Preparation method of high-strength high-modulus polyacrylonitrile-based filaments, polyacrylonitrile-based filaments and application

Abstract

The application discloses a preparation method of high-strength and high-modulus polyacrylonitrile-based filaments, polyacrylonitrile-based filaments and application. The preparation method of the high-strength and high-modulus polyacrylonitrile-based filaments comprises a steam drawing step, and the relationship between the steam drawing inlet speed and the steam drawing outlet filament tension satisfies the following relationship formula: 0.0024x+0.2975<=y<=‑1.9*10 ‑5 x 2 +0.0043*x+0.3487, wherein y represents the tension of a single fiber at the steam drawing outlet, and the unit is cN; and x represents the steam drawing inlet speed, and the unit is m / min. The method solves the problems of excessive hairiness and poor mechanical properties of carbon fibers in the preparation of polyacrylonitrile-based filaments under the existing conditions, and can be well used in the industrial production of high-strength and high-modulus carbon fiber polyacrylonitrile fibers.

Description

Technical Field

[0001] This invention relates to the field of polyacrylonitrile spinning technology, specifically to a method for preparing high-strength, high-modulus polyacrylonitrile-based precursor fibers, as well as the polyacrylonitrile-based precursor fibers and their applications. Background Technology

[0002] Carbon fiber possesses excellent properties such as high strength, high modulus, and light weight. Composite materials using carbon fiber as a reinforcing fiber have already achieved remarkable success in fields such as aerospace and new energy, becoming an important strategic material for the development of national defense and the national economy. Carbon fiber can be classified into three types according to its raw materials: polyacrylonitrile-based, pitch-based, and viscose-based. Among them, polyacrylonitrile-based carbon fiber, due to its readily available raw materials and excellent comprehensive mechanical properties, has become the main component of carbon fiber, accounting for over 90% of global carbon fiber production.

[0003] The preparation of carbon fiber can be mainly divided into two major processes: carbon fiber precursor preparation and precursor oxidation and carbonization treatment, involving thousands of process control points. Among them, the carbon fiber precursor is the key to determining the performance of carbon fiber. The structure and defects of the precursor can be inherited into the carbon fiber during the oxidation and carbonization process, which will have an irreversible impact on the structure and properties of the carbon fiber.

[0004] The production of carbon fiber precursor involves a series of steps, including coagulation, hot water drawing, washing, oiling, drying, steam drawing, and heat setting. Steam drawing is a crucial step in the preparation of polyacrylonitrile-based carbon fiber precursor, determining key structural characteristics such as orientation and crystallinity. Chinese patents CN111088543A and CN116024680A disclose methods for preparing polyacrylonitrile-based carbon fiber precursor, respectively controlling the tension on each fiber during steam drawing and the steam pressure to reduce fuzziness and improve carbon fiber performance; however, the former method still requires improvement in mechanical properties, while the latter method still results in a relatively large number of fuzzy fibers. During steam drawing, the precursor is subjected to significant stretching and rapid speed increases. At this point, the grooved structure on the surface of the precursor obtained by wet spinning increases the friction between the fiber bundles and increases surface defects, which is detrimental to the subsequent oxidation and carbonization processes in carbon fiber preparation, ultimately hindering the improvement of the carbon fiber's mechanical properties. Summary of the Invention

[0005] To address the problems of excessive fuzz and poor mechanical properties of carbon fibers produced by polyacrylonitrile-based precursor fibers under existing conditions, this invention provides a method for preparing high-strength, high-modulus polyacrylonitrile-based precursor fibers, as well as the resulting polyacrylonitrile-based precursor fibers and their applications. The method described in this invention effectively solves this problem and can be used in the industrial production of polyacrylonitrile fibers for high-strength, high-modulus carbon fibers.

[0006] One objective of this invention is to provide a method for preparing high-strength, high-modulus polyacrylonitrile-based precursor fibers, including a steam drawing step, wherein the relationship between the steam drawing inlet velocity and the steam drawing outlet precursor fiber tension satisfies the following equation:

[0007] 0.0024x + 0.2975 ≤ y ≤ -1.9 × 10 -5 x 2 +0.0043x+0.3487

[0008] Where y represents the tension of a single fiber at the steam drawing inlet, in cN; and x represents the steam drawing inlet velocity, in m / min.

[0009] In a preferred embodiment of the present invention,

[0010] The steam stretching inlet velocity is 5-80 m / min, preferably 8-65 m / min.

[0011] In a preferred embodiment of the present invention,

[0012] The steam pressure (in MPa) a used for steam drawing is 0.15-0.18 times the drawing ratio (in multiples) b, preferably 0.15-0.17 times, more preferably 0.15-0.16 times, wherein the drawing ratio is 1.5-3.0 times, preferably 1.8-2.7 times.

[0013] This invention provides the aforementioned relationship through extensive experimental research. By ensuring that the tension of a single fiber at the steam drawing exit and the steam drawing inlet velocity conform to the relationship expressed by this formula during the steam drawing process, the problems of excessive fuzz and poor mechanical properties of carbon fibers produced by polyacrylonitrile-based precursor fibers under existing conditions can be effectively solved.

[0014] In a preferred embodiment of the present invention,

[0015] The preparation method employs a wet spinning process, preferably including the steps of coagulating and forming a polyacrylonitrile raw solution, coagulating and stretching, hot water stretching, washing, oiling, drying and densifying, steam stretching, and steam heat setting to obtain the high-strength, high-modulus polyacrylonitrile-based precursor fiber.

[0016] In a preferred embodiment of the present invention,

[0017] The polyacrylonitrile stock solution has a polyacrylonitrile solid content of 10-40%, preferably 17-22%, and / or an intrinsic viscosity of 1.0-5.0 dL / g, preferably 1.7-2.5 dL / g.

[0018] In a preferred embodiment of the present invention,

[0019] The solidification and stretching process includes at least three stages; preferably,

[0020] In the solidification drawing process, the temperature of each solidification drawing is 25-95℃, preferably 30-80℃, more preferably 30-70℃, and / or the total draw ratio is 1.5-3.5, preferably 1-2.

[0021] In a preferred embodiment of the present invention,

[0022] The hot water stretching includes at least three stages; and / or,

[0023] The temperature of the hot water stretching is 90-100℃, preferably 95-99℃; more preferably,

[0024] The total draw ratio of the hot water stretching is greater than or equal to 3.5 times, preferably greater than or equal to 4.5 times, and the draw ratio of the third hot water stretching is greater than or equal to 1.3 times, preferably 1.6-2.7 times.

[0025] In a preferred embodiment of the present invention,

[0026] The oiling and drying densification process involves at least two stages; and / or,

[0027] The drying and densification temperature is 90-150℃, without stretching; preferably, the drying and densification temperature is 100-140℃.

[0028] In a preferred embodiment of the present invention,

[0029] The number of strands in a single bundle of the high-strength, high-modulus polyacrylonitrile-based precursor fiber is 1,000-320,000.

[0030] In the above technical solution, there are no special limitations on other aspects of the preparation method of polyacrylonitrile-based precursor fibers. They can be obtained from polyacrylonitrile raw materials commonly used in the art through commonly used spinning processes. There are no special limitations on the polyacrylonitrile raw materials and spinning processes. The polyacrylonitrile used in this application can be a polyacrylonitrile homopolymer or a polyacrylonitrile copolymer. The polyacrylonitrile copolymer can be prepared from a comonomer commonly used in the art. For example, but not limited to, the polyacrylonitrile comonomer is a vinyl-containing monomer. The comonomer is preferably one or more of acrylates, vinyl esters, acrylamides, sulfonates, carboxylic acids, and ammonium salts.

[0031] The second objective of this invention is to provide a polyacrylonitrile-based precursor fiber obtained by a preparation method according to one of the objectives of this invention.

[0032] The third objective of this invention is to provide a high-strength, high-modulus carbon fiber, which is prepared from the polyacrylonitrile-based precursor fiber described in the second objective of this invention; preferably, the high-strength, high-modulus carbon fiber is obtained by subjecting the polyacrylonitrile precursor fiber to steps including pre-oxidation, carbonization, and graphitization treatment.

[0033] The preparation process of the high-strength, high-modulus carbon fiber is not particularly limited and can be obtained from polyacrylonitrile-based precursor fibers through commonly used pre-oxidation, carbonization, and graphitization processes in the field.

[0034] In a preferred embodiment of the present invention,

[0035] The pre-oxidation temperature is 180-300℃; and / or,

[0036] The carbonization is divided into low-temperature carbonization and high-temperature carbonization; preferably, the temperature of the low-temperature carbonization is 300-700℃; and / or, the temperature of the high-temperature carbonization is 1000-1500℃; and / or,

[0037] The graphitization temperature is 2200-2800℃.

[0038] By employing the technical solution of this invention, the number of fiber filaments at the graphite furnace outlet every 30 hours during the carbon fiber preparation process can be as low as 8 using an online camera. The resulting carbon fiber has a tensile strength of up to 5.82 GPa and a modulus of up to 380 GPa, achieving good technical results. Detailed Implementation

[0039] The present invention will now be described in detail with reference to specific embodiments. It should be noted that the following embodiments are only used to further illustrate the present invention and should not be construed as limiting the scope of protection of the present invention. Some non-essential improvements and adjustments made by those skilled in the art based on the content of the present invention are still within the scope of protection of the present invention.

[0040] In this invention, the tension value borne by the fiber during the saturated steam drawing process is obtained by measuring the tension of the fiber bundle between the front and rear drawing rollers of the steam drawing machine using a handheld tension meter; the standard for testing the linear density of carbon fiber precursor is GB / T 14343, and the standard for testing the mechanical properties of carbon fiber multifilament is GB / T 3362-2017; the fuzzy fibers of the fiber bundle at the graphite furnace outlet during the carbon fiber preparation process are obtained by counting the number of fuzzy fibers over 10 hours using an online camera.

[0041] Unless otherwise specified, the raw materials used in the embodiments and comparative examples of this invention are all disclosed in the prior art, such as those that can be directly purchased or prepared according to the preparation methods disclosed in the prior art.

[0042] The polyacrylonitrile in the spinning solution used in Example 1 of this invention is a polyacrylonitrile copolymer, which is obtained by polymerization according to Example 1 of Chinese Patent CN110684149A; the preparation process of other examples and comparative examples is the same as that of Example 1 of Chinese Patent CN110684149A, only the mass ratio of acrylonitrile, itaconic acid and sodium methacrylate added is changed.

[0043]

Example 1

[0044] Preparation of polyacrylonitrile-based precursor fibers: Wet spinning technology was used, and the intrinsic viscosity of the spinning solution was 2.5 dL / g, with a solid content of 18%. The spinning solution, precisely metered and filtered by a metering pump, is extruded through a 3000-hole spinneret and sequentially enters four coagulation baths containing dimethyl sulfoxide aqueous solution at temperatures of 35℃, 55℃, 60℃, and 70℃, with a total draw ratio of 2.0 and concentrations of 85%, 67%, 53%, and 39%, respectively. It then undergoes three stages of hot water drawing at temperatures of 95℃, 96℃, and 99℃, with draw ratios of 1.84, 2.15, and 2.68, respectively. After oiling, it undergoes two stages of drying and densification treatment without drawing, at temperatures of 115℃ and 125℃. The steam drawing inlet velocity is 40 m / min, the steam pressure is 0.375 MPa, and the draw ratio is 2.5. At this point, the steam-drawn outlet filament tension is 1320 cN, and the tension of a single fiber is 0.44 cN. Finally, after heat setting and winding, high-strength, high-modulus polyacrylonitrile carbon fiber precursor is obtained.

[0045] Preparation of high-strength, high-modulus carbon fiber: The obtained precursor fiber was sequentially passed through four pre-oxidation temperature zones at 180℃, 240℃, 270℃, and 300℃, with draw ratios of 1.01, 1.0, 1.0, and 0.99, respectively, and held for 40 min in each zone; then, it was carbonized at a low temperature of 700℃ with a draw ratio of 1.03 and a holding time of 20 min; then, it was carbonized at a high temperature of 1500℃ with a draw ratio of 1.04 and a holding time of 20 min; finally, it was graphitized at 2500℃, and then subjected to surface treatment, washing, sizing, drying at 120℃, and winding to obtain high-strength, high-modulus carbon fiber.

[0046] The number of filaments at the graphite furnace outlet was counted using an online camera. The number of filaments in the fiber was 15 per 30 hours. The carbon fiber tensile strength was 5.82 GPa and the modulus was 380 GPa.

[0047]

Example 2

[0048] Preparation of polyacrylonitrile-based precursor fibers: Wet spinning technology was adopted. The intrinsic viscosity of the spinning solution (in the polyacrylonitrile copolymer, the mass ratio of acrylonitrile:itacic acid:sodium methacrylate was 90:8:2) was 2.0 dL / g, and the solid content was 19%. The spinning solution, precisely metered and filtered by a metering pump, is extruded through a 6000-hole spinneret and sequentially enters four coagulation baths containing dimethyl sulfoxide aqueous solution at temperatures of 30℃, 50℃, 55℃, and 60℃, with a total draw ratio of 1.95 and concentrations of 85%, 67%, 53%, and 39%, respectively. It then undergoes three stages of hot water drawing at temperatures of 97℃, 98℃, and 99℃, with draw ratios of 1.65, 1.90, and 2.25, respectively. After oiling, it undergoes two stages of drying and densification treatment without drawing, at temperatures of 118℃ and 120℃. The steam drawing inlet velocity is 35 m / min, the steam pressure is 0.3 MPa, and the draw ratio is 2.0. At this point, the steam-drawn outlet filament tension is 2580 cN, and the tension of a single fiber is 0.43 cN. Finally, after heat setting and winding, high-strength, high-modulus polyacrylonitrile carbon fiber precursor is obtained.

[0049] Preparation of high-strength, high-modulus carbon fiber: The obtained precursor fiber was sequentially passed through four pre-oxidation temperature zones at 180℃, 240℃, 270℃, and 300℃, with draw ratios of 1.01, 1.0, 1.0, and 0.99, respectively, for 40 min at each zone; then, it was carbonized at a low temperature of 480℃ with a draw ratio of 1.03 and a dwell time of 20 min; then, it was carbonized at a high temperature of 1400℃ with a draw ratio of 1.04 and a dwell time of 20 min; finally, it was graphitized at 2500℃, and then subjected to surface treatment, washing, sizing, drying at 120℃, and winding to obtain high-strength, high-modulus carbon fiber.

[0050] The number of filaments at the graphite furnace outlet was counted using an online camera. The number of filaments in the fiber was 18 per 30 hours. The carbon fiber tensile strength was 5.79 GPa and the modulus was 378 GPa.

[0051]

Example 3

[0052] Preparation of polyacrylonitrile-based precursor fibers: Wet spinning technology was used. The intrinsic viscosity of the spinning solution (in the polyacrylonitrile copolymer, the mass ratio of acrylonitrile:itacic acid:sodium methacrylate was 90:7:3) was 1.9 dL / g and the solid content was 17%. The spinning solution, precisely metered and filtered by a metering pump, is extruded through a 320,000-hole spinneret and sequentially enters four coagulation baths containing dimethyl sulfoxide aqueous solution at temperatures of 35℃, 60℃, 65℃, and 75℃, with a total draw ratio of 1.2 and concentrations of 85%, 67%, 53%, and 39%, respectively. It then undergoes three stages of hot water drawing at temperatures of 95℃, 96℃, and 97℃, with draw ratios of 1.35, 1.65, and 1.85, respectively. After oiling, it undergoes two stages of drying and densification treatment without drawing, at temperatures of 130℃ and 140℃. The steam drawing inlet velocity is 8 m / min, the steam pressure is 0.27 MPa, and the draw ratio is 1.8. At this point, the steam-drawn outlet filament tension is 108,800 cN, and the tension of a single fiber is 0.34 cN. Finally, after heat setting and winding, high-strength, high-modulus polyacrylonitrile carbon fiber precursor is obtained.

[0053] Preparation of high-strength, high-modulus carbon fiber: The obtained precursor fiber was sequentially passed through four pre-oxidation temperature zones at 180℃, 240℃, 270℃, and 300℃, with draw ratios of 1.01, 1.0, 1.0, and 0.99, respectively, for 40 min at each zone; then, it was carbonized at a low temperature of 480℃ with a draw ratio of 1.03 and a dwell time of 20 min; then, it was carbonized at a high temperature of 1400℃ with a draw ratio of 1.04 and a dwell time of 20 min; finally, it was graphitized at 2500℃, and then subjected to surface treatment, washing, sizing, drying at 120℃, and winding to obtain high-strength, high-modulus carbon fiber.

[0054] The number of filaments at the graphite furnace outlet was counted using an online camera. The number of filaments in the fiber was 32 per 30 hours. The carbon fiber tensile strength was 5.68 GPa and the modulus was 365 GPa.

[0055]

Example 4

[0056] Preparation of polyacrylonitrile-based precursor fibers: Wet spinning technology was used. The spinning solution (in the polyacrylonitrile copolymer, the mass ratio of acrylonitrile:itacic acid:sodium methacrylate was 90:6:4) had an intrinsic viscosity of 1.7 dL / g and a solid content of 22%. The spinning solution, precisely metered and filtered by a metering pump, is extruded through a 96,000-hole spinneret and sequentially enters four coagulation baths containing dimethyl sulfoxide aqueous solution at temperatures of 40℃, 60℃, 65℃, and 70℃, with a total draw ratio of 1.35 and concentrations of 85%, 67%, 53%, and 39%, respectively. It then undergoes three stages of hot water drawing at temperatures of 96℃, 97℃, and 98℃, with draw ratios of 1.60, 1.75, and 1.85, respectively. After oiling, it undergoes two stages of drying and densification treatment without drawing, at temperatures of 135℃ and 145℃. The steam drawing inlet velocity is 10 m / min, the steam pressure is 0.27 MPa, and the draw ratio is 1.8. At this point, the steam-drawn outlet filament tension is 33,600 cN, and the tension of a single fiber is 0.35 cN. Finally, after heat setting and winding, high-strength, high-modulus polyacrylonitrile carbon fiber precursor is obtained.

[0057] Preparation of high-strength, high-modulus carbon fiber: The obtained precursor fiber was sequentially passed through four pre-oxidation temperature zones at 180℃, 240℃, 270℃, and 300℃, with draw ratios of 1.01, 1.0, 1.0, and 0.99, respectively, for 40 min at each zone; then, it was carbonized at a low temperature of 480℃ with a draw ratio of 1.03 and a dwell time of 20 min; then, it was carbonized at a high temperature of 1400℃ with a draw ratio of 1.04 and a dwell time of 20 min; finally, it was graphitized at 2500℃, and then subjected to surface treatment, washing, sizing, drying at 120℃, and winding to obtain high-strength, high-modulus carbon fiber.

[0058] The number of filaments at the graphite furnace outlet was counted using an online camera. The number of filaments in the fiber was 28 per 30 hours. The carbon fiber tensile strength was 5.59 GPa and the modulus was 360 GPa.

[0059]

Example 5

[0060] Preparation of polyacrylonitrile-based precursor fibers: Wet spinning technology was used. The intrinsic viscosity of the spinning solution (in the polyacrylonitrile copolymer, the mass ratio of acrylonitrile:itacic acid:sodium methacrylate was 95:4:1) was 2.2 dL / g, and the solid content was 20%. The spinning solution, precisely metered and filtered by a metering pump, is extruded through a 48,000-hole spinneret and sequentially enters four coagulation baths containing dimethyl sulfoxide aqueous solution at temperatures of 30℃, 45℃, 55℃, and 65℃, with a total draw ratio of 1.45 and concentrations of 85%, 67%, 53%, and 39%, respectively. It then undergoes three stages of hot water drawing at temperatures of 95℃, 97℃, and 99℃, with draw ratios of 1.55, 1.85, and 2.05, respectively. After oiling, it undergoes two stages of drying and densification treatment without drawing, at temperatures of 135℃ and 150℃. The steam drawing inlet velocity is 25 m / min, the steam pressure is 0.3 MPa, and the draw ratio is 2.0. At this point, the steam-drawn outlet filament tension is 19200 cN, and the tension of a single fiber is 0.4 cN. Finally, after heat setting and winding, high-strength, high-modulus polyacrylonitrile carbon fiber precursor is obtained.

[0061] Preparation of high-strength, high-modulus carbon fiber: The obtained precursor fiber was sequentially passed through four pre-oxidation temperature zones at 180℃, 240℃, 270℃, and 300℃, with draw ratios of 1.01, 1.0, 1.0, and 0.99, respectively, for 40 min at each zone; then, it was carbonized at a low temperature of 480℃ with a draw ratio of 1.03 and a dwell time of 20 min; then, it was carbonized at a high temperature of 1400℃ with a draw ratio of 1.04 and a dwell time of 20 min; finally, it was graphitized at 2500℃, and then subjected to surface treatment, washing, sizing, drying at 120℃, and winding to obtain high-strength, high-modulus carbon fiber.

[0062] The number of filaments at the graphite furnace outlet was counted using an online camera. The number of filaments in the fiber was 22 per 30 hours. The carbon fiber tensile strength was 5.63 GPa and the modulus was 371 GPa.

[0063]

Example 6

[0064] Preparation of polyacrylonitrile-based precursor fibers: Wet spinning technology was used. The intrinsic viscosity of the spinning solution (in the polyacrylonitrile copolymer, the mass ratio of acrylonitrile:itacic acid:sodium methacrylate was 97:2:1) was 2.4 dL / g and the solid content was 21%. The spinning solution, precisely metered and filtered by a metering pump, is extruded through a 12,000-hole spinneret and sequentially enters four coagulation baths containing dimethyl sulfoxide aqueous solution at temperatures of 30℃, 50℃, 70℃, and 75℃, with a total draw ratio of 1.55 and concentrations of 85%, 67%, 53%, and 39%, respectively. It then undergoes three stages of hot water drawing at temperatures of 96℃, 96℃, and 99℃, with draw ratios of 1.45, 1.65, and 1.75, respectively. After oiling, it undergoes two stages of drying and densification treatment without drawing, at temperatures of 125℃ and 135℃. The steam drawing inlet velocity is 15 m / min, the steam pressure is 0.38 MPa, and the draw ratio is 2.5 times. At this point, the steam-drawn outlet filament tension is 4080 cN, and the tension of a single fiber is 0.34 cN. Finally, after heat setting and winding, high-strength, high-modulus polyacrylonitrile carbon fiber precursor is obtained.

[0065] Preparation of high-strength, high-modulus carbon fiber: The obtained precursor fiber was sequentially passed through four pre-oxidation temperature zones at 180℃, 240℃, 270℃, and 300℃, with draw ratios of 1.01, 1.0, 1.0, and 0.99, respectively, for 40 min at each zone; then, it was carbonized at a low temperature of 480℃ with a draw ratio of 1.03 and a dwell time of 20 min; then, it was carbonized at a high temperature of 1400℃ with a draw ratio of 1.04 and a dwell time of 20 min; finally, it was graphitized at 2500℃, and then subjected to surface treatment, washing, sizing, drying at 120℃, and winding to obtain high-strength, high-modulus carbon fiber.

[0066] The number of filaments at the graphite furnace outlet was counted using an online camera. The number of filaments in the fiber was 8 per 30 hours. The carbon fiber tensile strength was 5.54 GPa and the modulus was 373 GPa.

[0067]

Comparative Example 1

[0068] Preparation of polyacrylonitrile-based precursor fibers: Wet spinning technology was used, and the intrinsic viscosity of the spinning solution (obtained by polymerization according to Example 1 of Chinese Patent CN110684149A) was 2.5 dL / g, and the solid content was 18%. The spinning solution, precisely metered and filtered by a metering pump, is extruded through a 3000-hole spinneret and sequentially enters four coagulation baths containing dimethyl sulfoxide aqueous solution at temperatures of 35℃, 55℃, 60℃, and 70℃, with a total draw ratio of 2.0 and concentrations of 85%, 67%, 53%, and 39%, respectively. It then undergoes three stages of hot water drawing at temperatures of 95℃, 96℃, and 99℃, with draw ratios of 1.84, 2.15, and 2.68, respectively. After oiling, it undergoes two stages of drying and densification treatment without drawing, at temperatures of 115℃ and 125℃. The steam drawing inlet velocity is 40 m / min, the steam pressure is 0.27 MPa, and the draw ratio is 2.5. At this point, the steam-drawn outlet filament tension is 1740 cN, and the tension of a single fiber is 0.58 cN. Finally, after heat setting and winding, high-strength, high-modulus polyacrylonitrile carbon fiber precursor is obtained.

[0069] Preparation of high-strength, high-modulus carbon fiber: The obtained precursor fiber was sequentially passed through four pre-oxidation temperature zones at 180℃, 240℃, 270℃, and 300℃, with draw ratios of 1.01, 1.0, 1.0, and 0.99, respectively, and held for 40 min in each zone; then, it was carbonized at a low temperature of 700℃ with a draw ratio of 1.03 and a holding time of 20 min; then, it was carbonized at a high temperature of 1500℃ with a draw ratio of 1.04 and a holding time of 20 min; finally, it was graphitized at 2500℃, and then subjected to surface treatment, washing, sizing, drying at 120℃, and winding to obtain high-strength, high-modulus carbon fiber.

[0070] The number of filaments at the graphite furnace outlet was counted using an online camera. The number of filaments in the fiber was 35 per 30 hours. The carbon fiber tensile strength was 5.27 GPa and the modulus was 352 GPa.

[0071] [Comparative Example 2]

[0072] Preparation of polyacrylonitrile-based precursor fibers: Wet spinning technology was used, and the intrinsic viscosity of the spinning solution (obtained by polymerization according to Example 1 of Chinese Patent CN110684149A) was 2.5 dL / g, and the solid content was 18%. The spinning solution, precisely metered and filtered by a metering pump, is extruded through a 3000-hole spinneret and sequentially enters four coagulation baths containing dimethyl sulfoxide aqueous solution at temperatures of 35℃, 55℃, 60℃, and 70℃, with a total draw ratio of 2.0 and concentrations of 85%, 67%, 53%, and 39%, respectively. It then undergoes three stages of hot water drawing at temperatures of 95℃, 96℃, and 99℃, with draw ratios of 1.84, 2.15, and 2.68, respectively. After oiling, it undergoes two stages of drying and densification treatment without drawing, at temperatures of 115℃ and 125℃. The steam drawing inlet velocity is 40 m / min, the steam pressure is 0.35 MPa, and the draw ratio is 2.5 times. At this point, the steam-drawn outlet filament tension is 1050 cN, and the tension of a single fiber is 0.35 cN. Finally, after heat setting and winding, high-strength, high-modulus polyacrylonitrile carbon fiber precursor is obtained.

[0073] Preparation of high-strength, high-modulus carbon fiber: The obtained precursor fiber was sequentially passed through four pre-oxidation temperature zones at 180℃, 240℃, 270℃, and 300℃, with draw ratios of 1.01, 1.0, 1.0, and 0.99, respectively, and held for 40 min in each zone; then, it was carbonized at a low temperature of 700℃ with a draw ratio of 1.03 and a holding time of 20 min; then, it was carbonized at a high temperature of 1500℃ with a draw ratio of 1.04 and a holding time of 20 min; finally, it was graphitized at 2500℃, and then subjected to surface treatment, washing, sizing, drying at 120℃, and winding to obtain high-strength, high-modulus carbon fiber.

[0074] The number of filaments at the graphite furnace outlet was counted using an online camera. The number of filaments in the fiber was 55 per 30 hours. The carbon fiber tensile strength was 5.24 GPa and the modulus was 349 GPa.

[0075] [Comparative Example 3]

[0076] Preparation of polyacrylonitrile-based precursor fibers: Wet spinning technology was used, and the intrinsic viscosity of the spinning solution (polyacrylonitrile copolymer as in Example 2) was 2.0 dL / g, and the solid content was 19%. The spinning solution, precisely metered and filtered by a metering pump, is extruded through a 6000-hole spinneret and sequentially enters four coagulation baths containing dimethyl sulfoxide aqueous solution at temperatures of 30℃, 50℃, 55℃, and 60℃, with a total draw ratio of 1.95 and concentrations of 85%, 67%, 53%, and 39%, respectively. It then undergoes three stages of hot water drawing at temperatures of 97℃, 98℃, and 99℃, with draw ratios of 1.65, 1.90, and 2.25, respectively. After oiling, it undergoes two stages of drying and densification treatment without drawing, at temperatures of 118℃ and 120℃. The steam drawing inlet velocity is 35 m / min, the steam pressure is 0.55 MPa, and the draw ratio is 3.0. At this point, the steam-drawn outlet filament tension is 2880 cN, and the tension of a single fiber is 0.48 cN. Finally, after heat setting and winding, high-strength, high-modulus polyacrylonitrile carbon fiber precursor is obtained.

[0077] Preparation of high-strength, high-modulus carbon fiber: The obtained precursor fiber was sequentially passed through four pre-oxidation temperature zones at 180℃, 240℃, 270℃, and 300℃, with draw ratios of 1.01, 1.0, 1.0, and 0.99, respectively, for 40 min at each zone; then, it was carbonized at a low temperature of 480℃ with a draw ratio of 1.03 and a dwell time of 20 min; then, it was carbonized at a high temperature of 1400℃ with a draw ratio of 1.04 and a dwell time of 20 min; finally, it was graphitized at 2500℃, and then subjected to surface treatment, washing, sizing, drying at 120℃, and winding to obtain high-strength, high-modulus carbon fiber.

[0078] The number of filaments at the graphite furnace outlet was counted using an online camera. The number of filaments in the fiber was 34 per 30 hours. The carbon fiber tensile strength was 5.07 GPa and the modulus was 347 GPa.

[0079] [Comparative Example 4]

[0080] Preparation of polyacrylonitrile-based precursor fibers: Wet spinning technology was used, and the intrinsic viscosity of the spinning solution (polyacrylonitrile copolymer as in Example 6) was 2.4 dL / g, and the solid content was 21%. The spinning solution, precisely metered and filtered by a metering pump, is extruded through a 12,000-hole spinneret and sequentially enters four coagulation baths containing dimethyl sulfoxide aqueous solution at temperatures of 30℃, 50℃, 70℃, and 75℃, with a total draw ratio of 1.55 and concentrations of 85%, 67%, 53%, and 39%, respectively. It then undergoes three stages of hot water drawing at temperatures of 96℃, 96℃, and 99℃, with draw ratios of 1.45, 1.65, and 1.75, respectively. After oiling, it undergoes two stages of drying and densification treatment without drawing, at temperatures of 125℃ and 135℃. The steam drawing inlet velocity is 15 m / min, the steam pressure is 0.27 MPa, and the draw ratio is 2.5 times. At this point, the steam-drawn outlet filament tension is 5040 cN, and the tension of a single fiber is 0.42 cN. Finally, after heat setting and winding, high-strength, high-modulus polyacrylonitrile carbon fiber precursor is obtained.

[0081] Preparation of high-strength, high-modulus carbon fiber: The obtained precursor fiber was sequentially passed through four pre-oxidation temperature zones at 180℃, 240℃, 270℃, and 300℃, with draw ratios of 1.01, 1.0, 1.0, and 0.99, respectively, for 40 min at each zone; then, it was carbonized at a low temperature of 480℃ with a draw ratio of 1.03 and a dwell time of 20 min; then, it was carbonized at a high temperature of 1400℃ with a draw ratio of 1.04 and a dwell time of 20 min; finally, it was graphitized at 2500℃, and then subjected to surface treatment, washing, sizing, drying at 120℃, and winding to obtain high-strength, high-modulus carbon fiber.

[0082] The number of filaments at the graphite furnace outlet was counted using an online camera. The number of filaments in the fiber was 51 per 30 hours. The carbon fiber tensile strength was 4.68 GPa and the modulus was 340 GPa.

[0083] [Comparative Example 5]

[0084] Preparation of polyacrylonitrile-based precursor fibers: Wet spinning technology was employed. The spinning solution (in a polyacrylonitrile copolymer, the mass ratio of acrylonitrile:itacic acid:sodium methacrylate was 98:1:1) had an intrinsic viscosity of 3.5 dL / g and a solid content of 18%. The spinning solution was precisely metered and filtered by a metering pump, then extruded through a 6000-hole spinneret. It was sequentially coagulated in four dimethyl sulfoxide aqueous solutions at temperatures of 26℃, 30℃, 40℃, and 50℃, with a total draw ratio of 1.32 and concentrations of 85%, 67%, 53%, and 39%, respectively. Following this, it underwent four stages of hot water drawing at temperatures of 95℃, 96℃, 97℃, and 99℃, with draw ratios of 1.38 and 1.38, respectively. 1.40, 1.48, and 1.50; after oiling, they undergo two-stage drying and densification treatment without stretching, at temperatures of 110℃ and 120℃ respectively; the steam stretching inlet speed is 25m / min, the steam pressure is 0.3MPa, and the stretching ratio is 2.5 times. At this time, the tension of the steam-stretched outlet filament is 3000cN, and the tension of a single fiber is 0.5cN; finally, after heat setting and winding, high-strength, high-modulus polyacrylonitrile carbon fiber precursor is obtained.

[0085] Preparation of high-strength, high-modulus carbon fiber: The obtained precursor fiber was sequentially passed through four pre-oxidation temperature zones at 180℃, 240℃, 270℃, and 300℃, with draw ratios of 1.01, 1.0, 1.0, and 0.99, respectively, and held for 40 min in each zone; then, it was carbonized at a low temperature of 480℃ with a draw ratio of 1.03 and a holding time of 20 min; then, it was carbonized at a high temperature of 1400℃ with a draw ratio of 1.04 and a holding time of 20 min; finally, it was graphitized at 2800℃, and then subjected to surface treatment, washing, sizing, drying at 120℃, and winding to obtain high-strength, high-modulus carbon fiber.

[0086] The number of filaments at the graphite furnace outlet was counted using an online camera. The number of filaments in the fiber was 150 per 30 hours. The carbon fiber tensile strength was 4.56 GPa and the modulus was 345 GPa.

[0087] As can be seen from Example 1 and Comparative Examples 1-2, under the same conditions, the relationship between the steam drawing inlet velocity and the steam drawing outlet yarn tension in Comparative Examples 1-2 does not satisfy the following equation: 0.0024x + 0.2975 ≤ y ≤ -1.9 × 10⁻⁶ -5 x 2 +0.0043x+0.3487, therefore the number of filaments is significantly increased compared to Example 1, and the mechanical properties of the carbon fiber are also reduced compared to Example 1;

[0088] A comparison of Example 2 with Comparative Example 3, and Example 6 with Comparative Example 4, also shows that under the same conditions, only when the relationship between the steam drawing inlet velocity and the steam drawing outlet yarn tension during the steam drawing process satisfies the formula of the present invention (0.0024x + 0.2975 ≤ y ≤ -1.9 × 10⁻⁶). -5 x 2 Only when the value is +0.0043x+0.3487 can the number of filaments be reduced more effectively and the mechanical properties of carbon fiber be improved.

[0089] It should be noted that the embodiments described above are only for explaining the present invention and do not constitute any limitation on the present invention. The present invention has been described with reference to typical embodiments, but it should be understood that the words used therein are descriptive and explanatory terms, not limiting terms. Modifications can be made to the present invention within the scope of the claims, and revisions can be made to the present invention without departing from the scope and spirit of the present invention. Although the present invention described herein relates to specific methods, materials, and embodiments, it does not mean that the present invention is limited to the specific examples disclosed herein; on the contrary, the present invention can be extended to all other methods and applications with the same function.

[0090] All publications, patent applications, patents, and other references mentioned in this specification are incorporated herein by reference. Unless otherwise defined, all technical and scientific terms used in this specification have the meanings commonly understood by those skilled in the art. In case of conflict, the definitions in this specification shall prevail.

[0091] When this specification uses the prefixes “known to those skilled in the art,” “prior art,” or similar terms to derive materials, substances, methods, steps, apparatus, or components, the objects derived from such prefixes cover those commonly used in the art at the time of this application’s filing, but also include those that are not currently commonly used but will become generally recognized in the art as suitable for similar purposes.

[0092] The endpoints and any values ​​of the ranges disclosed in this application are not limited to the precise ranges or values; such ranges or values ​​should be understood to include values ​​close to them. 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. In principle, various technical solutions can be combined with each other to obtain new technical solutions, which should also be considered as specifically disclosed herein.

[0093] In the context of this specification, except where expressly stated otherwise, any matters or issues not mentioned shall apply directly to those known in the art without any modification.

[0094] Furthermore, any implementation described herein can be freely combined with one or more other implementations described herein, and the resulting technical solutions or technical ideas shall be regarded as part of the original disclosure or original record of the present invention, and should not be regarded as new content not disclosed or anticipated herein, unless those skilled in the art believe that the combination is obviously unreasonable.

Claims

1. A method for preparing high-strength, high-modulus polyacrylonitrile-based precursor fibers, comprising a steam drawing step, wherein the relationship between the steam drawing inlet velocity and the steam drawing outlet precursor fiber tension satisfies the following equation: 0.0024x+0.2975≤y≤-1.9×10 -5 x 2 +0.0043x+0.3487 in, y represents the tension of a single fiber at the steam drawing exit, in cN; x represents the steam drawing inlet speed, in m / min; the steam pressure a used for steam drawing is 0.15-0.18 times the drawing ratio b, where the unit of steam pressure a is MPa; the tension value borne by the fiber during steam drawing is obtained by measuring the tension of the filament bundle between the front and rear drawing rollers of the steam drawing machine using a handheld tension meter; the preparation method adopts a wet spinning process, including the steps of solidifying and forming polyacrylonitrile dope, solidifying and drawing, hot water drawing, washing, oiling, drying and densifying, steam drawing, and steam heat setting to obtain the high-strength, high-modulus polyacrylonitrile-based precursor fiber.

2. The preparation method according to claim 1, characterized in that: The steam stretching inlet velocity is 5-80 m / min.

3. The preparation method according to claim 2, characterized in that: The steam stretching inlet velocity is 8-65 m / min.

4. The preparation method according to claim 1, characterized in that: The draw ratio is 1.5-3.0 times.

5. The preparation method according to claim 4, characterized in that: The draw ratio is 1.8-2.7 times.

6. The preparation method according to claim 1, characterized in that: The polyacrylonitrile stock solution has a polyacrylonitrile solid content of 10-40% and / or an intrinsic viscosity of 1.0-5.0 dL / g.

7. The preparation method according to claim 6, characterized in that: The polyacrylonitrile stock solution has a polyacrylonitrile solid content of 17-22% and / or an intrinsic viscosity of 1.7-2.5 dL / g.

8. The preparation method according to claim 1, characterized in that: The solidification stretching process includes at least three stages.

9. The preparation method according to claim 8, characterized in that: In the solidification drawing process, the temperature of each solidification drawing is 25-95℃, and / or the total draw ratio is 1.5-3.

5.

10. The preparation method according to claim 9, characterized in that: In the solidification drawing process, the temperature of each solidification drawing is 30-80℃, and / or the total drawing ratio is 1-2.

11. The preparation method according to claim 1, characterized in that: The hot water stretching includes at least three stages; and / or, The temperature of the hot water stretching is 90-100℃.

12. The preparation method according to claim 11, characterized in that: The temperature of the hot water stretching is 95-99℃.

13. The preparation method according to claim 12, characterized in that: The total draw ratio of the hot water stretching is greater than or equal to 3.5 times, and the draw ratio of the third hot water stretching is greater than or equal to 1.3 times.

14. The preparation method according to claim 13, characterized in that: The total draw ratio of the hot water stretching is greater than or equal to 4.5 times, and the draw ratio of the third hot water stretching is 1.6-2.7 times.

15. The preparation method according to claim 1, characterized in that: The oiling and drying densification process involves at least two stages; and / or, The drying and densification temperature is 90-150℃, and no stretching is applied.

16. The preparation method according to claim 15, characterized in that: The drying and densification temperature is 100-140℃.

17. The preparation method according to claim 1, characterized in that: The number of strands in a single bundle of the high-strength, high-modulus polyacrylonitrile-based precursor fiber is 1,000-320,000.

18. A polyacrylonitrile-based precursor fiber obtained by any one of the preparation methods described in claims 1-17.

19. A high-strength, high-modulus carbon fiber, prepared from the polyacrylonitrile-based precursor fiber as described in claim 18; the high-strength, high-modulus carbon fiber is obtained by subjecting the polyacrylonitrile precursor fiber to steps including pre-oxidation, carbonization, and graphitization treatment.

20. The high-strength, high-modulus carbon fiber as described in claim 19, characterized in that, The pre-oxidation temperature is 180-300℃; and / or, The carbonization is divided into low-temperature carbonization and high-temperature carbonization; and / or, The graphitization temperature is 2200-2800℃.

21. The high-strength, high-modulus carbon fiber as described in claim 20, characterized in that, The low-temperature carbonization temperature is 300-700℃; and / or, the high-temperature carbonization temperature is 1000-1500℃.