Acid-resistant high-modulus para-aramid fiber and preparation method thereof

Abstract

The invention relates to the technical field of chemical fiber production, in particular to an acid-resistant high-modulus para-aramid fiber and a preparation method thereof.The preparation method comprises the steps that S1, a spinning solution of para-aramid is extruded through a spinneret plate to form nascent fibers; s2, immersing the nascent fiber into a coagulating bath containing diisocyanate for soaking reaction to obtain a modified tow; s3, the modified tows are subjected to tension merging and synchronous twisting, then multi-stage drying treatment is conducted, and the acid-resistant high-modulus para-aramid fibers are obtained. The high-model para-aramid fiber prepared by the method shows higher stability and longer service life in a strong acid environment, and is suitable for application fields requiring higher acid resistance, such as protective materials, corrosion-resistant coatings, high-performance composite materials and the like. The preparation method provided by the invention provides an innovative and effective improved technology for production of the para-aramid fiber, and has relatively high industrial application value.

Description

Technical Field

[0001] The invention relates to an acid-resistant high-modulus para-aramid fiber and a preparation method thereof, belonging to the technical field of chemical fiber production. Background Art

[0002] Para-aramid fiber, also known as poly(p-phenylenediamine terephthalamide) or aramid 1414, is a high-performance synthetic fiber. Due to its excellent mechanical properties, thermal stability, and chemical resistance, it is widely used in aerospace, military, automotive, and construction industries. Para-aramid fiber is prepared by polycondensing para-aramid monomers (such as p-phenylenediamine and terephthalic acid dichloride) to produce a polyamide solution, which is then processed into fibers through wet or dry spinning. The coagulation bath in this process typically contains a solvent and acid to promote fiber coagulation and orientation.

[0003] Traditional para-aramid fibers still face a high risk of dissolution in extremely acidic environments, especially in strong acid solutions like concentrated sulfuric acid. This is primarily because para-aramid's molecular structure contains multiple functional groups, such as amino and hydroxyl groups. These groups are prone to reaction in strong acid environments, causing molecular chain breakage or dissolution, thus affecting the fiber's performance and stability. The lack of adequate protection in the coagulation bath limits the application of prepared para-aramid fibers in these harsh environments.

[0004] However, para-aramid fiber is often used as raw material for pipes, cables, corrosion-resistant coatings, protective clothing, etc. used in some special environments with strong acid. However, the acid resistance of para-aramid fiber is poor, which greatly limits the application of para-aramid fiber. 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] In view of the deficiencies in the prior art, the present invention provides an acid-resistant high-modulus para-aramid fiber and a preparation method thereof. The para-aramid fiber has higher modulus and acid resistance and a simple preparation process.

[0006] The technical solution of the present invention to solve the above technical problems is as follows: a method for preparing acid-resistant high-modulus para-aramid fiber, the preparation method comprising: S1, extruding the spinning solution of para-aramid through a spinneret to form nascent fibers; S2, immersing the as-spun fibers in a coagulation bath containing diisocyanate for a reaction to obtain a modified tow; S3. The modified filament bundles are tensioned and twisted synchronously, and then subjected to multi-stage drying treatment to obtain acid-resistant high modulus para-aramid fibers.

[0007] Furthermore, the spinning solution includes poly(p-phenylene terephthalamide) resin and concentrated sulfuric acid, the concentration of the concentrated sulfuric acid is 99.8%-100.2%, and the mass ratio of the poly(p-phenylene terephthalamide) resin to the concentrated sulfuric acid is 1:(3.9-4.2).

[0008] 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-7.5 dL / g.

[0009] Furthermore, the spinneret specifications are 1-4 500-2000 hole spinnerets, and the diameter of each single hole is 0.5-2D.

[0010] Furthermore, the coagulation bath comprises diisocyanate, sulfuric acid and water, the mass concentration of the diisocyanate in the coagulation bath is 0.1%-5%, and the mass concentration of the sulfuric acid in the coagulation bath is 4.5%-6.5%.

[0011] Furthermore, the temperature of the coagulation bath is 5-10° C., and the soaking reaction time of the as-spun fibers in the coagulation bath is 1-60 minutes.

[0012] Furthermore, the diisocyanate is selected from at least one of hexamethylene diisocyanate, toluene diisocyanate, isophorone diisocyanate, and diphenylmethane diisocyanate.

[0013] Furthermore, in step S3, the modified tows are combined in groups of 2 to 8, with a tension of 0.1 to 5 N and a synchronous twisting condition of 0.5 to 10 T / m.

[0014] Furthermore, in step S3, a three-stage drying process is adopted, wherein the three-stage drying process is: The first stage of drying is oven drying, with a drying temperature of 80-180°C, a tension of 1 cN / dtex-5 cN / dtex, and a drying time of 3-7 seconds. The moisture content of the first stage dried tow is 6%-8%; The second stage of drying is a heated roller with a drying temperature of 200-300°C, a tension of 2cN / dtex-5cN / dtex, and a drying time of 1-3s; The third stage of drying is infrared radiation drying, with a drying temperature of 160-180°C and a drying time of 1-1.5s.

[0015] The invention also discloses an acid-resistant high-modulus para-aramid fiber. The acid-resistant high-modulus para-aramid fiber is prepared according to the preparation method of the invention.

[0016] The beneficial effects of the present invention are: The preparation method described herein produces an acid-resistant high-model para-aramid fiber through spinneret optimization, diisocyanate modification, and triple drying. The high-model para-aramid fiber produced using this method exhibits enhanced stability and a 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 method provides an innovative and effective improvement in the production of para-aramid fiber. Furthermore, the preparation process is simple to operate and has high industrial application value.

[0017] More specifically, in the preparation method described in the present invention, the spinneret configuration is optimized, the spinning solution is spun to form primary 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, thereby improving the acid resistance of the fiber; after the fiber is formed, the fiber is combined and treated, and a three-time drying technology is used to improve the uniformity and modulus of the fiber, and finally an acid-resistant high-model para-aramid fiber is obtained. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 The present invention provides a process flow chart for preparing the acid-resistant high-modulus para-aramid fiber. DETAILED DESCRIPTION

[0019] The present invention can be implemented in many other ways than those described herein, and those skilled in the art can make similar improvements without violating the scope of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed.

[0020] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which the present invention belongs. The terms used are only for describing specific embodiments and are not intended to limit the present invention.

[0021] like Figure 1 As shown, a method for preparing acid-resistant high modulus para-aramid fiber, the preparation method is: S1. Under sealed conditions, poly(p-phenylene terephthalamide) resin and concentrated sulfuric acid are mixed and stirred, degassed and filtered to obtain a spinning solution, and the spinning solution of para-aramid is extruded through a spinneret to form spun fibers; S2, immersing the as-spun fibers in a coagulation bath containing diisocyanate for a reaction to obtain a modified tow; S3. The modified filament bundles are tensioned and twisted synchronously, and then subjected to multi-stage drying treatment to obtain acid-resistant high modulus para-aramid fibers.

[0022] Specifically, the spinning solution includes poly(p-phenylene terephthalamide) resin and concentrated sulfuric acid, the concentration of the concentrated sulfuric acid 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).

[0023] 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-7.5 dL / g (at 25° C., the solvent is concentrated sulfuric acid).

[0024] Specifically, the spinneret specifications are 1-4 spinnerets with 500-2000 holes, and the diameter of each hole is 0.5-2D.

[0025] Specifically, the coagulation bath includes diisocyanate, sulfuric acid and water. The mass concentration of the diisocyanate in the coagulation bath is 0.1%-5%, and the mass concentration of the sulfuric acid in the coagulation bath is 4.5%-6.5%.

[0026] Specifically, the temperature of the coagulation bath is 5-10° C., and the spun fibers are immersed in the coagulation bath for a reaction time of 1-60 minutes.

[0027] Specifically, the diisocyanate is at least one selected from hexamethylene diisocyanate (HDI), toluene diisocyanate (TDI), isophorone diisocyanate (IPDI), and diphenylmethane diisocyanate (MDI).

[0028] Specifically, in step S3, the modified tows are combined in groups of 2 to 8, with a tension of 0.1 to 5 N and a synchronous twisting condition of 0.5 to 10 T / m.

[0029] Specifically, in step S3, a three-stage drying process is adopted, and the three-stage drying process is respectively: The first stage of drying is oven drying, with a drying temperature of 80-180°C, a tension of 1 cN / dtex-5 cN / dtex, and a drying time of 3-7 seconds. The moisture content of the first stage dried tow is 6%-8%; The second stage of drying is a heated roller with a drying temperature of 200-300°C, a tension of 2cN / dtex-5cN / dtex, and a drying time of 1-3s; The third stage of drying is infrared radiation drying, with a drying temperature of 160-180°C and a drying time of 1-1.5s.

[0030] Disclosed is an acid-resistant high-modulus para-aramid fiber, which is prepared according to the preparation method of the present invention.

[0031] Example 1 A method for preparing acid-resistant high-modulus para-aramid fiber, the preparation method comprising: (1) The water content of poly(p-phenylene terephthalamide) resin is 150 ppm, the salt content is 8.3%, and the intrinsic viscosity is 7.0 dL / g; the concentration of concentrated sulfuric acid is 99.8%; the mass ratio of poly(p-phenylene terephthalamide) resin and concentrated sulfuric acid is 1:4, and the spinning solution is obtained after degassing and filtration. The spun fibers are formed by extrusion using two spinnerets with 1000 holes and a single hole diameter of 1.5D.

[0032] (2) Immerse the as-spun fibers in a coagulation bath containing an aqueous solution of 2% hexamethylene diisocyanate (HDI) and 5% sulfuric acid at a temperature of 5°C for 30 minutes.

[0033] (3) The modified tows were combined in groups of four with a tension of 2 N and a synchronous twist of 5 T / m. Drying was divided into three stages: the first stage was oven drying at a drying temperature of 120°C, a tension of 3 cN / dtex, a drying time of 5 s, and a moisture content of 7%; the second stage was heating roller drying at a drying temperature of 250°C, a tension of 3 cN / dtex, and a drying time of 2 s; and the third stage was infrared radiation drying at a drying temperature of 180°C and a drying time of 1.2 s.

[0034] Example 2 A method for preparing acid-resistant high-modulus para-aramid fiber, the preparation method comprising: (1) The water content of poly(p-phenylene terephthalamide) resin is 100 ppm, the salt content is 8.0%, and the intrinsic viscosity is 6.5 dL / g; the concentration of concentrated sulfuric acid 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, and the spinning solution is obtained after degassing and filtration. The spinning solution is extruded using two spinnerets with 1000 holes and a single hole diameter of 1.5D to form primary fibers.

[0035] (2) Immerse the as-spun fibers in a coagulation bath containing 0.5% toluene diisocyanate (TDI) and 4.5% sulfuric acid solution at a coagulation bath temperature of 8°C for 60 minutes.

[0036] (3) The modified tows were combined in groups of two with a tension of 0.1 N and a synchronous twist of 0.5 T / m. Drying was divided into three stages: the first stage was oven drying at 80°C, a tension of 1 cN / dtex, a drying time of 7 s, and a moisture content of 6%; the second stage was heating roller drying at 200°C, a tension of 2 cN / dtex, and a drying time of 3 s; and the third stage was infrared radiation drying at 180°C and a drying time of 1 s.

[0037] Example 3 A method for preparing acid-resistant high-modulus para-aramid fiber, the preparation method comprising: (1) The water content of poly(p-phenylene terephthalamide) resin is 80 ppm, the salt content is 8.5%, and the intrinsic viscosity is 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 in a mass ratio of 1:4.2, and the spinning solution is obtained after degassing and filtration. The spinning solution is extruded through two spinnerets with 1000 holes and a single hole diameter of 1.5D to form primary fibers.

[0038] (2) Immerse the as-spun fiber in a coagulation bath containing 5% isophorone diisocyanate (IPDI) and 6.5% sulfuric acid in an aqueous solution at a coagulation bath temperature of 10°C for 1 minute.

[0039] (3) The modified tows 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 at a drying temperature of 180°C, a tension of 5cN / dtex, a drying time of 3s, and a moisture content of 8%; the second stage was heating roller drying at a drying temperature of 300°C, a tension of 5cN / dtex, and a drying time of 1s; and the third stage was infrared radiation drying at a drying temperature of 180°C and a drying time of 1.5s.

[0040] Example 4 A method for preparing acid-resistant high-modulus para-aramid fiber, the preparation method comprising: (1) The water content of poly(p-phenylene terephthalamide) resin is 120 ppm, the salt content is 8.2%, and the intrinsic viscosity is 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, and the spinning solution is obtained after degassing and filtration. The spinning solution is extruded through two spinnerets with 1000 holes and a single hole diameter of 1.5D to form primary fibers.

[0041] (2) Immerse the as-spun fiber in a coagulation bath containing 3% diphenylmethane diisocyanate (MDI) and 5.5% sulfuric acid in an aqueous solution at a coagulation bath temperature of 6°C for 20 minutes.

[0042] (3) The modified tows 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 a drying temperature of 150°C, a tension of 4cN / dtex, a drying time of 4s, and a moisture content of 7.5%; the second stage was heating roller drying at a drying temperature of 270°C, a tension of 4cN / dtex, and a drying time of 2s; and the third stage was infrared radiation drying at a drying temperature of 180°C and a drying time of 1.3s.

[0043] Example 5 A method for preparing acid-resistant high-modulus para-aramid fiber, the preparation method comprising: (1) The water content of poly(p-phenylene terephthalamide) resin is 180 ppm, the salt content is 8.4%, and the intrinsic viscosity is 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 in a mass ratio of 1:4.1, and the spinning solution is obtained after degassing and filtration. The spinning solution is extruded using two spinnerets with 1000 holes and a single hole diameter of 1.5D to form primary fibers.

[0044] (2) Immerse the as-spun fibers in a coagulation bath containing an aqueous solution of 1% hexamethylene diisocyanate (HDI), 4% toluene diisocyanate (TDI), and 6% sulfuric acid at a coagulation bath temperature of 7°C for 45 minutes.

[0045] (3) The modified tows 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 drying temperature of 130°C, a tension of 3.5 cN / dtex, a drying time of 6 seconds, and a moisture content of 7.2%; the second stage was heating roller drying at a drying temperature of 240°C, a tension of 3.5 cN / dtex, and a drying time of 2.5 seconds; and the third stage was infrared radiation drying at a temperature of 180°C and a drying time of 1.1 seconds.

[0046] Comparative Example 1 The difference between Comparative Example 1 and Example 1 is that hexamethyl diisocyanate is not added to the coagulation bath of Comparative Example 1. Other conditions are the same as those of Example 1. The specific steps are as follows: (1) The water content of poly(p-phenylene terephthalamide) resin is 150 ppm, the salt content is 8.3%, and the intrinsic viscosity is 7.0 dL / g; the concentration of concentrated sulfuric acid is 99.8%; the mass ratio of poly(p-phenylene terephthalamide) resin and concentrated sulfuric acid is 1:4, and the spinning solution is obtained after degassing and filtration. The spun fibers are formed by extrusion using two spinnerets with 1000 holes and a single hole diameter of 1.5D.

[0047] (2) Immerse the as-spun fiber in a coagulation bath containing 5% sulfuric acid in an aqueous solution at a temperature of 5°C for 30 minutes.

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

[0049] Comparative Example 2 The difference between Comparative Example 2 and Example 1 is that no drying is performed in Comparative Example 2, and other conditions are the same as those in Example 1. The specific steps are as follows: (1) The water content of poly(p-phenylene terephthalamide) resin is 150 ppm, the salt content is 8.3%, and the intrinsic viscosity is 7.0 dL / g; the concentration of concentrated sulfuric acid is 99.8%; the mass ratio of poly(p-phenylene terephthalamide) resin and concentrated sulfuric acid is 1:4, and the spinning solution is obtained after degassing and filtration. The spun fibers are formed by extrusion using two spinnerets with 1000 holes and a single hole diameter of 1.5D.

[0050] (2) Immerse the as-spun fibers in a coagulation bath containing an aqueous solution of 2% hexamethylene diisocyanate (HDI) and 5% sulfuric acid at a temperature of 5°C for 30 minutes.

[0051] (3) The modified tows were combined in groups of 4 with a tension of 2 N and a synchronous twist of 5 T / m.

[0052] Comparative Example 3 The difference between Comparative Example 2 and Example 1 is that only the first stage drying is performed in Comparative Example 2, and other conditions are the same as those in Example 1. The specific steps are as follows: (1) The water content of poly(p-phenylene terephthalamide) resin is 150 ppm, the salt content is 8.3%, and the intrinsic viscosity is 7.0 dL / g; the concentration of concentrated sulfuric acid is 99.8%; the mass ratio of poly(p-phenylene terephthalamide) resin and concentrated sulfuric acid is 1:4, and the spinning solution is obtained after degassing and filtration. The spun fibers are formed by extrusion using two spinnerets with 1000 holes and a single hole diameter of 1.5D.

[0053] (2) Immerse the as-spun fibers in a coagulation bath containing an aqueous solution of 2% hexamethylene diisocyanate (HDI) and 5% sulfuric acid at a temperature of 5°C for 30 minutes.

[0054] (3) The modified tows were combined in groups of four with a tension of 2 N and a synchronous twist of 5 T / m. The drying process was oven drying at a temperature of 120°C, a tension of 3 cN / dtex, a drying time of 5 s, and a moisture content of 7%.

[0055] Comparative Example 4 The difference between Comparative Example 4 and Example 1 is that two-stage drying is performed in Comparative Example 4, and other conditions are the same as those in Example 1. The specific steps are as follows: (1) The water content of poly(p-phenylene terephthalamide) resin is 150 ppm, the salt content is 8.3%, and the intrinsic viscosity is 7.0 dL / g; the concentration of concentrated sulfuric acid is 99.8%; the mass ratio of poly(p-phenylene terephthalamide) resin and concentrated sulfuric acid is 1:4, and the spinning solution is obtained after degassing and filtration. The spun fibers are formed by extrusion using two spinnerets with 1000 holes and a single hole diameter of 1.5D.

[0056] (2) Immerse the as-spun fibers in a coagulation bath containing an aqueous solution of 2% hexamethylene diisocyanate (HDI) and 5% sulfuric acid at a temperature of 5°C for 30 minutes.

[0057] (3) The modified tows were combined in groups of four with a tension of 2 N and a synchronous twist of 5 T / m. Drying was performed in two stages: the first stage was oven drying at a drying temperature of 120°C, a tension of 3 cN / dtex, a drying time of 5 s, and a moisture content of 7%; the second stage was heated roller drying at a drying temperature of 250°C, a tension of 3 cN / dtex, and a drying time of 2 s.

[0058] Comparative Example 5 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 specified in the present invention), and the other conditions are the same as those in Example 1. The specific steps are as follows: (1) The water content of poly(p-phenylene terephthalamide) resin is 150 ppm, the salt content is 8.3%, and the intrinsic viscosity is 7.0 dL / g; the concentration of concentrated sulfuric acid is 99.8%; the mass ratio of poly(p-phenylene terephthalamide) resin and concentrated sulfuric acid is 1:4, and the spinning solution is obtained after degassing and filtration. The spun fibers are formed by extrusion using two spinnerets with 1000 holes and a single hole diameter of 1.5D.

[0059] (2) Immerse the as-spun fibers in a coagulation bath containing an aqueous solution of 8% hexamethylene diisocyanate (HDI) and 5% sulfuric acid at a coagulation bath temperature of 5°C for 30 minutes.

[0060] (3) The modified tows were combined in groups of four with a tension of 2 N and a synchronous twist of 5 T / m. Drying was divided into three stages: the first stage was oven drying at a drying temperature of 120°C, a tension of 3 cN / dtex, a drying time of 5 s, and a moisture content of 7%; the second stage was heating roller drying at a drying temperature of 250°C, a tension of 3 cN / dtex, and a drying time of 2 s; and the third stage was infrared radiation drying at a drying temperature of 180°C and a drying time of 1.2 s.

[0061] Comparative Example 6 The difference between Comparative Example 6 and Example 1 is that in Comparative Example 6, after the primary fibers are coagulated and formed, they are then placed in a bath containing diisocyanate for treatment. The specific steps are as follows: (1) The water content of poly(p-phenylene terephthalamide) resin is 150 ppm, the salt content is 8.3%, and the intrinsic viscosity is 7.0 dL / g; the concentration of concentrated sulfuric acid is 99.8%; the mass ratio of poly(p-phenylene terephthalamide) resin and concentrated sulfuric acid is 1:4, and the spinning solution is obtained after degassing and filtration. The spun fibers are formed by extrusion using two spinnerets with 1000 holes and a single hole diameter of 1.5D.

[0062] (2) The spun fibers were immersed in a coagulation bath containing 5% sulfuric acid at a temperature of 5°C for 30 minutes to obtain coagulated fibers; the coagulated fibers were then immersed in a coagulation bath containing 2% hexamethylene diisocyanate (HDI) and 5% sulfuric acid at a temperature of 5°C for 30 minutes to obtain modified filaments.

[0063] (3) The modified tows were combined in groups of four with a tension of 2 N and a synchronous twist of 5 T / m. Drying was divided into three stages: the first stage was oven drying at a drying temperature of 120°C, a tension of 3 cN / dtex, a drying time of 5 s, and a moisture content of 7%; the second stage was heating roller drying at a drying temperature of 250°C, a tension of 3 cN / dtex, and a drying time of 2 s; and the third stage was infrared radiation drying at a drying temperature of 180°C and a drying time of 1.2 s.

[0064] Comparative Example 7 The difference between Comparative Example 7 and Example 1 is that the temperature of the second stage drying is increased (350°C) in Comparative Example 7, and the other conditions are the same as those in Example 1. The specific steps are as follows: (1) The water content of poly(p-phenylene terephthalamide) resin is 150 ppm, the salt content is 8.3%, and the intrinsic viscosity is 7.0 dL / g; the concentration of concentrated sulfuric acid is 99.8%; the mass ratio of poly(p-phenylene terephthalamide) resin and concentrated sulfuric acid is 1:4, and the spinning solution is obtained after degassing and filtration. The spun fibers are formed by extrusion using two spinnerets with 1000 holes and a single hole diameter of 1.5D.

[0065] (2) Immerse the as-spun fibers in a coagulation bath containing an aqueous solution of 2% hexamethylene diisocyanate (HDI) and 5% sulfuric acid at a temperature of 5°C for 30 minutes.

[0066] (3) The modified tows were combined in groups of four with a tension of 2 N and a synchronous twist of 5 T / m. Drying was divided into three stages: the first stage was oven drying at a drying temperature of 120°C, a tension of 3 cN / dtex, a drying time of 5 s, and a moisture content of 7%; the second stage was heating roller drying at a drying temperature of 350°C, a tension of 3 cN / dtex, and a drying time of 2 s; and the third stage was infrared radiation drying at a drying temperature of 180°C and a drying time of 1.2 s.

[0067] Comparative Example 8 The difference between Comparative Example 8 and Example 1 is that the temperature of the third stage drying is increased (200° C.) in Comparative Example 8, and the other conditions are the same as those in Example 1. The specific steps are as follows: (1) The water content of poly(p-phenylene terephthalamide) resin is 150 ppm, the salt content is 8.3%, and the intrinsic viscosity is 7.0 dL / g; the concentration of concentrated sulfuric acid is 99.8%; the mass ratio of poly(p-phenylene terephthalamide) resin and concentrated sulfuric acid is 1:4, and the spinning solution is obtained after degassing and filtration. The spun fibers are formed by extrusion using two spinnerets with 1000 holes and a single hole diameter of 1.5D.

[0068] (2) Immerse the as-spun fibers in a coagulation bath containing an aqueous solution of 2% hexamethylene diisocyanate (HDI) and 5% sulfuric acid at a temperature of 5°C for 30 minutes.

[0069] (3) The modified tows were combined in groups of four with a tension of 2 N and a synchronous twist of 5 T / m. Drying was divided into three stages: the first stage was oven drying at a drying temperature of 120°C, a tension of 3 cN / dtex, a drying time of 5 s, and a moisture content of 7%; the second stage was heating roller drying at a drying temperature of 250°C, a tension of 3 cN / dtex, and a drying time of 2 s; and the third stage was infrared radiation drying at a drying temperature of 200°C and a drying time of 1.2 s.

[0070] Comparative Example 9 The difference between Comparative Example 9 and Example 1 is that the temperature condition of the third stage drying is lowered (150° C.) in Comparative Example 9, and the other conditions are the same as those in Example 1. The specific steps are as follows: (1) The water content of poly(p-phenylene terephthalamide) resin is 150 ppm, the salt content is 8.3%, and the intrinsic viscosity is 7.0 dL / g; the concentration of concentrated sulfuric acid is 99.8%; the mass ratio of poly(p-phenylene terephthalamide) resin and concentrated sulfuric acid is 1:4, and the spinning solution is obtained after degassing and filtration. The spun fibers are formed by extrusion using two spinnerets with 1000 holes and a single hole diameter of 1.5D.

[0071] (2) Immerse the as-spun fibers in a coagulation bath containing an aqueous solution of 2% hexamethylene diisocyanate (HDI) and 5% sulfuric acid at a temperature of 5°C for 30 minutes.

[0072] (3) The modified tows were combined in groups of four with a tension of 2 N and a synchronous twist of 5 T / m. Drying was divided into three stages: the first stage was oven drying at a drying temperature of 120°C, a tension of 3 cN / dtex, a drying time of 5 s, and a moisture content of 7%; the second stage was heating roller drying at a drying temperature of 250°C, a tension of 3 cN / dtex, and a drying time of 2 s; and the third stage was infrared radiation drying at a drying temperature of 150°C and a drying time of 1.2 s.

[0073] Comparative Example 10 The difference between Comparative Example 10 and Example 1 is that a spinneret with 2000 holes and a single hole diameter of 1.5D is used in Comparative Example 10, and other conditions are the same as those in Example 1. The specific steps are as follows: (1) The water content of poly(p-phenylene terephthalamide) resin is 150 ppm, the salt content is 8.3%, and the intrinsic viscosity is 7.0 dL / g; the concentration of concentrated sulfuric acid is 99.8%; the mass ratio of poly(p-phenylene terephthalamide) resin and concentrated sulfuric acid is 1:4, and the spinning solution is obtained after degassing and filtration. The spinning solution is extruded through a spinneret with 2000 holes and a single hole diameter of 1.5D to form a primary fiber.

[0074] (2) Immerse the as-spun fibers in a coagulation bath containing an aqueous solution of 2% hexamethylene diisocyanate (HDI) and 5% sulfuric acid at a temperature of 5°C for 30 minutes.

[0075] (3) The modified tows were combined in groups of four with a tension of 2 N and a synchronous twist of 5 T / m. Drying was divided into three stages: the first stage was oven drying at a drying temperature of 120°C, a tension of 3 cN / dtex, a drying time of 5 s, and a moisture content of 7%; the second stage was heating roller drying at a drying temperature of 250°C, a tension of 3 cN / dtex, and a drying time of 2 s; and the third stage was infrared radiation drying at a drying temperature of 180°C and a drying time of 1.2 s.

[0076] The performance of the para-aramid fibers prepared in the above examples and comparative examples was tested. The specific test results are shown in Table 1 below. The test methods involved are as follows: Modulus and tensile strength performance test: GB / T 42823-2023 "Para-aramid filament standard"; Acid resistance test: The para-aramid fiber was immersed in concentrated sulfuric acid with a mass concentration of 98%. The tensile strength of the para-aramid fiber was measured after immersion for 48 hours, and the strength retention rate was calculated.

[0077] Table 1 Performance test results of aramid fibers of Examples and Comparative Examples

[0078] As can be seen from the above table data: Example 1-Example 5 The para-aramid fibers prepared by the preparation method of the present invention have better performance stability under strong acid conditions, and the acid resistance is effectively improved. The strength retention rate is not less than 90cN / dtex, which meets the acid resistance requirements of para-aramid. The present invention utilizes diisocyanate to improve the acid resistance of the fiber. After being treated with diisocyanate, the amino or hydroxyl groups in the aramid molecular chain form a three-dimensional cross-linked structure with the diisocyanate, thereby improving the strength retention rate of the para-aramid fiber and improving the acid resistance of the para-aramid fiber. After the fiber is formed, the fiber is combined and processed, and a three-stage drying technology is used to improve the uniformity and modulus of the fiber, and finally an acid-resistant high-model para-aramid fiber is obtained.

[0079] From the comparison of the experimental results of Comparative Example 1 and Example 1, it can be seen that in the preparation method of the present invention, the addition of diisocyanate to the coagulation bath can form a three-dimensional cross-linked structure with the amino or hydroxyl groups in the aramid molecular chain and the diisocyanate, thereby improving the strength retention rate of the para-aramid fiber and improving the acid resistance of the para-aramid fiber.

[0080] From the comparison of the experimental results of Comparative Examples 2 to 4 and Example 1, it can be seen that in the preparation method of the present invention, the provision of a three-stage drying technology helps to improve the modulus of the para-aramid fiber and at the same time makes the para-aramid fiber have better acid resistance.

[0081] From the comparison of the experimental results of Comparative Example 5 and Example 1, it can be seen that if the diisocyanate concentration in the coagulation bath is too high, a large number of holes and defects will be formed inside the fiber, because the excessively high diisocyanate concentration will change the solvent-nonsolvent equilibrium of the coagulation bath, causing the coagulation speed of the fiber surface to be too fast, forming a dense cortex, and hindering the diffusion of the internal solvent to the outside, thereby forming a large number of holes and defects inside the fiber.

[0082] Comparing the experimental results of Comparative Example 6 and Example 1, it can be seen that if the spun fibers are first coagulated and formed 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 and forming in a conventional coagulation bath and then subjecting to a coagulation bath containing diisocyanate" causes the spun fibers to form a dense, stable skin-core structure in the first coagulation bath. This dense structure acts as a barrier, severely hindering the subsequent diffusion and penetration of the diisocyanate solution into the fiber interior, making it difficult to fully react with the amide groups. As a result, the crosslinking reaction can only be confined to the surface or near-surface area of ​​the fiber and cannot occur uniformly across the entire fiber cross-section, thereby limiting the improvement in overall acid resistance.

[0083] From the comparison of the experimental results of Comparative Example 7 and Example 1, it can be seen that if the temperature conditions of the second-stage drying are increased, the residual solvent in the fiber core will increase, the surface will harden and microcracks will be generated. Because the second-stage drying is in the stage of "the surface has basically formed a film and the core solvent diffuses outward under control", the temperature is too high, causing the cortex to densify too quickly, hindering the further escape of the remaining solvent, forming internal stress cracks, making it easy for the acid to penetrate along the cracks, and reducing the acid resistance of the fiber.

[0084] From the comparison of the experimental results of Comparative Example 8 and Example 1, it can be seen 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; because the third stage is the "low solvent content, structural finalization" stage, it will lead to surface cracking, loss of the "flexibility-density" synergistic effect, excessive growth of the crystal region, resulting in fragile interfaces between microfibers, preferential breakage during acid etching, a significant reduction in strength retention, and worsening of acid resistance.

[0085] From the comparison of the experimental results of Comparative Example 9 and Example 1, it can be seen that if the temperature conditions of the third-stage drying are lowered, the residual solvent amount will be too high and the glass transition temperature of the fiber will decrease. This is because the third-stage temperature is insufficient to completely drive out the trace solvent. The residual solvent has a plasticizing effect, making the fiber prone to creep and accelerated acid-catalyzed hydrolysis during subsequent heat treatment and use, resulting in poor acid resistance and durability, and a decrease in the fiber modulus.

[0086] From the comparison of the experimental results of Comparative Example 10 and Example 1, it can be seen that if a 2000-hole spinneret is used for spinning, the transverse-longitudinal structural uniformity of the spun fiber will be poor and the fiber strength retention rate will decrease. Because two spinnerets with 1000 holes and 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 defect probability, the transverse-longitudinal structural uniformity of the spun fiber is better, thereby showing a higher strength retention rate and a longer service life in the subsequent acid etching environment.

[0087] The technical features of the above-described embodiments can be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above-described 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.

[0088] For those skilled in the art, several variations and improvements may be made without departing from the scope of the present invention, which all fall within the scope of protection of the present invention. The scope of protection of the present invention shall be based on the appended claims.

Claims

1. A method for preparing acid-resistant high modulus para-aramid fiber, characterized in that: The preparation method is: S1, extruding the spinning solution of para-aramid through a spinneret to form nascent fibers; S2, immersing the as-spun fibers in a coagulation bath containing diisocyanate for a reaction to obtain a modified tow; S3. The modified filament bundles are tensioned and twisted synchronously, and then subjected to multi-stage drying treatment to obtain acid-resistant high modulus para-aramid fibers.

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

3. The method for preparing an 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-7.5 dL / g.

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

5. The method for preparing an acid-resistant high modulus para-aramid fiber according to claim 1, characterized in that: The coagulation bath comprises diisocyanate, sulfuric acid and water. The mass concentration of the diisocyanate in the coagulation bath is 0.1%-5%, and the mass concentration of the sulfuric acid in the coagulation bath is 4.5%-6.5%.

6. The method for preparing an acid-resistant high modulus para-aramid fiber according to claim 1, characterized in that: The temperature of the coagulation bath is 5-10° C., and the soaking reaction time of the as-spun fibers in the coagulation bath is 1-60 minutes.

7. The method for preparing an 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.

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

9. The method for preparing an acid-resistant high modulus para-aramid fiber according to claim 1, characterized in that: In step S3, a three-stage drying process is adopted, wherein the three-stage drying process is: The first stage of drying is oven drying, with a drying temperature of 80-180°C, a tension of 1 cN / dtex-5 cN / dtex, and a drying time of 3-7 seconds. The moisture content of the first stage dried tow is 6%-8%; The second stage of drying is a heated roller with a drying temperature of 200-300°C, a tension of 2cN / dtex-5cN / dtex, and a drying time of 1-3s; The third stage of drying is infrared radiation drying, with a drying temperature of 160-180°C and a drying time of 1-1.5s.

10. 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 according to any one of claims 1 to 9.

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