Ultra-fine air fiber, and preparation method therefor and use thereof

Abstract

An ultra-fine air fiber, and a preparation method therefor and the use thereof. The ultra-fine air fiber is prepared from a polymer solution by means of wet spinning using the following steps: passing the polymer solution through a gradient phase separation bath, performing stepwise drawing, then performing coagulation in a coagulating bath and drying same at a normal temperature and pressure, so as to obtain an ultra-fine polymer air fiber. The fiber has an average diameter of less than 30 μm, and exhibits good mechanical properties and a good weavability. A continuously oriented polymer linear pore-wall skeleton is formed inside the fiber along the axial direction, thereby improving the strength of the fiber. The average pore diameter in a direction perpendicular to oriented pores is less than 60 nm, and therefore gas heat conduction can be effectively reduced. The preparation method has the advantages of simplicity, safety, environmental friendliness, a high speed and low costs; and thermal insulating textiles based on the ultra-fine fiber integrate a light weight, a high strength, good thermal insulation performance and good flexibility, and can be widely used in the field of thermal insulation.

Description

An ultrafine air fiber, its preparation method and application Technical Field

[0001] This invention relates to the field of aerogel preparation technology, specifically to an ultrafine air fiber, its preparation method, and its application. Background Technology

[0002] Aerogel fiber is a novel material with high porosity, low density, and excellent thermal insulation properties. Due to its diverse functions and ease of weaving or integration into textiles and composite materials, it is suitable for applications such as thermal clothing, filter materials, personal protective fabrics, and smart textiles. Furthermore, the fine diameter of aerogel fibers allows for the weaving of denser fabrics, effectively insulating against cold air and efficiently reflecting radiant heat from the human body, thus significantly enhancing the thermal insulation performance of textiles.

[0003] Currently, aerogel fibers prepared by cryo-spinning generally exhibit poor performance, with low strength of the porous skeleton, large pore size, and low pore wall orientation, resulting in poor mechanical properties. During preparation, the strength of the gel fibers is insufficient to withstand the tension of industrial spinning equipment, and their fragile mechanical properties severely limit continuous production. Therefore, it is difficult to achieve ultrafine fibers through high draw ratios during preparation, resulting in poor weavability. Aerogel fibers prepared by this method typically have large diameters and pore sizes, making it difficult to simultaneously achieve excellent mechanical properties and high-efficiency thermal insulation. Drawing on the advantages of high-throughput and continuous production of traditional wet spinning, stable preparation of ultrafine diameter fibers can be achieved through controllable draw of the gel-state fibers. By precisely controlling the phase separation process and draw ratio, the internal pore size and fiber diameter can be further optimized and reduced, the porosity and skeleton strength can be balanced, and the nanoporous structure can be stably maintained in the ultrafine fibers with the help of atmospheric pressure drying process. It is expected to create ultrafine aerogel fibers with ultralight, ultra-insulating properties and good mechanical properties, enabling them to achieve continuous mass spinning and complex weaving like conventional textile fibers, thereby promoting the large-scale application of aerogel materials in high-end textiles and flexible thermal insulation fields. Summary of the Invention

[0004] To address the challenge of existing technologies in preparing ultrafine aerogel fibers with small pore sizes and excellent mechanical properties, this invention provides an ultrafine air fiber, its preparation method, and its applications, resulting in air fibers with good mechanical strength, flexibility, and thermal insulation properties. The air fiber is an aerogel fiber composed of nanoscale pores and a continuous linear polymer network framework.

[0005] One of the technical solutions of this invention is to provide a method for preparing ultrafine air fibers. By performing traction stretching in a phase separation bath with high solvent content, the fiber exhibits low phase separation, resulting in greater distances between polymer chains and weaker intermolecular interactions. Under stretching force, the polymer chains undergo partial orientation. Subsequently, further stretching in a phase separation bath with lower solvent content leads to a denser arrangement of the polymer chains, thereby improving the strength of the porous polymer fiber skeleton. The stretching force during the stepwise phase separation process effectively suppresses the nucleation size of the polymer-depleted phase, ensuring the fine pore size inside the air fiber. Testing shows that this invention can effectively control the internal pore size of the air fiber within 60 nm. This structure forms a continuous and strong oriented pore wall skeleton along the fiber axis, providing excellent mechanical properties. Simultaneously, the ultrafine pore size effectively suppresses gas molecule movement, significantly reducing gas thermal conductivity. This synergistic mechanism enables the material to maintain its ultralight properties while achieving a balance and unity between mechanical strength and thermal insulation performance.

[0006] Specifically, the method includes: extruding a polymer solution, stretching it in a multi-stage phase separation bath system, then solidifying it in a coagulation bath to obtain nascent fibers, and drying the nascent fibers to obtain ultrafine polymer air fibers; the multi-stage phase separation bath system includes multiple phase separation baths, each phase separation bath being a mixed solution of polymer solvent and non-solvent, wherein the mass fraction of the solvent is 30% to 90%, the mass fraction of the solvent in the first phase separation bath is not less than 40%, and the mass fraction of the solvent in each phase separation bath decreases sequentially; the coagulation bath is a non-solvent of the polymer; the stretching ratio in each phase separation bath is 30% to 200%. The stretching ratio is defined as ((second roller speed - first roller speed) ÷ first roller speed) × 100%.

[0007] Further, the polymer solution is a 10wt%~15wt% polyamic acid solution, a 0.1wt%~2.5wt% heterocyclic aramid solution, a 15wt%~25wt% polyurethane solution, a 15wt%~25wt% polyacrylonitrile solution, or a 2%~10% sodium alginate solution.

[0008] Further, the solvent is one or more of DMF, DMAC, NMP, DMSO, HMPA, TEP, TMP, and TMU; the non-solvent is one or more of water, ethanol, isopropanol, methanol, diethyl ether, ethyl acetate, ethylene glycol, and glycerol.

[0009] When using sodium alginate spinning solution, the solvent is water, and the non-solvent is one or more of the following: ethanol, isopropanol, methanol, ethylene glycol, glycerol, n-hexane, etc.

[0010] Generally, the solvent used is the same as or miscible with the solvent in the polymer solution.

[0011] Furthermore, the drying process is carried out at room temperature and atmospheric pressure.

[0012] In some embodiments of the present invention, polyamic acid is used as a polymer solution to prepare polyimide air fibers. After the polyamic acid air fibers are dried, they need to be transferred to a tube furnace for imidization at 300°C for one hour to obtain polyimide air fibers.

[0013] The second technical solution of the present invention is to provide an ultrafine air fiber prepared by the above method.

[0014] The polymer air fibers prepared by the method described in this invention can have a diameter of 1-30 μm, a strength range of 20-500 MPa, and a porosity of 30-80%.

[0015] Preferably, the polymer air fiber has a diameter of 3µm to 10µm, a strength of 40MPa to 200MPa, and a porosity of 40% to 70%.

[0016] Furthermore, the polymer air fiber forms a continuous and tough pore wall skeleton inside, with pore size smaller than the mean free path of air molecules. The air inside the small pores is generally in a static state, which can effectively reduce gas heat conduction and play a huge role in thermal insulation.

[0017] The third technical solution of the present invention is to provide a filament bundle composed of the above-mentioned ultrafine air fibers.

[0018] The fourth technical solution of the present invention is to provide a woven fabric prepared from the above-mentioned filament bundles.

[0019] The beneficial effects of this invention are as follows: It breaks through the traditional design concept of random porous structures, achieving precise control of the pore structure of air fibers through multi-stage phase separation baths and step-by-step drawing processes. The resulting polymer air fibers have a fine diameter, possessing both good mechanical strength and flexibility, and are endowed with excellent weavability. The air fibers form a continuously oriented pore wall skeleton along the axial direction, improving fiber strength. The average pore diameter is less than 60 nm, effectively reducing gas heat conduction. This synergistic mechanism enables the material to maintain its ultra-lightweight properties while achieving a balance and unity between mechanical strength and thermal insulation performance. The preparation method of this invention is simple and efficient, enabling large-scale preparation of air fibers with excellent mechanical properties and thermal insulation effects at room temperature and atmospheric pressure. It is highly repeatable and shows broad application prospects in the field of thermal insulation textiles. Attached Figure Description

[0020] Figure 1 is a SEM image of the polyimide air fiber obtained in Example 1.

[0021] Figure 2 shows a picture of the polyimide air fiber knot in Example 1.

[0022] Figure 3 is a SEM image of the radial cross section of the polyimide air fiber obtained in Example 11.

[0023] Figure 4 is a SEM image of the axial cross section of the polyimide air fiber obtained in Example 11.

[0024] Figure 5 is an optical diagram of the polyimide air fiber bundle obtained in Example 11. Detailed Implementation

[0025] The following examples are provided to further illustrate the present invention and are intended to explain the invention, not to limit its scope. Unless otherwise specified, all figures are expressed in parts by weight and weight percentages.

[0026] Unless otherwise specified, the raw materials used in this invention are all conventional commercially available products; unless otherwise specified, the methods used in this invention are all conventional methods in the field.

[0027] The embodiments of the present invention will be further described below with reference to several examples.

[0028] The spinning needle described in this invention is a commercially available national standard needle.

[0029] It should be understood that the described embodiments are merely some, not all, of the embodiments in this application. All other embodiments obtained by those skilled in the art based on the embodiments in this application without inventive effort are within the scope of protection of this application.

[0030] The terminology used in the embodiments of this application is for the purpose of describing particular embodiments only and is not intended to be limiting of this application. The singular forms “a,” “the,” and “the” used in the embodiments of this application and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise. Example 1

[0031] (1) A 15% N,N-dimethylacetamide solution of polyamic acid was extruded through a 34G needle, passed through a three-stage gradient phase separation bath and drawn, and finally wet-spun through a pure water coagulation bath to obtain polyamic acid nascent fibers. The mass ratios of N,N-dimethylacetamide and water in the gradient phase separation bath were 9:1, 1:1, and 3:7, respectively, and the corresponding draw ratios in each bath were 50%, 200%, and 100%, respectively.

[0032] (2) Polyamic acid fibers were dried at room temperature and atmospheric pressure to obtain polyamic acid air fibers, which were then thermally imidized to obtain polyimide air fibers. The imidization temperature was 300℃ and the imidization time was 1h. The diameter of the prepared fibers was approximately 9μm. The microstructure of the obtained air fibers is shown in Figure 1, with an average pore size of 37nm, an orientation degree of 0.72, a porosity of 70%, and a tensile strength of 157MPa. The polyimide air fibers in Example 1 were knotted, and the results are shown in Figure 2. The fibers in Example 1 were prepared into tows and then woven into fabrics. The vertical thermal conductivity at room temperature was 39 mW / (m·K). Example 2

[0033] The only difference from Example 1 is the use of a 10 wt% polyamic acid N,N-dimethylacetamide solution. Example 3

[0034] (1) A 0.1% (w / w) heterocyclic aramid N,N-dimethylacetamide solution was extruded through a 32G needle, passed through a three-stage gradient phase separation bath and drawn, and finally wet-spun through a pure ethanol coagulation bath to obtain heterocyclic aramid nascent fibers. The mass ratios of dimethyl sulfoxide and ethanol in the gradient phase separation bath were 8:2, 6:4, and 4:6, respectively, and the corresponding draw ratios in each bath were 30%, 150%, and 100%, respectively.

[0035] (2) The heterocyclic aramid nascent fibers were dried at room temperature and normal pressure to obtain heterocyclic aramid air fibers. The average pore size was 51 nm, the fiber diameter was 3 μm, the orientation degree was 0.75, the porosity was 40%, and the tensile strength was 200 MPa. The fibers from Example 3 were prepared into tows and then woven into fabrics. The vertical thermal conductivity at room temperature was 55 mW / (m·K). Example 4

[0036] The only difference from Example 3 is the use of a 2.5 wt% heterocyclic aramid N,N-dimethylacetamide solution. Example 5

[0037] (1) A 15% N,N-dimethylformamide polyurethane solution was extruded through a 30G needle, passed through a four-stage gradient phase separation bath and stretched, and finally wet-spun through a pure ethanol coagulation bath to obtain polyurethane nascent fibers. The mass ratios of N,N-dimethylformamide to water in the gradient phase separation bath were 8:2, 6:4, 4:6, and 3:7, respectively, and the corresponding stretching ratios in each bath were 80%, 200%, 100%, and 100%, respectively. The coagulation bath consisted of ethanol and water in a 1:1 miscible ratio.

[0038] (2) The nascent polyurethane fibers were dried at room temperature and normal pressure to obtain polyurethane air fibers. The average pore size was 51 nm, the fiber diameter was 10 μm, the orientation degree was 0.87, and the tensile strength was 40 MPa. The fibers from Example 5 were prepared into tows and then woven into fabrics. The vertical thermal conductivity at room temperature was 45 mW / (m·K). Example 6

[0039] The only difference from Example 5 is the use of a 25% by mass solution of polyurethane N,N-dimethylformamide. Example 7

[0040] (1) A 15% (w / w) polyacrylonitrile dimethyl sulfoxide solution was extruded through a 34G needle, passed through a three-stage gradient phase separation bath and stretched, and finally wet-spun through a pure water coagulation bath to obtain nascent polyacrylonitrile fibers. The mass ratio of N-methylpyrrolidone solution to water in the gradient phase separation bath was 8:2, 6:4, and 1:1, with corresponding stretching ratios of 50%, 200%, and 100% in each bath.

[0041] (2) The nascent polyacrylonitrile fibers were dried at room temperature and normal pressure to obtain polyacrylonitrile air fibers. The average pore size was 37 nm, the fiber diameter was 6 μm, the orientation degree was 0.77, and the strength was 125 MPa. The fibers from Example 7 were prepared into tows and then woven into fabrics. The vertical thermal conductivity at room temperature was 38 mW / (m·K). Example 8

[0042] The only difference from Example 7 is the use of a 25% (w / w) polyacrylonitrile dimethyl sulfoxide solution. Example 9

[0043] (1) A 15% (w / w) polyacrylonitrile dimethyl sulfoxide solution was extruded through a 34G needle, passed through a three-stage gradient phase separation bath and stretched, and finally wet-spun through a pure water coagulation bath to obtain nascent polyacrylonitrile fibers. The mass ratio of N-methylpyrrolidone solution to water in the gradient phase separation bath was 4:6, 7:3, and 3:7, with corresponding stretching ratios of 50%, 200%, and 100% in each bath.

[0044] (2) Dry the nascent polyacrylonitrile fibers at room temperature and normal pressure to obtain polyacrylonitrile air fibers. Example 10

[0045] (1) A 4% sodium alginate aqueous solution was extruded through a 30G needle, passed through a three-stage gradient phase separation bath and stretched, and finally wet-spun through pure ethanol and n-hexane coagulation baths to obtain sodium alginate nascent fibers. The mass ratios of water and ethanol in the gradient phase separation baths were 4:6, 2:8, and 1:9, respectively, and the corresponding stretching ratios in each bath were 50%, 200%, and 100%, respectively.

[0046] (2) Sodium alginate nascent fibers were dried at room temperature and normal pressure to obtain sodium alginate air fibers. The average pore size was 60 nm, the fiber diameter was 30 μm, the orientation degree was 0.54, the porosity was 80%, and the tensile strength was 20 MPa. The fibers from Example 10 were prepared into tows and then woven into fabrics. The vertical thermal conductivity at room temperature was 25 mW / (m·K). Example 11

[0047] (1) A 15% N,N-dimethylacetamide solution of polyamic acid was extruded through a spinneret with a pore size of 100µm and 1000 pores. The solution was then drawn in a three-stage gradient phase separation bath and finally wet-spun in a pure water coagulation bath to obtain nascent polyamic acid fibers. The mass ratios of N,N-dimethylacetamide and water in the gradient phase separation bath were 6:4, 1:1, and 4:6, respectively, and the corresponding draw ratios in each bath were 150%, 200%, and 200%, respectively.

[0048] (2) The polyamic acid fiber was dried at room temperature and normal pressure to obtain polyamic acid air fiber bundles, which were then drawn and thermally imidized to obtain polyimide air fiber bundles. The imidization temperature was 300℃ and the imidization time was 1h. The diameter of the prepared single fiber was about 5µm. The radial cross-sectional micromorphology of the obtained air fiber is shown in Figure 3. It has a large number of nanoscale pores inside. An oriented flat hole array is formed along the axial direction. The microstructure is shown in Figure 4. The continuously oriented pore wall skeleton significantly improves the fiber strength. At the same time, it has a narrow pore structure with an anisotropy ratio of its major axis to minor axis of 3. The average pore diameter in the vertical direction of the flat holes is less than 60 nm, which effectively reduces gas heat conduction and has good thermal insulation performance. This structure enables the material to maintain its ultra-lightweight characteristics while achieving a balance and unity between mechanical strength and thermal insulation performance. Furthermore, the oriented flat-hole array generates multiple reflection / scattering interfaces, which can extend the thermal radiation propagation path, enhance absorption or backscattering, and effectively suppress radiative heat transfer. At the same time, the narrow and tortuous channels of the flat holes greatly increase the gas flow resistance, suppressing the convection effect. The average vertical pore diameter of the oriented holes is 45 nm, the orientation degree is 0.76, the porosity is 72%, and the tensile strength is 210 MPa.

[0049] The macroscopic dispersion structure of the filament bundle in Example 11 is shown in Figure 5. When woven into a fabric, its vertical thermal conductivity at room temperature is 27 mW / (m·K). Example 12

[0050] (1) A 15% N,N-dimethylacetamide solution of polyamic acid was extruded through a spinneret with a pore size of 75 µm and 1000 pores. The solution was then drawn in a three-stage gradient phase separation bath and finally wet-spun in a pure water coagulation bath to obtain nascent polyamic acid fibers. The mass ratios of N,N-dimethylacetamide and water in the gradient phase separation bath were 6:4, 1:1, and 4:6, respectively, and the corresponding draw ratios in each bath were 200%, 200%, and 200%, respectively.

[0051] (2) Polyamic acid fibers were dried at room temperature and normal pressure to obtain polyamic acid air fibers, which were then stretched and thermally imidized to obtain polyimide air fibers. The imidization temperature was 300℃ and the imidization time was 1h. The prepared fibers had a diameter of approximately 1μm, an anisotropy ratio of the long axis to the short axis of the flat pores of 6, an average vertical pore diameter of 30nm, an orientation degree of 0.8, a porosity of 64%, and a tensile strength of 287MPa. The fibers from Example 12 were prepared into tows and then woven into fabrics. The vertical thermal conductivity at room temperature was 42 mW / (m·K). Example 13

[0052] (1) A heterocyclic aramid N,N-dimethylacetamide solution with a mass fraction of 0.8% was extruded through a 32G needle, passed through a three-stage gradient phase separation bath and drawn, and finally wet-spun through a pure ethanol and a hexane coagulation bath to obtain heterocyclic aramid nascent fibers. The mass ratios of water and ethanol in the gradient phase separation baths were 8:2, 1:1, and 1:9, respectively, and the corresponding draw ratios in each bath were 50%, 200%, and 150%, respectively.

[0053] (2) The heterocyclic aramid nascent fibers were dried at room temperature and normal pressure to obtain heterocyclic aramid air fibers. The average pore size was 52 nm, the fiber diameter was 10 μm, the orientation degree was 0.78, the porosity was 50%, and the tensile strength was 500 MPa. The fibers from Example 13 were prepared into tows and then woven into fabrics. The vertical thermal conductivity at room temperature was 48 mW / (m·K). Comparative Example 1

[0054] The difference from Example 1 is that the mass ratios of N,N-dimethylacetamide and water in the three-stage gradient phase separation bath are 3:7, 2:8, and 1:9, respectively, and the corresponding stretching ratios in each bath are 50%, 200%, and 100%, respectively. The prepared fibers are solid fibers without porous structures. Comparative Example 2

[0055] The difference from Example 7 is that only one phase separation bath was used, in which the mass ratio of N-methylpyrrolidone to water was 4:6 and the stretching ratio was 100%, and the prepared fibers had a micron-scale finger-like pore structure.

[0056] The above embodiments describe in detail the structure, features, and effects of the present invention. The above description is only a preferred embodiment of the present invention. Any changes made in accordance with the concept of the present invention, or equivalent embodiments modified to have equivalent changes, shall still fall within the scope of protection of the present invention if they do not exceed the scope covered by the specification.

Claims

1. A method for preparing ultrafine air fibers, characterized in that, The polymer solution is extruded and drawn in a multi-stage phase separation bath system, then solidified in a coagulation bath to obtain nascent fibers. The nascent fibers are dried to obtain ultrafine air fibers. The multi-stage phase separation bath system includes multiple phase separation baths, each of which is a mixed solution of polymer solvent and non-solvent, wherein the mass fraction of the solvent is 30% to 90%, the mass fraction of the solvent in the first phase separation bath is not less than 40%, and the mass fraction of the solvent in each phase separation bath decreases sequentially. The coagulation bath is a non-solvent of the polymer. The drawing ratio in each phase separation bath is 30% to 200%.

2. The preparation method according to claim 1, characterized in that, The polymer solution is a 10wt%~15wt% polyamic acid solution, a 0.1wt%~2.5wt% heterocyclic aramid solution, a 15wt%~25wt% polyurethane solution, or a 15wt%~25wt% polyacrylonitrile solution.

3. The preparation method according to claim 1, characterized in that, The solvent is one or more of DMF, DMAC, NMP, DMSO, HMPA, TEP, TMP, and TMU; the non-solvent is one or more of water, ethanol, isopropanol, methanol, diethyl ether, ethyl acetate, ethylene glycol, and glycerol.

4. The preparation method according to claim 1, characterized in that, The drying process is carried out at room temperature and normal pressure.

5. An ultrafine air fiber prepared by the preparation method as described in claim 1.

6. The ultrafine air fiber according to claim 5, characterized in that, The air fiber has a diameter of 3µm to 10µm, a strength of 40Mpa to 200Mpa, and a porosity of 40% to 70%.

7. The ultrafine air fiber according to claim 6, characterized in that, The pores inside the air fiber are nanopores with an average pore size of less than 60 nm.

8. A filament bundle composed of the ultrafine air fibers as described in claim 5.

9. A woven fabric prepared from the filaments of claim 8.

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