Preparation method of vanillin-based flexible flame-retardant aromatic amine epoxy curing agent

Abstract

The invention relates to a preparation method of a vanillin-based flexible flame-retardant aromatic amine epoxy curing agent, which comprises the following steps: by taking N, N-dimethylformamide (DMF) as a solvent, carrying out epoxy ring-opening addition reaction on vanillin and glycidyl ether under the action of a 4-dimethylaminopyridine (DMAP) catalyst to obtain flexible vanillin VAN-EPO; the preparation method comprises the following steps: with tetrahydrofuran THF as a solvent, carrying out a Schiff base condensation reaction on flexible vanillin VAN-EPO and aromatic amine to obtain an imine intermediate; and carrying out addition reaction on the imine intermediate and a phosphorus-containing compound to obtain the vanillin-based flexible flame-retardant aromatic amine epoxy curing agent. The molecular structure of the vanillin-based flexible flame-retardant aromatic amine epoxy curing agent prepared by the method provided by the invention contains a biomass raw material vanillin, also contains a flexible polyethylene / propylene glycol structure and a flame-retardant element phosphorus, and has multiple effects of environmental protection, toughening and flame retardance. The vanillin-based flexible flame-retardant aromatic amine epoxy curing agent has the characteristics of mild reaction conditions and simple process.

Description

Technical Field

[0001] This invention relates to the field of epoxy resin and composite material technology, and in particular to a method for preparing a vanillin-based flexible flame-retardant aromatic amine epoxy curing agent and its application. Background Technology

[0002] Epoxy resin / fiber composites are widely used in marine equipment, aerospace, transportation, and other fields, and are mainly composed of epoxy resin, curing agent, and fiber. Traditional glass fiber and carbon fiber are gradually being replaced by natural fibers such as bamboo and wood, which also places higher demands on epoxy resins. Traditional epoxy resins and curing agents are prepared from petrochemical-based raw materials, which will gradually fade from the market due to their consumption of strategic petrochemical resources and potential environmental pollution. Therefore, the research and development of renewable, low-ecotoxicity, and bio-based epoxy curing agents that meet the needs of industry development has attracted the attention of researchers both domestically and internationally.

[0003] Vanillin is a widely used and affordable industrial lignin raw material, an important bio-based resource, and a crucial raw material and intermediate in pharmaceuticals, chemicals, and agriculture. Containing reactive aldehyde and phenolic hydroxyl groups, it can serve as a platform for building multifunctional renewable materials. Aromatic amine curing agents are widely used in epoxy / fiber composites due to their high temperature resistance, strong alkali resistance, and long pot life; however, they suffer from high brittleness. Furthermore, natural fibers such as bamboo and wood are flammable, posing safety hazards.

[0004] Therefore, the development of vanillin-based flexible flame-retardant aromatic amine epoxy curing agents is of great significance to the development of the industry. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing and applying a vanillin-based flexible flame-retardant aromatic amine epoxy curing agent. The vanillin-based flexible flame-retardant aromatic amine epoxy curing agent is cured with water-based epoxy to prepare epoxy / natural fiber composite materials, which have excellent flexibility, biodegradability, and environmental friendliness, and can be applied in the field of epoxy composite materials.

[0006] To achieve the above objectives, the present invention provides the following solution:

[0007] This invention provides a method for preparing a vanillin-based flexible flame-retardant aromatic amine epoxy curing agent, characterized by using an epoxy ring-opening addition reaction and a Schiff base condensation reaction to prepare the vanillin-based flexible flame-retardant aromatic amine epoxy curing agent, comprising the following steps: First, using N,N-dimethylformamide (DMF) as a solvent and 4-dimethylaminopyridine (DMAP) as a catalyst, vanillin and glycidyl ether undergo an epoxy ring-opening addition reaction to obtain flexible vanillin (VAN-EPO); Second, flexible vanillin (VAN-EPO) and an aromatic amine undergo a Schiff base condensation reaction in tetrahydrofuran (THF) to obtain an imine intermediate; the imine intermediate is then reacted with a phosphorus-containing compound through an addition reaction to obtain a vanillin-based flexible flame-retardant aromatic amine epoxy curing agent (VEPDM).

[0008] The epoxy curing agent prepared in this invention uses vanillin, a lignin derivative, as its raw material. It is combined with water-based epoxy and natural fibers to prepare bio-based epoxy / fiber composite materials. The raw materials are renewable, the products are biodegradable, the preparation process is simple, and the environmental pollution is small. On the other hand, the curing agent contains a flexible polyethylene / propylene glycol structure and the flame-retardant element phosphorus in its bulk structure. The multifunctional groups synergistically enhance the flexibility and flame-retardant properties of the epoxy composite material.

[0009] Preferably, in the preparation method of vanillin-based flexible flame-retardant aromatic amine epoxy curing agent, the molar ratio of vanillin to glycidyl ether is 2:1.

[0010] Preferably, in the preparation method of vanillin-based flexible flame-retardant aromatic amine epoxy curing agent, the molar ratio of flexible vanillin (VAN-EPO), aromatic amine and phosphorus-containing compound is 1:2:2.

[0011] Preferably, in the preparation method of vanillin-based flexible flame-retardant aromatic amine epoxy curing agent, the glycidyl ether is one of ethylene glycol diglycidyl ether, 1,4-butanediol diglycidyl ether, polypropylene glycol diglycidyl ether, and polyethylene glycol diglycidyl ether.

[0012] Preferably, in the preparation method of vanillin-based flexible flame-retardant aromatic amine epoxy curing agent, the aromatic amine is one of 3,3'-oxydiphenylamine, diethyltoluenediamine, 2,2'-(ethylenedioxy)diphenylamine, and 2,6-diethylaniline.

[0013] Preferably, in the preparation method of vanillin-based flexible flame-retardant aromatic amine epoxy curing agent, the phosphorus-containing compound is one of diethyl phosphite or 10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO).

[0014] Preferably, in the preparation method of vanillin-based flexible flame-retardant aromatic amine epoxy curing agent, the epoxy addition reaction temperature is 100℃~150℃ and the reaction time is 5h~10h.

[0015] Preferably, in the preparation method of vanillin-based flexible flame-retardant aromatic amine epoxy curing agent, the Schiff base condensation reaction temperature is 30℃~50℃ and the reaction time is 5h~10h; the addition reaction temperature is 50℃~80℃ and the reaction time is 3h~6h.

[0016] Preferably, in the preparation method of vanillin-based flexible flame-retardant aromatic amine epoxy curing agent, the amount of catalyst 4-dimethylaminopyridine (DMAP) added accounts for 1 wt% of the total mass of the reactants.

[0017] A vanillin-based flexible flame-retardant aromatic amine epoxy curing agent is prepared by the aforementioned preparation method.

[0018] This invention uses vanillin, a lignin derivative, as a raw material and employs reactions such as epoxy ring-opening addition and Schiff base condensation to prepare a vanillin-based flexible flame-retardant aromatic amine epoxy curing agent.

[0019] The preparation process of this invention is simple, using only biomass resources as raw materials with low ecotoxicity. The curing agent itself contains multiple functional groups, which can improve the overall performance of epoxy composites. Performance tests show that, compared with pure aromatic amine curing agents, the bio-based epoxy curing agent prepared by the method of this invention has superior flexibility. Therefore, the use of renewable, biodegradable, and environmentally friendly biomass resources in epoxy composites is of great significance.

[0020] The present invention discloses the following technical effects:

[0021] (1) The raw material lignin derivative vanillin involved in this invention is renewable and biodegradable.

[0022] (2) The reactions involved in this invention are ring-opening addition and Schiff base condensation reactions, and the process equipment and reaction process are simple.

[0023] (3) The vanillin-based flexible flame-retardant aromatic amine epoxy curing agent contains a polyethylene / propylene glycol structure and the flame-retardant element phosphorus, which has multiple effects of environmental protection, toughening and flame retardancy. It can achieve the purpose of "one agent with multiple effects". Attached Figure Description

[0024] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the accompanying drawings used in the embodiments will be briefly described below.

[0025] Figure 1 The images show the Fourier transform infrared (FTIR) spectra of vanillin, vanillin-based flexible flame-retardant aromatic amine epoxy curing agent (VEPDM), and intermediate products in Examples 1 and 2 of this invention. Detailed Implementation

[0026] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0027] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0028] Unless otherwise specified in the following embodiments, all process equipment or devices used are conventional equipment or devices in the art.

[0029] Example 1

[0030] This embodiment provides a method for preparing a vanillin-based flexible flame-retardant aromatic amine epoxy curing agent, comprising the following steps:

[0031] In the first step, vanillin and ethylene glycol diglycidyl ether were dissolved in N,N-dimethylformamide (DMF) at a molar ratio of 2:1. An epoxy ring-opening addition reaction was carried out under the catalysis of 4-dimethylaminopyridine (DMAP) at a temperature of 100°C for 10 h to obtain flexible vanillin (VAN-EPO).

[0032] In the second step, flexible vanillin (VAN-EPO) and 3,3'-oxydiphenylamine were dissolved in tetrahydrofuran and subjected to a Schiff base condensation reaction at 40°C for 8 hours to obtain an imine intermediate. The imine intermediate was then mixed with diethyl phosphite and subjected to an addition reaction at 80°C for 4 hours to obtain a vanillin-based flexible flame-retardant aromatic amine epoxy curing agent (VEPDM). The molar ratio of flexible vanillin (VAN-EPO), 3,3'-oxydiphenylamine, and diethyl phosphite was 1:2:2. The mechanical properties were tested, and the results are shown in Table 1.

[0033] Example 2

[0034] This embodiment provides a method for preparing a vanillin-based flexible flame-retardant aromatic amine epoxy curing agent, comprising the following steps:

[0035] In the first step, vanillin and polyethylene glycol diglycidyl ether were dissolved in N,N-dimethylformamide (DMF) at a molar ratio of 2:1. An epoxy ring-opening addition reaction was carried out under the catalysis of 4-dimethylaminopyridine (DMAP) at a temperature of 130°C for 8 h to obtain flexible vanillin (VAN-EPO).

[0036] In the second step, flexible vanillin (VAN-EPO) and diethyltoluene diamine were dissolved in tetrahydrofuran and subjected to a Schiff base condensation reaction at 50°C for 5 hours to obtain an imine intermediate. The imine intermediate was then mixed with diethyl phosphite and subjected to an addition reaction at 70°C for 3 hours to obtain a vanillin-based flexible flame-retardant aromatic amine epoxy curing agent (VEPDM). The molar ratio of flexible vanillin (VAN-EPO), diethyltoluene diamine, and diethyl phosphite was 1:2:2. The mechanical properties were tested, and the results are shown in Table 1.

[0037] Example 3

[0038] This embodiment provides a method for preparing a vanillin-based flexible flame-retardant aromatic amine epoxy curing agent, comprising the following steps:

[0039] In the first step, vanillin and polypropylene glycol diglycidyl ether were dissolved in N,N-dimethylformamide (DMF) at a molar ratio of 2:1. An epoxy ring-opening addition reaction was carried out under the catalysis of 4-dimethylaminopyridine (DMAP) at a temperature of 150°C for 5 h to obtain flexible vanillin (VAN-EPO).

[0040] In the second step, flexible vanillin (VAN-EPO) and 2,6-diethylaniline were dissolved in tetrahydrofuran and subjected to a Schiff base condensation reaction at 30°C for 10 hours to obtain an imine intermediate. The imine intermediate was then mixed with 10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) and subjected to an addition reaction at 80°C for 2 hours to obtain a vanillin-based flexible flame-retardant aromatic amine epoxy curing agent (VEPDM). The molar ratio of flexible vanillin (VAN-EPO), 2,6-diethylaniline, and DOPO was 1:2:2. The mechanical properties were tested, and the results are shown in Table 1.

[0041] Example 4

[0042] This embodiment provides a method for preparing a vanillin-based flexible flame-retardant aromatic amine epoxy curing agent, comprising the following steps:

[0043] In the first step, vanillin and polypropylene glycol diglycidyl ether were dissolved in N,N-dimethylformamide (DMF) with a molar ratio of vanillin to 1,4-butanediol diglycidyl ether of 2:1. An epoxy ring-opening addition reaction was carried out under the catalysis of 4-dimethylaminopyridine (DMAP) at a temperature of 120°C for 7 h to obtain flexible vanillin (VAN-EPO).

[0044] In the second step, flexible vanillin (VAN-EPO) and 2,2'-(ethylenedioxy)diphenylamine were dissolved in tetrahydrofuran and subjected to a Schiff base condensation reaction at 35°C for 8 hours to obtain an imine intermediate. The imine intermediate was then mixed with 10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) and subjected to an addition reaction at 50°C for 6 hours to obtain a vanillin-based flexible flame-retardant aromatic amine epoxy curing agent (VEPDM). The molar ratio of flexible vanillin (VAN-EPO), 2,2'-(ethylenedioxy)diphenylamine, and DOPO was 1:2:2. The mechanical properties were tested, and the results are shown in Table 1.

[0045] Example 5

[0046] This embodiment provides a method for preparing a vanillin-based flexible flame-retardant aromatic amine epoxy curing agent, comprising the following steps:

[0047] In the first step, vanillin and polyethylene glycol diglycidyl ether were dissolved in N,N-dimethylformamide (DMF) at a molar ratio of 2:1. An epoxy ring-opening addition reaction was carried out under the catalysis of 4-dimethylaminopyridine (DMAP) at a temperature of 140°C for 6 h to obtain flexible vanillin (VAN-EPO).

[0048] In the second step, flexible vanillin (VAN-EPO) and diethyltoluene diamine were dissolved in tetrahydrofuran and subjected to a Schiff base condensation reaction at 40°C for 6 hours to obtain an imine intermediate. The imine intermediate was then mixed with 10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) and subjected to an addition reaction at 70°C for 3 hours to obtain a vanillin-based flexible flame-retardant aromatic amine epoxy curing agent (VEPDM). The molar ratio of flexible vanillin (VAN-EPO), diethyltoluene diamine, and DOPO was 1:2:2. The mechanical properties were tested, and the results are shown in Table 1.

[0049] Example 6

[0050] This embodiment provides a method for preparing a vanillin-based flexible flame-retardant aromatic amine epoxy curing agent, comprising the following steps:

[0051] In the first step, vanillin and polypropylene glycol diglycidyl ether were dissolved in N,N-dimethylformamide (DMF) at a molar ratio of 2:1. An epoxy ring-opening addition reaction was carried out under the catalysis of 4-dimethylaminopyridine (DMAP) at a temperature of 120°C for 8 hours to obtain flexible vanillin (VAN-EPO).

[0052] In the second step, flexible vanillin (VAN-EPO) and 3,3'-oxydiphenylamine were dissolved in tetrahydrofuran and subjected to a Schiff base condensation reaction at 40°C for 6 hours to obtain an imine intermediate. The imine intermediate was then mixed with 10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) and subjected to an addition reaction at 80°C for 2 hours to obtain a vanillin-based flexible flame-retardant aromatic amine epoxy curing agent (VEPDM). The molar ratio of flexible vanillin (VAN-EPO), 3,3'-oxydiphenylamine, and DOPO was 1:2:2. The mechanical properties were tested, and the results are shown in Table 1.

[0053] The infrared spectra of vanillin, vanillin-based flexible flame-retardant aromatic amine epoxy curing agent (VEPDM), and intermediate products in Examples 1 and 2 of this invention are shown below. Figure 1 ,Depend on Figure 1 It can be seen that at 2426 cm -1 1678cm -1 907cm -1 The characteristic peaks at 1280 cm⁻¹ belong to pH, C=O, and the epoxy group disappears, respectively. -1 The characteristic peak at 960 cm⁻¹ belongs to P=O. -1 The characteristic peak belongs to P−OC. The results indicate that the target compound was successfully synthesized.

[0054] Pure aniline and pure aniline with 20 wt% of vanillin-based flexible flame-retardant aromatic amine epoxy curing agents prepared in Examples 1-6 (denoted as 1-2, 2-2, 3-3, 4-2, 5-2, 6-2, respectively) were cured with waterborne epoxy resin and their mechanical properties were tested using a universal testing machine, as shown in Table 1.

[0055]

[0056] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for preparing a vanillin-based flexible flame-retardant aromatic amine epoxy curing agent, characterized in that, A vanillin-based flexible flame-retardant aromatic amine epoxy curing agent is prepared by an epoxy ring-opening addition reaction and a Schiff base condensation reaction, comprising the following steps: First, using N,N-dimethylformamide (DMF) as a solvent and 4-dimethylaminopyridine (DMAP) as a catalyst, vanillin and glycidyl ether undergo an epoxy ring-opening addition reaction to obtain flexible vanillin VAN-EPO; Second, flexible vanillin VAN-EPO and an aromatic amine undergo a Schiff base condensation reaction in tetrahydrofuran (THF) to obtain an imine intermediate; The imine intermediate is then reacted with a phosphorus-containing compound through an addition reaction to obtain the vanillin-based flexible flame-retardant aromatic amine epoxy curing agent.

2. The preparation method of the vanillin-based flexible flame-retardant aromatic amine epoxy curing agent according to claim 1, characterized in that, The molar ratio of vanillin to glycidyl ether is 2:

1.

3. The preparation method of the vanillin-based flexible flame-retardant aromatic amine epoxy curing agent according to claim 1, characterized in that, The molar ratio of flexible vanillin (VAN-EPO), aromatic amine, and phosphorus-containing compound is 1:2:

2.

4. The preparation method of the vanillin-based flexible flame-retardant aromatic amine epoxy curing agent according to claim 1, characterized in that, The glycidyl ether is one of ethylene glycol diglycidyl ether, 1,4-butanediol diglycidyl ether, polypropylene glycol diglycidyl ether, and polyethylene glycol diglycidyl ether.

5. The preparation method of the vanillin-based flexible flame-retardant aromatic amine epoxy curing agent according to claim 1 or 3, characterized in that, The aromatic amine is one of 3,3'-oxydiphenylamine, diethyltoluenediamine, 2,2'-(ethylenedioxy)diphenylamine, or 2,6-diethylaniline.

6. The preparation method of the vanillin-based flexible flame-retardant aromatic amine epoxy curing agent according to claim 1 or 3, characterized in that, The phosphorus-containing compound is one of diethyl phosphite or 10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO).

7. The preparation method of the vanillin-based flexible flame-retardant aromatic amine epoxy curing agent according to claim 1, characterized in that, The epoxy ring-opening addition reaction temperature is 100℃~150℃, and the reaction time is 5h~10h.

8. The preparation method of the vanillin-based flexible flame-retardant aromatic amine epoxy curing agent according to claim 1, characterized in that, The Schiff base condensation reaction temperature is 30℃~50℃, and the reaction time is 5h~10h; the addition reaction temperature is 50℃~80℃, and the reaction time is 3h~6h.

9. The preparation method of the vanillin-based flexible flame-retardant aromatic amine epoxy curing agent according to claim 2, characterized in that, The amount of catalyst 4-dimethylaminopyridine (DMAP) added is 1 wt% of the total mass of the reactants.

10. A vanillin-based flexible flame-retardant aromatic amine epoxy curing agent, characterized in that, It is prepared by the preparation method described in any one of claims 1 to 8.

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