High-performance polyacrylonitrile-based carbon fiber and method for producing the same

Abstract

The application discloses a kind of high-performance polyacrylonitrile-based carbon fibers and preparation method thereof, comprising the following steps: polyacrylonitrile, solvent and plasticizer are mixed according to proportion, heated stirring, and obtain uniform spinning dope;The plasticizer is diphenyl phthalate, bisphenol A-bis (diphenyl) phosphate or resorcinol bis (diphenyl) phosphate;Spinning dope is spun, and polyacrylonitrile fiber precursor is prepared;After heat drawing treatment to polyacrylonitrile fiber precursor, pre-oxidation, carbonization treatment, and polyacrylonitrile-based carbon fiber is obtained;The temperature of pre-oxidation is 200-300 DEG C, and the time of pre-oxidation is 80-160 min.The carbon fiber preparation method of the application can effectively improve the spinnability and drawability of PAN fiber, can promote the improvement of the crystallinity and graphitization degree of carbon fiber, so as to enhance the mechanical properties of fiber.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of polyacrylonitrile-based carbon fiber preparation, and relates to high-performance polyacrylonitrile-based carbon fiber and a preparation method thereof. BACKGROUND

[0002] The statements herein are provided only to complement the background of the application and are not necessarily prior art.

[0003] Carbon fiber has excellent electrical conductivity, chemical stability, heat resistance, and large specific surface area, and has been widely used in various fields such as fuel cells, rail transit, and wind power generation. Although it has been widely used, the mechanical properties of the currently prepared carbon fiber, especially the tensile strength, are far from the theoretical value, which seriously hinders its more extensive commercial application.

[0004] In the production process of carbon fiber, drawing is a crucial step, which helps to optimize the microstructure of the fiber and improve its final mechanical properties. By applying appropriate heat drawing to PAN fiber, a denser fiber matrix can be obtained, and the formation of defect structures can be reduced. However, due to the strong hydrogen bonding and dipole interaction between PAN molecular chains, these intermolecular forces will limit their relative sliding, thereby posing a challenge to the drawing process of the precursor fiber. SUMMARY

[0005] In view of the deficiencies of the prior art, the purpose of the present application is to provide high-performance polyacrylonitrile-based carbon fiber and a preparation method thereof, which improves the drawability of the fiber by adding a special plasticizer, improves the graphite structure of the obtained carbon fiber, and significantly improves the tensile strength, which is expected to pave the way for its more extensive application.

[0006] In order to achieve the above-mentioned purpose, the present application is realized by the following technical scheme:

[0007] In the first aspect, the present application provides a preparation method of high-performance polyacrylonitrile-based carbon fiber, comprising the following steps:

[0008] Mixing polyacrylonitrile, solvent and plasticizer in proportion, heating and stirring to obtain a uniform spinning solution; the plasticizer is diphenyl phthalate, bisphenol A-bis(diphenyl) phosphate or resorcinol bis(diphenyl) phosphate;

[0009] Spinning the spinning solution to prepare a polyacrylonitrile fiber precursor;

[0010] The polyacrylonitrile fiber precursor is subjected to heat drawing treatment, pre-oxidation and carbonization treatment to obtain polyacrylonitrile-based carbon fiber.

[0011] The pre-oxidation temperature is 200-300 DEG C, and the pre-oxidation time is 80-160 min.

[0012] The inventors found in experiments that the plasticizer can weaken the interaction between molecular chains, which is conducive to the drawing process, so that adding a suitable plasticizer in the PAN precursor is expected to enhance the drawability of the fiber. However, the commonly used plasticizers have poor heat resistance and are prone to decomposition at high temperatures in the carbonization process, resulting in the formation of defect structures in the fiber matrix and reducing the mechanical properties of the carbon fiber.

[0013] In the present application, during the preparation of the polyacrylonitrile carbon fiber, a plasticizer such as diphenyl phthalate, bisphenol A-bis(diphenyl) phosphate or resorcinol bis(diphenyl) phosphate is added to the spinning dope to promote the crosslinking of linear PAN molecular chains to form graphite carbon layers during the pre-oxidation and carbonization of the fiber, ultimately resulting in improved structure and properties of the carbon fiber.

[0014] Further experiments found that when the fiber precursor is first pre-oxidized and then carbonized, the mechanical properties of the carbon fiber prepared are better.

[0015] In some embodiments, the solvent is one of dimethylformamide, dimethylacetamide, dimethyl sulfoxide or sodium thiocyanate.

[0016] Preferably, the solvent is dimethylformamide, and the plasticizer is resorcinol bis(diphenyl) phosphate.

[0017] When the solvent is dimethylformamide and the plasticizer is resorcinol bis(diphenyl) phosphate, the drawing properties of the polyacrylonitrile fiber precursor are better, and the mechanical properties of the prepared carbon fiber are best.

[0018] In some embodiments, the solid content in the spinning dope is 13wt%-25wt%.

[0019] Preferably, the mass of the plasticizer is 0.01-60wt% of the mass of the polyacrylonitrile.

[0020] Further preferably, the mass of the plasticizer is 1-60wt% of the mass of the polyacrylonitrile.

[0021] More preferably, the mass of the plasticizer is 10-50wt% of the mass of the polyacrylonitrile.

[0022] In some embodiments, the spinning is one of electrospinning, wet spinning, dry-jet wet spinning, melt spinning or gel spinning.

[0023] The electrostatic spinning condition is: temperature 40℃, voltage 20KV, liquid supply rate 2.5ml / h, and spinning roller rotating speed 1000rpm; the dry-wet spinning condition is: air layer thickness 4-12mm, coagulation bath water solution of the solvent used for the spinning dope, temperature 5-25℃, and concentration 10-60%. The PAN as-spun fiber prepared from the coagulation bath is washed and drawn to prepare the PAN precursor.

[0024] In some embodiments, the temperature of the heat drawing is 70-160℃; and the actual drawing multiple is 1-10.

[0025] Preferably, the temperature of the heat drawing is 100-160℃; and the actual drawing multiple is 3-8.

[0026] Further preferably, the temperature of the heat drawing is 120-150℃; and the actual drawing multiple is 3-6.

[0027] In some embodiments, the carbonization is carried out under nitrogen or argon, and the carbonization temperature is 400-2000℃.

[0028] In a second aspect, the present application provides a high-performance polyacrylonitrile-based carbon fiber prepared by the above method.

[0029] The beneficial effects of one or more embodiments of the present application are as follows:

[0030] The carbon fiber preparation method of the present application can effectively improve the spinnability and drawability of PAN fibers. The incorporation of the special plasticizer can weaken the van der Waals force between the molecules, and under the action of heat drawing, the fiber molecular chains containing the plasticizer are more easily moved along the fiber axis, which helps to reduce the fiber fineness and improve the structural orientation.

[0031] The carbon fiber preparation method of the present application can promote the improvement of the crystallinity and graphitization degree of the carbon fiber, thereby enhancing the mechanical properties of the fiber. The fiber porosity is reduced due to the closer arrangement of the molecular chains, and the microcrack diffusion energy is increased due to the increased graphitization degree, so the tensile strength and modulus of the carbon fiber with the plasticizer are improved compared with the carbon fiber prepared from pure PAN. BRIEF DESCRIPTION OF DRAWINGS

[0032] The drawings accompanying the specification of the present application form a part thereof, serve to provide further understanding of the present application, and together with the description, explain the present application. The present application is illustrated by way of example in the accompanying drawings in which:

[0033] Figure 1 SEM images of the fiber precursor after heat drawing obtained in Comparative Example 1 and Example 1 of the present application. Fig. a is the PAN fiber image of Comparative Example 1, and Fig. b is the fiber image of Example 1 with the plasticizer added.

[0034] Figure 2 Photographs of the electrospun fiber membranes obtained after thermal drawing in Inventive Comparative Example 1 and Example 1, wherein a is the PAN fiber membrane prepared in Inventive Comparative Example 1, and b is the fiber membrane prepared after adding plasticizer in Example 1;

[0035] Figure 3 Stress-strain curves (a) and tensile strength comparison graphs (b) of the carbon fibers obtained in Inventive Comparative Example 1 and Example 1. DETAILED DESCRIPTION

[0036] It should be noted that the following detailed description is illustrative only and is intended to provide further description of the present application. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs.

[0037] The present application is further described below with reference to examples.

[0038] Example 1

[0039] A PAN solution with a mass fraction of 19wt% was prepared using dimethylformamide as a solvent, and a plasticizer, resorcinol bis(diphenyl) phosphate RDP, was added in an amount of 40wt% of PAN. The obtained spinning dope was poured into a needle tube equipped with a spinning needle with an inner diameter of 0.5mm, and electrospinning was performed at a temperature of 40°C and an electric field strength of 20kV, and the nanofiber sample was collected by a spinning roller with a rotation speed of 1000rpm.

[0040] The electrospun nanofiber mat was cut along the orientation and subjected to thermal drawing treatment in an oven at 135°C with a draw ratio of 4, and then the fiber mat was pre-oxidized at 280°C in an air atmosphere and carbonized at 1400°C in a nitrogen atmosphere.

[0041] The tensile strength and modulus of the prepared carbon fibers were measured using a tensile testing machine. The steps were as follows: the carbonized fiber membrane was divided into strips (30mm x 1mm) along the fiber winding direction, the sample was fixed in a paper holder, and then the breaking strength and Young's modulus were measured by a tensile tester with an effective clamping distance of 20mm and a tensile rate of 5mm / min, and at least 10 tests were performed for each sample.

[0042] The tensile strength of the prepared carbon fibers was 10.78MPa, and the modulus was 3.25%.

[0043] Example 2

[0044] A PAN solution with a mass fraction of 25wt% was prepared using dimethylacetamide as solvent, and a plasticizer, diphenyl phthalate, was added in an amount of 20wt% of PAN. The obtained spinning dope was poured into a needle tube equipped with a spinning needle with an inner diameter of 0.5mm, and electrospinning was performed at a temperature of 40°C and an electric field strength of 20kV, and the nanofiber sample was collected by a rotating roller with a speed of 1000rpm.

[0045] The electrospun nanofiber mat was cut along the orientation and was subjected to heat drawing in an oven at 105°C. The draw ratio was 6, and then the fiber mat was pre-oxidized at 270°C in an air atmosphere and carbonized at 1200°C in an argon atmosphere.

[0046] The tensile strength of the prepared carbon fiber was 6.02MPa, and the modulus was 1.75%.

[0047] Example 3

[0048] A PAN solution with a mass fraction of 13wt% was prepared using sodium thiocyanate as solvent, and a plasticizer, bisphenol A-bis(diphenyl) phosphate, was added in an amount of 60wt% of PAN. The obtained spinning dope was subjected to defoaming treatment, and PAN protofilament was prepared by dry-jet wet spinning process. After the fiber was ejected, it first passed through an air layer of 8mm, and then entered a coagulation bath of 40% dimethyl sulfoxide aqueous solution at 15°C. After passing through the coagulation bath, the PAN protofilament was obtained by multi-stage water washing and heat drawing, and the drawing temperature was 160°C, and the total draw ratio was 8.

[0049] The drawn protofilament was pre-oxidized at 300°C in an air atmosphere and carbonized at 2000°C in a nitrogen atmosphere.

[0050] The tensile strength of the prepared carbon fiber was 4.30MPa, and the modulus was 2.18%.

[0051] Example 4

[0052] A PAN solution with a mass fraction of 18wt% was prepared using dimethyl sulfoxide as solvent, and a plasticizer, resorcinol bis(diphenyl) phosphate, was added in an amount of 5wt% of the mass of PAN. The obtained spinning dope was subjected to defoaming treatment, and PAN protofilament was prepared by dry-jet wet spinning process. After the fiber was ejected, it first passed through an air layer of 4mm, and then entered a coagulation bath of 20% dimethyl sulfoxide aqueous solution at 5°C. After passing through the coagulation bath, the PAN protofilament was obtained by multi-stage water washing and heat drawing, and the drawing temperature was 70°C, and the total draw ratio was 10.

[0053] The drawn protofilament was pre-oxidized at 200°C in an air atmosphere and carbonized at 450°C in a nitrogen atmosphere.

[0054] The tensile strength of the prepared carbon fiber is 5.98 MPa, and the modulus is 1.61%.

[0055] Example 5

[0056] A PAN solution with a mass fraction of 25wt% is prepared by using sodium thiocyanate as a solvent, wherein a composite plasticizer of diphenyl phthalate and bisphenol A-bis(diphenyl) phosphate is added, the mass ratio of diphenyl phthalate and bisphenol A-bis(diphenyl) phosphate in the composite plasticizer is 1:3, and the addition amount is 20wt% of PAN.

[0057] The obtained spinning dope is poured into a needle tube which is equipped with a spinning needle with an inner diameter of 0.5 mm, electrospinning is carried out at a temperature of 40°C and an electric field intensity of 20 kV, and the nanofiber sample is collected by a spinning roller with a rotating speed of 1000 rpm.

[0058] The electrospun nanofiber mat is cut along the orientation and subjected to heat drawing treatment in an oven at 105°C. The draw ratio is 6, and then the fiber mat is pre-oxidized at 270°C in an air atmosphere and carbonized at 1200°C in an argon atmosphere.

[0059] The tensile strength of the prepared carbon fiber is 5.48 MPa, and the modulus is 1.39%.

[0060] Example 6

[0061] A PAN solution with a mass fraction of 25wt% is prepared by using dimethyl formamide as a solvent, wherein a composite plasticizer of diphenyl phthalate and bisphenol A-bis(diphenyl) phosphate is added, the mass ratio of diphenyl phthalate and bisphenol A-bis(diphenyl) phosphate in the composite plasticizer is 1:3, and the addition amount is 20wt% of PAN.

[0062] The obtained spinning dope is poured into a needle tube which is equipped with a spinning needle with an inner diameter of 0.5 mm, electrospinning is carried out at a temperature of 40°C and an electric field intensity of 20 kV, and the nanofiber sample is collected by a spinning roller with a rotating speed of 1000 rpm.

[0063] The electrospun nanofiber mat is cut along the orientation and subjected to heat drawing treatment in an oven at 105°C. The draw ratio is 6, and then the fiber mat is pre-oxidized at 270°C in an air atmosphere and carbonized at 1200°C in an argon atmosphere.

[0064] The tensile strength of the prepared carbon fiber is 6.44 MPa, and the modulus is 1.98%.

[0065] Comparative Example 1

[0066] A PAN solution with a mass fraction of 19wt% was prepared using dimethylformamide as solvent without adding plasticizer. The obtained spinning dope was poured into a needle tube equipped with a spinning needle with an inner diameter of 0.5mm, and electrospinning was performed at a temperature of 40℃ and an electric field strength of 20kV, and the nanofiber sample was collected by a rotating roller with a rotating speed of 1000rpm.

[0067] The electrospun nanofiber mat was cut along the orientation and subjected to heat drawing treatment in an oven at 135℃. The draw ratio was 4, and then the fiber mat was pre-oxidized at 280℃ in an air atmosphere and carbonized at 1400℃ in a nitrogen atmosphere.

[0068] As shown in FIG. 1, the sample with the addition of plasticizer in Example 1 had a smaller fiber diameter and a more obvious orientation after drawing, indicating that the addition of plasticizer improved the drawability of the fiber. Figure 1

[0069] Figure 2 The stress-strain curve and tensile strength comparison chart of the carbon fiber obtained in the present application Comparative Example 1 and Example 1 can be seen, and it can be seen that the tensile strength of the carbon fiber prepared in Example 1 is obviously greater than that of the carbon fiber prepared in Comparative Example 1.

[0070] Figure 3 The stress-strain curve and tensile strength comparison chart of the carbon fiber obtained in the present application Comparative Example 1 and Example 1 can be seen, and it can be seen that the tensile strength of the carbon fiber prepared in Example 1 is obviously greater than that of the carbon fiber prepared in Comparative Example 1.

[0071] Comparative Example 2

[0072] The difference from Example 1 is that the plasticizer resorcinol bis(diphenyl) phosphate is replaced by dipentaerythritol ester, and the others are the same as Example 1.

[0073] The tensile strength of the prepared carbon fiber is 5.24MPa, and the modulus is 1.74%.

[0074] Comparative Example 3

[0075] The difference from Example 1 is that the pre-oxidation step is omitted, and the others are the same as Example 1.

[0076] The tensile strength of the prepared carbon fiber is 4.70MPa, and the modulus is 1.29%.

[0077] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. For those skilled in the art, the present application can have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.​

Claims

1. A method for producing high-performance polyacrylonitrile-based carbon fibers, characterized by: The method comprises the following steps: polyacrylonitrile, solvent and plasticizer are mixed in proportion, heated and stirred to obtain a uniform spinning dope; the plasticizer is diphenyl phthalate, bisphenol A-bis(diphenyl) phosphate or resorcinol bis(diphenyl) phosphate; The mass of the plasticizer is 5-60 wt% of the mass of the polyacrylonitrile. The spinning dope is spun to prepare a polyacrylonitrile fiber precursor; After heat drawing treatment of the polyacrylonitrile fiber precursor, pre-oxidation and carbonization treatment are performed to obtain a polyacrylonitrile-based carbon fiber. The pre-oxidation temperature is 200-300℃, and the pre-oxidation time is 80-160min.

2. The method for preparing high-performance polyacrylonitrile-based carbon fiber according to claim 1, characterized in that: The solvent is one of dimethylformamide, dimethylacetamide, dimethyl sulfoxide or sodium thiocyanate.

3. The method for preparing high-performance polyacrylonitrile-based carbon fiber according to claim 1, characterized in that: The solvent is dimethylformamide, and the plasticizer is resorcinol bis(diphenyl) phosphate.

4. The method for preparing high-performance polyacrylonitrile-based carbon fiber according to claim 1, characterized in that: In the spinning dope, the solid content is 13 wt%-25 wt%.

5. The method for preparing high-performance polyacrylonitrile-based carbon fiber according to claim 1, characterized in that: The mass of the plasticizer is 10-50 wt% of the mass of the polyacrylonitrile.

6. The method for preparing high-performance polyacrylonitrile-based carbon fiber according to claim 1, characterized in that: The spinning is one of electrospinning, wet spinning, dry-jet wet spinning, melt spinning or gel spinning.

7. The method for preparing high-performance polyacrylonitrile-based carbon fiber according to claim 1, characterized in that: The heat drawing temperature is 70-160℃, and the actual draw ratio is 1-10.

8. The method for preparing high-performance polyacrylonitrile-based carbon fiber according to claim 1, characterized in that: The heat drawing temperature is 100-160℃, and the actual draw ratio is 3-8.

9. The method for preparing high-performance polyacrylonitrile-based carbon fiber according to claim 8, characterized in that: The heat drawing temperature is 120-150℃, and the actual draw ratio is 3-6.

10. The method for preparing high-performance polyacrylonitrile-based carbon fiber according to claim 1, characterized in that: The carbonization is performed under nitrogen or argon, and the carbonization temperature is 400-2000℃.

11. A high performance polyacrylonitrile-based carbon fiber, characterized by: Prepared by the preparation method of any one of claims 1-10.

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