KR20260002581A - Polyacrylonitrile carbon fiber and yarn and method for producing the same - Google Patents

Abstract

The present invention relates to polyacrylonitrile carbon fibers, yarns thereof, and a method for producing the same. The polyacrylonitrile carbon fibers provided by the present invention have a groove structure on the surface, and the Si/C ratio of a region X between the top of a protrusion on the fiber surface and the bottom of the groove is in the range of 1% to 10%, the Si/C ratio of a region Y between the bottom of the groove and an inner distance of up to 100 nm is in the range of 0.1% to 1%, and the Si/C ratio of a region Z greater than 100 nm is 0.06% or less. The present invention further provides a method for producing polyacrylonitrile carbon fibers, polyacrylonitrile yarns, and a method for producing polyacrylonitrile yarns. The carbon fibers of the present invention have low ash content and high performance.

Description

Polyacrylonitrile carbon fiber and yarn and method for producing the same

The present invention relates to polyacrylonitrile carbon fibers and yarns, and a method for producing the same. The present invention also relates to polyacrylonitrile carbon fiber yarns for producing the carbon fibers, and a method for producing the same.

Carbon fiber is an inorganic polymer fiber material with a carbon content of over 90%. It has a stable chemical structure, high strength, high modulus, and low mass. It also has excellent heat and corrosion resistance, a low coefficient of thermal expansion, excellent heat transfer and chemical stability, and good conductivity. Carbon fiber can be used as a reinforcing material for high-performance composites and is widely used in aerospace, architectural reinforcement, sporting goods, automotive structures, wind power blades, the solar industry, and medical devices. However, the continuous development of aerospace and high-end equipment is placing new performance demands on carbon fiber materials, and these demands are no longer limited to basic indicators such as strength and modulus. In particular, aerospace applications are raising demands on carbon fiber ash content.

Carbon fiber performance is largely affected by defects. High-quality emulsions and a reasonable oiling process are effective means of preventing defects. Treating PAN yarn with a dedicated emulsion can form a heat-resistant protective film on the fiber surface, which separates the single filaments and prevents adhesion and braiding during the pre-oxidation process. Currently, silicone-containing emulsions are primarily used in the production of high-performance carbon fiber yarns. Some silicone-containing emulsions exhibit poor decomposition properties at high temperatures. This leads to incomplete decomposition during the pre-oxidation and carbonization process. This results in impurities such as silicon carbide and silicon nitride remaining within the carbon fiber, potentially creating weaknesses during drawing or bending, and thus seriously impacting the quality of the carbon fiber. Furthermore, silicon oxides generated during the pre-oxidation and carbonization process are a major source of ash. Ash not only contaminates equipment, but also shortens its production cycle and lifespan, reducing operating time, necessitating frequent shutdowns and cleaning.

There are numerous yarns that can be used to manufacture carbon fibers. Currently, more than 90% of carbon fibers on the market are made from PAN fibers. PAN-based carbon fibers have high carbon yields, excellent mechanical properties, and mature processes, making them a major carbon fiber product. Currently, PAN fibers are primarily manufactured through wet spinning and dry-jet wet spinning. In dry-jet wet spinning, the solution is extruded through a spinning nozzle, first passing through an air gap and then entering a coagulation bath for solidification and shaping. Due to these processes, wet-jet and dry-jet spinning differ significantly in their solution systems, spinning processes, and spinning equipment, and the resulting yarns and carbon fibers also differ in their morphology and structure. Wet and dry spun carbon fibers have a smooth surface and a denser structure, while the surface of carbon fibers obtained by wet spinning has a distinct groove structure, wherein the height difference between the top of the protrusion and the bottom of the groove can reach tens of nanometers, and the groove structure of the protrusions can cause the carbon fiber to break due to defects. Therefore, the main structural features that affect the breakage of wet and dry spun carbon fibers are also different. In the process of manufacturing PAN fiber, compared with wet and dry spinning, the wet spinning process is more mature, the spinning process is stable and easy to control, the residual solvent in the fiber is easy to remove, and the manufactured carbon fiber is easier to combine with composite materials, so it is an important method for manufacturing high-performance carbon fiber yarn.

High-quality carbon fiber yarns must have minimal surface defects, minimal pore structure, a dense structure, good elasticity, and high heat resistance. To produce high-quality carbon fibers with superior performance and controllable silicon content and silicon permeability, the yarns must possess low silicon content, low silicon permeability, and good coating properties that uniformly form an oil film on the fiber surface. During the production of carbon fiber yarn, the coagulation process is a double diffusion process, resulting in a large number of pores in the as-spun fiber. During subsequent drawing and washing, some pores gradually decrease or even close. During the oiling process, silicone-containing emulsions can penetrate these unclosed pores. Pores can become closed during the subsequent drying and densification process, making it difficult to completely remove the silicon-containing emulsions within the pores. These pores remain within the fibers, increasing ash content during the carbonization process. Furthermore, the infiltrated silicon remains difficult to completely remove, affecting the performance of the final carbon fiber.

Therefore, selecting a high-quality oiling agent and a reasonable oiling process is an important task in the production of low-ash, high-performance polyacrylonitrile carbon fiber and the carbon fiber yarn.

CN113597484A discloses a method for producing carbon fibers that suppresses the infiltration of emulsion into the fiber surface and suppresses the formation of pores in the surface layer, wherein SIMS (secondary ion mass spectrometry) is used to calculate the Si/C ratio at a certain depth from the fiber surface. The application clearly states that the invention cannot be applied to improving the strength of wet-spun carbon fibers. In addition, wet spinning generally uses a multi-stage coagulation process, and the concentration, temperature, and immersion time of the coagulation bath are completely different from those of dry and wet spinning, so the coagulation conditions and air residence time of dry and wet spinning, which are the invention points of CN113597484A, cannot be applied to the production of wet-spun carbon fiber yarns, and the infiltration of emulsion into the fiber surface layer during the wet spinning process cannot be suppressed, and the inter-fiber adhesion and pores in the carbon fiber surface layer cannot be suppressed. In addition, wet-spun primary fibers have a looser structure and larger pores than dry-spun primary fibers, and it is easier for oil to penetrate into the fiber during the oiling process, so a new method is needed to suppress Si penetration and improve the performance of carbon fibers.

CN111088559A discloses an oiling method in which an ultra-low silicone emulsion or a non-silicon emulsion is used for the first oiling, and after the first drying and densification, a general-purpose silicone-containing emulsion is used for the second oiling, in order to solve the problems of carbon fiber having a lot of fluff, poor mechanical performance, and high coke emission due to low carbon.

CN114622417A discloses a silicone-containing emulsion for carbon fibers. The emulsion reduces frictional damage between yarns and rollers, ensures uniform pre-oxidation of the fibers, and inhibits adhesion and braiding of carbonized monofilaments. However, the issues of carbonized ash and impurities in carbon fibers were not addressed.

CN112424418A discloses a silicone-containing emulsion for carbon fibers. This application effectively protects carbon fibers by resolving the problem of fluffing during the yarn spinning process. However, the resulting carbon fibers have relatively low strength, and the problems of carbonized ash and carbon fiber impurities are not addressed.

CN112726207A discloses a non-silicone emulsion for manufacturing carbon fiber yarn, which has a very low ash content and thus can significantly reduce damage to equipment such as carbon furnaces, but the obtained carbon fiber has a low strength and elastic modulus, making it unsuitable for the manufacturing process of high-strength, high-elasticity carbon fiber.

CN110863270A discloses a method for reducing ash content of high-strength polyacrylonitrile-based carbon fibers, which comprises an organic solvent immersion treatment and a hydrofluoric acid treatment step for the polyacrylonitrile-based carbon fibers, but the method may have a negative effect on the performance of the carbon fibers, such as tensile modulus.

CN103290527A discloses a method for reducing the ash content of polyacrylonitrile carbon fibers. The application comprises producing a PAN spinning solution with relatively high hydrophilicity based on a quaternary ammonia-modified copolymerization system. The application then controls the swelling degree and introduces a low-silicon emulsion before applying the emulsion to the yarn, thereby controlling the oil content of the fiber bundle. However, the modified copolymerization system of the application is not suitable for producing high-performance carbon fibers.

In conventional technology, reducing the ash content of carbon fibers in wet spinning production of high-performance carbon fibers often results in a decrease in the performance of the carbon fibers.

Through in-depth research, the inventors of the present invention have discovered that when a large amount of silicon is penetrated and distributed within the fiber, it becomes a major cause of increased ash during the subsequent pre-oxidation and carbonization processes, and can also increase the content of impurities within the final carbon fiber, thereby affecting the performance of the carbon fiber. On the other hand, if the Si content of the surface layer of the yarn is too low, problems such as braiding, adhesion, and increased fluff can easily occur during the pre-oxidation process, ultimately reducing the performance of the carbon fiber. Through further research, the inventors of the present invention have discovered that controlling the depth and gradient of silicon penetration within the carbon fiber can achieve both high performance and low ash content, thereby obtaining a carbon fiber with both low ash content and high performance, thereby completing the present invention.

Technical problem 1 to be solved by the present invention is to solve the problem that reducing the ash content of carbon fibers in conventional wet spinning results in a deterioration in the mechanical performance of the carbon fibers produced. Accordingly, the present invention provides a low-ash, high-performance polyacrylonitrile carbon fiber that can reduce the ash content of carbon fibers and improve the mechanical performance of carbon fibers by having a specific penetration gradient and silicon content in the carbon fiber surface.

Technical problem 2 to be solved by the present invention is to provide a method for manufacturing low-ash, high-performance carbon fiber corresponding to the technical problem 1 above. The method is characterized by low ash content during the carbonization process (only one stop for half a year or more is required to clean the ash content inside the equipment), and further, the silicon impurity content in the manufactured carbon fiber is low, and the carbon fiber strength, elastic modulus, and elongation are excellent.

Technical problem 3 to be solved by the present invention is to provide a polyacrylonitrile yarn for producing the low-ash, high-performance carbon fiber corresponding to the technical problem 1.

Technical problem 4 to be solved by the present invention is to provide a method for manufacturing polyacrylonitrile yarn corresponding to technical problem 3 above.

The present invention provides a polyacrylonitrile carbon fiber having a groove structure on a surface, wherein the carbon fiber is characterized in that the Si/C ratio in a region X between the top of a protrusion on the fiber surface and the bottom of a groove is in a range of 1% to 10%, the Si/C ratio in a region Y between the bottom of the groove and within 100 nm inward is in a range of 0.1% to 1%, and the Si/C ratio in a region Z greater than 100 nm is 0.06% or less.

The present invention also provides a method for producing polyacrylonitrile carbon fiber, preferably the polyacrylonitrile carbon fiber of the present invention, comprising the step of carbonizing polyacrylonitrile yarn to obtain the polyacrylonitrile carbon fiber; wherein the polyacrylonitrile yarn is characterized in that the Si/C ratio in a region from the top of the fiber surface protrusions to an inside area of 2 μm is in a range of 1.0% to 20%, and the Si/C ratio in a region of 2 μm or more is 0.15% or less.

The present invention provides a polyacrylonitrile yarn, wherein the polyacrylonitrile yarn is characterized in that the Si/C ratio in a region from the top of a protrusion on the surface of the fiber to an inside area of 2 μm is in a range of 1.0% to 20%, and the Si/C ratio in a region of 2 μm or more is 0.15% or less.

The present invention also provides a method for producing a polyacrylonitrile yarn, preferably a polyacrylonitrile yarn of the present invention, comprising wet spinning and oiling steps, wherein the oiling step comprises two consecutive oiling processes, with no dry compaction step between the two oiling processes, wherein the first oiling process uses a non-silicon emulsion, a low-silicon emulsion, or a combination thereof, and the second oiling process uses a silicone-containing emulsion.

In order to more clearly explain the technical solution of the present invention, the attached drawings are provided.
Figure 1 is a cross-sectional illustration of a single strand of carbon fiber of the present invention.
In Fig. 1, 1 is a protrusion structure on the surface of a carbon fiber; 2 is a groove structure on the surface of a carbon fiber; a and b are scanning lines of adjacent protrusion structures and groove structures from the center of the fiber to the surface of the fiber, respectively; X represents a region from the top of a protrusion on the surface of a carbon fiber to the bottom of a groove; Y represents a region from the bottom of a groove to 100 nm inside the carbon fiber (i.e., the depth of the region is 100 nm); and Z represents a region that is 100 nm or more inside the carbon fiber.
In the present invention, the upper part of the protrusion refers to the highest part of the protrusion structure, and the bottom part of the groove refers to the lowest part of the groove structure.

In one aspect, the present invention provides a polyacrylonitrile carbon fiber having a groove structure on a surface, wherein the carbon fiber has a Si/C ratio in a region X between the top of a protrusion on the fiber surface and the bottom of a groove in a range of 1% to 10%, a Si/C ratio in a region Y between the bottom of the groove and within 100 nm inward in a range of 0.1% to 1%, and a Si/C ratio in a region Z that is 100 nm or more (from the bottom of the groove on the surface) is 0.06% or less.

In the present invention, the Si/C ratio of the region X between the top of the protrusion on the fiber surface of the carbon fiber and the bottom of the groove is in the range of 1% to 10%. For example, the Si/C ratio may be in the range of 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 9.5%, 10%, or any two of the above values. In some embodiments, the Si/C ratio may be in the range of 2% to 10%, in the range of 3% to 10%, in the range of 4% to 10%, or in the range of 4% to 9.5%.

In the present invention, the Si/C ratio in the region Y between the groove bottom and the inner side of the carbon fiber is in the range of 0.1% to 1%. For example, the Si/C ratio may be 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 0.95%, 1.0%, or a range comprised of any two of the above values. In some embodiments, the Si/C ratio may be in the range of 0.2% to 1%, in the range of 0.3% to 1%, in the range of 0.4% to 1%, or in the range of 0.4% to 0.95%.

In the present invention, the Si/C ratio of a region Z of 100 nm or more (from the groove bottom of the surface) of the carbon fiber is 0.06% or less. For example, the Si/C ratio may be 0%, 0.005%, 0.01%, 0.02%, 0.03%, 0.04%, 0.05%, 0.06%, or a range comprised of any two of the above values, for example, 0% to 0.06%. In some embodiments, the Si/C ratio may be in a range of 0.005% to 0.06%, or in a range of 0.01% to 0.06%.

In the present invention, the Si/C ratio is the ratio of the number of Si atoms to the number of C atoms. In the present invention, the Si/C ratio was determined using the TEM-EDS method; see below for details.

In the present invention, the total silicon content in the carbon fiber may be 500 to 1500 ppm (weight). For example, calculated by weight, the total silicon content in the carbon fiber may be 500 ppm, 600 ppm, 700 ppm, 800 ppm, 900 ppm, 1000 ppm, 1100 ppm, 1200 ppm, 1300 ppm, 1400 ppm, 1500 ppm, or a range comprised of any two of the above values.

In some embodiments of the present invention, among the carbon fibers, the Si/C ratio of a region X between the top of a protrusion on the fiber surface and the bottom of a groove is at least 8.5 times the Si/C ratio of a region Y between the bottom of a groove and 100 nm inward. In some embodiments of the present invention, among the carbon fibers, the Si/C ratio of a region X between the top of a protrusion on the fiber surface and the bottom of a groove is 8.5 to 12 times the Si/C ratio of a region Y between the bottom of a groove and 100 nm inward.

In some embodiments of the present invention, for the carbon fiber of the present invention, the number of pores present in regions X and Y from the top of the protrusions on the fiber surface to 100 nm inward is less than 20, and preferably less than 16; wherein the average length of the pores is 10 to 50 nm, and the average width is 5 to 25 nm. In the present invention, 10 carbon fibers were observed by gallium focused ion beam cutting and transmission electron microscopy, and the number of pores, the average length of the pores, and the average width are average values of 10 carbon fibers.

In some embodiments of the present invention, the orientation deviation angle of the pores along the fiber axis direction obtained through small-angle X-ray scattering is 4° or less, preferably 3° or less.

The tensile strength of the above carbon fiber may be 5.6-5.8 GPa, the tensile modulus may be 360-390 GPa, and the elongation at break may be 1.45%-1.6%.

In the present invention, the polyacrylonitrile carbon fiber is obtained from a polyacrylonitrile yarn manufactured by wet spinning.

In another aspect, the present invention provides a method for producing a polyacrylonitrile carbon fiber, comprising the step of carbonizing a polyacrylonitrile yarn to obtain the polyacrylonitrile carbon fiber; wherein the Si/C ratio in a region from the top of a fiber surface protrusion of the polyacrylonitrile yarn to an inside area of 2 μm is in a range of 1.0% to 20%, and the Si/C ratio in a region of 2 μm or more is 0.15% or less.

In some embodiments, the Si/C ratio of a region 2 μm inward from the top of the fiber surface protrusions of the polyacrylonitrile yarn may be in the range of 2.0% to 20%, in the range of 3.0% to 20%, in the range of 4.0% to 20%, or in the range of 5.0% to 19%. In some embodiments, the Si/C ratio of a region 2 μm or more inward from the top of the fiber surface protrusions of the polyacrylonitrile yarn may be in the range of 0.01% to 0.15%, in the range of 0.02% to 0.15%, in the range of 0.03% to 0.15%, in the range of 0.04% to 0.15%, or in the range of 0.05% to 0.15%.

In some embodiments, the oil content of the yarn may be from 0.5% to 2.5%, preferably from 0.8% to 2.5%, preferably from 0.8% to 2.4%, and more preferably from 0.9% to 2.0%. For example, the oil content of the yarn may be from 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2.0%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, or a range comprised of any two of the foregoing values.

In some embodiments, the silicone content of the yarn may be 0.01 to 0.5%, preferably 0.05 to 0.5%. For example, the silicone content of the yarn may be 0.01%, 0.02%, 0.03%, 0.04%, 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, 0.45%, 0.5%, or a range comprised of any two of the foregoing values. In some embodiments, the monofilament linear density of the polyacrylonitrile yarn is 0.7 to 1.0 dtex. For example, the monofilament linear density of the polyacrylonitrile yarn may be in a range of 0.7 dtex, 0.8 dtex, 0.9 dtex, 1.0 dtex, or any two of the above values.

In the present invention, the polyacrylonitrile yarn is manufactured by wet spinning.

In the present invention, the polyacrylonitrile yarn is manufactured by wet spinning and further includes an oiling step, wherein the oiling step includes two consecutive oiling processes, wherein there is no dry densification step between the two oiling processes, the first oiling process uses a non-silicon emulsion, a low-silicon emulsion, or a combination thereof, and the second oiling process uses a silicone-containing emulsion.

In the present invention, the absence of a dry compaction step between two oiling processes means that after the first oiling process is completed, the second oiling process is continued without performing a dry compaction process on the fibers oiled in the first process.

In the process of manufacturing polycarbon fiber yarn, it is well known in the art to impart an emulsion to the fiber through an oiling step. As is known in the art, the emulsion used in the oiling step may include a non-silicone emulsion, a low-silicone emulsion, or a silicone-containing emulsion.

Regarding the non-silicone emulsion, the present invention has no particular limitation on the non-silicone emulsion, and various non-silicone emulsions commonly used in the art for producing polyacrylonitrile yarns can be used.

In some embodiments, the non-silicone emulsion comprises a non-siloxane component as a major component of the emulsion. For example, one or more of the following materials may be used as the major component of the non-silicone emulsion: polyesters of long-chain fatty acids and polyols, ethylene oxide adducts of long-chain fatty amines, polybutene, polyoxyethylene ether, neopentanol derivatives, fatty acid esters, amide compounds, ammonium salts of fatty acid esters, aromatic esters, amide compounds, etc.

Regarding the silicone-containing emulsion, the present invention has no particular limitation on the silicone-containing emulsion, and various silicone-containing emulsions used in the art for producing polyacrylonitrile yarns can be used. In some embodiments, the silicone-containing emulsion contains an organic polysiloxane and/or a derivative thereof. Examples thereof include polydimethylsiloxane, polyphenylmethylsiloxane, polymethylhydrosiloxane, alkylarylalkyl-modified polysiloxane, amino-modified polysiloxane, polyether-modified polysiloxane, epoxy-modified polysiloxane, and amide-modified polysiloxane.

Regarding the low-silicon emulsion, the present invention has no particular limitation on the low-silicon emulsion, and various low-silicon emulsions used in the art for producing polyacrylonitrile yarn can be used.

In the present invention, the silicone content of the silicone-containing emulsion may be 0.01 to 0.9% by weight, and the silicone content of the low-silicon emulsion may be 0.001% to less than 0.01% by weight. In some embodiments, the silicone component contained in the low-silicon emulsion accounts for 1% by weight or less of the total emulsion components.

In the present invention, there is no particular limitation on the form of the emulsion. In the present invention, the emulsion preferably used is an oil-in-water emulsion.

In some embodiments, the non-silicone emulsion may be an oil-in-water emulsion comprising an emulsion component and water, wherein the mass percentage content of the emulsion component is 1 to 40%; the emulsion component comprises at least one of an aromatic ester compound, an aromatic polyoxyethylene ether, an amine compound, an alcohol compound, an acid compound, and a nonionic surfactant, an emulsifier, an antioxidant, and an antistatic agent; Here, when the mass sum of the emulsion components is calculated as 100%, the content of the aromatic ester compound is 40 to 90%, the content of the aromatic polyoxyethylene ether is 10 to 30%, the content of the amine compound is 0 to 7%, the content of the alcohol compound is 0 to 7%, the content of the acid compound is 0 to 7%, the content of the nonionic surfactant is 10 to 65%, the content of the emulsifier is 10 to 30%, the content of the antioxidant is 1 to 10%, and the content of the antistatic agent is 1 to 10%.

In some embodiments, the silicone-containing emulsion may be an oil-in-water emulsion comprising an emulsion component and water, wherein the mass percentage content of the emulsion component is 1% to 40%; the emulsion component comprises dimethylsiloxane, modified siloxane, a nonionic surfactant, an emulsifier, an antioxidant, and an antistatic agent; wherein, when the mass sum of the emulsion components is calculated as 100%, the content of the dimethylsiloxane is 10% to 50%, the content of the modified siloxane is 10% to 75%, the content of the nonionic surfactant is 10% to 65%, the content of the emulsifier is 10% to 30%, the content of the antioxidant is 1% to 10%, and the content of the antistatic agent is 1% to 10%.

In some embodiments, the low-silicon emulsion is an oil-in-water emulsion comprising an emulsion component and water, wherein the mass percentage of the emulsion component is 1% to 40%; the emulsion component comprises a heat-resistant ester compound, a modified siloxane, a nonionic surfactant, an emulsifier, an antioxidant, and an antistatic agent; wherein, when the mass sum of the emulsion components is calculated as 100%, the content of the heat-resistant ester compound is 10% to 70%, the content of the modified siloxane is 0.1% to 1%, the content of the nonionic surfactant is 10% to 65%, the content of the emulsifier is 10% to 30%, the content of the antioxidant is 1% to 10%, and the content of the antistatic agent is 1% to 10%.

In the present invention, the emulsion component includes all substances in the emulsion except water.

There is no particular limitation on the concentration of the emulsion in the present invention. In the present invention, the first oiling process uses a non-silicone emulsion, a low-silicone emulsion, or a combination thereof, and the weight concentration thereof may be 0.1% to 5.0%. For example, the weight concentration of the non-silicone emulsion, the low-silicone emulsion, or a combination thereof used in the first oiling process may be 0.1%, 0.5%, 1.0%, 1.5%, 2.0%, 2.5%, 3.0%, 3.5%, 4.0%, 4.5%, 5.0%, or a range consisting of any two of the above values. In the present invention, a silicone-containing emulsion is used in the second oiling process, and the weight concentration thereof may be 0.1% to 5.0%. For example, the weight concentration of the silicone-containing emulsion used in the secondary oiling process may be 0.1%, 0.5%, 1.0%, 1.5%, 2.0%, 2.5%, 3.0%, 3.5%, 4.0%, 4.5%, 5.0%, or a range comprised of any two of the above values. In the present invention, the weight concentration of the emulsion means the ratio of the weight of all emulsion components in the emulsion to the weight of the emulsion.

In some embodiments, the average particle size of the non-silicone emulsion, the low-silicone emulsion, and the silicone-containing emulsion can each independently be from 50 nm to 500 nm. For example, the average particle size of the non-silicone emulsion, the low-silicone emulsion, and the silicone-containing emulsion can be from 50 nm, 100 nm, 150 nm, 200 nm, 250 nm, 300 nm, 350 nm, 400 nm, 450 nm, 500 nm, or a range comprised of any two of the above values, for example, from 100 nm to 400 nm, etc.

In the present invention, the silicone content of the silicone-containing emulsion used in the secondary oiling process may be 0.01 to 0.9% by weight. For example, the silicone content of the silicone-containing emulsion may be 0.01%, 0.05%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9% by weight, or a range comprised of any two of the above values.

In the present invention, there is no particular limitation on the method of applying the emulsion to the fiber, and various methods generally known in the art can be used. For example, dipping, roller dipping, spraying, etc. can be used.

In the present invention, there is no particular limitation on the pH values of the non-silicone emulsion, low-silicone emulsion, and silicone-containing emulsion, and a person skilled in the art can appropriately determine and select the pH values of the non-silicone emulsion, low-silicone emulsion, and silicone-containing emulsion. In some embodiments, the pH difference between the non-silicone emulsion or low-silicone emulsion and the silicone-containing emulsion may not be greater than 1. In some embodiments, the pH difference between the non-silicone emulsion or low-silicone emulsion and the silicone-containing emulsion may be 0 or more and 1 or less.

In the present invention, in some embodiments, the non-silicone emulsion, the low-silicone emulsion, and the silicone-containing emulsion each include a surfactant, wherein the surfactant of the non-silicone emulsion or the low-silicone emulsion and the surfactant of the silicone-containing emulsion do not have opposite polarities. In the present invention, surfactants that can be used in the emulsions include cationic surfactants, anionic surfactants, amphoteric surfactants, and nonionic surfactants. In the present invention, opposite polarities mean that the surfactant in the non-silicone emulsion or the low-silicone emulsion includes a cationic surfactant and the surfactant in the silicone-containing emulsion includes an anionic surfactant, or the surfactant in the non-silicone emulsion or the low-silicone emulsion includes an anionic surfactant and the surfactant in the silicone-containing emulsion includes a cationic surfactant; except for the two cases above, all cases are considered as cases where the polarities are not opposite to each other. Any of a variety of surfactants known in the art can be used, as long as the above polarity requirements are met. In some embodiments, the silicone-containing emulsion preferably includes a nonionic surfactant.

In the present invention, there is no particular limitation on the temperature of the emulsion during oiling, and any temperature of the emulsion commonly used in the art may be used. In some embodiments, the temperature of the emulsion during oiling may be 20 to 30°C.

In the present invention, there is no particular limitation on the time required for oiling, and a time commonly used in the art can be used. In some embodiments, the first oiling time, for example, the residence time in the oiling tank, may be 0.05 to 0.5 seconds, preferably 0.06 to 0.4 seconds, and more preferably 0.07 to 0.3 seconds. In some embodiments, the second oiling time, for example, the residence time in the oiling tank, may be 0.03 to 0.3 seconds, preferably 0.04 to 0.3 seconds, and more preferably 0.04 to 0.2 seconds.

In some embodiments, the secondary channel oiling residence time is shorter than the primary oiling residence time.

As is known in the art, a dry compaction process is performed after oiling. In the present invention, there are no specific limitations on the dry compaction process, and any dry compaction process known in the art can be used. In some embodiments, the dry compaction process may include multiple stages. In some embodiments, the dry compaction process may include four stages of drying and compaction, each at temperatures of 90°C, 100°C, 115°C, and 130°C.

In some embodiments, the swelling degree of the fiber after washing of the polyacrylonitrile yarn before oiling can be 80 to 150%. For example, the swelling degree of the fiber after washing of the polyacrylonitrile yarn before oiling can be 80%, 90%, 100%, 110%, 120%, 130%, 140%, or a range comprised of any two of the above values, for example, the swelling degree can be 90 to 140%.

In some embodiments, the manufacturing method may include wet coagulation forming, coagulation drawing, high-temperature water drawing, water washing, oiling, dry densification, steam drawing, and steam thermoforming of the polyacrylonitrile raw material to obtain the polyacrylonitrile yarn.

The production of yarn from polyacrylonitrile raw solution is generally known in the art. In the present invention, the production of the yarn employs a wet spinning process known in the art.

For polyacrylonitrile yarns manufactured from polyacrylonitrile concentrate, the manufacturing process may include drawing steps such as coagulation forming, coagulation drawing, drawing by high-temperature water drawing, washing steps such as water rinsing, oiling, dry densification, drawing by steam drawing, and thermoforming steps such as steam thermoforming. These steps are known in the art, and those skilled in the art can appropriately select and perform these steps. As described above, in the method of the present invention, the oiling step includes two consecutive oiling processes, wherein there is no dry densification step between the two oiling processes; wherein the first oiling process uses a non-silicon emulsion, a low-silicon emulsion, or a combination thereof, and the second oiling process uses a silicone-containing emulsion.

In some embodiments, in the coagulation forming step of the method of the present invention, the primary fibers, after leaving the spinneret hole, enter a first coagulation bath for coagulation of the primary fibers. Those skilled in the art can easily select the composition and temperature of the first coagulation bath. In some embodiments, the temperature of the first coagulation bath is 28°C and the first coagulation bath is a 51.5% dimethyl sulfoxide aqueous solution. After leaving the first coagulation bath, the filaments may be subjected to one or more subsequent coagulation baths to perform additional coagulation and drawing. In some embodiments, after leaving the first coagulation bath, the filaments are further subjected to a third coagulation drawing at concentrations of 30%, 20%, and 10%, at temperatures of 30°C, 40°C, and 50°C, respectively, and at draw ratios of 1.0, 1.1, and 1.2, respectively. In some embodiments, after leaving the final coagulation bath, the coagulated filaments may be drawn. This drawing may be performed, for example, in steam or hot water. Those skilled in the art can appropriately select the draw ratio. In some embodiments, a fourth hot water drawing may be performed at temperatures of 95°C, 96°C, 97°C, and 99°C, respectively, and draw ratios of 1.35, 1.50, 1.70, and 2.00, respectively. After drawing, the filaments may be washed, such as rinsed, to remove residual solvent. In some embodiments, a sixth washing process may be performed at temperatures of 70°C, 70°C, 80°C, 80°C, 90°C, and 90°C, respectively. The swelling degree of the fibers after washing may be 80% to 140%. In the method of the present invention, after washing, the filaments may be oiled and dried to densify. In the present invention, as described above, the oiling comprises two consecutive oiling processes, with no dry compaction step between the two oiling processes; the first oiling process uses a non-silicone oil, a low-silicone oil, or a combination thereof, and the second oiling process uses a silicone-containing oil. The oiling is performed using an oiling agent commonly used in the art, and the dry compaction can be performed by adopting a dry compaction operation commonly adopted in the art. In some embodiments, the dry compaction treatment can include a four-stage dry compaction treatment at temperatures of 90°C, 100°C, 115°C, and 130°C, respectively. In some embodiments, after the dry compaction, the obtained filaments can be further drawn, such as by steam drawing. Those skilled in the art can appropriately select the drawing ratio and drawing conditions. In some embodiments, steam drawing is adopted, with a drawing ratio of 3.0 and a steam pressure of 0.35 MPa. In some embodiments, after drawing, the resulting filaments can be thermoformed. For example, the filaments can be thermoformed through a multi-stage high-temperature roller or thermoformed with steam. After thermoforming, a yarn is obtained, which can be wound for subsequent use.

As will be known to those skilled in the art, one or more steps may be omitted or added, or the order of these steps may be adjusted.

In the present invention, there is no particular limitation on the linear density of the monofilament of the polyacrylonitrile yarn, and those skilled in the art can appropriately select and determine the linear density of the monofilament. In some embodiments, the linear density of the monofilament of the polyacrylonitrile yarn may be 0.7 to 1.0 dtex. For example, the linear density of the monofilament of the polyacrylonitrile yarn may be 0.7 dtex, 0.8 dtex, 0.9 dtex, 1.0 dtex, or a range comprised of any two of the above values.

After obtaining the yarn, the yarn can be manufactured into polyacrylonitrile carbon fibers. Processes for manufacturing polyacrylonitrile carbon fibers from polyacrylonitrile yarn are well known in the art, and the present invention can manufacture polyacrylonitrile carbon fibers from the yarn using processes known in the art.

In the present invention, the polyacrylonitrile yarn can be subjected to pre-oxidation treatment and carbonization treatment to obtain the polyacrylonitrile carbon fiber.

In some embodiments, the pre-oxidation treatment is performed in an air atmosphere, at a temperature of 170 to 300°C, and a total elongation of 5% or less.

In some embodiments, the pre-oxidation treatment can be performed in an air atmosphere using a gradient heating method, divided into multiple temperature zones, for example, 2 to 6 temperature zones. The start temperature of the pre-oxidation treatment can be 170 to 200°C, and the end temperature of the pre-oxidation treatment can be 260 to 300°C. A certain degree of elongation can be applied to the fiber during the pre-oxidation treatment, for example, the elongation can be 0 to 5%. The pre-oxidation treatment time can be 30 to 120 minutes.

In some embodiments, the carbonization treatment comprises a step of performing a low-temperature carbonization treatment in an inert atmosphere at a temperature of 300 to 750°C with a draw ratio of 0 to 4% of the total elongation, and a step of performing a high-temperature carbonization treatment in an inert atmosphere at a temperature of 800 to 1500°C with a draw ratio of -4 to -2% of the total elongation. The inert atmosphere can be implemented by using, for example, nitrogen, helium, argon, or xenon.

After carbonization, graphitization may optionally be performed. In the present invention, there are no particular limitations on the graphitization process, and any graphitization process known in the art may be used. In some embodiments, graphitization may be performed at 2800°C.

In some embodiments, the manufacturing method may include a surface treatment step, a washing step, and a sizing step.

As will be appreciated by those skilled in the art, the carbon fibers of the present invention may be surface treated prior to sizing. For example, oxidation treatment may be performed to improve the affinity and adhesion between the carbon fibers and matrix resin in a composite material.

Sizing can be performed using various sizing methods known in the art. The present invention does not specifically limit the sizing method, sizing agent, or sizing conditions, as long as the desired sizing agent can be imparted to the carbon fiber. After sizing, a drying process may be performed to remove the solvent or dispersion medium used in the sizing process. For example, drying may be performed at 120°C. Finally, the filaments may be finished to obtain carbon fibers.

In another aspect, the present invention provides a polyacrylonitrile yarn in which the Si/C ratio in a region from the top of a protrusion on the fiber surface to 2 μm inward is in a range of 1.0% to 20% and the Si/C ratio in a region greater than 2 μm is 0.15% or less.

In some embodiments, the Si/C ratio of a region 2 μm inward from the top of the fiber surface protrusion of the polyacrylonitrile yarn may be in the range of 2.0% to 20%, in the range of 3.0% to 20%, in the range of 4.0% to 20%, or in the range of 5.0% to 19%. In some embodiments, the Si/C ratio of a region 2 μm or more inward from the top of the fiber surface protrusion of the polyacrylonitrile yarn may be in the range of 0.01% to 0.15%, in the range of 0.02% to 0.15%, in the range of 0.03% to 0.15%, in the range of 0.04% to 0.15%, or in the range of 0.05% to 0.15%.

In some embodiments, the oil content of the yarn may be from 0.5% to 2.5%, preferably from 0.8% to 2.5%, preferably from 0.8% to 2.4%, and more preferably from 0.9% to 2.0%. For example, the oil content of the yarn may be from 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2.0%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, or a range comprised of any two of the foregoing values.

In some embodiments, the silicone content of the yarn may be from 0.01% to 0.5%, preferably from 0.05% to 0.5%. For example, the silicone content of the yarn may be 0.01%, 0.02%, 0.03%, 0.04%, 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, 0.1%, 0.15%, 0.25%, 0.35%, 0.45%, 0.5%, or a range comprised of any two of the above values.

In some embodiments, the monofilament linear density of the polyacrylonitrile yarn is 0.7 to 1.0 dtex. For example, the monofilament linear density of the polyacrylonitrile yarn may be 0.7 dtex, 0.8 dtex, 0.9 dtex, 1.0 dtex, or a range comprised of any two of the above values.

In the present invention, the polyacrylonitrile yarn of the present invention is manufactured by wet spinning.

Meanwhile, the present invention comprises wet spinning and two consecutive oiling processes, without a dry compaction step between the two oiling processes, wherein the first oiling process uses a non-silicon emulsion, a low-silicon emulsion, or a combination thereof, and the second oiling process uses a silicone-containing emulsion. In the present invention, the absence of a dry compaction step between the two oiling processes means that after the first oiling process is completed, the second oiling process is continued without performing a dry compaction process on the fibers oiled in the first process.

Each aspect and feature of the method for manufacturing polyacrylonitrile yarn of the present invention is the same as each aspect and feature of the method for manufacturing yarn in the section on the method for manufacturing polyacrylonitrile carbon fiber described above, and therefore will not be described again here.

In the present invention, polyacrylonitrile yarn is manufactured from a polyacrylonitrile stock solution. In the present invention, the polyacrylonitrile stock solution includes a polyacrylonitrile polymer and a solvent. There is no particular limitation on the concentration of the polyacrylonitrile polymer in the polyacrylonitrile stock solution, and any suitable concentration used in polyacrylonitrile spinning stock solutions generally known in the art can be used. In the present invention, for example, the concentration of the polyacrylonitrile polymer in the polyacrylonitrile spinning stock solution can be, for example, 15 to 30 wt%. In the present invention, various solvents used in the polyacrylonitrile stock solution can be used. For example, the solvent can be at least one of dimethyl sulfoxide (DMSO), dimethylformamide (DMF), dimethylacetamide (DMAC), and mixtures thereof.

In the present invention, the polyacrylonitrile raw solution can be obtained by dissolving a polyacrylonitrile polymer in a solvent or by polymerizing a monomer in a solvent.

Any polyacrylonitrile yarn of the present invention or any polyacrylonitrile yarn produced by the yarn production method of the present invention can be used to produce the low-ash, high-performance polyacrylonitrile carbon fiber of the present invention.

In the present invention, except for the limitations on oiling and densification described herein, there are no special limitations on other aspects of the production of the polyacrylonitrile yarn, and the polyacrylonitrile yarn can be produced through a spinning process commonly used or known in the art using a polyacrylonitrile spinning solution commonly used or known in the art, and there are no special requirements for the polyacrylonitrile spinning solution and spinning process. In the present invention, except for the limitations on oiling and densification described herein, the yarn can be produced from the polyacrylonitrile spinning solution using a generally known yarn production method and process parameters. Compared to the conventional technology for producing polyacrylonitrile carbon fibers, the present invention can achieve the purpose of improving the mechanical performance of the fiber and reducing ash content.

In the present invention, the polyacrylonitrile polymer in the polyacrylonitrile stock solution may include a polyacrylonitrile homopolymer, a polyacrylonitrile copolymer, or a mixture thereof. In the present invention, various polyacrylonitrile homopolymers, polyacrylonitrile copolymers, or mixtures thereof used in the production of carbon fibers may be used. For example, when a polyacrylonitrile copolymer is used, the copolymerization monomer may be a vinyl-containing monomer. In some embodiments, the copolymerization monomer is preferably one or more of acrylates, vinyl esters, acrylamides, sulfonates, and ammonium salt monomers. In some embodiments, the polyacrylonitrile polymer may include 90-100 mass% of acrylonitrile-derived monomer units and 0-10 mass% of structural units derived from a monomer copolymerizable with acrylonitrile. As monomers copolymerizable with acrylonitrile, various copolymerizable monomers generally known in the art can be used, including, for example, acrylic acid, methacrylic acid, itaconic acid and their alkali metal salts, ammonium salts and lower alkyl esters; acrylamide and its derivatives; allyl sulfonic acid, methylallyl sulfonic acid and their salts or alkyl esters; etc.

The present inventors unexpectedly found that by controlling the silicon penetration gradient and silicon content on the fiber surface, the ash content of carbon fibers can be reduced and the mechanical performance of carbon fibers can be improved. In the present invention, the Si/C ratio of a region X between the top of a fiber surface protrusion and the bottom of a groove of the carbon fiber is controlled to be in the range of 1% to 10%, the Si/C ratio of a region Y between the bottom of the groove and within 100 nm inward is controlled to be in the range of 0.1% to 1%, and the Si/C ratio of a region Z greater than 100 nm is controlled to be 0.06% or less, thereby solving the problems existing in the prior art.

On the other hand, the method of the present invention comprises two consecutive oiling processes without a dry densification step in between the two oiling processes, wherein the first oiling process uses a non-silicon emulsion, a low-silicon emulsion, or a combination thereof, and the second oiling process uses a silicone-containing emulsion, thereby controlling the silicone penetration gradient and silicone content on the fiber surface, thereby producing a carbon fiber yarn and carbon fiber having a low silicone content and a good silicone penetration gradient. The present invention can realize a long operating cycle, and can produce a carbon fiber having very low ash content and excellent performances such as strength and elastic modulus.

In the present invention, the swelling degree was measured using the following method:

About 10 g of wet washed fibers were taken, washed in running deionized water for 30 minutes, and evenly placed in a 50 ml centrifuge tube. The centrifuge tube was then placed in a centrifuge dehydrator (3000 r/min, 15 min) to dehydrate the fibers so that the water attached to the fiber surface and the water trapped between the fibers were removed. After centrifugation, the dehydrated fibers were obtained, the mass was measured, and this was designated as W. Afterwards, the dehydrated fibers were dried in a hot air drying oven at 110°C for 2 hours, placed in a desiccator, cooled to room temperature, and the mass was designated as W0. Swelling (wt%) = (W-W0)/W0×100%.

In the present invention, the silicon content of the yarn and carbon fiber was measured using the following method:

A 5g sample was placed in a quartz crucible, the quartz crucible was placed in a muffle furnace, heated to 400℃ for 2 hours, then heated to 960℃ for 3 hours; the ash in the crucible was transferred to a Teflon test tube, and hydrochloric acid, nitric acid, and hydrofluoric acid with concentrations of 37%, 68%, and 50%, respectively, were added in volumes of 3ml, 1ml, and 1ml, respectively, and heated at 120℃ for 5 hours, and then the Si content in the sample was confirmed by quantitative measurement using ICP-OES inductively coupled plasma emission spectroscopy.

In the present invention, the silicon content in the emulsion was measured using the following method:

0.5 g of the emulsion was placed in a quartz crucible, and the quartz crucible was placed in a muffle furnace, heated to 90°C for 2 hours, then heated to 150°C for 0.5 hours, continuously heated to 300°C for 0.5 hours, and finally heated to 400°C for 2 hours; the ash in the crucible was transferred to a Teflon test tube, and hydrochloric acid, nitric acid, and hydrofluoric acid with concentrations of 37%, 68%, and 50%, respectively, were added in volumes of 3 ml, 1 ml, and 1 ml, respectively, and heated at 120°C for 5 hours, diluted 100 times with water, and the Si content in the sample was confirmed by quantitative measurement using ICP-OES inductively coupled plasma emission spectroscopy.

In the present invention, linear density was measured using the following method:

Using a manual fiber linear density meter, yarn with K number N was wound 10 times straight around a hand roller with a circumference of 1 m, and the weight of the fiber (unit: g) was measured and expressed as W. Linear density (dtex) = W/N, and the average value was taken after measuring 10 times.

In the present invention, the mechanical properties including tensile strength, initial elastic modulus, and elongation at break of carbon fiber yarn were measured according to GB/T 14337~2008; and the mechanical properties including tensile strength, tensile modulus, and elongation at break of carbon fiber were measured according to GB/T 3362~2017.

In the present invention, the particle size of the emulsion was measured using a laser particle size analyzer - Mastersizer 2000, Malvern, UK.

In the present invention, the Si/C ratio and the number and size of pores in the fiber were measured using the following methods:

The fibers were cut into sheets 100 nm thick by a low-temperature FIB (Focused Gallium Ion Beam) and colorless transparent pores were observed in the region X and Y from the top of the protrusions on the fiber surface to the inside up to 100 nm by transmission electron microscopy (TEM), where the long side is the length and the short side is the width. Through coupling with the TEM-EDS module, 50 scan lines were taken from the fiber center to the outer surface in the circumferential direction, and among them, 25 scan lines were taken from the fiber center to the top of the adjacent protrusions and the bottom of the grooves on the fiber surface, and one point was taken every 20 nm to scan, thereby obtaining the ratio of Si/C atoms with different depth differences from the fiber center to the surface. Using the data of the X region of the scan line from the fiber center to the top of the protrusion on the fiber surface (indicated by the a scan line in Fig. 1), the average value of the Si/C atomic ratio in the region X between the top of the protrusion on the fiber surface and the bottom of the groove was calculated, and using the data of the Y and Z regions from the fiber center to the bottom of the groove on the fiber surface (indicated by the b scan line in Fig. 1), the average values of the Si/C atomic ratio in the region Y between the bottom of the groove and within 100 nm inward and the region Z greater than 100 nm were calculated, respectively. A total of 10 carbon fibers were measured, and the Si/C ratio, number of pores, average length and average width of pores in the present invention are average values obtained from 10 carbon fibers.

In the present invention, the oil content of the yarn was measured by the following method:

A 3g sample of yarn was taken, dried in an air atmosphere at 105°C for 2 hours, and its mass was measured and denoted as W1; the sample was placed in a Soxhlet extractor, cyclohexane was added, the temperature was raised to 100°C, and extraction was performed for 4 hours. The sample was taken out, dried in an air atmosphere at 105°C for 2 hours, and its mass was measured and denoted as W2. Oil content (wt%) = (W1-W2)/W1 × 100%.

In the present invention, the orientation deviation angle of pores along the axial direction of the carbon fiber was measured in the following manner according to the following literature [1]:

The carbon fiber bundles were taken and taped onto a metal frame with dimensions of 4 cm × 3 cm × 0.2 cm and a central opening dimension of 3 cm × 2 cm, and evenly spread out to the same width, and then the samples were measured by the small-angle X-ray scattering (SAXS) apparatus of the Shanghai Light Source (SSRF, BL16B) beam station. The distance from the sample to the detector was calibrated to 1980 mm using a standard sample cow tendon; the incident X-rays had a wavelength of 0.12398 nm. The SAXS data were collected using a Mar CCD 165 imaging board. The obtained data were processed using xPolar (Precision works NY, Inc., USA) software, and the average length ( L _f ) and orientation deviation angle ( B φ ) of the micropores along the fiber axis were calculated according to the Cauchy-Cauchy formula.

In the equation, s ( s = 2sin q / l ) is the scattering vector corresponding to the azimuth scan curve, and B _obs is the half-width angular width of the azimuth scan curve. The azimuth scan curve was obtained by processing the SAXS graph, where the air scattering was reasonably subtracted, and then scanning along the tangent parallel to the meridian direction, and then integrating to obtain the azimuth scan curve. The data was then fitted using a Gaussian distribution, Linear fitting was performed for the scattering vector s corresponding to each azimuth, and the values of L _f and B φ were calculated based on the intercept and slope data after linear fitting.

Literature[1] Andreas F. Th Nemann et al. Microvoids in Polyacrylonitrile Fibers: A Small-Angle X-ray Scattering Study [J]. Macromolecules, 2000, 33(5):1848-1852.

During the carbon fiber production process, if the strength of the carbon fiber decreases or equipment malfunctions occur, operation must be stopped, and the equipment must be cleaned and maintained. The method of the present invention enables continuous production for longer periods of time without the need for stopping operation, cleaning, or maintenance.

In the present invention, the yarn of the present invention exhibits a favorable silicon penetration gradient, significantly reducing ash content during the carbonization process. Furthermore, the silicon content of the resulting carbon fiber is low, effectively suppressing the depth of silicon penetration. Even after continuous production for over six months, the resulting carbon fiber still exhibits a tensile strength of at least 5.6 GPa, a tensile modulus of at least 360 GPa, and a break elongation of at least 1.5%.

The present invention is further explained through the following examples.

The raw materials and reagents used in the examples and comparative examples can be purchased directly or manufactured according to manufacturing methods disclosed in the prior art. If necessary, the raw materials or reagents are treated prior to use using methods known in the art to meet the reaction requirements. For example, acrylonitrile is distilled prior to use to remove the polymerization inhibitor.

For the silicon content testing of yarns, carbon fibers and emulsions, ICP-OES inductively coupled plasma emission spectroscopy tests were performed on a Varian 725-ES from Varian, and the samples were melted using a Digiblock ST36 electropyrolyzer from LabTech.

During the Si/C ratio testing, low-temperature FIB (Focused Ion Beam Gallium Ion) cutting was performed using a ZEISS Crossbeam Laser, and TEM and EDS examinations were performed using an FEI Titan Cubed Themis G2 300 and an Aztec X-Max 100 TLE Oxford Instruments.

The non-silicone emulsion used in the examples and comparative examples was TFA-1208 from Tianjin Institute of Technology Textile Auxiliary Co., Ltd.; and the silicone-containing emulsion used was JH88 from Matsumoto Yushi. In Examples 7, 8 and 12 and Comparative Examples 10 and 11, the non-silicone emulsions having different particle sizes were the TFA-1208 series synthesized by Tianjin Institute of Technology Textile Auxiliary Co., Ltd., and the silicone-containing emulsions having different particle sizes were the JSYJ series from China Petrochemical (Shanghai) Petroleum and Chemical Research Institute. The anionic non-silicone emulsion of Comparative Example 4 was TFA-1208, and the cationic silicone-containing emulsion was the JLQR emulsion from Jilin Qianren New Materials Co., Ltd. In Example 16, the pH of the emulsion was adjusted by adding an appropriate amount of diluted ammonia water. In Comparative Example 3, the pH of the non-silicone emulsion was adjusted by adding an appropriate amount of dilute ammonia water, and the acidic silicone-containing emulsion was ADVALON®CF3295 from Wacker Chemicals (China) Co., Ltd.

In the examples and comparative examples, in the production of the spinning stock solution, the molar ratio of acrylonitrile and itaconic acid was 99:1, the monomer concentration was 20 wt%, and after polymerization for 20 hours under a nitrogen atmosphere at 60°C, the conversion was 91.5%; thereafter, demonomerization and defoaming were performed to obtain the spinning stock solution.

In the examples and comparative examples, the spinning solution was accurately metered with a metering pump and then filtered using a 10 μm candle filter before extruding through a spinning plate.

[Example 1]

1. Production of yarn: A wet spinning method was adopted, and a spinning solution obtained by copolymerizing acrylonitrile and itaconic acid in dimethyl sulfoxide was used (characteristic viscosity 2.5 dL/g, solid content 18%). The spinning solution was accurately measured using a metering pump, filtered, and then extruded through a spinning plate with 6000 holes and a hole diameter of 60 μm, and entered into a first coagulation bath containing a dimethyl sulfoxide aqueous solution to coagulate at a coagulation temperature of 28°C and a concentration of 51.5%, and then third coagulation drawing was performed at concentrations of 30%, 20%, and 10%, at temperatures of 30°C, 40°C, and 50°C, and at draw ratios of 1.0, 1.1, and 1.2, respectively; After performing the fourth high-temperature water drawing at temperatures of 95℃, 96℃, 97℃, and 99℃, and draw ratios of 1.35, 1.50, 1.70, and 2.00, respectively, six washing processes were performed at temperatures of 70℃, 70℃, 80℃, 80℃, 90℃, and 90℃, respectively, and the swelling degree of the fiber after washing was 110%.

After washing, the fibers first passed through a first oiling tank containing a nonionic, non-silicone emulsion with a pH of 7.2, an emulsion concentration of 1.5%, and a particle size of 300 nm with a residence time of 0.15 s. Thereafter, they passed through a second oiling tank containing a nonionic, silicone-containing emulsion with a pH of 7.8, an emulsion concentration of 1.2%, a particle size of 300 nm, and a silicone content of 0.15% with a residence time of 0.1 s.

Afterwards, a four-step dry densification treatment was performed at temperatures of 90°C, 100°C, 115°C, and 130°C, respectively, followed by steam drawing at a draw ratio of 3.0 times and a steam pressure of 0.35 MPa; and finally, thermoforming was performed at a draw ratio of 0.95 and a steam pressure of 120 MPa, and then winding was performed to obtain polyacrylonitrile carbon fiber yarn.

The linear density of the yarn is 0.85 dtex, the oil content is 1.2%, and the silicon content is 0.15%. The Si/C ratio in the region from the top of the protrusions on the fiber surface to 2 μm inward is 10%, and the Si/C ratio in the region greater than 2 μm is 0.11%; the tensile strength, initial modulus, and elongation at break are 7.5 cN/dtex, 125 cN/dtex, and 12.0%, respectively.

2. Production of carbon fiber: The yarn obtained in step 1 was pre-oxidized in air at 180 to 260°C (the total pre-oxidation draw ratio was 0.95 times) to obtain pre-oxidized fiber; then low-temperature carbonization and high-temperature carbonization were performed at 300 to 750°C and 800 to 1500°C with a draw ratio of 0.96 times; then graphitization was performed at 2800°C, and finally, carbon fiber was obtained through surface treatment, washing, sizing, drying at 120°C, and winding.

The total silicon content of the carbon fiber is 800 ppm, the Si/C ratio of the region X between the top of the protrusion on the fiber surface and the bottom of the groove is 5.8%, the Si/C ratio of the region Y between the bottom of the groove and 100 nm inward is 0.5%, and the Si/C ratio of the region Z greater than 100 nm is 0.04%. The number of pores present in the carbon fiber surface layer (regions X and Y from the top of the protrusion on the fiber surface to 100 nm inward) is 10, the average length of the pores is 20 nm, and the average width is 15 nm. The orientation deviation angle of the pores along the fiber axis obtained by small-angle X-ray scattering is 2.3°. The tensile strength of the carbon fiber is 5.74 GPa, the tensile modulus is 370 GPa, and the elongation at break is 1.52%. After seven months of continuous production, the carbon fiber strength began to decline, the operation was stopped, and the ash in the equipment was cleaned once.

[Example 2]

1. Production of yarn: A wet spinning method was adopted, and a spinning solution obtained by copolymerizing acrylonitrile and itaconic acid in dimethyl sulfoxide was used (characteristic viscosity 2.5 dL/g, solid content 18%). The spinning solution was accurately measured through a metering pump, filtered, and then extruded through a spinning plate with 6000 holes and a hole diameter of 60 μm, and entered into a first coagulation bath containing a dimethyl sulfoxide aqueous solution, and solidified at a coagulation temperature of 28°C and a concentration of 51.5%, and then subjected to third coagulation drawing at concentrations of 30%, 20%, and 10%, temperatures of 30°C, 40°C, and 50°C, and draw ratios of 1.0, 1.1, and 1.2, respectively; After performing the fourth high-temperature water drawing at temperatures of 95℃, 96℃, 97℃, and 99℃, and draw ratios of 1.35, 1.50, 1.70, and 2.00, respectively, six washing processes were performed at temperatures of 70℃, 70℃, 80℃, 80℃, 90℃, and 90℃, respectively, and the swelling degree of the fiber after washing was 110%.

After washing, the fibers first passed through a first oiling tank containing a nonionic, non-silicone emulsion with a pH of 7.2, an emulsion concentration of 3.5%, and an emulsion particle size of 300 nm with a residence time of 0.15 s, and then passed through a second oiling tank containing a nonionic, silicone-containing emulsion with a pH of 7.8, an emulsion concentration of 3%, an emulsion particle size of 300 nm, and an emulsion silicon content of 0.35% with a residence time of 0.1 s.

Afterwards, a four-step dry densification treatment was performed at temperatures of 90°C, 100°C, 115°C, and 130°C, respectively, followed by steam drawing at a draw ratio of 3.0 times and a steam pressure of 0.35 MPa; and finally, thermoforming was performed at a draw ratio of 0.95 and a steam pressure of 120 MPa, and then winding was performed to obtain polyacrylonitrile carbon fiber yarn.

The linear density of the yarn is 0.85 dtex, the oil content is 2.2%, and the silicon content is 0.47%. The Si/C ratio in the region from the top of the protrusions on the fiber surface to 2 μm inward is 19%, and the Si/C ratio in the region greater than 2 μm is 0.14%; the tensile strength, initial modulus, and elongation at break are 7.2 cN/dtex, 120 cN/dtex, and 12.3%, respectively.

2. Production of carbon fiber: The yarn obtained in step 1 was pre-oxidized at 180-260°C with a pre-oxidation total draw ratio of 0.95 times to obtain pre-oxidized fiber; then low-temperature carbonization and high-temperature carbonization were performed at 300-750°C and 800-1500°C with a draw ratio of 0.96 times; then graphitization was performed at 2800°C, and finally, carbon fiber was obtained through surface treatment, washing, sizing, drying at 120°C, and winding.

The total silicon content of the carbon fiber is 1400 ppm, the Si/C ratio of region X from the top of the protrusion on the fiber surface to the bottom of the groove is 9%, the Si/C ratio of region Y from the bottom of the groove to the inside within 100 nm is 0.9%, and the Si/C ratio of region Z greater than 100 nm is 0.05%. The number of pores on the surface of the carbon fiber is 15, the average length of the pores is 42 nm, and the average width is 22 nm. The pore orientation deviation angle along the fiber axis obtained by small-angle X-ray scattering is 3.5°. The tensile strength of the carbon fiber is 5.63 GPa, the tensile modulus is 360 GPa, and the elongation at break is 1.56%. After 6 months of continuous production, the carbon fiber strength began to decrease, the operation was stopped, and the ash in the equipment was cleaned once.

[Example 3]

1. Manufacturing of yarn: A wet spinning method was adopted, and a spinning solution obtained by copolymerizing acrylonitrile and itaconic acid in dimethyl sulfoxide was used (characteristic viscosity 2.5 dL/g, solid content 18%). The spinning solution was accurately measured through a metering pump, filtered, and then extruded through a spinning plate with 6000 holes and a hole diameter of 60 μm. The spinning solution was introduced into a first coagulation bath containing a dimethyl sulfoxide aqueous solution, and solidified at a coagulation temperature of 28°C and a concentration of 51.5%. Then, third coagulation drawing was performed at concentrations of 30%, 20%, and 10%, at temperatures of 30°C, 40°C, and 50°C, and at draw ratios of 1.0, 1.1, and 1.2, respectively; After performing the fourth high-temperature water drawing at temperatures of 95℃, 96℃, 97℃, and 99℃, and draw ratios of 1.35, 1.50, 1.70, and 2.00, respectively, six washing processes were performed at temperatures of 70℃, 70℃, 80℃, 80℃, 90℃, and 90℃, respectively, and the swelling degree of the fiber after washing was 110%.

After washing, the fibers first passed through a first oiling tank containing a nonionic, non-silicone emulsion with a pH of 7.2, an emulsion concentration of 1.1%, and an emulsion particle size of 300 nm with a residence time of 0.15 s, and then passed through a second oiling tank containing a nonionic, silicone-containing emulsion with a pH of 7.8, an emulsion concentration of 0.8%, an emulsion particle size of 300 nm, and an emulsion silicon content of 0.1% with a residence time of 0.1 s.

Afterwards, a four-step dry densification treatment was performed at temperatures of 90°C, 100°C, 115°C, and 130°C, respectively, followed by steam drawing at a draw ratio of 3.0 times and a steam pressure of 0.35 MPa; and finally, thermoforming was performed at a draw ratio of 0.95 and a steam pressure of 120 MPa, and then winding was performed to obtain polyacrylonitrile carbon fiber yarn.

The linear density of the yarn is 0.85 dtex, the oil content is 0.85%, and the silicon content is 0.09%. The Si/C ratio in the region from the top of the protrusions on the fiber surface to 2 μm inward is 6%, and the Si/C ratio in the region greater than 2 μm is 0.07%; the tensile strength, initial modulus, and elongation at break are 8.1 cN/dtex, 137 cN/dtex, and 11.8%, respectively.

2. Production of carbon fiber: The yarn obtained in step 1 was pre-oxidized at 180-260°C with a pre-oxidation total draw ratio of 0.95 times to obtain pre-oxidized fiber; then low-temperature carbonization and high-temperature carbonization were performed at 300-750°C and 800-1500°C with a draw ratio of 0.96 times; then graphitization was performed at 2800°C, and finally, carbon fiber was obtained through surface treatment, washing, sizing, drying at 120°C, and winding.

The total silicon content of the carbon fiber is 620 ppm, the Si/C ratio of the region X between the top of the protrusion on the fiber surface and the bottom of the groove is 4.5%, the Si/C ratio of the region Y between the bottom of the groove and the inner side 100 nm is 0.47%, and the Si/C ratio of the region Z greater than 100 nm is 0.03%. The number of pores on the surface of the carbon fiber is 7, the average length of the pores is 15 nm, and the average width is 10 nm. The pore orientation deviation angle along the fiber axis obtained by small-angle X-ray scattering is 2.2°. The tensile strength of the carbon fiber is 5.75 GPa, the tensile modulus is 374 GPa, and the elongation at break is 1.51%. After 8 months of continuous production, the carbon fiber strength began to decrease, the operation was stopped, and the ash in the equipment was cleaned once.

[Example 4]

1. Production of yarn: A wet spinning method was adopted, and a spinning solution obtained by copolymerizing acrylonitrile and itaconic acid in dimethyl sulfoxide was used (characteristic viscosity 2.5 dL/g, solid content 18%). The spinning solution was accurately measured through a metering pump, filtered, and then extruded through a spinning plate with 6000 holes and a hole diameter of 60 μm, and entered into a first coagulation bath containing a dimethyl sulfoxide aqueous solution, and solidified at a coagulation temperature of 28°C and a concentration of 51.5%, and then subjected to third coagulation drawing at concentrations of 30%, 20%, and 10%, temperatures of 30°C, 40°C, and 50°C, and draw ratios of 1.0, 1.1, and 1.2, respectively; After performing the fourth high-temperature water drawing at temperatures of 95℃, 96℃, 97℃, and 99℃, and draw ratios of 1.35, 1.50, 1.70, and 2.00, respectively, six washing processes were performed at temperatures of 70℃, 70℃, 80℃, 80℃, 90℃, and 90℃, respectively, and the swelling degree of the fiber after washing was 110%.

After washing, the fibers first passed through a first oiling tank containing a nonionic, non-silicone emulsion with a pH of 7.2, an emulsion concentration of 1.1%, and a particle size of 300 nm with a residence time of 0.15 s, and then passed through a second oiling tank containing a nonionic, silicone-containing emulsion with a pH of 7.8, an emulsion concentration of 1.5%, an emulsion particle size of 300 nm, and a silicone content of 0.2% with a residence time of 0.05 s.

Afterwards, a four-step dry densification treatment was performed at temperatures of 90°C, 100°C, 115°C, and 130°C, respectively, followed by steam drawing at a draw ratio of 3.0 times and a steam pressure of 0.35 MPa; and finally, thermoforming was performed at a draw ratio of 0.95 and a steam pressure of 120 MPa, and then winding was performed to obtain polyacrylonitrile carbon fiber yarn.

The linear density of the yarn is 0.85 dtex, the oil content is 0.9%, and the silicon content is 0.13%. The Si/C ratio in the region from the top of the protrusions on the fiber surface to 2 μm inward is 9%, and the Si/C ratio in the region greater than 2 μm is 0.1%; the tensile strength, initial modulus, and elongation at break are 7.8 cN/dtex, 121 cN/dtex, and 11.8%, respectively.

2. Production of carbon fiber: The yarn obtained in step 1 was pre-oxidized at 180-260°C with a pre-oxidation total draw ratio of 0.95 times to obtain pre-oxidized fiber; then low-temperature carbonization and high-temperature carbonization were performed at 300-750°C and 800-1500°C with a draw ratio of 0.96 times; then graphitization was performed at 2800°C, and finally, carbon fiber was obtained through surface treatment, washing, sizing, drying at 120°C, and winding.

The total silicon content in the carbon fiber is 690 ppm, the Si/C ratio of region X from the top of the protrusion on the fiber surface to the bottom of the groove is 4.8%, the Si/C ratio of region Y from the bottom of the groove to 100 nm inward is 0.54%, and the Si/C ratio of region Z greater than 100 nm is 0.04%. The number of pores on the surface of the carbon fiber is 8, the average length of the pores is 17 nm, and the average width is 13 nm. The pore orientation deviation angle along the fiber axis obtained by small-angle X-ray scattering is 2.2°. The tensile strength of the carbon fiber is 5.75 GPa, the tensile modulus is 374 GPa, and the elongation at break is 1.55%. After 8 months of continuous production, the carbon fiber strength began to decrease, the operation was stopped, and the ash in the equipment was cleaned once.

[Example 5]

1. Production of yarn: A wet spinning method was adopted, and a spinning solution obtained by copolymerizing acrylonitrile and itaconic acid in dimethyl sulfoxide was used (characteristic viscosity 2.5 dL/g, solid content 18%). The spinning solution was accurately measured through a metering pump, filtered, and then extruded through a spinning plate with 6000 holes and a hole diameter of 60 μm, and entered into a first coagulation bath containing a dimethyl sulfoxide aqueous solution, and solidified at a coagulation temperature of 28°C and a concentration of 51.5%, and then subjected to third coagulation drawing at concentrations of 30%, 20%, and 10%, temperatures of 30°C, 40°C, and 50°C, and draw ratios of 1.0, 1.1, and 1.2, respectively; After performing the fourth high-temperature water drawing at temperatures of 95℃, 96℃, 97℃, and 99℃, and draw ratios of 1.35, 1.50, 1.70, and 2.00, respectively, six washing processes were performed at temperatures of 70℃, 70℃, 80℃, 80℃, 90℃, and 90℃, respectively, and the swelling degree of the fiber after washing was 110%.

After washing, the fibers first passed through a first oiling tank containing a nonionic, non-silicone emulsion with a pH of 7.2, an emulsion concentration of 1.5%, and a particle size of 300 nm with a residence time of 0.25 s, and then passed through a second oiling tank containing a nonionic, silicone-containing emulsion with a pH of 7.8, an emulsion concentration of 1.2%, an emulsion particle size of 300 nm, and a silicone content of 0.15% with a residence time of 0.13 s.

Afterwards, a four-step dry densification treatment was performed at temperatures of 90°C, 100°C, 115°C, and 130°C, respectively, followed by steam drawing at a draw ratio of 3.0 times and a steam pressure of 0.35 MPa; and finally, thermoforming was performed at a draw ratio of 0.95 and a steam pressure of 120 MPa, and then winding was performed to obtain polyacrylonitrile carbon fiber yarn.

The linear density of the yarn is 0.85 dtex, the oil content is 1.8%, and the silicon content is 0.39%. The Si/C ratio in the region from the top of the protrusions on the fiber surface to 2 μm inward is 14%, and the Si/C ratio in the region greater than 2 μm is 0.12%; the tensile strength, initial modulus, and elongation at break are 7.2 cN/dtex, 127 cN/dtex, and 11.8%, respectively.

2. Production of carbon fiber: The yarn obtained in step 1 was pre-oxidized at 180-260°C with a pre-oxidation total draw ratio of 0.95 times to obtain pre-oxidized fiber; then low-temperature carbonization and high-temperature carbonization were performed at 300-750°C and 800-1500°C with a draw ratio of 0.96 times; then graphitization was performed at 2800°C, and finally, carbon fiber was obtained through surface treatment, washing, sizing, drying at 120°C, and winding.

The total silicon content of the carbon fiber is 1340 ppm, the Si/C ratio of the region X from the top of the protrusion on the fiber surface to the bottom of the groove is 8%, the Si/C ratio of the region Y from the bottom of the groove to the inside 100 nm is 0.85%, and the Si/C ratio of the region Z greater than 100 nm is 0.04%. The number of pores on the surface of the carbon fiber is 15, the average length of the pores is 35 nm, and the average width is 20 nm. The pore orientation deviation angle along the fiber axis obtained by small-angle X-ray scattering is 3.0°. The tensile strength of the carbon fiber is 5.66 GPa, the tensile modulus is 361 GPa, and the elongation at break is 1.58%. After 6 months of continuous production, the carbon fiber strength began to decrease, the operation was stopped, and the ash in the equipment was cleaned once.

[Example 6]

1. Production of yarn: A wet spinning method was adopted, and a spinning solution obtained by copolymerizing acrylonitrile and itaconic acid in dimethyl sulfoxide was used (characteristic viscosity 2.5 dL/g, solid content 18%). The spinning solution was accurately measured through a metering pump, filtered, and then extruded through a spinning plate with 6000 holes and a hole diameter of 60 μm, and entered into a first coagulation bath containing a dimethyl sulfoxide aqueous solution, and solidified at a coagulation temperature of 28°C and a concentration of 51.5%, and then subjected to third coagulation drawing at concentrations of 30%, 20%, and 10%, temperatures of 30°C, 40°C, and 50°C, and draw ratios of 1.0, 1.1, and 1.2, respectively; After performing the fourth high-temperature water drawing at temperatures of 95℃, 96℃, 97℃, and 99℃, and draw ratios of 1.35, 1.50, 1.70, and 2.00, respectively, six washing processes were performed at temperatures of 70℃, 70℃, 80℃, 80℃, 90℃, and 90℃, respectively, and the swelling degree of the fiber after washing was 110%.

After washing, the fibers first passed through a first oiling tank containing a nonionic, non-silicone emulsion with a pH of 7.2, an emulsion concentration of 1.5%, and an emulsion particle size of 300 nm with a residence time of 0.08 s, and then passed through a second oiling tank containing a nonionic, silicone-containing emulsion with a pH of 7.8, an emulsion concentration of 1.2%, an emulsion particle size of 300 nm, and an emulsion silicon content of 0.15% with a residence time of 0.05 s.

Afterwards, a four-step dry densification treatment was performed at temperatures of 90°C, 100°C, 115°C, and 130°C, respectively, followed by steam drawing at a draw ratio of 3.0 times and a steam pressure of 0.35 MPa; and finally, thermoforming was performed at a draw ratio of 0.95 and a steam pressure of 120 MPa, and then winding was performed to obtain polyacrylonitrile carbon fiber yarn.

The linear density of the yarn is 0.85 dtex, the oil content is 0.9%, and the silicon content is 0.08%. The Si/C ratio in the region from the top of the protrusions on the fiber surface to 2 μm inward is 5%, and the Si/C ratio in the region greater than 2 μm is 0.05%; the tensile strength, initial modulus, and elongation at break are 7.4 cN/dtex, 126 cN/dtex, and 11.5%, respectively.

2. Production of carbon fiber: The yarn obtained in step 1 was pre-oxidized at 180-260°C with a pre-oxidation total draw ratio of 0.95 times to obtain pre-oxidized fiber; then low-temperature carbonization and high-temperature carbonization were performed at 300-750°C and 800-1500°C with a draw ratio of 0.96 times; then graphitization was performed at 2800°C, and finally, carbon fiber was obtained through surface treatment, washing, sizing, drying at 120°C, and winding.

The total silicon content of the carbon fiber is 560 ppm, the Si/C ratio of region X between the top of the protrusion on the fiber surface and the bottom of the groove is 4.3%, the Si/C ratio of region Y between the bottom of the groove and the inner side 100 nm is 0.41%, and the Si/C ratio of region Z greater than 100 nm is 0.02%. The number of pores on the surface of the carbon fiber is 10, the average length of the pores is 23 nm, and the average width is 18 nm. The pore orientation deviation angle along the fiber axis obtained by small-angle X-ray scattering is 2.8°. The tensile strength of the carbon fiber is 5.68 GPa, the tensile modulus is 364 GPa, and the elongation at break is 1.55%. After 8 months of continuous production, the carbon fiber strength began to decrease, the operation was stopped, and the ash in the equipment was cleaned once.

[Example 7]

1. Production of yarn: A wet spinning method was adopted, and a spinning solution obtained by copolymerizing acrylonitrile and itaconic acid in dimethyl sulfoxide was used (characteristic viscosity 2.5 dL/g, solid content 18%). The spinning solution was accurately measured through a metering pump, filtered, and then extruded through a spinning plate with 6000 holes and a hole diameter of 60 μm, and entered into a first coagulation bath containing a dimethyl sulfoxide aqueous solution, and solidified at a coagulation temperature of 28°C and a concentration of 51.5%, and then subjected to third coagulation drawing at concentrations of 30%, 20%, and 10%, temperatures of 30°C, 40°C, and 50°C, and draw ratios of 1.0, 1.1, and 1.2, respectively; After performing the fourth high-temperature water drawing at temperatures of 95℃, 96℃, 97℃, and 99℃, and draw ratios of 1.35, 1.50, 1.70, and 2.00, respectively, six washing processes were performed at temperatures of 70℃, 70℃, 80℃, 80℃, 90℃, and 90℃, respectively, and the swelling degree of the fiber after washing was 110%.

After washing, the fibers first passed through a first oiling tank containing TFA-1208-10 nonionic non-silicone emulsion synthesized by Tianjin Institute of Technology Textile Auxiliary Co., Ltd., which has a pH of 7.2, an emulsion concentration of 1.5%, an emulsion particle size of 100 nm, with a residence time of 0.15 s, and then passed through a second oiling tank containing JSYJ-20 nonionic silicone-containing emulsion synthesized by China Petrochemical (Shanghai) Petrochemical Research Institute, which has a pH of 7.8, an emulsion concentration of 1.2%, an emulsion particle size of 200 nm, and an emulsion silicone content of 0.15%, with a residence time of 0.1 s.

Afterwards, a four-step dry densification treatment was performed at temperatures of 90°C, 100°C, 115°C, and 130°C, respectively, followed by steam drawing at a draw ratio of 3.0 times and a steam pressure of 0.35 MPa; and finally, thermoforming was performed at a draw ratio of 0.95 and a steam pressure of 120 MPa, and then winding was performed to obtain polyacrylonitrile carbon fiber yarn.

The linear density of the yarn is 0.85 dtex, the oil content is 1.4%, and the silicon content is 0.14%. The Si/C ratio in the region from the top of the protrusions on the fiber surface to 2 μm inward is 9%, and the Si/C ratio in the region greater than 2 μm is 0.1%; the tensile strength, initial modulus, and elongation at break are 7.7 cN/dtex, 130 cN/dtex, and 11.5%, respectively.

2. Production of carbon fiber: The yarn obtained in step 1 was pre-oxidized at 180-260°C with a pre-oxidation total draw ratio of 0.95 times to obtain pre-oxidized fiber; then low-temperature carbonization and high-temperature carbonization were performed at 300-750°C and 800-1500°C with a draw ratio of 0.96 times; then graphitization was performed at 2800°C, and finally, carbon fiber was obtained through surface treatment, washing, sizing, drying at 120°C, and winding.

The total silicon content of the carbon fiber is 700 ppm, the Si/C ratio of the region X between the top of the protrusion on the fiber surface and the bottom of the groove is 5%, the Si/C ratio of the region Y between the bottom of the groove and the inner side 100 nm is 0.55%, and the Si/C ratio of the region Z greater than 100 nm is 0.04%. The number of pores on the surface of the carbon fiber is 8, the average length of the pores is 17 nm, and the average width is 13 nm. The pore orientation deviation angle along the fiber axis obtained by small-angle X-ray scattering is 2.2°. The tensile strength of the carbon fiber is 5.75 GPa, the tensile modulus is 374 GPa, and the elongation at break is 1.51%. After 8 months of continuous production, the carbon fiber strength began to decrease, the operation was stopped, and the ash in the equipment was cleaned once.

[Example 8]

1. Production of yarn: A wet spinning method was adopted, and a spinning solution obtained by copolymerizing acrylonitrile and itaconic acid in dimethyl sulfoxide was used (characteristic viscosity 2.5 dL/g, solid content 18%). The spinning solution was accurately measured through a metering pump, filtered, and then extruded through a spinning plate with 6000 holes and a hole diameter of 60 μm, and entered into a first coagulation bath containing a dimethyl sulfoxide aqueous solution, and solidified at a coagulation temperature of 28°C and a concentration of 51.5%, and then subjected to third coagulation drawing at concentrations of 30%, 20%, and 10%, temperatures of 30°C, 40°C, and 50°C, and draw ratios of 1.0, 1.1, and 1.2, respectively; After performing the fourth high-temperature water drawing at temperatures of 95℃, 96℃, 97℃, and 99℃, and draw ratios of 1.35, 1.50, 1.70, and 2.00, respectively, six washing processes were performed at temperatures of 70℃, 70℃, 80℃, 80℃, 90℃, and 90℃, respectively, and the swelling degree of the fiber after washing was 110%.

After washing, the fibers first passed through a first oiling tank containing a nonionic, non-silicone emulsion with a pH of 7.2, an emulsion concentration of 1.5%, and a particle size of 300 nm with a residence time of 0.15 s, and then passed through a second oiling tank containing a JSYJ-20 nonionic silicone-containing emulsion synthesized by the China Petrochemical (Shanghai) Petrochemical Research Institute with a pH of 7.8, an emulsion concentration of 1.2%, an emulsion particle size of 200 nm, and a silicone content of 0.15% with a residence time of 0.04 s.

Afterwards, a four-step dry densification treatment was performed at temperatures of 90°C, 100°C, 115°C, and 130°C, respectively, followed by steam drawing at a draw ratio of 3.0 times and a steam pressure of 0.35 MPa; and finally, thermoforming was performed at a draw ratio of 0.95 and a steam pressure of 120 MPa, and then winding was performed to obtain polyacrylonitrile carbon fiber yarn.

The linear density of the yarn is 0.85 dtex, the oil content is 1.1%, and the silicon content is 0.07%. The Si/C ratio in the region from the top of the protrusions on the fiber surface to the inside of 2 μm is 5%, and the Si/C ratio in the region greater than 2 μm is 0.06%; the tensile strength, initial modulus, and elongation at break are 8.4 cN/dtex, 130 cN/dtex, and 12.0%, respectively.

2. Production of carbon fiber: The yarn obtained in step 1 was pre-oxidized at 180-260°C with a pre-oxidation total draw ratio of 0.95 times to obtain pre-oxidized fiber; then low-temperature carbonization and high-temperature carbonization were performed at 300-750°C and 800-1500°C with a draw ratio of 0.96 times; then graphitization was performed at 2800°C, and finally, carbon fiber was obtained through surface treatment, washing, sizing, drying at 120°C, and winding.

The total silicon content of the carbon fiber is 550 ppm, the Si/C ratio of region X from the top of the protrusion on the fiber surface to the bottom of the groove is 4.3%, the Si/C ratio of region Y from the bottom of the groove to 100 nm inward is 0.4%, and the Si/C ratio of region Z greater than 100 nm is 0.02%. The number of pores on the surface of the carbon fiber is 7, the average length of the pores is 15 nm, and the average width is 9 nm. The pore orientation deviation angle along the fiber axis obtained by small-angle X-ray scattering is 2.1°. The tensile strength of the carbon fiber is 5.8 GPa, the tensile modulus is 390 GPa, and the elongation at break is 1.45%. After 8 months of continuous production, the carbon fiber strength began to decrease, the operation was stopped, and the ash in the equipment was cleaned once.

[Example 9]

1. Production of yarn: A wet spinning method was adopted, and a spinning solution obtained by copolymerizing acrylonitrile and itaconic acid in dimethyl sulfoxide was used (characteristic viscosity 2.5 dL/g, solid content 18%). The spinning solution was accurately measured through a metering pump, filtered, and then extruded through a spinning plate with 6000 holes and a hole diameter of 60 μm, and entered into a first coagulation bath containing a dimethyl sulfoxide aqueous solution, and solidified at a coagulation temperature of 28°C and a concentration of 51.5%, and then subjected to third coagulation drawing at concentrations of 30%, 20%, and 10%, temperatures of 30°C, 40°C, and 50°C, and draw ratios of 1.0, 1.1, and 1.2, respectively; After performing the fourth high-temperature water drawing at temperatures of 95℃, 96℃, 97℃, and 99℃, and draw ratios of 1.35, 1.50, 1.70, and 2.00, respectively, six washing processes were performed at temperatures of 70℃, 70℃, 80℃, 80℃, 90℃, and 90℃, respectively, and the swelling degree of the fiber after washing was 110%.

After washing, the fibers first passed through a first oiling tank containing a nonionic, non-silicone emulsion with a pH of 7.2, an emulsion concentration of 1.5%, and an emulsion particle size of 300 nm with a residence time of 0.15 s, and then passed through a second oiling tank containing a nonionic, silicone-containing emulsion with a pH of 7.8, an emulsion concentration of 2%, an emulsion particle size of 300 nm, and an emulsion silicon content of 0.3% with a residence time of 0.1 s.

Afterwards, a four-step dry densification treatment was performed at temperatures of 90℃, 100℃, 115℃, and 130℃, respectively, followed by steam drawing at a draw ratio of 3.0 times and a steam pressure of 0.35 MPa; and finally, thermoforming was performed at a draw ratio of 0.95 and a steam pressure of 120 MPa, followed by winding, to obtain polyacrylonitrile carbon fiber yarn.

The linear density of the yarn is 0.85 dtex, the oil content is 1.3%, and the silicon content is 0.34%. The Si/C ratio in the region from the top of the protrusions on the fiber surface to 2 μm inward is 13%, and the Si/C ratio in the region greater than 2 μm is 0.12%; the tensile strength, initial modulus, and elongation at break are 7.5 cN/dtex, 126 cN/dtex, and 11.7%, respectively.

2. Production of carbon fiber: The yarn obtained in step 1 was pre-oxidized at 180-260°C with a pre-oxidation total draw ratio of 0.95 times to obtain pre-oxidized fiber; then low-temperature carbonization and high-temperature carbonization were performed at 300-750°C and 800-1500°C with a draw ratio of 0.96 times; then graphitization was performed at 2800°C, and finally, carbon fiber was obtained through surface treatment, washing, sizing, drying at 120°C, and winding.

The total silicon content of the carbon fiber is 1200 ppm, the Si/C ratio of region X between the top of the protrusion on the fiber surface and the bottom of the groove is 6.7%, the Si/C ratio of region Y between the bottom of the groove and 100 nm inward is 0.7%, and the Si/C ratio of region Z greater than 100 nm is 0.04%. The number of pores on the surface of the carbon fiber is 14, the average length of the pores is 30 nm, and the average width is 19 nm. The pore orientation deviation angle along the fiber axis obtained by small-angle X-ray scattering is 2.8°. The tensile strength of the carbon fiber is 5.69 GPa, the tensile modulus is 365 GPa, and the elongation at break is 1.54%. After 6 months of continuous production, the carbon fiber strength began to decrease, the operation was stopped, and the ash in the equipment was cleaned once.

[Example 10]

1. Production of yarn: A wet spinning method was adopted, and a spinning solution obtained by copolymerizing acrylonitrile and itaconic acid in dimethyl sulfoxide was used (characteristic viscosity 2.5 dL/g, solid content 18%). The spinning solution was accurately measured through a metering pump, filtered, and then extruded through a spinning plate with 6000 holes and a hole diameter of 60 μm, and entered into a first coagulation bath containing a dimethyl sulfoxide aqueous solution, and solidified at a coagulation temperature of 28°C and a concentration of 51.5%, and then subjected to third coagulation drawing at concentrations of 30%, 20%, and 10%, temperatures of 30°C, 40°C, and 50°C, and draw ratios of 1.0, 1.1, and 1.2, respectively; After performing the fourth high-temperature water drawing at temperatures of 95℃, 96℃, 97℃, and 99℃, and draw ratios of 1.35, 1.50, 1.70, and 2.00, respectively, six washing processes were performed at temperatures of 70℃, 70℃, 80℃, 80℃, 90℃, and 90℃, respectively, and the swelling degree of the fiber after washing was 110%.

After washing, the fibers first passed through a first oiling tank containing a nonionic, non-silicone emulsion with a pH of 7.2, an emulsion concentration of 1.5%, and a particle size of 300 nm with a residence time of 0.15 s, and then passed through a second oiling tank containing a nonionic, silicone-containing emulsion with a pH of 7.8, an emulsion concentration of 1.5%, an emulsion particle size of 300 nm, and a silicone content of 0.2% with a residence time of 0.1 s.

Afterwards, a four-step dry densification treatment was performed at temperatures of 90℃, 100℃, 115℃, and 130℃, respectively, followed by steam drawing at a draw ratio of 3.0 times and a steam pressure of 0.35 MPa; and finally, thermoforming was performed at a draw ratio of 0.95 and a steam pressure of 120 MPa, followed by winding, to obtain polyacrylonitrile carbon fiber yarn.

The linear density of the yarn is 0.85 dtex, the oil content is 1.1%, and the silicon content is 0.08%. The Si/C ratio in the region from the top of the protrusions on the fiber surface to the inside of 2 μm is 7%, and the Si/C ratio in the region greater than 2 μm is 0.07%; the tensile strength, initial modulus, and elongation at break are 8.1 cN/dtex, 137 cN/dtex, and 11.8%, respectively.

2. Production of carbon fiber: The yarn obtained in step 1 was pre-oxidized at 180-260°C with a pre-oxidation total draw ratio of 0.95 times to obtain pre-oxidized fiber; then low-temperature carbonization and high-temperature carbonization were performed at 300-750°C and 800-1500°C with a draw ratio of 0.96 times; then graphitization was performed at 2800°C, and finally, carbon fiber was obtained through surface treatment, washing, sizing, drying at 120°C, and winding.

The total silicon content of the carbon fiber is 600 ppm, the Si/C ratio of the region X between the top of the protrusion on the fiber surface and the bottom of the groove is 4.5%, the Si/C ratio of the region Y between the bottom of the groove and the inner side 100 nm is 0.45%, and the Si/C ratio of the region Z greater than 100 nm is 0.03%. The number of pores on the surface of the carbon fiber is 7, the average length of the pores is 15 nm, and the average width is 10 nm. The pore orientation deviation angle along the fiber axis obtained by small-angle X-ray scattering is 2.2°. The tensile strength of the carbon fiber is 5.76 GPa, the tensile modulus is 379 GPa, and the elongation at break is 1.5%. After 8 months of continuous production, the carbon fiber strength began to decrease, the operation was stopped, and the ash in the equipment was cleaned once.

[Example 11]

1. Production of yarn: A wet spinning method was adopted, and a spinning solution obtained by copolymerizing acrylonitrile and itaconic acid in dimethyl sulfoxide was used (characteristic viscosity 2.5 dL/g, solid content 18%). The spinning solution was accurately measured through a metering pump, filtered, and then extruded through a spinning plate with 6000 holes and a hole diameter of 60 μm, and entered into a first coagulation bath containing a dimethyl sulfoxide aqueous solution, and solidified at a coagulation temperature of 28°C and a concentration of 51.5%, and then subjected to third coagulation drawing at concentrations of 30%, 20%, and 10%, temperatures of 30°C, 40°C, and 50°C, and draw ratios of 1.0, 1.1, and 1.2, respectively; After performing the fourth high-temperature water drawing at temperatures of 95℃, 96℃, 97℃, and 99℃, and draw ratios of 1.35, 1.50, 1.70, and 2.00, respectively, six washing processes were performed at temperatures of 70℃, 70℃, 80℃, 80℃, 90℃, and 90℃, respectively, and the swelling degree of the fiber after washing was 140%.

After washing, the fibers first passed through a first oiling tank containing a nonionic, non-silicone emulsion with a pH of 7.2, an emulsion concentration of 1.5%, and an emulsion particle size of 300 nm with a residence time of 0.15 s, and then passed through a second oiling tank containing a nonionic, silicone-containing emulsion with a pH of 7.8, an emulsion concentration of 1%, an emulsion particle size of 300 nm, and an emulsion silicon content of 0.11% with a residence time of 0.1 s.

Afterwards, a four-step dry densification treatment was performed at temperatures of 90℃, 100℃, 115℃, and 130℃, respectively, followed by steam drawing at a draw ratio of 3.0 times and a steam pressure of 0.35 MPa; and finally, thermoforming was performed at a draw ratio of 0.95 and a steam pressure of 120 MPa, followed by winding, to obtain polyacrylonitrile carbon fiber yarn.

The linear density of the yarn is 0.85 dtex, the oil content is 2.3%, and the silicon content is 0.4%. The Si/C ratio in the region from the top of the protrusions on the fiber surface to 2 μm inward is 16%, and the Si/C ratio in the region greater than 2 μm is 0.14%; the tensile strength, initial modulus, and elongation at break are 7.2 cN/dtex, 119 cN/dtex, and 12.5%, respectively.

2. Production of carbon fiber: The yarn obtained in step 1 was pre-oxidized at 180-260°C with a pre-oxidation total draw ratio of 0.95 times to obtain pre-oxidized fiber; then low-temperature carbonization and high-temperature carbonization were performed at 300-750°C and 800-1500°C with a draw ratio of 0.96 times; then graphitization was performed at 2800°C, and finally, carbon fiber was obtained through surface treatment, washing, sizing, drying at 120°C, and winding.

The total silicon content of the carbon fiber is 1350 ppm, the Si/C ratio of the region X between the top of the protrusion on the fiber surface and the bottom of the groove is 8%, the Si/C ratio of the region Y between the bottom of the groove and the inner side 100 nm is 0.85%, and the Si/C ratio of the region Z greater than 100 nm is 0.04%. The number of pores on the surface of the carbon fiber is 15, the average length of the pores is 38 nm, and the average width is 20 nm. The pore orientation deviation angle along the fiber axis obtained by small-angle X-ray scattering is 3.2°. The tensile strength of the carbon fiber is 5.66 GPa, the tensile modulus is 362 GPa, and the elongation at break is 1.55%. After 6 months of continuous production, the carbon fiber strength began to decrease, the operation was stopped, and the ash in the equipment was cleaned once.

[Example 12]

1. Production of yarn: A wet spinning method was adopted, and a spinning solution obtained by copolymerizing acrylonitrile and itaconic acid in dimethyl sulfoxide was used (characteristic viscosity 2.5 dL/g, solid content 18%). The spinning solution was accurately measured through a metering pump, filtered, and then extruded through a spinning plate with 6000 holes and a hole diameter of 60 μm, and entered into a first coagulation bath containing a dimethyl sulfoxide aqueous solution, and solidified at a coagulation temperature of 28°C and a concentration of 51.5%, and then subjected to third coagulation drawing at concentrations of 30%, 20%, and 10%, temperatures of 30°C, 40°C, and 50°C, and draw ratios of 1.0, 1.1, and 1.2, respectively; After performing the fourth high-temperature water drawing at temperatures of 95℃, 96℃, 97℃, and 99℃, and draw ratios of 1.35, 1.50, 1.70, and 2.00, respectively, six washing processes were performed at temperatures of 70℃, 70℃, 80℃, 80℃, 90℃, and 90℃, respectively, and the swelling degree of the fiber after washing was 90%.

After washing, the fibers first passed through a primary oiling tank containing TFA-1208-10 nonionic non-silicone emulsion synthesized by Tianjin Institute of Technology Textile Auxiliary Co., Ltd., which has a pH of 7.2, an emulsion concentration of 1.5%, an emulsion particle size of 100 nm, with a residence time of 0.15 s, and then passed through a secondary oiling tank containing JSYJ-10 nonionic silicone-containing emulsion synthesized by China Petrochemical (Shanghai) Petrochemical Research Institute, which has a pH of 7.8, an emulsion concentration of 1.2%, an emulsion particle size of 100 nm, and an emulsion silicone content of 0.15%, with a residence time of 0.1 s.

Afterwards, a four-step dry densification treatment was performed at temperatures of 90℃, 100℃, 115℃, and 130℃, respectively, followed by steam drawing at a draw ratio of 3.0 times and a steam pressure of 0.35 MPa; and finally, thermoforming was performed at a draw ratio of 0.95 and a steam pressure of 120 MPa, followed by winding, to obtain polyacrylonitrile carbon fiber yarn.

The linear density of the yarn is 0.85 dtex, the oil content is 1.4%, and the silicon content is 0.16%. The Si/C ratio in the region from the top of the protrusions on the fiber surface to 2 μm inward is 12%, and the Si/C ratio in the region greater than 2 μm is 0.12%; the tensile strength, initial modulus, and elongation at break are 7.5 cN/dtex, 134 cN/dtex, and 11.7%, respectively.

2. Production of carbon fiber: The yarn obtained in step 1 was pre-oxidized at 180-260°C with a pre-oxidation total draw ratio of 0.95 times to obtain pre-oxidized fiber; then low-temperature carbonization and high-temperature carbonization were performed at 300-750°C and 800-1500°C with a draw ratio of 0.96 times; then graphitization was performed at 2800°C, and finally, carbon fiber was obtained through surface treatment, washing, sizing, drying at 120°C, and winding.

The total silicon content of the carbon fiber is 900 ppm, the Si/C ratio of the region X between the top of the protrusion on the fiber surface and the bottom of the groove is 6%, the Si/C ratio of the region Y between the bottom of the groove and the inner side 100 nm is 0.63%, and the Si/C ratio of the region Z greater than 100 nm is 0.04%. The number of pores on the surface of the carbon fiber is 12, the average length of the pores is 26 nm, and the average width is 16 nm. The pore orientation deviation angle along the fiber axis obtained by small-angle X-ray scattering is 2.5°. The tensile strength of the carbon fiber is 5.7 GPa, the tensile modulus is 377 GPa, and the elongation at break is 1.52%. After 7 months of continuous production, the carbon fiber strength began to decrease, the operation was stopped, and the ash in the equipment was cleaned once.

[Example 13]

1. Production of yarn: A wet spinning method was adopted, and a spinning solution obtained by copolymerizing acrylonitrile and itaconic acid in dimethyl sulfoxide was used (characteristic viscosity 2.5 dL/g, solid content 18%). The spinning solution was accurately measured through a metering pump, filtered, and then extruded through a spinning plate with 6000 holes and a hole diameter of 60 μm, and entered into a first coagulation bath containing a dimethyl sulfoxide aqueous solution, and solidified at a coagulation temperature of 28°C and a concentration of 51.5%, and then subjected to third coagulation drawing at concentrations of 30%, 20%, and 10%, temperatures of 30°C, 40°C, and 50°C, and draw ratios of 1.0, 1.1, and 1.2, respectively; After performing the fourth high-temperature water drawing at temperatures of 95℃, 96℃, 97℃, and 99℃, and draw ratios of 1.35, 1.50, 1.70, and 2.00, respectively, six washing processes were performed at temperatures of 70℃, 70℃, 80℃, 80℃, 90℃, and 90℃, respectively, and the swelling degree of the fiber after washing was 110%.

After washing, the fibers first passed through a first oiling tank containing a nonionic, non-silicone emulsion with a pH of 8, an emulsion concentration of 1.5%, and an emulsion particle size of 300 nm with a residence time of 0.15 s, and then passed through a second oiling tank containing a nonionic, silicone-containing emulsion with a pH of 9, an emulsion concentration of 1.2%, an emulsion particle size of 300 nm, and an emulsion silicon content of 0.15% with a residence time of 0.1 s.

Afterwards, a four-step dry densification treatment was performed at temperatures of 90℃, 100℃, 115℃, and 130℃, respectively, followed by steam drawing at a draw ratio of 3.0 times and a steam pressure of 0.35 MPa; and finally, thermoforming was performed at a draw ratio of 0.95 and a steam pressure of 120 MPa, followed by winding, to obtain polyacrylonitrile carbon fiber yarn.

The linear density of the yarn is 0.85 dtex, the oil content is 1.2%, and the silicon content is 0.14%. The Si/C ratio in the region from the top of the protrusions on the fiber surface to 2 μm inward is 9%, and the Si/C ratio in the region greater than 2 μm is 0.11%; the tensile strength, initial modulus, and elongation at break are 7.7 cN/dtex, 135 cN/dtex, and 11.5%, respectively.

2. Production of carbon fiber: The yarn obtained in step 1 was pre-oxidized at 180-260°C with a pre-oxidation total draw ratio of 0.95 times to obtain pre-oxidized fiber; then low-temperature carbonization and high-temperature carbonization were performed at 300-750°C and 800-1500°C with a draw ratio of 0.96 times; then graphitization was performed at 2800°C, and finally, carbon fiber was obtained through surface treatment, washing, sizing, drying at 120°C, and winding.

The total silicon content of the carbon fiber is 700 ppm, the Si/C ratio of the region X between the top of the protrusion on the fiber surface and the bottom of the groove is 5%, the Si/C ratio of the region Y between the bottom of the groove and the inner side 100 nm is 0.55%, and the Si/C ratio of the region Z greater than 100 nm is 0.04%. The number of pores on the surface of the carbon fiber is 8, the average length of the pores is 17 nm, and the average width is 13 nm. The pore orientation deviation angle along the fiber axis obtained by small-angle X-ray scattering is 2.2°. The tensile strength of the carbon fiber is 5.75 GPa, the tensile modulus is 375 GPa, and the elongation at break is 1.51%. After 8 months of continuous production, the carbon fiber strength began to decrease, the operation was stopped, and the ash in the equipment was cleaned once.

[Comparative Example 1]

1. Production of yarn: A wet spinning method was adopted, and a spinning solution obtained by copolymerizing acrylonitrile and itaconic acid in dimethyl sulfoxide was used (characteristic viscosity 2.5 dL/g, solid content 18%). The spinning solution was accurately measured through a metering pump, filtered, and then extruded through a spinning plate with 6000 holes and a hole diameter of 60 μm, and introduced into a first coagulation bath containing a dimethyl sulfoxide aqueous solution, and solidified at a coagulation temperature of 28°C and a concentration of 51.5%, and then subjected to third coagulation drawing at concentrations of 30%, 20%, and 10%, temperatures of 30°C, 40°C, and 50°C, and draw ratios of 1.0, 1.1, and 1.2, respectively; After performing the fourth high-temperature water drawing at temperatures of 95℃, 96℃, 97℃, and 99℃, and draw ratios of 1.35, 1.50, 1.70, and 2.00, respectively, six washing processes were performed at temperatures of 70℃, 70℃, 80℃, 80℃, 90℃, and 90℃, respectively, and the swelling degree of the fiber after washing was 110%.

After washing, the fibers first passed through a first oiling tank containing a nonionic silicone-containing emulsion with a pH of 7.8, an emulsion concentration of 1.5%, and a particle size of 300 nm, with a residence time of 0.15 s, and then passed through a second oiling tank containing a nonionic silicone-containing emulsion with a pH of 7.8, an emulsion concentration of 1.2%, an emulsion particle size of 300 nm, and a silicone content of 0.15%, with a residence time of 0.1 s.

Afterwards, a four-step dry densification treatment was performed at temperatures of 90℃, 100℃, 115℃, and 130℃, respectively, followed by steam drawing at a draw ratio of 3.0 times and a steam pressure of 0.35 MPa; and finally, thermoforming was performed at a draw ratio of 0.95 and a steam pressure of 120 MPa, followed by winding, to obtain polyacrylonitrile carbon fiber yarn.

The linear density of the yarn is 0.85 dtex, the oil content is 3%, and the silicon content is 0.67%. The Si/C ratio in the region from the top of the protrusions on the fiber surface to 2 μm inward is 34%, and the Si/C ratio in the region greater than 2 μm is 0.5%; the tensile strength, initial modulus, and elongation at break are 8.1 cN/dtex, 131 cN/dtex, and 11.9%, respectively.

2. Production of carbon fiber: The yarn obtained in step 1 was pre-oxidized at 180-260°C with a pre-oxidation total draw ratio of 0.95 times to obtain pre-oxidized fiber; then low-temperature carbonization and high-temperature carbonization were performed at 300-750°C and 800-1500°C with a draw ratio of 0.96 times; then graphitization was performed at 2800°C, and finally, carbon fiber was obtained through surface treatment, washing, sizing, drying at 120°C, and winding.

The total silicon content of the carbon fiber is 3000 ppm, the Si/C ratio of the region X between the top of the protrusion on the fiber surface and the bottom of the groove is 77%, the Si/C ratio of the region Y between the bottom of the groove and the inner side 100 nm is 20%, and the Si/C ratio of the region Z greater than 100 nm is 2%. The number of pores on the surface of the carbon fiber is 40, the average length of the pores is 70 nm, and the average width is 45 nm. The pore orientation deviation angle along the fiber axis obtained by small-angle X-ray scattering is 4.1°. The tensile strength of the carbon fiber is 5.23 GPa, the tensile modulus is 355 GPa, and the elongation at break is 1.46%. After 2.5 months of continuous production, the carbon fiber strength began to decrease, the operation was stopped, and the ash in the equipment was cleaned once.

[Comparative Example 2]

1. Production of yarn: A wet spinning method was adopted, and a spinning solution obtained by copolymerizing acrylonitrile and itaconic acid in dimethyl sulfoxide was used (characteristic viscosity 2.5 dL/g, solid content 18%). The spinning solution was accurately measured through a metering pump, filtered, and then extruded through a spinning plate with 6000 holes and a hole diameter of 60 μm, and entered into a first coagulation bath containing a dimethyl sulfoxide aqueous solution, and solidified at a coagulation temperature of 28°C and a concentration of 51.5%, and then subjected to third coagulation drawing at concentrations of 30%, 20%, and 10%, temperatures of 30°C, 40°C, and 50°C, and draw ratios of 1.0, 1.1, and 1.2, respectively; After performing the fourth high-temperature water drawing at temperatures of 95℃, 96℃, 97℃, and 99℃, and draw ratios of 1.35, 1.50, 1.70, and 2.00, respectively, six washing processes were performed at temperatures of 70℃, 70℃, 80℃, 80℃, 90℃, and 90℃, respectively, and the swelling degree of the fiber after washing was 110%.

After washing, the fibers first passed through a primary oiling tank containing water with a pH of 7 with a residence time of 0.15 s, and then passed through a secondary oiling tank containing a nonionic silicone-containing emulsion with a pH of 7.8, an emulsion concentration of 1.2%, an emulsion particle size of 300 nm, and a silicone content of 0.15% with a residence time of 0.1 s.

Afterwards, a four-step dry densification treatment was performed at temperatures of 90℃, 100℃, 115℃, and 130℃, respectively, followed by steam drawing at a draw ratio of 3.0 times and a steam pressure of 0.35 MPa; and finally, thermoforming was performed at a draw ratio of 0.95 and a steam pressure of 120 MPa, followed by winding, to obtain polyacrylonitrile carbon fiber yarn.

The linear density of the yarn is 0.85 dtex, the oil content is 2.8%, and the silicon content is 0.55%. The Si/C ratio in the region from the top of the protrusions on the fiber surface to 2 μm inward is 24%, and the Si/C ratio in the region greater than 2 μm is 0.19%; the tensile strength, initial modulus, and elongation at break are 7.9 cN/dtex, 131 cN/dtex, and 11.5%, respectively.

2. Production of carbon fiber: The yarn obtained in step 1 was pre-oxidized at 180-260°C with a pre-oxidation total draw ratio of 0.95 times to obtain pre-oxidized fiber; then low-temperature carbonization and high-temperature carbonization were performed at 300-750°C and 800-1500°C with a draw ratio of 0.96 times; then graphitization was performed at 2800°C, and finally, carbon fiber was obtained through surface treatment, washing, sizing, drying at 120°C, and winding.

The total silicon content of the carbon fiber is 2600 ppm, the Si/C ratio of the region X between the top of the protrusion on the fiber surface and the bottom of the groove is 72%, the Si/C ratio of the region Y between the bottom of the groove and 100 nm inward is 18%, and the Si/C ratio of the region Z greater than 100 nm is 1.8%. The number of pores on the surface of the carbon fiber is 39, the average length of the pores is 66 nm, and the average width is 45 nm. The pore orientation deviation angle along the fiber axis obtained by small-angle X-ray scattering is 3.8°. The tensile strength of the carbon fiber is 5.35 GPa, the tensile modulus is 357 GPa, and the elongation at break is 1.48%. After 3 months of continuous production, the carbon fiber strength began to decrease, the operation was stopped, and the ash in the equipment was cleaned once.

[Comparative Example 3]

1. Production of yarn: A wet spinning method was adopted, and a spinning solution obtained by copolymerizing acrylonitrile and itaconic acid in dimethyl sulfoxide was used (characteristic viscosity 2.5 dL/g, solid content 18%). The spinning solution was accurately measured through a metering pump, filtered, and then extruded through a spinning plate with 6000 holes and a hole diameter of 60 μm, and entered into a first coagulation bath containing a dimethyl sulfoxide aqueous solution, and solidified at a coagulation temperature of 28°C and a concentration of 51.5%, and then subjected to third coagulation drawing at concentrations of 30%, 20%, and 10%, temperatures of 30°C, 40°C, and 50°C, and draw ratios of 1.0, 1.1, and 1.2, respectively; After performing the fourth high-temperature water drawing at temperatures of 95℃, 96℃, 97℃, and 99℃, and draw ratios of 1.35, 1.50, 1.70, and 2.00, respectively, six washing processes were performed at temperatures of 70℃, 70℃, 80℃, 80℃, 90℃, and 90℃, respectively, and the swelling degree of the fiber after washing was 110%.

After washing, the fibers first passed through a first oiling tank containing a nonionic, non-silicone emulsion with a pH of 8, an emulsion concentration of 1.5%, and a particle size of 300 nm inside the tank with a residence time of 0.15 s, and then passed through a second oiling tank containing a nonionic, silicone-containing emulsion with a pH of 6, an emulsion concentration of 1.2%, an emulsion particle size of 300 nm, and a silicone content of 0.15% inside the tank with a residence time of 0.1 s.

Afterwards, a four-step dry densification treatment was performed at temperatures of 90℃, 100℃, 115℃, and 130℃, respectively, followed by steam drawing at a draw ratio of 3.0 times and a steam pressure of 0.35 MPa; and finally, thermoforming was performed at a draw ratio of 0.95 and a steam pressure of 120 MPa, followed by winding, to obtain polyacrylonitrile carbon fiber yarn.

The linear density of the yarn is 0.85 dtex, the oil content is 3.1%, and the silicon content is 0.68%. The Si/C ratio in the area from the top of the protrusions on the fiber surface to the inside of 2 μm is 35%, and the Si/C ratio in the area greater than 2 μm is 0.5%; the tensile strength, initial modulus, and elongation at break are 7.5 cN/dtex, 128 cN/dtex, and 11.3%, respectively.

2. Production of carbon fiber: The yarn obtained in step 1 was pre-oxidized at 180-260°C with a pre-oxidation total draw ratio of 0.95 times to obtain pre-oxidized fiber; then low-temperature carbonization and high-temperature carbonization were performed at 300-750°C and 800-1500°C with a draw ratio of 0.96 times; then graphitization was performed at 2800°C, and finally, carbon fiber was obtained through surface treatment, washing, sizing, drying at 120°C, and winding.

The total silicon content of the carbon fiber is 3200 ppm, the Si/C ratio of the region X between the top of the protrusion on the fiber surface and the bottom of the groove is 80%, the Si/C ratio of the region Y between the bottom of the groove and the inner side 100 nm is 13%, and the Si/C ratio of the region Z greater than 100 nm is 1.5%. The number of pores on the surface of the carbon fiber is 50, the average length of the pores is 77 nm, and the average width is 52 nm. The pore orientation deviation angle along the fiber axis obtained by small-angle X-ray scattering is 4.3°. The tensile strength of the carbon fiber is 5.05 GPa, the tensile modulus is 361 GPa, and the elongation at break is 1.39%. After 3 months of continuous production, the carbon fiber strength began to decrease, the operation was stopped, and the ash in the equipment was cleaned once.

[Comparative Example 4]

1. Production of yarn: A wet spinning method was adopted, and a spinning solution obtained by copolymerizing acrylonitrile and itaconic acid in dimethyl sulfoxide was used (characteristic viscosity 2.5 dL/g, solid content 18%). The spinning solution was accurately measured through a metering pump, filtered, and then extruded through a spinning plate with 6000 holes and a hole diameter of 60 μm, and entered into a first coagulation bath containing a dimethyl sulfoxide aqueous solution, and solidified at a coagulation temperature of 28°C and a concentration of 51.5%, and then subjected to third coagulation drawing at concentrations of 30%, 20%, and 10%, temperatures of 30°C, 40°C, and 50°C, and draw ratios of 1.0, 1.1, and 1.2, respectively; After performing the fourth high-temperature water drawing at temperatures of 95℃, 96℃, 97℃, and 99℃, and draw ratios of 1.35, 1.50, 1.70, and 2.00, respectively, six washing processes were performed at temperatures of 70℃, 70℃, 80℃, 80℃, 90℃, and 90℃, respectively, and the swelling degree of the fiber after washing was 110%.

After washing, the fibers first passed through a primary oiling tank containing TFA-1208-Y anionic non-silicone emulsion synthesized by Tianjin Institute of Technology Textile Auxiliary Co., Ltd., which had a pH of 7.2, an emulsion concentration of 1.5%, an emulsion particle size of 300 nm, with a residence time of 0.15 s, and then passed through a secondary oiling tank containing JLQR-Y anionic silicone-containing emulsion synthesized by Jilin Qianren New Material Co., Ltd., which had a pH of 7.8, an emulsion concentration of 1.2%, an emulsion particle size of 300 nm, and an emulsion silicone content of 0.15%, with a residence time of 0.1 s.

Afterwards, a four-step dry densification treatment was performed at temperatures of 90℃, 100℃, 115℃, and 130℃, respectively, followed by steam drawing at a draw ratio of 3.0 times and a steam pressure of 0.35 MPa; and finally, thermoforming was performed at a draw ratio of 0.95 and a steam pressure of 120 MPa, followed by winding, to obtain polyacrylonitrile carbon fiber yarn.

The linear density of the yarn is 0.85 dtex, the oil content is 3.1%, and the silicon content is 0.69%. The Si/C ratio in the region from the top of the protrusions on the fiber surface to 2 μm inward is 35%, and the Si/C ratio in the region greater than 2 μm is 0.5%; the tensile strength, initial modulus, and elongation at break are 7.5 cN/dtex, 129 cN/dtex, and 11.3%, respectively.

2. Production of carbon fiber: The yarn obtained in step 1 was pre-oxidized at 180-260°C with a pre-oxidation total draw ratio of 0.95 times to obtain pre-oxidized fiber; then low-temperature carbonization and high-temperature carbonization were performed at 300-750°C and 800-1500°C with a draw ratio of 0.96 times; then graphitization was performed at 2800°C, and finally, carbon fiber was obtained through surface treatment, washing, sizing, drying at 120°C, and winding.

The total silicon content of the carbon fiber is 3300 ppm, the Si/C ratio of the region X between the top of the protrusion on the fiber surface and the bottom of the groove is 82%, the Si/C ratio of the region Y between the bottom of the groove and the inner side 100 nm is 15%, and the Si/C ratio of the region Z greater than 100 nm is 2%. The number of pores on the surface of the carbon fiber is 56, the average length of the pores is 80 nm, and the average width is 60 nm. The pore orientation deviation angle along the fiber axis obtained by small-angle X-ray scattering is 4.3°. The tensile strength of the carbon fiber is 5 GPa, the tensile modulus is 358 GPa, and the elongation at break is 1.37%. After 3 months of continuous production, the carbon fiber strength began to decrease, the operation was stopped, and the ash in the equipment was cleaned once.

[Comparative Example 5]

1. Production of yarn: A wet spinning method was adopted, and a spinning solution obtained by copolymerizing acrylonitrile and itaconic acid in dimethyl sulfoxide was used (characteristic viscosity 2.5 dL/g, solid content 18%). The spinning solution was accurately measured through a metering pump, filtered, and then extruded through a spinning plate with 6000 holes and a hole diameter of 60 μm, and entered into a first coagulation bath containing a dimethyl sulfoxide aqueous solution, and solidified at a coagulation temperature of 28°C and a concentration of 51.5%, and then subjected to third coagulation drawing at concentrations of 30%, 20%, and 10%, temperatures of 30°C, 40°C, and 50°C, and draw ratios of 1.0, 1.1, and 1.2, respectively; After performing the fourth high-temperature water drawing at temperatures of 95℃, 96℃, 97℃, and 99℃, and draw ratios of 1.35, 1.50, 1.70, and 2.00, respectively, six washing processes were performed at temperatures of 70℃, 70℃, 80℃, 80℃, 90℃, and 90℃, respectively, and the swelling degree of the fiber after washing was 110%.

After washing, the fibers first passed through a first oiling tank containing a nonionic, non-silicone emulsion with a pH of 7.2, an emulsion concentration of 1.5%, and a particle size of 300 nm with a residence time of 0.15 s, and then passed through a second oiling tank containing a nonionic, non-silicone emulsion with a pH of 7.2, an emulsion concentration of 1.2%, an emulsion particle size of 300 nm, and a silicon content of 0.15% with a residence time of 0.1 s.

Afterwards, a four-step dry densification treatment was performed at temperatures of 90℃, 100℃, 115℃, and 130℃, respectively, followed by steam drawing at a draw ratio of 3.0 times and a steam pressure of 0.35 MPa; and finally, thermoforming was performed at a draw ratio of 0.95 and a steam pressure of 120 MPa, followed by winding, to obtain polyacrylonitrile carbon fiber yarn.

The linear density of the yarn is 0.85 dtex, the oil content is 2.6%, and the silicone content is 0%. The Si/C ratio in the region from the top of the protrusions on the fiber surface to 2 μm inward is 0%, and the Si/C ratio in the region greater than 2 μm is 0%; the tensile strength, initial modulus, and elongation at break are 7.2 cN/dtex, 120 cN/dtex, and 11.6%, respectively.

2. Production of carbon fiber: The yarn obtained in step 1 was pre-oxidized at 180-260°C with a pre-oxidation total draw ratio of 0.95 times to obtain pre-oxidized fiber; then low-temperature carbonization and high-temperature carbonization were performed at 300-750°C and 800-1500°C with a draw ratio of 0.96 times; then graphitization was performed at 2800°C, and finally, carbon fiber was obtained through surface treatment, washing, sizing, drying at 120°C, and winding.

The total silicon content in the carbon fiber is 0 ppm, the Si/C ratio in the region X between the top of the protrusion on the fiber surface and the bottom of the groove is 0%, the Si/C ratio in the region Y between the bottom of the groove and 100 nm inward is 0%, and the Si/C ratio in the region Z greater than 100 nm is 0%. The number of pores in the carbon fiber surface layer is 64, the average length of the pores is 89 nm, and the average width is 71 nm. The pore orientation deviation angle along the fiber axis obtained by small-angle X-ray scattering is 4.8°. The tensile strength of the carbon fiber is 4.6 GPa, the tensile modulus is 340 GPa, and the elongation at break is 1.35%. After 7 months of continuous production, the carbon fiber strength began to decrease, the operation was stopped, and the ash in the equipment was cleaned once.

[Comparative Example 6]

1. Production of yarn: A wet spinning method was adopted, and a spinning solution obtained by copolymerizing acrylonitrile and itaconic acid in dimethyl sulfoxide was used (characteristic viscosity 2.5 dL/g, solid content 18%). The spinning solution was accurately measured through a metering pump, filtered, and then extruded through a spinning plate with 6000 holes and a hole diameter of 60 μm, and entered into a first coagulation bath containing a dimethyl sulfoxide aqueous solution, and solidified at a coagulation temperature of 28°C and a concentration of 51.5%, and then subjected to third coagulation drawing at concentrations of 30%, 20%, and 10%, temperatures of 30°C, 40°C, and 50°C, and draw ratios of 1.0, 1.1, and 1.2, respectively; After performing the fourth high-temperature water drawing at temperatures of 95℃, 96℃, 97℃, and 99℃, and draw ratios of 1.35, 1.50, 1.70, and 2.00, respectively, six washing processes were performed at temperatures of 70℃, 70℃, 80℃, 80℃, 90℃, and 90℃, respectively, and the swelling degree of the fiber after washing was 110%.

After washing, the fibers first passed through a first oiling tank containing a nonionic, non-silicone emulsion with a pH of 7.2, an emulsion concentration of 6%, and an emulsion particle size of 300 nm with a residence time of 0.15 s, and then passed through a second oiling tank containing a nonionic, silicone-containing emulsion with a pH of 7.8, an emulsion concentration of 2%, an emulsion particle size of 300 nm, and an emulsion silicon content of 0.3% with a residence time of 0.1 s.

Afterwards, a four-step dry densification treatment was performed at temperatures of 90℃, 100℃, 115℃, and 130℃, respectively, followed by steam drawing at a draw ratio of 3.0 times and a steam pressure of 0.35 MPa; and finally, thermoforming was performed at a draw ratio of 0.95 and a steam pressure of 120 MPa, followed by winding, to obtain polyacrylonitrile carbon fiber yarn.

The linear density of the yarn is 0.85 dtex, the oil content is 2.6%, and the silicon content is 0.01%. The Si/C ratio in the region from the top of the protrusions on the fiber surface to the inside of 2 μm is 0.8%, and the Si/C ratio in the region greater than 2 μm is 0.09%; the tensile strength, initial modulus, and elongation at break are 7.4 cN/dtex, 127 cN/dtex, and 11.6%, respectively.

2. Production of carbon fiber: The yarn obtained in step 1 was pre-oxidized at 180-260°C with a pre-oxidation total draw ratio of 0.95 times to obtain pre-oxidized fiber; then low-temperature carbonization and high-temperature carbonization were performed at 300-750°C and 800-1500°C with a draw ratio of 0.96 times; then graphitization was performed at 2800°C, and finally, carbon fiber was obtained through surface treatment, washing, sizing, drying at 120°C, and winding.

The total silicon content of the carbon fiber is 400 ppm, the Si/C ratio of region X between the top of the protrusion on the fiber surface and the bottom of the groove is 0.8%, the Si/C ratio of region Y between the bottom of the groove and the inner side 100 nm is 0.07%, and the Si/C ratio of region Z greater than 100 nm is 0.01%. The number of pores on the surface of the carbon fiber is 58, the average length of the pores is 75 nm, and the average width is 50 nm. The pore orientation deviation angle along the fiber axis obtained by small-angle X-ray scattering is 4.5°. The tensile strength of the carbon fiber is 4.92 GPa, the tensile modulus is 367 GPa, and the elongation at break is 1.32%. After 6 months of continuous production, the carbon fiber strength began to decrease, the operation was stopped, and the ash in the equipment was cleaned once.

[Comparative Example 7]

1. Production of yarn: A wet spinning method was adopted, and a spinning solution obtained by copolymerizing acrylonitrile and itaconic acid in dimethyl sulfoxide was used (characteristic viscosity 2.5 dL/g, solid content 18%). The spinning solution was accurately measured through a metering pump, filtered, and then extruded through a spinning plate with 6000 holes and a hole diameter of 60 μm, and entered into a first coagulation bath containing a dimethyl sulfoxide aqueous solution, and solidified at a coagulation temperature of 28°C and a concentration of 51.5%, and then subjected to third coagulation drawing at concentrations of 30%, 20%, and 10%, temperatures of 30°C, 40°C, and 50°C, and draw ratios of 1.0, 1.1, and 1.2, respectively; After performing the fourth high-temperature water drawing at temperatures of 95℃, 96℃, 97℃, and 99℃, and draw ratios of 1.35, 1.50, 1.70, and 2.00, respectively, six washing processes were performed at temperatures of 70℃, 70℃, 80℃, 80℃, 90℃, and 90℃, respectively, and the swelling degree of the fiber after washing was 110%.

After washing, the fibers first passed through a first oiling tank containing a nonionic, non-silicone emulsion with a pH of 7.2, an emulsion concentration of 3.5%, and an emulsion particle size of 300 nm with a residence time of 0.15 s, and then passed through a second oiling tank containing a nonionic, silicone-containing emulsion with a pH of 7.8, an emulsion concentration of 6%, an emulsion particle size of 300 nm, and an emulsion particle size of 1% with a residence time of 0.1 s.

Afterwards, a four-step dry densification treatment was performed at temperatures of 90℃, 100℃, 115℃, and 130℃, respectively, followed by steam drawing at a draw ratio of 3.0 times and a steam pressure of 0.35 MPa; and finally, thermoforming was performed at a draw ratio of 0.95 and a steam pressure of 120 MPa, followed by winding, to obtain polyacrylonitrile carbon fiber yarn.

The linear density of the yarn is 0.85 dtex, the oil content is 2.7%, and the silicon content is 0.53%. The Si/C ratio in the region from the top of the protrusions on the fiber surface to 2 μm inward is 23%, and the Si/C ratio in the region greater than 2 μm is 0.19%; the tensile strength, initial modulus, and elongation at break are 7.7 cN/dtex, 136 cN/dtex, and 11.3%, respectively.

2. Production of carbon fiber: The yarn obtained in step 1 was pre-oxidized at 180-260°C with a pre-oxidation total draw ratio of 0.95 times to obtain pre-oxidized fiber; then low-temperature carbonization and high-temperature carbonization were performed at 300-750°C and 800-1500°C with a draw ratio of 0.96 times; then graphitization was performed at 2800°C, and finally, carbon fiber was obtained through surface treatment, washing, sizing, drying at 120°C, and winding.

The total silicon content of the carbon fiber is 2400 ppm, the Si/C ratio of the region X between the top of the protrusion on the fiber surface and the bottom of the groove is 48%, the Si/C ratio of the region Y between the bottom of the groove and the inner side 100 nm is 15%, and the Si/C ratio of the region Z greater than 100 nm is 1%. The number of pores on the surface of the carbon fiber is 38, the average length of the pores is 65 nm, and the average width is 44 nm. The pore orientation deviation angle along the fiber axis obtained by small-angle X-ray scattering is 3.9°. The tensile strength of the carbon fiber is 5.3 GPa, the tensile modulus is 354 GPa, and the elongation at break is 1.47%. After 3 months of continuous production, the carbon fiber strength began to decrease, the operation was stopped, and the ash in the equipment was cleaned once.

[Comparative Example 8]

1. Production of yarn: A wet spinning method was adopted, and a spinning solution obtained by copolymerizing acrylonitrile and itaconic acid in dimethyl sulfoxide was used (characteristic viscosity 2.5 dL/g, solid content 18%). The spinning solution was accurately measured through a metering pump, filtered, and then extruded through a spinning plate with 6000 holes and a hole diameter of 60 μm, and entered into a first coagulation bath containing a dimethyl sulfoxide aqueous solution, and solidified at a coagulation temperature of 28°C and a concentration of 51.5%, and then subjected to third coagulation drawing at concentrations of 30%, 20%, and 10%, temperatures of 30°C, 40°C, and 50°C, and draw ratios of 1.0, 1.1, and 1.2, respectively; After performing the fourth high-temperature water drawing at temperatures of 95℃, 96℃, 97℃, and 99℃, and draw ratios of 1.35, 1.50, 1.70, and 2.00, respectively, six washing processes were performed at temperatures of 70℃, 70℃, 80℃, 80℃, 90℃, and 90℃, respectively, and the swelling degree of the fiber after washing was 110%.

After washing, the fibers first passed through a first oiling tank containing a nonionic, non-silicone emulsion with a pH of 7.2, an emulsion concentration of 1.5%, and a particle size of 300 nm with a residence time of 0.25 s, and then passed through a second oiling tank containing a nonionic, silicone-containing emulsion with a pH of 7.8, an emulsion concentration of 1.2%, an emulsion particle size of 300 nm, and a silicone content of 0.15% with a residence time of 0.3 s.

Afterwards, a four-step dry densification treatment was performed at temperatures of 90℃, 100℃, 115℃, and 130℃, respectively, followed by steam drawing at a draw ratio of 3.0 times and a steam pressure of 0.35 MPa; and finally, thermoforming was performed at a draw ratio of 0.95 and a steam pressure of 120 MPa, followed by winding, to obtain polyacrylonitrile carbon fiber yarn.

The linear density of the yarn is 0.85 dtex, the oil content is 2.7%, and the silicon content is 0.55%. The Si/C ratio in the region from the top of the protrusions on the fiber surface to the inside of 2 μm is 26%, and the Si/C ratio in the region greater than 2 μm is 0.25%; the tensile strength, initial modulus, and elongation at break are 7.6 cN/dtex, 132 cN/dtex, and 11.5%, respectively.

2. Production of carbon fiber: The yarn obtained in step 1 was pre-oxidized at 180-260°C with a pre-oxidation total draw ratio of 0.95 times to obtain pre-oxidized fiber; then low-temperature carbonization and high-temperature carbonization were performed at 300-750°C and 800-1500°C with a draw ratio of 0.96 times; then graphitization was performed at 2800°C, and finally, carbon fiber was obtained through surface treatment, washing, sizing, drying at 120°C, and winding.

The total silicon content of the carbon fiber is 2100 ppm, the Si/C ratio of region X between the top of the protrusion on the fiber surface and the bottom of the groove is 48%, the Si/C ratio of region Y between the bottom of the groove and 100 nm inward is 9%, and the Si/C ratio of region Z greater than 100 nm is 1%. The number of pores on the surface of the carbon fiber is 39, the average length of the pores is 66 nm, and the average width is 44 nm. The pore orientation deviation angle along the fiber axis obtained by small-angle X-ray scattering is 4.1°. The tensile strength of the carbon fiber is 5.28 GPa, the tensile modulus is 360 GPa, and the elongation at break is 1.41%. After 3 months of continuous production, the carbon fiber strength began to decrease, the operation was stopped, and the ash in the equipment was cleaned once.

[Comparative Example 9]

1. Production of yarn: A wet spinning method was adopted, and a spinning solution obtained by copolymerizing acrylonitrile and itaconic acid in dimethyl sulfoxide was used (characteristic viscosity 2.5 dL/g, solid content 18%). The spinning solution was accurately measured through a metering pump, filtered, and then extruded through a spinning plate with 6000 holes and a hole diameter of 60 μm, and entered into a first coagulation bath containing a dimethyl sulfoxide aqueous solution, and solidified at a coagulation temperature of 28°C and a concentration of 51.5%, and then subjected to third coagulation drawing at concentrations of 30%, 20%, and 10%, temperatures of 30°C, 40°C, and 50°C, and draw ratios of 1.0, 1.1, and 1.2, respectively; After performing the fourth high-temperature water drawing at temperatures of 95℃, 96℃, 97℃, and 99℃, and draw ratios of 1.35, 1.50, 1.70, and 2.00, respectively, six washing processes were performed at temperatures of 70℃, 70℃, 80℃, 80℃, 90℃, and 90℃, respectively, and the swelling degree of the fiber after washing was 110%.

After washing, the fibers first passed through a first oiling tank containing a nonionic, non-silicone emulsion with a pH of 7.2, an emulsion concentration of 1.5%, and a particle size of 300 nm with a residence time of 0.15 s, and then passed through a second oiling tank containing a nonionic, silicone-containing emulsion with a pH of 7.8, an emulsion concentration of 1.2%, an emulsion particle size of 300 nm, and a silicone content of 0.15% with a residence time of 0.02 s.

Afterwards, a four-step dry densification treatment was performed at temperatures of 90℃, 100℃, 115℃, and 130℃, respectively, followed by steam drawing at a draw ratio of 3.0 times and a steam pressure of 0.35 MPa; and finally, thermoforming was performed at a draw ratio of 0.95 and a steam pressure of 120 MPa, followed by winding, to obtain polyacrylonitrile carbon fiber yarn.

The linear density of the yarn is 0.85 dtex, the oil content is 1%, and the silicon content is 0.01%. The Si/C ratio in the region from the top of the protrusions on the fiber surface to the inside of 2 μm is 0.8%, and the Si/C ratio in the region greater than 2 μm is 0.05%; the tensile strength, initial modulus, and elongation at break are 7.4 cN/dtex, 130 cN/dtex, and 11.4%, respectively.

2. Production of carbon fiber: The yarn obtained in step 1 was pre-oxidized at 180-260°C with a pre-oxidation total draw ratio of 0.95 times to obtain pre-oxidized fiber; then low-temperature carbonization and high-temperature carbonization were performed at 300-750°C and 800-1500°C with a draw ratio of 0.96 times; then graphitization was performed at 2800°C, and finally, carbon fiber was obtained through surface treatment, washing, sizing, drying at 120°C, and winding.

The total silicon content of the carbon fiber is 400 ppm, the Si/C ratio of the region X between the top of the protrusion on the fiber surface and the bottom of the groove is 0.9%, the Si/C ratio of the region Y between the bottom of the groove and the inner side 100 nm is 0.07%, and the Si/C ratio of the region Z greater than 100 nm is 0.01%. The number of pores on the surface of the carbon fiber is 60, the average length of the pores is 87 nm, and the average width is 69 nm. The orientation deviation angle of the pores along the fiber axis obtained by small-angle X-ray scattering is 4.6°. The tensile strength of the carbon fiber is 4.9 GPa, the tensile modulus is 366 GPa, and the elongation at break is 1.31%. After 7 months of continuous production, the carbon fiber strength began to decrease, the operation was stopped, and the ash in the equipment was cleaned once.

[Comparative Example 10]

1. Production of yarn: A wet spinning method was adopted, and a spinning solution obtained by copolymerizing acrylonitrile and itaconic acid in dimethyl sulfoxide was used (characteristic viscosity 2.5 dL/g, solid content 18%). The spinning solution was accurately measured through a metering pump, filtered, and then extruded through a spinning plate with 6000 holes and a hole diameter of 60 μm, and entered into a first coagulation bath containing a dimethyl sulfoxide aqueous solution, and solidified at a coagulation temperature of 28°C and a concentration of 51.5%, and then subjected to third coagulation drawing at concentrations of 30%, 20%, and 10%, temperatures of 30°C, 40°C, and 50°C, and draw ratios of 1.0, 1.1, and 1.2, respectively; After performing the fourth high-temperature water drawing at temperatures of 95℃, 96℃, 97℃, and 99℃, and draw ratios of 1.35, 1.50, 1.70, and 2.00, respectively, six washing processes were performed at temperatures of 70℃, 70℃, 80℃, 80℃, 90℃, and 90℃, respectively, and the swelling degree of the fiber after washing was 110%.

After washing, the fibers first passed through a first oiling tank containing TFA-1208-80 nonionic, non-silicone emulsion synthesized by Tianjin Institute of Technology Textile Auxiliary Co., Ltd., which has a pH of 7.2, an emulsion concentration of 1.5%, an emulsion particle size of 800 nm, with a residence time of 0.15 s, and then passed through a second oiling tank containing a nonionic, silicone-containing emulsion containing pH of 7.8, an emulsion concentration of 1.2%, an emulsion particle size of 300 nm, and a silicone content of 0.15%, with a residence time of 0.1 s.

Afterwards, a four-step dry densification treatment was performed at temperatures of 90℃, 100℃, 115℃, and 130℃, respectively, followed by steam drawing at a draw ratio of 3.0 times and a steam pressure of 0.35 MPa; and finally, thermoforming was performed at a draw ratio of 0.95 and a steam pressure of 120 MPa, followed by winding, to obtain polyacrylonitrile carbon fiber yarn.

The linear density of the yarn is 0.85 dtex, the oil content is 2.6%, and the silicon content is 0.52%. The Si/C ratio in the region from the top of the protrusions on the fiber surface to 2 μm inward is 22%, and the Si/C ratio in the region greater than 2 μm is 0.16%; the tensile strength, initial modulus, and elongation at break are 7.3 cN/dtex, 128 cN/dtex, and 11.5%, respectively.

2. Production of carbon fiber: The yarn obtained in step 1 was pre-oxidized at 180-260°C with a pre-oxidation total draw ratio of 0.95 times to obtain pre-oxidized fiber; then low-temperature carbonization and high-temperature carbonization were performed at 300-750°C and 800-1500°C with a draw ratio of 0.96 times; then graphitization was performed at 2800°C, and finally, carbon fiber was obtained through surface treatment, washing, sizing, drying at 120°C, and winding.

The total silicon content of the carbon fiber is 2000 ppm, the Si/C ratio of the region X between the top of the protrusion on the fiber surface and the bottom of the groove is 45%, the Si/C ratio of the region Y between the bottom of the groove and the inner side 100 nm is 13%, and the Si/C ratio of the region Z greater than 100 nm is 0.08%. The number of pores on the surface of the carbon fiber is 45, the average length of the pores is 60 nm, and the average width is 40 nm. The pore orientation deviation angle along the fiber axis obtained by small-angle X-ray scattering is 5°. The tensile strength of the carbon fiber is 4.8 GPa, the tensile modulus is 350 GPa, and the elongation at break is 1.3%. After 4 months of continuous production, the carbon fiber strength began to decrease, the operation was stopped, and the ash in the equipment was cleaned once.

[Comparative Example 11]

1. Production of yarn: A wet spinning method was adopted, and a spinning solution obtained by copolymerizing acrylonitrile and itaconic acid in dimethyl sulfoxide was used (characteristic viscosity 2.5 dL/g, solid content 18%). The spinning solution was accurately measured through a metering pump, filtered, and then extruded through a spinning plate with 6000 holes and a hole diameter of 60 μm, and entered into a first coagulation bath containing a dimethyl sulfoxide aqueous solution, and solidified at a coagulation temperature of 28°C and a concentration of 51.5%, and then subjected to third coagulation drawing at concentrations of 30%, 20%, and 10%, temperatures of 30°C, 40°C, and 50°C, and draw ratios of 1.0, 1.1, and 1.2, respectively; After performing the fourth high-temperature water drawing at temperatures of 95℃, 96℃, 97℃, and 99℃, and draw ratios of 1.35, 1.50, 1.70, and 2.00, respectively, six washing processes were performed at temperatures of 70℃, 70℃, 80℃, 80℃, 90℃, and 90℃, respectively, and the swelling degree of the fiber after washing was 110%.

After washing, the fibers first passed through a first oiling tank containing TFA-1208-04 nonionic non-silicone emulsion synthesized by Tianjin Institute of Technology Textile Auxiliary Co., Ltd., which has a pH of 7.2, an emulsion concentration of 1.5%, an emulsion particle size of 40 nm, with a residence time of 0.15 s, and then passed through a second oiling tank containing JSYJ-04 nonionic silicone-containing emulsion synthesized by China Petrochemical (Shanghai) Petrochemical Research Institute, which has a pH of 7.8, an emulsion concentration of 1.2%, an emulsion particle size of 40 nm, and an emulsion silicone content of 0.15%, with a residence time of 0.1 s.

Afterwards, a four-step dry densification treatment was performed at temperatures of 90℃, 100℃, 115℃, and 130℃, respectively, followed by steam drawing at a draw ratio of 3.0 times and a steam pressure of 0.35 MPa; and finally, thermoforming was performed at a draw ratio of 0.95 and a steam pressure of 120 MPa, followed by winding, to obtain polyacrylonitrile carbon fiber yarn.

The linear density of the yarn is 0.85 dtex, the oil content is 2.7%, and the silicon content is 0.63%. The Si/C ratio in the region from the top of the protrusions on the fiber surface to the inside of 2 μm is 31%, and the Si/C ratio in the region greater than 2 μm is 0.28%; the tensile strength, initial modulus, and elongation at break are 7.5 cN/dtex, 129 cN/dtex, and 11.3%, respectively.

2. Production of carbon fiber: The yarn obtained in step 1 was pre-oxidized at 180-260°C with a pre-oxidation total draw ratio of 0.95 times to obtain pre-oxidized fiber; then low-temperature carbonization and high-temperature carbonization were performed at 300-750°C and 800-1500°C with a draw ratio of 0.96 times; then graphitization was performed at 2800°C, and finally, carbon fiber was obtained through surface treatment, washing, sizing, drying at 120°C, and winding.

The total silicon content of the carbon fiber is 2500 ppm, the Si/C ratio of the region X between the top of the protrusion on the fiber surface and the bottom of the groove is 50%, the Si/C ratio of the region Y between the bottom of the groove and the inner side 100 nm is 17%, and the Si/C ratio of the region Z greater than 100 nm is 1.3%. The number of pores on the surface of the carbon fiber is 48, the average length of the pores is 69 nm, and the average width is 50 nm. The pore orientation deviation angle along the fiber axis obtained by small-angle X-ray scattering is 4.2°. The tensile strength of the carbon fiber is 5.1 GPa, the tensile modulus is 351 GPa, and the elongation at break is 1.4%. After 3 months of continuous production, the carbon fiber strength began to decrease, the operation was stopped, and the ash in the equipment was cleaned once.

[Comparative Example 12]

1. Production of yarn: A wet spinning method was adopted, and a spinning solution obtained by copolymerizing acrylonitrile and itaconic acid in dimethyl sulfoxide was used (characteristic viscosity 2.5 dL/g, solid content 18%). The spinning solution was accurately measured through a metering pump, filtered, and then extruded through a spinning plate with 6000 holes and a hole diameter of 60 μm, and entered into a first coagulation bath containing a dimethyl sulfoxide aqueous solution, and solidified at a coagulation temperature of 28°C and a concentration of 51.5%, and then subjected to third coagulation drawing at concentrations of 30%, 20%, and 10%, temperatures of 30°C, 40°C, and 50°C, and draw ratios of 1.0, 1.1, and 1.2, respectively; After performing the fourth high-temperature water drawing at temperatures of 95℃, 96℃, 97℃, and 99℃, and draw ratios of 1.35, 1.50, 1.70, and 2.00, respectively, six washing processes were performed at temperatures of 70℃, 70℃, 80℃, 80℃, 90℃, and 90℃, respectively, and the swelling degree of the fiber after washing was 110%.

After washing, the fibers first passed through a first oiling tank containing a nonionic, non-silicone emulsion with a pH of 7.2, an emulsion concentration of 1.5%, and an emulsion particle size of 300 nm with a residence time of 0.15 s, and then passed through a second oiling tank containing a nonionic, silicone-containing emulsion with a pH of 7.8, an emulsion concentration of 6%, an emulsion particle size of 300 nm, and an emulsion particle size of 1% with a residence time of 0.1 s.

Afterwards, a four-step dry densification treatment was performed at temperatures of 90℃, 100℃, 115℃, and 130℃, respectively, followed by steam drawing at a draw ratio of 3.0 times and a steam pressure of 0.35 MPa; and finally, thermoforming was performed at a draw ratio of 0.95 and a steam pressure of 120 MPa, followed by winding, to obtain polyacrylonitrile carbon fiber yarn.

The linear density of the yarn is 0.85 dtex, the oil content is 2.7%, and the silicon content is 0.16%. The Si/C ratio in the region from the top of the protrusions on the fiber surface to 2 μm inward is 12%, and the Si/C ratio in the region greater than 2 μm is 0.12%; the tensile strength, initial modulus, and elongation at break are 7.8 cN/dtex, 130 cN/dtex, and 11.5%, respectively.

2. Production of carbon fiber: The yarn obtained in step 1 was pre-oxidized at 180-260°C with a pre-oxidation total draw ratio of 0.95 times to obtain pre-oxidized fiber; then low-temperature carbonization and high-temperature carbonization were performed at 300-750°C and 800-1500°C with a draw ratio of 0.96 times; then graphitization was performed at 2800°C, and finally, carbon fiber was obtained through surface treatment, washing, sizing, drying at 120°C, and winding.

The total silicon content of the carbon fiber is 1750 ppm, the Si/C ratio of the region X between the top of the protrusion on the fiber surface and the bottom of the groove is 30%, the Si/C ratio of the region Y between the bottom of the groove and the inner side 100 nm is 2.8%, and the Si/C ratio of the region Z greater than 100 nm is 0.07%. The number of pores on the surface of the carbon fiber is 36, the average length of the pores is 64 nm, and the average width is 30 nm. The pore orientation deviation angle along the fiber axis obtained by small-angle X-ray scattering is 3.6°. The tensile strength of the carbon fiber is 5.35 GPa, the tensile modulus is 356 GPa, and the elongation at break is 1.47%. After 3 months of continuous production, the carbon fiber strength began to decrease, the operation was stopped, and the ash in the equipment was cleaned once.

[Comparative Example 13]

1. Production of yarn: A wet spinning method was adopted, and a spinning solution obtained by copolymerizing acrylonitrile and itaconic acid in dimethyl sulfoxide was used (characteristic viscosity 2.5 dL/g, solid content 18%). The spinning solution was accurately measured through a metering pump, filtered, and then extruded through a spinning plate with 6000 holes and a hole diameter of 60 μm, and entered into a first coagulation bath containing a dimethyl sulfoxide aqueous solution, and solidified at a coagulation temperature of 28°C and a concentration of 51.5%, and then subjected to third coagulation drawing at concentrations of 30%, 20%, and 10%, temperatures of 30°C, 40°C, and 50°C, and draw ratios of 1.0, 1.1, and 1.2, respectively; After performing the fourth high-temperature water drawing at temperatures of 95℃, 96℃, 97℃, and 99℃, and draw ratios of 1.35, 1.50, 1.70, and 2.00, respectively, six washing processes were performed at temperatures of 70℃, 70℃, 80℃, 80℃, 90℃, and 90℃, respectively, and the swelling degree of the fiber after washing was 110%.

After washing, the fibers first passed through a first oiling tank containing a nonionic, non-silicone emulsion with a pH of 7.2, an emulsion concentration of 1.5%, and a particle size of 300 nm inside the tank with a residence time of 0.15 s, and then underwent a four-stage drying densification treatment at temperatures of 90°C, 100°C, 115°C, and 130°C, respectively, and then passed through a second oiling tank containing a nonionic, silicone-containing emulsion with a pH of 7.8, an emulsion concentration of 1.2%, a particle size of 300 nm, and a silicone content of 0.15% inside the tank with a residence time of 0.1 s.

Afterwards, a four-step dry densification treatment was performed at temperatures of 90℃, 100℃, 115℃, and 130℃, respectively, followed by steam drawing at a draw ratio of 3.0 times and a steam pressure of 0.35 MPa; and finally, thermoforming was performed at a draw ratio of 0.95 and a steam pressure of 120 MPa, followed by winding, thereby obtaining polyacrylonitrile carbon fiber yarn.

The linear density of the yarn is 0.85 dtex, the oil content is 2%, and the silicon content is 0.15%. The Si/C ratio in the area from the top of the protrusions on the fiber surface to the inside of 2 μm is 0.5%, and the Si/C ratio in the area greater than 2 μm is 0.05%; the tensile strength, initial modulus, and elongation at break are 7.6 cN/dtex, 132 cN/dtex, and 11.5%, respectively.

2. Production of carbon fiber: The yarn obtained in step 1 was pre-oxidized at 180-260°C with a pre-oxidation total draw ratio of 0.95 times to obtain pre-oxidized fiber; then low-temperature carbonization and high-temperature carbonization were performed at 300-750°C and 800-1500°C with a draw ratio of 0.96 times; then graphitization was performed at 2800°C, and finally, carbon fiber was obtained through surface treatment, washing, sizing, drying at 120°C, and winding.

The total silicon content of the carbon fiber is 450 ppm, the Si/C ratio of region X between the top of the protrusion on the fiber surface and the bottom of the groove is 0.9%, the Si/C ratio of region Y between the bottom of the groove and 100 nm inward is 0.03%, and the Si/C ratio of region Z greater than 100 nm is 0.01%. The number of pores on the surface of the carbon fiber is 43, the average length of the pores is 67 nm, and the average width is 41 nm. The pore orientation deviation angle along the fiber axis obtained by small-angle X-ray scattering is 4.1°. The tensile strength of the carbon fiber is 5.16 GPa, the tensile modulus is 359 GPa, and the elongation at break is 1.42%. After 6 months of continuous production, the carbon fiber strength began to decrease, the operation was stopped, and the ash in the equipment was cleaned once.

[Comparative Example 14]

1. Production of yarn: A wet spinning method was adopted, and a spinning solution obtained by copolymerizing acrylonitrile and itaconic acid in dimethyl sulfoxide was used (characteristic viscosity 2.5 dL/g, solid content 18%). The spinning solution was accurately measured through a metering pump, filtered, and then extruded through a spinning plate with 6000 holes and a hole diameter of 60 μm, and entered into a first coagulation bath containing a dimethyl sulfoxide aqueous solution, and solidified at a coagulation temperature of 28°C and a concentration of 51.5%, and then subjected to third coagulation drawing at concentrations of 30%, 20%, and 10%, temperatures of 30°C, 40°C, and 50°C, and draw ratios of 1.0, 1.1, and 1.2, respectively; After performing the fourth high-temperature water drawing at temperatures of 95℃, 96℃, 97℃, and 99℃, and at draw ratios of 1.10, 1.15, 1.15, and 1.2, respectively, six washing processes were performed at temperatures of 70℃, 70℃, 80℃, 80℃, 90℃, and 90℃, respectively, and the swelling degree of the fiber after washing was 170%.

After washing, the fibers first passed through a first oiling tank containing a nonionic, non-silicone emulsion with a pH of 7.2, an emulsion concentration of 1.5%, and a particle size of 300 nm with a residence time of 0.15 s, and then passed through a second oiling tank containing a nonionic, silicone-containing emulsion with a pH of 7.8, an emulsion concentration of 1.2%, an emulsion particle size of 300 nm, and a silicone content of 0.15% with a residence time of 0.1 s.

Afterwards, a four-step dry densification treatment was performed at temperatures of 90℃, 100℃, 115℃, and 130℃, respectively, followed by steam drawing at a draw ratio of 3.0 times and a steam pressure of 0.35 MPa; and finally, thermoforming was performed at a draw ratio of 0.95 and a steam pressure of 120 MPa, followed by winding, thereby obtaining polyacrylonitrile carbon fiber yarn.

The linear density of the yarn is 0.9 dtex, the oil content is 3.3%, and the silicon content is 0.74%. The Si/C ratio in the region from the top of the protrusions on the fiber surface to 2 μm inward is 46%, and the Si/C ratio in the region greater than 2 μm is 0.69%; the tensile strength, initial modulus, and elongation at break are 7.0 cN/dtex, 117 cN/dtex, and 12.7%, respectively.

2. Production of carbon fiber: The yarn obtained in step 1 was pre-oxidized at 180-260°C with a pre-oxidation total draw ratio of 0.95 times to obtain pre-oxidized fiber; then low-temperature carbonization and high-temperature carbonization were performed at 300-750°C and 800-1500°C with a draw ratio of 0.96 times; then graphitization was performed at 2800°C, and finally, carbon fiber was obtained through surface treatment, washing, sizing, drying at 120°C, and winding.

The total silicon content of the carbon fiber is 3500 ppm, the Si/C ratio of the region X between the top of the protrusion on the fiber surface and the bottom of the groove is 81%, the Si/C ratio of the region Y between the bottom of the groove and 100 nm inward is 20%, and the Si/C ratio of the region Z greater than 100 nm is 3.7%. The number of pores on the surface of the carbon fiber is 70, the average length of the pores is 84 nm, and the average width is 77 nm. The pore orientation deviation angle along the fiber axis obtained by small-angle X-ray scattering is 5.5°. The tensile strength of the carbon fiber is 4.58 GPa, the tensile modulus is 339 GPa, and the elongation at break is 1.34%. After two months of continuous production, the carbon fiber strength began to decrease, the operation was stopped, and the ash in the equipment was cleaned once.

Swelling degree of water-washed filament/% Non-silicone emulsion pH density/% Emulsion particle size/nm Residence time/s Silicone-containing emulsion pH density/% Emulsion particle size/nm Silicon content/% of the emulsion Residence time/s Example 1 110 7.2 1.5 300 0.15 7.8 1.2 300 0.15 0.1 Example 2 110 7.2 3.5 300 0.15 7.8 3 300 0.35 0.1 Example 3 110 7.2 1.1 300 0.15 7.8 0.8 300 0.1 0.1 Example 4 110 7.2 1.1 300 0.15 7.8 1.5 300 0.2 0.05 Example 5 110 7.2 1.5 300 0.25 7.8 1.2 300 0.15 0.13 Example 6 110 7.2 1.5 300 0.08 7.8 1.2 300 0.15 0.05 Example 7 110 7.2 1.5 100 0.15 7.8 1.2 200 0.15 0.1 Example 8 110 7.2 1.5 300 0.15 7.8 1.2 200 0.15 0.04 Example 9 110 7.2 1.5 300 0.15 7.8 2 300 0.3 0.1 Example 10 110 7.2 1.5 300 0.15 7.8 1.5 300 0.2 0.1 Example 11 140 7.2 1.5 300 0.15 7.8 1 300 0.11 0.1 Example 12 90 7.2 1.5 100 0.15 7.8 1.2 100 0.15 0.1 Example 13 110 8 1.5 300 0.15 9 1.2 300 0.15 0.1

Total silicon content/ppm Si/C/% of area X between the top of the protrusion and the bottom of the groove Si/C/% of the region Y between the bottom of the home and the inner surface up to 100 nm Si/C/% in region Z greater than 100 nm Number of pores/unit within the surface X and Y regions Average pore length/nm Average vhr/nm of pores Orientation deviation angle/° Tensile strength of carbon fiber/GPa Tensile modulus of carbon fiber/GPa Elongation at break/% Downtime/month Example 1 800 5.8 0.5 0.04 10 20 15 2.3 5.74 370 1.52 7 Example 2 1400 9 0.9 0.05 15 42 22 3.5 5.63 360 1.56 6 Example 3 620 4.5 0.47 0.03 7 15 10 2.2 5.75 374 1.51 8 Example 4 690 4.8 0.54 0.04 8 17 13 2.2 5.75 374 1.55 8 Example 5 1340 8 0.85 0.04 15 35 20 3.0 5.66 361 1.58 6 Example 6 560 4.3 0.41 0.02 10 23 18 2.8 5.68 364 1.55 8 Example 7 700 5 0.55 0.04 8 17 13 2.2 5.75 374 1.51 8 Example 8 550 4.3 0.4 0.02 7 15 9 2.1 5.8 390 1.45 8 Example 9 1200 6.7 0.7 0.04 14 30 19 2.8 5.69 365 1.54 6 Example 10 600 4.5 0.45 0.03 7 15 10 2.2 5.76 379 1.5 8 Example 11 1350 8 0.85 0.04 15 38 20 3.2 5.66 362 1.55 6 Example 12 900 6 0.63 0.04 12 26 16 2.5 5.7 377 1.52 7 Example 13 700 5 0.55 0.04 8 17 13 2.2 5.75 375 1.51 8

Swelling degree of water-washed filament/% Milk pH density/% Emulsion particle size/nm Residence time/s Silicone-containing emulsion pH density/% Emulsion particle size/nm Silicon content/% of the emulsion Residence time/s Comparative Example 1 110 Contains silicone, 7.8 1.5 300 0.15 7.8 1.2 300 0.15 0.1 Comparative Example 2 110 Water, 7.0 / / 0.15 7.8 1.2 300 0.15 0.1 Comparative Example 3 110 8 1.5 300 0.15 6 1.2 300 0.15 0.1 Comparative Example 4 110 Anion, 7.2 1.5 300 0.15 Anion, 7.8 1.2 300 0.15 0.1 Comparative Example 5 110 7.2 1.5 300 0.15 Non-silicon, 7.2 1.2 300 0.15 0.1 Comparative Example 6 110 7.2 6 300 0.15 7.8 2 300 0.3 0.1 Comparative Example 7 110 7.2 3.5 300 0.15 7.8 6 300 1 0.1 Comparative Example 8 110 7.2 1.5 300 0.25 7.8 1.2 300 0.15 0.3 Comparative Example 9 110 7.2 1.5 300 0.15 7.8 1.2 300 0.15 0.02 Comparative Example 10 110 7.2 1.5 800 0.15 7.8 1.2 300 0.15 0.1 Comparative Example 11 110 7.2 1.5 40 0.15 7.8 1.2 40 0.15 0.1 Comparative Example 12 110 7.2 1.5 300 0.15 7.8 6 300 1 0.1 Comparative Example 13 110 7.2 1.5 300 0.15 7.8 1.2 300 0.15 0.1 Comparative Example 14 170 7.2 1.5 300 0.15 7.8 1.2 300 0.15 0.1

Total silicon content/ppm Si/C/% of area X between the top of the protrusion and the bottom of the groove Si/C/% of the region Y between the bottom of the home and the inner surface up to 100 nm Si/C/% in region Z greater than 100 nm Number of pores/unit within the surface X and Y regions Average pore length/nm Average vhr/nm of pores Orientation deviation angle/° Tensile strength of carbon fiber/GPa Tensile modulus of carbon fiber/GPa Elongation at break/% Downtime/month Comparative Example 1 3000 77 20 2 40 70 45 4.1 5.23 355 1.46 2.5 Comparative Example 2 2600 72 18 1.8 39 66 45 3.8 5.35 357 1.48 3 Comparative Example 3 3200 80 13 1.5 50 77 52 4.3 5.05 361 1.39 3 Comparative Example 4 3300 82 15 2 56 80 60 4.3 5 358 1.37 3 Comparative Example 5 0 0 0 0 64 89 71 4.8 4.6 340 1.35 7 Comparative Example 6 400 0.8 0.07 0.01 58 75 50 4.5 4.92 367 1.32 6 Comparative Example 7 2400 48 15 1 38 65 44 3.9 5.3 354 1.47 3 Comparative Example 8 2100 48 9 1 39 66 44 4.1 5.28 360 1.41 3 Comparative Example 9 400 0.9 0.07 0.01 60 87 69 4.6 4.9 366 1.31 7 Comparative Example 10 2000 45 13 0.08 45 60 40 5 4.8 350 1.3 4 Comparative Example 11 2500 50 17 1.3 48 69 50 4.2 5.1 351 1.4 3 Comparative Example 12 1750 30 2.8 0.07 36 64 30 3.6 5.35 356 1.47 3 Comparative Example 13 450 0.9 0.03 0.01 43 67 41 4.1 5.16 359 1.42 6 Comparative Example 14 3500 81 20 3.7 70 84 77 5.5 4.58 339 1.34 2

Claims (18)

A polyacrylonitrile carbon fiber having a groove structure on a surface, wherein the carbon fiber has a Si/C ratio in a region X between the top of a protrusion on the fiber surface and the bottom of a groove in a range of 1% to 10%, a Si/C ratio in a region Y between the bottom of the groove and within 100 nm inward in a range of 0.1% to 1%, and a Si/C ratio in a region Z greater than 100 nm in a thickness of 0.06% or less. In the first paragraph,
The above polyacrylonitrile carbon fiber is characterized in that it is obtained from polyacrylonitrile yarn manufactured by wet spinning. In claim 1 or 2,
A polyacrylonitrile carbon fiber characterized in that the total silicon content of the carbon fiber is 500 to 1500 ppm, and/or the Si/C ratio of the region X between the top of the protrusion on the fiber surface and the bottom of the groove is 8.5 times or more the Si/C ratio of the region Y between the bottom of the groove and 100 nm inward. In any one of the first to third paragraphs,
A polyacrylonitrile carbon fiber characterized in that the number of pores present in regions X and Y from the top of the protrusions on the fiber surface to 100 nm inward is less than 20, preferably less than 16; and the average length of the pores is 10 to 50 nm, and the average width is 5 to 25 nm. In any one of claims 1 to 4,
The orientation deviation angle of the pores along the fiber axis obtained by the small-angle X-ray scattering method is 4° or less; and/or
Polyacrylonitrile carbon fiber characterized in that the tensile strength of the carbon fiber is 5.6-5.8 GPa, the tensile modulus is 360-390 GPa, and the elongation at break is 1.45%-1.6%. A method for producing polyacrylonitrile carbon fibers, preferably polyacrylonitrile carbon fibers according to any one of claims 1 to 5, comprising the step of carbonizing polyacrylonitrile yarn to obtain polyacrylonitrile carbon fibers,
A method for producing polyacrylonitrile carbon fiber, characterized in that the above polyacrylonitrile yarn has a Si/C ratio in the range of 1.0% to 20% in a region from the top of the fiber surface protrusions to 2 μm inward, and a Si/C ratio in the region of 2 μm or more is 0.15% or less. In paragraph 6,
The oil content of the above yarn is 0.5% to 2.5%, preferably 0.8% to 2.5%, preferably 0.8% to 2.4%, more preferably 0.9% to 2.0%; and/or
The silicone content of the above yarn is 0.01% to 0.5%; and/or
The monofilament linear density of the above polyacrylonitrile yarn is 0.7 to 1.0 dtex; and/or
A method for producing polyacrylonitrile carbon fiber, characterized in that the above polyacrylonitrile yarn is produced by wet spinning. In paragraph 6 or 7,
A method for producing polyacrylonitrile carbon fiber, characterized in that the above polyacrylonitrile yarn is manufactured by wet spinning and further includes an oiling step, wherein the oiling step includes two consecutive oiling processes, and there is no dry densification step between the two oiling processes; and the first oiling process uses a non-silicon emulsion, a low-silicon emulsion, or a combination thereof, and the second oiling process uses a silicone-containing emulsion. In paragraph 8,
The primary oiling process uses a non-silicone emulsion, a low-silicone emulsion, or a combination thereof with a weight concentration of 0.1% to 5.0%; and the secondary oiling process uses a silicone-containing emulsion with a weight concentration of 0.1% to 5.0%; and/or
The average particle size of the non-silicon emulsion, low-silicon emulsion and silicone-containing emulsion is each independently 50 nm to 500 nm; and/or
The silicone content of the silicone-containing emulsion used in the secondary oiling process is 0.01 wt% to 0.9 wt%; and/or
A method for producing polyacrylonitrile carbon fiber, characterized in that the secondary oiling residence time is shorter than the primary oiling residence time. In any one of the 6th to 9th clauses,
The pH difference between the non-silicone emulsion or low-silicone emulsion and the silicone-containing emulsion is not greater than 1; and/or
A method for producing polyacrylonitrile carbon fiber, characterized in that the surfactant in the non-silicone emulsion or low-silicone emulsion and the surfactant in the silicone-containing emulsion do not have opposite polarities, and preferably, the silicone-containing emulsion is an emulsion containing a nonionic surfactant. In any one of the 6th to 10th clauses,
A method for manufacturing polyacrylonitrile carbon fiber, characterized in that polyacrylonitrile yarn before oiling has a swelling degree of 80 to 150% after washing. In any one of the 6th to 11th clauses,
A method for producing polyacrylonitrile carbon fiber, characterized in that the above manufacturing method comprises the steps of wet coagulation molding, coagulation stretching, high-temperature water stretching, water washing, oiling, dry densification, steam stretching and steam thermoforming of a polyacrylonitrile raw material to obtain the above polyacrylonitrile yarn. In any one of the 6th to 12th clauses,
A method for producing polyacrylonitrile carbon fiber, characterized in that the above polyacrylonitrile yarn undergoes pre-oxidation treatment and carbonization to obtain the above polyacrylonitrile carbon fiber. In Article 13,
The above pre-oxidation treatment is performed in an air atmosphere, the temperature is 170 to 300°C, and the total elongation is 5% or less; and/or
A method for producing polyacrylonitrile carbon fiber, characterized in that the carbonization treatment comprises a step of performing low-temperature carbonization treatment in an inert atmosphere at a temperature of 300 to 750°C with a draw ratio of 0 to 4% of total elongation, and a step of performing high-temperature carbonization treatment in an inert atmosphere at a temperature of 800 to 1500°C with a draw ratio of -4 to -2% of total elongation. In polyacrylonitrile yarn,
The above polyacrylonitrile yarn is characterized in that the Si/C ratio in the region from the top of the protrusion on the fiber surface to 2 μm inward is in the range of 1.0% to 20%, and the Si/C ratio in the region greater than 2 μm is 0.15% or less. In Article 15,
The oil content of the above yarn is 0.5% to 2.5%, preferably 0.8% to 2.5%, preferably 0.8% to 2.4%, more preferably 0.9% to 2.0%; and/or
The silicone content of the above yarn is 0.01% to 0.5%; and/or
The monofilament linear density of the above polyacrylonitrile yarn is 0.7 to 1.0 dtex; and/or
A polyacrylonitrile carbon fiber yarn, characterized in that the above polyacrylonitrile yarn is manufactured by wet spinning. In a method for producing polyacrylonitrile yarn, preferably polyacrylonitrile yarn according to claim 15 or 16,
A method for producing polyacrylonitrile yarn, comprising wet spinning and an oiling step, wherein the oiling step comprises two consecutive oiling processes, there is no dry compaction step between the two oiling processes, the first oiling process uses a non-silicon emulsion, a low-silicon emulsion, or a combination thereof, and the second oiling process uses a silicone-containing emulsion. In Article 17,
The primary oiling process uses a non-silicone emulsion, a low-silicone emulsion, or a combination thereof with a weight concentration of 0.1% to 5.0%; and the secondary oiling process uses a silicone-containing emulsion with a weight concentration of 0.1% to 5.0%; and/or
The secondary oiling residence time is shorter than the primary oiling residence time; and/or
The average particle size of the above non-silicon emulsion, low-silicon emulsion and silicone-containing emulsion is each independently 50 nm to 500 nm; and/or
The silicone content of the silicone-containing emulsion used in the secondary oiling process is 0.01 wt% to 0.9 wt%; and/or
The pH difference between the non-silicone or low-silicone emulsion and the silicone-containing emulsion is not greater than 1; and/or
The surfactant in the non-silicone emulsion or low-silicone emulsion is not opposite in polarity to the surfactant in the silicone-containing emulsion, and preferably, the silicone-containing emulsion is an emulsion containing a nonionic surfactant; and/or
The swelling degree of the fiber after washing the polyacrylonitrile yarn before oiling is 80 to 150%; and/or
The above manufacturing method is characterized in that it includes the steps of wet coagulation molding, coagulation stretching, high-temperature water stretching, water washing, oiling, dry densification, steam stretching and steam thermoforming of the polyacrylonitrile raw material to obtain the above polyacrylonitrile yarn.