Aromatic polyamide fiber with high tensile strength and high elastic modulus and preparation method thereof

Abstract

The invention relates to the technical field of high-performance aromatic polyamide fibers, and discloses an aromatic polyamide fiber with high tensile strength and high elastic modulus and a preparation method thereof. The preparation method comprises the following steps: carrying out wet spinning on an aromatic polyamide spinning solution to obtain nascent fibers; obtaining energy storage modulus data, loss modulus data and loss angle tangent data of the nascent fiber in the heating process through a dynamic thermomechanical analysis device; according to the data, obtaining the tension limit, the viscosity characteristic and the relaxation time of the nascent fiber generating lossless plastic deformation in the corresponding temperature interval, and further obtaining the drafting tension and the retention time of the nascent fiber in different temperature intervals; and drafting the nascent fiber according to the process parameters to obtain the fiber. According to the method, the drafting tension of the fibers in each high-temperature interval is accurately metered, the drafting tension of the fibers in the high-temperature interval is controlled to be zero, the fibers are not suspended in the heating channel any more, and the heterocyclic aramid fibers with high tensile strength and high elastic modulus are obtained.

Description

Technical Field

[0001] This application relates to the field of high-performance aromatic polyamide fiber technology, specifically to an aromatic polyamide fiber with high tensile strength and high elastic modulus and its preparation method. Background Technology

[0002] Heterocyclic aramid fibers are widely used in important applications such as individual soldier protection, lightweight armor, and electrical insulation due to their lightweight, high strength, high toughness, and good electromagnetic permeability.

[0003] Currently, the typical production process for heterocyclic aramid fibers mainly involves wet spinning or wet-dry spinning. The common steps are to first spin and set the polymer solution of the heterocyclic aramid in a coagulation bath, then wash and preliminarily dry it to obtain nascent fibers; finally, after high-temperature drawing, the finished fibers are obtained. High-temperature drawing is a key step affecting the strength of aramid fibers. During high-temperature drawing, the molecular chain orientation in the nascent fibers is significantly improved, thereby significantly increasing its tensile strength and elastic modulus from approximately 1 GPa and 80 GPa to over 4 GPa and 120 GPa, respectively. For example, the invention patent with application number CN02133583.4 discloses a new post-processing process for aramid III precursor yarn bundles. By stretching the heterocyclic aramid precursor yarn bundles in a heating furnace at 320℃-500℃ with a tension of 0.2cN / dtex-1cN / dtex, the tensile strength and elastic modulus of heterocyclic aramid are effectively increased from 1.4GPa and 80GPa to 5.03GPa and 156GPa, respectively.

[0004] In recent years, by breaking down the high-temperature drawing process of heterocyclic aramid fibers from a single one-step drawing to a multi-step drawing process, the tensile strength and elastic modulus of the finished fibers have been significantly improved. For example, invention patent application number 201510131346.X discloses a hot drawing process for aramid III fiber precursor bundles. This process decomposes the traditional one-step hot drawing process for heterocyclic aramid fibers into a first step of high-tension drawing at 270℃-300℃ and a second step of low-tension drawing at 340℃-500℃. This process can increase the tensile strength of the fibers from 28 cN / dtex to 33 cN / dtex and the elastic modulus from 900 cN / dtex to 1050 cN / dtex. Invention patent application number 201910706716.6 discloses a process for hot drawing of heterocyclic aramid fibers. The three-stage heat setting method further decomposes the high-temperature drawing process of heterocyclic aramid nascent fibers into three steps: applying tensions of 5cN / dtex-30cN / dtex, 0.1cN / dtex-1cN / dtex, and 3cN / dtex-20cN / dtex to the nascent fibers in three temperature ranges of 230℃-360℃, 380℃-430℃, and 435℃-500℃, respectively. Unlike the traditional one-step high-temperature drawing process, this method can increase the tensile strength and elastic modulus of heterocyclic aramid from 4.3GPa and 112GPa to 6.5GPa and 145GPa, respectively.

[0005] The aforementioned studies indicate that multi-stage drawing of heterocyclic aramid nascent fibers at high temperatures can further improve their tensile strength and elastic modulus. However, due to the unclear structural evolution mechanism during the multi-stage drawing process, existing drawing process parameters are difficult to match well with the relaxation characteristics of heterocyclic aramid nascent fibers in different temperature ranges, resulting in the mechanical strength and modulus of the finished fibers still not reaching advanced levels. Furthermore, recent research by the applicant shows that due to the unique self-ordering and self-elongation phenomena of heterocyclic aramids at high temperatures, existing multi-stage high-temperature drawing processes for heterocyclic aramids suffer from over-drawing of nascent fibers at high temperatures and the introduction of macroscopic defects, ultimately resulting in relatively low mechanical strength and modulus of the finished fibers. For example, the invention patent with application number 201010158558.4 discloses an online heat treatment process and device for aramid III fiber. In the high-temperature section, the process adopts a method of consistent rotation speed of the front and rear rollers when stretching heterocyclic aramid. However, due to the self-elongation effect of the fiber, it actually presents a suspended state in the channel, further scraping and contacting the inner wall of the channel, which ultimately causes the fiber to overheat and pill, reducing the tensile strength of the fiber to a certain extent, which is only 5.91 GPa. Summary of the Invention

[0006] This application provides an aromatic polyamide fiber with high tensile strength and high elastic modulus and its preparation method, aiming to solve the technical problem that the existing process parameters for multi-stage high-temperature drawing of heterocyclic aramid fibers are difficult to match well with the relaxation characteristics of heterocyclic aramid nascent fibers in different temperature ranges, resulting in low fiber mechanical strength and modulus.

[0007] To achieve the above objectives, the present application adopts the following technical solution.

[0008] A first aspect of this application provides a method for preparing aromatic polyamide fibers with high tensile strength and high elastic modulus, comprising:

[0009] S1, providing an aromatic polyamide spinning solution, and wet spinning the aromatic polyamide spinning solution to obtain nascent fibers;

[0010] S2, Under an inert atmosphere, a dynamic thermomechanical analysis device is used to perform temperature scanning, stress scanning and frequency scanning on the nascent fiber during the heating process to obtain its energy storage modulus data, loss modulus data and loss tangent data during the heating process.

[0011] S3. Based on the energy storage modulus data, determine the tensile limit of the nascent fiber undergoing non-destructive plastic deformation in the corresponding temperature range; based on the loss modulus data and loss angle data, determine the viscous characteristics of the nascent fiber in the corresponding temperature range and its relaxation time in different temperature ranges; thereby obtaining the stretching tension and residence time of the nascent fiber in different temperature ranges.

[0012] S4, under an inert atmosphere, the nascent fibers are stretched according to the stretching tension and residence time of the nascent fibers in different temperature ranges to obtain aromatic polyamide fibers with high tensile strength and high elastic modulus.

[0013] Preferably, in step S3, in the temperature range below 380°C, the energy dissipation level of the nascent fiber undergoing relaxation transformation in this temperature range is calculated based on the integral area of ​​the loss tangent curve in different temperature ranges; combined with the average storage modulus of the nascent fiber in this temperature range, the tension level and load limit of the nascent fiber undergoing non-destructive plastic deformation are obtained, and the stretching tension of the nascent fiber in this temperature range is obtained; in the temperature range above 380°C, based on the self-elongation of the fiber, the stretching tension is controlled to be 0;

[0014] Based on the half-peak width of the loss tangent curve and the rate of decrease of the energy storage modulus curve within this temperature range, the relaxation time of the nascent fiber during the relaxation transition is obtained, thus yielding the residence time of the nascent fiber within this temperature range.

[0015] More preferably, the formula for calculating the energy dissipation level is as follows:

[0016]

[0017] Among them, W loss t0 and t1 are the initial and final values ​​of the temperature range, respectively. tanδ(t) is the change of the loss tangent with temperature in the temperature range. E is the average storage modulus in the temperature range. ε0 is the amplitude in a single sinusoidal loading cycle during dynamic thermomechanical analysis and testing.

[0018] The formula for calculating the relaxation time is as follows:

[0019]

[0020] Where τ is the relaxation time, f peak This is the frequency value corresponding to the highest loss tangent.

[0021] Preferably, the aromatic polyamide spinning solution in S1 is prepared by the following method:

[0022] Under an inert atmosphere, a diamine monomer is dissolved in a solvent to prepare a diamine solution; the diamine solution is cooled to -10℃ to 10℃, and the first batch of terephthaloyl chloride is added to it to react; then the diamine solution is heated to room temperature, and the second batch of terephthaloyl chloride is added to react, to obtain an aromatic polyamide spinning solution;

[0023] The diamine monomer includes 2-(4-aminophenyl)-5-aminobenzimidazole and a second monomer.

[0024] More preferably, the second monomer comprises at least one of p-phenylenediamine, 4,4'-diaminobiphenyl, 4,4'-diaminobenzonitaniline, 2-chloro-1,4-phenylenediamine, 4,4'-diaminodiphenyl ether, 2,5-dichloro-1,4-phenylenediamine, 2-(4-aminophenyl)-5-aminobenzoxazole, 2-(4-aminophenyl)-5-aminobenzothiazole, 2-(2-hydroxy-4-aminophenyl)-5-aminobenzimidazole, 2-(2-chloro-4-aminophenyl)-5-aminobenzimidazole, 2-chloro-4,4'-diaminobenzonitaniline, or 3,3'-dichlorobiphenylamine.

[0025] More preferably, the molar percentage of 2-(4-aminophenyl)-5-aminobenzimidazole in the diamine monomer is 20-100%.

[0026] More preferably, the solvent is an N,N-dimethylacetamide solution of LiCl; wherein the mass concentration of LiCl is 1-10%;

[0027] The aromatic polyamide spinning solution contains 1-10% aromatic polyamide solids.

[0028] More preferably, the molar ratio of the diamine monomer to terephthaloyl chloride is 1:1;

[0029] The first batch of terephthaloyl chloride accounted for 90-99% of the total molar amount of terephthaloyl chloride.

[0030] Preferably, the temperature of the stretching treatment in S4 is 100–450°C.

[0031] A second aspect of this application provides aromatic polyamide fibers with high tensile strength and high elastic modulus prepared by the above-described preparation method.

[0032] Compared with the prior art, the beneficial effects of this application are as follows:

[0033] This application utilizes dynamic thermomechanical analysis of nascent heterocyclic aramid fibers containing 2-(4-aminophenyl)-5-aminobenzimidazole to determine their relaxation scale at different temperature ranges. Based on the relaxation characteristics of heterocyclic aramid fibers at different temperature ranges, different tensions and holding times are applied to ensure sufficient orientation without excessive stretching at each temperature stage. Furthermore, based on the spontaneous elongation and ordered processing characteristics of nascent heterocyclic aramid fibers at high temperatures, this application accurately measures the stretching tension of the fibers in each high-temperature range and strictly controls the stretching tension to zero in the high-temperature range (>380℃) without causing sagging in the tunnel, ultimately producing finished heterocyclic aramid fibers with high tensile strength and high elastic modulus.

[0034] The heterocyclic aramid fibers prepared by this invention have an orientation degree ranging from 0.95 to 0.99, a tensile strength of 6.5 GPa to 7.5 GPa, and an elastic modulus of 135 GPa to 185 GPa. Attached Figure Description

[0035] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments recorded in this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0036] Figure 1 The image shows the test results of self-ordering and self-elongation of heterocyclic aramid fibers at high temperature.

[0037] Figure 2 The graph shows the changes in storage modulus, loss modulus, and loss tangent of the nascent fiber in Example 1 as temperature increases during dynamic thermomechanical analysis. Detailed Implementation

[0038] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0039] In the following description of this embodiment, the terms "including", "comprising", "having", and "containing" are all open-ended terms, meaning that they include but are not limited to.

[0040] In the following description of this embodiment, the term "and / or" is used to describe the association relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, B existing alone, and A and B existing simultaneously. A and B can be singular or plural. The character " / " generally indicates that the preceding and following related objects have an "or" relationship.

[0041] In the following description of this embodiment, the term "at least one" means one or more, and "more than one" means two or more. "At least one of the following" or similar expressions refer to any combination of these items, including any combination of single or multiple items. For example, "at least one of a, b, or c", or "at least one of a, b, and c", can both mean: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can be single or multiple.

[0042] The terminology used in the embodiments of this application is for the purpose of describing particular embodiments only and is not intended to be limiting of this application. The singular forms "a" and "the" as used in the embodiments of this application and the appended claims are also intended to include the plural forms, unless the context clearly indicates otherwise.

[0043] Those skilled in the art should understand that, in the following description of the embodiments of this application, the sequence of numbers does not imply the order of execution. Some or all steps may be executed in parallel or sequentially. 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 this application.

[0044] Those skilled in the art will understand that the numerical ranges in the embodiments of this application should be understood as each intermediate value between the upper and lower limits of the specifically disclosed range. Each smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this application. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0045] Unless otherwise stated, the technical / scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains. While this application describes only preferred methods and materials, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this application. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0046] In a first aspect, this application provides a method for preparing aromatic polyamide fibers with high tensile strength and high elastic modulus, comprising:

[0047] S1, providing an aromatic polyamide spinning solution, and wet spinning the aromatic polyamide spinning solution to obtain nascent fibers;

[0048] In this application, the aromatic polyamide spinning solution is prepared by the following method:

[0049] Under an inert atmosphere, a diamine monomer is dissolved in a solvent to prepare a diamine solution; the diamine solution is cooled to below 0°C, and the first batch of terephthaloyl chloride is added to it to react; then the diamine solution is heated to room temperature, and the second batch of terephthaloyl chloride is added to react, to obtain an aromatic polyamide spinning solution.

[0050] In this application, the diamine monomer comprises 2-(4-aminophenyl)-5-aminobenzimidazole and a second monomer. The molar percentage of 2-(4-aminophenyl)-5-aminobenzimidazole in the diamine monomer is 20-100%. The chemical structure of 2-(4-aminophenyl)-5-aminobenzimidazole is shown below:

[0051]

[0052] In this application, the second monomer is selected from at least one of p-phenylenediamine, 4,4'-diaminobiphenyl, 4,4'-diaminobenzonitaniline, 2-chloro-1,4-phenylenediamine, 4,4'-diaminodiphenyl ether, 2,5-dichloro-1,4-phenylenediamine, 2-(4-aminophenyl)-5-aminobenzoxazole, 2-(4-aminophenyl)-5-aminobenzothiazole, 2-(2-hydroxy-4-aminophenyl)-5-aminobenzimidazole, 2-(2-chloro-4-aminophenyl)-5-aminobenzimidazole, 2-chloro-4,4'-diaminobenzonitaniline, or 3,3'-dichlorobiphenylamine.

[0053] In this application, the solvent is an N,N-dimethylacetamide solution of LiCl. The mass concentration of LiCl is 1-10%. The aromatic polyamide spinning solution contains 1-10% aromatic polyamide solids.

[0054] In this application, the molar ratio of the diamine monomer to terephthaloyl chloride is 1:1; the first batch of terephthaloyl chloride accounts for 90-99% of the total molar amount of terephthaloyl chloride.

[0055] S2, Under an inert atmosphere, a dynamic thermomechanical analysis device is used to perform temperature scanning, stress scanning and frequency scanning on the nascent fiber during the heating process to obtain its energy storage modulus data, loss modulus data and loss tangent data during the heating process.

[0056] In this application, a dynamic thermomechanical analyzer was used to perform stress scanning and frequency scanning tests on the nascent fibers during the heating process from 25℃ to 500℃, collecting data on the changes in storage modulus, loss modulus, and loss tangent during the heating process. The test frequency was set to 0.5–5Hz, the stress control range was 10MPa–500MPa, and the strain control range was 0.5%–5%.

[0057] S3. Based on the energy storage modulus data, determine the tension limit for non-destructive plastic deformation of the nascent fiber in the corresponding temperature range; based on the loss modulus data and loss angle data, determine the viscous characteristics of the nascent fiber in the corresponding temperature range and its relaxation time in different temperature ranges; thus, obtain the drawing tension and residence time of the nascent fiber in different temperature ranges, i.e., the high-temperature drawing process parameters. In this application, the tension control is divided into two stages. In the temperature range below 380°C, the drawing tension is calculated according to the above method; while in the temperature range above 380°C, due to the self-elongation effect of heterocyclic aramid fibers, the drawing tension is controlled to be 0.

[0058] Specifically, based on the integral area of ​​the loss tangent curve in different temperature ranges, the energy dissipation level of the nascent fiber undergoing relaxation transformation in that temperature range is calculated.

[0059] The formula for calculating the energy dissipation level is as follows:

[0060]

[0061] Among them, W loss t0 and t1 are the initial and final values ​​of the temperature range, respectively. tanδ(t) is the change of the loss tangent with temperature in the temperature range. E is the average storage modulus in the temperature range. ε0 is the amplitude in a single sinusoidal loading cycle during dynamic thermomechanical analysis and testing.

[0062] By combining the average storage modulus of the nascent fiber within this temperature range, the tension level and load limit of the nascent fiber that undergoes non-destructive plastic deformation are obtained, and the stretching tension of the nascent fiber within this temperature range is obtained.

[0063] Based on the half-peak width of the loss tangent curve and the rate of decrease of the energy storage modulus curve within this temperature range, the relaxation time of the nascent fiber during the relaxation transition is obtained, thus yielding the residence time of the nascent fiber within this temperature range.

[0064] The formula for calculating the relaxation time is as follows:

[0065]

[0066] Where τ is the relaxation time, f peak This is the frequency value corresponding to the highest loss tangent.

[0067] S4, under an inert atmosphere, the nascent fibers are stretched according to the stretching tension and residence time of the nascent fibers in different temperature ranges to obtain aromatic polyamide fibers with high tensile strength and high elastic modulus.

[0068] The temperature of the stretching treatment is 100–450°C.

[0069] In this application, the inert atmosphere includes at least one of nitrogen, helium, neon, and argon atmospheres, preferably a nitrogen atmosphere.

[0070] The applicant's research indicates that heterocyclic aramids exhibit unique self-ordering and self-elongation phenomena at high temperatures, such as... Figure 1 As shown, the existing high-temperature stretching processes for heterocyclic aramid fibers all have shortcomings in overstretching the nascent heterocyclic aramid fibers at high temperatures and introducing macroscopic defects, ultimately resulting in low mechanical strength and modulus of the finished fibers.

[0071] This application utilizes dynamic thermomechanical analysis of nascent heterocyclic aramid fibers containing 2-(4-aminophenyl)-5-aminobenzimidazole to determine their relaxation scale at different temperature ranges. Based on the relaxation characteristics of heterocyclic aramid fibers at different temperature ranges, different tensions and holding times are applied to ensure sufficient orientation without excessive stretching at each temperature stage. Furthermore, based on the spontaneous elongation and ordered processing characteristics of nascent heterocyclic aramid fibers at high temperatures, this application accurately measures the stretching tension of the fibers in each high-temperature range and strictly controls the stretching tension to zero in the high-temperature range (>380℃) without causing sagging in the tunnel, ultimately producing finished heterocyclic aramid fibers with high tensile strength and high elastic modulus.

[0072] Secondly, this application provides aromatic polyamide fibers prepared by the above-described preparation method. The heterocyclic aramid fibers of this application have high tensile strength and high elastic modulus, with an orientation degree ranging from 0.95 to 0.99, a tensile strength of 6.5 GPa to 7.5 GPa, and an elastic modulus of 135 GPa to 185 GPa.

[0073] The present application will be further illustrated by the following examples.

[0074] Example 1

[0075] S1, under the protection of dry nitrogen, 82.32 g of 2-(4-aminophenyl)-5-aminobenzimidazole and 39.72 g of p-phenylenediamine were added to a 3.5% lithium chloride N,N-dimethylacetamide solution (6513.2 g by mass), and stirred until completely dissolved to obtain a diamine solution. The diamine solution was cooled to 2°C, and 141.77 g of terephthaloyl chloride was added, and the reaction was continued for 0.5 h. Then the cooling device was removed, and the reaction solution was heated to room temperature. Another 7.46 g of terephthaloyl chloride was added, and the reaction was continued for 1 h to obtain a heterocyclic aramid spinning solution. The heterocyclic aramid spinning solution was wet-spun to obtain nascent fibers.

[0076] S2, under dry nitrogen protection, a tensile stress of 50 MPa and a loading frequency of 1 Hz were set. A dynamic thermomechanical analyzer was used to perform temperature scanning, stress scanning and frequency scanning on the nascent fiber to determine the changes in storage modulus, loss modulus and loss tangent of the nascent fiber during the heating process from 25℃ to 500℃.

[0077] The storage modulus, loss modulus, and loss tangent of nascent fibers as a function of temperature in dynamic thermomechanical analysis are shown in the following curves. Figure 2 As shown.

[0078] S3, based on the integral area of ​​the loss tangent curve in different temperature ranges and the corresponding average storage modulus in the relaxation range, the energy dissipation level of the nascent fiber undergoing relaxation transition in this temperature range is calculated according to the following formula:

[0079]

[0080] In the formula, W loss t0 and t1 are the initial and final values ​​of the temperature range, respectively. tanδ(t) is the change of the loss tangent with temperature in the temperature range. E is the average storage modulus in the temperature range. ε0 is the amplitude in a single sinusoidal loading cycle during dynamic thermomechanical analysis and testing.

[0081] At the median of each of the above temperature ranges, stress scanning of heterocyclic aramid nascent fibers was performed using a dynamic thermomechanical analyzer. The change in storage modulus as the applied stress decreased was plotted, and the stress corresponding to the inflection point when the storage modulus decreased significantly was recorded as the tensile limit at which the nascent fiber underwent non-destructive plastic deformation in that temperature range.

[0082] Meanwhile, based on the frequency scanning of heterocyclic aramid nascent fibers in various temperature ranges, the frequency value f corresponding to the highest loss tangent was recorded. peak According to the Debye formula The relaxation time of the nascent fiber within this temperature range is calculated, which is the residence time of the nascent fiber within this temperature range.

[0083] Based on the relaxation characteristics of heterocyclic aramid in different temperature ranges reflected by the above dynamic thermomechanical analysis and test results, a segmented multi-stage hot drawing process for heterocyclic aramid was formulated as shown in Table 1.

[0084] S4. In a segmented high-temperature tunnel, the nascent fibers are heat-treated according to the above-mentioned segmented multi-stage hot stretching process to obtain heterocyclic aramid fibers.

[0085] Table 1. High-temperature drawing process parameters for Examples 1-5

[0086]

[0087] Example 2

[0088] S1, under the protection of dry nitrogen, 90.77 g of 2-(4-aminophenyl)-5-aminobenzimidazole and 43.74 g of p-phenylenediamine were added to a 3.5% lithium chloride N,N-dimethylacetamide solution (8239.4 g by mass), and stirred until completely dissolved to obtain a diamine solution. The diamine solution was cooled to 2°C, and 159.40 g of terephthaloyl chloride was added, and the reaction was carried out for 0.5 h. Then the cooling device was removed, and the reaction solution was heated to room temperature. Another 4.93 g of terephthaloyl chloride was added, and the reaction was carried out for 1 h to obtain a heterocyclic aramid spinning solution. The heterocyclic aramid spinning solution was wet-spun to obtain nascent fibers.

[0089] Steps S2, S3, and S4 of Example 2 are the same as those of Example 1. The segmented multi-stage hot drawing process of heterocyclic aramid in Example 2 is shown in Table 1.

[0090] Example 3

[0091] S1, under the protection of dry nitrogen, 42.10 g of 2-(4-aminophenyl)-5-aminobenzimidazole and 47.34 g of p-phenylenediamine were added to a 3.5% lithium chloride N,N-dimethylacetamide solution (mass 5968.4 g). The solution was stirred until completely dissolved to obtain a diamine solution. The diamine solution was cooled to 2°C, and 123.22 g of terephthaloyl chloride was added. The reaction was allowed to proceed for 0.5 h. The cooling device was then removed, and the reaction solution was heated to room temperature. 3.81 g of terephthaloyl chloride was added, and the reaction was allowed to proceed for 1 h to obtain a heterocyclic aramid spinning solution. The heterocyclic aramid spinning solution was then wet-spun to obtain nascent fibers.

[0092] Steps S2, S3, and S4 of Example 3 are the same as those of Example 1. The segmented multi-stage hot drawing process of the heterocyclic aramid in Example 3 is shown in Table 1.

[0093] Example 4

[0094] S1, under the protection of dry nitrogen, 73.39 g of 2-(4-aminophenyl)-5-aminobenzimidazole and 74.37 g of 4,4'-diaminobenzoylaniline were added to a 3.5% lithium chloride N,N-dimethylacetamide solution (7737.5 g by mass), and stirred until completely dissolved to obtain a diamine solution. The diamine solution was cooled to 2°C, and 128.89 g of terephthaloyl chloride was added, and the reaction was carried out for 0.5 h. Then the cooling device was removed, and the reaction solution was heated to room temperature. 3.99 g of terephthaloyl chloride was added, and the reaction was carried out for 1 h to obtain a heterocyclic aramid spinning solution. The heterocyclic aramid spinning solution was wet-spun to obtain nascent fibers.

[0095] Steps S2, S3, and S4 in Example 4 are the same as in Example 1. The segmented multi-stage hot drawing process of the heterocyclic aramid in Example 4 is shown in Table 1.

[0096] Example 5

[0097] S1, under the protection of dry nitrogen, 31.50 g of 2-(4-aminophenyl)-5-aminobenzimidazole and 127.67 g of 4,4'-diaminobenzoylaniline were added to a 3.5% lithium chloride N,N-dimethylacetamide solution (mass 8319.2 g). The solution was stirred until completely dissolved to obtain a diamine solution. The diamine solution was cooled to 2°C, and 138.29 g of terephthaloyl chloride was added. The reaction was allowed to proceed for 0.5 h. The cooling device was then removed, and the reaction solution was heated to room temperature. Another 4.28 g of terephthaloyl chloride was added, and the reaction was allowed to proceed for 1 h to obtain a heterocyclic aramid spinning solution. The heterocyclic aramid spinning solution was then wet-spun to obtain nascent fibers.

[0098] Steps S2, S3, and S4 of Example 5 are the same as those of Example 1. The segmented multi-stage hot drawing process of the heterocyclic aramid in Example 5 is shown in Table 1.

[0099] Example 6

[0100] S1, under the protection of dry nitrogen, 97.63 g of 2-(4-aminophenyl)-5-aminobenzimidazole and 104.60 g of 2-(2-hydroxy-4-aminophenyl)-5-aminobenzimidazole were added to a 3.5% lithium chloride N,N-dimethylacetamide solution (9095.7 g by mass). The solution was stirred until completely dissolved to obtain a diamine solution. The diamine solution was cooled to 2°C, and 171.46 g of terephthaloyl chloride was added. The reaction was allowed to proceed for 0.5 h. The cooling device was then removed, and the reaction solution was heated to room temperature. 5.30 g of terephthaloyl chloride was added, and the reaction was allowed to proceed for 1 h to obtain a heterocyclic aramid spinning solution. The heterocyclic aramid spinning solution was then wet-spun to obtain nascent fibers.

[0101] Steps S2, S3, and S4 of Example 6 are the same as those of Example 1. The segmented multi-stage hot drawing process of the heterocyclic aramid in Example 6 is shown in Table 2.

[0102] Table 2. High-temperature drawing process parameters for Examples 6-10

[0103]

[0104] Example 7

[0105] S1, under the protection of dry nitrogen, 84.25 g of 2-(4-aminophenyl)-5-aminobenzimidazole and 95.10 g of 3,3'-dichlorobenzidine were added to a 3.5% lithium chloride N,N-dimethylacetamide solution (7965.4 g by mass), and stirred until completely dissolved to obtain a diamine solution. The diamine solution was cooled to 2°C, and 147.97 g of terephthaloyl chloride was added, and the reaction was carried out for 0.5 h. Then the cooling device was removed, and the reaction solution was heated to room temperature. 4.58 g of terephthaloyl chloride was added, and the reaction was carried out for 1 h to obtain a heterocyclic aramid spinning solution. The heterocyclic aramid spinning solution was wet-spun to obtain nascent fibers.

[0106] Steps S2, S3, and S4 of Example 7 are the same as those of Example 1. The segmented multi-stage hot drawing process of heterocyclic aramid in Example 7 is shown in Table 2.

[0107] Example 8

[0108] S1, under the protection of dry nitrogen, 70.64 g of 2-(4-aminophenyl)-5-aminobenzimidazole and 81.49 g of 2-(2-chloro-4-aminophenyl)-5-aminobenzimidazole were added to a 3.5% lithium chloride N,N-dimethylacetamide solution (6720.6 g by mass). The solution was stirred until completely dissolved to obtain a diamine solution. The diamine solution was cooled to 2°C, and 124.06 g of terephthaloyl chloride was added. The reaction was allowed to proceed for 0.5 h. The cooling device was then removed, and the reaction solution was heated to room temperature. 3.84 g of terephthaloyl chloride was added, and the reaction was allowed to proceed for 1 h to obtain a heterocyclic aramid spinning solution. The heterocyclic aramid spinning solution was then wet-spun to obtain nascent fibers.

[0109] Steps S2, S3, and S4 in Example 8 are the same as in Example 1. The segmented multi-stage hot drawing process of the heterocyclic aramid in Example 8 is shown in Table 2.

[0110] Example 9

[0111] S1, under the protection of dry nitrogen, 99.30 g of 2-(4-aminophenyl)-5-aminobenzimidazole and 88.66 g of 4,4'-diaminodiphenyl ether were added to a 3.5% lithium chloride N,N-dimethylacetamide solution (8825.6 g by mass), and stirred until completely dissolved to obtain a diamine solution. The diamine solution was cooled to 2°C, and 174.38 g of terephthaloyl chloride was added, and the reaction was carried out for 0.5 h. Then the cooling device was removed, and the reaction solution was heated to room temperature. 5.39 g of terephthaloyl chloride was added, and the reaction was carried out for 1 h to obtain a heterocyclic aramid spinning solution. The heterocyclic aramid spinning solution was wet-spun to obtain nascent fibers.

[0112] Steps S2, S3, and S4 of Example 9 are the same as those of Example 1. The segmented multi-stage hot drawing process of the heterocyclic aramid in Example 9 is shown in Table 2.

[0113] Example 10

[0114] S1, under the protection of dry nitrogen, 146.26 g of 2-(4-aminophenyl)-5-aminobenzimidazole was added to a 3.5% lithium chloride N,N-dimethylacetamide solution (9865.3 g by mass), and stirred until completely dissolved to obtain a diamine solution. The diamine solution was cooled to 2°C, and 256.5 g of terephthaloyl chloride was added, reacting for 0.5 h. Then the cooling device was removed, and the reaction solution was heated to room temperature, followed by the addition of 7.94 g of terephthaloyl chloride, reacting for 1 h to obtain a heterocyclic aramid spinning solution. The heterocyclic aramid spinning solution was then wet-spun to obtain nascent fibers.

[0115] Steps S2, S3, and S4 of Example 10 are the same as those of Example 1. The segmented multi-stage hot drawing process of the heterocyclic aramid fiber in Example 10 is shown in Table 2.

[0116] Comparative Example 1

[0117] S1 is the same as in Example 1;

[0118] S2, the nascent fibers are placed freely in a high-temperature furnace under nitrogen protection without any load, and heat-treated at 360°C for 0.5 hours, and then naturally cooled to room temperature to obtain heterocyclic aramid fibers.

[0119] Comparative Example 2

[0120] S1 is the same as in Example 1;

[0121] S2, the nascent fiber is stretched at a tension of 15MPa at a uniform speed through a segmented high-temperature tunnel protected by nitrogen and at a temperature of 420℃, and the residence time of the fiber in the tunnel is controlled to be 2min to obtain heterocyclic aramid fiber.

[0122] Comparative Example 3

[0123] S1 is the same as in Example 1;

[0124] S2, the nascent fiber is stretched at a tension of 15 MPa at a constant speed through the 350°C temperature zone of the segmented high-temperature tunnel, with the residence time controlled at 1.5 min; then it is stretched at a tension of 40 MPa at a constant speed through the 420°C temperature zone of the segmented high-temperature tunnel, with the residence time controlled at 0.5 min; thus obtaining heterocyclic aramid fiber.

[0125] The orientation degree, tensile strength and elastic modulus of the heterocyclic aramid fibers in the examples and comparative examples were tested, and the test results are shown in Table 3.

[0126] Table 3. Orientation degree, tensile strength, and elastic modulus of heterocyclic aramid fibers in the examples and comparative examples.

[0127]

[0128]

[0129] As shown in Table 3, the heterocyclic aramid fibers prepared by the high-temperature drawing process of this application have an orientation degree of 0.95-0.99, which is significantly higher than that of the heterocyclic aramid fibers in the comparative example; their tensile strength is 6.5GPa-7.5GPa and their elastic modulus is 135GPa-185GPa, both of which have achieved a significant improvement.

[0130] Although this application has been described in detail in this specification with general descriptions and specific embodiments, some modifications or improvements can be made to it, which will be obvious to those skilled in the art. Therefore, such modifications or improvements made without departing from the spirit of this application are all within the scope of protection claimed in this application.

Claims

1. A method for preparing aromatic polyamide fibers with high tensile strength and high elastic modulus, characterized in that, include: S1, providing an aromatic polyamide spinning solution, and wet spinning the aromatic polyamide spinning solution to obtain nascent fibers; S2, Under an inert atmosphere, a dynamic thermomechanical analysis device is used to perform temperature scanning, stress scanning and frequency scanning on the nascent fiber during the heating process to obtain its energy storage modulus data, loss modulus data and loss tangent data during the heating process. S3. Based on the energy storage modulus data, determine the tensile limit of the nascent fiber undergoing non-destructive plastic deformation in the corresponding temperature range; based on the loss modulus data and loss angle data, determine the viscous characteristics of the nascent fiber in the corresponding temperature range and its relaxation time in different temperature ranges; thereby obtaining the stretching tension and residence time of the nascent fiber in different temperature ranges. S4, under an inert atmosphere, the nascent fibers are stretched according to the stretching tension and residence time of the nascent fibers in different temperature ranges to obtain aromatic polyamide fibers with high tensile strength and high elastic modulus.

2. The preparation method according to claim 1, characterized in that, In step S3, in the temperature range below 380℃, the energy dissipation level of the nascent fiber undergoing relaxation transformation in this temperature range is calculated based on the integral area of ​​the loss tangent curve in different temperature ranges; combined with the average storage modulus of the nascent fiber in this temperature range, the tension level and load limit of the nascent fiber undergoing non-destructive plastic deformation are obtained, and the stretching tension of the nascent fiber in this temperature range is calculated; in the temperature range above 380℃, the stretching tension is controlled to be 0 based on the self-elongation of the fiber. Based on the half-peak width of the loss tangent curve and the rate of decrease of the energy storage modulus curve within this temperature range, the relaxation time of the nascent fiber during the relaxation transition is obtained, thus yielding the residence time of the nascent fiber within this temperature range.

3. The preparation method according to claim 2, characterized in that, The formula for calculating the energy dissipation level is as follows: Among them, W loss t0 and t1 are the initial and final values ​​of the temperature range, respectively. tanδ(t) is the change of the loss tangent with temperature in the temperature range. E is the average storage modulus in the temperature range. ε0 is the amplitude in a single sinusoidal loading cycle during dynamic thermomechanical analysis and testing. The formula for calculating the relaxation time is as follows: Where τ is the relaxation time, f peak This is the frequency value corresponding to the highest loss tangent.

4. The preparation method according to claim 1, characterized in that, The aromatic polyamide spinning solution described in S1 is prepared by the following method: Under an inert atmosphere, a diamine monomer is dissolved in a solvent to prepare a diamine solution; the diamine solution is cooled to -10℃ to 10℃, and the first batch of terephthaloyl chloride is added to it to react; then the diamine solution is heated to room temperature, and the second batch of terephthaloyl chloride is added to react, to obtain an aromatic polyamide spinning solution; The diamine monomer includes 2-(4-aminophenyl)-5-aminobenzimidazole and a second monomer.

5. The preparation method according to claim 4, characterized in that, The second monomer includes at least one of p-phenylenediamine, 4,4'-diaminobiphenyl, 4,4'-diaminobenzonitaniline, 2-chloro-1,4-phenylenediamine, 4,4'-diaminodiphenyl ether, 2,5-dichloro-1,4-phenylenediamine, 2-(4-aminophenyl)-5-aminobenzoxazole, 2-(4-aminophenyl)-5-aminobenzothiazole, 2-(2-hydroxy-4-aminophenyl)-5-aminobenzimidazole, 2-(2-chloro-4-aminophenyl)-5-aminobenzimidazole, 2-chloro-4,4'-diaminobenzonitaniline, or 3,3'-dichlorobiphenylamine.

6. The preparation method according to claim 4, characterized in that, In the diamine monomer, the molar percentage of 2-(4-aminophenyl)-5-aminobenzimidazole is 20-100%.

7. The preparation method according to claim 4, characterized in that, The solvent is an N,N-dimethylacetamide solution of LiCl; wherein the mass concentration of LiCl is 1-10%; The aromatic polyamide spinning solution contains 1-10% aromatic polyamide solids.

8. The preparation method according to claim 4, characterized in that, The molar ratio of the diamine monomer to terephthaloyl chloride is 1:1; The first batch of terephthaloyl chloride accounted for 90-99% of the total molar amount of terephthaloyl chloride.

9. The preparation method according to claim 1, characterized in that, The temperature for the stretching treatment described in S4 is 100–450°C.

10. Aromatic polyamide fibers with high tensile strength and high elastic modulus prepared by the preparation method according to any one of claims 1-9.

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