A degradable glycidylamine epoxy resin containing an aminal structure and a preparation method thereof

Abstract

The present invention discloses a degradable glycidylamine epoxy resin containing an aminal structure and a preparation method thereof. The degradable glycidylamine epoxy resin containing an aminal structure has the following molecular structure formula: #imgabs0# wherein R1 and R2 are one of an alkyl group, a cycloalkyl group, a heterocyclic group, a heterocycloalkyl group, an aromatic group, and a heteroaromatic group. The present invention introduces the aminal structure into the epoxy resin cross-linked structure through a cross-linking and curing reaction. The aminal synthesis is simple and green, and the nitrogen heterocyclic hexahydropyrimidine structure of the epoxy resin gives it high mechanical properties and thermal stability. It can be degraded under acidic conditions and still maintains a certain degree of stability under normal temperature and low-concentration acidic conditions. This has significant economic and environmental advantages for the recycling and reuse of thermosetting resins.

Description

Technical Field

[0001] The present invention relates to a degradable epoxy resin and a preparation method thereof, and in particular to a degradable glycidylamine epoxy resin containing an aminal structure and a preparation method thereof. Background Art

[0002] my country currently has the largest demand for epoxy resins globally, accounting for two-thirds of global usage. With the continued growth of my country's industrialization, demand for epoxy resins is also expected to increase. However, the three-dimensional cross-linked network formed after curing epoxy resins is relatively stable, making them difficult to effectively degrade and recycle. Only 1% of composite materials are recycled and reused annually.

[0003] Common methods such as energy recovery, physical crushing recovery, and chemical recovery all have problems such as high energy consumption, environmental pollution, and low added value of recycled products. Among them, energy recovery methods are difficult to achieve the recycling of fibers and resins, physical crushing can only achieve low-value recovery, and chemical methods often destroy the stable chemical bonds in the resin cross-linked network through high temperature and high pressure, catalysts or harsh chemical treatments, which can achieve the recovery of carbon fibers. However, due to the harsh degradation conditions, the chemical structure of the recycled carbon fibers is usually damaged to a certain extent, resulting in a certain decline in mechanical properties and thermal stability. At the same time, the harsh degradation conditions bring about a large amount of energy consumption, and the recycling and reuse of the resin cannot be achieved. A series of degradable epoxy resins have been developed, including epoxy resin systems containing imine bonds, disulfide bonds, acetal bonds, and hexahydrotriazine structures. The degradation and recovery of the resin can be achieved through stimulation means such as acid, alkali, heat, and solvation. However, the above chemical bonds also have problems such as low bond energy, poor stability, and harsh synthesis conditions, making them difficult to commercialize. Summary of the Invention

[0004] To address the above technical problems, the present invention provides a degradable glycidylamine epoxy resin containing an aminal structure and a degradation method thereof. The present invention introduces the aminal structure into the epoxy resin cross-linked structure through a cross-linking and curing reaction. The aminal synthesis is simple and environmentally friendly, and the nitrogen heterocyclic hexahydropyrimidine structure of the epoxy resin imparts high mechanical properties and thermal stability. The epoxy resin can be degraded under acidic conditions and retains a certain degree of stability at room temperature and low-concentration acidic conditions, offering significant economic and environmental advantages for the recycling and reuse of thermosetting resins.

[0005] The purpose of the present invention is achieved through the following technical solutions:

[0006] A degradable glycidylamine epoxy resin containing an aminal structure has the following molecular structure formula:

[0007]

[0008] In the formula, R1 and R2 are one of alkyl, cycloalkyl, heterocyclic, heterocycloalkyl, aromatic, and heteroaromatic groups.

[0009] A method for preparing the above-mentioned degradable glycidylamine epoxy resin containing an aminal structure is prepared according to the following reaction process:

[0010]

[0011] The specific preparation steps are as follows:

[0012] Step 1: Compound I and Compound II are subjected to an amine-aldehyde condensation reaction in a solvent. After the reaction is completed, the solvent is evaporated to dryness to obtain an aminal compound, wherein:

[0013] The structural formula of the compound I is The structural formula of compound II is The equivalent ratio of the two is 1:2~2.1;

[0014] The solvent is at least one of toluene, xylene, dichloromethane, methanol, ethanol, ethylene glycol, propanol, isopropanol, ethyl acetate, ether, tetrahydrofuran, chloroform, acetone, and acetonitrile;

[0015] The temperature of the amine-aldehyde condensation reaction is 0 to 80° C. and the time is 4 to 12 hours;

[0016] Step 2: mixing the aminal compound with epichlorohydrin to react, wherein:

[0017] The molar ratio of the aminal compound to epichlorohydrin is 1:3 to 10;

[0018] The reaction temperature is 50-80°C and the reaction time is 3-8 hours;

[0019] Step 3: After the reaction is completed, alkali metal hydroxide is added dropwise to carry out a desalting ring-closing reaction, wherein:

[0020] The alkali metal hydroxide is sodium hydroxide or potassium hydroxide, and the molar ratio of the aminal compound to the alkali metal hydroxide is 1:2.1-2.5;

[0021] The desalination ring-closing reaction temperature is 20-40°C and the time is 2-4 hours;

[0022] Step 4: After the desalting and ring-closing reaction is completed, extraction, water washing, liquid separation and vacuum removal of the solvent are performed to obtain a degradable glycidylamine epoxy resin containing an aminal structure.

[0023] A method for preparing a degradable thermosetting epoxy resin comprises the following steps:

[0024] The above-mentioned degradable glycidylamine epoxy resin containing an aminal structure is subjected to a heat curing cross-linking reaction with a curing agent to generate a degradable thermosetting epoxy resin, wherein:

[0025] The weight ratio of the degradable glycidylamine epoxy resin containing an aminal structure to the curing agent is 0.1 to 10:1;

[0026] The curing agent is one of an amine curing agent, an acid anhydride curing agent, an anionic polymerization curing agent, a cationic polymerization curing agent, and the like;

[0027] The temperature of the heat curing cross-linking reaction is 30 to 200°C;

[0028] The degradable thermosetting epoxy resin contains the following breakable cross-linking structure:

[0029]

[0030] The degradable glycidylamine epoxy resin containing an aminal structure can be used as a matrix to prepare a degradable epoxy resin composite material.

[0031] A method for degrading the above-mentioned degradable glycidylamine epoxy resin containing an aminal structure and the degradable epoxy resin composite material includes the following two technical solutions:

[0032] Technical Solution 1: Under heating conditions, amines and solvents are used as degradation liquids, and degradation of degradable glycidylamine epoxy resins containing aminal structures and degradable epoxy resin composites is achieved under mechanical stirring, wherein:

[0033] The heating temperature is 40 to 200° C. and the heating time is 1 to 12 hours;

[0034] The mass concentration of the amine in the solvent is 20 to 100%;

[0035] The amine is at least one of aliphatic amines (such as ethylenediamine, propylenediamine, 3-methylaminopropylamine, etc.), alicyclic amines (such as isophoronediamine, 1,3-cyclohexanedimethylamine, etc.), aromatic amines (such as m-phenylenediamine, 4,4-diaminodiphenylmethane, etc.), etc.;

[0036] The solvent is at least one of water, isopentane, n-pentane, petroleum ether, hexane, cyclohexane, cyclopentane, heptane, carbon tetrachloride, benzene, toluene, xylene, chlorobenzene, o-dichlorobenzene, dichloromethane, carbon tetrachloride, methanol, ethanol, ethylene glycol, propanol, isopropanol, butanol, isobutanol, tert-butanol, amyl alcohol, benzyl alcohol, ethyl acetate, ethyl ether, petroleum ether, isopropyl ether, tetrahydrofuran, chloroform, dioxane, pyridine, acetone, acetonitrile, N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, and dimethyl sulfoxide;

[0037] Technical Solution 2: Under heating conditions, acid and solvent are used as degradation liquids, and degradation of degradable glycidylamine epoxy resins containing aminal structures and degradable epoxy resin composites is achieved under mechanical stirring, wherein:

[0038] The heating temperature is 40 to 200° C. and the heating time is 1 to 12 hours;

[0039] The mass concentration of the acid in the solvent is 20-40%;

[0040] The acid is at least one of hydrochloric acid, sulfuric acid, acetic acid, p-toluenesulfonic acid, phosphotungstic acid, nitric acid, etc.;

[0041] The solvent is at least one of water, isopentane, n-pentane, petroleum ether, hexane, cyclohexane, cyclopentane, heptane, carbon tetrachloride, benzene, toluene, xylene, chlorobenzene, o-dichlorobenzene, dichloromethane, carbon tetrachloride, methanol, ethanol, ethylene glycol, propanol, isopropanol, butanol, isobutanol, tert-butanol, amyl alcohol, benzyl alcohol, ethyl acetate, ethyl ether, petroleum ether, isopropyl ether, tetrahydrofuran, chloroform, dioxane, pyridine, acetone, acetonitrile, N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, and dimethyl sulfoxide.

[0042] Compared with the prior art, the present invention has the following advantages:

[0043] 1. The present invention prepares a degradable epoxy resin through an amine-aldehyde condensation reaction, introducing an aminal structure into the epoxy resin cross-linked structure through a crosslinking and curing reaction. In the presence of an acid or amine and a solvent, the aminal structure undergoes a reverse reaction of the amine-aldehyde condensation or an exchange reaction, degrading to produce an aldehyde compound and an amino-terminated epoxy resin prepolymer, thereby achieving the purpose of degrading the thermosetting epoxy resin while maintaining excellent mechanical and heat resistance.

[0044] 2. The degradable thermosetting epoxy resin of the present invention is used in fiber-reinforced composite materials. Under the degradation conditions provided by the present invention, the thermosetting epoxy resin matrix in the fiber-reinforced composite material is degraded into a polymer with a smaller molecular weight. This polymer is soluble in an organic solvent. A simple separation process can be performed to separate the epoxy resin matrix from the fiber, thereby achieving the purpose of recovering and reusing the fiber reinforcement. Furthermore, the degradation and recovery method provided by the present invention under amine conditions allows the curing agent, epoxy resin prepolymer, and solvent to be recovered and reused, without generating secondary pollution to the environment, thus providing an economically viable industrial production route. DETAILED DESCRIPTION

[0045] The technical solution of the present invention is further described below with reference to the embodiments, but is not limited thereto. Any modification or equivalent replacement of the technical solution of the present invention that does not depart from the spirit and scope of the technical solution of the present invention should be included in the scope of protection of the present invention.

[0046] Example 1: Preparation of Epoxy Resin I

[0047] 35.40 g of terephthalaldehyde and 17.60 g of 3-methylaminopropylamine were dissolved in 250 mL of anhydrous ethanol respectively. After complete dissolution, the mixture was transferred to a 1000 mL round-bottom flask and heated under reflux for 4 hours. The solvent was then removed in vacuo, the mixture was washed with cold water, and dried to obtain an acetal amine compound with a yield of up to 93%.

[0048] 27.4 g of the above-mentioned aminal compound was dissolved in 250 mL of anhydrous methanol and slowly added dropwise to 92.5 g of epichlorohydrin. The reaction was carried out at 50 ° C. After the addition was completed, the reaction was continued for 6 h, and then the temperature was lowered to 40 ° C. 14 g of 30 wt% sodium hydroxide solution was added dropwise. After the addition was completed, the reaction was continued for 2 h. 500 mL of dichloromethane was added, and the organic phase was taken and washed with saturated brine until neutral. After removing the solvent in vacuo, an amber viscous liquid was obtained, which is epoxy resin I, with the following structural formula:

[0049]

[0050] Example 2: Preparation of Epoxy Resin II

[0051] 17.60 g of 3-methylaminopropylamine and 0.35 g of p-toluenesulfonic acid were dissolved in 300 mL of toluene, and 20.00 g of a 50 wt% aqueous solution of glutaraldehyde was added dropwise to the above solution. The mixture was heated to 85°C and refluxed for 8 h. The solvent was then removed in vacuo, the mixture was washed with cold water, and dried to obtain an acetal amine compound with a yield of up to 90%.

[0052] 26.8 g of the above-mentioned aminal compound was dissolved in 250 mL of anhydrous methanol and slowly added dropwise to 46.25 g of epichlorohydrin. The reaction was carried out at 60 ° C. After the addition was completed, the reaction was continued for 5 h, and then the temperature was lowered to 30 ° C. 14 g of 30 wt% sodium hydroxide solution was added dropwise. After the addition was completed, the reaction was continued for 2 h. 500 mL of dichloromethane was added, and the organic phase was taken and washed with saturated brine until neutral. After removing the solvent in vacuo, an amber viscous liquid was obtained, which is epoxy resin II, with the following structural formula:

[0053]

[0054] Example 3: Preparation of Degradable Thermosetting Resin I from Epoxy Resin I

[0055] At room temperature, 38.6 g of epoxy resin I prepared in Example 1 and 11.5 g of polyetheramine D230 were mixed and stirred thoroughly to remove air bubbles. The mixture was then transferred to a stainless steel mold pre-coated with a release agent. The mixture was heated at 60°C for 1 hour to gel and then heated at 100°C for 4 hours to fully cure. After cooling to room temperature, degradable epoxy resin I was obtained. The thermodynamic properties are shown in Table 1.

[0056] Table 1 Thermodynamic properties of degradable epoxy resin I

[0057] project performance Tensile strength (MPa) 73.2±3.2 Tensile modulus (GPa) 2.7±0.5 Tensile strain (%) 4.5±0.5 Flexural strength (MPa) 127.6±5.2 Flexural modulus (GPa) 3.3±0.5 Tg(℃) 78-86

[0058] Example 4: Preparation of Degradable Thermosetting Resin II from Epoxy Resin II

[0059] At room temperature, 38.0 g of epoxy resin II prepared in Example 2 and 20 g of polyetheramine D400 were mixed and stirred thoroughly to remove air bubbles. The mixture was then transferred to a stainless steel mold pre-coated with a release agent. The mixture was heated at 60°C for 1 hour to gel and then heated at 100°C for 4 hours to fully cure. After cooling to room temperature, the biodegradable epoxy resin II was obtained. The thermodynamic properties are shown in Table 2.

[0060] Table 2 Thermodynamic properties of degradable epoxy resin II

[0061] project performance Tensile strength (MPa) 67.2±2.7 Tensile modulus (GPa) 2.3±0.8 Tensile strain (%) 4.8±0.5 Flexural strength (MPa) 117.3±4.3 Flexural modulus (GPa) 2.8±0.6 Tg(℃) 73-80

[0062] Example 5: Degradation and recovery of degradable thermosetting resin 1

[0063] In a 50 mL glass bottle, 20 mg of the degradable thermosetting resin I prepared in Example 3, 3 mL of 1,3-propylenediamine, and 12 mL of DMSO were added and stirred at 60° C. for 2 h. The degradable resin was completely degraded to obtain a clear and transparent yellow solution with a recovery rate of up to 92%.

[0064] Example 6: Degradation and recovery of degradable thermosetting resin II

[0065] 20 mg of the degradable thermosetting resin II prepared in Example 4 and 20 mL of 3-methylaminopropylamine were added to a 50 mL glass bottle and stirred at 60° C. for 1 h. The degradable resin was completely degraded to obtain a clear and transparent yellow solution with a recovery rate of up to 100%.

[0066] Example 7: Degradation and recovery of degradable thermosetting resin II

[0067] In a 50 mL glass bottle, 20 mg of the degradable thermosetting resin II prepared in Example 4, 10 mL of hydrochloric acid, and 12 mL of THF were added and stirred at 60°C for 1 hour. This resulted in complete degradation, yielding a clear, transparent yellow solution. This solution was then neutralized with saturated potassium carbonate solution, and the degradation product was recovered with a recovery rate of up to 75%.

[0068] Example 8: Preparation and Degradation Recovery of Thermosetting Resin II-Carbon Fiber Composite Material

[0069] The T300-grade carbon fiber was impregnated with the degradable thermosetting resin II prepared in Example 4 and then laid out in 5 layers. The carbon fiber was placed in a metal mold and pressurized and cured using a hot press. The gel was heated at 60°C for 1 hour and then pressurized to 1 MPa. The carbon fiber composite material was completely cured by heating at 100°C for 4 hours to obtain the obtained carbon fiber composite material.

[0070] The composite material was immersed in a mixed solution of hydrochloric acid / THF and stirred at 60°C for 3 hours to completely degrade it, obtaining a yellow solution and recycled carbon fibers with a clean surface.

Claims

1. A degradable glycidylamine epoxy resin containing an aminal structure, characterized in that The epoxy resin has the following molecular structure formula: In the formula, R1 is one of phenylene and pentylene, and R2 is methyl.

2. A method for preparing the degradable glycidylamine epoxy resin containing an aminal structure according to claim 1, characterized in that The method comprises the following steps: Step 1: Compound I and Compound II are subjected to an amine-aldehyde condensation reaction in a solvent. After the reaction is completed, the solvent is evaporated to dryness to obtain an aminal compound, wherein: The structural formula of the compound I is The structural formula of compound II is , the equivalent ratio of the two is 1:2~2.1; The amine-aldehyde condensation reaction is carried out at a temperature of 0 to 80° C. and for a time of 4 to 12 hours; Step 2: mixing the aminal compound with epichlorohydrin to react, wherein: The molar ratio of the aminal compound to epichlorohydrin is 1:3-10; The reaction temperature is 50-80°C and the reaction time is 3-8 hours; Step 3: After the reaction is completed, alkali metal hydroxide is added dropwise to carry out a desalting ring-closing reaction, wherein: The molar ratio of the aminal compound to the alkali metal hydroxide is 1:2.1-2.5; The desalination ring-closing reaction temperature is 20-40°C and the time is 2-4 hours; Step 4: After the desalting and ring-closing reaction is completed, extraction, water washing, liquid separation and vacuum removal of the solvent are performed to obtain a degradable glycidylamine epoxy resin containing an aminal structure.

3. The method for preparing the degradable glycidylamine epoxy resin containing an aminal structure according to claim 2, characterized in that The solvent is at least one of toluene, xylene, dichloromethane, methanol, ethanol, ethylene glycol, propanol, isopropanol, ethyl acetate, ether, tetrahydrofuran, chloroform, acetone, and acetonitrile; and the alkali metal hydroxide is sodium hydroxide or potassium hydroxide.

4. A method for preparing a degradable thermosetting epoxy resin, characterized in that The method comprises the following steps: subjecting the degradable glycidylamine epoxy resin containing an aminal structure according to claim 1 to a heat-curing cross-linking reaction with a curing agent to generate a degradable thermosetting epoxy resin, wherein: The weight ratio of the degradable glycidylamine epoxy resin containing an aminal structure to the curing agent is 0.1 to 10:1; The temperature of the heat curing cross-linking reaction is 30-200°C; The degradable thermosetting epoxy resin contains the following breakable cross-linking structure: .

5. The method for preparing a degradable thermosetting epoxy resin according to claim 4, wherein The curing agent is one of an amine curing agent, an acid anhydride curing agent, an anionic polymerization curing agent, and a cationic polymerization curing agent.

6. A method for degrading a degradable glycidylamine epoxy resin containing an aminal structure prepared by the method according to any one of claims 4 to 5, characterized in that The method comprises the following steps: using amine and solvent as degradation liquids under heating conditions, and achieving degradation of a degradable glycidylamine epoxy resin containing an aminal structure and a degradable epoxy resin composite material under mechanical stirring, wherein: The heating temperature is 40-200°C and the heating time is 1-12 hours; The mass concentration of the amine in the solvent is 20-100%.

7. The method for degrading a degradable glycidylamine epoxy resin containing an aminal structure according to claim 6, characterized in that The amine is at least one of aliphatic amines, alicyclic amines, and aromatic amines; and the solvent is at least one of water, isopentane, n-pentane, petroleum ether, hexane, cyclohexane, cyclopentane, heptane, carbon tetrachloride, benzene, toluene, xylene, chlorobenzene, o-dichlorobenzene, dichloromethane, carbon tetrachloride, methanol, ethanol, ethylene glycol, propanol, isopropanol, butanol, isobutanol, tert-butanol, amyl alcohol, benzyl alcohol, ethyl acetate, ethyl ether, petroleum ether, isopropyl ether, tetrahydrofuran, chloroform, dioxane, pyridine, acetone, acetonitrile, N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, and dimethyl sulfoxide.

8. A method for degrading a degradable glycidylamine epoxy resin containing an aminal structure prepared by the method according to any one of claims 4 to 5, characterized in that The method comprises the following steps: using an acid and a solvent as degradation liquid under heating conditions, and achieving degradation of a degradable glycidylamine epoxy resin containing an aminal structure and a degradable epoxy resin composite material under mechanical stirring, wherein: The heating temperature is 40-200°C and the heating time is 1-12 hours; The mass concentration of the acid in the solvent is 20-40%.

9. The method for degrading a degradable glycidylamine epoxy resin containing an aminal structure according to claim 8, characterized in that The acid is at least one of hydrochloric acid, sulfuric acid, acetic acid, p-toluenesulfonic acid, phosphotungstic acid, and nitric acid; and the solvent is at least one of water, isopentane, n-pentane, petroleum ether, hexane, cyclohexane, cyclopentane, heptane, carbon tetrachloride, benzene, toluene, xylene, chlorobenzene, o-dichlorobenzene, dichloromethane, carbon tetrachloride, methanol, ethanol, ethylene glycol, propanol, isopropanol, butanol, isobutanol, tert-butanol, amyl alcohol, benzyl alcohol, ethyl acetate, ethyl ether, petroleum ether, isopropyl ether, tetrahydrofuran, chloroform, dioxane, pyridine, acetone, acetonitrile, N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, and dimethyl sulfoxide.

10. Use of the degradable thermosetting epoxy resin prepared by the method of claim 5 as a matrix in a degradable epoxy resin composite material.

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