Dendritic micro-nano polyimide fiber cotton and preparation method thereof

Abstract

The application belongs to the technical field of fiber preparation, and relates to a preparation method of dendritic structure micro-nano polyimide fiber cotton, which comprises the following steps: (S1) preparing a polyamide acid solution through a solution polycondensation method; (S2) adding a rheological modifier into the polyamide acid solution to obtain a spinning solution with a non-Newtonian index of 0.50-0.95; (S3) preparing dendritic structure micro-nano polyamide acid fiber cotton through high-speed airflow spinning technology, wherein the shear rate of the high-speed airflow spinning is 5.0x10 4 ~1.0x10 7 s ‑1 ; (S4) performing thermal imidization on the polyamide acid fiber cotton to obtain dendritic structure micro-nano polyimide fiber cotton. The dendritic structure micro-nano polyimide fiber cotton is prepared through rheological property control of a spinning solution and a specific high-speed airflow spinning process, and has high efficient warmth retention, good sound absorption and high resilience, and is suitable for industrialized large-scale production.

Description

Technical Field

[0001] This invention belongs to the field of fiber preparation technology, specifically relating to a dendritic micro / nano polyimide fiber cotton and its preparation method. Background Technology

[0002] Fiber cotton, primarily composed of synthetic fibers, exhibits broad application prospects in warmth retention, heat insulation, and sound insulation due to its low density and high specific surface area. Examples include seven-hole and nine-hole cotton. Currently, the most common fiber cotton is made of polyester microfiber. However, polyester lacks intrinsic flame-retardant properties and is prone to dripping when melted at high temperatures, posing a significant safety risk. This is especially true for workers in industries such as coal mining, petrochemicals, and power generation, where non-flame-retardant cold-weather clothing increases safety hazards during work. Polyimide, with its unique aromatic heterocyclic rigid structure, possesses excellent intrinsic flame-retardant properties. Using polyimide to prepare fiber cotton will effectively reduce the risks of combustion and dripping, playing a crucial role in warmth retention and heat insulation.

[0003] Currently, there are two main technical routes for preparing fiber cotton using polyimide as the main material. One route uses polyimide fibers as raw materials and prepares them through processes such as opening, carding, and web laying, as shown in CN112359483A, CN115652652A, and CN102965846A. The other route directly prepares nanoscale polyimide wadding using electrospinning technology, as shown in CN105019141A and CN116219629A. However, both methods have certain problems. For example, the fiber diameter of polyimide fiber cotton prepared by the first method is mostly on the order of 10μm, which affects the specific surface area and warmth retention performance of the fiber cotton (wadding). The second method can produce polyimide fibers with diameters on the nanoscale. Theoretically, the finer the fiber and the larger the specific surface area, the better the heat insulation, sound absorption, and heat preservation effects should be. However, since all the fibers are nanoscale, the fiber cotton has poor resilience and low overall fluffiness, which will also affect the heat insulation and sound absorption effects. In addition, the electrospinning technology has low spinning efficiency, which is not conducive to large-scale engineering production. Summary of the Invention

[0004] In view of the above-mentioned problems in the prior art, the present invention provides a dendritic micro-nano polyimide fiber cotton and its preparation method. The polyimide fiber cotton has the advantages of high heat retention (low thermal conductivity and high thermal resistance), good sound absorption and high resilience, and is suitable for large-scale industrial production.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A method for preparing a dendritic micro / nano polyimide fiber cotton includes the following steps:

[0007] (S1) Polyamic acid solution was prepared by solution polycondensation;

[0008] (S2) A rheology modifier is added to a polyamic acid solution to obtain a spinning solution, wherein the non-Newtonian index of the spinning solution is 0.50~0.95;

[0009] (S3) The spinning solution is blown out of the spinneret through high-speed airflow spinning technology, heated, and collected using a collection device to obtain dendritic micro / nano polyamic acid fiber cotton; the shear rate of the high-speed airflow spinning is 5.0 × 10⁻⁶. 4 ~1.0×10 7 s -1 ;

[0010] (S4) Polyamic acid fiber cotton is thermally imidized to obtain dendritic micro-nano polyimide fiber cotton.

[0011] Further, in step (S1), the conditions for the solution polycondensation method are as follows: the dianhydride monomer and the diamine monomer are polycondensed in a polar aprotic solvent at a molar ratio of 1:(0.98~1.02); the solid content of the polyamic acid solution is 12~25wt%, and the intrinsic viscosity is 1.1~2.8dL / g.

[0012] Furthermore, the dianhydride monomer is at least one of pyromellitic dianhydride (PMDA), diphenyl ether tetracarboxylic dianhydride (ODPA), biphenyl tetracarboxylic dianhydride (BPDA), and 3,3',4,4'-triphenyl diether tetracarboxylic dianhydride (HQDPA); the diamine monomer is at least one of 4,4'-diaminodiphenyl ether (ODA), 3,4'-diaminodiphenyl ether (3,4'-ODA), p-phenylenediamine (p-PDA), m-phenylenediamine (m-PDA), 2-(4-aminophenyl)-5-aminobenzimidazole (BIA), and 4,4'-diaminobiphenyl; the polar aprotic solvent is at least one of N,N-dimethylacetamide (DMAc), N,N-dimethylformamide (DMF), and N-methylpyrrolidone (NMP), and its amount is 3 to 7 times the total mass of the dianhydride monomer and the diamine monomer; the polycondensation conditions are: temperature 0 to 20°C, time 6 to 10 h.

[0013] Further, in step (S2), the rheology modifier is at least one of deionized water, C2-C3 alcohol, acetone, and ethyl acetate; preferably, the content of the rheology modifier in the spinning solution is 0.1~1.5wt%.

[0014] Non-Newtonian exponents are parameters that quantify the deviation of a fluid from Newtonian fluid behavior, expressed through a power-law equation. The exponent n is defined in the formula, where σ is the shear stress. Where is the shear rate, and K is the consistency coefficient. The non-Newtonian index n is affected by the molecular chain structure, viscosity, and shear rate range. This invention introduces the "non-Newtonian index" to evaluate the rheological properties of the spinning solution.

[0015] The rheology modifier used in step (S2) is a non-solvent for polyamic acid and is miscible with the polar aprotic solvent in step (S1). A small amount of rheology modifier can significantly adjust the rheological properties of the spinning solution because its addition reduces the interaction between polyamic acid and the solvent (polyamic acid forms a strong hydrogen bond network in polar aprotic solvents such as DMAc), reducing the coil volume in the spinning solution and increasing the non-Newtonian index. Simultaneously, because the amount of rheology modifier added is small, it does not affect the overall solubility and stability of polyamic acid. The non-Newtonian index of the spinning solution is a key parameter affecting the formation of dendritic micro / nano polyamic acid fiber cotton. Although the mechanism is not fully understood, the inventors have found that only when the non-Newtonian index of the spinning solution is within the aforementioned range, combined with the specific high-speed airflow spinning process in step (S3), can dendritic micro / nano polyamic acid fiber cotton be obtained. It is speculated that when the non-Newtonian index of the spinning solution is within the aforementioned range, high shear rates can induce capillary instability, generating secondary jets and thus producing dendritic fibers. If the non-Newtonian index of the spinning solution is less than 0.50, high-speed spinning and dendritic fiber structure cannot be achieved; if the non-Newtonian index is greater than 0.95, the molecular chain orientation of the fiber is insufficient, its strength is low, and it may not even be able to form fibers in a high-speed airflow.

[0016] Preferably, the non-Newtonian index of the spinning solution in step (S2) is 0.65 to 0.85.

[0017] Further, the high-speed airflow spinning described in step (S3) is slit-type coaxial airflow spinning. Shear rate refers to the velocity gradient of a fluid perpendicular to the flow direction. In this invention, the shear rate refers to the velocity gradient at the interface between the high-speed airflow and the spinning liquid. The larger the value, the more intense the shearing action on the spinning liquid fluid. The calculation formula is shown in equation (1). This invention defines high-speed airflow spinning by shear rate. Shear rate is another key parameter affecting the formation of dendritic micro / nano polyamic acid fiber cotton. Its value is jointly affected by gas flow rate, slit width, spinneret diameter, and spinning liquid extrusion speed. The inventors found through research that when the shear rate is too low, the obtained fibers are mainly uniform micron-sized fibers, which are independent of each other and do not form a dendritic structure; when the shear rate is too high, the obtained fibers are mainly uniform nano-sized fibers, which are also not dendritic structures; only when the shear rate is within the above range can dendritic micro / nano fiber cotton be obtained.

[0018] (1)

[0019] In the formula, Δv is the shear rate of air-jet spinning, Δv is the velocity difference between the airflow and the spinning solution, and r is the spinneret radius.

[0020] Preferably, the shear rate of the high-speed airflow spinning in step (S3) is 6.5 × 10⁻⁶. 4 ~6.0×10 6 s -1 .

[0021] Furthermore, the other process parameters for high-speed airflow spinning in step (S3) are: airflow slit width 0.05~0.35mm, gas flow rate 1~80L / min, air pressure 0.01~0.4MPa, airflow temperature 20~30℃, spinneret diameter 0.4~1.0mm, single-hole extrusion speed of spinning solution 2~80ml / h, and fiber receiving distance 25~50cm.

[0022] Furthermore, the heat treatment conditions in step (S3) are: a temperature of 50~150℃. The purpose of the heat treatment is to remove some of the solvent and fix the fiber morphology. The collecting device is not particularly limited, and can be, for example, a mesh belt, a mesh curtain, or a rotating drum.

[0023] Further, the conditions for thermal imidization in step (S4) are: temperature 300~450℃, preferably 350~400℃, and time 5~50min.

[0024] A dendritic micro / nano polyimide fiber cotton, prepared by the above-described method, refers to fibers with a dendritic branching structure, including a trunk, branches, and nodes; a porous network structure is formed between the trunk, branches, and nodes; the diameter of the trunk fiber is 0.5~5μm, and the diameter of the branch fiber is 30~400nm. This dendritic micro / nano fiber cotton differs from uniform nanofiber cotton obtained by electrospinning. It not only possesses the rich porosity and large specific surface area inherent in nanofiber structures, which are beneficial for heat insulation and sound absorption, but also features a micron-sized trunk providing stable spatial support, which helps maintain its fluffy characteristics and better retain still air. The micron-sized trunk and nano-sized branches are an integrated growth structure, rather than a fused or adhered network formed by post-processing, resulting in better continuity and network stability, and giving the fiber cotton better resilience.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] 1. This invention obtains dendritic micro-nano polyimide fiber cotton by controlling the rheological properties of the spinning solution and combining it with a specific high-speed airflow spinning process.

[0027] 2. The dendritic micro-nano polyimide fiber cotton prepared by this invention has the advantages of high-efficiency heat retention (low thermal conductivity, high thermal resistance), good sound absorption and high resilience, and is suitable for industrial-scale production. Attached Figure Description

[0028] Figure 1 SEM image of the dendritic micro / nano polyimide fiber cotton prepared in Example 1;

[0029] Figure 2 SEM image of the polyimide fiber cotton prepared in Comparative Example 3.

[0030] Figure 3 SEM image of the polyimide fiber cotton prepared in Comparative Example 4.

[0031] Figure 4 This is a SEM image of the polyimide fiber cotton prepared in Comparative Example 5. Detailed Implementation

[0032] The present invention will be further described below with reference to specific embodiments, but the present invention is not limited to the following embodiments.

[0033] Unless otherwise specified, the experimental methods described in the following examples are conventional methods; unless otherwise specified, the reagents and materials are commercially available.

[0034] The following parameters are involved in the embodiments and are tested using the following methods:

[0035] Intrinsic viscosity: The intrinsic viscosity of the solution is measured using an Ubbelohde viscometer and is determined by extrapolating the specific viscosity at infinite dilution or the logarithmic viscosity at infinite dilution.

[0036] Non-Newtonian index: The change of shear stress in the spinning solution with shear rate was tested using a rheometer at a temperature of 30℃. The non-Newtonian index n was calculated according to the following formula.

[0037] (2)

[0038] Where σ is the shear stress. Where is the shear rate, and K is the consistency coefficient.

[0039] Example 1

[0040] (S1) Add 10g of 4,4'-diaminodiphenyl ether (ODA) and 5.4g of p-phenylenediamine (p-PDA) to 200g of N,N-dimethylacetamide (DMAc) solvent, then add 11g of pyromellitic dianhydride (PMDA) and 14.8g of biphenyl dianhydride (BPDA), and stir the mixture at 10°C for 10h to obtain a polyamic acid solution (intrinsic viscosity of 1.7dL / g).

[0041] (S2) Add 1.5g of deionized water to the polyamic acid solution obtained in step (S1) to obtain a spinning solution with a non-Newtonian index of 0.82;

[0042] (S3) The spinning solution obtained in step (S2) is blown out of the spinneret through high-speed airflow spinning technology, and after heat treatment at 80℃, it enters the collection device to obtain dendritic micro-nano polyamic acid fiber cotton; by adjusting the airflow slit width, gas (compressed air) flow rate, extrusion speed of the spinning solution, and spinneret diameter, the shear rate of airflow spinning is made to be 5.9 × 10⁻⁶. 6 s -1 (Airflow slit width 0.09mm, gas flow rate 25L / min, spinneret diameter 0.55mm, single-hole extrusion speed of spinning solution 20ml / h), air pressure 0.2MPa, airflow temperature 25℃, fiber receiving distance 30cm;

[0043] (S4) The polyamic acid fiber cotton obtained in step (S3) is treated at 350℃ for 30 minutes to obtain an areal density of approximately 100 g / m³. 2 The dendritic structure of micro-nano polyimide fiber cotton.

[0044] SEM image of the dendritic micro / nano polyimide fiber cotton prepared is shown below. Figure 1 As shown in the figure, polyimide fiber cotton has a dendritic structure, including a trunk, branches and nodes, which form a rich porous structure. The diameter of the trunk fiber is about 0.6~2.8μm, and the diameter of the branch fiber is about 35~290nm.

[0045] Example 2

[0046] The rest is the same as in Example 1, except that: the amount of deionized water used in step (S2) is 0.5g, and the non-Newtonian index of the resulting spinning solution is 0.50.

[0047] The dendritic micro / nano polyimide fiber cotton obtained by scanning electron microscopy exhibits similar characteristics. Figure 1 The structure has a main fiber diameter of about 0.8~3.5μm and a branch fiber diameter of about 35~310nm.

[0048] Example 3

[0049] The rest is the same as in Example 1, except that: the amount of deionized water used in step (S2) is 0.9g, and the non-Newtonian index of the resulting spinning solution is 0.65.

[0050] The dendritic micro / nano polyimide fiber cotton obtained by scanning electron microscopy exhibits similar characteristics. Figure 1The structure has a main fiber diameter of about 0.7~3.5μm and a branch fiber diameter of about 35~300nm.

[0051] Example 4

[0052] The rest is the same as in Example 1, except that the amount of deionized water used in step (S2) is 3.5g, and the non-Newtonian index of the spinning solution is 0.95.

[0053] The dendritic micro / nano polyimide fiber cotton obtained by scanning electron microscopy exhibits similar characteristics. Figure 1 The structure has a main fiber diameter of about 0.6~2.6μm and a branch fiber diameter of about 35~200nm.

[0054] Example 5

[0055] The rest is the same as in Example 1, except that: in step (S2), propanol of equal mass is used instead of deionized water, and the non-Newtonian index of the spinning solution is 0.85.

[0056] The dendritic micro / nano polyimide fiber cotton obtained by scanning electron microscopy exhibits similar characteristics. Figure 1 The structure has a main fiber diameter of approximately 0.6~2.7μm and a branch fiber diameter of approximately 35~260nm.

[0057] Example 6

[0058] The rest is the same as in Example 1, except that the spinning process parameters in step (S3) are different, specifically:

[0059] (S1) Same as Example 1;

[0060] (S2) Same as Example 1;

[0061] (S3) The spinning solution obtained in step (S2) is blown out of the spinneret through high-speed airflow spinning technology, and after heat treatment at 80℃, it enters the collection device to obtain dendritic micro-nano polyamic acid fiber cotton; by adjusting the airflow slit width, gas (compressed air) flow rate, extrusion speed of the spinning solution, and spinneret diameter, the shear rate of airflow spinning is made to be 1.5×10. 6 s -1 (Airflow slit width 0.3mm, gas flow rate 70L / min, spinneret diameter 1.0mm, single-hole extrusion speed of spinning solution 65ml / h), air pressure 0.09MPa, airflow temperature 25℃, fiber receiving distance 40cm;

[0062] (S4) Same as Example 1.

[0063] The dendritic micro / nano polyimide fiber cotton obtained by scanning electron microscopy exhibits similar characteristics. Figure 1 The structure has a main fiber diameter of about 0.6~2.8μm and a branch fiber diameter of about 37~300nm.

[0064] Example 7

[0065] The rest is the same as in Example 1, except that the spinning process parameters in step (S3) are different, specifically:

[0066] (S1) Same as Example 1;

[0067] (S2) Same as Example 1;

[0068] (S3) The spinning solution obtained in step (S2) is blown out of the spinneret through high-speed airflow spinning technology, and after heat treatment at 80℃, it enters the collection device to obtain dendritic micro-nano polyamic acid fiber cotton; by adjusting the airflow slit width, gas (compressed air) flow rate, extrusion speed of the spinning solution, and spinneret diameter, the shear rate of airflow spinning is made to be 6.5×10. 4 s -1 (Airflow slit width 0.335mm, gas flow rate 1L / min, spinneret diameter 0.46mm, single-hole extrusion speed of spinning solution 5ml / h), air pressure 0.01MPa, airflow temperature 25℃, fiber receiving distance 25cm;

[0069] (S4) Same as Example 1.

[0070] The dendritic micro / nano polyimide fiber cotton obtained by scanning electron microscopy exhibits similar characteristics. Figure 1 The structure has a main fiber diameter of about 0.6~4.0μm and a branch fiber diameter of about 55~350nm.

[0071] Example 8

[0072] The rest is the same as in Example 1, except that the spinning process parameters in step (S3) are different, specifically:

[0073] (S1) Same as Example 1;

[0074] (S2) Same as Example 1;

[0075] (S3) The spinning solution obtained in step (S2) is blown out of the spinneret through high-speed airflow spinning technology, and after heat treatment at 80℃, it enters the collection device to obtain dendritic micro-nano polyamic acid fiber cotton; by adjusting the airflow slit width, gas (compressed air) flow rate, extrusion speed of the spinning solution, and spinneret diameter, the shear rate of airflow spinning is made to be 7.3×10. 5 s -1(Airflow slit width 0.06mm, gas flow rate 2L / min, spinneret diameter 0.55mm, single-hole extrusion speed of spinning solution 10ml / h), air pressure 0.02MPa, airflow temperature 25℃, fiber receiving distance 30cm;

[0076] (S4) Same as Example 1.

[0077] The dendritic micro / nano polyimide fiber cotton obtained by scanning electron microscopy exhibits similar characteristics. Figure 1 The structure has a main fiber diameter of about 0.5~3.3μm and a branch fiber diameter of about 38~360nm.

[0078] Comparative Example 1

[0079] The rest is the same as in Example 1, except that deionized water is not added in step (S2), and the non-Newtonian index of the spinning solution is 0.45 at this time.

[0080] Experiments have shown that in step (S3), the spinning solution is extruded at the spinneret in the form of liquid spheres, gradually gathers, and is blown off after reaching a certain size, thus failing to produce fibers.

[0081] Comparative Example 2

[0082] The rest is the same as in Example 1, except that the amount of deionized water used in step (S2) is 4.5g, and the non-Newtonian index of the spinning solution is 0.98 at this time.

[0083] Experiments revealed that during step (S3), the spinning solution formed discontinuous droplets at the spinneret, thus failing to form continuous fibers.

[0084] Comparative Example 3

[0085] The rest is the same as in Example 1, except that the shear rate of the airflow spinning in step (S3) is different, specifically:

[0086] (S1) Same as Example 1;

[0087] (S2) Same as Example 1;

[0088] (S3) The spinning solution obtained in step (S2) is blown out of the spinneret through high-speed airflow spinning technology, and after heat treatment at 80°C, it enters the collection device to obtain polyamic acid fiber cotton; by adjusting the airflow slit width, gas (compressed air) flow rate, extrusion speed of the spinning solution, and spinneret diameter, the shear rate of airflow spinning is made to be 1.6 × 10⁻⁶. 4 s -1(Airflow slit width 0.4mm, gas flow rate 1L / min, spinneret diameter 1.0mm, single-hole extrusion speed of spinning solution 10ml / h), air pressure 0.01MPa, airflow temperature 25℃, fiber receiving distance 30cm;

[0089] (S4) Same as Example 1.

[0090] SEM image of the prepared polyimide fiber cotton is shown below. Figure 2 As shown in the figure, the fibers are mainly uniform micron-sized fibers with a diameter of approximately 0.8 to 5.5 μm.

[0091] Comparative Example 4

[0092] The rest is the same as in Example 1, except that the shear rate of the airflow spinning in step (S3) is different, specifically:

[0093] (S1) Same as Example 1;

[0094] (S2) Same as Example 1;

[0095] (S3) The spinning solution obtained in step (S2) is blown out of the spinneret through high-speed airflow spinning technology, and after heat treatment at 80°C, it enters the collection device to obtain polyamic acid fiber cotton; by adjusting the airflow slit width, gas (compressed air) flow rate, extrusion speed of the spinning solution, and spinneret diameter, the shear rate of airflow spinning is made to be 2.0 × 10⁻⁶. 7 s -1 (Airflow slit width 0.115mm, gas flow rate 85L / min, spinneret diameter 0.46mm, single-hole extrusion speed of spinning solution 10ml / h), air pressure 0.45MPa, airflow temperature 25℃, fiber receiving distance 30cm;

[0096] (S4) Same as Example 1.

[0097] SEM image of the prepared polyimide fiber cotton is shown below. Figure 3 As shown in the figure, the main fibers are uniform nanofibers with a diameter of approximately 70-250 nm.

[0098] Comparative Example 5

[0099] The rest is the same as in Example 1, except that electrospinning technology is used in step (S3), specifically:

[0100] (S1) Same as Example 1;

[0101] (S2) Same as Example 1;

[0102] (S3) Polyamic acid fibers are prepared by electrospinning using the spinning solution obtained in step (S2). The process parameters for electrospinning are: spinning solution feed speed of 0.2 ml / h, voltage of 25 kV, receiving distance of 20 cm, and spinning temperature of 25 °C.

[0103] (S4) Same as Example 1.

[0104] SEM image of the prepared polyimide fiber cotton is shown below. Figure 4 As shown in the figure, the main component is uniform nanofiber cotton, with a fiber diameter of approximately 100~320nm.

[0105] The fiber morphology and fiber diameter of the polyimide fiber cotton prepared in the above embodiments and comparative examples are summarized in Table 1.

[0106] Testing and Analysis

[0107] The polyimide fiber cotton prepared in the examples and comparative examples was subjected to the following performance tests, and the specific test results are shown in Table 1.

[0108] Thermal conductivity: Refer to GB / T10297-2015 Determination of thermal conductivity of non-metallic solid materials by hot wire method.

[0109] Thermal resistance: The thermal resistance is calculated based on the thermal conductivity and sample thickness, as shown in the following formula. Where R is the thermal resistance. l Where is the sample thickness, and k is the thermal conductivity.

[0110] (3)

[0111] The lower the thermal conductivity and the higher the thermal resistance, the better the insulation of the fiber cotton.

[0112] Sound absorption coefficient: Refer to GB / T 18696.2-2002 Measurement of sound absorption coefficient and acoustic impedance in acoustic impedance tubes - Part 2: Transfer function method. The sound absorption coefficient at 6300Hz is used to characterize the sound insulation and noise reduction performance. The larger the sound absorption coefficient, the better the sound insulation and noise reduction performance.

[0113] Compression resilience: The recovery rate is tested according to "FZ / T64003-2021 Spray-bonded cotton sheet". The recovery rate is used to characterize the compression resilience. The higher the recovery rate, the better the compression resilience.

[0114] Table 1 Performance Tests

[0115] .

[0116] As shown in Table 1, the polyimide fiber cotton prepared in the embodiments of the present invention has a dendritic structure, and micro and nanoscale structures coexist. This polyimide fiber cotton exhibits low thermal conductivity and high thermal resistance, indicating good warmth retention; simultaneously, it also possesses good sound absorption and high compression resilience. Furthermore, since the present invention utilizes high-speed airflow spinning technology, its spinning efficiency is higher than that of electrospinning, making it suitable for large-scale industrial production. In contrast, comparative examples 1-5 failed to obtain dendritic micro / nanofibers, resulting in correspondingly inferior warmth retention, sound absorption, and compression resilience.

Claims

1. A method for preparing a dendritic micro / nano polyimide fiber cotton, characterized in that, Includes the following steps: (S1) Polyamic acid solution was prepared by solution polycondensation; (S2) A rheology modifier is added to a polyamic acid solution to obtain a spinning solution, wherein the non-Newtonian index of the spinning solution is 0.50~0.95; (S3) The spinning solution is blown out of the spinneret through high-speed airflow spinning technology, heated, and collected using a collection device to obtain dendritic micro / nano polyamic acid fiber cotton; the shear rate of the high-speed airflow spinning is 5.0 × 10⁻⁶. 4 ~1.0×10 7 s -1 ; (S4) Polyamic acid fiber cotton is thermally imidized to obtain dendritic micro-nano polyimide fiber cotton.

2. The preparation method according to claim 1, characterized in that, In step (S1), the conditions for the solution polycondensation method are as follows: dianhydride monomer and diamine monomer are polycondensed in a polar aprotic solvent at a molar ratio of 1:(0.98~1.02); the solid content of the polyamic acid solution is 12~25wt%, and the intrinsic viscosity is 1.1~2.8dL / g.

3. The preparation method according to claim 2, characterized in that, The dianhydride monomer is at least one of pyromellitic dianhydride, diphenyl ether tetracarboxylic dianhydride, biphenyl tetracarboxylic dianhydride, and 3,3',4,4'-triphenyl diether tetracarboxylic dianhydride; the diamine monomer is at least one of 4,4'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, p-phenylenediamine, m-phenylenediamine, 2-(4-aminophenyl)-5-aminobenzimidazole, and 4,4'-diaminobiphenyl; the polar aprotic solvent is at least one of N,N-dimethylacetamide, N,N-dimethylformamide, and N-methylpyrrolidone, and its amount is 3 to 7 times the total mass of the dianhydride monomer and the diamine monomer; the polycondensation conditions are: temperature 0 to 20°C, time 6 to 10 h.

4. The preparation method according to claim 1, characterized in that, In step (S2), the rheology modifier is at least one of deionized water, C2-C3 alcohol, acetone, and ethyl acetate; the content of the rheology modifier in the spinning solution is 0.1~1.5 wt%.

5. The preparation method according to claim 1, characterized in that, The non-Newtonian index of the spinning solution in step (S2) is 0.65~0.

85.

6. The preparation method according to claim 1, characterized in that, The high-speed airflow spinning described in step (S3) is slit-type coaxial airflow spinning.

7. The preparation method according to claim 1, characterized in that, The shear rate of the high-speed airflow spinning in step (S3) is 6.5 × 10⁻⁶. 4 ~6.0×10 6 s -1 .

8. The preparation method according to claim 1, characterized in that, Other process parameters for high-speed airflow spinning in step (S3) are: airflow slit width 0.05~0.35mm, gas flow rate 1~80L / min, air pressure 0.01~0.4MPa, airflow temperature 20~30℃, spinneret diameter 0.4~1.0mm, single-hole extrusion speed of spinning solution 2~80ml / h, and fiber receiving distance 25~50cm.

9. The preparation method according to claim 1, characterized in that, The conditions for the heat treatment in step (S3) are: temperature 50~150℃.

10. The preparation method according to claim 1, characterized in that, The conditions for thermal imidization in step (S4) are: temperature 300~450℃, time 5~50min.

11. A dendritic micro / nano polyimide fiber cotton, prepared by the method according to any one of claims 1-10, characterized in that, The dendritic micro / nano polyimide fiber cotton refers to fibers with a dendritic branching structure, including a trunk, branches, and nodes; a porous network structure is formed between the trunk, branches, and nodes; the diameter of the trunk fiber is 0.5~5μm, and the diameter of the branch fiber is 30~400nm.

Images