A porous fiber and its preparation method

Abstract

This invention discloses a porous fiber and its preparation method. The porous fiber has elliptical pores inside, with the major axis of the pores along the fiber axis, the minor axis of the pores being 15-50 nm, the major axis being 100-250 nm, and the axial ratio being 3-15. By designing the anisotropic pore structure, the problem of the incompatibility between high tensile strength and high thermal insulation in porous fibers is solved. A high tensile strength of 115 MPa is achieved in the axial direction of the porous fiber, and a thermal insulation effect of 23.5 mW / mK in the radial direction is achieved.

Description

Technical Field

[0001] This invention belongs to the field of fiber preparation, specifically relating to a porous fiber and its preparation method. Background Technology

[0002] Porous fibers, with their ultra-low thermal conductivity (as low as 0.03-0.05 W / mK), lightweight (density 0.1-0.3 g / cm³), and multifunctional integration potential (flame retardancy, sound absorption), have become an ideal choice for high-efficiency thermal insulation materials, achieving full-scale thermal insulation across wide current and radiation. However, the tensile strength of porous fibers is often below 20 MPa, and the elongation at break is <5%, making them prone to breakage under bending or impact.

[0003] Porous fibers face significant bottlenecks in synergistically improving thermal insulation and mechanical strength. The core contradiction stems from the differential impact of porosity on these two aspects: as porosity increases, the low thermal conductivity of the air within the pores becomes more dominant, significantly reducing the overall thermal conductivity of the fiber and improving thermal insulation performance. However, increased porosity disrupts the fiber's continuous structure (e.g., causing microcracks and interface defects), leading to increased stress concentration under load and a simultaneous decrease in mechanical strength (e.g., tensile strength and modulus). This contradiction of "improved thermal insulation but weakened mechanical strength" makes it difficult for traditional porous fibers to meet the demands of applications requiring both high thermal insulation and high strength simultaneously—for example, polar protective clothing needs to withstand extreme low temperatures (relying on high thermal insulation) while also resisting friction and tension (relying on high strength); aerospace insulation layers need to block high-temperature heat flow (relying on high thermal insulation) while also withstanding complex stress environments (relying on high strength). This irreconcilable difference is the core defect limiting the further application of porous fibers in key fields. Summary of the Invention

[0004] To address the aforementioned problems, this invention provides a porous fiber and its preparation method. The porous fiber has elliptical pores inside, with the major axis of the pores along the fiber axis, the minor axis of the pores being 15-50 nm, the major axis being 100-250 nm, and the axial ratio being 3-15. Through anisotropic design of the pores, the problem of the incompatibility between high tensile strength and high thermal insulation in porous fibers is solved. A high tensile strength of 115 MPa is achieved in the axial direction of the porous fiber, while the thermal conductivity in the radial direction is 23.5 mW / mK, resulting in excellent thermal insulation. This porous fiber possesses extremely strong structural stress dispersion capabilities, achieving high specific strength with minimal weight, while also exhibiting low thermal conductivity. Its thermal insulation performance is significantly improved compared to traditional fiber structures. Through directional decoupling design of thermal conductivity and strength, the contradiction between low thermal conductivity and high tensile strength is successfully balanced.

[0005] This invention provides a method for preparing porous fibers, comprising the following steps:

[0006] (1) Prepare a polyacrylonitrile solution; the molecular weight of polyacrylonitrile is 100,000-300,000, the mass concentration is 10%-20%, and the solvent is an aqueous solution of one or more of DMSO, DMF or DMAC with a concentration of 90wt%-100wt%;

[0007] (2) The polyacrylonitrile solution is solution spun, and the spinning solution is coagulated sequentially through a primary coagulation bath, a secondary coagulation bath, ..., an Nth-stage coagulation bath; the coagulation bath is composed of a mixture of non-solvent and solvent, and the concentration of non-solvent increases sequentially from the primary to the Nth stage of coagulation; the non-solvent content of the primary coagulation bath is 5 wt%; the non-solvent content of the Nth-stage coagulation bath is 100 wt%; N = 4-6;

[0008] The solvent is one or more of DMSO, DMF, or DMAC; the non-solvent is water. Through slow phase separation, a small and uniform pore structure is obtained.

[0009] (3) The gel fiber is drawn into a stretching bath for stretching and orientation. The stretching bath is composed of water and the temperature is 70℃-90℃. The stretching ratio is 1-5 times. This is to make the pore structure of the porous fiber anisotropic.

[0010] (4) Dry at room temperature and pressure to obtain porous fibers.

[0011] Furthermore, the polyacrylonitrile solution also includes a silver nitrate solution, the mass concentration of which is 1-5 times the concentration of polyacrylonitrile. Silver nitrate increases the viscosity of the spinning solution by forming coordination bonds with the nitrile groups in the polyacrylonitrile, thereby slowing down the phase separation rate and obtaining a more uniform pore structure.

[0012] Furthermore, the temperature of the coagulation bath is 5℃-25℃.

[0013] Furthermore, the solvent in the coagulation bath is the same as the solvent in the polyacrylonitrile solution described in step 1.

[0014] The present invention also provides a porous fiber prepared by the above method, wherein the pores in the porous fiber are elliptical pores, and the major axis of the elliptical pores is along the fiber axis; wherein the minor axis length of the elliptical pores is 15nm to 50nm, the major axis length is 100nm to 250nm, and the axis ratio (major axis / minor axis) ranges from 3 to 15.

[0015] By designing the pores with anisotropy, the problem of simultaneously achieving high tensile strength and high thermal insulation in porous fibers was solved. A high tensile strength of 115 MPa was achieved in the axial direction of the porous fiber, while a thermal insulation effect of 23.5 mW / mK was achieved in the radial direction.

[0016] The ellipsoidal pores in porous fibers achieve decoupling of mechanics and thermal insulation through geometric asymmetry. Their long axis strengthens load-bearing capacity, while their short axis emphasizes thermal insulation. Specifically, in terms of mechanical property control, traditional isotropic pores (such as spherical pores) suffer from high structural symmetry and insufficient stress distribution uniformity, easily forming high stress concentration zones in localized areas of the pore wall, leading to a significant decrease in material strength with increasing porosity. Ellipsoidal pores, through directional design, effectively overcome this limitation: First, aligning the long axis of the ellipsoidal pores along the fiber axis reduces the axial radius of curvature, allowing stress to be transmitted smoothly along the pore wall, significantly alleviating localized stress concentration. Second, during stretching, it induces molecular chains to be highly oriented along the axial direction, forming a continuous load transfer path and enhancing the material's load-bearing capacity. Simultaneously, the asymmetric structure of the ellipsoidal pores forces crack propagation paths to deflect, further improving material toughness by increasing energy dissipation.

[0017] In terms of thermal insulation performance control, isotropic pores exhibit isotropic heat conduction paths, making it difficult to achieve directional thermal resistance control. Ellipsoidal pores, on the other hand, achieve efficient thermal insulation through multi-dimensional structural design: First, the pore structure along the short axis (perpendicular to the fiber axis) shortens the solid heat conduction path, and when the short axis dimension is less than 50 nm, the gas molecule free path limitation effect is significant, greatly reducing the gas thermal conductivity; second, the periodic nanoscale ellipsoidal pore interface significantly enhances phonon scattering, effectively suppressing solid heat conduction; furthermore, the asymmetric pore structure can further reduce thermal radiation heat transfer efficiency by extending the infrared reflection path.

[0018] The present invention also provides a woven fabric prepared from the aforementioned porous fibers. This fabric combines the lightness of silk with the heat insulation properties of down.

[0019] The advantages of this invention are: by stretching the fiber in a high-temperature stretching bath, an anisotropic elliptical pore structure is formed inside the porous fiber, and the mechanical strength of the porous fiber can reach 117.5 MPa, and the radial thermal conductivity of the resulting fabric can be reduced to 23.5 mW / mk, which is significantly lower than that of porous fibers prepared by conventional methods. Attached Figure Description

[0020] Figure 1 The radial cross-sectional microstructure of the polyacrylonitrile porous fiber in Example 1 is shown.

[0021] Figure 2 The image shows the axial cross-sectional microstructure of the polyacrylonitrile porous fiber from Example 1.

[0022] Figure 3 The radial cross-sectional microstructure of the polyacrylonitrile porous fiber in Example 2 is shown.

[0023] Figure 4The microstructure of the axial cross section of the polyacrylonitrile porous fiber in Example 2 is shown.

[0024] Figure 5 The radial cross-sectional microstructure of the polyacrylonitrile porous fiber in Example 3 is shown.

[0025] Figure 6 The image shows the axial cross-sectional microstructure of the polyacrylonitrile porous fiber in Example 3. Detailed Implementation

[0026] 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.

[0027] 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.

[0028] The embodiments of the present invention will be further described below with reference to several examples.

[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.

[0031] Example 1

[0032] (1) DMSO is used as a solvent to dissolve PAN powder with a molecular weight of 100,000 in the composite solvent. The mass concentration of PAN in the solution is 15%, and the mass concentration of silver nitrate is 30%.

[0033] (2) Place the spinning solution of PAN into a vacuum oven for thorough degassing treatment for 24 hours.

[0034] (3) The deaerated PAN spinning solution is quantitatively supplied to the spinneret by a metering pump. The spinneret is completely immersed in the coagulation bath. The diameter of the spinneret hole is 0.075 mm. The spinning temperature is 15℃. The coagulation bath is a composite solvent of DMSO and water. The coagulation bath has 5 stages. The mass ratio of water in different coagulation baths is 5%, 20%, 50%, 80% and 100%, respectively.

[0035] (4) The nascent gel fibers are stretched and oriented in a stretching bath. The stretching bath consists of water, the temperature is 80℃, and the stretching ratio is 1.

[0036] (5) The stretched porous fibers were dried and collected under an infrared lamp. The microstructure of the fibers along the radial section is shown in the figure. Figure 1 Microscopic morphology along the axial section is shown Figure 2 .like Figure 2 The diagram shows that the porous fiber has an oriented porous structure with a short axis length of 50 nm, a long axis length of 150 nm, and an axis ratio of 3. The porosity of the obtained fiber was measured to be 80.2%.

[0037] (6) The porous fiber was cut to a length of 0.5 mm and the mechanical strength of the fiber was measured to be 105.6 MPa and the elongation at break was 19.3% using a mechanical testing machine.

[0038] (7) The porous fibers were woven into a fabric in the same direction and their thermal conductivity was tested using a transient thermal analyzer. The radial thermal conductivity of the fibers was 27 mW / mk.

[0039] Example 2

[0040] (1) DMF and water are mixed in a mass ratio of 20:1 to prepare a composite solvent. PAN powder with a molecular weight of 250,000 is dissolved in the composite solvent. The mass concentration of PAN solution is 10% and the mass concentration of silver nitrate is 50%.

[0041] (2) Place the spinning solution of PAN into a vacuum oven for thorough degassing treatment for 24 hours.

[0042] (3) The defoamed PAN spinning solution is quantitatively supplied to the spinneret by a metering pump. The spinneret is completely immersed in the coagulation bath. The diameter of the spinneret hole is 0.075 mm, the spinning temperature is 25 °C, the coagulation bath is a composite solvent of DMF and water, and the coagulation bath has 4 stages. The mass ratio of water in different coagulation baths is 5%, 30%, 60%, and 100%, respectively.

[0043] (4) The nascent gel fibers are stretched and oriented in a stretching bath. The stretching bath consists of water, the temperature is 70°C, and the stretching ratio is 4 times.

[0044] (5) The stretched porous fibers were dried under an infrared lamp and collected. The microstructure of the fibers along the radial section is shown in [Figure number missing]. Figure 3 Microscopic morphology along the axial section is shown Figure 4 Its minor axis length is 15 nm, major axis length is 135 nm, and axial ratio is 9. The porosity of the obtained fiber was determined to be 83.2%.

[0045] (6) The porous fiber was cut to a length of 0.5 mm and the mechanical strength of the fiber was measured to be 110.3 MPa and the elongation at break was 17.5% using a mechanical testing machine.

[0046] (7) The porous fibers were woven into a fabric in the same direction and its thermal conductivity was tested using a transient thermal analyzer. The radial thermal conductivity of the fiber was 26.5 mW / mk.

[0047] Example 3

[0048] (1) DMAC and water were mixed in a mass ratio of 10:1 to prepare a composite solvent. PAN powder with a molecular weight of 300,000 was dissolved in the composite solvent. The mass concentration of PAN in the solution was 20%, and the mass concentration of silver nitrate was 20%.

[0049] (2) Place the spinning solution of PAN into a vacuum oven for thorough degassing treatment for 24 hours.

[0050] (3) The degassed PAN spinning solution is metered and supplied to the spinneret by a metering pump. The spinneret is completely immersed in the gel bath. The diameter of the spinneret hole is 0.075 mm. The spinning temperature is 5℃. The coagulation bath is a composite solvent of DMAC and water. The coagulation bath has 6 stages. The mass ratio of water in different coagulation baths is 5%, 10%, 20%, 40%, 70% and 100%, respectively.

[0051] (4) The nascent gel fibers are stretched and oriented in a stretching bath. The stretching bath consists of water, the temperature is 90℃, and the stretching ratio is 5 times.

[0052] (5) The stretched porous fibers were dried under an infrared lamp and collected. The microstructure of the fibers along the radial section is shown in [Figure number missing]. Figure 5 Microscopic morphology along the axial section is shown Figure 6 Its minor axis length is 17 nm, major axis length is 250 nm, and axial ratio is 14.7. The porosity of the obtained fiber was measured to be 83.2%.

[0053] (6) The porous fiber was cut to a length of 0.5 mm and the mechanical strength of the fiber was measured to be 115.3 MPa and the elongation at break was 16.6% using a mechanical testing machine.

[0054] (7) The porous fibers were woven into a fabric in the same direction and its thermal conductivity was tested using a transient thermal analyzer. The radial thermal conductivity of the fiber was 23.5 mW / mk.

[0055] Example 4

[0056] The difference from Example 1 is that a composite solvent of DMF and DMAC was used instead of DMSO. The resulting porous fibers had elliptical pores with a minor axis length of 20 nm, a major axis length of 100 nm, and an aspect ratio of 5. The porosity was 85.3%, the mechanical strength was 117.5 MPa, and the elongation at break was 15.8%. The radial thermal conductivity of the resulting fabric was 26.5 mW / mK.

[0057] Comparative Example 1

[0058] The difference from Example 1 is that the temperature of the stretching bath is 50°C. During the stretching process, due to the low temperature of the stretching bath, the fibers cannot be stretched and break.

[0059] Comparative Example 2

[0060] The difference from Example 1 is that the fibers were subjected to only one non-solvent 100wt% coagulation bath, resulting in fibers with irregular cross-sectional shapes, uneven pore size distribution, a dense shell on the surface, and finger-like pores of tens of micrometers inside. The resulting porous fibers had a porosity of 64.6%, a mechanical strength of 8.7 MPa, and an elongation at break of 55.2%. The resulting fabric had a radial thermal conductivity of 56.9 mW / mK.

[0061] 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 porous fibers, characterized in that, It includes the following steps: (1) Prepare a polyacrylonitrile solution; the molecular weight of polyacrylonitrile is 100,000-300,000, the mass concentration is 10%-20%, the solvent is an aqueous solution of one or more of DMSO, DMF or DMAC, and the concentration is 90wt%-100wt%; the polyacrylonitrile solution also includes a silver nitrate solution, the mass concentration of silver nitrate is 1-5 times the mass concentration of polyacrylonitrile; (2) The polyacrylonitrile solution is solution spun, and the spinning solution is coagulated sequentially through a primary coagulation bath, a secondary coagulation bath, ..., an Nth-stage coagulation bath; the coagulation bath is composed of a mixture of non-solvent and solvent, and the concentration of non-solvent increases sequentially from the primary to the Nth stage of coagulation; the non-solvent content of the primary coagulation bath is 5 wt%; the non-solvent content of the Nth-stage coagulation bath is 100 wt%; N = 4-6; The solvent is one or more of DMSO, DMF, or DMAC; the non-solvent is water. (3) The gel fiber is drawn into a stretching bath for stretching and orientation. The stretching bath is composed of water and the temperature of the stretching bath is 70℃-90℃. The stretching ratio is 1-5 times. (4) Dry at room temperature and pressure to obtain porous fibers.

2. The method according to claim 1, characterized in that, The temperature of the coagulation bath is 5℃-25℃.

3. The method according to claim 1, characterized in that, The solvent in the coagulation bath is the same as the solvent in the polyacrylonitrile solution described in step 1.

4. A porous fiber prepared by the method described in claim 1, characterized in that, The pores in the fiber are elliptical pores, with the major axis of the elliptical pores along the fiber axis; the minor axis length of the elliptical pores is 15nm to 50nm, the major axis length is 100nm to 250nm, and the ratio of the major axis to the minor axis ranges from 3 to 15.

5. A woven fabric, characterized in that, Prepared from the porous fiber described in claim 4.

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