Carbon fiber and preparation method thereof

Abstract

The present invention discloses a carbon fiber and a preparation method thereof, the method comprising: (1) subjecting polyacrylonitrile copolymer fiber to a tension-controlled preoxidation treatment in an air atmosphere to obtain a preoxidized fiber having an oxygen content of 6-9wt%; (2) subjecting the preoxidized fiber to a tension-controlled low-temperature carbonization treatment in a nitrogen atmosphere to obtain a low-temperature carbonized fiber; (3) subjecting the low-temperature carbonized fiber to a tension-controlled high-temperature carbonization to obtain a carbon fiber. The method can be used to prepare a carbon fiber having a tensile modulus of 340-380GPa and a carbon content of ≤98wt%, thereby effectively improving the interface performance of the composite material.

Description

Technical Field

[0001] The invention belongs to the field of carbon fibers, and in particular relates to a carbon fiber and a preparation method thereof. Background Art

[0002] Carbon fiber has the characteristics of high specific strength and high specific modulus. As an important reinforcement for composite materials, it can meet the needs of lightweight structure, high structural stiffness, dimensional stability and functional / structural integration of equipment in aviation and aerospace. It is the core key material of the primary and secondary structures of equipment, and the focus of future aerospace material development. With the continuous upgrading of composite materials, new requirements are constantly put forward for carbon fibers, especially composite materials are mainly designed for stiffness, so modulus is the key to achieving lightweight. In the traditional high modulus carbon fiber preparation process, after the modulus of carbon fiber is improved, the carbon content of carbon fiber increases, which leads to a decrease in active atoms such as nitrogen, oxygen and hydrogen on the surface, and the interface performance of the composite material deteriorates. The carbon content of high-strength T300, T700 grade (modulus of about 230GPa) and high-strength medium model T800 grade (modulus of about 290GPa) is between 93-95%, while the carbon content of high modulus carbon fiber (referring to modulus above 340GPa) is greater than 99.9%, which is basically close to 100%, resulting in low surface activity of high modulus carbon fiber, which directly affects the performance of composite materials, especially comprehensive performance indicators such as compressive strength and post-impact compressive strength. Therefore, reducing its carbon content while high modulus carbon fiber is the key to improving interface performance and thus achieving upgrading of composite materials. Summary of the invention

[0003] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a carbon fiber and a preparation method thereof. The method can be used to prepare carbon fiber with a tensile modulus of 340-380GPa and a carbon content of ≤98wt%, thereby effectively improving the interface performance of the composite material.

[0004] In one aspect of the present invention, the present invention provides a method for preparing carbon fiber, comprising:

[0005] (1) subjecting polyacrylonitrile copolymer fibers to a tension-controlled preoxidation treatment in an air atmosphere to obtain preoxidized fibers having an oxygen content of 6-9 wt %;

[0006] (2) subjecting the pre-oxidized fiber to a controlled tension low-temperature carbonization treatment in a nitrogen atmosphere to obtain a low-temperature carbonized fiber;

[0007] (3) The low-temperature carbonized fiber is subjected to tension-controlled high-temperature carbonization to obtain carbon fiber.

[0008] Preferably, in step (1), the raw material components of the polyacrylonitrile copolymer fiber include acrylonitrile and itaconic acid, and the fiber is spun by a wet method or a dry-wet method.

[0009] Preferably, in step (1), the molar fraction of acrylonitrile in the raw material component of the polyacrylonitrile copolymer fiber is ≥ 98%.

[0010] Preferably, in step (1), the polyacrylonitrile copolymer fiber has a single filament fineness of 0.5-0.8 dtex.

[0011] Preferably, in step (1), the pre-oxidation treatment conditions include: 200-280°C, 3-6 stages of gradient temperature increase for 40-80 minutes.

[0012] Preferably, in step (1), a tension of 0.4-0.5 cN / dtex is applied to each section of the pre-oxidation stage.

[0013] Preferably, in step (2), the low-temperature carbonization treatment includes 2-5 temperature zones, the temperatures of the 2-5 temperature zones are gradually increased, wherein the starting temperature of the first temperature zone is 350°C-400°C, the temperature of the last temperature zone is 550-650°C, and the total treatment time of the low-temperature carbonization treatment is 2-5 minutes.

[0014] Preferably, in step (2), each temperature zone applies a tension of 0.2-0.3 cN / dtex.

[0015] Preferably, in step (3), the high temperature carbonization includes two temperature zone treatment, the first temperature zone temperature is 1000-1400°C, the treatment time is 2-4 minutes, and a tension of 0.8-1.5 cN / dtex is applied; the second temperature zone temperature is 1400-1700°C, the treatment time is 2-4 minutes, and a tension of 1.5-2.1 cN / dtex is applied.

[0016] In yet another aspect of the present invention, the present invention provides a carbon fiber, which is prepared by the method described above.

[0017] Compared with the prior art, this application has the following advantages:

[0018] (1) The present application achieves reasonable control of the microstructure by regulating the tension of each process section, and performs tension control in stages, so as to achieve the purpose of high modulus at a lower carbonization temperature;

[0019] (2) The present application controls the oxygen content in the pre-oxidized fiber to be 6-9wt%, which can effectively inhibit the escape of nitrogen during the carbonization process, thereby reducing the carbon content of the carbon fiber. DETAILED DESCRIPTION

[0020] The present invention is further described in detail below in conjunction with examples. The following examples are only illustrative and not restrictive, and the protection scope of the present invention cannot be limited thereto.

[0021] In one aspect of the present invention, the present invention provides a method for preparing carbon fiber. According to an embodiment of the present invention, the method comprises:

[0022] S1: The polyacrylonitrile copolymer fiber is subjected to tension-controlled pre-oxidation treatment in air atmosphere.

[0023] In this step, the polyacrylonitrile copolymer fiber is subjected to a tension-controlled pre-oxidation treatment in an air atmosphere to obtain pre-oxidized fiber with an oxygen content of 6-9 wt %.

[0024] According to an embodiment of the present invention, the raw material components of the polyacrylonitrile copolymer fiber include acrylonitrile and itaconic acid, and are spun by a wet method or a dry-wet method. Specifically, the method for preparing the polyacrylonitrile copolymer fiber includes:

[0025] Using dimethyl sulfoxide (DMSO) as solvent and azobisisobutyl cyanide (AIBN) as initiator at 60-70°C, preferably 65°C, a binary solution copolymerization of acrylonitrile and itaconic acid is carried out for 12-36 hours, preferably 24 hours, to obtain a polymer spinning solution, wherein the molar fraction of acrylonitrile in the total amount of acrylonitrile and itaconic acid is not less than 98%, and then unreacted monomers in the polymer spinning solution are removed under stirring at 60-70°C, preferably 65°C and a vacuum degree greater than 0.095MPa. After 7-9 hours, preferably 8 hours, the stirring is stopped, and the solution is allowed to stand for degassing under the same vacuum conditions at 55-65°C, preferably 60°C. Then, a 60-80% dimethyl sulfoxide (DMSO) aqueous solution is used as a coagulation bath, preferably a 70% DMSO aqueous solution, and the polymer spinning solution is coagulated at a temperature of 20-65°C, preferably 45°C, and the polymer spinning solution is converted into a primary fiber. The primary fiber is then successively coagulated in a 40% and 20% DMSO aqueous solution at room temperature. Then, it is drawn 4-7 times, preferably 5 times, in boiling water, washed in water at a temperature of 50-90°C, and the washed fiber is oiled and dried, and drawn 2-3.2 times, preferably 2.4 times, in superheated steam, and finally heat-set to obtain a polyacrylonitrile copolymer fiber. And the monofilament fineness of the polyacrylonitrile copolymer fiber of the present application is 0.5-0.8dtex.

[0026] The polyacrylonitrile copolymer fiber is then subjected to a tension-controlled pre-oxidation treatment in an air atmosphere, wherein the pre-oxidation treatment conditions include: 200-280°C, 3-6 stages of gradient heating, a total treatment time of 40-80 minutes, and a tension of 0.4-0.5 cN / dtex is applied to each stage of the pre-oxidation stage to obtain pre-oxidized fibers with an oxygen content of 6-9wt%.

[0027] S2: The pre-oxidized fiber is subjected to a tension-controlled low-temperature carbonization treatment in a nitrogen atmosphere.

[0028] In this step, the pre-oxidized fiber obtained above is subjected to a tension-controlled low-temperature carbonization treatment in a nitrogen atmosphere, wherein the low-temperature carbonization treatment includes 2-5 temperature zones, the temperatures of the 2-5 temperature zones are gradually increased, wherein the starting temperature of the first temperature zone is 350°C-400°C, and the temperature of the last temperature zone is 550-650°C, the total treatment time of the low-temperature carbonization treatment is 2-5 minutes, and each temperature zone is subjected to a tension of 0.2-0.3 cN / dtex to obtain a low-temperature carbonized fiber.

[0029] S3: subjecting the low-temperature carbonized fiber to controlled tension high-temperature carbonization, wherein the high-temperature carbonization includes two temperature zone treatments, the first temperature zone having a temperature of 1000-1400°C, a treatment time of 2-4 minutes, and a tension of 0.8-1.5 cN / dtex; the second temperature zone having a temperature of 1400-1700°C, a treatment time of 2-4 minutes, and a tension of 1.5-2.1 cN / dtex, to obtain carbon fiber.

[0030] Therefore, the present application controls the temperatures of pre-oxidation, low-temperature carbonization and high-temperature carbonization and coordinates the regulation with the tension to achieve the preparation of high modulus carbon fibers with a modulus of 340-380 GPa at a temperature lower than the normal graphitization temperature (generally high modulus carbon fibers need to be graphitized at above 2000 degrees). At the same time, controlling the fiber tension according to different heat treatment stages and matching it with the heat treatment temperature spectrum can effectively control the carbon microcrystalline structure and element content in the fiber, so that the final carbonized carbon fibers have a high modulus and a carbon content of ≤98% for the high modulus carbon fibers.

[0031] The second aspect of the present invention provides a carbon fiber, which is prepared by the above method. It should be noted that the features and advantages described above for the method for preparing carbon fiber are also applicable to the carbon fiber, and will not be repeated here.

[0032] The present invention is described below with reference to specific embodiments. It should be noted that these embodiments are merely illustrative and do not limit the present invention in any way.

[0033] Example 1

[0034] The 12K polyacrylonitrile copolymer fiber with a single fiber fineness of 0.8dtex spun by the dry-wet method of Beijing University of Chemical Technology was used. In an air atmosphere, three heat stabilization treatments were performed at 200°C, 230°C, and 250°C for a total time of 60 minutes, and a tension of 0.4cN / dtex was applied to each section to obtain an air heat-stabilized fiber with an oxygen content of 7wt%. The obtained air heat-stabilized fiber was subjected to low-temperature carbonization at three temperatures of 350°C, 430°C, and 650°C in a nitrogen atmosphere for a total time of 2 minutes, and a tension of 0.2cN / dtex was applied to each section; then, high-temperature carbonization was performed in a nitrogen atmosphere, with a carbonization temperature of 1100°C for a period of 6 minutes and a tension of 0.8cN / dtex applied; the second carbonization temperature was 1500°C for a period of 6 minutes and a tension of 1.5cN / dtex was applied to obtain a high modulus carbon fiber. Its performance was tested, and the results are listed in Table 1.

[0035] Example 2

[0036] 12K polyacrylonitrile copolymer fiber with a single fiber fineness of 0.8 dtex spun by dry and wet methods of Beijing University of Chemical Technology was used. In air atmosphere, three stages of heat stabilization treatment were performed at 220°C, 230°C, and 235°C for a total time of 90 minutes. A tension of 0.4 cN / dtex was applied in each stage to obtain air heat stabilized fiber with an oxygen content of 6%. The other process conditions were the same as those in Example 1 to obtain high modulus carbon fiber. Its performance was tested and the results are listed in Table 1.

[0037] Example 3

[0038] 12K polyacrylonitrile copolymer fiber with a single fiber fineness of 0.5 dtex produced by dry-wet spinning of Beijing University of Chemical Technology was used, and other process conditions were the same as those in Example 1 to produce high modulus carbon fiber. Its properties were tested and the results are listed in Table 1.

[0039] Example 4

[0040] 12K polyacrylonitrile copolymer fiber with a single fiber fineness of 0.78 dtex produced by the Beijing University of Chemical Technology was used, and the other process conditions were the same as those in Example 1 to produce a high modulus carbon fiber. The performance of the carbon fiber was tested, and the results are listed in Table 1.

[0041] Example 5

[0042] The 12K polyacrylonitrile copolymer fiber with a single fiber fineness of 0.78 dtex spun by the dry-wet method of Beijing University of Chemical Technology was used. The heat stabilization process was the same as in Example 1. The obtained air heat-stabilized fiber was subjected to low-temperature carbonization at three stages of 400°C, 430°C and 550°C in a nitrogen atmosphere. The total treatment time was 2 minutes, and a tension of 0.25 cN / dtex was applied to each stage; then, high-temperature carbonization was carried out in a nitrogen atmosphere. The first stage carbonization temperature was 1100°C, the total treatment time was 6 minutes, and a tension of 0.8 cN / dtex was applied; the second stage carbonization temperature was 1400°C, the treatment time was 6 minutes, and a tension of 1.5 cN / dtex was applied to obtain a high modulus carbon fiber. Its performance was tested, and the results are listed in Table 1.

[0043] Example 6

[0044] 12K polyacrylonitrile copolymer fiber with a single fiber fineness of 0.78 dtex spun by dry-wet method of Beijing University of Chemical Technology was used. The heat stabilization and low temperature carbonization were the same as in Example 1. Then, high temperature carbonization was carried out in nitrogen atmosphere. The first stage carbonization temperature was 1100°C, the treatment time was 6 minutes, and the tension of 1.5 cN / dtex was applied; the second stage carbonization temperature was 1400°C, the total treatment time was 6 minutes, and the tension of 2.1 cN / dtex was applied to obtain high modulus carbon fiber. Its performance was tested and the results are listed in Table 1.

[0045] Example 7

[0046] 12K polyacrylonitrile copolymer fiber with a single fiber fineness of 0.78 dtex spun by dry-wet method of Beijing University of Chemical Technology was used, and four-stage heat stabilization treatment was carried out at 200°C, 220°C, 240°C and 260°C in air atmosphere for a total time of 60 minutes, and a tension of 0.5 cN / dtex was applied in each stage to obtain air heat-stabilized fiber with an oxygen content of 9wt%. The obtained air heat-stabilized fiber was subjected to low-temperature carbonization in sequence at four temperatures of 350°C, 430°C, 600°C and 650°C in nitrogen atmosphere for a total treatment time of 2 minutes, and a tension of 0.2 cN / dtex was applied in each stage; then, high-temperature carbonization was carried out in nitrogen atmosphere, with a carbonization temperature of 1100°C in the first stage, a treatment time of 4 minutes, and a tension of 1.0 cN / dtex applied; and a second carbonization temperature of 1500°C, a treatment time of 4 minutes, and a tension of 1.5 cN / dtex applied to obtain high modulus carbon fiber. Its performance was tested and the results are listed in Table 1.

[0047] Example 8

[0048] 12K polyacrylonitrile copolymer fiber with a single fiber fineness of 0.78 dtex spun by dry-wet method of Beijing University of Chemical Technology was used. The heat stabilization and low temperature carbonization were the same as those in Example 7. Then, high temperature carbonization was carried out in nitrogen atmosphere. The first stage carbonization temperature was 1200°C, the treatment time was 4 minutes, and the tension of 1.0 cN / dtex was applied; the second stage carbonization temperature was 1600°C, the treatment time was 4 minutes, and the tension of 1.5 cN / dtex was applied to obtain high modulus carbon fiber. Its performance was tested, and the results are listed in Table 1.

[0049] Example 9

[0050] 12K polyacrylonitrile copolymer fiber with a single fiber fineness of 0.78 dtex spun by dry-wet method of Beijing University of Chemical Technology was used. It was heat-stabilized in six stages at 200°C, 215°C, 230°C, 245°C, 260°C and 280°C in air atmosphere for a total time of 30 minutes. A tension of 0.4 cN / dtex was applied in each stage to obtain air-heat-stabilized fiber with an oxygen content of 8 wt%. The obtained air-heat-stabilized fiber was heat-stabilized in nitrogen atmosphere at 380°C, 430°C and 500°C. Low temperature carbonization was carried out in sequence at five stages of temperature: 500℃, 580℃, 620℃ and 650℃, with a total treatment time of 2 minutes and a tension of 0.2cN / dtex applied in each stage; then high temperature carbonization was carried out in a nitrogen atmosphere, with a carbonization temperature of 1400℃ for one stage, a treatment time of 2 minutes, and a tension of 0.8cN / dtex applied; a second carbonization temperature of 1700℃ for two minutes, and a tension of 1.5cN / dtex applied, to obtain high modulus carbon fiber. Its properties were tested and the results are listed in Table 1.

[0051] Example 10

[0052] 12K polyacrylonitrile copolymer fiber with a single fiber fineness of 0.78 dtex spun by dry-wet method of Beijing University of Chemical Technology was used. The heat stabilization and low temperature carbonization were the same as those in Example 9. Then, high temperature carbonization was carried out in nitrogen atmosphere. The first stage carbonization temperature was 1200°C, the treatment time was 2 minutes, and the tension of 1.4 cN / dtex was applied; the second stage carbonization temperature was 1600°C, the treatment time was 2 minutes, and the tension of 2.1 cN / dtex was applied to obtain high modulus carbon fiber. Its performance was tested, and the results are listed in Table 1.

[0053] Comparative Example 1

[0054] 12K polyacrylonitrile copolymer fiber with a single fiber fineness of 0.78 dtex spun by dry-wet method of Beijing University of Chemical Technology was used. The heat stabilization and low temperature carbonization were the same as those in Example 9. Then, high temperature carbonization was carried out in nitrogen atmosphere. The first stage carbonization temperature was 1100°C, the treatment time was 2 minutes, and the tension of 0.7 cN / dtex was applied; the second stage carbonization temperature was 1500°C, the treatment time was 2 minutes, and the tension of 1.3 cN / dtex was applied to obtain carbon fiber. Its performance was tested, and the results are listed in Table 1.

[0055] Comparative Example 2

[0056] 12K polyacrylonitrile copolymer fiber with a single fiber fineness of 0.78 dtex spun by dry-wet method of Beijing University of Chemical Technology was used. The heat stabilization and low temperature carbonization were the same as those in Example 9. Then, high temperature carbonization was carried out in nitrogen atmosphere. The first stage carbonization temperature was 1400°C, the treatment time was 2 minutes, and the tension of 0.6 cN / dtex was applied; the second stage carbonization temperature was 2000°C, the treatment time was 2 minutes, and the tension of 1.2 cN / dtex was applied to obtain high modulus carbon fiber. Its performance was tested, and the results are listed in Table 1.

[0057] Table 1 Mechanical properties and carbon content of high modulus carbon fibers obtained in Examples and Comparative Examples

[0058] Serial number <![CDATA[Linear density / g·m -1 > <![CDATA[Body density / g·cm 3 > Tensile modulus / GPa Carbon content / % Example 1 0.490 1.759 342 97.9 Example 2 0.462 1.783 357 97.4 Example 3 0.310 1.763 380 97.7 Example 4 0.478 1.800 354 98.0 Example 5 0.479 1.806 343 97.4 Example 6 0.469 1.811 371 97.3 Example 7 0.471 1.791 340 97.6 Example 8 0.476 1.788 352 97.8 Example 9 0.473 1.773 351 98.0 Example 10 0.471 1.779 364 97.6 Comparative Example 1 0.483 1.774 317 97.3 Comparative Example 2 0.473 1.787 343 99.8

[0059] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present invention. These improvements and modifications should also be regarded as not within the scope of protection of the invention.

Claims

1. A method for preparing carbon fiber, characterized in that: include: (1) subjecting polyacrylonitrile copolymer fibers to a tension-controlled preoxidation treatment in an air atmosphere to obtain preoxidized fibers having an oxygen content of 6-9 wt %; (2) subjecting the pre-oxidized fiber to a controlled tension low-temperature carbonization treatment in a nitrogen atmosphere to obtain a low-temperature carbonized fiber; (3) subjecting the low-temperature carbonized fiber to controlled tension high-temperature carbonization to obtain carbon fiber, Wherein, in step (1), the pre-oxidation treatment conditions include: 200-280°C, 3-6 stages of gradient temperature rise for 40-80 minutes, and a tension of 0.4-0.5 cN / dtex is applied to each stage of the pre-oxidation stage; In step (2), the low-temperature carbonization treatment includes 2-5 temperature zones, the temperatures of the 2-5 temperature zones are gradually increased, wherein the starting temperature of the first temperature zone is 350°C-400°C, the temperature of the last temperature zone is 550-650°C, the total treatment time of the low-temperature carbonization treatment is 2-5 minutes, and a tension of 0.2-0.3 cN / dtex is applied to each temperature zone during the low-temperature carbonization stage; In step (3), the high temperature carbonization includes two temperature zone treatment, the first temperature zone temperature is 1000-1400°C, the treatment time is 2-4 minutes, and a tension of 0.8-1.5 cN / dtex is applied; the second temperature zone temperature is 1400-1700°C, the treatment time is 2-4 minutes, and a tension of 1.5-2.1 cN / dtex is applied.

2. The method according to claim 1, characterized in that In step (1), the raw material components of the polyacrylonitrile copolymer fiber include acrylonitrile and itaconic acid, and the fiber is spun by a wet method or a dry-wet method.

3. The method according to claim 2, characterized in that In step (1), the molar fraction of acrylonitrile in the raw material component of the polyacrylonitrile copolymer fiber is ≥ 98%.

4. The method according to claim 1, characterized in that: In step (1), the fineness of the polyacrylonitrile copolymer fiber monofilament is 0.5-0.8 dtex.