropwise to ODA / ethanol solution within 20-30 minutes. After the addition is complete, stir the reaction to obtain a yellow precipitate. Filter, wash and dry to obtain vanillin-based epoxy resin precursor VAN-ODA. Step 2: VAN-ODA is mixed with epichlorohydrin and tetrabutylammonium bromide and placed in an oil bath at 100°C for reaction. After the reaction is complete, sodium hydroxide solution is added dropwise at 60-80°C. After the addition is complete, the reaction continues at 60-80°C. After the reaction is complete, the mixture is filtered, and the resulting pale yellow precipitate is recrystallized in ethyl acetate solution and dried to obtain vanillin-based epoxy resin VOEP.

[0012] Further specifying, the stoichiometric ratio of vanillin to ODA in step one is 2.5:1.

[0013] Further specified, the mass-to-volume ratio of vanillin to anhydrous ethanol in the vanillin / ethanol solution is (10.5~11) g : (50~100) mL.

[0014] Further specified, the mass-to-volume ratio of ODA to anhydrous ethanol in the ODA / ethanol solution is (8~9.5) g : (100~150) mL.

[0015] Further specifying, the stirring reaction time in step one is 2 hours.

[0016] Further specifying, the drying temperature in step one is 60℃.

[0017] Further specifying, step one can also be: adding ODA to a vanillin / ethanol solution, heating and reacting at 70~85℃ for 2 hours to obtain a yellow precipitate, filtering, washing and drying to obtain the vanillin-based epoxy resin precursor VAN-ODA.

[0018] Further specifying, in step two, the mass ratio of VAN-ODA to epichlorohydrin and tetrabutylammonium bromide is 1:(4~6):(0.15~0.2).

[0019] Further specifying, in step two, the reaction is carried out in an oil bath at 100°C for 6 hours.

[0020] Further specifying, the concentration of sodium hydroxide solution in step two is 40%.

[0021] To further specify, after the sodium hydroxide solution is added dropwise in step two, the reaction continues for 0.5 hours.

[0022] Further specifying, the drying temperature in step two is 60~70℃.

[0023] Further specifying, step two can also be: mixing VAN-ODA with epichlorohydrin and tetrabutylammonium bromide and reacting them in an oil bath at 100°C. After the reaction is complete, cooling the reaction solution to 0°C and adding sodium hydroxide solution dropwise. After the addition is complete, reacting at 60~80°C. After the reaction is complete, filtering is performed, and the resulting pale yellow precipitate is recrystallized in ethyl acetate solution and dried to obtain vanillin-based epoxy resin.

[0024] Further specifying, the curing process in (3) is as follows: first, cure at 120℃~130℃ for 1~2h, then cure at 140℃~150℃ for 2~3h, and finally cure at 160℃~170℃ for 1~2h.

[0025] The second objective of this invention is to provide a biodegradable and recyclable epoxy vitrimer prepared by the above method.

[0026] The third objective of this invention is to provide an application of the aforementioned biodegradable and recyclable epoxy Vitrimer, specifically as an adhesive for electronic packaging.

[0027] The fourth objective of this invention is to provide a method for recycling the aforementioned degradable and recyclable epoxy vitrimer, specifically by hot-pressing the cured, discarded, or used degradable and recyclable epoxy vitrimer to obtain a secondary product.

[0028] The fifth objective of this invention is to provide a method for degrading the aforementioned degradable and recyclable epoxy vitrimer. Specifically, the cured waste or used degradable and recyclable epoxy vitrimer is added to a dithiothreitol / DMF solution or a hexylamine solution and heated at 90-100°C for 3-4 hours to achieve complete degradation of the degradable and recyclable epoxy vitrimer.

[0029] Beneficial effects: (1) In this invention, 2,2'-diaminodiphenyl disulfide (2-AFD) is used as a curing agent for bisphenol A diglycidyl ether epoxy resin (DGEBA). Dynamic disulfide bonds are introduced during the curing process of DGEBA, which endows the epoxy resin with degradable and recyclable properties. Furthermore, vanillin-based epoxy resin (VOEP) is used to replace part of the bisphenol A diglycidyl ether epoxy resin, which can introduce more reversible dynamic covalent bonds (-C=N-) into the matrix. During physical hot-pressing recycling, more crosslinking point exchange reactions will occur. The metathesis reaction of disulfide bonds and imine bonds promotes the rapid rearrangement of the crosslinking network structure, thereby enabling the epoxy resin to achieve high performance retention during hot-pressing recycling. At the same time, it endows the epoxy resin to degrade in both thiol / DMF solution and n-hexylamine solution. Test results show that when the mass fraction of epoxy resin VOEP is 60%, the electrical properties of the epoxy resin are retained to 89.01% of the original value before physical hot pressing and recycling. In contrast, the electrical properties of the Pure sample without VOEP are only retained to 74.92% of the original value after recycling. This is because, during physical hot pressing, the sample containing vanillin-based epoxy resin has more reversible dynamic bonds that can undergo dynamic reversible reactions under high temperature and high pressure conditions compared to the sample without VOEP. This indicates that the synergistic effect of the two dynamic bonds effectively improves the recyclability of the epoxy resin.

[0030] (2) The present invention modifies bisphenol A diglycidyl ether epoxy resin by adding vanillin-based epoxy resin VOEP and curing agent containing dynamic reversible disulfide bonds. The mixed epoxy resin system can maintain stable performance under high temperature and harsh environment, and at the same time exhibits strong chemical corrosion resistance, making it suitable for applications under harsh working conditions.

[0031] (3) By adjusting the ratio of VOEP to bisphenol A diglycidyl ether epoxy resin, this invention not only retains its excellent thermodynamic properties but also improves the material's recyclability, solving the problems of insolubility and non-recyclability of traditional epoxy resins. Furthermore, the preparation method of this invention involves conventional stirring, casting, and drying steps, making the process simple and easy to implement, suitable for large-scale production. By controlling parameters such as temperature and time, the stability of the product can be ensured. Because this vanillin-based epoxy resin material has excellent thermodynamic and electrical properties, it has broad application prospects and is suitable for adhesives, composite materials, electronic packaging, industrial tools, and other fields. Since it can replace a portion of petroleum-based epoxy resins, it meets environmental and safety requirements. Attached Figure Description

[0032] Figure 1 The flowchart shows the synthesis process of vanillin-based epoxy resin VOEP and the preparation diagram of VOEP samples with different mass fractions. Figure 2 Infrared spectra of vanillin-based epoxy resin precursors and monomers; Figure 3 The 1H NMR spectrum of VAN-ODA, a vanillin-based epoxy resin precursor; Figure 4 The 1H NMR spectrum of the vanillin-based epoxy monomer VOEP; Figure 5 Infrared spectra of the epoxy resins prepared in Examples 1-4 and Comparative Example 1; Figure 6 Scanning electron microscope (SEM) images (at different locations) of the fracture surfaces of the epoxy resins prepared in Examples 3 and 7 and Comparative Examples 1 and 2. Figure 7 The AC breakdown field strength diagrams are for the epoxy resins prepared in Examples 1-4 and Comparative Example 1. Figure 8 AC breakdown field strength diagrams of the epoxy resins prepared in Examples 5-8 and Comparative Example 2; Figure 9 The DSC test results are for the epoxy resins prepared in Examples 1-4 and Comparative Example 1. Figure 10 The following are DSC test results for the epoxy resins prepared in Examples 5-8 and Comparative Example 2; Figure 11 The stress-strain curves of the epoxy resins prepared in Examples 1-4 and Comparative Example 1 are shown. Figure 12 The stress-strain curves of the epoxy resins prepared in Examples 5-8 and Comparative Example 2 are shown. Figure 13 Schematic diagram of the chemical degradation process of the epoxy resin prepared for Comparative Example 1 in dithiothreitol / DMF solution; Figure 14 The diagram shows the chemical degradation process of the epoxy resin prepared in Example 2 in a hexylamine solution. Detailed Implementation

[0033] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the examples in the specification.

[0034] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art may make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0035] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that is mutually exclusive with other embodiments.

[0036] Unless otherwise specified, the experimental methods used in the following examples are conventional methods. Unless otherwise specified, the materials, reagents, methods, and instruments used are all conventional materials, reagents, methods, and instruments in the art, and can be obtained commercially by those skilled in the art.

[0037] The epoxy resin DGEBA used in the following examples was purchased from Beijing Innocare Technology Co., Ltd., and the product is bisphenol A diglycidyl ether (DGEBA, ≥85%).

[0038] Example 1: The epoxy resin prepared in this embodiment is produced according to the following steps: Step S1: Under reflux conditions, 13 g of 4,4'-diaminodiphenyl ether (ODA) was added to 100 ml of anhydrous ethanol, heated to 85 °C with a magnetic stirrer, and stirred until all ODA was dissolved to obtain an ODA solution. 19.74 g of vanillin was added to 50 ml of anhydrous ethanol, and stirred magnetically until all vanillin was dissolved to obtain a vanillin solution.

[0039] Under magnetic stirring, vanillin solution was added dropwise to ODA solution, and all vanillin solution was added within 30 minutes. Then, the mixture was stirred on a magnetic stirrer and reacted for 2 hours to obtain a yellow precipitate. The yellow precipitate was filtered, washed, and placed in a 60°C forced-air oven for 12 hours. After drying, a bio-based epoxy resin intermediate (VAN-ODA) was obtained.

[0040] 30g of dried epoxy resin intermediate (VAN-ODA), 120g of epichlorohydrin, and 3g of tetrabutylammonium bromide were placed in a beaker. The magnetic stirrer was then set to 500 rpm and the reaction was carried out at 100℃ for 6 hours. After the reaction was complete, 30mL of a 40% sodium hydroxide solution was added dropwise at 70℃, with all the sodium hydroxide solution added within 30 minutes. During the addition, a pale yellow precipitate slowly appeared. The reaction was continued for another 0.5 hours. The resulting pale yellow precipitate was filtered and recrystallized in ethyl acetate solution, then dried in an oven at 65℃ to obtain bio-based epoxy resin (VOEP). The specific VOEP preparation process is as follows: Figure 1 As shown in the figure, VAN represents vanillin, ODA represents 4,4'-diaminodiphenyl ether, ECH is epichlorohydrin, C2H6O is anhydrous ethanol, VAN-ODA represents the vanillin epoxy resin intermediate synthesized from vanillin and 4,4'-diaminodiphenyl ether in a stoichiometric ratio of 2:1, and VOEP represents the vanillin epoxy resin obtained by epoxidation of the epoxy resin intermediate VAN-ODA and epichlorohydrin.

[0041] Step S2: Based on the total mass of epoxy resin DGEBA and vanillin-based epoxy resin VOEP in the target blend system, calculate the required mass of curing agent 2-AFD according to the stoichiometric ratio. Add 3.104g of 2-AFD to 7.421g of epoxy resin DGEBA, heat to 90℃, and continue stirring until a uniform, transparent premixed liquid is formed; Step S3: The premixed liquid obtained in step S2 is heated to 120°C. First, 1g of vanillin-based epoxy resin VOEP is added, and the mixture is reacted at 120°C for 20min. Then, 0.855g of vanillin-based epoxy resin VOEP is added, and the mixture is reacted at 120°C for another 20min. After the reaction is complete, the mixture is heated to 130°C and stirred for 10min until the two epoxy resins form a homogeneous mixture (wherein, the amount of vanillin-based epoxy resin VOEP added accounts for 20% of the total mass of vanillin-based epoxy resin VOEP and epoxy resin DGEBA).

[0042] Step S4: The mixed liquid obtained in step S3 was poured evenly into the polytetrafluoroethylene mold to be tested, and then placed in a forced-air drying oven for pre-curing at 120°C for 2 hours, followed by curing at 140°C for 2 hours, and finally curing at 160°C for 2 hours. After complete curing, a biodegradable and recyclable epoxy resin was obtained, named 20wt.

[0043] Example 2: The difference between this embodiment and embodiment 1 is that the amount of vanillin-based epoxy resin VOEP added in step S3 is 40wt% of the total mass of vanillin-based epoxy resin VOEP and epoxy resin DGEBA. The remaining process steps and parameter settings are the same as in embodiment 1, resulting in a biodegradable and recyclable epoxy resin, named 40wt%.

[0044] Example 3: The difference between this embodiment and embodiment 1 is that the amount of vanillin-based epoxy resin VOEP added in step S3 is 60wt% of the total mass of vanillin-based epoxy resin VOEP and epoxy resin DGEBA. The remaining process steps and parameter settings are the same as in embodiment 1, resulting in a biodegradable and recyclable epoxy resin, named 60wt%.

[0045] Example 4: The difference between this embodiment and embodiment 1 is that the amount of vanillin-based epoxy resin VOEP added in step S3 is 80wt% of the total mass of vanillin-based epoxy resin VOEP and epoxy resin DGEBA. The remaining process steps and parameter settings are the same as in embodiment 1, resulting in a biodegradable and recyclable epoxy resin, named 80wt%.

[0046] Comparative Example 1: The difference between this embodiment and embodiment 1 is that the premixed liquid obtained in step S2 is directly placed in an oven for curing, and after curing, a biodegradable and recyclable epoxy resin is obtained, named Pure.

[0047] Example 5: The 20 wt% obtained in Example 1 was hot-pressed for recovery, specifically: Take 5g of the 20wt% sample prepared in Example 1, pulverize it using a pulverizer, and collect epoxy resin powder with a mesh size ≤50. Place the powder in a square hot press mold and hot press it at 180°C and 15MPa for 4 hours. After cooling and demolding, a secondary product is obtained, named 20wt%-Re.

[0048] Example 6: The difference between this embodiment and embodiment 5 is that the 40wt% prepared in embodiment 2 is hot-pressed for recovery, while the remaining process steps and parameter settings are the same as in embodiment 5. The resulting secondary product is named 40wt%-Re.

[0049] Example 7: The difference between this embodiment and embodiment 5 is that the 60wt% prepared in embodiment 3 is hot-pressed for recovery, while the remaining process steps and parameter settings are the same as in embodiment 5. The resulting secondary product is named 60wt%-Re.

[0050] Example 8: The difference between this embodiment and embodiment 5 is that the 80wt% prepared in embodiment 4 is hot-pressed for recovery, while the remaining process steps and parameter settings are the same as in embodiment 5. The resulting secondary product is named 80wt%-Re.

[0051] Comparative Example 2: The difference between this comparative example and Example 5 is that the Pure prepared in Comparative Example 1 is hot-pressed for recycling, while the remaining process steps and parameter settings are the same as in Example 5. The resulting secondary product is named Pure-Re.

[0052] Example of effect: (1) Figure 2 This image shows the infrared spectrum of the vanillin-based epoxy resin VOEP prepared according to the present invention. As can be seen from the image, the peak value at 1672 cm⁻¹ in VAN-ODA is [missing value]. -1 The aldehyde group of vanillin disappears at 3212 cm⁻¹. -1 and 3462cm -1 The disappearance of the amino group in 4,4'-diaminodiphenyl ether proves that all the amino groups in ODA have been consumed. Simultaneously, at 1622 cm⁻¹... -1 The appearance of a new peak is due to the Schiff base reaction between the aldehyde group in vanillin and the amino group in 4,4'-diaminodiphenyl ether to form an imine bond, which occurs at 3515 cm⁻¹. -1 The presence of a peak at the hydroxyl group indicates that the hydroxyl group in vanillin is retained, as can be seen at 914 cm⁻¹ in VOEP. -1 A new peak appears, at 3515cm. -1 The disappearance of hydroxyl groups proves that epoxy groups were successfully introduced into VAN-ODA through epichlorohydrin epoxidation. At the same time, the hydroxyl groups in the vanillin-based epoxy resin precursor VAN-ODA were completely consumed, proving the successful synthesis of vanillin-based epoxy resin.

[0053] (2) Figure 3 and Figure 4 The figures show the 1H NMR spectra of the prepared vanillin-based epoxy resin precursor VAN-ODA and vanillin-based epoxy resin VOEP, respectively. As can be seen from the figures, in the vanillin-based epoxy resin precursor VAN-ODA, the chemical shift at 8.48 ppm is a characteristic peak specific to the imine bond proton, confirming the successful synthesis of the vanillin-based epoxy resin precursor. In the precursor VAN-ODA, the characteristic proton peak of the phenolic hydroxyl group at 9.74 ppm disappears, replaced by new proton characteristic peaks at 2.88-2.72 ppm and 3.86 ppm, confirming the successful synthesis of the vanillin-based epoxy resin VOEP.

[0054] (3) Figure 5The infrared spectra of the epoxy resins prepared in Examples 1-4 and Comparative Example 1 are shown in the figures. It can be seen from the figures that at 914 cm⁻¹... -1 The near-smooth peak of the epoxy groups indicates that the epoxy resin was completely cured, and the peak at 1622 cm⁻¹ is also significant. -1 With 550cm -1 The presence of an absorption band indicates that the imine bond and the disulfide bond in the curing agent are preserved.

[0055] (4) Figure 6 The images show scanning electron microscope (SEM) images (at different locations) of the fracture surfaces of the epoxy resins prepared in Comparative Examples 1 and 2 and Examples 3 and 7. Figures (a) and (c) show that the fracture surfaces of Pure and 60 wt% VOEP samples are relatively smooth and flat, exhibiting "river-like" crack propagation traces. The crack propagation is uniform, and the structure is dense, consistent with the brittle fracture characteristics of epoxy resin, indicating that the epoxy resin material preparation process is stable. Figure (b) shows the SEM image of the fracture surface of the Pure sample after physical hot-pressing recovery. The image shows that the recovered epoxy resin exhibits relatively dense crack propagation, but still conforms to the "river-like" crack propagation traces of epoxy resin. Figure (d) shows the SEM image of the fracture surface of the 60 wt% VOEP sample after physical hot-pressing recovery. The image shows that the recovered epoxy resin has a relatively smooth and flat fracture surface with fewer cracks, exhibiting "river-like" crack traces. The two groups of samples showed a significant difference in the number of cracks in their cross-sections after physical hot-pressing recovery. This is because the 60wt% VOEP sample, under high temperature and pressure, not only had disulfide bonds participating in the exchange reaction, but also imine bonds participating in the metathesis reaction. The synergistic effect of these two different reversible dynamic bonds made the epoxy resin after physical hot-pressing recovery more dense and resulted in fewer crack propagation.

[0056] (5) Figure 7The AC breakdown field strength diagrams are shown for the epoxy resins prepared in Examples 1-4 and Comparative Example 1. The measured 63.2% power frequency electrical strength (breakdown field strength) results are as follows: Pure: 62.05 kV / mm, 20wt%: 67.15 kV / mm, 40wt%: 67.85 kV / mm, 60wt%: 61.64 kV / mm, and 80wt%: 58.98 kV / mm. Analysis of the data shows that with the increase of VOEP mass fraction, the power frequency electrical strength of the blend system exhibits a trend of first increasing and then decreasing. When 20wt% and 40wt% VOEP are added, the breakdown field strength significantly increases from 62.05 kV / mm in the pure system to 67.15 kV / mm and 67.85 kV / mm, respectively, with increases of 8.22% and 9.34%. This enhancement effect is attributed to the two additional benzene ring structures in the VOEP molecule compared to the DGEBA molecule. These rigid benzene rings deepen the trap levels and reduce the free volume of the material, effectively suppressing carrier migration and ultimately leading to an increase in power frequency breakdown strength. However, when the VOEP mass fraction exceeds 40%, the power frequency electrical strength begins to decrease. This is because the different reaction rates of the two epoxy resins and the curing agent in the system lead to a looser material structure, i.e., a decrease in crosslinking density. This loose structure easily induces local electric field concentration, thereby reducing the power frequency breakdown strength of the material. It is worth noting that even at high VOEP contents (such as 60wt% and 80wt%), the breakdown strength (61.64kV / mm, 58.98kV / mm) remains high, indicating that the material still maintains good insulation performance. (6) Figure 8 The Weibull distribution of the power frequency electrical strength of epoxy resins (VOEP) with different mass fractions after pulverization and physical hot pressing recycling is shown. The measured breakdown field strengths are as follows: Pure-Re: 46.49 kV / mm, 20wt%-Re: 51.04 kV / mm, 40wt%-Re: 60.57 kV / mm, 60wt%-Re: 54.87 kV / mm, and 80wt%-Re: 54.06 kV / mm. Notably, the power frequency breakdown strength retention rate of the epoxy resin after physical hot pressing recycling shows an increasing trend, reaching 74.92%, 76.01%, 89.27%, 89.01%, and 91.65%, respectively. This is attributed to the gradual increase in the content of reversible dynamic imine bonds in the epoxy resin crosslinking network. During physical hot pressing, more chain segments undergo imine metathesis reactions, resulting in a more compact structure of the recycled epoxy resin, thereby improving its power frequency breakdown field strength retention rate.

[0057] (7) Figure 9The figures show the DSC test results of the epoxy resins prepared in Examples 1-4 and Comparative Example 1. It can be seen from the figures that as the amount of VOEP added gradually increases, the glass transition temperature (Tg) of the epoxy resin gradually increases. This is because the dynamic imine bonds and rigid benzene ring structures gradually increase, restricting the rotation and movement of the molecular chains, thereby enhancing the overall rigidity of the molecular chains and ultimately leading to an increase in the glass transition temperature.

[0058] (8) Figure 10 The images show the DSC test results of the epoxy resins prepared in Examples 5-8 and Comparative Example 2. The glass transition temperatures of the epoxy resins after hot-press recycling were all lowered. This is because during physical hot-press recycling, the dynamic bonds within the epoxy resin break and recombine under high temperature and pressure, leading to a decrease in crosslinking density, defects, and insufficient crosslinking in localized areas, resulting in a decrease in the overall glass transition temperature.

[0059] (9) Figure 11 The stress-strain curves of the epoxy resins prepared in Examples 1-4 and Comparative Example 1 are shown. As can be seen from the figures, with the increase of VOEP addition, the tensile strength of the epoxy resin first increases and then decreases, while the elongation at break continuously decreases. This phenomenon can be attributed to the imine bond and benzene ring structure in the VOEP molecule, which keeps the molecular chain segments in the same plane, forming a large π-bond conjugated system, thereby enhancing tensile strength while reducing elongation at break. However, when the VOEP content exceeds a certain threshold, the reaction rates between the two epoxy resins, VOEP and DGEBA, and the curing agent may differ, leading to an increase in internal defects in the material and a decrease in tensile properties.

[0060] (10) Figure 12 The stress-strain curves of the epoxy resins prepared in Examples 5-8 and Comparative Example 2 are shown. As can be seen from the figures, compared to before recycling, the tensile strength and elongation at break retention rates of the recycled epoxy resins both increase with increasing VOEP content. When the VOEP content is 60% and 80%, the tensile strength retention rates of the epoxy resins recycled by physical hot pressing reach 86.54% and 92.56%, respectively. This trend is mainly attributed to the increased content of dynamically reversible bonds within the material, thereby significantly improving its mechanical property retention capacity after recycling.

[0061] (11) 2 g of the epoxy resin prepared in Comparative Example 1 was placed in a 0.05 g / mL dithiothreitol (DTT) / DMF solution for chemical degradation. The degradation process is described in [the table below]. Figure 13The epoxy resin can degrade because its three-dimensional cross-linked network is bridged by the curing agent 2-AFD. DTT, as a strong reducing agent, has dithiol groups (-SH) in its molecules that can dissociate under weakly alkaline conditions to generate more nucleophilic thiolate anions (-S⁻). These anions attack the disulfide bonds (-SS-) introduced into the epoxy resin network by the curing agent, leading to the destruction of the cross-linked network. This process transforms the epoxy resin from a large-molecule cross-linked state to a small-molecule soluble state, thus achieving degradation.

[0062] (12) 4 g of the epoxy resin prepared in Example 2 was placed in a 98% pure n-hexylamine solution for chemical degradation. The degradation process is described in [the table below]. Figure 14 The epoxy resin can degrade because its three-dimensional cross-linked network contains vanillin-based epoxy resin (VOEP) structural units. The dynamic imine bonds (-C=N-) in VOEP can undergo reversible breakage and recombination under acidic conditions or the action of nucleophiles. Hexylamine, as a long-chain primary amine, attacks the carbon atoms of the imine bonds with its strongly nucleophilic amino group, initiating an amine exchange reaction. This reaction leads to the breakage of the original imine bonds and the generation of new imine bonds and free amines, thereby disrupting the epoxy resin cross-linked network, causing it to depolymerize into smaller molecular chains and dissolve, thus achieving degradation.

[0063] In summary, the addition of vanillin-based epoxy resin can improve the performance retention rate of bisphenol A diglycidyl ether epoxy resin (DGEBA) after physical hot pressing recovery while maintaining its performance. Furthermore, the addition of vanillin-based epoxy resin (VOEP) allows the epoxy resin to degrade in hexylamine solution.

[0064] The above description is only a preferred embodiment of the present invention. Given that those skilled in the art can make appropriate changes and modifications to the above embodiments, the present invention is not limited to the specific embodiments described above, and some modifications and changes to the present invention should also fall within the protection scope of the claims of the present invention.

Claims

1. A method for preparing a biodegradable and recyclable epoxy vitrimer, characterized in that, include: (1) Add curing agent 2-AFD to epoxy resin DGEBA, heat to 90~110℃, and continue stirring until a uniform and transparent premixed liquid is formed; (2) Heat the premixed liquid obtained in (1) to 120~130℃, add vanillin-based epoxy resin VOEP in batches, and after all the resin has been added, place it in an oven and heat it to obtain a mixed liquid; (3) Pour the mixed liquid obtained in (2) into a mold, place it in a forced-air oven, and cure it to obtain a biodegradable and recyclable epoxy Vitrimer.

2. The preparation method according to claim 1, characterized in that, (2) The amount of vanillin-based epoxy resin VOEP added is 20% to 80% of the total mass of vanillin-based epoxy resin VOEP and epoxy resin DGEBA.

3. The preparation method according to claim 1, characterized in that, (2) The proportion of the amount of vanillin-based epoxy resin VOEP added is 20%, 40%, 60% or 80% of the total mass of vanillin-based epoxy resin VOEP and epoxy resin DGEBA.

4. The preparation method according to claim 1, characterized in that, (2) The preparation methods of vanillin-based epoxy resin VOEP include: Step 1: Add vanillin / ethanol solution dropwise to ODA / ethanol solution within 20-30 minutes. After the addition is complete, stir the reaction to obtain a yellow precipitate. Filter, wash and dry to obtain vanillin-based epoxy resin precursor VAN-ODA. Step 2: VAN-ODA is mixed with epichlorohydrin and tetrabutylammonium bromide and reacted in an oil bath at 100°C. After the reaction is complete, sodium hydroxide solution is added dropwise. After the addition is complete, the reaction is carried out at 60~80°C. After the reaction is complete, the mixture is filtered, and the resulting pale yellow precipitate is recrystallized in ethyl acetate solution and dried to obtain vanillin-based epoxy resin VOEP.

5. The preparation method according to claim 4, characterized in that, In step one, the stoichiometric ratio of vanillin to ODA is 2.5:1; the mass-volume ratio of vanillin to anhydrous ethanol in the vanillin / ethanol solution is (10.5~11) g: (50~100) mL; and the mass-volume ratio of ODA to anhydrous ethanol in the ODA / ethanol solution is (8~9.5) g: (100~150) mL.

6. The preparation method according to claim 4, characterized in that, In step two, the mass ratio of VAN-ODA to epichlorohydrin and tetrabutylammonium bromide is 1:(4~6):(0.15~0.2).

7. A biodegradable and recyclable epoxy vitrimer prepared by the method of any one of claims 1 to 6.

8. An application of the biodegradable and recyclable epoxy Vitrimer as described in claim 7, characterized in that, Used as an adhesive in electronic packaging.

9. A method for recycling the biodegradable and recyclable epoxy vitrimer as described in claim 7, characterized in that, The cured, waste, or used biodegradable and recyclable epoxy Vitrimer is recycled by hot pressing to obtain secondary products.

10. A method for degrading the biodegradable and recyclable epoxy vitrimer as described in claim 7, characterized in that, The cured waste or used biodegradable and recyclable epoxy vitrimer is added to a dithiothreitol / DMF solution or a hexylamine solution and heated at 90~100℃ for 3~4 hours to achieve complete degradation of the biodegradable and recyclable epoxy vitrimer.

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