Preparation process and application of phthalonitrile-modified aramid fiber

Abstract

The present invention relates to the technical field of aramid fibers, and discloses a preparation process and application of phthalonitrile-modified aramid fibers. In the present invention, aramid fibers are irradiated and modified by ultraviolet light to generate abundant carboxyl groups on the surface of the aramid fibers, and then an amidation reaction occurs with one amino group of 4,5-bis(4-aminophenoxy)phthalonitrile to obtain amino-phthalonitrile-modified aramid fibers. During the curing process, the grafted amino groups on the aramid fibers can crosslink and cure with epoxy resin, so that a crosslinked network is formed between the aramid fibers and the epoxy resin, enhancing the interfacial bonding force between the aramid fibers and the epoxy resin. Moreover, the grafted phthalonitrile on the aramid fibers generates thermally stable structures such as triazine and phthalocyanine rings during the high-temperature curing process, thereby increasing the thermal decomposition temperature and residual carbon content of the epoxy resin, and enhancing the high-temperature resistance and flame retardancy of the epoxy resin.

Description

Technical Field

[0001] The present invention relates to the technical field of aramid fibers, and specifically to a preparation process and application of phthalonitrile-modified aramid fibers. Background Art

[0002] Aramid fibers have properties such as ultra-high strength, high modulus, high temperature resistance, flame retardancy, acid and alkali resistance, etc., and are widely used in various fields of the national economy such as aerospace, mechanical construction, and sports goods; epoxy resin is a thermosetting resin with excellent electrical insulation, high strength, good durability, and strong impact resistance, and can be made into products such as coatings and adhesives, and has important applications in civil construction, electronic appliances, etc. However, traditional epoxy resins have disadvantages such as poor high temperature resistance and lack of flame retardancy.

[0003] Using aramid fibers to fill and modify epoxy resin can effectively enhance the comprehensive performance of epoxy resin. The patent with publication number CN110372998B discloses an aramid fiber-reinforced epoxy resin matrix composite material and its preparation method. The dopamine aramid fibers are modified and then impregnated into the epoxy resin curing agent solution for curing to obtain good mechanical properties and processability. The patent with publication number CN115819921A discloses a preparation method and application of an interface-modified aramid fiber / epoxy resin composite material. Active groups are introduced onto the surface of aramid fibers through plasma surface treatment and silane coupling agents to achieve the interfacial bonding ability between the fiber-reinforced material aramid fiber woven fabric and the matrix material epoxy resin. The present invention provides a phthalonitrile-modified aramid fiber aiming to improve the high temperature resistance and flame retardancy of epoxy resin materials. Summary of the Invention

[0004] (1) Technical Problems to be Solved

[0005] The present invention provides a phthalonitrile-modified aramid fiber, which solves the problems of poor high temperature resistance and flame retardancy of epoxy resin materials.

[0006] (2) Technical Solutions

[0007] A preparation process of a phthalonitrile-modified aramid fiber is as follows:

[0008] Add the ultraviolet irradiation-modified aramid fiber into N,N-dimethylformamide, stir at room temperature for 12 - 24 h, then add 4,5-bis(4-aminophenoxy)phthalonitrile, N-hydroxysuccinimide, and 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride. After the reaction, filter the solvent, wash successively with deionized water and acetone, and dry to obtain the amino-phthalonitrile-modified aramid fiber.

[0009] Further, the dosages of 4,5-bis(4-aminophenoxy)phthalonitrile, N-hydroxysuccinimide, and 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride are 5-60%, 3-35%, and 8-90% of the mass of the aramid fiber in sequence.

[0010] Further, the reaction is stirred at a temperature of 25-50 °C for 6-24 h.

[0011] Further, the preparation method of the ultraviolet irradiated modified aramid fiber is as follows: the aramid fiber is placed in an acetone solvent, then washed by ultrasonic oscillation, the aramid fiber is taken out and dried, and irradiated with a 100-400 W ultraviolet lamp for 5-10 min to obtain the ultraviolet irradiated modified aramid fiber with carboxyl groups on the surface.

[0012] Further, the preparation process of 4,5-bis(4-aminophenoxy)phthalonitrile is as follows: 4,5-dichlorophthalonitrile, N-BOC-4-aminophenol, and potassium carbonate with a molar ratio of 1:1.8-2.6:2.2-3 are added to dimethyl sulfoxide, and the reaction is carried out at a temperature of 80-95 °C for 1-3 h. After the reaction, dilute hydrochloric acid solution is added dropwise to adjust the pH to 5-6, then ethyl acetate and deionized water are added, and after extraction and separation, the ethyl acetate solution is rotary evaporated to remove the solvent. The crude product is washed with ether, then placed in a dichloromethane solution of 25% trifluoroformic acid, stirred at room temperature for 2-5 h, rotary evaporated to remove the solvent, washed with ether, and the product is recrystallized from ethanol to obtain 4,5-bis(4-aminophenoxy)phthalonitrile; the reaction formula is as follows:

[0013]

[0014] Further, the application of the phthalonitrile modified aramid fiber in epoxy resin is characterized in that: the phthalonitrile modified aramid fiber is added to the epoxy resin, stirred evenly, and then an imidazole curing agent is added, and thermal curing is carried out to obtain an aramid fiber-epoxy resin composite material.

[0015] Further, the dosage of the phthalonitrile modified aramid fiber is 5-40% of the mass of the epoxy resin.

[0016] Further, the thermal curing process is 180 °C / 2 h, 200 °C / 3 h, 240 °C / 3 h, 270 °C / 2 h in sequence.

[0017] (III) Beneficial technical effects

[0018] The present invention irradiates and modifies aramid fibers with ultraviolet light to generate abundant carboxyl groups on the surface of the aramid fibers, and then undergoes an amidation reaction with one amino group of 4,5-bis(4-aminophenoxy)phthalonitrile to obtain amino-phthalonitrile modified aramid fibers, thereby grafting a phthalonitrile structure containing an amino group on the surface of the aramid fibers.

[0019] The amino-phthalonitrile modified aramid fibers are co-cured with epoxy resin. During the curing process, the grafted amino groups on the aramid fibers can crosslink and cure with the epoxy resin, so that the aramid fibers and the epoxy resin form a crosslinked network, enhancing the interfacial bonding strength between the aramid fibers and the epoxy resin. Moreover, the phthalonitrile grafted on the aramid fibers generates thermally stable structures such as triazine and phthalocyanine rings during the high-temperature curing process, thereby increasing the thermal decomposition temperature and the residual carbon content of the epoxy resin, and enhancing the high-temperature resistance and flame retardancy of the epoxy resin. Specific embodiments

[0020] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the protection scope of the present invention.

[0021] Example 1

[0022] Preparation of 4,5-bis(4-aminophenoxy)phthalonitrile: 4,5-dichlorophthalonitrile, N-BOC-4-aminophenol and potassium carbonate with a molar ratio of 1:1.8:2.2 are added to dimethyl sulfoxide, and the reaction is carried out at a temperature of 95 °C for 1 h. After the reaction, dilute hydrochloric acid solution is added dropwise to adjust the pH to 6, and then ethyl acetate and deionized water are added. After extraction and separation, the ethyl acetate solution is rotary evaporated to remove the solvent. After the crude product is washed with ether, it is placed in a dichloromethane solution of 25% trifluoroformic acid and stirred at room temperature for 5 h. The solvent is rotary evaporated and washed with ether, and the product is recrystallized from ethanol to obtain 4,5-bis(4-aminophenoxy)phthalonitrile.

[0023] Preparation of ultraviolet-irradiated modified aramid fibers with carboxyl groups on the surface: The aramid fibers are placed in an acetone solvent, then washed by ultrasonic oscillation, the aramid fibers are taken out and dried, and irradiated with a 400W ultraviolet lamp for 5 min to obtain ultraviolet-irradiated modified aramid fibers with carboxyl groups on the surface.

[0024] Preparation of amino-phthalonitrile modified aramid fiber: Add the ultraviolet irradiated modified aramid fiber into N,N-dimethylformamide, stir at room temperature for 24 h, then successively add 4,5-bis(4-aminophenoxy)phthalonitrile which is 5% of the mass of the aramid fiber, 3% of N-hydroxysuccinimide and 8% of 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride, stir and react at 40 °C for 12 h, filter the solvent after the reaction, wash successively with deionized water and acetone, and dry to obtain the amino-phthalonitrile modified aramid fiber.

[0025] Preparation of aramid fiber-epoxy resin composite: Add the phthalonitrile modified aramid fiber which is 5% of the mass of the epoxy resin into epoxy resin E51, stir evenly, then add 2-ethyl-4-methylimidazole curing agent which is 7% of the mass of the epoxy resin, and carry out thermal curing. The thermal curing process is 180 °C / 2 h, 200 °C / 3 h, 240 °C / 3 h, 270 °C / 2 h to obtain the aramid fiber-epoxy resin composite.

[0026] Example 2

[0027] Preparation of 4,5-bis(4-aminophenoxy)phthalonitrile: Add 4,5-dichlorophthalonitrile, N-BOC-4-aminophenol and potassium carbonate with a molar ratio of 1:2.6:3 into dimethyl sulfoxide, react at 85 °C for 2 h, adjust the pH to 6 by dropping dilute hydrochloric acid solution after the reaction, then add ethyl acetate and deionized water, extract and separate, evaporate the ethyl acetate solution to remove the solvent, wash the crude product with ether, then place it in a dichloromethane solution of 25% trifluoroformic acid, stir at room temperature for 2 h, evaporate the solvent, wash with ether, and recrystallize the product in ethanol to obtain 4,5-bis(4-aminophenoxy)phthalonitrile.

[0028] Preparation of ultraviolet irradiated modified aramid fiber with carboxyl groups on the surface: Place the aramid fiber in acetone solvent, then wash it by ultrasonic oscillation, take out the aramid fiber and dry it, and irradiate it with a 200 W ultraviolet lamp for 5 min to obtain the ultraviolet irradiated modified aramid fiber with carboxyl groups on the surface.

[0029] Preparation of amino-phthalonitrile modified aramid fiber: Add the ultraviolet irradiated modified aramid fiber into N,N-dimethylformamide, stir at room temperature for 18 h, then successively add 4,5-bis(4-aminophenoxy)phthalonitrile which is 60% of the mass of the aramid fiber, 35% of N-hydroxysuccinimide and 90% of 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride, stir and react at 40 °C for 24 h, filter the solvent after the reaction, wash successively with deionized water and acetone, and dry to obtain the amino-phthalonitrile modified aramid fiber.

[0030] Preparation of aramid fiber-epoxy resin composite: Add aramid fiber modified with phthalonitrile accounting for 15% of the mass of epoxy resin to epoxy resin E51. After stirring evenly, add 2-ethyl-4-methylimidazole curing agent accounting for 8% of the mass of epoxy resin, and carry out thermal curing. The thermal curing process is 180°C / 2h, 200°C / 3h, 240°C / 3h, 270°C / 2h to obtain the aramid fiber-epoxy resin composite.

[0031] Example 3

[0032] Preparation of 4,5-bis(4-aminophenoxy)phthalonitrile: Add 4,5-dichlorophthalonitrile, N-BOC-4-aminophenol and potassium carbonate with a molar ratio of 1:2.2:2.5 to dimethyl sulfoxide, react at 95°C for 1h. After the reaction, add dilute hydrochloric acid solution to adjust the pH to 6, then add ethyl acetate and deionized water. After extraction and separation, rotary evaporate the ethyl acetate solution to remove the solvent. After washing the crude product with ether, place it in a dichloromethane solution of 25% trifluoroformic acid and stir at room temperature for 5h. Rotary evaporate to remove the solvent, wash with ether, and recrystallize the product in ethanol to obtain 4,5-bis(4-aminophenoxy)phthalonitrile.

[0033] Preparation of aramid fiber modified by ultraviolet irradiation with carboxyl groups on the surface: Place aramid fiber in acetone solvent, then wash it by ultrasonic oscillation, take out the aramid fiber and dry it, and irradiate it with a 200W ultraviolet lamp for 5min to obtain the aramid fiber modified by ultraviolet irradiation with carboxyl groups on the surface.

[0034] Preparation of aramid fiber modified with amino-phthalonitrile: Add the aramid fiber modified by ultraviolet irradiation to N,N-dimethylformamide and stir at room temperature for 18h. Then successively add 4,5-bis(4-aminophenoxy)phthalonitrile accounting for 25% of the mass of aramid fiber, N-hydroxysuccinimide accounting for 12% and 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride accounting for 42%, and stir and react at 25°C for 24h. After the reaction, filter the solvent, wash successively with deionized water and acetone, and dry to obtain the aramid fiber modified with amino-phthalonitrile.

[0035] Preparation of aramid fiber-epoxy resin composite: Add aramid fiber modified with phthalonitrile accounting for 30% of the mass of epoxy resin to epoxy resin E51. After stirring evenly, add 2-ethyl-4-methylimidazole curing agent accounting for 10% of the mass of epoxy resin, and carry out thermal curing. The thermal curing process is 180°C / 2h, 200°C / 3h, 240°C / 3h, 270°C / 2h to obtain the aramid fiber-epoxy resin composite.

[0036] Example 4

[0037] Preparation of 4,5-bis(4-aminophenoxy)phthalonitrile: 4,5-dichlorophthalonitrile, N-BOC-4-aminophenol and potassium carbonate with a molar ratio of 1:2.6:2.8 were added to dimethyl sulfoxide, and reacted at a temperature of 95 °C for 1 h. After the reaction, dilute hydrochloric acid solution was added dropwise to adjust the pH to 6, then ethyl acetate and deionized water were added. After extraction and separation, the solvent of the ethyl acetate solution was removed by rotary evaporation. After the crude product was washed with ether, it was placed in a dichloromethane solution of 25% trifluoroformic acid and stirred at room temperature for 4 h. The solvent was removed by rotary evaporation. After washing with ether, the product was recrystallized from ethanol to obtain 4,5-bis(4-aminophenoxy)phthalonitrile.

[0038] Preparation of ultraviolet irradiated modified aramid fiber with carboxyl groups on the surface: The aramid fiber was placed in an acetone solvent, and then washed by ultrasonic oscillation. The aramid fiber was taken out and dried, and irradiated with a 200 W ultraviolet lamp for 8 min to obtain the ultraviolet irradiated modified aramid fiber with carboxyl groups on the surface.

[0039] Preparation of amino-phthalonitrile modified aramid fiber: The ultraviolet irradiated modified aramid fiber was added to N,N-dimethylformamide and stirred at room temperature for 18 h. Then, 40% of 4,5-bis(4-aminophenoxy)phthalonitrile, 24% of N-hydroxysuccinimide and 72% of 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride based on the mass of the aramid fiber were added in sequence, and the reaction was stirred at a temperature of 25 °C for 24 h. After the reaction, the solvent was filtered, and washed and dried with deionized water and acetone in sequence to obtain the amino-phthalonitrile modified aramid fiber.

[0040] Preparation of aramid fiber-epoxy resin composite: 40% of phthalonitrile modified aramid fiber based on the mass of the epoxy resin was added to epoxy resin E51. After stirring evenly, 10% of 2-ethyl-4-methylimidazole curing agent based on the mass of the epoxy resin was added, and thermal curing was carried out. The thermal curing process was 180 °C / 2 h, 200 °C / 3 h, 240 °C / 3 h, 270 °C / 2 h to obtain the aramid fiber-epoxy resin composite.

[0041] Comparative Example 1

[0042] Preparation of 4,5-bis(4-aminophenoxy)phthalonitrile: 4,5-dichlorophthalonitrile, N-BOC-4-aminophenol and potassium carbonate with a molar ratio of 1:2:2.7 were added to dimethyl sulfoxide, and reacted at a temperature of 80 °C for 3 h. After the reaction, dilute hydrochloric acid solution was added dropwise to adjust the pH to 5, then ethyl acetate and deionized water were added. After extraction and separation, the solvent of the ethyl acetate solution was removed by rotary evaporation. After the crude product was washed with ether, it was placed in a dichloromethane solution of 25% trifluoroformic acid and stirred at room temperature for 5 h. The solvent was removed by rotary evaporation. After washing with ether, the product was recrystallized from ethanol to obtain 4,5-bis(4-aminophenoxy)phthalonitrile.

[0043] Preparation of epoxy resin composite: Add 5% of 4,5-bis(4-aminophenoxy)phthalonitrile based on the mass of epoxy resin E51 to epoxy resin E51. After stirring evenly, add 8% of 2-ethyl-4-methylimidazole curing agent based on the mass of epoxy resin, and carry out thermal curing. The thermal curing process is 180 °C / 2 h, 200 °C / 3 h, 240 °C / 3 h, 270 °C / 2 h to obtain the epoxy resin composite.

[0044] Comparative Example 2

[0045] Preparation of ultraviolet irradiation modified aramid fiber with carboxyl groups on the surface: Place aramid fiber in acetone solvent, then wash it by ultrasonic oscillation, take out the aramid fiber and dry it, and irradiate it with a 200 W ultraviolet lamp for 10 min to obtain the ultraviolet irradiation modified aramid fiber with carboxyl groups on the surface.

[0046] Preparation of aramid fiber-epoxy resin composite: Add 5% of ultraviolet irradiation modified aramid fiber based on the mass of epoxy resin E51 to epoxy resin E51. After stirring evenly, add 7% of 2-ethyl-4-methylimidazole curing agent based on the mass of epoxy resin, and carry out thermal curing. The thermal curing process is 180 °C / 2 h, 200 °C / 3 h, 240 °C / 3 h, 270 °C / 2 h to obtain the aramid fiber-epoxy resin composite.

[0047] The thermal properties of the epoxy resin composite were tested in a thermogravimetric analyzer under a nitrogen atmosphere with a flow rate of 50 mL / min, a heating rate of 10 °C / min, and a maximum test temperature of 800 °C. T5% (°C) is the temperature at which the material loses 5% of its mass, T50% (°C) is the temperature at which the material loses 50% of its mass, and Weight (%) is the mass remaining rate of the material at 800 °C.

[0048] The flame retardant properties of the epoxy resin composite were tested by an oxygen index tester and a horizontal and vertical burning tester according to the test standards of GB / T 2406.1-2008 and UL-94 fire protection standard. LOI (%) is the limiting oxygen index.

[0049] Example 1 Example 2 Example 3 Example 4 Comparative Example 1 Comparative Example 2 T5％(℃) 394.2 401.2 408.2 409.4 381.4 386.2 T50％(℃) 457.2 460.7 469.7 464.2 426.5 439.4 Weight(%) 24.5 32.1 38.4 42.3 16.4 18.6 LOI(%) 27.8 29.7 32.9 33.2 26.4 25.1 UL-94 rating V-1 V-1 V-0 V-0 V-1 V-2

[0050] After the thermogravimetric analysis test, when the amount of phthalonitrile-modified aramid fiber is 40% of the mass of epoxy resin, the maximum T5% of the epoxy resin is 409.4 °C, and the maximum mass residue rate is 42.3%. When the amount of phthalonitrile-modified aramid fiber is 30% of the mass of epoxy resin, the maximum T50% of the epoxy resin is 469.7 °C. In Comparative Example 2, only aramid fiber without phthalonitrile was added, and the T5%, T50% and mass residue of the epoxy resin were only 386.2 °C, 439.4 °C, 18.6%; in Comparative Example 1, only 4,5-bis(4-aminophenoxy)phthalonitrile was added, and the thermal performance was the worst.

[0051] After the flame retardancy test, when the amount of phthalonitrile-modified aramid fiber is 5-40% of the mass of epoxy resin, the limiting oxygen index of the epoxy resin reaches 27.8-33.2%. When the amount of phthalonitrile-modified aramid fiber is 30-40%, the UL-94 rating of the epoxy resin reaches V-0 level, showing excellent flame retardancy. It is much higher than the epoxy resin materials prepared in Comparative Example 1 and Comparative Example 2.

[0052] Although the embodiments of the present invention have been shown and described, it will be understood by those of ordinary skill in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. Application of phthalonitrile-modified aramid fiber in epoxy resin, characterized in that: Add phthalonitrile-modified aramid fiber to epoxy resin, stir evenly, then add imidazole curing agent, and carry out thermal curing to obtain aramid fiber-epoxy resin composite material; The dosage of the phthalonitrile-modified aramid fiber is 5-40% of the mass of the epoxy resin; The preparation process of the phthalonitrile-modified aramid fiber is as follows: Add ultraviolet irradiation-modified aramid fiber to N,N-dimethylformamide, stir at room temperature for 12-24 h, then add 4,5-bis(4-aminophenoxy)phthalonitrile, N-hydroxysuccinimide and 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride, filter after reaction, wash and dry to obtain amino-phthalonitrile-modified aramid fiber; The preparation process of 4,5-bis(4-aminophenoxy)phthalonitrile is as follows: Add 4,5-dichlorophthalonitrile, N-BOC-4-aminophenol and potassium carbonate with a molar ratio of 1:1.8-2.6:2.2-3 to dimethyl sulfoxide, react at a temperature of 80-95 °C for 1-3 h, after the reaction, add dilute hydrochloric acid solution to adjust the pH to 5-6, carry out extraction and separation, wash the crude product, then place it in a dichloromethane solution of trifluoroformic acid, stir at room temperature for 2-5 h, and recrystallize the product in ethanol to obtain 4,5-bis(4-aminophenoxy)phthalonitrile.

2. Use of the phthalonitrile-modified aramid fiber according to claim 1 in epoxy resin, characterized in that: The thermal curing process is successively 180 °C / 2 h, 200 °C / 3 h, 240 °C / 3 h, 270 °C / 2 h.

3. The application of the phthalonitrile-modified aramid fiber according to claim 1 in epoxy resin, characterized in that: In the preparation process of the phthalonitrile-modified aramid fiber, the dosages of 4,5-bis(4-aminophenoxy)phthalonitrile, N-hydroxysuccinimide, and 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride are successively 5-60%, 3-35%, and 8-90% of the mass of the aramid fiber.

4. Use of the phthalonitrile-modified aramid fiber according to claim 1 in epoxy resin, characterized in that: In the preparation process of the phthalonitrile-modified aramid fiber, the reaction is stirred at a temperature of 25-50 °C for 6-24 h.

5. The application of the phthalonitrile-modified aramid fiber according to claim 1 in epoxy resin, characterized in that: The preparation method of the ultraviolet irradiation-modified aramid fiber is as follows: Place the aramid fiber in an acetone solvent, then wash it by ultrasonic oscillation, take out the aramid fiber and dry it, and irradiate it with a 100-400 W ultraviolet lamp for 5-10 min to obtain ultraviolet irradiation-modified aramid fiber with carboxyl groups on the surface.

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