Polyacrylonitrile dry densified fiber, steam drawn fiber and preparation method and application of polyacrylonitrile dry densified fiber and steam drawn fiber

Abstract

The invention provides a polyacrylonitrile dry densified fiber, a steam-drawn fiber, and a preparation method and application of the polyacrylonitrile dry densified fiber and the steam-drawn fiber. The polyacrylonitrile dry densified fiber is prepared by wet spinning and then drying and densifying; the drying densification is performed in one section and has four temperature zones; the temperature difference between every two adjacent temperature zones is 5-20 DEG C; the preparation method of the polyacrylonitrile dry densified fiber comprises the following steps: preparing a polyacrylonitrile copolymer spinning solution, carrying out wet spinning, and carrying out drying densification to obtain the polyacrylonitrile dry densified fiber. And carrying out steam drafting on the polyacrylonitrile dry densified fiber by 1.5-3 times to obtain the polyacrylonitrile steam drafting fiber. The polyacrylonitrile dry densified fiber prepared by the invention has the advantages of small quantity of broken filaments in the dry densification process, small dispersion coefficient of fineness and good mechanical property.

Description

Technical Field

[0001] The present invention relates to the field of carbon fibers, and more particularly, to a polyacrylonitrile dry densification fiber, a steam drawing fiber, and a preparation method and application thereof. Background Art

[0002] Polyacrylonitrile-based carbon fibers are widely used. A large number of studies have shown that the crystalline structure of fibers can directly affect the performance of fiber products. The more perfect the crystallization, the fewer internal defects of the fibers and the higher the strength. Comparing carbon fibers with different degrees of crystallinity, it is found that fibers with a higher degree of crystallinity have higher strength and initial modulus. This may be because when the degree of crystallinity is relatively low, there are more amorphous regions. The amorphous regions are composed of molecular chain entanglement points, free molecular chains, etc. squeezed in during the crystallization process, that is, the amorphous regions contain defect points of the polymer, and these defect points become weak points in mechanical properties. One of the factors directly affecting the degree of crystallinity during the spinning process is the draw ratio.

[0003] During the dry densification process, the macromolecular chains in the fibers will be initially arranged as the draw ratio increases. That is, as the draw ratio increases, the crystallinity of the carbon fibers can be seen to increase with the increase of the draw ratio, which may be the effect of orientation-induced crystallization. As the draw ratio increases, the distance between molecular chains continuously decreases. After reaching a certain level, crystallization will occur and the crystal region structure will be further improved. During the stretching process, the size of the draw ratio is determined by the speed ratio of the front and rear rollers. The larger the draw ratio, the greater the average strain rate, and the degree of orientation of the molecular chain segments increases with the increase of the draw ratio. And as the draw ratio is further increased, the original crystallization may be partially destroyed and then rebuilt first, so the increase in crystallinity will slow down and the fiber properties will begin to decline. When the draw ratio is too large, the entanglement and other forces between molecular chains are not enough to support the externally applied force, and the mechanical properties of the fibers further decline, resulting in fiber breakage and the generation of fuzz.

[0004] In the steam drawing step, compared with the process of directly performing steam drawing without dry densification, the strength and modulus of the fibers after densification will be significantly improved, and by increasing the steam drawing ratio, the fiber strength and modulus increase significantly. This is because the molecular chains in the amorphous region of PAN fibers are arranged orderly along the fiber axis under the action of drawing stress, and at the same time, the plasticizing effect of water vapor greatly reduces the intermolecular force, making the fibers easy to be drawn and oriented. Microscopically, the orientation of the raw filaments increases with the increase of the drawing ratio. When the steam drawing ratio is too high, the phenomenon of fiber breakage and fuzz increases significantly, which may be caused by the fact that the internal micropores or fibers with a relatively small diameter in the fibers cannot withstand too large a drawing tension. Therefore, reasonable control of the draw ratio during the dry densification process and the steam drawing ratio is particularly important for the preparation of carbon fiber precursor filaments.

[0005] The drying densification process is a process of pore closure, which plays a key role in improving the denseness of the precursor. How to better control the coagulation forming and drying densification processes has a great impact on the properties of the precursor, and further affects the corresponding carbon fiber. Under the curing conditions of other processes, good coordination of coagulation forming and drying densification can well complete the pore closure, which will help improve the tensile strength of the later-stage carbon fiber, but high denseness will make the oxidation process difficult.

[0006] Patent CN109023563A discloses a preparation method of building-reinforcing polyacrylonitrile short fibers, which mainly solves the problem of poor single-filament strength of short fibers in the prior art. The preparation method includes the following steps: the metered spinning dope undergoes coagulation forming, multi-stage coagulation drawing, multi-stage hot water drawing, water washing, primary oiling, drying densification, steam drawing, heat setting, secondary oiling, and re-drying of the oil agent to obtain polyacrylonitrile fiber precursors; the precursors are cut by a short cutter to obtain building-reinforcing polyacrylonitrile short fibers. Among them, the water washing process uses mechanical vibration water washing first and then ultrasonic vibration water washing, and the content of dimethyl sulfoxide in the fiber after water washing is less than or equal to 0.3 wt%, which preferably solves this problem and can be used in the industrial production of building-reinforcing polyacrylonitrile short fibers.

[0007] Patent CN109943921A discloses a polyacrylonitrile precursor spinning method for carbon fibers, including the following steps: the polyacrylonitrile spinning dope is extruded through a horizontal spinneret into a coagulation bath, and the precursor passes through a certain distance in the coagulation bath and then makes a U-turn to vertically downward, enters the air for gas-phase coagulation forming, then turns to the horizontal direction, and the nascent fiber is obtained in the coagulation bath; the nascent fiber undergoes cold drawing, solvent drawing, and hot drawing; then it undergoes water washing to obtain Fiber I; Fiber I is oiled and dried densified to obtain Fiber II; Fiber II is drawn and densified to obtain Fiber III; Fiber III is steam heat-set and then wound to obtain polyacrylonitrile precursor products.

[0008] Patent CN113862812A discloses a polyacrylonitrile carbon fiber precursor for carbon paper and its preparation method, belonging to the field of organic polymer materials. The method includes: using water as a solvent, ammonium persulfate - ammonium sulfite or ammonium persulfate - ammonium bisulfite as a redox initiator, the first monomer being acrylonitrile, the second monomer being itaconic acid, and the third monomer being an ethylenic unsaturated ester with a large side group, reacting at 50 - 60 °C for 8 - 14 h to obtain PAN polymer powder; preparing the obtained PAN polymer powder into a slurry to obtain a spinning dope; setting the coagulation bath temperature at 30 - 60 °C, and the coagulation bath draw ratio at -30% to -5%; adopting two-stage hot water drawing with the densification temperature increasing step by step, then performing steam drawing, and finally obtaining a polyacrylonitrile-based carbon fiber precursor for carbon paper. After carbonization, the carbon content of the carbon fiber precursor of the present invention is ≥95.6%, and the resistivity is ≤1.6 mΩ·cm, meeting the technical indicators of carbon paper for fuel cell diffusion layers.

[0009] Patent CN114232139A discloses a carbon fiber finish for dry-jet wet-spun precursor and its preparation method. The finish mainly consists of components such as amino-modified silicone oil, epoxy-modified silicone oil, polyether-modified silicone oil, terpolymerized silicone oil, compound emulsifier, and deionized water. It is an oil-in-water type aqueous microemulsion with a particle size of 50 - 500 nm, which can better match the dry-jet wet-spinning process, uniformly apply the finish to the precursor in a short time, and is not easy to stick to the roller during the drying densification and steam drawing stages, with no deformation during winding and less hairiness, having good spinning processability; not sticky during the pre-oxidation and low-temperature carbonization stages, less hairiness, high carbonization strength, and small coefficient of variation. This method has the characteristics of environmental protection, good safety, high production efficiency, and stable quality, and is suitable for large-scale use in the polyacrylonitrile dry-jet wet-spinning process.

[0010] Patent CN109023563A only stipulates one drying densification step without specifying the specific parameters in the specific range. At the same time, the corresponding draw ratio range far exceeds 0.98, and no specific detection description of the mechanical properties of the obtained precursor is made; Patent CN109943921A does not perform a steam drawing step after the drying densification process and directly performs steam heat setting, and the draw ratio during the drying densification process is 1 - 4 times, which is greater than the defined multiple in the present invention; Patent CN113862812A describes the temperatures of each zone but does not explain the difference in draw ratios; Patent CN114232139A mainly solves the problem of the discrete number of precursors by changing the organic formulation.

[0011] Therefore, it is necessary to study a polyacrylonitrile fiber and its preparation method, which can solve the problems of a large number of hairy filaments during the drying densification process and poor mechanical properties of the obtained polyacrylonitrile-based carbon fiber precursor in the prior art. Summary of the Invention

[0012] To solve the technical problems existing in the prior art, the present invention provides a polyacrylonitrile dry densification fiber, a steam drawing fiber, and their preparation methods and applications.

[0013] The present invention mainly solves the problems of a large number of hair filaments during the dry densification process in the prior art and poor mechanical properties of the obtained polyacrylonitrile-based carbon fiber precursor. The polyacrylonitrile dry densification fiber prepared by the method of the present invention has the advantages of few hair filaments and good mechanical properties.

[0014] One of the objectives of the present invention is to provide a polyacrylonitrile dry densification fiber, which is prepared by wet spinning followed by dry densification; the dry densification is in one stage and has four temperature zones; the temperature difference between every two adjacent temperature zones is 5-20°C, preferably 5-10°C.

[0015] In a preferred embodiment of the present invention,

[0016] The four temperature zones of the dry densification are respectively the first temperature zone, the second temperature zone, the third temperature zone, and the fourth temperature zone; preferably,

[0017] The temperature of the first temperature zone is 90-120°C, and the draw ratio is 0.95-1;

[0018] The temperature of the second temperature zone is 100-130°C, and the draw ratio is 0.96-1.01;

[0019] The temperature of the third temperature zone is 110-130°C, and the draw ratio is 0.98-1.02;

[0020] The temperature of the fourth temperature zone is 120-140°C, and the draw ratio is 0.99-1.03.

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

[0022] The fineness of the polyacrylonitrile dry densification fiber is 7-9 dtex;

[0023] The coefficient of variation of the fineness of the polyacrylonitrile dry densification fiber is 1.5-6%;

[0024] The breaking strength of the polyacrylonitrile dry densification fiber is 5.8-9.2 cN / dtex, preferably 5.8-7.5 cN / dte;

[0025] The initial modulus of the polyacrylonitrile dry densification fiber is 110 c-150 cN / dtex;

[0026] The average number of hair filaments in every 10,000 meters of fiber at the dry densification outlet roll is below 24, preferably below 20.

[0027] The second object of the present invention is to provide a method for preparing polyacrylonitrile dry densified fibers, comprising the following steps:

[0028] (1) Prepare a polyacrylonitrile copolymer spinning dope;

[0029] (2) Wet-spin the polyacrylonitrile copolymer spinning dope obtained in step (1), and after drying densification, obtain the polyacrylonitrile dry densified fibers.

[0030] In a preferred embodiment of the present invention,

[0031] Step (1),

[0032] The polyacrylonitrile copolymer spinning dope can be prepared by a spinning process commonly used in the art without special limitation. For example, but not limited to, the comonomer of polyacrylonitrile is a vinyl-containing monomer, preferably at least one of acrylate, vinyl ester, acrylamide, sulfonate, ammonium salt, etc.; preferably,

[0033] A polyacrylonitrile copolymer spinning dope is obtained by copolymerizing an acrylic compound and its derivatives and acrylonitrile in the presence of an initiator and a solvent; the acrylic compound and its derivatives are preferably at least one of acrylic acid, itaconic acid, methyl acrylate, methyl methacrylate; further preferably,

[0034] Based on the total mass of the acrylic compound and its derivatives and acrylonitrile being 100%, it includes:

[0035] The acrylic compound and its derivatives 2 - 5%;

[0036] Acrylonitrile 95 - 98%;

[0037] The dosage of the acrylic compound is 0 - 5%, the dosage of the methyl acrylate compound is 0 - 2%, and the dosage of acrylonitrile is 95 - 98%; preferably, the dosage of the acrylic compound is 0.5 - 2.5%, the dosage of the methyl acrylate compound is 0.2 - 1.5%, and the dosage of acrylonitrile is 95.5 - 98%;

[0038] Even more preferably,

[0039] The acrylonitrile is distilled acrylonitrile;

[0040] The initiator is an initiator commonly used in the prior art, such as azobisisobutyronitrile;

[0041] The solvent is a solvent commonly used in the prior art, preferably at least one of dimethyl sulfoxide, dimethylformamide, dimethylacetamide;

[0042] The dosage of the initiator is 0.1-1 wt% of the total mass of the reaction monomers, preferably 0.1-0.5 wt%;

[0043] The mass ratio of the solvent to the total mass of the reaction monomers is (1.5-7):1, preferably (2-6):1;

[0044] The reaction is carried out under a protective gas atmosphere, and the protective gas is at least one of nitrogen and inert gas;

[0045] The reaction temperature is 55-95 °C, preferably 60-90 °C;

[0046] The reaction time is 16-32 h, preferably 18-30 h;

[0047] The post-treatment is monomer removal, degassing and filtration.

[0048] In a preferred embodiment of the present invention,

[0049] Step (2),

[0050] The wet spinning includes spinning extrusion, coagulation forming, hot water drawing, water washing and oiling; preferably,

[0051] The spinning extrusion is carried out from a spinneret with a pore diameter of 50-55 μm;

[0052] The coagulation forming is carried out in a three-stage coagulation bath, and the three-stage coagulation bath includes a first coagulation bath, a second coagulation bath and a third coagulation bath; the first coagulation bath, the second coagulation bath and the third coagulation bath are aqueous solutions of organic solvents, and the organic solvent is the same as the solvent in step (1), and the concentration of the organic solvent in the first coagulation bath, the second coagulation bath and the third coagulation bath decreases step by step; preferably, the concentration of the organic solution in the first coagulation bath is 70-80 wt%; the concentration of the organic solution in the second coagulation bath is 50-60 wt%; the concentration of the organic solution in the third coagulation bath is 30-40 wt%;

[0053] The temperature of the hot water drawing is 80-95 °C, and the hot water drawing ratio is 1.5-3 times;

[0054] The temperature of the water washing is 60-80 °C, and the water washing drawing ratio is 1-1.5 times;

[0055] The residence time of the oiling is not higher than 2 seconds, and no drawing is carried out;

[0056] The polyacrylonitrile dry densified fiber is collected by a winding machine.

[0057] The third object of the present invention is to provide a polyacrylonitrile dry densified fiber obtained by the above preparation method.

[0058] A fourth object of the present invention is to provide a polyacrylonitrile steam drawn fiber, which is obtained by subjecting a polyacrylonitrile dry densified fiber to steam drawing; the polyacrylonitrile dry densified fiber is the above-mentioned polyacrylonitrile dry densified fiber;

[0059] The crystallinity and steam drawing ratio of the polyacrylonitrile steam drawn fiber satisfy the following relational expression:

[0060] 0.26x + 70 ≤ y ≤ 2x + 82;

[0061] wherein, y is the crystallinity, %; x is the drawing ratio; x is 1.5 to 3.

[0062] In a preferred embodiment of the present invention,

[0063] the fineness of the polyacrylonitrile steam drawn fiber is 0.61 to 1.3 dtex;

[0064] the coefficient of variation of the fineness of the polyacrylonitrile steam drawn fiber is 5 to 12%.

[0065] A fifth object of the present invention is to provide a method for preparing a polyacrylonitrile steam drawn fiber, comprising: subjecting a polyacrylonitrile dry densified fiber to steam drawing to obtain the polyacrylonitrile steam drawn fiber; the drawing ratio of the steam drawing is 1.5 to 3 times; preferably, the steam pressure of the steam drawing is 220 kPa; and / or, steam heat setting is performed after the steam drawing, and more preferably, the fiber is heat set with saturated water steam.

[0066] A sixth object of the present invention is to provide an application of a polyacrylonitrile dry densified fiber and a polyacrylonitrile steam drawn fiber in the fields of high-strength carbon fibers and composite materials.

[0067] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0068] In the prior art, during dry densification, too large a drawing ratio will cause a further decline in the mechanical properties of the fiber, resulting in fiber breakage and the generation of fuzz; in the process of pore closure during dry densification, the improvement of the denseness of the raw silk plays a key role, but high denseness will make the oxidation process difficult. During steam drawing, when the steam drawing ratio is too high, the fiber breakage and fuzz phenomenon increase significantly.

[0069] The dry densification of the present invention is divided into four temperature zones, and the four temperature zones have different temperatures and drawing ratios. By controlling the structure-activity relationship between the breaking elongation and the drawing ratio, the prepared polyacrylonitrile dry densified fiber has few fuzz, a small coefficient of variation of its fineness, and good mechanical properties.

[0070] In the technical solution of the present invention, the number of hairiness in 10,000 meters of continuous fibers at the drying densification outlet roller of the prepared polyacrylonitrile drying densified fibers is monitored by an on-line camera, and the number is counted as 11 to 19. The modulus of the prepared drying densified fibers is greater than 110 cN / dtex, the breaking strength is greater than 5.8 cN / dtex, and the coefficient of variation of the dry densified fineness is less than 5.3%, achieving better technical effects. Specific Embodiments

[0071] The present invention will be specifically described below in conjunction with specific embodiments. It is necessary to point out here that the following embodiments are only for further illustration of the present invention and cannot be construed as limiting the protection scope of the present invention. Some non-essential improvements and adjustments made by those skilled in the art based on the content of the present invention still fall within the protection scope of the present invention.

[0072] The raw materials used in the examples and comparative examples are all conventional commercially available raw materials.

[0073] Testing Method:

[0074] Freeze-drying treatment of polyacrylonitrile fibers: Since the as-spun fibers contain moisture, the true linear density cannot be obtained without treatment, and accurate mechanical properties cannot be obtained. Therefore, the as-spun fibers need to be freeze-dried. After the as-spun fibers are washed with water, they are placed on a tray, and then the tray is placed on the tray rack of the material cart. The material cart sends the tray to the heating plate in the vacuum freeze-drying chamber, closes the chamber door and starts freeze-drying. The vacuum pumping system directly starts pumping vacuum and continuously pumps vacuum until the fibers are completely frozen until the temperature drops below 0°C. Then, start heating the heating plate. At the same time, continuously pump vacuum in the vacuum freeze-drying chamber so that the vacuum degree in the vacuum freeze-drying chamber is in the range of 10 Pa to 800 Pa. At the same time, control the temperature of the heating plate at 30°C to 140°C. Finally, observe the temperature of the temperature probe on the fiber. When it reaches above 0°C, the fibers are completely dried.

[0075] Mechanical property testing of polyacrylonitrile drying densified fibers and polyacrylonitrile steam drawn fibers: The mechanical properties of the freeze-dried polyacrylonitrile as-spun fibers are tested according to the national standard GB / T-14337-2008. Take a fiber bundle with a length of 40 mm from the as-spun fibers, and take out about 500 fibers from it, and lay them evenly on the velvet board for measurement. Randomly take out an as-spun fiber from the test sample with tweezers, clamp one end of the fiber with a tension clip of 0.1 cN, place the fiber in the holder of the instrument, and ensure that the fiber elongates along the axis. Set the single-filament strength tester test mode, the distance between the upper and lower chucks (20 mm), the tensile speed (20 mm / min), and the number of samples (50). Start the single-filament strength tester and the data acquisition device, start the tensile test, and obtain the strength, modulus and stress-strain curve results of the as-spun fiber single filaments.

[0076] Crystallinity test of polyacrylonitrile steam-drawn fiber: The crystallinity of freeze-dried polyacrylonitrile steam-drawn fiber was tested according to the national standard GB / T 23413-2009. A fiber bundle with a length of about 50 mm was taken from the fiber, straightened and evenly laid on the tablet, fixed for measurement. Press the button on the sample chamber door. When a continuous "beep-beep" sound is heard and the indicator light flashes, gently open the sample chamber door with both hands, then insert the sample rack into the sample card slot, and then gently close the sample chamber door. Press the button on the door. After seeing that the indicator light no longer flashes and no more beeping sounds are emitted, it indicates that the sample chamber has been closed and the test can be carried out. After setting the sample name and test conditions (including starting and ending angles, scanning speed, slit width, tube voltage and tube current) in the computer program, click the execute button to start the test. After the instrument prompts that the test is completed, convert the saved raw file into a txt file, and then use origin to plot the graph to obtain the required crystallinity result.

[0077] Counting the number of hairiness during the drying densification process: Use an online camera to monitor the number of hairiness contained in the as-spun fiber within 10,000 meters continuously at the outlet roller of the drying densification.

[0078]

Example 1

[0079] (1) Preparation of spinning solution: Distilled acrylonitrile (AN) and itaconic acid (IA) were added to the reactor in a ratio of 98:2, with a solid content of 20%, and azobisisobutyronitrile (AIBN) accounting for 0.3 wt% of the comonomers. Dimethyl sulfoxide (DMSO) was used as the solvent. Under nitrogen protection, the reaction was carried out at a constant temperature of 70 °C for 24 hours to obtain a binary acrylonitrile copolymer. After degassing, defoaming, and re-filtering, a polyacrylonitrile copolymer spinning dope was obtained.

[0080] (2) Preparation of polyacrylonitrile dry-densified fiber: Wet spinning was used. The spinning dope was extruded through a spinneret with a pore size of 55 μm and then entered a three-stage coagulation bath. The first coagulation bath was an 80% aqueous solution of dimethyl sulfoxide, the second coagulation bath was a 53% aqueous solution of dimethyl sulfoxide, and the third coagulation bath was a 30% aqueous solution of dimethyl sulfoxide. Then the coagulated fiber was washed with water and hot water drawn. The hot water drawing temperature was 85 °C, and the draw ratio was 2.0. The oiling residence time was 2 s, and there was no drawing. The washing temperature was 70 °C, and the draw ratio was 1.0. Then the fiber was dried and densified using a stepwise heating method, divided into four temperature zones. Among them, the temperature in zone 1 was 100 °C, and the draw ratio was 0.98; the temperature in zone 2 was 110 °C, and the draw ratio was 0.98; the temperature in zone 3 was 120 °C, and the draw ratio was 0.99; the temperature in zone 4 was 130 °C, and the draw ratio was 1.02. The polyacrylonitrile dry-densified fiber obtained by using a winding machine was collected.

[0081] The average number of slubs in every 10,000 meters of fiber at the outlet roller of dry densification is counted by an online camera to be 14. The mechanical properties of the dry densified fiber are tested according to the national standard GB / T - 14337 - 2008. Its fineness is 8.76 dtex, the modulus is 150 cN / dtex, the breaking strength is 5.8 cN / dtex, and the coefficient of variation of fineness is 4.8%.

[0082] The obtained polyacrylonitrile dry densified fiber is subjected to steam drawing using saturated steam. The steam pressure is 220 kpa, and the drawing ratio is 1.5 times. After steam drawing, the fiber is subjected to steam heat setting with saturated steam to obtain polyacrylonitrile steam drawn fiber.

[0083] According to the national standard GB / T 23413 - 2009, the crystallinity of the freeze - dried polyacrylonitrile steam drawn fiber is tested. After measurement, the crystallinity of the obtained fiber fineness is 72.4%. According to the national standard GB / T - 14337 - 2008, the mechanical properties of the steam drawn fiber are tested. Its fineness is 1.25 dtex, and the coefficient of variation of fineness is 9.4%.

[0084]

Example 2

[0085] The differences from Example 1 are as follows: during dry densification, the temperatures and draw ratios of the four temperature zones are different; the steam drawing ratio is different;

[0086] Specifically:

[0087] The temperature of Zone 1 is 95 °C, and the draw ratio is 0.98; the temperature of Zone 2 is 105 °C, and the draw ratio is 1; the temperature of Zone 3 is 115 °C, and the draw ratio is 0.98; the temperature of Zone 4 is 125 °C, and the draw ratio is 1;

[0088] The steam drawing ratio is 3 times;

[0089] Except for the above differences, the other conditions of Example 2 are the same as those of Example 1. After dry densification, polyacrylonitrile dry densified fiber is obtained, and then polyacrylonitrile steam drawn fiber is obtained after steam drawing.

[0090] The average number of slubs in every 10,000 meters of fiber at the outlet roller of dry densification is counted by an online camera to be 16. According to the national standard GB / T - 14337 - 2008, the mechanical properties of the polyacrylonitrile dry densified fiber are tested. Its fineness is 7.95 dtex, the modulus is 110 cN / dtex, the breaking strength is 7.2 cN / dtex, and the coefficient of variation of fineness is 5.3%.

[0091] The crystallinity of the freeze-dried polyacrylonitrile steam-drawn fiber was tested according to the national standard GB / T 23413-2009. After measurement, the crystallinity of the fiber fineness obtained was 88.0%. The mechanical properties of the steam-drawn fiber were tested according to the national standard GB / T-14337-2008. Its fineness was 0.83 dtex, and the coefficient of variation of the fineness was 6.3%.

[0092]

Example 3

[0093] The differences from Example 1 are as follows: During drying densification, the temperatures and draw ratios in the 4 temperature zones are different; the steam drawing ratio is different;

[0094] Specifically:

[0095] The temperature in Zone 1 is 105 °C, and the draw ratio is 0.98; the temperature in Zone 2 is 115 °C, and the draw ratio is 0.98; the temperature in Zone 3 is 125 °C, and the draw ratio is 0.99; the temperature in Zone 4 is 135 °C, and the draw ratio is 1;

[0096] The steam drawing ratio is 2 times;

[0097] Except for the above differences, the other conditions in Example 3 are the same as those in Example 1. After drying densification, polyacrylonitrile dried and densified fibers were obtained, and then polyacrylonitrile steam-drawn fibers were obtained after steam drawing.

[0098] The average number of fly filaments in the fiber with a length of 10,000 meters at the outlet roller of drying densification was counted by an on-line camera and was 16. The mechanical properties of the dried and densified fiber were tested according to the national standard GB / T-14337-2008. Its fineness was 7.68 dtex, the modulus was 136 cN / dtex, the breaking strength was 6.1 cN / dtex, and the coefficient of variation of the fineness was 5.0%.

[0099] The crystallinity of the freeze-dried polyacrylonitrile steam-drawn fiber was tested according to the national standard GB / T 23413-2009. After measurement, the crystallinity of the fiber fineness obtained was 73.9%. The mechanical properties of the steam-drawn fiber were tested according to the national standard GB / T-14337-2008. Its fineness was 0.75 dtex, and the coefficient of variation of the fineness was 9.3%.

[0100]

Example 4

[0101] The differences from Example 1 are as follows: During drying densification, the temperatures and draw ratios in the 4 temperature zones are different; the steam drawing ratio is different;

[0102] Specifically:

[0103] The temperature in Zone 1 is 90 °C and the draw ratio is 0.95; the temperature in Zone 2 is 100 °C and the draw ratio is 0.96; the temperature in Zone 3 is 110 °C and the draw ratio is 0.98; the temperature in Zone 4 is 120 °C and the draw ratio is 0.99;

[0104] The steam drawing ratio is 2.5 times;

[0105] Except for the above differences, other conditions of Example 4 are the same as those of Example 1. Polyacrylonitrile dried and densified fibers are obtained through drying and densification, and then polyacrylonitrile steam drawn fibers are obtained after steam drawing.

[0106] The average number of hairiness in every 10,000 meters of fibers at the outlet roller of drying and densification is counted by an on-line camera and is 17. The mechanical properties of the dried and densified fibers are tested according to the national standard GB / T - 14337 - 2008. Its fineness is 8.12 dtex, the modulus is 143 cN / dtex, the breaking strength is 6.5 cN / dtex, and the coefficient of variation of fineness is 3.4%.

[0107] The crystallinity of the freeze-dried polyacrylonitrile steam drawn fibers is tested according to the national standard GB / T 23413 - 2009. After measurement, the crystallinity of the obtained fiber fineness is 76.2%. The mechanical properties of the steam drawn fibers are tested according to the national standard GB / T - 14337 - 2008. Its fineness is 0.84 dtex, and the coefficient of variation of fineness is 8.3%.

[0108]

Example 5

[0109] The differences from Example 1 are as follows: during drying and densification, the temperatures and draw ratios in the 4 temperature zones are different; the steam drawing ratio is different;

[0110] Specifically:

[0111] The temperature in Zone 1 is 120 °C and the draw ratio is 1; the temperature in Zone 2 is 128 °C and the draw ratio is 1.01; the temperature in Zone 3 is 130 °C and the draw ratio is 1.02; the temperature in Zone 4 is 140 °C and the draw ratio is 1.03;

[0112] The steam drawing ratio is 2.5 times;

[0113] Except for the above differences, other conditions of Example 5 are the same as those of Example 1. Polyacrylonitrile dried and densified fibers are obtained through drying and densification, and then polyacrylonitrile steam drawn fibers are obtained after steam drawing.

[0114] The average number of hairiness in every 10,000 meters of fibers at the drying densification outlet roller is counted by an online camera and is 12. The mechanical properties of the dried and densified fibers are tested according to the national standard GB / T - 14337 - 2008. Its fineness is 7.96 dtex, the modulus is 117 cN / dtex, the breaking strength is 7.2 cN / dtex, and the coefficient of variation of fineness is 2.1%.

[0115] According to the national standard GB / T 23413 - 2009, the crystallinity of the freeze - dried polyacrylonitrile steam - drawn fibers is tested. After measurement, the crystallinity of the obtained fiber fineness is 83.3%. According to the national standard GB / T - 14337 - 2008, the mechanical properties of the steam - drawn fibers are tested. Its fineness is 0.96 dtex, and the coefficient of variation of fineness is 5.7%.

[0116]

Example 6

[0117] The differences from Example 1 are as follows: during drying densification, the temperatures and draw ratios of the four temperature zones are different; the steam drawing ratio is different;

[0118] Specifically:

[0119] The temperature of the first zone is 110 °C, and the draw ratio is 0.95; the temperature of the second zone is 115 °C, and the draw ratio is 0.98; the temperature of the third zone is 120 °C, and the draw ratio is 1; the temperature of the fourth zone is 130 °C, and the draw ratio is 1.02;

[0120] The steam drawing ratio is 2.5 times;

[0121] Except for the above differences, the other conditions of Example 6 are the same as those of Example 1. After drying densification, polyacrylonitrile dried and densified fibers are obtained, and after steam drawing, polyacrylonitrile steam - drawn fibers are obtained.

[0122] The average number of hairiness in every 10,000 meters of fibers at the drying densification outlet roller is counted by an online camera and is 11. The mechanical properties of the dried and densified fibers are tested according to the national standard GB / T - 14337 - 2008. Its fineness is 8.03 dtex, the modulus is 119 cN / dtex, the breaking strength is 7.1 cN / dtex, and the coefficient of variation of fineness is 1.9%.

[0123] According to the national standard GB / T 23413 - 2009, the crystallinity of the freeze - dried polyacrylonitrile steam - drawn fibers is tested. After measurement, the crystallinity of the obtained fiber fineness is 81.4%. According to the national standard GB / T - 14337 - 2008, the mechanical properties of the steam - drawn fibers are tested. Its fineness is 1.03 dtex, and the coefficient of variation of fineness is 5.5%.

[0124]

Example 7

[0125] The differences from Example 1 are as follows: during drying and densification, the temperatures and draw ratios in the four temperature zones are different; the steam drawing ratio is different;

[0126] Specifically:

[0127] The temperature in Zone 1 is 110 °C and the draw ratio is 1; the temperature in Zone 2 is 115 °C and the draw ratio is 1; the temperature in Zone 3 is 120 °C and the draw ratio is 0.98; the temperature in Zone 4 is 130 °C and the draw ratio is 0.99;

[0128] The steam drawing ratio is 2 times;

[0129] Except for the above differences, other conditions of Example 7 are the same as those of Example 1. After drying and densification, polyacrylonitrile dried and densified fibers are obtained, and after steam drawing, polyacrylonitrile steam drawn fibers are obtained.

[0130] The average number of flyings in every 10,000 meters of fibers at the outlet roller of drying and densification is counted by an online camera to be 18. According to the national standard GB / T - 14337 - 2008, the mechanical properties of the dried and densified fibers are tested. Its fineness is 8.64 dtex, the modulus is 142 cN / dtex, the breaking strength is 6.4 cN / dtex, and the coefficient of variation of fineness is 3.6%.

[0131] According to the national standard GB / T 23413 - 2009, the crystallinity of the freeze - dried polyacrylonitrile steam drawn fibers is tested. After measurement, the crystallinity of the obtained fiber fineness is 75.2%. According to the national standard GB / T - 14337 - 2008, the mechanical properties of the steam drawn fibers are tested. Its fineness is 1.17 dtex, and the coefficient of variation of fineness is 9.7%.

[0132]

Example 8

[0133] The differences from Example 1 are as follows: during drying and densification, the temperatures and draw ratios in the four temperature zones are different; the steam drawing ratio is different;

[0134] Specifically:

[0135] The temperature in Zone 1 is 105 °C and the draw ratio is 0.98; the temperature in Zone 2 is 125 °C and the draw ratio is 0.99; the temperature in Zone 3 is 130 °C and the draw ratio is 0.99; the temperature in Zone 4 is 135 °C and the draw ratio is 1;

[0136] The steam drawing ratio is 2 times;

[0137] Except for the above differences, other conditions of Example 8 are the same as those of Example 1. After the above - mentioned steam drawing, steam drawn fibers are obtained.

[0138] The average number of hairiness in every 10,000 meters of fibers at the drying densification outlet roller is counted by an online camera to be 19. The mechanical properties of the dried and densified fibers are tested according to the national standard GB / T - 14337 - 2008. Its fineness is 7.46 dtex, the modulus is 115 cN / dtex, the breaking strength is 7.1 cN / dtex, and the coefficient of variation of fineness is 4.1%.

[0139] According to the national standard GB / T 23413 - 2009, the crystallinity of the freeze - dried polyacrylonitrile steam - drawn fibers is tested. After measurement, the crystallinity of the obtained fiber fineness is 85%. The mechanical properties of the steam - drawn fibers are tested according to the national standard GB / T - 14337 - 2008. Its fineness is 0.66 dtex, and the coefficient of variation of fineness is 10.4%.

[0140]

Example 9

[0141] (1) Spinning solution preparation: Acrylonitrile (AN) and itaconic acid (IA) with a mass ratio of 96:4, a solid content of 20 wt%, and azobisisobutyronitrile (AIBN) accounting for 0.4 wt% of the comonomers are distilled and added to a reactor with dimethyl sulfoxide (DMSO) as the solvent. Under nitrogen protection, the reaction is carried out at a constant temperature of 65 °C for 32 hours to obtain a binary acrylonitrile copolymer. After degassing, de - bubbling, and re - filtration, a polyacrylonitrile copolymer spinning dope is obtained.

[0142] (2) Preparation of polyacrylonitrile dry - densified fibers: Wet spinning is used. The spinning dope is extruded through a spinneret with a pore size of 55 μm and enters a three - stage coagulation bath. The first coagulation bath is an aqueous solution of 70% dimethyl sulfoxide, the second coagulation bath is an aqueous solution of 60% dimethyl sulfoxide, and the third coagulation bath is an aqueous solution of 40% dimethyl sulfoxide. Then the coagulated fibers are washed with water and hot - drawn. The hot - drawing temperature is 85 °C, and the draw ratio is 2.0. The oiling residence time is 2 s, without drawing. The washing temperature is 70 °C, and the draw ratio is 1.0. Then the fibers are dried and densified using a step - by - step temperature - rising method, which is divided into four temperature zones. Among them, the temperature in zone 1 is 100 °C, and the draw ratio is 0.98; the temperature in zone 2 is 110 °C, and the draw ratio is 0.98; the temperature in zone 3 is 120 °C, and the draw ratio is 0.99; the temperature in zone 4 is 130 °C, and the draw ratio is 1.02. The polyacrylonitrile dry - densified fibers are collected using a winder.

[0143] The average number of hairiness in every 10,000 meters of fiber at the drying densification outlet roller is counted by an online camera to be 18. The mechanical properties of the dried and densified fiber are tested according to the national standard GB / T - 14337 - 2008. Its fineness is 8.20 dtex, the modulus is 127 cN / dtex, the breaking strength is 5.6 cN / dtex, and the coefficient of variation of fineness is 4.8%.

[0144] After that, steam drawing is carried out using saturated steam. The steam pressure is 220 kpa, and the drawing ratio is 1.5 times. After steam drawing, the fiber is subjected to steam heat setting under saturated steam pressure.

[0145] According to the national standard GB / T 23413 - 2009, the crystallinity of the freeze - dried polyacrylonitrile steam - drawn fiber is tested. After measurement, the crystallinity of the obtained fiber fineness is 78.3%. The mechanical properties of the steam - drawn fiber are tested according to the national standard GB / T - 14337 - 2008. Its fineness is 1.16 dtex, and the coefficient of variation of fineness is 11.2%.

[0146]

Comparative Example 1

[0147] The differences from Example 1 are as follows: during drying densification, the temperatures and draw ratios in the 4 temperature zones are different; the steam drawing ratio is different;

[0148] Specifically:

[0149] The temperature in Zone 1 is 105 °C, and the draw ratio is 0.98; the temperature in Zone 2 is 115 °C, and the draw ratio is 0.98; the temperature in Zone 3 is 125 °C, and the draw ratio is 0.99; the temperature in Zone 4 is 135 °C, and the draw ratio is 1;

[0150] The steam drawing ratio is 1.3 times;

[0151] Except for the above differences, other conditions in Comparative Example 1 are the same as those in Example 1. After drying and densification, polyacrylonitrile dried and densified fiber is obtained, and after steam drawing, polyacrylonitrile steam - drawn fiber is obtained.

[0152] The average number of hairiness in every 10,000 meters of fiber at the drying densification outlet roller is counted by an online camera to be 29. The mechanical properties of the dried and densified fiber are tested according to the national standard GB / T - 14337 - 2008. Its fineness is 8.01 dtex, the modulus is 122 cN / dtex, the breaking strength is 3.7 cN / dtex, and the coefficient of variation of fineness is 7.5%.

[0153] The crystallinity of the freeze-dried polyacrylonitrile steam-drawn fiber was tested according to the national standard GB / T 23413-2009. After measurement, the crystallinity of the fiber fineness obtained was 65.5%. The mechanical properties of the steam-drawn fiber were tested according to the national standard GB / T-14337-2008. Its fineness was 1.04 dtex, and the coefficient of variation of the fineness was 16.1%.

[0154]

Comparative Example 2

[0155] The differences from Example 1 were as follows: during drying and densification, the temperatures and draw ratios in the 4 temperature zones were different; the steam draw ratio was different;

[0156] Specifically:

[0157] The temperature in Zone 1 was 105 °C, and the draw ratio was 0.98; the temperature in Zone 2 was 115 °C, and the draw ratio was 0.98; the temperature in Zone 3 was 125 °C, and the draw ratio was 0.99; the temperature in Zone 4 was 135 °C, and the draw ratio was 1;

[0158] The steam draw ratio was 3.5 times;

[0159] Except for the above differences, the other conditions in Comparative Example 2 were the same as those in Example 1. After drying and densification, polyacrylonitrile dried and densified fibers were obtained, and then polyacrylonitrile steam-drawn fibers were obtained after steam drawing.

[0160] The average number of flyings in the fibers with a length of 10,000 meters at the drying and densification outlet roller was counted by an on-line camera as 25. The mechanical properties of the dried and densified fibers were tested according to the national standard GB / T-14337-2008. Its fineness was 7.42 dtex, the modulus was 129 cN / dtex, the breaking strength was 4.6 cN / dtex, and the coefficient of variation of the fineness was 7.5%.

[0161] The crystallinity of the freeze-dried polyacrylonitrile steam-drawn fiber was tested according to the national standard GB / T 23413-2009. After measurement, the crystallinity of the fiber fineness obtained was 66.3%. The mechanical properties of the steam-drawn fiber were tested according to the national standard GB / T-14337-2008. Its fineness was 0.86 dtex, and the coefficient of variation of the fineness was 15.3%.

[0162]

Comparative Example 3

[0163] The differences from Example 1 were as follows: during drying and densification, the temperatures and draw ratios in the 4 temperature zones were different; the steam draw ratio was different;

[0164] Specifically:

[0165] The temperature in Zone 1 is 85 °C, and the draw ratio is 0.95; the temperature in Zone 2 is 98 °C, and the draw ratio is 0.98; the temperature in Zone 3 is 110 °C, and the draw ratio is 1; the temperature in Zone 4 is 120 °C, and the draw ratio is 1.02;

[0166] The steam drawing ratio is 2.5 times;

[0167] Except for the above differences, other conditions of Comparative Example 3 are the same as those of Example 1. After drying and densification, polyacrylonitrile dried and densified fibers are obtained, and then polyacrylonitrile steam drawn fibers are obtained after steam drawing.

[0168] The average number of fly filaments in the fibers per 10,000 meters in length at the outlet roller of drying and densification is counted by an on-line camera to be 26. The mechanical properties of the dried and densified fibers are tested according to the national standard GB / T - 14337 - 2008. Its fineness is 8.94 dtex, the modulus is 116 cN / dtex, the breaking strength is 5.4 cN / dtex, and the coefficient of variation of fineness is 6.3%.

[0169] The crystallinity of the freeze-dried polyacrylonitrile steam drawn fibers is tested according to the national standard GB / T 23413 - 2009. After measurement, the crystallinity of the obtained fiber fineness is 61.8%. The mechanical properties of the steam drawn fibers are tested according to the national standard GB / T - 14337 - 2008. Its fineness is 1.28 dtex, and the coefficient of variation of fineness is 14.9%.

[0170]

Comparative Example 4

[0171] The differences from Example 1 are as follows: during drying and densification, the temperatures and draw ratios in the 4 temperature zones are different; the steam drawing ratio is different;

[0172] Specifically:

[0173] The temperature in Zone 1 is 120 °C, and the draw ratio is 0.92; the temperature in Zone 2 is 130 °C, and the draw ratio is 0.94; the temperature in Zone 3 is 130 °C, and the draw ratio is 0.96; the temperature in Zone 4 is 140 °C, and the draw ratio is 0.98;

[0174] The steam drawing ratio is 2.5 times;

[0175] Except for the above differences, other conditions of Comparative Example 4 are the same as those of Example 1. After drying and densification, polyacrylonitrile dried and densified fibers are obtained, and then polyacrylonitrile steam drawn fibers are obtained after steam drawing.

[0176] The average number of hairiness in every 10,000 meters of fibers at the drying densification outlet roller was counted by an online camera to be 39. The mechanical properties of the dried and densified fibers were tested according to the national standard GB / T - 14337 - 2008. Its fineness was 7.12 dtex, the modulus was 103 cN / dtex, the breaking strength was 5.7 cN / dtex, and the coefficient of variation of fineness was 7.6%.

[0177] The crystallinity of the freeze - dried polyacrylonitrile steam - drawn fibers was tested according to the national standard GB / T 23413 - 2009. After measurement, the crystallinity of the obtained fiber fineness was 62.3%. The mechanical properties of the steam - drawn fibers were tested according to the national standard GB / T - 14337 - 2008. Its fineness was 0.67 dtex, and the coefficient of variation of fineness was 17.1%.

[0178]

Comparative Example 5

[0179] The differences from Example 1 were as follows: during drying densification, the temperatures and draw ratios in the 4 temperature zones were different; the steam draw ratio was different;

[0180] Specifically:

[0181] The temperature in Zone 1 was 88 °C and the draw ratio was 0.98; the temperature in Zone 2 was 97 °C and the draw ratio was 0.98; the temperature in Zone 3 was 108 °C and the draw ratio was 0.99; the temperature in Zone 4 was 115 °C and the draw ratio was 1;

[0182] The steam draw ratio was 2 times;

[0183] Except for the above differences, other conditions in Comparative Example 5 were the same as those in Example 1. After drying densification, polyacrylonitrile dried and densified fibers were obtained, and then polyacrylonitrile steam - drawn fibers were obtained after steam drawing.

[0184] The average number of hairiness in every 10,000 meters of fibers at the drying densification outlet roller was counted by an online camera to be 36. The mechanical properties of the dried and densified fibers were tested according to the national standard GB / T - 14337 - 2008. Its fineness was 8.08 dtex, the modulus was 121 cN / dtex, the breaking strength was 5.1 cN / dtex, and the coefficient of variation of fineness was 8.2%.

[0185] The crystallinity of the freeze - dried polyacrylonitrile steam - drawn fibers was tested according to the national standard GB / T 23413 - 2009. After measurement, the crystallinity of the obtained fiber fineness was 60.6%. The mechanical properties of the steam - drawn fibers were tested according to the national standard GB / T - 14337 - 2008. Its fineness was 0.98 dtex, and the coefficient of variation of fineness was 18.2%.

[0186]

Comparative Example 6

[0187] The differences from Example 1 are as follows: during dry densification, the temperatures and draw ratios in the four temperature zones are different; the steam drawing ratio is different;

[0188] Specifically:

[0189] The temperature in Zone 1 is 110 °C and the draw ratio is 0.90; the temperature in Zone 2 is 115 °C and the draw ratio is 0.95; the temperature in Zone 3 is 120 °C and the draw ratio is 0.97; the temperature in Zone 4 is 130 °C and the draw ratio is 0.98;

[0190] The steam drawing ratio is 2 times;

[0191] Except for the above differences, the other conditions of Comparative Example 6 are the same as those of Example 1. Polyacrylonitrile dry densified fibers are obtained through dry densification, and then polyacrylonitrile steam drawn fibers are obtained after steam drawing.

[0192] The average number of fly filaments in the fibers with a length of 10,000 meters at the dry densification outlet roller is counted by an on-line camera as 40. The mechanical properties of the dry densified fibers are tested according to the national standard GB / T - 14337 - 2008. Its fineness is 7.03 dtex, the modulus is 117 cN / dtex, the breaking strength is 5.4 cN / dtex, and the coefficient of variation of fineness is 7.8%.

[0193] The crystallinity of the freeze-dried polyacrylonitrile steam drawn fibers is tested according to the national standard GB / T 23413 - 2009. After measurement, the crystallinity of the obtained fiber fineness is 61.9%. The mechanical properties of the steam drawn fibers are tested according to the national standard GB / T - 14337 - 2008. Its fineness is 0.63 dtex, and the coefficient of variation of fineness is 17.9%.

[0194]

Comparative Example 7

[0195] The differences from Example 1 are as follows: during dry densification, the temperatures and draw ratios in the four temperature zones are different; the steam drawing ratio is different;

[0196] Specifically:

[0197] The temperature in Zone 1 is 88 °C and the draw ratio is 0.90; the temperature in Zone 2 is 95 °C and the draw ratio is 0.95; the temperature in Zone 3 is 108 °C and the draw ratio is 0.97; the temperature in Zone 4 is 115 °C and the draw ratio is 0.98;

[0198] The steam drawing ratio is 3.5 times;

[0199] Except for the above differences, the other conditions of Comparative Example 7 are the same as those of Example 1. Polyacrylonitrile dry densified fibers are obtained through dry densification, and then polyacrylonitrile steam drawn fibers are obtained after steam drawing.

[0200] The average number of hairiness in every 10,000 meters of fiber at the drying densification outlet roller is counted by an online camera to be 47. The mechanical properties of the dried and densified fibers are tested according to the national standard GB / T - 14337 - 2008. Its fineness is 6.57 dtex, the modulus is 103 cN / dtex, the breaking strength is 3.3 cN / dtex, and the coefficient of variation of fineness is 9.2%.

[0201] The crystallinity of the freeze - dried polyacrylonitrile steam - drawn fiber is tested according to the national standard GB / T 23413 - 2009. After measurement, the crystallinity of the obtained fiber fineness is 60.7%. The mechanical properties of the steam - drawn fiber are tested according to the national standard GB / T - 14337 - 2008. Its fineness is 0.86 dtex, and the coefficient of variation of fineness is 19.4%.

[0202]

Comparative Example 8

[0203] The differences from Example 1 are as follows: During wet spinning, the hot - water drawing temperature is 95 °C and the drawing ratio is 1.4; the water - washing temperature is 60 °C and the drawing ratio is 1.5;

[0204] Except for the above differences, other conditions of Comparative Example 8 are the same as those of Example 1. Polyacrylonitrile dried and densified fibers are obtained through drying densification, and then polyacrylonitrile steam - drawn fibers are obtained through steam drawing.

[0205] The average number of hairiness in every 10,000 meters of fiber at the drying densification outlet roller is counted by an online camera to be 19. The mechanical properties of the dried and densified fibers are tested according to the national standard GB / T - 14337 - 2008. Its fineness is 7.88 dtex, the modulus is 146 cN / dtex, the breaking strength is 5.5 cN / dtex, and the coefficient of variation of fineness is 5.9%.

[0206] The crystallinity of the freeze - dried polyacrylonitrile steam - drawn fiber is tested according to the national standard GB / T 23413 - 2009. After measurement, the crystallinity of the obtained fiber fineness is 64.8%. The mechanical properties of the steam - drawn fiber are tested according to the national standard GB / T - 14337 - 2008. Its fineness is 1.09 dtex, and the coefficient of variation of fineness is 12.7%.

[0207]

Comparative Example 9

[0208] The differences from Comparative Example 8 are as follows: during wet spinning, the pore diameter of the spinneret is 50 μm; in the three-stage coagulation bath, the first coagulation bath is an 80% aqueous solution of dimethyl sulfoxide, the second coagulation bath is a 53% aqueous solution of dimethyl sulfoxide, and the third coagulation bath is a 30% aqueous solution of dimethyl sulfoxide; the hot water drawing temperature is 95 °C, and the drawing ratio is 1.2; the water washing temperature is 80 °C, and the drawing ratio is 2.0;

[0209] Except for the above differences, other conditions of Comparative Example 9 are the same as those of Comparative Example 8. After drying and densification, polyacrylonitrile dried and densified fibers are obtained, and then polyacrylonitrile steam drawn fibers are obtained after steam drawing.

[0210] The average number of hairiness in the fibers per 10,000 meters in length at the drying and densification outlet roller is counted by an online camera to be 19. The mechanical properties of the polyacrylonitrile dried and densified fibers are tested according to the national standard GB / T - 14337 - 2008. Its fineness is 7.27 dtex, the modulus is 141 cN / dtex, the breaking strength is 5.5 cN / dtex, and the coefficient of variation of fineness is 5.9%.

[0211] The crystallinity of the freeze-dried polyacrylonitrile steam drawn fibers is tested according to the national standard GB / T 23413 - 2009. After measurement, the crystallinity of the obtained fiber fineness is 68.4%. The mechanical properties of the steam drawn fibers are tested according to the national standard GB / T - 14337 - 2008. Its fineness is 1.63 dtex, and the coefficient of variation of fineness is 13.5%.

[0212] By comparing with Comparative Examples 1 - 9, in Examples 1 - 9, drying and densification are carried out at four temperatures within a limited range of temperature and drawing ratio. The coefficient of variation of fineness of the obtained polyacrylonitrile dried and densified fibers is 1.9 - 5.9%, the breaking strength is 5.8 - 7.2 cN / dtex, the initial modulus is 110 - 150 cN / dtex, and the average number of hairiness in the fibers per 10,000 meters in length at the drying and densification outlet roller is 11 - 19. They have excellent properties, which proves that in Examples 1 - 9, by controlling the structure-activity relationship of the breaking elongation and the drawing ratio, the structure of the as-spun fibers can meet the requirements of less hairiness in the drying and densification stage and a small coefficient of variation of the fineness of the raw silk.

Claims

1. A polyacrylonitrile dry densified fiber is prepared by wet spinning followed by dry densification; the dry densification is in one stage and has four temperature zones; the temperature difference between every two adjacent temperature zones is 5-20°C, preferably 5-10°C.

2. The polyacrylonitrile dry densified fiber according to claim 1, characterized in that: The four temperature zones of the dry densification are respectively the first temperature zone, the second temperature zone, the third temperature zone and the fourth temperature zone; preferably, The temperature of the first temperature zone is 90-120°C, and the draw ratio is 0.95-1; and / or, The temperature of the second temperature zone is 100-130°C, and the draw ratio is 0.96-1.01; and / or, The temperature of the third temperature zone is 110-130°C, and the draw ratio is 0.98-1.02; and / or, The temperature of the fourth temperature zone is 120-140°C, and the draw ratio is 0.99-1.

03.

3. The polyacrylonitrile dry densified fiber according to claim 1 or 2, characterized in that: The fineness of the polyacrylonitrile dry densified fiber is 7-9 dtex; and / or, The coefficient of variation of the fineness of the polyacrylonitrile dry densified fiber is 1.5-6%; and / or, The breaking strength of the polyacrylonitrile dry densified fiber is 5.8-9.2 cN / dtex, preferably 5.8-7.5 cN / dtex; and / or, The initial modulus of the polyacrylonitrile dry densified fiber is 110 c-150 cN / dtex; and / or, The average number of fly filaments in every 10,000 meters of fiber at the dry densification exit roller is below 24, preferably below 20.

4. A method for preparing a polyacrylonitrile dry densified fiber according to any one of claims 1-3, comprising the following steps: (1) Prepare a polyacrylonitrile copolymer spinning dope; (2) Wet-spin the polyacrylonitrile copolymer spinning dope obtained in step (1), and after dry densification, obtain the polyacrylonitrile dry densified fiber.

5. The method for preparing a polyacrylonitrile dry densified fiber according to claim 4, characterized in that: Step (1), Copolymerize an acrylic acid compound and its derivatives, acrylonitrile in the presence of an initiator and a solvent to obtain a polyacrylonitrile copolymer spinning dope; the acrylic acid compound and its derivatives are preferably at least one of acrylic acid, itaconic acid, methyl acrylate, methyl methacrylate; further preferably, Based on the total mass of the acrylic acid compound and its derivatives, acrylonitrile being 100%, it includes: Acrylic acid compound and its derivatives 2-5%; Acrylonitrile 95-98%; Even more preferably, The solvent is at least one of dimethyl sulfoxide, dimethylformamide, dimethylacetamide; and / or, The dosage of the initiator is 0.1-1 wt% of the total mass of the reaction monomers, preferably 0.1-0.5 wt%; and / or, The mass ratio of the solvent to the total mass of the reaction monomers is (1.5-7):1, preferably (2-6):1; and / or, The reaction is carried out in a protective gas atmosphere, and the protective gas is at least one of nitrogen, inert gas; and / or, The reaction temperature is 55 to 95 °C, preferably 60 to 90 °C; and / or, The reaction time is 16 to 32 h, preferably 18 to 30 h; and / or, The post-treatment is degassing, defoaming, and filtration.

6. The method for preparing a polyacrylonitrile dry and densified fiber according to claim 4, wherein: Step (2), The wet spinning includes spinning extrusion, coagulation molding, hot water drawing, water washing, and oiling; preferably, The spinning extrusion is performed by extruding from a spinneret with a pore diameter of 50 to 55 μm; and / or, The coagulation molding is carried out in a three-stage coagulation bath, and the three-stage coagulation bath includes a first coagulation bath, a second coagulation bath, and a third coagulation bath; the first coagulation bath, the second coagulation bath, and the third coagulation bath are aqueous organic solvent solutions, and the organic solvent is the same as the solvent in step (1), and the concentration of the organic solvent in the first coagulation bath, the second coagulation bath, and the third coagulation bath decreases gradually; preferably, the concentration of the organic solution in the first coagulation bath is 70 to 80 wt%; and / or, the concentration of the organic solution in the second coagulation bath is 50 to 60 wt%; and / or, the concentration of the organic solution in the third coagulation bath is 30 to 40 wt%; and / or, The temperature of the hot water drawing is 80 to 95 °C, and the hot water drawing ratio is 1.5 to 3 times; and / or, The temperature of the water washing is 60 to 80 °C, and the water washing drawing ratio is 1 to 1.5 times; and / or, The residence time of the oiling is not higher than 2 seconds, and no drawing is performed; and / or, The polyacrylonitrile dry and densified fiber is collected by a winding machine.

7. A polyacrylonitrile dry and densified fiber obtained by the preparation method according to any one of claims 4 to 6.

8. A polyacrylonitrile steam-drawn fiber obtained by steam-drawing a polyacrylonitrile dry and densified fiber; the polyacrylonitrile dry and densified fiber is the polyacrylonitrile dry and densified fiber according to any one of claims 1 to 3, 7; The crystallinity and the steam drawing ratio of the polyacrylonitrile steam-drawn fiber satisfy the following relationship: 0.26x + 70 ≤ y ≤ 2x + 82; Among them, y is the crystallinity, %; x is the drawing ratio; x is 1.5 to 3.

9. The polyacrylonitrile steam-drawn fiber according to claim 8, wherein: The fineness of the polyacrylonitrile steam-drawn fiber is 0.61 to 1.3 dtex; and / or, The coefficient of variation of the fineness of the polyacrylonitrile steam-drawn fiber is 5 to 12%.

10. A method for preparing a polyacrylonitrile steam drawing fiber as described in claim 8 or 9, comprising: The polyacrylonitrile steam-drawn fiber is obtained by steam-drawing the polyacrylonitrile dry and densified fiber; the drawing ratio of the steam drawing is 1.5 to 3 times; preferably, The steam pressure of the steam drawing is 220 kpa; and / or, After the steam drawing, steam heat setting is performed, and more preferably, the fiber is heat-set with saturated water steam.

11. The application of the polyacrylonitrile dry and densified fiber according to any one of claims 1 to 3, 7 or the polyacrylonitrile steam-drawn fiber according to claim 8 or 9 or the polyacrylonitrile steam-drawn fiber obtained by the preparation method according to claim 10 in the fields of high-strength carbon fibers and composites.