Mesophase pitch carbon fiber and method for producing the same

Abstract

The application discloses mesophase pitch carbon fiber and a preparation method thereof, and the method comprises the following steps: 1) adding 0.1-0.3 wt.% of carbon nanotubes or graphene into molten mesophase pitch to obtain a composite; 2) adopting a melt electrospinning process, and performing melt spinning on the composite at 295-360 DEG C to obtain a raw yarn; and 3) performing pre-oxidation and carbonization on the raw yarn to obtain mesophase pitch carbon fiber. By adding a small amount of carbon nanotubes or graphene, the spinnability of the melt electrospinning of the mesophase pitch can be improved, and the orientation of carbon atoms along the axial direction can be enhanced, and the prepared carbon fiber has better performance.

Description

TECHNICAL FIELD

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

[0002] Carbon fiber is a kind of inorganic non-metallic reinforcing fiber with high strength, high modulus and low density. It is mainly used as a reinforcing agent and a functional additive in the manufacture of composite materials. Mesophase pitch carbon fiber is an important variety of carbon fiber, which has higher modulus and better thermal conductivity, and plays an irreplaceable role in aerospace and satellite fields. The diameter of the current carbon fiber product is about 10 microns, which is the mainstream of the product. Electrospinning is a new type of spinning method developed in recent years. Under the drafting of high-voltage static electricity, fibers of several hundred nanometers can be spun, and it has been applied to the spinning of various ultra-fine carbon fibers. Electrospinning is divided into solution and melt spinning. Solution electrospinning is to dissolve the material in a solvent, which is simple in parameter adjustment and is the current mainstream method. However, the premise of solution electrospinning is that the material can be dissolved in the related solvent.

[0003] Mesophase pitch is a kind of liquid crystal-like macromolecular substance, and there is no solvent that can completely dissolve it at present. Therefore, the current electrospinning of pitch solution is all electrospinning of pitch as an additive together with other materials. For example, He Yiting in "Preparation and Capacitance Performance of Pitch / PAN Composite Nanometer Carbon Fiber Nonwoven Fabric" (New Carbon Materials, 2021, 36(1) 227-234.) prepared nanometer carbon fiber by co-spinning of spinning pitch and polyacrylonitrile. However, pure spinning pitch solution electrospinning cannot be realized. Direct electrospinning of spinning pitch in a molten state to prepare a precursor, and then obtain ultra-fine pitch carbon fiber with better performance, has not been reported at present. SUMMARY

[0004] In order to solve the above-mentioned defects in the prior art, the present application provides a mesophase pitch carbon fiber and a preparation method thereof, which directly electrospins mesophase pitch in a molten state to prepare a precursor, and then processes it into nanometer ultra-fine pitch carbon fiber.

[0005] In order to achieve the above-mentioned application purposes, the first aspect of the present application provides a preparation method of mesophase pitch carbon fiber, comprising:

[0006] 1) adding 0.1-0.3wt.% of carbon nanotubes or graphene to the molten mesophase pitch to obtain a composite;

[0007] 2) using a melt electrospinning process, melt spinning the composite at 295-360℃ to obtain a precursor;

[0008] 3) The raw silk is pre-oxidized and carbonized to prepare mesophase pitch carbon fiber.

[0009] In the above technical solution of the present application, mesophase pitch is used as raw material, ultra-fine mesophase pitch raw silk is prepared by melt electrospinning, and after treatment, mesophase pitch ultra-fine carbon fiber is obtained. Among them, the melted mesophase pitch has poor conductivity and insufficient charge carrying capacity, which often leads to unstable melt electrospinning or even failure; to solve this problem, 0.1-0.3wt.% carbon nanotubes or graphene are added to the melted mesophase pitch. Carbon nanotubes and graphene are two high-orientation carbon materials with good conductivity, which can improve the charging capacity as an additive of mesophase pitch and have the effect of guiding the orientation of mesophase pitch in the process of forming fibers. Therefore, by adding a small amount of carbon nanotubes or graphene, the spinnability of mesophase pitch melt electrospinning can be improved, and the orientation of carbon atoms along the axial direction can be enhanced, and the performance of the prepared carbon fiber is better.

[0010] Further, the softening point of the mesophase pitch in step 1) is 260-320℃, and examples are: 263℃, 265℃, 268℃, 270℃, 272℃, 275℃, 278℃, 280℃, 283℃, 285℃, 288℃, 290℃, 293℃, 295℃, 298℃, 300℃, 305℃, 308℃, 310℃, 312℃, 315℃, 318℃, etc. By selecting the above softening point range, the mesophase content of the pitch can be greater than 85%, and the mesophase pitch has sufficient flowability to ensure that it still has spinnability after adding carbon nanotubes or graphene, and the spinning temperature is suitable and the operation is convenient. In the present application, the spinning temperature is exemplarily: 298℃, 300℃, 305℃, 310℃, 315℃, 320℃, 325℃, 330℃, 335℃, 340℃, 345℃, 350℃, 355℃, etc. The addition amount of carbon nanotubes or graphene is exemplarily: 0.12wt.%, 0.15wt.%, 0.18wt.%, 0.20wt.%, 0.22wt.%, 0.25wt.%, 0.28wt.%, etc.

[0011] Further, the length of the carbon nanotubes in step 1) is less than 30 nanometers, and the diameter is 20-50 nanometers. By selecting the above size range, the carbon nanotubes can have good assistance effect on the orientation of carbon fiber, while preventing the negative effects such as the loss of spinnability due to the excessive increase of softening point caused by the addition and the uneven mixing of carbon nanotubes with mesophase pitch due to the excessive size of carbon nanotubes. The length of the carbon nanotubes is preferably 1-5 micrometers.

[0012] Further, the length of the carbon nanotubes in step 1) is less than 30 nanometers, and the diameter is 20-50 nanometers. By selecting the above size range, the carbon nanotubes can have good assistance effect on the orientation of carbon fiber, while preventing the negative effects such as the loss of spinnability due to the excessive increase of softening point caused by the addition and the uneven mixing of carbon nanotubes with mesophase pitch due to the excessive size of carbon nanotubes. The length of the carbon nanotubes is preferably 1-5 micrometers.

[0013] Further, the length and width of the graphene in step 1) is 15-30 nanometers, the above size range is selected to ensure that the graphene has a good effect of assisting the orientation of carbon fibers, while preventing the negative effects of excessive increase in softening point due to the addition, loss of spinnability, and uneven mixing of the graphene with the mesophase pitch due to the excessive size of the graphene.

[0014] Further, the mesophase pitch in step 1) is pitch with a mesophase content of 85% (volume fraction) or more, preferably 90% or more.

[0015] Further, the molten mesophase pitch in step 1) is pitch that is heated to a temperature above the softening point to become a flowable liquid.

[0016] Further, the addition process in step 1) is performed under stirring. The stirring speed is preferably 200-300 revolutions per minute, and the stirring time is 20-30 minutes.

[0017] Further, the pre-oxidation process in step 3) is a molecular cross-linking process of the precursor using an oxidizing agent, the oxidation temperature is 220-330°C, and the oxidation time is 2-4 hours. The oxidizing agent is preferably air.

[0018] Further, the carbonization process parameters in step 3) include treatment under nitrogen protection at 1000-1300°C for 0.5-5 hours.

[0019] Further, considering the mesophase ratio of the mesophase pitch, the effect of the carbon nanotubes or graphene on the softening point of the mesophase pitch, and the effect of the carbon nanotubes or graphene on the orientation assistance, the further preferred parameters in steps 1)-3) include: the addition amount of the carbon nanotubes or graphene is 0.15-0.25 wt.%, the spinning temperature is 320-340°C, the softening point of the mesophase pitch is 270-295°C, the mesophase pitch content is less than 270 degrees, which affects the strength of the fiber, the mesophase softening point exceeds 295 degrees, the viscosity increases after melting, the spinning temperature needs to be increased, which affects the quality of the mesophase pitch and also puts higher requirements on the equipment.

[0020] The present application obtains the above feasible preparation method through process groping, wherein the mesophase pitch structure and softening point, the morphology and the adding amount of the carbon nanotube or graphene have influences on the performance of the final carbon fiber. The mesophase pitch carbon fiber is composed of graphite crystals which are highly oriented along the axial direction, and the higher the orientation is, the better the performance of the carbon fiber is. The mesophase pitch with the large fusion and bulk structure is an ideal raw material for converting into graphite crystals, and the mesophase content in the pitch is preferably more than 90%. Since the carbon nanotube and graphene are highly oriented carbon materials, the addition of the carbon nanotube and graphene promotes the orientation of the final carbon fiber, and the more perfect the structure of the carbon nanotube or graphene is and the better the orientation is, the greater the orientation effect on the carbon fiber is. Further, the size of the carbon nanotube and graphene is limited in a certain range, which ensures the excellent orientation of the carbon nanotube and graphene and prevents the difficulty in mixing due to the oversize. Moreover, since the carbon nanotube and graphene are solid substances, the addition of the carbon nanotube and graphene will reduce the fluidity of the mesophase pitch and have a negative influence on the spinning performance of the mesophase pitch, and therefore the adding amount needs to be controlled.

[0021] The present application provides a mesophase pitch carbon fiber prepared by the above method, and the diameter of the mesophase pitch carbon fiber is 150-280 nanometers.

[0022] Compared with the prior art, the present application has the following advantages:

[0023] The present application provides a preparation method of ultrafine mesophase pitch carbon fiber, which adds carbon nanotube or graphene into the molten mesophase pitch, adopts the melt electrospinning process to prepare ultrafine mesophase pitch original wire, and obtains the ultrafine mesophase pitch carbon fiber through pre-oxidation and carbonization post-processing. The diameter of the mesophase pitch carbon fiber is 150-280 nanometers. The thinner the diameter of the carbon fiber is, the higher the orientation of carbon atoms along the fiber axial direction is, and the better the various performances are. Therefore, the present application overcomes the difficulty that the solution electrospinning method cannot spin pure mesophase pitch. The ultrafine carbon fiber prepared after adding the carbon nanotube or graphene has good orientation, which leads to better mechanical properties and better electric and thermal conductive properties.

[0024] Other features and advantages of the present application will be described in detail through the following specific embodiments. DETAILED DESCRIPTION

[0025] The concept and the generated technical effects of the present application will be described clearly and completely through the following embodiments, so as to fully understand the purpose, features and effects of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, but not all the embodiments. Based on the embodiments of the present application, other embodiments obtained by those skilled in the art without creative labor are within the protection scope of the present application.

[0026] The following embodiments are used to illustrate the preparation method of the ultrafine mesophase pitch carbon fiber of the present application.

[0027] Example 1

[0028] The mesophase pitch with a softening point of 293°C and a mesophase content of 91% was used as raw material, and 0.1 wt.% carbon nanotubes were added. The diameter of the carbon nanotubes was 20-50 nm, and the length was 1-5 μm. The addition was completed under a melting state of the mesophase pitch by mechanical stirring for 20 minutes (stirring speed: 300 rpm). The original fiber was spun by a melt electrospinning process at a spinning temperature of 320°C. The original fiber was pre-oxidized by heating at a rate of 10°C / min to 240°C in air, and then heating at a rate of 3°C / h from 240°C to 330°C. Then, the mesophase pitch-based carbon fiber was obtained by carbonization at 1100°C for 2 h under nitrogen atmosphere. The fiber diameter was 192 nm.

[0029] Example 2

[0030] The mesophase pitch with a softening point of 293°C and a mesophase content of 91% was used as raw material, and 0.1 wt.% graphene was added. The length and width of the graphene were 15-25 nm. The addition was completed under a melting state of the mesophase pitch by mechanical stirring for 20 minutes (stirring speed: 280 rpm). The original fiber was spun by a melt electrospinning process at a spinning temperature of 323°C. The original fiber was pre-oxidized by heating at a rate of 10°C / min to 240°C in air, and then heating at a rate of 0.5°C / min from 240°C to 330°C. Then, the mesophase pitch-based carbon fiber was obtained by carbonization at 1100°C for 2 h under nitrogen atmosphere. The fiber diameter was 201 nm.

[0031] Example 3

[0032] The mesophase pitch with a softening point of 260°C and a mesophase content of 85% was used as raw material, and 0.1 wt.% carbon nanotubes were added. The diameter of the carbon nanotubes was 30-50 nm, and the length was 2-5 μm. The addition was completed under a melting state of the mesophase pitch by mechanical stirring for 20 minutes (stirring speed: 300 rpm). The original fiber was spun by a melt electrospinning process at a spinning temperature of 295°C. The original fiber was pre-oxidized by heating at a rate of 10°C / min to 240°C in air, and then heating at a rate of 0.5°C / min from 240°C to 330°C. Then, the mesophase pitch-based carbon fiber was obtained by carbonization at 1100°C for 2 h under nitrogen atmosphere. The fiber diameter was 150 nm.

[0033] Example 4

[0034] Mesophase pitch with a softening point of 260℃ and a mesophase content of 85% was used as raw material. 0.2 wt.% of graphene was added, with the graphene length and width being 20-30 nanometers. The addition was completed under molten mesophase pitch and mechanical stirring for 20 minutes (stirring speed of 260 rpm). The precursor fiber was spun using melt electrospinning at a spinning temperature of 297℃. The precursor fiber was heated to 240℃ in air at a rate of 10℃ / min, and then heated from 240℃ to 330℃ at a rate of 0.5℃ / min. Then, it was carbonized at 1100℃ for 2 hours under nitrogen protection to obtain ultrafine mesophase pitch carbon fiber with a fiber diameter of 159 nanometers.

[0035] Example 5

[0036] Mesophase pitch with a softening point of 320℃ and a mesophase content of 95% was used as raw material. 0.3 wt.% of carbon nanotubes were added. The diameter of the carbon nanotubes was 30-50 nanometers and the length was 2-5 micrometers. The addition was completed by mechanical stirring for 20 minutes (stirring speed of 300 rpm) in the molten state of the mesophase pitch. The precursor fiber was spun by melt electrospinning at a spinning temperature of 360℃. The precursor fiber was heated to 240℃ in air at a rate of 10℃ / min, and then heated from 240℃ to 330℃ at a rate of 0.5℃ / min. Then, it was carbonized at 1100℃ for 2 hours under nitrogen protection to obtain ultrafine mesophase pitch carbon fiber with a fiber diameter of 276 nanometers.

[0037] Example 6

[0038] Mesophase pitch with a softening point of 260℃ and a mesophase content of 85% was used as raw material. 0.3 wt.% of graphene was added, with the graphene length and width ranging from 15 to 25 nanometers. The addition was completed under molten mesophase pitch and mechanical stirring for 20 minutes (stirring speed of 300 rpm). The precursor fiber was spun using melt electrospinning at a spinning temperature of 358℃. The precursor fiber was heated to 240℃ in air at a rate of 10℃ / min, and then heated from 240℃ to 330℃ at a rate of 0.5℃ / min. Finally, it was carbonized at 1100℃ for 2 hours under nitrogen protection to obtain ultrafine mesophase pitch carbon fibers with a fiber diameter of 280 nanometers.

[0039] Example 7

[0040] The difference from Example 1 is that the carbon nanotubes have a diameter of 65 nanometers and a length of 6.2 micrometers. The experimental results are as follows: the stable spinning time is less than 1 minute, and there are nodules in the diameter. Compared with Example 1, Example 7 shows that because the size of the added carbon nanotubes is not within the preferred range of this invention, the spinning continuity is reduced, the diameter is uneven, and the spinning performance and fiber performance are slightly worse.

[0041] Example 8

[0042] Different from example 2 in that the graphene diameter is 70 nm, and compared with example 2 and example 8, since the graphene addition size is not in the preferred range of the application, the spinnability is poor, the fiber has nodules, and the spinning performance and fiber performance are slightly poor.

[0043] Example 9

[0044] Different from example 1 in that the mesophase pitch softening point is 340℃, and the experimental results are as follows: the spinning temperature is high, 390℃, and the continuity is poor.

[0045] Comparative example 1

[0046] Different from example 1 in that no carbon nanotubes are added, and the spinning fails.

[0047] Comparative example 2

[0048] Different from example 1 in that the amount of carbon nanotubes added is 1wt.%, and the experimental results are as follows: the strength of the fiber is affected, and nodules appear in the fiber after graphitization.

[0049] Comparative example 3

[0050] Different from example 1 in that the spinning temperature is 280℃, and the experimental results are as follows: the pitch viscosity is large, and the spinning cannot be performed.

[0051] As can be seen from the examples of the application, after adding carbon nanotubes or graphene in the mesophase pitch, a nanoscale ultrafine mesophase pitch carbon fiber is prepared by melt electrospinning, the diameter of the carbon fiber is greatly reduced compared with the conventional micron-level carbon fiber, and a high-orientation mesophase pitch carbon fiber is obtained.

[0052] Obviously, the above examples of the application are only examples for clearly illustrating the application, and are not intended to limit the implementation modes of the application. Based on the above description, other different forms of changes or variations can be made by those skilled in the art. It is impossible to enumerate all the implementation modes here. Any obvious changes or variations derived from the technical solutions of the application are within the scope of the spirit of the application.

Claims

1. A process for the production of mesophase pitch carbon fibers, characterized by, Comprising: 1) adding 0.1-0.3wt.% of carbon nanotubes or graphene into molten mesophase pitch, the mesophase pitch having a softening point of 260-320℃, the carbon nanotubes having a length of less than 30 nanometers and a diameter of 20-50 nanometers; the graphene having a length of 15-30 nanometers and a width of 15-30 nanometers; the mesophase pitch comprising a volume fraction of 85% or more mesophase content; 2) using a melt electrospinning process, melt spinning the composite at 295-360℃ to obtain a precursor fiber; 3) preparing mesophase pitch carbon fiber from the precursor fiber by pre-oxidation and carbonization, the mesophase pitch carbon fiber having a diameter of 150-280 nanometers.

2. The process for producing mesophase pitch carbon fibers according to claim 1, characterized by, The mesophase pitch in step 1) is a pitch comprising a volume fraction of 90% or more mesophase content.

3. The process for producing mesophase pitch carbon fibers according to claim 1, characterized by, The adding process in step 1) is performed under stirring; the stirring speed is 200-300 revolutions per minute, and the stirring time is 20-30 minutes.

4. The process for producing mesophase pitch carbon fibers according to claim 1, characterized by, The pre-oxidation process in step 3) is a molecular cross-linking of the precursor fiber using an oxidizing agent, the oxidation temperature is 220-330℃, the oxidation time is 2-4 hours, and the oxidizing agent is air.

5. The process for producing mesophase pitch carbon fibers according to claim 1, characterized by, The carbonization process in step 3) comprises a treatment under nitrogen protection at 1000-1300℃ for 0.5-5 hours.

6. The process for the production of mesophase pitch carbon fibers according to any one of claims 1 to 5, characterized in that, In steps 1)-3), the softening point of the mesophase pitch is 270-295℃, the amount of the carbon nanotubes or graphene added is 0.15-0.25wt.%, and the spinning temperature is 320-340℃.

7. A mesophase pitch carbon fiber prepared by the method of any one of claims 1-6.