Degradable epoxy resin based on diimine bond vanillin as well as preparation method and application of degradable epoxy resin

Abstract

The invention belongs to the technical field of degradable and recyclable epoxy resin, and discloses degradable epoxy resin based on diimine bond vanillin as well as a preparation method and application of the degradable epoxy resin. The epoxy resin chain extender containing the biimine bond bio-based is prepared through a Schiff base reaction, the epoxy resin chain extender and epoxy resin are subjected to ring opening, finally, the epoxy resin chain extender and the curing agent containing amido are subjected to high-temperature curing, and the degradable and recyclable thermosetting epoxy resin and the degradable carbon fiber composite material which have excellent mechanical properties are prepared. The problem of recycling the thermosetting epoxy resin and the composite material is solved, sustainable utilization of resources is realized, and environmental pollution is reduced.

Description

Technical Field

[0001] This invention belongs to the field of biodegradable and recyclable epoxy resin technology, and specifically relates to a biodegradable epoxy resin based on bisimine-linked vanillin, its preparation method and application. Background Technology

[0002] Traditional polymer materials are mainly divided into two categories: thermoplastics and thermosettings. Thermoplastic materials, due to the relatively weak non-covalent bonds between molecular chains, can be repeatedly processed and recycled by heating and melting or dissolving in solvents, but their heat resistance and structural stability are relatively limited. Thermosetting materials, on the other hand, form a three-dimensional cross-linked network structure through covalent bonds, giving them excellent mechanical strength, temperature resistance, and chemical stability. However, this irreversible cross-linked structure also makes them difficult to degrade or remodel after disposal. It requires cumbersome methods such as high temperature conditions, hot air flow, supercritical and subcritical fluids, and solvation effects to break down the cross-linked structure of epoxy resins, causing the resin molecular chains to decompose into volatile or soluble small molecules.

[0003] Carbon fiber composites prepared from thermosetting epoxy resins are widely used in high-end fields such as wind turbine blades, aerospace, and the automotive industry due to their lightweight, excellent dimensional stability, mechanical properties, and solvent resistance. However, their permanent cross-linked structure makes them difficult to recycle after use, leading to traditional disposal methods such as landfill and incineration, which not only waste valuable resources but also exacerbate the environmental burden. According to existing research, the degradation and recycling of epoxy resins requires harsh reaction conditions, resulting in uncontrollable degradation products, low efficiency, and significant decline in the performance, structure, and order of the recycled composite materials. Introducing easily fractured groups into epoxy resins weakens the material's mechanical properties and heat resistance, thus affecting its practical applications. Summary of the Invention

[0004] In order to overcome the shortcomings and deficiencies of existing technologies, such as the need for harsh conditions and low efficiency in epoxy resin degradation, the primary objective of this invention is to provide a method for preparing a biodegradable epoxy resin based on bisimine-linked vanillin.

[0005] Another object of the present invention is to provide a biodegradable epoxy resin based on bisimine-bonded vanillin prepared by the above preparation method.

[0006] Another object of the present invention is to provide an application of the above-mentioned biodegradable epoxy resin based on diimine-bonded vanillin.

[0007] The objective of this invention is achieved through the following technical solution:

[0008] A method for preparing a biodegradable epoxy resin based on bisimine-bonded vanillin includes the following steps:

[0009] S1. Vanillin, diamine monomer and organic solvent are reacted under stirring to obtain a yellow precipitate, which is then purified to obtain a chain extender containing a bio-based double imine bond.

[0010] S2. The chain extender containing biimine bonds, epoxy resin, catalyst and organic solvent obtained in step S1 are subjected to a ring-opening reaction under stirring to obtain an epoxy prepolymer containing imine bonds.

[0011] S3. Add the diamine monomer to the epoxy prepolymer containing imine bonds obtained in step S2, stir evenly, and remove bubbles under vacuum at room temperature to obtain the blend.

[0012] S4. Pour the blend into a mold and cure it to obtain a biodegradable epoxy resin based on bisimine-bonded vanillin.

[0013] The diamine monomer mentioned in step S1 is one or more of 1,2-cyclohexanediamine, 1,3-cyclohexanediamine, p-phenylenediamine, 1,4-cyclohexanediamine, 1,6-hexanediamine, 1,7-diaminoheptane, 1,8-octanediamine, 1,10-diaminodecane, and 1,3-propanediamine.

[0014] The organic solvent is one or more of the following: water, methanol, ethanol, isopropanol, tert-butanol, n-butanol, diethyl ether, tetrahydrofuran, 1,4-dioxane, acetone, butanone, methyl isobutyl ketone, cyclohexanone, ethyl acetate, methyl acetate, butyl acetate, isopropyl acetate, toluene, xylene, ethylbenzene, n-hexane, cyclohexane, petroleum ether, dichloromethane, trichloromethane, carbon tetrachloride, 1,2-dichloroethane, N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, dimethyl sulfoxide, and dimethyl sulfoxide acetonitrile.

[0015] The molar ratio of vanillin to diamine monomer is 1:1 to 3:1;

[0016] The reaction temperature is 30-70℃, and the reaction time is 1-12 hours.

[0017] The epoxy resin mentioned in step S2 is one or more of E-51, E-44, E-20, E-12 and F-51;

[0018] The catalyst is one or more of tetramethylammonium bromide, tetrapropylammonium bromide, benzyltriphenylphosphine bromide, tetrabutylammonium bromide, tetraethylammonium bromide, triphenylphosphine, and cobalt(II) acetylacetonate, and its amount is 0.1 to 2 wt% of the total mass of epoxy resin and chain extender containing biimine bond bio-based groups;

[0019] The organic solvent is one or more of the following: water, methanol, ethanol, isopropanol, tert-butanol, n-butanol, diethyl ether, tetrahydrofuran, 1,4-dioxane, acetone, butanone, methyl isobutyl ketone, cyclohexanone, ethyl acetate, methyl acetate, butyl acetate, isopropyl acetate, toluene, xylene, ethylbenzene, n-hexane, cyclohexane, petroleum ether, dichloromethane, trichloromethane, carbon tetrachloride, 1,2-dichloroethane, N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, dimethyl sulfoxide, and dimethyl sulfoxide acetonitrile.

[0020] The molar ratio of the bio-based chain extender containing double imine bonds to the bio-based chain extender is 1:3 to 3:1;

[0021] The reaction is carried out at 130–180°C for 1–10 hours.

[0022] The diamine curing agent mentioned in step S3 is one or more of 1,2-cyclohexanediamine, 1,3-cyclohexanediamine, p-phenylenediamine, 1,4-cyclohexanediamine, 4,4'-diaminodiphenylmethane, 1,6-hexanediamine, 1,7-diaminoheptane, 1,8-octanediamine, 1,10-diaminodecane, and 1,3-propanediamine.

[0023] The molar ratio of the imine-containing epoxy prepolymer to the diamine monomer is 1:1 to 3:1;

[0024] The vacuum level of the vacuum pump is less than or equal to 0.01 MPa.

[0025] The curing process described in step S4 involves prepolymerizing at 60-100℃ for 0.5-5 hours, then curing at 100-120℃ for 1-10 hours, then curing at 130-150℃ for 1-10 hours, and finally curing at 160-180℃ for 1-10 hours.

[0026] A biodegradable epoxy resin based on bisimine-linked vanillin, prepared by the above-described method, wherein the tensile strength of the biodegradable epoxy resin based on bisimine-linked vanillin reaches 70-110 MPa. d5％ When the temperature reaches 320℃ or above, the chemical recovery efficiency can reach over 100%.

[0027] The above-mentioned application of biodegradable epoxy resin based on bisimine-bonded vanillin in biodegradable epoxy resin composites.

[0028] A biodegradable epoxy resin composite material made from the above-mentioned biodegradable epoxy resin based on bisimine-linked vanillin, wherein the biodegradable epoxy resin composite material is prepared from a biodegradable epoxy resin based on bisimine-linked vanillin, a reinforcing agent, and an organic solvent;

[0029] The reinforcing material is one or more of the following: carbon fiber, glass fiber, natural fiber, chemical fiber, fabric made of fiber material, carbon nanomaterial, boron nitride nanomaterial, metal nanoparticle, metal oxide nanoparticle, and organic nanoparticle.

[0030] The organic solvent is one or more of the following: water, methanol, ethanol, isopropanol, tert-butanol, n-butanol, diethyl ether, tetrahydrofuran, 1,4-dioxane, acetone, butanone, methyl isobutyl ketone, cyclohexanone, ethyl acetate, methyl acetate, butyl acetate, isopropyl acetate, toluene, xylene, ethylbenzene, n-hexane, cyclohexane, petroleum ether, dichloromethane, chloroform, carbon tetrachloride, 1,2-dichloroethane, N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, dimethyl sulfoxide, and dimethyl sulfoxide acetonitrile.

[0031] A method for degrading the above-mentioned biodegradable epoxy resin or biodegradable epoxy resin composite material based on bisimine-linked vanillin, the method comprising the following steps: at room temperature or under heating conditions, using a mixture of a weak acid solution and a solvent as a degradation solution, adding the biodegradable epoxy resin or biodegradable epoxy resin composite material based on bisimine-linked vanillin, and under stirring conditions, achieving the degradation of the biodegradable epoxy resin or biodegradable epoxy resin composite material based on bisimine-linked vanillin;

[0032] The molar concentration of the weak acid solution is 0.1–5 mol / L; the volume ratio of the weak acid solution to the solvent is 1:5–1:20; the heating temperature is 0–100°C; and the heating time is 1–24 h.

[0033] The weak acid solution is one or more of the following: hydrochloric acid, nitric acid, sulfuric acid, acetic acid, hydrofluoric acid, lactic acid, formic acid, propionic acid, citric acid, p-toluenesulfonic acid, sulfurous acid, phosphoric acid, and perchloric acid.

[0034] The solvent is one or more selected from water, methanol, ethanol, isopropanol, tert-butanol, n-butanol, diethyl ether, tetrahydrofuran, 1,4-dioxane, acetone, butanone, methyl isobutyl ketone, cyclohexanone, ethyl acetate, methyl acetate, butyl acetate, isopropyl acetate, toluene, xylene, ethylbenzene, n-hexane, cyclohexane, petroleum ether, dichloromethane, chloroform, carbon tetrachloride, 1,2-dichloroethane, N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, dimethyl sulfoxide, and dimethyl sulfoxide acetonitrile.

[0035] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0036] (1) Vanillin, as an aromatic lignin-derived compound, accounts for up to 15% of the content in terrestrial plants, which makes it not only abundant in source but also more economical in cost compared to other bio-based monomers; in addition, the aromatic ring in its molecular structure gives the material better thermal stability and mechanical properties.

[0037] (2) This invention prepares a bi-imine bond bio-based epoxy resin chain extender by reacting vanillin with a diamine monomer via a Schiff base reaction. This chain extender then undergoes ring-opening with the epoxy resin, followed by high-temperature curing with a diamine curing agent to synthesize a biodegradable epoxy resin based on bi-imine bond vanillin. Because the imine bonds introduced in this invention have higher bond energies than other weak chemical bonds, they are less prone to breakage under external loads and high-temperature environments. Furthermore, the diamine curing agent forms a stable cross-linking network, spatially restricting and inhibiting the activity of the imine bonds. This allows the mechanical properties of the biodegradable epoxy resin to be comparable to, or even surpass, those of traditional epoxy resins. The system is rich in aromatic structures, giving the epoxy resin excellent heat resistance. Therefore, the prepared epoxy resin possesses superior mechanical properties and thermal stability.

[0038] (3) Imine bonds are highly sensitive in acidic or amine solvents, and their dynamic structure can be reversibly dissociated through bond exchange kinetics or equilibrium shift. Under acidic or amine solvent conditions, the imine crosslinking structure in this epoxy resin undergoes a reverse amine-aldehyde condensation reaction, degrading into a prepolymer, thereby achieving the degradation of the thermosetting epoxy resin. Simultaneously, when this degradable thermosetting epoxy resin is applied to fiber-reinforced composites, under specific degradation conditions, the matrix is ​​degraded into a low-molecular-weight linear polymer. This polymer is soluble in organic solvents, and the resin matrix can be easily separated from the fiber, thus achieving fiber recycling and reuse.

[0039] (4) Upon testing, the tensile strength of the biodegradable thermosetting epoxy resin prepared in this invention reaches 70–110 MPa. d5％ At temperatures above 320°C, the chemical recovery efficiency of biodegradable thermosetting epoxy resins can reach over 100%. Attached Figure Description

[0040] Figure 1 This is a tensile curve comparing the mechanical properties of the thermosetting epoxy resin prepared in Example 3 of the present invention with those of Comparative Example 1.

[0041] Figure 2 This is a tensile curve comparing the mechanical properties of the epoxy resin obtained in Example 19 of this invention after recycling with the original resin in Example 3.

[0042] Figure 3 This is a tensile curve comparing the mechanical properties of virgin carbon fiber filaments and recycled carbon fiber filaments. Detailed Implementation

[0043] The present invention will be further described in detail below with reference to the embodiments and accompanying drawings, but the embodiments of the present invention are not limited thereto.

[0044] Example 1

[0045] A biodegradable epoxy resin based on bisimine-linked vanillin, the preparation method of which includes the following steps:

[0046] (1) Dissolve 30.4g vanillin and 11.2g 1,2-cyclohexanediamine in 200mL of anhydrous ethanol, mix and heat and keep warm at 40℃, stir at high speed for 2h to obtain a yellow precipitate. After standing, perform solid-liquid separation, collect the solid, wash with anhydrous ethanol 3 times, and then dry in an oven at 60℃ to obtain a chain extender containing a bio-based double imine bond.

[0047] (2) Dissolve 38.0g of a chain extender containing a bio-based double imine bond, 78.4g of E-51 and 1.0g of tetrabutylammonium bromide in 200mL of 1,4-dioxane, mix and heat at 140℃, and stir at high speed for 1h to obtain an epoxy prepolymer containing an imine bond.

[0048] (3) The obtained epoxy prepolymer containing imine bonds was stirred with 5.7g of 1,2-cyclohexanediamine to obtain a blend, and the blend was degassed under a vacuum of 0.01Mpa at room temperature.

[0049] (4) Pour the blend after removing the air bubbles into a mold, prepolymerize at 60℃ for 0.5h, cure at 100℃ for 1h, cure at 130℃ for 1h, and cure at 160℃ for 2h to obtain a biodegradable epoxy resin based on bisimine-bonded vanillin.

[0050] Example 2

[0051] A biodegradable epoxy resin based on bisimine-linked vanillin, the preparation method of which includes the following steps:

[0052] (1) Dissolve 30.4g vanillin and 11.2g 1,3-cyclohexanediamine in 200mL of anhydrous ethanol, mix and heat and keep warm at 40℃, stir at high speed for 2h to obtain a yellow precipitate. After standing, perform solid-liquid separation, collect the solid, wash with anhydrous ethanol 3 times, and then dry in an oven at 60℃ to obtain a chain extender containing a bio-based double imine bond.

[0053] (2) Dissolve 38.0g of a chain extender containing a bio-based double imine bond, 78.4g of E-51 and 0.1g of tetrabutylammonium bromide in 200mL of N,N-dimethylformamide, heat and keep at 160℃, and stir at high speed for 1h to obtain an epoxy prepolymer containing an imine bond.

[0054] (3) The obtained epoxy prepolymer containing imine bonds was stirred with 5.7g of 1,3-cyclohexanediamine to obtain a blend, and the blend was degassed under a vacuum of 0.01Mpa at room temperature.

[0055] (4) Pour the bubble-free blend into a mold, prepolymerize at 70℃ for 0.5h, cure at 100℃ for 1.5h, cure at 130℃ for 1h, and cure at 160℃ for 2.5h to obtain a biodegradable epoxy resin based on bisimine-bonded vanillin.

[0056] Example 3

[0057] A biodegradable epoxy resin based on bisimine-linked vanillin, the preparation method of which includes the following steps:

[0058] (1) Dissolve 30.4g vanillin and 10.8g p-phenylenediamine in 200mL tetrahydrofuran, mix and heat and keep warm at 50℃, stir at high speed for 2h to obtain a yellow precipitate. After standing, perform solid-liquid separation, collect the solid, wash with tetrahydrofuran 3 times, and then dry in an oven at 60℃ to obtain a chain extender containing a bio-based double imine bond.

[0059] (2) 37.6g of a chain extender containing a bio-based double imine bond, 78.4g of E-51 and 1.0g of benzyltriphenylphosphine bromide were dissolved in 200mL of N,N-dimethylformamide, heated and kept at 160℃, and stirred at high speed for 1.5h to obtain an epoxy prepolymer containing an imine bond.

[0060] (3) The obtained epoxy prepolymer containing imine bonds was stirred with 9.9g of 4,4'-diaminodiphenylmethane to obtain a blend, and the blend was degassed under a vacuum of 0.01Mpa at room temperature.

[0061] (4) Pour the blend after removing the air bubbles into a mold, prepolymerize at 90℃ for 0.5h, cure at 100℃ for 2h, cure at 130℃ for 2h, and cure at 160℃ for 2h to obtain a biodegradable epoxy resin based on bisimine-bonded vanillin.

[0062] Example 4

[0063] A biodegradable epoxy resin based on bisimine-linked vanillin, the preparation method of which includes the following steps:

[0064] (1) Dissolve 30.4g vanillin and 10.8g p-phenylenediamine in 200mL tetrahydrofuran, mix and heat and keep warm at 50℃, stir at high speed for 2h to obtain a yellow precipitate. After standing, perform solid-liquid separation, collect the solid, wash with tetrahydrofuran 3 times, and then dry in an oven at 80℃ to obtain a chain extender containing a bio-based double imine bond.

[0065] (2) 37.6g of a chain extender containing a bio-based double imine bond, 78.4g of E-51 and 1.0g of benzyltriphenylphosphine bromide were dissolved in 200mL of N,N-dimethylacetamide, heated and kept at 150℃, and stirred at high speed for 1.5h to obtain an epoxy prepolymer containing an imine bond.

[0066] (3) The obtained epoxy prepolymer containing imine bonds was stirred with 5.4g of p-phenylenediamine to obtain a blend, and the blend was degassed under a vacuum of 0.01Mpa at room temperature.

[0067] (4) Pour the blend after removing the air bubbles into a mold, prepolymerize at 70℃ for 0.5h, cure at 110℃ for 1h, cure at 140℃ for 1h, and cure at 170℃ for 2h to obtain a biodegradable epoxy resin based on bisimine-bonded vanillin.

[0068] Example 5

[0069] A biodegradable epoxy resin based on bisimine-linked vanillin, the preparation method of which includes the following steps:

[0070] (1) Dissolve 30.4g vanillin and 11.6g 1,6-hexanediamine in 200mL isopropanol, mix and heat and keep warm at 40℃, stir at high speed for 2h to obtain a yellow precipitate. After standing, perform solid-liquid separation, collect the solid, wash with anhydrous ethanol 3 times, and then dry in a 60℃ oven to obtain a chain extender containing a bio-based double imine bond.

[0071] (2) Dissolve 38.4g of a chain extender containing a bio-based double imine bond, 78.4g of E-51 and 1.0g of triphenylphosphine in 200mL of dimethyl sulfoxide, mix and heat at 140℃, and stir at high speed for 1h to obtain an epoxy prepolymer containing an imine bond.

[0072] (3) The obtained epoxy prepolymer containing imine bonds was stirred with 5.8g of 1,6-hexanediamine to obtain a blend, and the blend was degassed under a vacuum of 0.01Mpa at room temperature.

[0073] (4) Pour the blend after removing the air bubbles into a mold, prepolymerize at 60℃ for 0.5h, cure at 100℃ for 1h, cure at 130℃ for 1h, and cure at 160℃ for 2h to obtain a biodegradable epoxy resin based on bisimine-bonded vanillin.

[0074] Example 6

[0075] A biodegradable epoxy resin based on bisimine-linked vanillin, the preparation method of which includes the following steps:

[0076] (1) Dissolve 30.4g vanillin and 13.0g 1,7-diaminoheptane in 200mL of anhydrous ethanol, mix and heat and keep warm at 55℃, stir at high speed for 4h to obtain a yellow precipitate. After standing, perform solid-liquid separation, collect the solid, wash with anhydrous ethanol 3 times, and then dry in an oven at 70℃ to obtain a chain extender containing a bio-based double imine bond.

[0077] (2) Dissolve 39.8g of a chain extender containing a bio-based double imine bond, 78.4g of E-51 and 1.0g of cobalt(II) acetylacetonate in 200mL of 1,4-dioxane, heat and keep at 155℃, and stir at high speed for 1h to obtain an epoxy prepolymer containing an imine bond.

[0078] (3) The obtained epoxy prepolymer containing imine bonds was stirred with 6.5g of 1,7-diaminoheptane to obtain a blend, and the blend was degassed under a vacuum of 0.01Mpa at room temperature.

[0079] (4) Pour the blend after removing the air bubbles into a mold, prepolymerize at 90℃ for 1 hour, cure at 100℃ for 1 hour, cure at 130℃ for 1 hour, and cure at 160℃ for 2 hours to obtain a biodegradable epoxy resin based on bisimine vanillin.

[0080] Example 7

[0081] A biodegradable epoxy resin based on bisimine-linked vanillin, the preparation method of which includes the following steps:

[0082] (1) Dissolve 30.4g vanillin and 17.2g 1,10-diaminodecane in 200mL of anhydrous ethanol, mix and heat and keep warm at 40℃, stir at high speed for 2h to obtain a yellow precipitate. After standing, perform solid-liquid separation, collect the solid, wash with anhydrous ethanol 3 times, and then dry in an oven at 60℃ to obtain a chain extender containing a bio-based double imine bond.

[0083] (2) 41.2g of a chain extender containing a double imine bond bio-based, 78.4g of E-51 and 1.0g of benzyltriphenylphosphine bromide were dissolved in 200mL of isopropyl acetate, heated and kept at 160℃, and stirred at high speed for 1h to obtain an epoxy prepolymer containing an imine bond.

[0084] (3) The obtained epoxy prepolymer containing imine bonds was stirred with 8.6g of 1,10-diaminodecane to obtain a blend, and the blend was degassed under a vacuum of 0.01Mpa at room temperature.

[0085] (4) Pour the blend after removing the air bubbles into a mold, prepolymerize at 85℃ for 0.5h, cure at 100℃ for 1h, cure at 130℃ for 1h, and cure at 160℃ for 2h to obtain a biodegradable epoxy resin based on bisimine-bonded vanillin.

[0086] Example 8

[0087] A biodegradable epoxy resin based on bisimine-linked vanillin, the preparation method of which includes the following steps:

[0088] (1) Dissolve 30.4g vanillin and 7.4g 1,3-propanediamine in 200mL of anhydrous ethanol, mix and heat and keep warm at 40℃, stir at high speed for 2h to obtain a yellow precipitate. After standing, perform solid-liquid separation, collect the solid, wash with anhydrous ethanol 3 times, and then dry in an oven at 60℃ to obtain a chain extender containing a bio-based double imine bond.

[0089] (2) Dissolve 34.2g of a chain extender containing a bio-based double imine bond, 78.4g of E-51 and 1.0g of tetrabutylammonium bromide in 200mL of dimethyl sulfoxide acetonitrile, mix and heat at 140℃, and stir at high speed for 1h to obtain an epoxy prepolymer containing an imine bond.

[0090] (3) The obtained epoxy prepolymer containing imine bonds was stirred with 3.7g of 1,3-propanediamine to obtain a blend, and the blend was degassed under a vacuum of 0.01Mpa at room temperature.

[0091] (4) Pour the blend after removing the air bubbles into a mold, prepolymerize at 60℃ for 0.5h, cure at 100℃ for 1h, cure at 130℃ for 1h, and cure at 160℃ for 2h to obtain a biodegradable epoxy resin based on bisimine-bonded vanillin.

[0092] Example 9

[0093] A biodegradable epoxy resin based on bisimine-linked vanillin, the preparation method of which includes the following steps:

[0094] (1) Dissolve 30.4g vanillin and 11.4g 1,4-cyclohexanediamine in 200mL of anhydrous ethanol, mix and heat and keep warm at 40℃, stir at high speed for 2h to obtain a yellow precipitate. After standing, perform solid-liquid separation, collect the solid, wash with anhydrous ethanol 3 times, and then dry in an oven at 60℃ to obtain a chain extender containing a bio-based double imine bond.

[0095] (2) 38.2g of a chain extender containing a double imine bond bio-based, 78.4g of E-51 and 1g of benzyltriphenylphosphine bromide were mixed in 200mL of N-methylpyrrolidone, heated and kept at 150℃, and stirred at high speed for 1h to obtain an epoxy prepolymer containing an imine bond.

[0096] (3) The obtained epoxy prepolymer containing imine bonds was stirred with 5.7g of 1,4-cyclohexanediamine to obtain a blend, and the blend was degassed under a vacuum of 0.01Mpa at room temperature.

[0097] (4) Pour the blend after removing the air bubbles into a mold, prepolymerize at 60℃ for 0.5h, cure at 100℃ for 1h, cure at 130℃ for 1h, and cure at 160℃ for 2h to obtain a biodegradable epoxy resin based on bisimine-bonded vanillin.

[0098] Example 10

[0099] A biodegradable epoxy resin based on bisimine-linked vanillin, the preparation method of which includes the following steps:

[0100] (1) Dissolve 30.4g vanillin and 11.4g 1,4-cyclohexanediamine in 200mL of anhydrous ethanol, mix and heat and keep warm at 40℃, stir at high speed for 2h to obtain a yellow precipitate. After standing, perform solid-liquid separation, collect the solid, wash with anhydrous ethanol 3 times, and then dry in an oven at 60℃ to obtain a chain extender containing a bio-based double imine bond.

[0101] (2) 38.2g of a chain extender containing a double imine bond bio-based, 78.4g of E-51 and 1g of benzyltriphenylphosphine bromide were mixed in 200mL of N-methylpyrrolidone, heated and kept at 150℃, and stirred at high speed for 1h to obtain an epoxy prepolymer containing an imine bond.

[0102] (3) The obtained epoxy prepolymer containing imine bonds was stirred with 5.7g of 1,4-cyclohexanediamine to obtain a blend, and the blend was degassed under a vacuum of 0.01Mpa at room temperature.

[0103] (4) Pour the blend after removing the air bubbles into a mold, prepolymerize at 60℃ for 0.5h, cure at 100℃ for 1h, cure at 130℃ for 1h, and cure at 160℃ for 2h to obtain a biodegradable epoxy resin based on bisimine-bonded vanillin.

[0104] Example 11

[0105] A biodegradable epoxy resin based on bisimine-linked vanillin, the preparation method of which includes the following steps:

[0106] (1) Dissolve 30.4g vanillin and 11.2g 1,2-cyclohexanediamine in 200mL of anhydrous ethanol, mix and heat and keep warm at 40℃, stir at high speed for 2h to obtain a yellow precipitate. After standing, perform solid-liquid separation, collect the solid, wash with anhydrous ethanol 3 times, and then dry in an oven at 60℃ to obtain a chain extender containing a bio-based double imine bond.

[0107] (2) Dissolve 38.0g of a chain extender containing a bio-based double imine bond, 78.4g of E-51 and 1.0g of tetrabutylammonium bromide in 200mL of 1,4-dioxane, mix and heat at 140℃, and stir at high speed for 1h to obtain an epoxy prepolymer containing an imine bond.

[0108] (3) The obtained epoxy prepolymer containing imine bonds was stirred with 3.7g of 1,3-propanediamine to obtain a blend, and the blend was degassed under a vacuum of 0.01Mpa at room temperature.

[0109] (4) Pour the blend after removing the air bubbles into a mold, prepolymerize at 60℃ for 0.5h, cure at 100℃ for 1h, cure at 130℃ for 1h, and cure at 160℃ for 2h to obtain a biodegradable epoxy resin based on bisimine-bonded vanillin.

[0110] Example 12

[0111] A biodegradable epoxy resin based on bisimine-linked vanillin, the preparation method of which includes the following steps:

[0112] (1) Dissolve 30.4g vanillin and 11.2g 1,3-cyclohexanediamine in 200mL of anhydrous ethanol, mix and heat and keep warm at 40℃, stir at high speed for 2h to obtain a yellow precipitate. After standing, perform solid-liquid separation, collect the solid, wash with anhydrous ethanol 3 times, and then dry in an oven at 60℃ to obtain a chain extender containing a bio-based double imine bond.

[0113] (2) Dissolve 38.0g of a chain extender containing a bio-based double imine bond, 78.4g of E-51 and 0.1g of tetrabutylammonium bromide in 200mL of N,N-dimethylformamide, heat and keep at 160℃, and stir at high speed for 1h to obtain an epoxy prepolymer containing an imine bond.

[0114] (3) The obtained epoxy prepolymer containing imine bonds was stirred with 8.6g of 1,10-diaminodecane to obtain a blend, and the blend was degassed under a vacuum of 0.01Mpa at room temperature.

[0115] (4) Pour the bubble-free blend into a mold, prepolymerize at 70℃ for 0.5h, cure at 100℃ for 1.5h, cure at 130℃ for 1h, and cure at 160℃ for 2.5h to obtain a biodegradable epoxy resin based on bisimine-bonded vanillin.

[0116] Example 13

[0117] A biodegradable epoxy resin based on bisimine-linked vanillin, the preparation method of which includes the following steps:

[0118] (1) Dissolve 30.4g vanillin and 14.4g 1,8-octanediamine in 200mL tetrahydrofuran, mix and heat and keep warm at 40℃, stir at high speed for 2h to obtain a yellow precipitate. After standing, perform solid-liquid separation, collect the solid, wash with tetrahydrofuran 3 times, and then dry in a 60℃ oven to obtain a chain extender containing a bio-based double imine bond.

[0119] (2) 41.2g of a chain extender containing a bio-based double imine bond, 78.4g of E-51 and 1.0g of benzyltriphenylphosphine bromide were dissolved in 200mL of 1,4-dioxane, heated and kept at 140℃, and stirred at high speed for 1h to obtain an epoxy prepolymer containing an imine bond.

[0120] (3) The obtained epoxy prepolymer containing imine bonds was stirred with 3.6g of 1,8-octanediamine to obtain a blend, and the blend was degassed under a vacuum of 0.01Mpa at room temperature.

[0121] (4) Pour the blend after removing the air bubbles into a mold, prepolymerize at 60℃ for 0.5h, cure at 100℃ for 1h, cure at 130℃ for 1h, and cure at 160℃ for 2h to obtain a biodegradable epoxy resin based on bisimine-bonded vanillin.

[0122] Example 14

[0123] A biodegradable epoxy resin based on bisimine-linked vanillin, the preparation method of which includes the following steps:

[0124] (1) Dissolve 30.4g vanillin and 10.8g p-phenylenediamine in 200mL tetrahydrofuran, mix and heat and keep warm at 50℃, stir at high speed for 2h to obtain a yellow precipitate. After standing, perform solid-liquid separation, collect the solid, wash with tetrahydrofuran 3 times, and then dry in an oven at 80℃ to obtain a chain extender containing a bio-based double imine bond.

[0125] (2) Dissolve 37.6g of a chain extender containing a diimine bond bio-based compound, 78.4g of E-51, and 1.0g of benzyltriphenylphosphine bromide in 200mL of N,N-dimethylacetamide, heat and maintain the temperature at 150℃, and stir at high speed for a period of time.

[0126] (3) The obtained epoxy prepolymer containing imine bonds was stirred with 6.5g of 1,7-diaminoheptane to obtain a blend, and the blend was degassed under a vacuum of 0.01Mpa at room temperature.

[0127] (4) Pour the blend after removing the air bubbles into a mold, prepolymerize at 70℃ for 0.5h, cure at 110℃ for 1h, cure at 140℃ for 1h, and cure at 170℃ for 2h to obtain a biodegradable epoxy resin based on bisimine-bonded vanillin.

[0128] Example 15

[0129] A biodegradable epoxy resin based on bisimine-linked vanillin, the preparation method of which includes the following steps:

[0130] (1) Dissolve 30.4g vanillin and 14.4g 1,8-octanediamine in 200mL of anhydrous ethanol, mix and heat and keep warm at 50℃, stir at high speed for 2h to obtain a yellow precipitate. After standing, perform solid-liquid separation, collect the solid, wash with anhydrous ethanol 3 times, and then dry in an oven at 50℃ to obtain a chain extender containing a bio-based double imine bond.

[0131] (2) 46.6g of a chain extender containing a double imine bond bio-based, 78.4g of E-51 and 1.0g of tetraethylammonium bromide were dissolved in 200mL of 1,4-dioxane, heated and kept at 140℃, and stirred at high speed for 1h to obtain an epoxy prepolymer containing an imine bond.

[0132] (3) The obtained epoxy prepolymer containing imine bonds was stirred with 5.4g of p-phenylenediamine to obtain a blend, and the blend was degassed under a vacuum of 0.01Mpa at room temperature.

[0133] (4) Pour the blend after removing the air bubbles into a mold, prepolymerize at 80℃ for 1 hour, cure at 110℃ for 2 hours, cure at 140℃ for 2 hours, and cure at 170℃ for 2 hours to obtain a biodegradable epoxy resin based on bisimine-linked vanillin.

[0134] Comparative Example 1

[0135] 39.2g of E-51 and 9.9g of 4,4'-diaminodiphenylmethane were mixed with 100ml of N,N-dimethylformamide to obtain a blend, which was then degassed under a vacuum of 0.01Mpa at room temperature.

[0136] The degassed blend was poured into a mold and prepolymerized at 80°C for 1 hour, cured at 110°C for 2 hours, cured at 140°C for 2 hours, and cured at 170°C for 2 hours to obtain the comparative epoxy resin.

[0137] Comparative Example 2

[0138] 39.2g of E-51, 5.4g of p-phenylenediamine and 100ml of N,N-dimethylformamide were stirred evenly to obtain a blend, which was then degassed under a vacuum of 0.01Mpa at room temperature.

[0139] The degassed blend was poured into a mold and prepolymerized at 90°C for 1 hour, cured at 120°C for 2 hours, cured at 160°C for 2 hours, and cured at 180°C for 2 hours to obtain the comparative epoxy resin.

[0140] Comparative Example 3

[0141] 39.2g of E-51, 5.8g of 1,6-hexanediamine and 100ml of N,N-dimethylformamide were stirred evenly to obtain a blend, which was then degassed under a vacuum of 0.01Mpa at room temperature.

[0142] The degassed blend was poured into a mold and prepolymerized at 70°C for 1 hour, cured at 110°C for 2 hours, cured at 140°C for 2 hours, and cured at 170°C for 2 hours to obtain the comparative epoxy resin.

[0143] The mechanical and thermal properties of the epoxy resins obtained in Examples 1-5 and Comparative Examples 1-3 were tested. The data were measured in triplicate, and the final values ​​are presented as averages. The results are shown in Table 1.

[0144] Table 1 shows the mechanical and thermal properties of Examples 1-15 and Comparative Examples 1-3.

[0145]

[0146] As shown in Table 1, introducing a chain extender containing a bio-based diimine bond into the epoxy resin resulted in a biodegradable epoxy resin based on diimine bond vanillin exhibiting excellent mechanical and thermal properties. In contrast, the mechanical and thermal properties of Comparative Examples 1-3, which did not incorporate a bio-based diimine bond chain extender, were significantly inferior to those of the Examples. This is because the aromatic ring in the vanillin molecule imparts superior thermal stability and mechanical properties to Examples 1-15, and in step (3) of Example 3, a robust crosslinking network was formed by using a 4,4'-diaminodiphenylmethane curing agent with more rigid groups, spatially restricting and inhibiting the activity of the imine bonds. This design not only endows the biodegradable epoxy resin based on diimine bond vanillin with optimal mechanical and thermal properties but also makes it dynamically reversible under specific stimuli.

[0147] Example 16

[0148] Degradation methods for biodegradable epoxy resins based on diimine-linked vanillin:

[0149] 10 mg of the biodegradable epoxy resin based on diimine-bonded vanillin obtained in Example 1, 2 mL of 0.1 mol / L hydrochloric acid solution, and 10 mL of ethanol were placed in a 50 mL beaker. The temperature was controlled at 60 °C and kept at that temperature for 1 h to complete the degradation, resulting in a brownish-yellow solution.

[0150] The obtained solution was cured at 110℃ for 2 hours, 140℃ for 2 hours, and 170℃ for 2 hours, resulting in a recovery efficiency of up to 92.3% for the recovered product.

[0151] Example 17

[0152] Degradation methods for biodegradable epoxy resins based on diimine-linked vanillin:

[0153] 10 mg of the biodegradable epoxy resin based on diimine-bonded vanillin obtained in Example 2, 2 mL of 0.5 mol / L sulfuric acid solution, and 10 mL of ethanol were placed in a 50 mL beaker. The temperature was controlled at 50 °C and kept at that temperature for 2 h to complete the degradation, resulting in a brownish-yellow solution.

[0154] The obtained solution was cured at 110℃ for 2 hours, 140℃ for 2 hours, and 170℃ for 2 hours, and the recovery efficiency of the recovered product was as high as 90.8%.

[0155] Example 18

[0156] Degradation methods for biodegradable epoxy resins based on diimine-linked vanillin:

[0157] 10 mg of the biodegradable epoxy resin based on diimine-bonded vanillin obtained in Example 3, 2 mL of 2.0 mol / L hydrochloric acid solution, and 10 mL of N,N-dimethylformamide were placed in a 50 mL beaker. The temperature was controlled at room temperature and kept at this temperature for 2 hours to complete the degradation, resulting in a brownish-yellow solution.

[0158] The obtained solution was cured at 110℃ for 2 hours, 140℃ for 2 hours, and 170℃ for 2 hours, resulting in a recovery efficiency of up to 101.3% for the recovered product.

[0159] Example 19

[0160] Degradation methods for biodegradable epoxy resins based on diimine-linked vanillin:

[0161] 10 mg of the biodegradable epoxy resin based on diimine-bonded vanillin obtained in Example 4, 2 mL of 1.5 mol / L p-toluenesulfonic acid solution, and 10 mL of ethanol were placed in a 50 mL beaker. The temperature was controlled at 80 °C and kept at that temperature for 5 h to complete the degradation, resulting in a brownish-yellow solution.

[0162] The obtained solution was cured at 110℃ for 2 hours, 140℃ for 2 hours, and 170℃ for 2 hours, resulting in a recovery efficiency of up to 98.1% for the recovered product.

[0163] Example 20

[0164] Degradation methods for biodegradable epoxy resins based on diimine-linked vanillin:

[0165] 10 mg of the biodegradable epoxy resin based on diimine-bonded vanillin obtained in Example 5, 2 mL of 1.0 mol / L hydrochloric acid solution, and 10 mL of tert-butanol were placed in a 50 mL beaker. The temperature was controlled at 60 °C and kept at that temperature for 1 h to complete the degradation, resulting in a brownish-yellow solution.

[0166] The obtained solution was cured at 110℃ for 2 hours, 140℃ for 2 hours, and 170℃ for 2 hours, resulting in a recovery efficiency of up to 97.3% for the recovered product.

[0167] Comparative Example 4

[0168] The degradation methods of thermosetting epoxy resins in comparison:

[0169] 10 mg of the thermosetting epoxy resin obtained in Comparative Example 1, 2 mL of 1.0 mol / L hydrochloric acid solution, and 10 mL of tert-butanol were placed in a 50 mL beaker. The temperature was controlled at 70 °C and kept at that temperature for 2 h. The sample failed to degrade completely.

[0170] Comparative Example 5

[0171] A comparative method for degrading thermosetting epoxy resins:

[0172] 10 mg of the thermosetting epoxy resin obtained in Comparative Example 2, 2 mL of 1.0 mol / L hydrochloric acid solution, and 10 mL of tetrahydrofuran were placed in a 50 mL beaker. The temperature was controlled at 70 °C and kept at that temperature for 2 h. The sample failed to degrade completely.

[0173] Comparative Example 6

[0174] A comparative method for degrading thermosetting epoxy resins:

[0175] 10 mg of the thermosetting epoxy resin obtained in Comparative Example 3, 2 mL of 1.0 mol / L hydrochloric acid solution, and 10 mL of N,N-dimethylformamide were placed in a 50 mL beaker. The temperature was controlled at 70 °C and kept at that temperature for 2 h. The sample failed to degrade completely.

[0176] Comparative analysis of Examples 16-20 and Comparative Examples 4-6 showed that Examples 16-20, which contain bidynamic imine-bonded vanillin, can be degraded in specific weak acid organic solvents with a recovery efficiency of over 90%; while Comparative Examples 4-6, which do not contain bidynamic imine-bonded vanillin, failed to degrade in weak acid organic solvents and did not have chemical recovery performance.

[0177] Example 21

[0178] Preparation of biodegradable carbon fiber reinforced epoxy resin matrix composites:

[0179] The blend obtained in Example 1 (3) was dissolved in 5 mL of N,N-dimethylformamide solution, poured into a mold with carbon fiber cloth laid flat, soaked at room temperature for 30 min, heated to 110℃ for 2 h, cured at 140℃ for 2 h, and cured at 170℃ for 2 h to obtain a biodegradable carbon fiber reinforced epoxy resin matrix composite material.

[0180] Example 22

[0181] Preparation of biodegradable carbon fiber reinforced epoxy resin matrix composites:

[0182] The blend obtained in Example 2 (3) was dissolved in 5 mL of dimethyl sulfoxide solution, poured into a mold with carbon fiber cloth laid flat, soaked at room temperature for 30 min, heated to 120°C for 2 h, cured at 150°C for 2 h, and cured at 180°C for 2 h to obtain a biodegradable carbon fiber reinforced epoxy resin matrix composite material.

[0183] Example 23

[0184] Degradation of biodegradable carbon fiber reinforced epoxy resin composites:

[0185] 2g of the biodegradable carbon fiber reinforced epoxy resin matrix composite material prepared in Example 21, 2mL of 0.1mol / L hydrochloric acid solution and 10mL of tert-butanol were placed into a 50mL beaker. The temperature was controlled at 60℃ and 1h to complete the degradation. The resin matrix was completely depolymerized from the carbon fiber, resulting in a brownish-yellow solution and carbon fiber bundles.

[0186] The carbon fiber bundles were removed, and the recovered fibers were found to be clean and undamaged.

[0187] Example 24

[0188] Degradation of biodegradable carbon fiber reinforced epoxy resin composites:

[0189] 2g of the biodegradable carbon fiber reinforced epoxy resin matrix composite material prepared in Example 22, 2mL of 0.1mol / L hydrochloric acid solution and 10mL of tert-butanol were placed in a 50mL beaker. The temperature was controlled at room temperature and kept at this temperature for 2h to complete the degradation. The resin matrix was completely depolymerized from the carbon fiber, resulting in a brownish-yellow solution and carbon fiber bundles.

[0190] The carbon fiber bundles were removed, and the recovered fibers were found to be clean and undamaged.

[0191] Test example:

[0192] Tensile properties

[0193] The mechanical properties of the film were tested using a SUST model electronic universal testing machine manufactured in Zhuhai, China, at 25℃ and a tensile speed of 20 mm / min. The samples were prepared in a dumbbell shape, measuring 75 × 4 × 0.5 mm, for tensile testing. Figure 1As can be seen, the tensile strength and elongation at break of the biodegradable epoxy resin based on diimine-linked vanillin prepared in Example 3 are 94.7 MPa and 6.5%, respectively, while the tensile strength and elongation at break of Comparative Example 1E-51 are 60.6 MPa and 3.7%, respectively. Therefore, the mechanical properties of the biodegradable epoxy resin based on diimine-linked vanillin prepared in this invention are significantly better than those of E-51.

[0194] The tensile properties of the recycled epoxy resin obtained in Example 19 of this invention were tested against those of the original resin in Example 3. The epoxy resin had dimensions of 75 × 4 × 0.5 mm and a tensile rate of 20 mm / min. The results are as follows: Figure 2 As shown in the figure, the tensile strength of the recycled epoxy resin reaches 96.1 MPa, and its mechanical properties are 101.5% of those of the original epoxy resin.

[0195] The tensile properties of the recycled carbon fiber filaments from Example 24 of this invention were tested against those of the original carbon fiber filaments. The length was 10 mm, and the tensile rate was 1 mm / min. The results are as follows: Figure 3 As shown, the tensile properties of the recycled carbon fiber filaments are basically unchanged from those of the original carbon fiber filaments.

[0196] The applicant declares that this invention illustrates a biodegradable epoxy resin based on bisimino-linked vanillin, its preparation method, and its application through the above embodiments. However, this invention is not limited to the above embodiments, meaning that this invention does not necessarily rely on the above embodiments for implementation. Those skilled in the art should understand that any improvements to this invention, equivalent substitutions of raw materials, additions of auxiliary components, and selection of specific methods, etc., all fall within the protection and disclosure scope of this invention.

[0197] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all fall within the protection scope of the present invention.

Claims

1. A method for preparing a biodegradable epoxy resin based on bisimine-linked vanillin, characterized in that... The following steps are included: S1. Vanillin, diamine monomer and organic solvent are reacted under stirring to obtain a yellow precipitate, which is then purified to obtain a chain extender containing a bio-based double imine bond. S2. The chain extender containing biimine bonds, epoxy resin, catalyst and organic solvent obtained in step S1 are subjected to a ring-opening reaction under stirring to obtain an epoxy prepolymer containing imine bonds. S3. Add the diamine monomer to the epoxy prepolymer containing imine bonds obtained in step S2, stir evenly, and remove bubbles under vacuum at room temperature to obtain the blend. S4. Pour the blend into a mold and cure it to obtain a biodegradable epoxy resin based on bisimine-bonded vanillin.

2. The method for preparing a biodegradable epoxy resin based on bisimine-bonded vanillin according to claim 1, characterized in that: The diamine monomer mentioned in step S1 is one or more of 1,2-cyclohexanediamine, 1,3-cyclohexanediamine, p-phenylenediamine, 1,4-cyclohexanediamine, 1,6-hexanediamine, 1,7-diaminoheptane, 1,8-octanediamine, 1,10-diaminodecane, and 1,3-propanediamine. The organic solvent is one or more of the following: water, methanol, ethanol, isopropanol, tert-butanol, n-butanol, diethyl ether, tetrahydrofuran, 1,4-dioxane, acetone, butanone, methyl isobutyl ketone, cyclohexanone, ethyl acetate, methyl acetate, butyl acetate, isopropyl acetate, toluene, xylene, ethylbenzene, n-hexane, cyclohexane, petroleum ether, dichloromethane, trichloromethane, carbon tetrachloride, 1,2-dichloroethane, N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, dimethyl sulfoxide, and dimethyl sulfoxide acetonitrile. The molar ratio of vanillin to diamine monomer is 1:1 to 3:1; The reaction temperature is 30-70℃, and the reaction time is 1-12 hours.

3. The method for preparing a biodegradable epoxy resin based on bisimine-bonded vanillin according to claim 1, characterized in that: The epoxy resin mentioned in step S2 is one or more of E-51, E-44, E-20, E-12 and F-51; The catalyst is one or more of tetramethylammonium bromide, tetrapropylammonium bromide, benzyltriphenylphosphine bromide, tetrabutylammonium bromide, tetraethylammonium bromide, triphenylphosphine, and cobalt(II) acetylacetonate, and its amount is 0.1 to 2 wt% of the total mass of epoxy resin and chain extender containing biimine bond bio-based groups; The organic solvent is one or more of the following: water, methanol, ethanol, isopropanol, tert-butanol, n-butanol, diethyl ether, tetrahydrofuran, 1,4-dioxane, acetone, butanone, methyl isobutyl ketone, cyclohexanone, ethyl acetate, methyl acetate, butyl acetate, isopropyl acetate, toluene, xylene, ethylbenzene, n-hexane, cyclohexane, petroleum ether, dichloromethane, trichloromethane, carbon tetrachloride, 1,2-dichloroethane, N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, dimethyl sulfoxide, and dimethyl sulfoxide acetonitrile. The molar ratio of the bio-based chain extender containing double imine bonds to the bio-based chain extender is 1:3 to 3:1; The reaction is carried out at 130–180°C for 1–10 hours.

4. The method for preparing a biodegradable epoxy resin based on bisimine-bonded vanillin according to claim 1, characterized in that: The diamine curing agent mentioned in step S3 is one or more of 1,2-cyclohexanediamine, 1,3-cyclohexanediamine, p-phenylenediamine, 1,4-cyclohexanediamine, 4,4'-diaminodiphenylmethane, 1,6-hexanediamine, 1,7-diaminoheptane, 1,8-octanediamine, 1,10-diaminodecane, and 1,3-propanediamine. The molar ratio of the imine-containing epoxy prepolymer to the diamine monomer is 1:1 to 3:1; The vacuum level of the vacuum pump is less than or equal to 0.01 MPa.

5. The method for preparing a biodegradable epoxy resin based on bisimine-bonded vanillin according to claim 1, characterized in that: The curing process described in step S4 involves prepolymerizing at 60-100℃ for 0.5-5 hours, then curing at 100-120℃ for 1-10 hours, then curing at 130-150℃ for 1-10 hours, and finally curing at 160-180℃ for 1-10 hours.

6. A biodegradable epoxy resin based on bisimine-bonded vanillin, prepared by the preparation method according to any one of claims 1-5, characterized in that: The tensile strength of the biodegradable epoxy resin based on diimine-bonded vanillin reaches 70–110 MPa. d5％ When the temperature reaches 320℃ or above, the chemical recovery efficiency can reach over 100%.

7. The application of the biodegradable epoxy resin based on bisimine-bonded vanillin according to claim 6 in biodegradable epoxy resin composites.

8. A biodegradable epoxy resin composite material made from the biodegradable epoxy resin based on diimine-bonded vanillin as described in claim 6, characterized in that: The biodegradable epoxy resin composite material is prepared from a biodegradable epoxy resin based on bisimine-bonded vanillin, a reinforcing agent, and an organic solvent; The reinforcing material is one or more of the following: carbon fiber, glass fiber, natural fiber, chemical fiber, fabric made of fiber material, carbon nanomaterial, boron nitride nanomaterial, metal nanoparticle, metal oxide nanoparticle, and organic nanoparticle. The organic solvent is one or more of the following: water, methanol, ethanol, isopropanol, tert-butanol, n-butanol, diethyl ether, tetrahydrofuran, 1,4-dioxane, acetone, butanone, methyl isobutyl ketone, cyclohexanone, ethyl acetate, methyl acetate, butyl acetate, isopropyl acetate, toluene, xylene, ethylbenzene, n-hexane, cyclohexane, petroleum ether, dichloromethane, chloroform, carbon tetrachloride, 1,2-dichloroethane, N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, dimethyl sulfoxide, and dimethyl sulfoxide acetonitrile.

9. A method for degrading the biodegradable epoxy resin based on bisimine-bonded vanillin as described in claim 6 or the biodegradable epoxy resin composite material as described in claim 8, characterized in that: The method follows these steps: at room temperature or under heating conditions, a mixture of a weak acid solution and a solvent is used as the degradation solution, and a biodegradable epoxy resin or biodegradable epoxy resin composite material based on bisimine-linked vanillin is added. Under stirring conditions, the degradation of the biodegradable epoxy resin or biodegradable epoxy resin composite material based on bisimine-linked vanillin is achieved. The molar concentration of the weak acid solution is 0.1–5 mol / L; the volume ratio of the weak acid solution to the solvent is 1:5–1:20; the heating temperature is 0–100°C; and the heating time is 1–24 h.

10. The method according to claim 9, characterized in that: The weak acid solution is one or more of the following: hydrochloric acid, nitric acid, sulfuric acid, acetic acid, hydrofluoric acid, lactic acid, formic acid, propionic acid, citric acid, p-toluenesulfonic acid, sulfurous acid, phosphoric acid, and perchloric acid. The solvent is one or more selected from water, methanol, ethanol, isopropanol, tert-butanol, n-butanol, diethyl ether, tetrahydrofuran, 1,4-dioxane, acetone, butanone, methyl isobutyl ketone, cyclohexanone, ethyl acetate, methyl acetate, butyl acetate, isopropyl acetate, toluene, xylene, ethylbenzene, n-hexane, cyclohexane, petroleum ether, dichloromethane, chloroform, carbon tetrachloride, 1,2-dichloroethane, N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, dimethyl sulfoxide, and dimethyl sulfoxide acetonitrile.

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