A method for recycling aramid fabric

Abstract

The present invention relates to the technical field of aramid recycling, and specifically to a recycling and reuse method for aramid fabrics, wherein the recycling and reuse method comprises: placing the aramid fabric to be recycled in an organic solvent containing a cosolvent for treatment to obtain a slurry; filtering the slurry to remove insoluble fibers and impurities therein; beating the filtered slurry in a poor solvent, precipitating solids and drying to obtain aramid pellets; placing the aramid pellets in an organic solvent containing a cosolvent to obtain a spinning solution after redissolving; and spinning to obtain regenerated meta-aramid fibers. The recycling and reuse method for aramid fabrics of the present invention solves the technical difficulty that aramid fibers are difficult to dissolve to a high solid content due to high orientation, thereby affecting subsequent spinning use. The meta-aramid obtained by recycling and reuse does not produce yellowing, has a strength close to that of the original fibers, and does not affect the product performance of the regenerated aramid fibers, and has a good application prospect.

Description

Technical Field

[0001] The invention relates to a method for recycling aramid fabric, belonging to the technical field of aramid recycling. Background Art

[0002] Meta-aramid fabric is a special fiber material made of poly(m-phenylene isophthalamide), also known as aramid 1313. At present, meta-aramid fabric is mainly made of meta-aramid, flame-retardant viscose, conductive fiber materials and other blends. The fiber ratio of each component varies depending on the usage scenario. Meta-aramid fabric has excellent thermal stability, flame retardancy, electrical insulation, chemical stability and textile properties, and has broad application prospects in many fields. With the continuous advancement of science and technology and the gradual increase in the use of high-performance fiber materials, the waste and pollution caused by waste meta-aramid fabrics are becoming increasingly serious. In addition, the introduction of relevant policies and documents on material recycling and reuse has made the field of primary material recycling a subject of widespread concern among researchers.

[0003] The recycling of aramid fabrics is an important part of the effective utilization of resources. It can effectively solve the waste and pollution caused by waste generated in the entire upstream and downstream of the aramid fiber production, clothing processing, and waste fabric industry chain, and improve resource utilization. However, there is currently no method suitable for industrial application for the recycling of aramid fabrics.

[0004] Chinese patent application CN102373639A discloses a method for recycling waste aramid paper, which comprises the following steps: shredding waste aramid paper into aramid shredded paper; soaking the aramid shredded paper and an organic solvent at normal pressure, and then soaking them at 0.1-1.0 MPa to obtain pulp; performing a decomposition treatment on the pulp to obtain a slurry; mixing the slurry with an additive, reacting at 60-120°C to obtain a stock solution; degassing and standing the stock solution to obtain a transparent precipitated stock solution; mixing the precipitated stock solution with a precipitated solvent to obtain precipitated fibers. However, this method is aimed at the recycling of aramid paper, which is made by hot pressing after wet papermaking of aramid. Aramid waste or fiber is relatively pure aramid, and the orientation degree and processing difficulty are relatively high compared with aramid fabrics blended with other fibers, while aramid fabrics are very dense, so this method cannot be applied to the recycling of aramid fabrics. Chinese patent application CN113802217A discloses a method for recycling meta-aramid fiber waste and recycled materials, comprising: (1) drying the meta-aramid fiber waste, cutting or crushing it into short fibers or precipitated fragments; (2) soaking the short fibers or precipitated fragments in step (1) with an organic solvent under normal pressure to obtain a slurry; (3) mixing the slurry with a co-solvent, stirring and reacting under closed conditions to obtain a colorless and transparent meta-aramid resin solution. However, the meta-aramid resin solution obtained by this method has a low solid content and cannot be recycled for spinning. Summary of the invention

[0005] The present invention aims at the deficiencies in the prior art and provides a method for recycling aramid fabrics, thereby solving the environmental pollution problem caused by aramid fabrics, realizing resource recycling and reducing production costs.

[0006] The technical solution of the present invention to solve the above technical problems is as follows: a method for recycling aramid fabrics, the recycling method comprising:

[0007] S1, placing the aramid fabric to be recycled in an organic solvent containing a co-solvent to obtain a slurry;

[0008] S2, filtering the slurry to remove insoluble fibers and impurities;

[0009] S3, beating the filtered slurry in a poor solvent, precipitating solids and drying them to obtain aramid pellets;

[0010] S4, placing the aramid pellets in an organic solvent containing a cosolvent, and mixing them evenly to obtain a spinning solution;

[0011] S5. Spinning is performed to obtain regenerated meta-aramid fibers.

[0012] Furthermore, in step S1, the organic solvent is at least one of methyl tert-butyl ether, tetrahydrofuran, dioxane, methyl isobutyl ketone trimethylpentane, dimethyl sulfoxide, N-methylpyrrolidone, N,N-dimethylacetamide, and a mixed solvent of benzene and acetone.

[0013] Furthermore, in step S1, the mass ratio of the aramid fabric, the co-solvent and the organic solvent is 1:(0.5-4):(20-90).

[0014] Furthermore, the specific operation of step S1 is: placing the dried aramid fabric fragments to be recycled in an organic solvent containing a co-solvent, immersing for 0.5 to 1 hour at room temperature and pressure, and then performing microwave digestion or sufficient stirring at 60 to 100° C. to obtain a slurry.

[0015] Furthermore, in step S1, when microwave digestion is used, the power of microwave radiation is 100-300W;

[0016] In step S1, when stirring treatment is used, the stirring speed is 50-200 rpm and the treatment time is 0.5-2 h.

[0017] Furthermore, in step S2, the slurry is subjected to three-stage filtration, the filtration pore size of the first-stage filtration is 50-100 mesh, the filtration pore size of the second-stage filtration is 100-300 mesh, and the filtration pore size of the third-stage filtration is ≥300 mesh; the mesh sizes of the first-stage filtration, the second-stage filtration, and the third-stage filtration are increased step by step.

[0018] Furthermore, in step S3, the poor solvent is a mixed solvent of the organic solvent and the second solvent in step S1, and in the poor solvent, the mass ratio of the organic solvent and the second solvent in step S1 is 1:(1-19);

[0019] The second solvent is at least one of water and ethylene glycol.

[0020] Furthermore, in step S4, the organic solvent is at least one of methyl tert-butyl ether, tetrahydrofuran, dioxane, methyl isobutyl ketone, trimethylpentane, dimethyl sulfoxide, N-methylpyrrolidone, N,N-dimethylacetamide, and a mixed solvent of benzene and acetone.

[0021] Furthermore, in step S4, the mass ratio of the aramid pellets, the cosolvent and the organic solvent is 1:(0.3-0.65):(4-5.6); the mixing temperature is 60-100° C., and the mixing time is 0.5-1 h.

[0022] Furthermore, the co-solvent is at least one of calcium chloride, zinc chloride, calcium bromide and lithium bromide.

[0023] The beneficial effects of the present invention are:

[0024] The recycling and reuse method of the aramid fabric of the present invention adopts a two-step dissolution process, reduces the difficulty of impurity removal and filtration in the aramid fabric, solves the technical difficulty that the aramid fiber is difficult to dissolve to a high solid content due to its high orientation degree, thereby affecting the subsequent spinning use, and the meta-aramid obtained by recycling does not produce yellowing, and its strength and temperature resistance are close to those of the original fiber, and will not affect the product performance of the regenerated aramid fiber, solves the environmental pollution problem caused by discarded aramid fabrics, and has a good application prospect.

[0025] The method for recycling and reusing aramid fabrics of the present invention adopts a method of swelling at room temperature and pressure and then microwave digestion in a closed environment to increase the processing efficiency of fabric recycling, reduce the cost of aramid recycling, and greatly reduce the problem of aramid yellowing and molecular weight reduction caused by oxidation of terminal amino groups, thereby affecting the quality of regenerated aramid yarn.

[0026] The method for recycling and reusing aramid fabrics of the present invention adopts a technical route of first dissolving with a low solid content and then filtering, then precipitating and then granulating, and finally dissolving with a high solid content and directly spinning. This solves the technical problem that aramid fabrics are difficult to dissolve into high-solid content spinning solution due to their high fiber orientation and regular structure after spinning and weaving, thus requiring high energy consumption or low recovery rate due to the need for reduced pressure distillation or filtering out a large amount of insoluble matter. This greatly improves the recovery rate of aramid fabrics and reduces energy consumption costs.

[0027] The recycling and reuse method of the aramid fabric of the present invention has a simple process flow, high recycling efficiency, is convenient for industrial application, and all the organic solvents used can be recycled without causing environmental pollution. The meta-aramid produced does not turn yellow, and the recycling process does not involve high temperature and high pressure, and the process route is mild, so that the meta-aramid does not degrade, ensuring that the regenerated aramid fiber has excellent performance. DETAILED DESCRIPTION

[0028] The specific implementation of the present invention is described in detail below. 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 connotation of the present invention, so the present invention is not limited by the specific embodiments disclosed.

[0029] 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.

[0030] A method for recycling aramid fabrics, characterized in that the recycling method comprises:

[0031] S1, placing the aramid fabric to be recycled in an organic solvent containing a co-solvent to obtain a slurry;

[0032] S2, filtering the slurry to remove insoluble fibers and impurities;

[0033] S3, beating the filtered slurry in a poor solvent, precipitating solids and drying them to obtain aramid pellets;

[0034] S4, placing the aramid pellets in an organic solvent containing a cosolvent, and redissolving them to obtain a spinning solution;

[0035] S5. Spinning is performed to obtain regenerated meta-aramid fibers.

[0036] More specifically, the aramid fabric to be recycled is broken into pieces and dried before the operation of step S1 is performed; wherein the area of ​​the pieces of aramid fabric is not larger than 2 cm 2 ; The drying method is vacuum oven drying, and the drying temperature is 50-90℃.

[0037] Specifically, in step S1, the organic solvent is at least one of methyl tert-butyl ether, tetrahydrofuran, dioxane, methyl isobutyl ketone trimethylpentane, dimethyl sulfoxide, N-methylpyrrolidone, N,N-dimethylacetamide, and a mixed solvent of benzene and acetone;

[0038] Wherein, when the organic solvent is a mixed solvent of benzene and acetone, the mass ratio of benzene to acetone is 9:1.

[0039] Specifically, in step S1, the mass ratio of the aramid fabric, the co-solvent and the organic solvent is 1:(0.5-4):(20-90).

[0040] Specifically, the specific operation of step S1 is: placing the dried aramid fabric fragments to be recycled in an organic solvent containing a co-solvent, immersing for 0.5 to 1 hour at room temperature and pressure, and then performing microwave digestion or sufficient stirring at 60 to 100° C. to obtain a slurry.

[0041] Specifically, in step S1, when microwave digestion is used, the power of microwave radiation is 100-300W;

[0042] In step S1, when stirring treatment is used, the stirring speed is 50-200 rpm and the treatment time is 0.5-2 h.

[0043] Specifically, in step S2, the slurry is subjected to three-stage filtration, the filtration aperture of the first-stage filtration is 50-100 mesh, the filtration aperture of the second-stage filtration is 100-300 mesh, and the filtration aperture of the third-stage filtration is ≥300 mesh; the mesh sizes of the first-stage filtration, the second-stage filtration, and the third-stage filtration are increased step by step.

[0044] Specifically, in step S3, the poor solvent is a mixed solvent of the organic solvent and the second solvent in step S1, and in the poor solvent, the mass ratio of the organic solvent and the second solvent in step S1 is 1:(1-19);

[0045] The second solvent is at least one of water and ethylene glycol.

[0046] More specifically, during pulping in step S3, the rotation speed of the pulping machine is 400~2000rpm.

[0047] More specifically, in step S3, the moisture content of the dried aramid pellets is less than 20 ppm.

[0048] Specifically, in step S4, the organic solvent is at least one of methyl tert-butyl ether, tetrahydrofuran, dioxane, methyl isobutyl ketone trimethylpentane, dimethyl sulfoxide, N-methylpyrrolidone, N,N-dimethylacetamide, and a mixed solvent of benzene and acetone;

[0049] Wherein, when the organic solvent is a mixed solvent of benzene and acetone, the mass ratio of benzene to acetone is 9:1.

[0050] Specifically, in step S4, the mass ratio of the aramid pellets, the cosolvent, and the organic solvent is 1:(0.3-0.65):(4-5.6); the mixing temperature is 60-100° C., and the mixing time is 0.5-1 h.

[0051] Specifically, the co-solvent is at least one of calcium chloride, zinc chloride, calcium bromide, and lithium bromide.

[0052] More specifically, in an embodiment of the present invention, wet spinning is used to prepare regenerated meta-aramid fiber, and the specific process method is: spinning the prepared regenerated meta-aramid stock solution in an aqueous solution made of the organic solvent described in step S4 with a mass concentration of 25%, the coagulation bath temperature is 10°C, and the heat treatment temperature is 350°C.

[0053] Example 1

[0054] Step (1): Disassemble and break the blended aramid fabric into 1 cm 2 The fragments were dried in a vacuum oven at 90°C for 1 h, and the dried aramid fabric was put into an N-methylpyrrolidone solution dissolved with zinc chloride, the mass ratio of the aramid fabric, zinc chloride and N-methylpyrrolidone being 1:4:90. After being immersed at room temperature and pressure for 1 h, the solution was heated to 60°C and treated with intermittent microwave radiation (300 W, 2450 MHz) for 0.5 h to obtain a slurry.

[0055] Step (2): filtering the slurry to remove insoluble viscose, polyester and other insoluble blended fibers to obtain an aramid solution, and filtering the slurry in three stages (first stage: 100 mesh, second stage: 300 mesh, third stage: 400 mesh).

[0056] Step (3): the aramid solution is beaten in a solution of N-methylpyrrolidone and water in a mass ratio of 1:1 to precipitate, the beater speed is set to 400 rpm, and the precipitated solid is dried and crushed to form aramid pellets.

[0057] Step (4): putting the prepared aramid pellets into an N-methylpyrrolidone solution dissolved with zinc chloride, wherein the mass ratio of the aramid pellets, zinc chloride and N-methylpyrrolidone is 1:0.3:4, and stirring at 60° C. for 0.5 hour to prepare a spinning solution.

[0058] Step (5): The spinning solution is spun into regenerated meta-aramid fiber.

[0059] Example 2

[0060] Step (1): Disassemble and break the blended aramid fabric into 2 cm pieces 2 The fragments were dried in a vacuum oven at 50°C for 2 h, and the dried aramid fabric was put into methyl tert-butyl ether dissolved with calcium chloride, the mass ratio of aramid fabric, calcium chloride and methyl tert-butyl ether being 1:4:20. After being immersed at room temperature and pressure for 0.5 h, the solution was heated to 100°C and treated with intermittent microwave radiation (100 W, 2450 MHz) for 0.5 h to obtain a slurry.

[0061] Step (2): filtering the slurry to remove insoluble viscose, polyester and other insoluble blended fibers to obtain an aramid solution, and filtering the slurry in three stages (first stage: 50 mesh, second stage: 100 mesh, third stage: 300 mesh).

[0062] Step (3): the aramid solution is beaten in a solution having a mass ratio of methyl tert-butyl ether to water of 1:19 to precipitate, the beater speed is set to 2000 rpm, and the precipitated solid is dried and crushed to form aramid pellets.

[0063] Step (4): adding the prepared aramid pellets into methyl tert-butyl ether dissolved with calcium chloride, wherein the mass ratio of the aramid pellets, calcium chloride and methyl tert-butyl ether is 1:0.35:4.5, and stirring at 100° C. for 1 hour to prepare a spinning solution.

[0064] Step (5): The spinning solution is spun into regenerated meta-aramid fiber.

[0065] Example 3

[0066] Step (1): Disassemble and break the blended aramid fabric into 0.5 cm 2 The fragments were dried in a vacuum oven at 70°C for 1.5 h, and the dried aramid fabric was placed in dimethyl sulfoxide dissolved with calcium bromide, the mass ratio of aramid fabric, calcium bromide and dimethyl sulfoxide being 1:0.5:90. After being immersed at room temperature and pressure for 1 h, the solution was heated to 90°C and stirred (at a stirring speed of 50 rpm) for 1 h to obtain a slurry.

[0067] Step (2): filtering the slurry to remove insoluble viscose, polyester and other insoluble blended fibers to obtain an aramid solution, and filtering the slurry in three stages (first stage: 100 mesh, second stage: 200 mesh, third stage: 400 mesh).

[0068] Step (3): The aramid solution is beaten in a solution of dimethyl sulfoxide and water in a ratio of 1:9 to precipitate, the beater speed is set to 800 rpm, and the precipitated solid is dried and crushed to form aramid pellets.

[0069] Step (4): putting the prepared aramid pellets into a dimethyl sulfoxide solution dissolved with calcium bromide, wherein the ratio of the aramid pellets, calcium bromide and dimethyl sulfoxide is 1:0.4:5, and stirring at 90° C. for 0.5 hour to prepare a spinning solution.

[0070] Step (5): The spinning solution is spun into regenerated meta-aramid fiber.

[0071] Example 4

[0072] Step (1): Disassemble and break the blended aramid fabric into 0.3 cm 2The fragments were dried in a vacuum oven at 80°C for 1.5 h, and the dried aramid fabric was placed in tetrahydrofuran dissolved with lithium bromide, the mass ratio of aramid fabric, lithium bromide and tetrahydrofuran being 1:3:90. After being immersed at room temperature and pressure for 1 h, the solution was heated to 75°C and stirred (at a stirring speed of 200 rpm) for 1 h to obtain a slurry.

[0073] Step (2): filtering the slurry to remove insoluble viscose, polyester and other insoluble blended fibers to obtain an aramid solution, and filtering the slurry in three stages (first stage: 100 mesh, second stage: 200 mesh, third stage: 400 mesh).

[0074] Step (3): the aramid solution is slurried in a solution of tetrahydrofuran and water in a ratio of 1:5, the beater speed is set to 500 rpm, and the precipitated solid is dried and crushed to form aramid pellets.

[0075] Step (4): putting the prepared aramid pellets into a tetrahydrofuran solution containing lithium bromide, wherein the mass ratio of the aramid pellets, lithium bromide and tetrahydrofuran is 1:0.65:5.6, and stirring at 80° C. for 0.5 hour to prepare a spinning solution.

[0076] Step (5): The spinning solution is spun into regenerated meta-aramid fiber.

[0077] Example 5

[0078] Step (1): Disassemble and break the blended aramid fabric into 1 cm 2 The fragments were dried in a vacuum oven at 60°C for 2 h, and the dried aramid fabric was put into N,N-dimethylacetamide dissolved with calcium bromide, the mass ratio of aramid fabric, calcium bromide and N,N-dimethylacetamide was 1:2:50. After impregnation at room temperature and pressure for 1.0 h, the solution was heated to 80°C and treated with intermittent microwave radiation (100 W, 2450 MHz) for 0.5 h to obtain a slurry.

[0079] Step (2): filtering the slurry to remove insoluble viscose, polyester and other insoluble blended fibers to obtain an aramid solution, and filtering the slurry in three stages (first stage: 100 mesh, second stage: 200 mesh, third stage: 300 mesh).

[0080] Step (3): the aramid solution is slurried in a solution in which the mass ratio of N,N-dimethylacetamide to ethylene glycol is 1:10, the beater speed is set to 2000 rpm, and the precipitated solid is dried and crushed to form aramid pellets.

[0081] Step (4): adding the prepared aramid pellets into N,N-dimethylacetamide dissolved with calcium bromide, wherein the mass ratio of the aramid pellets, calcium bromide and N,N-dimethylacetamide is 1:0.5:5.6, and stirring at 80° C. for 1 hour to prepare a spinning solution.

[0082] Step (5): The spinning solution is spun into regenerated meta-aramid fiber.

[0083] Comparative Example 1

[0084] The conventional one-time dissolution operation is adopted, and the specific process is as follows:

[0085] Step (1): Disassemble and break the blended aramid fabric into 0.1 cm 2 The fragments were dried in a vacuum oven at 50°C for 2 h, and the dried aramid fabric was placed in N-methylpyrrolidone dissolved with lithium bromide, the mass ratio of aramid fabric, lithium bromide and N-methylpyrrolidone was 1:1.5:6. After immersion at room temperature and pressure for 1 h, the solution was heated to 75°C and stirred (stirring speed was 200 rpm) for 1 h to obtain a slurry.

[0086] Step (2): filtering the slurry to remove insoluble viscose, polyester and other insoluble blended fibers to obtain an aramid solution, and filtering the slurry in three stages (first stage: 100 mesh, second stage: 200 mesh, third stage: 400 mesh).

[0087] Step (3): spinning the aramid solution.

[0088] In specific experiments, it was found that the aramid solution of Comparative Example 1 could not be spun into fiber because the solid content of the aramid solution was too low. However, if the amount of organic solvent used in step (1) was small, a large amount of aramid fabric could not be made into slurry, thereby affecting the recovery efficiency.

[0089] Comparative Example 2

[0090] The same method as in Example 1 is adopted to recycle the aramid fabric, except that: in step (3) of this comparative example 2, N-methylpyrrolidone is not added, and the aramid solution is directly pulped in water to precipitate solids.

[0091] Comparative Example 3

[0092] The same method as in Example 1 is adopted to recycle the aramid fabric, except that in step (3) of this comparative example 3, the mass ratio of N-methylpyrrolidone to water is 1:0.5 (the amount of water used is lower than the amount specified in the present invention).

[0093] Comparative Example 4

[0094] The same method as in Example 1 was adopted to recycle the aramid fabric, except that only one level of filtration was performed in step (2) of this comparative example 4, that is, only one 100-mesh filtration was performed directly.

[0095] Comparative Example 5

[0096] The same method as in Example 1 was adopted to recycle the aramid fabric, except that only one level of filtration was performed in step (2) of this comparative example 5, that is, only one 400-mesh filtration was performed directly.

[0097] The regenerated meta-aramid fibers prepared in the above examples and comparative examples were subjected to performance tests, and the specific test results are shown in Table 1. The test methods involved are as follows:

[0098] (1) Tensile strength and elongation at break

[0099] The tensile strength and elongation at break were tested using an INSTRON 34TM-30 electronic tensile testing machine, and the test standard referred to GB / T 14344 Test method for tensile properties of chemical fiber filaments.

[0100] (2) The color difference of the spun fibers was detected using an UltraScan Pro colorimeter to quantitatively characterize the color difference between the regenerated fibers and the original fibers.

[0101] (3) Thermal shrinkage

[0102] Measure the exact length of the sample (sample length greater than 15cm) and record it as L 0 Then put the sample into a weighing bottle and quickly put it into an oven heated to 300°C. When the oven temperature returns to 300°C, start recording the heat treatment time. After 15 minutes of treatment, take out the sample and balance it at room temperature for 15 minutes. Measure the sample length again and record it as L. 1 The calculation formula of thermal shrinkage is as follows, where S is the thermal shrinkage.

[0103] .

[0104] (4) Recovery rate

[0105] The recovery rate is calculated according to the following formula: the mass of the aramid fabric before recycling is weighed, the mass of the aramid fiber therein is calculated according to the blending ratio, and the mass of the recycled regenerated meta-aramid fiber or precipitate is dried and measured.

[0106] P = [(m 1 -m 2 ) / m 1 ]×100%;

[0107] Where: P—recovery rate (%);

[0108] m 1 —Mass of aramid before recycling (g);

[0109] m 2 —Mass of recycled aramid (g).

[0110] Table 1 Performance data of regenerated meta-aramid fibers in the examples and comparative examples

[0111]

[0112] It can be seen from the above table data that the recycling and reuse method of the aramid fabric of the present invention is adopted in Examples 1-5, which reduces the difficulty of impurity removal and filtration in the aramid fabric, solves the technical difficulty that the aramid fiber is difficult to dissolve to a high solid content due to its high orientation degree, thereby affecting the subsequent spinning use, and the meta-aramid obtained by recycling does not produce yellowing, and the strength, temperature resistance, etc. can meet the product use standards of meta-aramid fibers (the original meta-aramid fibers in the blended aramid fabrics used in the embodiments of the present invention have a tensile strength of >3.6 cN / dtex, an elongation at break of 25-40%, and a thermal shrinkage at 300°C of <2.5%; the regenerated meta-aramid fibers obtained in Examples 1-5 have a tensile strength of >3 cN / dtex, an elongation at break of more than 25%, and a thermal shrinkage at 300°C of <2.5%, all of which meet the product standards of meta-aramid fibers), and can achieve the reuse of regenerated aramid fibers, solve the environmental pollution problem caused by discarded aramid fabrics, and have good application prospects.

[0113] It can be seen from the experimental data and experimental process of Comparative Example 1 and Examples 1-5 that: if only one-step dissolution process is performed, a spinning solution with a high solid content cannot be obtained, and thus the spinning process cannot be carried out smoothly, and the recovery rate is reduced. This is because the fabric structure is relatively dense, and the fiber orientation and crystallinity are high during the spinning process, making it difficult to directly dissolve and recover. After dissolving to a high concentration, the high solution viscosity will cause great difficulty in filtering and removing impurities. Therefore, the two-step method for recycling aramid fabrics is more conducive to obtaining regenerated aramid fibers.

[0114] From the comparison of the data of Comparative Example 2 and Example 1, it can be seen that if no organic solvent is added in step (3) and the aramid solution is directly pulped in a poor solvent, the strength performance of the regenerated meta-aramid fiber will decrease and the recovery rate will be low. This is because the coagulation bath used for precipitation helps to regulate the microscopic morphology of the precipitated aramid particles. If the proportion of the poor solvent in the coagulation bath is high, the polymer will accumulate and form quickly after precipitation, and the molecular chain segments will tend to be densely stacked, which will cause great difficulty in the subsequent dissolution treatment.

[0115] From the comparison of the data of Comparative Example 3 and Example 1, it can be seen that if the proportion of water used in step (3) is too small, the precipitation speed of the aramid solution will be too slow, and even the surface layer will precipitate into a film but the inside will not be able to precipitate into a film, which will greatly affect the physical properties of the regenerated aramid fiber and reduce the recovery efficiency.

[0116] From the comparison of the data of Comparative Example 4 and Example 1, it can be seen that if only one 100-mesh filtration is performed, a large amount of insoluble fibers and impurities cannot be separated and removed, which affects the final spinning to prepare regenerated fibers.

[0117] From the data comparison of Comparative Example 5 and Example 1, it can be seen that if only one 400-mesh filtration is performed, the filter residue will quickly clog the filter, resulting in excessive filter resistance, and the subsequent solution cannot be filtered, affecting the continuity of the entire recovery process.

[0118] The technical features of the above-described embodiments may be arbitrarily combined. 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.

[0119] For those skilled in the art, several modifications and improvements may be made without departing from the concept of the present invention, all of which belong to the protection scope of the present invention. The protection scope of the present invention shall be based on the attached claims.

Claims

1. A method for recycling aramid fabrics, characterized in that: The recycling method is as follows: S1, placing the aramid fabric to be recycled in an organic solvent containing a co-solvent to obtain a slurry; S2, filtering the slurry to remove insoluble fibers and impurities; S3, beating the filtered slurry in a poor solvent, precipitating solids and drying them to obtain aramid pellets; S4, placing the aramid pellets in an organic solvent containing a cosolvent, and redissolving them to obtain a spinning solution; S5, spinning to obtain regenerated meta-aramid fiber; In step S1, the organic solvent is at least one of methyl tert-butyl ether, tetrahydrofuran, dioxane, methyl isobutyl ketone trimethylpentane, dimethyl sulfoxide, N-methylpyrrolidone, N,N-dimethylacetamide, and a mixed solvent of benzene and acetone; The specific operation of step S1 is: placing the dried aramid fabric fragments to be recycled in an organic solvent containing a co-solvent, immersing for 0.5 to 1 hour at room temperature and pressure, and then performing microwave digestion or sufficient stirring at 60 to 100° C. to obtain a slurry; In step S2, the slurry is subjected to three-stage filtration, the filtration aperture of the first-stage filtration is 50-100 mesh, the filtration aperture of the second-stage filtration is 100-300 mesh, and the filtration aperture of the third-stage filtration is ≥300 mesh; the mesh numbers of the first-stage filtration, the second-stage filtration, and the third-stage filtration are increased step by step; In step S3, the poor solvent is a mixed solvent of the organic solvent and the second solvent in step S1, wherein the mass ratio of the organic solvent and the second solvent in step S1 is 1:(1-19); the second solvent is at least one of water and ethylene glycol; In step S4, the organic solvent is at least one of methyl tert-butyl ether, tetrahydrofuran, dioxane, methyl isobutyl ketone trimethylpentane, dimethyl sulfoxide, N-methylpyrrolidone, N,N-dimethylacetamide, and a mixed solvent of benzene and acetone; The co-solvent is at least one of calcium chloride, zinc chloride, calcium bromide and lithium bromide.

2. The method for recycling aramid fabric according to claim 1, characterized in that: In step S1, the mass ratio of the aramid fabric, the co-solvent and the organic solvent is 1:(0.5-4):(20-90).

3. The method for recycling aramid fabric according to claim 1, characterized in that: In step S1, when microwave digestion is used, the power of microwave radiation is 100-300W; In step S1, when stirring treatment is used, the stirring speed is 50-200 rpm and the treatment time is 0.5-2 h.

4. The method for recycling aramid fabric according to claim 1, characterized in that: In step S4, the mass ratio of the aramid pellets, the cosolvent and the organic solvent is 1:(0.3-0.65):(4-5.6); the mixing temperature is 60-100° C., and the mixing time is 0.5-1 h.

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