A method for multi-level efficient drying of meta-aramid fibers

Abstract

A method for multi-level efficient drying of meta-aramid fibers according to the present invention relates to the field of fiber drying. The method comprises the following steps: mixing calcium chloride and molecular sieve powder and grinding for 15-20 minutes, then mixing the obtained mixture with the meta-aramid fibers to be dried and stirring for 6-12 hours under the action of a spiral stirrer to obtain the meta-aramid fibers after the first treatment; subjecting the meta-aramid fibers after the first treatment to wet stretching to obtain the meta-aramid fibers after the second treatment; first stretching the meta-aramid fibers after the second treatment, and then subjecting the obtained meta-aramid fibers to microwave drying in a vacuum to obtain the dried meta-aramid fibers, which have the advantages of short drying time, uniform temperature, low static electricity generation and low energy consumption.

Description

Technical Field

[0001] The present invention relates to the field of fiber drying, and specifically to a method for multi-level efficient drying of meta-aramid fibers. Background Art

[0002] Meta-aramid, also known as aramid 1313, is an organic polymer fiber synthesized from isophthaloyl chloride and m-phenylenediamine, and its amide bonds are connected to the 1st and 3rd positions of two benzene rings. Meta-aramid has excellent properties such as thermal stability, flame retardancy, electrical insulation, chemical stability, and radiation resistance, and is widely used in fields such as aerospace, military, chemical industry, and electronics. The drying process of fibers has an important impact on their quality and output.

[0003] Initially, the drying process of meta-aramid fibers usually adopted spray drying or natural drying methods. Currently, meta-aramid fibers are mainly dried by means of pneumatic drying, vacuum drying, microwave drying, and freeze drying. Among the above four drying methods, pneumatic drying heats the meta-aramid fibers through high-temperature air flow and uses hot air for drying. Vacuum drying utilizes water evaporation and sublimation in a vacuum environment. Microwave drying uses microwave heating to improve the drying speed and efficiency. Freeze drying dries the meta-aramid fibers by freezing the suspended fibers in a low-temperature area and then absorbing moisture by raising the temperature. For example, Zhang Xiufang et al. from Shanghai Zhanheng Environmental Protection Technology Co., Ltd. adopted microwave drying, placed nanofibers containing organic solvents in a microwave drying device, and continuously dried the nanofibers by combining microwave drying with a blowing process. The process has a fast drying speed, low energy consumption, and little damage to the nanofibers; Chen Yuesong from Zhangjiagang Tengxiang Machinery Manufacturing Co., Ltd. prepared a drum dryer for drying fiber fabrics, which is equipped with a microwave drying device, improving the drying efficiency.

[0004] However, the above different drying technologies have their own advantages and disadvantages. During spray drying, particle aggregation may occur in the material, resulting in uneven drying; natural drying is affected by seasonal weather, and the humidity, temperature, wind speed, etc. during the process cannot be precisely controlled, making the stability and consistency of the drying process poor; pneumatic drying may cause dust problems, and subsequent treatment of waste gas and dust emissions is required, with high energy consumption; vacuum drying has a long drying cycle and high energy consumption; microwave drying causes uneven heating of the material, resulting in uneven mechanical strength; freeze drying has a long drying cycle, high energy consumption, and expensive equipment. The combination of microwave drying and blowing process, as well as the drying method of the drum dryer, have high energy consumption. Summary of the Invention

[0005] Aiming at the problems existing in the prior art, the present invention provides a method for multi-level efficient drying of meta-aramid fibers, which has the advantages of short drying time, uniform temperature, low static electricity generation, and low energy consumption.

[0006] The present invention is realized through the following technical solutions:

[0007] A method for efficiently drying meta-aramid fibers at multiple levels, comprising the following steps:

[0008] S1. Mix calcium chloride and molecular sieve powder and grind them for 15 min - 20 min. Then, mix the obtained mixture with the meta-aramid fibers to be dried, and stir under the action of a spiral stirrer for 6 h - 12 h to obtain the meta-aramid fibers after the first treatment;

[0009] S2. Wet-stretch the meta-aramid fibers after the first treatment to obtain the meta-aramid fibers after the second treatment;

[0010] S3. First, stretch the meta-aramid fibers after the second treatment, and then microwave-dry the obtained meta-aramid fibers in a vacuum with a vacuum degree of 10 Pa - 200 Pa and a microwave power of 500 W - 800 W to obtain the dried meta-aramid fibers.

[0011] Preferably, the molecular sieve described in S1 is a 4A molecular sieve.

[0012] Furthermore, the mass ratio of the calcium chloride to the 4A molecular sieve powder described in S1 is 1:(1 - 9).

[0013] Preferably, the mass ratio of the mixture described in S1 to the meta-aramid fibers to be dried is (70 - 90):(10 - 30).

[0014] Preferably, in S2, the meta-aramid fibers after the first treatment are wet-stretched under the condition of a draw ratio of 1.2 - 1.5 to obtain the meta-aramid fibers after the second treatment.

[0015] Preferably, in S3, the meta-aramid fibers after the second treatment are stretched at a draw ratio greater than 1.0 and ≤ 1.4, and then the obtained meta-aramid fibers are microwave-dried in a vacuum.

[0016] Preferably, in S3, the stretched meta-aramid fibers are dried in a vacuum microwave drying oven to obtain the dried meta-aramid fibers.

[0017] Furthermore, in S3, after stretching the meta-aramid fibers after the second treatment, they are placed in a vacuum microwave drying oven, weights are placed at both ends of the stretched meta-aramid fibers, and then drying is carried out.

[0018] Furthermore, in S3, the obtained meta-aramid fibers are microwave-dried in a vacuum for 20 - 30 min to obtain the dried meta-aramid fibers.

[0019] Further, the moisture content of the dried meta-aramid fiber described in S3 is 0.2%-0.3%, and the tensile strength is 3632 MPa-4092 MPa.

[0020] Compared with the prior art, the present invention has the following beneficial technical effects:

[0021] In the method for multi-level efficient drying of meta-aramid fiber of the present invention, the meta-aramid fiber to be dried is generally the wet meta-aramid fiber after spinning and washing. Mixing it with a strong hygroscopic fiber desiccant composed of calcium chloride and molecular sieve powder and stirring for a long time can dry it more evenly, remove most of the moisture in the wet meta-aramid fiber, and provide better humidity control and drying effect. This is because the pore structure of the molecular sieve can physically adsorb moisture and impurities in the air, preventing the fiber from adsorbing impurities in the air during the drying process and resulting in a decrease in purity. Calcium chloride can react with the moisture in the fiber and the pores of the molecular sieve to prevent the problem of fiber rewetting caused by the physically adsorbed moisture in the molecular sieve. The combination of vacuum and microwave can make the remaining water more easily evaporate under the action of microwave. Since the energy consumed by vacuum pumping is much less than the energy consumed by microwave radiation, and most of the moisture has been removed by the strong hygroscopic fiber desiccant, the combination of vacuum and microwave drying only needs to remove a small amount of water, thus solving the problems of high energy consumption and long time consumption. After the microwave radiation is absorbed, heat will be generated. Maintaining tension during the combination of vacuum and microwave drying can prevent the occurrence of agglomeration and local overheating phenomena, and this part of the heat can be better transferred and dispersed to the entire wet meta-aramid fiber, making it heated more evenly, which can increase the diffusion rate of moisture, promote the entire wet meta-aramid fiber to evaporate moisture more evenly, improve the drying efficiency and effect, and can also solve the problems of poor orientation degree and surface adsorption of impurities caused by the shrinkage of wet meta-aramid fiber during drying. It is efficient and low in energy consumption, and the service life and mechanical strength of the prepared meta-aramid fiber are greatly increased, and it has good application prospects in the fields of rockets, airplanes, sports goods, safety protective clothing, etc. Description of the Drawings

[0022] Figure 1 It is a flow chart of the multi-level efficient drying of meta-aramid fiber of the present invention. Detailed Embodiments

[0023] The following further describes the present invention in detail with specific embodiments, which are only explanations of the present invention and do not limit the present invention.

[0024] The present invention provides a method for multi-level efficient drying of meta-aramid fiber, as Figure 1 shown, including the following steps:

[0025] Step 1: Prepare a strong hygroscopic fiber desiccant. Mix calcium chloride and 4A molecular sieve powder in a mass ratio of 1:(1 - 9), and then grind for 15 - 20 min to obtain the strong hygroscopic fiber desiccant. Dope and dry the wet meta-aramid fiber after wet spinning washing and the strong hygroscopic fiber desiccant in a mass ratio of (10 - 30):(70 - 90) for 6 - 12 h (i.e., make the strong hygroscopic fiber desiccant absorb 70 - 80% of the water), and perform the first wet stretching under the condition that the wet stretching ratio is 1.2 - 1.5 to obtain wet fiber A.

[0026] Step 2: After stretching wet fiber A with a stretching ratio greater than 1.0 and less than or equal to 1.4, put it into a vacuum microwave drying oven, place heavy objects at both ends. Since the mass of wet fiber A itself is relatively light, it can always maintain a stretched state. Under a vacuum degree of 10 - 200 Pa and a microwave power of 500 - 800 W, carry out combined vacuum and microwave drying for 20 - 30 min to remove the remaining water with a strong binding force to the fiber, and obtain dry meta-aramid fiber.

[0027] The present invention will be described in detail below in conjunction with specific embodiments:

[0028] Example 1:

[0029] Step 1: Mix calcium chloride and 4A molecular sieve powder in a mass ratio of 1:1, and then grind for 20 min to obtain the strong hygroscopic fiber desiccant.

[0030] Dope the wet meta-aramid fiber after wet spinning washing and the strong hygroscopic fiber desiccant in a mass ratio of 30:70, dry for 12 h, and absorb 76% of the water. Perform the first wet stretching under the condition that the wet stretching ratio is 1.5 to obtain wet fiber A.

[0031] Step 2: After stretching wet fiber A with a stretching ratio of 1.4, put it into a vacuum microwave drying oven. Under a vacuum degree of 10 Pa and a microwave power of 500 W, carry out combined vacuum and microwave drying for 20 min in a stretched state to remove the remaining water with a strong binding force to the fiber, and obtain dry meta-aramid fiber.

[0032] The properties of the product obtained in this example are as follows:

[0033] Moisture content of meta-aramid fiber: 0.3%.

[0034] Tensile strength of meta-aramid fiber: 4030 MPa.

[0035] Young's modulus of meta-aramid fiber: 60.7 GPa.

[0036] Example 2:

[0037] Step 1: Mix calcium chloride and 4A molecular sieve powder in a mass ratio of 1:1 and grind for 20 min to obtain a strong hygroscopic fiber desiccant.

[0038] Dope the wet meta-aramid fiber after wet spinning washing with the strong hygroscopic fiber desiccant in a mass ratio of 30:70, dry for 6 h, and absorb 70% of the moisture. Conduct the first wet stretching under the condition that the wet stretching ratio is 1.2 to obtain wet fiber A.

[0039] Step 2: Stretch wet fiber A at a stretching ratio of 1.4, then put it into a vacuum microwave drying oven. Under a vacuum degree of 100 Pa and a microwave power of 650 W, conduct combined vacuum and microwave drying for 25 min while in a stretched state to remove the remaining water with a strong binding force to the fiber, and obtain dry meta-aramid fiber.

[0040] The properties of the product obtained in this example are as follows:

[0041] Moisture content of meta-aramid fiber: 0.3%.

[0042] Tensile strength of meta-aramid fiber: 3632 MPa.

[0043] Young's modulus of meta-aramid fiber: 47.6 GPa.

[0044] Example 3:

[0045] Step 1: Mix calcium chloride and 4A molecular sieve powder in a mass ratio of 1:5 and grind for 20 min to obtain a strong hygroscopic fiber desiccant.

[0046] Dope the wet meta-aramid fiber after wet spinning washing with the strong hygroscopic fiber desiccant in a mass ratio of 30:70, dry for 12 h, and absorb 78% of the moisture. Conduct the first wet stretching under the condition that the wet stretching ratio is 1.5 to obtain wet fiber A.

[0047] Step 2: Stretch wet fiber A at a stretching ratio of 1.4, then put it into a vacuum microwave drying oven. Under a vacuum degree of 200 Pa and a microwave power of 800 W, conduct combined vacuum and microwave drying for 30 min while in a stretched state to remove the remaining water with a strong binding force to the fiber, and obtain dry meta-aramid fiber.

[0048] The properties of the product obtained in this example are as follows:

[0049] Moisture content of meta-aramid fiber: 0.2%.

[0050] Tensile strength of meta-aramid fiber: 3907 MPa.

[0051] Young's modulus of meta-aramid fiber: 53.1 GPa.

[0052] Example 4:

[0053] Step 1: Mix calcium chloride and 4A molecular sieve powder in a mass ratio of 1:5 and grind for 20 min to obtain a strong hygroscopic fiber desiccant.

[0054] Dope the wet meta-aramid fiber after wet spinning washing with the strong hygroscopic fiber desiccant in a mass ratio of 10:90, dry for 6 h, and absorb 80% of the moisture. Conduct the first wet drawing under the condition that the wet draw ratio is 1.5 to obtain wet fiber A.

[0055] Step 2: After drawing wet fiber A at a draw ratio of 1.4, place it in a vacuum microwave drying oven. Under a vacuum degree of 10 Pa and a microwave power of 800 W, conduct combined vacuum and microwave drying for 20 min while in a drawn state to remove the remaining water with a strong binding force to the fiber, and obtain dry meta-aramid fiber.

[0056] The properties of the product obtained in this example are as follows:

[0057] Moisture content of meta-aramid fiber: 0.2%.

[0058] Tensile strength of meta-aramid fiber: 4092 MPa.

[0059] Young's modulus of meta-aramid fiber: 65.5 GPa.

[0060] Example 5:

[0061] Step 1: Mix calcium chloride and 4A molecular sieve powder in a mass ratio of 1:5 and grind for 15 min to obtain a strong hygroscopic fiber desiccant.

[0062] Dope the wet meta-aramid fiber after wet spinning washing with the strong hygroscopic fiber desiccant in a mass ratio of 20:80, dry for 6 h, and absorb 78% of the moisture. Conduct the first wet drawing under the condition that the wet draw ratio is 1.5 to obtain wet fiber A.

[0063] Step 2: After drawing wet fiber A at a draw ratio of 1.2, place it in a vacuum microwave drying oven. Under a vacuum degree of 10 Pa and a microwave power of 500 W, conduct combined vacuum and microwave drying for 20 min while in a drawn state to remove the remaining water with a strong binding force to the fiber, and obtain dry meta-aramid fiber.

[0064] The properties of the product obtained in this example are as follows:

[0065] Moisture content of meta-aramid fiber: 0.3%.

[0066] Tensile strength of meta-aramid fiber: 3789 MPa.

[0067] The Young's modulus of meta-aramid fiber: 50.7 GPa.

[0068] Comparative Example 1:

[0069] Step 1: Mix calcium chloride and 4A molecular sieve powder in a mass ratio of 1:5 and grind for 15 min to obtain a strong hygroscopic fiber desiccant.

[0070] Dope the wet meta-aramid fiber after wet spinning washing with the strong hygroscopic fiber desiccant in a mass ratio of 20:80, dry for 6 h, absorb 78% of the moisture, and do not perform wet stretching to obtain wet fiber A.

[0071] Step 2: Place wet fiber A in a vacuum microwave drying oven in a natural state and perform combined vacuum and microwave drying for 20 min under a vacuum degree of 10 Pa and a microwave power of 500 W to remove the remaining water with a stronger binding force to the fiber and obtain dry meta-aramid fiber.

[0072] The properties of the product obtained in this example are as follows:

[0073] The moisture content of meta-aramid fiber: 0.3%.

[0074] The tensile strength of meta-aramid fiber: 3502 MPa.

[0075] The Young's modulus of meta-aramid fiber: 45.8 GPa.

[0076] Tensile was not performed in Comparative Example 1. It can be seen that the tensile strength of the prepared fiber is the worst, which is due to uneven heating resulting in partial agglomeration of the fiber and poor orientation degree, and the mechanical strength of the whole fiber decreases due to the plank effect.

[0077] Comparative Example 2:

[0078] Only dry the wet meta-aramid fiber after wet spinning washing according to the steps in Comparative Example 1. The water content is 1.2%, the tensile strength is 2956 MPa, and the Young's modulus is 23.6 GPa.

[0079] Comparative Example 3:

[0080] Dry the wet fiber obtained in Comparative Example 2 under the vacuum drying conditions in Step 2 for 24 h. The water content is 0.8%, the tensile strength is 3267 MPa, and the Young's modulus is 28.1 GPa.

[0081] Comparative Example 4:

[0082] Dry the wet fiber obtained in Comparative Example 2 under the microwave drying conditions in Step 2 for 24 h. The water content is 1.1%, the tensile strength is 3206 MPa, and the Young's modulus is 27.9 GPa.

[0083] The tensile strength of the meta-aramid fiber prepared by the multi-level drying of the present invention is 15-25% higher than that of the meta-aramid fiber dried alone.

[0084] The above are only the preferred embodiments of the present invention, and are not intended to limit the technical solutions of the present invention. Those skilled in the art should understand that, without departing from the spirit and principle of the present invention, the technical solutions can also be subject to several simple modifications and substitutions, and these modifications and substitutions also fall within the protection scope covered by the claims.

Claims

1. A method for multi - level efficient drying of meta - aramid fibers, characterized in that, it comprises the following steps: S1, Mix calcium chloride with molecular sieve powder and then grind for 15 min - 20 min. After that, mix the obtained mixture with the meta - aramid fibers to be dried, and stir for 6 h - 12 h under the action of a spiral stirrer to obtain the meta - aramid fibers after the first treatment; S2, Wet - stretch the meta - aramid fibers after the first treatment under the condition that the draw ratio is 1.2 - 1.5 to obtain the meta - aramid fibers after the second treatment; S3, First stretch the meta - aramid fibers after the second treatment at a draw ratio greater than 1.0 and ≤ 1.

4. Then, microwave - dry the obtained meta - aramid fibers in a vacuum, with the vacuum degree being 10 Pa - 200 Pa and the microwave power being 500 W - 800 W, to obtain the dried meta - aramid fibers.

2. The method for multi - level efficient drying of meta - aramid fibers according to claim 1, characterized in that, the molecular sieve described in S1 is a 4A molecular sieve.

3. The method for multi - level efficient drying of meta - aramid fibers according to claim 2, characterized in that, the mass ratio of the calcium chloride to the 4A molecular sieve powder described in S1 is 1:(1 - 9).

4. The method for multi - level efficient drying of meta - aramid fibers according to claim 1, characterized in that, the mass ratio of the mixture described in S1 to the meta - aramid fibers to be dried is (70 - 90):(10 - 30).

5. The method for multi - level efficient drying of meta - aramid fibers according to claim 1, characterized in that, in S3, dry the stretched meta - aramid fibers in a vacuum microwave drying oven to obtain the dried meta - aramid fibers.

6. The method for multi - level efficient drying of meta - aramid fibers according to claim 5, characterized in that, after stretching the meta - aramid fibers after the second treatment in S3, put them into a vacuum microwave drying oven, place heavy objects at both ends of the stretched meta - aramid fibers, and then dry them.

7. The method for multi - level efficient drying of meta - aramid fibers according to claim 6, characterized in that, in S3, microwave - dry the obtained meta - aramid fibers in a vacuum for 20 - 30 min to obtain the dried meta - aramid fibers.

8. The method for multi - level efficient drying of meta - aramid fibers according to claim 7, characterized in that, the moisture content of the dried meta - aramid fibers described in S3 is 0.2% - 0.3%, and the tensile strength is 3632 MPa - 4092 MPa.

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