Polyacrylonitrile steam-drawn fiber as well as preparation method and application thereof

Abstract

The invention provides a polyacrylonitrile steam-drawn fiber as well as a preparation method and application thereof. The polyacrylonitrile steam drafting fiber is prepared by wet spinning, drying densification and steam drafting; the orientation degree and the steam drafting rate of the polyacrylonitrile steam drafting fiber meet the following relational expression:-0.022 x < 2 > + 0.12 x + 0.58 < = y < =-0.033 x < 2 > + 0.18 x + 0.87; wherein y is the orientation degree, and x is the steam drafting ratio; 1 < = x < = 5; the preparation method comprises the following steps: preparing a polyacrylonitrile copolymer spinning solution, carrying out wet spinning, and carrying out drying densification and steam drafting to obtain the polyacrylonitrile steam drafting fiber. The technical problems that in the steam drafting process, the number of broken filaments is large, the elongation at break of fibers after steam drafting is low, and the dispersion coefficient is high are solved.

Description

Technical Field

[0001] The present invention relates to the field of carbon fibers, and more particularly, to a polyacrylonitrile steam-drawn fiber and its preparation method and application. Background Art

[0002] Carbon fiber is a fibrous graphite material with a carbon content of more than 90%, which is prepared by processes such as pre-oxidation, carbonization, and graphitization of fibrous organic compounds. It has a series of excellent properties such as high specific strength, high specific modulus, high temperature resistance, corrosion resistance, fatigue resistance, creep resistance, electrical conductivity, heat transfer, and small coefficient of thermal expansion. Its molecular structure is between graphite and diamond, with high axial strength and modulus, low density, high specific function, ultra-high temperature resistance in a non-oxidizing environment, good fatigue resistance, and good corrosion resistance. According to the industrial production raw material route, carbon fibers can be divided into three categories: polyacrylonitrile-based carbon fibers, pitch-based carbon fibers, and viscose-based carbon fibers. Polyacrylonitrile-based carbon fibers are widely used and promoted because of their relatively simple production process and better mechanical properties of the products.

[0003] The drying densification process is a process of pore closure, which plays a key role in improving the denseness of the precursor fiber. How to better control the solidification molding and drying densification processes has a great impact on the properties of the precursor fiber, and thus will also affect the corresponding carbon fiber. Under the conditions of other process curing, good cooperation between solidification molding and drying densification can well complete the pore closure, which will help improve the tensile strength of the later carbon fiber, but high denseness will make the oxidation process difficult.

[0004] Steam drawing is under the heating action of steam and the plasticizing action of water, so that the filament temperature is higher than the glass transition temperature. Under such thermal effects, the mobility of macromolecular chain segments increases. Then, by applying a certain tensile stress, the axial aggregation and rearrangement of structural units are improved, which is beneficial to the orientation of the precursor fiber and helps to obtain high-quality carbon fibers. Steam drawing is beneficial to the optimization of the optimal stress state of the molecular chain, plays an important role in the fineness reduction of the precursor fiber diameter, high fiber orientation and high strength, and is also beneficial to the improvement of the production speed of the precursor fiber. Therefore, it has become a key technology for producing high-quality carbon fibers.

[0005] Patent CN114687010A discloses a high-strength, high-modulus and high-elongation carbon fiber and its preparation method. The elongation at break of the precursor fiber prepared by this method is 9.5-11%. Although the subsequent properties of the prepared carbon fiber are good, the unevenness rate and cv value are not controlled, and the production stability cannot be completely guaranteed.

[0006] Patent CN109023593A discloses a method for improving the performance of polyacrylonitrile carbon fiber produced by the sodium thiocyanate method, which improves the performance of the precursor by controlling the three precursor drawing steps of cold drawing, hot water drawing and steam drawing to achieve a higher total drawing multiple. However, it only controls two factors, namely the temperature during drawing and the mass ratio of fiber to water, and does not control the drawing multiple of the steam drawing part. Moreover, although it explains the improvement of the precursor strength and modulus, the change of the elongation at break is not explained.

[0007] Patent CN111088543A discloses a method for manufacturing polyacrylonitrile carbon fiber precursor, which reduces the amount of hair produced during the pre-oxidation process by controlling the tension on each fiber during the steam drawing process, and limits the drying and densification temperature and drawing ratio involved in the method.

[0008] Patent CN115707801A discloses a method for preparing polyacrylonitrile pre-oxidized fibers, which controls the circulation flow of heat transfer oil to achieve control of the drying and densification temperature and the reduction of the CV value of the drying and densification hot roller surface temperature, thereby improving the pullability of polyacrylonitrile precursor during the pre-oxidation process and reducing the number of hairy fibers. This method only discloses the results of the orientation degree of the fiber after oiling, and does not disclose the specific improvement of the precursor obtained by using this method.

[0009] Patent CN109082730A discloses a large-diameter polyacrylonitrile carbon fiber and its preparation method, which improves mechanical properties such as tensile strength by controlling the fiber diameter during coagulation, washing, and drying. However, the tensile modulus of the carbon fiber obtained by this method is only 230-260GPa, the control of the number of hairs needs to be improved, and the high linear density will limit the application range of its carbon fiber products.

[0010] In view of this, the present invention is proposed. Summary of the invention

[0011] In order to solve the technical problems existing in the prior art, the present invention provides a polyacrylonitrile steam-drawn fiber and a preparation method and application thereof.

[0012] The invention solves the technical problems that the number of hairy filaments is large during steam drawing, the elongation at break of fibers is low and the dispersion coefficient is high after steam drawing.

[0013] The inventors have found through in-depth research that during the steam drawing process, as the draw ratio increases, the fiber orientation first increases and then decreases. At the same time, an excessively high draw ratio will increase the friction between the fiber and the roller, resulting in more surface defects of the fiber, an increase in the number of broken filaments, and a decline in fiber properties. The presence of tension will also change the friction between the tow and the roller. By controlling the magnitude of the tension, the surface defects of the fiber can be further reduced, the fiber properties can be improved, and the generation of broken filaments can be reduced.

[0014] The drying densification process is a process of pore closure, which plays a key role in improving the denseness of the precursor fiber. There are certain differences in the pore closure performance of the as-spun fiber at different temperatures. If the tow thickness is too thick, the surface temperature will be too high while the temperature inside the tow is insufficient, resulting in a larger non-uniformity rate of pore closure of the fiber and affecting the fiber properties. If the residence time is too long, the water content of the fiber will decrease, the swelling degree difference will be obvious, and the surface temperature of the roller will cause damage to the fiber and a decline in performance.

[0015] The inventors have found through further research that the results of the above factors can be comprehensively reflected in the relationship between the fiber orientation and the steam draw ratio. That is, the draw ratio control and tension control during the above steam drawing process, and the tow thickness control and residence time control during the drying densification process will make the fiber orientation and the steam draw ratio satisfy a specific relational expression, that is:

[0016] -0.022x2 + 0.12x + 0.58 ≤ y ≤ -0.033x2 + 0.18x + 0.87

[0017] Wherein, y is the orientation degree and x is the draw ratio.

[0018] One of the purposes of the present invention is to provide a polyacrylonitrile steam-drawn fiber, which is prepared by wet spinning followed by drying densification and steam drawing; the orientation degree of the polyacrylonitrile steam-drawn fiber and the steam draw ratio satisfy the following relational expression:

[0019] -0.022x 2 + 0.12x + 0.58 ≤ y ≤ -0.033x 2 + 0.18x + 0.87;

[0020] Wherein, y is the orientation degree and x is the steam draw ratio;

[0021] 1 ≤ x ≤ 5, preferably 1.5 ≤ x ≤ 4.

[0022] In a preferred embodiment of the present invention,

[0023] During the drying densification process, the tow thickness is 50 - 500 microns, and the tow thickness refers to the cross-sectional thickness of a bundle of filaments.

[0024] The starting temperature of the drying densification is not lower than 95 °C, and the ending temperature is not higher than 135 °C;

[0025] The time for the drying densification is 30 - 180 s, preferably 90 - 130 s;

[0026] The fiber swelling degree after the drying densification is 80 - 125%;

[0027] A winding machine is used to collect the fibers after the drying densification and then perform steam drawing;

[0028] The steam drawing uses saturated water vapor as the medium;

[0029] The tension of the fiber during the steam drawing process is 3400 - 9500 cN; under the condition of a fixed steam pressure, the higher the drawing ratio, the greater the tension. In the present invention, the drawing is preferably performed at a steam pressure of 220 kPa;

[0030] The specifications of the steam-drawn tow are 1k, 3k, 6k or 12k; the tow specification refers to the number of fibers in a bundle of tow;

[0031] The total drawing ratio does not exceed 9 times, preferably does not exceed 7 times; the total drawing ratio refers to the total drawing ratio of the polyacrylonitrile steam-drawn fiber during the processes of wet spinning, drying densification, and steam drawing.

[0032] In a preferred embodiment of the present invention,

[0033] The fineness of the polyacrylonitrile steam-drawn fiber is 0.6 - 1.3 dtex;

[0034] The coefficient of variation (cv value) of the fineness of the polyacrylonitrile steam-drawn fiber is 5 - 10%;

[0035] The breaking elongation of the polyacrylonitrile steam-drawn fiber is 8.5 - 13%;

[0036] The average number of flyings per 10,000 meters at the steam drawing outlet is less than 25.

[0037] The second object of the present invention is to provide a method for preparing a polyacrylonitrile steam-drawn fiber, comprising the following steps:

[0038] (1) Prepare a polyacrylonitrile copolymer spinning dope;

[0039] (2) Wet-spin the polyacrylonitrile copolymer spinning dope obtained in step (1), and after drying densification and steam drawing, obtain the polyacrylonitrile steam-drawn fiber.

[0040] In a preferred embodiment of the present invention,

[0041] Step (1),

[0042] The polyacrylonitrile copolymer spinning dope can be prepared by common spinning processes in the art without special limitation. For example, but not limited to, the comonomer of the polyacrylonitrile is a vinyl-containing monomer, preferably at least one of acrylate, vinyl ester, acrylamide, sulfonate, ammonium salt, etc.; preferably,

[0043] The polyacrylonitrile copolymer spinning dope is obtained by copolymerizing an acrylic compound and its derivative, and acrylonitrile in the presence of an initiator and a solvent; the acrylic compound and its derivative are preferably at least one of acrylic acid, itaconic acid, methyl acrylate, methyl methacrylate; further preferably,

[0044] Based on the total mass of the acrylic compound and its derivative, and acrylonitrile being 100%, it includes:

[0045] The acrylic compound and its derivative: 2 - 5%;

[0046] Acrylonitrile: 95 - 98%;

[0047] 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, in the polyacrylonitrile copolymer, 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%;

[0048] Even more preferably,

[0049] The acrylonitrile is distilled acrylonitrile;

[0050] The initiator is a commonly used initiator in the prior art, such as azobisisobutyronitrile;

[0051] The solvent is a commonly used solvent in the prior art, preferably at least one of dimethyl sulfoxide, dimethylformamide, dimethylacetamide;

[0052] The dosage of the initiator is 0.1 - 1 wt% of the total mass of the reaction monomers, preferably 0.1 - 0.5 wt%;

[0053] The mass ratio of the solvent to the total mass of the reaction monomers is (1.5 - 7):1, preferably (2 - 6):1;

[0054] The reaction is carried out in a protective gas atmosphere, and the protective gas is at least one of nitrogen and inert gas;

[0055] The reaction temperature is 55 - 95°C, preferably 60 - 90°C;

[0056] The reaction time is 16 to 32 h, preferably 18 to 30 h;

[0057] The post-treatment is degassing, defoaming and filtering.

[0058] In a preferred embodiment of the present invention,

[0059] Step (2),

[0060] The wet spinning includes spinning extrusion, coagulation molding, hot water drawing, water washing and oiling; preferably,

[0061] The spinning extrusion is carried out from a spinneret with a pore size of 50 to 60 μm;

[0062] 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 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 from 80 wt% to 30 wt%; preferably, the concentration of the first coagulation bath is 70 to 80 wt%; and / or, the concentration of the second coagulation bath is 45 to 60 wt%; and / or, the concentration of the third coagulation bath is 30 to 40 wt%; and / or, the total residence time in the three-stage coagulation bath is 30 to 180 s, more preferably 40 to 120 s;

[0063] The temperature of the hot water drawing is not lower than 80 °C, and the total drawing ratio is not higher than 3 times;

[0064] The temperature of the water washing is 50 to 75 °C, and no drawing is carried out;

[0065] The residence time of the oiling is not higher than 3 s, and no drawing is carried out.

[0066] The thickness of the tow and the fiber swelling degree are controlled by the three-stage coagulation bath and the multiple of the hot water drawing. The higher the multiple of the hot water drawing, the smaller the thickness, and the lower the concentration of the coagulation bath, the smaller the thickness.

[0067] In a preferred embodiment of the present invention,

[0068] Step (2),

[0069] The drying densification is divided into two temperature zones and adopts a stepped heating method. Preferably, the temperature of the first temperature zone is 95 to 110 °C, and the drawing ratio is 0.95 to 1; the temperature of the second temperature zone is 115 to 135 °C, and the drawing ratio is 0.98 to 1.02;

[0070] During the drying densification process, the thickness of the tow is 50 to 500 microns;

[0071] The starting temperature of the drying densification is not lower than 95 °C, and the ending temperature is not higher than 135 °C;

[0072] The time of the drying densification is 30 to 180 s, preferably 90 to 130 s;

[0073] The swelling degree of the fiber after the drying densification is 80 to 125%;

[0074] A winding machine is used to collect the fiber after the drying densification and then perform steam drawing.

[0075] In a preferred embodiment of the present invention,

[0076] Step (2),

[0077] Saturated water vapor is used as the medium for the steam drawing;

[0078] The tension of the fiber during the steam drawing process is 3400 to 9500 cN;

[0079] The specifications of the steam-drawn tow are 1k, 3k, 6k or 12k;

[0080] The total drawing ratio does not exceed 9 times, preferably does not exceed 7 times.

[0081] The third object of the present invention is to provide a polyacrylonitrile steam-drawn fiber obtained by the above preparation method.

[0082] The fourth object of the present invention is to provide an application of the polyacrylonitrile steam-drawn fiber in the preparation of polyacrylonitrile-based carbon fiber.

[0083] Compared with the prior art, the beneficial effects of the present invention:

[0084] The steam drawing ratio, tension control, hot water drawing temperature and ratio, tow thickness, drying densification time and temperature, residence time and drawing ratio during the oiling process, and total drawing ratio have a significant impact on the number of hairiness, the breaking elongation rate and the coefficient of variation of the polyacrylonitrile steam-drawn fiber. The polyacrylonitrile steam-drawn fiber prepared by the method of the present invention has the advantages of few hairiness, high breaking elongation rate and low coefficient of variation.

[0085] Adopting the technical scheme of the present invention, the number of hairiness contained in the fiber within 10000 meters continuously at the outlet roller of the steam-drawn green fiber is monitored by an on-line camera to be less than 25, the breaking elongation rate of the prepared steam-drawn fiber is greater than 8.5%, and the cv value is less than 10%, achieving good technical effects. Specific Embodiments

[0086] 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 used for further illustration of the present invention and cannot be understood as limiting the protection scope of the present invention. Some non-essential improvements and adjustments made by those skilled in the art to the present invention based on the content of the present invention still fall within the protection scope of the present invention.

[0087] The raw materials used in the examples and comparative examples are all conventional commercially available raw materials.

[0088] Testing method:

[0089] Mechanical property test of polyacrylonitrile steam-stretched fiber: The mechanical properties of the steam-stretched fiber were tested according to the national standard GB / T - 14337 - 2008. Take a fiber bundle with a length of 40 mm from the steam-stretched fiber bundle, and take out about 500 fibers from it, and lay them evenly on the velvet board for measurement. Randomly take out a nascent fiber from the sample to be tested with tweezers, clamp one end of the fiber with a tension clamp of 0.1 cN, and place the fiber in the holder of the instrument to 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 stretching speed (20 mm / min), and the number of samples (50). Start the single-filament strength tester and the data acquisition device, start the stretching test, and obtain the strength, modulus, and stress-strain curve results of the single filament of the steam-stretched fiber.

[0090] Orientation degree test of polyacrylonitrile steam-stretched fiber: The crystallinity of the polyacrylonitrile steam-stretched fiber was tested according to the national standard GB / T 23413 - 2009. Take a fiber bundle with a length of about 50 mm from the fiber, straighten it and lay it evenly on the tablet, fix it for measurement. Press the button on the sample chamber door. When you hear a continuous "beep-beep" sound and the indicator light flashes, gently open the sample chamber door with both hands, then insert the sample holder 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 means that the sample chamber has been closed and the test can be carried out. After setting the sample name and test conditions (including the 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 orientation degree result.

[0091] Test of the swelling degree of polyacrylonitrile dried and densified fiber: Take a section of dried and densified fiber bundle (≥3 g), weigh it as W, and dry it in a hot air drying oven at 105°C for 2 h. Take out the fiber bundle and cool it to room temperature in a desiccator, weigh it as W0, and calculate the swelling degree BG of the dried and densified fiber bundle according to the following formula, that is

[0092] Swelling degree BG(%) = (W - W0) / W0 × 100%

[0093] Wherein, W is the weight of the dried and densified fiber bundle itself + the weight of water in the pores of the dried and densified fiber bundle, and W0 is the weight of the dried and densified fiber bundle itself after drying.

[0094] The thickness of the tow during the drying and densification process: measured by a vernier caliper.

[0095] Statistics of the number of hairiness after steam drawing: Use an online camera to monitor the number of hairiness contained in the fibers within 10,000 meters continuously at the outlet roller of the steam drawing.

[0096]

Example 1

[0097] (1) Preparation of the spinning solution: The distilled acrylonitrile (AN) and itaconic acid (IA) were added to the reactor according to a mass ratio of 98:2, with a solid content of 20%, and azobisisobutyronitrile (AIBN) accounting for 0.3 wt% of the comonomers. Using dimethyl sulfoxide (DMSO) as the solvent, the reaction was carried out at a constant temperature of 70°C for 24 hours under nitrogen protection to obtain a binary acrylonitrile copolymer. After degassing, defoaming, and re-filtration, a polyacrylonitrile copolymer spinning dope was obtained.

[0098] (2) Preparation of polyacrylonitrile steam-drawn fibers: Wet spinning was used. The spinning dope was extruded through a spinneret with a pore diameter of 55 μm and then entered a three-stage coagulation bath. The first coagulation bath was an aqueous solution of dimethyl sulfoxide with a concentration of 80%, the second coagulation bath was an aqueous solution of dimethyl sulfoxide with a concentration of 55%, and the third coagulation bath was an aqueous solution of dimethyl sulfoxide with a concentration of 30%; the total residence time in the three-stage coagulation bath was 80 s. Then, the coagulated fibers were subjected to hot water drawing and water washing treatments. Among them, the hot water drawing temperature was 85°C, the drawing ratio was 2.0, and the temperature was maintained at 70°C during the water washing process without drawing. Then, oiling was carried out in an oil bath with an oil concentration of 4% for a residence time of 2 s without drawing. Then, the fibers were dried and densified, which was divided into two temperature zones. The temperature of the first temperature zone was 95°C, the drawing ratio was 0.95, the temperature of the second temperature zone was 120°C, the drawing ratio was 1.0, and the drying and densification time was 120 s. The thickness of the tow and the fiber swelling degree were controlled by the multiples of the coagulation bath and hot water drawing. The thickness of the tow measured by a vernier caliper at the outlet roller of the drying and densification was 0.46 mm. A winding machine was used to collect the dried and densified fibers, and the swelling degree of the dried and densified fibers was measured to be 120.96%. Saturated steam was used to carry out steam drawing on the dried and densified fibers, and the drawing ratio was 1.5 times. The temperature was adjusted by controlling the steam pressure, thereby indirectly controlling the tension. During the process, the tow tension was maintained at 3591 cN, and the total drawing ratio was 3 times to obtain steam-drawn fibers. The steam-drawn tow specification was 12k.

[0099] (3) Fiber property evaluation and testing: According to the national standard GB / T 23413-2009, the orientation test of polyacrylonitrile steam-stretched fiber was carried out. After measurement, the orientation degree of the obtained fiber was 0.78. According to the national standard GB / T-14337-2008, the mechanical property test of the steam-stretched fiber was carried out. Its fineness was 1.29 dtex, the coefficient of variation of fineness was 6.74%, and the elongation at break was 12.48%. The average number of hairiness per 10,000 meters at the steam-stretching outlet was counted by an online camera as 13.

[0100]

Example 2

[0101] The difference from Example 1 was that when using saturated steam to perform steam stretching on the dried and densified fiber, the tow tension was maintained at 5181 cN and the stretching ratio was 2 times; the first coagulation bath was an aqueous solution of dimethyl sulfoxide with a concentration of 80%, the second coagulation bath was an aqueous solution of dimethyl sulfoxide with a concentration of 55%, and the third coagulation bath was an aqueous solution of dimethyl sulfoxide with a concentration of 40%.

[0102] Except for the above differences, other conditions of Example 2 were the same as those of Example 1. The tow thickness was measured by a vernier caliper at the dried and densified outlet roll to be 0.28 mm, and the swelling degree of the dried and densified fiber at this time was measured to be 117.67%; the steam-stretched fiber was obtained after the above steam stretching.

[0103] According to the national standard GB / T 23413-2009, the orientation test of polyacrylonitrile steam-stretched fiber was carried out. After measurement, the orientation degree of the obtained fiber was 0.81. According to the national standard GB / T-14337-2008, the mechanical property test of the steam-stretched fiber was carried out. Its fineness was 0.96 dtex, the coefficient of variation of fineness was 6.83%, and the elongation at break was 10.63%. The average number of hairiness per 10,000 meters at the steam-stretching outlet was counted by an online camera as 14.

[0104]

Example 3

[0105] The difference from Example 1 was that when using saturated steam to perform steam stretching on the dried and densified fiber, the tow tension was maintained at 7058 cN and the stretching ratio was 2.5 times; the first coagulation bath was an aqueous solution of dimethyl sulfoxide with a concentration of 75%, the second coagulation bath was an aqueous solution of dimethyl sulfoxide with a concentration of 58%, and the third coagulation bath was an aqueous solution of dimethyl sulfoxide with a concentration of 35%.

[0106] Except for the above differences, other conditions of Example 3 were the same as those of Example 1. The tow thickness was measured by a vernier caliper at the dried and densified outlet roll to be 0.15 mm, and the swelling degree of the dried and densified fiber at this time was measured to be 105.82%; the steam-stretched fiber was obtained after the above steam stretching.

[0107] The orientation of the polyacrylonitrile steam-drawn fiber was tested according to the national standard GB / T 23413-2009. After measurement, the orientation degree of the obtained fiber was 0.86. The mechanical properties of the steam-drawn fiber were tested according to the national standard GB / T-14337-2008. Its fineness was 0.76 dtex, the coefficient of variation of fineness was 7.35%, and the elongation at break was 10.23%. The average number of fly filaments per 10,000 meters at the steam-drawing outlet was counted by an online camera to be 11.

[0108]

Example 4

[0109] The difference from Example 1 was that when using saturated steam to perform steam drawing on the dried and densified fiber, the tow tension was maintained at 8272 cN and the drawing ratio was 3 times; the first coagulation bath was an aqueous solution of dimethyl sulfoxide with a concentration of 80%, the second coagulation bath was an aqueous solution of dimethyl sulfoxide with a concentration of 48%, and the third coagulation bath was an aqueous solution of dimethyl sulfoxide with a concentration of 32%. The total residence time in the three-stage coagulation bath was 60 s;

[0110] Except for the above differences, other conditions of Example 4 were the same as those of Example 1. The tow thickness was measured by a vernier caliper at the dried and densified outlet roll to be 0.10 mm, and the swelling degree of the dried and densified fiber at this time was measured to be 94.28%; the steam-drawn fiber was obtained after the above steam drawing.

[0111] The orientation of the polyacrylonitrile steam-drawn fiber was tested according to the national standard GB / T 23413-2009. After measurement, the orientation degree of the obtained fiber was 0.92. The mechanical properties of the steam-drawn fiber were tested according to the national standard GB / T-14337-2008. Its fineness was 0.67 dtex, the coefficient of variation of fineness was 5.80%, and the elongation at break was 9.73%. The average number of fly filaments per 10,000 meters at the steam-drawing outlet was counted by an online camera to be 14.

[0112]

Example 5

[0113] The difference from Example 1 was that when using saturated steam to perform steam drawing on the dried and densified fiber, the tow tension was maintained at 9302 cN and the drawing ratio was 3.5 times; the first coagulation bath was an aqueous solution of dimethyl sulfoxide with a concentration of 80%, the second coagulation bath was an aqueous solution of dimethyl sulfoxide with a concentration of 48%, and the third coagulation bath was an aqueous solution of dimethyl sulfoxide with a concentration of 32%. The residence time was 40 s;

[0114] Except for the above differences, other conditions of Example 5 were the same as those of Example 1. The tow thickness was measured by a vernier caliper at the dried and densified outlet roll to be 0.07 mm, and the swelling degree of the dried and densified fiber at this time was measured to be 82.71%; the steam-drawn fiber was obtained after the above steam drawing.

[0115] According to the national standard GB / T 23413-2009, the orientation test of polyacrylonitrile steam-drawn fiber was carried out. After measurement, the orientation degree of the obtained fiber was 0.88. According to the national standard GB / T-14337-2008, the mechanical properties of the steam-drawn fiber were tested. Its fineness was 0.61 dtex, the coefficient of variation of fineness was 6.25%, and the elongation at break was 9.04%. The average number of flyings per 10,000 meters at the steam-drawing outlet was counted by an online camera to be 16.

[0116]

Example 6

[0117] The difference from Example 1 is that when using saturated steam to perform steam drawing on the dried and densified fiber, the tow tension is maintained at 6363 cN and the drawing ratio is 2.5 times; the first coagulation bath is an aqueous solution of dimethyl sulfoxide with a concentration of 75%, the second coagulation bath is an aqueous solution of dimethyl sulfoxide with a concentration of 50%, and the third coagulation bath is an aqueous solution of dimethyl sulfoxide with a concentration of 35%, and the total residence time is 120 s;

[0118] Except for the above differences, the other conditions of Example 6 are the same as those of Example 1. The tow thickness was measured by a vernier caliper at the dried and densified outlet roll to be 0.18 mm. At this time, the swelling degree of the dried and densified fiber was measured to be 110.75%, and the steam-drawn fiber was obtained.

[0119] According to the national standard GB / T 23413-2009, the orientation test of polyacrylonitrile steam-drawn fiber was carried out. After measurement, the orientation degree of the obtained fiber was 0.82. According to the national standard GB / T-14337-2008, the mechanical properties of the steam-drawn fiber were tested. Its fineness was 0.85 dtex, the coefficient of variation of fineness was 8.41%, and the elongation at break was 10.26%. The average number of flyings per 10,000 meters at the steam-drawing outlet was counted by an online camera to be 17.

[0120]

Example 7

[0121] The difference from Example 1 is that when using saturated steam to perform steam drawing on the dried and densified fiber, the tow tension is maintained at 8561 cN and the drawing ratio is 2.5 times; the first coagulation bath is an aqueous solution of dimethyl sulfoxide with a concentration of 75%, the second coagulation bath is an aqueous solution of dimethyl sulfoxide with a concentration of 50%, and the third coagulation bath is an aqueous solution of dimethyl sulfoxide with a concentration of 35%. The residence time is 120 s;

[0122] Except for the above differences, the other conditions of Example 7 are the same as those of Example 1. The tow thickness was measured by a vernier caliper at the dried and densified outlet roll to be 0.34 mm. At this time, the swelling degree of the dried and densified fiber was measured to be 93.85%; after the above steam drawing, the steam-drawn fiber was obtained.

[0123] According to the national standard GB / T 23413-2009, the orientation of polyacrylonitrile steam-stretched fiber was tested. After measurement, the orientation degree of the obtained fiber was 0.82. According to the national standard GB / T-14337-2008, the mechanical properties of the steam-stretched fiber were tested. Its fineness was 0.81 dtex, the coefficient of variation of fineness was 9.94%, and the elongation at break was 8.62%. The average number of hairiness per 10,000 meters at the steam-stretching outlet was counted by an online camera to be 21.

[0124]

Example 8

[0125] (1) The preparation of the spinning solution was the same as that in Example 1 to obtain a polyacrylonitrile copolymer spinning dope.

[0126] (2) Preparation of polyacrylonitrile steam-stretched fiber: Wet spinning was used. The spinning dope was extruded through a spinneret with a pore size of 60 μm and then entered a three-stage coagulation bath. The first coagulation bath was an aqueous solution of dimethyl sulfoxide with a concentration of 79%, the second coagulation bath was an aqueous solution of dimethyl sulfoxide with a concentration of 50%, and the third coagulation bath was an aqueous solution of dimethyl sulfoxide with a concentration of 32%. The total residence time in the three-stage coagulation bath was 120 s. Then, the coagulated fiber was subjected to hot water stretching and water washing treatments. Among them, the hot water stretching temperature was 85 °C, the stretching ratio was 2.5, and the temperature was maintained at 52 °C during the water washing process without stretching. Then, oiling was carried out in an oil bath with an oil concentration of 4% for a residence time of 2 s without stretching. Then, the fiber was dried and densified. The drying and densification stage was divided into two temperature zones. The temperature of the first temperature zone was 98 °C, the stretching ratio was 0.98, the temperature of the second temperature zone was 110 °C, the stretching ratio was 1.0, and the drying and densification time was 120 s. The thickness of the tow was measured by a vernier caliper at the drying and densification outlet roller to be 0.32 mm. The winding machine was used to collect the dried and densified fiber. At this time, the swelling degree of the dried and densified fiber was measured to be 110.68%. The dried and densified fiber was steam-stretched using saturated steam with a stretching ratio of 1.5 times. The temperature was indirectly controlled by controlling the steam pressure to control the tension. During the process, the tow tension was maintained at 3491 cN, and the total stretching ratio was 3.75 times to obtain the steam-stretched fiber. The steam-stretched tow specification was 12k.

[0127] (3) Fiber property evaluation and testing: According to the national standard GB / T 23413-2009, the orientation of the polyacrylonitrile steam-stretched fiber was tested. After measurement, the orientation degree of the obtained fiber was 0.88. According to the national standard GB / T-14337-2008, the mechanical properties of the steam-stretched fiber were tested. Its fineness was 1.15 dtex, the coefficient of variation of fineness was 8.71%, and the elongation at break was 14.28%. The average number of hairiness per 10,000 meters at the steam-stretching outlet was counted by an online camera to be 18.

[0128]

Comparative Example 1

[0129] The differences from Example 1 are as follows: When using saturated steam to perform steam drawing on the dried and densified fiber, the tow tension is maintained at 2649 cN, and the drawing ratio is 1.2 times; the first coagulation bath is an aqueous solution of dimethyl sulfoxide with a concentration of 75%, the second coagulation bath is an aqueous solution of dimethyl sulfoxide with a concentration of 50%, and the third coagulation bath is an aqueous solution of dimethyl sulfoxide with a concentration of 35%. The residence time is 178 s;

[0130] Except for the above differences, other conditions of Comparative Example 1 are the same as those of Example 1. The tow thickness measured by a vernier caliper at the dried and densified outlet roller is 0.55 mm, and the swelling degree of the dried and densified fiber at this time is measured to be 160.61%; the steam-drawn fiber is obtained after the above steam drawing.

[0131] According to the national standard GB / T 23413-2009, the orientation of the polyacrylonitrile steam-drawn fiber is tested and measured, and the orientation degree of the obtained fiber is 0.66. According to the national standard GB / T-14337-2008, the mechanical properties of the steam-drawn fiber are tested. Its fineness is 1.54 dtex, the coefficient of variation of fineness is 17.68%, and the elongation at break is 7.37%. The average number of hairiness per 10,000 meters at the steam-drawn outlet is counted by an online camera to be 33.

[0132]

Comparative Example 2

[0133] The differences from Example 1 are as follows: When using saturated steam to perform steam drawing on the dried and densified fiber, the tow tension is maintained at 10454 cN, and the drawing ratio is 4.5 times; the first coagulation bath is an aqueous solution of dimethyl sulfoxide with a concentration of 80%, the second coagulation bath is an aqueous solution of dimethyl sulfoxide with a concentration of 50%, and the third coagulation bath is an aqueous solution of dimethyl sulfoxide with a concentration of 30%. The residence time is 20 s;

[0134] Except for the above differences, other conditions of Comparative Example 2 are the same as those of Example 1. The tow thickness measured by a vernier caliper at the dried and densified outlet roller is 0.04 mm, and the swelling degree of the dried and densified fiber at this time is measured to be 62.53%; the steam-drawn fiber is obtained after the above steam drawing.

[0135] The orientation of the polyacrylonitrile steam-drawn fiber was tested according to the national standard GB / T 23413-2009. After measurement, the orientation degree of the obtained fiber was 0.64. The mechanical properties of the steam-drawn fiber were tested according to the national standard GB / T-14337-2008. Its fineness was 0.53 dtex, the coefficient of variation of fineness was 19.68%, and the elongation at break was 7.03%. The average number of flyings per 10,000 meters at the steam-drawing outlet was counted by an online camera to be 36.

[0136]

Comparative Example 3

[0137] The differences from Example 1 were as follows: When using saturated steam to perform steam drawing on the dry densified fiber, the tow tension was maintained at 3048 cN, and the drawing ratio was 2.5 times; the first coagulation bath was an aqueous solution of dimethyl sulfoxide with a concentration of 70%, the second coagulation bath was an aqueous solution of dimethyl sulfoxide with a concentration of 55%, and the third coagulation bath was an aqueous solution of dimethyl sulfoxide with a concentration of 38%. The residence time was 120 s;

[0138] Except for the above differences, other conditions of Comparative Example 3 were the same as those of Example 1. The tow thickness was measured by a vernier caliper at the dry densification outlet roll to be 0.19 mm. At this time, the swelling degree of the dry densified fiber was measured to be 93.35%; the steam-drawn fiber was obtained after the above steam drawing.

[0139] The orientation of the polyacrylonitrile steam-drawn fiber was tested according to the national standard GB / T 23413-2009. After measurement, the orientation degree of the obtained fiber was 0.70. The mechanical properties of the steam-drawn fiber were tested according to the national standard GB / T-14337-2008. Its fineness was 0.79 dtex, the coefficient of variation of fineness was 10.83%, and the elongation at break was 8.87%. The average number of flyings per 10,000 meters at the steam-drawing outlet was counted by an online camera to be 26.

[0140]

Comparative Example 4

[0141] The differences from Example 1 were as follows: When using saturated steam to perform steam drawing on the dry densified fiber, the tow tension was maintained at 9826 cN, and the drawing ratio was 2.5 times; the first coagulation bath was an aqueous solution of dimethyl sulfoxide with a concentration of 75%, the second coagulation bath was an aqueous solution of dimethyl sulfoxide with a concentration of 50%, and the third coagulation bath was an aqueous solution of dimethyl sulfoxide with a concentration of 35%. The residence time was 120 s;

[0142] Except for the above differences, other conditions of Comparative Example 4 were the same as those of Example 1. The tow thickness was measured by a vernier caliper at the dry densification outlet roll to be 0.13 mm. At this time, the swelling degree of the dry densified fiber was measured to be 88.63%; the steam-drawn fiber was obtained after the above steam drawing.

[0143] According to the national standard GB / T 23413-2009, the orientation of the polyacrylonitrile steam-drawn fiber was tested. After measurement, the orientation degree of the obtained fiber was 0.71. According to the national standard GB / T-14337-2008, the mechanical properties of the steam-drawn fiber were tested. Its fineness was 0.73 dtex, the coefficient of variation of fineness was 9.64%, and the elongation at break was 9.01%. The average number of hairiness per 10,000 meters at the steam-drawing outlet was counted by an online camera and was 25.

[0144]

Comparative Example 5

[0145] (1) The spinning solution was prepared in the same way as in Example 1 to obtain a polyacrylonitrile copolymer spinning dope.

[0146] (2) Preparation of polyacrylonitrile steam-drawn fiber: Wet spinning was used. The spinning dope was extruded through a spinneret with a pore size of 60 μm and then entered a three-stage coagulation bath. The first coagulation bath was an aqueous solution of dimethyl sulfoxide with a concentration of 79%, the second coagulation bath was an aqueous solution of dimethyl sulfoxide with a concentration of 50%, and the third coagulation bath was an aqueous solution of dimethyl sulfoxide with a concentration of 32%. Then, the coagulated fiber was subjected to hot water drawing and water washing treatments. The hot water drawing temperature was 85 °C, the drawing ratio was 2.0, and the temperature was maintained at 52 °C during the water washing process without drawing. Then, it was oiled in an oil bath with an oil concentration of 4% for 2 s without drawing. Then, the fiber was dried and densified. The drying and densification stage was divided into two temperature zones. The temperature of the first temperature zone was 92 °C, the drawing ratio was 0.95, the temperature of the second temperature zone was 137 °C, and the drawing ratio was 1.0. The drying and densification time was 100 s. The thickness of the tow was measured by a vernier caliper at the outlet roller of the drying and densification, and it was 0.16 mm. The dried and densified fiber was collected by a winding machine. At this time, the swelling degree of the dried and densified fiber was measured to be 130.68%. The dried and densified fiber was steam-drawn using saturated steam, and the drawing ratio was 2.5 times. The temperature was adjusted by controlling the steam pressure to indirectly control the tension. During the process, the tow tension was maintained at 4591 cN, and the total drawing ratio was 5 times to obtain the steam-drawn fiber. The steam-drawn tow specification was 6k.

[0147] (3) Fiber property evaluation and testing: According to the national standard GB / T 23413-2009, the orientation of the polyacrylonitrile steam-drawn fiber was tested. After measurement, the orientation degree of the obtained fiber was 0.58. According to the national standard GB / T-14337-2008, the mechanical properties of the steam-drawn fiber were tested. Its fineness was 0.93 dtex, the coefficient of variation of fineness was 10.74%, and the elongation at break was 9.48%. The average number of hairiness per 10,000 meters at the steam-drawing outlet was counted by an online camera and was 23.

[0148] During the spinning process, in the steam drawing process, as the draw ratio increases, the fiber orientation first increases and then decreases. At the same time, an excessive draw ratio will increase the friction between the fiber and the roller, resulting in more surface defects of the fiber, an increase in the number of flyings, and a decline in fiber properties. The existence of tension will also change the friction between the tow and the roller. By controlling the magnitude of the tension, the surface defects of the fiber can be further reduced, the fiber orientation can be improved, the fiber strength can be increased, and the generation of flyings can be reduced. The drying densification process is a process of pore closure, which also plays a key role in improving the denseness of the raw silk. There are certain differences in the pore closure performance of the nascent fiber at different temperatures. If the tow thickness is too thick, the surface temperature will be too high while the temperature inside the tow is insufficient, resulting in a larger non-uniformity rate of pore closure of the fiber, and stress concentration at larger defect points, affecting the fiber properties. If the residence time is too long, the moisture content of the fiber will decrease, and the swelling degree difference will be obvious. The temperature on the roller surface will damage the fiber and the performance will decline. Therefore, even if the draw ratio is the same, different processes will result in significant differences in the results.

[0149] The tow thicknesses of Comparative Examples 1 to 2 are relatively large, the tensions of Comparative Examples 1 and 3 are relatively small, the tensions of Comparative Examples 2 and 4 are relatively large, the starting temperature of the drying densification of Comparative Example 5 is relatively low, and the ending temperature is relatively high. The orientation degrees of Comparative Examples 1 to 5 do not satisfy the relationship between the fiber orientation degree and the steam draw ratio given in the present invention. Compared with Comparative Examples 1 to 5, the polyacrylonitrile steam-drawn fibers prepared in Examples 1 to 8 have the advantages of fewer flyings, higher elongation at break, and lower coefficient of variation, achieving better technical effects.

Claims

1. A polyacrylonitrile steam-drawn fiber is prepared by wet spinning followed by drying densification and steam drawing; the orientation degree and steam drawing ratio of the polyacrylonitrile steam-drawn fiber satisfy the following relational expression: -0.022x 2 +0.12x+0.58≤y≤-0.033x 2 +0.18x+0.87; Among them, y is the orientation degree and x is the steam drawing ratio; 1 ≤ x ≤ 5, preferably 1.5 ≤ x ≤ 4.

2. The polyacrylonitrile steam-drawn fiber according to claim 1, wherein: During the drying densification process, the tow thickness is 50 - 500 microns; and / or, The starting temperature of the drying densification is not lower than 95°C and the ending temperature is not higher than 135°C; and / or, The time of the drying densification is 30 - 180 s, preferably 90 - 130 s; and / or, The swelling degree of the fiber after the drying densification is 80 - 125%; and / or, The steam drawing uses saturated water vapor as the medium; and / or, The tension of the fiber during the steam drawing process is 3400 - 9500 cN; and / or, The specifications of the steam-drawn tow are 1k, 3k, 6k or 12k; and / or, The total drawing ratio does not exceed 9 times, preferably does not exceed 7 times.

3. The polyacrylonitrile steam-drawn fiber according to claim 1 or 2, wherein: The fineness of the polyacrylonitrile steam-drawn fiber is 0.6 - 1.3 dtex; and / or, The coefficient of variation of the fineness of the polyacrylonitrile steam-drawn fiber is 5 - 10%; and / or, The breaking elongation of the polyacrylonitrile steam-drawn fiber is 8.5 - 13%; and / or, The average number of hairiness in every 10,000 meters of fiber at the steam drawing outlet is less than 25.

4. A method for preparing a polyacrylonitrile steam-drawn 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 drying densification and steam drawing, obtain the polyacrylonitrile steam-drawn fiber.

5. The method for preparing a polyacrylonitrile steam-drawn fiber according to claim 4, wherein: Step (1), Copolymerize an acrylic acid compound and its derivatives, and 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, and methyl methacrylate; further preferably, Based on the total mass of the acrylic acid compound and its derivatives and 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, and 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 and 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 de-single, de-bubbling, and filtration.

6. The method for preparing a polyacrylonitrile steam drawing 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 extruded from a spinneret with a pore diameter of 50 to 60 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 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 from 80 wt% to 30 wt%; preferably, the concentration of the first coagulation bath is 70 to 80 wt%; and / or, the concentration of the second coagulation bath is 45 to 60 wt%; and / or, the concentration of the third coagulation bath is 30 to 40 wt%; and / or, the total residence time in the three-stage coagulation bath is 30 to 180 s, more preferably 40 to 120 s; and / or, The temperature of the hot water drawing is not lower than 80 °C, and the total drawing ratio is not higher than 3 times; and / or, The temperature of the water washing is 50 to 75 °C, without drawing; and / or, The residence time of the oiling is not higher than 3 seconds, without drawing.

7. The method for preparing a polyacrylonitrile steam drawing fiber according to claim 4, wherein: Step (2), The drying densification is divided into two temperature zones and adopts a stepwise heating method. Preferably, the temperature of the first temperature zone is 95 to 110 °C, and the drawing ratio is 0.95 to 1; the temperature of the second temperature zone is 115 to 135 °C, and the drawing ratio is 0.98 to 1.02; and / or, The thickness of the fiber bundle during the drying densification is 50 to 500 microns; and / or, The starting temperature of the drying densification is not lower than 95 °C, and the ending temperature is not higher than 135 °C; and / or, The time of the drying densification is 30 to 180 s, preferably 90 to 130 s; and / or, The swelling degree of the fiber after the drying densification is 80 to 125%.

8. The method for preparing a polyacrylonitrile steam drawing fiber according to claim 4, wherein: Step (2), The steam drawing uses saturated water vapor as the medium; and / or, The tension of the fiber during the steam drawing process is 3400 to 9500 cN; and / or, The specifications of the steam drawing fiber bundle are 1k, 3k, 6k, or 12k; and / or, The total drawing ratio does not exceed 9 times, preferably does not exceed 7 times.

9. A polyacrylonitrile steam drawing fiber obtained by the preparation method according to any one of claims 4 to 8.

10. An application of a polyacrylonitrile steam drawing fiber according to any one of claims 1 to 3, 9 in the preparation of polyacrylonitrile-based carbon fibers.