Polyacrylonitrile-based fiber precursor, method for producing the same, carbon fiber, and method for producing the same

Abstract

The present application relates to the field of carbon fibers, in particular to a polyacrylonitrile-based fiber precursor, a preparation method thereof, a carbon fiber and a preparation method thereof, wherein the grain size A, the crystalline region orientation B and the crystallinity C of the polyacrylonitrile-based fiber precursor satisfy the following formula: 0≤[-(A-10.8)*(A-13.5)*1.1]-[(B-91)*(B-95)*0.55]-[(C-55)(C-60) / 100*C 0.5 ] / 100, A / nm, B / %, C / %. The carbon fiber prepared by using the polyacrylonitrile fiber precursor satisfying the grain size, the crystalline region orientation and the crystallinity as described above has a high tensile-compressive ratio and other mechanical properties close to those of the existing high-strength medium-modulus carbon fiber, and has high adaptability to subsequent processes in actual use.

Description

Technical Field

[0001] This invention relates to the field of carbon fiber, specifically to a polyacrylonitrile-based fiber precursor and its preparation method, and carbon fiber and its preparation method. Background Technology

[0002] Carbon fiber is a fibrous engineering material primarily composed of carbon. Compared to metallic materials, it possesses properties such as low density, high temperature resistance, friction resistance, electrical conductivity, thermal conductivity, and corrosion resistance. The carbon in carbon fibers exists in a complex form, with graphitized microcrystals preferentially oriented along the fiber axis, thus giving carbon fibers high strength and modulus in that direction. Carbon fibers, used as a matrix, can be combined with resins to create composite materials with very high specific strength and specific modulus, leading to their widespread application in weight-sensitive fields such as aerospace since their emergence.

[0003] Carbon fiber composites are produced by impregnating bundled carbon fibers with resin and then processing them through winding, lay-up, and molding. Therefore, the mechanical properties of the carbon fiber bundles are the core factors affecting the performance of the composites. Current research in the carbon fiber field often focuses on the tensile strength of the fibers, using it as a classification standard. After long-term technological development, the tensile strength of commercial carbon fiber products has reached up to 8.0 GPa, more than double that of the same period in the last century. Simultaneously, with the expansion of production scale, the manufacturing cost of carbon fiber has also decreased significantly. As carbon fiber continues to improve in quality and reduce in cost, its application areas are gradually expanding to consumer goods, such as sports equipment and wind turbine blades, where carbon fiber composites are used to replace glass fiber. With the increasing application scenarios of carbon fiber, other mechanical properties besides tensile strength have also received more attention. In many applications, the compressive strength of carbon fiber is significantly lower than its tensile strength, leading to material failure. Therefore, the compressive strength of carbon fiber has gradually become a research hotspot. Materials typically experience various stress states during use, including tension, compression, bending, and shear. Failure under any stress state can lead to material damage, making the material's equilibrium crucial. Simply increasing tensile strength is no longer very meaningful. For example, the compression-to-tension ratio of high-strength intermediate-modulus carbon fiber is usually 0.4, which is no longer sufficient to meet the design requirements of most spacecraft.

[0004] In existing research schemes, CN111218733B improves the strength and compressive strength of carbon fibers by increasing the diameter of the carbon fibers; CN111621878A improves the mechanical properties of carbon fibers by finely controlling the oxidation and carbonization process of carbon fibers; and CN111936681B regulates the crystallite size by controlling the compressive strength and initial elastic modulus of single fibers. Summary of the Invention

[0005] The purpose of this invention is to provide a new polyacrylonitrile-based fiber precursor, which can be used to obtain carbon fibers that simultaneously meet the requirements of high tensile strength and high pressure pull ratio.

[0006] As mentioned earlier, the aforementioned research schemes mainly control the final crystallite size of carbon fibers or single fibers to increase the performance of the final carbon fibers. However, in the process of carbon fiber preparation, the characteristics of the precursor fiber have a decisive influence on the performance of carbon fibers. Based on this, the inventors of this invention propose a new polyacrylonitrile-based fiber precursor fiber. This polyacrylonitrile-based fiber precursor fiber has a unique precursor fiber microstructure. The inventors have found that using this polyacrylonitrile-based fiber precursor fiber with a unique precursor fiber microstructure to prepare corresponding carbon fibers can improve its tensile-compression ratio without changing other mechanical properties of the carbon fibers, thus expanding the application prospects of carbon fibers.

[0007] Further improving the compression-to-tension ratio will be a key focus for advancing carbon fiber technology. Research indicates that the compression-to-tension ratio of carbon fiber is determined by its multi-level structure, including factors such as fiber diameter, graphite grain size, orientation angle, and degree of graphitization, all of which influence the compression-to-tension properties of carbon fiber to varying degrees. Studies have found that, from the perspective of carbon fiber processing, it is not feasible to alter a single structural characteristic without changing other properties; therefore, improving compression-to-tension properties often requires comprehensive optimization of the process.

[0008] The first aspect of this invention provides a polyacrylonitrile fiber precursor, wherein the grain size A, the degree of orientation of the crystalline region B, and the degree of crystallinity C of the polyacrylonitrile fiber precursor satisfy the following formula:

[0009] 0≤[-(A-10.8)*(A-13.5)*1.1]-[(B-91)*(B-95)*0.55]-[(C-55)(C-60) / 100*C 0.5 ], A / nm, B / %, C / %.

[0010] The second aspect of the present invention provides a method for preparing the polyacrylonitrile-based fiber precursor described in the first aspect of the present invention. The preparation method includes: solidifying and molding the polyacrylonitrile spinning solution, hot water drawing, washing, oiling, and steam drawing; wherein, in the polyacrylonitrile spinning solution, the molar content of the vinyl comonomer in the acrylonitrile copolymer is not higher than 2%; and the ratio of the draw ratio of the steam drawing to the draw ratio of the hot water drawing is 1-2 times.

[0011] A third aspect of the present invention provides a carbon fiber, which is prepared from the polyacrylonitrile-based fiber precursor described in the first aspect of the present invention or the polyacrylonitrile-based fiber precursor prepared by the preparation method described in the second aspect of the present invention.

[0012] The fourth aspect of the present invention provides a method for preparing carbon fiber, the method comprising: pre-oxidizing and carbonizing the polyacrylonitrile-based fiber precursor as described in the first aspect of the present invention or the polyacrylonitrile-based fiber prepared by the method described in the second aspect of the present invention.

[0013] The fifth aspect of the present invention provides a carbon fiber prepared by the preparation method described in the fourth aspect of the present invention.

[0014] Through the above technical solution, the carbon fiber prepared by using polyacrylonitrile carbon fiber precursor that meets the above-mentioned grain size, crystal orientation degree and crystallinity of the present invention has a high tensile-compression ratio, while its other mechanical properties are similar to those of existing high-strength intermediate modulus carbon fibers, and it has high adaptability to subsequent processes in actual use. Detailed Implementation

[0015] 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.

[0016] The first aspect of this invention provides a polyacrylonitrile fiber precursor, characterized in that the grain size A, crystalline region orientation B, and crystallinity C of the polyacrylonitrile fiber precursor satisfy the following formula:

[0017] 0≤[-(A-10.8)*(A-13.5)*1.1]-[(B-91)*(B-95)*0.55]-[(C-55)(C-60) / 100*C 0.5 A / nm; B / %, C / %.

[0018] As an upstream raw material for carbon fiber, polyacrylonitrile fiber precursor has been discovered by the inventors of this invention. Carbon fibers prepared using polyacrylonitrile fiber precursor with grain size, orientation degree of crystallization region, and crystallinity satisfying the above formula have a high tensile-compression ratio, while other mechanical properties are similar to those of existing high-strength intermediate-modulus carbon fibers.

[0019] According to a preferred embodiment of the present invention, the grain size A (nm), crystalline orientation degree B (%), and crystallinity C (%) of the polyacrylonitrile-based fiber precursor satisfy the formula: 1.5≤[-(A-10.8)*(A-13.5)*1.1]-[(B-91)*(B-95)*0.55]-[(C-50)(C-60) / 100*C 0.5 ≤4.5.

[0020] According to a preferred embodiment of the present invention, the grain size A (nm), crystalline orientation degree B (%), and crystallinity C (%) of the polyacrylonitrile-based fiber precursor satisfy the following formula: [-(A-10.8)*(A-13.5)*1.1]-[(B-91)*(B-95)*0.55]-[(C-50)(C-60) / 100*C 0.5 = 2-4.5 (e.g., 2, 2.5, 2.8, 3, 3.5, 3.8, 4, 4.3, or 4.5).

[0021] The carbon fibers prepared using polyacrylonitrile fiber precursors with grain size, crystalline region orientation, and crystallinity satisfying the above formula have superior overall performance, especially a high tensile-to-compression ratio.

[0022] In this invention, the crystallinity of the polyacrylonitrile-based fiber precursor is required to be within a wide range. The following is an illustrative description, but it does not limit the scope of the invention. According to a preferred embodiment of the invention, the crystallinity of the polyacrylonitrile-based fiber precursor is 40-75%, for example, 40%, 45%, 48%, 50%, 53%, 56%, 58%, 60%, 65%, 68%, 70%, 72%, or 75%, preferably 50-60%.

[0023] The crystal size, orientation degree of the crystalline region, and crystallinity of the polyacrylonitrile-based fiber precursor in this invention, while satisfying the above formula, further control of the crystallinity of the precursor within the above range can make the carbon fiber prepared using the precursor have better overall performance.

[0024] In this invention, the grain size requirement of the polyacrylonitrile-based fiber precursor is relatively wide. The following is an illustrative description, but it does not limit the scope of the invention. According to a preferred embodiment of the invention, the average grain size of the polyacrylonitrile-based fiber precursor is 10-14 nm, for example, 10 nm, 10.8 nm, 11 nm, 11.5 nm, 12 nm, 12.5 nm, 12.6 nm, 12.7 nm, 13 nm, 13.1 nm, 13.2 nm, 13.5 nm, 13.8 nm or 14 nm, preferably 10.8-13.5 nm.

[0025] The grain size, orientation degree of the crystalline region, and crystallinity of the polyacrylonitrile-based fiber precursor in this invention, while satisfying the above formula, further control of the grain size of the precursor within the above range can make the carbon fiber prepared using the precursor have better overall performance.

[0026] In this invention, the grain orientation degree of the polyacrylonitrile-based fiber precursor is required to be within a wide range. The following is an illustrative description, but it does not limit the scope of the invention. According to a preferred embodiment of the invention, the grain orientation degree of the polyacrylonitrile-based fiber precursor is 88-96%, for example, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95% or 96%, preferably 91-95%.

[0027] The grain size, orientation degree of the crystalline region, and crystallinity of the polyacrylonitrile-based fiber precursor in this invention, while satisfying the above formula, further control of the grain orientation degree of the precursor within the above range can make the carbon fiber prepared using the precursor have better overall performance.

[0028] In this invention, the fineness requirement of the polyacrylonitrile-based fiber precursor is relatively wide. The following is an illustrative description, but it does not limit the scope of the invention. According to a preferred embodiment of the invention, the fineness of the polyacrylonitrile-based fiber precursor is 1-1.5 dtex, for example, 1 dtex, 1.1 dtex, 1.2 dtex, 1.3 dtex, 1.4 dtex or 1.5 dtex, preferably 1.1-1.2 dtex.

[0029] In this invention, the monofilament modulus of the polyacrylonitrile-based fiber precursor is required to be within a wide range. The following is an illustrative description, but it does not limit the scope of the invention. According to a preferred embodiment of the invention, the monofilament modulus of the polyacrylonitrile-based fiber precursor is 130-160 cN / dtex, for example, 130 N / dtex, 135 N / dtex, 140 N / dtex, 145 N / dtex, 150 N / dtex, 152 N / dtex, 157 N / dtex or 160 N / dtex, preferably 152-160 cN / dtex.

[0030] In this invention, the boiling water shrinkage rate of the polyacrylonitrile-based fiber precursor is required to be within a wide range. The following is an illustrative description, but it does not limit the scope of the invention. According to a preferred embodiment of the invention, the boiling water shrinkage rate of the polyacrylonitrile-based fiber precursor is 3-6%, for example, 3%, 3.5%, 3.7%, 3.8%, 4%, 4.2%, 4.5%, 5% or 6%, preferably 3.7-4.5%.

[0031] According to the present invention, as long as the purpose of the present invention can be achieved, the preparation method of the polyacrylonitrile-based fiber precursor is not particularly limited. Preferably, the second aspect of the present invention provides a method for preparing the polyacrylonitrile-based fiber precursor, the method comprising: solidifying and molding the polyacrylonitrile spinning solution, hot water drawing, washing, oiling, and steam drawing; wherein, in the polyacrylonitrile spinning solution, the molar content of the vinyl comonomer in the acrylonitrile copolymer is not higher than 2%; and the ratio of the drawing ratio of the steam drawing to the drawing ratio of the hot water drawing is 1-2 times.

[0032] The polyacrylonitrile-based fiber precursor prepared by the above-mentioned method in this invention has an excellent crystal microstructure, which satisfies the following formula for the grain size A (nm), crystalline orientation degree B (%), and crystallinity C (%) of the polyacrylonitrile-based fiber precursor: 0≤[-(A-10.8)*(A-13.5)*1.1]-[(B-91)*(B-95)*0.55]-[(C-55)(C-60) / 100*C 0.5 The polyacrylonitrile-based fiber precursor prepared using this method can produce carbon fibers with high tensile-to-compression ratios while maintaining other mechanical properties that are similar to existing high-strength, medium-modulus carbon fibers.

[0033] According to the present invention, those skilled in the art will understand that the polyacrylonitrile spinning solution is a solution for spinning formed by dissolving an acrylonitrile copolymer in an organic solvent. The acrylonitrile copolymer refers to a polymer prepared by acrylonitrile with other vinyl comonomers containing vinyl groups; that is, the acrylonitrile copolymer contains acrylonitrile structural units and vinyl comonomer structural units. The vinyl comonomer structural units can be structural units of vinyl comonomers conventionally available in the art that can copolymerize with ethylene and acrylonitrile. In a preferred embodiment, the vinyl comonomer structural unit is selected from at least one of itaconic acid structural units, methacrylic acid structural units, methyl methacrylate structural units, and vinyl acetate structural units. The advantages of the present invention are illustrated by using the itaconic acid structural unit as an example, but the present invention is not limited thereto.

[0034] In this invention, the molar content of acrylonitrile structural units in the acrylonitrile copolymer can be selected within a wide range, as long as the purpose of this invention can be achieved. The following is an illustrative description, but it does not limit the scope of this invention. According to a preferred embodiment of this invention, the molar content of acrylonitrile structural units in the copolymer is 98.2-99.4%, for example, 98.2%, 98.3%, 98.5%, 98.8%, 99%, 99.2%, or 99.4%.

[0035] According to a preferred embodiment of the present invention, the molar content of the vinyl comonomer structural unit in the acrylonitrile copolymer is 0.6-1.8%, for example, 0.6%, 0.8%, 1%, 1.2%, 1.4%, 1.5%, 1.6% or 1.8%.

[0036] According to the present invention, the stock solution containing acrylonitrile copolymer is obtained by dissolving the acrylonitrile copolymer in a corresponding organic solvent. As long as the purpose of the present invention can be achieved, there is no special limitation on the type of organic solvent. Commonly used organic solvents are applicable to the present invention. This is an illustrative description, but does not limit the scope of the present invention. According to a preferred embodiment of the present invention, the organic solvent is selected from at least one of dimethyl sulfoxide, dimethylformamide, and dimethylacetamide, preferably dimethyl sulfoxide.

[0037] In this invention, the mass content of acrylonitrile copolymer in the raw solution is required to be within a wide range. The following is an illustrative description, but it does not limit the scope of the invention. According to a preferred embodiment of the invention, the mass content of acrylonitrile copolymer in the raw solution is 22-24 wt%, preferably 22.5-23 wt%. By adopting the aforementioned preferred embodiment, the quality of the fiber can be further improved.

[0038] In this invention, coagulation molding is a conventional method in the art. The specific operation method includes: extruding the polyacrylonitrile spinning solution through a spinneret, and then coagulating it in a coagulation bath to obtain nascent fibers. This invention does not have any special limitations on the specific operation method and conditions of coagulation molding. The following is a brief description of the conventional coagulation molding method in the art used in this invention.

[0039] In this invention, during the coagulation molding process, the coagulation bath is a mixture of organic solvent and water in the polyacrylonitrile spinning solution (i.e., a coagulation bath formed by mixing organic solvent and water). The mass content of the organic solvent in the coagulation bath has a wide range of requirements. The following is an illustrative description, but it does not limit the scope of this invention. According to a preferred embodiment of this invention, the organic solvent content in the coagulation bath is 25-40 wt%, preferably 30-35 wt%.

[0040] According to a preferred embodiment of the present invention, the solidification conditions include: a solidification bath temperature of 20-80°C, preferably 40-60°C.

[0041] According to a preferred embodiment of the present invention, the solidification molding conditions include: a solidification bath draw ratio of 0.6-0.8, for example, 0.6, 0.65, 0.7 or 0.8.

[0042] According to a preferred embodiment of the present invention, the total draw ratio is 5-8 times, for example, 5 times, 5.5 times, 6 times, 6.5 times, 7 times or 8 times.

[0043] In this invention, the total draw ratio refers to the sum of the draw ratio during hot water draw and the draw ratio during steam draw.

[0044] According to the present invention, there are no special limitations on the conditions for hot water drawing, as long as the purpose of the present invention can be achieved. In a preferred embodiment, the conditions for hot water drawing include a temperature of 90-95°C. The polyacrylonitrile carbon fiber precursor prepared in the foregoing embodiments exhibits a superior crystal microstructure.

[0045] According to a preferred embodiment of the present invention, the hot water stretching conditions include a stretching ratio of 1-3 times, for example, 1, 1.5, 2, 2.5, or 3 times, preferably 2-2.5 times. In the aforementioned embodiments, the prepared polyacrylonitrile carbon fiber precursor exhibits a superior crystal microstructure.

[0046] According to the present invention, there are no special restrictions on the conditions for steam drawing, as long as the purpose of the present invention can be achieved. In a preferred embodiment,

[0047] According to the present invention, as long as the purpose of the present invention can be achieved, the specific conditions for steam drawing are not particularly limited. In a preferred embodiment, the conditions for steam drawing include: the temperature of the drawing chamber during the steam drawing process is 150-170°C, i.e., the drawing temperature.

[0048] According to a preferred embodiment of the present invention, the conditions for steam drawing include: drawing outlet temperature ≥ drawing temperature - 30°C, for example, drawing outlet temperature - drawing chamber temperature (i.e., drawing temperature) during steam drawing + 30°C = 0-20°C, for example, 0°C, 15°C, 20°C, 25°C or 30°C.

[0049] According to a preferred embodiment of the present invention, the conditions for steam stretching include a stretching ratio of 3-5 times, for example, 3 times, 3.5 times, 4 times, 4.5 times or 5 times.

[0050] The washing, oiling, and drying processes in this invention are performed according to conventional methods in the art, as illustrated below. For example, the washing temperature is 40-95°C, and the oiling is performed using an oiling agent containing amino-modified silicone oil and / or epoxy-modified silicone oil.

[0051] In this invention, after steam drawing, the final polyacrylonitrile fiber precursor can be obtained by conventional heat setting and winding methods in the art.

[0052] A third aspect of the present invention provides a carbon fiber, which is prepared from the polyacrylonitrile-based fiber precursor described in the first aspect of the present invention or the polyacrylonitrile-based fiber precursor prepared by the preparation method described in the second aspect of the present invention.

[0053] The carbon fiber in this invention has a high tensile-compression ratio, while its other mechanical properties are similar to those of existing high-strength intermediate-modulus carbon fibers.

[0054] The fourth aspect of the present invention provides a method for preparing carbon fiber, the method comprising: pre-oxidizing and carbonizing the polyacrylonitrile-based fiber precursor as described in the first aspect of the present invention or the polyacrylonitrile-based fiber prepared by the method described in the second aspect of the present invention.

[0055] According to the present invention, the method for preparing carbon fiber by pre-oxidation and carbonization using the polyacrylonitrile-based fiber precursor of the present invention is a conventional method in the art. For example, the pre-oxidation conditions include: the pre-oxidation temperature is 200-255°C, wherein the pre-oxidation can be carried out sequentially in multiple temperature zones, and the pre-oxidation time can be selected according to the pre-oxidation temperature, preferably 40-100 min.

[0056] According to a preferred embodiment of the invention, the carbonization is carried out in an inert atmosphere, such as a nitrogen atmosphere.

[0057] According to the present invention, the carbonization can be carried out in a conventional manner in the art, first by low-temperature carbonization and then by high-temperature carbonization. Preferably, the carbonization includes a first carbonization and a second carbonization performed sequentially. Preferably, the temperature of the first carbonization is lower than the temperature of the second carbonization, and preferably the temperature difference between the first carbonization and the second carbonization is 300-800°C.

[0058] According to a preferred embodiment of the present invention, the conditions for the first carbonization include: a temperature of 350-750°C, preferably 375-700°C, more preferably 380-680°C, and specifically, the carbonization can be carried out within a temperature range that increases sequentially, for example, it can be divided into 5 temperature ranges. The time for the first carbonization can be selected according to the temperature of the first carbonization, preferably 60-600s, more preferably 60-120s.

[0059] According to a preferred embodiment of the present invention, the conditions for the second carbonization include: a temperature of 1200-1500℃, preferably 1200-1450℃, more preferably 1375-1450℃, and specifically, the carbonization can be carried out in a temperature range with progressively increasing temperatures, for example, it can be divided into 3 temperature ranges. The time for the second carbonization can be selected according to the temperature of the second carbonization, preferably 60-600s, more preferably 60-120s.

[0060] The fifth aspect of the present invention provides a carbon fiber prepared by the preparation method described in the fourth aspect of the present invention.

[0061] The carbon fiber in this invention has a high compressive-to-tensile ratio, preferably greater than or equal to 0.52, and more preferably 0.58-0.62.

[0062] The carbon fiber in this invention maintains both high compressive-to-tensile ratio and high tensile strength. Preferably, the tensile strength of the carbon fiber is 5.3-5.9 GPa, and more preferably 5.6-5.8 GPa.

[0063] In this invention, the diameter of the carbon fiber can be the same as that of ordinary carbon fiber, for example, the diameter of the carbon fiber is 6-7 μm.

[0064] The present invention will be described in detail below through examples. In the following examples, the number-average molecular weight of polyacrylonitrile was measured by GPC, and the fiber crystallinity, orientation, and grain size parameters were measured by XRD, with a test wavelength of 0.154 nm and a scanning range of 5-40°.

[0065] The fiber compressive strength test method is as follows: a monofilament is wound into a loop, and both ends are stretched outward under motor control. The shape of the loop gradually deforms as the stretching proceeds, and its major and minor axis distances are monitored in real time using an optical microscope. The fiber diameter loop and minor axis diameter (horizontal axis) are measured using an optical microscope, and the fiber compressive strength is calculated using the following formula.

[0066]

[0067] Where σ is the compressive strength; d is the fiber diameter; D is the minor axis diameter of the ring; E t For tensile modulus

[0068] All raw materials used in this invention are commercially available products, and acrylonitrile, dimethyl sulfoxide, and itaconic acid are all chemically pure.

[0069] Examples of preparation of carbon fiber precursor

[0070] Example 1

[0071] Polyacrylonitrile copolymer (obtained by polymerization of acrylonitrile and itaconic acid copolymer in a molar ratio of 99.4:0.6, with a number average molecular weight of 23,000) was dissolved in dimethyl sulfoxide to prepare a 23 wt% polyacrylonitrile spinning solution. This solution was extruded through a 48K spinneret and sprayed at a speed of 6 m / min into a coagulation bath (30 wt% dimethyl sulfoxide aqueous solution) for coagulation and shaping. The coagulation bath temperature was 60℃, and the coagulation bath draw ratio was 0.65. After coagulation, the fiber was drawn twice in hot water at 93℃, then washed with water at 60℃, and subsequently oiled with amino-modified silicone oil and epoxy-modified silicone oil. It was dried at 125℃ and then drawn 3.5 times in steam at 155℃ with a drawout temperature of 140℃ to obtain polyacrylonitrile fiber precursor A with a fineness of 1.1 dtex.

[0072] After testing, the crystallinity of polyacrylonitrile fiber precursor A was 58%, the average grain size was 12.7 nm, the orientation degree was 93%, the modulus was 152 cN / dtex, and the boiling water shrinkage rate was 3.7%.

[0073] Example 2

[0074] Polyacrylonitrile copolymer (obtained by polymerization of acrylonitrile and itaconic acid copolymer in a molar ratio of 99.4:0.6, with a number average molecular weight of 2.1w) was dissolved in dimethyl sulfoxide to prepare a 23.5wt% polyacrylonitrile spinning dope. This dope was extruded through a 48K spinneret and sprayed at a speed of 6 m / min into a coagulation bath (30wt% dimethyl sulfoxide aqueous solution) for coagulation and shaping. The coagulation bath temperature was 60℃, and the coagulation bath draw ratio was 0.65. After coagulation, the fiber was drawn twice in hot water at 93℃, then washed with water at 60℃, and subsequently oiled with amino-modified silicone oil and epoxy-modified silicone oil. It was dried at 125℃ and then drawn 3.5 times in steam at 155℃ with a drawout temperature of 145℃ to obtain polyacrylonitrile fiber precursor B with a fineness of 1.1 dtex.

[0075] After testing, the crystallinity of polyacrylonitrile fiber precursor B was 58%, the average grain size was 12.6 nm, the orientation degree was 94%, the modulus was 157 cN / dtex, and the boiling water shrinkage rate was 3.8%.

[0076] Example 3

[0077] Polyacrylonitrile copolymer (obtained by polymerization of acrylonitrile and itaconic acid copolymer in a molar ratio of 99.4:0.6, with a number average molecular weight of 2.3w) was dissolved in dimethyl sulfoxide to prepare a 23wt% polyacrylonitrile spinning dope. This dope was extruded through a 48K spinneret and sprayed at a speed of 6 m / min into a coagulation bath (30wt% dimethyl sulfoxide aqueous solution) for coagulation and shaping. The coagulation bath temperature was 60℃, and the coagulation bath draw ratio was 0.70. After coagulation, the fiber was drawn twice in hot water at 93℃, then washed with water at 60℃, followed by oiling with amino-modified silicone oil and epoxy-modified silicone oil. The fiber was dried at 125℃ and then drawn four times in steam at 160℃, with an exit temperature of 140℃, to obtain polyacrylonitrile fiber precursor C with a fineness of 1.1 dtex.

[0078] After testing, the crystallinity of polyacrylonitrile fiber precursor C was 58%, the average grain size was 13.2 nm, the orientation degree was 95%, the modulus was 157 cN / dtex, and the boiling water shrinkage rate was 4.2%.

[0079] Example 4

[0080] Polyacrylonitrile copolymer (polymerized from acrylonitrile and itaconic acid copolymer in a molar ratio of 99:1, with a number average molecular weight of 2.3w) was dissolved in dimethyl sulfoxide to prepare a 23wt% polyacrylonitrile spinning solution. This solution was extruded through a 48K spinneret and sprayed at a speed of 6 m / min into a coagulation bath (30wt% dimethyl sulfoxide aqueous solution) for coagulation and shaping. The coagulation bath temperature was 60℃, and the coagulation bath draw ratio was 0.65. After coagulation, the fiber was drawn twice in hot water at 93℃, then washed with water at 60℃, and subsequently oiled with amino-modified silicone oil and epoxy-modified silicone oil. It was dried at 125℃ and then drawn 3.5 times in steam at 155℃ with an exit temperature of 125℃ to obtain polyacrylonitrile fiber precursor D with a fineness of 1.1 dtex.

[0081] After testing, the crystallinity of polyacrylonitrile fiber precursor D was found to be 56%, the average grain size was 13.1 nm, the orientation degree was 93%, the modulus was 152 cN / dtex, and the boiling water shrinkage rate was 4.5%.

[0082] Comparative Example 1

[0083] Polyacrylonitrile copolymer (polymerized from acrylonitrile and itaconic acid copolymer in a molar ratio of 98:2, with a number average molecular weight of 2.6w) was dissolved in dimethyl sulfoxide to prepare a 23wt% polyacrylonitrile spinning solution. This solution was extruded through a 48K spinneret and sprayed at a speed of 6 m / min into a coagulation bath (30wt% dimethyl sulfoxide aqueous solution) for coagulation and shaping. The coagulation bath temperature was 60℃, and the coagulation bath draw ratio was 0.65. After coagulation, the fiber was drawn twice in hot water at 93℃, then washed with water at 60℃, and subsequently oiled with amino-modified silicone oil and epoxy-modified silicone oil. It was dried at 125℃ and then drawn 3.5 times in steam at 155℃ with a drawout temperature of 90℃ to obtain polyacrylonitrile fiber precursor D1 with a fineness of 1.1 dtex.

[0084] After testing, the crystallinity of polyacrylonitrile fiber precursor D1 was 53%, the average grain size was 10.8 nm, the orientation degree was 91%, the modulus was 144 cN / dtex, and the boiling water shrinkage rate was 3.1%.

[0085] Comparative Example 2

[0086] Polyacrylonitrile copolymer (obtained by polymerization of acrylonitrile and itaconic acid copolymer in a molar ratio of 99.4:0.6, with a number average molecular weight of 2.6w) was dissolved in dimethyl sulfoxide to prepare a 23wt% polyacrylonitrile spinning solution. This solution was extruded through a 48K spinneret and sprayed at a speed of 6 m / min into a coagulation bath (30wt% dimethyl sulfoxide aqueous solution) for coagulation and shaping. The coagulation bath temperature was 60℃, and the coagulation bath draw ratio was 0.65. After coagulation, the fiber was drawn twice in hot water at 93℃, then washed with water at 60℃, and subsequently oiled with amino-modified silicone oil and epoxy-modified silicone oil. It was dried at 125℃ and then drawn 4.5 times in steam at 155℃ with a drawout temperature of 140℃ to obtain polyacrylonitrile fiber precursor D2 with a fineness of 1.1 dtex.

[0087] After testing, the crystallinity of polyacrylonitrile fiber precursor D2 was 58%, the average grain size was 13.8 nm, the orientation degree was 96%, the modulus was 161 cN / dtex, and the boiling water shrinkage rate was 6.5%.

[0088] Comparative Example 3

[0089] Polyacrylonitrile copolymer (obtained by polymerization of acrylonitrile and itaconic acid copolymer in a molar ratio of 99.4:0.6, with a number average molecular weight of 2.6w) was dissolved in dimethyl sulfoxide to prepare a 23wt% polyacrylonitrile spinning solution. This solution was extruded through a 48K spinneret and sprayed at a speed of 6 m / min into a coagulation bath (30wt% dimethyl sulfoxide aqueous solution) for coagulation and shaping. The coagulation bath temperature was 60℃, and the coagulation bath draw ratio was 0.65. After coagulation, the fiber was drawn twice in hot water at 93℃, then washed with water at 60℃, and subsequently oiled with amino-modified silicone oil and epoxy-modified silicone oil. It was dried at 125℃ and then drawn 3.5 times in steam at 155℃ with a drawout temperature of 70℃ to obtain polyacrylonitrile fiber precursor D3 with a fineness of 1.1 dtex.

[0090] After testing, the crystallinity of polyacrylonitrile fiber precursor D3 was 58%, the average grain size was 12.7 nm, the orientation degree was 93%, the modulus was 152 cN / dtex, and the boiling water shrinkage rate was 3.7%.

[0091] Example of carbon fiber preparation

[0092] Preparation Example 1

[0093] Polyacrylonitrile fiber precursor A is oxidized and carbonized at a temperature of 200-255℃ (temperatures increase sequentially to 201℃, 212℃, 224℃, 235℃, and 253℃) for a total processing time of 60 min. Low-temperature carbonization is carried out in an N2 atmosphere at a temperature of 380-680℃ (the carbonization furnace is divided into five temperature zones with temperatures of 380℃, 420℃, 480℃, 580℃, and 680℃, for a total processing time of 90 s). High-temperature carbonization is carried out in an N2 atmosphere at a temperature of 1375-1450℃ (the carbonization furnace is divided into three temperature zones with temperatures of 1375℃, 1475℃, and 1450℃, for a total processing time of 90 s).

[0094] After testing, carbon fiber A has a tensile strength of 5.8 GPa and a compressive strength of 3.4 GPa, with a compression-to-tension ratio of 0.59.

[0095] Preparation Example 2

[0096] Carbon fiber B was prepared using polyacrylonitrile fiber precursor B according to the method in Preparation Example 1.

[0097] After testing, carbon fiber B has a tensile strength of 5.6 GPa and a compressive strength of 3.4 GPa, with a compression-to-tension ratio of 0.61.

[0098] Preparation Example 3

[0099] Carbon fiber C was prepared using polyacrylonitrile fiber precursor C according to the method in Preparation Example 1.

[0100] After testing, carbon fiber C has a tensile strength of 5.8 GPa and a compressive strength of 3.3 GPa, with a compression-to-tension ratio of 0.57.

[0101] Preparation Example 4

[0102] Carbon fiber D was prepared using polyacrylonitrile fiber precursor D according to the method in Preparation Example 1.

[0103] After testing, carbon fiber D has a tensile strength of 5.8 GPa, a compressive strength of 3.6 GPa, and a compression-to-tension ratio of 0.62.

[0104] Comparative Preparation Example 1

[0105] Carbon fiber D1 was prepared using polyacrylonitrile fiber precursor D1 according to the method in Preparation Example 1.

[0106] After testing, carbon fiber D1 has a tensile strength of 5.6 GPa, a compressive strength of 2.9 GPa, and a compression-to-tension ratio of 0.52.

[0107] Preparation of Comparative Example 2

[0108] Carbon fiber D2 was prepared using polyacrylonitrile fiber precursor D2 according to the method of Preparation Example 1.

[0109] After testing, carbon fiber D2 has a tensile strength of 4.9 GPa, a compressive strength of 2.2 GPa, and a compression-to-tension ratio of 0.45.

[0110] Preparation of Comparative Example 3

[0111] Carbon fiber D3 was prepared using polyacrylonitrile fiber precursor D3 according to the method of Preparation Example 1.

[0112] After testing, carbon fiber D3 has a tensile strength of 5.9 GPa and a compressive strength of 3.0 GPa, with a compression-to-tension ratio of 0.51.

[0113] 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 polyacrylonitrile fiber precursor, characterized in that, The grain size A, crystalline orientation B, and crystallinity C of the polyacrylonitrile-based fiber precursor satisfy the following formula: 0≤[-(A-10.8)*(A-13.5)*1.1]-[(B-91)*(B-95)*0.55]-[(C-55)(C-60) / 100*C 0.5 ], A / nm, B / %, C / %.

2. The polyacrylonitrile-based fiber precursor according to claim 1, wherein, The grain size A (nm), orientation degree B (%), and crystallinity C (%) of the polyacrylonitrile-based fiber precursor satisfy the formula: 1.5≤[-(A-10.8)*(A-13.5)*1.1]-[(B-91)*(B-95)*0.55]-[(C-50)(C-60) / 100*C 0.5 ≤4.5; and / or The crystallinity of the polyacrylonitrile-based fiber precursor is 40-75%, preferably 50-60%; and / or The average grain size of the polyacrylonitrile-based fiber precursor is 10-14 nm, preferably 10.8-13.5 nm; and / or The grain orientation degree of the polyacrylonitrile-based fiber precursor is 88-96%, preferably 91-95%.

3. The polyacrylonitrile-based fiber precursor according to claim 1 or 2, wherein, The fineness of the polyacrylonitrile-based fiber precursor is 1-1.5 dtex; and / or The monofilament modulus of the polyacrylonitrile-based fiber precursor is 130-160 cN / dtex, preferably 152-160 cN / dtex; and / or The boiling water shrinkage rate of the polyacrylonitrile-based fiber precursor is 3-6%, preferably 3.7-4.5%.

4. A method for preparing polyacrylonitrile-based fiber precursor according to any one of claims 1-3, characterized in that, The preparation method includes: solidifying and molding the polyacrylonitrile spinning solution, hot water drawing, water washing, oiling, and steam drawing; Wherein, in the acrylonitrile copolymer in the polyacrylonitrile spinning solution, the molar content of vinyl comonomer is not higher than 2%; the ratio of the draw ratio of steam drawing to the draw ratio of hot water drawing is 1-2 times.

5. The preparation method according to claim 4, wherein, The vinyl comonomer structural unit is selected from at least one of itaconic acid structural units, methacrylic acid structural units, methyl methacrylate structural units, and vinyl acetate structural units; and / or In the acrylonitrile copolymer, the molar content of acrylonitrile structural units is 98.2-99.4%; and / or In the acrylonitrile copolymer, the molar content of the vinyl comonomer structural unit is 0.6-1.8%; and / or The organic solvent in the polyacrylonitrile spinning solution is selected from at least one of dimethyl sulfoxide, dimethylformamide, and dimethylacetamide; and / or The acrylonitrile copolymer content in the polyacrylonitrile spinning solution is 22-24 wt%, preferably 22.5-23 wt%.

6. The preparation method according to claim 4 or 5, wherein, In the coagulation molding process, the coagulation bath is a mixture of organic solvent and water in the polyacrylonitrile spinning solution. Preferably, the coagulation bath has an organic solvent content of 25-40 wt%, and more preferably 30-35 wt%. and / or The solidification conditions include: a solidification bath temperature of 20-80℃, preferably 40-60℃, and a solidification bath draw ratio of 0.6-0.

8.

7. The preparation method according to any one of claims 4-6, wherein, The total draw ratio is 5-8 times; and / or The conditions for hot water stretching include: The temperature is 90-95℃; and / or The draw ratio is 1-3 times, preferably 2-2.5 times; and / or The conditions for steam drawing include: During steam drawing, the temperature of the drawing chamber is 150-170℃, the drawing outlet temperature is ≥ the drawing temperature -30℃, and the drawing ratio is 3-5 times.

8. A carbon fiber, characterized in that, The carbon fiber is prepared from the polyacrylonitrile-based fiber precursor as described in any one of claims 1-3 or the polyacrylonitrile-based fiber precursor prepared by the preparation method described in any one of claims 4-7.

9. A method for preparing carbon fiber, characterized in that, The preparation method includes: The polyacrylonitrile-based fiber precursor obtained by any one of claims 1-3 or by any one of claims 4-7 is subjected to pre-oxidation and carbonization. Preferably, The pre-oxidation conditions include: a pre-oxidation temperature of 200-255℃; and / or a pre-oxidation time of 40-100 min; and / or The carbonization is carried out in an inert atmosphere; and / or The carbonization includes a first carbonization and a second carbonization performed sequentially, wherein, preferably, the temperature of the first carbonization is lower than the temperature of the second carbonization, and preferably the temperature difference between the first carbonization and the second carbonization is 300-800℃; More preferably, The conditions for the first carbonization include: a temperature of 350-750°C; and / or a time of 60-600 s; and / or The conditions for the second carbonization include: a temperature of 1200-1500℃; and / or a time of 60-600s.

10. A carbon fiber prepared by the preparation method of claim 9; Preferably, The carbon fiber has a compression-to-tension ratio greater than or equal to 0.52, preferably 0.58-0.62; and / or The tensile strength of the carbon fiber is 5.3-5.9 GPa, preferably 5.6-5.8 GPa.

Images