High-strength high-modulus carbon fiber and method for producing the same

Abstract

The application relates to the technical field of carbon fiber preparation, and discloses a high-strength and high-modulus carbon fiber and a preparation method thereof. The method comprises pre-oxidation treatment of polyacrylonitrile-based original filaments; wherein the pre-oxidation treatment is provided with at least three temperature zones; in the first temperature zone, the ratio of the static value of the polyacrylonitrile-based original filament to the width of the polyacrylonitrile-based original filament is 0.005-0.032 V / mm. According to the method, the static value of the polyacrylonitrile-based original filament in the pre-oxidation process is controlled, high-strength and high-modulus carbon fibers are prepared, and the interlaminar shear strength of the composite material is high.

Description

Technical Field

[0001] This invention relates to the field of carbon fiber preparation technology, specifically to a high-strength, high-modulus carbon fiber and its preparation method. Background Technology

[0002] Carbon fiber is an inorganic high-performance fiber with a carbon content of over 90%. It is a microcrystalline graphite material obtained by carbonizing and graphitizing organic fibers. It possesses advantages such as low density, high axial strength modulus, good fatigue resistance, rapid electrical and thermal conductivity, good corrosion resistance, low coefficient of thermal expansion, and strong adaptability to sudden environmental changes. It is widely used in various sectors of the national economy. Carbon fiber not only possesses the inherent properties of carbon materials but also combines the flexibility and processability of textile fibers, making it a new generation of high-performance fibers.

[0003] Carbon fiber, with its superior properties of high strength, high modulus, and light weight, has become an important strategic material for the development of national defense and the national economy. It not only holds an irreplaceable position in military fields such as aerospace, but also shines in areas such as wind turbine blades, sports and leisure, pressure vessels, building protection, and automotive transportation.

[0004] Based on performance differences, carbon fibers can be divided into general-purpose and high-performance types (including high-strength, high-strength medium-modulus, and high-strength high-modulus types). According to their raw materials, carbon fibers can be divided into three types: polyacrylonitrile-based, pitch-based, and viscose-based. Among them, polyacrylonitrile-based carbon fibers, due to their readily available raw materials and excellent overall mechanical properties, have become the main component of carbon fibers, accounting for over 90% of global carbon fiber production.

[0005] High-strength, high-modulus carbon fiber typically refers to high-performance carbon fiber with a modulus above 350 GPa and a tensile strength above 3.5 GPa. The preparation process of polyacrylonitrile-based carbon fiber includes three main processes: solution preparation, precursor fiber preparation, and oxidative carbonization. Each of these three main processes involves multiple steps. The preparation process of high-strength, high-modulus carbon fiber usually involves further high-temperature treatment (also known as graphitization) of carbon fiber after high-temperature treatment. After graphitization, the carbon content of high-strength, high-modulus carbon fiber can reach over 99%, and its elongation at break is significantly lower than that of ungraphitized carbon fiber, typically below 0.9%. The higher the modulus, the lower the elongation at break.

[0006] In the conversion of polyacrylonitrile (PA) fibers into carbon fibers, pre-oxidation is a crucial process that controls both the quality and yield of the carbon fibers. During pre-oxidation, the PA precursor fibers undergo a series of physical and chemical changes in hot air at 200-300℃, transforming their linear molecules into a heat-resistant trapezoidal structure. Simultaneously, friction occurs between the PA fiber bundles and the driving force, between the bundles themselves, between the bundles and the hot air, and within and between the molecular chains of the fibers. This leads to the accumulation of static electricity, which in turn affects the fiber surface, mechanical properties, and processing difficulty. Excessive static electricity causes significant wear on the fiber surface during pre-oxidation, damaging the morphology; insufficient static electricity hinders polarization during surface treatment.

[0007] Carbon fiber is rarely used directly; it is mostly processed into intermediate products or composite materials. This requires carbon fiber to have a strong bonding ability with other resin materials to meet the requirements of practical applications. Interlaminar shear strength (ILSS) is a crucial indicator of the bonding between carbon fiber and resin, directly determining the strength and toughness of the composite material. It is defined as the ultimate strength under pure shear load, i.e., the interlaminar shear stress at which the specimen fails or the load reaches its maximum value. After high-temperature furnace carbonization, the surface activity of carbon fiber decreases, weakening its bonding ability with resin and reducing the ILSS of the composite material, which severely affects its application performance. Currently, the mainstream solution is to surface treat the carbon fiber to improve the ILSS of the composite material. Electrochemical technology has attracted much attention from researchers due to its ease of operation and significant effects; however, research has been limited to the influence of electrolyte type and process parameters on interfacial properties.

[0008] Patent applications CN109161947A and CN114086386A respectively improve the ILSS of high-modulus carbon fiber composites through multi-stage anodizing and parallel multi-stage electrolytic cells. Patent application CN112709064A uses multi-stage strong acid surface treatment to improve the surface activity of carbon fibers, thereby increasing their wettability with the matrix resin and obtaining carbon fiber composites with higher ILSS. Chen Qiufeng et al. (Influence of surface treatment process on ILSS and interface morphology of carbon fiber composites [J]. Fiberglass / Composite Materials, 2016(03):60-64+22.) explored the influence of different electrical conductivity on the tensile strength of carbon fibers, the ILSS of composites, and interfacial adhesion. The above patents and papers all improve the ILSS of carbon fiber composites by studying parameters such as the type of electrolyte, the number and arrangement of electrolytic cells, and electrical conductivity during the surface treatment process. The book "Carbon Fiber and Graphite Fiber" (Chemical Industry Press, He Fu, September 2010, pp. 303-311) mentions that the main influencing factors in the anodizing process include electrolyte, two-stage anodizing, and electrolytic cell process. However, it neglects the influence of the aforementioned processing on the static electricity of the carbon fiber surface, which in turn affects its anodizing process. Summary of the Invention

[0009] The purpose of this invention is to overcome the problems of low strength and modulus of carbon fibers and low interlaminar shear strength of composite materials in the prior art, and to provide a high-strength, high-modulus carbon fiber and its preparation method.

[0010] To achieve the above objectives, the present invention provides a method for preparing high-strength, high-modulus carbon fibers, the method comprising pre-oxidizing polyacrylonitrile precursor fibers;

[0011] The pre-oxidation treatment is provided with at least three temperature zones. In the first temperature zone, the ratio of the electrostatic value of the polyacrylonitrile precursor fiber bundle to the width of the polyacrylonitrile precursor fiber bundle is 0.005-0.032V / mm.

[0012] Preferably, during the pre-oxidation treatment in the first temperature zone, the bundle width of the polyacrylonitrile-based precursor fiber is 0.0001-0.0008 times the number of single bundles of polyacrylonitrile-based precursor fiber, and the bundle width of the polyacrylonitrile-based precursor fiber is measured in millimeters.

[0013] Preferably, within the first temperature zone, the electrostatic value y of the polyacrylonitrile-based precursor fiber bundle satisfies the following formula:

[0014] -1.3x 3 +2.4x 2 -0.65x+0.03 <y<-3.4x 3 +6.5x 2 -0.12x+0.23;

[0015] Where y is in V, and x represents the percentage of the pre-oxidation time in the first temperature zone to the total pre-oxidation time, with a value ranging from 25% to 85%.

[0016] Preferably, during the pre-oxidation treatment, the width of the polyacrylonitrile-based precursor fiber bundle is 4-80 mm.

[0017] Preferably, the number of strands in a single bundle of polyacrylonitrile precursor fibers is 1,000-320,000.

[0018] Preferably, the temperature of the first temperature zone is 200-270℃;

[0019] Preferably, the pre-oxidation residence time in the first temperature zone is 20-100 min;

[0020] Preferably, the draw ratio of the first temperature zone is 1-1.1.

[0021] The polyacrylonitrile-based precursor fiber is prepared by a wet spinning process;

[0022] Preferably, the fineness of the polyacrylonitrile precursor fiber is 0.7-6 dtex.

[0023] Preferably, the method further includes: subjecting the pre-oxidized oxidized fiber to low-temperature carbonization, high-temperature carbonization, graphitization, electrochemical treatment, washing, sizing, and drying in sequence.

[0024] Preferably, the temperature of the low-temperature carbonization treatment is 400-800℃, and the total draw ratio is 0.95-1.08 times;

[0025] Preferably, the high-temperature carbonization treatment is carried out at a temperature of 1200-1600℃, and the total draw ratio is 0.97-1.08 times.

[0026] Preferably, the graphitization treatment temperature is 2200-2800℃.

[0027] A second aspect of the present invention provides high-strength, high-modulus carbon fibers prepared by the method described above.

[0028] The method described in this invention produces high-strength, high-modulus carbon fibers by controlling the electrostatic value of polyacrylonitrile precursor fibers during the pre-oxidation process, and the composite material has high interlaminar shear strength. Detailed Implementation

[0029] The following provides a detailed description of specific embodiments of the present invention. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of the invention.

[0030] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0031] This invention provides a method for preparing high-strength, high-modulus carbon fibers, the method comprising pre-oxidizing polyacrylonitrile precursor fibers;

[0032] The pre-oxidation treatment is provided with at least three temperature zones. In the first temperature zone, the ratio of the electrostatic value of the polyacrylonitrile precursor fiber bundle to the width of the polyacrylonitrile precursor fiber bundle is 0.005-0.032V / mm.

[0033] In the method described in this invention, by rationally controlling the ratio of the electrostatic value of the precursor fiber bundle to the width of the precursor fiber bundle during the pre-oxidation process in the first temperature zone, surface wear of the fibers and the minor defects generated during this process are reduced, thereby facilitating the acquisition of higher-strength carbon fibers. The weak electric field between the fiber bundles can affect the physicochemical reactions during the pre-oxidation process. An appropriate electrostatic value can slow down the oxidation process and the formation of the core-sheath structure, which is beneficial to improving the mechanical properties of the carbon fiber. At the same time, appropriate electrostatics can polarize the surface of the carbon fiber, improving the interlaminar shear strength of its composite material.

[0034] In a specific implementation, within the first temperature zone, the ratio of the electrostatic value of the polyacrylonitrile-based precursor fiber bundle to the width of the polyacrylonitrile-based precursor fiber bundle can be 0.005V / mm, 0.006V / mm, 0.007V / mm, 0.008V / mm, 0.009V / mm, 0.01V / mm, 0.012V / mm, 0.015V / mm, 0.016V / mm, 0.018V / mm, 0.02V / mm, 0.022V / mm, 0.025V / mm, 0.026V / mm, 0.028V / mm, 0.03V / mm, or 0.032V / mm.

[0035] To further improve the mechanical properties of carbon fibers and the interlaminar shear strength of composite materials, in a preferred embodiment, during the first temperature zone pre-oxidation treatment, the bundle width of the polyacrylonitrile-based precursor is 0.0001-0.0008 times the number of single bundles of polyacrylonitrile-based precursor fibers, and the bundle width of the polyacrylonitrile-based precursor is measured in millimeters; specifically, the bundle width of the polyacrylonitrile-based precursor can be 0.0001, 0.0002, 0.0003, 0.0004, 0.0005, 0.0006, 0.0007, or 0.0008 times the number of single bundles of fibers.

[0036] To further improve the mechanical properties of carbon fibers and the interlaminar shear strength of composite materials, in a preferred embodiment, during the pre-oxidation process in the first temperature zone, the electrostatic value y of the fiber bundle is controlled to satisfy the following formula:

[0037] -1.3x 3 +2.4x 2 -0.65x+0.03 <y<-3.4x 3 +6.5x 2 -0.12x+0.23;

[0038] Where y is in V, and x represents the percentage of the pre-oxidation time in the first temperature zone to the total pre-oxidation time, with a value range of 25%-85%; specifically, x can be 25%, 30%, 40%, 45%, 50%, 65%, 75%, or 80%.

[0039] In a preferred embodiment, during the pre-oxidation treatment, the width of the polyacrylonitrile-based precursor fiber is controlled to be 4-80 mm; specifically, it can be 4 mm, 5 mm, 6 mm, 7 mm, 8 mm, 9 mm, 10 mm, 15 mm, 20 mm, 25 mm, 30 mm, 35 mm, 40 mm, 45 mm, 50 mm, 55 mm, 60 mm, 65 mm, 70 mm, or 80 mm.

[0040] In a preferred embodiment, during the pre-oxidation treatment, the number of single bundles of polyacrylonitrile precursor fibers is controlled to be 1,000-320,000; specifically, it can be 1,000, 2,000, 3,000, 4,000, 5,000, 8,000, 10,000, 12,000, 20,000, 240,000, 40,000, 48,000, 50,000, 60,000, 70,000, 80,000, 96,000, 100,000, 120,000, 200,000, 300,000, or 320,000.

[0041] In a preferred embodiment, the temperature of the pre-oxidation treatment is 200-300℃, and the total residence time is in the range of 100-140 min; specifically, it can be 100 min, 120 min, or 140 min.

[0042] In a preferred embodiment, the pre-oxidation treatment is carried out in an air atmosphere.

[0043] In a preferred embodiment, the temperature of the pre-oxidation treatment in the first temperature zone is controlled to be 200-270°C; specifically, it can be 200°C, 210°C, 220°C, 230°C, 240°C, 250°C, 260°C, or 270°C.

[0044] In a preferred embodiment, the pre-oxidation residence time in the first temperature zone is 20-100 min; specifically, it can be 20 min, 25 min, 30 min, 35 min, 40 min, 45 min, 50 min, 60 min, 70 min, 80 min, 90 min, or 100 min.

[0045] In a preferred embodiment, the stretching ratio of the polyacrylonitrile precursor fiber during the first temperature zone pre-oxidation treatment is 1-1.1.

[0046] In a specific implementation, the pre-oxidation process is set with three temperature zones: the first temperature zone has a pre-oxidation temperature of 200-270℃; the second temperature zone has a pre-oxidation temperature of 220-280℃; and the third temperature zone has a pre-oxidation temperature of 240-300℃; and the temperatures of the three temperature zones are set in ascending order.

[0047] In the method described in this invention, the polyacrylonitrile-based precursor fiber can be any polyacrylonitrile-based precursor fiber conventionally used in the art for preparing carbon fibers. In a preferred embodiment, the polyacrylonitrile-based precursor fiber is prepared by a wet spinning process.

[0048] More preferably, the fineness of the polyacrylonitrile-based precursor fiber is 0.7-6 dtex; specifically, it can be 0.7 dtex, 0.8 dtex, 0.83 dtex, 0.95 dtex, 1 dtex, 2 dtex, 3 dtex, 4 dtex, 5 dtex or 6 dtex.

[0049] Preferably, the method for preparing high-strength, high-modulus carbon fibers further includes: subjecting the pre-oxidized oxidized fibers to low-temperature carbonization, high-temperature carbonization, graphitization, electrochemical treatment, washing, sizing, and drying in sequence.

[0050] More preferably, the temperature of the low-temperature carbonization treatment is 400-800℃, and the total draw ratio is 0.95-1.08 times.

[0051] More preferably, the high-temperature carbonization treatment is carried out at a temperature of 1200-1600℃ and the total draw ratio is 0.97-1.08 times.

[0052] More preferably, the graphitization treatment temperature is 2200-2800℃.

[0053] In this invention, the method for testing the electrostatic value of the polyacrylonitrile-based precursor fiber bundle in the first temperature zone is as follows: the measurement is performed using a Keyence SK series handheld electrostatic detector, with the measurement position being 5cm from the outlet of the pre-oxidation furnace and the detection spot located in the center of the fiber bundle.

[0054] A second aspect of this invention provides high-strength, high-modulus carbon fibers prepared by the method described above. The high-strength, high-modulus carbon fibers have a tensile strength ≥3.98 GPa, a tensile modulus ≥526 GPa, and an interlaminar shear strength ≥55 MPa for the composite material.

[0055] The present invention will be described in detail below through embodiments, but the scope of protection of the present invention is not limited thereto.

[0056] The polyacrylonitrile precursor fibers used in the following examples and comparative examples were prepared according to the following method: the spinning solution was precisely metered by a metering pump, filtered again, and then wet-spun; subsequently, two-stage coagulation drawing, four-stage hot water drawing, washing, oiling, drying and densification, steam drawing, and steam heat setting were performed sequentially, and finally, carbon fiber precursor fibers were obtained by winding. The draw ratios for the two-stage coagulation drawing were 1.05 and 1.15, respectively; the four-stage hot water drawing was carried out in hot water at 80-95℃, with a total draw ratio of 3.5 times; the washing process was carried out at 75℃ without drawing; the drying and densification process used a five-temperature gradient heating method, namely 90℃, 105℃, 120℃, 130℃, and 135℃; the steam drawing pressure was 0.55MPa, and the draw ratio was 3.25 times; the steam heat setting temperature was 105℃.

[0057] The fineness test of polyacrylonitrile-based precursor fibers shall be performed in accordance with the method described in the national standard GB / T 14343.

[0058] The mechanical properties of carbon fiber were tested according to the method described in the national standard GB / T 3362-2017, and the interlaminar shear strength of carbon fiber composites was tested according to the short beam method described in standard ISO 14130.

[0059] Example 1

[0060] Polyacrylonitrile-based precursor fiber bundles (self-made, 12000 strands per bundle, fineness 0.83 dtex) were sequentially subjected to pre-oxidation, low-temperature carbonization, high-temperature carbonization, graphitization, surface treatment, washing, oiling, and drying, finally winding to obtain high-strength, high-modulus carbon fibers. The pre-oxidation process was carried out in air, sequentially passing through three temperature zones. The first temperature zone had a pre-oxidation temperature of 220℃ and a residence time of 30 min, accounting for 25% of the total pre-oxidation time (x = 25%). The draw ratio of the polyacrylonitrile precursor fiber during the first temperature zone pre-oxidation treatment was 1.0. The second temperature zone had a pre-oxidation temperature of 235℃ and a residence time of 60 min. The third temperature zone had a pre-oxidation temperature of 250℃ and a residence time of 30 min, for a total residence time of 120 min. During the first temperature zone pre-oxidation, the width of the polyacrylonitrile-based precursor fiber bundle was controlled at 5 mm, and the electrostatic value of the polyacrylonitrile-based precursor fiber bundle was y = 0.05 (in V). y and x satisfy the following relationship: -1.3x 3+2.4x 2 -0.65x+0.03 <y<-3.4x 3 +6.5x 2 -0.12x+0.23; the low-temperature carbonization process was carried out at 400℃ in the presence of inert gas, with a total draw ratio of 1.05; the high-temperature carbonization process was carried out at 1200℃ in the presence of inert gas, with a total draw ratio of 1.06; the graphitization process was carried out at 2200℃ in the presence of inert gas; the surface treatment adopted the electrochemical pulse method, with ammonium bicarbonate as the electrolyte, an electrolyte concentration of 2%, an electrolyte temperature of room temperature, and a surface treatment time of 60s. The obtained carbon fiber tensile strength was 4.05 GPa, the tensile modulus was 540 GPa, and the interlaminar shear strength of the carbon fiber composite was 55 MPa.

[0061] Example 2

[0062] Polyacrylonitrile-based precursor fiber bundles (self-made, 24,000 strands per bundle, 0.95 dtex fineness) were sequentially subjected to pre-oxidation, low-temperature carbonization, high-temperature carbonization, graphitization, surface treatment, washing, oiling, and drying, finally winding to obtain high-strength, high-modulus carbon fibers. The pre-oxidation process was carried out in air, sequentially passing through three temperature zones. The first temperature zone had a pre-oxidation temperature of 200℃ and a residence time of 60 min, accounting for 50% of the total pre-oxidation time (x = 50%). The draw ratio of the polyacrylonitrile precursor fiber during the first temperature zone pre-oxidation treatment was 1.08. The second temperature zone had a pre-oxidation temperature of 220℃ and a residence time of 20 min. The third temperature zone had a pre-oxidation temperature of 245℃ and a residence time of 40 min, for a total residence time of 120 min. During the first temperature zone pre-oxidation, the width of the polyacrylonitrile-based precursor fiber bundle was controlled at 9 mm, and the electrostatic value of the polyacrylonitrile-based precursor fiber bundle was y = 0.2 (in V). y and x satisfy the following relationship: -1.3x 3 +2.4x 2 -0.65x+0.03 <y<-3.4x 3 +6.5x 2 -0.12x+0.23; the low-temperature carbonization process was carried out at 550℃ in the presence of inert gas, with a total draw ratio of 1.07; the high-temperature carbonization process was carried out at 1250℃ in the presence of inert gas, with a total draw ratio of 1.04; the graphitization process was carried out at 2350℃ in the presence of inert gas; the surface treatment adopted the electrochemical pulse method, the electrolyte was ammonium bicarbonate, the electrolyte concentration was 1.8%, the electrolyte temperature was room temperature, and the surface treatment time was 60s. The obtained carbon fiber tensile strength was 4.12GPa, the tensile modulus was 547GPa, and the interlaminar shear strength of the carbon fiber composite was 55.7MPa.

[0063] Example 3

[0064] Polyacrylonitrile-based precursor fiber bundles (self-made, 48,000 strands per bundle, 0.86 dtex fineness) were sequentially subjected to pre-oxidation, low-temperature carbonization, high-temperature carbonization, graphitization, surface treatment, washing, oiling, and drying, finally winding to obtain high-strength, high-modulus carbon fibers. The pre-oxidation process was carried out in air, sequentially passing through three temperature zones. The first temperature zone had a pre-oxidation temperature of 215℃ and a residence time of 36 min, accounting for 30% of the total pre-oxidation time (x = 30%). The draw ratio of the polyacrylonitrile precursor fiber during the first temperature zone pre-oxidation treatment was 1.06. The second temperature zone had a pre-oxidation temperature of 220℃ and a residence time of 60 min. The third temperature zone had a pre-oxidation temperature of 230℃ and a residence time of 24 min, for a total residence time of 120 min. During the first temperature zone pre-oxidation, the width of the polyacrylonitrile-based precursor fiber bundle was controlled at 37 mm, and the electrostatic value of the polyacrylonitrile-based precursor fiber bundle was y = 0.5 (in V). y and x satisfy the following relationship: -1.3x 3 +2.4x 2 -0.65x+0.03 <y<-3.4x 3 +6.5x 2 -0.12x+0.23; the low-temperature carbonization process was carried out at 650℃ in the presence of inert gas, with a total draw ratio of 1.08; the high-temperature carbonization process was carried out at 1400℃ in the presence of inert gas, with a total draw ratio of 1.03; the graphitization process was carried out at 2500℃ in the presence of inert gas; the surface treatment adopted the electrochemical pulse method, the electrolyte was ammonium bicarbonate, the electrolyte concentration was 2.4%, the electrolyte temperature was room temperature, and the surface treatment time was 60s. The obtained carbon fiber tensile strength was 4.18GPa, the tensile modulus was 534GPa, and the interlaminar shear strength of the carbon fiber composite was 58.8MPa.

[0065] Example 4

[0066] Polyacrylonitrile-based precursor fiber bundles (self-made, with 96,000 strands per bundle and a fineness of 2.76 dtex) were subjected to pre-oxidation, low-temperature carbonization, high-temperature carbonization, graphitization, surface treatment, water washing, oiling, and drying in sequence, and finally the fibers were wound up to obtain high-strength and high-modulus carbon fibers. The pre-oxidation process was carried out in air, sequentially passing through three temperature zones. The first zone had a pre-oxidation temperature of 210℃ and a residence time of 60 min, representing 50% of the total pre-oxidation time (x = 50%). The draw ratio of the polyacrylonitrile precursor fiber during the first zone pre-oxidation was 1.05. The second zone had a pre-oxidation temperature of 225℃ and a residence time of 30 min. The third zone had a pre-oxidation temperature of 240℃ and a residence time of 30 min, for a total residence time of 120 min. During the first zone pre-oxidation, the width of the polyacrylonitrile precursor fiber bundle was controlled at 68 mm, and the electrostatic value of the polyacrylonitrile precursor fiber bundle was y = 1.5 (in V). y and x satisfy the following relationship: -1.3x 3 +2.4x 2 -0.65x+0.03 <y<-3.4x 3 +6.5x 2 -0.12x+0.23; the low-temperature carbonization process was carried out at 800℃ in the presence of inert gas, with a total draw ratio of 1.08; the high-temperature carbonization process was carried out at 1550℃ in the presence of inert gas, with a total draw ratio of 1.04; the graphitization process was carried out at 2750℃ in the presence of inert gas; the surface treatment adopted the electrochemical pulse method, the electrolyte was ammonium bicarbonate, the electrolyte concentration was 1.8%, the electrolyte temperature was room temperature, and the surface treatment time was 60s. The obtained carbon fiber tensile strength was 4.17GPa, the tensile modulus was 537GPa, and the interlaminar shear strength of the carbon fiber composite was 59.6MPa.

[0067] Example 5

[0068] Polyacrylonitrile-based precursor fiber bundles (self-made, with 320,000 strands per bundle and a fineness of 5.77 dtex) were sequentially subjected to pre-oxidation, low-temperature carbonization, high-temperature carbonization, graphitization, surface treatment, water washing, oiling, and drying, and finally filament winding to obtain high-strength, high-modulus carbon fibers. The pre-oxidation process was carried out in air, sequentially passing through three temperature zones. The first zone had a pre-oxidation temperature of 215℃ and a residence time of 96 min, accounting for 80% of the total pre-oxidation time (x = 80%). The draw ratio of the polyacrylonitrile precursor fiber during the first zone pre-oxidation was 1.1. The second zone had a pre-oxidation temperature of 235℃ and a residence time of 12 min. The third zone had a pre-oxidation temperature of 240℃ and a residence time of 12 min, for a total residence time of 120 min. During the first zone pre-oxidation, the width of the polyacrylonitrile precursor fiber bundle was controlled at 80 mm, and the electrostatic value of the polyacrylonitrile precursor fiber bundle was y = 2.5 (in V). y and x satisfy the following relationship: -1.3x 3 +2.4x 2 -0.65x+0.03 <y<-3.4x 3 +6.5x 2 -0.12x+0.23; the low-temperature carbonization process was carried out at 750℃ in the presence of inert gas, with a total draw ratio of 1.05; the high-temperature carbonization process was carried out at 1800℃ in the presence of inert gas, with a total draw ratio of 1.06; the graphitization process was carried out at 2800℃ in the presence of inert gas; the surface treatment adopted the electrochemical pulse method, the electrolyte was ammonium bicarbonate, the electrolyte concentration was 2%, the electrolyte temperature was room temperature, and the surface treatment time was 60s. The obtained carbon fiber tensile strength was 3.98GPa, the tensile modulus was 534GPa, and the interlaminar shear strength of the carbon fiber composite was 60.5MPa.

[0069] Example 6

[0070] Polyacrylonitrile-based precursor fiber bundles (self-made, with 48,000 strands per bundle and a fineness of 1.87 dtex) were subjected to pre-oxidation, low-temperature carbonization, high-temperature carbonization, graphitization, surface treatment, water washing, oiling, and drying in sequence, and finally the fibers were wound up to obtain high-strength and high-modulus carbon fibers. The pre-oxidation process was carried out in air, sequentially passing through three temperature zones. The first zone had a pre-oxidation temperature of 215℃ and a residence time of 30 min, representing 25% of the total pre-oxidation time (x = 25%). The draw ratio of the polyacrylonitrile precursor fiber during the first zone pre-oxidation process was 1.08. The second zone had a pre-oxidation temperature of 235℃ and a residence time of 45 min. The third zone had a pre-oxidation temperature of 250℃ and a residence time of 45 min, for a total residence time of 120 min. During the first zone pre-oxidation, the width of the polyacrylonitrile precursor fiber bundle was controlled at 37 mm, and the electrostatic value of the polyacrylonitrile precursor fiber bundle was y = 0.6 (in V). y and x satisfy the following relationship: -1.3x 3 +2.4x 2 -0.65x+0.03 <y<-3.4x 3 +6.5x 2 -0.12x+0.23; the low-temperature carbonization process was carried out at 700℃ in the presence of inert gas, with a total draw ratio of 1.05; the high-temperature carbonization process was carried out at 1450℃ in the presence of inert gas, with a total draw ratio of 1.06; the graphitization process was carried out at 2650℃ in the presence of inert gas; the surface treatment adopted the electrochemical pulse method, with ammonium bicarbonate as the electrolyte, an electrolyte concentration of 2%, an electrolyte temperature of room temperature, and a surface treatment time of 60s. The obtained carbon fiber tensile strength was 4.04 GPa, the tensile modulus was 539 GPa, and the interlaminar shear strength of the carbon fiber composite was 62.2 MPa.

[0071] Example 7

[0072] Polyacrylonitrile-based precursor fiber bundles (self-made, 96,000 strands per bundle, 2.94 dtex fineness) were sequentially subjected to pre-oxidation, low-temperature carbonization, high-temperature carbonization, graphitization, surface treatment, washing, oiling, and drying, finally winding to obtain high-strength, high-modulus carbon fibers. The pre-oxidation process was carried out in air, sequentially passing through three temperature zones. The first zone had a pre-oxidation temperature of 210℃ and a residence time of 60 min, with x = 50% of the total pre-oxidation time. The draw ratio of the polyacrylonitrile precursor fiber during the first pre-oxidation process was 1.06. The second zone had a pre-oxidation temperature of 230℃ and a residence time of 20 min, and the third zone had a pre-oxidation temperature of 250℃ and a residence time of 40 min, for a total residence time of 120 min. During the first pre-oxidation process, the width of the polyacrylonitrile-based precursor fiber bundle was controlled at 76 mm, and the electrostatic value of the polyacrylonitrile-based precursor fiber bundle was y = 1.2 (in V). y and x satisfy the following relationship: -1.3x 3 +2.4x 2 -0.65x+0.03 <y<-3.4x 3 +6.5x 2 -0.12x+0.23; the low-temperature carbonization process was carried out at 750℃ in the presence of inert gas, with a total draw ratio of 1.05; the high-temperature carbonization process was carried out at 1650℃ in the presence of inert gas, with a total draw ratio of 1.06; the graphitization process was carried out at 2750℃ in the presence of inert gas; the surface treatment adopted the electrochemical pulse method, with ammonium bicarbonate as the electrolyte, an electrolyte concentration of 2%, an electrolyte temperature of room temperature, and a surface treatment time of 60s. The obtained carbon fiber tensile strength was 4.02 GPa, the tensile modulus was 526 GPa, and the interlaminar shear strength of the carbon fiber composite was 61.1 MPa.

[0073] Example 8

[0074] Polyacrylonitrile-based precursor fiber bundles (self-made, with 200,000 strands per bundle and a fineness of 4.87 dtex) were sequentially subjected to pre-oxidation, low-temperature carbonization, high-temperature carbonization, graphitization, surface treatment, water washing, oiling, and drying, and finally filament winding to obtain high-strength, high-modulus carbon fibers. The pre-oxidation process was carried out in air, sequentially passing through three temperature zones. The first zone had a pre-oxidation temperature of 210℃ and a residence time of 42 min, representing 35% of the total pre-oxidation time (x = 35%). The draw ratio of the polyacrylonitrile precursor fiber during the first zone pre-oxidation was 1.08. The second zone had a pre-oxidation temperature of 215℃ and a residence time of 40 min. The third zone had a pre-oxidation temperature of 220℃ and a residence time of 38 min, for a total residence time of 120 min. During the first zone pre-oxidation, the width of the polyacrylonitrile precursor fiber bundle was controlled at 78 mm, and the electrostatic value of the polyacrylonitrile precursor fiber bundle was y = 0.768 (in V). y and x satisfy the following relationship: -1.3x 3 +2.4x 2 -0.65x+0.03 <y<-3.4x 3 +6.5x 2 -0.12x+0.23; The low-temperature carbonization process was carried out at 800℃ in the presence of inert gas, with a total draw ratio of 1.05; the high-temperature carbonization process was carried out at 1550℃ in the presence of inert gas, with a total draw ratio of 1.0; the graphitization process was carried out at 2500℃ in the presence of inert gas; the surface treatment adopted the electrochemical pulse method, with ammonium bicarbonate as the electrolyte, an electrolyte concentration of 2%, an electrolyte temperature of room temperature, and a surface treatment time of 60s. The obtained carbon fiber tensile strength was 4.04 GPa, the tensile modulus was 538 GPa, and the interlaminar shear strength of the carbon fiber composite was 64.7 MPa.

[0075] Example 9

[0076] Polyacrylonitrile-based precursor fiber bundles (self-made, 60,000 strands per bundle, fineness 2.74 dtex) were sequentially subjected to pre-oxidation, low-temperature carbonization, high-temperature carbonization, graphitization, surface treatment, water washing, oiling, and drying, and finally filament winding to obtain high-strength, high-modulus carbon fibers. The pre-oxidation process was carried out in air, sequentially passing through three temperature zones. The first zone had a pre-oxidation temperature of 200℃ and a residence time of 36 min, representing 30% of the total pre-oxidation time (x = 30%). The draw ratio of the polyacrylonitrile precursor fiber during the first zone pre-oxidation was 1.04. The second zone had a pre-oxidation temperature of 225℃ and a residence time of 42 min, and the third zone had a pre-oxidation temperature of 250℃ and a residence time of 42 min, for a total residence time of 120 min. During the first zone pre-oxidation, the width of the polyacrylonitrile precursor fiber bundle was controlled at 68 mm, and the electrostatic value of the polyacrylonitrile precursor fiber bundle was y = 0.837 (in V). y and x satisfy the following relationship: -1.3x 3 +2.4x 2 -0.65x+0.03 <y<-3.4x 3 +6.5x 2 -0.12x+0.23; the low-temperature carbonization process was carried out at 700℃ in the presence of inert gas, with a total draw ratio of 1.05; the high-temperature carbonization process was carried out at 1200℃ in the presence of inert gas, with a total draw ratio of 1.06; the graphitization process was carried out at 2200℃ in the presence of inert gas; the surface treatment adopted the electrochemical pulse method, with ammonium bicarbonate as the electrolyte, an electrolyte concentration of 2%, an electrolyte temperature of room temperature, and a surface treatment time of 60s. The obtained carbon fiber tensile strength was 4.03 GPa, the tensile modulus was 541 GPa, and the interlaminar shear strength of the carbon fiber composite was 65.2 MPa.

[0077] Example 10

[0078] Polyacrylonitrile-based precursor fiber bundles (self-made, with 48,000 strands per bundle and a fineness of 1.86 dtex) were subjected to pre-oxidation, low-temperature carbonization, high-temperature carbonization, graphitization, surface treatment, water washing, oiling, and drying in sequence, and finally the fibers were wound up to obtain high-strength and high-modulus carbon fibers. The pre-oxidation process was carried out in air, sequentially passing through three temperature zones. The first zone had a pre-oxidation temperature of 210℃ and a residence time of 30 min, representing 25% of the total pre-oxidation time (x = 25%). The draw ratio of the polyacrylonitrile precursor fiber during the first zone pre-oxidation was 1.1. The second zone had a pre-oxidation temperature of 235℃ and a residence time of 35 min. The third zone had a pre-oxidation temperature of 240℃ and a residence time of 65 min, for a total residence time of 120 min. During the first zone pre-oxidation, the width of the polyacrylonitrile precursor fiber bundle was controlled at 16 mm, and the electrostatic value of the polyacrylonitrile precursor fiber bundle was y = 0.243 (V). y and x satisfy the following relationship: -1.3x 3 +2.4x 2 -0.65x+0.03 <y<-3.4x 3 +6.5x 2 -0.12x+0.23; the low-temperature carbonization process was carried out at 650℃ in the presence of inert gas, with a total draw ratio of 1.05; the high-temperature carbonization process was carried out at 1400℃ in the presence of inert gas, with a total draw ratio of 1.06; the graphitization process was carried out at 2200℃ in the presence of inert gas; the surface treatment adopted the electrochemical pulse method, the electrolyte was ammonium bicarbonate, the electrolyte concentration was 2%, the electrolyte temperature was room temperature, and the surface treatment time was 60s. The obtained carbon fiber tensile strength was 4.04 GPa, the tensile modulus was 551 GPa, and the interlaminar shear strength of the carbon fiber composite was 62.4 MPa.

[0079] Comparative Example 1

[0080] Polyacrylonitrile-based precursor fibers (self-made, 6000 strands per bundle, 0.80 dtex fineness) were sequentially subjected to pre-oxidation, low-temperature carbonization, high-temperature carbonization, graphitization, surface treatment, washing, oiling, and drying, finally winding to obtain high-strength, high-modulus carbon fibers. The pre-oxidation process was carried out in air, sequentially passing through three temperature zones. The first temperature zone had a pre-oxidation temperature of 220℃ and a residence time of 30 min, accounting for 25% of the total pre-oxidation time. The draw ratio of the polyacrylonitrile precursor fibers during the first temperature zone pre-oxidation treatment was 1.08. The second temperature zone had a pre-oxidation temperature of 235℃ and a residence time of 35 min, and the third temperature zone had a pre-oxidation temperature of 250℃ and a residence time of 55 min, for a total residence time of 120 min. During the oxidation process, the width of the polyacrylonitrile precursor fiber bundle was controlled at 10 mm, and the electrostatic value of the polyacrylonitrile precursor fiber bundle was y = 0.006 (in V). The low-temperature carbonization process was carried out at 400℃ in the presence of an inert gas; the high-temperature carbonization process was carried out at 1200℃ in the presence of an inert gas, with a total draw ratio of 1.06; the graphitization process was carried out at 2200℃ in the presence of an inert gas; the surface treatment adopted the electrochemical pulse method, with ammonium bicarbonate as the electrolyte, an electrolyte concentration of 2%, an electrolyte temperature of room temperature, and a surface treatment time of 60 s. The obtained carbon fiber tensile strength was 3.84 GPa, the tensile modulus was 476 GPa, and the interlaminar shear strength of the carbon fiber composite was 42 MPa.

[0081] Comparative Example 2

[0082] Polyacrylonitrile-based precursor fibers (self-made, 80,000 fibers per bundle, 1.75 dtex fineness) were sequentially subjected to pre-oxidation, low-temperature carbonization, high-temperature carbonization, graphitization, surface treatment, washing, oiling, and drying, finally winding to obtain high-strength, high-modulus carbon fibers. The pre-oxidation process was carried out in air, sequentially passing through three temperature zones. The first zone had a pre-oxidation temperature of 200℃ and a residence time of 48 min, accounting for 40% of the total pre-oxidation time. The draw ratio of the polyacrylonitrile precursor fibers during the first zone pre-oxidation process was 1.05. The second zone had a pre-oxidation temperature of 215℃ and a residence time of 36 min, and the third zone had a pre-oxidation temperature of 220℃ and a residence time of 36 min, for a total residence time of 120 min. During the first zone pre-oxidation process... The width of the polyacrylonitrile precursor fiber bundle was controlled at 72 mm, and the electrostatic value of the polyacrylonitrile precursor fiber bundle was y = 2.8 (in V). The low-temperature carbonization process was carried out at 550℃ in the presence of an inert gas, with a total draw ratio of 1.05. The high-temperature carbonization process was carried out at 1250℃ in the presence of an inert gas, with a total draw ratio of 1.06. The graphitization process was carried out at 2350℃ in the presence of an inert gas. Surface treatment was performed using an electrochemical pulse method, with ammonium bicarbonate as the electrolyte at a concentration of 2%, at room temperature, and for 60 seconds. The obtained carbon fiber tensile strength was 3.85 GPa, the tensile modulus was 381 GPa, and the interlaminar shear strength of the carbon fiber composite was 38.4 MPa.

[0083] Comparative Example 3

[0084] Polyacrylonitrile-based precursor fibers (self-made, 1000 fibers per bundle, 0.83 dtex fineness) were sequentially subjected to pre-oxidation, low-temperature carbonization, high-temperature carbonization, graphitization, surface treatment, washing, oiling, and drying, finally winding to obtain high-strength, high-modulus carbon fibers. The pre-oxidation process was carried out in air, sequentially passing through three temperature zones. The first temperature zone had a pre-oxidation temperature of 220℃ and a residence time of 60 min, accounting for 50% of the total pre-oxidation time. The draw ratio of the polyacrylonitrile precursor fibers during the first temperature zone pre-oxidation process was 1.0. The second temperature zone had a pre-oxidation temperature of 240℃ and a residence time of 30 min, and the third temperature zone had a pre-oxidation temperature of 250℃ and a residence time of 30 min, for a total residence time of 120 min. During the first temperature zone pre-oxidation process... The width of the polyacrylonitrile precursor fiber bundle was controlled to be 1 mm, and the electrostatic value of the polyacrylonitrile precursor fiber bundle was y = 0.05 (in V). The low-temperature carbonization process was carried out at 650℃ in the presence of inert gas, with a total draw ratio of 1.05. The high-temperature carbonization process was carried out at 1400℃ in the presence of inert gas, with a total draw ratio of 1.06. The graphitization process was carried out at 2500℃ in the presence of inert gas. The surface treatment adopted the electrochemical pulse method, with ammonium bicarbonate as the electrolyte, an electrolyte concentration of 2%, an electrolyte temperature of room temperature, and a surface treatment time of 60 s. The obtained carbon fiber tensile strength was 3.74 GPa, the tensile modulus was 381 GPa, and the interlaminar shear strength of the carbon fiber composite was 19.5 MPa.

[0085] Comparative Example 4

[0086] Polyacrylonitrile-based precursor fibers (self-made, 320,000 fibers per bundle, 6.12 dtex fineness) were sequentially subjected to pre-oxidation, low-temperature carbonization, high-temperature carbonization, graphitization, surface treatment, washing, oiling, and drying, finally winding to obtain high-strength, high-modulus carbon fibers. The pre-oxidation process was carried out in air, sequentially passing through three temperature zones. The first temperature zone had a pre-oxidation temperature of 220℃ and a residence time of 72 min, accounting for 60% of the total pre-oxidation time. The draw ratio of the polyacrylonitrile precursor fibers during the first temperature zone pre-oxidation treatment was 1.03. The second temperature zone had a pre-oxidation temperature of 235℃ and a residence time of 20 min. The third temperature zone had a pre-oxidation temperature of 250℃ and a residence time of 28 min, for a total residence time of 120 min. During the first temperature zone pre-oxidation process... The width of the polyacrylonitrile precursor fiber bundle was controlled at 101 mm, and the electrostatic value of the polyacrylonitrile precursor fiber bundle was y = 0.015 (in V). The low-temperature carbonization process was carried out at 800℃ in the presence of an inert gas, with a total draw ratio of 1.05. The high-temperature carbonization process was carried out at 1550℃ in the presence of an inert gas, with a total draw ratio of 1.06. The graphitization process was carried out at 2750℃ in the presence of an inert gas. Surface treatment was performed using an electrochemical pulse method, with ammonium bicarbonate as the electrolyte at a concentration of 2%, at room temperature, and for 60 seconds. The obtained carbon fiber tensile strength was 4.08 GPa, the tensile modulus was 467 GPa, and the interlaminar shear strength of the carbon fiber composite was 17.5 MPa.

[0087] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for preparing high-strength, high-modulus carbon fibers, characterized in that, The method includes pre-oxidizing polyacrylonitrile precursor fibers; The pre-oxidation treatment is provided with at least three temperature zones. In the first temperature zone, the ratio of the electrostatic value of the polyacrylonitrile precursor fiber bundle to the width of the polyacrylonitrile precursor fiber bundle is 0.005-0.032V / mm. Within the first temperature zone, the electrostatic value y of the polyacrylonitrile precursor fiber bundle satisfies the following formula: -1.3x 3 +2.4x 2 -0.65x+0.03<y<-3.4x 3 +6.5x 2 -0.12x+0.23; Where y is in V, and x represents the percentage of the pre-oxidation time in the first temperature zone to the total pre-oxidation time, with a value ranging from 25% to 85%; The temperature of the pre-oxidation treatment is 200-300℃, and the total residence time ranges from 100-140 min.

2. The method according to claim 1, characterized in that, During the first temperature zone pre-oxidation treatment, the bundle width of the polyacrylonitrile-based precursor fiber is 0.0001-0.0008 times the number of single bundles of polyacrylonitrile-based precursor fiber, and the bundle width of the polyacrylonitrile-based precursor fiber is measured in millimeters.

3. The method according to any one of claims 1-2, characterized in that, During the pre-oxidation process, the width of the polyacrylonitrile precursor fiber bundle is 4-80 mm.

4. The method according to claim 1, characterized in that, The number of strands per bundle of polyacrylonitrile precursor fibers ranges from 1,000 to 320,000.

5. The method according to claim 1, characterized in that, The temperature in the first temperature zone is 200-270℃.

6. The method according to claim 5, characterized in that, The pre-oxidation residence time in the first temperature zone is 20-100 min.

7. The method according to claim 5, characterized in that, The draw ratio for the first temperature zone is 1-1.

1.

8. The method according to any one of claims 1-2, characterized in that, The polyacrylonitrile-based precursor fiber is prepared by a wet spinning process.

9. The method according to claim 8, characterized in that, The fineness of the polyacrylonitrile-based precursor fiber is 0.7-6 dtex.

10. The method according to claim 1, characterized in that, The method further includes: subjecting the pre-oxidized oxidized fibers to low-temperature carbonization, high-temperature carbonization, graphitization, electrochemical treatment, washing, sizing, and drying in sequence.

11. The method according to claim 10, characterized in that, The low-temperature carbonization treatment is carried out at a temperature of 400-800℃, and the total draw ratio is 0.95-1.08 times.

12. The method according to claim 11, characterized in that, The high-temperature carbonization treatment is carried out at a temperature of 1200-1600℃, and the total draw ratio is 0.97-1.08 times.

13. The method according to claim 11, characterized in that, The graphitization treatment temperature is 2200-2800℃.