A polyacrylonitrile precursor fiber and a method for producing the same, and a polyacrylonitrile-based pre-oxidized fiber and a polyacrylonitrile-based carbon fiber

Abstract

This invention relates to the field of chemical fiber manufacturing technology, and particularly to a polyacrylonitrile precursor fiber and its preparation method, as well as polyacrylonitrile-based pre-oxidized fibers and polyacrylonitrile-based carbon fibers. The method for preparing polyacrylonitrile precursor fiber provided by this invention involves dissolving polyacrylonitrile in a solvent to obtain a spinning solution; mixing dimethyl sulfoxide with water to prepare a basic coagulation bath, and introducing a zinc source and an ammonia-based coagulation agent to maintain the pH of the coagulation bath at 9.5-10.5, obtaining a zinc-ammonia coordination coagulation bath; spraying the spinning solution into the above zinc-ammonia coordination coagulation bath to coagulate and form nascent fibers; then washing, hot water drawing, oiling, drying and densifying, and steam drawing of the nascent fibers to obtain polyacrylonitrile precursor fiber. This invention can effectively improve the mechanical properties, structural stability, and pre-oxidation effect of polyacrylonitrile precursor fiber.

Description

Technical Field

[0001] This invention relates to the field of chemical fiber manufacturing technology, and in particular to a polyacrylonitrile precursor fiber and its preparation method, as well as polyacrylonitrile-based pre-oxidized fiber and polyacrylonitrile-based carbon fiber. Background Technology

[0002] Polyacrylonitrile (PAN) precursor fibers are key precursors for high-performance carbon fibers and flame-retardant pre-oxidized fibers. The uniformity of their microstructure and the integrity of their surface directly determine the mechanical properties, thermal stability, and structural uniformity of the final product. In the spinning process of wet or dry-jet wet spinning, the dual diffusion behavior of the coagulation bath is the core factor controlling the microstructure of the nascent fibers.

[0003] Traditional PAN spinning processes typically employ a neutral or weakly acidic coagulation bath system using solvent and water. When the spinning solution stream comes into contact with the coagulation bath, the surface organic solvent rapidly diffuses into the coagulation bath, causing rapid precipitation of polymer molecular chains and forming a dense skin structure. This dense skin acts as a physical barrier, severely blocking the channels for solvent diffusion from the core, leading to internal solvent retention and a severe imbalance in the core-skin structure. Simultaneously, the rapid coagulation process generates numerous defects on the fiber surface, such as grooves, pores, and wrinkles. These defects become stress concentration points during subsequent pre-oxidation and carbonization stages, significantly weakening the fiber's mechanical strength and greatly increasing the breakage rate, ultimately exacerbating the core-skin differences and structural inhomogeneity in the product.

[0004] To improve the solidification process, existing technologies mainly slow down the phase separation rate by adjusting the solidification bath temperature or concentration (e.g., using a low-temperature or high-concentration system), or by introducing alkaline additives to optimize solidification behavior through precise pH control. Ammonium bicarbonate can form a buffer system under weakly alkaline conditions, and partial ionization produces... Adjusting the ionic strength of the coagulation bath can slow down the double diffusion rate of DMSO and water, thereby inhibiting rapid densification of the cortex to some extent. However, these methods can only provide limited macroscopic regulation of the coagulation process and cannot fundamentally solve the problem of solvent channel blockage caused by cortex densification. While an alkaline environment helps regulate double diffusion behavior, improper pH control may trigger hydrolysis of PAN cyano groups, leading to polymer backbone breakage and significantly reducing fiber breaking strength and elongation. Given the coordination properties of cyano groups on the PAN molecular chain, some studies have attempted to introduce metal ions to construct a temporary cross-linked network in the cortex through coordination. However, in practical applications, due to the uncontrollable coordination reaction, the spinning solution is prone to premature gelation at the spinneret or excessive cross-linking of the cortex, which exacerbates fiber brittleness. The limitation of existing technologies lies in the lack of a mechanism that can achieve precise molecular-scale control. It is impossible to form dynamic support in the cortex to maintain solvent permeability, and it is difficult to achieve a balance between process stability and structural homogeneity, resulting in significant differences between fiber cortex and core and still significant surface defects. Summary of the Invention

[0005] In view of this, the present invention provides a polyacrylonitrile precursor fiber and its preparation method, as well as polyacrylonitrile-based pre-oxidized fibers and polyacrylonitrile-based carbon fibers. The preparation method of polyacrylonitrile precursor fiber provided by the present invention can effectively improve the mechanical properties, structural stability, and pre-oxidation effect of polyacrylonitrile precursor fiber.

[0006] This invention provides a method for preparing polyacrylonitrile precursor fibers, comprising the following steps:

[0007] S1. Dissolve polyacrylonitrile in a solvent to obtain a spinning solution;

[0008] Wherein, the polyacrylonitrile is a copolymer;

[0009] S2. Mix dimethyl sulfoxide with water to prepare a basic coagulation bath; add a zinc source and a complexing agent to the basic coagulation bath, and maintain the pH of the coagulation bath at 9.5~10.5 to obtain a zinc-ammonia complexation coagulation bath.

[0010] The ligand is ammonia gas and / or ammonia water;

[0011] S3. The spinning solution obtained in step S1 is sprayed into the zinc-ammonia coordination coagulation bath obtained in step S2 through a spinning device to obtain nascent fibers.

[0012] S4. The nascent fibers are washed, hot water drawn, oiled, dried and densified, and steam drawn to obtain polyacrylonitrile precursor fibers.

[0013] There is no order restriction between steps S1 and S2.

[0014] Preferably, in step S2, the zinc source is at least one of zinc chloride and zinc oxide;

[0015] The amount of zinc source added is 0.5-2.0 wt%, based on zinc ions.

[0016] Preferably, in step S2, the ligand is ammonia gas and / or ammonia water;

[0017] The molar ratio of NH3 in the ligand to Zn in the zinc source is ≥4:1.

[0018] Preferably, in step S2, the mass ratio of dimethyl sulfoxide to water is 5:5 to 7:3.

[0019] Preferably, in step S2, the temperature of the zinc-ammonia coordination coagulation bath is 10-25°C.

[0020] Preferably, in step S1:

[0021] The polyacrylonitrile is a copolymer of acrylonitrile and itaconic acid; the content of itaconic acid in the polyacrylonitrile is 1-5 wt%.

[0022] The solvent is dimethyl sulfoxide;

[0023] The solid content of the spinning solution is 18-22 wt%, and the viscosity at 50°C is 50-150 Pa·s.

[0024] Preferably, in step S4:

[0025] The washing process is a multi-stage washing process, which includes: a first acid wash and a subsequent water wash; wherein the first acid wash uses a dilute acid solution; the concentration of the dilute acid solution is 0.5-2.0 wt%, and the pH value is 3-5;

[0026] The temperature of the hot water stretching is 95-98℃, and the stretching ratio is 4.0-6.0 times;

[0027] The drying and densification temperature is 130-150℃;

[0028] The steam pressure for the steam stretching is 0.3-0.7 MPa, the steam temperature is 140-170℃, and the stretching ratio is 2.5-3.5 times.

[0029] The present invention also provides a polyacrylonitrile precursor fiber prepared by the preparation method described in the above technical solution.

[0030] The present invention also provides a polyacrylonitrile-based pre-oxidized fiber, which is obtained by a pre-oxidation process of polyacrylonitrile precursor; wherein the polyacrylonitrile precursor is the polyacrylonitrile precursor described in the above technical solution.

[0031] The present invention also provides a polyacrylonitrile-based carbon fiber, which is obtained by pre-oxidation and carbonization of polyacrylonitrile precursor; wherein the polyacrylonitrile precursor is the polyacrylonitrile precursor described in the above technical solution.

[0032] The present invention provides a method for preparing polyacrylonitrile (PAN) precursor fibers, which is a homogenization molding method that achieves precise control of the skin structure through the dynamic dissociation and in-situ coordination of zinc-ammonia complexes. The method involves dissolving polyacrylonitrile in a solvent to obtain a spinning solution; mixing dimethyl sulfoxide with water to prepare a basic coagulation bath, and introducing a zinc source and an ammonia-based coagulating agent to maintain the pH of the coagulation bath at 9.5-10.5, thus obtaining a zinc-ammonia coordination coagulation bath; spraying the spinning solution into the zinc-ammonia coordination coagulation bath to coagulate and form nascent fibers; then washing, hot water drawing, oiling, drying and densification, and steam drawing of the nascent fibers to obtain PAN precursor fibers. This invention introduces a zinc-ammonia complex system and utilizes the dynamic reversible properties of coordination bonds to construct a temporary scaffold in the fiber skin, resulting in a smooth surface, reduced groove defects, a dense and uniform cross-sectional structure, and minimal skin-core differences in the obtained PAN precursor fibers. Ultimately, PAN precursor fibers with excellent mechanical properties, structural stability, and pre-oxidation effects are obtained.

[0033] The test results show that the PAN precursor fiber obtained by this invention has a breaking strength of over 6.8 cN / dtex, a breaking elongation of over 31%, a boiling water shrinkage of less than 4.3%, and a pre-oxidation breakage rate of less than 5%, exhibiting excellent mechanical properties, structural stability, pre-oxidation effect, and excellent overall performance. Attached Figure Description

[0034] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0035] Figure 1 This is a schematic diagram of the testing instrument used in the tests of fracture strength and elongation at break;

[0036] Figure 2 This is a schematic diagram of the sample being tested on the machine during the fracture strength and elongation at break tests.

[0037] Figure 3 This is a schematic diagram of the sample breaking during the fracture strength and elongation at break tests.

[0038] Figure 4 SEM image of the sample obtained in Example 1;

[0039] Figure 5 SEM image of the sample obtained in Example 2;

[0040] Figure 6 SEM image of the sample obtained in Example 3;

[0041] Figure 7The image shows the SEM image of the sample obtained in Comparative Example 1.

[0042] Figure 8 The image shows the SEM image of the sample obtained in Comparative Example 2.

[0043] Figure 9 The image shows the SEM image of the sample obtained in Comparative Example 3. Detailed Implementation

[0044] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application.

[0045] In this document, the terms “comprising,” “including,” “having,” “containing,” or any other similar terms are open-ended conjunctions intended to cover non-exclusive inclusions. For example, a composition or article containing a plurality of elements is not limited to those listed herein, but may also include other elements not explicitly listed but typically inherent to the composition or article. Furthermore, unless explicitly stated to the contrary, the term “or” is inclusive, not exclusive. For example, the condition “A or B” is satisfied in any of the following cases: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); A and B are both true (or exist). Moreover, in this document, the terms “comprising,” “including,” “having,” and “containing” should be interpreted as specifically disclosed and simultaneously cover closed or semi-closed conjunctions such as “composed of” and “substantially composed of.”

[0046] As used herein, the term "and / or" includes any and all combinations of one or more of the related listed items.

[0047] In this document, all features or conditions defined in the form of numerical ranges or percentage ranges are for the sake of brevity and convenience only. Accordingly, descriptions of numerical ranges or percentage ranges should be considered as covering and specifically disclosing all possible secondary ranges and individual values ​​within those ranges, particularly integer values. For example, a range description of "1 to 8" should be considered as specifically disclosing all secondary ranges such as 1 to 7, 2 to 8, 2 to 6, 3 to 6, 4 to 8, 3 to 8, etc., particularly secondary ranges defined by all integer values, and should be considered as specifically disclosing individual values ​​within those ranges such as 1, 2, 3, 4, 5, 6, 7, 8, etc. Unless otherwise specified, the foregoing interpretation applies to all content throughout this invention, regardless of its scope.

[0048] If a quantity or other numerical value or parameter is expressed as a range, a preferred range, or a series of upper and lower limits, it should be understood that this document has specifically disclosed all ranges consisting of any upper or preferred value of that range and the lower or preferred value of that range, regardless of whether such ranges are separately disclosed. Furthermore, when a range of numerical values ​​is mentioned herein, unless otherwise stated, the range shall include its endpoints and all integers and fractions within the range.

[0049] In this article, when referring to units of data ranges, if the unit is only followed by the right endpoint, it means that the units of the left and right endpoints are the same. For example, 50-150 Pa.s means that the units of the left endpoint "50" and the right endpoint "150" are both Pa.s.

[0050] In a first aspect, the present invention provides a method for preparing polyacrylonitrile precursor fibers, comprising the following steps:

[0051] S1. Dissolve polyacrylonitrile in a solvent to obtain a spinning solution;

[0052] Wherein, the polyacrylonitrile is a copolymer;

[0053] S2. Mix dimethyl sulfoxide with water to prepare a basic coagulation bath; add a zinc source and a complexing agent to the basic coagulation bath, and maintain the pH of the coagulation bath at 9.5~10.5 to obtain a zinc-ammonia complexation coagulation bath.

[0054] The ligand is ammonia gas and / or ammonia water;

[0055] S3. The spinning solution obtained in step S1 is sprayed into the zinc-ammonia coordination coagulation bath obtained in step S2 through a spinning device to obtain nascent fibers.

[0056] S4. The nascent fibers are washed, hot water drawn, oiled, dried and densified, and steam drawn to obtain polyacrylonitrile precursor fibers.

[0057] There is no order restriction between steps S1 and S2.

[0058] To address the problems of excessively rapid cortex densification, significant core-sheath structure, and low elongation at break in existing PAN precursor fibers due to differences in diffusion rates, this invention provides a method for preparing PAN precursor fibers based on dynamic coordination regulation of metal-ammonia complexes. This invention introduces a zinc-ammonia complex system, utilizing the dynamic reversibility of coordination bonds to construct a temporary scaffold in the fiber cortex, eliminating the core-sheath structure. By precisely controlling the solidification kinetics, this invention achieves an upgrade from physical parameter optimization to molecular mechanism control, providing a reliable technical path for the industrial production of high-performance PAN precursor fibers.

[0059] Regarding step S1 :

[0060] S1. Dissolve polyacrylonitrile in a solvent to obtain a spinning solution.

[0061] In this invention, the polyacrylonitrile is a copolymer, preferably a copolymer of acrylonitrile and itaconic acid. The itaconic acid content in the polyacrylonitrile is preferably 1-5 wt%, specifically 1 wt%, 2 wt%, 3 wt%, 4 wt%, or 5 wt%. This invention does not impose any special restrictions on the source of the polyacrylonitrile; it can be a commercially available product.

[0062] In this invention, the solvent is dimethyl sulfoxide (DMSO). Using this solvent avoids the use of toxic solvents such as DMF. DMSO has extremely strong dissolving power for PAN copolymers (especially those containing acidic comonomers such as itaconic acid), enabling the preparation of uniform, stable, and high-solids-content spinning solutions. More importantly, DMSO has excellent miscibility with water, but its compatibility with PAN changes drastically within a certain concentration range. This provides a clear thermodynamic boundary for phase separation (coagulation); this boundary can be precisely and gently triggered by a ligand, rather than occurring violently. In an alkaline (pH 9.5-10.5) zinc-ammonia coordination environment, DMSO is stable and does not undergo side reactions, while some other solvent systems (such as certain ionic liquids or strong acid / base systems) may interfere with its operation. and The coordination balance of DMSO may be disrupted, or it may cause corrosion to the equipment. DMSO is associated with zinc salts (such as...) ZnO also has certain solubility and dispersibility, which helps it to be evenly distributed in the coagulation bath and form a uniform coordination environment. Therefore, the use of DMSO in this invention can achieve the best results.

[0063] This invention involves dissolving polyacrylonitrile in a solvent to prepare a homogeneous spinning solution. In this invention, the solid content of the spinning solution is 18-22 wt%, specifically 18 wt%, 19 wt%, 20 wt%, 21 wt%, or 22 wt%. The viscosity of the spinning solution (at 50°C) is 50-150 Pa·s, specifically 50 Pa·s, 60 Pa·s, 70 Pa·s, 80 Pa·s, 90 Pa·s, 100 Pa·s, 110 Pa·s, 120 Pa·s, 130 Pa·s, 140 Pa·s, or 150 Pa·s.

[0064] Regarding step S2 :

[0065] S2. Mix dimethyl sulfoxide with water to prepare a basic coagulation bath; add a zinc source and a complexing agent to the basic coagulation bath, and maintain the pH of the coagulation bath at 9.5-10.5 to obtain a zinc-ammonia complexation coagulation bath.

[0066] In this invention, the mass ratio of dimethyl sulfoxide to water is preferably 5:5 to 7:3, specifically 5:5, 6:4, 7:3, and more preferably 6:4.

[0067] In this invention, the zinc source is preferably at least one of zinc chloride and zinc oxide. The amount of zinc source added (i.e., the amount of zinc source added in the basic coagulation bath) is preferably 0.5-2.0 wt%, specifically 0.5 wt%, 1.0 wt%, 1.5 wt%, or 2.0 wt%, based on zinc ions.

[0068] In this invention, the ligand is ammonia gas and / or ammonia water. The ammonia water is high-concentration ammonia water, preferably 25-28 wt%, specifically 25 wt%, 26 wt%, 27 wt%, or 28 wt%.

[0069] In this invention, the amounts of the ligand and the zinc source meet dual control conditions: First, the molar ratio of NH3 in the ligand to Zn in the zinc source is controlled to be ≥4:1 to ensure that zinc ions are completely converted into tetraamminezinc complex ions. Secondly, the pH value of the coagulation bath is maintained stable at 9.5-10.5 to provide a stable environment for the coordinating ions. The pH value can be monitored through an online monitoring system, and the specific pH values ​​can be 9.5, 9.6, 9.7, 9.8, 9.9, 10.0, 10.1, 10.2, 10.3, 10.4, or 10.5. In this invention, the temperature of the coagulation bath is maintained at 10-25℃, that is, maintained at the above temperature during the introduction of the zinc source and coordinating agent. The resulting zinc-ammonia coordination coagulation bath is also at the above temperature, specifically 10℃, 15℃, 20℃, or 25℃.

[0070] Regarding step S3 :

[0071] S3. The spinning solution obtained in step S1 is sprayed into the zinc-ammonia coordination coagulation bath obtained in step S2 through a spinning device to obtain nascent fibers.

[0072] In this invention, the spinning solution is preferably defoamed and filtered before spinning. There are no special limitations to this treatment; it can be performed according to conventional practices in the field.

[0073] In this invention, the spinning equipment can be a dry-jet wet spinning equipment or a wet spinning equipment. In this invention, the spinning solution is sprayed into the zinc-ammonia coordination coagulation bath obtained in step S2 through the spinning equipment and then coagulated to form nascent fibers. During this process, the gradient change in interfacial ammonia concentration induces partial dissociation of the complex, releasing... It undergoes in-situ coordination crosslinking with the cyano (-CN) and carboxyl (-COOH) groups on the PAN molecular chain, which delays the shrinkage of the skin layer, helps to reduce spinning defects, and makes the cross-sectional structure dense and uniform with small differences between the skin and the core.

[0074] Regarding step S4 :

[0075] S4. The nascent fibers are washed, hot water drawn, oiled, dried and densified, and steam drawn to obtain polyacrylonitrile precursor fibers.

[0076] In this invention, the washing process is a multi-stage washing process, comprising: a first acid wash and subsequent water washes. The first acid wash uses a dilute acid solution, preferably dilute acetic acid or dilute hydrochloric acid; the concentration of the dilute acid solution is preferably 0.5-2.0 wt%, specifically 0.5 wt%, 1.0 wt%, 1.5 wt%, or 2.0 wt%. The pH value of the dilute acid solution is preferably 3-5, specifically 3, 4, or 5. Specifically, the first water wash tank is set as an acidic de-complexing tank. Under the aforementioned dilute acid environment, the zinc-PAN coordination bonds temporarily stored inside the fiber break, and zinc ions are re-dissolved and re-enter the aqueous phase, thereby restoring the flexibility of the PAN molecular chains and washing away excess metal ions. After the first acid wash, subsequent water washes are performed. The water wash is preferably deionized water. The subsequent water washes can be performed multiple times, thoroughly washing until neutral.

[0077] In this invention, after the above washing, hot water stretching is performed, which can be carried out in a hot water stretching tank. The preferred temperature for hot water stretching is 95-98℃, specifically 95℃, 96℃, 97℃, or 98℃. The preferred stretching ratio for hot water stretching is 4.0-6.0 times, specifically 4.0 times, 4.5 times, 5.0 times, 5.5 times, or 6.0 times.

[0078] In this invention, after the above-mentioned hot water stretching, oiling is performed. This step has no special limitations and can be carried out according to conventional processes in the field. Then, drying and densification are performed. In this invention, the drying and densification temperature is preferably 130-150℃, specifically 130℃, 135℃, 140℃, 145℃, or 150℃. The drying and densification time is preferably 5-10 minutes, specifically 5 minutes, 6 minutes, 7 minutes, 8 minutes, 9 minutes, or 10 minutes.

[0079] In this invention, after the above-mentioned drying and densification, steam drawing is performed, which can be carried out in a steam drawing machine. In this invention, the steam pressure for steam drawing is preferably 0.3-0.7 MPa, more preferably 0.5 MPa. The steam temperature for steam drawing is preferably 140-170℃, specifically 140℃, 145℃, 150℃, 155℃, 160℃, 165℃, or 170℃. The steam drawing ratio is preferably 2.5-3.5 times, specifically 2.5 times, 3 times, or 3.5 times.

[0080] In this invention, the total draw ratio is preferably controlled between 12.5 and 17.5 times, specifically 12.5 times, 13 times, 14 times, 15 times, 16 times, 17 times, and 17.5 times. After processing in step S4, polyacrylonitrile precursor fibers are obtained.

[0081] Secondly, the present invention also provides a polyacrylonitrile precursor fiber prepared by the preparation method described in the above technical solution.

[0082] Thirdly, the present invention also provides a polyacrylonitrile-based pre-oxidized fiber, which is obtained from polyacrylonitrile precursor fiber through a pre-oxidation process; wherein the polyacrylonitrile precursor fiber is the polyacrylonitrile precursor fiber described in the above-mentioned technical solution. In the present invention, the pre-oxidation process is not particularly limited and can be a conventional pre-oxidation process in the art.

[0083] Fourthly, the present invention also provides a polyacrylonitrile-based carbon fiber, which is obtained by pre-oxidation and carbonization of polyacrylonitrile precursor; wherein the polyacrylonitrile precursor is the polyacrylonitrile precursor described in the above-mentioned technical solution. In the present invention, the pre-oxidation is not particularly limited and can be a conventional pre-oxidation process in the art. The carbonization is not particularly limited and can be a conventional carbonization process in the art.

[0084] This invention, for the first time, utilizes the dynamic dissociation and in-situ coordination mechanism of zinc-ammonia complexes to achieve precise control of coagulation kinetics under a weakly alkaline environment, solving the problem of premature densification of the outer layer in wet spinning. Its mechanism of action is as follows:

[0085] (1) In the coagulation bath, zinc exists in a stable complex ion form; when the feed stream contacts the interface of the coagulation bath, the local ammonia concentration decreases, leading to Dissociation, release It forms coordination bonds with PAN side groups, constructs a temporary cross-linked network in the cortex, effectively supports the structure, prevents collapse, and maintains cortex permeability;

[0086] (2) The coordination network increases the rigidity of the chain segments, which offsets the shrinkage stress caused by the rapid outflow of solvent, allowing the DMSO in the core to have sufficient time to diffuse out and achieve homogenized solidification inside and outside.

[0087] (3) The coordination effect is reversible. Zinc ions can be efficiently removed by acidic water washing. It has both temporary support function and ensures the purity of the raw yarn, ultimately obtaining high-performance PAN raw yarn with no core-sheath difference and high breaking elongation.

[0088] Compared with the prior art, the present invention has the following beneficial effects:

[0089] The PAN precursor fibers obtained by this invention have a smooth surface, reduced groove defects, a dense and uniform cross-sectional structure, and minimal core-sheath difference. The fiber's breaking strength is improved, especially the elongation at break, and the fiber toughness is significantly enhanced. The precursor fibers with a uniform structure and fewer defects exhibit a lower breakage rate and a more uniform degree of pre-oxidation during subsequent pre-oxidation processes, which is beneficial for preparing high-performance pre-oxidized fibers and carbon fibers. Using DMSO as the sole solvent avoids the use of toxic solvents such as DMF. Furthermore, the zinc and ammonia sources are readily available and environmentally friendly, facilitating large-scale production by controlling the coagulation bath. In addition, by adjusting the pickling conditions, trace amounts of zinc can be selectively retained as a carbonization catalyst, giving the product multifunctional potential.

[0090] To further understand the present invention, preferred embodiments of the present invention are described below in conjunction with examples. However, it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, and not for limiting the scope of the claims of the present invention.

[0091] Example 1

[0092] S1. Preparation of spinning solution:

[0093] 4.0g of commercially available polyacrylonitrile (acrylonitrile-itaconic acid copolymer, itaconic acid unit content 1.5wt%) was dissolved in 78.0g of dimethyl sulfoxide to prepare a spinning solution with a solid content of 20wt% and a viscosity of 110 Pa·s (50℃).

[0094] S2. Preparation of the coagulation bath:

[0095] Mix 60.0 g of dimethyl sulfoxide with 40.0 g of water to obtain a basic coagulation bath. Add 0.8 g of zinc chloride to the basic coagulation bath. This is equivalent to 0.39 wt% Zn. 2+ ) and 3.2g of 25% ammonia water (NH3:Zn molar ratio = 4.2:1), the pH value was stably controlled at 10.2±0.1 and the temperature was 20℃ by an online pH monitoring system to obtain a zinc-ammonia coordination coagulation bath.

[0096] S3, spinning:

[0097] After degassing and filtration, the spinning solution obtained in step S1 is sprayed into the zinc-ammonia coordination coagulation bath obtained in step S2 through a dry-jet wet spinning device (air gap height 5 mm) to obtain nascent fibers.

[0098] S4. Post-processing:

[0099] The nascent fibers obtained in step S3 are first placed in an acidic de-winding tank (1.0wt% acetic acid aqueous solution, pH=4.0) for acid washing and de-winding treatment, then washed with deionized water until neutral, and then successively subjected to hot water drawing (98℃, 5 times), oiling, drying and densification (140℃, 10min) and steam drawing (0.5MPa, 150℃, 3.0 times), with a total drawing ratio of 15.0 times, to obtain PAN precursor yarn.

[0100] Example 2

[0101] S1. Preparation of spinning solution: Same as in Example 1.

[0102] S2. Preparation of the coagulation bath:

[0103] Mix 55.0 g of dimethyl sulfoxide with 45.0 g of water to obtain a basic coagulation bath. Add 1.0 g of zinc oxide (ZnO, equivalent to 0.80 wt% Zn) to the basic coagulation bath. 2+ ) and 3.5g of 25% ammonia water (NH3:Zn molar ratio = 4.5:1), the pH value was stably controlled at 10.0±0.1 and the temperature was 15℃ by an online pH monitoring system to obtain a zinc-ammonia coordination coagulation bath.

[0104] S3, Spinning: Same as in Example 1.

[0105] S4. Post-processing: Same as in Example 1.

[0106] Example 3

[0107] S1. Preparation of spinning solution: Same as in Example 1

[0108] S2. Preparation of the coagulation bath:

[0109] 58.0 g of dimethyl sulfoxide was mixed with 42.0 g of water to obtain a basic coagulation bath. 1.2 g of zinc oxide (ZnO, equivalent to 0.96 wt% Zn) was added to the basic coagulation bath. 2+ Ammonia gas (NH3) was introduced into the solution under continuous stirring, and the pH value was precisely and stably controlled at 10.1±0.1 using an online pH monitoring system. At this point, the molar ratio of NH3 to Zn was approximately 4.0:1. The coagulation bath temperature was controlled at 18℃, resulting in a zinc-ammonia coordination coagulation bath.

[0110] S3, Spinning: Same as in Example 1.

[0111] S4. Post-processing: Same as in Example 1.

[0112] Comparative Example 1

[0113] S1. Preparation of spinning solution: Same as in Example 1.

[0114] S2. Preparation of the coagulation bath:

[0115] Mix 60.0 g of dimethyl sulfoxide with 40.0 g of water to obtain a basic coagulation bath (pH≈6.5).

[0116] S3, Spinning: Same as in Example 1.

[0117] S4. Post-processing: Same as in Example 1.

[0118] Comparative Example 2

[0119] S1. Preparation of spinning solution: Same as in Example 1.

[0120] S2. Preparation of the coagulation bath:

[0121] Mix 60.0 g of dimethyl sulfoxide with 40.0 g of water to obtain a basic coagulation bath. Add 3.2 g of 25% ammonia solution to the basic coagulation bath to obtain a coagulation bath.

[0122] S3, Spinning: Same as in Example 1.

[0123] S4. Post-processing: Same as in Example 1.

[0124] Comparative Example 3

[0125] The procedure is carried out according to Example 1, except that acid washing is not performed in step S4, and water washing begins directly.

[0126] Product Testing :

[0127] The results of tests performed on each embodiment and comparative example are shown in Table 1.

[0128] (1) The breaking strength and elongation at break were tested using the XQ-2N fiber strength and elongation tester (e.g., Figure 1 (As shown), the test conditions were as follows: temperature 20℃, humidity 65% ​​RH%, tensile speed 10mm / min, clamping distance 10mm. Twenty parallel tests were performed, and the average value was taken as the test result. The samples were subjected to tensile testing and fracture testing as shown below. Figures 2-3 As shown.

[0129] (2) Monofilament diameter testing: Using SEM, the monofilaments were arranged parallel to each other on a sample stage with conductive adhesive, ensuring that multiple fibers did not overlap. Gold or carbon sputtering was applied to enhance conductivity and eliminate charge accumulation. Measurements were taken perpendicular to the fiber axis on clear SEM images using Nano Measurer 1.2 image analysis software. Ten measurements were taken from each sample, and the average value was used as the result.

[0130] (3) Boiling water shrinkage rate test: Refer to standard GB / T 6505-2017 to test the boiling water shrinkage rate of the sample. Take a sample with an original length of 20cm, treat it in boiling water at 100℃ for 30 min, take it out and let it air dry for 10 min, treat it in a vacuum oven at 55℃ for 1 h, and then apply a load of 0.05 cN / dtex to test the fiber length. The formula for calculating the boiling water shrinkage rate is as follows:

[0131]

[0132] In the formula, BWS is the boiling water shrinkage rate, %; L0 is the original length of the sample, cm; and L1 is the length of the sample after boiling water treatment, cm.

[0133] (4) Pre-oxidation breakage rate test: According to standard ASTM D3379, the strength of individual fiber filaments was tested using an XQ-2N fiber tensile strength tester. The main tests included the breaking strength and elongation at break of the PAN pre-oxidized fiber. A single fiber was attached to a specially designed clamp with a spacing of 25 mm, and the tensile speed was 1 mm / min. Fifty filaments were tested for each sample. The strength dispersion coefficient was calculated as follows:

[0134]

[0135] Where s is the standard deviation. The CV value is a direct and preliminary indicator of "end breakage risk": the larger the CV value, the more uneven the fiber strength, and the higher the risk of random breakage (end breakage) during processing.

[0136] Table 1: Performance Test Results

[0137]

[0138] The surface morphologies of the PAN precursor fibers obtained in Examples 1-3 and Comparative Examples 1-3 are respectively referred to as follows: Figures 4-9 .

[0139] As can be seen from the test results in the table above, the PAN precursor fibers obtained in Examples 1-3 of this invention have a breaking strength of over 6.9 cN / dtex, a breaking elongation of over 31%, a boiling water shrinkage of less than 4.2%, and a pre-oxidation breakage rate of less than 5%, exhibiting excellent mechanical properties, structural stability, and pre-oxidation effect. They have excellent overall performance and are suitable for subsequent pre-oxidation fiber and carbon fiber preparation.

[0140] Compared with Example 1, the properties of Comparative Examples 1-2 all deteriorated, proving that the specific zinc-ammonia coordination coagulation bath used in this invention is beneficial to improving the overall performance of PAN precursor fibers. Compared with Example 1, the properties of Comparative Example 3 deteriorated, proving that the acid washing and de-networking process after spinning in this invention is beneficial to improving the performance of PAN precursor fibers.

[0141] This document uses specific examples to illustrate the principles and implementation methods of the present invention. The descriptions of these embodiments are merely to aid in understanding the method and core ideas of the present invention, including the best mode, and to enable any person skilled in the art to practice the present invention, including manufacturing and using any device or system, and implementing any combined method. It should be noted that those skilled in the art can make various improvements and modifications to the present invention without departing from its principles, and these improvements and modifications also fall within the scope of protection of the claims. The scope of protection of this patent is defined by the claims and may include other embodiments that can be conceived by those skilled in the art. If these other embodiments have structural elements similar to those expressed in the claims, or if they include equivalent structural elements that are not substantially different from those expressed in the claims, then these other embodiments should also be included within the scope of the claims.

Claims

1. A method for preparing polyacrylonitrile precursor fibers, characterized in that, Includes the following steps: S1. Dissolve polyacrylonitrile in a solvent to obtain a spinning solution; Wherein, the polyacrylonitrile is a copolymer; S2. Mix dimethyl sulfoxide with water to prepare a basic coagulation bath; add a zinc source and a complexing agent to the basic coagulation bath, and maintain the pH of the coagulation bath at 9.5~10.5 to obtain a zinc-ammonia complexation coagulation bath. The ligand is ammonia gas and / or ammonia water; S3. The spinning solution obtained in step S1 is sprayed into the zinc-ammonia coordination coagulation bath obtained in step S2 through a spinning device to obtain nascent fibers. S4. The nascent fibers are washed, hot water drawn, oiled, dried and densified, and steam drawn to obtain polyacrylonitrile precursor fibers; the washing is a multi-stage washing process; the multi-stage washing includes: an initial acid wash and subsequent water washes. There is no order restriction between steps S1 and S2.

2. The preparation method according to claim 1, characterized in that, In step S2, the zinc source is at least one of zinc chloride and zinc oxide; The amount of zinc source added is 0.5-2.0 wt%, based on zinc ions.

3. The preparation method according to claim 1, characterized in that, In step S2, the ligand is ammonia gas and / or ammonia water; The molar ratio of NH3 in the ligand to Zn in the zinc source is ≥4:

1.

4. The preparation method according to claim 1, characterized in that, In step S2, the mass ratio of dimethyl sulfoxide to water is 5:5 to 7:

3.

5. The preparation method according to claim 1, characterized in that, In step S2, the temperature of the zinc-ammonia coordination coagulation bath is 10-25℃.

6. The preparation method according to claim 1, characterized in that, In step S1: The polyacrylonitrile is a copolymer of acrylonitrile and itaconic acid; the content of itaconic acid in the polyacrylonitrile is 1-5 wt%. The solvent is dimethyl sulfoxide; The solid content of the spinning solution is 18-22 wt%, and the viscosity at 50°C is 50-150 Pa·s.

7. The preparation method according to claim 1, characterized in that, In step S4: The washing solution used in the first pickling process is a dilute acid solution; the concentration of the dilute acid solution is 0.5-2.0 wt%, and the pH value is 3-5; The temperature of the hot water stretching is 95-98℃, and the stretching ratio is 4.0-6.0 times; The drying and densification temperature is 130-150℃; The steam pressure for the steam stretching is 0.3-0.7 MPa, the steam temperature is 140-170℃, and the stretching ratio is 2.5-3.5 times.

8. A polyacrylonitrile precursor fiber prepared by any one of claims 1-7.

9. A polyacrylonitrile-based pre-oxidized fiber, characterized in that, It is prepared by a pre-oxidation process of polyacrylonitrile precursor fiber, wherein the polyacrylonitrile precursor fiber is the polyacrylonitrile precursor fiber as described in claim 8.

10. A polyacrylonitrile-based carbon fiber, characterized in that, It is prepared by pre-oxidation and carbonization of polyacrylonitrile precursor fiber, wherein the polyacrylonitrile precursor fiber is the polyacrylonitrile precursor fiber as described in claim 8.

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