Bi-component polyimide nanofiber flocculus and preparation method thereof

Abstract

The invention relates to a bi-component polyimide nanofiber flocculus and a preparation method thereof. The method comprises the following steps: (1) preparing a hot-melt polyamide acid spinning solution; (2) preparing a thermosetting polyamide acid spinning solution; (3) combining the hot melt type polyamide acid spinning solution and the thermosetting type polyamide acid spinning solution to form composite spinning liquid drops with phase interfaces, then performing electrostatic spinning to form polyamide acid nanofibers, and stacking the polyamide acid nanofibers to obtain a polyamide acid nanofiber membrane; (4) opening the polyamide acid nanofiber membrane to obtain a fluffy polyamide acid nanofiber flocculus; and (5) carrying out thermal imidization treatment on the fluffy polyamide acid nanofiber flocculus to obtain the bi-component polyimide nanofiber flocculus. The method is simple in process, and rapid large-scale production can be carried out. The flocculus has excellent warmth retention property, compressibility and rebound resilience.

Description

Technical Field

[0001] The present invention relates to the field of thermal insulation materials for textiles, and particularly to a bicomponent polyimide nanofiber flake and a preparation method thereof. Background Art

[0002] Electrospinning is an efficient and low-cost method for preparing nanofibers, which has been widely concerned by people in recent years. The nanofibers prepared by it have many advantages, such as fine fiber diameter, large specific surface area, etc., and have great application value in the fields of filtration, sound absorption and noise reduction, tissue engineering, thermal insulation materials, etc.

[0003] Among the electrospinnable materials, polyimide is a polymer material with excellent comprehensive properties. It has excellent properties such as high and low temperature resistance, flame retardancy, low thermal conductivity, antibacterial property, far-infrared property, etc. Therefore, the application fields of its nanofiber products are expanding year by year, and the military and civilian markets are broad.

[0004] The nanofibers obtained by traditional electrospinning are generally linear and have a relatively single structure. They are closely packed to form a dense fiber membrane with a thickness of less than 1 mm, which limits the application of nanofibers in many aspects.

[0005] Chinese Patent Application CN111455474A discloses that a mixed spinning solution of two polymers with different elasticities is used for electrospinning in a high-humidity (relative humidity of 70-95%) environment to prepare curly nanofibers, and then stacked to form a three-dimensional nanofiber material. However, this invention requires the use of two completely different polymers (such as polyurethane and polyacrylonitrile) and has high requirements for environmental conditions, resulting in an increase in preparation cost.

[0006] Therefore, it is necessary to develop a new method with simple process and capable of large-scale production, and the prepared new material can meet the application requirements in the thermal insulation field. Summary of the Invention

[0007] Technical problem

[0008] The first object of the present invention is to provide a method for preparing a bicomponent polyimide nanofiber flake. The method has a simple process and can carry out rapid large-scale production.

[0009] The second object of the present invention is to provide a new type of bicomponent polyimide nanofiber flake, wherein each polyimide nanofiber contains a plurality of random bending parts, and the flake has excellent thermal insulation, compressibility and resilience, and can be used for a long time.

[0010] Technical solution

[0011] According to a first aspect of the present invention, there is provided a method for preparing a bicomponent polyimide nanofiber floc, the method comprising the following steps:

[0012] (1) Prepare a hot-melt polyamic acid spinning solution containing polyamic acid A;

[0013] (2) Prepare a thermosetting polyamic acid spinning solution containing polyamic acid B;

[0014] (3) Combine the hot-melt polyamic acid spinning solution and the thermosetting polyamic acid spinning solution to form a composite spinning solution droplet in which a phase interface exists, then perform electrospinning to form polyamic acid nanofibers, and stack the polyamic acid nanofibers to obtain a polyamic acid nanofiber membrane,

[0015] wherein the polyamic acid nanofibers contain the polyamic acid A and the polyamic acid B extending side by side along the fiber axis;

[0016] (4) Place the polyamic acid nanofiber membrane between two fiber meshes, and pass compressed hot gas through the polyamic acid nanofiber membrane to loosen it, thereby obtaining a fluffy polyamic acid nanofiber floc;

[0017] (5) Perform thermal imidization treatment on the fluffy polyamic acid nanofiber floc to obtain a bicomponent polyimide nanofiber floc.

[0018] In one embodiment, in step (1),

[0019] The hot-melt polyamic acid spinning solution is prepared by using a diamine monomer, a dianhydride monomer and a solvent,

[0020] The diamine monomer is one or more selected from bisphenol A type diamine (BAPP), meta-trisphenylene diamine (1,3,3-APB), diaminodiphenyl ether diamine (ODA) and m-phenylenediamine (MPD),

[0021] The dianhydride monomer is one or more selected from benzophenone dianhydride (BTDA), diphenyl ether dianhydride (ODPA), trisphenylene dianhydride (HQPDA), bisphenol A type dianhydride (BPADA), hexafluorodiacid dianhydride (6FDA) and diphenyl sulfide dianhydride (TDPA),

[0022] The solvent is one or more selected from N,N-dimethylacetamide (DMAC), N,N-dimethylformamide (DMF), N-methylpyrrolidone (NMP).

[0023] In one embodiment, in step (2),

[0024] The thermosetting polyamic acid spinning solution is prepared by using a diamine monomer, a dianhydride monomer, and a solvent.

[0025] The diamine monomer is one or more selected from p-phenylenediamine (PPD), benzidine (Bz), 4,4-diamino-2,2-dimethylbiphenyl (DMB), 4,4-diaminodiphenyl sulfone (DDS), and 2-(4-aminophenyl)-5-aminobenzimidazole (APBIA).

[0026] The dianhydride monomer is one or more selected from p-phthalic anhydride (PMDA), biphenyl dianhydride (BPDA), and 4,4'-(ethynyl diphenoxy) diphenyl dianhydride (EDA).

[0027] The solvent is one or more selected from N,N-dimethylacetamide (DMAC), N,N-dimethylformamide (DMF), and N-methylpyrrolidone (NMP).

[0028] In one embodiment, in step (3),

[0029] The hot-melt polyamic acid spinning solution and the thermosetting polyamic acid spinning solution are simultaneously supplied to a co-jet spinning nozzle with a double channel, and a composite spinning liquid droplet is formed at the spinning liquid outlet of the nozzle.

[0030] In the polyamic acid nanofibers, the weight ratio of polyamic acid A to polyamic acid B is 2:8 to 8:2.

[0031] In one embodiment, in step (4),

[0032] The two fiber meshes are two horizontally arranged and parallel fiber meshes.

[0033] The fiber mesh is one or more selected from a stainless steel fiber mesh, an aramid fiber mesh, a polyimide fiber mesh, and a polytetrafluoroethylene fiber mesh, and the mesh size is 0.5 to 2 cm.

[0034] The distance between the two fiber meshes is 5 to 20 mm.

[0035] The compressed hot gas is one or more selected from hot air, nitrogen, and argon, the temperature is 60 to 150 °C, and the pressure is 0.2 to 1 Mpa.

[0036] The compressed hot gas is passed from below the two fiber meshes upward through the polyamic acid nanofiber membrane to loosen it.

[0037] In one embodiment, in step (5), the temperature of the thermal imidization treatment is 300 to 450 °C.

[0038] According to a second aspect of the present invention, there is provided a bicomponent polyimide nanofiber flake prepared by the above method, wherein,

[0039] the flake is obtained by stacking bicomponent polyimide nanofibers,

[0040] and the bicomponent polyimide nanofibers are randomly bent.

[0041] In one embodiment, the average diameter of the bicomponent polyimide nanofibers is 200-900 nm.

[0042] In one embodiment, the density of the flake is less than 5 mg / cm 3 , the porosity is greater than 99%, and the average pore diameter is less than 3 μm.

[0043] Beneficial effect

[0044] The preparation method of the present invention prepares bicomponent composite polyamic acid nanofibers with a specific structure by electrospinning specific bicomponent composite spinning droplets, and further prepares bicomponent composite polyimide nanofibers with an obvious bending structure.

[0045] Specifically, the preparation method of the present invention combines two polyamic acid spinning solutions in step (3) to form a composite spinning droplet with a phase interface therein, and then performs electrospinning. The obtained composite polyamic acid nanofibers include a hot-melt polyamic acid A and a thermosetting polyamic acid B (two components) extending side by side along the fiber axis.

[0046] Furthermore, during the thermal imidization treatment in step (5), the composite polyamic acid nanofibers are converted into composite polyimide nanofibers, wherein the hot-melt polyamic acid A and the thermosetting polyamic acid B are respectively converted into a hot-melt polyimide A and a thermosetting polyimide B. During the formation of the composite polyimide nanofibers, due to the different thermal shrinkage rates of the above two components (i.e., the thermal shrinkage rate of the hot-melt polyimide A is significantly greater than that of the thermosetting polyimide B), asymmetric shrinkage occurs, and then multiple random bending parts are generated, so that the obtained flake has an increased porosity and fluffiness, increases the static air content, and improves the heat preservation effect.

[0047] Moreover, during the thermal imidization treatment, at the overlapping points of the nanofibers, the hot-melt polyimide B will undergo melting and bonding to form crosslinks, adding elastic rebound support points to the flake, so that the flake has high compressibility and resilience. Thus, the flake will not collapse significantly after being subjected to an external force and maintains a stable structure.

[0048] In addition, the preparation method of the present invention can carry out the electrospinning step (Step 3) in a conventional electrospinning environment (for example, the temperature is 20 to 30 °C and the humidity is 30 to 50%). Throughout the entire process flow of the present invention, there is no need to use a high-humidity environment (for example, a relative humidity of 70 to 95%), thus avoiding the phenomenon of flying flocs.

[0049] The preparation method of the present invention is simple to operate, has a one-time forming, is easy to realize mass production, and has good industrialization prospects.

[0050] In addition, the floc of the present invention has excellent heat preservation, compressibility and resilience, and can be used for a long time. Brief Description of the Drawings

[0051] Figure 1 It is a schematic diagram of the bicomponent polyamic acid nanofibers of the present invention.

[0052] Figure 2-1 It is a scanning electron microscope (SEM) image of the bicomponent polyimide nanofiber floc of Example 1.

[0053] Figure 2-2 It is an SEM image of the single-component polyimide nanofiber floc of Comparative Example 2.

[0054] Figure 2-3 It is an SEM image of the single-component polyimide nanofiber floc of Comparative Example 3.

[0055] Figure 2-4 It is an SEM image of the blended polyimide nanofiber floc of Comparative Example 4. Detailed Description of the Embodiments

[0056] Hereinafter, the present invention will be described in detail with reference to the accompanying drawings. The terms or words used in this specification and claims should not be construed restrictively as ordinary or dictionary definitions, and should be interpreted as meanings and concepts corresponding to the technical idea of the present invention on the basis of the principle that the inventor can appropriately define the concept of the term so as to describe the invention in the best possible way.

[0057] When the conditions and methods for measuring the properties or parameters described in this specification are not specifically described, the measurement conditions and methods commonly used by those skilled in the art are used to measure the properties or parameters.

[0058] Unless otherwise specified, "%" used herein refers to weight %.

[0059] Method for Preparing Bicomponent Polyimide Nanofiber Floc

[0060] According to one aspect of the present invention, the present invention provides a method for preparing a bicomponent polyimide nanofiber floc, and the method includes the following steps:

[0061] (1) Prepare a hot-melt polyamic acid spinning solution containing polyamic acid A;

[0062] (2) Prepare a thermosetting polyamic acid spinning solution containing polyamic acid B;

[0063] (3) Combine the hot-melt polyamic acid spinning solution and the thermosetting polyamic acid spinning solution to form a composite spinning solution droplet in which a phase interface exists, then perform electrospinning to form polyamic acid nanofibers, and stack the polyamic acid nanofibers to obtain a polyamic acid nanofiber membrane,

[0064] wherein the polyamic acid nanofibers contain the polyamic acid A and the polyamic acid B extending side by side along the fiber axis;

[0065] (4) Place the polyamic acid nanofiber membrane between two fiber meshes, and pass compressed hot gas through the polyamic acid nanofiber membrane to loosen it, thereby obtaining a fluffy polyamic acid nanofiber floc;

[0066] (5) Perform thermal imidization treatment on the fluffy polyamic acid nanofiber floc to obtain a bicomponent polyimide nanofiber floc

[0067] Hereinafter, each step will be described in detail.

[0068] Step (1): Prepare a hot-melt polyamic acid spinning solution

[0069] A hot-melt polyamic acid spinning solution containing polyamic acid A can be prepared using a diamine monomer, a dianhydride monomer, and a solvent. Suitable diamine monomers, dianhydride monomers, and solvents can be determined according to conventional selection.

[0070] The diamine monomer is a compound containing two amino groups and is a conventional component for preparing a polyamic acid spinning solution. The diamine monomer can be one or more selected from bisphenol A type diamine (BAPP), meta-trisphenylene diamine (1,3,3-APB), diaminodiphenyl ether diamine (ODA), and meta-phenylenediamine (MPD),

[0071] The dianhydride monomer is a compound containing two carboxylic anhydride groups and is a conventional component for preparing a polyamic acid spinning solution. The dianhydride monomer can be one or more selected from benzophenone dianhydride (BTDA), diphenyl ether dianhydride (ODPA), trisphenylene dianhydride (HQPDA), bisphenol A type dianhydride (BPADA), hexafluorodiacid anhydride (6FDA), and diphenyl sulfide dianhydride (TDPA).

[0072] The solvent may be one or more selected from N,N-dimethylacetamide (DMAC), N,N-dimethylformamide (DMF), and N-methylpyrrolidone (NMP).

[0073] The polyamic acid A is a hot-melt polyamic acid and can be used in subsequent steps to prepare a hot-melt polyimide A.

[0074] Step (2): Prepare a thermosetting polyamic acid spinning solution

[0075] A thermosetting polyamic acid spinning solution containing polyamic acid B can be prepared using a diamine monomer, a dianhydride monomer, and a solvent. Suitable diamine monomers, dianhydride monomers, and solvents can be determined according to conventional selection.

[0076] The diamine monomer may be one or more selected from p-phenylenediamine (PPD), benzidine (Bz), 4,4-diamino-2,2-dimethylbiphenyl (DMB), 4,4-diaminodiphenyl sulfone (DDS), and 2-(4-aminophenyl)-5-aminobenzimidazole (APBIA).

[0077] The dianhydride monomer may be one or more selected from p-phthalic anhydride (PMDA), biphenyl dianhydride (BPDA), and 4,4'-(ethynyl diphenoxy) diphenyl dianhydride (EDA).

[0078] The solvent may be one or more selected from N,N-dimethylacetamide (DMAC), N,N-dimethylformamide (DMF), and N-methylpyrrolidone (NMP).

[0079] The polyamic acid B is a thermosetting polyamic acid and can be used in subsequent steps to prepare a thermosetting polyimide B.

[0080] The order of the above steps (1) and (2) is not particularly limited and can be arranged as needed.

[0081] Step (3): Electrospinning (electrospinning)

[0082] The hot-melt polyamic acid spinning solution and the thermosetting polyamic acid spinning solution prepared in steps (1) and (2) are combined to form a composite spinning solution droplet with a phase interface therein, and then electrospinning is carried out to form polyamic acid nanofibers, and the polyamic acid nanofibers are stacked to obtain a polyamic acid nanofiber membrane.

[0083] Wherein the polyamic acid nanofibers comprise the polyamic acid A and the polyamic acid B extending side by side along the fiber axis.

[0084] In one embodiment, a hot-melt polyamic acid spinning solution and a thermosetting polyamic acid spinning solution are independently supplied to a coaxial spinning nozzle with a double channel, and respectively pass through the corresponding channels, and then the two spinning solutions are combined at the spinning liquid outlet of the nozzle, so as to form a composite spinning liquid droplet with a phase interface therein, wherein the two spinning solutions are not mixed, but are combined in the form of two phases. Then, electrospinning is carried out to obtain polyamic acid nanofibers, which contain polyamic acid A and polyamic acid B (two components) extending side by side along the fiber axis.

[0085] The weight ratio of polyamic acid A and polyamic acid B in the polyamic acid nanofibers can be changed by adjusting the liquid supply amount in the double channel. For example, the weight ratio of polyamic acid A to polyamic acid B can be 2:8 to 8:2, preferably 3:7 to 7:3, and most preferably 4:6 to 6:4.

[0086] If the proportion of polyamic acid A is too low, during the later thermal imidization process, the degree of fiber shrinkage is insufficient, and it is difficult to form a bending part, thus affecting the warmth retention property.

[0087] If the proportion of polyamic acid A is too high, during the later thermal imidization process, the fiber melts severely, and the three-dimensional network structure is prone to collapse, affecting its heat preservation performance.

[0088] In the obtained polyamic acid nanofibers, polyamic acid A and polyamic acid B are not mixed together, but form two independent phases. For example, when the weight ratio of polyamic acid A and polyamic acid B is 1:1, the two are arranged in approximately equal parts along the fiber axis, as Figure 1 shown.

[0089] Electrospinning is a simple and effective conventional technique for producing fibers in the micro- to nano-scale range. It makes a charged polymer solution flow and deform in an electrostatic field, and solidifies through solvent evaporation to form fibrous substances. In the present invention, electrospinning can be carried out for an appropriate time as needed, and the obtained polyamic acid nanofibers can be stacked to obtain a polyamic acid nanofiber membrane.

[0090] There is no limit to the length of the polyamic acid nanofiber membrane, and it can be of any length, such as 1 m or more, 10 m or more, 100 m or more, or 1000 m or more, etc.

[0091] There is no limit to the width of the polyamic acid nanofiber membrane, which can be adjusted by the width of the receiving belt or by subsequent cutting.

[0092] The thickness of the polyamic acid nanofiber membrane can be determined as needed, and generally can be 0.1 to 1 mm.

[0093] Step (4): Carding

[0094] Place the polyamic acid nanofiber membrane between two fiber meshes, and pass compressed hot gas through the polyamic acid nanofiber membrane to loosen it, thereby obtaining a fluffy polyamic acid nanofiber floc.

[0095] The length and width of the polyamic acid nanofiber membrane obtained in step (3) can be appropriately cut to be less than the length and width of the fiber mesh respectively, so as to be suitable for placement between two fiber meshes.

[0096] In one embodiment, two fiber meshes are arranged horizontally and parallel to each other up and down. Then, place the nanofiber membrane between the two fiber meshes, and the nanofiber membrane is located above the lower fiber mesh due to the action of gravity. Next, pass compressed hot gas from bottom to top through the two fiber meshes to loosen the nanofiber membrane therebetween to a fluffy state.

[0097] The gas can be hot air or an inert gas, preferably one or more selected from hot air, nitrogen, and argon. Considering the manufacturing cost, hot air is more preferred.

[0098] The fiber mesh is used to allow compressed hot gas to pass through and fix the floc obtained after loosening. The fiber mesh can be one or more of a stainless steel fiber mesh, an aramid fiber mesh, a polyimide fiber mesh, and a polytetrafluoroethylene fiber mesh, and it does not deform when gas passes through. The length, width, and thickness of the fiber mesh can be determined according to conventional selections, and the mesh size can be 0.5 - 2 cm, preferably 0.6 - 1.8 cm, more preferably 1 - 1.5 cm.

[0099] The compressed hot gas can form a high-speed air flow to impact and overcome the static friction force and entanglement force between the fibers in the polyamic acid nanofiber membrane. In addition, the surface of the fibers can be softened by the action of heat to reduce the cohesive force. Under this synergistic effect, the polyamic acid nanofiber membrane is loosened to form a fluffy polyamic acid nanofiber floc, which fills the space between the two fiber meshes.

[0100] The loosening means that the polyamic acid nanofiber membrane expands (i.e., the volume increases) to form a fluffy polyamic acid nanofiber floc. Generally, the volume of the fluffy polyamic acid nanofiber floc obtained after loosening can be 10 - 100 times that of the polyamic acid nanofiber membrane before loosening, preferably 20 - 80 times, more preferably 30 - 60 times. The fluffy floc can store a large amount of static air, which is beneficial to achieving excellent heat preservation effects.

[0101] By setting the distance between two fiber meshes, the degree of loosening of the nanofiber floc can be controlled. The distance between the two fiber meshes can be 5-20 mm, preferably 7-18 mm, more preferably 8-15 mm. The said distance can be appropriately determined according to the weight of the floc to facilitate maintaining an appropriate fluffiness and forming thickness of the floc.

[0102] If the above distance is too small, it may lead to insufficient fluffiness of the floc and poor heat preservation effect.

[0103] If the above distance is too large, it may lead to difficulty in forming the floc.

[0104] Hot gas can soften the fiber surface through heat, reduce the cohesive force, and is conducive to loosening. The temperature of the compressed hot gas can be 60-150 °C, preferably 80-140 °C, more preferably 100-120 °C.

[0105] If the temperature of the hot gas is too low, the degree of fiber softening is insufficient, affecting its loosening degree.

[0106] If the temperature of the hot gas is too high, the thermoplastic polyamic acid A component nanofibers may undergo preliminary melting, which will also affect the loosening effect of the fiber membrane.

[0107] The compressed hot gas can form a high-speed air flow, thereby impacting and overcoming the static friction force and entanglement force between the fibers to achieve a loosening effect. The pressure of the compressed hot gas can be 0.2-1 Mpa, preferably 0.3-0.9 Mpa, more preferably 0.4-0.8 Mpa.

[0108] If the pressure is too low, the impact force is too weak to overcome the static friction force and entanglement force between the fibers, resulting in insufficient loosening degree and affecting the fluffiness of the floc.

[0109] If the pressure is too high, it may blow the fiber membrane, resulting in difficulty in forming the floc.

[0110] Step (5): Thermal imidization

[0111] The obtained fluffy polyamic acid nanofiber floc is subjected to thermal imidization treatment to obtain a bicomponent polyimide nanofiber floc.

[0112] Thermal imidization means dehydrating and cyclizing polyamic acid at high temperature to obtain polyimide, which is a conventional step for preparing polyimide.

[0113] Through thermal imidization treatment, the polyamic acid floc can be dehydrated and cyclized to obtain a polyimide floc, in which the polyamic acid nanofibers are transformed into polyimide nanofibers, and the thermoplastic polyamic acid A and thermosetting polyamic acid B are respectively transformed into thermoplastic polyimide A and thermosetting polyimide B.

[0114] In addition, through thermal imidization treatment, the two-component polyimide nanofibers can undergo asymmetric shrinkage due to the different thermal shrinkage rates of the two components (i.e., the thermal shrinkage rate of polyimide component A is significantly greater than that of polyimide component B), thereby generating a bent structure (including a twisted structure). The resulting polyimide flake has a higher porosity and fluffiness, increasing the still air content and improving the thermal insulation effect.

[0115] Meanwhile, during the thermal imidization treatment, at the overlapping points of the nanofibers, the hot-melt polyimide B will undergo melting and bonding, thus forming crosslinks, which provide support points for elastic rebound of the flake, enabling the flake to have high compressibility and resilience. As a result, the flake will not undergo obvious collapse after being subjected to external forces and maintains a stable structure.

[0116] The temperature of thermal imidization can be 300 - 450 °C, preferably 320 - 420 °C, more preferably 350 - 400 °C.

[0117] If the temperature is too low, incomplete imidization of polyamic acid will occur, the formed bent structure will not be obvious, and the melting crosslinking of the hot-melt polyimide A at the overlapping points of the fibers will be insufficient, thus affecting the thermal insulation and compression resilience.

[0118] If the temperature is too high, the polyimide will degrade, and the melting crosslinking of the hot-melt polyimide A will be excessive, causing the fluffy structure to collapse, which will also affect the thermal insulation.

[0119] Polyimide nanofiber flake

[0120] According to another aspect of the present invention, the present invention provides a two-component polyimide nanofiber flake, wherein the flake is obtained by stacking two-component polyimide nanofibers having a bent structure, and the two-component polyimide nanofibers are randomly bent. The two-component polyimide nanofibers comprise a hot-melt polyimide A and a thermosetting polyimide B. The flake can be prepared by the above method of the present invention.

[0121] In one embodiment, the average diameter of the two-component polyimide nanofibers can be 200 - 900 nm, preferably 300 - 800 nm, more preferably 400 - 600 nm.

[0122] If the average diameter is less than 100 nm, the fiber rigidity is poor, the packing is too dense, the fluffiness of the flake after carding is insufficient, the retention of still air is insufficient, and at the same time, the three-dimensional structure is prone to collapse, resulting in poor thermal insulation;

[0123] If the average diameter is greater than 900 nm, the pore size of the flake after carding is too large, which is likely to cause air to flow therein, resulting in heat loss and thus a decrease in its thermal insulation.

[0124] In one embodiment, the density of the flake is less than 5 mg / cm 3 , the porosity is greater than 99%, and the average pore size is less than 3 μm.

[0125] The density of the flake can be measured as follows: First, measure its areal density according to GB / T 24218.1-2009 (Textiles - Test methods for nonwovens - Part 1: Determination of mass per unit area); then, measure its thickness according to GB / T 24218.2-2009 (Textiles - Test methods for nonwovens - Part 2: Determination of thickness); then, divide the areal density by the thickness to obtain the density.

[0126] The porosity of the flake can be measured according to the provisions of T / CSTM 00553-2022.

[0127] The average pore size of the flake can be measured according to GB / T 42269-2022 (Test method for pore size of separation membrane - Gas permeation method).

[0128] The porosity of the flake of the present invention can be greater than 99%, the compression ratio can be greater than 90%, and the recovery rate can be 90% or more.

[0129] The porosity of the flake can be measured according to the provisions of T / CSTM 00553-2022.

[0130] The compression ratio and recovery rate of the flake can be measured according to the test method in Appendix A of FZ / T 64003-2021 (Spray-bonded cotton flake).

[0131] The thickness of the flake of the present invention can be 1 - 20 mm, preferably 3 - 16 mm, more preferably 4 - 12 mm.

[0132] If the thickness of the flake is less than 1 mm, the static air retention is insufficient, resulting in reduced warmth retention;

[0133] If the thickness of the flake is greater than 20 mm, the flake is too bulky, resulting in reduced wearing comfort.

[0134] Examples

[0135] Hereinafter, the present invention will be described in detail with reference to examples to specifically describe the present invention. However, the examples of the present invention can be modified into various other forms, and the scope of the present invention should not be construed as limited to the examples described below. The examples of the present invention are provided to more completely describe the present invention to those of ordinary skill in the art.

[0136] Unless otherwise specified, the experimental methods in the following examples are generally conventional conditions in the art or conditions recommended by the manufacturer; the raw materials and equipment used, unless otherwise stated, are all raw materials and equipment that can be obtained from commercial channels such as the conventional market.

[0137] The following prepares polyimide nanofiber flocs of Examples 1-6 and Comparative Examples 1-4 based on the same areal density (also known as grammage, g / m 2 ), and compares their heat retention and compression resilience.

[0138] Example 1

[0139] A bicomponent polyimide nanofiber floc is prepared by a method including the following steps.

[0140] Step (1): Prepare a hot-melt polyamic acid spinning solution

[0141] Prepare 410.5 g (1 mol) of bisphenol A diamine (BAPP) and 322.2 g (1 mol) of benzophenone dianhydride (BTDA) in a molar ratio of 1:1. Additionally, prepare 4152.0 g of the solvent N,N-dimethylacetamide (DMAC). Stir them in a polymerization reactor for 12 h to obtain a hot-melt polyamic acid spinning solution containing 15% by mass of polyamic acid A.

[0142] Step (2): Prepare a thermosetting polyamic acid spinning solution

[0143] Prepare 108.1 g (1 mol) of p-phenylenediamine (PPD), 109.1 g (0.5 mol) of p-phthalic anhydride (PMDA), and 147.1 g (0.5 mol) of biphenyl dianhydride (BPDA) in a molar ratio of 1:0.5:0.5. Additionally, prepare 2064.4 g of the solvent N,N-dimethylacetamide (DMAC). Stir them in a polymerization reactor for 10 h to obtain a thermosetting polyamic acid spinning solution containing 15% by mass of polyamic acid B.

[0144] Step (3): Electrospinning

[0145] Independently supply the hot-melt polyamic acid spinning solution and the thermosetting polyamic acid spinning solution to a coaxial nozzle spinning head with a double channel, and pass them through the corresponding channels respectively. Then, merge the two spinning solutions at the spinning liquid outlet of the nozzle to form a composite spinning liquid droplet with a phase interface. Then, perform electrospinning in an electric field with an electric field strength of 20 KV / m. Among them, the feeding speed of the hot-melt polyamic acid spinning solution and the feeding speed of the thermosetting polyamic acid spinning solution are both 0.5 ml / min, so that in the obtained polyamic acid nanofibers, the weight ratio of polyamic acid A to polyamic acid B is 1:1.

[0146] The polyamic acid nanofibers formed by electrospinning are successively deposited on a conductive stainless-steel belt moving at a speed of 0.02 m / min. The electrospinning time is 200 min, forming a bicomponent polyamic acid nanofiber membrane with a length of 2 m, a width of 0.8 m, and a thickness of 200 μm.

[0147] Step (4): Carding

[0148] Prepare two stainless-steel fiber meshes, each with a length of 2.2 m, a width of 0.9 m, a thickness of 0.5 mm, and a mesh size of 1.2 cm. Place the above-mentioned bicomponent polyamic acid nanofiber membrane between the two stainless-steel fiber meshes. The stainless-steel fiber meshes are horizontally arranged and parallel to each other, and the fixed distance between the fiber meshes is 8 mm.

[0149] Let the compressed hot air with a pressure of 0.5 MPa and a temperature of 105 °C pass through the nanofiber membrane from the bottom up through the stainless-steel fiber mesh, card it, and fill the space between the two stainless-steel fiber meshes to obtain a fluffy polyamic acid nanofiber flake with a thickness of 8 mm.

[0150] Step (5): Thermal imidization

[0151] Feed the above-mentioned fluffy polyamic acid nanofiber flake into an 8-m long chain furnace for thermal imidization treatment. The chain furnace has 4 temperature zones, and the temperatures from the inlet end to the outlet end are 100 - 390 °C in sequence, and the moving speed of the flake is 1.2 m / min. Through the thermal imidization treatment, a bicomponent polyimide nanofiber flake is obtained.

[0152] After measurement, the average diameter of the obtained polyimide nanofibers is 500 nm.

[0153] The areal density of the obtained flake is 16 g / m 2 , the thickness is 6.4 mm, the density is 2.5 mg / cm 3 , the porosity is 99.8%, and the average pore diameter is 2.0 μm.

[0154] Example 2 (using different monomers from Example 1 to prepare two spinning solutions)

[0155] Prepare a bicomponent polyimide nanofiber flake by the same method as in Example 1, with the differences in the following steps.

[0156] Step (1): Prepare a hot-melt polyamic acid spinning solution

[0157] Prepare 292.3 g (1 mol) of meta - terphenyl diamine (1,3,3 - APB) and 310.2 g (1 mol) of diphenyl ether dianhydride (ODPA) in a molar ratio of 1:1. Additionally, prepare 3414.2 g of the solvent N,N - dimethylacetamide (DMAC). Stir them in a polymerization reactor for 16 h to obtain a hot - melt polyamic acid spinning solution with a mass fraction of 15%.

[0158] Step (2): Prepare a thermosetting polyamic acid spinning solution

[0159] Prepare 108.1 g (1 mol) of p - phenylenediamine (PPD) and 294.2 g (1 mol) of biphenyl dianhydride (BPDA) in a molar ratio of 1:1. Additionally, prepare 2279.7 g of the solvent N,N - dimethylacetamide (DMAC). Stir them in a polymerization reactor for 11 h to obtain a thermosetting polyamic acid spinning solution with a mass fraction of 15%.

[0160] The average diameter of the obtained polyimide nanofibers is 480 nm.

[0161] The areal density of the obtained flake is 16 g / m 2 , with a thickness of 5.9 mm, a density of 2.7 mg / cm 3 , a porosity of 99.8%, and an average pore diameter of 2.0 μm.

[0162] Example 3 (preparing two spinning solutions using monomers different from those in Example 1)

[0163] Prepare a bicomponent polyimide nanofiber flake by the same method as in Example 1, with the differences in the following steps.

[0164] Step (1): Prepare a hot - melt polyamic acid spinning solution

[0165] Prepare 200.2 g (1 mol) of diaminodiphenyl ether diamine (ODA) and 310.2 g (1 mol) of diphenyl ether dianhydride (ODPA) in a molar ratio of 1:1. Additionally, prepare 2892.3 g of the solvent N,N - dimethylacetamide (DMAC). Stir them in a polymerization reactor for 14 h to obtain a hot - melt polyamic acid spinning solution with a mass fraction of 15%.

[0166] Step (2): Prepare a thermosetting polyamic acid spinning solution

[0167] Prepare 184.2 g (1 mol) of benzidine (Bz) and 294.2 g (1 mol) of biphenyl dianhydride (BPDA) in a molar ratio of 1:1. Additionally, prepare 2710.9 g of the solvent N,N - dimethylacetamide (DMAC). Stir them in a polymerization reactor for 12 h to obtain a thermosetting polyamic acid spinning solution with a mass fraction of 15%.

[0168] The average diameter of the obtained polyimide nanofibers is 460 nm.

[0169] The areal density of the obtained floc is 16 g / m 2 , the thickness is 5.5 mm, and the density is 2.9 mg / cm 3 , the porosity is 99.8%, and the average pore diameter is 2.6 μm.

[0170] Example 4 (preparing two kinds of spinning solutions using monomers different from those in Example 1)

[0171] A bicomponent polyimide nanofiber floc was prepared by the same method as in Example 1, with the differences in the following steps.

[0172] Step (1): Prepare a hot-melt polyamic acid spinning solution

[0173] Prepare 200.2 g (1 mol) of diaminodiphenyl ether diamine (ODA) and 402.3 g (1 mol) of triphenyl ether dianhydride (HQPDA) according to a molar ratio of 1:1. Additionally, prepare 3414.2 g of the solvent N,N-dimethylacetamide (DMAC). Stir them in a polymerization reactor for 14 h to obtain a hot-melt polyamic acid spinning solution with a mass fraction of 15%.

[0174] Step (2): Prepare a thermosetting polyamic acid spinning solution

[0175] Prepare 106.1 g (0.5 mol) of 4,4-diamino-2,2-dimethylbiphenyl (DMB), 54.1 g (0.5 mol) of p-phenylenediamine (PPD), and 218.1 g (1 mol) of phthalic anhydride (PMDA) according to a molar ratio of 0.5:0.5:1. Additionally, prepare 2143.7 g of the solvent N,N-dimethylacetamide (DMAC). Stir them in a polymerization reactor for 12 h to obtain a thermosetting polyamic acid spinning solution with a mass fraction of 15%.

[0176] The average diameter of the obtained polyimide nanofibers is 510 nm.

[0177] The areal density of the obtained floc is 16 g / m 2 , the thickness is 5.9 mm, and the density is 2.7 mg / cm 3 , the porosity is 99.8%, and the average pore diameter is 2.8 μm.

[0178] Example 5 (preparing two kinds of spinning solutions using monomers different from those in Example 1)

[0179] A bicomponent polyimide nanofiber floc was prepared by the same method as in Example 1, with the differences in the following steps.

[0180] Step (1): Prepare a hot-melt polyamic acid spinning solution

[0181] Prepare 200.2 g (1 mol) of diaminodiphenyl ether diamine (ODA) and 520.5 g (1 mol) of bisphenol A dianhydride (BPADA) in a molar ratio of 1:1. Additionally, prepare 4084.0 g of the solvent N,N-dimethylacetamide (DMAC). Stir them in a polymerization reactor for 14 h to obtain a hot-melt polyamic acid spinning solution with a mass fraction of 15%.

[0182] Step (2): Prepare a thermosetting polyamic acid spinning solution

[0183] Prepare 173.8 g (0.7 mol) of 4,4'-diaminodiphenyl sulfone (DDS), 63.7 g (0.3 mol) of 4,4'-diamino-2,2'-dimethylbiphenyl (DMB), 147.1 g (0.5 mol) of biphenyl dianhydride (BPDA), and 109.1 g (0.5 mol) of phthalic anhydride (PMDA) in a molar ratio of 0.7:0.3:0.5:0.5. Additionally, prepare 2797.6 g of the solvent N,N-dimethylacetamide (DMAC). Stir them in a polymerization reactor for 12 h to obtain a thermosetting polyamic acid spinning solution with a mass fraction of 15%.

[0184] The average diameter of the obtained polyimide nanofibers is 520 nm.

[0185] The areal density of the obtained floc is 16 g / m 2 , the thickness is 6.1 mm, the density is 2.6 mg / cm 3 , the porosity is 99.8%, and the average pore diameter is 2.9 μm.

[0186] Example 6 (Preparing two spinning solutions using monomers different from those in Example 1)

[0187] Prepare a bicomponent polyimide nanofiber floc by the same method as in Example 1, except for the following steps.

[0188] Step (1): Prepare a hot-melt polyamic acid spinning solution

[0189] Prepare 200.2 g (1 mol) of diaminodiphenyl ether diamine (ODA), 266.5 g (0.6 mol) of hexafluorodiacid anhydride (6FDA), and 160.9 g (0.4 mol) of triphenyl ether dianhydride (HQPDA) in a molar ratio of 1:0.6:0.4. Additionally, prepare 3556.4 g of the solvent N,N-dimethylacetamide (DMAC). Stir them in a polymerization reactor for 14 h to obtain a hot-melt polyamic acid spinning solution with a mass fraction of 15%.

[0190] Step (2): Prepare a thermosetting polyamic acid spinning solution

[0191] Prepare 169.8 g (0.8 mol) of 4,4-diamino-2,2-dimethylbiphenyl (DMB), 44.9 g (0.2 mol) of 2-(4-aminophenyl)-5-aminobenzimidazole (APBIA), and 218.1 g (1 mol) of phthalic anhydride (PMDA) according to a molar ratio of 0.8:0.2:1. Additionally, prepare 2452.5 g of the solvent N,N-dimethylacetamide (DMAC). Stir them in a polymerization reactor for 12 h to obtain a thermosetting polyamic acid spinning solution with a mass fraction of 15%.

[0192] The average diameter of the obtained polyimide nanofibers is 450 nm.

[0193] The areal density of the obtained floc is 16 g / m 2 , with a thickness of 6.4 mm, a density of 2.5 mg / cm 3 , a porosity of 99.8%, and an average pore diameter of 2.6 μm.

[0194] Comparative Example 1 (omitting Step (4) (opening step))

[0195] Prepare a polyimide nanofiber floc by the same method as in Example 1, except that Step (4) (opening step) is omitted.

[0196] The average diameter of the obtained polyimide nanofibers is 480 nm.

[0197] The areal density of the obtained floc is 16 g / m 2 , with a thickness of 0.1 mm, a density of 160 mg / cm 3 , a porosity of 88.6%, and an average pore diameter of 1.9 μm.

[0198] Comparative Example 2 (only using the thermosetting spinning solution in Step (2) and omitting the hot-melt spinning solution in Step (1))

[0199] Prepare a polyimide nanofiber floc by the same method as in Example 1, except that Step (1) is omitted, and the thermosetting polyamic acid spinning solution in Step (2) is supplied to both channels of the coaxial spinning nozzle in Step (3), and electrospinning is carried out after forming droplets at the spinning liquid outlet.

[0200] The average diameter of the obtained polyimide nanofibers is 530 nm.

[0201] The areal density of the obtained floc is 16 g / m 2 , with a thickness of 4.2 mm, a density of 3.8 mg / cm 3, the porosity is 99.7%, and the average pore size is 2.4 μm.

[0202] Comparative Example 3 (only using the hot-melt spinning solution in step (1) and omitting the thermosetting spinning solution in step (2))

[0203] A polyimide nanofiber flake was prepared by the same method as in Example 1, except that step (2) was omitted, and the hot-melt polyamic acid spinning solution in step (1) was supplied to both channels of the coaxial spinning nozzle in step (3), and electrospinning was carried out after forming droplets at the spinning liquid outlet.

[0204] The average diameter of the obtained polyimide nanofibers is 470 nm.

[0205] The areal density of the obtained flake is 16 g / m 2 , the thickness is 0.025 mm, and the density is 640 mg / cm 3 , the porosity is 54.3%, and the average pore size is 1.0 μm.

[0206] Comparative Example 4 (changing the combination method of the two spinning solutions in step (3))

[0207] A polyimide nanofiber flake was prepared by the same method as in Example 1, except that step (3) was changed.

[0208] Step (3): Electrospinning

[0209] The hot-melt polyamic acid spinning solution in step (1) and the thermosetting polyamic acid spinning solution in step (2) were mixed evenly by mechanical stirring according to a weight ratio of 1:1 to obtain a blended polyamic acid spinning solution. Then, the blended polyamic acid spinning solution was supplied to both channels of the coaxial spinning nozzle, and spinning liquid droplets (without an interface) were formed at the spinning liquid outlet. Then, electrospinning was carried out. The conditions of electrospinning were the same as in Example 1.

[0210] The average diameter of the obtained polyimide nanofibers is 550 nm.

[0211] The areal density of the obtained flake is 16 g / m 2 , the thickness is 4.4 mm, and the density is 3.6 mg / cm 3 , the porosity is 99.7%, and the average pore size is 2.2 μm.

[0212] In Experimental Example 1, a scanning electron microscope was used to observe the morphology of the flake.

[0213] Using a scanning electron microscope (TESCAN, model VEGA3), SEM morphological observations of the microstructures of the flakes in Example 1 and Comparative Examples 2-4 were carried out in accordance with GB / T 36422-2018 (Determination of the microscopic morphology and diameter of chemical fibers - Scanning electron microscopy method), as Figures 2-1 to 2-4 shown. Among them,

[0214] Figure 2-1 is the SEM image of the bicomponent polyimide nanofiber flake of Example 1,

[0215] Figure 2-2 is the SEM image of the single-component polyimide nanofiber flake of Comparative Example 2,

[0216] Figure 2-3 is the SEM image of the single-component polyimide nanofiber flake of Comparative Example 3.

[0217] Figure 2-4 is the SEM image of the blended polyimide nanofiber flake of Comparative Example 4.

[0218] From Figure 2-1 it can be seen that all the nanofibers constituting the flake of Example 1 have an obviously curved structure, which can construct a better three-dimensional network structure and retain a large amount of static air, having excellent warmth retention. In addition, it can be seen that at the overlapping points of the nanofibers, melting bonding cross-linking has occurred, increasing the support points for elastic resilience, so that the flake has high compressibility and resilience and will not collapse significantly under the action of external forces.

[0219] From Figure 2-2 it can be seen that the nanofibers constituting the flake of Comparative Example 2 are basically in a linear state, and the three-dimensional fluffy network structure constructed by them is poor. Moreover, no cross-linking phenomenon occurs at the overlapping points of the nanofibers, and its fluffy structure is prone to collapse, resulting in poor resilience.

[0220] From Figure 2-3 it can be seen that the nanofibers constituting the flake of Comparative Example 3 have undergone severe melting bonding, and its fluffy structure has collapsed, and the amount of static air retained is low, thus resulting in poor warmth retention.

[0221] From Figure 2-4 it can be seen that some of the nanofibers constituting the flake of Comparative Example 4 are slightly bent, which is not enough to construct a better three-dimensional fluffy network structure. Moreover, no cross-linking phenomenon occurs at the overlapping points of the nanofibers, and its fluffy structure has a collapse problem, resulting in poor resilience of the flake.

[0222] Measurement of warmth retention in Experimental Example 2

[0223] Based on the same areal density (also known as grammage, g / m 2)The warmth retention properties of the waddings of Examples 1 to 6 and Comparative Examples 1 to 4 were compared. The warmth retention property of the wadding is expressed by the clo value, which can be measured according to GB / T 11048-2008 (Determination of Thermal Resistance and Moisture Resistance under Steady-State Conditions of Physiological Comfort of Textiles).

[0224] Specifically, the clo values of the polyimide nanofiber waddings of Examples 1 to 6 and Comparative Examples 1 to 4 were measured using a fabric warmth retention tester (Wenzhou Darong Textile Instrument Co., Ltd., model YG(B)606E) according to GB / T 11048-2018. The results are shown in Table 1 below.

[0225] Table 1: Clo values of polyimide nanofiber waddings

[0226]

[0227] As can be seen from Table 1, the clo values of the bicomponent polyimide nanofiber waddings of Examples 1 to 6 prepared by the method of the present invention are significantly larger, indicating excellent warmth retention effect.

[0228] In particular, compared with Comparative Example 1, the clo value of the wadding of Example 1 is significantly increased. From this, it can be seen that the carding step can significantly improve the warmth retention property of the obtained wadding;

[0229] Compared with Comparative Example 2, the clo value of the wadding of Example 1 is significantly increased. From this, it can be seen that the nanofibers containing two components and having a bent structure are beneficial to improving the warmth retention property of the wadding;

[0230] From the clo value of the wadding of Comparative Example 3, it can be seen that due to severe melting, the fluffy structure of the single-component hot-melt wadding collapses, and the amount of static air stored is low, resulting in poor warmth retention property;

[0231] From the clo value of the wadding of Comparative Example 4, it can be seen that although the polyimide nanofibers of Comparative Document 4 have two components, their degree of bending is low, resulting in poor warmth retention property of the wadding.

[0232] Measurement of compression ratio and recovery rate in Experimental Example 3

[0233] The compression ratio and recovery rate of the polyimide nanofiber waddings of Examples 1 to 6 and Comparative Examples 1 to 4 were measured according to the test method in Appendix A of FZ / T 64003-2021 Spray-Adhesive Cotton Wadding. The results are shown in Table 2 below.

[0234] Table 2: Compression ratio and recovery rate of polyimide nanofiber waddings

[0235] Compression ratio % Recovery rate % Example 1 96 97 Example 2 94 96 Example 3 93 95 Example 4 92 96 Example 5 93 93 Example 6 94 95 Comparative Example 1 16 10 Comparative Example 2 88 35 Comparative Example 3 4 3 Comparative Example 4 90 40

[0236] As can be seen from Table 2, the compression rate and recovery rate of the bicomponent polyimide nanofiber flocs of Examples 1 to 6 of the present invention are relatively high, which are suitable for the field of thermal insulation;

[0237] The compression rate and recovery rate of the flocs of Comparative Examples 1 and 3 are significantly lower, with poor fluffy structure, and are not suitable for the field of thermal insulation materials either.

[0238] The compression rate of the flocs of Comparative Examples 2 and 4 is relatively high, but the recovery rate is relatively low, indicating that there is an obvious collapse in the three-dimensional fluffy structure, and it is not suitable for the field of thermal insulation materials.

[0239] The description of the above embodiments is only used to help understand the core idea of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and modifications can be made to the present invention, and these improvements and modifications also fall within the protection scope of the present invention.

Claims

1. A method for preparing a bicomponent polyimide nanofiber flake, the method comprising the following steps: (1) Prepare a hot-melt polyamic acid spinning solution containing polyamic acid A; (2) Prepare a thermosetting polyamic acid spinning solution containing polyamic acid B; (3) Combine the hot-melt polyamic acid spinning solution and the thermosetting polyamic acid spinning solution to form a composite spinning solution droplet with a phase interface therein, then perform electrospinning to form polyamic acid nanofibers, and stack the polyamic acid nanofibers to obtain a polyamic acid nanofiber membrane, wherein the polyamic acid nanofibers contain the polyamic acid A and the polyamic acid B extending side by side along the fiber axis; (4) Place the polyamic acid nanofiber membrane between two fiber meshes, and pass compressed hot gas through the polyamic acid nanofiber membrane to loosen it, thereby obtaining a fluffy polyamic acid nanofiber flake; (5) Perform thermal imidization treatment on the fluffy polyamic acid nanofiber flake to obtain a bicomponent polyimide nanofiber flake.

2. The method according to claim 1, wherein In step (1), The hot-melt polyamic acid spinning solution is prepared by using a diamine monomer, a dianhydride monomer, and a solvent, The diamine monomer is one or more selected from bisphenol A type diamine (BAPP), meta-triphenylene diamine (1,3,3-APB), diaminodiphenyl ether diamine (ODA), and m-phenylenediamine (MPD), The dianhydride monomer is one or more selected from benzophenone dianhydride (BTDA), diphenyl ether dianhydride (ODPA), triphenylene dianhydride (HQPDA), bisphenol A type dianhydride (BPADA), hexafluorodiacid dianhydride (6FDA), and diphenyl sulfide dianhydride (TDPA), The solvent is one or more selected from N,N-dimethylacetamide (DMAC), N,N-dimethylformamide (DMF), and N-methylpyrrolidone (NMP).

3. The method according to claim 1, wherein In step (2), The thermosetting polyamic acid spinning solution is prepared by using a diamine monomer, a dianhydride monomer, and a solvent, The diamine monomer is one or more selected from p-phenylenediamine (PPD), biphenyl diamine (Bz), 4,4-diamino-2,2-dimethylbiphenyl (DMB), 4,4-diaminodiphenyl sulfone (DDS), and 2-(4-aminophenyl)-5-aminobenzimidazole (APBIA), The dianhydride monomer is one or more selected from p-phthalic anhydride (PMDA), biphenyl dianhydride (BPDA), and 4,4'-(ethynyl diphenoxy) diphenyl dianhydride (EDA), The solvent is one or more selected from N,N-dimethylacetamide (DMAC), N,N-dimethylformamide (DMF), and N-methylpyrrolidone (NMP).

4. The method according to claim 1, wherein, In step (3), Simultaneously supply the hot-melt polyamic acid spinning solution and the thermosetting polyamic acid spinning solution to a coaxial nozzle spinning head with a double channel to form the composite spinning solution droplet at the spinning liquid outlet of the nozzle; In the polyamic acid nanofibers, the weight ratio of polyamic acid A to polyamic acid B is 2:8 to 8:

2.

5. The method according to claim 1, wherein, In step (4), The two fiber meshes are two horizontally arranged and parallel fiber meshes; The fiber mesh is one or more selected from a stainless steel fiber mesh, an aramid fiber mesh, a polyimide fiber mesh, and a polytetrafluoroethylene fiber mesh, and the mesh size thereof is 0.5 to 2 cm, The distance between the two fiber meshes is 5 to 20 mm, The compressed hot gas is one or more selected from hot air, nitrogen, and argon, the temperature is 60 to 150 °C, and the pressure is 0.2 to 1 Mpa; The compressed hot gas is passed upward from below through the polyamic acid nanofiber membrane between the two fiber meshes to loosen it.

6. The method according to claim 1, wherein In step (5), The temperature of the thermal imidization treatment is 300 to 450 °C.

7. A bicomponent polyimide nanofiber flake prepared by the method according to claim 1, wherein, The flake is obtained by stacking bicomponent polyimide nanofibers, The bicomponent polyimide nanofibers are randomly curved.

8. The flake according to claim 7, wherein, The average diameter of the bicomponent polyimide nanofibers is 200 to 900 nm.

9. The flake according to claim 7, wherein, The density of the batting is less than 5 mg / cm 3 , the porosity is greater than 99%, and the average pore diameter is less than 3 μm.

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