Preparation method and application of aromatic polyamide fiber with high tensile strength and high compounding property

Abstract

The invention relates to the technical field of preparation of high-performance aromatic fibers, and discloses a preparation method and application of aromatic polyamide fibers with high tensile strength and high compounding performance. The preparation method comprises the following steps: carrying out a removal reaction on nascent fibers of aromatic polyamide fibers containing benzimidazole rings and a removal solution to remove hydrogen chloride complexed on the surfaces of the nascent fibers, and drying to obtain an intermediate product; and carrying out high-temperature annealing on the intermediate product in a nitrogen atmosphere to obtain the aromatic polyamide fiber with high tensile strength and high compounding property. According to the application, through a strategy of inhibiting fiber skin layer orientation and keeping core layer orientation, the high-performance fiber with a brand-new aggregation state and a skin layer low-orientation structure is prepared; the aromatic polyamide fiber prepared by the invention can simultaneously realize excellent mechanical properties and compounding properties, the tensile strength of the aromatic polyamide fiber reaches 5.5-7.0 GPa, and the interlaminar shear strength of a composite material prepared from the aromatic polyamide fiber and epoxy resin reaches 64-71 MPa.

Description

Technical Field

[0001] The present application relates to the technical field of high-performance aromatic fiber preparation, and specifically to a preparation method and application of aromatic polyamide fiber with high tensile strength and high compositeness. Background Art

[0002] Aromatic polyamide fibers (aramid fibers) are widely used in defense, military, vehicle engineering, and sports equipment due to their advantages such as light weight, high strength and toughness, and good electromagnetic transmittance. During the aramid fiber spinning process, the significantly different solidification rate gradient in the radial direction of the fiber results in a distinct "skin-core" structure in the aramid fiber, which is retained during the subsequent thermal stretching process. The high orientation of the fiber core gives it high strength and high modulus mechanical properties, while the high orientation of the fiber cortex results in poor tear resistance. This is because the highly oriented fiber cortex will first break during the stretching process and form stress concentration points, making it difficult to further increase the tensile strength of the fiber. At the same time, the interfacial failure of aramid fiber-reinforced composites is often manifested as cortex tearing rather than resin debonding, which is extremely detrimental to the interface design and overall mechanical properties of aramid fiber-reinforced composites. As the performance requirements for aramid fibers in various applications increase, the tensile strength of aramid fibers and their insufficient interfacial bonding with the polymer resin matrix have become two major difficulties limiting the application of aramid fibers.

[0003] Currently, the tensile strength of aramid fibers is usually improved by copolymerizing new monomers and blending nanofillers. Patent application CN202411779888.3 discloses a heterocyclic aramid block copolymer containing a PBO structure and a preparation method thereof. The modified heterocyclic aramid prepared by wet spinning has a tensile strength of up to 5.8 GPa. However, due to the large amount of highly corrosive polyphosphoric acid used as a reaction solvent during the polymerization process, the depreciation cost of the equipment is greatly increased, which is not conducive to further industrial production. Patent application CN202210524030.7 discloses a single-walled carbon nanotube reinforced heterocyclic aramid fiber and a preparation method thereof. By modifying the ports of single-walled carbon nanotubes with amine-containing functional groups, the aminated single-walled carbon nanotubes react with heterocyclic aramid monomers through -NH2 to form a copolymer. The resulting modified heterocyclic aramid fiber has a tensile strength of up to 36 cN / dtex. However, due to the extremely high raw material cost and lengthy process of modifying single-walled carbon nanotubes, the production efficiency of the fiber is greatly reduced and the production cost is increased.

[0004] At the same time, in order to improve the composite properties of aramid, active groups are usually introduced on the fiber surface to enhance its compatibility with the matrix resin. For example, patent application CN201210240025.X discloses a method for improving the surface activity of aramid fibers. By etching the aramid with a hydrogen peroxide solution, the interlaminar shear strength of the composite material made of aramid and epoxy resin can be increased from 40 MPa to about 60 MPa, but the tensile strength of the fiber is significantly reduced from 24 cN / dtex to 21 cN / dtex. The invention patent of patent application CN202010602028.8 discloses a method for modifying aramid fibers with plasma combined with dopamine. The aramid fibers are first etched with plasma, and then dopamine is coated on the active sites introduced therein. The interfacial shear strength between the modified fibers and the epoxy resin can be increased by 20.6%, but the breaking strength of the monofilament is reduced from 42.2 cN to 39.5 cN. Existing methods for improving the interfacial bonding strength between aramid fibers and matrix resins usually damage the fiber's inherent excellent mechanical strength and fail to solve the fundamental problem that the highly oriented cortex of the fiber is easily torn, thus causing premature failure of the composite material interface.

[0005] The study found that during the synthesis of aramid, the hydrogen chloride by-product of the reaction between diamine and acyl chloride will be stably complexed on the imidazole unit and completely removed during the later heat treatment process of the spun fiber. These stably complexed hydrogen chloride molecules just occupy the hydrogen bond interaction sites on the fiber macromolecular chain, thereby greatly weakening the intermolecular interaction in the spun fiber, allowing it to be smoothly oriented in the later thermal annealing process. Based on this, changing the hydrogen bond interaction of hydrogen chloride molecules may be a strategy to improve composite performance. Patent application CN202210084317.2 discloses a post-treatment process in the production of poly(p-phenylene terephthalamide), which mainly performs multi-stage countercurrent washing on ultra-low particle size poly(p-phenylene terephthalamide) resin powder, which can reduce the content of hydrogen chloride by-products therein to below 200ppm. However, since hydrogen chloride has no obvious binding sites with poly(p-phenylene terephthalamide), it has no obvious effect on the aggregation structure formation and mechanical properties of its fibers. It does not improve the composite properties of aramid fibers, but only reduces environmental pollution during the production process of para-aramid fibers. Summary of the Invention

[0006] The present application provides a preparation method and application of aromatic polyamide fibers with high tensile strength and high compositeness, aiming to solve the technical problems of low tensile strength of existing aromatic polyamide fibers and low interfacial bonding strength with polymer resin matrices.

[0007] In order to achieve the above objectives, this application adopts the following technical solutions.

[0008] In a first aspect of the present application, a method for preparing an aromatic polyamide fiber with high tensile strength and high compositeness is provided, comprising:

[0009] The as-spun aromatic polyamide fiber containing a benzimidazole ring is subjected to a stripping reaction with a stripping liquid to remove the hydrogen chloride complexed on the surface thereof, and then dried to obtain an intermediate product;

[0010] The intermediate product is subjected to high-temperature annealing in a nitrogen atmosphere to obtain aromatic polyamide fibers with high tensile strength and high compositeness.

[0011] Preferably, the high-temperature annealing comprises: heating the intermediate product to 270-360° C. in a nitrogen-protected reactor and keeping the temperature for 10-60 minutes.

[0012] Preferably, the high temperature annealing comprises: continuously passing the intermediate product through a channel protected by nitrogen, the temperature in the channel is 270-360° C., and the residence time of the intermediate product in the channel is 10 min to 60 min.

[0013] Preferably, the temperature of the removal reaction is 10° C. to 80° C., and the reaction time is 10s to 300s.

[0014] Preferably, the removal liquid is an alkaline solution with a mass concentration of 0.1 to 20 wt%.

[0015] Further preferably, the solute of the alkaline solution includes at least one of sodium bicarbonate, potassium bicarbonate, sodium carbonate, potassium carbonate, sodium hydroxide, potassium hydroxide, calcium hydroxide, ammonia water or triethylamine;

[0016] The solvent of the alkaline solution is any one of ethanol, acetonitrile, dimethylformamide, dimethylacetamide, dimethyl sulfoxide, methyl pyrrolidone or water.

[0017] Preferably, the spun fibers are subjected to a stripping reaction by being immersed in a stripping liquid or by being continuously drawn through a stripping liquid.

[0018] Preferably, the mass percentage of imidazole diamine in the aromatic polyamide fiber containing benzimidazole rings to the total amount of diamines is 30 to 100 wt %.

[0019] The second aspect of the present application provides the use of high tensile strength and high composite aromatic polyamide fibers prepared by the above preparation method in fiber-reinforced composite materials.

[0020] The third aspect of the present application provides a fiber-reinforced composite material, which includes reinforcing fibers and a resin matrix, wherein the reinforcing fibers are aromatic polyamide fibers with high tensile strength and high compositeness prepared by the above preparation method; and the resin matrix is epoxy resin.

[0021] Compared with the prior art, the present invention has the following advantages:

[0022] This application uses a strategy to suppress the orientation of the fiber cortex while maintaining the orientation of the core layer to produce a new aggregated high-performance fiber with a low-orientation cortex structure. This preparation method does not require changes to existing industrial production equipment or increase production costs, and has good industrial application prospects.

[0023] The present application removes the hydrogen chloride molecules complexed in the benzimidazole-containing aromatic polyamide fiber cortex, thereby effectively inhibiting the self-orientation behavior of the fiber cortex and greatly improving the tear resistance of the fiber cortex during the subsequent heat treatment process of the primary fiber, thereby optimizing the interfacial failure behavior of the fiber-reinforced composite material and improving the overall mechanical strength of the composite material; while retaining the complexed hydrogen chloride molecules in the benzimidazole-containing aromatic polyamide fiber core layer, the overall orientation of the fiber after thermal annealing treatment is retained, achieving the excellent effect of non-destructive modification of the fiber to obtain high composite performance.

[0024] The aromatic polyamide fiber prepared in this application can simultaneously achieve excellent mechanical properties and composite properties. Its tensile strength reaches 5.5-7.0GPa, and the interlaminar shear strength of the composite material prepared by it and epoxy resin reaches 64MPa-71MPa. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] To more clearly illustrate the technical solutions of the embodiments of this application, the following briefly introduces the drawings required for describing the embodiments. Obviously, the drawings described below are only some of the embodiments described in this application. For those skilled in the art, other drawings can be derived from these drawings without inventive effort.

[0026] Figure 1 1 is a graph showing the test results of the fiber cortex orientation of the aromatic polyamide fibers of Example 1 and Comparative Example 1;

[0027] Figure 2 2D wide-angle X-ray diffraction spectra of the aromatic polyamide fibers of Example 1 and Comparative Example 1;

[0028] Figure 3 These are SEM images of the interface failure of the fiber-reinforced composite materials of Example 1 and Comparative Example 1. DETAILED DESCRIPTION

[0029] The following will be combined with the accompanying drawings in the embodiments of this application to clearly and completely describe the technical solutions in the embodiments of this application. Obviously, the described embodiments are part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0030] In the following description of this embodiment, the terms "include", "comprising", "having" and "containing" are open-ended terms, meaning including but not limited to.

[0031] In the following description of this embodiment, the term "and / or" is used to describe the association relationship between associated objects, indicating that three possible relationships exist. For example, A and / or B can represent: A exists alone, B exists alone, and both A and B exist. A and B can be singular or plural. The character " / " generally indicates that the associated objects are in an "or" relationship.

[0032] In the following description of this embodiment, the term "at least one" refers to one or more, and "plurality" refers to two or more. "At least one of the following" or similar expressions refers to any combination of these items, including any combination of single items or plural items. For example, "at least one of a, b, or c", or "at least one of a, b, and c" can all represent: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can be single or multiple.

[0033] The terms used in the embodiments of the present application are only for the purpose of describing specific embodiments and are not intended to limit the present application. The singular forms "a", "an" and "the" used in the embodiments of the present application and the appended claims are also intended to include plural forms unless the context clearly indicates otherwise.

[0034] Those skilled in the art should understand that in the following description of the embodiments of the present application, the order of serial numbers does not mean the order of execution, some or all of the steps can be executed in parallel or sequentially, and the execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present application.

[0035] It will be understood by those skilled in the art that the numerical ranges in the examples of the present application are to be understood as specifically disclosing each intermediate value between the upper and lower limits of the range. Each smaller range between any intermediate value within a stated value or stated range and any other stated value or intermediate value within the stated range is also included in the present application. The upper and lower limits of these smaller ranges may independently be included or excluded in the range.

[0036] Unless otherwise indicated, the technical / scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which this application belongs. Although this application describes only preferred methods and materials, any methods and materials similar or equivalent to those described herein may also be used in the implementation or testing of this application. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials related to the documents. In the event of any conflict with any incorporated document, the content of this specification shall prevail.

[0037] In a first aspect, the present application provides an aromatic polyamide fiber with high tensile strength and high compositeness by suppressing the orientation of the fiber cortex and maintaining the orientation of the core layer. The preparation method includes:

[0038] The as-spun aromatic polyamide fiber containing a benzimidazole ring is subjected to a stripping reaction with a stripping liquid to remove the hydrogen chloride complexed on the surface thereof, and then dried to obtain an intermediate product;

[0039] The intermediate product is subjected to high-temperature annealing in a nitrogen atmosphere to obtain aromatic polyamide fibers with high tensile strength and high compositeness.

[0040] In the present application, the mass percentage of imidazole diamine in the raw fiber of the aromatic polyamide fiber containing benzimidazole rings to the total amount of diamines is 30-100wt%. The aromatic polyamide fiber containing benzimidazole rings used in the present application can be directly purchased or prepared according to existing methods.

[0041] In the present application, the removal liquid is an alkaline solution, preferably with a mass concentration of 0.1 to 20 wt %. The solute of the alkaline solution can be at least one of sodium bicarbonate, potassium bicarbonate, sodium carbonate, potassium carbonate, sodium hydroxide, potassium hydroxide, calcium hydroxide, ammonia water, or triethylamine, preferably sodium hydroxide, potassium hydroxide, sodium bicarbonate, ammonia water, or triethylamine; and the solvent of the alkaline solution can be any one of ethanol, acetonitrile, dimethylformamide, dimethylacetamide, dimethyl sulfoxide, methylpyrrolidone, or water.

[0042] In the alkaline solution of the present application, when the solute is an inorganic base or an alkaline salt, the solvent is preferably water; when the solute is an organic base, the solvent is preferably any one of ethanol, acetonitrile, dimethylformamide, dimethylacetamide, dimethyl sulfoxide or methyl pyrrolidone.

[0043] In the present application, a stripping reaction can be performed by a continuous or intermittent method to remove hydrogen chloride complexed on the surface of spun fibers of aromatic polyamide fibers containing benzimidazole rings. The intermittent method involves immersing the spun fibers in a stripping solution to perform the stripping reaction; the continuous method involves continuously drawing the spun fibers through the stripping solution and allowing them to remain in the solution for a period of time to perform the stripping reaction. The stripping reaction temperature is 10°C to 80°C, and the reaction time is 10s to 300s.

[0044] In this application, the intermediate product is subjected to high temperature annealing, which can be performed by any of the following methods:

[0045] Heat the intermediate product to 270-360°C in a nitrogen-protected reactor and keep it warm for 10-60 minutes;

[0046] Alternatively, the intermediate product is continuously passed through a corridor protected by nitrogen, the temperature in the corridor is 270-360° C., and the residence time of the intermediate product in the corridor is 10 min to 60 min.

[0047] The present invention suppresses the sheath orientation of the fiber while maintaining the core orientation by removing the complexed hydrogen chloride molecules in the sheath of the aromatic polyamide fiber containing benzimidazole and retaining the complexed hydrogen chloride molecules in the core.

[0048] By removing the complexed hydrogen chloride molecules from the benzimidazole-containing aromatic polyamide fiber cortex, the present application can effectively inhibit the self-orientation behavior of the fiber cortex and greatly improve the tear resistance of the fiber cortex during the subsequent heat treatment process of the primary fiber, thereby optimizing the interfacial failure behavior of the fiber-reinforced composite material and improving the overall mechanical strength of the fiber-reinforced composite material.

[0049] At the same time, the present application retains the complexed hydrogen chloride molecules in the core layer of the aromatic polyamide fiber containing benzimidazole, thereby retaining the overall orientation of the fiber after thermal annealing treatment, thereby achieving the excellent effect of non-destructive modification of the fiber to obtain high composite performance.

[0050] The preparation method of the present application does not change the existing industrial production equipment and does not increase production costs, and has good industrial application prospects.

[0051] The high-tensile-strength and high-complexity aromatic polyamide fiber prepared in this application has a structure with low-orientation of the skin and high-orientation of the core, which can simultaneously achieve excellent mechanical properties and composite properties. Its tensile strength reaches 5.5-7.0GPa, and it can be used to prepare fiber-reinforced composite materials with a resin matrix.

[0052] This application also provides a fiber-reinforced composite material, which is prepared by combining reinforcing fibers and a resin matrix. The reinforcing fibers are the high-tensile-strength, highly complex aromatic polyamide fibers prepared herein, and the resin matrix can be a commonly used resin, preferably an epoxy resin. The fiber-reinforced composite material with an epoxy resin matrix exhibits an interlaminar shear strength of 64 MPa to 71 MPa.

[0053] The present application is further described below through specific examples.

[0054] Example 1

[0055] The raw aromatic polyamide fiber containing 40% by mass of imidazole diamine in the total amount of diamine was immersed in a 1wt% NaOH aqueous solution at a temperature of 15°C for 10 seconds and dried; then, the fiber was heated to 270°C in a nitrogen-protected reactor, kept warm for 10 minutes, and then cooled to obtain an aromatic polyamide fiber with high tensile strength and high compositeness.

[0056] The fiber is composited with epoxy resin to obtain a fiber-reinforced composite material, wherein the volume fraction of the fiber in the composite material is 65%.

[0057] Example 2

[0058] The raw aromatic polyamide fiber containing 40% by mass of imidazole diamine in the total amount of diamine was immersed in a 3wt% KOH aqueous solution at a temperature of 25°C for 10 seconds and dried; then, the fiber was heated to 270°C in a nitrogen-protected reactor, kept warm for 10 minutes, and then cooled to obtain an aromatic polyamide fiber with high tensile strength and high compositeness.

[0059] The fiber is composited with epoxy resin to obtain a fiber-reinforced composite material, wherein the volume fraction of the fiber in the composite material is 65%.

[0060] Example 3

[0061] The raw aromatic polyamide fiber containing 60% by mass of imidazole diamine in the total amount of diamine was immersed in a 3wt% KOH aqueous solution at a temperature of 25°C for 10 seconds and dried; then, the fiber was heated to 270°C in a nitrogen-protected reactor, kept warm for 10 minutes, and then cooled to obtain an aromatic polyamide fiber with high tensile strength and high compositeness.

[0062] The fiber is composited with epoxy resin to obtain a fiber-reinforced composite material, wherein the volume fraction of the fiber in the composite material is 65%.

[0063] Example 4

[0064] The raw aromatic polyamide fiber containing 60% by mass of imidazole diamine in the total amount of diamine was immersed in a 10wt% NaHCO3 aqueous solution at a temperature of 25°C for 10s and dried; then, it was heated to 270°C in a nitrogen-protected reactor, kept warm for 10 minutes and then cooled to obtain an aromatic polyamide fiber with high tensile strength and high compositeness.

[0065] The fiber is composited with epoxy resin to obtain a fiber-reinforced composite material, wherein the volume fraction of the fiber in the composite material is 65%.

[0066] Example 5

[0067] The raw aromatic polyamide fiber containing 70% by mass of imidazole diamine in the total amount of diamine was immersed in a 5wt% NaHCO3 aqueous solution at a temperature of 30°C for 30s and dried; then, it was heated to 270°C in a nitrogen-protected reactor, kept warm for 10 minutes and then cooled to obtain an aromatic polyamide fiber with high tensile strength and high compositeness.

[0068] The fiber is composited with epoxy resin to obtain a fiber-reinforced composite material, wherein the volume fraction of the fiber in the composite material is 65%.

[0069] Example 6

[0070] The raw aromatic polyamide fiber containing 75% by mass of imidazole diamine in the total amount of diamine was immersed in a 10wt% NaHCO3 aqueous solution at a temperature of 60°C for 30s and dried; then, it was heated to 270°C in a nitrogen-protected reactor, kept warm for 10 minutes and then cooled to obtain an aromatic polyamide fiber with high tensile strength and high compositeness.

[0071] The fiber is composited with epoxy resin to obtain a fiber-reinforced composite material, wherein the volume fraction of the fiber in the composite material is 65%.

[0072] Example 7

[0073] The raw aromatic polyamide fiber containing 75% by mass of imidazole diamine in the total amount of diamine was immersed in a 15wt% NaHCO3 aqueous solution at a temperature of 60°C for 20s and dried; then, it was heated to 270°C in a nitrogen-protected reactor, kept warm for 10 minutes and then cooled to obtain an aromatic polyamide fiber with high tensile strength and high compositeness.

[0074] The fiber is composited with epoxy resin to obtain a fiber-reinforced composite material, wherein the volume fraction of the fiber in the composite material is 65%.

[0075] Example 8

[0076] The raw aromatic polyamide fiber containing 75% by mass of imidazole diamine in the total amount of diamine is immersed in a methyl pyrrolidone solution of triethylamine at a temperature of 50°C and a concentration of 10wt% for 20s and then dried; then the fiber is heated to 270°C in a nitrogen-protected reactor, kept warm for 10 minutes and then cooled to obtain an aromatic polyamide fiber with high tensile strength and high compositeness.

[0077] The fiber is composited with epoxy resin to obtain a fiber-reinforced composite material, wherein the volume fraction of the fiber in the composite material is 65%.

[0078] Example 9

[0079] Aromatic polyamide spun fibers containing 75% by mass of imidazole diamine in the total amount of diamines are immersed in an acetonitrile solution of triethylamine at a temperature of 50°C and a concentration of 10wt% for 20 seconds and then dried; then the fibers are heated to 270°C in a nitrogen-protected reactor, kept warm for 10 minutes, and then cooled to obtain aromatic polyamide fibers with high tensile strength and high compositeness.

[0080] The fiber is composited with epoxy resin to obtain a fiber-reinforced composite material, wherein the volume fraction of the fiber in the composite material is 65%.

[0081] Example 10

[0082] The raw aromatic polyamide fiber containing 80% by mass of imidazole diamine in the total amount of diamine is immersed in a 20wt% ammonia solution at a temperature of 60°C for 40 seconds and dried; then, it is heated to 270°C in a nitrogen-protected reactor, kept warm for 10 minutes, and then cooled to obtain an aromatic polyamide fiber with high tensile strength and high compositeness.

[0083] The fiber is composited with epoxy resin to obtain a fiber-reinforced composite material, wherein the volume fraction of the fiber in the composite material is 65%.

[0084] Example 11

[0085] The raw aromatic polyamide fiber containing 80% by mass of imidazole diamine in the total amount of diamine is immersed in a dimethylformamide solution of triethylamine with a concentration of 20wt% at a temperature of 40°C for 40s and then dried; then the fiber is heated to 350°C in a nitrogen-protected reactor, kept warm for 10 minutes and then cooled to obtain an aromatic polyamide fiber with high tensile strength and high compositeness.

[0086] The fiber is composited with epoxy resin to obtain a fiber-reinforced composite material, wherein the volume fraction of the fiber in the composite material is 65%.

[0087] Example 12

[0088] The difference between Example 12 and Example 11 is that the reaction is heated to 250° C. in a nitrogen-protected reactor. The rest is the same as Example 11.

[0089] Example 13

[0090] The difference between Example 13 and Example 11 is that the temperature is heated to 300° C. in a nitrogen-protected reactor. The rest is the same as Example 11.

[0091] Example 14

[0092] The as-spun aromatic polyamide fiber containing 100% imidazole diamine by mass in the total amount of diamine is immersed in a dimethylformamide solution of triethylamine with a concentration of 40wt% at a temperature of 80°C for 60s and then dried; then the as-spun aromatic polyamide fiber is heated to 270°C in a nitrogen-protected reactor, kept warm for 10 minutes, and then cooled to obtain an aromatic polyamide fiber with high tensile strength and high compositeness.

[0093] The fiber is composited with epoxy resin to obtain a fiber-reinforced composite material, wherein the volume fraction of the fiber in the composite material is 65%.

[0094] Example 15

[0095] The raw aromatic polyamide fiber containing 100% imidazole diamine by mass in the total amount of diamine was immersed in a 15wt% NaHCO3 aqueous solution at a temperature of 80°C for 120s and dried; then, it was heated to 320°C in a nitrogen-protected reactor, kept warm for 10 minutes and then cooled to obtain an aromatic polyamide fiber with high tensile strength and high compositeness.

[0096] The fiber is composited with epoxy resin to obtain a fiber-reinforced composite material, wherein the volume fraction of the fiber in the composite material is 65%.

[0097] Example 16

[0098] The difference between Example 16 and Example 15 is that the reaction mixture is heated to 270° C. in a nitrogen-protected reactor. The rest is the same as Example 15.

[0099] Example 17

[0100] Aromatic polyamide spun fibers containing 100% imidazole diamine by mass in the total amount of diamines are passed continuously through a 15wt% NaHCO3 aqueous solution at a temperature of 30°C at a speed of 0.5m / s and dried; then, they are passed continuously through a nitrogen-protected channel at a temperature of 360°C at a speed of 0.5m / s, with a residence time of 6 minutes in the channel, to obtain aromatic polyamide fibers with high tensile strength and high compositeness.

[0101] The fiber is composited with epoxy resin to obtain a fiber-reinforced composite material, wherein the volume fraction of the fiber in the composite material is 65%.

[0102] Example 18

[0103] Aromatic polyamide spun fibers containing 100% imidazole diamine by mass in the total amount of diamines are passed continuously through a NaHCO3 aqueous solution with a temperature of 80°C and a concentration of 15wt% at a speed of 1 m / s and dried; then, they are passed continuously through a nitrogen-protected channel with a temperature of 360°C at a speed of 1 m / s and a residence time in the channel of 3 minutes to obtain aromatic polyamide fibers with high tensile strength and high compositeness.

[0104] The fiber is composited with epoxy resin to obtain a fiber-reinforced composite material, wherein the volume fraction of the fiber in the composite material is 65%.

[0105] Example 19

[0106] Aromatic polyamide spun fibers containing 50% by mass of imidazole diamine in the total amount of diamines are continuously passed through an acetonitrile solution of triethylamine at a temperature of 80°C and a concentration of 20wt% at a speed of 1 m / s and dried; then, they are continuously passed through a nitrogen-protected channel at a temperature of 360°C at a speed of 1 m / s and a residence time in the channel of 3 minutes to obtain aromatic polyamide fibers with high tensile strength and high compositeness.

[0107] The fiber is composited with epoxy resin to obtain a fiber-reinforced composite material, wherein the volume fraction of the fiber in the composite material is 65%.

[0108] Comparative Example 1

[0109] Comparative Example 1 is compared with Example 1, in which the complexed hydrogen chloride on the surface is removed without undergoing a removal reaction, and the annealing treatment is performed directly. The preparation method of Comparative Example 1 is:

[0110] Aromatic polyamide nascent fibers containing 40% by mass of imidazole diamine in the total amount of diamines are heated to 270° C. in a nitrogen-protected reactor, kept warm for 10 minutes, and then cooled to obtain aromatic polyamide fibers with high tensile strength and high compositeness.

[0111] The fiber is composited with epoxy resin to obtain a fiber-reinforced composite material, wherein the volume fraction of the fiber in the composite material is 65%.

[0112] Comparative Example 2

[0113] Compared with Comparative Example 1, Comparative Example 2 is the same as Comparative Example 1, except that the mass percentage of the imidazole-containing diamine in the total amount of diamine is 50%.

[0114] Comparative Example 3

[0115] Compared with Comparative Example 1, Comparative Example 3 is the same as Comparative Example 1, except that the mass percentage of the imidazole-containing diamine in the total amount of diamine is 60%.

[0116] Comparative Example 4

[0117] Compared with Comparative Example 1, Comparative Example 4 is the same as Comparative Example 1, except that the mass percentage of the imidazole-containing diamine in the total amount of diamine is 70%.

[0118] Comparative Example 5

[0119] Compared with Comparative Example 1, Comparative Example 5 is the same as Comparative Example 1, except that the mass percentage of the imidazole-containing diamine in the total amount of diamine is 75%.

[0120] Comparative Example 6

[0121] Compared with Comparative Example 1, Comparative Example 6 is the same as Comparative Example 1, except that the mass percentage of the imidazole-containing diamine in the total amount of diamine is 80%.

[0122] Comparative Example 7

[0123] Compared with Comparative Example 1, Comparative Example 7 is the same as Comparative Example 1, except that the mass percentage of the imidazole-containing diamine in the total amount of diamines is 100%.

[0124] The fiber cortex orientation of the aromatic polyamide fibers prepared in Example 1 and Comparative Example 1 was tested by the following method:

[0125] Take the polarization infrared curves of two aromatic polyamide fibers at each polarization angle of 1020cm -1 The signal intensity at the wave number is similar to that at 700cm -1 The ratio of the signal intensity under the wave number is plotted into a pole figure to calculate the fiber cortex orientation. The test results are as follows: Figure 1 shown.

[0126] from Figure 1 It can be seen that the fiber cortex orientation degree of Comparative Example 1 is 13.51, while the fiber cortex orientation degree of Example 1 is 7.41, indicating that heat treatment after removing the hydrochloric acid from the cortex can significantly reduce the fiber cortex orientation degree.

[0127] The two-dimensional wide-angle X-ray diffraction spectra of the aromatic polyamide fibers prepared in Example 1 and Comparative Example 1 were measured to calculate the orientation degree of the core layer. Figure 2 As shown, Figure 2 The left figure in the middle is a two-dimensional wide-angle X-ray diffraction spectrum of the aromatic polyamide fiber prepared in Comparative Example 1, and the right figure is a two-dimensional wide-angle X-ray diffraction spectrum of the aromatic polyamide fiber prepared in Example 1.

[0128] from Figure 2 As can be seen, the fiber core orientation of Example 1 is 0.82, while that of Comparative Example 1 is 0.81. The fiber core orientation remains essentially unchanged before and after the removal of hydrogen chloride from the fiber surface. This is because the hydrogen chloride molecules in the fiber core are retained while the hydrogen chloride molecules on the fiber surface are removed. Consequently, the overall orientation of the fiber after thermal annealing is preserved, achieving non-destructive fiber modification and achieving high composite properties.

[0129] The interfacial shear strength of the fiber reinforced composite materials of Example 1 and Comparative Example 1 was measured by the fiber single filament pulling method. The SEM images of the interface failure sites are shown in FIG. Figure 3 As shown. Among them, Figure 3 The left picture in the middle is the SEM picture of the interface damage of comparative example 1, and the right picture is the SEM picture of the interface damage of embodiment 1.

[0130] from Figure 3 It can be seen that the interfacial failure of the fiber-reinforced composite material of Example 1 manifests as resin debonding, while its cortical fibers remain intact; whereas the interfacial failure of the fiber-reinforced composite material of Comparative Example 1 manifests as cortical tearing. This indicates that by removing the hydrogen chloride molecules complexed with the cortical layer of the benzimidazole-containing aromatic polyamide fibers, the self-orientation behavior of the fiber cortical layer can be effectively suppressed during the subsequent heat treatment of the as-spun fibers, significantly improving the tear resistance of the fiber cortical layer. This optimizes the interfacial failure behavior of the fiber-reinforced composite material and enhances the overall mechanical strength of the composite material.

[0131] The fiber-reinforced composite materials prepared in Examples 1-19 and Comparative Examples 1-7 were evaluated for interlaminar shear strength and the tensile strength of the aromatic polyamide fibers. The interlaminar shear strength of the fiber-reinforced composites was determined using the NOL ring test method, using ASTM D2344. The tensile strength of the aromatic polyamide fibers was determined according to GJB 348A-2018. The test results are shown in Table 1.

[0132] Table 1 Performance test data of fiber reinforced composite materials

[0133]

[0134] As shown in Table 1, the high-tensile-strength, highly composite aromatic polyamide fibers prepared in this application achieved tensile strengths of 5.5-7.0 GPa, both exceeding those of the comparative aromatic polyamide fibers without low-orientation treatment in the skin layer. The interlaminar shear strength of the fiber-reinforced composites prepared with these fibers was also significantly increased, reaching 64 MPa-71 MPa, both exceeding those of the comparative fiber-reinforced composites. The high-tensile-strength, highly composite aromatic polyamide fibers prepared in this application exhibit both excellent mechanical and composite properties.

[0135] Although this specification has been used to fully describe the present application using general descriptions and specific embodiments, it is obvious to those skilled in the art that modifications or improvements may be made based on the present application. Therefore, such modifications or improvements made without departing from the spirit of the present application are within the scope of protection claimed in this application.

Claims

1. A method for preparing aromatic polyamide fibers with high tensile strength and high compositeness, characterized in that: include: The as-spun aromatic polyamide fiber containing a benzimidazole ring is subjected to a stripping reaction with a stripping liquid to remove the hydrogen chloride complexed on the surface thereof, and then dried to obtain an intermediate product; The intermediate product is subjected to high-temperature annealing in a nitrogen atmosphere to obtain aromatic polyamide fibers with high tensile strength and high compositeness.

2. The preparation method according to claim 1, characterized in that The high temperature annealing comprises: heating the intermediate product to 270-360° C. in a nitrogen-protected reactor and keeping the temperature for 10-60 minutes.

3. The preparation method according to claim 1, characterized in that The high-temperature annealing comprises: continuously passing the intermediate product through a channel protected by nitrogen, the temperature in the channel is 270-360° C., and the residence time of the intermediate product in the channel is 10 min to 60 min.

4. The preparation method according to claim 1, characterized in that The temperature of the removal reaction is 10° C. to 80° C., and the reaction time is 10s to 300s.

5. The preparation method according to claim 1, characterized in that The removal liquid is an alkaline solution with a mass concentration of 0.1 to 20 wt%.

6. The preparation method according to claim 5, characterized in that The solute of the alkaline solution includes at least one of sodium bicarbonate, potassium bicarbonate, sodium carbonate, potassium carbonate, sodium hydroxide, potassium hydroxide, calcium hydroxide, ammonia water or triethylamine; The solvent of the alkaline solution is any one of ethanol, acetonitrile, dimethylformamide, dimethylacetamide, dimethyl sulfoxide, methyl pyrrolidone or water.

7. The preparation method according to claim 1, characterized in that The spun fibers are subjected to a stripping reaction by being immersed in a stripping liquid or by being continuously drawn through a stripping liquid.

8. The preparation method according to claim 1, characterized in that The mass percentage of imidazole diamine in the aromatic polyamide fiber containing benzimidazole rings to the total amount of diamines is 30 to 100 wt %.

9. Use of the high tensile strength and high composite aromatic polyamide fiber prepared by the preparation method according to any one of claims 1 to 8 in fiber-reinforced composite materials.

10. A fiber-reinforced composite material comprising reinforcing fibers and a resin matrix, characterized in that: The reinforcing fiber is an aromatic polyamide fiber with high tensile strength and high compositeness prepared by the preparation method according to any one of claims 1 to 8; and the resin matrix is an epoxy resin.

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