Polyacrylonitrile pre-oxidized fiber, preparation method therefor and use thereof

Abstract

A polyacrylonitrile fiber pre-oxidized fiber, a preparation method therefor and the use thereof. The pre-oxidized fiber comprises a core part and a skin part wrapping the core part, wherein the characteristic tensile parameter of the polyacrylonitrile pre-oxidized fiber is 475.0-580.0 cN / μm. Polyacrylonitrile-based carbon fibers prepared from the polyacrylonitrile pre-oxidized fibers reduce or eliminate chemical defects and structural defects, thereby improving the mechanical properties of carbon fibers.

Description

Polyacrylonitrile pre-oxidized yarn and its preparation method and use Technical Field

[0001] The present invention relates to polyacrylonitrile-based fibers, in particular to polyacrylonitrile preoxidized yarns and a preparation method and use thereof, and also to polyacrylonitrile-based carbon fibers and a preparation method thereof. Background Art

[0002] High-strength and high-modulus polyacrylonitrile (PAN)-based carbon fibers have a variety of excellent properties, and are therefore widely used in various fields, especially in high-end fields such as aerospace. The excellent properties of high-strength and high-modulus polyacrylonitrile (PAN)-based carbon fibers can be reflected in the following three aspects: (1) High-strength and high-modulus polyacrylonitrile-based carbon fibers can be used to form composite materials with high stiffness. The specific modulus of unidirectional composite materials prepared from high-strength and high-modulus polyacrylonitrile-based carbon fibers is usually 5-7 times greater than that of aluminum alloys. (2) Polyacrylonitrile-based high-strength and high-modulus carbon fibers can form composite materials with good dimensional stability. For example, using high-strength and high-modulus polyacrylonitrile-based carbon fibers as reinforcement materials, a composite material with a thermal expansion coefficient of nearly zero can be obtained through reasonable layer design, which has excellent dimensional stability in high and low temperature alternating environments. (3) Composite materials prepared from high-strength and high-modulus carbon fibers have a significant lightweight effect.

[0003] The preparation of polyacrylonitrile-based carbon fibers typically involves preparing polyacrylonitrile precursor fibers; pre-oxidizing the polyacrylonitrile precursor fibers to obtain pre-oxidized polyacrylonitrile fibers; and carbonizing and graphitizing the pre-oxidized polyacrylonitrile fibers to obtain polyacrylonitrile-based carbon fibers. Polyacrylonitrile precursor fibers have a straight, long molecular chain structure, which results in poor heat resistance, making them impractical for direct carbonization and graphitization. Therefore, pre-oxidation of the polyacrylonitrile precursor fibers plays a crucial role. During the pre-oxidation process, the straight polyacrylonitrile molecular chains within the polyacrylonitrile precursor fibers gradually form a "trapezoidal" polymer structure with excellent heat resistance, resulting in significantly improved heat resistance for the resulting pre-oxidized polyacrylonitrile fibers. During the subsequent carbonization and graphitization processes, the pre-oxidized polyacrylonitrile fibers gradually release non-carbon elements by releasing small molecules of gas. This trapezoidal polymer structure then forms the basis of a graphene-like structure, which gradually connects to form a network of graphite sheets.

[0004] The pre-oxidation process of polyacrylonitrile precursor is essentially a process of oxygen diffusion and reaction in the radial direction of the polyacrylonitrile precursor. Accordingly, the degree of pre-oxidation of the polyacrylonitrile precursor depends on a series of factors, such as the process conditions, temperature, and atmosphere. Consequently, pre-oxidation of polyacrylonitrile precursor will result in a common and unavoidable "skin-core" structure, a structural defect in the fiber itself. This defective structure can be further inherited into the resulting polyacrylonitrile-based carbon fibers after carbonization and graphitization, thereby affecting the quality of the resulting carbon fibers.

[0005] Summary of the Invention

[0006] In order to overcome the problems of chemical defects and structural defects in polyacrylonitrile preoxidized yarn and polyacrylonitrile-based carbon fibers in the prior art, the present invention provides a polyacrylonitrile preoxidized yarn and its preparation method and application, wherein the polyacrylonitrile preoxidized yarn has appropriate "characteristic tensile parameters" that are conducive to alleviating the formation of structural defects in the preoxidation stage. Therefore, the polyacrylonitrile-based carbon fibers prepared from the polyacrylonitrile preoxidized yarn alleviate or eliminate chemical defects and structural defects, thereby improving the mechanical properties of the carbon fibers. Accordingly, the present invention also provides a polyacrylonitrile-based carbon fiber and its preparation method.

[0007] In one aspect, the present invention provides a polyacrylonitrile pre-oxidized yarn, comprising a core and a sheath wrapping the core, wherein the characteristic tensile parameter A of the polyacrylonitrile pre-oxidized yarn is 475.0-580.0 cN / μm, and the characteristic tensile parameter A is shown in formula (1):

[0008] In formula (1), A represents the characteristic tensile parameter of the polyacrylonitrile pre-oxidized yarn (cN / μm), T represents the breaking strength of the polyacrylonitrile pre-oxidized yarn (cN), η represents the area ratio of the radial cross-section of the sheath to the radial cross-section of the entire polyacrylonitrile pre-oxidized yarn, and d represents the diameter of the polyacrylonitrile pre-oxidized yarn (μm).

[0009] In another aspect, the present invention provides a polyacrylonitrile-based carbon fiber, which is prepared from the polyacrylonitrile pre-oxidized yarn of the present invention and has a tensile strength greater than or equal to 5000 MPa and a tensile modulus of 500-600 GPa.

[0010] In another aspect, the present invention provides a method for preparing polyacrylonitrile preoxidized yarn, preferably for preparing the polyacrylonitrile preoxidized yarn of the present invention, the preparation method comprising at least: preoxidizing the polyacrylonitrile precursor in a low-temperature section, preoxidizing the polyacrylonitrile in a medium-temperature section, and preoxidizing the polyacrylonitrile in a high-temperature section in sequence to obtain the polyacrylonitrile preoxidized yarn;

[0011] Among them, the process parameters of controlling low temperature pre-oxidation, medium temperature pre-oxidation and high temperature pre-oxidation are To satisfy the following formula (2): N i,min ≤Ci≤N i,max (2)

[0012] Wherein, i=1, 2, 3, corresponding to low temperature pre-oxidation, medium temperature pre-oxidation and high temperature pre-oxidation respectively; P i is the pre-oxidation pressure (Pa); T i is the pre-oxidation temperature (℃); t i is the duration of pre-oxidation (min),

[0013] Wherein, for the low temperature pre-oxidation, C1 satisfies: 1.0≤C1≤10.0 (i.e., i=1, N in the above formula (2) 1,min =1.0 and N 1,max =10), preferably 1.90≤C1≤8.33 (i.e., i=1, N in the above formula (2) 1,min =1.90 and N 1,max =8.33); For the medium temperature pre-oxidation, C2 satisfies: 0.1≤C2≤2.5 (i.e., i=2, N in the above formula (2) 2,min =0.1 and N 2,max =2.5), preferably 0.48≤C2≤1.25 (i.e., i=2, N in the above formula (2) 2,min =0.48 and N 2,max =1.25); and, for the high temperature pre-oxidation, C3 satisfies: 0.5≤C3≤4.0 (i.e., i=3, N in the above formula (2) 3,min =0.5 and N 3,max =4), preferably 0.85≤C3≤2.13 (i.e. i=3, N in the above formula (2) 3,min =0.85 and N 3,max =2.13).

[0014] In another aspect, the present invention provides a polyacrylonitrile pre-oxidized fiber obtained by the preparation method of the present invention.

[0015] In yet another aspect, the present invention provides use of the polyacrylonitrile pre-oxidized yarn of the present invention in the preparation of carbon fibers.

[0016] In another aspect, the present invention provides a method for preparing polyacrylonitrile-based carbon fibers, comprising: sequentially subjecting polyacrylonitrile preoxidized fibers to low-temperature carbonization treatment, high-temperature carbonization treatment, and graphitization treatment, wherein the polyacrylonitrile preoxidized fibers are the polyacrylonitrile preoxidized fibers of the present invention or the polyacrylonitrile preoxidized fibers prepared according to the method of the present invention.

[0017] Compared with the prior art, the present invention has the following advantages:

[0018] (1) The polyacrylonitrile preoxidized yarn of the present invention has characteristic tensile parameters within a specific range. The inventor unexpectedly discovered that the polyacrylonitrile preoxidized yarn with characteristic tensile parameters within this range has a small amount of structural defects and chemical defects, and can simultaneously have a radial structure with a large sheath ratio and a more suitable fiber breaking strength. During the preoxidation process of the polyacrylonitrile precursor, as oxygen propagates from the outside to the inside of the precursor and undergoes a thermal oxidation stabilization reaction, it will inevitably form a gradient difference in the degree of stabilization between the inside and the outside, and the sheath ratio will gradually increase. However, under such circumstances, most of the ordered structure inside the precursor and the polyacrylonitrile molecular crystal structure will usually be destroyed to a certain extent, resulting in a decrease in the internal crystallinity, molecular cohesion, and rigidity, thereby causing the breaking strength of the obtained polyacrylonitrile preoxidized yarn to be adversely affected. The polyacrylonitrile preoxidized yarn of the present invention can not only achieve a high "sheath ratio" of the fiber, but also a small loss in the breaking strength of the preoxidized yarn, which is obviously unexpected compared to the polyacrylonitrile preoxidized yarn obtained by the prior art. More importantly, the oxygen element distribution in the sheath of the polyacrylonitrile preoxidized yarn of the present invention is also more uniform. The uniform distribution of oxygen can be characterized by SEM-EDS. A more uniform distribution of oxygen in the cortex means that local oxygen accumulation can be avoided. The more oxygen the polyacrylonitrile precursor absorbs, the more oxygen accumulates in that area, and accordingly, the denser the area is, and the smaller the intermolecular force is. In addition, the degree of molecular reaction inside the polyacrylonitrile precursor will reduce the structure supporting the mechanical properties due to excessive oxygen intake. At the same time, it will further hinder the subsequent diffusion of oxygen into the precursor. This series of negative effects will cause excessive chemical defects and structural defects to be concentrated in the outer area of ​​the polyacrylonitrile pre-oxidized fiber and a decrease in the overall pre-oxidized fiber breaking strength. During the pre-oxidation process, the long straight polyacrylonitrile molecular chains in the polyacrylonitrile precursor gradually form a trapezoidal polymer structure and cross-linked macromolecules. However, in areas where local oxygen accumulation occurs, excessive oxygen intake on the molecular chain will cause the trapezoidal polymer structure to release excessive small molecular gases containing oxygen elements, such as CO2, H2O, NO, during the subsequent carbonization process. x Etc., so that the longer polyacrylonitrile molecular chain can therefore break, shorten, cause the undersize forming graphite embryonic structure, finally be difficult to form more regular graphite large lamellar structure and can leave the hole of bubble shape on fiber structure after carbonization and graphitization.They all can become the site of stress concentration of carbon fiber when bearing external load, thereby fracture in advance, and then affect carbon fiber performance.Therefore, by the carbon fiber of preparation of polyacrylonitrile pre-oxidized silk of the present invention, chemical defect and structural defect in gained carbon fiber will be reduced or eliminated, and this improves the mechanical property of this carbon fiber.

[0019] (2) The present invention controls the range of the process parameter Ci during the preparation of polyacrylonitrile preoxidized yarn, thereby controlling the temperature, pressure, and time of the preoxidation process. The applicant unexpectedly discovered that the control of the process parameters, especially the optimized selection of the range of the preoxidation temperature, pressure, and time in each stage of preoxidation in the preferred embodiment, makes it easier for oxygen to diffuse into the interior of the polyacrylonitrile precursor. Therefore, during the preoxidation preparation process, excessive accumulation of oxygen elements in the outer surface area of ​​the polyacrylonitrile precursor is avoided, and accordingly, chemical defects and structural defects in the polyacrylonitrile preoxidized yarn are avoided, as described above. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The accompanying drawings are used to provide a further understanding of the present application and constitute a part of the specification. Together with the following detailed description, they are used to explain the present application but do not constitute a limitation of the present application. In the accompanying drawings:

[0021] FIG1 shows an optical microscope image of a cross section of the pre-oxidized polyacrylonitrile fiber obtained in Example 16.

[0022] FIG2 shows an optical microscope image of a cross section of the pre-oxidized polyacrylonitrile fiber obtained in Comparative Example 1.

[0023] FIG3 shows a cross-sectional scanning electron microscope (SEM) image of the polyacrylonitrile pre-oxidized filament obtained in Example 16, in which the linear scanning path of the EDS spectrum is marked.

[0024] FIG4 shows the energy spectrum of the outer region of the sheath of the polyacrylonitrile pre-oxidized yarn obtained in Example 16.

[0025] FIG5 shows the energy spectrum of the inner region of the sheath of the polyacrylonitrile pre-oxidized yarn obtained in Example 16.

[0026] FIG6 shows the energy spectrum of the core of the polyacrylonitrile pre-oxidized yarn obtained in Example 16. DETAILED DESCRIPTION

[0027] The present application will be further described in detail below through the accompanying drawings and examples, through which the features and advantages of the present application will become more clear and distinct.

[0028] Any specific numerical value disclosed herein (including the endpoints of a numerical range) is not limited to the exact value of the numerical value, but should be understood to also include values ​​close to the exact value, such as all possible values ​​within ±5% of the exact value. Moreover, for a disclosed numerical range, any combination of the endpoints of the range, between the endpoints and the specific points in the range, and between the specific points can be used to generate one or more new numerical ranges, and these new numerical ranges should also be considered to be specifically disclosed herein.

[0029] Except in the examples, all numerical values ​​of parameters herein are to be understood as being modified in all instances by the term "about", whether or not "about" actually precedes the numerical value.

[0030] In one aspect, the present invention provides a polyacrylonitrile pre-oxidized yarn, comprising a core and a sheath wrapping the core, wherein the characteristic tensile parameter A of the polyacrylonitrile pre-oxidized yarn is 475.0-580.0 cN / μm, and the characteristic tensile parameter A is shown in formula (1):

[0031] In formula (1), A represents the characteristic tensile parameter of the polyacrylonitrile pre-oxidized yarn (cN / μm), T represents the breaking strength of the polyacrylonitrile pre-oxidized yarn (cN), η represents the area ratio of the radial cross-section of the sheath to the radial cross-section of the entire polyacrylonitrile pre-oxidized yarn, and d represents the diameter of the polyacrylonitrile pre-oxidized yarn (μm).

[0032] In the present invention, the breaking strength is obtained by testing according to GB / T 14337-2008.

[0033] In the present invention, η can be obtained as follows: obtain a cross-sectional image of the polyacrylonitrile pre-oxidized yarn and calculate the area ratio of the cortex cross section to the entire pre-oxidized yarn cross section, wherein the cortex cross section is the dark part on the periphery of the cross-sectional image of the polyacrylonitrile pre-oxidized yarn.

[0034] In a preferred embodiment, 1.5 cN≤T≤8.0 cN, preferably, 2.5 cN≤T≤5.2 cN.

[0035] In a preferred embodiment, 55%≤η≤95%, preferably, 74%≤η≤91%, for example, η=55%, 60%, 65%, 70%, 75%, 80%, 85%, 90% or 95%.

[0036] In a preferred embodiment, 5.0 μm≤d≤15.0 μm, preferably, 7.0 μm≤d≤10.0 μm, for example, d=5.0 μm, 6.0 μm, 8.0 μm, 10.0 μm, 12.0 μm, 14.0 μm or 15.0 μm.

[0037] In a preferred embodiment, the characteristic tensile parameter of the polyacrylonitrile pre-oxidized yarn is 480.0-575.0 cN / μm, preferably 482.5-571.5 cN / μm, for example, 480.0 cN / μm, 490.0 cN / μm, 500.0 cN / μm, 510.0 cN / μm, 520.0 cN / μm, 530.0 cN / μm, 540.0 cN / μm, 550.0 cN / μm, 560.0 cN / μm, 570.0 cN / μm or 575.0 cN / μm.

[0038] In a preferred embodiment, the difference in oxygen content between the outer area and the inner area of ​​the sheath of the polyacrylonitrile pre-oxidized yarn is 1.5wt%-3.2wt%, preferably 1.8wt%-2.9wt%; preferably, the oxygen content of the outer area of ​​the sheath of the pre-oxidized yarn is 9.0wt%-14.0wt%, preferably 10.5wt%-12.0wt%; the oxygen content of the inner area of ​​the pre-oxidized yarn is 9.0wt%-11.5wt%, preferably 9.5wt%-10.2wt%. In the cross section of the polyacrylonitrile pre-oxidized yarn, the sheath is roughly annular, the outer side of which is the surface layer of the pre-oxidized yarn, and the inner side is connected to the core. There is a midpoint on the radial line segment connecting the inner and outer sides of the sheath. The area covered from the outer side to the midpoint is the outer area of ​​the sheath, and the area covered from the midpoint to the inner side is the inner area of ​​the sheath.

[0039] In one variation, the difference in oxygen content between any two points in the sheath of the polyacrylonitrile pre-oxidized yarn is 1.5 wt%-3.2 wt%, preferably 1.8 wt%-2.9 wt%.

[0040] The polyacrylonitrile pre-oxidized yarn of the present invention has a small difference in oxygen content between the outer and inner regions of the cortex. Preferably, the difference in oxygen content between any two points in the cortex is small. Accordingly, oxygen is more evenly distributed in the cortex, rather than being locally enriched. The oxygen content can be measured by SEM-EDS.

[0041] In another aspect, the present invention provides a polyacrylonitrile-based carbon fiber, which is prepared from the polyacrylonitrile pre-oxidized yarn of the present invention, and has a tensile strength greater than or equal to 4000 MPa, preferably greater than or equal to 5000 MPa, and a tensile modulus of 500-600 GPa, preferably 540-570 GPa.

[0042] In one aspect, the present invention provides a method for preparing polyacrylonitrile preoxidized yarn, which is preferably used to prepare the polyacrylonitrile preoxidized yarn of the present invention, and the preparation method comprises the steps of: preoxidizing the polyacrylonitrile precursor in a low temperature section, preoxidizing the polyacrylonitrile precursor in a medium temperature section, and preoxidizing the polyacrylonitrile precursor in a high temperature section in sequence to obtain the polyacrylonitrile preoxidized yarn; wherein the process parameters of the low temperature section, the medium temperature section, and the high temperature section are controlled. To satisfy the following formula (2): N i,min ≤Ci≤N i,max (2)

[0043] Wherein, i=1, 2, 3, corresponding to low temperature pre-oxidation, medium temperature pre-oxidation and high temperature pre-oxidation respectively; P i is the pre-oxidation pressure (Pa); T i is the pre-oxidation temperature (℃); t i is the duration of pre-oxidation (min),

[0044] Among them, for the low-temperature pre-oxidation, 1.00≤C1≤10.00, preferably 1.90≤C1≤8.33; for the medium-temperature pre-oxidation, 0.10≤C2≤2.50, preferably 0.48≤C2≤1.25; and for the high-temperature pre-oxidation, 0.50≤C3≤4.00, preferably 0.85≤C3≤2.13.

[0045] In one embodiment, the conditions for pre-oxidation in the low-temperature stage include: temperature T1 of 200-210°C; time t1 of no more than 10 minutes, preferably 3-5 minutes; pressure P1 of 18-55 Pa, preferably 20-50 Pa. The conditions for pre-oxidation in the medium-temperature stage include: temperature T2 of 240-250°C, time t2 of 20-35 minutes, preferably 20-25 minutes; pressure P2 of 25-65 Pa, preferably 30-60 Pa. The conditions for pre-oxidation in the high-temperature stage include: temperature T3 of 245-280°C, time t3 of 15-25 minutes, preferably 15-18 minutes; pressure P3 of 35-85 Pa, preferably 40-80 Pa.

[0046] In one variation, T2=(1.20-1.22)*T1, preferably 20°C≤T2-T1≤50°C, more preferably 30°C≤T2-T1≤40°C; 0°C≤T3-T2≤20°C, preferably 5°C≤T3-T2≤15°C, more preferably 10°C≤T3-T2≤15°C.

[0047] Preferably, for the low temperature pre-oxidation, N in the above formula (2) 1,min It can be, for example, 1.90, 2.00, 2.50, 3.00, 3.50, 4.00, etc., and N 1,maxIt can be, for example, 8.33, 8.00, 7.50, 7.00, 6.50, 6.00, 5.50, 5.00, etc. For the medium temperature pre-oxidation, N in the above formula (2) 2,min It can be, for example, 0.48, 0.50, 0.55, 0.60, etc., and N 2,max It can be, for example, 1.25, 1.24, 1.23, 1.22, 1.21, 1.20, etc.; and, for the high temperature pre-oxidation, N in the above formula (2) 3,min It can be, for example, 0.85, 0.90, 0.95, 1.00, etc., and N 3,max It can be 2.13, 2.10, 2.05, 2.00, etc.

[0048] In the method of the present invention, the "polyacrylonitrile precursor" can be replaced by a tow of polyacrylonitrile precursor. In one embodiment, the number of roots of the tow of polyacrylonitrile precursor is 1-20K, preferably, the number of roots of the tow of polyacrylonitrile precursor is 3-12K,

[0049] Preferably, the polyacrylonitrile precursor is obtained by dry spinning or wet spinning, preferably wet spinning. In one embodiment, the method for preparing the polyacrylonitrile precursor comprises the steps of: mixing acrylonitrile and a comonomer to form a monomer mixture; polymerizing the monomer mixture to obtain polyacrylonitrile; and spinning the polyacrylonitrile to obtain the polyacrylonitrile precursor. Examples of comonomers include acrylic acid, methacrylic acid, methyl acrylate, ethyl acrylate, methyl methacrylate, ethyl methacrylate, itaconic acid, etc. The process conditions for each step of the preparation method can be those commonly used in the art.

[0050] In one embodiment, the diameter of the polyacrylonitrile precursor is 5.0-15.0 μm, preferably 7.0-11.0 μm. When a tow composed of polyacrylonitrile precursor is used, the average diameter of the polyacrylonitrile precursor is 5.0-15.0 μm, preferably 7.0-11.0 μm.

[0051] In a preferred embodiment, during the low-temperature pre-oxidation, the medium-temperature pre-oxidation, and the high-temperature pre-oxidation, the drafting ratio of the polyacrylonitrile precursor is independently 0.80-1.20, preferably 0.90-1.10.

[0052] The polyacrylonitrile pre-oxidized yarn obtained by the preparation method of the present invention has the properties described above for the polyacrylonitrile pre-oxidized yarn, which will not be described in detail here.

[0053] In one aspect, the present invention provides a polyacrylonitrile pre-oxidized fiber obtained by the preparation method of the present invention.

[0054] In one aspect, the present invention provides a method for preparing polyacrylonitrile-based carbon fibers, comprising: sequentially subjecting polyacrylonitrile preoxidized fibers to low-temperature carbonization treatment, high-temperature carbonization treatment, and graphitization treatment, wherein the polyacrylonitrile preoxidized fibers are the polyacrylonitrile preoxidized fibers of the present invention or the polyacrylonitrile preoxidized fibers prepared according to the method of the present invention.

[0055] The present invention has no particular restrictions on the conditions for low-temperature carbonization treatment, high-temperature carbonization treatment and graphitization treatment, and the common conditions in this field can be adopted. In one embodiment, the conditions for the low-temperature carbonization treatment include: a temperature of 200-1000°C, a time of 0.5-10min, and a draft ratio of 0.80-1.20. Preferably, the conditions for the low-temperature carbonization treatment include: a temperature of 400-1000°C, a time of 1-4min, and a draft ratio of 1.00-1.06. More preferably, the low-temperature carbonization is carried out in multiple (e.g., 2-8 or 3-6) temperature zones, wherein the temperature of the latter temperature zone is higher than the temperature of the previous temperature zone.

[0056] In one embodiment, the high-temperature carbonization treatment conditions include: a temperature of 800-1800°C, a treatment time of 0.5-10 min, and a draft ratio of 0.80-1.00. Preferably, the high-temperature carbonization treatment conditions include: a temperature of 1000-1500°C, a treatment time of 1-4 min, and a draft ratio of 0.96-0.99. More preferably, the high-temperature carbonization is performed in multiple (e.g., 2-8 or 3-6) temperature zones, wherein the temperature of each subsequent temperature zone is higher than that of the preceding temperature zone.

[0057] In one embodiment, the graphitization treatment conditions include: a temperature of 2200-3000° C., a treatment time of 0.2-15 min, and a draw ratio of 0.90-1.50. Preferably, the graphitization treatment conditions include: a temperature of 2500-2700° C., a treatment time of 1-5 min, and a draw ratio of 1.04-1.15.

[0058] In one variation, the preparation method comprises:

[0059] (1) subjecting the polyacrylonitrile preoxidized yarn of the present invention or the polyacrylonitrile preoxidized yarn obtained by the preparation method of the present invention to a low-temperature carbonization treatment, wherein the conditions of the low-temperature carbonization treatment include: a temperature of 300-800° C., a time of about 1-4 minutes, and a draft ratio of 1.00-1.06;

[0060] (2) subjecting the polyacrylonitrile pre-oxidized filament obtained in step (1) to a high-temperature carbonization treatment, wherein the conditions of the high-temperature carbonization treatment include: a temperature of 1000-1500° C., a time of 1-4 minutes, and a draft ratio of 0.96-0.99;

[0061] (3) graphitizing the polyacrylonitrile pre-oxidized filaments obtained in step (2), wherein the graphitization treatment conditions include: a temperature of 2500-2700° C., a time of 1-5 min, and a draft ratio of 1.04-1.15.

[0062] In one aspect, the present invention provides the use of the polyacrylonitrile preoxidized filament of the present invention in the preparation of carbon fibers. Specifically, the polyacrylonitrile preoxidized filament is sequentially subjected to low-temperature carbonization treatment, high-temperature carbonization treatment and graphitization treatment to obtain the polyacrylonitrile-based carbon fibers. Preferably, the conditions for the low-temperature carbonization treatment include: a temperature of 400-1000°C, a time of 0.5-10min, and a draft ratio of 0.80-1.20. The conditions for the high-temperature carbonization treatment include: a temperature of 800-1800°C, a time of 0.5-10min, and a draft ratio of 0.80-1.02. The conditions for the graphitization treatment include: a temperature of 2200-3000°C, a time of 0.2-15min, and a draft ratio of 0.90-1.50.

[0063] The polyacrylonitrile preoxidized yarn of the present invention has characteristic tensile parameters within a specific range, particularly a more uniform oxygen distribution, thereby reducing and avoiding chemical and structural defects. Accordingly, when polyacrylonitrile-based carbon fibers are prepared from the polyacrylonitrile preoxidized yarn, the resulting carbon fibers have improved mechanical properties, with a tensile strength of greater than or equal to 4000 MPa, preferably greater than or equal to 5000 MPa, and a tensile modulus of 500-600 GPa, preferably 540-570 GPa.

[0064] Example

[0065] The following examples will further illustrate the present application, but are not intended to limit the present application.

[0066] The polyacrylonitrile precursor used in the examples and comparative examples is a tow consisting of 6K polyacrylonitrile precursors prepared by a conventional method. The polyacrylonitrile precursor contains 95.5 wt % acrylonitrile, 3.5 wt % methyl acrylate and 1.0 wt % itaconic acid, and has a fineness of 0.8551 d / tex.

[0067] Parameter testing and calculation:

[0068] η and d: The polyacrylonitrile pre-oxidized wire was ultra-thinly sliced ​​along the radial direction to obtain its optical microscope image, the average diameter d of the polyacrylonitrile pre-oxidized wire was measured, and the proportion η of the concentric circle endothelial part of the polyacrylonitrile pre-oxidized wire section (i.e. all parts with dark contrast) to the concentric circle area of ​​the entire polyacrylonitrile pre-oxidized wire section was quantified.

[0069] T: The single-filament breaking strength of polyacrylonitrile pre-oxidized yarn is tested according to GB / T 14337-2008.

[0070] Characteristic tensile parameters: Using the obtained T, η and d, the characteristic tensile parameters of the polyacrylonitrile pre-oxidized yarn are calculated according to formula (1).

[0071] The difference in oxygen content between the outer and inner areas of the pre-oxidized silk skin, △O: Zeiss's scanning electron microscope analysis and characterization instrument Merlin was used to perform SEM-EDS cross-sectional morphology characterization and radial element energy spectrum analysis on the polyacrylonitrile pre-oxidized silk slices. 10 sampling points were selected along the radial direction of the polyacrylonitrile pre-oxidized silk. The peak area of ​​the oxygen element peak obtained at the sampling point was integrated to obtain its oxygen element content (wt%). The average value of the oxygen element content of the sampling points located in the outer area was taken as the oxygen element content of the outer area, and the average value of the oxygen element content of the sampling points located in the inner area was taken as the oxygen element content of the inner area, and the difference in oxygen element content between the outer and inner areas of the pre-oxidized silk skin was calculated therefrom.

[0072] Tensile strength and tensile modulus of polyacrylonitrile-based carbon fibers: The mechanical properties of polyacrylonitrile-based carbon fiber tows were tested in accordance with the national standard GB / T25749-2011 to obtain their tensile strength and tensile modulus.

[0073] [Comparative Example 1]

[0074] The polyacrylonitrile precursor was pre-oxidized in the low-temperature section under the following process conditions: temperature of 180°C, pressure of 15Pa, time of 15min, process parameter C1 corresponding to pre-oxidation in the low-temperature section was 0.55, and the draft ratio was 1.03; then pre-oxidation in the medium-temperature section was carried out under the following process conditions: temperature of 230°C, pressure of 20Pa, time of 30min, process parameter C2 corresponding to pre-oxidation in the medium-temperature section was 0.29, and the draft ratio was 1.03; finally, pre-oxidation in the high-temperature section was carried out under the following process conditions: temperature of 250°C, pressure of 25Pa, time of 20min, process parameter C3 corresponding to pre-oxidation in the high-temperature section was 0.50, and the draft ratio was 1.00, to obtain PAN pre-oxidized yarn.

[0075] The polyacrylonitrile pre-oxidized filaments were subjected to low-temperature carbonization, high-temperature carbonization, and graphitization in high-purity nitrogen in sequence to obtain polyacrylonitrile-based carbon fibers. The low-temperature carbonization treatment was carried out in four temperature zones, with temperatures ranging from 320°C to 400°C to 550°C to 700°C, for a total time of 3 minutes and a draft ratio of 1.06; the high-temperature carbonization treatment was carried out in four temperature zones, with temperatures ranging from 1100°C to 1200°C to 1300°C to 1450°C, for a total time of 2 minutes and a draft ratio of 0.96; the graphitization treatment conditions were: temperature of 2500°C, draft ratio of 1.04, and time of 3 minutes.

[0076] As mentioned above, the parameters of PAN pre-oxidized filaments and polyacrylonitrile-based carbon fibers were tested and calculated, and the results are shown in Table 1.

[0077] [Comparative Example 2]

[0078] Comparative Example 1 was repeated, except that the process conditions for low-temperature pre-oxidation of the polyacrylonitrile precursor were: temperature of 160°C, pressure of 20 Pa, and time of 15 min. The process parameter C1 corresponding to the low-temperature pre-oxidation was 0.83, and the drawing ratio was 1.03.

[0079] [Comparative Example 3]

[0080] Comparative Example 1 was repeated, except that the process conditions for low-temperature pre-oxidation of the polyacrylonitrile precursor were: temperature of 160°C, pressure of 20 Pa, and time of 20 min. The process parameter C1 corresponding to the low-temperature pre-oxidation was 0.62, and the drawing ratio was 1.07.

[0081] [Comparative Example 4]

[0082] Comparative Example 1 was repeated, except that the process conditions for low-temperature pre-oxidation of the polyacrylonitrile precursor were: temperature of 180°C, pressure of 20 Pa, and time of 8 min. The process parameter C1 corresponding to the low-temperature pre-oxidation was 1.39, and the drawing ratio was 1.13.

[0083] [Comparative Example 5]

[0084] Comparative Example 1 was repeated, except that the process conditions for low-temperature pre-oxidation of the polyacrylonitrile precursor were: temperature of 180°C, pressure of 20 Pa, and time of 5 min, corresponding to the process parameter C1 of low-temperature pre-oxidation of 2.22, and the stretching ratio of 1.03; the process conditions for medium-temperature pre-oxidation were: temperature of 255°C, pressure of 35 Pa, and time of 10 min, corresponding to the process parameter C2 of medium-temperature pre-oxidation of 1.37, and the stretching ratio of 1.02.

[0085] [Comparative Example 6]

[0086] Comparative Example 1 was repeated, except that the process conditions for pre-oxidation of the polyacrylonitrile precursor in the low-temperature section were: temperature of 180°C, pressure of 20 Pa, and time of 5 min, the process parameter C1 corresponding to pre-oxidation in the low-temperature section was 2.22, and the stretching ratio was 1.03; the process conditions for pre-oxidation in the medium-temperature section were: temperature of 240°C, pressure of 30 Pa, and time of 10 min, the process parameter C2 corresponding to pre-oxidation in the medium-temperature section was 1.25, and the stretching ratio was 1.02; the process conditions for pre-oxidation in the high-temperature section were: temperature of 250°C, pressure of 30 Pa, and time of 30 min, the process parameter C3 corresponding to pre-oxidation in the high-temperature section was 0.40, and the stretching ratio was 1.00.

[0087] [Comparative Example 7]

[0088] Comparative Example 1 was repeated, except that the process conditions for pre-oxidation of the polyacrylonitrile precursor in the medium temperature section were as follows: temperature of 253°C, pressure of 25 Pa, and time of 7 min, corresponding to the process parameter C2 of pre-oxidation in the medium temperature section being 1.41, and the stretching ratio being 1.03; the process conditions for pre-oxidation in the high temperature section were as follows: temperature of 265°C, pressure of 35 Pa, and time of 5 min, corresponding to the process parameter C3 of pre-oxidation in the high temperature section being 2.64, and the stretching ratio being 1.00.

[0089] [Comparative Example 8]

[0090] Comparative Example 1 was repeated, except that the process conditions for pre-oxidation of the polyacrylonitrile precursor in the medium temperature section were as follows: temperature of 240°C, pressure of 78 Pa, and time of 15 min, corresponding to the process parameter C2 of pre-oxidation in the medium temperature section being 2.17, and the drawing ratio being 1.03; the process conditions for pre-oxidation in the high temperature section were as follows: temperature of 265°C, pressure of 35 Pa, and time of 5 min, corresponding to the process parameter C3 of pre-oxidation in the high temperature section being 2.64, and the drawing ratio being 1.00.

[0091] [Comparative Example 9]

[0092] Comparative Example 1 was repeated, except that the process conditions for the low-temperature pre-oxidation of the polyacrylonitrile precursor were: temperature 217°C, pressure 150 Pa, time 8 min, process parameter C1 corresponding to the low-temperature pre-oxidation was 8.64, and the draft ratio was 1.07; the process conditions for the medium-temperature pre-oxidation were: temperature 255°C, pressure 110 Pa, time 30 min, process parameter C2 corresponding to the medium-temperature pre-oxidation was 1.43, and the draft ratio was 1.02. The process conditions for the high-temperature pre-oxidation were: temperature 262°C, pressure 35 Pa, time 30 min, process parameter C3 corresponding to the high-temperature pre-oxidation was 0.44, and the draft ratio was 1.00.

[0093] [Comparative Example 10]

[0094] Comparative Example 9 was repeated, except that the process conditions for high-temperature pre-oxidation of the polyacrylonitrile precursor were: temperature of 265°C, pressure of 160 Pa, time of 12 min, process parameter C3 corresponding to high-temperature pre-oxidation was 5.03, and the drawing ratio was 1.00.

[0095] [Comparative Example 11]

[0096] Comparative Example 1 was repeated, except that the process conditions for the low-temperature pre-oxidation of the polyacrylonitrile precursor were: temperature 185°C, pressure 16 Pa, time 5 min, process parameter C1 corresponding to the low-temperature pre-oxidation was 1.59, and the draft ratio was 1.00; the process conditions for the medium-temperature pre-oxidation were: temperature 235°C, pressure 30 Pa, time 8 min, process parameter C2 corresponding to the medium-temperature pre-oxidation was 1.43, and the draft ratio was 1.03. The process conditions for the high-temperature pre-oxidation were: temperature 265°C, pressure 105 Pa, time 18 min, process parameter C3 corresponding to the high-temperature pre-oxidation was 2.20, and the draft ratio was 1.00.

[0097] [Comparative Example 12]

[0098] Comparative Example 1 was repeated, except that the process conditions for the low-temperature pre-oxidation of the polyacrylonitrile precursor were: temperature 195°C, pressure 18 Pa, time 6 min, process parameter C1 corresponding to the low-temperature pre-oxidation was 1.53, and the draft ratio was 1.03; the process conditions for the medium-temperature pre-oxidation were: temperature 238°C, pressure 27 Pa, time 8 min, process parameter C2 corresponding to the medium-temperature pre-oxidation was 1.42, and the draft ratio was 1.03. The process conditions for the high-temperature pre-oxidation were: temperature 260°C, pressure 125 Pa, time 20 min, process parameter C3 corresponding to the high-temperature pre-oxidation was 2.40, and the draft ratio was 1.00.

[0099] [Example 1]

[0100] The polyacrylonitrile precursor was subjected to low-temperature pre-oxidation, and the process conditions were: temperature of 200°C, pressure of 20Pa, time of 3min, process parameter C1 corresponding to low-temperature pre-oxidation was 3.33, and the drawing ratio was 1.06; then medium-temperature pre-oxidation was carried out, and the process conditions were: temperature of 240°C, pressure of 30Pa, time of 20min, process parameter C2 corresponding to medium-temperature pre-oxidation was 0.625, and the drawing ratio was 1.03; finally, high-temperature pre-oxidation was carried out, and the process conditions were: temperature of 250°C, pressure of 40Pa, time of 15min, process parameter C3 corresponding to high-temperature pre-oxidation was 1.06, and the drawing ratio was 1.00, thereby obtaining polyacrylonitrile pre-oxidized yarn.

[0101] Polyacrylonitrile pre-oxidized filaments were subjected to low-temperature carbonization, high-temperature carbonization, and graphitization in high-purity nitrogen to obtain polyacrylonitrile-based carbon fibers. The low-temperature carbonization treatment was carried out in four temperature zones, with temperatures ranging from 320°C to 400°C to 550°C to 700°C, for a total time of 3 minutes and a draft ratio of 1.06; the high-temperature carbonization treatment was carried out in four temperature zones, with temperatures ranging from 1100°C to 1200°C to 1300°C to 1450°C, for a total time of 2 minutes and a draft ratio of 0.96; and the graphitization treatment conditions were: temperature of 2500°C, draft ratio of 1.04, and time of 3 minutes.

[0102] As mentioned above, the parameters of polyacrylonitrile pre-oxidized yarn and polyacrylonitrile-based carbon fiber were tested and calculated, and the results are shown in Table 1.

[0103] [Example 2]

[0104] Example 1 was repeated, except that the process conditions for low-temperature pre-oxidation of the polyacrylonitrile precursor were: temperature of 200°C, pressure of 35 Pa, and time of 3 min. The process parameter C1 corresponding to the low-temperature pre-oxidation was 5.83, and the drawing ratio was 1.03.

[0105] [Example 3]

[0106] Example 1 was repeated, except that the process conditions for low-temperature pre-oxidation of the polyacrylonitrile precursor were: temperature of 200°C, pressure of 50 Pa, and time of 3 min, the process parameter C1 corresponding to low-temperature pre-oxidation was 8.33, and the drawing ratio was 1.05.

[0107] [Example 4]

[0108] Example 1 was repeated, except that the process conditions for low-temperature pre-oxidation of the polyacrylonitrile precursor were: temperature of 210°C, pressure of 35 Pa, and time of 4 min. The process parameter C1 corresponding to the low-temperature pre-oxidation was 4.17, and the drawing ratio was 1.05.

[0109] [Example 5]

[0110] Example 1 was repeated, except that the process conditions for low-temperature pre-oxidation of the polyacrylonitrile precursor were: temperature of 210°C, pressure of 50 Pa, and time of 5 min. The process parameter C1 corresponding to the low-temperature pre-oxidation was 4.76, and the drawing ratio was 1.05.

[0111] [Example 6]

[0112] Example 1 was repeated, except that the process conditions for low-temperature pre-oxidation of the polyacrylonitrile precursor were: temperature of 200°C, pressure of 20 Pa, and time of 3 min, the process parameter C1 corresponding to low-temperature pre-oxidation was 3.33, and the stretching ratio was 1.05; the process conditions for medium-temperature pre-oxidation were: temperature of 245°C, pressure of 30 Pa, and time of 20 min, the process parameter C2 corresponding to medium-temperature pre-oxidation was 0.61, and the stretching ratio was 1.02.

[0113] [Example 7]

[0114] Example 1 was repeated, except that the process conditions for pre-oxidation of the polyacrylonitrile precursor in the low-temperature section were as follows: temperature of 200°C, pressure of 20 Pa, and time of 3 min, the process parameter C1 corresponding to pre-oxidation in the low-temperature section was 3.33, and the stretching ratio was 1.02; the process conditions for pre-oxidation in the medium-temperature section were as follows: temperature of 245°C, pressure of 50 Pa, and time of 20 min, the process parameter C2 corresponding to pre-oxidation in the medium-temperature section was 1.02, and the stretching ratio was 1.02.

[0115] [Example 8]

[0116] Example 1 was repeated, except that the process conditions for low-temperature pre-oxidation of the polyacrylonitrile precursor were: temperature of 210°C, pressure of 50 Pa, and time of 5 min, the process parameter C1 corresponding to low-temperature pre-oxidation was 4.76, and the stretching ratio was 1.05; the process conditions for medium-temperature pre-oxidation were: temperature of 250°C, pressure of 60 Pa, and time of 22 min, the process parameter C2 corresponding to medium-temperature pre-oxidation was 1.09, and the stretching ratio was 1.03.

[0117] [Example 9]

[0118] Example 1 was repeated, except that the process conditions for low-temperature pre-oxidation of the polyacrylonitrile precursor were: temperature of 210°C, pressure of 50 Pa, and time of 5 min, the process parameter C1 corresponding to low-temperature pre-oxidation was 4.76, and the stretching ratio was 1.05; the process conditions for medium-temperature pre-oxidation were: temperature of 250°C, pressure of 60 Pa, and time of 25 min, the process parameter C2 corresponding to medium-temperature pre-oxidation was 0.96, and the stretching ratio was 1.02.

[0119] [Example 10]

[0120] Example 1 was repeated, except that the process conditions for pre-oxidation of the polyacrylonitrile precursor in the low-temperature section were as follows: temperature of 200°C, pressure of 20 Pa, and time of 3 min, the process parameter C1 corresponding to pre-oxidation in the low-temperature section was 3.33, and the stretching ratio was 1.01; the process conditions for pre-oxidation in the medium-temperature section were as follows: temperature of 245°C, pressure of 30 Pa, and time of 20 min, the process parameter C2 corresponding to pre-oxidation in the high-temperature section was 0.61, and the stretching ratio was 1.01; the process conditions for pre-oxidation in the high-temperature section were as follows: temperature of 255°C, pressure of 40 Pa, and time of 15 min, the process parameter C3 corresponding to pre-oxidation in the high-temperature section was 1.04, and the stretching ratio was 1.00.

[0121] [Example 11]

[0122] Example 1 was repeated, except that the process conditions for low-temperature pre-oxidation of the polyacrylonitrile precursor were as follows: temperature of 200°C, pressure of 20 Pa, and time of 3 min, the process parameter C1 corresponding to low-temperature pre-oxidation was 3.33, and the stretching ratio was 1.08; the process conditions for medium-temperature pre-oxidation were as follows: temperature of 245°C, pressure of 30 Pa, and time of 20 min, the process parameter C2 corresponding to low-temperature pre-oxidation was 0.61, and the stretching ratio was 1.04; the process conditions for high-temperature pre-oxidation were as follows: temperature of 250°C, pressure of 60 Pa, and time of 15 min, the process parameter C3 corresponding to high-temperature pre-oxidation was 1.60, and the stretching ratio was 1.00.

[0123] [Example 12]

[0124] Example 1 was repeated, except that the process conditions for pre-oxidation of the polyacrylonitrile precursor in the low-temperature section were as follows: temperature of 200°C, pressure of 20 Pa, and time of 3 min, the process parameter C1 corresponding to pre-oxidation in the low-temperature section was 3.33, and the stretching ratio was 1.06; the process conditions for pre-oxidation in the medium-temperature section were as follows: temperature of 245°C, pressure of 30 Pa, and time of 20 min, the process parameter C2 corresponding to pre-oxidation in the medium-temperature section was 0.61, and the stretching ratio was 1.03; the process conditions for pre-oxidation in the high-temperature section were as follows: temperature of 250°C, pressure of 80 Pa, and time of 15 min, the process parameter C3 corresponding to pre-oxidation in the high-temperature section was 2.13, and the stretching ratio was 1.00.

[0125] [Example 13]

[0126] Example 1 was repeated, except that the process conditions for pre-oxidation of the polyacrylonitrile precursor in the low-temperature section were as follows: temperature of 200°C, pressure of 20 Pa, and time of 3 min, the process parameter C1 corresponding to pre-oxidation in the low-temperature section was 3.33, and the stretching ratio was 1.05; the process conditions for pre-oxidation in the medium-temperature section were as follows: temperature of 245°C, pressure of 30 Pa, stretching ratio of 1.02, and time of 20 min, the process parameter C2 corresponding to pre-oxidation in the medium-temperature section was 0.61, and the stretching ratio was 1.03; the process conditions for pre-oxidation in the high-temperature section were as follows: temperature of 255°C, pressure of 60 Pa, and time of 17 min, the process parameter C3 corresponding to pre-oxidation in the low-temperature section was 1.38, and the stretching ratio was 1.00.

[0127] [Example 14]

[0128] Example 1 was repeated, except that the process conditions for pre-oxidation of the polyacrylonitrile precursor in the low-temperature section were as follows: temperature of 200°C, pressure of 20 Pa, and time of 3 min, the process parameter C1 corresponding to pre-oxidation in the low-temperature section was 3.33, and the stretching ratio was 1.05; the process conditions for pre-oxidation in the medium-temperature section were as follows: temperature of 245°C, pressure of 30 Pa, and time of 20 min, the process parameter C2 corresponding to pre-oxidation in the medium-temperature section was 0.61, and the stretching ratio was 1.02; the process conditions for pre-oxidation in the high-temperature section were as follows: temperature of 260°C, pressure of 60 Pa, and time of 18 min, the process parameter C3 corresponding to pre-oxidation in the high-temperature section was 1.28, and the stretching ratio was 1.00.

[0129] [Example 15]

[0130] Example 1 was repeated, except that the process conditions for pre-oxidation of the polyacrylonitrile precursor in the low-temperature section were as follows: temperature of 200°C, pressure of 20 Pa, and time of 3 min, corresponding to the process parameter C1 of pre-oxidation in the low-temperature section being 3.33, and the stretching ratio being 1.08; the process conditions for pre-oxidation in the medium-temperature section were as follows: temperature of 245°C, pressure of 30 Pa, and time of 20 min, corresponding to the process parameter C2 of pre-oxidation in the medium-temperature section being 0.61, and the stretching ratio being 1.05; the process conditions for pre-oxidation in the high-temperature section were as follows: temperature of 260°C, pressure of 70 Pa, and time of 18 min, that is, the process parameter C3 of pre-oxidation in the high-temperature section was 1.58, and the stretching ratio was 1.00.

[0131] [Example 16]

[0132] Example 1 was repeated, except that the process conditions for pre-oxidation of the polyacrylonitrile precursor in the low-temperature section were as follows: temperature of 210°C, pressure of 40 Pa, and time of 3 min, the process parameter C1 corresponding to pre-oxidation in the low-temperature section was 6.35, and the stretching ratio was 1.05; the process conditions for pre-oxidation in the medium-temperature section were as follows: temperature of 245°C, pressure of 50 Pa, and time of 22 min, the process parameter C2 corresponding to pre-oxidation in the medium-temperature section was 0.93, and the stretching ratio was 1.02; the process conditions for pre-oxidation in the high-temperature section were as follows: temperature of 258°C, pressure of 75 Pa, and time of 15 min, the process parameter C3 corresponding to pre-oxidation in the high-temperature section was 1.94, and the stretching ratio was 1.00.

[0133] [Example 17]

[0134] Example 1 was repeated, except that the process conditions for pre-oxidation of the polyacrylonitrile precursor in the low-temperature section were as follows: temperature of 210°C, pressure of 40 Pa, and time of 5 min, corresponding to the process parameter C1 of pre-oxidation in the low-temperature section being 3.81, and the stretching ratio being 1.07; the process conditions for pre-oxidation in the medium-temperature section were as follows: temperature of 245°C, pressure of 60 Pa, and time of 22 min, corresponding to the process parameter C2 of pre-oxidation in the medium-temperature section being 1.11, and the stretching ratio being 1.05; the process conditions for pre-oxidation in the high-temperature section were as follows: temperature of 258°C, pressure of 75 Pa, and time of 17 min, corresponding to the process parameter C3 of pre-oxidation in the high-temperature section being 1.71, and the stretching ratio being 1.00.

[0135] [Example 18]

[0136] Example 1 was repeated, except that the process conditions for pre-oxidation of the polyacrylonitrile precursor in the low-temperature section were as follows: temperature of 210°C, pressure of 50 Pa, and time of 5 min, the process parameter C1 corresponding to pre-oxidation in the low-temperature section was 4.76, and the stretching ratio was 1.10; the process conditions for pre-oxidation in the medium-temperature section were as follows: temperature of 248°C, pressure of 60 Pa, and time of 25 min, the process parameter C2 corresponding to pre-oxidation in the medium-temperature section was 0.97, and the stretching ratio was 1.05; the process conditions for pre-oxidation in the high-temperature section were as follows: temperature of 258°C, pressure of 80 Pa, and time of 17 min, the process parameter C3 corresponding to pre-oxidation in the high-temperature section was 1.82, and the stretching ratio was 1.00.

[0137] [Example 19]

[0138] Example 1 was repeated, except that the process conditions for pre-oxidation of the polyacrylonitrile precursor in the low-temperature section were as follows: temperature of 200°C, atmosphere pressure of 50 Pa, and time of 5 min, the process parameter C1 corresponding to pre-oxidation in the low-temperature section was 5.00, and the stretching ratio was 1.10; the process conditions for pre-oxidation in the medium-temperature section were as follows: temperature of 250°C, pressure of 60 Pa, and time of 20 min, the process parameter C2 corresponding to pre-oxidation in the medium-temperature section was 1.20, and the stretching ratio was 1.05; the process conditions for pre-oxidation in the high-temperature section were as follows: temperature of 260°C, pressure of 80 Pa, and time of 15 min, the process parameter C3 corresponding to pre-oxidation in the high-temperature section was 2.05, and the stretching ratio was 1.00.

[0139] Table 1. Parameter test and calculation results of comparative examples and embodiments

[0140] It can be seen from the above results that the polyacrylonitrile pre-oxidized yarn of the present invention has characteristic tensile parameters within a specific range, and the carbon fiber prepared therefrom has improved mechanical properties.

[0141] The preferred embodiments of the present application are described in detail above. However, the present application is not limited to the specific details of the above embodiments. Within the technical concept of the present application, various simple modifications can be made to the technical solution of the present application, and these simple modifications all fall within the scope of protection of the present application.

[0142] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any appropriate manner unless there is any contradiction. In order to avoid unnecessary repetition, this application will not further describe various possible combinations.

[0143] In addition, the various implementation methods of the present application can be arbitrarily combined, as long as they do not violate the concept of the present application, they should also be regarded as the content of the invention of the present application.

Claims

1. A polyacrylonitrile pre-oxidized yarn, comprising a core and a sheath covering the core, wherein: The characteristic tensile parameter A of the polyacrylonitrile preoxidized yarn is 475.0-580.0 cN / μm, and the characteristic tensile parameter is shown in formula (1): In formula (1), A represents the characteristic tensile parameter of the polyacrylonitrile pre-oxidized yarn (cN / μm); T represents the breaking strength of the polyacrylonitrile pre-oxidized yarn (cN); η represents the area ratio of the radial cross-section of the sheath to the radial cross-section of the entire polyacrylonitrile pre-oxidized yarn; and d represents the diameter of the polyacrylonitrile pre-oxidized yarn (μm).

2. The polyacrylonitrile pre-oxidized yarn according to claim 1, characterized in that: In formula (1): 1.5 cN≤T≤8.0 cN, preferably, 2.5 cN≤T≤5.2 cN; and / or, 55%≤η≤95%, preferably, 74%≤η≤91%; and / or, 5.0 μm≤d≤15.0 μm, preferably, 7.0 μm≤d≤10.0 μm.

3. The polyacrylonitrile preoxidized yarn according to claim 1 or 2, characterized in that: The characteristic tensile parameter of the polyacrylonitrile preoxidized yarn is 480.0-575.0 cN / μm, preferably 482.5-571.5 cN / μm.

4. The polyacrylonitrile pre-oxidized yarn according to claim 1, characterized in that: The difference in oxygen content between the outer region and the inner region of the sheath of the polyacrylonitrile pre-oxidized yarn is 1.5wt%-3.2wt%, preferably 1.8wt%-2.9wt%; preferably, the oxygen content of the outer region of the sheath of the pre-oxidized yarn is 9.0wt%-14.0wt%, preferably 10.5wt%-12.0wt%; The oxygen content of the inner region of the pre-oxidized fiber sheath is 9.0wt%-11.5wt%, preferably 9.5wt%-10.2wt%.

5. A polyacrylonitrile-based carbon fiber, which is prepared from the polyacrylonitrile preoxidized yarn according to claim 1, and has a tensile strength greater than or equal to 4000 MPa, preferably greater than or equal to 5000 MPa, and a tensile modulus of 500-600 GPa, preferably 540-570 GPa.

6. A method for preparing polyacrylonitrile preoxidized yarn, preferably used for preparing the polyacrylonitrile preoxidized yarn according to claim 1, the method comprising the steps of: preoxidizing the polyacrylonitrile precursor yarn in a low temperature section, preoxidizing the polyacrylonitrile precursor yarn in a medium temperature section and preoxidizing the polyacrylonitrile precursor yarn in a high temperature section in sequence to obtain the polyacrylonitrile preoxidized yarn; wherein: Control the process parameters of low temperature pre-oxidation, medium temperature pre-oxidation and high temperature pre-oxidation To satisfy the following formula (2): Wherein, i=1, 2, 3, which correspond to low temperature pre-oxidation, medium temperature pre-oxidation and high temperature pre-oxidation respectively; P i is the pre-oxidation pressure (Pa); T i is the pre-oxidation temperature (℃); t i is the duration of pre-oxidation (min), Among them, for the low-temperature pre-oxidation, 1.0≤C1≤10.0, preferably 1.90≤C1≤8.33; for the medium-temperature pre-oxidation, 0.1≤C2≤2.5, preferably 0.48≤C2≤1.25; and for the high-temperature pre-oxidation, 0.5≤C3≤4.0, preferably 0.85≤C3≤2.

13.

7. The preparation method according to claim 6, characterized in that: The conditions for pre-oxidation in the low temperature stage include: temperature T1 of 200-210° C., time t1 of no more than 10 min, preferably 3-5 min, pressure P1 of 18-55 Pa, preferably 20-50 Pa; and / or, The conditions for pre-oxidation in the medium temperature stage include: temperature T2 of 240-250° C., time t2 of 20-35 min, preferably 20-25 min, pressure P2 of 25-65 Pa, preferably 30-60 Pa; and / or, The conditions for pre-oxidation in the high temperature stage include: temperature T3 of 245-280° C., time t3 of 15-25 min, preferably 15-18 min, and pressure P3 of 35-85 Pa, preferably 40-80 Pa.

8. The preparation method according to claim 7, characterized in that: T2 = (1.20-1.22) * T1, preferably 20°C ≤ T2-T1 ≤ 50°C, more preferably 30°C ≤ T2-T1 ≤ 40°C; and / or 0℃≤T3-T2≤20℃, preferably 5℃≤T3-T2≤15℃, more preferably 10℃≤T3-T2≤15℃.

9. The preparation method according to any one of claims 6 to 8, characterized in that: In the low-temperature pre-oxidation, the medium-temperature pre-oxidation and the high-temperature pre-oxidation, the drafting ratio of the polyacrylonitrile precursor is independently 0.80-1.20, preferably 0.90-1.

10.

10. Polyacrylonitrile pre-oxidized yarn obtained by the preparation method according to any one of claims 6 to 9.

11. A method for preparing polyacrylonitrile-based carbon fiber, characterized in that: Includes steps: The polyacrylonitrile preoxidized fibers are subjected to low-temperature carbonization treatment, high-temperature carbonization treatment and graphitization treatment in sequence to obtain polyacrylonitrile-based carbon fibers. The polyacrylonitrile pre-oxidized yarn is the polyacrylonitrile pre-oxidized yarn according to claim 1 or the polyacrylonitrile pre-oxidized yarn prepared by the method according to claim 6.

12. The preparation method according to claim 11, characterized in that: The conditions of the low-temperature carbonization treatment include: a temperature of 400-1000°C, a time of 0.5-10 min, and a draft ratio of 0.80-1.20; and / or, The conditions of the high temperature carbonization treatment include: temperature of 800-1800°C, time of 0.5-10 min, and draft ratio of 0.80-1.00; and / or, The graphitization treatment conditions include: temperature of 2200-3000° C., time of 0.2-15 min, and stretching ratio of 0.90-1.

50.

13. Use of the polyacrylonitrile preoxidized yarn according to any one of claims 1 to 4 in the preparation of polyacrylonitrile-based carbon fibers, comprising the steps of: subjecting the polyacrylonitrile preoxidized yarn to a low-temperature carbonization treatment, a high-temperature carbonization treatment and a graphitization treatment in sequence to obtain the polyacrylonitrile-based carbon fibers.

14. The use according to claim 13, characterized in that: The conditions of the low-temperature carbonization treatment include: a temperature of 400-1000°C, a time of 0.5-10 min, and a draft ratio of 0.80-1.20; and / or, The conditions of the high temperature carbonization treatment include: temperature of 800-1800°C, time of 0.5-10 min, and draft ratio of 0.80-1.02; and / or, The graphitization treatment conditions include: temperature of 2200-3000° C., time of 0.2-15 min, and stretching ratio of 0.90-1.50.

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