A bio-based flame-retardant epoxy resin and its preparation method

Abstract

This invention discloses a bio-based flame-retardant epoxy resin and its preparation method, belonging to the field of epoxy resin material technology. The epoxy resin is prepared using vanillin as a bio-based raw material through a two-step reaction of phosphating modification and epoxidation. The phosphorus-based flame-retardant groups are covalently embedded in the molecular structure, forming an intrinsically flame-retardant system. The preparation process of this invention is simple, the reaction is highly efficient and controllable, and the product requires no additional flame retardant. It solves the problems of non-renewable and flammable raw materials in traditional epoxy resins, as well as the damage to mechanical properties caused by adding flame retardants. It also avoids the shortcomings of existing vanillin-based epoxy resin preparation processes, low product purity, and difficulty in industrial production. It combines environmental friendliness, excellent flame retardancy, and mechanical properties, and can be used in fields such as electronic and electrical packaging and composite material matrices, showing broad prospects for industrial application.

Description

Technical Field

[0001] This invention relates to the field of epoxy resin materials technology, specifically to a bio-based flame-retardant epoxy resin and its preparation method. Background Technology

[0002] Epoxy resins are widely used in electronics, aerospace, building materials, adhesives and other fields due to their excellent mechanical properties, adhesive properties, chemical stability and molding processability. However, traditional epoxy resins have a key shortcoming: insufficient flame retardancy. Unmodified epoxy resins typically have a limiting oxygen index of less than 25%, and their vertical flammability rating can only reach UL94HB, which cannot meet the high flame retardancy requirements of electronics, aerospace and other fields. To improve the flame retardant properties of epoxy resin, existing technologies mainly employ additive flame retardant modification, which involves adding inorganic or organic flame retardants to the epoxy resin. However, inorganic flame retardants require high addition levels to achieve the desired flame retardant effect, which can easily lead to a decrease in the mechanical properties and processing performance of the epoxy resin. Brominated flame retardants release toxic and harmful gases during combustion, posing serious environmental risks and health hazards, and their use has been gradually restricted. With the popularization of green and environmentally friendly concepts and the increasing demand for renewable resource utilization, the research and development of bio-based epoxy resins has become a hot topic in the industry. Among them, the development of bio-based flame-retardant epoxy resins using renewable vanillin as raw material has become the direction of industry development. However, the existing phosphating modification process of vanillin-based flame-retardant epoxy resins all require first synthesizing an imine intermediate from vanillin and diamine compounds, and then performing phosphating modification on the imine structure. This process has problems such as complicated synthesis steps, low product purity, and difficulty in industrial-scale production. Therefore, it is essential to design a bio-based flame-retardant epoxy resin and its preparation method. Summary of the Invention

[0003] The purpose of this invention is to provide a bio-based flame-retardant epoxy resin and its preparation method, in order to solve the problems mentioned in the background art, such as the non-renewable and flammable nature of traditional epoxy resins and the fact that adding flame retardants can easily damage their performance, as well as the cumbersome preparation process, low product purity, and difficulty in industrial production of existing vanillin-based flame-retardant epoxy resins.

[0004] To achieve the above objectives, the present invention provides the following technical solution: In one aspect, a method for preparing a bio-based flame-retardant epoxy resin is provided, wherein the raw materials include vanillin, phosphorus modifier, organic solvent, epichlorohydrin, phase transfer catalyst and alkaline substance; The molar ratio of vanillin, phosphorus modifier, and organic solvent is 0.8~1:1.0~1.2:5~20; The method includes the following steps: S1. Vanillin, phosphorus modifier and organic solvent are mixed and heated under inert gas protection to react. The reaction product is separated and dried to obtain phosphorus modified vanillin. S2. The phosphorus-modified vanillin, epichlorohydrin, phase transfer catalyst and alkaline substance obtained in S1 are mixed in a molar ratio of 0.8~1.2:5~25:0.05~0.15:2.5~5 and epoxidation reaction is carried out under inert gas protection. The reaction product is separated and dried to obtain bio-based flame-retardant epoxy resin.

[0005] As a further technical solution of the present invention, the temperature of the heating reaction in S1 is from room temperature to reflux temperature, and the reaction time is 2~24h.

[0006] As a further technical solution of the present invention, the epoxidation reaction in S2 includes: premixing at room temperature for 30 min, heating to 70~110℃ and reacting for 5~10 h, cooling to 40~80℃, adding an alkaline substance dropwise and continuing the reaction for 2 h.

[0007] As a further technical solution of the present invention, the phosphorus modifier is selected from one of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, diphenylphosphine, diphenylphosphine, diethyl phosphite, phosphorous acid, dimethyl phosphite, diisopropyl phosphite, diisobutyl phosphite, and diphenyl phosphite.

[0008] As a further technical solution of the present invention, the organic solvent includes one or more combinations of ethanol, methanol, acetone, dioxane, N,N-dimethylacetamide, DMAC, N-methylpyrrolidone (NMP), tetrahydrofuran, dichloromethane, chloroform, carbon tetrachloride, petroleum ether, toluene, ethyl acetate, triethylamine, and water.

[0009] As a further technical solution of the present invention, the phase transfer catalyst is selected from one or more of quaternary ammonium salts, polyethers, and quaternary phosphorus salts; The alkaline substance is an aqueous solution of sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, or sodium bicarbonate.

[0010] As a further technical solution of the present invention, the separation is performed by vacuum filtration or solvent extraction; the drying is performed by desiccant drying, vacuum distillation or vacuum drying.

[0011] As a further technical solution of the present invention, the quaternary ammonium salt is one or more of benzyltriethylammonium chloride, tetrabutylammonium bromide, tetrabutylammonium chloride, tetrabutylammonium hydrogen sulfate, trioctylmethylammonium chloride, dodecyltrimethylammonium chloride or tetradecyltrimethylammonium chloride; The polyether is selected from chain polyethylene glycol; the quaternary phosphine salt is one or more of tetraphenylphosphine chloride, triphenylphosphine and its derivatives.

[0012] As a further technical solution of the present invention, the desiccant is one or more of anhydrous sodium sulfate, anhydrous sodium carbonate, anhydrous potassium carbonate, anhydrous calcium chloride, anhydrous calcium sulfate, anhydrous calcium oxide, and anhydrous magnesium sulfate.

[0013] In a second aspect, a bio-based flame-retardant epoxy resin is provided, prepared by any one of the methods described in the first aspect, wherein a phosphorus-based flame-retardant group R is attached to the vanillin aldehyde group site in its molecular structure, and an epoxy group is attached to the phenolic hydroxyl group site; wherein R is selected from one of DOPO group, diphenyl phosphate group, diphenyl phosphine group, diethyl phosphite group, phosphite group, dimethyl phosphite group, diisopropyl phosphite group, diisobutyl phosphite group, and diphenyl phosphite group.

[0014] Compared with existing technologies, the beneficial effects of this bio-based flame-retardant epoxy resin and its preparation method are: Using vanillin as a renewable bio-based raw material, bio-based flame-retardant epoxy resin is prepared through a simple two-step process of phosphorylation modification and epoxidation. There is no need to synthesize imine intermediates. The reaction process is efficient and controllable, which effectively simplifies the production steps, improves the purity of the product, and is more suitable for the needs of large-scale industrial production. Phosphorus-based flame-retardant groups are covalently embedded in the epoxy resin molecule to form an intrinsic flame-retardant system. No additional flame retardant is required, which avoids the problems of decreased material mechanical properties, poor processability, and release of toxic and harmful substances during combustion caused by traditional additive flame retardants. At the same time, it significantly improves the flame-retardant performance of the material and meets the high flame-retardant requirements of the electronics, electrical appliances, composite materials and other fields. Replacing non-renewable fossil-based bisphenol A raw material with vanillin, a downstream product of lignin, effectively reduces the consumption of fossil resources and carbon emissions during the production process, which aligns with the concepts of green environmental protection and sustainable development, and is both environmentally friendly and economical. The prepared bio-based flame-retardant epoxy resin achieves high-efficiency flame retardancy while significantly improving the tensile strength and elongation at break of the material. It breaks through the technical bottleneck of traditional epoxy resins, which are difficult to balance flame retardant performance and mechanical properties. With excellent comprehensive performance, it can be widely used in many fields such as electronic and electrical packaging, composite matrix, adhesives and flame-retardant building materials, and has broad application prospects. With mild process conditions, precise raw material ratios, simple purification process, high reaction yield, and low production cost, it possesses excellent operability and market promotion value, and can effectively promote the commercial application of bio-based flame-retardant epoxy resins. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the method flow of the present invention; Figure 2 This is a schematic diagram of the molecular structure of the bio-based flame-retardant epoxy resin of the present invention. Figure 3 This is a schematic diagram of the molecular structure of the phosphorylated modified vanillin of the present invention; Figure 4 This is a schematic diagram of the molecular structure of DOPO-modified vanillin in an embodiment of the present invention. Figure 5 The infrared spectrum of the bio-based flame-retardant epoxy resin compound in the embodiments of the present invention; Figure 6 This is a schematic diagram of the molecular structure of the DOPO-modified vanillin epoxy resin in an embodiment of the present invention. Figure 7 This is a schematic diagram of the molecular structure of diethyl phosphite-modified vanillin in an embodiment of the present invention. Figure 8 This is a schematic diagram of the molecular structure of the bio-based flame-retardant epoxy resin in this embodiment of the invention. Figure 9 This is a comparison graph of the heat release rate (HRR) curves of the embodiments and comparative examples of the present invention; Figure 10 This is a comparison chart of the total heat release (THR) curves of the embodiments and comparative examples of the present invention; Figure 11 This is a comparison chart of the total smoke production (TSP) curves of the embodiments and comparative examples of the present invention; Figure 12 The tensile stress-tensile strain diagrams are shown for the bio-based flame-retardant epoxy resin system in the embodiments of the present invention and the comparative example E51 type epoxy resin after curing with 4,4-diaminodiphenylmethane as curing agent. Detailed Implementation

[0016] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0017] Please see Figures 1-3 One embodiment of the present invention provides a method for preparing a bio-based flame-retardant epoxy resin, wherein the raw materials include vanillin, phosphorus modifier, organic solvent, epichlorohydrin, phase transfer catalyst and alkaline substance; The molar ratio of vanillin, phosphorus modifier, and organic solvent is 0.8~1:1.0~1.2:5~20; Furthermore, the phosphorus modifier is selected from one of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, diphenylphosphine, diphenylphosphine, diethyl phosphite, phosphorous acid, dimethyl phosphite, diisopropyl phosphite, diisobutyl phosphite, and diphenyl phosphite. Furthermore, the organic solvent is selected from one or more combinations of ethanol, methanol, acetone, dioxane, N,N-dimethylacetamide, DMAC, N-methylpyrrolidone (NMP), tetrahydrofuran, dichloromethane, chloroform, carbon tetrachloride, petroleum ether, toluene, ethyl acetate, triethylamine, and water. Furthermore, the phase transfer catalyst is selected from one or more of quaternary ammonium salts, polyethers, and quaternary phosphonium salts; Furthermore, the quaternary ammonium salts are one or more of benzyltriethylammonium chloride, tetrabutylammonium bromide, tetrabutylammonium chloride, tetrabutylammonium hydrogen sulfate, trioctylmethylammonium chloride, dodecyltrimethylammonium chloride, or tetradecyltrimethylammonium chloride; Polyethers are chain-like polyethylene glycols; Quaternary phosphine salts are one or more of tetraphenylphosphine chloride, triphenylphosphine and their derivatives; Furthermore, the alkaline substance is an aqueous solution of sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, or sodium bicarbonate; The method includes the following steps: S1. Vanillin, phosphorus modifier and organic solvent are mixed and heated under inert gas protection to react. The reaction product is separated and dried to obtain phosphorus modified vanillin. The heating temperature for the reaction is from room temperature to reflux temperature, and the reaction time is 2 to 24 hours. S2. The phosphorus-modified vanillin, epichlorohydrin, phase transfer catalyst and alkaline substance obtained in S1 are mixed in a molar ratio of 0.8~1.2:5~25:0.05~0.15:2.5~5 and epoxidation reaction is carried out under inert gas protection. The reaction product is separated and dried to obtain bio-based flame retardant epoxy resin. The epoxidation reaction includes: premixing at room temperature for 30 min, heating to 70~110℃ and reacting for 5~10 h, cooling to 40~80℃, adding an alkaline substance dropwise and continuing the reaction for 2 h; Further separation is achieved through vacuum filtration or solvent extraction; drying is achieved through desiccant drying, vacuum distillation, or vacuum drying. Furthermore, the desiccant is one or more combinations of anhydrous sodium sulfate, anhydrous sodium carbonate, anhydrous potassium carbonate, anhydrous calcium chloride, anhydrous calcium sulfate, anhydrous calcium oxide, and anhydrous magnesium sulfate.

[0018] One embodiment of the present invention provides: a bio-based flame-retardant epoxy resin, prepared by any of the methods in the above embodiments, wherein the vanillin aldehyde group is connected to a phosphorus-based flame-retardant group R, and the phenolic hydroxyl group is connected to an epoxy group; R is selected from one of DOPO group, diphenylphosphine group, diphenylphosphine group, diethyl phosphite group, phosphite group, dimethyl phosphite group, diisopropyl phosphite group, diisobutyl phosphite group, and diphenyl phosphite group.

[0019] Another embodiment provided: A method for preparing a bio-based flame-retardant epoxy resin, comprising the following steps: 15.2 g of vanillin and 21.6 g of DOPO were added to a 500 mL three-necked flask, and 250 mL of toluene was added as a solvent. Under nitrogen protection, the mixture was heated to 110 °C and reacted for 12 h. After the reaction was completed, the mixture was filtered under reduced pressure to obtain a white solid, which was washed three times with toluene at 90 °C and dried under vacuum at 60 °C for 5 h. The resulting white solid was DOPO-modified vanillin; its molecular structure is shown below. Figure 4 As shown; 25g of the obtained DOPO-modified vanillin was added to a three-necked flask, along with 92.56g of epichlorohydrin and 1.75g ​​of tetrabutylammonium bromide. The mixture was stirred for 30min at room temperature under nitrogen protection, then heated to 110℃ and maintained at this temperature for 6h. The reaction temperature was then lowered to 40℃, and 30ml of sodium hydroxide solution (10mol / L) was slowly added dropwise at a rate of 10ml / min using a peristaltic pump. The reaction was allowed to proceed for 2h. After the reaction, the mixture was washed four times with 200ml of deionized water. The lower organic phase was collected, dried with anhydrous magnesium sulfate, and then excess epichlorohydrin was removed by vacuum distillation. The mixture was then vacuum dried in a vacuum drying phase at 80℃ for 5h. The resulting reddish-brown transparent liquid was the bio-based flame-retardant epoxy resin. Figure 5 As can be seen from the data, after DOPO modification, the characteristic peak of the aldehyde group at 1668 cm⁻¹ disappeared, and after epoxidation, the characteristic peak of the epoxy functional group appeared at 916 cm⁻¹, indicating that DOPO-modified vanillin epoxy resin was successfully prepared with a yield of approximately 94.6%; the molecular structure formula is as follows. Figure 6 As shown; In another embodiment provided, a method for preparing a bio-based flame-retardant epoxy resin includes the following steps: 15.8 g vanillin and 23.8 g DOPO were added to a 500 mL three-necked flask, and 250 mL toluene was added as a solvent. Under nitrogen protection, the temperature was raised to 110 °C and the reaction was maintained for 12 h. After the reaction was completed, the mixture was filtered under reduced pressure to obtain a white solid, which was washed three times with dichloromethane and dried under vacuum at 60 °C for 5 h. The white solid obtained was DOPO-modified vanillin. The obtained 37.0 g was added to a three-necked flask, along with 203.5 g of epichlorohydrin and 3.87 g of tetrabutylammonium bromide. The mixture was stirred for 30 min at room temperature under nitrogen protection, then heated to 80 °C and maintained at this temperature for 6 h. The reaction temperature was then lowered to 40 °C, and 35 ml of sodium hydroxide solution (10 mol / L) was slowly added dropwise at a rate of 1 ml / min using a peristaltic pump. The reaction was continued for 2 h. After the reaction was complete, the mixture was washed four times with 200 ml of deionized water. The lower organic phase was collected, dried with anhydrous magnesium sulfate, and then excess epichlorohydrin was removed by vacuum distillation. The mixture was then vacuum dried in a vacuum drying phase at 80 °C for 5 h. The resulting reddish-brown transparent liquid was the bio-based flame-retardant epoxy resin, with a yield of approximately 93.6%.

[0020] In another embodiment provided, a method for preparing a bio-based flame-retardant epoxy resin includes the following steps: 15.2 g of vanillin and 13.4 g of diethyl phosphite were added to a 500 mL three-necked flask, along with 150 mL of toluene and 10 g of triethylamine as solvents. Under nitrogen protection, the mixture was heated to 110 °C and reacted for 12 h. After the reaction, the mixture was washed three times with toluene, allowed to stand for 1 h in a separatory funnel, and the lower layer of brownish-red liquid was collected. This liquid was then distilled under reduced pressure at -0.09 MPa and 80 °C for 2 h to remove the toluene solvent. Finally, it was dried under vacuum in a 60 °C vacuum oven for 5 h to obtain a brownish-red transparent liquid, which was modified with diethyl phosphite. The molecular structure is shown below. Figure 7 As shown; 20 g of the obtained diethyl phosphite-modified vanillin was added to a three-necked flask, along with 92.56 g of epichlorohydrin and 1.85 g of tetrabutylammonium bromide. The mixture was stirred for 30 min at room temperature under nitrogen protection, then heated to 80 °C and maintained at this temperature for 6 h. The reaction temperature was then lowered to 40 °C, and 30 ml of 10 mol / L sodium hydroxide solution was slowly added dropwise at a rate of 2 ml / min using a peristaltic pump. The reaction was continued for 2 h. After the reaction was complete, the mixture was washed four times with 200 ml of deionized water. The lower organic phase was collected, dried with anhydrous magnesium sulfate, and then excess epichlorohydrin was removed by vacuum distillation. The final product was then vacuum dried in a vacuum drying oven at 80 °C for 5 h to obtain a yellowish-brown, transparent, bio-based flame-retardant epoxy resin with a yield of approximately 91.2%. The molecular structure is as follows: Figure 8 As shown; In another embodiment provided, a method for preparing a bio-based flame-retardant epoxy resin includes the following steps: 16.7 g vanillin and 17.6 g diethyl phosphite were added to a 500 mL three-necked flask, along with 150 mL toluene and 15 g triethylamine as solvents. Under nitrogen protection, the mixture was heated to 110 °C and reacted for 6 h. After the reaction was complete, the mixture was washed three times with toluene, allowed to stand for 1 h in a separatory funnel, and the lower layer of brownish-red liquid was collected. The liquid was then distilled under reduced pressure at -0.09 MPa and 80 °C for 2 h to remove the toluene solvent. Finally, the mixture was vacuum dried in a vacuum drying oven at 60 °C for 5 h to obtain a brownish-red transparent liquid, which was modified vanillin with diethyl phosphite. 20 g of the obtained diethyl phosphite-modified vanillin was added to a three-necked flask, along with 92.56 g of epichlorohydrin and 1.9 g of tetrabutylammonium bromide. The mixture was stirred for 30 min at room temperature and under nitrogen protection, then heated to 110 °C and maintained at this temperature for 6 h. The reaction temperature was then lowered to 80 °C, and 25 ml of sodium hydroxide solution (10 mol / L) was slowly added dropwise at a rate of 2 ml / min using a peristaltic pump. The reaction was allowed to proceed for 2 h. After the reaction was completed, the mixture was washed four times with 200 ml of deionized water. The lower organic phase was collected, dried with anhydrous magnesium sulfate, and then excess epichlorohydrin was removed by vacuum distillation. The mixture was then vacuum dried in a vacuum drying phase at 80 °C for 3 h to obtain a yellowish-brown transparent bio-based flame-retardant epoxy resin with a yield of approximately 93.3%.

[0021] A comparative example provided: 100g of E51 epoxy resin and 25g of 4,4'-diaminodiphenylmethane (DDM) were melt-mixed uniformly at 100℃, cured at 120℃ for 2 hours and then cured at 150℃ for 2 hours to obtain the epoxy cured product, named EP. According to the standard ASTM D3801-20, the UL-94 test of this cured product showed no rating. The flame retardant properties of E51 epoxy resin were tested using a cone calorimeter under a radiation intensity of 35kW / m2. Depend on Figures 9-11 The peak heat release rate (HRR), total heat release (THR), and total smoke production (TSP) of E51 epoxy resin are 1085.54 kW / m2, 133.24 MJ / m2, and 25.14 m2, respectively. These results indicate that E51 epoxy resin is prone to combustion and generates a large amount of heat and toxic and harmful smoke during combustion.

[0022] In another embodiment, 20g of successfully synthesized DOPO modified vanillin epoxy resin and 80g of E51 epoxy resin were mixed with DDM at a mass ratio of 100:25, cured at 120°C for 2 hours, and then cured at 150°C for 2 hours to obtain an epoxy cured product named EP / DVEP-20; the UL94 rating of this epoxy resin system was determined to be V0 according to the standard ASTM D3801-20. Depend on Figure 12It can be seen that the tensile strength of EP / DVEP-20 with the addition of intrinsic flame-retardant epoxy resin is increased by about 56.9% and the tensile strain is increased by about 86% compared with EP; this indicates that the system with the addition of intrinsic flame-retardant epoxy resin has superior mechanical properties. Depend on Figures 9-11 It can be seen that the heat release rate (HRR), total heat release (THR), and total smoke production (TSP) of EP / DVEP-20 with the addition of intrinsic flame-retardant epoxy resin are 815.3 kW / m2, 86.5 MJ / m2, and 20.8 m2, respectively, which are reduced by 13.3%, 53.9%, and 20.7% respectively; this indicates that the system with the addition of intrinsic flame-retardant epoxy resin has better flame-retardant properties.

[0023] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

Claims

1. A method for preparing a bio-based flame-retardant epoxy resin, characterized in that: The raw materials include vanillin, phosphorus modifier, organic solvent, epichlorohydrin, phase transfer catalyst and alkaline substances; The molar ratio of vanillin, phosphorus modifier, and organic solvent is 0.8~1:1.0~1.2:5~20; The method includes the following steps: S1. Vanillin, phosphorus modifier and organic solvent are mixed and heated under inert gas protection to react. The reaction product is separated and dried to obtain phosphorus modified vanillin. S2. The phosphorus-modified vanillin, epichlorohydrin, phase transfer catalyst and alkaline substance obtained in S1 are mixed in a molar ratio of 0.8~1.2:5~25:0.05~0.15:2.5~5 and epoxidation reaction is carried out under inert gas protection. The reaction product is separated and dried to obtain bio-based flame-retardant epoxy resin.

2. The method for preparing a bio-based flame-retardant epoxy resin according to claim 1, characterized in that: The heating reaction in S1 is carried out at a temperature ranging from room temperature to reflux temperature, and the reaction time is 2 to 24 hours.

3. The method for preparing a bio-based flame-retardant epoxy resin according to claim 1, characterized in that: The epoxidation reaction described in S2 includes: premixing at room temperature for 30 minutes, heating to 70-110°C and reacting for 5-10 hours, cooling to 40-80°C, adding an alkaline substance dropwise, and continuing the reaction for 2 hours.

4. The method for preparing a bio-based flame-retardant epoxy resin according to claim 1, characterized in that: The phosphorus modifier is selected from one of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, diphenylphosphine, diphenylphosphine, diethyl phosphite, phosphorous acid, dimethyl phosphite, diisopropyl phosphite, diisobutyl phosphite, and diphenyl phosphite.

5. The method for preparing a bio-based flame-retardant epoxy resin according to claim 1, characterized in that: The organic solvents include one or more combinations of ethanol, methanol, acetone, dioxane, N,N-dimethylacetamide, DMAC, N-methylpyrrolidone (NMP), tetrahydrofuran, dichloromethane, chloroform, carbon tetrachloride, petroleum ether, toluene, ethyl acetate, triethylamine, and water.

6. The method for preparing a bio-based flame-retardant epoxy resin according to claim 1, characterized in that: The phase transfer catalyst is selected from one or more of quaternary ammonium salts, polyethers, and quaternary phosphorus salts; The alkaline substance is an aqueous solution of sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, or sodium bicarbonate.

7. The method for preparing a bio-based flame-retardant epoxy resin according to claim 1, characterized in that: The separation is performed by vacuum filtration or solvent extraction; the drying is performed by desiccant drying, vacuum distillation, or vacuum drying.

8. The method for preparing a bio-based flame-retardant epoxy resin according to claim 6, characterized in that: The quaternary ammonium salts are one or more of benzyltriethylammonium chloride, tetrabutylammonium bromide, tetrabutylammonium chloride, tetrabutylammonium hydrogen sulfate, trioctylmethylammonium chloride, dodecyltrimethylammonium chloride, or tetradecyltrimethylammonium chloride; The polyether is selected from chain polyethylene glycol; the quaternary phosphine salt is one or more of tetraphenylphosphine chloride, triphenylphosphine and its derivatives.

9. The method for preparing a bio-based flame-retardant epoxy resin according to claim 7, characterized in that: The desiccant is one or more of the following: anhydrous sodium sulfate, anhydrous sodium carbonate, anhydrous potassium carbonate, anhydrous calcium chloride, anhydrous calcium sulfate, anhydrous calcium oxide, and anhydrous magnesium sulfate.

10. A bio-based flame-retardant epoxy resin, characterized in that: Prepared by the method according to any one of claims 1 to 6, wherein the molecule has a vanillin aldehyde group connected to a phosphorus-based flame retardant group R and a phenolic hydroxyl group connected to an epoxy group; wherein R is selected from one of DOPO group, diphenylphosphine group, diphenylphosphine group, diethyl phosphite group, phosphite group, dimethyl phosphite group, diisopropyl phosphite group, diisobutyl phosphite group, and diphenyl phosphite group.

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