Preparation method of recyclable and easy-to-repair epoxy resin, product and recycling process thereof

Abstract

The application discloses a preparation method of a recyclable and easy-to-repair epoxy resin, and the recyclable and easy-to-repair epoxy resin is prepared from an epoxy resin containing a borate ester structure or a mixed resin composed of the epoxy resin containing the borate ester structure and a conventional epoxy resin after curing; the structural formula of the epoxy resin containing the borate ester structure is shown in the following formula (I), wherein R is selected from one or more of the following formula (II-1), (II-2) and (II-3); the preparation method disclosed by the application is suitable for conventional types of epoxy resins in the field and has universality; and the prepared product has recyclability and repairability and also has high strength.

Description

Technical Field

[0001] This invention relates to the technical field of epoxy resin modification, and in particular to a method for preparing recyclable and easily repairable epoxy resin, its products, and recycling processes. Background Technology

[0002] Epoxy resin, as one of the three traditional thermosetting resins (epoxy, phenolic, and unsaturated polyester), possesses excellent mechanical and adhesive properties and is widely used in various industries, such as coatings, adhesives, electronic packaging, engineering plastics, and composite materials. Because epoxy resin is a thermosetting resin, it forms a permanent cross-linked network structure after curing, resulting in excellent thermal stability and mechanical properties. However, this also leads to difficulties in reprocessing and recycling. With product iteration and reaching the end of its service life, a large amount of epoxy resin faces disposal. Therefore, achieving green and efficient recycling of epoxy resin is an inevitable development trend for the epoxy resin industry.

[0003] In 2011, Leibler's research group discovered that adding alkaline metal salts to carboxylic acid-cured epoxy resins resulted in cured products exhibiting thermosetting polymer properties at room temperature, but showing significant stress relaxation at high temperatures. Further research revealed that the ester bonds in the crosslinked network were in dynamic exchange equilibrium. Professor Leibler named this type of thermosetting polymer containing reversible dynamic bonds "vitrimer," which Academician Zhang Xi translated as "glass-like polymer." Based on this concept, many dynamic covalent bonds, such as C / C bonds (Diels-Alder reaction), disulfide bonds, ester bonds, borate ester bonds, and silicon-oxygen bonds, have been found to induce topological network rearrangement at the molecular level even after polymer crosslinking, under appropriate conditions such as light and heat, achieving structural adjustment or recombination, thereby endowing them with self-healing, weldable, reprocessable, and recyclable properties.

[0004] Boronate bonds can be exchanged at lower temperatures and without catalysts, so introducing boronate bonds into epoxy resins can achieve efficient recycling of epoxy resins.

[0005] For example, Chinese patent document CN112608452 A discloses a high-performance, recyclable, and easily repairable epoxy resin and its preparation method. This resin is prepared by a curing reaction of epoxy resin, a curing agent, and an accelerator. The curing agent is a dynamically borate ester-bridged modified polyamine curing agent, prepared by reacting an organic amine molecule A1 with a phenylboronic acid group at one end with a polydiol molecule B1, or by reacting an organic amine molecule A2 with a monodiol group at one end with a polyphenylboronic acid molecule B2. The resin prepared by this method can achieve good recycling and repair performance under certain heating conditions, but according to the description, the recycling time is at least 6 hours. More importantly, the specific curing agent used in this technical solution limits the processing conditions and application range of the epoxy resin. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention discloses a method for preparing recyclable and easily repairable epoxy resin. This method is applicable to conventional epoxy resin types in the field and has universality. The prepared product is recyclable, repairable, and also has high strength.

[0007] The specific technical solution is as follows:

[0008] A method for preparing a recyclable and easily repairable epoxy resin involves curing an epoxy resin with a borate ester structure, or a mixed resin composed of an epoxy resin with a borate ester structure and a conventional epoxy resin, to obtain the recyclable and easily repairable epoxy resin.

[0009] The structural formula of the epoxy resin containing the borate ester structure is shown in formula (Ⅰ) below:

[0010]

[0011] In the formula, R is selected from one or more of the following formulas (II-1), (II-2), and (II-3);

[0012]

[0013] The borate ester-containing epoxy resin disclosed in this invention has a novel structure with end groups of eugenol glycidyl ether, allyl glycidyl ether, or 1,2-epoxy-4-vinylcyclohexane. It is liquid at room temperature and has excellent compatibility with various types of epoxy resins. It can be cured alone or mixed with a certain proportion of various types of conventional epoxy resins before curing. The resulting cured epoxy resin has excellent transparency and significantly improved tensile strength. Furthermore, the cured epoxy resin can be repaired and recycled under certain conditions.

[0014] The preparation method of the epoxy resin containing the borate ester structure specifically includes:

[0015] Step 1: Mix 1-thioglycerol, epoxy monomer containing unsaturated double bonds, photoinitiator and solvent I evenly, and carry out mercapto-alkene click chemistry reaction;

[0016] The epoxy monomer containing unsaturated double bonds is selected from one or more of eugenol glycidyl ether, allyl glycidyl ether, and 1,2-epoxy-4-vinylcyclohexane.

[0017] Step 2: Add 1,4-phenylenediboric acid, desiccant and solvent II to the reactor, and obtain an epoxy resin with borate ester structure after dehydration condensation reaction.

[0018] In step 1:

[0019] The molar ratio of 1-thioglycerol to epoxy monomers containing unsaturated double bonds is (0.95–1.05):1; preferably, the molar ratio is equal.

[0020] The photoinitiator is selected from commercially available free radical photoinitiators, such as phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide, ethyl 2,4,6-trimethylbenzoylphosphonate, 2-methyl-1-[4-(methylthio)phenyl]-2-(4-morpholino)-1-propanone, 2-hydroxy-2-methyl-1-phenyl-1-propanone, etc.

[0021] Preferably, the proportion of photoinitiator is 0.3 to 2.0 wt% based on the total mass of 1-thioglycerol and epoxy monomers containing unsaturated double bonds, specifically 0.3 wt%, 0.4 wt%, 0.5 wt%, 0.6 wt%, 0.7 wt%, 0.8 wt%, 0.9 wt%, 1.0 wt%, 1.1 wt%, 1.2 wt%, 1.3 wt%, 1.4 wt%, 1.5 wt%, 1.6 wt%, 1.7 wt%, 1.8 wt%, 1.9 wt%, 2.0 wt%, or any value within the range.

[0022] Solvent I is selected from one or more of methanol, tetrahydrofuran, toluene, and acetone;

[0023] The mass ratio of solvent to total mass of 1-thioglycerol and epoxy monomers containing unsaturated double bonds is (0.5–10):1; specifically, such as 0.5:1, 1:1, 1.5:1, 2:1, 2.5:1, 3:1, 3.5:1, 4:1, 4.5:1, 5:1, 5.5:1, 6:1, 6.5:1, 7:1, 7.5:1, 8:1, 8.5:1, 9:1, 9.5:1, 10:1 or any ratio within the range.

[0024] In step 1, the mercapto-alkene click chemistry reaction is carried out under ultraviolet light irradiation. The ultraviolet light irradiation conditions can be selected according to the absorption wavelength of the photoinitiator, preferably 395 nm or 405 nm. The reaction temperature is 10–50 °C, and the reaction time is 1–5 h; preferably, it is carried out at room temperature.

[0025] In step 2:

[0026] The molar amount of 1,4-phenylenediboronic acid added is (48-52)% of the molar amount of 1-thioglycerol in step 1, specifically 48%, 49%, 50%, 51%, 52% or any value within the range; preferably 50%.

[0027] The desiccant is selected from conventional types in the art, such as anhydrous sodium sulfate, anhydrous magnesium sulfate, molecular sieves, etc.

[0028] The desiccant has a mass of (50-150) wt% of the sum of the masses of 1-thioglycerol, epoxy monomers containing unsaturated double bonds, and 1,4-phenylenediboronic acid. Specifically, it can be 50 wt%, 60 wt%, 70 wt%, 80 wt%, 90 wt%, 100 wt%, 110 wt%, 120 wt%, 130 wt%, 140 wt%, 150 wt%, or any value within the range.

[0029] Solvent II is selected from one or more of methanol, tetrahydrofuran, toluene, and acetone;

[0030] Based on the total mass of 1-thioglycerol, the epoxy monomer containing unsaturated double bonds, and 1,4-phenylenediboric acid, the mass ratio of solvent II to the total mass of the three is (2-10):1, specifically such as 2:1, 2.5:1, 3:1, 3.5:1, 4:1, 4.5:1, 5:1, 5.5:1, 6:1, 6.5:1, 7:1, 7.5:1, 8:1, 8.5:1, 9:1, 9.5:1, 10:1, or any ratio within the range; preferably (3-6):1.

[0031] In step 2, the dehydration condensation reaction is carried out at a temperature of 10–50°C for 12–48 hours; preferably at room temperature.

[0032] In step 2, after the dehydration condensation reaction, the reaction solution is filtered.

[0033] The solvent is recovered by rotary evaporation of the filtrate, and the desiccant obtained after filtration can be recycled.

[0034] The epoxy resin with borate ester structure prepared by this method is liquid at room temperature, and the borate ester bonds in the structure can undergo reversible exchange under certain conditions. This preparation method conforms to the principles of green chemistry, generates no waste, and the solvents and desiccants used can be recycled and reused.

[0035] When preparing recyclable and easily repairable epoxy resins, conventional epoxy resins in this field are used, such as aromatic epoxy resins, aliphatic epoxy resins, alicyclic epoxy resins, etc.

[0036] Aromatic epoxy resins are selected from common types in this field, such as bisphenol A type epoxy resin, bisphenol F epoxy resin, bisphenol S epoxy resin, phenolic epoxy resin, etc.

[0037] Aliphatic epoxy resins are selected from common types in this field, such as aliphatic glycidyl ether epoxy resins, epoxidized soybean oil, etc.

[0038] Alicyclic epoxy resins are selected from common types in the art, such as 3,4-epoxycyclohexylmethyl 3,4-epoxycyclohexylcarboxylate, bis(7-oxabicyclo[4.1.0]3-heptylmethyl) hexadiote, etc.

[0039] Experiments have shown that the preparation method disclosed in this invention is universal and can be applied to conventional epoxy resins in the field.

[0040] When preparing recyclable and easily repairable epoxy resin, a curing agent is also added to the raw materials. In this invention, there are no special requirements for the type of curing agent, which can be selected from common types in the art, such as polyamine type and acid anhydride type.

[0041] The polyamine curing agent is selected from common types in the field, such as 4,4'-diaminodiphenylmethane, isophorone diamine, and diethylenetriamine.

[0042] Anhydride-type curing agents are selected from common types in this field, such as methyl hexahydrophthalic anhydride, phthalic anhydride, dodecenyl succinic anhydride, polyadenosine anhydride, etc.

[0043] When using anhydride-based curing agents, additional accelerators are required to speed up the curing reaction.

[0044] The accelerator is selected from conventional types in the art, such as 2,4,6-tris(dimethylaminomethyl)phenol, benzyldimethylamine, N,N-dimethylaniline, etc.

[0045] Preferably, the epoxy resin containing the borate ester structure is selected from allyl glycidyl ether-borate ester structure epoxy resin.

[0046] Experiments have shown that cured products made from epoxy resins with an allyl glycidyl ether-boronate structure have superior recyclability and shorter reprocessing time.

[0047] Preferred:

[0048] The mass ratio of the borate ester-structured epoxy resin to the conventional epoxy resin is (10-100):(0-90).

[0049] Further optimization:

[0050] When the epoxy resin containing the borate ester structure is selected from eugenol glycidyl ether-borate ester structure epoxy resin and 1,2-epoxy-4-vinylcyclohexane-borate ester structure epoxy resin, the mass ratio of the epoxy resin containing the borate ester structure to the conventional epoxy resin is (20-100):(0-80), specifically such as 20:80, 25:75, 30:70, 35:65, 40:60, 45:55, 50:50, 55:45, 60:40, 65:35, 70:30, 75:25, 80:20, 85:15, 90:10, 95:5, 100:0 (i.e., no conventional epoxy resin is added) or any ratio within the range.

[0051] When the epoxy resin containing the borate ester structure is selected from the epoxy resin with the allyl glycidyl ether-borate ester structure, the mass ratio of the epoxy resin containing the borate ester structure to the conventional epoxy resin is (10-100):(0-90), specifically such as 10:90, 15:85, 20:80, 25:75, 30:70, 35:65, 40:60, 45:55, 50:50, 55:45, 60:40, 65:35, 70:30, 75:25, 80:20, 85:15, 90:10, 95:5, 100:0 (i.e., no conventional epoxy resin is added) or any ratio within the range.

[0052] This invention also discloses a recyclable and easily repairable epoxy resin prepared according to the above method. This resin possesses high strength and is recyclable and repairable.

[0053] This invention discloses a recycling process for the recyclable and easily repairable epoxy resin, specifically as follows:

[0054] The recyclable and easily repairable epoxy resin is heated and molded at a temperature of 160-200°C, a pressure of 2-10 MPa, and a time of ≤240 min.

[0055] The molding temperature can be 160℃, 165℃, 170℃, 175℃, 180℃, 185℃, 190℃, 185℃, 200℃ or any value within this range.

[0056] The molding pressure can be 2 MPa, 3 MPa, 4 MPa, 5 MPa, 6 MPa, 7 MPa, 8 MPa, 9 MPa, 10 MPa or any value within the range.

[0057] As the molding temperature increases, the reprocessing time will be further shortened, with the shortest reprocessing time being only 7 minutes.

[0058] It is evident that the recyclable and easily repairable epoxy resin prepared by this invention has the advantage of short reprocessing time.

[0059] Compared with the prior art, the present invention has the following beneficial effects:

[0060] 1. This invention discloses a novel epoxy resin with a borate ester structure and its preparation method. The structure is liquid at room temperature, and the borate ester bonds in the structure can undergo reversible exchange under certain conditions. The preparation method conforms to the principles of green chemistry, generates no waste, and the solvents and desiccants used can be recycled and reused.

[0061] 2. The borate ester-structured epoxy resin disclosed in this invention can improve the mechanical properties of the cured epoxy resin after being blended and cured with commercial epoxy resin in a certain proportion.

[0062] 3. The epoxy resin cured product disclosed in this invention can be reprocessed and molded under certain conditions, and can also self-heal under certain conditions. The processing time required is short, which changes the shortcomings of traditional epoxy resin that cannot be repaired or recycled after curing.

[0063] 4. Adding the borate ester structure epoxy resin disclosed in this invention to most epoxy resin and curing agent formulations can give the cured epoxy resin high strength, recyclability, and repairability. This invention has universal applicability. Attached Figure Description

[0064] Figure 1 The 1H NMR spectrum of the eugenol glycidyl ether-boron ester structured epoxy resin prepared in Example 1 1 H-NMR;

[0065] Figure 2 The 1H NMR spectrum of the allyl glycidyl ether-boronate structured epoxy resin prepared in Example 2 1 H-NMR;

[0066] Figure 3 The 1H NMR spectrum of the 1,2-epoxy-4-vinylcyclohexane-borate ester epoxy resin prepared in Example 3. 1 H-NMR;

[0067] Figure 4 Optical photographs of the cured and reprocessed specimens prepared in Example 1; Figure 5 Optical photographs showing scratches and heat repair on the cured sample prepared in Example 2. Detailed Implementation

[0068] The present invention will be described in further detail below with reference to embodiments and comparative examples, but the implementation of the present invention is not limited thereto.

[0069] Example 1

[0070] Step 1: 13.14 g (60 mmol) of eugenol glycidyl ether, 6.50 g (60 mmol) of 1-thioglycerol, 0.2 g of phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide, and 20 mL of tetrahydrofuran were mixed thoroughly and reacted at room temperature under 405 nm UV irradiation for 3 h. Then, 5 g (30 mmol) of 1,4-phenylenediboronic acid, 100 mL of tetrahydrofuran, and 15 g of anhydrous magnesium sulfate were added, and the reaction was continued at room temperature for 24 h. The mixture was filtered to remove anhydrous magnesium sulfate, and the filtrate was rotary evaporated to recover tetrahydrofuran, yielding the eugenol glycidyl ether-boron ester epoxy resin, denoted as EUEP-DBD.

[0071] Figure 1 The 1H NMR spectrum of the eugenol glycidyl ether-boron ester epoxy resin prepared in step one. 1 H-NMR.

[0072] Step 2: Mix 20 parts by weight of EUEP-DBD with 80 parts by weight of bisphenol A epoxy resin (E51), then add 25 parts by weight of 4,4'-diaminodiphenylmethane (DDM) curing agent. After mixing evenly, pour the mixture into a sample for curing. The curing conditions are 100℃ / 2h and 150℃ / 2h.

[0073] After curing, the sample was subjected to tensile testing, then crushed into powder and molded at 160℃ and 5MPa pressure. The shortest time required for reprocessing (i.e., recycling time) was tested, and the tensile strength of the recycled epoxy resin was tested. The recycling efficiency (the ratio of the recycled tensile strength to the cured tensile strength) was calculated. The data are listed in Table 1 below.

[0074] Figure 4 Optical photographs of the cured and reprocessed samples prepared in this embodiment show that the cured sample prepared in this embodiment has excellent transparency, and the sample prepared after crushing and reprocessing also has good transparency.

[0075] Example 2

[0076] The preparation process is basically the same as in Example 1, except that in step two, the raw material ratio is replaced as follows:

[0077] After mixing 50 parts by weight of EUEP-DBD and 50 parts by weight of E51, add 19.5 parts by weight of DDM curing agent.

[0078] The performance tests of the cured specimens were the same as those in Example 1, and the performance data are listed in Table 1 below.

[0079] Figure 5Optical photographs of the cured specimens prepared in this embodiment were taken to show scratches and heat repair. It was observed that the surface cracks of the epoxy cured material could be repaired after heating for a certain period of time.

[0080] Example 3

[0081] The preparation process is exactly the same as in Example 2.

[0082] The performance tests of the cured specimens were basically the same as those in Example 1, except that the molding temperature was replaced with 200℃. The data are listed in Table 1 below.

[0083] Example 4

[0084] The preparation process is basically the same as in Example 1, except that in step two, the raw material ratio is replaced as follows:

[0085] Mix 100 parts by weight of EUEP-DBD with 12 parts by weight of DDM curing agent.

[0086] The performance tests of the cured specimens were the same as in Example 1, and the performance data are listed in Table 1 below.

[0087] Example 5

[0088] Step 1: 6.84 g (60 mmol) of allyl glycidyl ether, 6.50 g (60 mmol) of 1-thioglycerol, 0.2 g of ethyl 2,4,6-trimethylbenzoylphosphonate, and 20 mL of methanol were mixed thoroughly and reacted at room temperature under 395 nm UV irradiation for 3 h. Then, 5 g (30 mmol) of 1,4-phenylenediboronic acid, 100 mL of methanol, and 13 g of anhydrous sodium sulfate were added, and the reaction was continued at room temperature for 24 h. The mixture was filtered to remove the anhydrous sodium sulfate, and the methanol was recovered by rotary evaporation of the filtrate to obtain the allyl glycidyl ether-boronate epoxy resin, denoted as AGE-DBD.

[0089] Figure 2 The 1H NMR spectrum of the allyl glycidyl ether-boronate structured epoxy resin prepared in step one. 1 H-NMR.

[0090] Step 2: Mix 10 parts by weight of AGE-DBD with 90 parts by weight of glycerol triglycidyl ether (GTE), then add 44 parts by weight of isophorone diamine (IPDA) curing agent. After mixing evenly, pour the mixture into a sample for curing. The curing conditions are 100℃ / 2h and 120℃ / 2h.

[0091] The performance tests of the cured specimens were the same as in Example 1, and the performance data are listed in Table 1 below.

[0092] Example 6

[0093] The preparation process is basically the same as in Example 5, except that in step two, the raw material ratio is replaced as follows:

[0094] After mixing 20 parts by weight of AGE-DBD and 80 parts by weight of GTE, 41 parts by weight of IPDA curing agent were added.

[0095] The performance tests of the cured specimens were the same as in Example 1, and the performance data are listed in Table 1 below.

[0096] Example 7

[0097] The preparation process is basically the same as in Example 5, except that in step two, the raw material ratio is replaced as follows:

[0098] After mixing 50 parts by weight of AGE-DBD and 50 parts by weight of GTE, add 31 parts by weight of IPDA curing agent.

[0099] The performance tests of the cured specimens were the same as in Example 1, and the performance data are listed in Table 1 below.

[0100] Example 8

[0101] The preparation process is exactly the same as in Example 7.

[0102] The performance tests of the cured specimens were basically the same as those in Example 1, except that the molding temperature was replaced with 200℃. The data are listed in Table 1 below.

[0103] Example 9

[0104] The preparation process is basically the same as in Example 5, except that in step two, the raw material ratio is replaced as follows:

[0105] 100 parts by weight of AGE-DBD and 14.2 parts by weight of IPDA curing agent were mixed evenly.

[0106] The performance tests of the cured specimens were the same as in Example 1, and the performance data are listed in Table 1 below.

[0107] Example 10

[0108] The preparation process is exactly the same as in Example 9.

[0109] The performance tests of the cured specimens were basically the same as those in Example 1, except that the molding temperature was replaced with 200℃. The data are listed in Table 1 below.

[0110] Example 11

[0111] Step 1: 7.70 g (60 mmol) of 1,2-epoxy-4-vinylcyclohexane, 6.50 g (60 mmol) of 1-thioglycerol, 0.2 g of ethyl 2,4,6-trimethylbenzoylphosphonate, and 20 mL of toluene were mixed thoroughly and reacted at room temperature under 405 nm UV irradiation for 4 h. Then, 5 g (30 mmol) of 1,4-phenylenediboronic acid, 100 mL of toluene, and 13 g of anhydrous sodium sulfate were added, and the reaction was continued at room temperature for 36 h. The mixture was filtered to remove the anhydrous sodium sulfate, and the toluene was recovered by rotary evaporation of the filtrate to obtain the 1,2-epoxy-4-vinylcyclohexane-boronate structure epoxy resin, denoted as EVC-DBD.

[0112] Figure 3 The 1H NMR spectrum of the 1,2-epoxy-4-vinylcyclohexane-borate ester epoxy resin prepared in step one. 1 H-NMR.

[0113] Step 2: Mix 20 parts by weight of EVC-DBD with 80 parts by weight of 3,4-epoxycyclohexylmethyl 3,4-epoxycyclohexylcarboxylate (2021P), then add 130 parts by weight of methylhexahydrophthalic anhydride (MHHPA) curing agent and 0.3 parts by weight of accelerator DMP-30. After mixing evenly, pour the mixture into a sample for curing. The curing conditions are 100℃ / 1h, 120℃ / 2h, and 150℃ / 2h.

[0114] The performance tests of the cured specimens were the same as in Example 1, and the performance data are listed in Table 1 below.

[0115] Example 12

[0116] The preparation process is basically the same as in Example 11, except that in step two, the raw material ratio is replaced as follows:

[0117] After mixing 50 parts by weight of EVC-DBD and 50 parts by weight of 2021P, add 103 parts by weight of MHHPA curing agent and 0.3 parts by weight of DMP-30.

[0118] The performance tests of the cured specimens were the same as in Example 1, and the performance data are listed in Table 1 below.

[0119] Example 13

[0120] The preparation process is exactly the same as in Example 12.

[0121] The performance tests of the cured specimens were basically the same as those in Example 1, except that the molding temperature was replaced with 200℃. The data are listed in Table 1 below.

[0122] Example 14

[0123] The preparation process is basically the same as in Example 11, except that in step two, the raw material ratio is replaced as follows:

[0124] Mix 100 parts by weight of EVC-DBD with 70 parts by weight of MHHPA curing agent and 0.3 parts by weight of DMP-30 until homogeneous.

[0125] The performance tests of the cured specimens were the same as in Example 1, and the performance data are listed in Table 1 below.

[0126] Comparative Example 1

[0127] 100 parts by weight of bisphenol A epoxy resin (E51) and 27 parts by weight of 4,4'-diaminodiphenylmethane (DDM) curing agent were mixed evenly and then poured into a sample for curing. The curing conditions were 100℃ / 2h and 150℃ / 2h.

[0128] The performance tests of the cured specimens were the same as in Example 1, and the performance data are listed in Table 1 below.

[0129] Comparative Example 2

[0130] The preparation process is basically the same as in Example 1, except that in step two, the raw material ratio is replaced as follows:

[0131] After mixing 10 parts by weight of EUEP-DBD and 90 parts by weight of E51, add 26 parts by weight of DDM curing agent.

[0132] The performance tests of the cured specimens were the same as in Example 1, and the performance data are listed in Table 1 below.

[0133] Comparative Example 3

[0134] After mixing 100 parts by weight of glycerol triglycidyl ether (GTE) with 48 parts by weight of isophorone diamine (IPDA) curing agent, the mixture was poured into a sample for curing. The curing conditions were 100℃ / 1h, 120℃ / 2h, and 150℃ / 2h.

[0135] The performance tests of the cured specimens were the same as in Example 1, and the performance data are listed in Table 1 below.

[0136] Comparative Example 4

[0137] 100 parts by weight of 3,4-epoxycyclohexylmethyl 3,4-epoxycyclohexylcarboxylate (2021P), 148 parts by weight of methyl hexahydrophthalic anhydride (MHHPA) curing agent and 0.3 parts by weight of accelerator DMP-30 were mixed evenly and then poured into a sample for curing. The curing conditions were 100℃ / 1h, 120℃ / 2h and 150℃ / 2h.

[0138] The performance tests of the cured specimens were the same as in Example 1, and the performance data are listed in Table 1 below.

[0139] Comparative Example 5

[0140] The preparation process is basically the same as in Example 11, except that in step two, the raw material ratio is replaced as follows:

[0141] After mixing 10 parts by weight of EVC-DBD and 90 parts by weight of 2021P, add 144 parts by weight of MHHPA curing agent and 0.3 parts by weight of DMP-30.

[0142] The performance tests of the cured specimens were the same as in Example 1, and the performance data are listed in Table 1 below.

[0143] Table 1

[0144]

[0145] Table 1, comparing Examples 1-4 with Comparative Examples 1-2, shows that increasing the amount of EUEP-DBD added improves the tensile strength of the epoxy resin. However, the tensile strength of the pure EUEP-DBD cured product decreases slightly due to the reduced crosslinking density. Furthermore, as the EUEP-DBD content increases, the molding time for reprocessing gradually shortens, indicating that the improved borate ester structure increases the transesterification probability, leading to better epoxy resin recovery. Therefore, the tensile strength recovery rate gradually increases. Reprocessing is not possible without EUEP-DBD or with only a small amount (10 parts). Comparing the epoxy resin cured product with 50 parts EUEP-DBD, different molding temperatures reveal that increasing the molding temperature further shortens the reprocessing time without affecting the recovery efficiency.

[0146] As can be seen from Examples 5-10 and Comparative Example 3, the strength of the epoxy resin cured product gradually increases with the increase of AGE-DBD content. Among them, the pure AGE-DBD epoxy resin has the highest mechanical strength, reaching 76.2 MPa, and can be reprocessed in just 7 minutes of molding. Moreover, when the amount of AGE-DBD added is greater than or equal to 10 parts, the reprocessing function can be achieved while improving the tensile strength of the epoxy resin.

[0147] As can be seen from Examples 11-14 and Comparative Examples 4-5, the strength of the epoxy resin cured product gradually increases with the increase of EVC-DBD content. When the EVC-DBD content is greater than or equal to 20 parts, the reprocessing function can be achieved. Among them, pure EVC-DBD epoxy resin has the highest mechanical strength, reaching 55.3 MPa, and reprocessing can be achieved in just 26 minutes of molding. If the molding temperature is increased, the reprocessing time can be further shortened.

[0148] The above-described embodiments are preferred embodiments, but the scope of protection of the present invention is not limited thereto. Those skilled in the art can easily understand the spirit of the present invention based on the above embodiments and make different extensions and variations, but as long as they do not depart from the spirit of the present invention, they are all within the scope of protection of the present invention.

Claims

1. A method for preparing a recyclable and easily repairable epoxy resin, characterized in that, The recyclable and easily repairable epoxy resin is prepared by curing an epoxy resin with a borate ester structure or a mixed resin composed of an epoxy resin with a borate ester structure and a conventional epoxy resin. The structural formula of the epoxy resin containing the borate ester structure is shown in formula (Ⅰ) below: （Ⅰ）； In the formula, R is selected from one or more of the following formulas (II-1), (II-2), and (II-3); （Ⅱ-1） （Ⅱ-2） （Ⅱ-3）； The preparation method of the epoxy resin containing the borate ester structure specifically includes: Step 1: Mix 1-thioglycerol, epoxy monomer containing unsaturated double bonds, photoinitiator and solvent I evenly, and carry out mercapto-alkene click chemistry reaction; The epoxy monomer containing unsaturated double bonds is selected from one or more of eugenol glycidyl ether, allyl glycidyl ether, and 1,2-epoxy-4-vinylcyclohexane. Step 2: Add 1,4-phenylenediboric acid, desiccant and solvent II to the reactor, and obtain an epoxy resin with borate ester structure after dehydration condensation reaction; The conventional epoxy resin is selected from one or more of aromatic epoxy resins, aliphatic epoxy resins, and cycloaliphatic epoxy resins.

2. The method for preparing recyclable and easily repairable epoxy resin according to claim 1, characterized in that, In step 1: The molar ratio of 1-thioglycerol to epoxy monomers containing unsaturated double bonds is (0.95~1.05):1; The proportion of photoinitiator is 0.3~2.0 wt% based on the total mass of 1-thioglycerol and epoxy monomers containing unsaturated double bonds; Solvent I is selected from one or more of methanol, tetrahydrofuran, toluene, and acetone; The mass ratio of solvent I to the total mass of the two is (0.5~10):1, based on the total mass of 1-thioglycerol and epoxy monomers containing unsaturated double bonds.

3. The method for preparing recyclable and easily repairable epoxy resin according to claim 1, characterized in that, In step 1, the mercapto-alkene click chemistry reaction is carried out under ultraviolet light irradiation, the reaction temperature is 10~50℃, and the reaction time is 1~5h.

4. The method for preparing recyclable and easily repairable epoxy resin according to claim 1, characterized in that, In step 2: The molar amount of 1,4-phenylenediboric acid added is (48~52)% of the molar amount of 1-thioglycerol in step 1; The desiccant is selected from one or more of anhydrous sodium sulfate, anhydrous magnesium sulfate, and molecular sieves; The desiccant mass is (50~150) wt% of the sum of the masses of 1-thioglycerol, the epoxy monomer containing unsaturated double bonds, and 1,4-phenylenediboric acid. Solvent II is selected from one or more of methanol, tetrahydrofuran, toluene, and acetone; Based on the total mass of 1-thioglycerol, epoxy monomers containing unsaturated double bonds, and 1,4-phenylenediboric acid, the mass ratio of solvent II to the total mass of the three is (2~10):

1.

5. The method for preparing recyclable and easily repairable epoxy resin according to claim 1, characterized in that, In step 2, the temperature of the dehydration condensation reaction is 10~50℃ and the time is 12~48 h.

6. The method for preparing recyclable and easily repairable epoxy resin according to claim 1, characterized in that, A curing agent is also added to the raw materials.

7. A recyclable and easily repairable epoxy resin prepared by the method according to any one of claims 1 to 6.

8. A recycling process for recyclable and easily repairable epoxy resin according to claim 7, characterized in that, The recyclable and easily repairable epoxy resin is heated and molded at a temperature of 160~200℃, a pressure of 2~10 MPa, and a time of ≤240 min.

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