Porous fiber and preparation method thereof

Abstract

The invention discloses a porous fiber and a preparation method thereof, the interior of the porous fiber is an elliptical hole, the long axis of the elliptical hole is along the axial direction of the fiber, the short axis of the elliptical hole is 15-50nm, the long axis of the elliptical hole is 100-250nm, and the axial ratio is 3-15. Through anisotropic design of pores, the problem that high tensile strength and high heat insulation performance of porous fibers cannot be achieved at the same time is solved. The high tensile strength of 115 Mpa is achieved in the axial direction of the porous fiber, and the heat insulation effect of 23.5 mW / mk is achieved in the radial direction.

Description

Technical Field

[0001] The invention belongs to the field of fiber preparation, and in particular relates to a porous fiber and a preparation method thereof. Background Art

[0002] Porous fibers have become an ideal choice for efficient thermal insulation materials due to 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 retardant, sound absorption), and can achieve full-scale thermal insulation through wide-flow and radiation. However, the tensile strength of porous fibers is often less than 20 MPa, and the elongation at break is less than 5%, and they are easy to break under bending or impact.

[0003] Porous fibers face significant bottlenecks in the synergistic improvement of thermal insulation performance and mechanical strength. The core contradiction stems from the differential effects of porosity on the two: when the porosity increases, the dominant role of the low thermal conductivity of the air in the pores is enhanced, the overall thermal conductivity of the fiber is significantly reduced, and the thermal insulation performance is improved; but the increase in porosity will destroy the continuous structure of the fiber (such as the generation of microcracks and interface defects), resulting in increased stress concentration when the material is loaded, and a simultaneous decrease in mechanical strength (such as tensile strength and modulus). This contradiction of "increasing thermal insulation performance while weakening mechanical strength" makes it difficult for traditional porous fibers to meet the needs of application scenarios that require both high thermal insulation and high strength - for example, polar protective clothing needs to withstand extreme low temperatures (relying on high thermal insulation) and withstand friction and pulling (relying on high strength); aerospace thermal insulation layers need to block high-temperature heat flow (relying on high thermal insulation) and withstand complex stress environments (relying on high strength). The irreconcilability of the two has become a core defect that restricts the further application of porous fibers in key areas. Summary of the invention

[0004] In view of the above problems, the present invention provides a porous fiber and a preparation method thereof, wherein the porous fiber has an elliptical hole inside, the major axis of the elliptical hole is along the fiber axial direction, the minor axis of the elliptical hole is 15-50nm, the major axis is 100-250nm, and the axial ratio is 3-15. The problem that the high tensile strength and high thermal insulation of the porous fiber cannot be achieved at the same time is solved by the anisotropic design of the pores. A high tensile strength of 115Mpa is achieved in the axial direction of the porous fiber, and a thermal insulation effect of 23.5mW / mk in the radial direction is achieved. The porous fiber has a very strong structural stress dispersion ability, can achieve high specific strength at the lightest weight, and has low thermal conductivity characteristics. Its thermal insulation performance is significantly improved compared with traditional fiber structures, and the contradiction between low thermal conductivity and high tensile strength is successfully balanced through the directional decoupling design of thermal conductivity and strength.

[0005] The present invention provides a method for preparing a porous fiber, comprising the following steps: (1) Prepare a polyacrylonitrile solution; the molecular weight of the 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%; (2) Perform solution spinning on the polyacrylonitrile solution. The spinning solution passes through a primary coagulation bath, a secondary coagulation bath,..., an N - th coagulation bath in sequence for coagulation; the coagulation bath is composed of a non - solvent and a solvent, and from the primary to the N - th coagulation, the non - solvent concentration increases successively; the non - solvent content of the primary coagulation bath is 5wt%; the non - solvent content of the N - th coagulation bath is 100wt%; N = 4 - 6; The solvent is one or more of DMSO, DMF or DMAC; the non - solvent is water. Through slow phase separation, a pore structure with small and uniform pores is obtained.

[0006] (3) Draw the gel fiber into a stretching bath for stretching and orientation. The stretching bath is composed of water, the temperature of the stretching bath is 70°C - 90°C, and the draw ratio is 1 - 5 times; so that the pore structure of the porous fiber has anisotropy.

[0007] (4) Dry at normal temperature and pressure to obtain porous fibers.

[0008] Further, the polyacrylonitrile solution further includes a silver nitrate solution, and the mass concentration of the nitrate is 1 - 5 times that of the polyacrylonitrile concentration. The silver nitrate salt forms a coordination bond with the nitrile group in the polyacrylonitrile to increase the viscosity of the spinning solution, thereby slowing down the phase separation speed and obtaining a more uniform pore structure.

[0009] Further, the temperature of the coagulation bath is 5°C - 25°C.

[0010] Further, the solvent in the coagulation bath is the same as the solvent of the polyacrylonitrile solution in step 1.

[0011] The present invention also provides a porous fiber prepared by the above method. The pores in the porous fiber are elliptical pores, and the long axis of the elliptical pores is along the fiber axis; the short - axis length of the elliptical pores is 15nm to 50nm, the long - axis length is 100nm to 250nm, and the axis ratio (long axis / short axis) ranges from 3 to 15.

[0012] Through the anisotropic design of the pores, the problem that the high tensile strength and high heat insulation of the porous fiber cannot be both achieved is solved. A high tensile strength of 115 Mpa is achieved in the axial direction of the porous fiber, and a heat insulation effect of 23.5 mW / mk is achieved in the radial direction.

[0013] The ellipsoidal pores in the porous fibers achieve the decoupling of mechanics and heat insulation through geometric asymmetry, with the major axis enhancing load-bearing capacity and the minor axis emphasizing heat insulation. Specifically, in terms of mechanical property regulation, traditional isotropic pores (such as spherical pores) have high structural symmetry and insufficient stress distribution uniformity, easily forming high-stress concentration areas in local regions of the pore walls, resulting in a significant decrease in material strength as the porosity increases. The ellipsoidal pores effectively break through this limitation through directional design: Firstly, arranging the major axis of the ellipsoidal pores along the fiber axis can reduce the axial curvature radius, enabling stress to be transferred smoothly along the pore walls and significantly alleviating the local stress concentration phenomenon; Secondly, during the stretching process, it induces the molecular chains to be highly oriented along the axis, forming a continuous load transfer path and strengthening the load-bearing capacity of the material; At the same time, the asymmetric structure of the ellipsoidal pores can also force the crack propagation path to deflect, further enhancing the material toughness by increasing energy dissipation.

[0014] In terms of heat insulation property regulation, the heat conduction path of isotropic pores exhibits isotropic characteristics, making it difficult to achieve directional thermal resistance regulation. The ellipsoidal pores achieve efficient heat insulation through multi-dimensional structural design: Firstly, the pore structure in the minor axis direction (perpendicular to the fiber axis) can shorten the solid heat conduction path, and when the minor axis size is less than 50 nm, the gas molecule mean free path limitation effect is significant, and the gas thermal conductivity is greatly reduced; Secondly, the periodic nano-scale ellipsoidal pore interfaces can significantly enhance phonon scattering and effectively inhibit solid heat conduction; In addition, the asymmetric pore structure can further reduce the heat radiation heat transfer efficiency by extending the infrared reflection path.

[0015] The present invention also provides a woven fabric prepared from the above-mentioned porous fibers. This fabric is both light and thin like silk and has the heat preservation and insulation effects like down.

[0016] The advantages of the present invention are as follows: By performing stretching in a high-temperature stretching bath, an anisotropic elliptical pore structure is formed inside the porous fibers. The mechanical strength of the provided porous fibers can reach 117.5 Mpa, and the radial thermal conductivity of the obtained fabric can be reduced to 23.5 mW / mk, and its thermal conductivity is significantly lower than that of the porous fibers prepared by conventional means. Description of the Drawings

[0017] Figure 1 It is the microscopic morphology of the cross-section along the radial direction of the polyacrylonitrile porous fiber in Example 1; Figure 2 It is the microscopic morphology of the cross-section along the axial direction of the polyacrylonitrile porous fiber in Example 1; Figure 3 It is the microscopic morphology of the cross-section along the radial direction of the polyacrylonitrile porous fiber in Example 2; Figure 4 It is the microscopic morphology of the cross-section along the axial direction of the polyacrylonitrile porous fiber in Example 2; Figure 5The microscopic morphology of the polyacrylonitrile porous fiber of Example 3 along the radial section; Figure 6 The microscopic morphology of the polyacrylonitrile porous fiber of Example 3 along the axial section. Detailed implementation manners

[0018] The following examples are used to further illustrate the present invention, and the purpose is to explain the present invention rather than to limit the scope of the present invention. Unless otherwise specified, all are in parts by weight and weight percentages.

[0019] The raw materials used in the present invention are all conventional commercially available products unless otherwise specified; the methods used in the present invention are all conventional methods in the art unless otherwise specified.

[0020] The following further illustrates the embodiments of the present invention through multiple examples.

[0021] It should be clear that the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present application without creative efforts belong to the scope of protection of the present application.

[0022] 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", "the" and "said" used in the embodiments of the present application and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise.

[0023] Example 1 (1) Using DMSO as the solvent, PAN powder with a molecular weight of 100,000 was dissolved in the composite solvent. The mass concentration of the PAN solution was 15%, and the mass concentration of silver nitrate was 30%.

[0024] (2) The spinning solution of PAN was placed in a vacuum oven for sufficient degassing treatment, and the degassing time was 24 h.

[0025] (3) The degassed PAN spinning solution was quantitatively supplied to the spinneret by a metering pump. The spinneret was completely immersed in the coagulation bath. The diameter of the spinneret hole was 0.075 mm, the spinning temperature was 15 °C, the coagulation bath was a composite solvent of DMSO and water, the number of coagulation bath stages was 5, and the mass ratios of water in different coagulation baths were 5%, 20%, 50%, 80% and 100% respectively.

[0026] (4) The as - spun gel fiber was subjected to stretching orientation in the stretching bath. The stretching bath composition was water, the temperature was 80 °C, and the draw ratio was 1 time.

[0027] (5) The stretched porous fibers are dried under an infrared lamp and collected. The microscopic morphology of the fibers along the radial section is shown in Figure 1 , and the microscopic morphology along the axial section is shown in Figure 2 . As shown in Figure 2 , it shows that the porous fibers have 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. After measurement, the porosity of the obtained fibers is 80.2%.

[0028] (6) The porous fibers are cut into lengths of 0.5 mm, and the mechanical strength of the fibers is measured using a mechanical testing machine to be 105.6 Mpa, and the elongation at break is 19.3%.

[0029] (7) The porous fibers are woven into a fabric in the same direction, and its thermal conductivity is tested using a transient thermal analyzer. The radial thermal conductivity of the fibers is 27 mW / mk.

[0030] Example 2 (1) A composite solvent is prepared by mixing DMF and water at a mass ratio of 20:1. PAN powder with a molecular weight of 250,000 is dissolved in the composite solvent. The mass concentration of the PAN solution is 10%, and the mass concentration of silver nitrate is 50%.

[0031] (2) The PAN spinning solution is placed in a vacuum oven for sufficient degassing treatment, and the degassing time is 24 h.

[0032] (3) The degassed 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 holes is 0.075 mm, the spinning temperature is 25 °C, the coagulation bath is a composite solvent of DMF and water, the number of coagulation bath stages is 4, and the mass ratios of water in different coagulation baths are 5%, 30%, 60%, and 100% respectively.

[0033] (4) The as-spun gel fibers are stretched and oriented in the stretching bath. The composition of the stretching bath is water, the temperature is 70 °C, and the draw ratio is 4 times.

[0034] (5) The stretched porous fibers are dried under an infrared lamp and collected. The microscopic morphology of the fibers along the radial section is shown in Figure 3 , and the microscopic morphology along the axial section is shown in Figure 4 . Its short-axis length is 15 nm, its long-axis length is 135 nm, and its axis ratio is 9. After measurement, the porosity of the obtained fibers is 83.2%.

[0035] (6) The porous fibers are cut into 0.5 mm lengths, and the mechanical strength of the fibers is measured using a mechanical testing machine to be 110.3 MPa, and the elongation at break is 17.5%.

[0036] (7) Weave the porous fibers into a fabric in the same direction and measure its thermal conductivity using a transient thermal analyzer. The radial thermal conductivity of the fibers is 26.5 mW / mk.

[0037] Example 3 (1) Prepare a composite solvent by mixing DMAC and water in a mass ratio of 10:1. Dissolve PAN powder with a molecular weight of 300,000 in the composite solvent. The mass concentration of the PAN solution is 20%, and the mass concentration of silver nitrate is 20%. (2) Place the PAN spinning solution in a vacuum oven for sufficient degassing. The degassing time is 24 h.

[0038] (3) The degassed 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 holes is 0.075 mm, the spinning temperature is 5 °C, the coagulation bath is a composite solvent of DMAC and water, and the number of coagulation bath stages is 6. The mass ratios of water in different coagulation baths are 5%, 10%, 20%, 40%, 70%, and 100% respectively.

[0039] (4) Perform stretching and orientation on the nascent gel fibers in the stretching bath. The composition of the stretching bath is water, the temperature is 90 °C, and the draw ratio is 5 times.

[0040] (5) Dry and collect the stretched porous fibers under an infrared lamp. The microscopic morphology of the fibers along the radial section is shown in Figure 5 , and the microscopic morphology along the axial section is shown in Figure 6 . Its short axis length is 17 nm, the long axis length is 250 nm, and the axis ratio is 14.7. After measurement, the porosity of the obtained fibers is 83.2%.

[0041] (6) Cut the porous fibers into 0.5 mm lengths and measure the mechanical strength of the fibers using a mechanical testing machine. The mechanical strength is 115.3 MPa, and the elongation at break is 16.6%.

[0042] (7) Weave the porous fibers into a fabric in the same direction and measure its thermal conductivity using a transient thermal analyzer. The radial thermal conductivity of the fibers is 23.5 mW / mk.

[0043] Example 4 The difference from Example 1 is that a composite solvent of DMF and DMAC is used instead of DMSO. The short axis length of the elliptical holes of the obtained porous fibers is 20 nm, the long axis length is 100 nm, and the axis ratio is 5. The porosity is 85.3%, the mechanical strength is 117.5 Mpa, and the elongation at break is 15.8%. The radial thermal conductivity of the obtained fabric is 26.5 mW / mk.

[0044] Comparative Example 1 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, stretching cannot be carried out and the fiber breaks.

[0045] Comparative Example 2 The difference from Example 1 is that the fiber only passes through a coagulation bath with 100 wt% of non-solvent. The cross-sectional shape of the obtained fiber is irregular, the pore size distribution is uneven, a dense shell layer appears on the surface, and finger-like pores of more than ten microns appear inside. The porosity of the obtained porous fiber is 64.6%, the mechanical strength is 8.7 Mpa, and the elongation at break is 55.2%. The radial thermal conductivity of the obtained fabric is 56.9 mW / mk.

[0046] The above examples have detailed the structure, characteristics and effects of the present invention. The above are only the preferred embodiments of the present invention. Any changes made according to the concept of the present invention, or equivalent embodiments modified into equivalent changes, still within the scope covered by the specification, shall be within the protection scope of the present invention.

Claims

1. A method for preparing a porous fiber, characterized in that, It has 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%; (2) Perform solution spinning on the polyacrylonitrile solution, and the spinning solution passes through a primary coagulation bath, a secondary coagulation bath,..., an N - th coagulation bath in sequence for coagulation; the coagulation bath is composed of a non - solvent and a solvent, and from the primary to the N - th coagulation, the non - solvent concentration increases in sequence; the non - solvent content of the primary coagulation bath is 5wt%; the non - solvent content of the N - th coagulation bath is 100wt%; N = 4 - 6; The solvent is one or more of DMSO, DMF or DMAC; the non - solvent is water; (3) Pull the gel fiber into a stretching bath for stretching and orientation. The stretching bath is composed of water, the temperature of the stretching bath is 70°C - 90°C, and the draw ratio is 1 - 5 times; (4) Dry at normal temperature and pressure to obtain porous fibers.

2. The method according to claim 1, wherein The polyacrylonitrile solution further includes a silver nitrate solution, and the mass concentration of the nitrate is 1 - 5 times that of the polyacrylonitrile concentration.

3. The method according to claim 1, wherein The temperature of the coagulation bath is 5°C - 25°C.

4. 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 in step 1.

5. A porous fiber prepared by the method according to claim 1, characterized in that, The pores in the fiber are elliptical pores, and the major axis of the elliptical pores is along the fiber axis; among them, 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.

6. A knitted fabric, characterized in that, Prepared from the porous fiber according to claim 5.

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