Flame-retardant bio-based epoxy resin monomers, bio-based epoxy resins, and methods of making the same

Abstract

The application belongs to the technical field of bio-based polymer materials, and provides a flame-retardant bio-based epoxy resin monomer, a bio-based epoxy resin and a preparation method thereof.The flame-retardant bio-based epoxy resin monomer is prepared from vanillin and tyramine as raw materials, through a condensation reaction to introduce a DOPO flame retardant to generate a bisphenol monomer, and then through epoxidation and ring closure reaction.The bio-based epoxy resin can be prepared by mixing the monomer with an amino-containing curing agent and then performing first curing and second curing.The flame-retardant bio-based epoxy resin monomer provided by the application has a rigid benzene ring and a phosphorus-containing structure, which can not only improve the thermal stability and mechanical properties of the epoxy resin, but also synergistically flame-retard with nitrogen elements to form a dense and continuous expanded carbon layer during combustion, thereby exhibiting excellent flame retardancy.The monomer is prepared from renewable bio-based raw materials vanillin and tyramine, and the process steps are simple, green and environmentally friendly.The bio-based epoxy resin prepared has excellent comprehensive performance, can reduce the dependence on petroleum resources, and meets the demand for green development.

Description

Technical Field

[0001] This invention belongs to the field of bio-based polymer materials technology, and particularly relates to flame-retardant bio-based epoxy resin monomers, bio-based epoxy resins and their preparation methods. Background Technology

[0002] Epoxy resin is a type of organic polymer containing two or more epoxy groups in its molecular structure. Compared with most thermosetting materials, epoxy resin has excellent dimensional stability, high modulus, high strength, and good heat resistance and chemical resistance. With these excellent properties, it is widely used in coatings, adhesives, composite materials, electronic packaging and other fields.

[0003] While traditional petrochemical-based epoxy resins exhibit outstanding performance, their non-renewable and non-degradable nature contradicts the development philosophy of modern green manufacturing, severely restricting their further application in this field. Against this backdrop, bio-based epoxy resins, with their wide availability of raw materials and good biodegradability, align with the needs of green development and have gradually become a research hotspot in the industry, providing a new direction for the green development of epoxy resins. However, the natural molecular structure of bio-based epoxy resins determines their insufficient flame retardant properties, a problem that greatly limits their promotion and application in high-performance fields. Conversely, the industry typically uses halogenated flame retardants to improve the flame retardant properties of traditional epoxy resins, but these flame retardants pollute the natural environment and have potential negative impacts on human health during use, contradicting environmental and health principles. To address the dual problems of insufficient flame retardant properties in bio-based epoxy resins and the drawbacks of traditional flame retardant methods, this invention proposes a flame-retardant bio-based epoxy resin monomer, a bio-based epoxy resin, and its preparation method. Summary of the Invention

[0004] The purpose of this invention is to provide flame-retardant bio-based epoxy resin monomers, bio-based epoxy resins, and their preparation methods, in order to solve the problems mentioned in the background art.

[0005] The objective of this invention is achieved through the following technical solution:

[0006] Flame-retardant bio-based epoxy resin monomer, the structure of which is shown in Formula I:

[0007] Formula I: .

[0008] The preparation method of flame-retardant bio-based epoxy resin monomers as described above includes the following steps:

[0009] Vanillin, tyramine, and an alcohol solvent were mixed and subjected to a condensation reaction. Then, DOPO was dissolved in the alcohol solvent and added dropwise to the reaction system to obtain a bisphenol monomer with the structure shown in Formula II.

[0010] Formula II: ;

[0011] The bisphenol monomer, catalyst, and epichlorohydrin were mixed and subjected to an epoxidation reaction. The resulting epoxidation reaction solution was then mixed with sodium hydroxide to carry out a ring-closing reaction. After the reaction was completed, the monomer was purified by extraction, washing, drying, distillation, and column chromatography to obtain the flame-retardant bio-based epoxy resin monomer with the structure shown in Formula I.

[0012] Furthermore, the molar ratio of vanillin to tyramine is 1:1 to 1.5; the molar ratio of vanillin to DOPO is 1:1 to 1.5.

[0013] Furthermore, the condensation reaction is carried out at a temperature of 40-80°C for a time of 20-26 hours.

[0014] Furthermore, the molar ratio of the bisphenol monomer to the catalyst is 1:0.001~0.1; the molar ratio of the bisphenol monomer to epichlorohydrin is 1:8~30; and the molar ratio of the bisphenol monomer to sodium hydroxide is 1:0.1~0.7.

[0015] Furthermore, the catalyst is a quaternary ammonium salt, selected from one or more of tetrabutylammonium bromide, tetrabutylammonium chloride, tetrabutylammonium iodide and hexadecyltrimethylammonium bromide; the sodium hydroxide is used in the form of an aqueous sodium hydroxide solution with a mass concentration of 5-50%.

[0016] Furthermore, the epoxidation reaction is carried out at a temperature of 50~100℃ for 2~7h, and the stirring speed is 100~500r / min; the ring-closing reaction is carried out at a temperature of -5~10℃ for 2~7h, and the stirring speed is 100~500r / min.

[0017] Bio-based epoxy resin is prepared from epoxy resin monomers and curing agents. The epoxy resin monomers are the flame-retardant bio-based epoxy resin monomers described above or the flame-retardant bio-based epoxy resin monomers prepared by the above-described preparation method. The curing agent is one or more of the following: amino-containing curing agents, amino-disulfide bond-containing curing agents, and amino-siloxane-silicon bond-containing curing agents.

[0018] Furthermore, the amino-containing curing agent is 4,4'-diaminodiphenylmethane and / or 1,6-hexanediamine; the amino-disulfide bond-containing curing agent is 4,4'-diaminodiphenyl disulfide and / or 3,3'-dithiodipropionic acid; and the amino-siloxane bond-containing curing agent is 1,3-bis(3-aminopropyl)tetramethyldisiloxane and / or bis(4-aminophenoxy)dimethylsilane.

[0019] The preparation method of the bio-based epoxy resin as described above includes the following steps:

[0020] Flame-retardant bio-based epoxy resin monomers and curing agents are mixed, and then the mixture is poured into a mold for curing to obtain bio-based epoxy resin.

[0021] The molar ratio of the flame-retardant bio-based epoxy resin monomer to the curing agent is 1:0.1~1;

[0022] The curing process includes sequentially performing a first curing and a second curing. The temperature of the first curing is 60~120℃ and the time is 4~12h. The temperature of the second curing is 120~160℃ and the time is 2~12h.

[0023] Compared with the prior art, the beneficial effects of the present invention are:

[0024] The flame-retardant bio-based epoxy resin monomer provided by this invention contains a rigid benzene ring structure, which helps improve the thermal stability and mechanical properties of the epoxy resin. Furthermore, this monomer structure contains phosphorus, which, through synergistic flame retardancy with nitrogen elements in the epoxy network, allows the resin to form a dense and continuous expanded carbon layer during combustion, thereby endowing it with excellent flame-retardant properties. This monomer is prepared from tyramine (derived from tyrosine decarboxylation, green and non-toxic) and vanillin (derived from lignin depolymerization, abundant in source), both of which are renewable bio-based materials. The process is simple and reduces the consumption and dependence on petrochemical products, promoting the sustainable development of the epoxy resin industry. The resulting bio-based epoxy resin combines good thermal stability, mechanical properties, and excellent flame-retardant properties, reducing petroleum resource consumption and meeting the needs of green development. Attached Figure Description

[0025] Figure 1 The image shows the 1H NMR spectrum of the bisphenol monomer synthesized in Example 1.

[0026] Figure 2 The image shows the 1H NMR spectrum of the flame-retardant bio-based epoxy resin monomer synthesized in Example 2.

[0027] Figure 3 The image shows the infrared spectrum of the bio-based epoxy resin obtained after curing in Example 3.

[0028] Figure 4 This is a diagram showing the flexural properties of bio-based epoxy resin. Detailed Implementation

[0029] In order to provide a clearer understanding of the technical features, objectives and beneficial effects of the present invention, the technical solution of the present invention will now be described in detail below, but it should not be construed as limiting the scope of implementation of the present invention.

[0030] This invention provides a flame-retardant bio-based epoxy resin monomer, the structure of which is shown in Formula I:

[0031] Formula I: ;

[0032] This invention also provides a method for preparing the flame-retardant bio-based epoxy resin monomer described above, comprising the following steps:

[0033] Step 1: Vanillin, tyramine and alcohol solvents are mixed for condensation reaction. Then, DOPO (9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide) is dissolved in alcohol solvent and added dropwise to the reaction system to obtain a bisphenol monomer with the structure shown in Formula II.

[0034] Formula II: ;

[0035] The synthetic route for bisphenol monomers is as follows:

[0036] .

[0037] The molar ratio of vanillin to tyramine is preferably 1:1 to 1.5, specifically 1:1.05; the molar ratio of vanillin to DOPO is preferably 1:1 to 1.5, specifically 1:1.05; and the alcohol solvent is preferably methanol.

[0038] The preferred reaction temperature is 40-80℃, specifically 50℃, 60℃, or 70℃; the preferred reaction is carried out under reflux conditions; and the preferred reaction time is 20-26 hours, specifically 22 hours, 23 hours, 24 hours, or 25 hours. Under the above conditions, the synthesis of bisphenol monomers in this invention can promote efficient reaction.

[0039] Step 2: The bisphenol monomer, catalyst and epichlorohydrin are mixed to carry out an epoxidation reaction. Then the resulting epoxidation reaction solution is mixed with sodium hydroxide to carry out a ring-closure reaction to obtain the flame-retardant bio-based epoxy resin monomer with the structure shown in Formula I.

[0040] The combined reaction processes of epoxidation and ring-closing reactions are shown below:

[0041] .

[0042] The molar ratio of the bisphenol monomer to the catalyst is preferably 1:0.001~0.1, specifically 1:0.02, 1:0.03, 1:0.04, 1:0.06, or 1:0.08. The catalyst is preferably one or more quaternary ammonium salts; the quaternary ammonium salt is preferably one or more of tetrabutylammonium bromide, tetrabutylammonium chloride, tetrabutylammonium iodide, and hexadecyltrimethylammonium bromide. The catalyst used in this invention can promote the reaction, accelerate the reaction rate, and improve selectivity.

[0043] The molar ratio of the bisphenol monomer to epichlorohydrin is preferably 1:8 to 30, specifically 1:10, 1:13, 1:14, or 1:15; the molar ratio of the bisphenol monomer to sodium hydroxide is preferably 1:0.1 to 0.7, specifically 1:0.06, 1:0.08, 1:0.1, 1:0.2, 1:0.3, 1:0.4, or 1:0.5; the sodium hydroxide is used in the form of an aqueous solution, the mass concentration of which is preferably 5% to 50%, specifically 40%; the sodium hydroxide aqueous solution is preferably added dropwise.

[0044] The preferred temperature for the epoxidation reaction is 50-100℃, specifically 80℃, and the preferred time is 2-7 hours, specifically 6 hours; the stirring speed is 400 r / min. After the epoxidation reaction is completed, it is preferable to cool the resulting reaction solution and add sodium hydroxide aqueous solution dropwise to carry out the ring-closing reaction.

[0045] The preferred temperature for the ring-closure reaction is -5 to 10°C, specifically 0°C; the preferred time is 2 to 7 hours, specifically 3 hours, 4 hours, 5 hours, or 6 hours; the stirring speed is 400 r / min. After the ring-closure reaction is completed, the resulting reaction solution is preferably extracted with ethyl acetate, then washed with deionized water until neutral, and the washed solution is then dried by vacuum distillation and purified by column chromatography to obtain the flame-retardant bio-based epoxy resin monomer with the structure shown in Formula I; the preferred eluent for the column chromatography purification is petroleum ether.

[0046] In this invention, the preferred steps of the preparation method are as follows:

[0047] Vanillin was first dissolved in an alcohol solvent and then added dropwise to a three-necked round-bottom flask containing tyramine. After stirring at 50°C for 5 hours, DOPO dissolved in the alcohol solvent was added to the system. After the reaction was completed, the resulting reaction solution was filtered, and the resulting solid product was washed with methanol and dried to obtain bisphenol monomer. Then, the bisphenol monomer, catalyst, and epichlorohydrin were mixed for an epoxidation reaction. The resulting epoxidation reaction solution was mixed with sodium hydroxide for a ring-closing reaction to obtain a flame-retardant bio-based epoxy resin monomer with the structure shown in Formula I.

[0048] The present invention also provides a bio-based epoxy resin, which is prepared from an epoxy resin monomer and a curing agent. The epoxy resin monomer is the flame-retardant bio-based epoxy resin monomer described above or the flame-retardant bio-based epoxy resin monomer prepared by the preparation method described above. The curing agent is one or more of the following: an amino-containing curing agent, an amino-disulfide bond-containing curing agent, and an amino-siloxane-silicon bond-containing curing agent.

[0049] The amino-containing curing agent is preferably 4,4'-diaminodiphenylmethane (DDM) and / or 1,6-hexanediamine; the amino-disulfide bond-containing curing agent is preferably 4,4'-diaminodiphenyl disulfide and / or 3,3'-dithiodipropionic acid; the amino-siloxane bond-containing curing agent is preferably 1,3-bis(3-aminopropyl)tetramethyldisiloxane and / or bis(4-aminophenoxy)dimethylsilane.

[0050] The preferred molar ratio of the flame-retardant bio-based epoxy resin monomer to the curing agent is 1:1 to 3, and more specifically, it can be 1:2.

[0051] This invention also provides a method for preparing the above-described bio-based epoxy resin, comprising the following steps:

[0052] Flame-retardant bio-based epoxy resin monomers and a curing agent are mixed, and then the mixture is poured into a mold for curing to obtain a bio-based epoxy resin. The curing process includes a first curing and a second curing, wherein the first curing temperature is 60~120℃ and the time is 4~12h, and the second curing temperature is 120~160℃ and the time is 2~12h.

[0053] In this invention, it is preferred to first stir and mix the flame-retardant bio-based epoxy resin monomer and the curing agent evenly, then perform vacuum degassing, and finally pour it into a mold for curing.

[0054] Taking DDM as the curing agent as an example, the structure of the resulting bio-based epoxy resin after curing is shown in Formula III:

[0055] Formula III: .

[0056] The specific implementation of the present invention will be described in detail below with reference to specific embodiments. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0057] Example 1: Preparation of bisphenol monomers;

[0058] In a three-necked round-bottom flask equipped with a thermometer and a reflux condenser, tyramine (28.80 g, 0.21 mol) was dissolved in 100 mL of methanol at 50 °C with magnetic stirring at 400 rpm. Vanillin (37.93 g, 0.2 mol) dissolved in 50 mL of methanol was then added dropwise to the flask, and the mixture was refluxed for 5 h. DOPO (45.36 g, 0.21 mol) dissolved in 100 mL of methanol was then added, and the mixture was refluxed for 20 h. After the reaction was complete, the mixture was filtered, and the resulting white powder was washed three times with methanol and dried overnight to obtain the bisphenol monomer (VD).

[0059] The proton NMR spectrum of the obtained bisphenol monomer is as follows: Figure 1 As shown, by Figure 1 It can be seen that the signal peak at 4.3 ppm belongs to the hydrogen signal peak on the carbon bonded to DOPO, indicating the successful synthesis of the bisphenol monomer.

[0060] Example 2: Preparation of flame-retardant bio-based epoxy resin monomer;

[0061] 20 g (0.041 mol) of bisphenol monomer prepared in Example 1, 65 mL (0.83 mol) of epichlorohydrin, and 1 g (0.0031 mol) of tetrabutylammonium bromide catalyst were added to a three-necked flask equipped with a mechanical stirrer and a condenser. The mixture was thoroughly mixed (stirring speed was 400 r / min). After heating to 80 °C and reacting for 6 h, heating was stopped, and the reaction system was placed in a 0 °C ice-water bath. 1.64 g of sodium hydroxide aqueous solution (mass concentration of 40%) was added dropwise to the reaction system, and the reaction was continued at 400 r / min for 3 h. After the reaction was completed, ethyl acetate was added for extraction, and the reaction solution was washed several times with deionized water until neutral. The washed product was purified by vacuum distillation, and then purified by drying and column chromatography to obtain a light yellow liquid, namely the flame-retardant bio-based epoxy resin monomer (VDEP) with the structure shown in Formula I.

[0062] The proton NMR spectrum of the obtained flame-retardant bio-based epoxy resin monomer is as follows: Figure 2 As shown, by Figure 2 It can be seen that the position of 6.5~8ppm is the hydrogen resonance peak in the benzene ring structure, indicating the successful synthesis of flame-retardant bio-based epoxy resin monomer (VDEP).

[0063] Example 3: Preparation of bio-based epoxy resin;

[0064] The raw materials used in the preparation include component A and component B. Component A is the flame-retardant bio-based epoxy resin monomer prepared in Example 2, and component B is the curing agent 4,4-diaminodiphenylmethane (DDM). The molar ratio of component A to component B is 1:0.5.

[0065] The specific preparation process of bio-based epoxy resin is as follows: First, add component A to a 25mL beaker, add the weighed component B at 110℃, stir for 10min to make it evenly mixed; then degas in a vacuum oven at 80℃ for 10min, then pour the mixture into a mold, cure at 80℃ for 8h, and then cure at 140℃ for 4h to obtain bio-based epoxy resin (VDEP-DDM).

[0066] The infrared spectrum of the obtained bio-based epoxy resin is shown below. Figure 3 As shown, by Figure 3 It can be seen that: 3200cm -1 The characteristic peak at 1235 cm⁻¹ belongs to the hydroxyl group in VDEP-DDM. -1 The presence of a characteristic peak belonging to CN in VDEP-DDM indicates the successful synthesis of bio-based epoxy resin (VDEP-DDM).

[0067] Example 4: Flexural performance test of bio-based epoxy resin;

[0068] The cured sample of the bio-based epoxy resin obtained in Example 3 was subjected to a bending test at room temperature on an electronic universal material machine.

[0069] Figure 4 The results of flexural strength and flexural modulus of the bio-based epoxy resin are presented. It can be seen that the flexural strength of the bio-based epoxy resin prepared in Example 3 is 160 MPa, and the flexural modulus is 4.91 GPa. Due to the presence of a large number of rigid structures such as aromatic rings in the epoxy network, this bio-based epoxy resin exhibits high mechanical strength, and its mechanical properties are comparable to those of commercial epoxy resins, meeting the requirements for use as a structural material.

[0070] Example 5: Flame retardant performance test of bio-based epoxy resin;

[0071] To comprehensively evaluate the performance of the bio-based epoxy resin prepared in Example 3, flame retardant performance tests were conducted. The test methods are as follows:

[0072] (1) Limiting oxygen index: According to GB / T 2406.2-2009 "Determination of combustion behavior of plastics by oxygen index method", the limiting oxygen index instrument was used for testing;

[0073] (2) UL-94 vertical flammability rating: Tested using a JT-HVR5455 flammability tester according to GB / T 2408-2008 "Determination of flammability of plastics by horizontal and vertical methods".

[0074] The test results are shown in Table 1:

[0075] Table 1. Test results of the bio-based epoxy resin prepared in Example 3

[0076]

[0077] As shown in Table 1, the flame-retardant bio-based epoxy resin prepared in Example 3 has a limiting oxygen index of 35.1% and a UL-94 vertical flammability rating of V-0. Combined with the mechanical properties of 160 MPa flexural strength and 4.91 GPa flexural modulus in Example 4, this demonstrates that it possesses both good mechanical properties and excellent flame retardancy. Because the monomer structure of the flame-retardant bio-based epoxy resin contains a rigid benzene ring structure, it ensures the resin's mechanical properties and thermal stability. Simultaneously, this monomer structure contains phosphorus, which can form a synergistic flame-retardant effect with nitrogen elements in the epoxy network, promoting the formation of a dense and continuous expanded carbon layer during combustion, thereby achieving highly efficient flame retardancy. Furthermore, the raw material is a renewable bio-based material, and the resin can meet the requirements of structural materials, providing a new method for the sustainable development of epoxy resin materials.

[0078] The above are merely preferred embodiments of the present invention. It should be noted that those skilled in the art can make several modifications and improvements without departing from the concept of the present invention, and these should also be considered within the scope of protection of the present invention. These modifications and improvements will not affect the effectiveness of the implementation of the present invention or the practicality of the patent.

Claims

1. A flame-retardant bio-based epoxy resin monomer, characterized in that, Its structure is shown in Equation I: Formula I: .

2. The method for preparing flame-retardant bio-based epoxy resin monomer as described in claim 1, characterized in that, Includes the following steps: Vanillin, tyramine, and an alcohol solvent were mixed and subjected to a condensation reaction. Then, DOPO was dissolved in the alcohol solvent and added dropwise to the reaction system to obtain a bisphenol monomer with the structure shown in Formula II. Formula II: ; The bisphenol monomer, catalyst, and epichlorohydrin were mixed and subjected to an epoxidation reaction. The resulting epoxidation reaction solution was then mixed with sodium hydroxide to carry out a ring-closing reaction. After the reaction was completed, the monomer was purified by extraction, washing, drying, distillation, and column chromatography to obtain the flame-retardant bio-based epoxy resin monomer with the structure shown in Formula I.

3. The preparation method according to claim 2, characterized in that, The molar ratio of vanillin to tyramine is 1:1 to 1.5; the molar ratio of vanillin to DOPO is 1:1 to 1.

5.

4. The preparation method according to claim 2, characterized in that, The condensation reaction is carried out at a temperature of 40-80°C for 20-26 hours.

5. The preparation method according to claim 2, characterized in that, The molar ratio of bisphenol monomer to catalyst is 1:0.001~0.1; the molar ratio of bisphenol monomer to epichlorohydrin is 1:8~30; and the molar ratio of bisphenol monomer to sodium hydroxide is 1:0.1~0.

7.

6. The preparation method according to claim 2, characterized in that, The catalyst is a quaternary ammonium salt, selected from one or more of tetrabutylammonium bromide, tetrabutylammonium chloride, tetrabutylammonium iodide, and hexadecyltrimethylammonium bromide; the sodium hydroxide is used in the form of an aqueous sodium hydroxide solution with a mass concentration of 5-50%.

7. The preparation method according to claim 2, characterized in that, The epoxidation reaction is carried out at a temperature of 50~100℃ for 2~7h, and the stirring speed is 100~500r / min; the ring-closing reaction is carried out at a temperature of -5~10℃ for 2~7h, and the stirring speed is 100~500r / min.

8. A bio-based epoxy resin, characterized in that, It is prepared from epoxy resin monomer and curing agent, wherein the epoxy resin monomer is the flame-retardant bio-based epoxy resin monomer of claim 1 or the flame-retardant bio-based epoxy resin monomer prepared by any one of claims 2 to 7; and the curing agent is an amino-containing curing agent.

9. The bio-based epoxy resin according to claim 8, characterized in that, The amino-containing curing agent is selected from 4,4'-diaminodiphenylmethane and / or 1,6-hexanediamine, 4,4'-diaminodiphenyl disulfide and / or 3,3'-dithiodipropionic acid, 1,3-bis(3-aminopropyl)tetramethyldisiloxane and / or bis(4-aminophenoxy)dimethylsilane.

10. The method for preparing the bio-based epoxy resin as described in claim 8 or 9, characterized in that, Includes the following steps: Flame-retardant bio-based epoxy resin monomers and curing agents are mixed, and then the mixture is poured into a mold for curing to obtain bio-based epoxy resin. The molar ratio of the flame-retardant bio-based epoxy resin monomer to the curing agent is 1:0.1~1; The curing process includes a first curing and a second curing, wherein the temperature of the first curing is 60~120℃ and the time is 4~12h, and the temperature of the second curing is 120~160℃ and the time is 2~12h.

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