Acid-resistant high-modulus para-aramid fiber and method of making same

Abstract

The present application relates to the technical field of chemical fiber production, and in particular to an acid-resistant high-modulus para-aramid fiber and a preparation method thereof, the preparation method comprising the following steps: S1, extruding a spinning dope of para-aramid through a spinneret to form nascent fibers; S2, immersing the nascent fibers in a coagulation bath containing diisocyanate for soaking reaction to obtain modified filaments; S3, synchronously twisting the modified filaments after tensioning, and then performing multi-stage drying treatment to obtain the acid-resistant high-modulus para-aramid fiber. The high-modulus para-aramid fiber prepared by the method has higher stability and longer service life in a strong acid environment, and is suitable for application fields with high acid resistance requirements, such as protective materials, corrosion-resistant coatings and high-performance composite materials. The preparation method provides an innovative and effective improvement technology for the production of para-aramid fibers, and has high industrial application value.

Description

Technical Field

[0001] This invention relates to an acid-resistant, high-modulus para-aramid fiber and its preparation method, belonging to the field of chemical fiber production technology. Background Technology

[0002] Para-aramid fiber is a high-performance synthetic fiber, also known as poly(p-phenylene terephthalamide) fiber or aramid 1414. Due to its excellent mechanical properties, thermal stability, and chemical resistance, it has been widely used in aerospace, military, automotive, and construction industries. The preparation method for para-aramid fiber involves a polycondensation reaction of para-aramid monomers (such as p-phenylenediamine and terephthalic acid dichloroisocyanurate) to obtain a polyamide solution, which is then processed into fibers through wet spinning or dry spinning. The coagulation bath in this process typically uses a solution containing solvents and acids to promote fiber coagulation and orientation.

[0003] Traditional para-aramid fibers still face a high risk of dissolution under extremely acidic environments, especially in strong acid solutions such as concentrated sulfuric acid. This is mainly because the molecular structure of para-aramid contains multiple functional groups such as amino and hydroxyl groups, which are prone to reaction in strong acid environments, leading to molecular chain breakage or dissolution, thus affecting the fiber's performance and stability. The lack of sufficient protective measures in the coagulation bath limits the application of the prepared para-aramid fibers in special environments such as strong acids.

[0004] However, para-aramid fibers are often used as raw materials for pipes, cables, corrosion-resistant coatings, protective clothing, etc., which are used in some strong acid special environments. However, the poor acid resistance of para-aramid fibers will greatly limit their application. Therefore, it is of great value to develop an acid-resistant high-modulus para-aramid fiber and its preparation method. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides an acid-resistant, high-modulus para-aramid fiber and its preparation method. The para-aramid fiber has higher modulus and acid resistance, and the preparation process is simple.

[0006] The technical solution of this invention to solve the above-mentioned technical problems is as follows: A method for preparing acid-resistant high-modulus para-aramid fiber, wherein the preparation method is as follows:

[0007] S1. The spinning solution of para-aramid is extruded through a spinneret to form nascent fibers.

[0008] S2. Immerse the nascent fibers in a coagulation bath containing diisocyanate to obtain the modified fiber bundle.

[0009] S3. The modified filament bundles are tensioned and twisted simultaneously, and then subjected to multi-stage drying treatment to obtain acid-resistant high-modulus para-aramid fibers.

[0010] Furthermore, the spinning solution comprises poly(p-phenylene terephthalamide) resin and concentrated sulfuric acid, the concentration of which is 99.8%-100.2%, and the mass ratio of which is 1:(3.9-4.2).

[0011] Furthermore, the poly(p-phenylene terephthalamide) resin has a water content of less than 200 ppm, a salt content of 8.0%-8.6%, and an intrinsic viscosity of 6.5 dL / g to 7.5 dL / g.

[0012] Furthermore, the spinneret specifications are 1-4 spinnerets with 500-2000 holes, and the diameter of each hole is 0.5-2D.

[0013] Furthermore, the coagulation bath includes diisocyanate, sulfuric acid and water, wherein the mass concentration of diisocyanate in the coagulation bath is 0.1%-5% and the mass concentration of sulfuric acid in the coagulation bath is 4.5%-6.5%.

[0014] Furthermore, the temperature of the coagulation bath is 5-10℃, and the nascent fibers are immersed in the coagulation bath for 1-60 minutes.

[0015] Furthermore, the diisocyanate is selected from at least one of hexamethylene diisocyanate, toluene diisocyanate, isophorone diisocyanate, and diphenylmethane diisocyanate.

[0016] Furthermore, in step S3, the modified filament bundles are combined in groups of 2-8, with a tension of 0.1-5 N and a synchronous twisting condition of 0.5-10 T / m.

[0017] Furthermore, in step S3, a three-stage drying process is employed, wherein the three stages of drying are as follows:

[0018] The first stage of drying is oven drying, with a drying temperature of 80-180℃, a tension of 1cN / dtex-5cN / dtex, and a drying time of 3-7s. The moisture content of the first-stage dried filament bundle is 6%-8%.

[0019] The second stage of drying involves heated rollers, with a drying temperature of 200-300℃, a tension of 2cN / dtex-5cN / dtex, and a drying time of 1-3 seconds.

[0020] The third stage of drying is infrared radiation drying, with a drying temperature of 160-180℃ and a drying time of 1-1.5s.

[0021] The present invention also discloses an acid-resistant high-modulus para-aramid fiber, wherein the acid-resistant high-modulus para-aramid fiber is prepared according to the preparation method described in the present invention.

[0022] The beneficial effects of this invention are:

[0023] The preparation method described in this invention involves optimizing the spinneret, modifying with diisocyanate, and performing three drying processes to produce a high-modulus para-aramid fiber with superior acid resistance. The high-modulus para-aramid fiber obtained using this method exhibits higher stability and longer service life in strong acid environments, making it suitable for applications requiring high acid resistance, such as protective materials, corrosion-resistant coatings, and high-performance composite materials. This invention provides an innovative and effective improvement technology for the production of para-aramid fibers, and the preparation process is simple to operate, possessing high industrial application value.

[0024] More specifically, in the preparation method described in this invention, the spinneret configuration is optimized, the spinning solution is spun to form nascent fibers, and diisocyanate is added to the coagulation bath during the fiber formation process. The diisocyanate reacts with the amino or hydroxyl groups in the aramid molecular chain to form a three-dimensional cross-linked network, which improves the acid resistance of the fiber. After the fiber is formed, the fiber is subjected to a merging treatment and a three-stage drying technology is used to improve the uniformity and modulus of the fiber, ultimately obtaining a high-modulus para-aramid fiber with high acid resistance. Attached Figure Description

[0025] Figure 1 This is a flowchart illustrating the preparation process of the acid-resistant high-modulus para-aramid fiber described in this invention. Detailed Implementation

[0026] The specific embodiments of the present invention will be described in detail below. The present invention can be implemented in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed.

[0027] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used is for describing particular embodiments only and is not intended to limit the invention.

[0028] like Figure 1 As shown, a method for preparing acid-resistant, high-modulus para-aramid fiber is described, wherein the preparation method is as follows:

[0029] S1. Under sealed conditions, poly(p-phenylene terephthalamide) resin is mixed and stirred with concentrated sulfuric acid, degassed and filtered to obtain spinning solution, and the spinning solution of para-aramid is extruded through a spinneret to form nascent fibers.

[0030] S2. Immerse the nascent fibers in a coagulation bath containing diisocyanate to obtain the modified fiber bundle.

[0031] S3. The modified filament bundles are tensioned and twisted simultaneously, and then subjected to multi-stage drying treatment to obtain acid-resistant high-modulus para-aramid fibers.

[0032] Specifically, the spinning solution includes poly(p-phenylene terephthalamide) resin and concentrated sulfuric acid, the concentration of which is 99.8%-100.2% (including fuming sulfuric acid with free SO3), and the mass ratio of the poly(p-phenylene terephthalamide) resin to the concentrated sulfuric acid is 1:(3.9-4.2).

[0033] Specifically, the poly(p-phenylene terephthalamide) resin has a water content of less than 200 ppm, a salt content of 8.0%-8.6%, and an intrinsic viscosity of 6.5 dL / g to 7.5 dL / g (at 25°C, with concentrated sulfuric acid as the solvent).

[0034] Specifically, the spinneret specifications are 1-4 spinnerets with 500-2000 holes, and the diameter of each hole is 0.5-2D.

[0035] Specifically, the coagulation bath includes diisocyanate, sulfuric acid and water, wherein the mass concentration of diisocyanate in the coagulation bath is 0.1%-5% and the mass concentration of sulfuric acid in the coagulation bath is 4.5%-6.5%.

[0036] Specifically, the temperature of the coagulation bath is 5-10℃, and the nascent fibers are immersed in the coagulation bath for 1-60 minutes.

[0037] Specifically, the diisocyanate is selected from at least one of hexamethylene diisocyanate (HDI), toluene diisocyanate (TDI), isophorone diisocyanate (IPDI), and diphenylmethane diisocyanate (MDI).

[0038] Specifically, in step S3, the modified filament bundles are combined in groups of 2-8, with a tension of 0.1-5 N and a synchronous twisting condition of 0.5-10 T / m.

[0039] Specifically, in step S3, a three-stage drying process is adopted, wherein the three-stage drying processes are as follows:

[0040] The first stage of drying is oven drying, with a drying temperature of 80-180℃, a tension of 1cN / dtex-5cN / dtex, and a drying time of 3-7s. The moisture content of the first-stage dried filament bundle is 6%-8%.

[0041] The second stage of drying involves heated rollers, with a drying temperature of 200-300℃, a tension of 2cN / dtex-5cN / dtex, and a drying time of 1-3 seconds.

[0042] The third stage of drying is infrared radiation drying, with a drying temperature of 160-180℃ and a drying time of 1-1.5s.

[0043] An acid-resistant high-modulus para-aramid fiber, wherein the acid-resistant high-modulus para-aramid fiber is prepared according to the preparation method described in this invention.

[0044] Example 1

[0045] A method for preparing acid-resistant, high-modulus para-aramid fiber, wherein the preparation method comprises:

[0046] (1) The poly(p-phenylene terephthalamide) resin has a water content of 150 ppm, a salt content of 8.3%, and an intrinsic viscosity of 7.0 dL / g; the concentrated sulfuric acid concentration is 99.8%; the poly(p-phenylene terephthalamide) resin and concentrated sulfuric acid are mixed and stirred at a mass ratio of 1:4, degassed and filtered to obtain the spinning solution, and extruded using two spinnerets with 1000 holes and a single hole diameter of 1.5D to form nascent fibers.

[0047] (2) Immerse the nascent fibers in a coagulation bath containing 2% hexamethylene diisocyanate (HDI) and 5% sulfuric acid. The coagulation bath temperature is 5°C, and the soaking reaction is carried out for 30 minutes.

[0048] (3) The modified filament bundles were combined in groups of four, with a tension of 2N and a synchronous twist of 5T / m. The drying process was divided into three stages: the first stage was oven drying at 120℃, a tension of 3cN / dtex, and a drying time of 5s, with a moisture content of 7%; the second stage was heated roller drying at 250℃, a tension of 3cN / dtex, and a drying time of 2s; and the third stage was infrared radiation drying at 180℃ and a drying time of 1.2s.

[0049] Example 2

[0050] A method for preparing acid-resistant, high-modulus para-aramid fiber, wherein the preparation method comprises:

[0051] (1) The poly(p-phenylene terephthalamide) resin has a water content of 100 ppm, a salt content of 8.0%, and an intrinsic viscosity of 6.5 dL / g; the concentrated sulfuric acid concentration is 100.2%; the poly(p-phenylene terephthalamide) resin and concentrated sulfuric acid are mixed and stirred at a mass ratio of 1:3.9, degassed, filtered and the resulting spinning solution is used to extrude the nascent fibers using two spinnerets with 1000 holes and a single hole diameter of 1.5D.

[0052] (2) Immerse the nascent fibers in a coagulation bath containing 0.5% toluene diisocyanate (TDI) and 4.5% sulfuric acid solution at a temperature of 8°C for 60 minutes.

[0053] (3) The modified filament bundles were combined in groups of two, with a tension of 0.1 N and a synchronous twist of 0.5 T / m. The drying process was divided into three stages: the first stage was oven drying at 80 ℃, a tension of 1 cN / dtex, and a drying time of 7 s, with a moisture content of 6%; the second stage was heated roller drying at 200 ℃, a tension of 2 cN / dtex, and a drying time of 3 s; and the third stage was infrared radiation drying at 180 ℃ and a drying time of 1 s.

[0054] Example 3

[0055] A method for preparing acid-resistant, high-modulus para-aramid fiber, wherein the preparation method comprises:

[0056] (1) The poly(p-phenylene terephthalamide) resin has a water content of 80 ppm, a salt content of 8.5%, and an intrinsic viscosity of 7.5 dL / g; the concentration of concentrated sulfuric acid is 99.9%; the poly(p-phenylene terephthalamide) resin and concentrated sulfuric acid are mixed and stirred at a mass ratio of 1:4.2, degassed and filtered to obtain the spinning solution, which is then extruded using two spinnerets with 1000 holes and a single hole diameter of 1.5D to form nascent fibers.

[0057] (2) Immerse the nascent fibers in a coagulation bath containing 5% isophorone diisocyanate (IPDI) and 6.5% sulfuric acid. The coagulation bath temperature is 10°C, and the immersion reaction is carried out for 1 minute.

[0058] (3) The modified filament bundles were combined in groups of 8, with a tension of 5N and a synchronous twist of 10T / m. The drying process was divided into three stages: the first stage was oven drying, with a drying temperature of 180℃, a tension of 5cN / dtex, a drying time of 3s, and a moisture content of 8%; the second stage was heated roller drying, with a drying temperature of 300℃, a tension of 5cN / dtex, and a drying time of 1s; and the third stage was infrared radiation drying, with a drying temperature of 180℃ and a drying time of 1.5s.

[0059] Example 4

[0060] A method for preparing acid-resistant, high-modulus para-aramid fiber, wherein the preparation method comprises:

[0061] (1) The poly(p-phenylene terephthalamide) resin has a water content of 120 ppm, a salt content of 8.2%, and an intrinsic viscosity of 7.2 dL / g; the concentration of concentrated sulfuric acid is 99.85%; the poly(p-phenylene terephthalamide) resin and concentrated sulfuric acid are mixed and stirred at a mass ratio of 1:4.05, degassed, filtered and the resulting spinning solution is extruded using two spinnerets with 1000 holes and a single hole diameter of 1.5D to form nascent fibers.

[0062] (2) Immerse the nascent fibers in a coagulation bath containing 3% diphenylmethane diisocyanate (MDI) and 5.5% sulfuric acid at a temperature of 6°C for 20 minutes.

[0063] (3) The modified filament bundles were combined in groups of 5, with a tension of 3N and a synchronous twist of 8T / m. The drying process was divided into three stages: the first stage was oven drying at 150℃, a tension of 4cN / dtex, and a drying time of 4s, with a moisture content of 7.5%; the second stage was heated roller drying at 270℃, a tension of 4cN / dtex, and a drying time of 2s; and the third stage was infrared radiation drying at 180℃ and a drying time of 1.3s.

[0064] Example 5

[0065] A method for preparing acid-resistant, high-modulus para-aramid fiber, wherein the preparation method comprises:

[0066] (1) The poly(p-phenylene terephthalamide) resin has a water content of 180 ppm, a salt content of 8.4%, and an intrinsic viscosity of 7.3 dL / g; the concentration of concentrated sulfuric acid is 100%; the poly(p-phenylene terephthalamide) resin and concentrated sulfuric acid are mixed and stirred at a mass ratio of 1:4.1, degassed, filtered and the resulting spinning solution is extruded using two spinnerets with 1000 holes and a single hole diameter of 1.5D to form nascent fibers.

[0067] (2) Immerse the nascent fibers in a coagulation bath containing 1% hexamethylene diisocyanate (HDI), 4% toluene diisocyanate (TDI) and 6% sulfuric acid. The coagulation bath temperature is 7°C, and the soaking reaction is carried out for 45 minutes.

[0068] (3) The modified filament bundles were combined in groups of 6, with a tension of 4N and a synchronous twist of 7T / m. The drying process was divided into three stages. The first stage was oven drying at a temperature of 130℃, a tension of 3.5cN / dtex, and a drying time of 6s, with a moisture content of 7.2%. The second stage was heated roller drying at a temperature of 240℃, a tension of 3.5cN / dtex, and a drying time of 2.5s. The third stage was infrared radiation drying at a temperature of 180℃ and a time of 1.1s.

[0069] Comparative Example 1

[0070] The difference between Comparative Example 1 and Example 1 is that hexamethyl diisocyanate was not added to the coagulation bath of Comparative Example 1, while the other conditions were the same as those of Example 1. The specific steps are as follows:

[0071] (1) The poly(p-phenylene terephthalamide) resin has a water content of 150 ppm, a salt content of 8.3%, and an intrinsic viscosity of 7.0 dL / g; the concentrated sulfuric acid concentration is 99.8%; the poly(p-phenylene terephthalamide) resin and concentrated sulfuric acid are mixed and stirred at a mass ratio of 1:4, degassed and filtered to obtain the spinning solution, and extruded using two spinnerets with 1000 holes and a single hole diameter of 1.5D to form nascent fibers.

[0072] (2) Immerse the nascent fibers in a coagulation bath containing 5% sulfuric acid at a temperature of 5°C for 30 minutes.

[0073] (3) The modified filament bundles were combined in groups of four, with a tension of 2N and a synchronous twist of 5T / m. The drying process was divided into three stages: the first stage was oven drying at 120℃, a tension of 3cN / dtex, and a drying time of 5s, with a moisture content of 7%; the second stage was heated roller drying at 250℃, a tension of 3cN / dtex, and a drying time of 2s; and the third stage was infrared radiation drying at 180℃ and a drying time of 1.2s.

[0074] Comparative Example 2

[0075] The difference between Comparative Example 2 and Example 1 is that no drying is performed in Comparative Example 2, while the other conditions are the same as in Example 1. The specific steps are as follows:

[0076] (1) The poly(p-phenylene terephthalamide) resin has a water content of 150 ppm, a salt content of 8.3%, and an intrinsic viscosity of 7.0 dL / g; the concentrated sulfuric acid concentration is 99.8%; the poly(p-phenylene terephthalamide) resin and concentrated sulfuric acid are mixed and stirred at a mass ratio of 1:4, degassed and filtered to obtain the spinning solution, and extruded using two spinnerets with 1000 holes and a single hole diameter of 1.5D to form nascent fibers.

[0077] (2) Immerse the nascent fibers in a coagulation bath containing 2% hexamethylene diisocyanate (HDI) and 5% sulfuric acid. The coagulation bath temperature is 5°C, and the soaking reaction is carried out for 30 minutes.

[0078] (3) The modified filament bundles are combined in groups of 4, with a tension of 2N and a synchronous twist of 5T / m.

[0079] Comparative Example 3

[0080] The difference between Comparative Example 2 and Example 1 is that only the first stage of drying was performed in Comparative Example 2, while the other conditions were the same as those in Example 1. The specific steps are as follows:

[0081] (1) The poly(p-phenylene terephthalamide) resin has a water content of 150 ppm, a salt content of 8.3%, and an intrinsic viscosity of 7.0 dL / g; the concentrated sulfuric acid concentration is 99.8%; the poly(p-phenylene terephthalamide) resin and concentrated sulfuric acid are mixed and stirred at a mass ratio of 1:4, degassed and filtered to obtain the spinning solution, and extruded using two spinnerets with 1000 holes and a single hole diameter of 1.5D to form nascent fibers.

[0082] (2) Immerse the nascent fibers in a coagulation bath containing 2% hexamethylene diisocyanate (HDI) and 5% sulfuric acid. The coagulation bath temperature is 5°C, and the soaking reaction is carried out for 30 minutes.

[0083] (3) The modified filament bundles were combined in groups of 4, with a tension of 2N and a synchronous twist of 5T / m. The drying process was carried out in an oven at a temperature of 120℃, a tension of 3cN / dtex, and a drying time of 5s, with a moisture content of 7%.

[0084] Comparative Example 4

[0085] The difference between Comparative Example 4 and Example 1 is that Comparative Example 4 involves two-stage drying, while other conditions are the same as in Example 1. The specific steps are as follows:

[0086] (1) The poly(p-phenylene terephthalamide) resin has a water content of 150 ppm, a salt content of 8.3%, and an intrinsic viscosity of 7.0 dL / g; the concentrated sulfuric acid concentration is 99.8%; the poly(p-phenylene terephthalamide) resin and concentrated sulfuric acid are mixed and stirred at a mass ratio of 1:4, degassed and filtered to obtain the spinning solution, and extruded using two spinnerets with 1000 holes and a single hole diameter of 1.5D to form nascent fibers.

[0087] (2) Immerse the nascent fibers in a coagulation bath containing 2% hexamethylene diisocyanate (HDI) and 5% sulfuric acid. The coagulation bath temperature is 5°C, and the soaking reaction is carried out for 30 minutes.

[0088] (3) The modified filament bundles were combined in groups of 4, with a tension of 2N and a synchronous twist of 5T / m. The drying was divided into two stages: the first stage was oven drying, with a drying temperature of 120℃, a tension of 3cN / dtex, a drying time of 5s, and a moisture content of 7%; the second stage was heated roller drying, with a drying temperature of 250℃, a tension of 3cN / dtex, and a drying time of 2s.

[0089] Comparative Example 5

[0090] The difference between Comparative Example 5 and Example 1 is that the mass concentration of hexamethylene diisocyanate (HDI) in the coagulation bath of Comparative Example 5 is 8% (higher than the concentration range defined in this invention), while other conditions are the same as those in Example 1. The specific steps are as follows:

[0091] (1) The poly(p-phenylene terephthalamide) resin has a water content of 150 ppm, a salt content of 8.3%, and an intrinsic viscosity of 7.0 dL / g; the concentrated sulfuric acid concentration is 99.8%; the poly(p-phenylene terephthalamide) resin and concentrated sulfuric acid are mixed and stirred at a mass ratio of 1:4, degassed and filtered to obtain the spinning solution, and extruded using two spinnerets with 1000 holes and a single hole diameter of 1.5D to form nascent fibers.

[0092] (2) Immerse the nascent fibers in a coagulation bath containing 8% hexamethylene diisocyanate (HDI) and 5% sulfuric acid. The coagulation bath temperature is 5°C, and the soaking reaction is carried out for 30 minutes.

[0093] (3) The modified filament bundles were combined in groups of four, with a tension of 2N and a synchronous twist of 5T / m. The drying process was divided into three stages: the first stage was oven drying at 120℃, a tension of 3cN / dtex, and a drying time of 5s, with a moisture content of 7%; the second stage was heated roller drying at 250℃, a tension of 3cN / dtex, and a drying time of 2s; and the third stage was infrared radiation drying at 180℃ and a drying time of 1.2s.

[0094] Comparative Example 6

[0095] The difference between Comparative Example 6 and Example 1 is that in Comparative Example 6, after the nascent fibers are solidified, they are then treated in a bath containing diisocyanate. The specific steps are as follows:

[0096] (1) The poly(p-phenylene terephthalamide) resin has a water content of 150 ppm, a salt content of 8.3%, and an intrinsic viscosity of 7.0 dL / g; the concentrated sulfuric acid concentration is 99.8%; the poly(p-phenylene terephthalamide) resin and concentrated sulfuric acid are mixed and stirred at a mass ratio of 1:4, degassed and filtered to obtain the spinning solution, and extruded using two spinnerets with 1000 holes and a single hole diameter of 1.5D to form nascent fibers.

[0097] (2) Immerse the nascent fiber in a coagulation bath containing 5% sulfuric acid at a temperature of 5°C for 30 minutes to obtain the coagulated fiber; then immerse the coagulated fiber in a coagulation bath containing 2% hexamethylene diisocyanate (HDI) and 5% sulfuric acid at a temperature of 5°C for 30 minutes to obtain the modified filament bundle.

[0098] (3) The modified filament bundles were combined in groups of four, with a tension of 2N and a synchronous twist of 5T / m. The drying process was divided into three stages: the first stage was oven drying at 120℃, a tension of 3cN / dtex, and a drying time of 5s, with a moisture content of 7%; the second stage was heated roller drying at 250℃, a tension of 3cN / dtex, and a drying time of 2s; and the third stage was infrared radiation drying at 180℃ and a drying time of 1.2s.

[0099] Comparative Example 7

[0100] The difference between Comparative Example 7 and Example 1 is that the temperature of the second-stage drying in Comparative Example 7 is increased (to 350°C), while other conditions are the same as in Example 1. The specific steps are as follows:

[0101] (1) The poly(p-phenylene terephthalamide) resin has a water content of 150 ppm, a salt content of 8.3%, and an intrinsic viscosity of 7.0 dL / g; the concentrated sulfuric acid concentration is 99.8%; the poly(p-phenylene terephthalamide) resin and concentrated sulfuric acid are mixed and stirred at a mass ratio of 1:4, degassed and filtered to obtain the spinning solution, and extruded using two spinnerets with 1000 holes and a single hole diameter of 1.5D to form nascent fibers.

[0102] (2) Immerse the nascent fibers in a coagulation bath containing 2% hexamethylene diisocyanate (HDI) and 5% sulfuric acid. The coagulation bath temperature is 5°C, and the soaking reaction is carried out for 30 minutes.

[0103] (3) The modified filament bundles were combined in groups of 4, with a tension of 2N and a synchronous twist of 5T / m. The drying process was divided into three stages: the first stage was oven drying at a temperature of 120℃, a tension of 3cN / dtex, and a drying time of 5s, with a moisture content of 7%; the second stage was heated roller drying at a temperature of 350℃, a tension of 3cN / dtex, and a drying time of 2s; and the third stage was infrared radiation drying at a temperature of 180℃ and a drying time of 1.2s.

[0104] Comparative Example 8

[0105] The difference between Comparative Example 8 and Example 1 is that the temperature of the third stage of drying in Comparative Example 8 is increased (200°C), while other conditions are the same as in Example 1. The specific steps are as follows:

[0106] (1) The poly(p-phenylene terephthalamide) resin has a water content of 150 ppm, a salt content of 8.3%, and an intrinsic viscosity of 7.0 dL / g; the concentrated sulfuric acid concentration is 99.8%; the poly(p-phenylene terephthalamide) resin and concentrated sulfuric acid are mixed and stirred at a mass ratio of 1:4, degassed and filtered to obtain the spinning solution, and extruded using two spinnerets with 1000 holes and a single hole diameter of 1.5D to form nascent fibers.

[0107] (2) Immerse the nascent fibers in a coagulation bath containing 2% hexamethylene diisocyanate (HDI) and 5% sulfuric acid. The coagulation bath temperature is 5°C, and the soaking reaction is carried out for 30 minutes.

[0108] (3) The modified filament bundles were combined in groups of four, with a tension of 2N and a synchronous twist of 5T / m. The drying process was divided into three stages: the first stage was oven drying at a temperature of 120℃, a tension of 3cN / dtex, and a drying time of 5s, with a moisture content of 7%; the second stage was heated roller drying at a temperature of 250℃, a tension of 3cN / dtex, and a drying time of 2s; and the third stage was infrared radiation drying at a temperature of 200℃ and a drying time of 1.2s.

[0109] Comparative Example 9

[0110] The difference between Comparative Example 9 and Example 1 is that the temperature condition for the third stage of drying in Comparative Example 9 is reduced (150°C), while other conditions are the same as in Example 1. The specific steps are as follows:

[0111] (1) The poly(p-phenylene terephthalamide) resin has a water content of 150 ppm, a salt content of 8.3%, and an intrinsic viscosity of 7.0 dL / g; the concentrated sulfuric acid concentration is 99.8%; the poly(p-phenylene terephthalamide) resin and concentrated sulfuric acid are mixed and stirred at a mass ratio of 1:4, degassed and filtered to obtain the spinning solution, and extruded using two spinnerets with 1000 holes and a single hole diameter of 1.5D to form nascent fibers.

[0112] (2) Immerse the nascent fibers in a coagulation bath containing 2% hexamethylene diisocyanate (HDI) and 5% sulfuric acid. The coagulation bath temperature is 5°C, and the soaking reaction is carried out for 30 minutes.

[0113] (3) The modified filament bundles were combined in groups of four, with a tension of 2N and a synchronous twist of 5T / m. The drying process was divided into three stages: the first stage was oven drying at a temperature of 120℃, a tension of 3cN / dtex, and a drying time of 5s, with a moisture content of 7%; the second stage was heated roller drying at a temperature of 250℃, a tension of 3cN / dtex, and a drying time of 2s; and the third stage was infrared radiation drying at a temperature of 150℃ and a drying time of 1.2s.

[0114] Comparative Example 10

[0115] The difference between Comparative Example 10 and Example 1 is that Comparative Example 10 uses a spinneret with 2000 holes and a single hole diameter of 1.5D, while other conditions are the same as in Example 1. The specific steps are as follows:

[0116] (1) The poly(p-phenylene terephthalamide) resin has a water content of 150 ppm, a salt content of 8.3%, and an intrinsic viscosity of 7.0 dL / g; the concentrated sulfuric acid concentration is 99.8%; the poly(p-phenylene terephthalamide) resin and concentrated sulfuric acid are mixed and stirred at a mass ratio of 1:4, degassed and filtered to obtain the spinning solution, and extruded using a spinneret with 2000 holes and a single hole diameter of 1.5D to form nascent fibers.

[0117] (2) Immerse the nascent fibers in a coagulation bath containing 2% hexamethylene diisocyanate (HDI) and 5% sulfuric acid. The coagulation bath temperature is 5°C, and the soaking reaction is carried out for 30 minutes.

[0118] (3) The modified filament bundles were combined in groups of four, with a tension of 2N and a synchronous twist of 5T / m. The drying process was divided into three stages: the first stage was oven drying at 120℃, a tension of 3cN / dtex, and a drying time of 5s, with a moisture content of 7%; the second stage was heated roller drying at 250℃, a tension of 3cN / dtex, and a drying time of 2s; and the third stage was infrared radiation drying at 180℃ and a drying time of 1.2s.

[0119] The performance of the para-aramid fibers prepared in the above embodiments and comparative examples was tested. The specific test results are shown in Table 1 below. The test methods involved are as follows:

[0120] Modulus and tensile strength performance testing: GB / T 42823-2023 "Standard for Para-aramid Filaments";

[0121] Acid resistance test: Para-aramid fibers were immersed in concentrated sulfuric acid with a mass concentration of 98%, and the tensile strength of the para-aramid fibers after immersion for 48 hours was measured and the strength retention rate was calculated.

[0122] Table 1. Performance test results of aramid fibers in the examples and comparative examples.

[0123]

[0124] As can be seen from the data in the table above, the para-aramid fibers prepared by the method described in this invention in Examples 1-5 exhibit better performance stability under strong acid conditions, with effectively improved acid resistance and a strength retention rate of no less than 90 cN / dtex, meeting the requirements for the acid resistance of para-aramid. This invention utilizes diisocyanate to improve the acid resistance of the fiber. After diisocyanate treatment, the amino or hydroxyl groups in the aramid molecular chain form a three-dimensional cross-linked structure with the diisocyanate, improving the strength retention rate of the para-aramid fiber and thus enhancing its acid resistance. After fiber forming, the fiber undergoes a merging treatment and a three-stage drying process, improving the fiber uniformity and modulus, ultimately obtaining high-modulus para-aramid fibers with excellent acid resistance.

[0125] A comparison of the experimental results of Comparative Example 1 and Example 1 shows that the addition of diisocyanate to the coagulation bath in the preparation method of the present invention can enable the amino or hydroxyl groups in the aramid molecular chain to form a three-dimensional cross-linked structure with the diisocyanate, thereby improving the strength retention rate of para-aramid fibers and enhancing the acid resistance of para-aramid fibers.

[0126] A comparison of the experimental results of Comparative Examples 2-4 and Example 1 shows that the three-stage drying technology in the preparation method of the present invention helps to improve the modulus of para-aramid fibers and also makes the para-aramid fibers have better acid resistance.

[0127] A comparison of the experimental results of Comparative Example 5 and Example 1 shows that if the diisocyanate concentration in the coagulation bath is too high, it will lead to the formation of a large number of pores and defects inside the fiber. This is because an excessively high diisocyanate concentration will change the solvent-nonsolvent balance of the coagulation bath, causing the coagulation rate on the fiber surface to be too fast, forming a dense skin layer that hinders the diffusion of the internal solvent outward, thereby forming a large number of pores and defects inside the fiber.

[0128] A comparison of the experimental results from Comparative Example 6 and Example 1 shows that if the nascent fibers are first coagulated in a conventional coagulation bath and then subjected to a coagulation bath containing diisocyanate, the improvement in acid resistance is relatively limited. This is because the sequence of "first coagulation in a conventional coagulation bath, then treatment in a coagulation bath containing diisocyanate" results in the nascent fibers forming a dense and stable core-sheath structure in the first coagulation bath. This dense structure acts as a barrier, severely hindering the diffusion and penetration of the diisocyanate solution into the fiber interior, making it difficult to fully react with the amide groups. Therefore, the cross-linking reaction can only occur on the surface or near the surface of the fiber, and cannot occur uniformly across the entire fiber cross-section, thus limiting the overall improvement in acid resistance.

[0129] A comparison of the experimental results of Comparative Example 7 and Example 1 shows that if the temperature conditions of the second-stage drying are increased, it will lead to an increase in the residual solvent in the fiber core, surface hardening and the generation of microcracks. This is because the second-stage drying is in the stage where "the surface has basically formed a film and the outward diffusion of the core solvent is controlled". If the temperature is too high, the skin layer will become too dense, which will hinder the further escape of the remaining solvent, form internal stress cracks, and make it easy for acid to penetrate along the cracks, thus reducing the acid resistance of the fiber.

[0130] A comparison of the experimental results of Comparative Example 8 and Example 1 shows that if the temperature conditions of the third-stage drying are increased, it will lead to thermal oxidation of the fibers, abnormal increase in crystallinity, and embrittlement of the cross-linked layer. Since the third stage is the "low solvent content, structural fixation" stage, it will lead to surface cracking, loss of the "flexibility-density" synergistic effect, excessive growth of crystal regions, resulting in a fragile interface between microfibers, preferential fracture during acid etching, significantly reduced strength retention rate, and deterioration of acid resistance.

[0131] The comparison of the experimental results of Comparative Example 9 and Example 1 shows that if the temperature conditions of the third-stage drying are reduced, the residual solvent content will be higher and the glass transition temperature of the fiber will decrease. This is because the insufficient temperature of the third stage cannot completely remove the trace solvent. The residual solvent plays a plasticizing role, making the fiber prone to creep and accelerating acid-catalyzed hydrolysis during subsequent heat treatment and use. The acid resistance and durability will be worse, and the fiber modulus will also decrease.

[0132] A comparison of the experimental results of Comparative Example 10 and Example 1 shows that if a single 2000-hole spinneret is used for spinning, the uniformity of the transverse and longitudinal structure of the nascent fibers will be poor, and the fiber strength retention rate will decrease. This is because two 1000-hole spinnerets with a single hole diameter of 1.5D reduce the flow field pressure drop, thin the heat transfer boundary layer, homogenize the tensile stress field, and dilute the probability of defects, resulting in better uniformity of the transverse and longitudinal structure of the nascent fibers. Consequently, the fibers exhibit a higher strength retention rate and a longer service life in the subsequent acid etching environment.

[0133] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are exhaustively listed. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0134] For those skilled in the art, various modifications and improvements can be made without departing from the concept of the present invention, and these modifications and improvements are all within the scope of protection of the present invention. The scope of protection of the present invention is defined by the appended claims.

Claims

1. A method for preparing acid-resistant, high-modulus para-aramid fiber, characterized in that, The preparation method is as follows: S1. The spinning solution of para-aramid is extruded through a spinneret to form nascent fibers. S2. Immerse the nascent fibers in a coagulation bath containing diisocyanate to obtain the modified fiber bundle. S3. The modified filament bundles are tensioned and twisted simultaneously, and then subjected to multi-stage drying treatment to obtain acid-resistant high-modulus para-aramid fibers. The coagulation bath comprises diisocyanate, sulfuric acid, and water, wherein the mass concentration of diisocyanate in the coagulation bath is 0.1%-5%, and the mass concentration of sulfuric acid in the coagulation bath is 4.5%-6.5%. The temperature of the coagulation bath is 5-10℃, and the nascent fibers are immersed in the coagulation bath for 1-60 minutes. In step S3, a three-stage drying process is adopted, wherein the three-stage drying processes are as follows: The first stage of drying is oven drying, with a drying temperature of 80-180℃, a tension of 1cN / dtex-5cN / dtex, and a drying time of 3-7s. The moisture content of the first-stage dried filament bundle is 6%-8%. The second stage of drying involves heated rollers, with a drying temperature of 200-300℃, a tension of 2cN / dtex-5cN / dtex, and a drying time of 1-3 seconds. The third stage of drying is infrared radiation drying, with a drying temperature of 160-180℃ and a drying time of 1-1.5s.

2. The method for preparing acid-resistant high-modulus para-aramid fiber according to claim 1, characterized in that, The spinning solution comprises poly(p-phenylene terephthalamide) resin and concentrated sulfuric acid, the concentration of which is 99.8%-100.2%, and the mass ratio of which is 1:(3.9-4.2).

3. The method for preparing acid-resistant high-modulus para-aramid fiber according to claim 2, characterized in that, The poly(p-phenylene terephthalamide) resin has a water content of less than 200 ppm, a salt content of 8.0%-8.6%, and an intrinsic viscosity of 6.5 dL / g to 7.5 dL / g.

4. The method for preparing acid-resistant high-modulus para-aramid fiber according to claim 1, characterized in that, The spinneret specifications are 1-4 spinnerets with 500-2000 holes, and the diameter of each hole is 0.5-2D.

5. The method for preparing acid-resistant high-modulus para-aramid fiber according to claim 1, characterized in that, The diisocyanate is selected from at least one of hexamethylene diisocyanate, toluene diisocyanate, isophorone diisocyanate, and diphenylmethane diisocyanate.

6. The method for preparing acid-resistant high-modulus para-aramid fiber according to claim 1, characterized in that, In step S3, the modified filament bundles are combined in groups of 2-8, with a tension of 0.1-5 N and a synchronous twisting condition of 0.5-10 T / m.

7. An acid-resistant, high-modulus para-aramid fiber, characterized in that, The acid-resistant, high-modulus para-aramid fiber is prepared according to the preparation method described in any one of claims 1-6.

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