Preparation method of high-modulus para-aramid

Abstract

The invention belongs to the technical field of high polymer material processing, and discloses a preparation method of high-modulus para-aramid, which comprises the following steps: dipping para-aramid wet fibers obtained by dry-jet wet spinning in acetone at room temperature, taking out and airing, and then carrying out constant-tension heat treatment in a dry nitrogen atmosphere to obtain the high-modulus para-aramid. The high-modulus para-aramid fiber is prepared; the temperature of the constant tension heat treatment is 325-350 DEG C, and the tension is 0.80-1.10 cN / dtex; compared with a contrast sample, the tensile modulus of the high-modulus para-aramid fiber is increased by 17-32%; the contrast sample is prepared by directly carrying out constant-tension heat treatment on para-aramid wet fibers in a dry nitrogen atmosphere without acetone dipping treatment. According to the preparation method, the tensile modulus of the para-aramid can be greatly improved, the operation is simple, the production cost is low, and the preparation method can be used for a large-scale industrial production line of the high-modulus para-aramid.

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 is also called para-aramid fiber. It is one of the three high-performance fibers in the world along with ultra-high molecular weight polyethylene fiber and carbon fiber. Thanks to the conjugation of a large number of benzene rings and amide groups, the PPTA molecular chain segments are difficult to rotate internally and present a rod-like structure. The macromolecular chain shows a high degree of order, which perfectly meets the straight chain structure of high-performance fibers. Therefore, it has been used in many 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 on 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 the existing technology: one is to improve the technology and equipment of the entire process from monomer synthesis to spinning; the other is to add an additional treatment process for the finished fiber after heat treatment.

[0005] For example, patent CN117604668A discloses a high modulus aramid 1414 fiber for optical cable and its preparation method, which is to mix and dissolve poly(p-phenylene terephthalamide) resin and sulfuric acid, degassing, filtering, spinning, washing and drying to obtain fiber precursor with a fineness of 1500-6000D and a moisture content of 20-30%, and then obtain a high modulus aramid 1414 fiber with a modulus of 110-130GPa and a breaking strength of 18.0-20.0cN / dtex through first oiling, heat treatment, second oiling and winding. However, although the patent has improved the heat treatment tension, temperature and oiling method, the maximum tensile modulus of the product has only increased by 18.75% compared with the unimproved one, and the equipment requirements are high, and the production cost is large.

[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. The method is to place the aramid fibers in a closed container and apply a tension of 10 to 500 cN, introduce carbon dioxide at 80 to 120°C, and make them in a supercritical CO2 state under a certain pressure. After swelling for 5 to 15 minutes, the highly stretched and oriented aramid fibers are taken out. The tensile strength of the para-aramid fibers obtained is increased by 11 to 17%, and the tensile modulus is increased by 13 to 16%. However, the entire preparation process has high equipment requirements and high production costs, and the process flow is complicated. There are production safety risks in the high temperature and high pressure state, which is not suitable for large-scale production lines.

[0007] For example, patent application CN110042664A discloses the application of PPTA oligomer in para-aramid fiber reinforcement, which is to first prepare PPTA oligomer with controlled end groups, then disperse it in a nitrogen methyl pyrrolidone solution at a concentration of 0.1-1.05 mg / mL, then immerse the para-aramid fiber in the dispersion solution at 10-50°C with the aid of ultrasound for 20-60 minutes for swelling, and then take it out and dry it to obtain high-performance para-aramid fiber. Compared with the original para-aramid fiber, its tensile modulus is increased by 6.47-13.27%, but the synthesis of PPTA oligomers has strict requirements, complex processes and high costs, and it is difficult to recycle the reinforcing materials, which is also not suitable for large-scale production lines.

[0008] Therefore, it is of great significance to study a method for preparing high modulus para-aramid fiber, and obtain high modulus para-aramid fiber by directly subjecting wet fibers obtained by dry-jet wet spinning to a heat treatment process, so as 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] 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, comprising: dipping the para-aramid wet 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 the constant tension heat treatment is 325-350°C, 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 17-32%; the control sample is prepared by subjecting the wet para-aramid fiber to a constant tension heat treatment in a dry nitrogen atmosphere without being impregnated with acetone.

[0014] The present invention displaces part of the water molecules and residual solvent in the wet para-aramid fiber by immersing the wet para-aramid fiber in a low-boiling-point acetone solvent, and the internal solution system of the para-aramid fiber after immersion is changed from water to a mixed solution of water and acetone, and this solution system has a lower boiling point. The internal solution of the wet fiber vaporizes at the moment of entering the high-temperature heat pipe, and the macromolecular chains are instantly rearranged and approach each other under the state of high temperature and high tension, forming a crystal region and a hydrogen bond network at the position of the original liquid molecules. The low-boiling-point solution system allows the changes of vaporization and condensed state to occur almost simultaneously, so more orderly crystal regions are formed. In addition, a small amount of acetone molecules may enter the micropores of the fiber to replace the original water molecules. Under the high temperature and high tension state of heat treatment, the acetone molecules are more likely to evaporate quickly, thereby establishing a hydrogen bond network at the defect, forming a more orderly molecular arrangement, and reducing the number of fiber defects.

[0015] During the process of drying after immersion, 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 to rearrange the molecular chains, protecting the macromolecular chains from breaking under high temperature and high tension conditions.

[0016] Due to the above-mentioned 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 prior art is to prepare para-aramid wet fiber by dry-jet wet spinning, 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, and then powdered p-phenylenediamine is added thereto at room temperature, the temperature is lowered to -5 to 0°C, and then a slightly excessive amount of powdered terephthaloyl chloride is added, the molar ratio of terephthaloyl chloride to p-phenylenediamine being 1.001 to 1.002:1, the stirring speed is increased until a yellow gel mass is crushed, and then the mass is allowed to stand for more than 6 hours, a small amount of water is added to the resulting polymer, the mass is crushed and filtered, and then 8 to 15% NaOH is added thereto until the washing liquid is neutral, and then the mixture is washed with water for multiple times to remove residual solvent, impurities such as LiCl, pyridine and HCl, and then dried at 100°C to obtain a dry PPTA polymer;

[0019] (2) Preparation of spinning solution: PPTA polymer and concentrated sulfuric acid are mixed to prepare a spinning solution with a PPTA mass fraction of 19 to 19.5%, and the mixture is 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 through a metering pump, passes through an air layer of 2 to 7 mm, and has a draft ratio of 4 to 10. It then enters a coagulation bath with a temperature of 0 to 5°C and a sulfuric acid concentration of 0 to 10%. The solution is coagulated into filaments. The filaments are then washed with water and neutralized to neutrality by adding Ca(OH)2, followed by multiple washings and preliminary drying, and then wound to obtain wet fibers.

[0021] As the preferred technical solution:

[0022] In the method for preparing high modulus para-aramid fiber as described above, 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 method for preparing high modulus para-aramid fiber as described above, the immersion treatment time is 20 to 40 minutes, and the immersion 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 method for preparing high modulus para-aramid fiber as described above, the drying time does not exceed 6 hours.

[0026] In the method for preparing high modulus para-aramid fiber as described above, 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 changed 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, the macromolecular chains will rearrange and approach each other, and crystal regions and hydrogen bond networks will be formed 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 fiber, is simple to operate, and has low production cost, and can be used in large-scale high-modulus para-aramid industrial production lines. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1The 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 are shown. DETAILED DESCRIPTION

[0031] The present invention will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and are not intended to limit the scope of the present invention. In addition, it 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 within the scope limited by the appended claims of the application equally.

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

[0033] Tensile modulus, elongation at break, tensile strength: The mechanical properties of high modulus para-aramid and para-aramid in each embodiment and each comparative example were tested according to GB / T 14337-2008 using an XQ-1 fiber tensile tester; wherein the fiber clamping distance was 20 mm, the descent rate was 10 mm / min, the modulus elongation range was 0.1% to 2%, and each group was tested 30 times to take the average value.

[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 evaporates naturally, and then constant tension heat treatment was carried out in a dry nitrogen atmosphere to obtain high modulus para-aramid; wherein, the drying time is 2 hours, the constant tension heat treatment temperature is 325°C, the tension is 1.05 cN / dtex, and the time is 5 minutes.

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

[0038] A comparative sample was prepared according to the same steps as those 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 comparative sample;

[0039] The prepared high modulus para-aramid was compared with a control sample, and 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 tensile modulus of the prepared para-aramid fiber is 780.52 cN / dtex, the tensile strength is 13.05 cN / dtex, the elongation at break is 2.21%, and the crystallinity is 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 evaporates naturally, and then constant tension heat treatment was carried out in a dry nitrogen atmosphere to obtain high modulus para-aramid; wherein, the drying time is 4 hours, the constant tension heat treatment temperature is 325°C, the tension is 1.05 cN / dtex, and the time is 5 minutes.

[0047] The tensile modulus of the prepared high modulus para-aramid fiber is 990.46 cN / dtex, the tensile strength is 19.7 cN / dtex, the elongation at break is 2.15%, and the crystallinity is 88.73%;

[0048] A comparative sample was prepared according to the same steps as those 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 comparative sample;

[0049] The prepared high modulus para-aramid was compared with a control sample, and 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 tensile modulus of the prepared para-aramid fiber is 748.32 cN / dtex, the tensile strength is 19.23 cN / dtex, the elongation at break is 2.80%, and the crystallinity is 76.68%;

[0053] By comparing Example 1 and Comparative Example 2, it can be seen that the crystallinity of the para-aramid fiber 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 by D8Advance in-situ electrochemical X-ray diffractometer, respectively. The test voltage was 40KV, 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-width of the diffraction peaks of the fiber (110) and (200) planes 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 evaporates naturally, and then constant tension heat treatment was carried out in a dry nitrogen atmosphere to obtain high modulus para-aramid; wherein, the drying time is 6 hours, the constant tension heat treatment temperature is 325°C, the tension is 1.05 cN / dtex, and the time is 5 minutes.

[0058] The tensile modulus of the prepared high modulus para-aramid fiber is 929.71 cN / dtex, the tensile strength is 19.12 cN / dtex, the elongation at break is 2.1%, and the crystallinity is 80.66%;

[0059] A comparative sample was prepared according to the same steps as those 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 comparative sample;

[0060] The prepared high modulus para-aramid was compared with a control sample, and 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 (manufacturer: Sinochem High Performance Fiber Materials Co., Ltd.) with a moisture content of 25% is 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 evaporates naturally, and then a constant tension heat treatment is performed in a dry nitrogen atmosphere to obtain high modulus para-aramid; wherein, the drying time is 4 hours, the constant tension heat treatment temperature is 335°C, the tension is 0.8 cN / dtex, and the time is 3 minutes.

[0064] The tensile modulus of the prepared high modulus para-aramid fiber is 937.29 cN / dtex, the tensile strength is 19.58 cN / dtex, the elongation at break is 2.3%, and the crystallinity is 80.93%;

[0065] A comparative sample was prepared according to the same steps as those 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 comparative sample;

[0066] The prepared high modulus para-aramid fiber was compared with a control sample, and the tensile modulus of the high modulus para-aramid fiber 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 (manufacturer: Sinochem High Performance Fiber Materials Co., Ltd.) with a moisture content of 35% is 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 evaporates naturally, and then a constant tension heat treatment is performed in a dry nitrogen atmosphere to obtain high modulus para-aramid; wherein, the drying time is 4 hours, the constant tension heat treatment temperature is 350°C, the tension is 1.1 cN / dtex, and the time is 4 minutes.

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

[0071] A comparative sample was prepared according to the same steps as those 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 comparative sample;

[0072] The prepared high modulus para-aramid was compared with a control sample, and 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 in that: The p-aramid wet fiber obtained by dry-jet wet spinning is 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 p-aramid. The temperature of constant tension heat treatment is 325-350°C, 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 17-32%; the control sample is prepared by subjecting the wet para-aramid fiber to a constant tension heat treatment in a dry nitrogen atmosphere without being impregnated with acetone.

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

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

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

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