A method for preparing high modulus para-aramid

Abstract

The present invention belongs to the field of polymer material processing technology and discloses a method for preparing high-modulus para-aramid. The preparation method comprises: soaking wet para-aramid fibers obtained by dry-jet wet spinning in acetone at room temperature, removing them from the fibers and air-drying them; and then subjecting them to a constant-tension heat treatment in a dry nitrogen atmosphere to produce the high-modulus para-aramid fibers. The constant-tension heat treatment temperature is 325-350°C and the tension is 0.80-1.10 cN / dtex. Compared with a control sample, the tensile modulus of the high-modulus para-aramid fibers is increased by 17-32%. The control sample is produced by directly subjecting the wet para-aramid fibers to a constant-tension heat treatment in a dry nitrogen atmosphere without undergoing an acetone soaking treatment. The preparation method of the present invention can significantly improve the tensile modulus of the para-aramid fibers, is simple to operate, and has low production costs. The method can be used in large-scale high-modulus para-aramid industrial production lines.

Description

Technical Field

[0001] The invention belongs to the technical field of polymer material processing and relates to a method for preparing high-modulus para-aramid. Background Art

[0002] Poly(p-phenylene terephthalamide) (PPTA) fiber, also known as para-aramid fiber, is considered one of the world's three major high-performance fibers, along with ultra-high molecular weight polyethylene fiber and carbon fiber. Thanks to the conjugation of numerous benzene rings and amide groups, PPTA molecular segments resist internal rotation, resulting in a rod-like structure. The macromolecular chain exhibits a high degree of order, perfectly matching the straight-chain structure required for high-performance fibers. Consequently, it has found application in a wide range of fields.

[0003] At present, the domestic market demand for para-aramid is mainly in the fields of safety protection and optical fiber reinforcement. However, these two fields have very high requirements for the modulus of the fiber. The tensile modulus of the produced para-aramid only reaches 80% of the theoretical value, which still cannot meet their needs.

[0004] There are two main methods for improving the tensile strength of para-aramid fibers in existing technologies: one is to improve the technology and equipment of the entire process from monomer synthesis to spinning; the other is to add additional processing steps to the finished fibers after heat treatment.

[0005] For example, patent CN117604668A discloses a high-modulus aramid 1414 fiber for optical cables and its preparation method. This patent involves dissolving poly(p-phenylene terephthalamide) resin and sulfuric acid in a mixture, followed by degassing, filtration, spinning, washing, and drying to obtain fiber precursors with a fineness of 1500-6000D and a moisture content of 20-30%. The fiber is then subjected to a first oiling, heat treatment, second oiling, and winding to obtain a high-modulus aramid 1414 fiber with a modulus of 110-130 GPa and a breaking strength of 18.0-20.0 cN / dtex. However, although this patent improves the heat treatment tension, temperature, and oiling method, the maximum tensile modulus of the product is only increased by 18.75% compared to the original method. Furthermore, the patent places high demands on equipment and production costs.

[0006] For example, patent application CN103469602A discloses a method for improving the mechanical properties of aramid fibers by stretching and orienting them in a supercritical fluid. This method involves placing the aramid fibers in a sealed container and applying a tension of 10 to 500 cN. Carbon dioxide is then introduced at 80 to 120°C, causing them to reach a supercritical CO2 state under a certain pressure. After swelling for 5 to 15 minutes, the highly stretched and oriented aramid fibers are removed. The resulting para-aramid fibers exhibit an 11 to 17% increase in tensile strength and a 13 to 16% increase in tensile modulus. However, the entire preparation process requires high equipment and production costs, is complex, and the high-temperature and high-pressure conditions pose production safety risks, making it unsuitable for use in large-scale production lines.

[0007] For example, patent application CN110042664A discloses the use of PPTA oligomers in para-aramid fiber reinforcement. This involves first preparing a PPTA oligomer with controlled end groups, dispersing it in a nitrogen-methylpyrrolidone solution at a concentration of 0.1 to 1.05 mg / mL. The para-aramid fiber is then immersed in the dispersion and swelled with ultrasound at 10 to 50°C for 20 to 60 minutes. The resulting high-performance para-aramid fiber is then dried. Compared to the original para-aramid fiber, the resulting tensile modulus is increased by 6.47 to 13.27%. However, the synthesis of PPTA oligomers requires stringent requirements, is complex and expensive, and the reinforcing material is difficult to recycle, making it unsuitable for use in large-scale production lines.

[0008] Therefore, it is of great significance to study a preparation method of high modulus para-aramid, in which the wet fibers obtained by dry-jet wet spinning are directly subjected to a heat treatment process to obtain high modulus para-aramid, in order to solve the above problems. Summary of the Invention

[0009] The purpose of the present invention is to solve the problems existing in the prior art and provide a method for preparing high modulus para-aramid. The wet fibers obtained by dry-jet wet spinning are directly subjected to a heat treatment process to obtain high modulus para-aramid.

[0010] In order to achieve the above object, the technical solution adopted by the present invention is as follows:

[0011] A method for preparing high-modulus para-aramid fiber comprises: soaking wet para-aramid fiber obtained by dry-jet wet spinning in acetone at room temperature, taking it out and drying it, and then performing a constant tension heat treatment in a dry nitrogen atmosphere to obtain the high-modulus para-aramid fiber;

[0012] The temperature of constant tension heat treatment is 325-350℃, and the tension is 0.80-1.10 cN / dtex;

[0013] Compared with the control sample, the tensile modulus of the high modulus para-aramid fiber is increased by 17 to 32%; the control sample is prepared by subjecting the wet para-aramid fiber to a constant tension heat treatment in a dry nitrogen atmosphere without acetone impregnation treatment.

[0014] The present invention involves immersing wet para-aramid fiber in a low-boiling-point acetone solvent, displacing some of the water molecules and residual solvent in the wet para-aramid fiber. The resulting internal solution of the impregnated para-aramid fiber is transformed from water into a blend of water and acetone, a solution with a lower boiling point. The instant the wet fiber enters the high-temperature heat pipe, the internal solution vaporizes. Under the high-temperature, high-tension conditions, the macromolecular chains instantly rearrange and approach each other, forming crystalline regions and hydrogen-bonded networks at the locations of the original liquid molecules. The low-boiling-point solution system allows for nearly simultaneous vaporization and condensed-state changes, resulting in more ordered crystalline regions. Furthermore, a small amount of acetone molecules may enter the fiber's micropores, replacing the original water molecules. Under the high-temperature, high-tension conditions of the heat treatment, the acetone molecules evaporate more easily and rapidly, establishing a hydrogen-bonded network at the defects, creating a more ordered molecular arrangement and reducing the number of fiber defects.

[0015] During the process of drying after dipping, the blended solution inside the fiber evaporates, and the small liquid molecules remaining between the microfibers play a role of lubrication and plasticization when the fiber is subjected to tension heat treatment and the molecular chains are rearranged, protecting the macromolecular chains from breaking under high temperature and high tension conditions.

[0016] Due to the above effects, it is beneficial to form a more perfect high-performance fiber structure (straightened chain), and when the fiber is stretched, there is a stronger intermolecular force to counteract the stress, thereby greatly improving the mechanical properties of the fiber.

[0017] The dry-jet wet spinning method is used to prepare para-aramid wet fiber, and the specific steps are as follows:

[0018] (1) Low-temperature polycondensation: An N-methylpyrrolidone solution containing anhydrous LiCl and pyridine is added to a polymerization reactor equipped with a stainless steel stirrer and supplied with dry N2, followed by adding powdered p-phenylenediamine at room temperature, cooling to -5 to 0°C, followed by adding a slightly excessive amount of powdered terephthaloyl chloride, with the molar ratio of terephthaloyl chloride to p-phenylenediamine being 1.001 to 1.002:1, and accelerating the stirring speed until a yellow gel mass is crushed. The mixture is then allowed to stand for more than 6 hours, and a small amount of water is added to the resulting polymer, which is then crushed and filtered, followed by adding 8 to 15% NaOH until the washing liquid is neutral, and then washed with water several times to remove impurities such as residual solvent, LiCl, pyridine, and HCl, and then dried at 100°C to obtain a dry PPTA polymer;

[0019] (2) Preparation of spinning solution: PPTA polymer was mixed with concentrated sulfuric acid to prepare a spinning solution with a PPTA mass fraction of 19 to 19.5%, and the mixture was stirred and heated to 75°C to obtain a uniform nematic liquid crystal solution;

[0020] (3) Dry-jet wet spinning: The spinning solution is extruded from the spinneret by a metering pump, passes through an air layer of 2-7 mm, and has a draft ratio of 4-10. It then enters a coagulation bath with a temperature of 0-5°C and a sulfuric acid concentration of 0-10%. The solution is then coagulated into filaments. The filaments are then washed with water and neutralized to neutrality by adding Ca(OH)2. The fibers are then washed multiple times and initially dried, and then wound to obtain wet fibers.

[0021] As the preferred technical solution:

[0022] In the above-mentioned method for preparing high modulus para-aramid, the moisture content of the para-aramid wet fiber obtained by dry-jet wet spinning (the percentage of the mass of water contained in the para-aramid wet fiber to the total mass of the para-aramid wet fiber) is 25-35%.

[0023] In the above-mentioned method for preparing high modulus para-aramid, the dipping treatment time is 20 to 40 minutes, and the dipping bath ratio is 10 to 15 mL / g fiber.

[0024] In the above-mentioned method for preparing high modulus para-aramid fiber, drying refers to placing the fiber in a fume hood to allow the liquid in the wet para-aramid fiber to evaporate naturally.

[0025] In the above-mentioned method for preparing high modulus para-aramid, the drying time does not exceed 6 hours.

[0026] In the above-mentioned method for preparing high modulus para-aramid, the time of constant tension heat treatment is 3 to 5 minutes.

[0027] Beneficial effects:

[0028] (1) The present invention immerses the wet para-aramid fiber in a low-boiling-point acetone solvent, so that the internal solution system of the para-aramid fiber after immersion is converted from water to a mixed solution of water and acetone with a lower boiling point. Then, under high temperature and high tension, the solution inside the fiber will vaporize, and the macromolecular chains will rearrange and approach each other, forming crystal regions and hydrogen bond networks at the positions of the original liquid molecules, thereby improving the mechanical properties of the fiber.

[0029] (2) The present invention can significantly improve the tensile modulus of aramid fibers, is simple to operate, and has low production costs. It can be used in large-scale high-modulus para-aramid industrial production lines. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1These are the X-ray diffraction patterns of the high modulus para-aramid and para-aramid prepared in Example 2 of the present invention and Comparative Example 2. DETAILED DESCRIPTION

[0031] Below in conjunction with specific embodiment, further set forth the present invention.Should be understood that these embodiments are only used to illustrate the present invention and are not used in limiting the scope of the present invention.In addition, should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms fall equally within the scope limited by the appended claims of the application.

[0032] The testing methods for the relevant performance indicators in the following embodiments and comparative examples are as follows:

[0033] Tensile modulus, elongation at break, and tensile strength: The mechanical properties of the high modulus para-aramid and para-aramid fibers in each embodiment and comparative example were tested using an XQ-1 fiber tensor-extensometer in accordance with GB / T 14337-2008. The fibers were clamped at a distance of 20 mm, at a descent rate of 10 mm / min, and with a modulus elongation range of 0.1% to 2%. Each test was repeated 30 times, and the average value was taken.

[0034] Example 1

[0035] A method for preparing high modulus para-aramid fiber, the specific process is as follows:

[0036] First, wet para-aramid fiber (manufacturer: Sinochem High Performance Fiber Materials Co., Ltd.) with a moisture content of 30.34% was immersed in acetone with a bath ratio of 15 mL / g fiber at 25°C for 30 minutes, then taken out and placed in a fume hood to dry, so that the liquid in the wet para-aramid fiber evaporated naturally, and then constant tension heat treatment was performed in a dry nitrogen atmosphere to obtain high modulus para-aramid; wherein, the drying time was 2 hours, the constant tension heat treatment temperature was 325°C, the tension was 1.05 cN / dtex, and the time was 5 minutes.

[0037] The obtained high modulus para-aramid fiber has a tensile modulus of 882.84 cN / dtex, a tensile strength of 21.21 cN / dtex, an elongation at break of 2.45%, and a crystallinity of 78.50%.

[0038] A control sample was prepared according to the same steps as in the embodiment, except that in step (2), the wet para-aramid fiber was not impregnated with acetone and subsequently air-dried, but was directly subjected to a constant tension heat treatment in a dry nitrogen atmosphere to obtain the control sample.

[0039] The prepared high modulus para-aramid was compared with a control sample. The tensile modulus of the high modulus para-aramid was increased by 17.98%.

[0040] Comparative Example 1

[0041] A method for preparing para-aramid is basically the same as that in Example 1, except that the acetone used in the impregnation in step (2) is replaced by dichloromethane.

[0042] The prepared para-aramid fiber has a tensile modulus of 780.52 cN / dtex, a tensile strength of 13.05 cN / dtex, an elongation at break of 2.21%, and a crystallinity of 72.54%.

[0043] By comparing Example 1 with Comparative Example 1, it can be seen that the tensile strength of the para-aramid fiber prepared in Comparative Example 1 is reduced by 32.14% and the tensile modulus is increased by 4.30% compared with the control sample. This is because dichloromethane has an etching effect on the para-aramid fiber, resulting in partial etching of the fiber cortex, thereby affecting the mechanical properties of the para-aramid fiber.

[0044] Example 2

[0045] A method for preparing high modulus para-aramid fiber, the specific process is as follows:

[0046] First, wet para-aramid fiber (manufacturer: Sinochem High Performance Fiber Materials Co., Ltd.) with a moisture content of 30.34% was immersed in acetone with a bath ratio of 15 mL / g fiber at 25°C for 30 minutes, then taken out and placed in a fume hood to dry, so that the liquid in the wet para-aramid fiber evaporated naturally, and then constant tension heat treatment was performed in a dry nitrogen atmosphere to obtain high modulus para-aramid; wherein, the drying time was 4 hours, the constant tension heat treatment temperature was 325°C, the tension was 1.05 cN / dtex, and the time was 5 minutes.

[0047] The obtained high modulus para-aramid fiber has a tensile modulus of 990.46 cN / dtex, a tensile strength of 19.7 cN / dtex, an elongation at break of 2.15%, and a crystallinity of 88.73%.

[0048] A control sample was prepared according to the same steps as in the embodiment, except that in step (2), the wet para-aramid fiber was not impregnated with acetone and subsequently air-dried, but was directly subjected to a constant tension heat treatment in a dry nitrogen atmosphere to obtain the control sample.

[0049] The prepared high modulus para-aramid was compared with a control sample. The tensile modulus of the high modulus para-aramid was increased by 32.36%.

[0050] Comparative Example 2

[0051] A method for preparing para-aramid is basically the same as that in Example 1, except that the acetone used in the impregnation in step (2) is replaced by tetrahydrofuran.

[0052] The prepared para-aramid fiber has a tensile modulus of 748.32 cN / dtex, a tensile strength of 19.23 cN / dtex, an elongation at break of 2.80%, and a crystallinity of 76.68%.

[0053] Comparing Example 1 and Comparative Example 2, it can be seen that the crystallinity of the para-aramid prepared in Comparative Example 2 is significantly lower than that in Example 2, and the tensile modulus of Comparative Example 2 is not improved compared with the control sample.

[0054] The high modulus para-aramid and para-aramid prepared in Example 2 and Comparative Example 2 were tested using a D8Advance in-situ electrochemical X-ray diffractometer. The test voltage was 40 kV, the scanning range was 5° to 90°, and the scanning speed was 5° / min. The test results are shown in FIG. Figure 1 As shown in the figure, it can be seen that the half-height width of the diffraction peaks of the fiber (110) and (200) prepared in Comparative Example 2 is smaller than that in Example 2, and the crystallinity is also reduced, which shows that the present invention has an improving effect on the crystallinity of the fiber and can shape a more perfect high-performance straight chain structure, thereby significantly improving the tensile modulus.

[0055] Example 3

[0056] A method for preparing high modulus para-aramid fiber, the specific process is as follows:

[0057] First, wet para-aramid fiber (manufacturer: Sinochem High Performance Fiber Materials Co., Ltd.) with a moisture content of 30.34% was immersed in acetone with a bath ratio of 15 mL / g fiber at 25°C for 30 minutes, then taken out and placed in a fume hood to dry, so that the liquid in the wet para-aramid fiber evaporated naturally, and then constant tension heat treatment was performed in a dry nitrogen atmosphere to obtain high modulus para-aramid; wherein, the drying time was 6 hours, the constant tension heat treatment temperature was 325°C, the tension was 1.05 cN / dtex, and the time was 5 minutes.

[0058] The obtained high modulus para-aramid fiber has a tensile modulus of 929.71 cN / dtex, a tensile strength of 19.12 cN / dtex, an elongation at break of 2.1%, and a crystallinity of 80.66%.

[0059] A control sample was prepared according to the same steps as in the embodiment, except that in step (2), the wet para-aramid fiber was not impregnated with acetone and subsequently air-dried, but was directly subjected to a constant tension heat treatment in a dry nitrogen atmosphere to obtain the control sample.

[0060] The prepared high modulus para-aramid was compared with a control sample. The tensile modulus of the high modulus para-aramid was increased by 24.24%.

[0061] Example 4

[0062] A method for preparing high modulus para-aramid fiber, the specific process is as follows:

[0063] First, wet para-aramid fiber with a moisture content of 25% (manufacturer: Sinochem High Performance Fiber Materials Co., Ltd.) was immersed in acetone with a bath ratio of 15 mL / g fiber at 25°C for 20 minutes, then taken out and placed in a fume hood to dry, so that the liquid in the wet para-aramid fiber evaporated naturally, and then subjected to constant tension heat treatment in a dry nitrogen atmosphere to obtain high modulus para-aramid; wherein, the drying time was 4 hours, the constant tension heat treatment temperature was 335°C, the tension was 0.8 cN / dtex, and the time was 3 minutes.

[0064] The obtained high modulus para-aramid fiber has a tensile modulus of 937.29 cN / dtex, a tensile strength of 19.58 cN / dtex, an elongation at break of 2.3%, and a crystallinity of 80.93%.

[0065] A control sample was prepared according to the same steps as in the embodiment, except that in step (2), the wet para-aramid fiber was not impregnated with acetone and subsequently air-dried, but was directly subjected to a constant tension heat treatment in a dry nitrogen atmosphere to obtain the control sample.

[0066] The prepared high modulus para-aramid was compared with a control sample. The tensile modulus of the high modulus para-aramid was increased by 25.25%.

[0067] Example 5

[0068] A method for preparing high modulus para-aramid fiber, the specific process is as follows:

[0069] First, wet para-aramid fiber with a moisture content of 35% (manufacturer: Sinochem High Performance Fiber Materials Co., Ltd.) was immersed in acetone with a bath ratio of 15 mL / g fiber at 25°C for 40 minutes, then taken out and placed in a fume hood to dry, so that the liquid in the wet para-aramid fiber evaporated naturally, and then subjected to constant tension heat treatment in a dry nitrogen atmosphere to obtain high modulus para-aramid; wherein, the drying time was 4 hours, the constant tension heat treatment temperature was 350°C, the tension was 1.1 cN / dtex, and the time was 4 minutes.

[0070] The obtained high modulus para-aramid fiber has a tensile modulus of 922.27 cN / dtex, a tensile strength of 19.1 cN / dtex, an elongation at break of 2.25%, and a crystallinity of 80.19%.

[0071] A control sample was prepared according to the same steps as in the embodiment, except that in step (2), the wet para-aramid fiber was not impregnated with acetone and subsequently air-dried, but was directly subjected to a constant tension heat treatment in a dry nitrogen atmosphere to obtain the control sample.

[0072] The prepared high modulus para-aramid was compared with a control sample. The tensile modulus of the high modulus para-aramid was increased by 23.25%.

Claims

1. A method for preparing high modulus para-aramid fiber, characterized by: The para-aramid wet fibers obtained by dry-jet wet spinning were immersed in acetone at room temperature, taken out and dried, and then subjected to constant tension heat treatment in a dry nitrogen atmosphere to obtain high modulus para-aramid fibers. The temperature of constant tension heat treatment is 325-350℃, and the tension is 0.80-1.10 cN / dtex; Compared with the control sample, the tensile modulus of the high modulus para-aramid fiber is increased by 17 to 32%; the control sample is prepared by subjecting the wet para-aramid fiber to a constant tension heat treatment in a dry nitrogen atmosphere without acetone impregnation treatment.

2. The method for preparing high modulus para-aramid according to claim 1, wherein: The moisture content of the para-aramid wet fiber obtained by dry-jet wet spinning is 25-35%.

3. The method for preparing high modulus para-aramid according to claim 1, wherein: The immersion treatment time is 20 to 40 minutes, and the immersion bath ratio is 10 to 15 mL / g fiber.

4. The method for preparing high modulus para-aramid according to claim 1, wherein: Drying means placing the wet para-aramid fiber in a fume hood to allow the liquid in the fiber to evaporate naturally.

5. The method for preparing high modulus para-aramid according to claim 4, characterized in that: The drying time should not exceed 6 hours.

6. The method for preparing high modulus para-aramid according to claim 1, wherein: The time for constant tension heat treatment is 3 to 5 minutes.

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