Polyimide aerogel fiber with skin-core structure and preparation method of polyimide aerogel fiber

Abstract

The invention discloses a polyimide aerogel fiber with a skin-core structure and a preparation method of the polyimide aerogel fiber. The retention time of the gel fiber in a phase separation bath is regulated and controlled by a polyimide acid solution through a phase separation wet spinning method, and the aerogel fiber with a skin-core structure is generated in one step. The polyimide aerogel fiber disclosed by the invention can be continuously and integrally formed and prepared on a large scale, has a continuous skin-core structure and also has relatively low density, relatively high porosity and good tensile property, bending resistance and compression resistance.

Description

Technical Field

[0001] The invention relates to the technical field of aerogel preparation, and specifically relates to a sheath-core structured polyimide aerogel fiber and a preparation method thereof. Background Art

[0002] Aerogel is a new type of material with high porosity, low density, large specific surface area, and good thermal insulation performance, while aerogel fiber combines the advantages of aerogel and fiber materials. It is a lightweight, porous, flexible and multifunctional material with broad application prospects in thermal insulation, pollution adsorption, biomedicine, energy storage, aerospace and other fields. Compared with bulk aerogel, aerogel fiber is highly flexible and weavable, and can be more easily integrated into applications of various shapes and sizes. However, due to its high porosity and large pore structure, aerogel fiber inevitably has lower tensile strength and compressive strength and is relatively soft and difficult to resist bending. For this reason, aerogel fiber often needs to add a layer of dense skin in some application scenarios.

[0003] The existing methods for preparing a skin-core structure are usually coaxial spinning and coating sizing. Coaxial spinning usually uses a coaxial spinning needle to infuse different spinning solutions into the skin layer and the core layer, and then coagulate them in the same coagulation bath to prepare aerogel fibers with different skin-core structures. Coating sizing is to prepare the aerogel fiber after it is sized with a slurry or manually coated with other thermoplastic resins. Since the skin layer and the core layer are two or more different materials, this will inevitably lead to gaps caused by the loose combination of the internal aerogel fiber and the external skin layer, defects caused by poor interface compatibility, etc., which greatly weakens the excellent performance it should have. Summary of the invention

[0004] In view of the defect that the preparation of aerogel fibers with a sheath-core structure in the prior art inevitably requires coaxial spinning or sizing, the present invention provides a sheath-core polyimide aerogel fiber and a preparation method thereof, which overcomes the problems of the traditional sheath-core aerogel fiber process being cumbersome, discontinuous, high cost and many defects.

[0005] One of the technical solutions of the present invention is to provide a sheath-core structured polyimide aerogel fiber, wherein the fiber core has a sponge pore structure, the sheath has a long strip pore structure, and the length direction of the long strip pore structure is distributed along the circumference of the fiber; the fiber diameter is 200-300µm, and the sheath thickness is 3µm-12µm.

[0006] The long strip hole structure distributed in the circumferential direction can better disperse the stress and bending moment brought by the outside world to the fiber, and the continuous skin-core structure allows the external stress to be better transmitted to the inside of the fiber to avoid the stress concentration and interface effect caused by defects at the skin-core interface. At the same time, the orientation of the long strip hole structure in the circumferential direction makes it have higher compression resistance in the radial direction, so that the fiber has a stronger modulus and higher compressive stress.

[0007] The second technical solution of the present invention is to provide a method for preparing the above-mentioned aerogel fiber. Specifically, the method comprises: first passing a 10wt%~15wt% polyimide acid solution through a phase separation bath for phase separation to form a gel fiber with a skin-core structure, and after the gel fiber is shaped and dried, an aerogel fiber is obtained; the phase separation bath is a mixed solution of a solvent and a non-solvent of polyimide acid, and the mass fraction of the solvent of polyimide acid is 40%~60%; the coagulation bath is a non-solvent for polyimide acid; and the time of the phase separation bath is 15s-45s.

[0008] Furthermore, the shaping drying is freeze drying, supercritical drying, or first coagulation in a coagulation bath and then drying at room temperature and pressure.

[0009] Furthermore, the solvent is one or more of DMF, DMAC, NMP, DMSO, and the non-solvent is one or more of water, ethanol, isopropanol, methanol, ether, ethyl acetate, ethylene glycol, and glycerol.

[0010] In the phase separation bath, the solvent inside the fiber diffuses from the inside to the outside, and the non-solvent diffuses from the outside to the inside. At the beginning of the phase separation, the external polymer chains first contact the non-solvent, resulting in a high degree of entanglement of the molecular chains and a slower and more difficult movement of the polymer chains. In a short period of time, the external pores are denser, while the internal solvent content is higher, and the polymer chains form a loose porous structure; as the phase separation time increases, the internal solvent gradually diffuses outward, so that the entangled chains in the cortex are untied to form a loose porous structure. At the same time, the cortex of the fiber is squeezed into a long strip-shaped pore structure distributed in the circumferential direction due to the formation of the internal porous structure. Therefore, regulating the residence time of the viscose fiber in the phase separation bath can obtain a skin-core structure aerogel fiber with a continuous skin layer of different thicknesses. Furthermore, the residence time in the phase separation bath is 15s-45s.

[0011] In some embodiments of the present invention, polyimide acid is used as a polymer solution to prepare polyimide aerogel fibers. After drying, the polyimide acid aerogel fibers need to be moved to a tubular furnace for imidization at 300° C. for one hour to obtain polyimide aerogel fibers.

[0012] The beneficial effect of the present invention is that aerogel fibers with a continuous skin-core structure are prepared in one step by regulating the phase separation behavior of the fibers in a phase separation bath. The prepared aerogel has uniform pore size, low density, high porosity, and good tensile properties, bending resistance, and compression resistance. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 This is the SEM image of the polyimide aerogel fiber obtained in Example 1; Figure 2 This is the SEM image of the polyimide aerogel fiber obtained in Example 2; Figure 3 This is the SEM image of the polyimide aerogel fiber obtained in Example 3; Figure 4 This is a comparison chart of the skin thickness of the polyimide aerogel fibers obtained in Example 2, Example 1, and Example 3. DETAILED DESCRIPTION

[0014] Non-solvent induced phase separation is a common basic scientific principle in the field of polymer membrane materials. Its process is to dissolve the polymer in the solvent to form a homogeneous solution, then slowly add a reagent that is more miscible with the solvent (called an extractant) to extract the solvent, forming a two-phase structure with the polymer as the continuous phase and the solvent as the dispersed phase. Then, the solvent is removed by normal pressure drying to obtain a polymer with a certain pore structure. In the traditional wet spinning process, the skin and core of the fiber often show obvious structural differences, forming a structural feature of dense outside and loose inside. Combining the above principles and detailed regulation of the residence time of the gel fiber in the phase separation bath, a skin-core structure aerogel fiber with small pores on the outside and large pores on the inside can be achieved.

[0015] The following examples are used to further illustrate the present invention, and their purpose is to illustrate the present invention and should not be construed as limiting the scope of the present invention. Unless otherwise specified, all parts by weight and weight percentages are used below.

[0016] The raw materials used in the present invention, unless otherwise specified, are conventional commercially available products; the methods used in the present invention, unless otherwise specified, are conventional methods in the art.

[0017] The embodiments of the present invention are further described below with reference to a plurality of embodiments.

[0018] It should be clear that the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in the field without creative work are within the scope of protection of the present application.

[0019] The terms used in the embodiments of the present application are only for the purpose of describing specific embodiments, and are not intended to limit the present application. The singular forms "a", "said" and "the" used in the embodiments of the present application and the appended claims are also intended to include plural forms, unless the context clearly indicates other meanings.

[0020] Example 1 (1) A 15 wt% polyimide acid N,N-dimethylacetyl solution was extruded through a 25G needle and wet-spun through a phase separation bath and a coagulation bath to obtain polyimide acid primary fibers. The phase separation bath consisted of a 1:1 mass ratio of N,N-dimethylacetyl solution to water, the coagulation bath was water, and the residence time of the gel fiber in the phase separation bath was 30 s.

[0021] (2) Drying the polyimide acid as-spun fibers at room temperature and normal pressure to obtain polyimide acid aerogel fibers.

[0022] (3) The polyimide acid aerogel fiber is thermally imidized to obtain polyimide aerogel. The imidization temperature is 300 °C and the imidization time is 1 h. Figure 1 As shown, the fiber core has a sponge pore structure, the skin has a long strip pore structure, and the length direction of the long strip pore structure is distributed along the fiber circumference.

[0023] (4) The fiber diameter is 200 µm, the skin thickness is 5.4 µm, the tensile strength is 25.8 MPa, the tensile modulus is 288 MPa, the elongation at break is 27.5%, and the compression modulus at a strain of 30% is 1.31 MPa.

[0024] Example 2 The difference between Example 2 and Example 1 is that the composition of the phase separation bath is N, N-dimethylacetyl solution and water in a mass ratio of 6:4, and the residence time of the gel fiber in the phase separation bath is 45s. The skin thickness is 3.5µm, the tensile strength is 18.6MPa, the tensile modulus is 255MPa, the elongation at break is 12.5%, and the compression modulus at a strain of 30% is 0.85MPa. The obtained polyimide aerogel fiber is as follows Figure 2 shown.

[0025] Example 3 The difference between Example 3 and Example 1 is that the composition of the phase separation bath is N,N-dimethylacetyl solution and water in a mass ratio of 4:6, and the residence time of the gel fiber in the phase separation bath is 15 seconds. Figure 3 As shown. The skin thickness is 12.1µm, the tensile strength is 24.2MPa, the tensile modulus is 352MPa, the elongation at break is 15.5%, and the compression modulus at a strain of 30% is 1.74MPa. The thickness comparison of the fiber skin in the three embodiments is shown in Figure 4 As shown, from left to right are Example 2, Example 1, and Example 3. It can be seen that as the residence time of the phase separation bath increases, the skin thickness of the aerogel fiber becomes thinner and the internal structure becomes more uniform.

[0026] Example 4 The only difference from Example 1 is that a 10 wt% polyimide acid solution is used. The fiber diameter is 300 µm and the skin thickness is 3 µm.

[0027] Comparative Example 1 The only difference from Example 1 is that the residence time of the gel fiber in the phase separation bath is 120s. The pore structure and size of the obtained polyimide aerogel fiber are relatively uniform on the outside and inside, without obvious skin-core structure, and the tensile modulus is very low, only about 200MPa, and the compression modulus at a strain of 30% is only 0.62MPa. It is not the longer and smaller strip-shaped pores on the outside and the rounder and larger sponge pores on the inside obtained in the embodiment.

[0028] Comparative Example 2 (1) A 15 wt% water-soluble polyimide acid aqueous solution was directly extruded into liquid nitrogen using a 25G needle, and after quick freezing, it was transferred to a freeze dryer for freeze drying to obtain polyimide acid aerogel fibers.

[0029] (2) The polyimide aerogel fiber was thermally imidized to obtain polyimide aerogel, the imidization temperature was 300°C, and the imidization time was 1 hour. The pore structure and size of the external and internal pores of the obtained polyimide aerogel fiber were relatively uniform, and there was no obvious skin-core structure.

Claims

1. A sheath-core structured polyimide aerogel fiber, characterized in that: The core has a sponge pore structure, the skin has a long strip pore structure, and the length direction of the long strip pore structure is distributed along the fiber circumference.

2. The fiber according to claim 1, characterized in that The diameter of the aerogel fibers is 200-300µm, and the skin thickness is 3µm-12.1µm.

3. A method for preparing a sheath-core structured polyimide aerogel fiber, characterized in that: A 10wt%~15wt% polyimide acid solution is first passed through a phase separation bath for phase separation to form a gel fiber with a skin-core structure, and the gel fiber is shaped and dried to obtain an aerogel fiber; the phase separation bath is a mixed solution of a solvent and a non-solvent for polyimide acid, and the mass fraction of the solvent for polyimide acid is 40%~60%; the coagulation bath is a non-solvent for polyimide acid; and the time of the phase separation bath is 15s-45s.

4. The preparation method according to claim 3, characterized in that: The shaping drying is freeze drying, supercritical drying, or first coagulation in a coagulation bath and then drying at room temperature and pressure.

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

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