Coumarin eleostearate type epoxy curing agent as well as preparation method and application thereof

Abstract

The invention discloses a coumarin eleostearate type epoxy curing agent as well as a preparation method and application thereof. The coumarin eleostearate type epoxy curing agent has a structural formula as shown in a formula I, wherein R1 is H or Me. The natural tung oil fat long chain is introduced into the epoxy resin, so that the toughness of the epoxy resin is improved, the elongation at break and the fatigue resistance of the epoxy resin are enhanced, and meanwhile, the natural extracted components do not generate toxic volatile matters in the use process and are environment-friendly. The coumarin derivative is added, so that the material can be endowed with higher tensile strength, and meanwhile, the application of the epoxy resin in the field of cultural relic repair adhesives is expanded by utilizing the luminescence characteristic of the parent nucleus structure of the coumarin derivative. Natural products are adopted as raw materials, the curing agent is obtained through simple esterification and Diels-Alder reaction, the process is simple, the reaction condition is mild, and the raw materials are green and free of pollution.

Description

Technical Field

[0001] The invention belongs to the field of epoxy resins, and particularly relates to a coumarin tung oil ester type epoxy curing agent, a preparation method and an application thereof. Background Art

[0002] As products of long-term natural evolution, plant oils and fats, rich in long aliphatic chains, provide a unique molecular foundation for material flexibility. Tung oil, a typical non-edible plant oil, boasts a unique conjugated triene structure and long carbon chain in its main component, eleostearic acid. This not only imparts excellent flexibility and thermal stability, but also, due to its high degree of unsaturation, makes it an ideal platform for chemical modification. However, current plant oil resource utilization faces significant challenges: According to statistics, approximately 80% of global plant oil processing products remain at the low-value-added stage, such as primary fatty acids and biodiesel, while the development of high-end materials with functional structures is severely lacking. This extensive utilization model significantly lags behind the demand for high-value bio-based materials within my country's "dual carbon" strategy. There is an urgent need to develop new material systems that combine functionality and sustainability through molecular design.

[0003] In the field of epoxy curing agents, anhydride curing agents have become an important alternative to amine curing agents due to their low irritation, long operating window, and excellent dielectric properties. In recent years, innovative research on biomass-based anhydride curing agents has shown that cardanol-based systems can improve corrosion resistance by 40%, rosin-based modification can increase heat deformation temperature by more than 25°C, and soybean oil-based systems can achieve an elongation at break that is up to three times that of traditional curing agents. These advances reveal the structure-activity relationship between the structural characteristics of biomass molecules and material properties: alicyclic structures enhance thermal stability, long alkyl chains impart flexibility, and aromatic groups contribute to mechanical strength. This provides important insights into the development of multifunctional curing agents through molecular assembly strategies.

[0004] Coumarin compounds, naturally occurring benzo-α-pyrone derivatives, exhibit a rigid planar structure that can produce significant fluorescence effects and mechanical reinforcement. Studies have shown that the conjugated coumarin ring system can increase the tensile strength of materials by up to 200%, while its multiple active sites (positions 3, 4, 7, and 8) provide a multi-dimensional design space for molecular functionalization. However, existing research has primarily focused on the application of coumarin monomers in optoelectronics, while their synergistic enhancement effects in epoxy-curing systems have not been fully explored. Based on this, this study innovatively combines the long-chain flexibility of eleostearic acid with the rigid fluorescent backbone of coumarin through a molecular engineering strategy: the long alkyl chains of eleostearic anhydride act as "flexible buffer units" to effectively disperse stress and inhibit crack propagation; the coumarin structure acts as a "rigid reinforcement unit" to form a physical cross-linked network through π-π stacking, while its fluorescent properties impart self-radiographic properties to the material. This combination of rigidity and flexibility not only breaks through the technical bottleneck of the trade-off between strength and toughness of traditional epoxy resins, but also, through functional integration, enables the material to demonstrate unique application value in cutting-edge fields such as wind turbine blade stress visualization monitoring and microcrack self-diagnosis in cultural relics restoration, opening up a new dimension for the high-end utilization of vegetable oils. Summary of the Invention

[0005] Technical problem solved: The present invention introduces coumarin into a tung oil-based anhydride curing agent to enhance the strength and fluorescence of epoxy resin. A coumarin tung oil ester-type epoxy curing agent and its preparation method and application are designed. The molecular structure contains a longer alkyl chain of tung oil, which is expected to improve the toughness of the epoxy resin. At the same time, the coumarin molecular skeleton is spliced ​​to enhance the strength and fluorescence of the epoxy resin, making the epoxy resin have broad application prospects in wind turbine blades, cultural relics restoration, coatings, aerospace, electronics, construction and other fields.

[0006] Technical solution: A coumarin tung oil ester type epoxy curing agent having the following structural formula I

[0007]

[0008] , where R 1 It is H or Me.

[0009] The preparation method of the above-mentioned coumarin tungoleate-type epoxy curing agent comprises the following steps: first, adding dichloromethane, tungoleic acid and coumarin derivatives to a reaction vessel and fully dissolving them, wherein the concentration of the dichloromethane is 0.05-0.1M, and the molar ratio of tungoleic acid to the coumarin derivative is (1-4):1; then adding a condensing agent, wherein the molar ratio of the condensing agent to the coumarin derivative is (1.1-1.5):1, and a catalyst accounting for 10% to 15 mol% of the coumarin derivative; reacting at room temperature for 5-10 hours; after the reaction is completed, removing the solvent by concentrating under reduced pressure; adding ethyl acetate in an amount equal to that of the dichloromethane, washing three times with hot water at 85-95°C, drying the organic layer, and concentrating under reduced pressure to obtain a curing agent precursor whose main component is an intermediate represented by formula V: In the second step, the compound of formula V and maleic anhydride are mixed and stirred, wherein the molar ratio of the compound of formula V to maleic anhydride is 1:(1-1.5), and a Diels-Alder reaction is carried out at 70-90° C. for 3-5 hours. After the reaction is completed, a coumarin tung oil ester type epoxy curing agent can be obtained.

[0010] The above coumarin derivative is any one of the following: umbelliferone 4-Methylumbelliferone 4-Hydroxycoumarin

[0011] The condensing agent is any one of 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride (EDCI) and N,N'-dicyclohexylcarbodiimide (DCC).

[0012] The catalyst is 4-dimethylaminopyridine (DMAP).

[0013] Preferably, the molar ratio of the eleostearic acid to the coumarin derivative is 2:1.

[0014] Application of the above-mentioned coumarin tung oil ester type epoxy curing agent in the preparation of fluorescent epoxy resin.

[0015] The application steps are as follows: mix the coumarin tung oil ester type epoxy curing agent with epoxy E51 or E44 in a molar ratio of 1:1, add 0.3wt.% to 1wt.% of accelerator DMP-30, N,N-dimethylbenzylamine or benzylamine, mix well and pour into the mold, degas at 60°C for 10 hours, cure at 100°C for 2 hours, and then cure at 180°C for 2 hours.

[0016] Beneficial effects: 1) The introduction of natural tung oil fatty long chains into epoxy resin improves the toughness of epoxy resin, which is beneficial to enhancing the elongation at break and fatigue resistance of epoxy resin. At the same time, the natural extracts do not produce toxic volatiles during use and are environmentally friendly. 2) The addition of coumarin derivatives can give the material higher tensile strength, while utilizing the luminescent properties of its own parent core structure to expand the application of epoxy resin in the field of cultural relics restoration adhesives. 3) The curing agent is obtained by using natural products as raw materials through simple esterification and Diels-Alder reaction. The process is simple, the reaction conditions are mild, and the raw materials are green and pollution-free. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is the infrared spectrum of the umbelliferone-eleostearic acid curing agent intermediate.

[0018] Figure 2 This is the H NMR spectrum of the umbelliferone-eleostearic acid curing agent intermediate.

[0019] Figure 3 It is the luminescence characteristic of the curing agent under ultraviolet light. DETAILED DESCRIPTION

[0020] Some examples are given below to further illustrate the present invention, but the following examples are not intended to limit the scope of protection of the present invention. Non-essential improvements and adjustments made by technicians in this field based on the content of the present invention still fall within the scope of protection of the present invention.

[0021] Example 1

[0022] Umbelliferone (20 mmol, 3.3 g) and eleostearic acid were added to a flask according to the amounts listed in Table 1. Dichloromethane (0.05 M, 400 mL), EDCI (30 mmol, 5.9 g), and DMAP (3 mmol, 370 mg) were then added. The reaction was allowed to proceed at room temperature for 5 to 10 hours. After completion of the reaction, the solvent was removed by concentrating under reduced pressure. 400 mL of ethyl acetate was added, and the mixture was washed three times with hot water. The organic layer was dried over anhydrous magnesium sulfate or anhydrous sodium sulfate, and then concentrated under reduced pressure to obtain a curing agent precursor.

[0023] The curing agent precursor and maleic anhydride were mixed and stirred according to the amounts shown in Table 1, and a Diels-Alder reaction was carried out at 60-90° C. for 3-5 hours. After the reaction was completed, a coumarin tung oil ester type epoxy curing agent was obtained.

[0024] Table 1 Preparation ratio of curing agent 1-6

[0025] Umbelliferone Eleuropein Maleic anhydride Curing agent 1 3.3g 6.0g 2.4g Curing agent 2 3.3g 12.0g 4.8g Curing agent 3 3.3g 15.0g 6.0g Curing agent 4 3.3g 18.0g 7.2g Curing agent 5 3.3g 21.0g 8.4g Curing agent 6 3.3g 24.0g 9.6g

[0026] Example 2

[0027] 4-Methylumbelliferone (20 mmol, 3.6 g) and eleostearic acid (60 mmol, 18.0 g) were added to a flask, followed by dichloromethane (400 mL), a condensing agent (DCC) (30 mmol, 6.2 g), and a catalyst (3 mmol, 370 mg). The mixture was reacted at room temperature for 5-10 h. After completion of the reaction, the solvent was removed by concentrating under reduced pressure. Ethyl acetate (400 mL) was added and washed three times with hot water. The organic layer was dried over anhydrous magnesium sulfate or anhydrous sodium sulfate and concentrated under reduced pressure to obtain a curing agent precursor. The curing agent precursor was mixed with maleic anhydride (7.2 g) and stirred. A Diels-Alder reaction was carried out at 60-90°C for 3-5 h. After completion of the reaction, a coumarin eleostearate-type epoxy curing agent 7 was obtained.

[0028] Comparative Example:

[0029] Experimental Group 1: 5.2 g of curing agent 1 prepared in Example 1 was accurately weighed, and then 1% of the curing agent mass of the accelerator benzylamine was added, followed by 3.75 g of E51. After mixing evenly, the sample was poured into a 50 × 10 × 4 mm mold. The sample was first left overnight or vacuum dried at 50°C to eliminate bubbles, and then cured at high temperature. The curing procedure was: curing at 100°C for 2 hours and curing at 180°C for 2 hours.

[0030] Experimental Group 2: 6.28 g of curing agent 2 prepared in Example 1 was accurately weighed, and then 1% of the mass of the curing agent, benzylamine, an accelerator, was added. Then, 5.26 g of E51 was added and mixed evenly. The sample was poured into a 50 × 10 × 4 mm mold. The sample was first left overnight or vacuum dried at 50°C to eliminate bubbles, and then cured at high temperature. The curing procedure was: curing at 100°C for 2 hours and curing at 180°C for 2 hours.

[0031] Experimental Group 3: 6.08 g of curing agent 3 prepared in Example 1 was accurately weighed, and then 1% of the mass of the curing agent, benzylamine, an accelerator, and 5.26 g of E51 were added. After mixing evenly, the sample was poured into a 50×10×4 mm mold. The sample was first left overnight or vacuum-dried at 50°C to eliminate bubbles, and then cured at high temperature. The curing procedure was: curing at 100°C for 2 hours and curing at 180°C for 2 hours.

[0032] Experimental Group 4: 6.3 g of curing agent 4 prepared in Example 1 was accurately weighed, and then 1% of the mass of the curing agent, benzylamine, an accelerator, and 5.59 g of E51 were added. After mixing evenly, the sample was poured into a 50×10×4 mm mold. The sample was first left overnight or vacuum-dried at 50°C to eliminate bubbles, and then cured at high temperature. The curing procedure was: curing at 100°C for 2 hours and curing at 180°C for 2 hours.

[0033] Experimental Group 5: 4.24 g of curing agent 4 prepared in Example 1 was accurately weighed, and then 1% of the mass of the curing agent, benzylamine, an accelerator, was added. Then, 4.55 g of E44 was added and mixed evenly. The sample was poured into a 50 × 10 × 4 mm mold. The sample was first left overnight or vacuum dried at 50°C to eliminate bubbles, and then cured at high temperature. The curing procedure was: curing at 100°C for 2 hours and curing at 180°C for 2 hours.

[0034] Experimental Group 6: 5.84 g of curing agent 5 prepared in Example 1 was accurately weighed, and then 1% of the mass of the curing agent, benzylamine, an accelerator, was added. Then, 5.26 g of E51 was added and mixed evenly. The sample was poured into a 50 × 10 × 4 mm mold. The sample was first left overnight or vacuum dried at 50°C to eliminate bubbles, and then cured at high temperature. The curing procedure was: curing at 100°C for 2 hours and curing at 180°C for 2 hours.

[0035] Experimental Group 7: 5.84 g of curing agent 6 prepared in Example 1 was accurately weighed, and then 1% of the curing agent mass of the accelerator benzylamine was added, followed by 5.26 g of E51. After mixing evenly, the sample was poured into a 50×10×4 mm mold. The sample was first left overnight or vacuum-dried at 50°C to eliminate bubbles, and then cured at high temperature. The curing procedure was: curing at 100°C for 2 hours and curing at 180°C for 2 hours.

[0036] Experimental Group 8: Accurately weigh 6.44 g of curing agent 7 prepared in Example 2, then add 1% of the curing agent mass of the accelerator benzylamine, and then add 5.64 g of E51. After mixing evenly, the sample is poured into a 50×10×4 mm mold. First, the sample is left overnight or vacuum-dried at 50°C to eliminate bubbles, and then cured at high temperature. The curing procedure is: curing at 100°C for 2 hours and curing at 180°C for 2 hours.

[0037] The mechanical properties of the above 8 thermosetting materials were analyzed, and the test results are shown in Table 2.

[0038] Table 2 Comparison of mechanical properties of experimental groups

[0039]

[0040]

[0041] Example 3

[0042] Accurately weigh 6.28g of curing agent 2, then add 1% of the curing agent's mass as accelerator benzylamine, followed by 5.26g of E51. After mixing thoroughly, pour the mixture into a silicone mold, impregnate the cut carbon fiber sample into the mixture, and stack it layer by layer. After stacking three layers, let it sit overnight to eliminate bubbles, then high-temperature cure at 100°C for 2 hours and 180°C for 2 hours. Mechanical testing shows that the prepared coumarin tung oil ester-based epoxy curing agent can significantly improve the tensile strength of carbon fiber materials.

[0043] Table 3 Comparison of mechanical properties

[0044] project Tensile strength (MPa) Elongation at break (%) Elastic modulus (MPa) Three-layer carbon fiber 9.62 34.8695 640.63 Composite Spline 68.38 2.1336 1567.05

Claims

1. A coumarin tung oil ester type epoxy curing agent, characterized in that, It has the following structural formula I: ， where R 1 It is H or Me.

2. The method for preparing the coumarin tung oil ester type epoxy curing agent according to claim 1, characterized in that: The steps are as follows: first, adding dichloromethane, eleostearic acid and coumarin derivatives into a reaction vessel and fully dissolving them, wherein the concentration of the dichloromethane is 0.05-0.1M, and the molar ratio of eleostearic acid to the coumarin derivative is (1-4):1; then adding a condensing agent, wherein the molar ratio of the condensing agent to the coumarin derivative is (1.1-1.5):1, and a catalyst accounting for 10% to 15 mol% of the coumarin derivative; reacting at room temperature for 5-10 hours; after the reaction is completed, removing the solvent by concentrating under reduced pressure; adding ethyl acetate in an amount equal to that of the dichloromethane, washing three times with hot water at 85-95°C, drying the organic layer, and concentrating under reduced pressure to obtain a curing agent precursor whose main component is an intermediate represented by formula V: In the second step, the compound of formula V and maleic anhydride are mixed and stirred, wherein the molar ratio of the compound of formula V to maleic anhydride is 1: (1-1.5), a Diels-Alder reaction is carried out at 70-90° C. for 3-5 h. After the reaction is completed, a coumarin tung oil ester type epoxy curing agent can be obtained.

3. The method for preparing the coumarin tung oil ester type epoxy curing agent according to claim 2, characterized in that: The coumarin derivative is any one of the following: umbelliferone 4-Methylumbelliferone 4-Hydroxycoumarin 4. The method for preparing the coumarin tung oil ester type epoxy curing agent according to claim 2, wherein: The condensing agent is any one of 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride (EDCI) and N,N'-dicyclohexylcarbodiimide (DCC).

5. The method for preparing the coumarin tung oil ester type epoxy curing agent according to claim 2, characterized in that: The catalyst is 4-dimethylaminopyridine (DMAP).

6. The method for preparing the coumarin tung oil ester type epoxy curing agent according to claim 2, characterized in that: The molar ratio of the eleostearic acid to the coumarin derivative is 2:

1.

7. Use of the coumarin tung oil ester type epoxy curing agent according to claim 1 in the preparation of fluorescent epoxy resin.

8. The use according to claim 7, characterized in that The method comprises the following steps: mixing a coumarin tung oil ester type epoxy curing agent with epoxy E51 or E44 at a molar ratio of 1:1, adding 0.3 wt.% to 1 wt.% of an accelerator DMP-30 and N,N-dimethylbenzylamine or benzylamine, mixing evenly and pouring the mixture into a mold, degassing at 60°C for 10 hours, curing at 100°C for 2 hours, and then curing at 180°C for 2 hours.

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