Carbon nanotube modified aramid Ⅲ fiber and preparation method thereof

Abstract

The application discloses carbon nanotube modified aramid fiber III, wherein the carbon nanotube modified aramid fiber III contains carbon nanotubes with a tube length less than 200 nm. The application is directed to the high aspect ratio characteristics of carbon nanotubes and the agglomeration phenomenon such as easy aggregation and winding of the carbon nanotubes. The carbon nanotubes are subjected to shortening treatment to improve the dispersibility of the carbon nanotubes in a polymerization system, thereby improving the uniformity of the dispersion of the carbon nanotubes in the modified fiber. Furthermore, the carbon nanotubes after the shortening treatment are subjected to functionalization treatment to further improve the dispersibility of the carbon nanotubes in the polymerization system. The functionalized carbon nanotubes are added to the modified aramid fiber III through in-situ polymerization, and the covalent combination of the carbon nanotubes and aramid III polymer molecules can be realized, so that the performance of the carbon nanotube modified aramid fiber III is improved by using the effective dispersion and chemical bond connection of the carbon nanotube material.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of aramid, in particular to carbon nanotube modified aramid III fiber and a preparation method thereof. BACKGROUND

[0002] Aromatic polymer fiber belongs to high-strength and high-modulus organic fiber, mainly including aramid fiber and polyimide fiber, etc. Aramid III is a modified aramid, which has a heterocyclic structure in the molecular chain, and is also called heterocyclic aramid. Heterocyclic aramid has more excellent mechanical properties than para-aramid (aramid 1414). It has excellent properties such as light weight, high strength, wave transmission, corrosion resistance, radiation resistance, high and low temperature resistance, high flame resistance, and high flexibility, and is a core basic material in high-end industries such as aerospace, ships, automobile industry, bulletproof products, cables, infrastructure and IT industry, and a strategic material for national security, which has broad market prospects and practical needs in both military and civilian markets. However, its mechanical properties are still inferior to those of poly-p-phenylene benzobisoxazole fiber (PBO fiber) and carbon fiber, and it lacks functional properties such as electrical conductivity and thermal conductivity in actual application, which limits its application in special demand fields. Therefore, in order to further improve the mechanical properties of aromatic polymer fiber and give aramid III fiber more functionality, it needs to be modified, so as to ultimately optimize the comprehensive performance of aramid III.

[0003] Carbon nanotube is a one-dimensional nanocarbon material with sp 2 hybrid structure, which has ultra-high specific surface area, excellent mechanical properties, electrical conductivity and thermal conductivity. The composite of carbon nanotube material and aromatic polymer material can effectively modify the mechanical, thermal and electrical properties of the latter. However, as the aramid III fiber has more excellent comprehensive performance, its polymerization and spinning process mainly involves organic solvent system, and ordinary blending method is difficult to realize the effective dispersion of carbon nanotube, and the dispersion of carbon nanotube in the aramid III polymerization liquid matrix seriously affects the spinnability and comprehensive mechanical properties of the subsequent fiber. How to improve the dispersion of carbon nanotube in the aramid III polymerization and spinning organic solvent system becomes a problem to be solved. SUMMARY

[0004] The present application aims to provide a carbon nanotube in-situ modified aramid III fiber and a preparation method thereof.

[0005] In one aspect, the present application provides a carbon nanotube modified aramid III fiber, which contains carbon nanotubes with a tube length of less than 200 nm.

[0006] According to an embodiment of the present application, the carbon nanotube is connected to the aramid III polymer by covalent bond.

[0007] According to another embodiment of the present application, the covalent bond is an amide bond and / or a carboxyl bond.

[0008] According to another embodiment of the present application, the diameter of the carbon nanotube is less than 30 nm.

[0009] According to another embodiment of the present application, the mass of the carbon nanotube in the fiber accounts for 0.1-3% of the mass of the aramid III matrix.

[0010] According to another embodiment of the present application, the breaking strength of the modified fiber is 32-36 cN / dtex, the elastic modulus is 800-1000 cN / dtex, and the breaking elongation is 3.5-5%.

[0011] Another aspect of the present application provides a preparation method of the above carbon nanotube modified aramid III fiber, comprising: S1, performing a short-cut treatment on the carbon nanotube to obtain a carbon nanotube with a predetermined size; S2, performing a functionalization on the carbon nanotube after the S1 step to graft a functional group on the carbon nanotube; S3, dispersing the functionalized carbon nanotube in N,N-dimethylacetamide to form a dispersion liquid; S4, adding the dispersion liquid into an N,N-dimethylacetamide solution of a monomer forming aramid III and performing a polymerization reaction to obtain a polymerization liquid; and S5, performing a spinning on the polymerization liquid to obtain the carbon nanotube modified aramid III fiber.

[0012] According to an embodiment of the present application, the functional group comprises an amino group.

[0013] According to another embodiment of the present application, the functional group is grafted onto the carbon nanotube by reacting a diamine type substance with an oxygen-containing functional group on the carbon nanotube, and the diamine type substance is selected from one or more of ethylenediamine, 1,3-propanediamine, 1,4-butanediamine and 1,6-hexanediamine.

[0014] According to another embodiment of the present application, the viscosity of the polymerization liquid is 300-1200 centipoise.

[0015] The present application is directed to the high aspect ratio characteristics of the carbon nanotube itself, and its easy aggregation, entanglement and other aggregation phenomena, performs a short-cut treatment on the carbon nanotube, improves the dispersibility of the carbon nanotube in the polymerization system, thereby improving the uniformity of the dispersion of the carbon nanotube in the modified fiber. Furthermore, performs a functionalization treatment on the short-cut carbon nanotube, further improves the dispersibility of the carbon nanotube in the polymerization system, and the functionalized carbon nanotube is added into the modified fiber through in-situ polymerization, which can realize the covalent combination of the carbon nanotube and the aramid III polymer molecule, thereby realizing the performance improvement of the carbon nanotube modified aramid III fiber by using the effective dispersion and chemical bond connection of the carbon nanotube material. BRIEF DESCRIPTION OF DRAWINGS

[0016] Figure 1is a laser particle size test chart of the carbon nanotube dispersion solution after shortening in Example 1.

[0017] Figure 2 is a length contrast scanning electron microscope chart of the carbon nanotubes before (left) and after (right) ultrasonic shortening treatment in Example 1.

[0018] Figure 3 is a scanning electron microscope contrast chart of the original carbon nanotube modified fiber (left) and the short carbon nanotube modified fiber (right). DETAILED DESCRIPTION

[0019] The technical solutions of the present application will be described in detail below in combination with the drawings and examples. However, the description of the examples is only a part of the examples of the present application, and is not limited to this.

[0020] The carbon nanotube modified aramid III fiber of the present application contains carbon nanotubes with a tube length of less than 200 nm. By shortening the carbon nanotubes with a high aspect ratio, the present application avoids the defects of poor dispersibility in solvents caused by the aggregation, entanglement and other agglomeration phenomena of carbon nanotubes with a high aspect ratio. After shortening, the dispersibility of carbon nanotubes in the polymerization system can be improved, thereby significantly improving the mechanical properties of the carbon nanotube modified aramid III fiber formed.

[0021] In an optional embodiment, the carbon nanotubes are connected to the aramid III polymer by covalent bonds. By functionalizing the shortened carbon nanotubes, the functionalized carbon nanotube dispersion liquid is added to the polymerization system during the polymerization reaction of aramid III, and the functionalized carbon nanotubes are in-situ polymerized with the monomers forming aramid III, thereby being connected to the aramid III polymer molecules by covalent bonds, further improving the performance of the modified aramid III fiber. The covalent bond is an amide bond and / or a carboxyl bond. Since the carbon nanotubes are connected to the aramid III by covalent bonds, the viscosity of the polymerization liquid will decrease slightly. Since the content of the added carbon nanotubes directly affects the viscosity of the polymerization liquid, the spinning process of the subsequent carbon nanotube modified aramid III fiber polymerization liquid needs to be adjusted during the spinning process. The skilled person modifies the spinning process parameters according to the specific viscosity of the spinning liquid.

[0022] In an optional embodiment, the diameter of the carbon nanotubes is less than 30 nm.

[0023] In an optional embodiment, the mass of the carbon nanotubes in the fiber accounts for 0.1-3% of the mass of the aramid III matrix.

[0024] In an optional embodiment, the breaking strength of the modified fiber is 32-36 cN / dtex, the elastic modulus is 800-1000 cN / dtex, and the breaking elongation is 3.5-5%.

[0025] The carbon nanotube modified aramid III fiber can be prepared by the following method. It comprises: S1, shortening the carbon nanotube to obtain a carbon nanotube of a predetermined size; S2, functionalizing the carbon nanotube after S1 to graft a functional group on the carbon nanotube; S3, dispersing the functionalized carbon nanotube in N,N-dimethylacetamide to form a dispersion liquid; S4, adding the dispersion liquid to an N,N-dimethylacetamide solution of a monomer forming aramid III and performing a polymerization reaction to obtain a polymerization liquid; and S5, spinning the polymerization liquid to obtain a carbon nanotube modified aramid III fiber.

[0026] In the S1 step, the carbon nanotube is shortened. The shortening method can be any method that can form a carbon nanotube of a predetermined size. The addition of the shortening process is intended to improve the uniform dispersion of the carbon nanotube in the spinning liquid and the subsequent production stability. For example, it can be, but is not limited to, the following method.

[0027] First, the carbon nanotube is subjected to acid treatment to form multiple defects on the tube wall and the port. The acid treatment can be a method of acidizing the carbon nanotube material in a concentrated acid solution by heating reflux and magnetic stirring. Other acid treatment methods can be used. The carbon nanotube can be a multi-walled carbon nanotube with a diameter of <30 nm and a length of 0.5-30 μm, and the average wall number of the multi-walled carbon nanotube is 2-6. The concentrated acid can be one or more of concentrated sulfuric acid, concentrated nitric acid, and concentrated hydrochloric acid. The heating temperature is 70-90°C, the stirring reflux time is 2-8 h, and the stirring speed is controlled at 800-1000 r / min. After sufficient stirring and mixing, the multi-walled carbon nanotube surface is activated, and multiple defects are formed on the tube wall and the port.

[0028] Next, the carbon nanotube is subjected to shortening treatment. The multi-walled carbon nanotube concentrated acid solution obtained by the above step is subjected to centrifugation and water washing treatment to obtain a multi-walled carbon nanotube water dispersion liquid with a concentration of 1 wt%-3 wt%, and then one of a cell crushing ultrasonic instrument, a nano sand mill, or a high-pressure homogenizer is used to shorten the multi-walled carbon nanotube. The power of the cell crushing ultrasonic instrument is 800-1500 W, the rotation speed of the nano sand mill is adjusted to 600-1800 r / min, and the working pressure of the high-pressure homogenizer is adjusted to 800-1500 Bar. The shortening time is 1-5 h. The length of the carbon nanotube after shortening is less than 200 nm.

[0029] In the S2 step, the short-cut carbon nanotubes are functionalized to graft functional groups on the carbon nanotubes. The functional groups grafted on the carbon nanotubes are used to improve the dispersibility of the carbon nanotubes in the solvent required for the preparation of aramid III, that is, to improve the dispersibility of the carbon nanotubes in the polymerization system, and the functional groups can react with the monomers to form aramid III, so that the performance of the carbon nanotube modified aramid III fiber is improved due to the high dispersibility and chemical bond connection. The functional groups can include amino groups. The specific grafting process can be, but is not limited to, adding an excess of a diamine substance to the short-cut carbon nanotube aqueous solution obtained in the S1 step, refluxing at 90-120°C for 6-24h, cooling, dialysis, and removing excess amine substances and other impurity ions, etc., followed by drying treatment to obtain amino-functionalized short-cut carbon nanotube powder. The diamine substance can be one or more of ethylenediamine, 1,3-propanediamine, 1,4-butanediamine, and 1,6-hexanediamine.

[0030] In the S3 step, the functionalized carbon nanotubes are dispersed in N,N-dimethylacetamide (DMAc) to form a dispersion liquid. The dispersion process can use a high-power ultrasonic device to disperse the carbon material under inert gas protection, with a dispersion concentration of 0.1-5wt%, an ultrasonic power of 300-600W, and an ultrasonic time of 1-5h. The inert gas can be one or more of nitrogen, argon, helium, and carbon dioxide.

[0031] In the S4 step, the dispersion liquid is added to an N,N-dimethylacetamide solution of aramid III-forming monomers, and a polymerization reaction is performed to obtain a polymerization liquid. The N,N-dimethylacetamide solution of aramid III-forming monomers can be prepared from p-phthaloyl chloride, p-phenylenediamine, and 5(6)-amino-2-(p-aminophenyl)benzimidazole monomers, with a molar ratio of p-phthaloyl chloride, p-phenylenediamine, and benzimidazole monomers being 1:0.7-0.3:0.3-0.7, and lithium chloride as a cosolvent, and the aramid III resin solution is synthesized by polycondensation in a polymerization reactor. The carbon nanotube dispersion liquid is added to the polymerization system in 3-5 portions during the monomer dissolution stage. The final aramid III resin solution has a specific viscosity of 3-120,000 centipoise.

[0032] Due to the good dispersibility of the short-cut carbon nanotubes, the viscosity gradually increases as the polymerization process proceeds, and the carbon nanotubes can form a uniform polymerization liquid with a covalent bond connection with the aramid matrix.

[0033] Finally, in S5, the polymerization liquid (aramid III resin solution) is spun to obtain carbon nanotube modified aramid III fiber. Specifically, but not limited to, the polymerization liquid obtained in S4 is poured into a spinning host, and spinning is performed under a certain pressure. The extruded yarn is coagulated in a coagulation bath and then coagulated again in a hot water tank. After water washing at 60-80°C and drying at 100-120°C, the carbon nanotube modified aramid III fiber is obtained by heat stretching at 350-400°C and finally winding.

[0034] The present application is further described by specific examples below. However, these examples are merely exemplary and do not constitute any limitation on the scope of protection of the present application.

[0035] In the following examples and comparative examples, the reagents, materials and instruments used are commercially available unless otherwise specified.

[0036] Example 1

[0037] First, the multi-walled carbon nanotubes (tube diameter 5-30 nm, tube length 0.5-20 μm) are heated to 90°C in concentrated nitric acid and stirred for 6 h under reflux. Then, centrifugation and washing are performed to obtain a 3 wt% acidified carbon nanotube aqueous dispersion.

[0038] The carbon nanotube aqueous dispersion is placed in a cell crushing ultrasonic instrument for shortening treatment. The ultrasonic power is adjusted to 1000 W, and the ultrasonic time is 3 h. The obtained sample is tested and analyzed by a laser particle size instrument. The test results are shown in Figure 1 The carbon nanotube particle size distribution is less than 200 nm, and D90 is 150 nm. At the same time, the test and analysis by a scanning electron microscope are shown in Figure 2 The length of the carbon nanotubes is observed to be less than 200 nm, which meets the expected effect of shortening treatment. In the above carbon nanotube aqueous dispersion, an excess of ethylenediamine is added at a mass ratio of 1:3.5, and refluxed at 90°C for 6 h. After sufficient cooling and dialysis, the excess ethylenediamine residue is removed, and freeze-drying treatment is performed to obtain amino-functionalized short carbon nanotube powder.

[0039] The short-cut carbon nanotube powder is dispersed in DMAc solvent under anhydrous condition, and a carbon nanotube DMAc dispersion liquid with a concentration of 3wt% is obtained under ultrasonic dispersion. In the polymerization process of aramid III, the above dispersion liquid is added in three times during the dissolving stage of p-phenylenediamine and 5(6)-amino-2-(p-aminophenyl) benzimidazole monomer, the mass proportion of carbon nanotube in aramid III matrix is 0.1%, and low-temperature polymerization is carried out after the addition of carbon nanotube dispersion liquid is completed. An appropriate amount of terephthaloyl chloride is added, the viscosity of the polymerization liquid is adjusted to 50,000 centipoises, and the in-situ polymerization reaction is ended.

[0040] The composite polymerization liquid is added to the spinning host, the circulating water temperature of the host is adjusted to 40°C for defoaming treatment, and the polymerization liquid is leveled after defoaming treatment. The conventional spinning, primary coagulation bath, secondary coagulation bath, washing and drying are carried out. The nascent yarn is heat stretched at 400°C for 30s. Then the yarn is wound into a silk, and the silk is carbon nanotube modified aramid III fiber, the breaking strength of which is 35.67 cN / dtex, the elastic modulus is 958.81 cN / dtex, and the breaking elongation is 4.71%.

[0041] Example 2

[0042] First, the multi-walled carbon nanotubes (tube diameter 5-30 nm, tube length 0.5-20 μm) are heated to 80°C in a mixture of concentrated nitric acid and concentrated sulfuric acid (volume ratio 2:1) and stirred for 4 h. Then, centrifugation and washing are carried out to obtain a 3wt% acidified carbon nanotube water dispersion liquid.

[0043] The carbon nanotube water dispersion liquid is placed in a cell crushing ultrasonic instrument for short-cut treatment, and the ultrasonic power is adjusted to 1000W and the ultrasonic time is 3h. The obtained sample is tested by a laser particle size instrument, and it is found that the particle size of the obtained carbon nanotube is less than 400nm, and the D90 is 250nm. In the above carbon nanotube water dispersion liquid, an excess of 1,3-propanediamine is added in a mass ratio of 1:2.5, and refluxed at 90°C for 6h, and then cooled and dialyzed. After removing the excess 1,3-propanediamine residue, freeze-drying treatment is carried out to obtain amino-functionalized short-cut carbon nanotube powder.

[0044] The short-cut carbon nanotube powder is dispersed in DMAc solvent under anhydrous condition, and a carbon nanotube DMAc dispersion liquid with a concentration of 3wt% is obtained under ultrasonic dispersion. In the polymerization process of aramid III, the above dispersion liquid is added in three times during the dissolving stage of p-phenylenediamine and 5(6)-amino-2-(p-aminophenyl) benzimidazole monomer, the mass proportion of carbon nanotube in aramid III matrix is 0.1%, and low-temperature polymerization is carried out after the addition of carbon nanotube dispersion liquid is completed. An appropriate amount of terephthaloyl chloride is added, the viscosity of the polymerization liquid is adjusted to 50,000 centipoises, and the in-situ polymerization reaction is ended.

[0045] The composite polymerization solution is added to the spinning host, the circulating water temperature of the host is adjusted to 40°C for defoaming treatment, and after the polymerization solution is leveled, the conventional spinning, primary coagulation bath, secondary coagulation bath, washing, and drying are performed. The nascent yarn is heat stretched at 380°C for 30s. Then the yarn is wound into a fiber, which is a carbon nanotube modified aramid III fiber, the breaking strength of which is 33.62 cN / dtex, the elastic modulus is 839.52 cN / dtex, and the breaking elongation is 3.85%.

[0046] Example 3

[0047] First, the multi-walled carbon nanotubes (tube diameter 5-30 nm, tube length 0.5-20 μm) are heated to 70°C in a mixed solution of concentrated hydrochloric acid and concentrated nitric acid (volume ratio 3:1) and stirred for 3h, and then centrifuged and washed to obtain an acidified carbon nanotube water dispersion solution with a concentration of 2wt%.

[0048] The carbon nanotube water dispersion solution is placed in a horizontal nanometer sand mill for shortening treatment, the rotating speed is adjusted to 1500r / min, the dispersion time is 2h, and the dispersion temperature is 40°C. The obtained sample is tested by a laser particle size analyzer, and the carbon nanotube particle size is less than 5μm, and the D90 is 2.8μm. Excess ethylenediamine is added to the above-mentioned carbon nanotube water dispersion solution at a mass ratio of 1:3, and refluxed at 90°C for 8h, and then cooled and dialyzed. After removing the excess ethylenediamine, freeze-drying treatment is performed to obtain amino-functionalized short carbon nanotube powder.

[0049] The short carbon nanotube powder is dispersed in DMAc solvent under anhydrous conditions, and a 3wt% carbon nanotube DMAc dispersion solution is obtained under ultrasonic dispersion. In the aramid III polymerization process, the above-mentioned dispersion solution is added in three times during the dissolution stage of p-phenylenediamine and 5(6)-amino-2-(p-aminophenyl) benzimidazole monomer, and the mass ratio of carbon nanotubes in the aramid III matrix is 0.75%. After the addition of the carbon nanotube dispersion solution is completed, low-temperature polymerization is performed, and an appropriate amount of terephthaloyl chloride is added, and the viscosity of the polymerization solution is adjusted to 70,000 centipoise, and the in-situ polymerization reaction is completed.

[0050] The composite polymerization solution is added to the spinning host, the circulating water temperature of the host is adjusted to 40°C for defoaming treatment, and after the polymerization solution is leveled, the conventional spinning, primary coagulation bath, secondary coagulation bath, washing, and drying are performed. The nascent yarn is heat stretched at 395°C for 30s. Then the yarn is wound into a fiber, which is a carbon nanotube modified aramid III fiber, the breaking strength of which is 34.22 cN / dtex, the elastic modulus is 879.85 cN / dtex, and the breaking elongation is 3.95%.

[0051] Example 4

[0052] Firstly, multi-walled carbon nanotubes (tube diameter 5-30 nm, tube length 0.5-20 μm) were heated to 90°C in concentrated nitric acid and stirred for reflux for 6 h, followed by centrifugation, washing, to obtain a 3 wt% acidified carbon nanotube aqueous dispersion.

[0053] The carbon nanotube aqueous dispersion was placed in a cell crushing ultrasonic instrument for shortening treatment, the ultrasonic power was adjusted to 1000 W, and the ultrasonic time was 3 h. The obtained sample was tested by a laser particle size analyzer, and the carbon nanotube particle size was less than 200 nm, and the D90 was 150 nm. Excess ethylenediamine was added to the above carbon nanotube aqueous dispersion at a mass ratio of 1:3.5, and reflux treatment was carried out at 90°C for 6 h, and sufficient cooling and dialysis were carried out. After removing the excess ethylenediamine residue, freeze-drying treatment was carried out, to obtain amino-modified short carbon nanotube powder.

[0054] The short carbon nanotube powder was dispersed in DMAc solvent under anhydrous conditions, and a 3 wt% carbon nanotube DMAc dispersion was obtained under ultrasonic dispersion. In the polymerization process of aramid III, the above dispersion was added in three times during the dissolution stage of p-phenylenediamine and 5(6)-amino-2-(p-aminophenyl) benzimidazole monomers. The mass ratio of carbon nanotubes in aramid III matrix was 3%, and after the addition of carbon nanotube dispersion was completed, low-temperature polymerization was carried out, and an appropriate amount of terephthaloyl chloride was added, the viscosity of the polymerization solution was adjusted to 50,000 centipoise, and the in-situ polymerization reaction was completed.

[0055] The composite polymerization solution was added to the spinning host, the circulating water temperature of the host was adjusted to 40°C for defoaming treatment, and after the polymerization solution was flat, conventional spinning, primary coagulation bath, secondary coagulation bath, washing, and drying were carried out. The nascent yarn was heat stretched at 400°C for 30 s. Then the yarn was wound into a silk, and the silk was carbon nanotube modified aramid III fiber, the breaking strength was 32.14 cN / dtex, the elastic modulus was 821.33 cN / dtex, and the breaking elongation was 3.98%.

[0056] Comparative Example 1

[0057] The carbon nanotube powder (tube diameter 5-30 nm, tube length 0.5-20 μm) was dispersed in DMAc solvent under anhydrous conditions, and a 1 wt% carbon nanotube DMAc dispersion was obtained under ultrasonic dispersion. The carbon nanotube particle size D90 was 5 μm obtained by particle size analysis. In the polymerization process of aramid III, the above dispersion was added in three times during the dissolution stage of p-phenylenediamine and 5(6)-amino-2-(p-aminophenyl) benzimidazole monomers. The mass ratio of carbon nanotubes in aramid III matrix was 0.1%, and after the addition of carbon nanotube dispersion was completed, low-temperature polymerization was carried out, and an appropriate amount of terephthaloyl chloride was added, the viscosity of the polymerization solution was adjusted to 40,000 centipoise, and the in-situ polymerization reaction was completed.

[0058] The composite polymer solution is added to the spinning host machine, the circulating water temperature of the host machine is adjusted to 40°C for defoaming treatment, and after the polymer solution is flat, the conventional spinning, primary coagulation bath, secondary coagulation bath, washing, and drying are carried out. The nascent yarn is heat stretched at 400°C for 30s. Then it is wound into yarn. The yarn is carbon nanotube modified aramid fiber III. Since the short carbon nanotubes are not dispersed, the yarn is prone to breakage during spinning. The obtained fiber has a breaking strength of 27.64 cN / dtex, an elastic modulus of 769.62 cN / dtex, and an elongation at break of 2.85%. The obtained composite fiber is characterized by scanning electron microscopy, as shown in Figure 3 The prepared fiber has poor surface uniformity, resulting in decreased mechanical properties and spinnability.

[0059] Comparative Example 2

[0060] First, the multi-walled carbon nanotubes (tube diameter 5-30 nm, tube length 0.5-20 μm) are heated to 70°C in a mixture of concentrated hydrochloric acid and concentrated nitric acid (volume ratio 3:1) and stirred for 3h. Then centrifugation and washing are carried out to obtain a 2wt% acidified carbon nanotube water dispersion.

[0061] The carbon nanotube water dispersion is placed in a horizontal nanometer sand mill for shortening treatment. The rotation speed is adjusted to 1500r / min, the dispersion time is 2h, and the dispersion temperature is 40°C. The obtained sample is tested by laser particle size instrument. The carbon nanotube particle size is less than 5μm, and the D90 is 2.8μm. Excess ethylenediamine is added to the above carbon nanotube water dispersion at a mass ratio of 1:3, and refluxed at 90°C for 8h, and cooled and dialyzed. After removing the excess ethylenediamine, freeze-drying treatment is carried out to obtain amino-functionalized short carbon nanotube powder.

[0062] The short carbon nanotube powder is dispersed in DMAc solvent under anhydrous conditions, and a 3wt% carbon nanotube DMAc dispersion is obtained under ultrasonic dispersion. After the aramid III polymerization is completed, the above dispersion is added to the polymer solution and stirred for 1h. The mass fraction of carbon nanotubes in the aramid III matrix is 0.75%. The viscosity of the polymer solution is adjusted to 40,000 centipoise by adding solvent to obtain a physical blending composite polymer solution.

[0063] The composite polymerization solution is added to a spinning host machine, the circulating water temperature of the host machine is adjusted to 40℃ for defoaming treatment, and after the polymerization solution is leveled, conventional spinning, primary coagulation bath, secondary coagulation bath, washing, and drying are performed. The nascent yarn is heat-drawn at 395℃ for 30s. Subsequently, the yarn is wound into a silk, and the silk is carbon nanotube modified aramid fiber III, the breaking strength of which is 29.31 cN / dtex, the elastic modulus is 812.74 cN / dtex, and the breaking elongation is 3.45%. Since the carbon nanotube dispersion liquid is added after polymerization and does not form covalent connection with the aramid matrix, the mechanical property is not obviously improved compared with the original aramid.

[0064] The parameters and the properties of the fibers of Examples 1-4 and Comparative Examples 1-2 are shown in Table 1.

[0065] Table 1

[0066]

[0067]

[0068] As can be seen from Table 1, it can be seen from Comparative Examples 1-4 and Comparative Example 1 that the carbon nanotubes not subjected to short-cutting treatment added to aramid III through in-situ polymerization process do not have as good effect on enhancing the performance of aramid III as the carbon nanotubes subjected to short-cutting treatment, and the breaking strength, elastic modulus, and breaking elongation are all reduced, indicating that the carbon nanotubes subjected to short-cutting treatment have obvious effect on enhancing aramid III fiber; it can be seen from Comparative Examples 1-4 and Comparative Example 2 that the carbon nanotubes do not covalently connect with the aramid matrix, which will result in that the mechanical property is not obviously improved; it can be seen from Comparative Examples 1 and 4 that with the increase of the content of carbon nanotubes, the strength of aramid III fiber is reduced, and the content of short-cut carbon nanotubes should not be too much for enhancing aramid III fiber.

[0069] The preferred embodiments of the application disclosed above are only used to help explain the application. The preferred embodiments do not describe all the details, and the application is not limited to the specific embodiments described. Obviously, many modifications and changes can be made according to the content of the specification. The specification selects and specifically describes these embodiments in order to better explain the principles and practical applications of the application, so that those skilled in the art can well understand and utilize the application. The application is limited only by the claims and their full scope and equivalents.

Claims

1. A method for preparing carbon nanotube-modified aramid III fibers, characterized in that, include: S1, carbon nanotubes are chopped to obtain carbon nanotubes of a predetermined size; S2, Functionalize the carbon nanotubes after step S1 by grafting amino-containing functional groups onto the carbon nanotubes. S3, functionalized carbon nanotubes are dispersed in N,N-dimethylacetamide to form a dispersion; S4, the dispersion is added to an N,N-dimethylacetamide solution containing the monomer that forms aramid III, and a polymerization reaction is carried out to obtain a polymer solution; S5, the polymerization liquid is spun to obtain carbon nanotube modified aramid III fiber; The carbon nanotube-modified aramid III fiber contains carbon nanotubes with a length of less than 200 nm and a diameter of less than 30 nm. The carbon nanotubes are covalently connected to the aramid III polymer. The carbon nanotube-modified aramid III fiber has a breaking elongation of 3.85~5%.

2. The preparation method according to claim 1, characterized in that, The functional groups are grafted onto the carbon nanotubes via a reaction between diamines and oxygen-containing functional groups on the carbon nanotubes. The diamines are selected from one or more of ethylenediamine, 1,3-propanediamine, 1,4-butanediamine, and 1,6-hexanediamine.

3. The preparation method according to claim 1, characterized in that, The covalent bond is an amide bond.

4. The preparation method according to claim 1, characterized in that, The viscosity of the polymerization liquid is 30,000 to 120,000 centipoise.

5. A carbon nanotube-modified aramid III fiber, characterized in that, Prepared by the preparation method according to any one of claims 1-4.

6. The carbon nanotube-modified aramid III fiber according to claim 5, characterized in that, The modified fiber has a tensile strength of 32~36 cN / dtex and an elastic modulus of 800~1000 cN / dtex.

Images